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# European Biomass Heating Technologies: An overview of combustion principles and performance characteristics of commercially available systems

Written by Birgit Musil-Schlaeffer birgit.musil@bioenergy2020.eu

Date 28 th January 2010 Report Number 372 TR nK-I-1-65 01II 

### European Biomass Heating Technologies

commercial partner New York State Energy Resear ch and Development Authority

Project manager Birgit Musil-Schlaeffer birgit.musil@bioenergy2020.eu Collaborator Aislinn McCarry aislinn.mccarry@bioenergy2020.eu Christoph Schmidl christoph.schmidl @bioenergy2020.eu Walter Haslinger walter.haslinger@bioenergy2020.eu

Project number nK-1-I-65 Project duration 01 August 2009 - 31 December 2009III 

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# Executive Summary

In an effort to develop a hi gh-efficiency biomass heating ma rket of technologies with acceptable emissions performance, the New York State Energy Research and Development Authority’s (NYSERDA’s) Environmental R&D and Building R&D Programs have jointly developed the Biomass Heatin g R&D program. The objectives of this program are to:

• Evaluate the energy-efficiency and emi ssions performance of a wide range of conventional and advanced biom ass-fired heating technologies;

• Evaluate the energy, moisture, and chemic al composition of biomass fuel feed stocks;

• Develop advanced boiler technologies by supporting R&D and commercialization efforts with New Yo rk manufacturers;

• Demonstrate advanced technologies in representative applications; and

• Provide objective scientific information for the developm ent of high-efficiency and low emission biomass heating initiatives in New York State. Currently the United States Environmental Protection Agency (EPA) is updating the emissions performance required of all residential wood heating technologies. These New Source Performance Standards (NSPS) revisions will require that all newly manufactured heating systems meet emission levels that represent the current best demonstrated technology; i.e., all new units in the United States will have to meet the level of performance of today's best designs. This document, prepared by BIOENERGY 202 0+ surveys the current state of biomassfired heating technology in use in Austria, Germany, and Scandinavian countries Denmark, Norway and Sweden. The report provides critical information to assist NYSERDA develop a high-efficiency biomass he ating market and help EPA assess current best demonstrated technology on which to ba se revisions to the residential wood heater NSPS. A key aspect of this study is the descr iption of the European methodology for determining thermal efficiency using the net calorific value (lower heating value) of the wood fuel and the conversion of this value to the gross calorific value (high heating value) used to determine thermal efficiencies by the U.S. heating industry. Throughout this report thermal efficiency values are converted to the Americ an convention using gross calorific value. The emissions for “d ust” or Total Suspended Particulates are converted to pounds per million British th ermal unit (lb/MMBtu), the common unit used in the United States. Other em issions are normalized to values at standard conditions at 12% O 2 levels in the flue gas. Legislative regulations and incentives on national and European levels are used in the European Union to continuously improve the performance of biomass appliances. In the European Standard EN 303-5, which regulate s performance requirements for solid fuel boilers, three classes (class 1 to 3) for effi ciency requirements an d emission limits are defined in order to embrace the diverse techno logy stages of the EU member states. InIV 

### European Biomass Heating Technologies

the revision of EN 303-5, which is current ly under discussion, more stringent classes (class 3 to 5) will be introduced, thereby resulting in the steady increase of the performance of installed biomass appliances . In addition to the EN 303-5, national regulations and eco-labels may request even higher efficiencies and lower emissions. Regional and national financial incentives for the installation of biomass appliances are very often linked to eco-label requirements.

45% 50% 55% 60% 65% 70% 75% 80% 85% 90%

0 300 600 900 1200 1500 nominal load in mBTU/h class 3

class 2

class 1 class 4 class 5efficiency based on GCV Blue Angel (G)/Umweltzeichen (A) Nordic Swan (Scandinavia) Figure 0-1 efficiency requirements for boilers from EN 303-5 (class 1 to class 5) and efficiency requirements from Austrian, German and Scandinavian eco-labels; efficiencies based on GCV were converted for pellets fuel

Austrian biomass boiler technology is a pe rfect example of how the improvements in combustion technology can be driven by legislative requirements and incentives. Figure 0-2 shows the technological improvem ent of boilers for solid wood, wood chips and pellets (starting in 1998) through test data from FJ-BLT. Over the last 30 years average efficiencies of bioma ss boilers have increased from approximately 55% to more than 90% based on the NCV and the averag e CO-emissions have decreased from 15,000 to less than 50 mg/m3 at 13% O 2 in Austria.

Figure 0-2 Small scale wood combustion systems: Efficiencies and CO emissions measured at the test bench through cert ification tests since 1980 - data according (FJ-BLT 2005), compilation in (Voglauer 2005) Modern combustion technology for biomass is based on staged combustion in order to enable maximum burnout rates. In the primary zone located on the grate, drying, devolatilization and solid combustion take place. In the secondary combustion zone, which is situated in the combustion chamber, the volatile gases are burnt with secondary air. In order to minimize emi ssions, combustion must be as complete as possible in the secondary zone. In Figure 0-3, Figure 0-4 and Figure 0-5 the fu nction principles of a solid wood boiler, an underfeed pellet boiler with condensing technology and a pellet boiler with top feed technology are illustrated.V 

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Figure 0-3 Under-burning solid

wood boiler (Froeling 2005) Figure 0-4 Condensing boiler for wood pellets with underfeed burner (Oekofen 2007)

Figure 0-5 Top feed pellets boiler (Evotherm 2010)

The development of solid bio-fuel standards in Europe is linked to the beginning of wood pellet production. In order to gain a co mmon understanding between the manufacturers and the users, codes of good practice, qua lity guidelines and later national standards have been developed. For the development of high performing combustion appliances, harmonized fuel properties are advantageo us because the optimi zation of operating conditions is only possible if the fuel properties are known. Although modern solid wood bo ilers are able to modulate their operation load from 100 to 50%, the use of heat storage is strongly recommended in order to reach high efficiencies and keep emissions low. Even though pellet and wood chip boilers can modulate their operation load from 100 to 30%, some studies also recommend the integration of accumulator tanks in these heat ing systems in order to increase the annual efficiencies of the heating syst ems. In addition to improved performance, the design of heat storage systems also influences the n eed for maintanance and the durability of boilers. Due to their high availability, non-wood biom asses are very attractive fuels. They may however have certain general physical and ch emical properties that may cause problems during combustion. In addition to the possible increase of NO X , HCl, SO 2 , and other emissions in comparison to wood biomass, hi gher ash contents combined with lower ash melting temperatures and corrosive effects negatively influence the failure rate and durability of the boilers. The summary of performance data from Europe an biomass applications and of European regulation schemes for boilers themselves as well as for its periphery (bio-fuel, heat storage, emission control) shows that stringent regulati ons and financial incentivesVI 

### European Biomass Heating Technologies

encourage technology development resulting in higher performance levels in the European Union sustainably. The TOP 25% performing biomass appliances that were identified with in this study reach high efficiencies and low emissions. Table 0-1 summary of average efficiency and emission data from considered biomass technologiesηGCV1)(% )CO(mg/m312% O2)TSP1)(lb/MM BtuNOx(mg/m312%O2)

< 55 87 43 0.022 140 12221 55 - 100 86 39 0.024 136 13659 100 - 170 87 38 0.023 132 16844 170 - 340 86 24 0.036 154 23537

> 340 86 17 0.031 133 - < 85 83 174 0.039 139 10116 85 - 120 83 220 0.044 126 10319 120 - 170 83 152 0.066 115 12672

> 170 82 97 0.033 119 14089 < 100 76 60 0.046 157 14350 100 - 200 79 39 0.027 134 25504 200 - 340 78 30 0.038 138 31581 340 - 680 80 22 0.042 125 34056

> 680 78 34 0.092 131 65180 pellets 82 34 0.027 145 solid wood 79 252 0.027 120 stove with hot water pellets 25 - 50 85 117 0.019 143 9843

< 30 88 164 0.045 88 8113 > 30 87 180 0.043 110 4820 solid wood 20 - 130 73 1069 0.050 126 - stove pellets

solid wood

wood chips

pellets 16870 data at nominal loadload range(M Btu/h)avg. retailprice (US $)

50 - 150 boiler

combined

boilertechnologyfuel

1) related to the Gross Calorific Value (upper heating value) Figure 0-6 and Figure 0-7 exhi bit clearly, that e fficiencies of the TOP 25% performing biomass appliances are far beyond and emissi ons are far below the future requirements of EN 303-5, class 5.

75% 80% 85% 90%

0 200 400 600 800 1000 nominal load in mBTU/h class 3 class 4 class 5efficiency based on GCV TOP 25% pellet boilers

TOP 25% solid wood boilers* TOP 25% wood chip boilers*

* conversion from efficiency based on NCV to efficiency based on GCV was performed based on pellets fuel, therefore a correction factor for wood chip boiler (+10.6%) and for wood chip boilers (+3.1%) was used to enable comparability, efficiencies for wood chip and solid wood boilers are not exact. Figure 0-6 efficiency classes 3 to 5 from EN 303-5 and efficiency performance of TOP 25% pellet, solid wood and wood chips boilers; efficiencies from solid wood and wood chip boilers were corrected because efficiency limits based on the GCV were converted for pellets fuelVII 

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0.000 0.050 0.100 0.150 0.200

0 200 400 600 800 1000 nominal load in mBTU/h class 3

class 4

class 5

TOP 25% pellet boilers TOP 25% solid wood boilers*

TOP 25% wood chip boilers* class 2

* conversion from dust emission limits from mg/m3 to lb/MMBTU was performed for pellets fuel, therefore a correction factor for wood chip boiler (0.754) and for wood chip boilers (0.911) was used to enable comparab ilitydust emissions in lb/MMBtu Figure 0-7 dust emission limit classes 2 to 5 from EN 303-5 and dust emissions from TOP 25% pellet, solid wood and wood chips boilers; emissions from solid wood and wood chip boilers were corrected because dust emission conversion from mg/m3 to lb/MMBtu was performed for pellets fuel

Figure 0-8 shows the average efficiencies at nominal and partial load for the TOP 25% performing pellet, solid wood and wood chip appliances. For solid wood boilers partial load equals 50% of nominal load, for pellets and wood chip boilers the partial load is 30% of the nominal load. Efficiencies for nominal and partial load are almost identical. Solid wood and wood chip boilers sometimes even reac h higher efficiencies at partial load operation.

75% 80% 85% 90%< 5555 - 100100 - 170170 - 340> 340< 8585 - 120120 - 170> 170< 100100 - 200200 - 340340 - 680> 680

pellet boilers solid wood boilers wood chip boilers nominal load partial loadefficiency based on GCV

load categor y (MBtu/h ) Figure 0-8 average efficiencies based on GCV at nominal and partial heat load for the TOP 25% performing boilers

By making careful conversions of conven tional methodology an d units, the energy efficiency and emissi ons performance of the European heating systems can be more easily summarized in the context of the Am erican nomenclature. After conversions, differences in evaluation duty-cycle and th e emissions sampling and analysis protocols still exist in the regulatory test methods be tween the European Commission and the U.S. For example, the European Commission evalua tion duty cycles do not include operation for the very low burn rates (low heat demand rates) that U.S. evaluation duty cycles typically include. The U.S. evaluation duty cycles incl ude these low burn rates because many U.S. designs do not alwa ys automatically minimize or eliminate idle modes that have poor combustion characteristics. There is considerable interest in the U.S. in this opportunity for much improved performanc e. Also, the U.S. sa mpling and analysis typically include condensable particulate matter that is not included in the European tests because the high-efficiency de signs combust virtually all of the organic precursors toVIII 

### European Biomass Heating Technologies

condensable aerosol particles. Thus one must be very careful in comparing results and recognize that not all results are directly comparable. Even considering the differences described abov e, it is clear that by using fuels with lower water content (only 22.5% for wood ch ips and 14.5% for solid wood), improved staged combustion design, requirements for minimum thermal efficiency, and sophisticated controls that optimize combusti on and minimize or eliminate idle modes, the top 25% performing commercially availabl e European technologies greatly exceed not only the current classes (1, 2, and 3) of boilers but also the proposed classes (4 and 5) for thermal efficiency and emissions. Tech nology forcing policies, regulations, and Ecolabeling efforts have clearly resulted in greatly improved technology now available in Europe which is starting to make its way into the American wood heating market as well.IX 

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# Table of Content

1 Introduction - Calorific Value and Efficiency Discussion 1

1.1 Chemical composition 1

1.2 Calorific Value 3
1.2.1 Measurement and conversion 3
1.2.2 Formula from Boie 5

1.3 Conversion factors 6



### 2 Biomass combustion technology 9

2.1 Overview – combustion principles 9
2.1.1 Staged combustion 9
2.1.2 Manual stoking 9
2.1.3 Automated stoking 10

2.2 Small scale combustion systems 13
2.2.1 Room heaters 13 2.2.1.1 Fireplaces 14 2.2.1.2 Pellet stoves 14 2.2.1.3 Pellet stoves with hot water production 15 2.2.1.4 Wood stoves 16 2.2.1.5 Masonry heaters 17 2.2.2 Boilers 19 2.2.2.1 Pellet boilers 19 2.2.2.2 Solid wood boilers 21 2.2.2.3 Wood chip boilers 21 2.2.2.4 Combined boiler technologies 22
2.3 Medium to large scale combustion 23
2.3.1 Fixed-bed combustion 23 2.3.1.1 Underfeed stokers 23 2.3.1.2 Grate furnaces 24 2.3.2 Fluidised bed combustion 26 2.3.2.1 Bubbling fluidised bed combustion (BFB) 27 2.3.2.2 Circulating fluidised be d (CFB) combustion 27 2.3.3 Dust combustion 28



### 3 Emissions 30

3.1 Conversion factors 30

3.2 Carbon Monoxide (CO) 31
3.2.1 General 31X 

### European Biomass Heating Technologies

3.2.2 Measurement 32
3.2.3 Reduction 32

3.3 Total Organic Bound Carbon/Organic Gaseous Substances (OGC) 34
3.3.1 General 34
3.3.2 Measurement 34
3.3.3 Reduction 35

3.4 Dust · Particulate Matter (PM) · Totals Suspended Particulate Matter (TSP) 35
3.4.1 General 35
3.4.2 Measurement 38
3.4.3 Reduction 38 3.4.3.1 Primary measures 38 3.4.3.2 Secondary measures 39
3.5 Nitroxen Oxides (NO X ) 43
3.5.1 Measurement 44
3.5.2 Reduction 45 3.5.2.1 Primary measures 45 3.5.2.2 Secondary measures 46



### 4 European Test Methods 48

4.1 Residential heating systems 49
4.1.1 EN 303-5: Heating boilers for solid fuels, hand and automatically stoked 49
4.1.2 EN 12809: Residential independent boilers fired by solid fuel 51
4.1.3 EN 12815: Residential cookers fired by solid fuel 51
4.1.4 EN 13229: Inset appliances including open fires fired by solid fuels 51
4.1.5 EN 13240: Room-heaters fired by solid fuel 53
4.1.6 EN 14785: Residential space heating appliances fired by wood pellets 55
4.1.7 EN 15250: Slow heat release appliances fired by solid fuel 56

4.2 Commercial heating systems 58

4.3 Summary 59



### 5 Regulations for biom ass installations 60

5.1 European level 61
5.1.1 Regulations for boilers 61
5.1.2 Regulations for room heaters 63

5.2 National levels 63
5.2.1 Austria 64
5.2.2 Germany 67XI 

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5.2.3 Denmark 71
5.2.4 Finland 73
5.2.5 Sweden 74



### 6 Performance of biomass installations 76

6.1 Introduction 76
6.1.1 Data sources 76
6.1.2 Selection method for TOP 25% performing appliances 77

6.2 Stoves/room-heaters 77
6.2.1 Pellet stoves 77
6.2.2 Wood stoves 80
6.2.3 Masonry heaters 81

6.3 Boilers 81
6.3.1 Pellet boiler 82
6.3.2 Solid wood boiler 83
6.3.3 Wood chip boiler 85
6.3.4 Combined technologies 87
6.3.5 Summary 89

6.4 Commercial biomass installations 91
6.4.1 Data collection of Austrian me dium scale biomass appliances (Musil et al. 2006) 92
6.4.2 Data collection of Swiss automated biomass appliances (Hasler et al. 2000) 93
6.4.3 Emission factors 96
6.4.4 Summary 97



### 7 Emission control technologies 99

7.1 Emission control technology for PM/dust 99
7.1.1 Small scale appliances 99
7.1.2 Medium scale appliances 101



### 8 European Biomass Fuel Requirements 102

8.1 General remarks 102

8.2 European Bio-fuel standards 104
8.2.1 Origin of Bio-fuels 104
8.2.2 Specification of solid bio-fuels base d on traded forms and properties105
8.2.3 Revision of EN14961:2005 105

8.3 European countries with na tional pellet standards 106XII 

### European Biomass Heating Technologies

8.3.1 Austria 106 8.3.1.1 OeNORM M 7135 106 8.3.1.2 OeNORM M 7136 107 8.3.1.3 OeNORM M 7137 107 8.3.2 Germany 107 8.3.2.1 DIN 51731 107 8.3.2.2 DIN plus Standard 107 8.3.2.3 Certification of pellet logistics 107 8.3.3 Sweden 108
8.3.4 Italy 108
8.3.5 United Kingdom 108

8.4 Additional environmental or quality labels 108

8.5 Summary of European and national prop erty specifications for bio-fuels 110



### 9 Heat storage (accumulator tank) 113

9.1 Introduction 113

9.2 Dimensioning 114
9.2.1 General aspects 114
9.2.2 Sizing guidelines 115
9.2.3 EN 303-5 116



### 10 Energy from non-Wood y Biomass Fuels 117

10.1 Emissions and effici encies of solid non wood biomasses 117
10.1.1 Fuels & fuel properties 117
10.1.2 Emissions 118
10.1.3 Efficiencies 119
10.1.4 Slagging & Corrosion 120XIII 

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# Introduction

Austria is a leading country in biomass combustion technology due to its long tradition of using biomass for heating purposes as well as the high environmental awareness of its population. Approximately 30 ye ars ago, the first efforts were started towards improving combustion technology for biomass appliances. At this time, the first measurements of efficiencies and CO em issions from boilers were performe d by national authorities and a competition was arranged amongst Austrian producers of biomass boilers in order to encourage technology development. Figure 0-9 shows the technological improvement of boilers for solid wood, wood chips and pellets (starting in 1998) th rough test data from FJ-BLT. Over the last 30 years, the average efficiencies of bioma ss boilers have increased from approximately 55% to more than 90% based on the NCV and the averag e CO-emissions have decreased from 15,000 to less than 50 mg/m3.

Figure 0-9 Small scale wood combustion systems: Efficiencies and CO emissions measured at the test bench through cert ification tests since 1980 - data according (FJ-BLT 2005), compilation in (Voglauer 2005) In the European Union, effici ency requirements and emission limits (CO, OGC and dust) for solid fuel boilers are regulated by one standard: EN 303-5. In order to include the differing technology levels within the EU, different classes are defined for emission limits and efficiency requirements. In the new re vision, which is currently under discussion, more stringed efficiency and em ission performances will be introduced in order to raise the overall performance of bi omass appliances in Europe.
All EU member states are allowed to in troduce additional and more stringent requirements than those given in the European standards for combustion appliances. This possibility is used for example by Austria, Germany and the Scandina vian Countries. In addition to legal requirements, environmental labels with very high requirments for efficiency and emissi ons are also introduced by some countries. These eco-labels encourage the population to purchase high performing biomass a ppliances by giving additional financial incentives.XIV 

### European Biomass Heating Technologies

This report provides a description of:

• combustion principles of modern biomass heating systems and commonly employed designs;

• combustion emission formations and reduction concepts;

• European test methods for various appliances;

• European regulations for bi omass heating systems;

• a survey of current technology perfor mance for commercially available heating systems;

• a summary of the best performing units based on thermal efficiency and CO emissions;

• emission control technology;

• fuel requirements;

• heat storage; and

• heating systems for non- woody biomass fuels. A key aspect of this study is that it describes the European methodology for determining thermal efficiency using the net calorific value (lower heating value) of the wood fuel and how this is converted to the gross calorific value (high heating value) used to determine thermal efficiencies by the U.S. heating industry. Throughout this report thermal efficiency values are converted to the Americ an convention using gross calorific value. The emissions for “dust” or Total Suspended Particulates are converted to pounds per million British thermal unit (lb/MMBtu), the common unit used in the United States. Other emissions are normalized to values at standard conditions at 12% O 2 levels in the flue gas. By making these careful conversions of conv entional methodology an d units, the energy efficiency and emissi ons performance of the European heating systems can be more easily summarized in the context of the Am erican nomenclature. After conversions, differences in evaluation duty-cycle and th e emissions sampling and analysis protocols still exist in the regulatory test methods be tween the European Comm ission and the U.S. For example, the European Commission evaluati on duty cycles do not include operation for the very low burn rates (low heat demand rates) that U.S. ev aluation du ty cycles typically include. The U.S. evaluation duty cycles include these low burn rates because many U.S. designs do not alwa ys automatically minimize or eliminate idle modes that have poor combustion characteristics. There is considerable interest in the U.S. in this opportunity for much improved performanc e. Also, the U.S. sa mpling and analysis typically include condensable particulate matter that is not included in the European tests because the high-efficiency de signs combust virtually all of the organic precursors of condensable aerosol particles. Thus one must be very careful in comparing results and recognize that not all results are directly comparable.XV 

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# List of Abbreviations

a Ash in kg/kg
Btu British Thermal Unit CHP Combined heat and power
CO Carbon Monoxide d.b. dry basis FJ-BLT Biomass · Logistics · Technology Francisco Josephinum (test house in Wieselburg)

g gramm GCV gross calorific value (upper heating value) h hydrogen content of the fuel in kg/kg HC Hydro Carbons
J Joule lb pound

m meter NCV net calorific value (lower heating value) Nm3 m3 at normal conditions (1 atm, 32 °F) NO Nitrogen Monoxide

NO 2 Nitrogen Dioxide

NO X Nitrogen Oxides

O 2 Oxygen OGC Oganic Gaseous Substances
PM Particulate Matter

P nominal load in MBtu/h TSP Total Suspended Particulates w water content of the fuel related to the mass of wet biomass in kg/kg (w.b.)

W Watt
w.b. wet basis

η Efficiency

η GCV Efficiency based on GCV

η NCV Efficiency based on NCVXVI 

### European Biomass Heating Technologies



# Units and basic conversion factors

Prefixes according to DIN 1301

Abbreviation Name Value M Mega 10 6 k Kilo 103 d Deci 10 -1 c Centi 10 -2 m Milli 10 -3

Example: 1 MW (1 Megawatt) = 103 kW (1,000 Kilowatt) = 10 6 W (1,000,000 Watt) Custom prefixes for North Amer ica (in correlation with Btu)

Abbreviation Value MBtu 10 3 ·Btu MMBtu 10 6 ·Btu

Calorific value [CV] [CV] = 1 J/g = 0.43 Btu/lb Density [ ρ ] [ ρ ] = 1 g/m3 = 6.5·10 -8 lb/oz Energy [E] [E] = 1 J = 9.4782·10 -4 Btu Length [l] [l] = 1 m = 39.2701 in = 3.28084 ft Mass [m] [m] = 1 g = 2.2046·10 -3 lb Power [P] [P] = 1 W = 3.4121 Btu/h Volume [V] [V] = 1 m3 = 1·103 l = 2.641·10 3 fl gal = 3.381·10 4 fl oz

Exchange rate Euro – Dollar 1 € = 1.478 US$1 

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# 1 Introduction - Calorific Value and Efficiency Discussion

1.1 Chemical composition

Biomass is an inhomogeneous raw material. Pr operties and therefore the composition of biomass influence its combustion behavior. A complete analysis of the biomass fuel would be time extensive and very expensive. For the characterization of the biomass with regard to its combustion behavior, proxim ate analysis is common. It comprised the determination of the content of water, ash and volatiles in the fuel. Additionally the heating value of the fuel is determined (see afterwards).
Biomass fuel can be divided into burning and not burning substances (Figure 1-1). Non burning substances are water and substanc es which are converted to ash during combustion.



### BIOMASS - FUEL

NOT burning

substances burning substances

volatiles charcoal water ash
Figure 1-1 classification of biomass fuel with regard to its combustion behaviour (Marutzky, Seeger 1999) Burning substances can be divided into volati les and charcoal (fixed carbon). Volatiles equal the fraction of biomass, which is tran sferred to gaseous stat e when the biomass is heated up hermetically sealed. The amount of volatile matter in biomass fuels is higher than in coals and usually varies between 76 and 86 wt.% (d.b.). As a result of this high amount of volatiles, the major part of a bi omass fuel is vaporize d before homogeneous gas phase combustion reactions take place; the remaining char then undergoes heterogeneous combustion reactions. Therefor e, the amount of volatile matter strongly influences the thermal deco mposition and combustion be havior of solid fuels. Figure 1-2 shows the mass and energy ratio of ash, volatile matter and charcoal from biomass. From ash forming substances, no ener gy is gained. Charcoal contributes to the energy quantity in a high degree.2 

### Introduction - Calorific Value and Efficiency i i

energy ratio minerals = ash

charcoal 1 %

83 %

16 % 67 %

33 % volatiles

mass ratio Figure 1-2 Mass and energy ratio of ash, charcoal and volatiles from biomass (Ebert, 1998)

Looking at the elemental composition of biomass, main elements, macro and micro nutrients and others can be identified (F igure 1-3). Figure 1- 4 shows the average elemental compositions of plants.

