R I GA T E C HNI C A L U N I VE R S I T Y

Faculty of Power and Electrical EngineeringInstitute of Energy Systems and Environment

Environmental Monitoring Laboratory

Energy Efficient and Ecological Housing“ECOHOUSING”

Project Report

NON-WOODY BIOMASS BRIQUETTES.FUEL ANALYSIS AND COMBUSTION TESTS

Riga

June 2013

Table of Contents

Introduction .......................................................................................................... 3

Acknowledgements .............................................................................................. 3

1. The gathering of biomass samples .............................................................. 4

1.1. Description of the analysed samples.................................................... 5

1.1. Briquetting process .............................................................................. 5

2. Biofuel analysis ........................................................................................... 7

2.1. Methodology........................................................................................ 8

2.2. Results.................................................................................................. 8

3. Combustion tests ....................................................................................... 11

3.1. Methodology...................................................................................... 11

3.1. Results................................................................................................ 12

Main findings ..................................................................................................... 17

References .......................................................................................................... 18

Annexes.............................................................................................................. 19

Summary: biofuel analysis [2] ........................................................................... 20

Summary: combustion tests [2].......................................................................... 21

3

IntroductionThe governments of Finland, Estonia and Latvia have proposed plans for energy

efficiency measures and the substitution of fossil energy resources by renewable energysources. An important source of renewable energy is locally available wood resources andother forms of biomass.

ECOHOUSING is a European project within the Central Baltic Region INTERREGIVA framework. The goal of the project is to increase the use of high efficiency heatingsystems and to expand the use of energy efficient domestic appliances and locally producedbiofuels. Within the framework of the project partners are collecting information aboutbiomass heating technologies (boilers, stoves, burners), made for woody biomass and/or otherforms of bioenergy. The information is collected in three partner states where the project isimplemented: Finland, Estonia and Latvia.

The main tasks of the Institute of Energy Systems and Environment (IESE) within theECOHOUSING project are following:

1) to compare characteristics of biofuels, which are produced in various regions ofLatvia, by providing a fuel analysis accordingly to the Technical Specifications of theEuropean Commission for Standardization (CEN/TS);

2) to identify the potential of non-woody biomass in Latvia and to collect differentsamples of non-woody biomass useful for production of briquettes;

3) to produce a briquettes from prepared mixtures of non-woody biomass and wood.Quality assessment should be based on laboratory analysis of the briquettes;

4) to perform combustion tests with small scale solid biomass heating appliances in orderto determine, how properties of various types of biofuels affect the efficiency, capacityand the emission rates of the appliances.

This report is focused on results related with the production, analysis and combustion ofbriquettes partly or fully made from non-woody biomass. The results of analysis andcombustion of wood logs, pellets and briquettes produced in Latvia are presented in theproject report “FUEL ANALYSIS AND COMBUSTION TESTS” (http://www.ecohousing-project.eu/wp-content/uploads/2012/11/Ecohousing_report_final-230312.pdf).

AcknowledgementsThe work was supported by the European Regional Development Fund from the

European Commission within the framework of “Central Baltic INTERREG IV Programme2007-2013” for the implementation of the project “Energy Efficient and Ecological Housing”(ECOHOUSING).

The authors would like to express a special acknowledgement to the project partners inTyötehoseura (TTS) (Work Efficiency Institute) in Rajamäki, Finland and EstonianUniversity of Life Sciences (EULS) in Tartu, Estonia. The authors express a specialacknowledgement to the Andres Menind and Mart Hovi for their assistance within thepreparation of the biomass briquettes and support on the scientific analysis of the results.

4

1. The gathering of biomass samplesDifferent types of biomass were gathered to create biomass briquettes that were

afterwards tested in a room heating stove. The gathered materials are leftovers from differentproduction processes with the exception of the Common reed that is a widespread wild plantspecie. During the collection of these materials a study on the availability of herbaceousresources for production of solid biomass fuels in Latvia was carried out, identifying theavailability of these materials in Latvia. The results are summarized in the Table 1.

