Energy Efficient and Ecological Housing ECOHOUSING. Project Report FUEL ANALYSIS AND COMBUSTION TESTS

Transcription

1 R I GA TECHNICAL UNIVE R S I T Y Faculty of Power and Electrical Engineering Institute of Energy Systems and Environment Environmental Monitoring Laboratory Energy Efficient and Ecological Housing ECOHOUSING Project Report FUEL ANALYSIS AND COMBUSTION TESTS Riga March 2012

2 Table of Contents Introduction... 3 Dissemination of the project results... 4 Acknowledgements The gathering of biofuel samples Territorial distribution of the analysed samples Description of the analysed samples Biofuel analysis Methodology Results Conclusions Combustion tests Methodology Results Flue gas composition Capacity and efficiency Conclusions Main findings References Appendix Summary: biofuel analysis for pellets Summary: biofuel analysis for briquettes and wood logs Summary: combustion tests using pellets Summary: combustion test using briquettes Summary: combustion test using wood logs... 33

3 Introduction The governments of Finland, Estonia and Latvia have proposed plans for energy efficiency measures and the substitution of fossil energy resources by renewable energy sources. An important source of renewable energy is locally available wood resources and other forms of biomass. ECOHOUSING is a European project within the Central Baltic Region INTERREG IVA framework. The goal of the project is to increase the use of high efficiency heating systems and to expand the use of energy efficient domestic appliances and locally produced biofuels. Within the framework of the project partners are collecting information about biomass heating technologies (boilers, stoves, burners), made for woody biomass and/or other forms of bioenergy. The information is collected in three partner states where the project is implemented: Finland, Estonia and Latvia. The main tasks of the Institute of Energy Systems and Environment (IESE) within the ECOHOUSING project are following: to compare characteristics of biofuels, which are produced in various regions of Latvia, by providing a fuel analysis accordingly to the Technical Specifications of the European Commission for Standardization (CEN/TS); to perform combustion tests with small scale solid biomass heating appliances in order to determine, how properties of various types of biofuels affect the efficiency, capacity and the emission rates of the appliances. During the project in total 13 samples of pellets, 9 samples of wood logs and 9 samples of briquettes were examined. The samples were gathered from local producers and resellers in Latvia and as well received from the Finnish and Estonian partners. Physical parameters were determined for various types of biomass, such as, wood, straw, peat and grass. Combustion tests with 25 kw pellet boiler and 9 kw stove were performed at the Laboratory of Environmental Monitoring of the IESE. The testing was done using the previously gathered samples of biofuel. The aim of the testing was to reveal the relationship between the emission rates, the efficiency and capacity of the appliances and the quality of the biofuels. Within the frame of the project, IESE is participating in the implementation of a market research regarding the current situation within the sector of the biomass heating appliances. A questionnaire oriented on acquiring information on technical and environmental parameters and costs of different biomass-based combustion technologies has been developed. Moreover the IESE is carrying out the analysis and optimization of the first solar and pellet combisystem installed for a multi-family building in Latvia. The IESE is taking part in the activities of developing a database of online learning materials. The main objective of the database is to provide information about energy efficient and ecological measures for households sector, but, in fact the oriented target groups are wider: end-users, energy experts, scientists and students. 3