Carbon (C) Hydrogen (H)

Oxygen (O) MAIN ELEMENTSMACRO NUTRIENTMICRO NUTRIENT

OTHERS Sulphur (S) Nitrogen (N) Potassium (K) Phosphor (P) Magnesium (Mg) Calcium (Ca) Ferrite * (Fe) Boron (B) Ferrite * (Fe) Manganese (Mn) Molybdenum (Mo) Copper (Cu) Chlorine (Cl) Zink (Zn) Selenium (Se)

Cobalt (Co) Silicon (Si) Sodium (Na), Aluminium (Al)

micro elements and heavy metals Carbon (C) Hydrogen (H)

Oxygen (O) MAIN ELEMENTSMACRO NUTRIENTMICRO NUTRIENT

OTHERS Sulphur (S) Nitrogen (N) Potassium (K) Phosphor (P) Magnesium (Mg) Calcium (Ca) Ferrite * (Fe) Boron (B) Ferrite * (Fe) Manganese (Mn) Molybdenum (Mo) Copper (Cu) Chlorine (Cl) Zink (Zn) Selenium (Se)

Cobalt (Co) Silicon (Si) Sodium (Na), Aluminium (Al)

micro elements and heavy metals

Figure 1-3 concentration and function of elements in biomass (Kaltschmitt, Hartmann 2001) composition of plants (wt% d.b.)

Figure 1-4 average elemental composition of plants (Kaltschmitt, Hartmann 2001)
While the macro and micro nutrients are import ant for the growth of the plant, they can influence the combustion process negatively . Table 1-1 shows the guiding values and guiding ranges for elements in biomass fuels and biomass ashes for unproblematic thermal utilisation.3 

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Table 1-1 Guiding values and guiding rang es for elements in biomass fuels and biomass ashes for unproblematic thermal utilisation

Element Guiding concentration in fuel

(wt% d.b.) Limiting parameter Outside guiding concentration ranges, problems can occur for
< 0.6 Straw, cereals, grass N < 2.5 NO x emissions Waste wood, fibre boards < 0.1 Corrosion Stra w, cereals, grass < 0.1 HCl emissions St raw, cereals, grass Cl < 0.3 PCDD/F emissions Straw, cereals, grass < 0.1 Corrosion Stra w, cereals, grass S < 0.2 SOx emissions Grass, hay Ca 15 - 35 Ash-melting poin t Straw, cereals, grass

< 7.0 Ash-melting point, depositions, corrosion Straw, cereals, grass K -- Aerosol formation St raw, cereals, grass < 0.08 Ash recycling Bark, wood chips, sawdust Zn -- Particulate emissions Bark, wood chips, sawdust < 0.0005 Ash recycling Bark, wood chips, sawdust Cd -- Particulate emissions Bark, wood chips, sawdust Guiding values for ashes related to the bioma ss fuel ashes according to ISO 1171-1981 at 1022 °F


## 1.2 Calorific Value

1.2.1 Measurement and conversion

Gross calorific value (upper heating value) The wet based GCV is determined by measurement in bomb calorimeter:

• Temperature of fuel before combustion and of combusti on products: 77 °F. Before and after combustion all water (water in fuel and formed water by h) is liquid

• complete oxidation of c and s in the fuel (CO 2 and SO 2 )

• no oxidation of n in the fuel 

# ( )

m H GCV R b w 

### Δ

− =

. . F 1

GCV w.b. wet based gross calorific value Btu/lb enthalpy of reaction Btu

m fuel mass lb In order to calculate the dry based GCV, th e moisture content w has to be considered: R H Δ4 

### Introduction - Calorific Value and Efficiency i i

w GCV GCV b w b d



### − ⋅ = 1 1

. . . . F 2

GCV w.b. wet based gross calorific value Btu/lb

GCV d.b. dry based gross calorific value Btu/lb
w moisture content in the fuel lb/lb

Net calorific value (lower heating value) In the NCV the water in the fuel and the form ed water by h is gaseous after combustion, but still at a temperature of 77 °F (25 °C). Therefore the difference between NCV and GCV is the evaporation heat of the water amo unt after combustion at 77 °F. In order to determine the dry based NCV from the dry based GCV, the evaporation heat of the hydrogen in the fuel has to be subtracted:

. . . . . . 

### 9 b d b d b d 

### h r GCV NCV

⋅ ⋅ − = F 3

NCV d.b. dry based net calorific value Btu/lb

GCV d.b. dry based gross calorific value Btu/lb r evaporation heat of water at 77 °F (= 1,050) Btu/lb

h d.b. dry based hydrogen in the fuel lb/lb
w moisture in the fuel lb/lb

For calculation of the wet based NCV, the ma ss and the evaporation he at of the moisture in the fuel has to be considered:



### w r w NCV NCV b d b w 

### ⋅ − − ⋅ = ) 1 (

. . . . F 4

NCV w.b. wet based net calorific value Btu/lb

NCV d.b. dry based net calorific value Btu/lb r evaporation heat of water at 77 °F (= 1,050) Btu/lb h hydrogen in the fuel lb/lb
w moisture in the fuel lb/lb

Conversion from dry based GCV to wet based NCV If direct conversion of dry based GCV to wet based NCV is wished, combination of F 3 and F 4 result in:



### w r w h r GCV NCV b d b d b w 

### ⋅ − − ⋅ ⋅ ⋅ − = ) 1 ( ) 9 (

. . . . . . F 5

NCV w.b. wet based net calorific value Btu/lb

NCV d.b. dry based net calorific value Btu/lb r evaporation heat of water at 77 °F (= 1,050) Btu/lb

h d.b. dry based hydrogen in the fuel lb/lb
w moisture in the fuel lb/lb5 

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In Figure 1-5 the relationship of the net calorific value as well as the gross calorific value and the dry based water content is given. Addi tionally typical water contents for pellets, log wood (seasoned wood) and fresh wood are drawn in.

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 9,000

0% 20% 40% 60% 80% 100% water content w in % w.b. GCV BTU/lb
NCV BTU/lbseasoned woodCalorific Value in BTU/lbwoodpelletsfresh wood

Figure 1-5 relationship of Net and Gr oss Calorific Value and water content



### 1.2.2 Formula from Boie

The heating value can only be determined ex actly by measurement. If measurement is not possible or only estimation is requested, the experiment ally developed Formula from Boie can be used to approximate the heating value of the biomass. Although this Formula considers the nitrogen in the fuel, which is hardly oxidized, it still furnishes reasonable results for bio-fuels:



### w n s o h c NCV

b w b w b w b w b w b w



### ⋅ − ⋅ + ⋅ + ⋅ − ⋅ + ⋅ ≈ 050 , 1 709 , 2 515 , 4 644 , 4 377 , 40 964 , 14

. . . . . . . . . . . . F 6

NCV w.b. wet based net calorific value Btu/lb

c w.b. wet based carbon in the fuel lb/lb

h w.b. wet based hydrogen in the fuel lb/lb

o w.b. wet based oxygen in the fuel lb/lb

s w.b. wet based sulfur in the fuel lb/lb

n w.b. wet based nitrogen in the fuel lb/lb
w water content lb/lb6 

### Introduction - Calorific Value and Efficiency i i



## 1.3 Conversion factors

For the conversion of efficienci es and emissions, it is nece ssary to assume the elemental composition, the calorific value and the water content of the considered biofuels. In Table 1-2 the considered values ar e shown. The elemental compos ition and the gross calorific value of the biofuels corresp ond to the standard values that are used for emission calculations by BE2020+, Bran ch Wieselburg. The average wa ter contents of the fuels from all input data (w NCV ) are assumed to be equal to the average water content of each fuel from the FJ-BLT 1 test reports. The water contents of the biofuels for the calculation of the efficiencies based on the GCV (w GCV ) were provided by NYSERDA. Table 1-2 assumed elemental composition, gr oss calorific value and water content for conversion

GCV 1) (d.b.) c 1,2) h 1,2) a 1,2) w NCV 3) w GCV 4) NCV 3) (w.b.) GCV 4) (w.b.) Btu/lb % (d.b.) % Btu/lb pellets 7.5 5 7 300 8 200 solid wood 14.5 20 6 700 6 900 wood chips 8 600 50.70 6.23 0.20 22.5 40 6 000 5 200

1) standard values for emission calculation of BE2020+, Wieselburg 2) c: carbon in the fuel, h: hydrogen in the fuel, a: ash in the fuel 3) averaged from FJ-BLT test reports 4) given from NYSERDA

In the test reports that were used for this st udy, the efficiencies we re based on the lower heating value (net calorific va lue NCV). These efficiencies we re achieved with test fuels having the assumed averaged water content of the test fuels as shown inTable 1-2.
The efficiencies must however be based on the GCV which is calculated with new water contents of the fuels given by NYSERDA (see Table 1-2). In order to convert the efficiencies based on the GCV values with the new water contents provided in the test reports by NYSERDA, the correlation between the water content of the fuel and the efficiency have to be considered.
In order to calculate the conversion factor s, the excess air rati o of the combustion conditions must be determined, whereby it is assumed to equal the average excess air ratio found in the data available from FJ-BLT:

• pellets: λ = 1.50

• solid wood: λ = 1.42

• wood chips: λ = 1.43 Figure 1-6 shows the efficienci es which were reached for water contents of 0, 22.5 and 40% at an excess air ratio of 1.43 (these valu es correspond to wood chips). In Figure 1-6 only losses by heat in the flue gas are cons idered. Losses by radiation, un-burnt gases in

1 FJ-BLT is the test house fo r wood boilers in Wieseburg7 

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the flue gas or un-burnt material in the ash are not considered. Theses losses are however small in comparison to the flue gas losses.

65% 70% 75% 80% 85% 90% 95% 100%

0 100 200 300 400 500 600 700 flue gas temperature in °F water content 40.00% water content 22.50% water content 0.00%efficiency based on GCV

Figure 1-6 correlation between the efficiency and corresponding flue gas temperature for different water contents of the fuel at an excess air ratio of 1.43 (only losses by heat in the flue gas considered) An efficiency of 85% with a fuel water content of 22.5% will be reduced to 80% if the fuel water content is increased to 40%, assu ming that the fuel gas temperature stays constant (about 220 °F).
In order to convert the efficiencies based on the NCV and the average water contents of the test fuels to the efficiencies based on the GCV and the water contents provided by NYSERDA, the graphs for each fuel correspon ding to Figure 1-6 were determined. F 7 shows the approximaed equation that was us ed for conversion and in Table 1-3 the factors for F 7 are given.



### ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛

⋅ −

⋅ − = 2 1 2 1 

### X f X Y Y BLT

NYSERDA NCV CV GCV 

### η η F 7

η GCV,NYSERDA efficiency based on GCV and water contents from NYSERDA -

η NCVBLT efficiency based on NCV an d averaged water contents of the test fuel -8 

### Introduction - Calorific Value and Efficiency i i

Table 1-3 factors for conversion from effici ency determined on basis of the NCV and averaged water contents of the test fuel s to efficiency based on GCV and water content of NYSERDA

fuel X 1 (-) X 2 (-) Y 1 (-) Y 2 (-) f CV (-) pellets 9.32·10 -1 5.37·10 -4 9.36·10 -1 5.35·10 -4 9.22·10 -1

solid wood 9.21·10 -1 5.21·10 -4 9.12·10 -1 5.28·10 -4 9.11·10 -1
wood chips 9.07·10 -1 5.35·10 -4 8.62·10 -1 5.70·10 -4 8.96·10 -1

Figure 1-7 exhibits the resulting conversion functions.

60% 65% 70% 75% 80% 85% 90% 95% 100%

75% 80% 85% 90% 95% 100% efficiency based on NCV and averaged water contents of the fuels solid wood (14.5% -> 20%) pellets (7.5% -> 5%) wood chips (22.5% -> 40%)efficiency based on GCV and watercontent from NYSERDA

Figure 1-7 conversion function for the conver sion of the efficienci es based on the NCV and average water contents of test fuel to efficiencies based on the GCV and average water contents provided by NYSERDA When converting from NCV with a 7.5% wate r content pellet to the American convention of GCV with a pellet having 5% water content, a loss of approximately 5% is observed. This is due to the water formed from h in the wood fuel. In the case of changing from a wood chip fuel with 22.5% water content to one with 40% water content, not only is the 5% loss of energy from the fuel h conversi on to water accounted for but the loss in energy efficiency of an additi onal 10% due to the loss of energy required to heat the water in the fuel is also apparent.9 

### Report



# 2 Biomass combustion technology

2.1 Overview – combustion principles

2.1.1 Staged combustion

Combustion technology for biom ass appliances is based on staged combustion in order to enable maximum burnout rates. Figure 2-1 illustrates the st ages of biomass combustion that take place in the primary and secondary combustion zones.

combustion of biomass

reaction in firebed reaction in comb. chamber

gas combustion drying

solid combustion

devolatilization combustion air

primary combustion zone secondary combustion zone combustion air combustion of biomass

reaction in firebed reaction in comb. chamber

gas combustion drying

solid combustion

devolatilization combustion air

primary combustion zone secondary combustion zone combustion air

Figure 2-1 primary and secondary comb ustion zone in biomass combustion In the primary combustion zone, the bio-fuel is first dried from the heat within the combustion chamber followed by devolatilization, whereby the volatile substances are set free from the solid fuel and ascend to th e secondary combustion zone. Finally, the remaining solid charcoal is burnt in the firebed. Primary air is needed for devolatilization and solid combustion. In the secondary combustion zone, the volat ile gases from devola tilization and gases from solid combustion are burnt with secondar y air. In order to achieve low emissions, the reaction in the secondary combustion zone must be as complete as possible.



### 2.1.2 Manual stoking

Manually stoked furnaces can burn logs (from 10 in up to 40 in in length) as well as briquettes. Some log wood furnaces also work with coarse wood ch ips. There are three common, basic classifications wh ich are determined by the airflow of the primary air: top burning, through burning or under burning furnace. These designs are illustrated in Figure 2-2. Numerous combin ations and modifications of these three principles are available.10 

### Biomass combustion

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Figure 2-2 Classification of log wood combustion principles (FNR I 2007) In through-burning systems, the primary ai r enters the combustion chamber through a grate. The wood logs are then ignited at the bottom of the batch, thus heating the entire stack and commencing the burnin g. This combustion system is suitable for stoves frequently fed with small batches of log wood. For log wood boilers, this combustion principle is no longer a state-of-the-art technology. In top burning systems, the primary air enters the combustion zone sideways. The stack is ignited at the top or in the middle and as such, the combustion reactions are slower than those in through-burning systems. The combustion process is nevertheless discontinuous. This combustion system is su itable for small or medium batches of log wood. Both combustion systems, through and top-burning, are usually operated with natural draught, meaning that no auxiliary ventilation devices are needed. Under-burning systems are the latest development in log wood combustion technologies. This principle is a state-of-the-art technology for log wood boilers. The fuel is ignited at the bottom and the combustion gases are draw n downwards or sideways, resulting in a relatively continuous combustion process. The continuous combustion process and separation of the primary and secondary combus tion zones result in very low emissions; a fan is however necessary to ensure proper op eration. This fan is usually placed at the flue gas exit of the furnace.



### 2.1.3 Automated stoking

Automatically stoking furnaces can be divide d into furnaces with fixed bed combustion, fluidised bed combusti on and dust combustion. The ba sic principles of these three technologies are shown in Figure 2-3 (Marutzky, Seeger 1999).11 

### Report

Fuel Ash

Air

Fixed bed furnace

(grate furnace) Fuel

Ash

Air

bubbling fluidised

bed furnace circulating fluidised bed furnace Air Air Fuel

Fuel

dust firing
Figure 2-3 Diagram of principle combustion technologies for biomass (Marutzky, Seeger 1999) Fixed-bed combustion systems include grate fu rnaces and underfeed stokers. Primary air passes through a fixed bed, in which drying, gasification, an d charcoal combustion takes place. The combustible gases produced are bu rnt after secondary air addition has taken place, usually in a combustion zo ne separated from the fuel bed. Within a fluidised bed furnace, biomass fuel is burnt in a self-mixing suspension of gas and solid-bed material into which combusti on air enters from below. The type of combustion can be distinguishe d depending on the fluidisation velocity, bubbling fluidised bed and circulatin g fluidised bed Dust combustion is suitable for fuels available as small particles (average diameter smaller than 0.1 in). For this type of combustion, a mixture of fuel and primary combustion air is injected into the combusti on chamber, whereby the combustion takes place while the fuel is in su spension. The gas burnout is ac hieved after the addition of secondary air. For small scale appliances, fixed bed combustion technology is used in medium to large scale appliances, inclusive for all technologies.

Small scale appliances - pellets Existing combustion technologies for wood chips have been adopted for pellet combustion, and a new principle has been de veloped. The development of small-scale pellet burners has taken place to a great exte nt in Sweden and Aust ria. Pellet burners are divided according to the feed direction of th e pellets into three main types: top feed, underfeed and horizontal f eed (Alakamgas, Paju 2002).12 

### Biomass combustion

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Figure 2-4: Classification of pellet combustion principles (Alakamgas, Paju 2002) In underfeed burners (underfeed stoker or unde rfeed retort burners), the fuel is fed into the bottom of the combustion chamber or co mbustion retort. These burners are best suited for fuels with low ash content (wood pellets, wood chips). They are built for a nominal power between 35 MBtu/h and 8 MMBtu/h or greater. In horizontal feed burners, the combustion chamber is either fitted with a grate or a pusher plate. The fuel is introduced horizontally into the combustion chamber. During combustion, the fuel is moved or pushed hori zontally from the feeding zone to the other side of the pusher plate or the grate. While the fuel is drying, gasification and solid combustion take place; following this the remaining ash drops into an ash container. Horizontal feed burners can burn wood chips and pellets and are built for nominal heat flows from 50 MBtu/h to more than 50 MMBtu /h. Purpose-built hori zontal feed systems (with moving grate, with water cooling) are fitted for the use of bark, straw or grain as well. Top feed burners have been specifically developed for pellet combustion in small-scale units. The pellets fall through a shaft onto the fi re bed, consisting of either a grate or a retort. The separation of the feeding syst em and the fire bed ensures the effective protection against back-burn into the fuel storage. The proper distance between the combustion retort and the feedin g system prevents early igniti on of pellets in the feeding system (Obernberger, Thek 2002). The ash is removed manually or mechanically by a dumping grate. This feeding sy stem allows very accurate f eeding of pellets according to the current power demand and is thus often used in furnaces with very small nominal heat flows.13 

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Pellet burner systems are always operated wi th a forced draught. The fan can be placed at the combustion air inlet or at the flue gas exit of the furnace.



## 2.2 Small scale combustion systems

Common small scale combustion systems for w oody biomass are listed in Table 2-1 and are categorized in two groups: Room heat ers and boilers. Small scale combustions systems are used in the residential and commerci al sectors as well as in district heating systems. Table 2-1 Types and features of small-scale wood combustions systems, modified from (FNR I 2007)

type nominal heat load in MBtu/h combustion principle feature

ROOM HEATERS fireplaces 0 - 15 through- / top burning inappropriate for permanent heating

pellet stoves 10 – 35 top feed automatically operated, regulated fuel and combustion air input (fan), with or without hot water
wood stoves 10 – 40 through- / top burning fired from living room no water installations

Masonry heaters 5 – 60 through- / top burning diverse heat storing/release characteristics , with or without hot water, combined technologies with pellets

BOILERS

pellet boilers ≥ 10 top feed / horizontally feed / underfeed burner fully automated operation, induced draught

solid wood boilers ≥ 35 through/ under burning up to 40 in log wood length, natural or induced draught, buffer accumulator is needed
wood chip boilers ≥ 35 through burning / horizontally feed / underfeed burner fully automated operation possible, induced draught, buffer accumulator advantageous



### 2.2.1 Room heaters

Room heaters are intended to heat a space directly, unlike central heating furnaces or boilers, which supply heat to the house thro ugh a system of ducts or pipes. Varying concepts for space heaters have been deve loped and are still in use. Common space heaters are:14 

### Biomass combustion

technology

• Open and closed fireplaces

• Log wood stoves

• Masonry heaters (Heat storing (tiled) stoves)

• Pellet stoves

2.2.1.1 Fireplaces

Conventional fireplaces have a long history in home heating. They are built from masonry materials such as brick, block and stone. More recently, factory-built models are constructed mainly of steel. Conventional open fireplaces (Figure 2-5, left) do not heat a home effectively and th eir use for permanent heating is thus not recommended. In many settlement areas and especially urban areas, the use of open fireplaces is even forbidden. Factory-built closed fireplaces combine the beauty of an open fire with modern wood stove features, such as controlled and st aged combustion air supply, baffle plates, properly dimensioned combustion chambers and fireclay lining. Burnout rate and efficiency clearly exceed those of open fireplaces. Many closed fireplaces provide heat by direct flame radiation and by co nvection (Figure 2-5, right).

Figure 2-5 Open fireplace (left) and clos ed fireplace with convection casing (right)(Kachelofenbauerinnung 2007) Fireplaces will not be considered in this study because they are not an appropriate technology for heating purposes.

2.2.1.2 Pellet stoves

Pellet stoves are suitable for continuous operation; their minimum heat output is usually 30 % of the nominal heat flow. Underfeed ing and top feeding are the most common combustion technologies for pellet stoves.15 

### Report

Figure 2-6 shows the principle of a pellet stove with a top feed burner. The pellets are conveyed by the fuel screw into the shaft from where they fall into the combustion retort. The pellets are usually ignited automatically with a glow-plug. The supply of primary and secondary combustion air is co ntrolled by a low-noise fan. External air supply is also possible for some pellet stoves, which is important for houses with controlled ventilation. The storage compartment is placed in the rear of the stove and can hold up to 110 lb of pellets.

Figure 2-6 Functional principle of a pellet stove with top feed burner (Calimax 2007)

In latest technological developments, the quality of combustion is regulated by a carbon monoxide sensor, which ensures optimal comb ustion air supply at all times. Excess air ratio sensors are used less often for the control of ventilators in pellet stoves as they are quite expensive. They are however frequent ly used for control in boiler furnaces.

2.2.1.3 Pellet stoves with hot water production

The heat output of pellet stoves can usually be varied from 30 to 100 %. This enables pellet stoves to produce exactly the heat and, with integrated heat exchangers, also the hot water required. In these pellet stoves up to 80 % of the heat produced can be stored in the water (FNR I 2007). Figure 2-7 shows an example of a pellet stove with integrated hot water production. The combination of a pellet stove and solar hot water production allows the complete heat and hot water demand of a (low-energy) hous e to be covered without the need of an additional boiler.16 

### Biomass combustion

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Figure 2-7 Pellet stove with integrated hot water production (Calimax 2007)

2.2.1.4 Wood stoves

Figure 2-8 Functional principle of a log wood stove (Westfeuer 2005) Figure 2-9 Example of a log wood stove (Heinz Aberle 2007)

In contrast to fireplaces, log wood stoves ar e floor mounted (free-st anding) in the living room. In general, they are built of cast iron and designed for logs with a length of 10 and 15 in. Wide variations in design, such as door s with or without viewin g glass or casings of tiles or soapstone are available. Wood stov es are usually based on the through-burning17 

### Report

principle. Conventional wood stoves are equipped with up to three doors; the upper door serves for loading the logs, the middle door is used for manual grate cleaning and the third for ash removal. Combus tion air supply can be regula ted manually by dampers or push handles. In simple designs, there is no separation of primary and secondary combustion air. Figure 2-8 and Figure 2-9 show the functional pr inciple as well as an example of modern log wood stoves ba sed on the through- burning principle.
Solid wood stoves are still sold without test certification.

2.2.1.5 Masonry heaters

Two different basic types of masonry heaters, the fully handcrafted model and the prefabricated model, can be distinguished. The traditional type of masonry heater, the tiled base stove, is a fully handcrafted heating device. With the exception of the fire door and possibly some parts of the combustion ch amber, it is completely built with ceramic materials such as chamotte, so apstone, clay and/or tiles. Due to its large heat storing mass, it is a slow reacting heating system; Figure 2-10 shows the function al principle of tiled base stoves and Figure 2-11 shows a design example of a tiled base stove. This stove is fed from another room (mostly from the anteroom).

Figure 2-10 Functional principle of a tiled base stove (Kachelofenbauerinnung 2007) Figure 2-11 Example of a tiled base stove (Kachelofenverband 2007)

The second type of masonry heaters consists of a prefabricated combustion chamber; the combustion gas channel (heat exchangers) can be built by hand or be prefabricated as well. A hot-air tiled stove has only a small heat storage mass. This type of stove consists of a prefabricated heater and optionally, a steel or cast-iron heat exchanger. Most of the heat is transferred by convection. Hot-air tile d stoves can react quickly to changing heat demands, but are not designed for long-la sting heat transfer. Depending on their dimensions, hot-air tiled stoves have similar heating characteristics as conventional wood stoves with convection casings. Combined tiled stoves are a combination of tiled base stoves and hot-air tiled stoves, consisting of a prefabricated heater and a ceramic heat storage unit (Figure 2-12 and Figure 2-13).18 

### Biomass combustion

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Figure 2-12 Functional principle of a combined tiled stove (Kachelofenbauerinnung 2007) Figure 2-13 Example of a combined tiled stove (Kachelofenverband 2007)

Masonry heaters are based on the top and through-burning combustion principles. Combustion air is supplied in stages as primary and secondary combustion air.

Combined masonry heaters Different technologies have b een developed for the combustion of pellets in tiled stoves over the past few years. Prefabricated heat ers enable the optional combustion of log wood and pellets or have an integrated boiler function. Figure 2-14 shows a prefabricated heater for pellet combustion in a combined tiled stove. No auxiliary devices such as a fan or motor are needed for operation. Figure 2-15 shows a fully automated prefabricated heater with an underfeed pell ets burner. Both prefabricated heaters can burn log wood as well.

