The Torrefaction Of Biomass

Name : William Helliker,

Sun: 050768688,

Supervisors: Dr. D. J. Nowakowski,Prof. A. V. Bridgwater

1

Abstract

This report looks into the torrefaction process, over a range of torrefaction

temperatures (200oC-300oC) for a variety of biomass: hard wood (Beech

Wood), soft wood (Willow), a herbaceous energy crop (Miscanthus) and an

agricultural waste (Rape Straw). The torrefaction process was carried out

using a Thermogravimetric analyser, to measure mass losses that occur during

the process. Samples of each biomass were produced for torrefaction

temperatures of 200, 225, 250, 275 and 300 centigrade. Ashing and pyrolysis

was conducted using the TGA apparatus, to compare volatiles content and

char content (fixed carbon and ash) in all samples. In addition PY-GC-MS

apparatus was also used to determine the volatiles released from the

torrefaction process, this allowed for the analysis of which lignocellulosic

components were affected by the torrefaction process. H,C,N analysis was

used to allow calculations and estimations of the heating values and energy

improvements of the fuels, after the torrefaction process. This report finds that

the torrefaction majorly affected the hemicellulose component, as well as a

smaller affect on the lignin and cellulose of the biomass. Thermal Degradation

of the hemicellulose caused an improvement in energy density seen within the

torrifeied biomass, and hence the level of hemicellulose present in biomass

was a key factor in determining how well the torrefaction process improved the

biomass. In addition the fixed carbon content was very important to the energy

retained in the biomass. The Biomass varieties that yielded the best energy

density increase had a good balance between moderate/high levels of

hemicellulose and fixed carbon.

2

Table of contents

1 Introduction........................................................................................................................ 42 Background and Review of Related Literature...................................................................52.1 The Chemistry of Biomass.............................................................................................5

2.1.1 Lignocellulose................................................................................................................62.1.1.1 Cellulose................................................................................................................72.1.1.2 Hemicellulose.......................................................................................................102.1.1.3 Lignin................................................................................................................... 13

2.1.2 Extractives................................................................................................................... 142.2 Thermal Conversion Processes of Biomass.......................................................................15

2.2.1 pyrolysis...................................................................................................................... 152.2.1.1 Fast Pyrolysis.......................................................................................................172.2.1.2 Slow pyrolysis......................................................................................................18

2.2.2 Gasification.................................................................................................................192.2.3 Combustion of Biomass..............................................................................................212.3 Torrefaction of Biomass.................................................................................................22

2.3.1 The Torrefaction Process........................................................................................222.3.2 The Result & Gains of Torrefaction.........................................................................272.3.3 The Economic Potential of the Torrefaction Process..............................................29

3 Experiments and Planning...............................................................................................343.1 Sample Preparation.................................................................................................343.2 High Temperature Pyrolysis of Feed Stocks...........................................................353.3 Slow Ashing of Samples..........................................................................................363.4 Pyrolysis of Prepared Samples & Feed stocks........................................................373.5 H,C,N Analysis........................................................................................................373.6 PY-GC-MS of Feed Stocks......................................................................................38

4 Results and Discussion....................................................................................................394.1 Comparison of Biomass Feed Stocks.....................................................................394.2 The Effects of Torrefaction on Mass and Energy of the Biomass............................434.3 Chemical Analysis of the Torrefaction process........................................................51

4.3.1 Slow Ashing of the Raw and Torrified Biomass Samples........................................514.3.2 Pyrolysis of the Torrified Biomass Samples............................................................554.3.3 PY-GC-MS Analysis of the Volatiles Produced During Torrefaction.......................574.3.3.1 Volatiles Produced During the Torrefaction of Beech Wood...........................604.3.3.2 Volatiles Produced During the Torrefaction of Rapestraw..............................624.3.3.3 Volatiles Produced During the Torrefaction of Green Miscanthus..................634.3.3.4 Volatiles Produced During the Torrefaction of Willow.....................................64

5 Conclusions.....................................................................................................................656 Reccomendations............................................................................................................677 Glossary........................................................................................................................... 698 References.......................................................................................................................719 Appendicies ..................................................................................................................... 74

9.1 Appendix A .............................................................................................................. 75 9.2 Appendix B .............................................................................................................. 77 9.3 Appendix C .............................................................................................................. 81 9.4 Appendix D .............................................................................................................. 83

3

1 IntroductionThere is a realisation that the natural resources around the globe, such as

coal, oil and gas, are slowly depleting. These slowly depleting resources are

key feed stocks in the production of many different fuels and chemicals.

Therefore there has been an increasing necessity to look for alternatives feed

stocks to replace them.

One alternative for consideration Is Biomass, the use of plants and crops

grown specifically for use as the base for bio-fuels or bio-chemicals. Crops

such as short rotation woody crops, or herbaceous energy crops, are grown

specifically for use as a biomass resource[1], although there is also research

into agricultural wastes such as a few various types of straw.

Biomass as a fuel has several undesirable properties, it has a low calorific, a

high moisture content, due to its hygroscopic nature, and smokes when

combusted[2,3] It is because of this poorer calorific value/lower energy density

that fuel biomass treatments, such as pyrolysis, have been used to increase

the energy density of the fuel. For examples fast pyrolysis of biomass to form

bio-oils, one advantage of converting the biomass to a bio-oil is its easier to

transport and store, and there is greater potential for use as a fuel or a base for

chemical production.[4]

This report will focus on the treatment of biomass making use of a mild form of

pyrolysis, known as torrefaction. The report aims to look at what effect this

process has on different forms of biomass. With references to any beneficial

results achieved, and the actual affect the process has on the biomass.

1 Brown R.C. “Biorenewable Resources, engineering new products from agriculture”, Ames, Iowa (2003)

2 Pentananunt R. Mizanur Rahman A.N.M., and Bhattacharya S.C. ‘Upgrading biomass by means of torrefaction’ J. Energy, Vol. 15, No 12 (1990) pp. 1175-1179

3 Felfi F. Luengo C. Bezzon G. and Beaton P., “Bench Unit for Biomass Residues Torrefaction” Preceedings conf. on Biomass for Energy and Industry (1998) pp. 1593

4 Bridgwater A.V., Czernik S.and Piskorz J. “Progress in Thermochemical Biomass Conversion” Vol. 2, Blackwell science, (2001) pp 979-997

4

2 Background and Review of Related Literature

2.1 The Chemistry of BiomassShort rotation woody crops (SRWC): short rotation woody crop is the term

used to describe woody biomass that is fast growing, and suitable for use in

dedicated feedstock supply systems.[Error: Reference source not found] The SRWC are

grown on a sustainable basis and are harvested on a rotation of around 3

years in the uk. Woody crops include hard woods and softwoods [Error: Reference source

not found]

Hardwoods (deciduous species) are trees classified as angiosperms; [Error: Reference

source not found,5] they have the ability to resprout from stumps, a process known as

coppicing, which reduces their production costs relative to softwoods. [Error:

Reference source not found]

There are many other advantages of hard woods in processing including high

density for many species; the presence of hemicellulose high in xylan, which

can be removed relatively easily; low ash content (particularly silica relative to

softwood and herbaceous crops); hardwood lignin has a lower degree of

polymerisation than softwood and contains a greater methoxyl content [Error:

Reference source not found]

Softwoods (Coniferous species) are trees classified as gymnosperms [Error:

Reference source not found,Error: Reference source not found], softwood is generally faster growing, but

their carbohydrate is not as accessible for chemical processing as the

carbohydrates in hardwood.[Error: Reference source not found] Also softwoods tend to have

a higher cellulose and higher lignin content than that of hardwoods. [Error: Reference

source not found]Since softwoods are frequently used in construction lumber and

pulpwood, they are more readily available as waste material in the form of

logging and manufacturing residues.[Error: Reference source not found]

Herbacious energy crops (HEC): herbaceous energy crops are plants that

have little or no woody tissue, the above ground growth of these plants usually

lasts for only a single growing season. [Error: Reference source not found] However

herbaceous crops include both annuals and perennials, Annuals die at the end

5

of each growing season, and hence must be replanted in spring, where as

Perennials die back each year in temperate climates, but establish themselves

each spring from rootstock.[Error: Reference source not found]

Recent development work with the herbaceous energy crops has focused on

grasses due to their higher yields of lignocellulose. There are two types of

these grasses either thick stemmed of thin stemmed. [Error: Reference source not found]

Thick stemmed grasses are generally seen as more labour intensive and may

require more specialist equipment, hence there is a preference to thin

stemmed grasses as they can be harvested with conventional hay equipment. [Error: Reference source not found]

2.1.1 Lignocellulose

In general Biomass is comprised of three major constituents which form the

lignocellulose material that makes up the plant. [Error: Reference source not found] It consists

of variable amounts of cellulose, hemicellulose, and Lignin, the ratio of each

component within the plant varies dependant if it is Hardwoods (from

deciduous trees), softwood (from coniferous trees), or herbaceous material

(from plants and agricultural crops) [Error: Reference source not found]

For woody biomasses about half is cellulose, a quarter hemicellulose and

extractives, and a quarter lignin.[6] but this is subject to change dependant on

the type of biomass. Table 2.1.1.0.1 shows various types of biomass and their

approximate compositions based on a weight %

Table 2.1.1.0.1 Organic components of lignocellulosic crops (dry basis)[Error: Reference source not found]

Feed StockCellulose (wt

%)Hemicellulose

(wt%)Lignin (wt%) Other (wt%)

Bagasse 35 25 20 20

Corn Stover 53 15 16 16

Corncobs 32 44 13 11

Wheat Straw 38 36 16 10

Wheat Chaff 38 36 16 11

S.R.W.C. 50 23 22 5

H.E.C. 45 30 15 10

Waste Paper 76 13 11 0

(Sources: Bull S.R. 1991, “The U.S. Department of Energy Biofuels Research Program” in

Energy Sources, Vol. 13 pp. 433-442; Wayman M. and Parcekh S., “Biotechnology of Biomass

6

Conversion: Fuels and Chemicals from Renewable Resources”,Philadelphia: Open university

Press)

2.1.1.1 Cellulose

Cellulose is a “homopolysaccharide of glucose, and is an important constituent

within the plant”[Error: Reference source not found]. The base constituent of the cellulose

polymer is cellobiose[Error: Reference source not found,7], the repeating unit of cellobiose is

composed of two glucose anhydride molecules[Error: Reference source not found,Error: Reference

source not found]. The number of glucose molecules within a cellulose chain is known

as the degree of polymerization. The average degree of polymerisation for

native cellulose is in the order of 10,000 “chemical pulping” can reduce this to

range between 500-2000. [Error: Reference source not found] It is these long polymer chains

forming the cellulose that give the lignocellulosic biomass material much of its

tough fibrous nature.

Figure 2.1.1.1.1 shows the previously mention cellobiose unit, composed of the

two repeating Glucose Anhydride molecules. whilst figure 2.1.1.1.2 shows the

chemical structure of the cellulose with intra- and interchain hydrogen-bonded

bridging[8]

Figure 2.1.1.1.1 The Conformational Structure of the cellulbiose[Error: Reference source not found,Error: Reference

source not found]

7

Figure 2.1.1.1.2: The intra- and inter-chain hydrogen bonded bridging of the cellubiose

unit[Error: Reference source not found]

Cellulose pyrolysis: the generally accepted model for the pyrolysis of the

cellulose is represented by the Broido-Shafizadeh model, the mechanism was

originally suggested by Broido[9], was later simplified by Bradbury, Sakai and

Shafizadeh[10] shown below in figure 2.1.1.1.2

Figu

re 2.1.1.1.2 Broido-Shafizadeh model of cellulose pyrolysis[11]

Although the model seems to over simplify the nature of the chemical reactions

and physical interactions taking place it is still considered a good model to

represent the kinetic process of cellulose pyrolysis.

9 Broido A. and Weinstein M., “Kinetics of solid phase cellulose pyrolysis”. In Wiedemann (Ed.). Proc. 3rd Int. Conf. Thermal Anal., Birkhauser Verlag, Basel. (1971), pp. 285-296

10 Bradbury A.G.W., Sakai Y. and Shafizadeh F. “A Kinetic Model for Pyrolysis of Cellulose”. J. App. Pol. Sci., Vol. 23, Issue 11 (1979) pp. 3271 – 3280

11 Varhegyi G., Antal M., Jakab E., Szabo P.. “Kinetic Modeling of Biomass Pyrolysis”, J. Anal. and App. Pyrolysis, (1997) pp 73-87

Kc Char & Gases

K1 Cellulose Active Cellulose

Volatiles “tars” Kv

8

As suggested by Varhegyi et al.[Error: Reference source not found] This is because one

stage in the model may well represent a group of reactions working in parallel

or even the slowest (rate determining) step in a reaction sequence.

Varhegyi et al. also states that at around 250oC the reaction rate is slow and

yields both char and gasses equally, “as the temperature increases, the lower

branch of the reaction scheme becomes dominant.” [Error: Reference source not found] This

agrees with the findings of Bergman and his colleagues [12] that the

Depolymerisation of cellulose does occur at low temperature, but “at higher

temperature, this process takes place faster and to a larger extent.” [Error: Reference

source not found] Also the main volatiles formed varies with the torrefaction conditions

but “Higher temperatures lead to increased formation of these

components.”[Error: Reference source not found] Mohan et al. states cellulose degradation

occurs between 240-350 oC, and produces anhydrocellulose and levglucosan.[Error: Reference source not found]

These findings concur with the concept that the hemicellulose is the more

volatile component of the lignincellulosic biomass material, decomposing at

lower temperatures and being responsible for the majority of the volatiles and

gases released at the lower temperatures of torrefaction. Where as the

cellulose does not significantly depolymerise without the higher temperature

range of the torrefaction process, which could be why there is a further

increase in volatiles at these higher temperature ranges (>250oC).

Cellulose Use in the plant: In terms of physical properties cellulose creates

the tough, stringy, fibrous structure of woody biomass [Error: Reference source not found]. It is

this property that makes the biomass hard to grind up and mill into smaller

particles for use in applications like fluidised bed gasification.

The cellulose is grouped in bundles as shown in figure1.1.3.3. The cellulose

bundles are held together mainly through the hemicellulose, and partially

through the lignin

9

Figure 1.1.1.3 Typical Plant Cell Wall Arrangement [13]

2.1.1.2 Hemicellulose

Hemicellulose consists of a large number of heteropolysaccharides built from

six carbon sugars, hexoses (D-glucose, D-mannose, and D-galactose), five

carbon sugars, pentoses (D-xylose, and L-arabinose,) and 4-O-methyl

Glucuronic acid [Error: Reference source not found,Error: Reference source not found,Error: Reference source not

found,14,15]

Figure 1.1.2.1 shows the chemical structure of these monomers that make up

the hemicellulose biomass material.

a) b) c)

d) e) f)

10

Figure 1.1.2.1 Sugar monomer components of hemicellulose found in wood, (a)b-D-Glucose,

(b)B-D-Mannose, (c)B-D-Galactose, (d)B-D-Xylose (e)B-L-Arabinose (f)4-O-Methylglucuronic

acid[Error: Reference source not found]

There are also some amounts of other sugars, deoxyhexoses [Error: Reference source not

found,Error: Reference source not found].

The primary Hemicellulose components are formed from the sugars in figure

1.1.2.1, these are galactoglucomannans(glucomannan) and

glucuronoxylan(xylan). [Error: Reference source not found, Error: Reference source not found]

These components and their chemical structure within hemicellulose can be

seen in figures 1.1.2.2 and 1.1.2.3. Showing the major hardwood and major

softwood hemicellulose respectively

Figure 1.1.2.2: Major hardwood hemicellulose[Error: Reference source not found]

Figure 1.1.2.3 Major softwood hemicellulose[Error: Reference source not found]

11

Softwood hemicellulose have more mannose and galactose units but have less

xylose units, meaning galactoglucomannan(mannan) is the major softwood

hemicellulose.[Error: Reference source not found, Error: Reference source not found, Error: Reference source not found] as

well as having less acetylated hydroxyl groups than hardwood.[Error: Reference source not

found] Where as hard woods are high in glucuronoxylan(xylan), formed from the

xylose sugar monomer[Error: Reference source not found, Error: Reference source not found]

The chemical and thermal stability of hemicellulose is lower than that of

cellulose causing it to decompose at lower temperatures [Error: Reference source not

found,Error: Reference source not found]. Hemicellulose decompose over the temperature

range 130-194oC (with the majority of the weight loss occurring at

temperatures >180oC)[16] This is believed to be due to the lack of crystallinity

and lower degree of polymerisation, which is only 100-200, compared to

Cellulose’s in the order of 10,000 degree of polymerisation for woody

biomass[Error: Reference source not found,Error: Reference source not found].