Table 1. Availability and energy potential of herbaceous biomass in Latvia [1]

Biomass typeAmount,

fresh weight(t/year)

Moisturecontent (%

fresh weight)

Gross calorificvalue per dry

weight (MJ/kg)

Amount,dry weight

(t/year)

Total amount ofenergy per dryweight (TJ)

Straw 107 000 8.5 18.78 97 905 1 839Common reed 46 500 8.2 18.88 4 2687 806Grain husks 500 10.1 19.20 450 9Rapeseed dust 4 526 8.4 22.11 4 146 92Buckwheat hulls 1 500 14.4 19.64 1 284 25Grain dusts 83 10.1 19.20 75 1Potato pulp 2 661 88 15.47 319 5Hogweed 625 000 90 19.25 62 500 1 203TOTAL 787 770 459 366 4 810

The area where the biomass was collected can be seen in the Figure 1.

Figure 1. Sources of biomass materials [source of the map - http://www.grupa93.lv]

Rapeseed

Oat and wheatmiddlings

Straw

DraffBuckwheat

Commonreed

Source: agriculture or non-arableland

Source: industry

5

1.1. Description of the analysed samplesFor the experiments a total number of 6 herbaceous types of biomass were gathered in

Latvia and 3 more samples received from the partners in Estonia. Mixtures of herbaceousbiomass and different shares of wood were made and briquetted. The ratios of biomass towood for the briquettes were 100:0, 75:25, 50:50, 25:75, in specific the ratio 0:100 representspure wood used as a benchmarking threshold. The original sources of the biomass anddesignation used to describe the biomass mixtures are given in the Table 2.

Table 2. Description of the biomass used [2]Biomass Source DesignationDraff Residue of husks after fermentation, beer production DRCommon reed Pure material, wetlands CROat and wheatmiddlings By-product from sieving of grains, agriculture OWM

Straw By-product from grain cultivation, agriculture STBuckwheat hulls By-product from production of buckwheat BH

Rapeseeds By-product from biofuel production (excludingrapeseed cake) RB

Wood Saw dust from sawmilling process WO

The numbers after the designations are describing the mass percentage of non-woodybiomass in the mixture:

- Draff – DR (DR25, DR50, DR75, DR100);- Common reed – CR (CR25, CR50, CR75, CR100);- Oat and wheat middlings –OWM (OWM25, OWM50, OWM75, OWM100);- Straw – ST (ST25, ST50, ST75, ST100);- Buckwheat hulls – BH (BH25, BH50, BH75, BH100);- Rapeseed by-product from biofuel production (excluding rapeseed cake) – RB

(RB25, RB50, RB75, RB100);- Wood – WO (WO100).

The materials from the Estonian partners were briquetted as pure materials with noaddition of wood. These materials were bark, hay and manure.

1.1. Briquetting processThe briquetting operations and the energy consumption measurements for processing

were performed in the Biofuel Laboratory at Estonian University of Life Sciences. Abriquetting experiment was carried out by using the briquetting press Weima C-150. Theapplied compressive force to the sample in a 50mm press chamber was ~20 tons. Thebriquetting process has been carried out with constant output rate - 50 kg h-1. The longitudeof the briquettes on the machine is adjusted automatically by the analogue controller. Thisguarantees to have briquettes of approximately equal size (i.e. between 5-6 cm) during anormal production phase. The electricity consumption was measured with 1 Wh resolutionand logged for all the tested samples. Particle density (density of a single briquette) wasdetermined by weighting together with the stereometric volume estimation for sevenrandomly chosen briquettes from every sample of biomass [2].

6

The measured energy consumption of the briquetting process for the studied casesvaried in the range of 51.1 - 101.1 kWh/t (see Fig. 2.). This means that energy consumptionmay vary two times in function of biomass used [2].