Figure 2-14 Prefabricated heater Pellets Power (Wienerberger Ofenkachel 2007) Figure 2-15 Prefabricated heater Pellet module (Brunner 2007)19 

### Report

2.2.2 Boilers

In contrast to space heaters, boilers are intended to produce hot water for heating remote rooms. Usually, they are placed in special heating rooms in the cellar, in the garage or even in heating containers ou tside the house. Modern boilers achieve efficiencies beyond 80 % (based on the upper heating value).

2.2.2.1 Pellet boilers

Pellet boilers operate fully automatically wi th top feed, underfeed and horizontal feed burners. Manufacturers have typically spec ialized in a certain technology. Devices exclusively designed for wood pellets are ty pically used for a heat output range from 25 MBtu/h. For higher heat flows, wood chip furnaces are usually used, which are often approved for wood pellets as well (see 2.2. 2.3). Figure 2-16 and Figure 2-17 and show two different top feed boiler s for wood pellets. This comb ustion principle allows for accurate feeding and is suitable for small heat demands as well as on/off-operation modes. In order to ensure proper operation, the grate must be au tomatically cleaned. Slagging can occur if low-quality pellets ar e used (Regionalenergie Steiermark 2005).

Figure 2-16 Top feed boiler (Evotherm 2010) Figure 2-17 Top feed boiler (Windhager 2005)
Underfeed boilers are used for small to larg e heat flows. Underfeed boilers are less sensitive to low-quality pellets than top f eed burners (Regionalenergie Steiermark 2005). An example of an underfeed boil er is shown in Figure 2-18. A horizontal feed boiler is demonstrated in Figure 2-19.20 

### Biomass combustion

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Figure 2-18 Underfeed boiler ( Guntamatic 2007 ) Figure 2-19 Horizontal feed boiler ( Hargassner 2005 )

Flue gas condensing With proper flue gas condensing technology the moisture can be removed from the flue gas to further reduce the exhaust gas temperature, thus achieve higher efficiencies

. Figure 2-20 shows the function al principle of the first cond ensing boiler for wood pellets available on the European market. Its efficiency of over 100 % is of course only due to the chosen definition for the determination of the efficiency, which is based on the net calorific value of the used fuel. The measured total dust emissions are very low, most likely due to the effect of the flue gas condensation.

Figure 2-20 Functional principle of a condensing boiler for wood pellets (Oekofen 2007)21 

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2.2.2.2 Solid wood boilers

Log wood boilers with natural draught based on the through- burning combustion principle were a state-of-the-art technology in the 1 970s. Modern log wood boilers are based on the under-burning combustion principle and induced draught. Usually a fan, which is placed at the flue gas exit of the boiler, is used to suck primary and secondary combustion air into the corresponding combus tion zones. The wood storage compartment may be filled during combustion without the risk of combustion gases leaving the boiler. The high degree of turbulence needed for the mixing of the fuel gas and the combustion air is ensured by the proper design of the combustion ai r inlet zone and the nozzles. Figure 2-21 and Figure 2-22 show two different log wood boilers with induced draught airflow and flue gas exits on the si de and at the top of the boiler. Log wood boilers are usually designed for a heat output range from 50 to 135 MBtu/h. There are some specialty companies that ma ke systems up to 3 MMBtu/h such as the Lopper company.

Figure 2-21 Under-burning boiler with induced draught, flue gas exit sideways(Buderus 2005) Figure 2-22 Under-burning boiler with induced draught, vertical flue gas exit (Froeling 2005)

2.2.2.3 Wood chip boilers

For wood chip furnaces, underfeed burners and horizontal feed burners with or without a grate are fairly common in various designs. W ood chip furnaces are therefore used in a wide nominal power capacity range from 50 MBtu/h up to over 70 MMBtu/h.22 

### Biomass combustion

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Concerning small scale systems, the advantag es of wood chip boilers over log wood boilers include automatic operation and low em issions due to conti nuous combustion. On the other hand, the process of producing, st oring and, if necessary, drying wood chips requires more investment in machinery and st orage space than is the case for log wood. In comparison to pellets, wood chips are less expensive and can be produced on site. Wood chip furnaces are often approved for wood pellets as well; specially designed pellet boilers can however not be fired with wood chips. Figure 2-23 shows an example of an underfe ed burner for wood ch ips and pellets. The principle of a horizontal stoker burner is shown in Figure 2-24.

Figure 2-23 Underfeed burner for wood chips and pellets (KWB 2007) Figure 2-24 Horizontal feed burner for wood chips, pellets and grain (BAXI 2007)

2.2.2.4 Combined boiler technologies

Special boilers have been developed to comb ine the comfortable combustion system for wood pellets with the combustion system for log wood. In some boilers manual rearrangements are necessary, while others offer a fully automati c switch. Figure 2-25 shows a combined boiler with a fully automa tic switch. When heat is demanded, the pellet burner is started automatically. Any log wood fed into the boiler will be ignited by the pellet flame. As soon as the log wood is ignited, the pellet burner stops and the log wood stack is burnt (under-burning principle). If there is no log wood in the fuel storage compartment, the pellet burner will continue combustion and the log wood compartment is used as secondary combustion zone for pellet combustion.23 

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Figure 2-25 Combined boiler technology for pellet and log wood combustion (left: log wood mode, right: pellet mode) (sht 2007)



## 2.3 Medium to large scale combustion

In Table 2-2 the characteristics of common me dium to large combustion technologies for woody biomass are listed. Table 2-2 Types and characteristics of medium to large combustions systems suitable for woody biomass (FNR II 2007)

Combustion technology Stoking Fuel Nominal power Moisture content (% w.b.)

Underfeed stoker Mechanic Pellets and wood chips (ash content ≤ 1%) 35 MBtu/h – 9 MMBtu/h 5-40

Moving grate Mechanic All wood fuels (ash content up to 50%) 510 MBtu/h – 170 MMBtu/h 5-60

Bubbling fluidised bed combustion Mechanic Particle size <3.6 in 20 MMBtu/h – 120 MMBtu/h 5-60 Circulating fluidised bed combustion Mechanic Particle size <1.5 in 50 MMBtu/h850 Btu/h 5-60

Dust firing Pneumatic Particle size <0.20 in 1700 MBtu/h170 MMBtu/h Usually <20



### 2.3.1 Fixed-bed combustion

2.3.1.1 Underfeed stokers

In addition to small scale combustion sy stems where underfeed stokers are a common technology (see 2.2.2.1 and 2.2. 2.3), they are also an inexpe nsive and operationally safe24 

### Biomass combustion

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technology for medium-scale systems up to 20 MMBtu/h. They are suitable for biomass fuels with low ash content (wood chips, sa wdust, pellets) and small particle sizes (particle dimension up to 2.0 in). Ash-rich biomass fuels such as bark, straw and grain need more efficient ash removal systems. Mo reover, sintered or melted ash particles covering the upper surface of the fuel bed can cause problems in underfeed stokers due to unstable combustion conditions when the fuel and the air are breaking through the ash-covered surface. An advantage of unde rfeed stokers is their good partial-load behaviour and their simple load control. Load changes can be achieved more easily and quickly than in grate combustion plants beca use the fuel supply can be controlled more easily (Loo, Koppejan, 2002).

Figure 2-26 Combustion chamber of an underfeed stoker furnace (BINDER 2007)

2.3.1.2 Grate furnaces

There are different grate furnace technologies available: fixed grates, travelling grates, moving grates, rotating grates, vibrating gr ates etc. All of these technologies have specific advantages and disadvantages dependin g on the fuel properti es; as such careful selection and planning is necessa ry. Based on the flow directions of fuel and the flue gas, there are different systems for grat e combustion plan ts (Figure 2-27):

• counter-current flow (flame in the opposite direction as the fuel)

• co-current flow (flame in the same direction as the fuel)

• cross-flow (flue gas removal in the middle of the furnace)

Counter-current combustion is most suitable for fuels with low heating values (wet bark, wood chips or sawdust). Co-current combusti on is applied for dry fuels such as waste wood or straw, or in systems where pre-heat ed primary air is used. Cross-flow systems are a combination of co-current and counter-cu rrent units and are also especially applied in combustion plants with vertical secondary combustion chambers (Loo, Koppejan, 2002).25 

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Cross-current Co-current Counter-current

Figure 2-27 Classification of grate combus tion technologies: co-current, cross-current and counter-current (Nussbaumer 1995)

Moving grate systems Moving grate furnaces usually have an inclined grate consisting of fixed and moveable rows of grate bars (see Figure 2-27 and Figu re 2-28). They are made of heat-resistant steel alloys and are equipped with small cha nnels in their side-walls for primary air supply. By alternating horizo ntal forward and backward movements of the moveable sections, the fuel is transported along th e grate, whereby un-bu rnt and burnt fuel particles are mixed and the surfac e of the fuel bed is steadily renewed. The fuel is evenly distributed over the grate surface (Loo, Koppejan, 2002).

Figure 2-28 Combustion chamber of a moving grate furnace (Polytechnik 2007 )

In moving grate furnaces a wide variety of biofuels can be burnt. Air-cooled moving grate furnaces use primary air for cooling the grat e and are suitable for wet bark, sawdust andwood chips. For dry biofuels or biofuels with low ash-sintering temperatures, watercooled moving grate systems are re commended (Loo, Koppejan, 2002).

Travelling grate Travelling grate furnaces are built of grate bars forming an endless band (like a moving staircase) moving through the combustion ch amber. Fuel is supplie d at one end of the combustion chamber onto the grate, by screw conveyors for example or is distributed26 

### Biomass combustion

technology

over the grate by spreader-stokers injecting the fuel into the comb ustion chamber (see Figure 2-29). The fuel bed itself does not move, but is transported through the combustion chamber by the grate, contrary to moving grate furnaces where the fuel bed is moved over the grate. The advantages of travelling grate systems are that they provide uniform combustion conditions and low dust emissions due to th e stable and almost unmoving bed of embers. Furthermore, the maintenance or replacement of grate bars is easy to handle. In comparison to moving grate furnaces however, the fact that the bed of embers is not stoked results in a longer burn -out time (Loo, Koppejan, 2002).

Figure 2-29 Diagram of a travelling grate furnace fed by spreader-stokers (Detroit Stoker Company 1998)



### 2.3.2 Fluidised bed combustion

Fluidised bed (FB) combustion systems have been applied since 1960 for the combustion of municipal and industrial wastes. Regarding technological applications, bubbling fluidised beds (BFB) an d circulating fluidise d beds (CFB) have to be distinguished. Due to the good mixing achieved, FB combustion plants can provide flexibly with different fuel mixtures but are limited in terms of fuel particle size and impurities contained in the fuel. Therefore, an appropriate fuel pre-treatm ent system covering pa rticle size reduction and separation of metals is necessary for fail-safe operation. Usually a particle size less than 1.6 in is recommended for CFB units and less than 3.1 in for BFB units. Moreover, partial load operation of FB combustion plants is limited due to the need of bed fluidisation. The low excess air quantities necessary increa se combustion effici ency and reduce theflue gas volume flow. This makes FB combustion plants especially interesting for largescale applications. One disadvantage of FB co mbustion plants is posed by the high dust27 

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loads carried along with the fl ue gas, which make efficient dust precipitators and boiler cleaning systems necessar y (Loo, Koppejan, 2002).

2.3.2.1 Bubbling fluidised be d combustion (BFB)

In BFB furnaces (see Figure 2-30) a bed mate rial is located in the bottom part of the furnace. The primary air is supplied over a no zzle distributor plate an d fluidises the bed. The bed material is usually silica sand. The ad vantage of BFB furnaces is their flexibility concerning particle size and moisture content of the biomass fuels. Furt hermore, it is also possible to use mixtures of different kinds of biomass or to co-fire th em with other fuels. A large disadvantage of BFB furnaces is th e difficulties they have at partial load operation, a problem which is solved in modern furnaces by splitting or staging the bed. BFB furnaces are typically used for nomi nal outputs of more than 17-34 MMBtu/h (Loo, Koppejan, 2002).

bed partitioning section A-A 1 3 2 1 A A

Fuel

Fluidised bed Flue gas ash

tertiary air

primary air

bed 1 secundary air bed 2,3 2 3

Figure 2-30 Diagram of a BFB furnace (Hein, Schmitz 1995)

2.3.2.2 Circulating fluidised bed (CFB) combustion

By increasing the fluidising velocity to 16 to 33 ft/s and using smaller sand particles (0.008 in to 0.02 in diameter), a CFB system is achieved. The sand particles will be carried with the flue gas, separated in a hot cyclone or a U-beam separator, and fed back into the combustion chamber (see Figure 2-31) . The higher turbulen ce in CFB furnaces leads to a better heat transfer and a very homogeneous temperature distribution in the bed. The disadvantages of CFB furnaces are th eir larger size and therefore higher price, the even greater dust load in the flue gas leaving the sand pa rticle separator than in BFB systems, the higher loss of be d material in the ash, and the small fuel particle size28 

### Biomass combustion

technology

required (between 0.004 and 1.6 in in diameter). This often causes higher investments in fuel pre-treatment. Moreover, their operation at partial load is problematic. CFB furnaces are usually applied in a power range of mo re than 100 MMBtu/h (Loo, Koppejan, 2002).

to baghouse Economizer Generator banks Primary superheaters Secondary superheater Tertiary superheater Gas flow

790-890°C 870°C Cyclone

Furnace

Air

Fuel 910°C

Figure 2-31 Diagram of a CFB furnace (NREL 1996)



### 2.3.3 Dust combustion

Fuel quality in dust combustion systems has to be quite constant. Fuels such as sawdust and fine shavings are pneumatically injected into the furnace. The transportation air is used as primary air. Start-up of the furnace is achieved by an au xiliary burner. Due to the explosion-like gasification of the fine and small biomass particles, the fuel feeding needs to be controlled very carefully and forms a key technological unit within the overall system. Fuel gasification and charcoal combus tion take place at the same time because of the small particle size. Therefore, quick lo ad changes and an efficient load control can be achieved. Figure 2-32 show s a muffle dust furnace in combination with a water tube steam boiler. This technology is available for thermal capacity between 6.8 and 27 MMBtu/h (Loo, Koppejan, 2002).29 

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1...primary air supply, 2...fuel feed, 3...gasification and partial combustion, 4...flue gas recirculation, 5...ash disposal, 6...secondary air supply, 7...tertiary air supply, 8...water tube boiler.

Figure 2-32 Diagram of a dust combustion plant (muffle furnace) in combination with a water-tube steam boiler (Marutzky, Seeger 1999)30 

### Emissions



# 3 Emissions

In this section, a short summary of the emissions from bioma ss combustion to be considered in this report is given. Additionally, measurement and reduction methods are summariesed. With regard to the reduction methods, primary and seconary measures have to be distinguished: While primary me asures are implemented in the combustion process and/or design of the combustion ch amber, secondary measures are implemented after combustion process has ended, mostly adjacent to the boiler. More detailed information on formation mechanisms, impacts on health and the environment, measurement and reduction methods can for example be found in Nussbaumer 1989, Kaltschmitt, Hart mann 2001, Marutzky, Seeger 1999 or Loo, Koppejan, 2002.



## 3.1 Conversion factors

Emissions are usually given in a co ncentration related to a certain O 2 -concentration in the flue gas at normal conditions 2 (mg/m3 at 13% O 2 or ppm/m3 at 13% O 2 ); this relation of the emissions to certain O 2 -concentrations enables compar ability of data. For biomass appliances, the normal O 2 -concentrations range from 10 to 13%. Sometimes emissions are related to the fuel input (mg/MJ). Sinc e the measurement of the exact energy input is impossible, especially in medium to larg e scale appliances, this measurement method is limited to small scale appliances.
The most recent emission limits from th e European Commission are usually given in mg/m3 based on 10 % oxygen in the dry fl ue gas; older regula tions refer to 13 % oxygen in the dry flue gas. In this report, gaseous emissions will be given in mg/m3 at XX%O 2 , which always means that emissions are related to the dry volume in m3 at normal conditions (Nm3) at a certain oxygen level in the flue gas (XX % O 2 ). According to NYSERDA’s specifications, emissions are to be based on an oxygen content of 12 %

. In Table 3-1 the factors fo r the conversion of the O 2 -based emissions in mg/Nm3 for various oxygen levels are shown.
Table 3-1 conversion factor s for the conversion of O 2 -based emissions in mg/m3 mg/m3 at 10% O2 1 0 9

. 0 & & 1 8

. 0 & & 2 7

. 0 & & mg/m3 at 11% O2 1.1 1 0.9 0.8 mg/m3 at 12% O2 2

. 1 & 1

. 1 & 1 8

. 0 & mg/m3 at 13% O2 1.375 1.25 1.125 1 mg/m3 at 10% O2 mg/m3 at 11% O2 mg/m3 at 12% O2 mg/m3 at 13% O2 read the table from the first column to the last row: Emissions in mg/m3 at 10%O2 · 0 9

. 0 & & = Emissions in mg/m3 at 11%O2

2 pressure of 1 atm and temperature of 32 °F31 

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The European Commission also pr ovides emission limits for du st in mg/m3 at a certain O 2 level. The factors for the conv ersion from mg /m3 at 12% O 2 to mg/kg fuel and lb/MMBtu are shown in Table 3-2. For the conv ersion from mg/m2 at a certain O 2 level to mg/kg fuel and lb/MMBtu, the elemental composition and th e calorific value of the considered fuels have to be assumed. These assumption s are given in Table 1-2 on page 6.
Table 3-2 conversion factors for the conver sion of dust emissi ons from mg/m3 to mg/kg fuel and lb/MMBtu

fuel 2 % 12 3 / /

O at fuel
m mg kg mg
2 % 12 3 / /

O at m mg mmBTU

lb

pellets 10.08 1.23·10 -3 solid wood 9.31 1.35·10 -3 wood chips 8.44 1.64·10 -3



## 3.2 Carbon Monoxide (CO)

3.2.1 General

Carbon monoxide emissions can be regarded as the indicator of the combustion quality. Conversion of fuel carbon to CO 2 takes place through several elementary steps, and through several different reaction paths. CO is the most important final derivative. It is oxidised to CO 2 if oxygen is available. The rate at which CO is oxidised to CO 2 depends primarily on te mperature. In addition, sufficient residence time is important to achieve low CO emission levels, mainly because CO is generally a later intermediate than hydrocarbons. Furtherm ore, enough Oxygen must be available and mixed with the fuel for the combustion process. CO emissions are caused by in complete combustion which is mainly a result of either:

• inadequate mixing of the combustion air and the fuel in the combustion chamber, producing local fuel-rich combustion zones;

• an overall lack of available oxygen;

• combustion temperatures too low;

• residence times too short; These variables are all linked together thro ugh the reaction rate expressions for the elementary combustion reactions. However, in cases in which sufficient oxygen is available, temperature is the most important variable due to its exponential influence on the reaction rates. An optimisation of these va riables will in general contribute to reduced levels of all emissions from incomplete combustion. Figure 3-1 shows the CO emissi on level as a function of excess air ratio for different biomass combustion applications. For each system an optimum excess air ratio exists: higher excess air ratios will result in a decreased combustion temperature while lower excess air ratios will result in inadequate mixing conditions.32 

### Emissions

CO [mg/m 3 ]

0

excess air ratio 10 100 1000 10,000 100,000

12345 a

b

d c a) simple, manually charged wood boiler; b) downdraught wood log boiler; c) automatic furnace with combustion technology as of 1990; d) automatic furnace with enhanced combustion technology as of 1995

Figure 3-1 CO- emissions - CO vs . excess air ratio (Nussbaumer 1989)



### 3.2.2 Measurement

CO emissions are measured directly after the flue exit of the appliance in an insolated pipe. Results are given in ppm pe r dry flue volume (m3) at no rmal conditions. In order to reference the emissions to an oxygen content of 10, 12 or 13 %, the O 2 and/or the CO 2 concentration have to be measured as well.



### 3.2.3 Reduction

In order to keep CO and correspondingly OGC emissions low (see chapter 3.2 and 3.3), optimal conditions for a high burnout rate of CO must be ensured. These conditions are often summarized as the 3T-rule (Time, Temperature, Turbulence) for combustion quality. In addition, the correct amount of oxygen (air) must participate in the combustion.

Residence TIME of fuel and oxygen in the combustion zone Figure 3-2 shows the correlati on between CO burnout and re sidence time in an ideal stirring reactor. The higher the combustion temperature and the oxygen content, the lower residence times are necessary to reach high CO burnout rate.
The residence time is a function of the co mbustion chamber volume and combustion gas flow. The combustion chamber ha s to be designed to guarant ee high residence times also at high load operation and to avoid fluidic disadvantageous conditions (e.g. dead zones, insufficient mixing, ...)

High TEMPERATURES of the gases in the combustion zone The reaction rate of CO to CO 2 depends primarily on temperat ure if the mixture of fuel and oxygen as well as a certain residence time are given. The temperature of the combustion zone is amongst others influenced by the materials used for the combustion33 

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chamber. If ceramics are used to line the combustion chamber, temperatures will be higher than if the combustion chamber was built of steel (must be cooled with water). In addition, the air fuel ra tio relevancies of extreme importance for the combustion temperature, as shown in Figure 3-3. The higher the air fuel ratio, the lower combustion temperatures will be.

Leuckel, Römer, 1979 

### 0,1 1,0 10,0 100,0

0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6 

## residence time in [s]share of remainingCO in [%] 1300 °F, 18%O2
1300 °F, 2%O2
1200 °F, 18%O2
1200 °F, 2%O2

Figure 3-2 CO-rest as function of residence time, combustion temperature and oxygen-concentration in an ideal sti rring reactor (Leuckel, Roemer 1979)

400 600 800 1,000 1,200 1,400 1,600 1,800 2,000

0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3 3.2 Excess air ratioadiabatic comb. temp. [°C] 20 wt% w.b.
30 wt% w.b.
40 wt% w.b.
50 wt% w.b. fuel moisture content

400 600 800 1,000 1,200 1,400 1,600 1,800 2,000

0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3 3.2 Excess air ratioadiabatic comb. temp. [°C] 20 wt% w.b.
30 wt% w.b.
40 wt% w.b.
50 wt% w.b. fuel moisture content

Figure 3-3 relationship between the adiabatic combustion temperature and the excess air (air fuel) ratio (Nussbaumer 1989)34 

### Emissions

High TURBULENCE in combustion zone The mixing quality of fuel and oxygen is de scribed by the turbulence in the combustion zone. The turbulence is primarily influenced by the flow velocity of the combustion air. With increasing flow velocities , the mixing of fuel and air be comes increasingly ideal. This again results in lower amounts of air needed for the combustion and thus higher combustion temperatures (see Figure 3-3).



## 3.3 Total Organic Bound Ca rbon/Organic Gaseous Substances (OGC)

3.3.1 General

OGC emissions from biomass appliances are di rectly linked to high CO emissions. In Figure 3-4 the measurement results of th e correlation between hydrocarbon and COemissions for wood appliances are shown. If CO-emissions are low, hydrocarbon emissions will be 1/10 to 1/100 of the CO-emissions.

a) Wood stove, b) solid wood boiler with underburning technology, c) Wood chips boiler with horizontal feed (Nussbaumer) 1 10 100 1.000 10.000

10 100 1.000 10.000 100.000 

### Carbon monoxide in [mg/m n 

### 3]Hydrocarbons[m g/mn3] a)

b)

c)

1 10 100 1.000 10.000

10 100 1.000 10.000 100.000 

### Carbon monoxide in [mg/m n 

### 3]Hydrocarbons[m g/mn3] a)

b)

c)

Figure 3-4 Correlation of hydrocarbon and CO-emissions in wood appliances (Nussbaumer 1989)



### 3.3.2 Measurement

OGC emissions are measured directly after the flue exit of the appliance in an insolated pipe. Results are given in ppm pe r dry flue volume (m3) at no rmal conditions. In order to reference the emissions to an oxygen content of 10, 12 or 13 %, the O 2 and/or the CO 2 concentration have to be measured as well.35 

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3.3.3 Reduction

If CO emissions are low, also OGC emissions will be low for biomass combustion processes. Therefore, no separate reductio n concepts for OGC emissions are necessary for biomass combustion.



## 3.4 Dust · Particulate Matter (PM) · Totals Suspended Particulate Matter (TSP)

3.4.1 General

Particulates formed during biomass combusti on can be divided into bottom ashes and fly ashes. The fly ash fraction typically consis ts of a coarse and a fine mode. While the coarse mode (particles larger than some μm ) is simply due to the ash entrainment from the fuel bed, the formation pathways of the fi ne mode (so-called aerosols, with a particle diameter <1 μm) are much more complex.



### Bottom ash K, Na, S, Cl, easily volatile heavy metals released from the fuel to the gas phase Condensation on coarse fly ash particles

Coarse fly ash particles entrained from the fuel bed Gas phase reactions Cooling phase

Nucleation Condensation

Figure 3-5 ash and aerosol formation processes during biomass combustion The basic mechanisms concerning aerosol fo rmation in combustion processes are in general well known from former research wo rk (Friedlander 1977). Volatile ash forming compounds specific to biomass combustion su ch as K, Na, S and Cl as well as easily volatile heavy metals (Zn and Cd), are released from the fuel into the gas phase and subsequently undergo gas phase reactions. As soon as the vapour pressure of a compound exceeds the saturation pressure , which can happen either due to a high formation ratio of this compound or by cool ing of the flue gas, particle formation by nucleation or condensation of these vapours on existing surfaces ta kes place. Nucleation36 

### Emissions

and condensation are always competing processes, and if enough surface for condensation is available, nucleation can part ly or even totally be suppressed. Otherwise, very small (some nm) aerosol particles are formed. As soon as these particles are formed, they start to coagulate with other aero sols or with coarse fly ashes. Figure 3-5 gives an overview of the different ash and aerosol format ion processes, for more details see (Brunner et al 2004). Next to the formation path of the fly ash fraction by low volatile minerals, heavy metals and salt, aerosols can also be formed due to incomplete combustion. In this case unburnt carbon, fine wood particles, charcoal, soot, tar, ... are emitted as dust. Therefore complete combustion (low CO emissions) are necessary to k eep also dust emissions as low as possible. In Figure 3-6 the chemic al compostions of dust samples from an appliance that was operated under optimal conditions (low CO emissions) and from a wood stove that was operated under poor co nditions (high CO emissions) are shown.