Hemicellulose use in the plant: As shown in figure 1.1.1.3 hemicellulose

works to hold together the cellulose bundles within the lingnocellulose biomass

structure [Error: Reference source not found]. Bergman [Error: Reference source not found] also states that

the hemicellulose (as well as the lignin) is responsible for the “tenacity” of the

biomass. Hence this is why the torrefaction process works to weaken the

biomasses strength and resilience.

In addition to the hemicellulose destruction, torrefaction causes the previously

mentioned depolymerisation of the cellulose (the component responsible for

the biomasses fibrous nature) which adds to further weaken the biomass and

reduce its fiberous structure [Error: Reference source not found], increasing its ability to be

processed further.

12

2.1.1.3 Lignin

Lignin is a phenylpropane based polymer, it is the largest non carbohydrate

faction found within the lignocellulose.[Error: Reference source not found] It is constructed of

three monomers(as shown in figure 2.1.1.3.1): coniferyl alcohol, sinapyl

alcohol, and coumaryl alcohol, each of which has an aromatic ring with

different substituents[Error: Reference source not found,Error: Reference source not found]. The functional

groups associated with lignin (eg alderhyde groups, methoxy groups, alcoholic

hydroxyl groups) result in highly reactive molecules.[Error: Reference source not found]

A) B) C)

Figure 2.1.1.3.1: The monomers that form lignin; (A) P-Coumaryl alcohol, (B)Coniferyl alcohol, (C) Sinapyl alcohol [Error: Reference source not found]

It is the lignin component in the plant that classifies it as ‘woody’ [Error: Reference source

not found]. The lignin component works with the hemicellulose to form a sheath

that surrounds the cellulosic portion of the lignocellulosic biomass. [Error: Reference

source not found] The lignin is an amorphous cross-linked resin, cementing between

the woody cellulose fibre bundles and causing stiffening within the fibres [17].

This effect most likely results from covalent linking between ligning and

polysaccharides, which enhances the bond strength between the cellulose

fibers[Error: Reference source not found]. Unlike Cellulose, lignin cannot be depolymerised to

its original monomers.[Error: Reference source not found] Lignin is also designed to protect

the lignincellulose against insect attack.[Error: Reference source not found]

13

2.1.2 Extractives

Within the biomass there are a range of organic extractives, which can be

removed with the use of polar and non polar solvents.[Error: Reference source not found] The

extractives generally come from the cell wall of the biomass, the chemicals

include fats, fatty acids, waxes, alkaloids, phenols, proteins, terpenes, steroids,

simple sugars, pectins and many other chemicals and essential oils. [Error: Reference

source not found,18] In general softwoods will have a higher extractive content than

hardwoods.[Error: Reference source not found] Within the softwood Pinene is one of the most

common terpenes. (figure 2.1.2.1, structure A) [Error: Reference source not found] “Polymeric

esters of gallic-acid are usually associated with sugars”(Figure 2.1.2.1,

structure B) [Error: Reference source not found] conidendrin another example of an extractive

is found in spruce and hemlock(figure 2.1.2.1, structure C) [Error: Reference source not found]

and the extract Pinosylvin is an example of a polyphenol (Figure 2.1.2.1,

structure D) [Error: Reference source not found]

A) B)

C) D)

Figure 2.1.2.1: Chemical structure of some wood extractives (A)Pinene, (B)Gallic Acid, (C)Pineresinol, (D)Pinosylvin

14

2.2 Thermal Conversion Processes of Biomass

There are several different biomass conversion processes. Some of the

processes, such as combustion and co-combustion, aim to get energy directly

out of the biomass. The other processes tend to focus on creation of an

improved fuel/product, converting the biomass into a more useful product

depending on the application. In general the energy density of the fuel is

improved, along with other properties that are tailored to the desired

application of the product. For example fast pyrolysis is used to produce high

yields of bio-oil which has applications in chemical production and automotive

bio-fuels, where as gasification is used to produce a gas that can be used to

raise steam to create power, and drive gas turbines.

2.2.1 pyrolysis

Pyrolysis is a complicated series of thermally driven chemical reactions that

decompose organic compounds with the biomass. [Error: Reference source not found]

Pyrolysis occurs when biomass is heated in an inert atmosphere, (an absence

of oxygen) the aim is to produce a mixture of solid char, condensable liquids,

and gases.[Error: Reference source not found]

When the biomass is heated, like it is in pyrolysis, the biomass particle can

shrink. It has been found that the reduction in volume can be between 45-70%

though this is dependant on the type of biomass. [19] It has also been found that

the shrinkage affects the pyrolysis products. There is a trend to increase the

production of tars and reduce the production of the light hydrocarbon volatiles. [20] It is believed that initial shrinkage forms cracks on the surface of the

biomass particle which allows heat to much more quickly and easily penetrate

the biomass.[Error: Reference source not found] Cracks enhance the pyrolysis affect reducing

the thermal conversion time21

Pyrolysis proceeds at medium-high temperatures, and affects different

components of the biomass at varying temperatures dependant on the type of

plant material. Hemicellulose begins to pyrolyze at temperatures between 225

and 325 oC, and lignin pyrolysis is initiated between 250 and 500 oC [Error: Reference

source not found]

15

The resulting product composition contains various volatile organic and

inorganic compounds, the types and amounts depend on the type of biomass

processed, and the heating rate used.[Error: Reference source not found]

Some pyrolysis products include carbon monoxide, carbon dioxide, methane,

hydrogen and some light hydrocarbons, all of which are given off as a gas.

Some “vapour products with higher molecular weight can also be condensed to

a tarry liquid.”[Error: Reference source not found]

Table 2.2.1.0.1 Typical product yields (dry wood basis) obtained by different modes of

pyrolysis and wood thermal treatment[22]

Mode Conditions Liquid Char Gas

22 Bridgwater A.V., “Biomass Pyrolysis”, IEA Bioenergy Update 27, International Energy Agency, Biomass and Bioenergy,

6 Diebold J.P. and Bridgwater A.V. “Overview of fast Pyrolysis of biomass for the production of liquid fuels,” Developments in thermochemical biomass conversion, Volume 1, IEA bioenergy, edited by A.V. Bridgwater & D.G.B Boocock., Blackie Academic and professional, London (1994) pp. 5-18

8 Mohan D. Pittman C. U. and Steele P. H., “Pyrolysis of Wood/Biomass for Bio-oil:  A Critical Review” J. Energy Fuels, Vol. 20, American Chemical Society, Washington (2006), pp.848-889

13 Murphy J. D. and McCarthy K.” Ethanol production from energy crops and wastes for use as a transport fuel in Ireland” J. Appl. Energy (2005) Vol.82, pp.148-166

5 Rowell R.M. ‘Handbook of wood chemistry and wood composites’ CRC Press, New York (2005) pp.36-37

7 Yu Y. Lou X. and Wu H. “Some Recent Advances In Hydrolysis of Biomass in Hot-Compressed Water and Its Comparisons with Other Hydrolysis Methods” J. Energy and Fuels, Vol. 22, No.1 American Chemical Society, Washington (2007), 22 (1) pp. 46-60

12 Bergman P.C.A., Boersma A.R., and Kiel J.H.A., “Torrefaction For Entrained – Flow Gasification of Biomass” In: “The 2nd World Conf. and Technology Exhibition on Biomass for Energy, Industry and Climate Protection” Rome, Italy (2004) ECN-RX-04-04614 Rowell R.M., “The Chemistry of solid wood”; American Chemical Society, (1984)

15 Ebringerove A., Hromaθkova Z. and Heinze T., “Hemicellulose”, J. Adv. Pol. Sci.(2005) Vol. 186 pp. 1-67

16 Runkel R. O. H. and Wilke K. D., ‘ chemical composition and properties of wood heated at 140-200oC in a closed system without free space. Part II’ Holz Roh-u. Werkstoff (1951) pp. 260-270

17 Goldstein I. S., “Organic Chemicals from biomass” CRC Press, Inc.,Boca Raton, FL, (1981) pp 9-19

18 Rowell R.M. ‘Handbook of wood chemistry and wood composites’ CRC Press, New York (2005) pp.45-46

19 Davidsson K.O., Pettersson J.B.C., ‘Birch Wood Particle Shrinkage During Rapid Pyrolysis’ J. Fuel Vol. 81, Issue 3, (2002) pp. 263-270

20 Hagge M.J.and Bryden K. M. ‘ Modeling The Impact of Shrinkage on The Pyrolysis of Dry Biomass’ J. Chem. Eng. Sci. Vol. 57 Issue 14 (2002) pp. 2811-2823

21 Shen D.K., Luo K.H, Gu S., and Bridgwater A.V. ‘Analysis of wood structural changes under thermal radiation’ J. Energy and Fuels Vol. 23, Issue 2, (2009) pp. 1081-1088

16

FastModerate temperature, around 500C, short

hot vapour residents time ~ 1 sec75% 2% 13%

Intermediate

Moderate temperature, around 500C,

moderate hot vapour residents time ~ 10-20

sec

0% 20% 30%

Slowlow temperature, around 400C, long vapour

residents time30% 35% 35%

Gasificationhigh temperature, around 800C, long vapour

residents time5% 10% 85%

(source: Bridgwater A.V., “Biomass Pyrolysis”, IEA Bioenergy Update 27, International Energy

Agency, Biomass and Bioenergy)

17

2.2.1.1 Fast Pyrolysis

Fast Pyrolysis is utilized to optimize the production of condensable organic

vapors(bio-oils) from the biomass, with minimum production of gases and char.[Error: Reference source not found] The advantage of producing a liquid bio-oil is that it is

easier to transport and store as well as having the potential to be used as a

fuel or a base for chemical production. [Error: Reference source not found] With the potential

to hopefully replace its fossil fuel derived counter part. In addition Bio-oils are

counted as being CO2/GHG neutral, with relatively insignificant SOx emissions

due to the minimal sulfur in plant/wood biomass. [Error: Reference source not found] Bio-fuels

also produce 50% less NOx emmisions than diesel oil when used in a gas

turbine. [Error: Reference source not found]

Pyrolysis is defined as the thermal decomposition occurring in the absence of

oxygen[Error: Reference source not found] Fast pyrolysis has a residence time of, at most, a

few seconds.[23] Due to this short residence time the higher temperatures used

in fast pyrolysis are reached prior to the decomposition of the biomass. [Error:

Reference source not found] These higher temperatures cause a tendency towards a

mechanism involving depolymerization, as appose to what is believed to be a

melt[Error: Reference source not found]. Under the faster heating conditions and higher

temperatures the regular dehydration reactions that occur to form char become

less dominant and instead Organic volatiles are formed by cracking reactions,[Error: Reference source not found] due to this it is key to the process to bring the biomass

particle to the process temperature as quickly as possible, minimizing its

exposure to the lower temperatures that cause the formation of char. [Error: Reference

source not found,Error: Reference source not found] The fast pyrolysis reaction temperature is

normally around 500oC, with vapour phase temperature of 400-450oC[Error:

Reference source not found] The residences time as previously stated is under 2 seconds.[Error: Reference source not found] Rapid removal and cooling of the pyrolysis vapors form

bio-oil,[Error: Reference source not found,Error: Reference source not found] and prevents further cracking

of the desired product caused by the char, which acts as a cracking catalyst.[Error: Reference source not found] The desired product from this process is the bio-oil, which

can be generated in yields up to 75%(wt) of the feed, on a dry feed basis. [Error:

Reference source not found]

23 Bridgewater A. V. “The Production of Biofuels and Renewable Chemicals by fast Pyrolysis of Biomass” Int. J. Global Energy Issues, Vol. 27, No. 2, (2007) pp. 160-202

18

The process of fast pyrolysis process itself requires around 15% of the energy

stored in the feed.[Error: Reference source not found] The process creates char and gases

which can be used to supply this required energy, In this way process effluent

is minimized to just ash and flue gases. [Error: Reference source not found]

Some of the main chemicals from bio oil formed from fast pyrolysis include

levoglucosan (formed by the Pyrolysis of the cellulose in the absence of a

catalysts), hydroxyacetalderhyde, organic acids, and furfurals There are many

other oxygenated compounds, and they vary greatly depending on the

temperature, heating rate, biomass and reactor used. Water should be

removed from the biomass to minimize the water content of the bio-oil product [Error: Reference source not found, Error: Reference source not found,Error: Reference source not found,24,25]

2.2.1.2 Slow pyrolysis

As previously mentioned pyrolysis is a series of thermally driven chemical

reactions that occur in the absences of oxygen. Slow pyrolysis conditions tend

to emphasise char production most likely due to the long residence times. In

general slow pyrolysis can be achieved with lower process temperatures

ranging from 400-800oC[26] and longer residence times.[27]

Research has shown that temperature from 500-600oC seem to maximise the

production of volatiles/liquids[Error: Reference source not found,28] where as past these

temperatures the liquid yield seems to decrease marginally but there is a

noticeable decrease in the char production as more gases are produced. [Error:

Reference source not found,Error: Reference source not found]

24 Meier D., Oasmaa A., Peacocke G.V.C. “Properties of fast Pyrolysis of liquids: status of test Methods” Developments in thermochemical biomass conversion, Vol. 1, IEA bioenergy, edited by A.V. Bridgwater & D.G.B Boocock., Blackie Academic and professional, London (1994) pp 391-408

25 Milne T., Agblevor F., Davis M., Deutch S. and Johnson D. “A Review of Chemical Composition of Fast-Pyrolysis Oils from Biomass” Developments in thermochemical biomass conversion, Volume 1, IEA bioenergy, edited by A.V. Bridgwater & D.G.B Boocock., Blackie Academic and professional, London (1994) pp 409-424

26 Ucar S. and Karagoz S. ‘The Slow Pyrolysis of Pomegranate Seeds: The effect of temperature on the product yields and bio-oil properties’ J. Anal. Appl. Pyrolysis (2009) - article in press -

27 Mesa-Perez J.M., Cortez L.A.B., Rocha J.D., Bossard-Perez L.E. and Olivares-Gomez E. ‘unidimensional heat transfer analysis of elephant grass and sugar cane bagasse slow pyrolysis in a fixed bed reactor’ J. Fuel Processing Tech. Vol. 86 (2005) pp.565-575

28 Apaydin-Varol E., Putun E., and Putun A.E. ‘Slow pyrolysis of pistachio shell’ J. Fuel Vol 86 (2007) pp. 1892-1899

19

Research also shows that during the slow pyrolysis there are three main zones

that form within the particle. The outer most zone allows for char formation, this

zone will slowly deepen/thicken and inhibit heat transfer further into the

particle.[Error: Reference source not found] There is another zone beyond this char layer

where the heat has penetrated deep enough and the pyrolysis reactions are

taking place.[Error: Reference source not found] Then finally the inner zone where the

pyrolysis hasn’t occurred. [Error: Reference source not found]

It is also shown that increasing particle size with Slow pyrolysis leads to a

decrease in gas formation, this could likely be due to the char layer formed

reducing the heat transfer coefficient into the particle[Error: Reference source not found, 29]

20

2.2.2 Gasification

Gasification is the high temperature (>750oC) conversion of solid, carbon

based fuels into flammable gas mixtures. This gas, sometimes called produce

gas, consists of carbon monoxide, hydrogen, methane, nitrogen, carbon

dioxide and smaller quantities of longer chained hydrocarbons. [Error: Reference source

not found] The process is designed to produce a low to medium energy fuel gas, or

can also be used to produce synthesis gases for the manufacture of chemicals

or hydrogen. [30] The fuel gas produced from biomass tends to have a relatively

low heating value 5-10(MJ/Nm3) [31] which stems from the low energy density of

the biomass, wood for example has an energy density of around 18MJ/Nm3. [32]

This energy density is not idea for gasification fuels, and instead it is

suggested that gasifiers running at temperatures slightly above 900oC should

use fuels that have a LHV of around 23MJ/Nm3.[Error: Reference source not found]