50

60

70

80

90

100

110

OWM DR BH CR RB ST25% 50% 75% 100% 100% Wood

a) Energy consumption, kWhe/t

600

700

800

900

1000

OWM DR BH CR RB ST25% 50% 75% 100% 100% wood

b) Particle density, kg/m3

Figure 2. Indicators of briquetting process: a – energy consumption of the machinery, b –density of briquettes (particle density) [2]

Particle density of the produced briquettes is described in Fig. 2.b. All the samples ofpure grainy materials (oat and wheat middlings, draff, rapeseed by-product, buckwheat hulls)do not suit well for producing of good quality briquettes. From mixtures with a sawdust ratioof 50% or higher all the materials were possible to be pressed into solid and well-shapedbriquettes. In order to guarantee the quality and mechanical durability of briquettes (requiredby standard for solid biofuels fuels LVS EN 14961-1:2010 [3]) it is recommended to useadditional binding materials. In this specific case straw, hay or some other material rich inlignin may be used instead of sawdust [2].

An illustrative view of the briquettes produced using collected samples is presented inTable 3.

Table 3. The appearance of the tested briquette samples

WO100 OWM25 OWM50 OWM75 OWM100

7

WO100 DR25 DR50 DR75 DR100

WO100 BH25 BH50 BH75 BH100

WO100 CR25 CR50 CR75 CR100

WO100 RB25 RB50 RB75 RB100

WO100 ST25 ST50 ST75 ST100

2. Biofuel analysisThe gathered different biomass types were tested before and after the briquetting

process. No considerable changes in the test results were noticed. The moisture content, ashcontent, net and gross calorific value for the samples were determined according to the

8

methods described in the LVS EN standards. The analysis was carried out in theEnvironmental Monitoring Laboratory at Riga Technical University.

2.1. MethodologyThe terminology and definitions are used according to the LVS EN 14588:2011

standard “Solid biofuels - Terminology, definitions and descriptions” [4]. The methodologyused for biofuel analysis is presented in Table 3.

Table 3. Methodology used for laboratory analysis of the biomass samplesParameter, unit Method Repeatability limitMoisture content,

w-%* LVS EN 14774-3 [5] < 0.2 % absolute

Ash content, w-%,d** LVS EN 14775 [6] < 2 % of the mean result (A ≥ 10 %)

< 0.2 % absolute (A < 10 %)Net calorific value,

MJ kg-1 LVS EN 14918 [7] < 120 J g-1

Gross calorificvalue, MJ kg-1 LVS EN 14918 [7] < 120 J g-1

* w-% - weight-percentage** w-%,d - weight-percentage, dry basis

2.2. ResultsNumerical results of the biofuel analysis results are summarised in the Annex I. The

comparison of the results for the tested types of briquettes is presented in the Figures 3 to 5.

Figure 3. Moisture content in the briquettes samples [2]

9

The moisture content of the samples used for combustion tests is presented in Figure 3.Moisture content is used for the calculation of ash content and calorific value. The moisturecontent for all the analysed samples varied from 6.39 w-% to 12.4 w-%.

Figure 4. Ash content in the briquettes samples [2]

The unconventional biomass used for the experiments has much higher ash content incomparison with wood sawdust. For studied types of herbaceous biomass ash content vary inrange of 2-5 w-%,d, but for rapeseeds it was 11.3 w-%, d and 7.39 w-%, d for hay [2].

Figure 5. Gross calorific value of the samples [2]

10

The gross calorific values of the samples vary in the range of 18.3 to 21.3 MJ/kg. Thehighest gross calorific values of the draff, rapeseed hulls and bark are similar with wood.

Figure 6. Net calorific value, constant pressure, moisture as received for the briquettessamples [2]

The net caloric values of the samples vary from 15.6 to 17.9 MJ/kg. Briquettes samplesfrom common reed, oat and wheat middlings and straw have the lowest net caloric values.

11

3. Combustion testsAll collected samples were combusted in order to determine the concentration of

emissions and thermal performance of the stove.