Automatic appliance, optimum operation conditions CO < 50 ppm Wood stove, poor operation conditions

CO > 10 000 ppm

Figure 3-6 chemical composition of dust samples from differen t biomass appliances and operation conditions (Klippel 2007) While the un-burnt fraction of an automatic appliance under optimum operation conditions is about 2 wt%, the un-burnt frac tion of the wood stov e that was operated under poor conditions is about 98 wt%. Considering that the amount of salts is approximately equal for the automatically an d the manually stoked appliances, overall dust emissions from the wood stoves will be a multiple higher than those of the automatic system.
Definition and characte ristics of coarse fl y ashes and aerosols:

• Coarse fly ashes:

o ashes entrained from the fuel bed

o particle sizes < 100 μm

o mainly consist of refractory species such as Ca, Mg, Si as well as smaller amounts of K, Na, Al37 

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• Aerosols:

o Latin: solvere = solute

o colloidal solid (dust) or fluid (fog) particulate matter in gases

o formed from condensed ash vapours released from the fuel to the gas phase during combustion

o particle sizes between 1 nm and 1 μm

o mainly consist of K, Na, S, Cl, Zn and Pb

• Fly ashes = coarse fl y ashes + aerosols

0 100 200 300 400 500 600 700 800 900

0.01 0.10 1.00 10.00 100.00 1,000.00 xm [μm ae.d.] wood chips [mg/Nm3] bark [mg/Nm3] waste wood [mg/Nm3]

aerodynamic diameter d ae [ μ m]Δm/Δlg(dae) [mg/Nm3]

Figure 3-7 Particle size distributions of fly as hes in the flue gas at boiler outlet in dry flue gas at 13% O 2 (Brunner et al 2004)

Figure 3-8 SEM images of coarse fly- ash (left) and aerosol particles (right) Description: Samples from wood combustion in a grate furnace; biomass fuel: wood (beech). Equipment used: Scanning Electron Microscopy (SEM) (Brunner et al 2004)38 

### Emissions

3.4.2 Measurement

The dust content is determined discontinuous ly (usually over a period of 30 Minutes) using a gravimetric or electrostatic method. Suitable test equipment is shown in Figure 3-9. 1. removable sampling probe 2. union nut 3. seal 4. filtering bush 5. quartz wool 6. filter housing 7. union nut 8. clamping ring 9. flat filter support 10. flat filter 11. end case

Figure 3-9 tubular filter device for dust measurement With this method the total coarse and a portio n of the fine dust fraction in the flue gas can be measured. Depending on the plugging me thod of the quartz wool into the filter housing, particulates down to 1 μ m are collected in the filter and therefore considered in this measurement. In order to avoid the co ndensing of semi-volati les, a minimum flue gas temperature is required. More informat ion about measurement methods for dust can be found in VDI 2066, EN 13284-1 or Nussbaumer 2008. Results are given in mg per dry flue volume (m3) at normal conditions. In order to reference the emissions to an oxygen content of 10, 12 or 13 %, the O 2 and/or the CO 2 concentration have to be measured as well.



### 3.4.3 Reduction

3.4.3.1 Primary measures

The study of the primary reduction of dust em issions is quite a young field of research. Oser, Nussbaumer 2004 developed a low-particle concept for biomass appliances:

• operation at very low air-fuel ratio in th e firebed (Excess air ratio in firebed: 0.2- 0.4)

• gas tightness of combustion and fuel stoking unit

• operation at low overall air-fuel ratio (Excess air ratio 1.3-1.6)

• clear staging of secondary air and prevention of backflow of secondary air into the firebed.

• adequate large dimensioned combusti on chamber for a high firebed

• high burnout rate of OGC

• sufficient high temperatures in primary combustion zone39 

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3.4.3.2 Secondary measures

To reduce dust emissions dive rse technologies with different efficiencies and function principles were developed. Since costs for investment, operation and maintenance are, depending on the technology, quite high and limits are given to operation conditions, these technologies were primarily used in large and mediums scale appliances.
Due to strict dust emission limits in small scale appliances, dust control technologies were recently adopted for the utilisation in small appliances as well. Table 3-3 gives an overview of particle sizes removed and effi ciencies reached by medium to large scale dust control technologies. Table 3-3 summary of typical sizes of part icles removed by various particle control technologies

Particle control technology Particle size ( μ m) Efficiency (%) Settling chambers > 50 < 50 Cyclones > 5 < 80 Multicyclones > 5 < 90 Electrostatic precipitator < 1 > 99 Baghouse filters < 1 > 99 Spray chambers > 10 < 80 Impingement scrubbers > 3 < 80 Cyclone spray chambers > 3 < 80 Venturi scrubbers > 0.5 < 99

3.4.3.2.1 Cyclones

Particle separation in a cyclone is based on the principle of gravity in combination with centrifugal forces. Gas and solid particles are exposed to centrifugal forces, whereby heavy particles experience high er centrifugal forces and th erefore hit the wall and slide down into a container. The gas flow into the cyclone can be tangential (Figure 3-10) or axial . In the second case a fan is necessa ry to bring the gas into rotation. The separation efficiency of a cyclone can be improved by in creasing the centrifugal force through reduction of the cyclone diameter. In order to prevent the loss of capacity, several cyclones can be used in parallel; this is called a multicyclone and is illustrated in Figure 3-11. There are however disadvantages of multicyclones in that they are more complicated, requiring a more complicated construction, and are as a result more expensive. They also require an increased pressure drop, an d thus have a higher energy consumption. Cyclones represent a simple technology wh ich are high reliable and require little maintenance. The requirements regarding the flue gas quality are low. Cyclones are used at pressure levels from 0.01 to 100 atm an d can withstand temperatures of up to 1650 °F. The efficiency from 80 – 90% is quit e low and corresponds to dust loads of40 

### Emissions

0.150 to 0.075 lb/MMBtu when biomass is used. This technology is therefore quite often used as pre-precipitator.

Figure 3-10 tangential cyclone (Jirkowsky et Al, 2002) Figure 3-11 axial multicyclone (Jirkowsky et Al, 2002)

3.4.3.2.2 Electrostatic precipitator

In an electrostatic filter, the particles are first electrically charged and then exposed to an electrical field whereby they are attracted to an electrode. Periodical ly, this electrode is cleaned through vibration, where the dust falls off the electrode into a collection unit. This operation principle is shown in Figure 3-12.

Figure 3-12 operation principle of electros tatic precipitator (Jirkowsky et Al, 2002)
Different variations of electrosta tic precipitators are available:
The dry electrostatic precipitator works as illustrated in Figure 3-12. In order to collect the precipitated particles, di scontinuous operating rappers are used.41 

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In wet electrostatic precipitators, the flue gas is completely saturated before entering the precipitator. This saturation reduces th e electrical charging of the particles and increases the efficiency. Condensing wet electrostatic precipitators are cooled by ambient air, which leads to the cooling of the flue gas an d the condensation of water on the inner surface of the precipitator. The condensed water flows down the electrode and cleans it at the same time. Electrostatic precipitators reach efficiencies greater than 99%.

3.4.3.2.3 Baghouse filters

Baghouse filters consist of a filter or cloth tightly woven from special fibres and hung in a closed construction through which flue gas passe s. The separation effi ciency of bag filters is quite high, even with high flue gas flow rates an d high particle content. The first layer of particles actually improves the filtration efficiency. However, as more particles settle on the cloth, the pressure dr op increases. The cloth is th us periodically cleaned by vibration or pressurised air (Figure 3-13).

Figure 3-13 pulse jet baghouse filter (Jirkowsky et Al, 2002)

The operating temperature range is limited to approximately 480 °F; there is a significant risk of fire if this temperature is exceeded or when un-burnt carbon is present in the fly ash. In order to limit the amount of particles settling on the filter and to reduce the chance of fire through sparks, a cyclone ca n be used. When the operating temperatures are too low, tars present in the flue gas ma y condense and clog th e cloth. In addition, the moisture in the flue gas is limited to a maximum of 20 %. Baghouse filters reach efficiencies of gr eater than 99% and therefore reduce the emissions of wood appliances below 0.010 lb/MMBtu.

3.4.3.2.4 Scrubbers

In scrubbers, particles are scrubbed out from the flue gas by water droplets of various sizes depending on the type of scrubber used . The particles are removed by the collision and interception between droplets and partic les. Upon impact, the particles are wetted and carried by the water droplet, thus effect ing removal. The more droplets formed, the42 

### Emissions

more efficient the unit will be. The droplets must therefor e be small. Smaller diameter spray nozzles will produce smaller droplets, but will also result in higher pressure drops, consuming more energy. Since efficiency increases as the droplet size decreases, the efficiency also incr eases with increasing pressure drop. Several types of scrubbers exist. In a countercurrent scrubber for example, the flue gas is introduced at the bottom side of the unit and flows upward against the current with respect to the settling of the atomised liquid droplets. In a cross-flow scrubber , the flue gas flows perpendicula r with respect to the settling of the atomised spray water droplets. Although two sets of sprays atomise the water in horizontal directions, the settling of the resulting droplets is still downward, perpendicular to the direction of the flue gas. A cyclone spray chamber (Figure 3-14) is a combination of an ordinary spray and a cyclone. A venturi scrubber (Figure 3-14) works with a high pressure nozzle in which the flue gas and the liquid are atomised.

Figure 3-14 venturi scrubber (left), cyclone spray chamber (right) (Corbitt 1999) Scrubbers reach efficiencies of up to 99%. They are usually only used if acid components in the flue gas (HCl, SO 2 ) have to be precipitated as well (FNR 2005). This is necessary for contaminated biomass or for non wood bi omass with high chlorine and/or sulphur contents. For medium and large scale wood biomasses appliances this technology is not relevant, but some scrubber systems – always combined with flue gas condensation – have recently been developed for small scale appliances.

3.4.3.2.5 Flue gas condensation

The primary aim of flue gas co ndensation is the heat recove ry from fuels with a high water content. An additional effect of flue gas condensation is that the dust load is precipitated by the condensing water an d dust loads can be reduced down to 0.060 lb/MMBtu (FNR 2005). In medium to larg e scale appliances a cyclone should be used before flue gas condensation. In order to enable flue gas condensation, a return temperature of about 85 °F should be possible.43 

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## 3.5 Nitroxen Oxides (NO X 

## )

NO X emissions from biomass combustion applic ations are mainly a result of complete oxidation of nitrogen in the fuel. Additional NO X may be formed from nitrogen in the air given certain conditions. However, these reac tion mechanisms are not considered to be of significant importance in most biomass combustion applications. The main nitric oxide emitted is NO, which is converted to NO 2 in the atmosphere. In Figure 3-15 the diverse reaction paths of the nitrogen in the fuel are exhibited. It shows that most of the nitrogen in the fuel is converted to N 2 , and some N is bound in the ash, but there is also a fraction of nitrogen in the fuel that is converted to NO and N 2 O.

N in ash N 2 O

NO

N 2 biomass volatile HCN

coke

N NH i i=0,1,2,3 NO

N 2 N 2 O

O, OH O, OH

NO CH i („NO-Recycle“) NCO NH

NH i CO, CH i C, ash H OH pyrolysis and gasification intermediate products oxidation products in flue gas

Figure 3-15 formation paths of biomass fuel nitrogen

Besides the fuel NO X mechanism described in Figure 3-15, two further mechanisms – the thermal NO X mechanism and the prompt NO X mechanism - result in increased NO X emissions. These two NO X mechanisms gain relevance at combustion temperatures above 2300 °F (1300 °C), as shown in Figure 3-16. Since these temperatures are hardly ever reached during biomass comb ustion, the thermal and prompt NO X mechanisms are not considered to be relevant for biomas s combustion. Figure 3-16 also shows that typical NO X -emissions for wood combustion are in the range of approximately 90 to 250 mg/m3. For herbaceous biofuels, the typical NO X emissions are between 250 and 550 mg/m3, because the nitrogen in the fuel is generally higher in herbaceous fuels than in wood fuels. As Figure 3-16 shows, the nitrogen content of the fuel and the NO X -emissions are directly related for biomass combustion, meaning that if the nitrogen content of the fuel is high, the NO X -emissions will be high as well. This relationship is however not linear. Conversion rate of Nitrogen in the fuel to NO X decreases with increasing Nitrogen content.44 

### Emissions

1600 0 100 200 300 400 500 600 700 800 900

800 1200 1400 Prompt- NO x

1600 0 100 200 300 400 500 600 700 800 900

800 1200 1400 Prompt- NO x time, O 2 Thermal NO x for t=0.5 s, O 2 = 11 vol %

Fuel NO x , wood Fuel NO x , herbacious biofuels Fuel NO x , UF-Chip board

temperature [°C] NO x as NO 2 at 11% O 2 [mg/m 3 ] Typical biomass combustion Thermal NO x and prompt NO x

Figure 3-16 NO x -emissions - dependence on the fu el and the furnace temperature (Nussbaumer 1997)

Figure 3-17 correlation of the nitrogen content of the fuel and NO X emissions (Wopienka et al. 2007)



### 3.5.1 Measurement

NO X emissions equal the sum of NO and NO 2 -emissions. They are measured directly after the flue exit of the appliance in an insolated pipe. Results are given in ppm per dry flue volume (m3) at normal conditions. In order to refer the emissions to an oxygen content of 10, 12 or 13 %, the O 2 and/or the CO 2 concentration have to be measured as well.45 

### Report

3.5.2 Reduction

3.5.2.1 Primary measures

To reduce NO X emissions by primary measures, thr ee different concepts are available.

Air staging Primary and secondary combustion air is injected in clearly separated zones or combustion chambers. Between these zones the NO is redu ced in the reduction zone, where a excess air ratio of 0.7 – 0.8 and te mperatures from 2000 to 2200 F are required. With this technology, a NO X reduction in the range of 30 – 60% can be reached. In Figure 3-18 the concept for air stagin g and flue gas recirculation is shown.

Flue gas recirculation The recirculation of flue gas is primaril y used to reduce or control combustion temperatures and therefore the formation of thermal NO X . Thermal NO X is however not considered to be a relevant formation me chanism for biomass combustion (see chapter 3.5). Some reduction of fuel NO X is nevertheless achieved by flue gas recirculation.

pyrolysis

λ << 1 1650 F fuel

prim. air reduction zone λ 0.7 – 0.8 2000 – 2200 F oxidation zone λ > 2 1500 F secondary air flue gas

ash ash heat exchanger

flue gas recirculation pyrolysis

λ << 1 1650 F fuel

prim. air reduction zone λ 0.7 – 0.8 2000 – 2200 F oxidation zone λ > 2 1500 F secondary air flue gas

ash ash heat exchanger

flue gas recirculation Figure 3-18 concept of air staging and flue gas recirculation (adopted from Zuberbuehler 2002)

Fuel staging The concept of fuel staging ai ms at the same mechanisms as air staging by producing a reduction zone where NO is re duced. In the reduction zone, a excess air ratio from 0.6 – 0.8 is required. Approximately 70% of the fuel is stoked as primary fuel. As secondary fuel, biomass producer gas, shavings, sawd ust, ... are possible. With this reduction mechanism, a NO X reduction in the range of 50 to 70% can be achieved. In Figure 3-19 the concept for fuel staging is shown.

devolitalisation and oxidation λ > 1 primary

fuel

prim. air reduction zone λ < 1 secondary fuel

oxidation zone λ > 1 secondary air flue gas

ash ash devolitalisation and oxidation λ > 1 primary

fuel

prim. air reduction zone λ < 1 secondary fuel

oxidation zone λ > 1 secondary air flue gas

ash ash heat exchanger

Figure 3-19 concept of fuel staging for primary NO X

reduction46 

### Emissions

3.5.2.2 Secondary measures

To reduce NO X emissions by secondary measures , two different concepts were developed. Both concepts are applied in la rge scale appliances only because operation requirements and costs are too high for smal l and medium scale appliances. Figure 3-20 shows typical NO X emissions for biomasses and the NO X reduction potential of primary and secondary measures. For wood biomass combustion, secondary cleaning measures for NO X are usually not necessary because sufficient NO X reduction can be achieved by primary measures (FNR 2005).

Figure 3-20 NOx-emissions and reduction potential – overview ( Hasler et al. 2000 )
Explanations: NOx calculated as NO 2 and related to the dry flue gas at 11 vol.% O2

SNCR: selective non catalytic reduction In the SNCR process a reducing agent (ammonia or urea) is injected into the hot flue gas (in the afterburner chamber). The reducing agent reacts with the NO X to create elemental Nitrogen. The temperature range for optima l reaction is between 1550 and 1750 °F. If the temperature is too low, the reaction will be slow and if temperature is too high, side reactions will become more prominent and NO and N 2 O will be formed. To reach the maximum NO X removal, the reducing agents have to be added hyperstoichiometrically (1.5 for ammonia and 2 for urea). This leads to the emission of ammonia or urea in the flue gas. To keep these emissions low, the re ducing agents have to be metered exactly. A NO X reduction of 60 to 70% can be reached.47 

### Report

SCR: selective catalytic reduction The SCR process works at the same principle as the SNCR process, but catalysts are used to accelerate the reaction and to keep reac tion temperatures lower. Platinum, tungsten, titanium or vanadium oxide based materials are used as catalysts. The optimum temperature level for ammonia is between 430 and 520 °F, and between 750 and 840 °F for urea. Due to the higher reaction rate, the reducing agents can be added nearly stoichiometric thus resulting in low emissions of ammonia or urea. A NO X reduction of 80 – 95% can be achieved. A drawback of this technology is however the danger of the deactivation of the catalyst by alkaline compounds and heavy metals.48 

### European Test Methods



# 4 European Test Methods

Table 4-1 gives an overview of the Euro pean standards for biomass (solid fuel) combustion technologies. These standards consider requirements with respect to materials, design and construction, safety, pe rformance, appliance instructions, marking, evaluation of conformity and type test ing of the appliance. The performance requirements indluce a minimum thermal efficiency as well as limits for CO and optionally for OGC and dust. Table 4-1 European standards applied for biomass combustion technologies type Standard comments B OILERS pellets, solid wood, wood chips, combined technologies EN 303-5 <1000 MBtu/h Solid fuels max. water temperature: 100 °C, max. operating pressure: 6 bar boiler also providing direct heat EN 12809 < 170 MBtu/h solid fuels (except for pellets) max. operating pressure: 2 bar R OOM
- HEATERS

cook stoves EN 12815 solid fuels (except for pellets) manual stoking hot water production also possible fireplace insets with or without doors

masonry heaters (insets) EN 13229 solid fuels (except for pellets) manual stoking with or without combus tion chamber doors, no fan hot water production also possible

wood stoves (continuous or intermitted operation) EN 13240 solid fuels (except for pellets) manual stoking with combustion chamber doors no fan hot water production also possible

pellet stoves EN 14785 < 170 MBtu/h pellets only with or without fan closed fire doors only hot water production also possible

masonry heaters (handcrafted) EN 15250 solid fuels (pellets stoked manually) intermittend buring no fan no boiler function49 

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## 4.1 Residential heating systems

4.1.1 EN 303-5: Heating boilers for solid fuels, hand and automatically stoked

Full title: EN 303-5. Heating boilers for solid fuels, hand and automatically stocked, nominal heat output of up to 1025MBtu - Terminology, requirements, testing and marking Prepared by/approved/amends: Prepared by CEN TC 57 Central heating boilers

. Approved on 12 November 1998 and published in April 1999. The standard is to be revised: a first proposal has been elaborated and the discussion at CEN-level started in spring 2008. Appliances: Boilers for hydronic heating systems up to nominal heat output of 1025 MBtu/h with manual and au tomatic stoking. Minimum heat loss of boilers has to stay within the requirements of the standard; otherwise th e standard does not apply.
Fuels: Wood (logs, chops, briquettes, pellets , sawdust) and fossil fuels (coal, coke, anthracite)
Test Methods: Specifies test methods for heat ou tput, efficiency and emissions (CO, OGC, dust); measurement methods for emissions are not defined. Availability: Sharing is restricted; English version purchasable: https://www.onnorm.at/shopV5/search/Details.a ction?showDetails=&dokkey=70316 Table 4-2 summary of EN 303-5 with regard to testing procedure

MANUALLY STOKED BOILERS AUTOMATICALLY STOKED BOILERS T EST DURATION AND NUMBER OF TESTS

o Before the tests may begin, the boiler

has to be brought to its normal working condition using a complete fuel load (up to the maximum filling height). Testing can start when the necessary basic firebed is established.

o Test duration starts immediately after

placing the fuel on the basic firebed and ends with the refill.

o For the nominal and partial heat

loads , two nominal combustion periods and one combustion period are required respectively. o Before the tests may begin, the boiler has to be heated up to its normal working condition . Testing can start when the necessary basic firebed is established.

o For the nominal and partial heat

loads, test duration has to be at least 6 hours.50 

### European Test Methods

MANUALLY STOKED BOILERS AUTOMATICALLY STOKED BOILERS H EAT FLOW
- EFFICIENCY

o At nominal heat load the mean value of th e flow temperature has to lie in the range

of 155 to 195 °F and the average temperature difference of flow an d return has to lie in the range of 50 and 75 °F. In addition , the difference valu e between the ambient air temperature and the mean value of flow and return temperature has to be not less than 105 °F.

o At partial heat load the same conditions as for nominal heat load have to be

fulfilled, except for the requested temperature difference of flow and return temperature.

o The efficiency is determined on the basis of th e net calorific value and has to be

calculated with the direct method. The indirect calculation enables control of the measurement accuracy of the test rig an d determination of the single losses. E MISSIONS

o At nominal heat load, the test period

covers two successive combustion periods (includi ng refill), CO 2 or O 2 , CO and OGC (and NO X where appropriate) are measured during the complete test duration.

o At partial heat load the test period

covers one combustion period, CO 2 or O 2 , CO and OGC are measured.

o For the measurement of TSP at

nominal heat load, every combustion period is split into two equal time segments. Measurements start in each case at the beginning of a time segment, with the first measurement beginning imme diately after the fuel is placed and the door closed. The suction time per filter is limited to 30 min. The average TSP content is determined from the 4 minimum half-hour values taken at half our intervals. o At nominal heat, CO 2 or O 2 , CO and OGC (and NO X where appropriate) are measured over the entire test duration.

o At partial heat load CO 2 or O 2 , CO and

OGC are measured over the entire test duration.

o For the measurement of TSP at

nominal heat load, the test period is divided into at mi nimum 4 equal time segments. The measurements begin in each case at the start of the segment, with the first measurement taken when the test begins. The suction time per filter is limited to 30 min. The average dust content is determined from the 4 minimum values taken at half hour intervals.

o For the calculation of the emissions from a combustion period, the measured data

sets are first averaged over the complete combustion period. Afterwards transformation to the desired units (mg/m3 at certain oxygen level or lb/MMBtu) is performed. The ambient air temperature during testing procedure hast to be between 60 and 85 °F. Partial load is 50% of nominal heat load for manually stoked boilers and 30% of nominal heat load for automatically stoked boilers.51 

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4.1.2 EN 12809: Residential independent boilers fired by solid fuel

Full title: EN 12809. Residential independent boilers fired by solid fuel – Nominal heat output up to 170 Btu/h – Requ irements and test methods. Prepared by/approved/amends: Prepared by CEN TC 295 Residential solid fuel burning appliances , approved on 7 April 2001, amends: EN 12809:2001/A1:2004 Appliances: Hand and automatically fired, manual fuelled solid fuel appliances up to a nominal heat output of 170 MBtu/h for hydron ic heating systems also providing direct heat at the place of installation.
Fuels: Solid mineral fuels, peat briquettes, natural or manufactured wood logs or multifuel in accordance with the operation instructions of the appliance
Test Methods: Specifies test methods for total heat output, water heating output, space heating output, efficiency and emissions (CO, dust, OG C); measurement methods for dust and OGC are not defined Availability: Sharing is restricted; English version purchasable: https://www.onnorm.at/shopV5/search/Details.a ction?showDetails=&dokkey=223590



### 4.1.3 EN 12815: Residential cookers fired by solid fuel

Full title: EN 12815. Residential cookers fired by solid fuel – Requirements and test methods Prepared by/approved/amends: Prepared by CEN TC 295 Residential solid fuel burning appliances , approved on 7 April 2001, amendments: EN 12815: 2001/A1: 2004 Appliances: Hand fired appliances which primary function is to cook and secondary function is direct heating. In case of conne cting these appliances to a boiler, they also provide domestic hot water and/or central heating.
Fuels: Solid mineral fuels, peat briquettes, wood logs or multi-fuel in accordance with the operation instructions of the appliance.
Test Methods: Specifies test methods for total heat output, water heating output, space heating output, efficiency and emissions (CO, dust, OG C); measurement methods for dust and OGC are not defined Availability: Sharing is restricted; preview is a ttached, English version purchasable: https://www.on-norm.at/shopV5/search/ Details.action?showDetails=&dokkey=233243



### 4.1.4 EN 13229: Inset appliances includ ing open fires fired by solid fuels

Full title: EN 13229. Inset appliances includin g open fires fired by solid fuels – Requirements and testing methods52 

### European Test Methods

Prepared by/approved/amends: Prepared by CEN TC 295 Residential solid fuel burning appliances , approved on 7 April 2001, amendments: EN 13229: 2001/A1: 2003, EN 13229:2001/A2:2004 Appliances: Freestanding or inset hand fired appliances which have functional modification or inset appliances for firepl aces: recessed and enclosed. Where connected to a boiler, also domestic hot water and/or central heating are provided.
Fuels: Solid mineral fuels, peat briquettes, wood logs or multi-fuel in accordance with the operation instructions of the appliance.
Test Methods: Specifies test methods for total heat output, water heating output, space heating output, efficien cy and emissions (CO) Availability: Sharing is restricted; preview is a ttached, English version purchasable: https://www.on-norm.at/shopV5/search/ Details.action?showDetails=&dokkey=233241

Table 4-3 shows the categorisations of appliances to EN 13229 and EN 13240. Table 4-3 Categorisation of appliances (EN 13229 versus EN 13240)
a) Freestanding or inset appliances without functional modification b) Freestanding or inset appliances with functional modification c) Inset appliances for fireplace recess and enclosure

1. Appliances operating with firedoors closed EN 13240 EN 13229 EN 13229

2. Appliances operating with firedoors closed or open EN 13240 EN 13229 EN 13229

3. Open fires without firedoors EN 13229 EN 13229 EN 13229

NOTE: Without functional modification mean s “modification of the surrounding of an appliance, which only changes the transmission of heat without affe cting combustion”.53 

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Table 4-4 summary of EN 13229 with regard to testing procedure

NOMINAL HEAT LOAD PARTIAL LOAD T EST DURATION

o Before tests may begin, the appliance

has to be operated until steady state is reached; at least one combustion period at nominal heat load is necessary before testing. Prefabricated heaters have to be operated before testing until the ceramics has completely dried (usually 10 hours or more).

o Testing starts immediate after refilling

the fuel onto the fi rebed and ends when all fuel except th e ash is burnt.

o At least two tests in two different

combustion periods ha ve to be carried out for nominal heat load

.
o minimum combustion times with closed

doors for wood fuel:

o 1 hour for continuous operating stoves

o 0.75 hours for intermittent operating stoves

o 90 (+10/-20) min. for prefabricated heaters o Before test may begin, the appliance has to be operated at nominal heat load.

o Testing starts when operating conditions

are stable for not less than 15 min.

o For prefabricated heaters the test

duration ends when an ignitable firebed is left, for continuous operating stoves the test is finished when the mass of the firebed equals the mass of the firebed before start of the test.

o minimum combustion times with closed

doors for wood fuel:

o 3 hours for continuous operating stoves

o (50 ± 10)% of time at nominal load

H EAT FLOW

– EFFICIENCY

o Efficiency is calculat ed as the average of

the two test periods.

o If appliance is equipped with water

circulation, flow temperature during test must be 175 ± 40 F and flow rate of water has to vary less then ± 5 %. o If appliance is equipped with water circulation, flow temperature must be below 185 F and flow rate of water has to vary less then ± 5 %.

o Efficiency is calculated by the indirect method, considering flue gas loss from heat,

un-burnt matter and losses in the ash from un-burnt combustible matter. If appliance has water circulation, the hot water output is considered as well.