The overall process is endothermic, the heat required may be provided from

an external source to the gasifier, or alternatively it can be provided by

internally burning part of the fuel entering the gasifier.[Error: Reference source not found]

The high volatile content of biomass (70-90 wt%) compared to coal (typically

30-40 wt%),along with the high reactivity of its char, gives biomass good

potential gasification fuel [Error: Reference source not found]. The main problem with biomass

though is its thermal instability, which can cause the formation of condensable

tars.[Error: Reference source not found] Tars will cause problems in the down stream

equipment, ‘such as choking and blockage’[Error: Reference source not found]

Due to this problem there have been issues with the cost and convenience of

biomass gasification, which in turn have limited its application to special

situations and niche markets. [Error: Reference source not found]

30 Klass L.D. ‘Biomass for Renewable Energy, Fuels and Chemicals’ Academic Press., California (1998) pp. 271-332

31 Brammer J. G. ‘Combustion Gasification and Co-firing’, CP4008 Energy Products From Biomass, Aston University, Chemical engineering and applied science building, on 21st October 2008

32 Prins M. J., Ptasinski K. J. and Janssen F. J. J. G. “From coal to biomass gasification: Comparison of thermodynamic efficiency” J. of Energy (2007) Vol. 32 Issue 7 pp.1248-1259

21

Heating and Drying Pyrolysis Gas-Solid ReactionsGas-Phase Reactions

Thermal front penetrates Porosity increases

Figure 2.2.2.1 The four main stages of gasification.[Error: Reference source not found]

The gasification process has four main stages; shown above in figure 2.2.2.1

Drying, Pyrolysis (devolatilisation), Volatile Combustion, and finally Char

Gasification and Gas Reforming. [Error: Reference source not found] The figure above shows

the several steps that occur during the gasification of biomass.. [Error: Reference source

not found]

22

Volatile gasses:CO, CO2, H2, H2O, light hydrocarbons

and tar

Exothermic reactions

Endothermic reactions

CO + H2OCO2 +H2

CO+ 3H2CH4 +H2O

2.2.3 Combustion of Biomass

Right up to the early 20th century most of industrialised society relied on the

combustion of biomass and related thermal processes for heating, cooking,

chemical production, creating charcoal, generating steam and hence also the

generation of mechanical and electrical power.[33]

Combustion of wood based biomass can be represented by the oxidation of

the empirical formula of cellulose[Error: Reference source not found] (C6H10O5)n:

(C6H10O5)n + 6nO2 6nCO2 + 5nH2O

This formula represents the complete combustion of the wood based biomass.

With complete combustion only CO2 and water are formed, and the reactant is

completely consumed producing radiant and thermal energy. [Error: Reference source not

found] This complete combustion ideal is very hard to achieve. Much research

has been carried out in the field of solid fuel combustion to understand the true

mechanism and kinetics of the process.

“An empirical view of combustion involves the evaporation of high energy

volatiles such as terpenes, which burn in the gas phase with flaming

combustion” [Error: Reference source not found] the lignocellulose components under the

influence of high temperatures decompose to form pyrolysis products, the

cellulose components are converted to combustible (and some non

combustible volatiles), which are then burnt in the gas phase with flaming

combustion. [Error: Reference source not found] The lignin contributes to the residual char,

which burns at a lower rate by surface oxidation, represented by glowing

combustion. [Error: Reference source not found]

In industry one of the largest wood fuelled power stations is located in

Burlington, Vermont. It generates 50MW of net production, and requires an

equivalent dry wood rate of 925 t/day With a thermal energy consumption of

13MJ of fuel per kWh produced, and a thermal efficiency of around 27.5% [34]

33 Klass L.D. ‘Biomass for Renewable Energy, Fuels and Chemicals’ Academic Press., California (1998) pp.191-224

34 Tewksbury C. ‘Energy from Biomass and Wastes X’ (D.L.Klass ed.) Elsevier applied science publishers, London, and institute of gas technology, Chicago (1987) p.555

29 Hu G., Fan H., Liu Y., ‘Experimntal studies on pyrolysis of Datong coal with solid heat carrier in a fixed bed’ J. Fuel Processing Tech. Vol. 69 (2001) pp. 221-228

23

If this is compared to other power stations, which make use of fossil fuels, the

overall thermal efficiencies at such power stations range from 28-40% and an

average thermal energy consumption of 11MJ of fuel per kWh produced. [Error:

Reference source not found] Which clearly shows the potential for fuel savings that

conventional fossil fuels based power stations have over those that would run

purely on biomass.

24

2.3 Torrefaction of Biomass

2.3.1 The Torrefaction Process

Biomass as a fuel has several undesirable properties, it has a low

calorific/heating value, a high moisture content, it is hygroscopic in nature and

smokes when combusted[Error: Reference source not found,Error: Reference source not found] These

unwanted properties are vastly improved with the torrefaction process.

Torrefaction is a process for the thermal treatment of biomass. The process

heats biomass in an inert atmosphere up to a maximum temperature of

300oC[Error: Reference source not found,35] past this recommended limit (300oC) pyrolysis

processes start[36]. Torrefaction may also be referred to as mild pyrolysis.

Torrefaction is generally seen as a pre-treatment step, the aim of which is to

improve the properties of the biomass. Torrified biomass has similar

characteristics to that of low grade coal in terms of the van Krevelen coal rank

parameter,[37] and could be used as a substitute for charcoal in a range of

applications[Error: Reference source not found]

There are other possible uses of torrefaction as a pre treatment.

Untreated biomass will retain its fibrous nature due to the cellulose present in

the lignincellulosic material the biomass is made from. This means the

biomass will not be easily reduced into small spherical particles, (which would

be necessary for use in a fluidised bed gasifier or fluidised bed pyrolysis

reactor) hence the size reduction process is expensive. The torrefaction

process, particularly at higher temperatures (250-300oC) will depolymerise the

cellulose within the biomass.[Error: Reference source not found] This gives the biomass many

improved properties. One such property is the biomass becomes much easier

to grind/cut into smaller particles. The heat treated biomass has improved

grind-ability because the long cellulose chains have been depolymerised, [Error:

Reference source not found] resulting in an increase in cellulose crystalinity[38] The

35 Zanzi R., Tito Ferro D., Torres A., Beaton Soler P. and Bjornbom E. “Biomass Torrefaction” [accessed 26th Jan. 09] available from ‘http://hem.fyristorg.com/zanzi/paper/zanziV2A-17.pdf’

36 Bourgeois, J.P. and Doat J., Torrefied wood from temperate and tropical species: Advantages andprospects, Bioenergy 84, Proceedings of an Int. Conf. on bionergy in Göteborg, Vol.3, 1985, pp.153-159,

37. Bridgeman T.G, Jones J.M., Shield I., Williams P.T. “Torrefaction of reed canary grass, wheat straw and willowto enhance solid fuel qualities and combustion properties”. J. Fuel (2008) Vol.87, pp.844-856

25

torrefaction of woody biomass can reduce the power consumption of the size

reduction process by 50%-85% depending on the conditions used [Error: Reference

source not found]. In addition “because of the shortening of the fibres through

torrefaction, the particles resulting from the size reduction process become

more spherical” [Error: Reference source not found]

The torrefaction process also weakens the tenacious nature of the biomass at

all temperature ranges because of the degradation of the hemicellulose which

is responsible for holding together the cellulose bundles. [Error: Reference source not found]

Bergman et al. also showed the higher the temperatures used in the

torrefaction process the better the ability of the biomass to be mechanically

processed[Error: Reference source not found]. This leads to the conclusion that torrefaction

has Ideal use as a pre treatment, in particular for use in a fluidised bed

biomass processes such as gasification or possibly in certain types of pyrolysis

processes, because of the improved physical properties of the torrified

biomass. There may also be considerations for use in suspension firing

combustors, though this will be limited to co-combustion with coal in such

applications because the suspension fired combustors are generally in a size

range of over 100MW. [Error: Reference source not found] Due to this scale the possibility of

using torrified biomass as the only feed becomes unlikely, the collection and

transport of the required quantity of biomass will be expensive and may not

allow for a reasonable net energy gain. The torrefaction processing on such a

large scale would also require more research.

In addition to the improved physical properties, the torrified biomass has

improved chemical properties. These improved chemical properties could

potentially be utilised effectively in applications within gasification.

Some of the disadvantages of wood biomass for use in gasification include the

low energy density of wood, typically 18MJ/kg and its high moisture content as

a result of its hygroscopic character, which even after drying are around 10wt%[39] It has also been found that higher gasification efficiencies can be achieved

by using fuels with lower O/C ratios.[40] Woody biomass has been found to have

around 50 wt% carbon and 45 wt% oxygen[41], compared to torrified biomass

that has around 60-64wt% carbon and 30-33wt% oxygen. [Error: Reference source not found]

26

As previously mentioned the decreased O/C ratio would give the torrified

biomass better potential for use in a gasifier due to the improved efficiency

over the woody biomass. Although torrefaction is an improvement on the

woody biomass the O/C ratio is still greater than that of charcoal (82 wt%

carbon, 12wt% oxygen[Error: Reference source not found]) or coal, which has around 60–85

wt% carbon and 5–20 wt% oxygen.[Error: Reference source not found] The Van krevelen

scale can be used to compare this relation ship between biomass and coal and

their relative O/C ratios as shown below in figure 2.3.2.1.

Figure 2.3.2.1 Van Krevelen diagram showing various fuels’ relative energy

densities.[Error: Reference source not found]

The decreasing O/C ratio represents an increase in the energy density of the

fuel on the scale. The higher biomass O/C ratios would have a negative effect

on the efficiency of a gasifier running on biomass. Another problem with the

wood biomass feedstock is its optimum gasification temperature is rather low

caused by its high O/C ratio this means that the wood is generally over-

oxidized in conventional gasifiers leading to thermodynamic losses. [Error: Reference

source not found] Research shows that generally the optimum gasification

temperature for woody biomass is around 782oC(for biomass with average

composition CH1.4O0.6)[Error: Reference source not found] which is reflected in figure 2.3.2.2

27

FIGURE 2.3.2.2: Gasification temperatures for fuels of varying O/C and H/C ratios[Error: Reference

source not found]

This could be where the torrefaction process could help, the torrefaction

process will lower the O/C ratio of the biomass[Error: Reference source not found,42] and

reduce the moisture content to around 0-3% [Error: Reference source not found] Hence it is

possible to reduce the thermodynamic losses by prior thermal pre-treatment,[Error: Reference source not found] which should in turn improve the efficiency of gasification

of the fuel at higher temperatures. Research also shows higher temperatures

of torrefaction (250-300oC) achieve more favourable results for gasification

feed stocks in a shorter time span.[Error: Reference source not found]

42 Nguila Inari G., Pétrissans M., Lambert J., Ehrhardt JJ. and Gérardin P. “XPS characterization of wood chemical composition after heat-treatment.”Surface Interface Anal. (2006) Vol.38, pp1336-1342.

38 Gérardin P., Nguila Inari G., Mounguengui S., Dumarcay S. and Pétrissans M., “Evidence of Char Formation During Wood Heat Treatment by Mild Pyrolysis” J. pol. Degredation and stability,(2007) Vol. 97, pp.997-1002

39 Prins M.J., Ptasinski K.J. and Janssen F.J.J.G. “More Efficient Biomass Gasification Via torrefaction” J. Energy (2006) Vol.31, pp.3458-3470

40 Prins M.J., Ptasinski K.J., Janssen F.J.J.G. “coal to biomass gasification: comparison of thermodynamic efficiencies.”, Proceedings of the 16th Int. Conf. on Efficiencies, Cost, Opimization, Simulation and Environmental Impact of Energy Systems(2003) pp. 1097–103

41 Prins M. J., Ptasinski K. J. and Janssen F. J. J. G. “From coal to biomass gasification: Comparison of thermodynamic efficiency” J. of Energy (2007) Vol. 32 Issue 7 pp.1248-1259

28

Process gases and volatiles released: As the biomass is heated it undergoes a series of physical and chemical

processes. Firstly the biomass dries out with the removal of moisture from the

biomass. At temperatures over 160oC further water removal occurs, the water

is formed from chemical reactions, and removed through a thermo-

condensation process[Error: Reference source not found] at this temperature range carbon

dioxide gas is also formed. Between 180 and 270oC hemicellulose

degrades[Error: Reference source not found] and from temperatures over 250OC the cellulose

depolymerises to a much greater degree than previously. [Error: Reference source not found]

There is little mention of the torrefaction process having any significant affect

on the lignin within the biomass, hence it is reasonable to assume that the mild

pyrolysis (torrefaction) process does not reach high enough temperatures to

significantly breakdown this part of the lignocellulosic biomass material.

Although there is some mention of lignin undergoing thermal cross linking [Error:

Reference source not found] which would most likely disrupt the previously formed

covalent linking between the ligning and polysaccharides [Error: Reference source not found],

this disruption may well further weaken the bond strength between the

cellulose fibers, if it were to occur.

The main volatiles produced from the torrefaction process consists of Water,

acetic acid, methanol, carbon monoxide, carbon dioxide, and furan derivatives.[Error: Reference source not found] In addition to these products there are also some phenols

produced.[Error: Reference source not found] Mamleev et al.[43] shows that low-molecular

acids play a significant catalytic role in the products produced during pyrolysis.

This is expanded on in a proposal by Géradin et al. [Error: Reference source not found] who

proposes that Acid degradation catalysed by the formation of acetic acid during

the hemicellulose degredation is the key step in the formation of furfural,

alderhydes and other volatile by-products.

At the higher temperature scale of the torrefaction process, with temperatures

in excess of 270oC, there is more formation of phenols as well as cresols and

other heavier products.[Error: Reference source not found] It is likely due to the process

beginning to become more like pyrolysis in its nature at this high temperature

29

range, causing increased breakdown of the cellulose and even possibly to a

lesser extent the lignin.

The relative yields of the volatiles depend on the conditions of the torrefaction

process and the type of biomass used. Whether the biomass is a hard wood or

soft wood can depict whether the hemicellulose is xylan or mannan based. [Error:

Reference source not found,Error: Reference source not found,Error: Reference source not found] Hence It is expected

that the type of woody biomass used will have a big effect on the volatiles

released, because of research[Error: Reference source not found,44] that shows hemicellulose

to be the main reactant in the torrefaction process.

30

2.3.2 The Result & Gains of Torrefaction

Torrefied biomass has been found to retain between 70-95% of its original

mass.[Error: Reference source not found,Error: Reference source not found,45] depending on the type of

biomass, the temperatures it was exposed to and the time it was exposed to

that temperature. The product from the torrefaction process is dry and

hydrophobic,[Error: Reference source not found] having an equilibrium moisture reduction of

about 73%[46] The torrefied biomass will also have an increased energy density

relative to the original biomass.[Error: Reference source not found] The moisture content of

the torrified biomass is below that of the dried biomass feed, dropping from

around 10% to between 0-3%[Error: Reference source not found] and the heating value has

increased by 5-25%[Error: Reference source not found,Error: Reference source not found] The energy

retained in the biomass can range between 80-97% (and most commonly is

around 90%)once again dependant on the temperature ranges and biomass

used. [Error: Reference source not found,Error: Reference source not found] The energy remaining in the

torrified sample could be calculated using a method developed by S.W.

Channiala & P.P. Parikh that can accurately predicted by the higher heating

value (HHV) of a fuel, for a range of different fuels. [47] The experimentally

derived formulae calculates this value from the fuel composition with an

average absolute error of 1.45% [Error: Reference source not found] The equation is shown

below:

Higher heating Value equation (1)[Error: Reference source not found]

HHV = 0.3491C + 1.1783H + 0.1005S -0.1034O – 0.0151N – 0.0211A

(Where:C=carbon weight%, H=hydrogen weight%, S=Sulphur weight%,

O=Oxygen weight%, N=nitrogen weight% and A=ash weight%)

Another HHV correlation produced by Friedl et al.[48] calculated Linear

regression models to predict a HHV of a biomass fuel from its elemental

45 Arcate, J. “New process for torrefied wood manufacturing” Bioenergy update, vol. 2, No. 4, April 2000

46 Felfi F.F., Luengo C.A., Beaton P.A. & Suarez J.A. ’Wood Briquette Torrefeaction’ J. Energy For Sustainable Development, Vol. 9, No 3, (2005) pp. 19-22

47 Channiwala S. W., and Parikh P. P. ‘A Unified Correlation for Estimating HHV of Solid, Liquid and Gaseous Fuels’ J. Fuel Vol. 81 (2002) pp. 1051-1063

31

composition. The models were calculated by ordinary least squares regression

(OLS) and by partial least squares regression (PLS).