3.1. MethodologyThe combustion tests were performed using a stove for samples of briquettes.

Combustion tests were done according to the standard LVS EN 13240:2002 “Room heatersfired by solid fuel – Requirements and test methods” [8]. All tests were performed incontrolled conditions and using same mass of fuel. Oxygen, carbon dioxide, carbonmonoxide, nitrogen oxide and flue gas temperature values were measured during all the testusing infrared/electrochemical flue gas analyzer was. The chimney draught was monitoredusing differential manometer. The amount of consumed fuel was monitored too usingweighting platform.

The heat output was calculated by using the mass of the fuel consumed during the test,the net calorific value of the test fuel and the stove efficiency. Heat losses are determinedfrom the mean values of flue gases and room temperature, the flue gas composition and theamount of combustibles in the residue. Efficiency of the stove is determined from heat losses.All calculations are done according to methodology of the LVS EN 13240:2002 standard [8].

The room heating stove was used for combustion tests Skladova Tehnika Torino K. Thestove is equipped with grates, ash collecting box, glazed doors, buffer plate in the top of theburning chamber and ceramic plane in the bottom of the stove, see Figure 7.

a) b)Figure 7. a) Room heating stove Skladova Tehnika Torino K, b) Principial scheme of the

combustion chamber (P – primary air supply; S – secondary air supply; E – exhaust to stack)

Air supply is ensured through two air intakes: above of the front door and on the lid ofthe ash box, see Figure 7 b. The air intakes can be regulated manually.

12

3.1. ResultsThe photos from each combustion test are visible in the Table 4. Photos are made every five minute of the test in order to provide basic visual

information on the duration and intensity of the combustion process.

Table 4. Visualization of the combustion tests00:05 00:10 00:15 00:20 00:25 00:30 00:35 00:40 00:45 00:50 00:55 01:00

DR25

DR50

DR75

DR100

CR25

CR50

CR75

CR100

13

OWM25

OWM50

OWM75

OWM100

ST25

ST50

ST75

ST100

BH25

BH50

14

BH75

BH100

RB25

RB50

RB75

RB100

WO100

Hay

Bark

Manure

15

The differences in duration of the combustion process are presented in Figure 8. Results fromthe combustion tests showed the strong correlation between share of non-woody biomass inbriquettes and duration of combustion tests. Samples with common reed have greatly longercombustion test duration that all the other samples.

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

25% 50% 75% 100%Share of non-wood biomass, %

DR CR OWM ST BH RB WO

Combustion time, hour

Figure 8. The duration of the combustion process [2]

Also the temperature of the flue gas has correlation with duration of the combustion tests. Thecomparison of flue gas temperature is presented in Figure 9.

Figure 9. Flue gas temperature [2]

The function between the duration of combustion process and the flue gas temperature isinvers - the greater is the time of combustion the lower is temperature of flue gases. In general fluegas temperatures differ from 331 °C to 474 °C. The thermal efficiency is presented in Figure 10.

16

6465666768697071727374

25% 50% 75% 100%

Efficiency,%

Share of non-wood biomass, %DR CR OWM ST BH RB WO

Figure 10. Thermal efficiency of the stove [2]

The briquettes from the common reed have higher efficiency between all the tested samples.The briquettes from the buckwheat hulls, oat and wheat middlings and pure wood represents thelowest efficiency. Heat output from the stove is mainly dependent from the amount of fuel energyand duration of the combustion process. Thermal power of the stove is presented in Figure 11.

0

2

4

6

8

10

12

14

25% 50% 75% 100%

Power, kW

Share of non-wood biomass, %DR CR OWM ST BH RB WO

Figure11. Thermal power of the stove [2]

The power of the stove varied from 6.55 kW to 13.02 kW. There is obvious correlationbetween the heat output and share of non-woody biomass in briquettes.

The summary of the results for combustion tests including the results for hay, bark andmanure briquettes is given in the Annex II.