EMISSIONS

o CO 2 or O 2 and CO are measured during the complete test durations.

o For the calculation of the emissions from a combustion period, the measured data

sets are first averaged over the complete combustion period. Afterwards transformation to the desired units (mg/m3 at certain oxygen level or lb/MMBtu) is performed.



### 4.1.5 EN 13240: Room-heaters fired by solid fuel

Full title: EN 13240. Room-heaters fired by solid fuel – Requirements and test methods54 

### European Test Methods

Prepared by/approved/amends: Prepared by CEN TC 295 Residential solid fuel burning appliances , approved on 7 April 2001, amendments: EN 13240: 2001/A2: 2004 Appliances: Manually stoked appliances which are operated with firedoors closed or firedoors closed or open, providing direct spac e heat. Standard also applies to slow heat release appliances which are av ailable as complete units or pre-fabricated parts designed to be built on site.
Fuels: Solid mineral fuels, peat briquettes, wood logs or multi-fuel in accordance with the operation instructions of the appliance.
Test Methods: Specifies test methods for total heat output, water heating output, space heating output, efficiency and emissions (CO, dust, OG C); measurement methods for dust and OGC are not defined Availability: Sharing is restricted; preview is a ttached, English version purchasable: https://www.on-norm.at/shopV5/search/ Details.action?showDetails=&dokkey=233239 Table 4-5 summary of EN 13240 with regard to testing procedure

NOMINAL HEAT LOAD PARTIAL LOAD T EST DURATION

o Before the test may begin, the

appliance has to be operated until steady state is reached; minimum combustion times and number of combustion periods for wood fuel are:

o 1.5 hours / 2 periods for continuous operating stoves

o 0.75 hours / 3 periods for intermitted operating stoves

o Testing starts immediate after refilling

the fuel onto the fi rebed and ends when all the fuel except the ash is burnt. o Before the test may begin, the appliance has to be operated at nominal heat load or the ne cessary firebed can be reached within one hour after ignition in the cold appliance.

o Testing starts when operating conditions

are stable for no less than 15 min.

o Testing is finished for continuous

operating stoves when the minimum combustion time of 10 hours (or longer time claimed by manufacturer) is reached. The firebed at the end of the test duration has to equal the mass of the firebed before start of the test. H EAT FLOW

– EFFICIENCY

o Efficiency is calculat ed as the average of

the two test periods.

o If appliance is equipped with water

circulation, flow temperature during test must be 175 ± 40 F and flow rate of water has to vary less then ± 5 %. o If appliance is equipped with water circulation, flow temperature must be below 185 F and flow rate of water has to vary less then ± 5 %.

o Efficiency is calculated by the indirect method, considering flue gas loss from heat

and un-burnt matter and losses in the ash from un-burnt combustible matter. If appliance has water circulation, the hot water output is considered as well.55 

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NOMINAL HEAT LOAD PARTIAL LOAD T EST DURATION
EMISSIONS

o CO 2 or O 2 and CO are measured during the complete test durations.

o For the calculation of the emissions from a combustion period, the measured data

sets are first averaged over the complete combustion period. Afterwards transformation to the desired units (mg/m3 at certain oxygen level or lb/MMBtu) is performed.



### 4.1.6 EN 14785: Residential space heatin g appliances fired by wood pellets

Full title: EN 14785. Residential space heating a ppliances fired by wood pellets – Requirements and test methods Prepared by/approved/amends: Prepared by CEN TC 295 Residential solid fuel burning appliances , approved on 3 May 2006. Appliances: Residential space heaters fired by wood pellets. Appliances may be freestanding or inset appliances and provide di rect heat. They can be operated by either a natural draught or fan-assisted combustion air. Where combined with a boiler, they also provide domestic hot water and/or central heating. These appliances are only operated with fire-doors closed.
Fuels: wood pellets
Test Methods: Specifies test methods for total/ nominal/reduced heat output, water heating output, space heating output, efficiency and emissions (CO, dust, OGC); measurement methods for dust and OGC are not defined Availability: Sharing is restricted, English version purchasable: https://www.onnorm.at/shopV5/search/Details.a ction?showDetails=&dokkey=22178556 

### European Test Methods

Table 4-6 summary of EN 14785 with regard to testing procedure

NOMINAL HEAT LOAD PARTIAL HEAT LOAD T EST DURATION

o Before the tests may begin, the

appliance has to be de-ashed and operated for at least 30 min. in its steady state (normal working conditions). Steady state is reached when flue temperature varies less than ± 40 °F.

o Test starts with the refill of the

appliance and has to last for at least 3 hours. If manufacturer claims a longer combustion period, the test has to be prolonged according to the manufacturer’s declaration.

o At least two tests in two different

combustion periods ha ve to be carried out. o Before the tests may begin, the appliance has to be operated at nominal heat load. After de-ashing the appliance has to be operated at partial load for at least one hour in steady state. Refill of appliance is possible before start of test.

o Test duration has to last at least 6

hours.

o No partial heat load tests are carried

out, if the appliance works in the on/off – mode only.

o One test is required.

H EAT FLOW
- EFFICIENCY

o Efficiency is calculat ed as the average of

the two test periods.

o If appliance is equipped with water

circulation, flow temperature during test must be 175 ± 40 °F and flow rate of water has to vary less then ± 5 %. o If appliance is equipped with water circulation, flow temperature must be below 185 °F and flow rate of water has to vary less then ± 5 %.

o Efficiency is calculated by the indirect method, considering flue gas loss from heat

and un-burnt matter and losses in the ash from un-burnt combustible matter. If appliance has water circulation, the hot water output is considered as well. E MISSIONS

o CO 2 or O 2 and CO are measured during the complete test durations.

o For the calculation of the emissions from a combustion period, the measured data

sets are first averaged over the complete combustion period. Afterwards transformation to the desired units (mg/m3 at certain oxygen level or lb/MMBtu) is performed.



### 4.1.7 EN 15250: Slow heat release app liances fired by solid fuel

Full title: EN 15250. Slow heat release appliances fired by solid fuel – Requirements and test methods Prepared by/approved/amends: Prepared by CEN TC 295 Residential solid fuel burning appliances , approved on 13 January 2007.57 

### Report

Appliances: Manually stoked, intermittent burning, slow heat release appliances with thermal storage capacity. Appliances are alwa ys built on site, either completely hand crafted or assembled with pre-fabricated part s. This standard spec ifies the minimum time period within which the maxi mum differential surface temperature may be reduced to half of its original value.
Fuels: Solid mineral fuels, peat briquettes, wood logs or multi-fuel in accordance with the operation instructions of the appliance. Manually stoked wood pellets can also be burnt either on the existing grate on in special insets.
Test Methods: Specifies test methods for total he at output, efficiency and emissions (CO, dust, OGC); measurement methods for dust and OGC are not defined Availability: Sharing is restricted, preview is attached, English version purchasable: https://www.on-norm.at/shopV5/search/ Details.action?showDetails=&dokkey=278524 Table 4-7 summary of EN 15250 with regard to testing procedure

NOMINAL HEAT LOAD PARTIAL HEAT LOAD T EST DURATION

o The test is to be started cold without a

pre-test period, wher eby ignition is to be performed either according to the manufacturer’s instructions or using kindling of mass of 500g or 10% of the fuel load, whichever is greater. Any bottom air entry is to be open during ignition.

o The adding of further batch charges

should not exceed 3 hours

o Any batch charges shall not be less than

20% of the total fuel loading.

o The test is over once 25% of the mean

maximum differential surface temperature of the ap pliance’s external surfaces has been reached.

o One test is required.

o A Temperature Safety Test is also

required o The test is to be started cold without a pre-test period, wher eby ignition is to be performed either according to the manufacturer’s instructions or using kindling of mass of 500g or 10% of the fuel load, whichever is greater. Any bottom air entry is to be open during ignition.

o Any batch charges shall not be less than

20% of the total fuel loading.

o The adding of further batch charges

should not exceed 3 hours

o Any batch charges shall not be less than

20% of the total fuel loading.

o One test is required.

o A Temperature Safety Test is also

required.

H EAT FLOW
- EFFICIENCY

o If the test fuel is wood logs, the

combustible constituen ts of the residue need not be measured, but can be taken as 0,5 % points of efficiency. o If the test fuel is wood logs, the combustible constituen ts of the residue need not be measured, but can be taken as 0,5 % points of efficiency.

o Efficiency is calculated by the indire ct method, considering the heat losses

determined from the mean value of the flue gas and room temperature, the flue gas composition and the combustibl e matter in the residue.58 

### European Test Methods

NOMINAL HEAT LOAD PARTIAL HEAT LOAD E MISSIONS

o CO 2 or O 2 and CO are measured during the complete test duration.

o For the calculation of the emissions from a combustion period, the measured data

sets are first averaged over the complete combustion period. Afterwards transformation to the desired units (mg/m3 at certain oxygen level or lb/MMBtu) is performed.



## 4.2 Commercial heating systems

For commercial heating systems > 1025 MBtu, no European standards are defined. These plants undergo individual commissioning procedures. An example of a commissioning report is added in the annex.59Report4.3SummaryTable 4-8 summary ofstandards for residential heating systems303-5 12809 12815 13229 13240 15250 14785full title Heating boilers for solidfuels, hand andautomatically stocked,nominal heat output of upto 300 kW - Terminology,requirements, testing andmarkingResidentialindependent boilersfired by solid fuel –Nominal heat outputup to 50 kW –Requirements andtest methodsResidentialcookers fired bysolid fuel –Requirementsand testmethodsInset appliancesincluding openfires fired by solidfuels –Requirements andtesting methodsRoom-heatersfired by solid fuel– Requirementsand test methodsSlow heat releaseappliances firedby solid fuel –Requirements andtest methodsResidential spaceheatingappliances firedby wood pellets –Requirements andtest methodsAppliance Boilers for hydronic heatingwithout direct spaceheating outputResidentialindependent solidfuel fired boilerswith heat direct toliving roomCookers (withor withoutwater circulate)Freestanding orinset appliancesRoom-heaters(with or withoutwater circulate)Hand fuelledintermittentburning slow heatrelease appliancesResidential spaceheatingappliances firedby wood pellets(with and withoutwater circulate)Fuel wood and fossil fuels Solid mineral fuels, peat briquettes, natural or manufactured wood logs or multi-fuel in accordancewith the operation instructions of the appliancewood pelletsHeatOutputdetermined on the basis ofwater flow andtemperaturestotal heat output: based on efficiency, fuel input and calorific valuehot water output: based onwater flow and temperaturesspace heating output: difference of total heat output and hot water outputon the basis ofefficiency, fuelinput and calorificvaluesee 12809Efficiency Direct method: Quotient ofheat output and heat input.Indirect method for controlpurposes onlyIndirect method: flue gas loss from heat, un-burnt matter and losses in theash from un-burnt combustible matterEmissions CO2or O2, CO, OGC, TSP(NOXwhere appropriate)CO2or O2and CO60 

### Regulations for biomass installations



# 5 Regulations for biomass installations

Performance regulations for biomass installati ons (emission limits an d thermal efficiency requirements) aim at increasing the numbe r of newly installed, state-of-the-arte appliances, thus decreasing the number of ol d technologies in operation. The end result is thereby the continuous improvement in performance of biomass appliances in operation. These regulations have to consider the different performance levels of appliances in Europe and at the same time encourage a ll countries to improve their technologies, regardless if the country is leading or laging behind in combustion technology. In order to embrace all technology stages in the European Union, different emi ssion and efficiency classes are defined for boilers in the EN 303-5. Additi onally, national requirements and eco labeling programs also encourage techno logy development to increase performance levels. Figure 5-1 shows efficiency re quirements for boilers in the EN 303-5 (classes 1 to 3 are currently in practice and classes 3 to 5 are under discussion) and effi ciency requirements from Austrian, German and Scandi navian eco-labels. A continuo us increase of efficiency requirements is one major driving force for technology developments.

45% 50% 55% 60% 65% 70% 75% 80% 85% 90%

0 300 600 900 1200 1500 nominal load in mBTU/h class 3

class 2

class 1 class 4 class 5efficiency based on GCV Blue Angel (G)/Umweltzeichen (A) Nordic Swan (Scandinavia)

Figure 5-1 efficiency requirements for boile rs from EN 303-5 (class 1 to class 5) and efficiency requirements from Austrian , German and Scandinavian eco-labels; efficiencies based on GCV were converted for pellets fuel61 

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## 5.1 European level

5.1.1 Regulations for boilers

EN 303-5 sets the standards for solid fuel boilers with a nominal heat load up to 1025 MBtu/h. In EN 303-5 emission limits fo r CO, OGC and dust as well as thermal efficiency requirements for solid fuel boile rs are specified. In order to embrace the diverse combustion standards from EU memb er states, three different emission and efficiency classes were defined. Table 5-1 shows the emi ssion limits for wood fuel and fossil fuel boilers in the valid standard. Table 5-1 emission limits for biogenic fuels in EN 303-5

Emission limits at 12% O 2
CO in mg/m3 OGC in mg/m3 Dust 3) in mg/m3 (and lb/MMBtu) class class cla ss class class class class class classStoking Nominal heat load in MBtu/h 1 2 3 1 2 3 1 2 3

≤ 170 20455 6545 4090 1635 245 120 165 (0.22) 145 (0.20) 125 (0.17) 170 - 510 10227 4090 2045 1230 165 80 165 (0.22) 145 (0.20) 125 (0.17)Manual1)

510 - 1025 10227 1635 980 1230 165 80 165 (0.22) 145 (0.20) 125 (0.17)

≤ 170 12270 4090 2455 1430 165 80 165 (0.20) 145 (0.18) 125 (0.15) 170 - 510 10230 3680 2045 1020 120 65 165 (0.20) 145 (0.18) 125 (0.15)Automatic2)

510 - 1025 10230 1635 980 1020 120 65 165 (0.20) 145 (0.18) 125 (0.15)

1) Based on the higher heat value (GCV) and the heat value for solid wood (dust values only) 2) Based on the higher heat value (GCV) and the heat value for pellets (dust values only) 3) Dust emission limits are identical for automati cal and manual systems in EN 303-5, conversion from mg/m3 to lb/MMBtu results in higher emission limits for manually stoked appliances, though (see Table 3-2 on page 31)

The emission limits for fossil fuels will be identical to the emission limits for biogenic fuels, except for dust – emissi ons (brown coal fuel assumed):

• class 1: 145 mg/m at 12% O 2 and 0.185 lb/MMBtu

• class 2: 125 mg/m at 12% O 2 and 0.160 lb/MMBtu

• class 3: 100 mg/m at 12% O 2 and 0.130 lb/MMBtu62 

### Regulations for biomass installations

The efficiency requirements in the valid EN 303-5 are calculat ed as follows (based on the GCV):

• 41 + 5.5·log P n for class 1

• 50 + 5.5 log P n for class 2

• 59 + 5.5 log P n for class 3
where P n is the nominal heat load of the boiler in MBtu/h. A revision of the EN 303-5 is currently in progress and new emission classes (class 4 and 5) are being discussed. Class 1 and 2 will be phased out as more stringent class 4 and 5 are phased in. The actual status of the discussion regarding w ood fuel boilers is shown in Table 5-2. In addition to lower emission levels, the future standard will be valid for higher loads (1025 – 1700 MBtu/h) as well. Table 5-2 proposed future emission li mits for biogenic fuels in EN 303-5

Emission at 12% O 2
CO limits in mg/m3 OGC limits in mg/m3 Dust 3) in mg/m3 (and lb/MMBtu) class class cla ss class class class class class classStoking Nominal heat load in MBtu/h 3 4 5 3 4 5 3 4 5

≤ 170 4090 820 410 125 60 40 125 (0.17) 60 (0.08) 50 (0.07) 170 - 510 2045 615 245 80 40 25 125 (0.17) 60 (0.08) 50 (0.07) 510 - 1025 980 410 205 80 10 10 125 (0.17) 60 (0.08) 50 (0.07)Manual1)

1025 – 1710 980 410 205 80 10 10 125 (0.17) 60 (0.08) 50 (0.07)

≤ 170 2455 820 410 80 60 40 125 (0.15) 60 (0.08) 50 (0.06) 170 - 510 2045 615 245 65 60 40 125 (0.15) 60 (0.08) 50 (0.06) 510 - 1025 980 410 205 65 40 20 125 (0.15) 60 (0.08) 50 (0.06)Automatic2)

1025 – 1710 980 410 205 65 40 20 125 (0.15) 60 (0.08) 50 (0.06)

1) Based on the higher heat value (GCV) and the heat value for solid wood (dust values only) 2) Based on the higher heat value (GCV) and the heat value for pellets (dust values only) 3) Dust emission limits are identical for automatica l and manual systems in EN 303-5, conversion from mg/m3 to lb/MMBtu results in higher emission limits for manually stoked applianc es, though (see Table 3-2 on page 31)63 

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The emission limits for fossil fuels will be identical to the emission limits for biogenic fuels, except for dust – emissi ons (brown coal fuel assumed):

• class 4

o manual stoking: 60 mg/m at 12% O 2 /0.075 lb/MMBtu

o automatic stoking: 50 mg/m at 12% O 2 /0.060 lb/MMBtu

• class 5: 40 mg/m at 12% O 2 /0.050 lb/MMBtu In the future EN 303-5, the following effi ciency requirements are being discussed for classes 4 and 5 (based on the GCV):

• 76 + log P n for class 4

• 80 + log P n for class 5
where P n is the nominal heat load of the boiler in MBtu/h.



### 5.1.2 Regulations for room heaters

For room-heaters a number of standards appl y, providing efficien cy requirements and limits for CO-emission. In Table 5-3 a summary of efficiency and em ission requirements of these standards are given. This summary shows the broa d range of emission limits and efficiency requirements for d iverse room-heating technologies. Table 5-3 Summary of efficiency and CO-req uirements in standards for room-heating appliances

type of appliance Standard minimum efficiency 1) in % CO limits in mg/m3 at 12% O 2 cookers EN 12815 55 2) 14065 slow heat release inset 65 2) 280 fireplace insets (closed doors) EN 13229 25 2) 1410

room-heater EN 13240 for closed doors class 1: class 2: class 3: 60 2) 55 2) 45 2) class 1: class 2: 420 1410

pellet stove EN 14785 nominal load: partial load: 70 65 nominal load: partial load: 565 845 slow heat release appliances EN 15250 60 2) 4220

1) related to higher heating value (GCV) 2) based on heat value for solid wood


## 5.2 National levels

All EU member states are allowed to introduc e stricter and addition al requirements for combustion appliances than they are given in the standards. In the following section,64 

### Regulations for biomass installations

national regulations for emissi ons and efficiencies of biom ass appliances are shown for Austria, Germany and the Scandinavian countries. Re gulations for small scale (residential) appliances and, if available, for medium to large scale (commercial) appliances are quoted. Additional legal requirements and environmental labels, which are often linked to additional financial incentives, are also being introduced by some countries.



### 5.2.1 Austria

Currently, two regulations apply to the emission limits and energy-efficiency requirements of residual smal l combustion installations:

• The Vereinbarung gemaeß Art. 15a B- VG ueber Schutzmaßnahmen betreffend Kleinfeuerungen sets emi ssion limits for combusti on units < 1365 MBtu/h.