HHV(OLS model) = 1.87C2 − 144C − 2820H + 63.8C

×H + 129N + 20147

HHV(PLS model) = 5.22C2 − 319C − 1647H + 38.6C

×H + 133N + 21028 (5)

After analyzing the OLS and PLS models and results a final model for the

prediction of the HHV of biomass from elemental data was produced

Higher heating value equation (2):

HHV = 3.55C2 − 232C − 2230H +51.2CH + 131N + 20, 600

(Where: C=carbon weight%, H=hydrogen weight%, O=Oxygen weight% and

N=nitrogen weight%)

In the equation coefficients were rounded to three significant digits. The model

claims to give a standard error of calibration of 337 kJ/kg. [Error: Reference source not found]

The carbon content of the solid torrified biomass product shows a trend to

increases with higher temperatures of torrefaction, and longer resident times.[Error: Reference source not found] whilst the hydrogen and oxygen content deceases.[Error:

Reference source not found] This is what causes the increased energy density of the

product. The decrease in the O/C ratio after the heat treatment[Error: Reference source not

found] could be due to the degradation of the hemicellulose to volatile by-

products, and the thermal cross linking of the lignin [Error: Reference source not found], but it

is suggested by Géradin et al. [Error: Reference source not found] that these aren’t the sole

factors contributing to the decrease in the O/C ratio, and on analysis believes

that there is some char formation during the torrefaction process, despite this

having been well documented occurring at temperatures above that of the

torrefaction process(300-450oC).

32

2.3.3 The Economic Potential of the Torrefaction Process

The torrefaction process increases the energy density of a fuel; the biomass

will lose mass, but retain higher amounts of its energy relative to the mass lost.

Figure 2.3.3.1 shows how the process can lead to this energy densification.

Figure 2.3.3.1: the effect of torrefaction on the energy density of biomass[49]

Increasing a fuels energy density can save costs on transportation and

storage, because it allows for storing and transporting higher amounts of

energy within the same volume. F. Felfi et al.[Error: Reference source not found] carried out a

range of torrefaction experiments on wood briquettes, table 2.3.3.1 show some

results from the torrefaction process carried out over a range of temperatures

and residence times.

Table 2.3.3.1: Energy and Weight yields of wood briquettes after the torrefaction process

Temperature(oC) Time (hr) Weight yield (%) Energy Yield (%)220 0.5 94 97

1 90 94

49

? Kiel J. ‘Torrefeaction for biomass upgrading into commodity fuels’ ECN, IEA Bioenergy task32 workshop “fuel shortage, handling and preparation and system analysis for biomass combustion technologies” Berlin, (2007)

43 Mamleev V., Bourbigot S., Les Bras M., and Yvon J. “The facts and Hypotheses relating to the Phenomenological model of cellulose pyrolysis: interdependence of the steps” J. of anal. and app. pyrolysis, Vol 84, Issue 1, (2009) pp. 1-17

44 Gaur S. and Reed T.B. “Thermal Data for Natural and Synthetic Materials” Marcel Dekker (1998)

48 Friedl A., Padouvas E., Rotter H. and Varmuza K. ’Prediction of heating values of biomass fuel from elemental composition’ J. analytica Chimica Acta, Vol. 544 (2005) pp. 191-198

Gas & volatiles

Torrefaction

BiomassTorrified Biomass

MassEnergy

0.1

1 0.9

1

0.3

0.7

Energy densification (E/kg) = 1 x ( / ) = 1.30.9 0.7

33

1.5 72 77

2500.5 74 801 65 72

1.5 60 67270 0.5 56 65

1 54 621.5 43 50

(source: Felfi F.F., Luengo C.A., Beaton P.A. & Suarez J.A. ’Wood Briquette Torrefeaction’ J. Energy For Sustainable Development, Vol. 9, No 3, (2005) pp. 19-22)

The data shows that the energy loss is noticeably less than the mass loss, and

hence that energy densification has been achieved. If torrified biomass was to

then under go pelletisation the energy density of the fuel could be further

increased. Giving further reductions to storage and transportation cost.

Kiel et al. also looked into pelletisation, and the preliminary findings indicated

that the pelletisation process was easy, and had a low energy input

requirement, and the quality of the pellet was dependant heavily on the

conditions used in the process, but was generally very good. [Error: Reference source not

found]

Pellets formed from torrified biomass retained their hydrophobic nature. In

addition further increases in energy density and heating value were seen.

Table 2.3.3.2 shows a comparison between the treated and untreated biomass

fuels.

Table 2.3.3.2: property comparison between treated and raw biomass[Error:

Reference source not found]

Properties Unit Wood Torrified biomass Wood pellets

Torrified biomass pellets

Low High Low HighLower Heating

value (dry basis)

MJ/kg 17.7 20.4 17.7 17.7 20.4 22.7

Mass density Kg/m3 550 230 500 650 750 850

Energy density GJ/m3 5.8 4.6 7.8 10.5 14.9 18.4

(source: Felfi F.F., Luengo C.A., Beaton P.A. & Suarez J.A. ’Wood Briquette Torrefaction’ J. Energy For Sustainable Development, Vol. 9, No 3, (2005) pp. 19-22)

34

As table 2.3.3.2 shows there is a marked increase in energy density through

pelletisation and torrefaction. Combining the processes show an increase in

energy density of 250-300% with the product reaching a respectable LHV of up

to 22.7 MJ/kg. [Error: Reference source not found] This kind of improvement in the fuels

properties should noticeably improve the economics of transportation and fuel

storage.

35

As well as the experimental work previously mentioned kiel et al. & ECN have

looked into a possible process for the production of torrified biomass pellets.

The process shown in figure 2.3.3.2 makes use of the volatiles released from

the torrefaction process as a fuel to assist the torrefaction & pelletisation

process. The volatiles are separated from the inert gas used in torrefaction and

mixed with air and a utility fuel, the fuels are then combusted producing a flue

gas. The heat produced in the form of a flue gas is then used to drive the

torrefaction process itself, with waste heat being used to dry the biomass feed

prior to torrefaction. Producing the pellets in this way gives high energy

efficiency. (over 90%)[Error: Reference source not found]

Figure 2.3.3.2: Torrified biomass pellet production flow diagram [Error: Reference source

not found,50]

Kiel et al. have also produced a cost comparison between this proposed

process, and pelletisation of the biomass without the torrefaction step. Figure

2.3.3.3 shows a capital investment comparison between the two processes.

50 Bergman P.C. A. and Kiel J. H. A. ‘Torrerfaction for Biomass upgrading’ Puiblished at 14th European conference and exhibition, Fracne (2005)

36

Figure 2.3.3.3: Total Capital Investment Comparison between Torrified Pelletisation and Conventional Pelletisation[Error: Reference source not

found]

Figure 2.3.3.3 clearly shows that all though the extra torrefaction process

accounts for nearly 3million euros of total capital investment (half the cost of

the conventional process) savings on storage and processing costs make the

overall impact of the process less expensive than might have otherwise been

expected.[Error: Reference source not found] The combined torrefaction and pelletisation

(T&P / TOP) process is shown to only cost around an extra 20%-25% capital

cost. [Error: Reference source not found] When the saving on transportation costs are also

considered the TOP process has been shown to have favorable economics

over conventional pelletisation, for certain applications [Error: Reference source not found], as

reflected in figure 2.3.3.4

37

Sawdust

0.7 €/GJ

TOP Process(South Africa)

2.0 €/GJ

Logistics

< 2.0 €/GJ

Sawdust

0.7 €/GJ

Conventional Pelletisation

(South Africa)2.3 €/GJ

Logistics

2.9 €/GJ

Co-firing coal fired power stations or

entrained flow gasifiers North-west Europe

< 4.7 €/GJ

5.9 €/GJ

Figure 2.3.3.4: economic comparison of the TOP process and the conventional biomass pelletisation process[Error: Reference source not

found]

Summary of Torrified Biomass Properties:

Hydrophobic Nature and lower moisture content[Error: Reference source not

found,Error: Reference source not found,Error: Reference source not found,Error: Reference source not found]

Higher calorific value achieved, compare to the untreated

Biomass[Error: Reference source not found,Error: Reference source not found]

Less smoke when burnt[51]

Suitable for various applications as a fuel (co-combustion &

gasification)[Error: Reference source not found,Error: Reference source not found,Error: Reference

source not found,Error: Reference source not found,Error: Reference source not found,52]

Can substitute charcoal/wood briquettes/biomass for use as a

domestic fuel[Error: Reference source not found,Error: Reference source not found]

Increased energy density, leading to improved storage and

transportation cost efficiencies over untreated biomass[Error: Reference

source not found,Error: Reference source not found,Error: Reference source not found,Error: Reference source

not found,Error: Reference source not found,Error: Reference source not found,Error: Reference source not

found,Error: Reference source not found]

Pelletisation further improves torrified biomasses properties[Error:

Reference source not found]

Significantly improved/easier cutting and grinding ability over

untorrified biomass, leading to reduced energy costs for

51 Prins M J., Ptansinski K. J. and Janssen F. J. J. G. ‘torrefaction of wood part 2. analysis of products’ J. Anal. Appl. Pyrolysis Vol. 77 (2006) pp. 35-40

52 Bergman P. C. A., Boersma A. R., Kiel J. H. A., Prins M. J., Ptasinski K. J. and Janssen F. J. J. G. ‘Torrefaction For entrained-Flow Gasification of Biomass’ presented at “ the 2nd World Conference and Technology Exhibition on Biomass for Energy, Industy and Climate Protection” Italy, (2004)

38

processing.[Error: Reference source not found,Error: Reference source not found,Error: Reference

source not found]

39

3 Experiments and Planning

In this report four different types of biomass will be tested on, Beech wood, a

hard wood, Willow, a soft wood, Green Miscanthus, an energy crop and Rape

straw, an agricultural waste.

3.1 Sample Preparation

Each one of the four feed stocks will be a homogenous sample of particles

ranging in size from 0.15mm to 0.25 mm. The raw feed stocks will then

undergo torrefaction sample preparation in a thermogravimetric analyser; the

Pyris 1 TGA apparatus will torrify the four different feed stocks in an inert

nitrogen atmosphere, at torrefaction temperatures: 200oC, 225oC, 250oC,

275oC and 300oC. The high-precision balance will be able to accurately

measure the mass losses of each sample as the torrefaction process takes

place. The torrefaction samples will be prepared in this way, to record the

mass losses for comparison between feed stocks.

The heating rate on the thermal gravitational machine will be as follows:

[I] The raw biomass feedstock will enter the reactor which will be around

50oC, The feedstock will be held at this temperature for five minutes.

[II] From here the biomass will be heated up in the reactors miniature

electric oven to a temperature of 105oC at a heating rate of 10oC/minute

[III] The TGA will hold at 105oC for 5minutes. This stage removes the

moisture from the biomass, and allows the moisture content of the

feedstock to be accurately measured, for each of the torrified samples.

[IV] The sample is then heated from 105 oC up to the desired torrefaction

temperature. The heating rate is once again 10oC/min.

40

[V] Once the desired torrefaction temperature is reached the

thermogravimetric analyser will hold at the desired temperature for

15minutes.

[VI] Once the sample has been torrified the reactor will be cooled down to

50oC so when the sample is removed it does not undergo any

combustion reactions.

Figure 3.1.1 shows a graphical representation of the heating profile.

Figure 3.1.1: torrefaction heating rate applied to the biomass feed stocks

3.2 High Temperature Pyrolysis of Feed Stocks

As well as carrying out the torrefaction process on the raw feed stocks the

TGA will be used to carry out feedstock pyrolysis in a nitrogen atmosphere up

to a temperature of 900oC. The standard BERG pyrolysis method will be used

for the pyrolysis of the feed stocks. This will allow the accurate measurement

of the char present in each of the feed stocks, and also allow the water content

of the raw feed stocks to be measured. After calculating the char and water

content of the feed stocks the volatile content can also be worked out by

Heating Rate Profile

0 10 20 30 40 50 60 70

Time (min)

Torrefaction Temperature

105oC

41

I

II

III

IV

V

VI

Tem

pera

ture

(o C)

difference, giving the over all composition of the feed stocks. The heating rates

applied in this experiment will be exactly the same as those used in the

torrefaction process, and the hold times will also be the same. The difference

will be the peak temperature reached will be 900oC as appose to the range

used in torrefaction (200-300oC)

3.3 Slow Ashing of Samples

Slow ashing will be conducted using the Thermogravimetric analyser, with the

prepared set of samples being slowly heated in air. The heating rate will be

5oC/min, but follow the standard BERG heating profile used for the torrefaction

of the feed stocks. The reactor will be held at 50oC for 5minutes, then heated

up to 105oC at 5oC/min, held at 105oC for 5 minutes, then further heated

(5oC/min) up to a peak temperature of 575oC. The peak temperature is then

held for 15minutes, before the sample is cooled back down to 50oC. The peak

temperature is set to 575oC because past this temperature the inorganics that

form the ash may begin to combust affecting the mass loss of the samples.

The samples will consist of the raw biomass, 200oC, 225oC, 250oC, 275oC &

300oC across the four varieties of biomass. By combustion of all the volatiles

and fixed carbon in an air atmosphere it will be possible to accurately measure

the inorganics/ash content present in the char of all the samples, and hence

calculate the fixed carbon in each of the biomass sample sets. The derivative

of the slow ashing mass loss profile (d mass/d time) will give the rate of mass

loss over the temperature range 50-575oC, this should allow the identification

of the regions/temperatures where the volatiles are combusted, and where the

char is combusted, as mentioned by klass [Error: Reference source not found] hopefully, with

clear distinction between these two regions, it will be possible to see how the

balance between relative volatile content and char content (weight %) is shifted

with the torrefaction process.

42

3.4 Pyrolysis of Prepared Samples & Feed stocks

Once again the TGA can be utilised with the standard BERG pyrolysis method

to pyrolyse the sample sets. The heating rate will be 10oC/min. in a nitrogen

atmosphere and the heating profile will once again follow the profile used for

torrefaction, the exception is this time the peak temperature reached will be

600oC, to ensure each torrified and raw feed stocks are pyrolysed. This will

allow a comparison between feed stocks after torrefaction, and analyse how

the torrefaction process affects the biomass with respect to volatile content.

Pyrolysis should show the torrified biomass contain less volatiles than the raw

biomass and increasing torrefaction temperatures further reduce volatile

content.

3.5 H,C,N Analysis

H,C,N analysis will be conducted on the raw biomass feed stocks as well as

the prepared torrified samples of each feedstock. Analysis will find the

elemental chemical make up of the biomass and torrified biomass, allowing the

carbon content, hydrogen content, and nitrogen content to be found as a

weight percentage of the sample. The oxygen content is assumed to constitute

the remainder of the biomass, and shall be calculated by difference.

This elemental analysis will allow calculations to be carried out to work out the

energy content of the samples. The equations mentioned in section 2.3.2 can

be utilised with the ash content derived from slow ashing, to calculate the

Higher Heating Value (HHV) of the samples. This will allows a comparison of

the feed stocks and how torrefaction affects the heating value of the feedstock

over the torrefaction temperature ranges proposed in section 3.1.

In addition to the higher heating value, atomic ratios of O/C and H/C can be

calculated by converting the weight percentage values to a mole basis. The

atomic ratios are then able to be used to compare the samples to each other

and to existing fuels on a Van Krevelen diagram

43

3.6 PY-GC-MS of Feed Stocks

A CDS-2000 pyroprobe and CDS AS-2500 auto sampler coupled to a gas

chromatograph mass spectrometer will be utilized to recreate the effect of

pyrolysis and torrefaction on the feed stocks, allowing for the analysis of the

volatiles that are released from both processes, and a comparison between

them.