4 Dissemination of the project results The project results are generally intended for two different target groups. Firstly, other researchers can acquire information about the project in forms of scientific publications, abstracts and poster presentations at conferences. Secondly, general public is acquainted with the project outcomes through the mass media and the internet. Scientific publications 1. Beloborodko A., Timma L., Žandeckis A., Romagnoli F. The regression model for the evaluation of the quality parameters for pellets. Submitted paper for the proceedings of International scientific conference "Biosystems Engineering", May 10-11, 2012, Tartu, Estonia. 2. Kirsanovs V., Timma L., Žandeckis A., Romagnoli F. The quality of pellets available on the market in Latvia: classification according EN requirements. Submitted paper for the proceedings of 53rd International Scientific Conference of Riga Technical University and 1st World Congress of RPI-RTU Engineering Alumni, October 11-12, 2012, Riga, Latvia. 3. Žandeckis A., Timma L., Rochas C., Rošā M., Blumberga D. Solar and pellet combisystem for an apartment buildings: analysis of solar loop thermal performance // Submitted paper for Latvian Journal of Physics and Technical Sciences, March Žandeckis A., Timma L., Rochas C., Rošā M., Blumberga D. Solar and pellet combisystem for an apartment buildings. Heat losses and efficiency improvements of the pellet boiler // Re-submitted peer reviewed paper for the international journal - Applied Energy, March Žandeckis A., Rochas C., Blumberga D., Timma L. Possibilities for Utilization of Solar Thermal Energy in Multi-Family Buildings in Latvia // RTU scientific proceedings Ser.13, Environmental and climate technologies. Vol.6, Riga Technical University, 2011, Riga, Latvia. 6. Žandeckis A., Rochas C., Blumberga D., Rošā M., Siliņš K., Timma L. Solar, Pellet Combisystem for Apartment Buildings // 6th Dubrovnik Conference on Sustainable Development of Energy, Water and Environment Systems, Online Proceedings, September 25-29, 2011, Dubrovnik, Croatia. Abstracts 7. Žandeckis A., Timma L., Blumberga D., Rochas C. [In Latvian] Saules siltuma izmantošanas iespējas daudzdzīvokļu ēkās // Apvienotā Pasaules latviešu zinātnieku 3. kongresa un letonikas 4. kongresa sekcijas Vides kvalitāte Latvijā: esošais stāvoklis, izaicinājumi, risinājumi Book of abstracts, 2011, Riga, Latvia. 8. Žandeckis A., Rochas C., Rošā M., Blumberga D., Siliņš K., Timma L. Solar, pellet combisystem for apartment buildings // 6th Dubrovnik conference on sustainable development of energy, water and environment systems, Book of abstracts, Faculty of Mechanical Engineering and Naval Architecture, p , 2011, Zagreb, Croatia. 4

5 Poster presentations 9. Žandeckis A., Timma L., Rochas C., Blumberga D. [In Latvian] Saules siltuma izmantošanas iespējas daudzdzīvokļu ēkās Latvijā // Poster presentation at Riga Technical University 52 nd International scientific conference, Section Environmental and Climate Technologies, October 12, 2011, Riga, Latvia. 10. Žandeckis A., Timma L., Blumberga D., Rochas C. [In Latvian] Saules siltuma izmantošanas iespējas daudzdzīvokļu ēkās Latvijā // Poster presentation Apvienotā pasaules latviešu zinātnieku III kongresa un Letonikas IV kongresa «Zinātne, sabiedrība un nacionālā identitāte» ietvaros, Sekcija Enerģētika un elektrotehnika, October 25, 2011,, Riga, Latvia. 11. Žandeckis A., Timma L., Blumberga D., Rochas C. [In Latvian] Saules siltuma izmantošanas iespējas daudzdzīvokļu ēkās Latvijā// Poster presentation seminārā Zaļās enerģijas ceļš Latvijā: no tehnoloģiskiem risinājumiem līdz politikai, December 14, 2011, Riga, Latvia. Appearance on the television 12. The costs of heating: which fuel to use for cost efficient heating?, prepared by Latvian Independent Television JSC, 2011, available on Innovations for residential building heating solutions, prepared by Hansamedia Ltd., 2011, available on Quality analysis of different pellets, prepared by Vides Projekti Ltd., 2011, available on [Starts at: 01:40] 15. Solar pellet combisystem for multi-family building in Sigulda, prepared by Vides Projekti Ltd., 2011, available on [starts at 10:15] 16. Solar pellet combisystem for multi-family building in Sigulda, prepared by Latvian Independent Television JSC, 2011, available on Project ECOHOUSING the determination of quality parameters and combustion efficiency of local biofuels in Latvia, prepared by Latvian Independent Television JSC, to be aired in March

6 Acknowledgements The work was supported by the European Regional Development Fund from the European Commission within the framework of Central Baltic INTERREG IV Programme 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 in Työtehoseura (TTS) (Work Efficiency Institute) in Rajamäki, Finland and Estonian University of Life Sciences (EULS) in Tartu, Estonia for their assistance, provided biomass samples and conducting alternative analysis for comparison. Compact solar and pellet combisystem was built with financial support of the European Economic Area Financial Mechanism, the Environmental Policy and Integration of Latvia. 6