17

Main findingsThe combination of woody biomass with other type of biomass is giving a several

opportunities. Results of the combustion tests prove that several types of herbaceous biomasscan stabilize the combustion process by reducing combustion intensity. This results muchlonger, safer and more efficient combustion. High ash content should not create anysignificant mechanical problems in the case than herbaceous biomass is used in the appliancesdesigned for wood logs and briquettes. This aspect is not related to appliances with automatedfuel supply and ash removal systems.

Higher ash and nitrogen contents, resulting in an elevated emission of dust and NOx, arestill a matter of investigation on the use of herbaceous biomass in small scale householdappliances.

The quality of compressed biofuels depends on both: production process and parametersof raw materials. Due to diverse properties of herbaceous biomass, it can be effectively usedin mixtures to improve specific parameters of the final product. At the same time results ofthis study shows that energy consumption for the specific case should be investigated.

A full scientific perspective of the tests carried out is reported within the scientific paperBriquettes from mixtures of herbaceous biomass and wood: biofuel investigation andcombustion tests” by A.Žandeckis, F. Romagnoli, A. Beloborodko, V.Kirsanovs, A. Menind,M. Hovi, D.Blumberga [2].

18

References

1. Beloborodko, A., Kļaviņa, K., Romagnoli, F., Ķenga, K., Rošā, M., Blumberga, D.Study on Availability of Herbaceous Resources for Production of Solid Biomass Fuelsin Latvia. Agronomy Research, 2013, Vol.11, No.2, pp.283-294. ISSN 1406-894X;

2. A.Žandeckis, F. Romagnoli, A. Beloborodko, V.Kirsanovs, A. Menind, M. Hovi,D.Blumberga Briquettes from mixtures of herbaceous biomass and wood: biofuelinvestigation and combustion tests. Submitted for proceedings of the The 8thConference on Sustainable Development of Energy, Water and Environment Systems,2013;

3. LVS EN 14961-1:2010 “Solid biofuels - Fuel specifications and classes - Part 1:General requirements”;

4. LVS EN 14588:2011 “Solid biofuels - Terminology, definitions and descriptions”;5. LVS EN 14774-3:2010 “Solid biofuels - Determination of moisture content - Oven dry

method - Part 3: Moisture in general analysis sample”;6. LVS EN 14775-2010 “Solid biofuels - Determination of ash content”;7. LVS EN 14918:2010 “Solid biofuels - Determination of calorific value”;8. LVS EN 13240:2002 “Room heaters fired by solid fuel – Requirements and test

methods”.

19

Annexes

20

Annex 1Summary: biofuel analysis [2]

Unit DR25

DR50

DR75

DR100

CR25

CR50

CR75

CR100

OWM25

OWM50

OWM75

OWM100

ST25

ST50

ST75

ST100

Ash content Ad;w-%, d 1.66 2.65 4.01 4.91 1.61 2.93 3.93 4.89 1.30 1.97 2.87 3.61 1.51 2.54 3.69 4.72

Moisturecontent

Mar;w-% 2.65 7.50 7.49 7.82 6.70 6.84 6.61 6.65 7.50 7.95 8.42 8.66 6.95 7.06 7.33 6.97

Gross calorificvalue

qgr,v,d;MJ/kg, d 20.8 20.7 20.8 21.0 20.2 19.6 19.1 18.8 20.2 19.7 19.4 19.0 20.2 19.8 19.2 18.9

Net calorificvalue

qnet,p,ar;MJ/kg, 17.7 17.5 17.8 17.7 17.4 16.9 16.6 16.2 16.9 16.4 16.0 15.6 17.2 17.1 16.3 16.2

Gross calorificvalue

qgr,v,d;kWh/kg, d 5.78 5.77 5.79 5.84 5.62 5.46 5.31 5.22 5.62 5.49 5.39 5.27 5.60 5.49 5.35 5.25

Net calorificvalue

qnet,p,ar;kWh/kg, 4.93 4.87 4.95 4.93 4.85 4.69 4.60 4.49 4.70 4.56 4.44 4.34 4.77 4.75 4.52 4.52