The samples will be 1mg and 3mg of the feed stocks for the pyrolysis runs and

torrefaction runs respectively. The sample is loaded into a quartz tube and

placed in the centre of an inductive heated coil. The samples are heated with a

heating rate of 3000oC/s up to a temperature of 300oC which is held for 45

seconds for torrefaction. For replication of pyrolysis conditions the samples is

heated to 600oC and held for 15 seconds. The difference in residence time is

such that adequate amounts of volatiles are released for measurement.

The gas chromatograph will use a split ratio of 1:25 to separate the molecules,

the injector and detector temperatures were both at 280oC and the carrier

velocity was at 38cm/s. Separation was achieved using a semi polar column

DB-1701 60m by 25 m, an a film thickness of 0.025 m, with a chemical

composition 14% cyanopropyl-phenyl 86%dimethylpolysiloxane, which

produces a different selectivity to (phenyl) dimethylsiloxane phases because of

the function cyano groups. In order to give good separation the temperature

progam started at 45oC for 4minutes, followed by a 4oC/minute heating rate to

240oC and 39oC/minute up to 280oC

A Perkin Elmer MS GOLD (UK) electron impact mass spectrometer set at 70

eV will produce the mass spectra. The mass range from 28-300 m/z will be

scanned, and data processed by Perkin Elmer Turbo mass spectrometer

version 6.0. The Perkin Elmer NIST98 computer library will be used to identify

the compounds

44

4 Results and Discussion

4.1 Comparison of Biomass Feed Stocks

Thanks to the experimentation as described in section 3 it is possible to

compile a table of the feed stocks and their relative component compositions.

Table 4.1.1: The composition of the raw feed stocks on a dry basis

Biomass: Beech Wood (Dry Basis)

Willow (Dry Basis)

Green Miscanthus (Dry Basis)

Rape Straw (Dry Basis)

Moisture % (Wa) - - - -

Volatiles % (Va) 85.88 77.7 82.24 89.64

Char % (Cha) 14.12 22.3 17.76 10.36

Fixed Carbon % (Cfix

a) 13.12 17.55 11.8 3.28

Ash % (Aa) 1 4.75 5.96 7.08

Table 4.1.1 shows that willow, the softwood, has the highest char content and

the highest levels of fixed carbon, beech wood the hard wood has the lowest

ash content and also a very high level of fixed. The herbaceous energy crop

green miscanthus is not quite as rich in fixed carbon, but higher levels of

inorganics give a larger ash content than the woody biomasses. Rapestraw is

shown to have the lowest levels of char and fixed carbon, yet the highest levels

of ash.

Because of this rape straw is shown to have the highest volatile content, and

as such it could be expected that rape straw would be most affected by the

torrefaction process, until Figure 4.1.1 is considered. Where it is shown the

volatile mass losses of rape straw happen towards the later stages of the high

temperature pyrolysis process.

45

As mentioned Figure 4.1.1 shows the rape straw to contain the lowest amount

of char. This is interesting when considering the energy that will remain in the

biomass after torrefaction is directly affected by the fixed carbon. It would be

expected that the higher the levels of fixed carbon (and hence char) a

feedstock has, the better it will retain its energy when the more volatile

components of the biomass are removed. Hence according to table 4.1.1 and

figure 4.1.1 Willow contains the highest amount of char and fixed carbon and

therefore could be most likely to retain the highest levels of energy after

torrefaction.

Figure 4.1.1: The mass loss of the biomass feed stocks during high temperature (900oC) pyrolysis

The rate of mass loss of each of the feed stocks, relative to the temperature,

should also be considered during the high temperature pyrolysis. This will

allow better analysis of how each of the feed stocks will be affected by

torrefaction. this can be seen in figure 4.1.2

46

Biomass Feedstocks Pyrolysis Mass Loss Comparison

0

20

40

60

80

100

120

0 50 100 150 200 250

Time (m)

Wei

ght (

%)

Beech WoodWillowRape StrawGreen Miscanthus

Figure 4.1.2: High temperature (900oC) pyrolysis feedstock analysis, comparing rate of mass loss to pyrolysis temperature

Figure 4.1.2 shows beech wood loses less weight over the torrefaction

temperature range. It may be assumed this is due to relatively lower levels of

hemicellulose and higher ratios of lignin and cellulose present in woody

biomass when compared to agricultural wastes, grasses and other herbaceous

energy crops.[Error: Reference source not found]

From figure 4.1.2 it would be expect that torrefaction will give the biggest mass

loss to green miscanthus, followed by rape straw then willow. Once again most

likely due to the higher levels of hemicellulose relative to those present in

beech wood. This mass loss relation may mean that the torrefaction process

gives hemicellulose rich feed stocks a much more noticeable increase in

heating value. Also note the shape of beech wood and willow peaks and the

way they shift to the right, possibly contributable to higher lignin contents.

Figure 4.1.3 shows lignin degrades at a higher temp range, and as stated by

Y. Yu et al.[Error: Reference source not found] lignin is responsible for woody character of

biomass, which supports the higher content of lignin within the woody

biomasses.

47

Comparison of Mass Loss Rates of The Biomass Feedstocks.

-10

-8

-6

-4

-2

0

2

100 150 200 250 300 350 400 450 500 550 600

Temperature (C)

rate

of m

ass

loss

( d%

wt.

/ dt.)

Beech WoodGreen MiscanthusWillowRape Straw

The cellulose peak at around 320oC in figure 4.1.3 could also contribute to the

shape of the willow and beech wood peaks in figure 4.1.2. hence the

combination of cellulose and lignin degradation around 350-400oC explains the

large secondary peaks seen in beech wood and willow in figure 4.1.2, all of

which supports the idea that the woody feed stocks will show least mass loss

from the torrefaction process due to their relatively lower levels of

hemicellulose.

Although it is Expected that the beech wood mass will remain largely the least

affected by the process this may change towards the higher temperatures of

torrefaction where it is claimed pyrolysis reactions begin to occur.[Error: Reference

source not found]

Pyrolysis of the Lignocellulose Components

-25

-20

-15

-10

-5

0100 200 300 400 500 600

Temperature (C)

rate

of m

ass

loss

(d%

wt /

dt)

CelluloseHemicelluloseLignin

Figure 4.1.3: A comparison between the lignocellulose components pyrolysis temperatures (lignocellulose components derived from a beech wood feedstock)

48

4.2 The Effects of Torrefaction on Mass and Energy of the Biomass

As expected the hemicellulose rich herbaceous energy crop and agricultural

waste showed the greatest mass losses (see appendix A for exact details)

retaining less than 60% of their original mass. The beech wood showed the

least mass loss overall.

Table 4.2.1 shows the relative atomic ratio of the biomasses constituent

elements and the higher heating value calculated using these ratios. The two

equations mentioned in section 2.3.2; equation 1 by S.W. Channiala & P.P.

Parikh [Error: Reference source not found] and equation 2 by Friedl et al.[Error: Reference source not found]

were used to calculate the higher heating values HHV1 and HHV2

respectively. The equation proposed by Friedl et al. Only considered the CHN

(and by difference oxygen) chemical make up, which could lead to some errors

in values for feed stocks with higher inorganic content being unaccounted for.

The equation proposed by S.W. Channiala & P.P. Parikh accounts for the

inorganics(ash) and other constituents such as sulphur, nitrogen, hydrogen,

carbon, in both cases the oxygen was calculated by difference could well

cause some slight errors and anomalies in the results.

The trends seemed to be a constant increase in the carbon wt% and decrease

in the Hydrogen and Oxygen. Thus an increase in HHV. (as shown graphically

in van krevelen diagram fig.4.2.3) the decrease of Hydrogen in the torrified

samples was inconsistent at times. Which most likely caused errors because of

the nature of the equations, in addition the assumption of Oxygen by difference

would further compound any slight error in the hydrogen content, leading to

some samples not following the trend of increased HHV.

49

Table 4.2.1: The affect torrefaction has on the feed stocks composition and heating value

Torrefaction Temperatures ( C )

  Raw 200 225 250 275 300Beech WoodMoisture (Wa) 4.49 4.17 4.11 4.19 4.28 4.29

C 47.96 48.12 48.66 49.25 50.33 51.62H 5.87 5.75 5.79 5.9 5.87 5.69N 0 0 0 0 0 0O 45.169 45.102 44.390 43.599 42.376 41.179

Ash (An) 0.956 0.985 1.112 1.199 1.363 1.446dry ash basis (Aa) 1.001 1.028 1.160 1.251 1.424 1.511HHV {1} (MJ/kg) 18.97 18.89 19.20 19.61 20.08 20.44HHV {2} (MJ/kg) 18.96 19.00 19.23 19.51 19.95 20.43

Willowmoisture (Wa) 6.34 6.08 6.26 6.27 5.87 5.94

C 47.71 48.44 48.91 49.89 51.92 53.94H 5.43 5.67 5.62 5.54 5.26 5.10N 1.59 1.54 1.80 1.78 1.92 2.02O 40.52 39.15 38.89 37.35 35.24 31.64

Ash 4.45 4.88 4.48 5.10 5.33 6.87dry ash basis (Aa) 4.754 5.195 4.777 5.437 5.657 7.301HHV {1} (MJ/kg) 18.74 19.41 19.55 19.94 20.53 21.38HHV {2} (MJ/kg) 18.98 19.31 19.52 19.89 20.63 21.39

Green Miscanthusmoisture (Wa) 4.03 0.67 4.26 4.14 4.17 4.15

C 45.24 45.89 47.16 47.75 49.64 51.85H 5.68 5.6 5.28 5.63 5.43 4.89N 1.92 1.72 2 1.98 2.05 2.15O 41.199 39.693 37.725 36.060 33.363 29.947

Ash 5.721 7.049 7.501 8.225 9.121 10.700dry ash basis (Aa) 5.961 7.097 7.835 8.580 9.517 11.163HHV {1} (MJ/kg) 18.07 18.34 18.59 19.36 20.05 20.50HHV {2} (MJ/kg) 18.11 18.32 18.79 19.08 19.79 20.47

Rape Strawmoisture (Wa) 4.53 5.10 4.91 4.92 4.97 4.97

C 45.55 45.16 46.08 47.26 48.44 50.5H 5.42 5.07 5.18 5.17 5.56 5.19N 1.26 1.15 1.21 1.08 1.2 1.34O 40.693 40.171 37.217 34.867 36.159 31.815

Ash 6.756 8.018 9.807 11.051 8.212 10.601dry ash basis (Aa) 7.077 8.449 10.313 11.623 8.641 11.155HHV {1} (MJ/kg) 17.912 17.390 18.106 18.723 19.522 20.200HHV {2} (MJ/kg) 18.117 17.930 18.276 18.687 19.240 19.958

50

A comparison between the raw biomass HHV and the relative increase in HHV

achieved through the torrefaction temperature range showed some evidence

that the high hemicellulose containing green miscanthus showed the biggest

increase in energy relative to the raw biomass, (as shown in figure 4.2.1 and

4.2.2.) On the other hand the increase in higher heating value seen in the

willow was greater than that of rape straw, yet rape straw was shown to have a

larger mass loss (appendix A). This could show that the mass losses, and

hemicellulose content of the biomass is not the only deciding factor in the

increase in HHV, and it is quite likely the low char/fixed carbon content shown

in rapestraw also affected the relatively low HHV increase. Though the

comparison is not fully conclusive due to the anomalies witnessed in the rape

straw runs, this may stem from the low char content and high ash content

which could have had an adverse affect on the HHV equations used.

Effect of Torrefact on Increasing The Energy of Biomass

-4

-2

0

2

4

6

8

10

12

14

16

200 210 220 230 240 250 260 270 280 290 300

Torrefaction Temperature (C)

Incr

ease

in E

nerg

y re

lativ

e to

the

raw

bio

mas

s (%

)

Green MiscanthusWillowRape StrawBeech Wood

Figure 4.2.1: Relative increase in HHV(equation 1 used) of the feed stocks, over the torrefaction temperature range

51

Effect of Torrefact on Increasing The Energy of Biomass

-2

0

2

4

6

8

10

12

14

200 210 220 230 240 250 260 270 280 290 300

Torrefaction Temperature (C)

Incr

ease

in E

nerg

y re

lativ

e to

the

raw

bio

mas

s (%

)

Green MiscanthusWillowRape StrawBeech Wood

Figure 4.2.2: Relative increase in HHV(equation 2 used) of the feed stocks, over the torrefaction temperature range

The mass and energy yields of the feed stocks, across the range of

torrefaction temperatures, were also analysed. The results, shown in table

4.2.2 show a trend of a decreasing mass yield with increasing torrefaction

temperatures this trend was mimicked by the energy yield, but to a lesser

extent, such that there was a noticeable retention in energy yield greater than

that of mass yield with the higher temperatures of torrefaction.

52

Table 4.2.2: The mass and energy yields of the four different biomass feed stocks, seen over the range of torrefaction temperatures

    Mass yield

Energy yield {1}

Energy yield {2}

Beech Wood 200 94.9 94.5 94.7225 93.7 94.9 96.2250 89.8 92.9 95.5275 80.6 85.3 89.7

  300 69.2 74.5 80.3Willow 200 91.0 94.2 92.6

225 88.3 92.1 90.9250 83.3 88.7 87.3275 75.8 83.1 82.5

  300 66.8 76.2 75.3grn.

Miscanthus 200 98.3 99.8 99.5

225 87.4 89.9 90.7250 81.3 87.1 85.6275 71.5 79.3 78.1

  300 58.3 66.2 65.9Rape Straw 200 92.5 89.8 91.5

225 89.9 90.9 90.7250 83.9 87.7 86.5275 74.2 80.9 78.8300 59.2 66.7 65.2

Table 4.2.2 is interesting because although green miscanthus and rape straw

were shown to have good mass losses this did not relate to a great energy

yield, probably due to the speculated relatively high levels of hemicellulose.

Although they had high mass loss because of the high levels of hemicellulose,

and Green Miscanthus even had one of the biggest marked improvent in HHV

(relative to the raw biomass), the high levels of hemicellulose meant it was

hard to retain high levels of energy due to subsequently lower levels of char

and fixed carbon. So the large mass losses of over 40% didn’t allow for high

levels of energy to be retained unlike beech wood and willow. Beech wood and

willow were shown to retain the higher levels of energy content, and this is

attributable to the woody nature of their lignocellulose being richer in lignin and

hence richer in fixed carbon.

Although the beech wood retained the highest levels of energy the torrefaction

process relatively increased the higher heating value of the beech wood least.

(fig.4.2.1 & fig.4.2.2)

53

On the basis of these results it is expected that willow and possibly other soft

woods as well as green miscanthus and possibly other HEC, will gain the most

benefit from the torrefaction process. This is most likely due to the balance of

hemicellulose and lignin, such that there is a large enough mass loss to show

a significantly marked improvement in HHV, at the same time as having the

right ratio of lignocellulose components and fixed carbon to allow for the

retention of energy. This is shown to some degree by looking at the energy

densification of the biomass feed stocks in question, shown in Table 4.2.3.

Table 4.2.3: The comparison of energy densification caused by torrefaction

HHV eq.1 HHv eq. 2Torrefaction Temp. (oC)

Energy Densification

Energy Densification

Beech Wood 200 1.00 1.00225 1.01 1.03250 1.03 1.06275 1.06 1.11300 1.08 1.16

Willow 200 1.04 1.02225 1.04 1.03250 1.06 1.05275 1.10 1.09300 1.14 1.13

grn. Miscanthus 200 1.01 1.01

225 1.03 1.04250 1.07 1.05275 1.11 1.09300 1.13 1.13

Rape Straw 200 0.97 0.99225 1.01 1.01250 1.05 1.03275 1.09 1.06300 1.13 1.10

The energy densification of the biomasses are close, and show that higher

temperature torrefaction is beneficial for all the biomasses experimented on,

with a tendency to have the optimum effect on biomasses with higher fixed

carbon contents and possibly relatively medium/high hemicellulose contents.

54

The Van Kreveln Diagram compares the atomic ratios of Oxygen Hydrogen

and Carbon within a fuel, this allows for a relative comparison of the fuel to that

of existing fuels. There is also a trend of increasing heating value with

decreasing atomic O/C and H/C ratios. Table 4.2.4 shows these relative ratios

and how they decrease with the increasing torrefaction temperatures, leading

to an increase in heating value as shown in Figure 4.2.3.

