LIFE CYCLE ANALYSIS OF

SYNGAS PRODUCTION FROM

BIOMASS GASIFICATION 02/04/2014

ABSTRACT Biomass is an alternative power

generation fuel coming from forest

reserves or agricultural wastes that has

immense potential for energy production.

Considering the importance of biomass

as fuel source it has become imperative

to study the combustion characteristic

and emission rates. The technical and

environmental performance of biomass

gasification upto syngas production is

examined using life cycle analysis. A

proposed plant is setup in British

Columbia, Canada. The classification of

impact from this plant is analysed based

on ECO-99 indicator. The global

warming potential from various biomass

sources is compared to that of

conventional natural sources of energy.

Satarupa Dhir CHE 594

1

Contents 1. INTODUCTION ................................................................................................................................. 2

2. BIOMASS IN CANADA ................................................................................................................... 2

2.1 BIOMASS FROM AGRICULTURAL RESIDUES .................................................................... 2

2.2 BIOMASS FROM FOREST ......................................................................................................... 3

3. GASIFICATION OF BIOMASS ........................................................................................................ 3

3.1 GASIFIACTION REACTIONS ................................................................................................... 3

4. TYPES OF GASIFIER ....................................................................................................................... 4

4.1 UPDRAFT FIXED BED GASIFIER ............................................................................................ 4

4.2 DOWNDRAFT FIXED BED GASIFIER .................................................................................... 4

4.3 BUBBLING FLUIDIZED BED GASIFIER ................................................................................ 5

4.4 CIRCULATING FLUIDIZED BED GASIFIER .......................................................................... 5

5. SYNGAS APPLICATIONS ............................................................................................................... 5

6. PROCESS DESCRIPTION ................................................................................................................ 6

7. JUSTIFICATION ............................................................................................................................... 6

8. LIFE CYCLE ASSESSMENT ........................................................................................................... 7

8.1 GOAL AND SCOPE DEFINITION ............................................................................................. 7

8.2 INVENTORY ANALYSIS........................................................................................................... 8

8.3 IMPACT ASSESSMENT ............................................................................................................. 8

8.4 INTERPRETATION ..................................................................................................................... 9

9. DISCUSSION ..................................................................................................................................... 9

10. SOLUTION TO THE PROBLEMS ............................................................................................... 10

11. CONCLUSION ............................................................................................................................... 10

REFERENCES ..................................................................................................................................... 11

APPENDIX ........................................................................................................................................... 12

2

1. INTODUCTION

With recent price rise and depletion of fossil fuels there has been trend towards use of

alternate energy resources. Syngas produced from renewable resource like biomass has the

potential to be put to various use. Gasification of various forms of biomass like wood,

agricultural matter is helpful in generation of power and electricity or manufacture of

chemical or fuel cells. Biomass is cheap, indigenous and easily available. It has the ability to

convert solid waste, like agricultural residues or forest residues to readily usable fuel or other

forms of energy. The increasing availability and the advancement in technology has made it

possible for biomass to be used effectively and efficiently with low level of emissions.

Although biomass gasification might be a new and developing concept in North America, it

has been extensively used in Europe since the time of World War II[1].

2. BIOMASS IN CANADA

Biomass is a renewable fuel derived from currently living or any product of living organism.

It is typically referred as plant or plant based materials and they can be used as an energy

source. Conversion of biomass into bio fuel can be achieved by various thermal, chemical or

biochemical means.

Biomass contributes to about 15% energy used by people globally. At present, Canada meets

to about 5-6% of its total energy from biomass. In Canada, millions of tonnes biomass is

harvested each year in the form of trees, crops or agricultural residues from farms. Biomass

forms the second most renewable form of energy after hydro energy. Popularity of biomass

usage can be evident from the application of wood as heating systems in Canadian homes or

from usage of corn and agricultural products to generate ethanol and biodiesels.

Agricultural residues and whole forest are the major resources of biomass in Canada. About

42% of Canadas land is forested and 6.8% make up the agricultural land of which 3.6% are

cropland[2].

Details of Various resources of biomass have been described below:

2.1 BIOMASS FROM AGRICULTURAL RESIDUES

According to survey by BIOCAP Canada foundation the total crop production was estimated

at 78.3Million oven dry tonnes (M Odt) of which 70% was wheat and barley and 56.1 M Odt

was straw, some of which was used as feed supplement while letting the remaining to rot in

3

field. Agricultural residues can be used as fuel for heat and combined heat and power plants

as well as feedstock for ethanol production[2][3].