Particle density kg/m3 922 945 881 889 832 733 668 662 937 960 989 890 843 810 788 754

Unit BH25

BH50

BH75

BH100

RB25

RB50

RB75

RB100

WO100 Hay Bark Manure

Ash content Ad;w-%, d 1.23 1.50 1.92 2.19 3.95 6.57 8.71 11.3 0.82 7.39 4.62 5.95

Moisturecontent

Mar;w-% 7.10 7.75 8.01 12.4 6.93 7.10 7.30 7.52 6.39 7.09 7.20 7.83

Gross calorificvalue

qgr,v,d;MJ/kg, d 20.3 20.0 20.0 19.8 21.0 21.0 21.1 21.3 20.7 18.3 20.5 18.9

Net calorificvalue

qnet,p,ar;MJ/kg, 17.3 16.9 16.9 15.9 17.9 17.9 17.9 17.9 17.8 16.7 19.1 17.6

Gross calorificvalue

qgr,v,d;kWh/kg, d 5.65 5.55 5.55 5.50 5.83 5.85 5.86 5.93 5.77 5.08 5.70 5.26

Net calorificvalue

qnet,p,ar;kWh/kg, 4.80 4.70 4.70 4.41 4.97 4.98 4.97 4.99 4.96 4.64 5.29 4.89

Particle density kg/m3 969 878 820 732 992 981 978 925 899 - - -

21

Annex 2Summary: combustion tests [2]

Unit DR25

DR50

DR75

DR100

CR25

CR50

CR75

CR100

OWM25

OWM50

OWM75

OWM100

ST25

ST50

ST75

ST100

Testduration h:mm 0:37 0:39 0:46 0:46 0:39 0:48 0:50 1:00 0:30 0:34 0:41 0:45 0:37 0:38 0:39 0:44

Applied fuelquantity kg 1.97 2.01 2.02 2.01 1.98 1.99 2.00 2.01 2.01 1.99 2.01 2.01 1.99 1.98 1.99 1.99

Hourly fuelconsumption kg/h 3.19 3.09 2.63 2.62 3.05 2.49 2.40 2.02 4.02 3.51 2.94 2.68 3.23 3.13 3.06 2.71

Fuel heatinput kWh 9.69 9.79 9.99 9.89 9.59 9.32 9.20 9.07 9.45 9.06 8.91 8.72 9.49 9.40 8.98 8.98

Capacity kW 11.4 10.5 9.23 9.20 10.6 8.40 7.88 6.55 13.0 10.9 8.76 8.16 10.8 10.5 9.41 8.94Stove

efficiency % 72.6 69.9 70.8 71.3 71.7 72.2 71.4 72.2 68.9 67.9 67.2 70.2 70.5 70.7 68.1 73.1

Flue gastemp.

oC 430 427 412 412 442 409 396 331 474 451 421 496 437 429 430 392

Unit BH25

BH50

BH75

BH100

RB25

RB50

RB75

RB100

WO100 Hay Bark Manure

Testduration h:mm 0:35 0:38 0:45 0:41 0:33 0:38 0:44 0:46 0:33 0:36 0:32 1:10

Applied fuelquantity kg 2.00 2.01 2.01 2.00 1.99 1.98 2.00 2.01 1.97 2.07 2.05 1.99

Hourly fuelconsumption kg/h 3.43 3.17 2.68 2.93 3.62 3.13 2.73 2.62 3.58 3.45 3.84 1.71

Fuel heatinput kWh 9.59 9.43 9.44 8.82 9.87 9.85 9.93 10.0 9.77 9.24 10.64 9.77

Capacity kW 11.3 10.1 8.37 8.37 12.5 10.7 9.43 9.25 11.9 12.7 12.1 5.63Stove

efficiency % 68.9 67.9 66.5 64.9 69.4 69.1 69.6 70.8 67.2 71.7 69.7 67.2

Flue gastemp.

oC 436 450 424 403 459 448 421 426 466 443 462 379

22