• In the Vereinbarung gemaeß Art. 15a B-VG ueber die Einsparung von Energie minimum efficiency requirem ents are defined for combustion installations < 1365 MBtu/h. The regulation for combusti on units of < 1365 MBtu/h makes a distinction between manually and automatically stoked appliances as well as fossil fu els and biofuels. The Austrian limits for these installations are in any case lower than th e emissions levels in EN 303-5, class 3. There are also additional limits set for NO X . Emission limit values for appliances < 1365 MBtu/h are presented in Table 5-4.
Table 5-4 Austrian emission limits for installations < 1365 MB tu/h (Vereinbarung Art. 15a B-VG)

Emission limits in mg/m3 12 % O 2 Stoking and fuel types CO NO X OGC dust Dust in lb/MMBtu Biogenic solid fuels 2) 1840 1) 2510 135 100 0.135 Manual Fossil solid fuels 3) 1840 185 135 100 0.125 Biogenic solid fuels 4) 8470 2540 70 100 0.125 Automatic Fossil solid fuels 3) 8470 185 70 75 0.095
1) At partial load (30 %) the limit may be exceeded by 50 % 2) solid wood fuel assumed 3) brown coal fuel assumed 4) pellets fuel assumed

The adoption of these emission limits due to improved comb ustion technologies and an increasing variety of biomass fuels is curre ntly under discussion. The present status of this discussion is shown in Table 5-5.65 

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Table 5-5 Future Austrian em ission limits for installations < 1365 MBtu – present status of discussion Emission limits in mg/m3 12 % O 2 fuel types and appliances CO NO X OGC dust Dust in lb/MMBtu room-heaters 1) 1840 250 145/85 100/60 0.135/0.080 wood fuels boilers 2) 850 250/170 85/50 85/50 0.105/0.060 < 170 mBUT/h 1860 505 85 100/60 0.125/0.075 other standardised biog. fuels 2) > 170 mBUT/h 850 500 50 100/60 0.125/0.075 < 170 mBUT/h 2020 185 145 90/65 0.115/0.080 fossil fuels 3) > 170 mBUT/h 920 185 55 90/65 0.115/0.080 XX/YY: values valid from coming into force/values vallid from 2015 1) solid wood fuel assumed 2) pellet fuel assumed 3) brown coal fuel assumed

Regulations for the minimum e fficiency distinguish between room-heating appliances and boilers. For room heating appliances the minimum efficiency is 70 %, whereas it is 62 % for cookers. For boilers, the minimum effici ency depends on the type of stoking and the nominal heat load, as shown in Table 5-6. Table 5-6 minimum efficiency requirements for boilers < 1365 MBtu/h (Vereinbarung Art. 15a B-VG) Stoking Nominal heat load in MBtu/h Efficiency 1) in %

< 35 65 % 35 – 680 (57 + 7.1 log P n 2) ) % Manual stoking 3) > 680 75 % < 35 70 % 35 – 680 (60 + 7.1 log P n ) % Automatic stoking 4) > 680 80 %

1) related to the higher heating value (GCV) 2) nominal heat load in MBtu/h 3) based on the heat value for solid wood 4) Based on the heat value for pellets

Environmental label – Umweltzeichen The Umweltzeichen (environmental label) was introduced by the Austrian Government. For wood appliances (boilers and room he aters) the Environmental Label number 37 specifies emission and e fficiency requirements.
In Table 5-7 the emission limits for bo ilers and room heaters according to the Environmental Label are shown.66 

### Regulations for biomass installations

Table 5-7 Austrian Environmental Label emission limits for boilers and room-heaters (Umweltzeichen) Emission limits in mg/m3 at 12 % O 2 Appliance fuel CO/OGC (nominal load) CO/OGC (partial load 2) ) NO X dust Dust in lb/MMBtu pellets 100/5 230/5 170 25 0.030 wood chips 250/10 495/15 200 50 0.080 Boiler solid wood 420/50 1250 200 50 0.070 pellets 205/10 450/20 170 35 0.042 Room- heater solid wood 1170/85 -/- 200 50 0.070

1) related to the lower heating value (NCV) 2) for pellets and wood chips: 30% of nominal load, for solid wood: 50% of nominal load

Table 5-8 shows the efficiency requirements for boilers an d room-heaters according to the Austrian Environmental Label.
Table 5-8 Austrian Environmental Label effi ciency requirements for room-heaters and boilers (Umweltzeichen) Efficiency in % related to upper heating value (GCV) stoking Boilers Roomheaters Manual 2) 62 + 7.1 log P n 1) 70 Automatic 3) 85 85

1) nominal heat load in MBtu/h 2) based on heat value for solid wood 3) based on the heat value for pellets

In addition to these requirements, the losse s due to radiation of the boilers are also limited:

• up to 340 MBtu/h: maximum lo sses of 2.5 % by radiation

• 340 – 1365 MBtu/h: maximum losses of 1.5 % by radiation

Medium to large scale (commercial) applications The Feuerungsanlagen-Verordnung, BGBl. II Nr. 331/1997, which came into force on June 1 st 1998, covers residential installation s with a nominal heat capacity > 1365 MBtu/h kW as well as commercial combustion units > 170 MBtu/h. Table 5-9 and Table 5-10 show the emission limits for CO, dust, NO X and HC for biomass appliances and emission limits for CO, dust, NO X and SO 2 for coal and coke appliances according to the Feuerungsanlagenverordnung.67 

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Table 5-9 Austrian emission limits for comm ercial biomass appliances according to the Feuerungsanlagenverordnung (FAV) Emission limits in mg/m3 at 12% O 2 NO X Installation heat load in MBtu/h CO HC fuel1 fuel2 fuel3 dust Dust lb/MMBtu

170 – 340 900 1) 55 340 280 565 170 0.210 3) 340 – 1195 900 55 340 280 565 170 0.210 3) 1,195 – 6,830 280 25 340 280 565 170 0.275 4) 6,830 – 17,075 280 25 340 280 565 55 2) 0.090 2), 4) 17,075 – 34,150 115 25 340 280 395 55 0.090 4) > 34,150 115 25 340 225 395 55 0.090 4)

1) at 30 % load limit may be exceeded by 50 % 2) from 1 st January 2010 fuel1: beech, oak, non-tr eated bark, brushwood, cones fuel1: other non-treated wood fuel1: derived timber products (no heavy metals or halogen organic compounds in binder, hardener und coating) 3) Based on the higher heat value (GCV) of the fuel, pellets assumed 4) Based on the higher heat value (GCV) of the fuel, wood chips assumed

Table 5-10 Austrian emission limits for comm ercial coal and coke appliances according to the Feuerungsanlagenverordnung (FAV) Emission limits in mg/m3 at 12% O 2 Installation heat load in MBtu/h CO NO X SO 2 dust Dust 1) lb/MMBtu

170 – 340 1125 - - 170 0.215 340 – 1195 1125 450 - 170 0.215 1,195 – 6,830 170 450 - 170 0.215 6,830 – 17,075 170 450 - 55 0.070 17,075 – 34,150 170 395 450 55 0.070 > 34,150 170 115 225 55 0.070

4) Based on the higher heat value (G CV) of the fuel, brown coal assumed

In the Feuerungsanlagenverordnung, a minimum efficiency of 75 % based on the GCV for automatically stoked solid fuel appliances used for room heating or domestic hot water production is required.



### 5.2.2 Germany

In Germany, the 1. BImSchV ( Bundes Immissions Schutz Verordnung fuer Kleinfeuerungsanlagen ) regulates the Emissions for small scale installations. It was implemented in 1988 and has since then been revised twice (in 1997 and 2003) and is currently undergoing a third revision. In Table 5-11 the valid emission limits for biomass combustion appliances with nominal heat loads > 50 MBtu/h is shown.68 

### Regulations for biomass installations

Table 5-11 German Emission li mits for biomass combustion appliances according to the valid 1 st BImSchV (1st BImSchV) Emissions in mg/m3 at 12 % O 2 fuel nominal heat load in MBtu/h CO dust dust in lb/MMBtu 50 – 170 4500 170 0.230 1) 170 – 510 2250 170 0.230 1) 510 – 1705 1125 170 0.275 2) non-treated wood in pieces, i.e. shavings, and straw or other plant products > 1705 565 170 0.275 2) 50 – 340 900 170 0.275 2) 340 – 1705 565 170 0.275 2) painted, coated or laminated wood, plywood and chipboards > 1705 340 170 0.275 2)

1) Based on the higher heat value (GCV) of the fuel, solid wood assumed 2) Based on the higher heat value (GCV) of the fuel, wood chips assumed No specific efficiency requ irements are given in the 1. BImSchV for biomass boilers.
Table 5-12 future German em ission limits for biomass boilers according to the 1 st BImSchV (1st BImSchV – Draft from July 2009)

Installation built after 1 st BImSchV came into force Installations built after 2014 1)

E-limits in mg/m3 at

12% O 2 E-limits in mg/m3 at

12% O 2 fuel nominal heat load (MBtu/h) CO dust dust in lb/ MMBtu nominal heat load

(Btu/h) CO dust dust in lb/ MMBtu

15 – 1705 1125 115 0.185 7) non treated wood 2) > 1705 565 115 0.185 7)

15 – 1705 900 70 0.085 8) pellets 3) > 1705 565 70 0.085 8) 15 – 1705 1125 100 0.125 9) coal > 1705 565 100 0.125 9) ≥ 15 450 25 0.040 7) 0.030 8) 0.030 9)

170 – 340 900 115 0.185 7) 340 – 1705 565 115 0.185 7) 170 – 1705 450 25 0.040 7) pre treated wood 4) > 1705 340 115 0.185 7) > 1705 340 25 0.040 7) straw 15 - 340 1125 115 - 15 – 340 450 25 -

1) Solid wood emission limits instated in 2017 2) Non-treated wood (pieces, shavings), straw or other pl ant products – wood chips assumed for dust emissions 3) Pressed untreated wood (b riquettes, pellets, ...) 4) painted, varnished or coated wood; plywood, chipboards , fibre boards (no reservatives used, no heavy metals of halogen organic compounds – soli d wood assumed for dust emissions 5) straw and similar plant materials 6) All dust emissions based on the higher heating value (GCV) 7) Based on the higher heat value (G CV) of the fuel, wood chips assumed 8) Based on the higher heat value (GCV) of the fuel, pellets assumed 9) Based on the higher heat value (G CV) of the fuel, brown coal assumed69 

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Table 5-12 shows the recent status of th e discussion for the new emission (and efficiency) requirements for biomass boilers. No specific efficiency requirements are given in the draft version of the 1 st BImSchV for biomass boilers.
Table 5-13 shows the recent discussion stat us for new emission (and efficiency) requirements for room-heaters.
Room-heaters which were in stalled before the future 1 st BImSchV was implemented are only allowed to be operated, if

• dust emissions are < 0.228 lb /MBtu (150 mg/m3 at 13% O 2 ) and

• CO-emissions are < 6.090 lb/M Btu (4000 mg/m3 at 13% O 2 ) Otherwise they must be upgrad ed with emission control te chnology or placed out of operation corresponding to a time schedule.
Table 5-13 future German emission and e fficiency requirements for room-heaters according to 1 st BImSchV (1st BImSchV – Draft)

Installation built after 1 st BImSchV came into force Installations built after 2014

Emission in mg/m3 limits

at 12% O 2 Emission in mg/m3 limits at 12% O 2 type of appliance Standard Efficiency 1)

(%) CO dust dust in lb/ MMBtu CO dust dust in lb/ MMBtu

room heater (intermittent operation) 65 2250 115 0.150 2) 1405 45 0.061

room heater (continuous operation) EN 13240 60 2810 115 0.150 2) 1405 45 0.061

slow heat release appliances EN 15250 65 2250 115 0.150 2) 1405 45 0.061

closed inset 65 2250 115 0.150 2) 1405 45 0.061 slow heat release inset (intermittent) 70 2250 115 0.150 2) 1405 45 0.061

slow heat release inset (continuous) EN 13229 70 2815 115 0.150 2) 1405 45 0.061

cookers 60 3375 115 0.150 2) 45 0.061 cookers (with room heater function) EN 12815 65 3940 115 0.150 2) 1690 45 0.061

pellet stove 80 450 55 0.070 3) 280 35 0.040 pellet stove with boiler EN 14785 85 450 35 0.040 3) 280 25 0.030

1) related to the higher heating value (GCV)70 

### Regulations for biomass installations

Environmental Label – The Blue Angel The Blue Angel label is sponsored an d administered by the German Federal Environmental Agency and the Quality Assurance and Product Labeling Institute RAL Deutsches Institut fuer Guetesicherung und Kennzeichnung e.V. This label provides additional emission and effi ciency requirements for pell et stoves and pellet boilers (Table 5-14).
Table 5-14 Emission limits for the German Blue Angel label (Blue Angel) Emission limits in mg/m3 at 12% O 2 for nominal/partial load appliance Efficiency (%) 1) CO NO X TOC dust dust in lb/mmBtu
pellet stove 200/450 170/- 10/20 30/- 0.035/- pellet boiler ≥ 85 100/225 170/- 5/5 25/- 0.030/-

1) related to the higher heating value (GCV) XXX/YYY: values for nominal load/values for partial load

Medium to large scale applications In the TA Luft, emission limits for CO, dust, NO X and OGC are given fo r medium to large scale appliances. The emission limits for non treated and pret reated biomass are given in Table 5-15. The installation heat load for installations which burn pretreated wood is limited to 170 MMBtu/h.
Table 5-15 German emission limits for medium to large scale appliances according to the TA Luft Emission limits in mg/m3 at 12 % O 2 fuel heat load in MMBtu/h CO OGC NO X dust Dust 3) lb/MMBtu
non treated biomass ≤ 8.5 135 1) 10 225 90 0.150 other biomass 2) 135 1) 10 360 45 0.075 non treated biomass 8.5 – 17 135 10 225 45 0.075 other biomass 2) 135 10 360 45 0.075 non treated biomass > 17 135 10 225 20 0.030 other biomass 2) 135 10 360 20 0.030

1) emission limit only valid for nominal load 2) painted, varnished or coated wood; plywood, chipbo ards, fibre boards (no preservatives used, no heavy metals or halogen organic compounds) 3) based on heat value for wood chips

For non treated biomass applia nces, TA Luft requires continuous measurement of dust emissions:

• from 17 to 85 MMBtu/h: qualitative measurement

• from 85 MMBtu/h: measurement of mass concentration In addition, the continuous measurement of CO-emissions for heat loads > 9 MMBtu/h is required. No efficiency requiremen ts are specified in the TA Luft.71 

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For fossil solid fuels emission limits are identical to the emission limits for “other biomass” in Table 5-16. Additionally emission limits for SO 2 are requested:

• fluidised bed co mubstion: 315 mg/m3 at 12% O 2

• other combustion technology

o mineral coal: 1170 mg/m3 at 12% O 2

o other fossil fuels: 900 mg/m3 at 12% O 2 (TA Luft)



### 5.2.3 Denmark

The Danish Guidelines for Air Emission Regulation (Environmental Guidelines no. 1, 2002) apply to all emitting installations, while the Statutory Order, regulating air pollution from wood burners and boilers and certain other fixed energy producing installations applies to combustion installations with a total input of < 1025 MBtu/h. Handcrafted masonry heaters are excluded from this regulation. In Table 5-16 the Danish emission limits for biomass boilers are shown.
Table 5-16 Danish emission limits for biomas s boilers (according to EN 303-5, Class 3) (Statutory Order) Emission limits in mg/m3 at 12% O 2 Appliance and fuel types nominal heat load MBtu/h CO OGC dust dust in lb/MMBtu < 170 4090 125 125 0.165 3) 170 – 510 2045 80 125 0.165 3) Biomass 1) 510 – 1025 980 80 125 0.165 3) < 170 4090 125 100 0.125 4) 170 – 510 2045 80 100 0.125 4) Manual stoking Fossil 2) 510 – 1025 980 80 100 0.125 4) < 170 2455 80 125 0.150 5) 170 – 510 2045 65 125 0.125 5) Biomass 1) 510 - 1025 980 65 125 0.125 5) < 170 2455 80 100 0.210 4) 170 – 510 2045 65 100 0.210 4) Automatic stoking Fossil 2) 510 – 1025 980 65 100 0.210 4)

1) wood, plant seed and other residual products 2) fixed carbon or coal 3) based on the higher heat value (GCV) of the fuel, solid wood assumed 4) based on the higher heat value (G CV) of the fuel, brown coal assumed 5) based on the higher heat value (GCV) of the fuel, pellets assumed In addition, the efficiency re quirements according to EN 3 03-5 are requested (based on the GCV):

• η GCV ≥ 59 + 5.5 log P n where P n is the nominal heat load of the boiler in MBtu/h. For room-heaters, dust emissi ons are limited depending on the method of measurement:72 

### Regulations for biomass installations

• Measurement in dilution tunnel: 0.16 oz/lb (10 g/kg) fuel; max. 0.32 oz/lb (20 g/kg) fuel in the individual testing intervals

• Measurement in the flue gas pipe (according to EN 13240): 0.115 lb/MMBtu (75 mg/m3 at 13 % O 2 ) Efficiency and emissions re quirements for room heaters according to EN 13240:

• η GCV ≥ 44 % (class 3)

• CO < 1405 mg/m 3 at 12 % O 2 (class 2)

Environmental label – The Nordic Swan The Nordic Swan was introduced by the Nordic Council of Ministers and it is a common system for Sweden, Norway , Denmark and Finland . It provides criteria for closed fireplaces and solid biomass boilers. Table 5-17 presents efficiency and emission requirements for (closed) room-heaters.
Table 5-17 Nordic Swan effici ency and emission requirements for closed room-heaters (Nordic Swan)

emission limits in mg/m3 at 12 % O 2 at nominal load Appliance Efficiency 1) (%) CO OGC dust in g/kg fuel and (lb/MMBtu) at nominal load/ partial load/ for each individual test slow heat release appliance 2) ≥ 70 170 2250 1/-/- (0.020/-/-) inset (manual stoking) 2) 170 2815 3/8/15 (0.050/0.120/0.230) stove (manual stoking) 2) ≥ 65 170 2815 3/5/10 (0.045/0.080/0.150)
stove (automatic stoking) 3) ≥ 70 55 1125 2/5/10 (0.030/0.070/0.135)

1) related to the lower heating value (NCV) 2) based on heat value for solid wood 3) based on heat value for pellets XXX/YYY/ZZZ: values for nominal lo ad/values for partial load/val ues for each individual test

In Table 5-18 emission requiremen ts for boilers are exhibited.73 

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Table 5-18 Nordic Swan emission requirements for boilers (Nordic Swan) Emission limits in mg/m3 at 12 % O 2 Stoking nominal heat load in kW CO NO 2 OGC dust dust in lb/MMBtu Automatic ≤ 1025 330 280 20 35 0.040 1)
≤ 340 1640 280 60 55 0.080 2) Manual 340 - 1025 820 280 40 55 0.080 2)

1) based on heat values for pellets 2) based on heat values for solid wood Dust and NO X emissions are tested only at nominal load Testing procedure for OGC and CO-emissions:

- nominal heat load for manually stoked boilers

- nominal load and partial load for automatically stoked boilers

Efficiency requirements for bo ilers are shown in Table 5-19. Table 5-19 Nordic Swan efficiency requirements for boiler (Nordic Swan) Stoking Efficiency 1) in % Manual 3) at nominal load: 65 + 5.5 log P n 2)

Automatic 4) at nominal load: 70 + 5.5 log P n 2) and η x ≥ 80 % where η x = ( η 20 + η 40 + η 60)/3 with η 20, η 40, η 60 are measured efficiencies at 20, 40 and 60% load

1) related to the higher heating value (GCV) 2) nominal heat load in MBtu/h 3) based on heat values for pellets 4) based on heat values for solid wood

Medium to large scale appliances For medium to large scale appliances, effi ciency and fuel qua lity requirements are defined, but there are no requirements for em issions. Medium to la rge scale appliances have to reach efficiencies larger th an 68% based on the GCV (Brønnum 2009).



### 5.2.4 Finland

In Finland, a proposal for the regulation of emissions and effici encies for heating appliances using wood fuels has been in the works, under discussion and review since 2006. This regulation will appl y to new biomass installations that provide heat, domestic hot water or other energy services with a nominal heat load up to 1025 MBtu/h. The proposal distinguishes primary and secondar y heating systems. Pr imary heating systems provide all required heat/hot water on thei r own, while secondary heating systems have another (main) heat source. Table 5-20 show s the suggested emission and efficiency requirements for Finland.74 

### Regulations for biomass installations

Table 5-20 Proposed Finnish emission and ef ficiency requirements for biomass boilers < 1025 MBtu/h kW (EuP Lot 15, Task1) Emission limits in mg/m3 at 12% O 2 heating system nominal heat load (MBtu/h) efficiency 1) (%) CO OGC ≤ 170 2455 80 170 – 510 2045 65 primary > 510 59+ 5.5 log P n 2) 980 65 ≤ 170 4090 125 170 – 510 2045 80 secondary > 510 59 + 5.5 log P n 2) 980 80

1) related to the higher heating value (GCV ), based on heat value for solid wood 2) nominal heat load in MBtu/h

In Table 5-21 the Finnish emission and effi ciency requirements for fireplaces (room heaters) is shown. Fireplaces which do not fu lfill the requirements are still allowed, but they have to be marked as usea ble only for decorative purposes. Table 5-21 Proposed Finnish emission and efficiency requirements for fireplaces (room-heaters) (EuP Lot 15, Task1)

heating system nominal heat load (MBtu/h) efficiency 1) (%) CO (mg/m3) at 12% O 2 primary 2455 secondary ≤ 170 60 4220

1) related to the higher heating value (GCV ), based on heat value for solid wood

Medium to large scale appliances For medium to large scale applications, national dust requir ements are given:

• 3.4 – 17 MMBtu/h: < 0.465 lb/MMBtu

• 17 – 170 MMBtu/h: < 0.200 - 4 / 3 ·(P n -0.01) lb/MMBtu Additionally, emission limits can be requested by local authorities for heating plants > 17 MMBtu/h. For appliances > 170 MMBtu/h approval is needed by even higher authorities and these li mits are open to public (Oravainen 2009).

Environmental label – The Nordic Swan



### 5.2.5 Sweden

In Sweden emission limits for sm all scale solid fuel appliances are included in the building regulation (BFS 2006:12). The re gulation applies to solid fuel installations with nominal heat loads < 1025 MBtu/h. The em ission limits for solid fuel appliances are shown in Table 5-22. The CO requirements do not apply to open fireplaces, tiled stoves (masonry heaters) and cook stoves.75 

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Table 5-22 Swedish emissi on limits for solid fuel appliances < 1025 MBtu/h (EuP Lot 15, Task1)

stoking nominal heat load (MBtu/h) OGC in mg/m3 at 12% O 2

≤ 170 125 manual 170 – 1025 80 ≤ 170 80 automatic 170 – 1025 65

For secondary heating systems (another main heat source is used), limits for COemission are given:

• for stoves and fireplaces inse rts: CO < 3300 mg/m3 at 12% O 2

• for pellet stoves: CO < 440 mg/m3 at 12% O 2 These CO requirements do not apply to open fireplaces, tiled stoves (masonry heaters) and cook stoves. For efficiency requirements on ly recommendations are given:

• for stoves: η > 53 % (on GCV basis)

• for fireplace inserts: η > 44 % (on GCV basis)

• for pellet stoves: η > 65 % (on GCV basis)

Environmental label – The Nordic Swan76 

### Performance of biomass installations



# 6 Performance of biomass installations

Technology forcing efforts of regulations, technology cluster investment, competition among manufacturers and Eco-labeling efforts have resulted in commercially available technologies with performance far exceedin g regulatory requirem ents. This chapter describes the top performing biomass technolo gies based on thermal efficiency, CO , NO X and dust (fine particles) emissions. Additionally retail prices are given. For selection of the TOP 25% performing tec hnologies in each si ze category, thermal efficiency and CO data at full load is used due to the availability of this information. Recall that for many technologies, especially boilers the thermal efficiency curve is linear down to very low part loads with these technologies (Figure 6-3).



## 6.1 Introduction

6.1.1 Data sources

Before installation of biomass appliances is a llowed, they have to pa ss the efficiency and emission requirements of the current European standards as well as the national/regional regulations. Small scale appliances are usually type-tested by certified testing houses. Results of these tests are property of biomass appliances’ manufacturer and are therefore not usually publicly available. However, some local and national organisations collect and publish test data which they whet her collect from manufacturers or from test houses. In order to receive test data of bi omass appliances in the considered countries, the following sources were used:

• Website of FJ-BLT ( http://www.josephinum.at ), an Austrian testing laboratory

• Publications of the Fachagentur Nachwachsende Rohstoffe (FNR) on biomass boilers and pellet stoves av ailable on the German market

• Webpage of Teknologisk Institut ( http://www.teknologisk.dk ), a Danish testing house

• Webpage of the Dani sh Environmental Protection Agency ( http://www.mst.dk )

• Written information of the Teknikfoer etagens Branschgrupper AB, the Swedish Heating Boilers and Burners Association (contact person: Magnus Davidsson)

• Website and written information of the HKI Industrieverband Haus-, Heiz und Kuechentechnik e.V., the German heat technology association (contact person: Frank Kienle)

• Written information of following manufacturers of biomass appliances:

o Veljekset Ala-Talkkari (Finland)

o Nunnauuni Oy (Finland)

o Rika (Austria)

o Calimax (Austria)

o ...77 

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Information from these sources about test da ta varies from the simple statement that the appliances have passed the efficiency and emission requirements to detailed data on efficiency and emissions at nominal and partial load as well as investment costs.



### 6.1.2 Selection method for TOP 25% performing appliances

For the selection of the TOP 25% performing biomass appliances, the efficiency and CO-emissions at full load (nominal heating load) were considered:

• The efficiency of an appliance provides informat ion regarding the extend the fuel input is used to produce hot water and/or room heat. It is therefore one of the most important quality criteria.

• CO-emissions are the prime indicators of the combustion quality of biomass appliances (chapter 3.2). If CO-emissions are low, the emissions of OGC as well as the organic fraction of the TSP (total suspended particul ate matter) will also be low. NOx-emissions depend primarily on the nitrogen content of the fuel (chapter 3.5); therefore, they are not co nsidered for the selection of the TOP 25% performing appliances.

• The full load range is chosen for the selection method, because most data is available at this load. The appliances with the high est efficiencies an d CO-emissions lower than the average CO-emissions of the considered technology and load range represent the TOP 25% performing appliances.



## 6.2 Stoves/room-heaters

6.2.1 Pellet stoves

The European pellet stove market is quit e manageable, because pellets combustion technology is a relatively young technology. Manufacturers of pellet stoves are used to having their products tested and are as such usually willing to publish their test data. As a result, a very broad database was able to be compiled for this study. Therefore, the data given in the list of the TOP 25% perfor ming pellet stoves is considered to be representative of the current market. Table 6-1 shows a summary of the minimu m, maximum and average efficiency and emission values at full load for all the cons idered pellet stoves and Table 6-5 shows a summary of the minimum, maxi mum and average efficiency an d emissions values at full load for the TOP 25% pellet stoves with and without water circulation equipment. A total of 79 data sets were recorded, of whic h 53 were not identical. Identical data sets are a result of manufacturers producing two or more appliances, which are identical in terms of all technical aspects and combustion systems, but have diffe rent designs for the housing as well as different model names. However, due to the identical technical design, separate performance tests are not necessary.78 

### Performance of biomass installations

Table 6-1 summary of extreme and averaged values for all considered pellet stoves

yes < 30 > 30 all

34 18 27 17 16 19 445 min. 8 30 25 max. 29 132 51 avg. 23 66 38 min. 86 85 84 max. 89 87 85 avg. 87 86 84 min. 75 153 39 max. 844 1316 460 avg. 249 449 174 min. 0.011 0.027 0.014 max. 0.104 0.082 0.087 avg. 0.040 0.052 0.031 min. 15 92 84 max. 259 213 162 avg. 101 139 119 5262 3757 8820 load range (MBtu/h) no water circulate

nominal load

(MBtu/h)

η GCV 1) at full load (%) No. of all test data No. of unequal test data No. of top 25% appliances

CO at full load (mg/m 3 12%O2 )

TSP 1) at full load (lb/MMBtu)

NOx at full load

(mg/m3 12%O2 ) avg. retail price (US$)

1) related to the Gross Calorific Value (upper heating value)

Pellet stoves with and without water circulat ion equipment are built in a load range from approximately 10 to 130 MBtu/h, whereby the e fficiency of these a ppliances is 86% on average. Pellet stoves with hot water produc tion attain slightly lower efficiencies.
The measured CO-emissions exhibit a very broad range from 75 to 1350 mg/m3 at 12% O 2 . This broad variation is due to diff erent combustion chamber materials and diverse control concepts used for the stoves:

• If ceramics are used in the combustion ch amber, the combustion temperature will be higher than if steel only is used – the combustion temperature is the most important indicator for low CO -emissions (chapter 3.2).