2.2 BIOMASS FROM FOREST

Canadian sawmills are responsible for majority of forest mill residues. Lumber production is

maximum in the province of British Columbia followed by Quebec. Sawmill residues can be

in form of bark, sawdust and shavings. Rich distribution of lumber production around Canada

can be shown in the following figure[2].

Figure 1: Lumber production distribution in Canada.

3. GASIFICATION OF BIOMASS

Biomass gasification is the process of conversion of any organically derived feedstock by

partial oxidation into syngas (CO and H2) and some lesser amounts of CO2, H2O, CH4 ,

hydrocarbons and N2. The reactions are carried at temperatures of 500-1400C and at

atmospheric or elevated pressure (upto 33bar). Gasification can take place in presence of air,

pure oxygen , steam or mixture of these gases. Air based gasifiers result in low heating value

of the product gas(4-6 MJ/m3) with high concentration of nitrogen while oxygen and steam

based gasifiers produce a product gas with high concentration of CO and H2 and high heating

value(10-20 MJ/m3).

3.1 GASIFIACTION REACTIONS

Biomass gasification takes place via two steps: pyrolysis followed by gasification. Pyrolysis

occurs in presence of inert medium like N2. Its an endothermic reaction which produces lots

British Columbia

52%Quebec26%

Alberta11%

Ontario11%

Lumber Production

British Columbia Quebec Alberta Ontario

4

of volatiles (70-90%) and char. These products are further used as feed for gasification and

subsequently convert it to syngas[2].

Commonly occurring reactions in gasification are:

Partial Oxidation C + O2 CO

Combustion C + O2 CO2

Methanation C + H2 CH4

Water Gas Shift reaction CO + H2O CO2 + H2

Boudouard reaction C + CO2 CO

Steam Carbon reaction C + H2O CO + H2

When pyrolysis and gasification occurs in the same vessel its called directly heated

gasification. In this system the reactor temperature is controlled by the oxidant feed rate.

While in indirectly heated gasification two separate reactors are used for pyrolysis and

gasification. Pyrolysis may occur in a fluidised bed and the bed particles are separated from

char by cyclone separator.

4. TYPES OF GASIFIER

4.1 UPDRAFT FIXED BED GASIFIER

Updraft or counterflow gasification is the oldest and simplest form of gasifier. In this type of

gasifier biomass is introduced from top of the gasifier while air/oxygen/steam is introduced

from below the grate and diffuses up through the bed of biomass. Complete combustion

occurs at the bottom of the bed liberating CO2 and H2O at 1000C. These hot gases are

reduced to CO and H2 and they pyrolyse the descending dry biomass. The syngas leave the

reactor at relatively low temperature of 500C. The primary disadvantage of this gasifier is

that the syngas produced needs extensive clean-up before subsequent use in power plant or

chemical synthesis[4].

4.2 DOWNDRAFT FIXED BED GASIFIER

It is a simple and low cost gasifier where the biomass and the oxidant flow concurrently

down the reactor. The feed should have low moisture content (< 20%) for proper gasification.

Syngas formed exits the reactor at high temperature (800C) and requires heat recovery

system .One the disadvantage of this gasification process is that 4-7% of the carbon/feed may

remain unreacted[4].

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4.3 BUBBLING FLUIDIZED BED GASIFIER

It is one the popular forms of gasifier as it has the ability to accept wide range of fuels and

fuel particle sizes including the fines. A bubbling fluidized bed consists of fine particles of

sand or alumina and gas is forced from below the bed. Slowly the velocity of the gas is

increased till the drag force and the weight of the solid counterbalance ( ie state of minimum

fluidisation). This state is called the boiling state where the inert particles attain enough

energy to break the biomass fed. A BFB provides uniform temperature distribution, high heat

transfer rates between the particles and fuel gas and the product formed is uniform in

nature[4].

4.4 CIRCULATING FLUIDIZED BED GASIFIER

Circulating fluidised bed is operated at gas velocities higher than minimum fluidisation

velocity. This causes entrainment of bed particles along with the product gas. An additional

cyclone separator is employed to remove the bed particles from the product syngas. High

velocities might lead to erosion of the equipment and heat exchange efficiency is less as

compared to BFB gasifier.