7 1. The gathering of biofuel samples The main objective for the biofuel gathering process was to collect samples produced in various regions of Latvia covering different types of locally available biomass fuels Territorial distribution of the analysed samples In order to compare the characteristics of different locally produced biomass fuels a total of 27 samples of various types of biomass fuel were gathered. The analysis was performed for 12 samples of pellets, 6 samples of briquettes and 9 samples of wood logs. The gathered samples represented two different types of trade forms directly purchased from producers and purchased from resellers and four types of biomass resources wood, straw, peat and grass. The location of producers, resellers and the price for the analysed biofuels were obtained for further comparison. The territorial distribution of the collected samples is presented in Figure 1. Pellets Briquettes Wood logs Figure 1. Territorial distribution of collected biomass samples In addition to the locally gathered samples, four biofuel samples were received directly from the project partners. The same type of analysis was performed for these samples as for the locally gathered samples. Two samples of grass briquettes were obtained from EULS; one pellet sample and one briquette sample were received from TTS. Moreover in order to investigate and analyse the same type of biomass among the project partners one sample of wood pellets was sent to TTS. 7

8 1.2. Description of the analysed samples An overview of the analysed samples of pellets The trade form, the type of biomass, price and geometrical dimensions of the collected biomass pellets are presented in Table 1. Table 1 The characteristics of the tested samples of pellets Geometrical dimensions Sample Biomass Price, /ton Trade form ID type excl. VAT Mean Mean diameter, mm length, mm 1PP Producer Wood PP Producer Wood PS Reseller Wood PP Producer Wood PS Reseller Wood PP Producer Wood PS Reseller Wood PS Reseller Wood PP Producer Peat PS Reseller Wood PP Producer Straw PP Producer Straw PF Received from the partners in Finland Wood n/a All gathered pellets were sold in plastic bags (for pellets with 6 mm in diameter in 15 kg bags and for pellet with 8 mm pellets in 16 kg bags). The appearance of the gathered pellets varies depending on the biomass type and the geometrical dimensions, see Table 2. The appearance of the tested samples of pellets Table 2 1PP 2PP 3PS 4PP 5PS 6PP 8

9 7PS 8PS 9PP 10PS 11PP 12PP 13PF 9

10 An overview of analysed samples of briquettes The trade form, biomass type, price and geometrical dimensions of the collected biomass briquettes are presented in Table 3. Table 3 The characteristics of the tested samples of briquettes Geometrical dimensions Sample Biomass Price, /ton Trade form ID type excl. VAT Mean Mean diameter, mm length, mm 1BS Reseller Wood BS Reseller Wood BP Producer Straw BP Producer Wood BP Producer Wood BS Reseller Wood BF Received from the partners in Finland Wood n/a BE Received from the Grass n/a BE partners in Estonia Grass n/a All gathered briquettes were sold in plastic bags. Usually one bag contained 12 briquettes and weighed approximately 10 kg. An illustrative review on the collected samples of briquettes is presented in Table 4. The appearance of the tested samples of briquettes Table 4 1BS 2BS 3BP 4BP 5BS 6BS 7BF 8BE 9BE 10

11 An overview of analysed samples of wood logs The trade form, price and geometrical dimensions of the collected samples of wood logs are presented in Table 5. Table 5 The characteristics of the tested wood log samples Sample ID Trade form Price, /m 3 Geometric dimensions excl. VAT Diameter, cm Length, cm 1WLS Reseller (shop) WLP Producer WLP Producer WLP Producer WLS Reseller (shop) WLS Reseller (shop) WLP Producer WLP Producer WLS Reseller (shop) The samples of wood logs were gathered in various packing forms. Some of the samples were packed in plastic mesh bags; others were stored in piles at the site of the producer and transported in cardboard boxes. The pre-packaged units were sold in plastic mesh bags; these bags usually had a capacity from 20 up to 40 litres. The appearance of the collected samples of the wood logs is shown in Table 6. The appearance of the tested samples of wood logs Table 6 1WLS 2WLP 3WLP 4WLP 5WLS 6WLS 7WLP 8WLP 9WLS 11