• If the control concept of the stove invo lves CO or air ratio-measurement, CO emissions can be minimized more easily than if only the combustion gas temperature is measured. If no concepts for combustion condition optimisation are implemented, the control of the stove is not able to adopt to the operation mode.
The measures for the reduction of CO described above will however result in an increase in cost of the stoves. This is clearly shown in a comparis on of the CO emissions in relation to the costs of stoves without wate r installations having head loads of <30 and >30 Btu/h. The average pell et stove with a heat load of < 30 MBtu/h emits approximately 250 mg/m3 CO at 12% O 2 and costs approximately 5250 US$. On the other hand, the average pellet stove with a heat load > 30 MBtu/H emits nearly twice as much CO (450 mg/m3 at 12% O 2 ), but costs one quarter less (3750 US$).79 

### Report

Emissions of TSP vary from 0.015 to 0.100 lb/ MMBtu. This broad range can be attributed to the same factors mentioned above. A low co mbustion temperature will result in a high organic fraction of TSP and the (control) concept for the air supply influences the amount of fly ash.

NO X emissions range from 100 to 360 mg/m3 at 12% O 2 and the average value is approximately 120 mg/m3 at 12% O 2 . These are typical values for wood combustion. Table 6-2 summary of extrem e and averaged values for TOP 25% performing pellet stoves

yes < 30 > 30 all

34 18 27 17 16 19 445 min. 8 30 25 max. 29 34 51 avg. 21 32 38 min. 88 86 85 max. 89 87 85 avg. 88 87 85 min. 86 153 39 max. 236 234 169 avg. 164 180 117 min. 0.033 0.035 0.014 max. 0.072 0.050 0.025 avg. 0.045 0.043 0.019 min. 88 106 125 max. 88 114 162 avg. 88 110 143 8113 4820 9843 no

CO at full load (mg/m 3 12%O2 )

TSP 1) at full load (lb/MMBtu)

NOx at full load

(mg/m3 12%O2 ) avg. retail price (US$) water circulate

nominal load

(MBtu/h)

η GCV 1) at full load (%) No. of all test data No. of unequal test data No. of top 25% appliances load range (MBtu/h)

1) related to the Gross Calorific Value (upper heating value) The TOP 25% performing pellet stoves reach average efficiencies from 85 to 87% based on the GCV. Their CO-emissions vary from 40 to 240 mg/m3 at 12% O 2 and the average CO emissions are approximately 155 mg/m3 at 12% O 2 . The difference between the CO emissions from pellet stoves without water circulations having heat loads of < 30 MBtu/h and those with heat loads of > 30 MBtu/h still exists, but is definitely smaller. The average dust emissions range from 0. 020 to 0.045 lb/MMBtu, a range which is slightly smaller than the averag e dust emissions calculated fr om all of the collected data. The NO X emissions from the TOP 25% performing pellet st oves are essentially no different than those from all the other pellet stoves collected for this study. For pellet stoves without water circulation having heat loads of < 30 MBtu/h in particular, a quite notable increase in price for the TOP 25% is observed in comparison to the average price of all the collected data. Detailed performance data of the TOP 25% performing pellet stoves and contact information of the manufacturers is given in the annex.80 

### Performance of biomass installations

6.2.2 Wood stoves

The wood stove market is extremely broad and diverse as manufacturers come from many different backgrounds (masonry heater industry, steel indu stry, biomass boiler industry...) and as such define the main pu rposes for their produc ts differetly (e.g., efficient heating, stove design , lifestyle product...). Moreover, many uncertified products, which do not conform to the according stan dard (EN 13240) are also offered on the market. The publishing of test data is not common fo r wood stoves. The fact that the emissions from wood stoves are difinitively higher th ose from pellet stoves or biomass boilers discourages manufacturers fr om publishing test data. For these reasons, only a small group of wood stoves data could be collected and evaluated. In addition to the detailed data collected for this study, a list of EN 13240 certified wood stoves from German manufacturers is provided in the annex.
Table 6-3 and Table 6-4 show the minimu m, maximum and average efficiency and emissions values at full load for all an alysed wood stoves and for the TOP 25% performing wood stoves.
A total of 51 data sets were record ed, of which 40 were not identical.

Table 6-3 summary of extreme and average values for selected wood stoves

51 40 10 min. 25 max. 128 avg. 57 min. 64 max. 76 avg. 71 min. 776 max. 2535 avg. 1521 min. 0.009 max. 0.128 avg. 0.059 min. 59 max. 225 avg. 139

- NOx at full load

(mg/m3 12%O2 ) avg. retail price (US$) nominal load

(MBtu/h)

η GCV 1) at full load (%)

CO at full load (mg/m 3 12%O2 )

TSP 1) at full load (lb/MMBtu) No. of all test data No. of unequal test data No. of top 25% appliances

1) related to the GCV Table 6-4 summary of extreme and average values for TOP 25% performing wood stoves

51 40 10 min. 25 max. 128 avg. 57 min. 71 max. 76 avg. 73 min. 776 max. 1340 avg. 1069 min. 0.020 max. 0.081 avg. 0.050 min. 59 max. 197 avg. 126

- nominal load

(MBtu/h)

η GCV 1) at full load (%)

CO at full load (mg/m 3 12%O2 )

TSP 1) at full load (lb/MMBtu)

NOx at full load

(mg/m3 12%O2 ) avg. retail price (US$)

No. of all test data No. of unequal test data No. of top 25% appliances81 

### Report

The heat loads of the wood stoves vary fr om 25 to 130 MBtu/h and achieve an average efficiency of 71 % based on the GCV. CO emissions fall into a rather wide range between 750 to 2550 mg/m3 at 12% O 2 . Since dust emissions are related to CO emissions due to un-bur nt particles in the fly ash fraction, dust emission s also widely vary from 0.010 to 0.130 lg/MMBtu. The average NO X emissions are approximately 140 mg/m3 at 12% O 2 , which is a typical value for wood combustion. The TOP 25% performing wood stoves reach e fficiencies of approximately 73% and emit on average 1050 mg/m3 CO at 12% O 2 , a 33% reduction with respect to the entire data set. The dust emissions still show quite broad variations from 0.020 to 0.080 lb/MMBtu; however, the average data chan ges marginally in comparison to the entire data set. Altogether, the average data of the TOP 25% performing wood stoves does not exhibit significant improvements in comparison to the entire data set. Detailed performance data of all considered wood stoves and contact information of the manufacturers is given in the annex. This summary should give an idea of the average emissions as well as the performance of wood stoves. It does not imply that test data from other manufacturers is bette r or worse than the given data.



### 6.2.3 Masonry heaters

The masonry heater market is similar to th at of wood stoves. Data from only two manufacturers (LEDA and Brunner) could be co llected. For this reason, performance and emission data will not be summarized for masonry heaters. In the annex, a list of EN 13229 certified prefabricated masonry heaters from German manufacturers is provided. Additionally contact information of manufacturers is also given.



## 6.3 Boilers

The European biomass boiler market is quit e large. A very compet itive environment and local/national grant schemes for biomass appliances (see diverse environmental labels mentioned in chapter 5.2) lead to a high transparency of perf ormance and emission data. Test data can be found on webpages from national authorities. It is estimated that approximately 90% of Austrian and German boilers were collected for this study. Therefore, the data given in the list of the TOP 25% performing pellet stoves is considered to be an accurate repr esentation of the current market. A total of 954 data sets were recorded, of which 787 were not identical. These identical data sets are a result of manufacturers producing two or more appliances, which are identical in terms of all tec hnical aspects and combustion systems, but have different designs for the housing as well as different model names. Due to the identical technical design, a separate performa nce test is not necessary.82 

### Performance of biomass installations

6.3.1 Pellet boiler

Table 6-5 shows a summary of the minimu m, maximum and average efficiency and emission values at full load for all the consid ered pellet boilers and Table 6-6 shows test data of the TOP25% performing app liances at the defined load ranges.
A total of 433 data sets were recorded , of which 362 were not identical.

Table 6-5 overview of extrem e and averaged values for a ll considered pellet boilers

< 55 55 - 100 100 - 170 170 - 340 > 340 124 142 83 52 32 102 130 66 45 29 26 33 17 11 7 min. 26 55 99 171 342 max. 54 98 169 338 997 avg. 45 78 134 254 568 min. 78 73 80 81 81 max. 89 88 89 88 88 avg. 85 84 85 85 85 min. 7 1 3 4 1 max. 371 603 281 338 543 avg. 91 116 76 66 62 min. 0.003 0.008 0.006 0.014 0.004 max. 0.069 0.348 0.377 0.377 0.058 avg. 0.023 0.028 0.030 0.047 0.031 min. 84 12 63 63 63 max. 398 365 378 293 247 avg. 154 168 144 151 133 11359 12149 16052 24795 30244 load range (MBtu/h)

nominal load

(MBtu/h)

η GCV 1) at full load (%) No. of all test data No. of unequal test data No. of top 25% appliances

CO at full load (mg/m 3 12%O2 )

TSP 1) at full load (lb/MMBtu)

NOx at full load

(mg/m3 12%O2 ) avg. retail price (US$)

1) related to the Gross Calorific Value (upper heating value)
Pellet boilers are built for heat loads starti ng at 25 MBtu/h and re ach high e fficiencies independent of their load, in the range of 73 to 89 %. The average efficiency for these boilers is 85 %. CO emissions vary from very small amounts to elevated values of 600 mg/m3 at 12% O 2. The average CO-emissions for all load ra ngs are however below 120 mg/m3 at 12% O 2 . Higher loads give rise to lower CO emissions, a fact that can be attributed to the higher combustion temperatures reached in larger appliances as a result of the favourable relationship between combustion chamber vo lume and combustion chamber surface as well as the better materials that are used. It can be stated that CO-emissions are generally low in pellet boilers. TSP-emissions vary from 0.003 to 0.377 lb/ MMBtu; the average emissions are in the range of 0.025 to 0.045 lb/MMBtu, which are very low values.

NO X -emissions fall within a range of 60 to 400 mg/m3 at 12% O 2 ; the average value is approximately 150 mg/m3 at 12% O 2 , which can be considered normal NO X -emissions for wood fuel.83 

### Report

Table 6-6 overview of extr eme and average values for TOP 25% performing pellet boilers

< 55 55 - 100 100 - 170 170 - 340 > 340 124 142 83 52 32 102 130 66 45 29 26 33 17 11 7 min. 27 55 102 171 342 max. 53 92 169 331 885 avg. 44 78 141 258 524 min. 86 85 86 86 85 max. 89 88 89 88 88 avg. 87 86 87 86 86 min. 7 1 5 4 5 max. 77 105 73 59 41 avg. 43 39 38 24 17 min. 0.008 0.010 0.006 0.014 0.008 max. 0.043 0.056 0.057 0.053 0.056 avg. 0.022 0.024 0.023 0.036 0.031 min. 95 39 63 105 118 max. 230 260 183 198 171 avg. 140 136 132 154 133 12221 13659 16844 23537 0 nominal load

(MBtu/h)

η GCV 1) at full load (%)

CO at full load (mg/m 3 12%O2 )

TSP 1) at full load (lb/MMBtu) load range (MBtu/h) No. of all test data No. of unequal test data No. of top 25% appliances

avg. retail price (US$) NOx at full load

(mg/m3 12%O2 )

1) related to the Gross Calorific Value (upper heating value)
The TOP 25% performing pellet bo ilers exhibit average efficien cies 2% higher than that of the entire data set. The CO emissions ar e 50% less that of all considered appliances, and varying from nearly no CO emissions to 105 mg/m3 at 12% O 2 . The average dust emissions are slightly lower th an the emission values of the entire data and range from 0.02 to 0.035 lb/MMBtu. Detailed performance data of the TOP 25% performing pellet boilers and contact information of the manufacturers is given in the annex.



### 6.3.2 Solid wood boiler

Table 6-7 shows a summary of the minimu m, maximum and average efficiency and emission values at full load for all the consid ered solid wood boilers. Table 6-8 shows test data of the TOP25% performing app liances for the defined load ranges.
A total of 279 data sets were recorded , of which 229 were not identical.84 

### Performance of biomass installations

Table 6-7 overview of extrem e and average values from all considered solid wood boilers

< 85 85 - 120 120 - 170 > 170 69 81 72 57 65 64 54 46 16 16 14 12 min. 40 85 120 171 max. 82 116 167 348 avg. 63 98 141 199 min. 62 73 73 73 max. 84 85 84 84 avg. 80 81 81 81 min. 64 20 18 44 max. 3912 4137 2878 2009 avg. 612 417 399 308 min. 0.008 0.009 0.008 0.012 max. 0.175 0.189 0.324 0.166 avg. 0.034 0.035 0.041 0.036 min. 20 57 34 75 max. 206 225 242 199 avg. 129 133 135 149 8436 9683 11965 14104 CO at full load (mg/m 3 12%O2 )

NOx at full load

(mg/m3 12%O2 ) avg. retail price (US$) TSP 1) at full load (lb/MMBtu) load range (MBtu/h)

nominal load

(MBtu/h)

η GCV 1) at full load (%) No. of all test data

No. of top 25% appliances

No. of unequal test data

1) related to the Gross Calorific Value (upper heating value)

Solid wood boilers are built for heat loads st arting at 50 MBtu/h and reach efficiencies from 60 to 85 %. The average efficiencies are approximately 81%, which is 3% lower than the efficiencies reac hed by pellet boilers. CO-emissions vary from 20 to 4140 mg/m3 at 12% O 2 which exhibits a very broad variation. This may be attributed to the broad range of control (or no control) concepts 3 for solid wood boilers as well as the materials used in the combustion zone. The average values are approximately 400 mg/m3 at 12% O 2 and decrease with higher load ranges. This can be attributed to the same phen omenon discussed for the pellet boilers. Dust emissions range from 0.010 to 0.325 lb/ MMBtu, whereby the average emissions are approximately 0.035 lb/MMBtu, which is nearly as low as the dust emissions from pellet boilers. The average NO X -emissions are approximately 130 mg/m3 at 12% O 2 and thus lie in the normal range for wood combustion.

3 The solid wood boiler is the oldest biomass boiler technology. There are thus a large number of traditional manufacturers who use very traditional design concepts without proper control conc epts, thus resulting in a broad variation.85 

### Report

Table 6-8 overview of extr eme and average values from TOP 25% performing solid wood boilers

< 85 85 - 120 120 - 170 > 170 69 81 72 57 65 64 54 46 16 16 14 12 min. 40 85 123 171 max. 75 116 167 239 avg. 63 97 143 189 min. 82 82 82 81 max. 84 83 84 84 avg. 83 83 83 82 min. 64 40 50 44 max. 353 298 343 282 avg. 174 220 152 97 min. 0.014 0.014 0.021 0.015 max. 0.175 0.189 0.324 0.076 avg. 0.039 0.044 0.066 0.033 min. 90 100 34 75 max. 182 186 181 194 avg. 139 126 115 119 10116 10319 12672 14089 NOx at full load

(mg/m3 12%O2 ) avg. retail price (US$) nominal load

(MBtu/h)

η GCV 1) at full load (%)

CO at full load (mg/m 3 12%O2 )

TSP 1) at full load (lb/MMBtu) load range (MBtu/h) No. of all test data No. of unequal test data No. of top 25% appliances

1) related to the Gross Calorific Value (upper heating value) The TOP 25% performing solid wood boilers reach average efficien cies which are 2% higher than the average values from the entire data set.
The variation of CO emissions is significantly lower and varies from 40 to 350 mg/m3 at 12% O 2 . The average CO emissions decrease by 50 to 75% and range from 100 to 220 mg/m3 at 12% O 2 . A decrease of CO emi ssions with higher loads can also be observed for the TOP 25% performing appliances. Surprisingly and also inconsiste nt with the statement that lo w CO emissions result in low dust emissions, the dust em issions of the TOP 25% performing appliances are higher than the dust emissions for the entire data set. This could be attributed to quality variations of the dust measurement methods. Detailed performance data of the TOP 25% pe rforming solid wood boilers and contact information of the manufacturers is given in the annex.



### 6.3.3 Wood chip boiler

Table 6-9 shows a summary of the minimu m, maximum and average efficiency- and emission values at full load of all considered wood chip boilers and Table 6-10 shows test data for the TOP25% performing appliances at the defined load ranges.
A total of 213 data sets were recorded , of which 174 were not identical.86 

### Performance of biomass installations

Table 6-9 overview of extrem e and averaged values from all considered wood chip boilers

< 100 100 - 200 200 - 340 340 - 680 > 680 35 65 44 39 30 26 49 42 33 26 7 12 11 8 7 min. 34 102 205 342 683 max. 96 188 340 666 5123 avg. 74 150 265 444 1459 min. 73 68 69 70 46 max. 86 86 86 86 86 avg. 77 77 76 77 75 min. 22 4 7 3 6 max. 489 649 641 368 369 avg. 128 117 106 74 86 min. 0.011 0.009 0.011 0.004 0.024 max. 0.134 0.258 0.237 0.127 0.460 avg. 0.058 0.051 0.052 0.048 0.106 min. 91 45 51 45 45 max. 438 394 411 371 235 avg. 180 145 146 150 122 15921 21887 26468 32373 54890 load range (MBtu/h)

NOx at full load

(mg/m3 12%O2 ) avg. retail price (US$) nominal load

(MBtu/h)

η GCV 1) at full load (%)

CO at full load (mg/m 3 12%O2 )

TSP 1) at full load (lb/MMBtu) No. of all test data No. of unequal test data No. of top 25% appliances

1) related to the Gross Calorific Value (upper heating value) Wood chip boilers are available from a nominal load of 35 MBtu/h. The efficiencies vary from 70 to 86% and the average is approxim ately 77%, meaning that their performance is 4% lower than that of the solid wood boilers. The CO-emissions range from very sm all amounts to 650 mg/m3 at 12% O 2; the average value is approximately 100 mg/m3 at 12% O 2 . Due to the continuous operation conditions, these emission values are similar to the CO-emissions of pe llet boilers. It can also be observed that the CO-emissions decrease as the load range increases. TSP-emissions vary from 0.004 to 0.460 lb/M MBtu; the average is approximately 0.052 lb/MMBtu. Emissions in the largest load ra nge (> 680 MBtu/h) are significantly higher, which can be attributed to the small amo unt of appliance data. Overall, the TSPemissions are slightly higher than the TSP-emissions for soli d wood boilers, which may be due to the characteristics of the fuel as wood chips have more fine parts are more inhomogeneous than pellets.
The NO X -emissions fall into the rang e of 50 to 440 mg/m3 at 12% O 2 ; the average value is approximately 150 mg/m3 at 12% O 2 . This value is slightly higher than the NO X emissions from pellets and solid wood stoves, which can attrib uted to the characteristics of wood chips (bark).87 

### Report

Table 6-10 overview of extreme and averag ed values from TOP 25% performing wood chip boilers

< 100 100 - 200 200 - 340 340 - 680 > 680 35 65 44 39 30 26 49 42 33 26 7 12 11 8 7 min. 51 102 205 342 751 max. 96 171 340 666 2220 avg. 78 147 276 449 1322 min. 73 75 77 77 76 max. 78 81 80 86 79 avg. 76 79 78 80 78 min. 28 10 7 9 15 max. 108 93 87 40 68 avg. 60 39 30 22 34 min. 0.017 0.009 0.020 0.009 0.053 max. 0.110 0.053 0.075 0.072 0.156 avg. 0.046 0.027 0.038 0.042 0.092 min. 91 90 106 45 90 max. 185 179 180 180 178 avg. 157 134 138 125 131 14350 25504 31581 34056 65180 nominal load

(MBtu/h)

η GCV 1) at full load (%)

CO at full load (mg/m 3 12%O2 )

TSP 1) at full load (lb/MMBtu)

NOx at full load

(mg/m3 12%O2 ) avg. retail price (US$)

load range (MBtu/h) No. of all test data No. of unequal test data No. of top 25% appliances

1) related to the Gross Calorific Value (upper heating value) The TOP 25% performing wood chip boilers reach efficiencies of approximately 78%, which is 1% higher than the average emissions of the entire data set. In comparison to the CO emi ssions of the entire data set, decreases of 50 – 70% can be observed in that the averag e CO emissions are very low at approximately 35 mg/m3 at 12% O 2 . Dust emissions are approximately 20% lo wer than the emissions of the entire data set. The average dust emission s are approximately 0.040 lb/MMBtu/h. Detailed performance data of the TOP 25% pe rforming wood chip boilers and contact information of the manufacturers is given in the annex.



### 6.3.4 Combined technologies

Table 6-11 shows a summary of the minimum, maximum an d average efficiency- and emission values at full load of all considered combined technology boilers (pellets & solid wood) and Table 6-12 shows test data of the TOP25% performing appliances at the defined load ranges.
A total of 29 data sets were record ed, of which 22 were not identical.88 

### Performance of biomass installations

Table 6-11 overview of extreme and averag e values from all considered combined technology boilers (pellets & solid wood)
pellets solid wood

min. 51 51 max. 205 205 avg. 80 92 min. 79 72 max. 89 87 avg. 84 80 min. 1 158 max. 294 1384 avg. 109 367 min. 0.008 0.021 max. 0.139 0.079 avg. 0.036 0.035 min. 92 96 max. 218 174 avg. 131 135 fuel No. of all test data No. of unequal test data No. of top 25% appliances

NOx at full load

(mg/m3 12%O2 ) avg. retail price (US$) nominal load

(MBtu/h)

η GCV 1) at full load (%)

CO at full load (mg/m 3 12%O2 )

TSP 1) at full load (lb/MMBtu)

15675 29 22 6

1) related to the Gross Calorific Value (upper heating value) Combined boilers are built in load ranges from 50 to 200 MBtu/h. For pellets mode and solid wood mode, average efficiencies of 84% and 80% are respectively achieved. CO emissions in pellets mode ar e approximately 110 mg/m3 at 12% O 2 , meaning that CO emissions are similar to the emissions from pellet boilers. In solid wood mode, CO emissions are approximately 370 mg/m3 at 12% O 2 . These emissions are comparable to emissions from solid wood boilers. Dust emissions range from 0.010 to 0.140 lb/MMBtu and are approximately 0.036 lb/MMBtu on average. These values also co rrespond closely with emission data from pellets and solid wood boilers. NOx emissions are approximately 130 mg/m3 at 12% O 2, which can be considered normal NO X -emissions for wood fuel.89 

### Report

Table 6-12 overview of extreme and av erage values from TOP 25% performing combined technology boilers (pellets & solid wood)
pellets solid wood 29 22

6 min. 51 51 max. 126 153 avg. 75 88 min. 79 72 max. 84 83 avg. 82 79 min. 6 158 max. 104 530 avg. 34 252 min. 0.017 0.023 max. 0.040 0.038 avg. 0.027 0.027 min. 92 96 max. 218 150 avg. 145 120 16870 nominal load

(MBtu/h) fuel No. of all test data No. of unequal test data No. of top 25% appliances

η GCV 1) at full load (%)

CO at full load (mg/m 3 12%O2 )

TSP 1) at full load (lb/MMBtu)

NOx at full load

(mg/m3 12%O2 ) avg. retail price (US$)

1) related to the Gross Calorific Value (upper heating value)
The emissions and efficiencies of the TOP 25% performing appliances correspond to the increase of efficiency and de crease of CO and TSP emission s as discussed for the pellets and solid wood boilers. Detailed performance data of all combined technology boilers and contact information of the manufacturers is given in the annex.



### 6.3.5 Summary

In Figure 6-1 and Figure 6-2 the average effi ciencies and dust emi ssions of the TOP 25% performing appliances are summarized. The e fficiencies and emission s for classes 3 to 5 in EN 303-5 are also illustrated. In order to enable the comparability of pellet, wood chip and solid wood appliances, a correction factor for wood chip and solid wood boilers was used because the efficiency re quirements and dust emission limits fr om EN 303-5 were converted for pellets fuel. Figure 6-1 and Figure 6-2 clearly show th at the average perfor mance of the TOP 25% performing appliances identified in this repo rt greatly exceed the efficiency requirements and are below the dust emission limits of class 5 from EN 303-5 (currently still under discussion and has not yet been introduced). At present, class 3 represents the most stringent requirements for biomass boilers.90 

### Performance of biomass installations

75% 80% 85% 90%

0 200 400 600 800 1000 nominal load in mBTU/h class 3 class 4 class 5efficiency based on GCV TOP 25% pellet boilers

TOP 25% solid wood boilers* TOP 25% wood chip boilers*

* conversion from efficiency based on NCV to efficiency based on GCV was performed based on pellets fuel, therefore a correction factor for wood chip boiler (+10.6%) and for wood chip boilers (+3.1%) was used to enable comparability, efficiencies for wood chip and solid wood boilers are not exact.
Figure 6-1 efficiency classes 3 to 5 from EN 303-5 and efficiency performance of TOP 25% pellet, solid wood and wood chips boilers; efficiencies from solid wood and wood chip boilers were corrected because efficien cy limits based on the GCV were converted for pellets fuel

0.000 0.050 0.100 0.150 0.200

0 200 400 600 800 1000 nominal load in mBTU/h class 3

class 4

class 5

TOP 25% pellet boilers TOP 25% solid wood boilers*

TOP 25% wood chip boilers* class 2

* conversion from dust emission limits from mg/m3 to lb/MMBTU was performed for pellets fuel, therefore a correction factor for wood chip boiler (0.754) and for wood chip boilers (0.911) was used to enable comparabilitydust emissions in lb/MMBtu

Figure 6-2 dust emissi on limit classes 2 to 5 from EN 303-5 and dust emissions from TOP 25% pellet, solid wood and wood chip s boilers; emissions from solid wood and wood chip boilers were corrected because dust emission conver sion from mb/m3 to lb/MMBtu was performed for pellets fuel91 

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Figure 6-3 shows the efficien cies from the TOP 25% performing boilers for nominal and partial loads. For pellet and wood chips boilers partial load equals 30% of nominal load, for solid wood boilers partial load is 50% of nominal load.