5. SYNGAS APPLICATIONS

Highly pure Syngas has application in fuel and chemical synthesis. Supporting process

equipment such as scrubbers, compressors and coolers are required to condition the syngas

for further usage. An extensive use of syngas is its use as fuel gas. Biomass represents 4% of

primary use in USA, 17% in Finland and 21% in Sweden. About 13% of the world energy

demands is met with biomass fuels. Syngas generated from biomass when subjected to

combustion engine, combustion turbine or steam turbine helps in power generation. Biomass

integrated gasification combined cycle (BIGCC) technology can be considered for electricity

generation from sugarcane and pulp industries. Large amount of H2 gas can be produced

when syngas is subjected to Water gas shift reaction. Reacting syngas with steam over copper

oxide catalyst in presence of small amount of CO2 at temperature of about 260C and

pressure of 70bar helps in synthesis of commercial methanol. Synthetic fuels such as gasoline

and diesel can also be produced from syngas by Fischer-Tropsch process[2][4].

6

Figure 2: Distribution of various usage of syngas[9]

6. PROCESS DESCRIPTION

The forest residues are collected by means of forwarder and transported to plant site by

means of long hauls in forms of bales or loafing. Biomass is then resized and given various

shapes (chips, pellets) using various methods like rollers, chopping, shredding and rotating

knives. The resized biomass is either stored in huge silos or transported directly to the gasifier

using pneumatic belts. The biomass is kept in minimum fluidised condition in the bubbling

fluidized bed. The inert bed particles are in boiling state and they help in combustion of

incoming biomass. The syngas formed might be further used in power generation plant and

the ash formed passes through the grate at the bottom of the gasifier and is collected in a

storage bin.

7. JUSTIFICATION

This project would help us to analyze environmental impacts due to the biomass gasification

plant located at British Columbia, Canada. Presence of ample forest reserves as well as beetle

infested forest reserves makes it a better choice for plant location. About 47% of forest

lumber production occurs in BC itself[2]. The emission from biomass plant due to forest

residues is compared to that of other feeds including fossil fuel like coal. Life cycle Analysis

helps us to evaluate and analyze different types of emissions, material consumption and other

important factors of the related process from environmental point of view.

Ammonia53%Refinery

23%

Methanol11%

Electricity4%

Gas to Liquid8%

Others1% Syngas Market

Ammonia Refinery Methanol Electricity Gas to Liquid Others

7

8. LIFE CYCLE ASSESSMENT

8.1 GOAL AND SCOPE DEFINITION

The aim of this project is to assess and analyse the environmental impact due to generation of

syngas in a biomass fired gasifier. LCA helps us to estimate the greenhouse gas emission,

depletion of reserves and effects of acidification and eutrophication on ecosystem. The

damage due to various emission on human health, ecosystems and reserves was analysed

under Eco 99 methodology. A layout if the biomass gasification plant is shown in Figure 3.

The system boundary for this process includes the material transport, material production,

biomass transport and combustion in gasifier. Energy input to the system as well as further

application of syngas in other process is neglected. The plant life is assumed to be 30 years

with 7tons of biomass(wood pellets) feed in a day.

Figure 3: Boundary Line for Life Cycle Assessment of the process

Manufacturing of eraw material

TransportationGasification of

biomass

Decommissioning of gasification

plant

Emission Syngas production

8

Figure 4: General schematic diagram of BFB biomass gasifier[12].

8.2 INVENTORY ANALYSIS

The working principle of the gasifier is same as that of bubbling fluidized bed gasifier as

discussed earlier[7][8]. The material of construction of the plant along with the emission due to

its transport is mentioned in Table. Composition of the flue gas obtained is tabulated in Table

3[5]. Emission due to electricity consumption as well as dismantling of the plant is omitted in

the LCA study. For calculation of emission per kwh it was assumed that 30% energy of the

syngas produced might be used to produce electricity in a syngas turbine run power plant.

8.3 IMPACT ASSESSMENT

The air emission has been evaluated by using ECO 99 methodology. Impact assessment was

done using Hierarchist point of view. Global warming potential, Acidification and

Eutrophication and Ground level Ozone depletion values were calculated from the total

emissions including the material handling and gasification stage. The emissions calculated

were multiplied with suitable weighted damage factor using ECO 99 Indicator. All the values

have been tabulated in Table 4-7. The Global warming potential helps us to quantitatively

measure the global warming potential due to contribution from various gases like Carbon

Dioxide, Methane, Nitrous Oxide. This GWP values from different energy resources as well

as that from different types of biomass was compared.