12 Pellets only All samples 2. Biofuel analysis The moisture content, ash content, net and gross calorific value, mechanical durability, bulk and energy density and the amount of fines for the pellets were determined accordingly to the methods described in the CEN/TS Methodology The terminology and definitions are used according to the LVS EN 14588:2011 standard Solid biofuels - Terminology, definitions and descriptions [1]. The enumeration of the tested parameters and the precision for each method are summarized in Table 7. Table 7 CEN/TS methodology for determination of the physical parameters for solid biofuels Parameter Method Repeatability limit Moisture content, w-% * CEN/TS [2] < 0.2 % absolute < 2 % of the mean result Ash content, w-%,d ** CEN/TS [3] (A 10 %) < 0.2 % absolute (A < 10 %) Mean diameter, mm Mean length, mm Net calorific value, MJ kg -1 CEN/TS [4] < 120 J g -1 Gross calorific value, MJ kg -1 CEN/TS [4] < 120 J g -1 Bulk density, kg m -3 LVS EN [5] < 4 % (BD 300 kg m -3 ) < 6 % (BD < 300 kg m -3 ) Durability, w-% CEN/TS [6] < 0.4 % absolute (DU 97.5 %) < 2 % absolute (DU < 97.5 %) Fines, w-% LVS EN [7] < 2 w-% Energy density, MWh m -3 LVS EN [8] --- * w-% - weight-percentage ** w-%,d - weight-percentage, dry basis The determination of the moisture content was performed accordingly to the standard LVS EN :2010 Solid biofuels Determination of moisture content Oven dry method Part 3: Moisture in general analysis sample [2]. The procedure included drying of the sample in an oven at 105 ºC until constant mass is reached. The determination of ash content was performed accordingly to the LVS EN 14775:2010 standard Solid biofuels Determination of ash content [3]. The ash content was determined by combustion of biofuel sample in a muffle furnace at 550 ºC. The gross and net calorific values of biomass samples were determined accordingly to the method for automated bomb calorimeters described in the LVS EN 14918:2010 standard Solid biofuels Determination of calorific value [4]. For the samples of pellets bulk density was determined by using the LVS EN 15103:2010 methodology Solid biofuels Determination of bulk density [5]. The standard describes a method of filling a container with sample and repeatedly dropping container from fixed height to achieve the compaction of the pellets. 12

13 Moisture content, w-% Calorific value, MJ kg-1 The durability was determined by agitation of pellets in a rotating drum accordingly to the standard LVS EN :2010 Solid biofuels Determination of mechanical durability of pellets and briquettes Part 1: Pellets [6]. The amount of fines was determined by using the LVS EN :2011 Solid biofuels Determination of particle size distribution Part 1: Oscillating screen method using sieve apertures of 1 mm and above [7] methodology. The calculations of energy density of pellets were done by using the results for net calorific value at constant pressure and bulk density values accordingly to the LVS EN :2010 Solid biofuels - Fuel specifications and classes - Part 1: General requirements [8] Results From all of the gathered pellet samples, the sample 7PS that was purchased from a reseller had the lowest moisture content 4.4 w-%, the moisture content for all analysed pellet samples varied from 4.4 w-% to 12.2 w-% (see Figure 2). Of all the collected briquettes the lowest moisture content 5.7 w-% was determined for sample 2BS (see Figure 3). Due to different storage conditions of obtained wood logs the moisture content for all samples varied from 8.7 w-% to 43.4 w-%. All gathered straw and grass samples presented moisture content slightly over 8%, but the net calorific value due to biomass type was lower than for wood samples with the same moisture content. The net calorific value for pellets varied in the range between 16.0 and 18.4 MJ kg -1. The net calorific value for briquettes varied in the range between 15.2 and 18.8 MJ kg -1. The net calorific value of the driest wood sample was 16.6 MJ kg -1, but for wood logs with the highest moisture content 9.9 MJ kg -1. More detailed results for all analysed parameters of the collected biofuels are presented in Appendix 1 and Appendix PP 2PP 3PS 4PP 5PS 6PP 7PS 8PS 9PP 10PS 11PP 12PP 13PF Pellets Moisture content Net calorific value Gross calorific value Figure 2. Moisture content, gross and net calorific value of pellet samples