Table 4.2.4: The effect of torrefaction on the atomic O/C and H/C ratios

    Torrefaction Temperatures ( C )  Raw 200 225 250 275 300

Beech WoodAtomic O/C ratio 0.71 0.70 0.68 0.66 0.63 0.60Atomic H/C ratio 1.47 1.43 1.43 1.44 1.40 1.32

WillowAtomic O/C ratio 0.64 0.61 0.60 0.56 0.51 0.44Atomic H/C ratio 1.37 1.40 1.38 1.33 1.22 1.13

Green Miscanthus

Atomic O/C ratio 0.68 0.65 0.60 0.57 0.50 0.43Atomic H/C ratio 1.51 1.46 1.34 1.41 1.31 1.13

Rape StrawAtomic O/C ratio 0.67 0.66 0.61 0.55 0.56 0.47Atomic H/C ratio 1.43 1.43 1.35 1.31 1.38 1.23

55

Figure 4.2.3: Van Krevelen diagram showing raw and torrified biomass samples’ atomic O/C and H/C ratio compared to existing fuels

The van krevelen diagram in fig.4.2.3 much more clearly conveys how Willow

and Green Miscanthus benefitted the most from the torrefaction. Figure 4.2.3

also shows how the high torrefaction temperatures cause the torrified biomass

to become more like peat.

Figure 4.2.3 shows the beech wood being least affected by the torrefaction

process, something that is also clearly shown in the Van krevelen diagram

figure 4.2.4 where the raw biomass, high temperature torrified biomass and

other known compounds have been marked.

Van Krevelen Diagram

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80

Atomic O/C ratio

Beech woodWillowGreen MiscanthusRape Straw

atomic H/C ratio

Bio

mas

s

Peat

Incr

eas

ing to

rre

fact

ion

te

mp

erat

ure

ligni

te

Coa

l

Ant

hra

cite

In cr ea si ng

H ea tin g va lu e

56

Figure 4.2.4: A Van Krevelen diagram, showing the raw biomass and torrified (300oC) biomass in comparison to some other known fuels

Van Krevelen Diagram

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80

Atomic O/C ratio

Ato

mic

H/C

ratio

Beech woodWillowGreen MiscanthusRape Straw

Raw Biomass

Rape Straw

Beech woodWillowGreen Miscanthus

Torrified Biomass (300oC)

In cr ea si ng

H ea tin g va lu e

Charcoal

LigniteBituminious coalAnthracite

Other Known Fuels

57

4.3 Chemical Analysis of the Torrefaction process

4.3.1 Slow Ashing of the Raw and Torrified Biomass Samples

The data from the slow ashing of the different biomass varieties over the range

of the torrefaction temperatures can be manipulated to give the combustion

rate of mass loss against temperature. Figure 4.3.1.1 shows the beech wood

mass loss rate against the combustion temperature. It can be clearly seen that

there are two main peaks that have formed for all the beech wood samples,

raw and torrified. The trend shows that as the biomass progresses through the

torrefaction temperatures these peaks change. The first peak narrows and

deepens with the increase of torrefaction temperature, and represents the

volatiles that are being combusted, as explained by klass.[Error: Reference source not found]

As the first peak progresses through the range of torrefaction temperature the

volatiles released between 220-300oC dramatically reduce, this nicely

represents the reduction in hemicellulose volatiles that remain in the biomass.

The first peak narrows and this most likely represents that most of the volatiles

that burn at the lower temperatures are being produced by the cellulose

especially if the 300oC torrified sample is compare to cellulose peak shown in

figure 4.1.3

Mass loss Rates of raw and heat treated Beechwood

-8

-7

-6

-5

-4

-3

-2

-1

0

1

2

150 200 250 300 350 400 450 500 550

Temp (C)

Rat

e of

mas

s lo

ss (d

%w

t /dt

)

Raw200225250275300

58

Figure 4.3.1.1: The slow ashing mass loss rate of beech wood during combustion

The second peak in figure 4.3.1.1 is representing the relative char percentage

of each of the samples, as more volatiles are removed during the higher

torrefaction temperatures the samples contains more char relative to the total

mass of the sample. This causes the gradual increase in peak size in both the

higher torrefaction temperature volatile peaks and the char peaks. These

increasing peaks also reflect how the energy density of the biomass increases

as there is more char and fixed carbon present relative to the overall mass of

the product.

The trend of an increasing fixed carbon peak, and narrowing volatile peak was

reflected in all of the slow ashing experiments. Showing the hemicellulose was

decomposing and the volatile components were being released. When looking

at the willow sample though there was an interesting difference with the high

temperature torrefaction profile. At torrefaction temperature of 300oC the peak

dramatically dropped in size, this shows that more of the volatiles in the

biomass had been removed, not just the hemicellulose components but most

likely cellulose and possibly even some lignin decomposition had taken place.

Py-GC-MS Analysis of the products released at this higher 300oC torrefaction

temperature will allow the evaluation of which biomass components are being

affected.

59

Mass loss Rates of raw and heat treated Willow

-8

-7

-6

-5

-4

-3

-2

-1

0

1

150 200 250 300 350 400 450 500 550

Temp (C)R

ate

of m

ass

loss

(d%

wt /

dt)

Raw200225250275300

Figure 4.3.1.2: The slow ashing mass loss rate of Willow during combustion

It is mentioned in the literature[Error: Reference source not found] that as the torrefaction

process begins to approach the 300oC the reaction becomes more like

pyrolysis in nature. This may be due to the cellulose composition in the soft

wood (galactoglucomannan based[Error: Reference source not found,Error: Reference source not found,Error:

Reference source not found]) decomposing at a lower temperature and more readily,

meaning some pyrolysis reactions occur at lower temperatures due to the

willows lignocellulose composition, hence why the volatile peak in figure

4.3.1.2 drops dramatically at 300oC torrefaction temperature.

This same anomaly was seen in the HEC Green Miscanthus, as shown in

figure 4.3.1.3. Once again, likely due to the plants lignocellulose composition,

past 250oC torrefaction temperature the volatile peak of the combustion profile

began to reduce. This indicates more than the hemicellulose was

decomposing, and volatiles from the cellulose and possibly even some

components of the lignin were being removed in the higher temperature

torrefaction process. This will be looked at more in section 4.3.2. Once again

like in willow the green miscanthus biomass could have began to undergo

pyrolysis reactions, but this time at a lower temperature range than seen in the

willow. This may be what gave both willow and green miscanthus slightly

60

superior (relative) increases in heating value. And also their relative positions

on the Van Krevelen diagram

Mass loss Rates of raw and heat treated Green Miscanthus

-8

-7

-6

-5

-4

-3

-2

-1

0

1

2

100 150 200 250 300 350 400 450 500 550 600

Temp (C)

Rat

e of

mas

s lo

ss (d

%w

t /dt

)

RAW200225250275300

Figure 4.3.1.3: The slow ashing mass loss rate of Green Miscanthus during combustion

61

When the rape straw was examined the rape straw’s profile was most similar

to that of the beech wood. The increasing torrefaction temperature caused a

narrowing and deepening of the volatile peak as shown below in figure 4.3.4.

Once again less volatiles were combusted over the lower temperature range,

showing the more unstable hemicellulose volatiles were being removed during

the increasing torrefaction temperatures.

Mass loss Rates of raw and heat treated Rape Straw

-8

-7

-6

-5

-4

-3

-2

-1

0150 200 250 300 350 400 450 500 550

Temp (C)

Rat

e of

mas

s lo

ss (d

%w

t /dt

)

Raw200225250275300

Figure 4.3.1.4: The slow ashing mass loss rate of Rape straw during combustion

One way the Rape Straw’s rate of combustion profile was quite different was

the small/negligible peak of fixed carbon seen during the slow-ashing. This

stems from a very low amount of fixed carbon, especially compared to the

other varities of biomass tested, something that is reflected in Table 4.1.1.

This low amount of fixed carbon is quite likely to be responsible for the slightly

poor energy yield shown by the rape straw seen in table 4.2.3, despite the

large mass loss observed.

62

4.3.2 Pyrolysis of the Torrified Biomass Samples

The pyrolysis of the torrified biomasses allows further analysis of the volatiles

removed during torrefaction, with regards to the different types of biomass over

the range of torrefaction temperatures. Manipulating the data to give the mass

loss rate during pyrolysis clearly shows the trends and differences between the

varities of biomass and the range of torrefaction temperatures. The rate of

mass loss curves are shown in Appendix C.

The Beech Wood curve (Appendix C, figure C1) shows that the rate of volatiles

being lost between 200-340oC decreases with increasing torrefaction

temperature, this reflects what was seen in the slow ashing experiments, the

more unstable hemicellulose polymers are decomposing more readily with the

increasing torrefaction temperatrues. The narrowing and deepening of the

peak also indicates that in the case of beech wood, the cellulose and lignin are

likely to be hardly affected.

The Willow curve (Appendix C, figure C2) reflects a similar trend as the beech

wood; a decrease in volatiles being produced at the lower pyrolysis

temperatures as the torrefaction temperature of the sample is increased. This

is representative of the decrease in hemicellulose remaining in the product as

the torrefaction temperatures increase. There is also a noticeable drop in the

peak depth between the 275oC and 300oC torrefaction samples. This may

represent the suspected cellulose degredation has began to take place as the

torrefaction process becomes more like pyrolysis in nature, though this cant be

confirmed without PY-GC-MS analysis

63

The Green Miscanthus curve (Appendix C, figure C3) is very similar to that of

willow. The curve has the same trends that have been shown before (the

degredation of hemicellulose increasing with torrefaction temperature)

represented by less volatiles being produced in the lower temperatures as the

samples are treated with higher torrefaction temperatures. And once again

there may well be some cellulose degradation also taking place, as there is a

drop in peak depth (rate of volatiles released during pyrolysis) at the higher

torrefaction temperatures. This will be investigated further by the mass spectra

of the volatiles released.

The Rape Straw curve (Appendix C, figure C4) has an unusual rate of mass

loss profile. In the previous curves there was a clear narrowing of the peak,

and the lower torrefaction temperature curves had a clear step between 200-

320oC, (particularly visible with beech wood, fig C1) indicating volatiles are

being released from hemicellulose degradation, then as the temperature

increases the cellulose (and possibly partial lignin) degradation peak was

seen.

This stepped peak was not seen in the rate of mass loss curve for rape straw

pyrolysis. This could indicate that there are lower levels of cellulose and/or

lignin relatively, hence why there is no clear stepped peak. This makes it hard

to tell if there is any cellulose degradation, as the drop in the 300 oC torrefaction

sample peak could just represent that there is less volatiles remaining in the

product, due to low levels of cellulose and lignin relative to the high levels of

inorganics present within the rape straw. Once again the PY-GC-MS analysis

of the volatiles produced during torrefaction should indicate what is happening

to the biomass during torrefaction.

64

4.3.3 PY-GC-MS Analysis of the Volatiles Produced During Torrefaction

Table 4.3.3.1 shows the major volatile peaks Identified from the torrefection

process, the table gives each compounds details along with which type of

biomass sample it was released from. Chemicals that represent Major peaks

from any sample are marked in bold

Table 4.3.3.1: Analysis of the Volatiles Released During Torrefaction

Molecule Molecular Weight Formula Structure Volatile Released

From:

Acetic acid anhydride, with

formic acid88 C3H4O3

Beech WoodWillow

Green MiscanthusRape Straw

acetic acid methylester 74 C3H6O3 Beech WoodRape Straw

1,2-ethandiol, monoacetate 104 C4H8O3

Beech WoodGreen Miscanthus

Rape Straw

2-oxo,methylester, propanoic acid 102 C4H6O3

Beech WoodGreen Miscanthus

Rape Straw

acetic acid anhydride 102 C4H6O3Beech Wood

3-Furaldehyde 96 C5H4O2

Beech WoodWillow

Green MiscanthusRape Straw

2-Furan methanol 98 C5H4O2

Beech WoodWillow

Green MiscanthusRape Straw

1-(acetyloxy)-2-propanone 116 C5H8O3

Beech WoodWillow

Green MiscanthusRape Straw

2-cyclopentene-1,4-dione 96 C5H4O2

Beech WoodWillow

Green MiscanthusRape Straw

2-hydroxy-2-cyclopenten-1-one 98 C5H6O2 Beech Wood

Rape Straw

65

4-hydroxy-butanoic acid 104 C4H8O3

Green MiscanthusRape Straw

5-methyl-2-furancarboxaldehyde 110 C6H6O2

Beech WoodWillow

Green Miscanthus

(s)-5-hydroxymethyl-2[5H]-furanone 114 C5H6O3

Green MiscanthusRape Straw

benzylalcohol 108 C7H8O Willow

phenol 94 C6H6O Willow

methyl- -D-ribopyranoside

164 C6H9O5 Beech Wood

1,6:3,4-dianhydro-2-deoxy- -D-ribo-

hexopyranose128 C5H8O3 Willow

propionaldehyde 58 C3H6O

Beech WoodWillow

Green MiscanthusRape Straw

guaiacol 128 C7H8O2Beech Wood

Green Miscanthus

2,5-dimethyl-4-hydroxy-3(2H)-

furanone128 C6H8O3

WillowGreen Miscanthus

1,6:3,4-dianhydro-2-O-acetyl- -D-

Galactopyranose186 C8H10O5 Willow

pentanal 86 C5H10O

Beech WoodWillow

Green MiscanthusRape Straw

66

2,3-dihydro-3,5-dihydroxy-6-methyl-

4H-pyran-4-one144 C6H8O4 Green Miscanthus

3-methyl butanal 86 C5H10O Green Miscanthus

2-methoxy-4-vinylphenol 153 C9H9O2

Beech WoodWillow

Green Miscanthus

levoglucosan (1,6-anhydro- -D-

glucopyranose);162 C6H10O5 Willow

2,6-dimethoxy-4-(2propenyl)-phenol 194 C11H14O3 Willow

1-(4-hydroxy-3,5-dimethoxyphenyl)-

ethanone268 C16H12O4 Willow

2-hydroxy-phenylmethylester

benzoic acid228 C14H12O3 Willow

2-methoxy-5-(1-propenyl) 164 C10H12O2 Beech Wood

3-hydroxy-4-methoxy mandelic acid 198 C9H10O5 Beech Wood

4,5-dimethyl-4-hexen-3-one 126 C8H14O Green Miscanthus

67

Analysis of the volatiles released during torrefaction showed some of the

products formed were common among all the different feedstocks, particularly

at the lower retention times that were analysed. There was clear production of

low molecular acids, caused by hemicellulose degredation. [Error: Reference source not

found] The low molecular, acids are believed to be responsible for the formation

of furfural, alderhydes and other volatile by-products, as they play an

important catalytic role in the acid degredation reactions that form these

products.[Error: Reference source not found,Error: Reference source not found]

The acetic acid, 3-Furaldehyde and 2-Furan methanol compounds and their

commonality among the varieties of biomass tested seemed to agree with the

literature, that torrefaction causes degradation of hemicellulose as the major

lignocellulosic component affected by the process , [Error: Reference source not found,Error:

Reference source not found,Error: Reference source not found,Error: Reference source not found,Error: Reference source not found,44]

and the acetic acid formed by the hemicellulose degredation has some role in

the production of furan and furfural products.

4.3.3.1 Volatiles Produced During the Torrefaction of Beech Wood

When analysing the peaks of the PY-GC-MS torrefaction data for beech wood

there were not only signs of hemicellulose degredation but also some very

slight cellulose degredation and lignin degredation.

There are several small peaks [figure 4.3.3.1] which indicate the compounds:

3-hydroxy-4-methoxy mandelic acid, 2-methoxy-5-(1-propenyl), 2-methoxy-4-

vinylphenol and guaiacol, these compounds represent lignin degredation

having taken place. There was also a slightly bigger methyl- -D-

ribopyranoside peak, indicating the degredation of cellulose.

These peaks showed that although there was some degredation of cellulose

and lignin during torrefaction, for beech wood it was only a very small amount.

This is what was expected, especially with the evidence provided by

figure4.1.3 which showed cellulose degredation barely started by 300oC and

68

the lignin degredation was a lot less than that of hemicellulose and cellulose.

The mass loss profiles (appendix A) also indicated that beech wood was the

least affected by the torrefaction process, and hence possibly contained lower

levels of hemicellulose and less volatile cellulose/lignin components. The

amount and types of volatiles collected from the mass spectra back up this

belief.