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8.4 INTERPRETATION

Biomass is one of the abundant, cheaply available and cleaner source of energy. It was be

seen from Table 4-5 and Figure 6 that the maximum emission in biomass is due to Carbon

dioxide and Methane. Combustion of biomass in the gasifier contributes maximum to these

emission.

It can be seen that emission from biomass types like rice husk, nutshell( in general

agricultural products) is less compared to that from forest residues. It might be attributed to

the high carbon content of the wood than the agricultural wastes. However wood is preferred

as it has high energy content(11-15 MJ) than others which helps to increase the power

generation in plants.

Carbon dioxide emitted from the process contributes to the damage to human health. But the

majority of the impact is to the human(4.4E+04 and 7.337E+03 DALYs)and

ecosystem(7.8E+05 and 4.19E+02 DALYs)is due to NOx and SOx emission[11]. Depletion to

natural resources is mostly due to fossil fuel and Manganese ore content coming from the

material of construction from plant(Carbon Steel Grade 70) and not from biomass.

Comparison of GWP shows that biomass has low gram equivalent emission of carbon

dioxide(365 g/kwh) compared to other fossil fuels whose range can be as high as 1000g/kwh.

9. DISCUSSION

One of the major disadvantages of the biomass gasification is that it has low calorific value

compared to other conventional energy resources. High moisture content in biomass

decreases its gross calorific value. Secondly drying this biomass is not cost effective.

The main challenges in future for utilisation of forest based biomass is relayed to availability

of labour and machinery resources, behaviour of forest owners and their willingness to sell

the wood. Given high demand of the forest based biomass there might be a problem in future

as it is not possible to grow large patches of trees in a short time. A lot of expenditure is

involved in sizing, shredding and baling of biomass bundles.

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10. SOLUTION TO THE PROBLEMS

One of the popular methods to increase the energy content of the biomass is co-firing with

coal. This also helps in reduction of total emissions from the plant. Using hybrid crops/fast

growing trees and vines improves the gasification condition in the plant.

Since the biomass plant is far away from the forest it becomes obvious that lot of money is

involved during transportation. It would be effective to build a centralised plant and connect

to all the nearby sawmill or other sources of biomass production. The little Carbon dioxide

emission in the plant can also be controlled by recycling it to the gasifier

11. CONCLUSION

From the LCA results it can be concluded that the energy inputs and emissions from the

biomass are extremely low compared with the conventional system. Gram equivalent of

Carbon dioxide emission is 365.73 g/kwh compared to that of Coal and Heavy oil fired plant

having emissions around 1000 g/kwh and 800g/kwh respectively.

Even if it is considered a clean resource it has considerable impacts to human health and

ecosystem due to NOx and SOx. Particulate matter emission is very low and has been

contributed only due to transportation of the materials.

The LCA methodology is a very useful tool to measure the environmental impact of any

activity. ECO 99 is one of the tools which helps us to determine the damage to human health

(respiratory, climate change), ecosystems(acidification and eutrophication) and natural

reserves.

Addressing cost as well as availability and emission impacts biomass has all the potential to

generate power and be an attractive energy fuel.

11

REFERENCES

[1] D.Yogi Goswami, Alternative Energy in Agriculture , Chapter 4, Vol II Ed, 1986, Pg

83-102 .

[2] Birgit Kajat, Bioenergy and biofuels: Canadian industry and market opportunities,

Compiled for IRAP Pacific, Clean Technology Group.

[3] Amit Kumar, Jay B. Cameron and Peter C.Flynn, Biomass power cost and optimum

plant size in western Canada , Biomass and Bioenergy 24,2003, 445-464.

[4] Jared P. Ciferno and John J. Marano, Benchmarking biomass gasification technologies

for fuels, chemicals and hydrogen production , U.S Department of Energy, National Energy

Technology Laboratory.

[5] C. Koroneos, A.Dompros and G.Roumbas, Hydrogen production via biomass

gasification A life cycle assessment approach, Chemical Engineering and Processing 47,

2008, 1261-1268

[6] Average In-Use Emissions from Heavy Duty Trucks, United States Environmental

Protection Agency.

[7] Richard Venditti, Environmental Life Cycle Assessment.

[8] Handbook of Biomass Downdraft Gasifier Engine Systems.

[9] A.Van der Drift and H. Boerrigter, Synthesis gas from biomass for fuels and chemicals

[10] Nuno Couto, Abel Rouba and Valter Silva, Influence of the biomass gasification

processes on the final composition of syngas ,Energy Procedia 36, 2013, 596-606.