14 Moisture content, w-% Calorific value, MJ kg BS 2BS 3BP 4BP 5BP 6BS 7BF 8BE 9BE 1WLS 2WLP 3WLP 4WLP 5WLS 6WLS 7WLP 8WLP 9WLS Briquettes Wood logs Moisture content Net calorific value Gross calorific value Figure 3. Moisture content, gross and net calorific value of briquette and wood log samples 2.3. Conclusions It was observed that pellets with higher ash content had lower gross calorific value, only peat pellets are an exception to this statement. This can be explained by higher content of carbon in peat in comparison to woody biomass. The highest ash content was observed for non-woody biomass samples: peat, straw and grass. This could be explained by the origin of biomass as there are additional nutrients added in fields where straw and grass is harvested and therefore more micro and macro elements are fixed in the biomass. Non-woody biomass usually is more contaminated with inorganic components as sand, dust and soil. The gross calorific value for peat was higher than for wood, which is due to higher content of carbon, but the net calorific value was in typical range of tested woody biomass pellets because of elevated moisture and ash content for peat pellets. The net calorific value is dependent on the moisture content of the biomass; pellets with lower moisture content had higher calorific value. Lower moisture content was observed for pellets purchased from resellers in comparison to ones purchased from producers. This could be due to the storage conditions in both cases. It was observed that most producers store their pellets in warehouses near to the production site, while the resellers store the pellets at their facilities, where the indoor climate is usually adjusted for thermal comfort of customers. In regard to this, the storage conditions would mainly explain the differences for samples obtained in two trade forms, assuming that in reseller s facilities the relative air moisture is lower than in producer s warehouses. Three of the collected briquette samples had high gross calorific value, all more than 21 MJ kg -1, this could be explained by lower amount of the unburning mass ash per mass unit e.g. sample 2BS, or by the use of coniferous wood e.g. sample 5BP. Biomass of three different tree species birch, pine and alder was collected in the form of wood logs. Pine as coniferous wood had slightly higher gross calorific value, but the sample had high moisture content, therefore relatively low net calorific value. The net calorific value of the driest wood log sample was 1.7 times higher than for the sample with 14

15 the highest moisture content. In order to use biomass resources efficiently, it is important for typical households to buy and use dried wood logs or dry wood logs before combustion. The results for the physical parameters: mechanical durability, bulk density and the amount of fines, for the tested pellets varied in a wide range, which can be explained by different manufacturing technologies of pellets, various origins of the used biomass, storage time and condition and transportation distance of the samples. 15

16 3. Combustion tests All collected samples were combusted in order to determine level of emissions and performance of the appliances for each type of biofuel Methodology The combustion tests were performed using a boiler for samples of pellets and a stove for samples of briquettes and wood logs. Since two different heat appliances were used combustion tests were done according to two different methodologies: the standard LVS EN 303-5:2001 Heating boilers - Part 5: Heating boilers for solid fuels, hand and automatically stocked, nominal heat output of up to 300 kw - Terminology, requirements, testing and marking [9] and the standard LVS EN 13240:2002 Roomheaters fired by solid fuel Requirements and test methods [10] Combustion tests for pellets The combustion tests for pellets were performed according to the standard LVS EN 303-5:2001 [9]. The same amount of fuel and air supply was applied for all combustion tests. The laboratory stand consisted of a 25 kw pellet boiler, monitoring equipment, a heat accumulation tank and a heat exchanger for boiler cooling (see Figure 4). Figure 4. The principal scheme for the 25 kw boiler stand [11] Nomenclature used in Figure 3: B mass of the test fuel (kg h -1 ), M w water flow rate (kg h -1 ), Q heat output (kw), B heat input (kw), Q b chemical heat losses in the flue gases, referred to the unit of mass of the test fuel, (kj kg -1 ) t a flue gas temperature ( C), p a draught in the chimney (Pa), t b.in boiler input temperature ( C), t b.out boiler output temperature ( C). Temperature and chemical composition of the flue gases, the thermal performance of the boiler, the chimney draught and the amount of consumed fuel were monitored during the tests. Oxygen, carbon dioxide, carbon monoxide and nitrogen oxide values were measured during all testing time. Flue gas temperature was measured with grounded K-type 16

17 thermocouples. The thermocouples were located in the flue gas stack according to standard LVS EN 304:2001 Heating boilers Test code for heating boilers for atomizing oil burners [12]. Water flow was controlled manually; flow rate was measured using magnetic flow meter. Water temperatures were measured using PT 100 temperature sensors. All data was gathered using data logger and transferred to PC for data processing. For dust content determinations the extraction time per filter was limited to 30 minutes. During each test three dust samplings were taken. Dust content was determined using an isokinetic gas sampler accordingly to the standard ISO 9096:2006 Stationary source emissions - Manual determination of mass concentration of particulate matter [13]. The boiler efficiency was calculated according to standard EN 303-5:2001 [9] using the direct method. The amount of the used fuel, produced heat and the net calorific value was taken into account for the boiler efficiency calculations. Boiler description Experiments were performed using 25 kw fire-tube boiler Grandeg GD-BIO 25, which is produced in Latvia (see Figure 5). Figure 5. The Grandeg GD-BIO 25 boiler The operation of the boiler is semi-automatic; the user must manually ignite the fuel in the furnace and has to regularly clean ashes from the boiler. After a manual ignition, the burning process is regulated automatically. In automatic regime, the amount of supplied pellets and control of on/off sequences is a function of the water temperature in the boiler. Fuel is stored in a container next to the boiler. Pellets are fed with horizontal screw type conveyor into the vertical, bottom fed burner. The required amount of air is supplied with the fan. The amount of air supplied to the combustion chamber was controlled by manually changing ON/OFF intervals of the air blower. 17