Figure 4.3.3.1.1: PY-GC-MS Chromatogram for Beech wood under torrefaction conditions (300oC)

The main peaks identified in the mass spectrum are as follows:1: Acetic acid anhydride, with formic acid; 2: acetic acid methylester 3: 2-oxo,methylester, propanoic acid;4: 1,2-ethandiol, mono acetate; 5: acetic acid anhydride; 6: 3-Furaldehyde; 7: 2-Furan methanol; 8: 1-acetyloxy-2-propanone; 9: 2-cyclopentene-1,4-dione; 10: 2-hydroxy-2-cyclopenten-1-one; 11: 5-methyl-2-furancarboxaldehyde; 12:methyl- -D-ribopyranoside; 13: propionaldehyde; 14:unknown; 15:Guaiacol; 16: unknown; 17: pentanal; 18: 2-methoxy-4-vinylphenol; 19:2-methoxy-5-(1-propenyl); 20:3-hydroxy-4-methoxy mandelic acid

69

4.3.3.2 Volatiles Produced During the Torrefaction of Rapestraw

The major peaks seen in rape straw were the low molecular weight acids, from

hemicellulose, and some subsequent believed reaction derivatives [Error: Reference

source not found,Error: Reference source not found]

3-furaldehyde & 2-furan methanol. This indicated high levels of hemicellulose

present within the rape straw, which was backed up by the major peak seen

marking acetic acid. In addition there was only limited cellulose marker peaks,

and no clear lignin markers seen at the high torrefaction temperatures. These

results coincide with the low levels of fixed carbon seen in table 4.1.1. This

backs up the the other results which were indicating the rape straw was rich in

hemicellulose, but lacking lignin content, and due to this the torrefaction

process was unable to have any major affect on the lignin or cellulose present

in the rape straw.

Figure 4.3.3.2.1: PY-GC-MS Chromatogram for Rape Straw under torrefaction conditions (300oC)

The main peaks identified in the mass spectrum are as follows:

1: acetic acid, anhydride with formic acid; 2: acetic acid methylester; 3: 1,2-ethandiol, monoacetate; 4: methylester, 2-oxo-propanoic acid; 5: 3-furaldehyde; 6: 2-furan methanol; 7: 1-(acetyloxy)-2-propanone; 8: 2-cyclopentene-1,4-dione; 9: 2-hydroxy-2-cyclopenten-1-one; 10: 4-hydroxy-butanoic acid; 11: (s)-5-hydroxymethyl-2-[5H]-furanone; 12: propionaldehyde; 13: unknown; 14: pentanal

70

4.3.3.3 Volatiles Produced During the Torrefaction of Green Miscanthus

Green miscanthus interestingly had a much smaller acetic acid peak than

rapestraw or beech wood during torrefaction, one that was much closer to

Willow’s, the largest peak was identified as 2-methoxy-4-vinylphenol. Which

was very interesting as this component is a marker for lignin, another lignin

compound seen but with a smaller peak was guaiacol. There was also a

moderate 2,3-dihydro-3,5-dihydroxy-6-methyl-4H-pyran-4-one peak, this

seems to indicate some cellulose degredation had occurred. The release of

these volatiles clearly indicates there has been more than just hemicellulose

degredation occurring, cellulose, and most definitely some lignin

decomposition has taken place, and to a much more noticeable extent than

that seen in beech wood, as shown by the height of the volatile’s peaks. This

Indicates the literature[Error: Reference source not found,Error: Reference source not found] is correct in

stating the high temperature end of the torrefaction process causes the thermal

reactions to become more like pyrolysis in nature.

Figure 4.3.3.3.1: PY-GC-MS Chromatogram for Green Miscanthus under torrefaction conditions (300oC)

The main peaks identified in the mass spectrum are as follows:1: acetic acid anhydride with formic acid; 2: 1,2-ethandiol, monoacetate; 3: methylester-2-oxo,propanoic acid; 4: 3-furaldehyde; 5: 2-furan methanol; 6: 1-(acetyloxy)-2-propanone; 7: 2-cyclopentene-1,4-dione; 8: 5-methyl-2-furancarboxaldehyde; 9: 4-hydroxy- butanoic acid; 10: (s)-5-hydroxymethyl-2[5H]-furanone; 11: propionaldehyde; 12: unknown; 13: guaiacol; 14: 2,5-dimethyl-4-hydroxy-3(2H)-furanone; 15: pentanal; 16: 2,3-dihydro-3,5-dihydroxy-6-methyl-4H-pyran-4-one; 17: 3-methyl butanal; 18: 2-methoxy-4-vinylphenol; 19: 4,5-dimethyl-4-hexen-3-one; 20: C20 hydrocarbon chain.(formed by radicals from the process, and can be ignored)

71

4.3.3.4 Volatiles Produced During the Torrefaction of Willow

Willow showed one of the biggest ranges of different volatiles during

torrefaction conditions. Like beech wood the main decomposition product was

hemicellulose, but there was a wider variety of smaller peaks showing clear

cellulose degredation and lignin degredation too. Some of the cellulose volatile

indicators [Error: Reference source not found,53] included: 2,5-dimethyl-4-hydroxy-3(2H)-

furanone, 1,6:3,4-dianhydro-2-deoxy- -D-ribo-hexopyranose, 1,6:3,4-53

? Nowakoski D. J., Woodbridge C. R., and Jones J. M. ‘Phosphorus catalysis in the pyrolysis behaviour of biomass’ J. anal. & app. Pyrolysis, Vol 83, issue 2, pp.197-204

9 Appendices

9.1 Appendix A – feedstock mass loss data

9.2 Appendix B – calculations and equations utilized in data manipulation

9.3 Appendix C – the effect of pyrolysis on the torrified samples

72

dianhydro-2-O-acetyl- -D-Galactopyranose, andlevoglucosan (1,6-anhydro- -

D-glucopyranose).

As well as some of the medium and smaller peaks on the spectra indicating

lignin degredation: phenol, benzylalcohol, 2,6-dimethoxy-4-(2propenyl)-phenol,

1-(4-hydroxy-3,5-dimethoxyphenyl)-ethanone, 2-hydroxy-phenylmethylester

benzoic acid,

9.4 Appendix D- Mass spectra for torrefaction and pyrolysis conditions

9.1 Appendix AMass losses during torrefaction: all masses are based on weight percentage

73

Table A1: Beech Wood mass losses over torrefaction temperature rangeTemperature (C)200225250275300moisture (Wa)4.174.114.194.284.29Mass loss (Mlw)4.916.009.7618.5829.51mass loss dry basis (Mld)5.126.2610.1919.4130.84

Table A2: Willow mass losses over torrefaction temperature rangeTemperature (C)200225250275300moisture (Wa)6.086.266.275.875.94Mass loss

(Mlw)8.4710.9515.6322.7431.21mass loss dry basis (Mld)9.0211.6816.6824.1633.18

Table A3: Green Miscanthus mass losses over torrefaction temperature rangeTemperature (C)200225250275300moisture (Wa)0.674.264.144.174.15Mass loss

(Mlw)1.6612.0717.9527.3439.93mass loss dry basis (Mld)1.6712.6118.7228.5341.66

Table A4: Rape straw mass losses over torrefaction temperature rangeTemperature (C)200225250275300moisture (Wa)5.104.914.924.974.97Mass loss

(Mlw)7.159.6215.3224.5138.81mass loss dry basis (Mld)7.5410.1116.1225.7940.83

74

Figure 4.3.3.4.1: PY-GC-MS Chromatogram for Willow under torrefaction conditions (300oC)

The main peaks identified in the mass spectrum are as follows:1: acetic acid anhydride with formic acid; 2: acetic acid, methylester 3: 3-furaldehyde; 4: 2-furanmethanol; 5: 1-(acetyloxy)-2-propanone; 6: 2-cyclopentene-1,4-dione; 7: 5-methyl-2-furancarboxaldehyde; 8: benzylalcohol;9: phenol; 10: 1,6:3,4-dianhydro-2-deoxy- -D-ribo-hexopyranose; 11: propionaldehyde; 12: 2,5-dimethyl-4-hydroxy-3(2H)-furanone; 13: 1,6:3,4-dianhydro-2-O-acetyl- -D-Galactopyranose; 14: pentanal; 15: 2-methoxy-4-vinylphenol; 16: levoglucosan (1,6-anhydro- -D-glucopyranose);17: 2,6—dimethoxy-4-(2propenyl)-phenol; 18: 1-(4-hydroxy-3,5-dimethoxyphenyl)-ethanone; 19: 2-hydroxyphenylmethylester benzoic acid

75

5 Conclusions

The literature has indicated there is a potential to use the torrefaction process

to improve biomass for applications such as gasification, because of the

improved ease of ‘grindability’ and increased energy density achieved through

torrefaction.

9.2 Appendix B

Dry Basis Calculations:

Wa = Moisture contentVa = volatile contentCha= Char content

Va(dry basis) =

Cha(dry basis) =

Biomass:Green MiscanthusGreen Miscanthus (dry basis) Moisture (Wa)4.07-Calculated mass loss (at 105oC) from 900oC pyrolysis of feed stock Volatiles

(Va)78.8982.24remaining =100-(Cha+Wa)Char (Cha)17.0317.76Mass remaining after 900oC pyrolysis of biomass (in Nitrogen atmosphere)Fixed Carbon (Cfix

a)-11.80char - ash = Fixed CarbonAsh (Aa)5.725.96Mass remaining after slow ashing of BiomassAshing

Moisture Content4.03 Calculated mass loss (at 105oC) during slow ashing of Feed stock

76

In addition it has been noted that a pelletisation process could further improve

the energy density of the torrified fuel, and allow use in co-firing and the

domestic sector, replacing current biomass/wood pellets due to the storage,

transportation and machining savings, achieved once the biomass is torrified.

This report shows that it is indeed the case that torrified biomass shows a

marked improvement over the raw biomass, and improves a fuels energy

Higher Heating Value Calculations:

Equation 1:

Channiala & P.P. Parikh[47]

HHV = 0.3491C + 1.1783H + 0.1005S -0.1034O – 0.0151N – 0.0211A

(Where:C=carbon weight%, H=hydrogen weight%, S=Sulphur weight%,

O=Oxygen weight%, N=nitrogen weight% and A=ash weight%)

Raw Green Miscanthus biomass data:moisture (Wa)4.03C45.24H5.68N1.92O41.199Ash5.721dry ash basis

(Aa)5.961(oxygen calculated by difference)

HHV = 0.3491C + 1.1783H + 0.1005S -0.1034O – 0.0151N – 0.0211A

HHV =17.226 (MJ/kg)

Equation 2:

Friedl et al.[48]

HHV = 3.55C2 − 232C − 2230H +51.2CH + 131N + 20, 600

(Where: C=carbon weight%, H=hydrogen weight%, O=Oxygen weight% and

N=nitrogen weight%)

Raw Green Miscanthus biomass data:

moisture (Wa)4.03C45.24H5.68N1.92O41.199Ash5.721dry ash basis (Aa)5.961

HHV = 3.55C2 − 232C − 2230H +51.2CH + 131N + 20, 600

HHV = 18,099 (kJ/kg)

Mass & Energy Yield and Energy Density Calculations:Mass & Energy Yield calculations:

77

density and heating value. Increases in energy densities of around 13% were

estimated for the (300oC) torrified fuel when compared to the raw biomass.

When energy improvements were focused on, in terms of improvement in

HHV, it was shown that the HEC, SWRC and even agricultural wastes were

more susceptible to improving HHV, showing improvements between 10-14%

this was not achieved by the hardwood (in this study beech wood). When this

was compared to the mass losses observed it was indicated that the

Ymass(%) = mass yieldYenergy(%) = mass yieldM = massHHV = higher heating value

Ymass(%) =

Beech wood mass loses:

Temperature (C)raw200225250275300moisture (Wa)4.494.174.114.194.284.29Mass loss (wt %) 4.916.009.7618.5829.51mass loss dry basis (Mld) 5.126.2610.1919.4130.84Example -

(200 torrefaction temperature):

Ymass(%) = = 94.9

(data was already collected on a weight % basis, hence the mass yield is already calculated)

Yenergy(%) =

Beech wood HHV (eq. 1)Temperature (C)raw200225250275300HHV {1}

(MJ/kg)18.96818.88919.19519.61120.07520.435Example - (200 torrefaction temperature):

Energy yield {1} = = 94.5

  Mass yieldEnergy yield {1}Energy yield {2}Beech Wood20094.994.594.722593.794.996.225089.892.995.527580.685.389.7 30069.274.580.3

N.B. energy yield {1} reflects the answers produced by HHV equation 1 were used in the calculation

energy yield {2} reflects the answers produced by HHV equation 2 were used in the calculation

Energy Density calculations:

78

hemicellulose content was a key factor in deciding improvement in higher

heating value. The feed stocks with higher hemicellulose content such as the

rape straw and green miscanthus showed the biggest mass losses. Followed

by willow, with its moderate hemicellulose content relative to the other fuels.

This mass loss was roughly translated to an improvement in heating value.

Energy density =

  Mass yieldEnergy yield {1}Energy yield {2}Beech Wood 30069.274.580.3Example - (300 torrefaction temperature):

Energy density [1] = = 1.08

HHV eq.1HHv eq. 2  Energy DensificationEnergy DensificationBeech Wood2001.001.002251.011.032501.031.062751.061.11 3001.081.16

9.3 Appendix C

79

Although hemicellulose was a key factor, it was not the only aspect controlling

energy densification and improvement in the fuels heating value after

torrefaction. It was also noted despite being rich in hemicellulose the Rape

Straw did not perform as well as the Willow did when comparing heating value

improvement, and when comparing the fuels on a Van Krevelen diagram this

was further emphasized.

It was also shown that the higher the level of fixed carbon in the biomass the

better the fuel retained its energy during torrefaction, as shown by a

comparison between the energy densification and energy yield results of the

different feed stocks. This shows that the amount of fixed carbon is also

important, and shows why the rapestraw (which had a very low Fixed carbon

content) performed surprisingly poorly on the van krevelen diagram, in spite of

the large mass drop that was observed, and willow, containing the highest

content of fixed carbon performed far better.

On these results this report concludes that the fuel that will gain the most from

the torrefaction process should have a balance between having a high

Pyrolysis of Torrified Beech Wood

-14

-12

-10

-8

-6

-4

-2

0

2

200 250 300 350 400 450 500 550 600

Temperature (c)

Rat

e of

mas

s lo

ss (d

M/d

t)

200225250275300

Figure C1: Comparison of pyrolysis mass loss rates of torrified beech wood,

over a range of torrefaction temperatures

80

hemicellulose content, and a high fixed carbon content, it is crucial to strike a

balance between these two factors. Too little hemicellulose, like in the beech

wood, or to little fixed carbon, like the rapestraw, will lead to a poorer increase

in energy density.

Pyrolysis of Torrified Willow

-7.5

-6.5

-5.5

-4.5

-3.5

-2.5

-1.5

-0.5

0.5

200 250 300 350 400 450 500 550 600

Temperature (C)

Rat

e of

mas

s lo

ss (d

wt%

/dt)

200225250275300

Figure C2: Comparison of pyrolysis mass loss rates of torrified Willow,

over a range of torrefaction temperatures

81

6 Recommendations

The research done so far indicates that the torrefaction process will have the

most beneficial affect on HEC and soft wood SRWC, with high levels of

hemicellulose and fixed carbon. Therefore I recommend further research into

which aspect, hemicellulose or fixed carbon, is most beneficial to the

improvement of energy densification after torrefaction. A comparison between

the different feed stocks to get a good range of samples, and the comparison

between the relative ratio of each component (fixed carbon / lignin, and

hemicellulose) and the gain in energy density achieved from torrefaction. This

will then allow estimations on which is the optimum ratio of these components

within the biomass, and allow it to be calculated from the biomasses

composition if torrefaction is a viable process, both economically and in terms

of energy conservation, for the biomass fuels of interest. It would also be

beneficial to research further into the energy requirements and energy costs of

Pyrolysis of Torrified Green Miscanthus

-9

-7

-5

-3

-1

1

200 250 300 350 400 450 500 550 600

Temperature (C)

Rat

e of

mas

s lo

ss (d

wt%

/dt)

200225250275300

Figure C3: Comparison of pyrolysis mass loss rates of torrified Green Miscanthus, over a range of torrefaction temperatures

82

torrefaction, against benefits yielded from a variety residence times, to allow

the calculation of which torrefaction resident time gives the optimum increase

in energy density, relative to the energy costs incurred.