[11] Mark Huijbregts, Life cycle impact assessment of acidifying and eutrophying air

pollutants: Calculation of equivalency factors with RAINS-LCA.

[12] http://www.cset.iastate.edu/research/current-research/bench-top-fluidized-bed-reactor

12

APPENDIX

Table 1: Gasifier specification

Biomass Feed 7 tons/day

Temperature 700C

Air 0.8kg/kg feed

Steam 0.5 kg/kg feed

Plant life time 30 years

Distance from Forest to Plant 250km

Table 2: Material Specification

Carbon Steel Grade 70 150 tons

Concrete 1000 tons

Epoxy Paint 2 tons

Table 3: Properties of Products from Gasifier

Component % mol

Hydrogen 21.28

Carbon Monoxide 43.16

Methane 15.83

Carbon dioxide 13.45

Acetylene 0.36

Ethylene 4.62

Ethane 0.62

Tars 0.4

SOx 0.08

NOx 0.37

Table 4: Emissions due to Material of Construction

Materials kg

CO2

kg

CO

kg

CH4

kg N2O kg SO2 kg

VOC

kg

NOx

Steel 491250 139.5 6 10.5 2175 1425 24

Concrete 363600 220 141 1 372 16 517

Epoxy paint 10876 6.094 41.94 0.3 13.66 1.86 19.084

Emissions due to recyling

Recycling kg

CO2

kg

CO

kg

CH4

kg N2O kg SO2 kg

VOC

kg

NOx

Steel 218280 0 0 0 0 0 0

Landfill 207 2.3 9.2 0 0.46 2.3 2.3

Emission due to transportation of Materials

13

Transportation kg

CO2

kg

CO

kg

CH4

kg

PM2.5

kg

PM10

kg

VOC

kg

NOx

Heavy Duty

Vehicle

3.075 1.025 0.511 0.014 0.016 0.496 0.911

Table 5: Emission due to Combustion of Biomass

Materials kg

CO2

kg CO kg

CH4

kg N2O kg SO2 kg

VOC

kg

NOx

Biomass 604296 123377

1

258489

0 5082

0 17325

Emission due to transportation of Biomass

Transportation kg

CO2

kg CO kg

CH4

kg

PM2.5

kg

PM10

kg

VOC

kg

NOx

Heavy Duty

Vehicle 768.75 256.25 127.73 3.44 3.98 123.91 227.66

Table 6: Environmental impact due to biomass gasification

Global Warming Potential 365.73 g CO2/ kwh

Acidification and Eutrophication 0.4847g SO2/ kwh

Ground level Ozone 0.4924 g VOC and NOx/kwh

Table 7: Impacts using EcoIndicator 99(H,A)

Respiratory effects on human by inorganic substances

Substance Weighted damage factor DALYs

PM10 9.74 33.61

PM2.5 1.82E+01 72.8

NOx 2.3 4.041E+04

SOx 1.42 7.337E+03

Damage to human health by climate change

Substance Weighted damage factor

DALYs

CO2 5.45E-03

3.59E+04

Damage to Ecosystem

Substances Weighted damage

factor

PDF

NOx 4,45E0-1

7.82E+05

SOx 8,12E-02 4.19E+02

14

Depletion to the fossil fuels and ores

Substances

Weighted damage

factor

MJ

Mn 1.88E-01 4.27

Fe 3.87E-02 0.155

C(Coal) 2.785

Figure 5: Respiratory Impact by ECO 99.

Figure 6: Emission Comparison in various stages of operation.

PM100% PM2.5

0%

Nox85%

Sox15%

Respiratory Impact by ECO 99

PM10 PM2.5 Nox Sox

050

100150200250300350400450500550600

g CO2 eq/kwh g Nox/kwh g Sox/kwh g PM2.5/kwh g PM10/kwh g VOC/kwh

Emission Comparison in Material Handling and Combustion

Material handling Combustion

15

Figure 7: GWP comparison for various types Biomass.

Figure 8: GWP comparison of biomass with various energy resources.

0

50

100

150

200

250

300

350

400

Wood Rice husk Nutshell

g C

O2

eq

/kw

h

various biomass

GWP for Various Biomass

0

200

400

600

800

1000

1200

Biomass Heavy Oil Coal Natural gas Coal(SO2scrubbing

g C

O2

eq

/KW

H

Various Feed for gasification

GWP