18 Combustion tests for briquettes and wood logs The combustion tests for wood logs and briquettes were done according to the standard LVS EN 13240:2002 Roomheaters fired by solid fuel Requirements and test methods [10]. All tests were performed with the same amount of air supply. Oxygen, carbon dioxide, carbon monoxide, nitrogen oxide and flue gas temperature values were measured during all testing time. The flue gas analyser and K-type thermocouple probes were used. Temperature data was gathered using data logger and transferred to PC for data processing. For dust content determinations the extraction time per filter was limited to 30 minutes. The dust content was determined using an isokinetic gas sampler accordingly to the standard method ISO 9096:2006 Stationary source emissions - Manual determination of mass concentration of particulate matter [13]. The heat output was calculated according to the LVS EN 13240:2002 [12] 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 determined from the mean values of flue gases and room temperature, the flue gas composition and the amount 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 [10]. Stove description The stove is equipped with grates, ash collecting box, glazed doors and buffer plate in the top of the burning chamber, see Figure 6a. a) b) Figure 6. a) Wood log stove Thermo-Bull Energetic TB7/12AC, b) Air supply in the stove (P primary air supply; S secondary air supply; E exhaust to stack) In order to facilitate heat transfer to the surrounding air, eight vertical air convection tubes are incorporated into the design of the stove. Air supply is ensured through four air intakes: above and below of the front door, on the lid of the ash box and at the back of the stove, see Figure 6b. Flue gas damper allows adjusting the total amount of air intake o the combustion chamber. The air intakes above and below the door were closed during the tests. 18

19 3.2. Results Flue gas composition CO, NO x, PM, mg/nm 3 at 10% O PP 2PP 3PS 4PP 5PS 6PP 7PS 8PS 9PS 10P 11PP 12PP 13PP CO NOx PM Figure 7. Flue gas composition, (carbon monoxide, nitric oxides concentration and dust content) for wood pellets tests 19

20 CO, NO x, PM, mg/nm 3 at 10% O BS 2BS 3BP 4BP 5BP 6BS 7B 8B 9B CO NOx PM Figure 8. Flue gas composition (carbon monoxide, nitric oxides concentration and dust content) for briquettes tests 20

21 CO, NO x, PM, mg/nm 3 at 10% O WLS 2WLP 3WLP 4WLP 5WLP 6WLP 7WLP 8WLP 9WLP CO NOx PM Figure 9. Flue gas composition, carbon monoxide concentration, nitric oxide concentration and dust content for wood logs tests 21

22 Capacity and efficiency Figure 10. Capacity and efficiency for pellets tests 22

23 Figure 11. Capacity and efficiency for briquettes tests 23

24 Figure 12. Capacity and efficiency for wood logs tests 24

25 3.3. Conclusions The most noticeable influence on the performance of the boiler occurred when biomass with high ash content was used. In this case, peat and straw pellets had highest ash content from tested samples. When peat or straw pellets were used it was not possible to operate the boiler properly without adjustments in boiler air and fuel supply systems. In case of pellet burners without automatic ash cleaning it is recommended to perform boiler cleaning several times per day. This will allow to keep high efficiency and to avoid high emissions from the combustion process of peat and straw pellets. Other solution could be found in form of woody and non-woody biomass fuel mixtures. The duration of the combustion tests and the amount of fuel supplied to the heat appliances was constant during pellet combustion tests. For wood logs and briquettes the duration of combustion tests was in the range from 30 minutes to more than 1 hour and 30 minutes. The test duration was influenced, firstly, by the moisture content of wood logs. The longest test duration was with wood log samples with highest moisture content. The moisture content of briquettes was lower and did not noticeably affect the test duration. Secondly, the duration of combustion of wood logs and briquettes with larger sizes was longer. Since the tested wood briquettes had uniform properties, the range of flue gas temperature was narrow the heat output and oxygen concentration in the flue gases was similar in all preformed tests. Also wood pellets had uniform properties and similar combustion process therefore occurred. The difference between the briquettes and pellets combustion tests was in the oxygen concentration in the flue gases. Since the pellet boiler is semi-automatic it is possible to adjust the air supplied to the combustion chamber more precisely than in case of the stove. The efficiency of the stove was significantly lower when using wood log samples with higher moisture content. The stove efficiently varied from 57.8% to 62.6% when using logs with moisture content more than 20%. The efficiency of the stove was about 70% and more with wood logs with moisture content about 10%. It is therefore important for typical households to buy and use dried wood logs or dry wood logs before combustion. The mean dust content was about 26 mg/nm 3 for wood pellets and 58 mg/nm 3 for wood briquettes. The dust content was more than 150 mg/nm 3 for straw pellets, more than 60 mg/nm 3 for peat pellet and about 115 mg/nm 3 for grass briquettes. Straw, grass and peat biofuels have higher ash content than wood biofuels which is one of the main reasons for higher dust content. 25