Another suggestion would be to investigate the level of tars that remain in

different fuels after the torrefaction process. This would be for applications

within gasification, because as is mentioned in the literature [Error: Reference source not

found] the formation of condensable tars can lead to choking and blocking, which

is one of the major problems currently inhibiting the use of biomass within

gasification. This will bring another aspect into considering which fuels to

torrify, not just the energy densification achieved being optimum, but tar

content, for use in gasifiers.

Pyrolysis of Torrified Rapes Straw

-9

-7

-5

-3

-1

1

200 250 300 350 400 450 500 550 600

Temperature (C)

Rat

e of

mas

s lo

ss (d

wt%

/dt)

200225250275300

Figure C4: Comparison of pyrolysis mass loss rates of torrified Rape Straw,over a range of torrefaction temperatures

9.4 Appendix D

83

Ash melting point could also be investigated, for use in combustion, as low

melting point ashes, common in HECs such as grasses can also cause a

problem when used in certain fuel burners, [Error: Reference source not found] and as such

may be a very important area to investigate if looking at using torrified wood

pellets in small or domestic scale application.

The final recommendation would be to form an extensive catalogue for the

multiple varities of biomass available. Looking at agricultural/process wastes,

SRWC & HEC. The key data & characteristics of interest are likely to be

Lignocellulosic component composition, the degradation temperature range for

the biomasses specific lignocellulosic components, fixed carbon content, ash

content, ash melting point and Energy density. If this data was tabulated for a

range of biomass then it would be easier to make assumptions about trends

that relate to these characteristics, and make it easier to find which biomasses

are best suited to specific processes and applications.

Figure D1: PY-GC-MS Chromatogram for Beech wood under torrefaction conditions (300oC)The main peaks identified in the mass spectrum are as follows:

1: Acetic acid anhydride, with formic acid; 2: acetic acid methylester 3: 2-oxo,methylester, propanoic acid; 4: 1,2-ethandiol, mono acetate; 5: acetic acid anhydride; 6: 3-Furaldehyde; 7: 2-Furan methanol; 8: 1-acetyloxy-2-propanone; 9: 2-cyclopentene-1,4-dione; 10: 2-hydroxy-2-cyclopenten-1-one; 11: 5-methyl-2-furancarboxaldehyde; 12:methyl- -D-ribopyranoside; 13: propionaldehyde; 14:unknown; 15:Guaiacol; 16: unknown; 17: pentanal; 18: 2-methoxy-4-vinylphenol; 19:2-methoxy-5-(1-propenyl); 20:3-hydroxy-4-methoxy mandelic acid

84

7 Glossary

Angiosperms: a flowering plant whose seed is enclosed/develops in a pod or

endosperm after the plant is fertilised. The ability to flower helped angiosperms

become the most common and diverse land plant, by enabling a wider range

evolutionary relationships and broadening the variety of species. Hardwoods

are classed as angiosperms.

Cellulose: Cellulose is found within the plant cell wall and is a constituent of

lignocellulose. Chemically it is comprised of long polymer chains that form long

fibrous bundles within the cell wall.

Figure D2: PY-GC-MS Chromatogram for Beech wood under pyrolysis conditions (600oC)The main peaks identified in the mass spectrum are as follows:1: acetic acid anhydride with formic acid; 2: acetic acid methylester; 3: 1,2-ethandiol,monoacetate; 4: 4-hydroxy-2-pentanone; 5: propionaldehyde; 6: 3-furaldehyde; 7: 2-furan methanol; 8: 1-(acetyloxy)-2-propanone 9: 2-hydroxy-2-cyclopenten-1-one; 10: cis-1,2,cyclohexanediol; 11: 4-pentenoic acid; 12: propionaldehyde; 13: 2-hydroxy-3-methyl-2-cyclopenten-1-one; 14: mequinol; 15: tetrahydro-5-methyl-trans, 2-furanmethanol; 16: 2-methoxy-6-methylphenol; 17: pentenal; 18: 4-ethyl-2-methoxy-phenol; 19: tetrahydro-3,6-dimethyl-2H-pyran-2-one; 20: 2-methoxy-4-vinylphenol; 21: 2-methoxy-3-(2-propenyl)-phenol; 22: 4,5-dimethyl-4-hexen-3-one; 23: 2,6-dimethoxy-phenol; 24: 2-methoxy-4-(1-propenyl) phenol; 25: 2-methoxy-5-(1-propenyl) phenol; 26: 1,2,4-tri methoxy benzene; 27: 3-hydroxy-4-methoxy-benzaldehyde; 28: 1,2,3-tri-methoxy-5-methyl-benzene; 29: 1-(4-hydroxy-3-methoxyphenyl)-ethanone; 30: 3,5-dimethoxy acetophenone; 31: unknown; 32: 2,5-dimethoxy-4-ethylbenzaldehyde;33: 2,6-dimethoxy-4-(2-propenyl)-phenol; 34: 4-hydroxy-3,5-dimethoxy-benzaldehyde; ]35: 1-(4-hydroxy-3,5-dimethoxyphenol)-ethanone;

85

Endosperm: The endosperm is the plant tissue produced from the majority of

flowering plants, it acts to provide the seed with nutrients. It develops around

the time of fertilization.

Gymnosperms: The distinguishing feature of gymnosperms is the plant’s seed

is considered “naked” and does not develop in an enclosed (endosperm)

Figure D3: PY-GC-MS Chromatogram for Willow under torrefaction conditions (300oC)The main peaks identified in the mass spectrum are as follows:1: acetic acid anhydride with formic acid; 2: acetic acid, methylester 3: 3-furaldehyde; 4: 2-furanmethanol; 5: 1-(acetyloxy)-2-propanone; 6: 2-cyclopentene-1,4-dione; 7: 5-methyl-2-furancarboxaldehyde; 8: benzylalcohol; 9: phenol; 10: 1,6:3,4-dianhydro-2-deoxy- -D-ribo-hexopyranose; 11: propionaldehyde; 12: 2,5-dimethyl-4-hydroxy-3(2H)-furanone;

13: 1,6:3,4-dianhydro-2-O-acetyl- -D-Galactopyranose; 14: pentanal; 15: 2-methoxy-4-vinylphenol;

16: levoglucosan (1,6-anhydro- -D-glucopyranose); 17: 2,6—dimethoxy-4-(2propenyl)-phenol; 18: 1-(4-hydroxy-3,5-dimethoxyphenyl)-ethanone; 19: 2-hydroxyphenylmethylester benzoic acid

86

environment. The most common gymnosperms being the conifer family.

Softwoods are classified as gymnosperms

HEC: Herbaceous Energy Crop. A HEC can be considered as a crop grown for

a source of carbon and energy for the use in a variety of applications. The term

herbaceous refers to the plants tissue, where a HEC has little or no woody

tissue in its above ground growth.

Hemicellulose: A component lignocellulose and part of the plant cell wall.

Chemically it is a polymer comprised of multiple different sugars, with a shorter

polymer chain length than that found in cellulose. It is used to hold together the

cellulose bundles.

Figure D4: PY-GC-MS Chromatogram for Willow under pyrolysis conditions (600oC)The main peaks identified in the mass spectrum are as follows:1: 2-methyl furan; 2: 3-penten-2-one; 3: Acetic acid anhydride with formic acid; 4: acetic acid methylester; 5: toluene; 6: acetic acid anhydride; 7: 3-methyl furan; 8: 1,2-ethandiol monoacetate; 9: propionaldehyde; 10: 2-oxo-methylester propanoic acid; 11: 3-furaldehyde; 12: 2-furan methanol; 13: 1-(acetyloxy)-2-propanone; 14: 1-propen-2-ol, acetate; 15: 2-methyl-2-cyclopenten-1-one; 16: 1-(2-furanyl) ethanone; 17: 2-cyclopenten-1,4-one; 18: 2-hydroxy-2-cyclopenten-1-one; 19: 3-methyl-2-cyclopenten-1-one; 20: 4-hydroxy-butanoic acid; 21: (s)-5-hydroxymethyl-2-[5H]-furanone; 22: propionaldehyde; 23: 2-hydroxy-3-methyl-2-cyclopenten-1-one; 24: phenol; 25: mequinol; 26: 2-methyl phenol; 27: 3-ethyl-2-hydroxy-2-cyclopenten-1-one; 28: 3-butene-1,2-diol; 29: 3-methyl phenol; 30: 3-hydroxy-benzenethanol; 31: cyclopentane; 32: 4-hydroxy-2-pentenoic acid; 33: 20methoxy-4-methylphenol; 34: pentenal; 35: 2,5-dimethyl phenol;36: 4-ethyl-2-methoxy-phenol; 37: 3,4-anhydro-D-galactosan; 38: dihydro-2H-pyran-3(4H)-one; 39: anhydro-D-mannosan; 40: 1,4:3,6-dianhydro- -D-glucopyranose; 41: 2-methoxy-4vinylphenol; 42: 2-methoxy-3-(2-propenyl)-phenol; 43: 4,5-dimethyl-4-hexen-3-one; 44:2,6-dimethoxy-phenol; 45: 2-methoxy-5-(1-propenyl)-phenol; 46: 2-methoxy-4-(1-propenyl)-phenol; 47: 1,2,4-trimethoxy benzene; 48: 3-hydroxy-4methoxy-benzaldehyde; 49: unknown; 50: 1-(4-hydroxy-3-methoxyphenyl)-ethanone; 51: 1-(2-hydroxy-5-methoxy-4-methylphenyl)-ethanone; 52: 1-(4-hydroxy-3-methoxyphenyl)-2-propanone; 53: unknown; 54: 2,5-dimethoxy-4-ethylbenzaldehyde; 55: levoglucosan (1,6-anhydro- -D-glucopyranose); 56: 2,6-dimethyl-4-(2propenyl)phenol; 57: 4-hydroxy-3,5-dimethoxy-benzaldehyde; 58: 1-(4-hydroxy-3,5-dimethoxyphenyl)-ethanone; 59:unknown

Figure D5: PY-GC-MS Chromatogram for Green Miscanthus under torrefaction conditions (300oC)

The main peaks identified in the mass spectrum are as follows:1: acetic acid anhydride with formic acid; 2: 1,2-ethandiol, monoacetate; 3: methylester-2-oxo,propanoic acid; 4: 3-furaldehyde; 5: 2-furan methanol; 6: 1-(acetyloxy)-2-propanone; 7: 2-cyclopentene-1,4-dione; 8: 5-methyl-2-furancarboxaldehyde; 9: 4-hydroxy- butanoic acid; 10: (s)-5-hydroxymethyl-2[5H]-furanone; 11: propionaldehyde; 12: unknown; 13: guaiacol; 14: 2,5-dimethyl-4-hydroxy-3(2H)-furanone; 15: pentanal; 16: 2,3-dihydro-3,5-dihydroxy-6-methyl-4H-pyran-4-one; 17: 3-methyl butanal; 18: 2-methoxy-4-vinylphenol; 19: 4,5-dimethyl-4-hexen-3-one; 20: C20 hydrocarbon chain.(formed by radicals from the process, and can be ignored)

87

HHV: Higher Heating Value, also referred to as gross calorific value is the

enthalpy of complete combustion of a fuel. (Where all carbon forms carbon

dioxide and all hydrogen forms water), the higher heating value is given for

standard temperature and pressure, and includes the condensation enthalpy of

water

Figure D6: PY-GC-MS Chromatogram for Green Miscanthus under pyrolysis conditions (600oC)

The main peaks identified in the mass spectrum are as follows:1: acetic acid, anhydride with formic acid; 2: acetic acid, methylester; 3: unknown; 4: 1,2-ethandiol monoacetate; 5: unknowon; 6: 3-butene-1,2-diol; 7: methylester,-2-oxo-propanoic acid; 8: 3-furaldehyde; 9: 2-furan methanol; 10: 1-(acetyloxy)-ethanone; 11: 2-methyl-2-cyclopenten-1-one; 12: 1-propen-2-ol, acetate; 13: 1-(2-furanyl)-ethanone; 14: unknown; 15: 2-cyclopenten-1,4-dione; 16: 2-hydroxy-2-cyclopenten-1-one; 17: cis,1,2-cyclohexendiol; 18: 5-methyl-2-furancaboxaldehyde; 19: 3-methyl-2-cyclopenten-1-one; 20: 4-hydroxy-butanoic acid; 21: (s)-5-hydroxymethyl-2-[5H]-furanone; 22: propionaldehyde; 23: 2-hydroxy-3-methyl-2-cyclopenten-1-one; 24: phenol; 25: 2-methoxy-phenol; 26: 2-methyl phenol; 27: 3-ethyl-2-hydroxy-2-cyclopenten-1-one; 28: unknown; 29: 4-methyl-phenol; 30: 2-methoxy-4-methyl-phenol; 31: pentanal; 32: 4-ethyl-phenol; 33: 2-methoxy-4-ethyl-phenol; 34: 2-methoxy-4-vinylphenol; 35: 4,5-dimethyl-4-hexen-3-one; 36: 2,6-dimethoxy-phenol; 37: 2-methoxy-5-(1-propenyl)-(e)-phenol

88

LHV: The Lower Heating Value Is obtained when the condensation enthalpy

of the water formed from the combustion is neglected.

Lignin: A component of lignocellulose, it is seen as the cement between the

cellulose bundles holding them in place.

Lignocellulose: part of the plants cell wall, providing stability and strength to the

cell wall. It is comprised of three major components cellulose, hemicellulose

and lignin.

SRWC: Short rotation woody crop, also can be classed as short rotation

energy crop. A woody crop, an example of which might be willow, or poplar,

that is grown in a relatively short growing period, 3yrs in the U.K. Commonly

Figure D7: PY-GC-MS Chromatogram for Rape Straw under torrefaction conditions (300oC)The main peaks identified in the mass spectrum are as follows:

1: acetic acid, anhydride with formic acid; 2: acetic acid methylester; 3: 1,2-ethandiol, monoacetate; 4: methylester, 2-oxo-propanoic acid; 5: 3-furaldehyde; 6: 2-furan methanol; 7: 1-(acetyloxy)-2-propanone; 8: 2-cyclopentene-1,4-dione; 9: 2-hydroxy-2-cyclopenten-1-one; 10: 4-hydroxy-butanoic acid; 11: (s)-5-hydroxymethyl-2-[5H]-furanone; 12: propionaldehyde; 13: unknown; 14: pentanal

1

2

3

4

56

7

8

9

10

11

12

1314

15

16

17

18

19

20

21

22

23

24

25

26

5 .0 10.0 15.0 2 0.0 25.0 30.0 35.0 40.0 45.0 50.0 55.0 60.0 65.0 7 0.0 Tim e (m in) 0

100

%

Figure D8: PY-GC-MS Chromatogram for Rape Straw under pyrolysis conditions (600oC)The main peaks identified in the mass spectrum are as follows:

1: 3-methyl-2-butanone; 2: acetic acid, anhydride with formic acid; 3: acetic acid methylester; 4: 1-hydroxy-2-butanone; 5: 1,2-ethandiol, monoacetate; 6: 3-buten-1,2-diol; 7: methyl ester, 2-oxo-propanoic acid; 8: 3-furaldehyde; 9: 2-furan methanol; 10: 1-(acetyloxy)-2-propanone; 11: 1-propen-2-ol, acetate; 12: 2-hydroxy-2-cyclopenten-1-one; 13: 2(5H)-furanone; 14: propionaldehyde; 15: 2-hydroxy-3-methyl-2-cyclopenten-1-one; 16: phenol; 17: mequinol; 18: 2-methoxy-4-methyl-phenol; 19: pentanal; 20: unknown; 21: 2-methoxy-4-vinylphenol; 22: 2,6-dimethoxy phenol; 23: 2-methoxy-4-(1-propenyl)-phenol; 24: 1,2,4-trimethoxy benzene; 25: 3,5-dimethoxyacetophenone; 26: 2-methoxy-4-(2-propenyl)-phenol

89

the crop is grown for use as a fuel, or raw material for fuel or chemical

production.

90

8 References

91