26 Main findings The price of acquired wood logs varied in a wide range, due to trade form and pre-treatment of the biofuel. In most cases, the price per cubic meter of wood logs was lower than for pellets (considering the determined bulk density of pellets). Lower and uniform price was observed for both non-woody briquettes and pellets, though for wood pellets and briquettes there was significant variation in price. All of the pellets purchased from producers and most of the ones purchased from the resellers were less expensive than wood briquettes. Considering only the purchased amount of biofuel the nonwoody pellets are the less expensive choice for the end users, but more parameters should be evaluated. From the tested biofuels the highest ash content was presented in non-woody biomass peat pellets, followed by straw and grass biofuels. High ash content will lead to elevated emission rates from the boilers or stoves. The heat appliance will need maintenance more often, because of the ash depositions on internal surfaces. By using various types of biomass in the same heat appliance the combustion efficiency can vary a lot. The efficiency of the heat appliance will be lower using straw and grass biofuel, if compared with woody biomass. The moisture content of the fuel influences the amount of energy needed for water evaporation inside the burner and it is affecting formation of harmful emissions. Lower moisture content was observed for pellets purchased from resellers in comparison to ones purchased from producers. Similar observations were made for briquettes, thought these observations are not conclusive, because only few briquette samples were gathered from resellers. The wood log samples gathered from producers were both raw and pre-dried logs, but the samples purchased from resellers were all pre-dried and with low moisture content. The difference in moisture content of pellets could be due to the storage conditions in both cases. It was observed that most producers store their pellets in warehouses near to the production site, while the resellers store the pellets at their facilities, where the indoor climate is usually adjusted for thermal comfort of customers. In regard to this, the storage conditions would mainly explain the differences for samples obtained in two trade forms, assuming that in reseller s facilities the relative air moisture is lower than in producer s warehouses. Due to different storage conditions and pre-treatment of obtained wood logs the moisture content for all samples varied in a wide range from 8.7 w-% to 43.4 w-%. The net calorific value of the driest sample was 1.7 times higher than for the sample with the highest moisture content. In order to use the biomass resources efficiently, it is therefore important for typical households to buy and use dried wood logs or dry wood logs before combustion. The sustainable solution for utilization of locally available biomass is the production of mixtures of various types of biomass and the usage of as much as possible waste products from industries, which deals with biomass. A mixture of straw and woody biomass or other wastes (e.g. paper) could provide reduction of ash content per mass unit of pellets and increase the gross calorific value and durability of such pellets. 26

27 References 1. LVS EN 14588:2011 Solid biofuels - Terminology, definitions and descriptions 2. LVS EN :2010 Solid biofuels Determination of moisture content Oven dry method Part 3: Moisture in general analysis sample 3. LVS EN 14775:2010 Solid biofuels Determination of ash content 4. LVS EN 14918:2010 Solid biofuels Determination of calorific value 5. LVS EN 15103:2010 Solid biofuels Determination of bulk density 6. LVS EN :2010 Solid biofuels Determination of mechanical durability of pellets and briquettes Part 1: Pellets 7. LVS EN :2011 Solid biofuels Determination of particle size distribution Part 1: Oscillating screen method using sieve apertures of 1 mm and above 8. LVS EN :2010 Solid biofuels Fuel specifications and classes Part 1: General requirements 9. LVS EN 303-5:2001 Heating boilers - Part 5: Heating boilers for solid fuels, hand and automatically stocked, nominal heat output of up to 300 kw - Terminology, requirements, testing and marking 10. LVS EN 13240:2002 Roomheaters fired by solid fuel Requirements and test methods 11. Žandeckis A., Timma L., Rochas C., Rošā M., Blumberga D. Solar and pellet combisystem for an apartment buildings. Heat losses and efficiency improvements of the pellet boiler // Re-submitted peer reviewed paper for the international journal - Applied Energy, March LVS EN 304:2001 Heating boilers Test code for heating boilers for atomizing oil burners 13. LVS ISO 9096:2006 Stationary source emissions - Manual determination of mass concentration of particulate matter 27

28 Appendix 28

29 Appendix 1 Sample ID Ash content Moisture content Net calorific value A d; w-%, d M ar; w-% q v,net,ar; MJ/kg Summary: biofuel analysis for pellets Gross calorific value q V,gr,d; MJ/kg, d Net calorific value q v,net,ar; kwh/kg, Gross calorific value q V,gr,d; kwh/kg, d Bulk density Energy density Fines Durability BD; kg/m 3 MWh/m 3 F; w-% DU ar ; w-% 1PP PP PS PP PS PP PS PS PP PS PP PP PF

30 Wood logs Briquettes Fuel type Sample ID Summary: biofuel analysis for briquettes and wood logs Ash content Moisture content Net calorific value Gross calorific value Net calorific value Gross calorific value A d; w-%, d M ar; w-% q v,net,ar; MJ/kg q V,gr,d ; MJ/kg, d q v,net,ar; kwh/kg, q V,gr,d; kwh/kg, d 1BS BS BP BP BP BS BF BE BE WLS WLP WLP WLP WLS WLS WLP WLP WLS Appendix 2 30

31 Flue gas composition Summary: combustion tests using pellets Appendix 3 Unit 1PP 2PP 3PS 4PP 5PS 6PP 7PS 8PS 9PS 10P 11PP 12PP 13PP Test duration h:mm 6:00 6:00 6:00 6:00 6:00 6:00 6:00 6:00 4:00 6:00 6:00 5:00 6:00 Applied fuel quantity kg Fuel consumption kg h Fuel heat input kwh Capacity kw Boiler efficiency % Flue gas temp. (average) o C O 2 % CO 2 % CO ppm CO, 10% O 2 ppm * CO, 10% O 2 mg Nm -3** NO x ppm NO x, 10% O 2 ppm NO x, 10% O 2 mg Nm Dust, 10% O 2 mg Nm *Emission values in mg/m 3 (relating to 10 % O 2, dry flue gas) ** Emission values in mg/nm 3 (relating to 10 % O 2, 0 C temperature, dry flue gas) 31

32 Flue gas composition Summary: combustion test using briquettes Appendix 4 Unit 1 BS 2BS 3BP 4BP 5BP 6BS 7BF 8BE 9BE Test duration h:mm 1:08 1:03 0:37 1:08 1:01 0:58 1:04 0:52 0:37 Applied fuel quantity kg Hourly fuel consumption kg/h Fuel heat input kwh Capacity kw Stove efficiency % Flue gas temp. (average) o C Flue gas temp. (max) o C O 2 % CO 2 % CO ppm CO, 10% O 2 ppm * CO, 10% O 2 mg/nm 3 ** Nitric oxides ppm NO x, 10% O 2 ppm* NO x, 10% O 2 mg/nm 3 ** Dust, 10% O 2 mg/nm *Emission values in mg/m 3 (relating to 10 % O 2, dry flue gas) ** Emission values in mg/nm 3 (relating to 10 % O 2, 0 C temperature, dry flue gas) 32

33 Flue gas composition Summary: combustion test using wood logs Appendix 5 Unit 1WLS 2WLS 3WLS 4WLS 5WLS 6WLS 7WLS 8WLS 9WLS Test duration h:mm 0:30 0:54 1:08 1:35 0:37 0:38 0:37 0:47 0:44 Applied fuel quantity kg Hourly fuel consumption kg/h Fuel heat input kwh Capacity kw Stove efficiency % Flue gas temp. (average) o C Flue gas temp. (max) o C O 2 % CO 2 % CO ppm CO, 10% O 2 ppm * CO, 10% O 2 mg/nm 3 ** Nitric oxides ppm NO x, 10% O 2 ppm* NO x, 10% O 2 mg/nm 3 ** Dust, 10% O 2 mg/nm *Emission values in mg/m 3 (relating to 10 % O 2, dry flue gas) ** Emission values in mg/nm 3 (relating to 10 % O 2, 0 C temperature, dry flue gas) 33