75% 80% 85% 90%< 5555 - 100100 - 170170 - 340> 340< 8585 - 120120 - 170> 170< 100100 - 200200 - 340340 - 680> 680

pellet boilers solid wood boilers wood chip boilers nominal load partial loadefficiency based on GCV

load categor y (MBtu/h )

Figure 6-3 average efficiencies based on GCV at nominal an d partial heat load for the TOP 25% performing boilers
Efficiencies that are reached at nominal and partial load are nearly identical, solid wood and wood chip appliances sometimes even re ach higher efficiencies at partial load.



## 6.4 Commercial biomass installations

Medium to large scale commercial biom ass installations undergo individual commissioning, meaning that th ese plants are dimensioned an d built individually with respect to the technical requirements of the buyer. Commisioning is performed in order to guarantee that the emission and efficien cy requirements (see chapter 5) are met. Depending on the local regulations, emission s and efficiencies ha ve to be controlled periodically by consulting engineers. Resu lts of these measurements are usually not published; therefore, no database on emis sions and efficiencies of medium commercial biomass appliances is available. In order to give an idea of emissions and efficiencies of medium scale biomass plants, results from various studies on th is topic will be cited in this section. In addition, national emission factors for biomass combustion uni ts shall show which average emissions are assumed for the Austrian biomass plants.92 

### Performance of biomass installations

6.4.1 Data collection of Austrian medium scale biomass appliances (Musil et al. 2006)

Emission data for Austrian biomass combustion and CHP pl ants was collected directly from the operators of medium scale biomass units using a standard questionnaire. In addition, the measurement results of one consulting engineer were used for the estimation of emissions from medium scale biomass applia nces. Approximately 100 data sets in total were collected, all appliances were operated with wood chips, saw shavings or wood residues. In Figure 6-4 the average em ission results for TSP and NO X assigned in three load ranges are shown.

163 180

148

76 82

33

0 20 40 60 80 100 120 140 160 180 200

≤ 3.4 mmBTU/h 3.4 - 6.8 mmBTU/h 6.8 - 17.1 mmBTU/h

nominal heat load NOx TSP sd.: 79

sd.: 40 sd.: 92

sd.: 31 sd.: 33 sd.: standard deviationemissions in mg/m313%O2

sd.: 33

Figure 6-4 TSP and NOx emissions of medium scale biomass appliances in Austria

While the NO X emissions were quite constant for these load categories (from 170 – 205 mg/m3 at 12% O 2 ), dust emissions decreased significan t with increasing load because of stricter emission limits for lo ads from 6.9 MMBtu/h. Up to a load range of 6.8 MMBtu/h, TSP emissions were found to be around 80 mg/m3 at 13% O 2 (0.150 lb/MMBtu), TSP emissions for higher loads ar e around 35 mg/m3 at 13% O 2 (0.065 lb/MMBtu). Figure 6-5 shows the TSP emi ssions and the emission limit s of the analysed biomass appliances in more detail including the utilised emission control technology.93 

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0 20 40 60 80 100 120 140 160

1 2 35 1 35 2 3 45

≤ 3.4 mmBTU/h 3.4 - 6.8 mmBTU/h 6.8 - 17.1 mmBTU/hTSP in mg/m3@ 13% O2

technology:

heat load:

blue dots: emission limits for the appliance technology 1: cyclone technology 2: cyclone + electrostatic precipitator technology 3: cyclone + flue gas condensation technology 4: cyclone + flue gas cond ensation + electrostatic precipitator technology 5: electrostatic precipitator Figure 6-5 dust emissions an d emission limits of Aust rian medium scale biomass appliances (Musil et al. 2006) For appliances of up to 6.8 MMBtu/h, cycl ones are the most commonly used emission control technology. This is due to the relati vely high emission limi ts of 150 mg/m at 13% O 2 (0.275 lb/MMBtu) in comparison to emissi on limits for combus tion units from 6.8 MMBtu/h (50 mg/m3 at 13% O 2 and 0.090 lb/MMBtu). Next to cyclones, electrostatic precipitators combined with cy clones are the second most common. No bag-house filters were used for appliances of this load range.



### 6.4.2 Data collection of Swiss automated biomass appliances (Hasler et al. 2000)

In a large data survey, approximately 1000 measurement results of 250 biomass appliances installed in Switzerland were co llected and analyzed. Untreated wood chips (LRV Kat. b), wood residues (LRV Kat. c) and urban waste wood (Altholz) were used. For comparison, a small number of data from solid wood appliances (LRV Kat. a) were also considered. Figure 6-6 shows the number of the considered wood chip appliances by heat load and fuel category.94 

### Performance of biomass installations

Figure 6-6 number of considered wood chip boilers by heat load and fuel category from 100 to 2000 kW (340-6820 MB tu/h); fuels: untreated w ood chips (LRV Kat. b), wood residues (LRV Kat. c) and urban waste wood (Altholz) how to read the graph: the first range of values (1 st field of the X-axis) includes all appliances in the range from 0 to 100 kW (0-340 MBtu/h) (Hasler et al. 2000) Figure 6-6 shows the CO emissi ons and the excess air ratio of the considered boilers with untreated wood chips fuel (LRV Kat. b).

Figure 6-7 CO emissions in mg/m3 at 11%O2 and the excess air ratio of the considered boilers with untreated wood chips fuel (LRV Kat. a) (Hasler et al. 2000) How to read the graph: the first range of values (1 st field of the X-axis) includes all measurement points in the rang e from 0 to 100 mg/m3 at 11%O 2 (0 to 90mg/m 3 at 12%O 2 ) respectively 0 to 1.2 Two thirds of the considered appliances ha ve CO emissions of < 250 mg/m3 at 11% O 2 (225 mg/m3 at 12% O 2 ); CO emissions > 1000 mg/m3 at 11% O 2 (900 mg/m3 at 12% O 2 ) are only measured in appliances with heat loads below 500 kW (1706 MBtu/h). The excess air ratio shows broad variations from 1.2 < λ < 5. Most of the appliances reach excess air ratios between 1.8 and 2.4 and abou t one third of the app liances are operated with excess air ratios > 2.4.95 

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Figure 6-8 shows the NO X emissions of all considered wood chip appliances (untreated wood chips (LRV Kat. b), wood residues (LRV Kat. c) and urban waste wood (Altholz)).

Figure 6-8 NO X

-emissions from wood chip appliances (fuels: untreated wood chips (LRV Kat. b), wood residues (LRV Kat. c) and urban waste wood (Altholz)) (Hasler et al. 2000) How to read the graph: the first range of values (1 st field of the X-axis) includes NO X emissions in the range from 0 to 50 mg/m3 at 11% O 2 (45 mg/m3 at 12% O 2 )

NO X emissions from untreated wood chips (L RV Kat. b) exhibit a nearly Gaussian distribution in the range from 100 to 400 mg/m3 at 11% O 2 . For urban waste wood, NO X emissions fall into a similar range. NO X emissions from wood residues (LRV Kat. c) fall into a broader range of up to 850 mg/m3 at 11% O 2 due to higher N contents in some wood residues appliances. Figure 6-9 shows the TSP/dust emissions of w ood chip appliances (untreated wood chips (LRV Kat. b), wood residues (LRV Kat. c) and of solid wood appliances (LRV Kat. a)).96 

### Performance of biomass installations

Figure 6-9 TSP/dust emissions from wood chips and solid wood appliances (fuels: solid wood (LRV Kat. a) untreated wood chips (LRV Kat. b), wood residues (LRV Kat. c)) How to read the graph: the first range of values (1 st field of the X-axis) includes dust emissions in the range from 0 to 25 mg/m3 at 11% O 2 (0-0.030 lb/MMBtu for solid wood and 0-0.037 lb/MMBtu) (Hasler et al. 2000) For all solid wood appliances (LRV Kat. a) the dust emissions are below 150 mg/m3 at 11% O 2 (0.185 lb/MMBtu); most dust loads are in the range from 25 to 50 mg/m3 at 11% O 2 (0.030 – 0.060 lb/MMBtu). For untreated wood chips (LRV Kat. b) and wood residues (LRV Kat. c) the averaged dust emissions are between 100 and 150 mg/m3 at 11% O 2 (0.150- 0.220 lb/MMBtu).



### 6.4.3 Emission factors

While measurement results of emissions are re lated to the input load, emission factors are related to the annual ener gy use. Therefore a direct co nversion from emissions to emission factors is not possible.
Emission factors are used to calculate th e national annual overall emissions of CO 2 , CO, NO X and other pollutants.
Calculation methods for emission factors va ry from country to country and depend strongly on the availabel data sources. Emission factors are supposed to represent the average annual emissions of the considered appliance type, including start- and stop emissions as well as summer and winter oper ation modes. Emission factors are derived as a function of plant size an d fuel type and are combined in different cla sses which differ from country to country. To calculate the an nual overall emissions, the shares of the diverse emission classes in the total en ergy consumption has to be determined.
In order to estimate nationwide emissions of diverse facilities, emission factors are specified for diverse facilities and fuels. Each country identifi es emission categories on its own, which means that emissions from biom ass combustion units are often mixed with emissions from other combusti on units. Table 7-4 shows emi ssion factors from Austria, Germany and Switzerland.97 

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Table 6-13 Austrian, German and Swiss emission factors

CO (lb/MMBtu) TSP (lb/MMBtu) NO X (lb/MMBtu) A USTRIA ( SOURCE : B OEHMER ET AL . 2007) biomass district heating/CHP facilities < 170 MMBtu/h wood chips including bark and wood residues 0.115 0.050 0.215

G ERMANY ( SOURCE : S TRUSCHKA ET AL . 2008) manual boilers > 170 MBtu/h 1.400 0.145 0.200 pellet boilers > 170 MBtu/h 0.255 0.075 0.230 wood chip boilers > 170 MBtu/h 2.305 0.150 0.370 S WITZERLAND ( SOURCE : H ASLER ET AL . 2000) solid wood (LRV Kat. a) 0.105 0.235 untreated wood chips (LRV Kat. b) 0.205 0.375 wood residues (LRV Kat. c) 0.215 0.665 urban waste wood (Altholz) 0.005 0.485

Table 6-13 clearly shows that each country looks at different co mbustion systems and fuel categories in order to calculate the national emission fact ors. Therefore, the comparability of these emission factors is limited. CO emissions vary from 0.100 to 2.300 lb/ MMBtu. While wood chip appliances are considered to reach low CO emissions in th e Austrian study, very high emissions are considered in the German study. Except for the Swiss emission factors fo r urban waste wood (0.005 lb/MMBtu), TSP emissions vary from 0.050 to 0.220 lb/MMB tu. Since TSP emissions depend on the emission control system installed, this variation seems reasonable due to different TSP control concepts and/or limits. For medium scale biomass applia nces, emission controls for NO X are usually not installed. Since NO X emissions result primarily from nitrogen in the fuel and the fuel quality is quite constant, NO X emission factors should be very similar. This is true for the emission factors shown in Table 6-13 where NO X emission factors are with in the range of 0.200 to 0.375 lb/MMBtu. Since wood residues and urban waste wood usually contain more nitrogen then the other biomass fuels, NO X emissions are thus higher for these appliances.



### 6.4.4 Summary

In two studies, emission data from medium scale biomass appliances were collected and analysed, whereby an emphasis was placed on NO X and dust emissions. In the Austrian study (Musil et al. 2006), biomass district heating/CHP facilities with heat loads of up to 17 MMBtu/h were analysed, wh ile the Swiss study (Hasler et al. 2000) considered all sizes of biomass appliances from residential stoves up to 17 MMBtu/h. In addition,98 

### Performance of biomass installations

emission factors are presented for Au stria (Boehmer et al. 2007), Germany (Struschka et al. 2008) and Switzerland (Has ler et al. 2000). Since emission factors are based on the annual heat demand, they canno t be directly compared with measured average emission values. CO emissions were only anaysed in the study from Hasler et al. 2000. It was shown that two thirds of the appliances emit CO < 225 mg/m3 at 12% O 2 . Emission factors for CO show very broad variations from 0.100 to 2.300 lb/MMBtu ( ≈ 70 to 1400 mg/m3 at 12% O 2 ). While the Austrian study shows averaged dust emissions (the following values are based on those for pellets) of about 0.097 lb/ MMBtu for appliances < 6830 Btu/h and about 0.060 lb/MMBtu for appliances > 6830 Btu/h, th e Swiss study results in averaged dust emissions of 0.150 – 0.200 lb/MMBtu for all fu els. Emission factors for dust vary from 0.050 to 0.220 lb/MMBtu. Since du st emissions depend greatly on the installed emission control technology, variations of these em issions may be attrib uted to different technologies. Average NO X emissions which were given in the studies vary from 150 to 220 mg/m3 for untreated wood. For wood residues the NO X emissions can be higher due to a higher nitrogen content of the wood fuel . Also the emission factors for NO X show high correlation. They are in a rang e from 0.200 to 0.375 lb/MMBtu ( ≈ 120 to 230 mg/m3 at 12% O 2 ) for untreated wood. For urban waste wood and wood residues , higher emission factors were fixed because of the higher nitrogen content of these fuels.99 

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# 7 Emission control technologies

For biomass appliances, emission control techno logies usually aim at the reduction of CO, OGC, dust and NO X emissions. Two different concepts for emission reduction, both primary and secondary measures have to be considered. While primary measures are implemented in the combustion process and/ or design of the combustion chamber, secondary measures are implemented after combustion process has ended, mostly adjacent to the boiler. Table 7-1 gives a su mmary indicating which reductions measures are available for small and medium to large scale biomass appliances. Table 7-1 overview of primary and second ary emission control technologies for biomass appliances scale small medium to large measures primary secondary primary secondary CO/OGC X - X - PM/dust X X X X NO X - - X X 1)

1) in biomass appliances NO X emissions are usually below the limit by primary measures



## 7.1 Emission control technology for PM/dust

Secondary measures for emission control in biomass appliances usually aim at the reduction of dust emissions. CO/OGC and NO X emissions are reduced below the limits by primary measures, as was shown above.



### 7.1.1 Small scale appliances

Due to stricter dust emission limits for small scale applianc es, special solutions for dust reduction in this load range were recently developed. These developments were mostly performed by small companies (business star t-ups) and manufacturers of small scale appliances, who were aware of this need. Smal l scale dust emission control is based on the technology of scrubbers and electrostatic precipitators. For heat loads > 650 MBtu/h, baghouse filter systems were also develo ped. Scrubber systems are always combined with flue gas condensation. Table 7-2 gives an overview of commercia lly available secondary dust reduction technology for small scale appliances; the cont act data of the manufacturers is available in the annex.100 

### Emission control technologies

Table 7-2 commercial small scale dust co ntrol technologies (summarised from Bischof 2008)

name heat load in MBtu/h efficiency

in % life time in years market launch sold systems price in US$ producer

S CRUBBER / CONDENSATION Hydrocube 50 – 3400 ≤ 70 15 - 20 2007 250 7400 Schraeder Abgastechnologie ≤ 85 2500 Power Condenser ≤ 170 75 1) 20 2008 20 3700 Powerkondens AG

2100 2) Carbonizer 75 - 1700 ≤ 86 > 20 2003 500 7400 3) Bschor GmbH

3400 4) Profitherm 50 - 500 50 > 20 - - 6600 3) BOMAT Heiztechnik GmbH E LECTROSTATIC PRECIPITATOR
Zumik®on ≤ 120 60 - 90 15 - 20 2006 > 140 1600 Rueegg Cheminée AG ≤ 120 ≤ 170 Trion ≤ 12000 90 15-20 2005 300 - 400 1500 - 3000 5) Trion Luftfiltersysteme GmbH OekoTube ≤ 240 90 15 2008 0 2000 OekoSolve AG Airbox ≤ 50 > 60 - 2008 10 2100 Spartherm B AGHOUSE FILTERKeramikfilter > 680 99 15 - 20 - - - Herding GmbH Filtertechnik Koeb Winkel 680 - 2000 < 10 mg/m3 - - - - Koeb & Schaefer GmbH

1) 50 without scrubber (condensing only) 2) 75 MBtu/h 3) 340 MBtu/h 4) 70 MBtu/h 5) depends on length

As Table 7-2 shows, dust removal technolo gies for small scale appliances were not introduced to the market before 2003. Furt hermore, the number of systems sold shows that this is a very young technology. A large number of prototypes are currently being tested. Scrubbers with flue gas conden sing and electrostatic precipit ators are available for very small heat loads. In general, electrostati c precipitators are less expensive and reach higher efficiencies. While for scrubber technology low return temperatures of about 85 °F are necessary for flue gas condensation, el ectrostatic precipitators have a maximum energy demand of 100 Btu/h (Bischof 2008).101 

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7.1.2 Medium scale appliances

For medium to large scale appliances, industri al solutions for emissi on control are used. These technologies are usually produced by plant or system manufacturers who are either specialists of flue ga s cleaning technology or build complete (energy) plants. Emission control technologies for medium and large scale appliances are individually fit to the design data of the biomass appliance. For medium scale biomass appliances the cyclones for dust removal are usually built by the boiler manufacturers themselves. Table 7-3 shows important European manufacturers of dust emission control technologies for me dium scale biomass appliances including their special fields. Table 7-3 European manufacturers for dust control technologies for medium scale biomass appliances( Brunner 2009, Lundgren 2009, Oravainen 2009)

company cyclone scrubber electrostatic precipitator baghouse filter Beth X X Scheuch GmbH X X X X VAS - Verfahrenstechnik & Anlagensysteme X

JM Stoftteknik AB X X Jaernforsen Energi System AB X Dust Control Systems Oy X X

In Table 7-4 an overview of prices for the dust removal technologies is given. Table 7-4 prices for medium to large sca le dust control tec hnologies (FNR 2005) technology heat load in MMBtu/h costs in US$/MBtu/h 0.3 – 1.7 7 – 11 multicyclone 1.7 – 6.8 4 – 7 3.4 – 6.8 20 - 30 6.8 - 17 15 - 22 baghouse filters or electrostatic precipitators 17 - 68 9 - 18 flue gas condensation 3.4 - 17 20 - 30102 

### European Biomass Fuel Requirements



# 8 European Biomass Fuel Requirements

8.1 General remarks

The development of solid bio-fuel standards in Europe is linked to the beginning of wood pellet production, which started in Sweden in the late 1980s. Other countries such as Finland, Denmark and Austri a followed in the early 1990s. In order to gain a common understanding between the manufacture rs and the users, codes of good practice, quality guidelines and later national standards have been developed. In Europe the first national st andards on pellet quality were developed in Sweden and Austria in 1998 – other countries followed. In general these fuel quality standards should:

• guarantee a common, offi cial, national quality of a certain bio-fuel

• ensure legal compliance and security for all involved market participants by defining responsibi lities and duties

• help to avoid problems at interface-poin ts along the supply chain by defining quality standards an d threshold values

• inform the consumers about quality char acteristics and therefore support the dissemination of a new biom ass fuel to the market. In addition to the national efforts, the deve lopment of quality guide lines was also pushed on the European level. The Technical Committee 335 (TC335) of the European Committee for Standardization (CEN) developed the European standards CEN/TC 14558:2003 Solid bio-fuels – Terminology, defini tions and descriptions as well as CEN/TC 14961:2005 Solid bio-fuels – Fuel specifications and classes which allow a differentiation of terminologically defined solid bio- fuels by means of defined parameters. Additionally, a series of te chnical standards dealing with determination methods of specific fuel properties or sampling meth ods have been worked out by the TC335. Table 8-1 lists all standards develo ped by this technical committee. Moreover, national standards fo r wood pellets logistics and st orage have been developed. The definition of quality parameters for lo gistics and storage was also found to be important so as to avoid any problems along the supply chain. Furthe rmore, the end-user should have a clear guideline of how to ensure product quality and user safety during the storage of bio-fuels.103 

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Table 8-1 List of standards developed by CEN/TC 335

S TANDARD REFERENCE T ITLE CEN/TS 14588:2004 Solid bio- fuels - Terminology, defi nitions and descriptions
CEN/TS 14774-1:2004 Solid bio-fuels - Meth ods for determination of moisture content - Oven dry method - Part 1: Total moisture - Reference method

CEN/TS 14774-2:2004 Solid bio-fuels - Methods for the determination of moisture content - Oven dry method - Part 2: Total moisture - Simplified method

CEN/TS 14774-3:2004 Solid bio-fuels - Methods for the determination of moisture content - Oven dry method - Part 3: Moisture in general analysis sample CEN/TS 14775:2004 Solid bio-fu els - Method for the dete rmination of ash content CEN/TS 14778-1:2005 Solid bi o-fuels - Sampling - Part 1: Methods for sampling
CEN/TS 14778-2:2005 Solid bio-fuels - Sampling - Part 2: Methods for sampling particulate material transported in lorries
CEN/TS 14779:2005 Solid bio-fuels - Sampling - Methods for preparing sampling plans and sampling certificates CEN/TS 14780:2005 Solid bio-fuels - Methods for sample preparation CEN/TS 14918:2005 Solid Bio-fu els - Method for the determ ination of calorific value CEN/TS 14961:2005 Solid bio-fuels - Fuel specifications and classes CEN/TS 15103:2005 Solid bio-fu els - Methods for the determ ination of bulk density
CEN/TS 15104:2005 Solid bio-fuels - Determination of total content of carbon, hydrogen and nitrogen - Instrumental methods
CEN/TS 15105:2005 Solid bio-fuels - Methods for determination of the water soluble content of chloride, sodium and potassium
CEN/TS 15148:2005 Solid bio-fuels - Method for the determination of the content of volatile matter

CEN/TS 15149-1:2006 Solid bio-fuels - Methods for the determination of particle size distribution - Part 1: Oscillating screen method using sieve apertures of 3,15 mm and above

CEN/TS 15149-2:2006 Solid bio-fuels - Methods for the determination of particle size distribution - Part 2: Vibrating screen method using sieve apertures of 3,15 mm and below
CEN/TS 15149-3:2006 Solid bio-fuels - Methods for the determination of particle size distribution - Part 3: Rotary screen method
CEN/TS 15150:2005 Solid bio-fuels - Methods for the determination of particle density
CEN/TS 15210-1:2005 Solid bio-fuels - Meth ods for the determination of mechanical durability of pellets and br iquettes - Part 1: Pellets
CEN/TS 15210-2:2005 Solid bio-fuels - Meth ods for the determination of mechanical durability of pellets and br iquettes - Part 2: Briquettes CEN/TS 15234:2006 Solid bio-fuel s - Fuel quality assurance
CEN/TS 15289:2006 Solid Bio-fuels - Determination of total content of sulphur and chlorine104 

### European Biomass Fuel Requirements

S TANDARD REFERENCE T ITLE CEN/TS 15290:2006 Solid Bio-fuels - Determination of major elements CEN/TS 15296:2006 Solid Bio-fuels - Calcul ation of analyses to different bases CEN/TS 15297:2006 Solid Bio-fuels - Determination of minor elements
CEN/TS 15370-1:2006 Solid Bio-fuels - Method for the determination of ash melting behavior - Part 1: Characte ristic temperatures method



## 8.2 European Bio-fuel standards

The technical standard EN14961 from 2005 defines the fuel quality classes and specifications for solid bio-fuels originating from the following sources:

• Products from agriculture and forestry,

• Vegetable waste from agriculture and forestry

• Vegetable waste from the f ood processing industry,

• Wood waste, with the exception of wood waste which may contain halogenated organic compounds or heavy metals as a result of treatment with wood preservatives or coatings

• waste originated from construction and demolition waste

• Fibrous vegetable waste from virgin pulp production and from production of paper from pulp, if it is co-incinerated at the place of production an d heat generated is recovered.

• Cork waste NOTE: Demolition wood is not included in the scope of this standard. Demolition wood is defined as “used wood arising from demoli tion of buildings or civil engineering installations” (CEN/TS 14588).



### 8.2.1 Origin of Bio-fuels

The first step in the classifica tion of solid bio-fuels accord ing to En14961 is based on the bio-fuel origin and source. In the hierarchical classification system, the main origin-based solid bio-fuel groups are:

• Woody biomass

• Herbaceous biomass

• Fruit biomass

• Blends and mixtures Each group has several subdi visions to allow for a more detailed specification.105 

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8.2.2 Specification of solid bio-fuels based on traded forms and properties

Solid bio-fuels are traded in many different forms (sizes and shapes). The European standard EN14961:2005 distinguis hes between solid bio-fuel trading forms, which are listed in Table 8-2. Table 8-2 Trading forms of solid bio-fuels and their preparation methods according to EN14961:2005.

F UEL NAME T YPICAL PARTICLE SIZE C OMMON PREPARATION METHOD Briquettes Ø>25 mm Mechanical compression Pellets Ø<25 mm Mechanical compression Fuel powder <1 mm Milling Sawdust 1 – 5 mm Cutting with sharp tools Wood chips 5 – 100 mm Cutting with sharp tools Hog fuel Varying Crushing with blunt tools Logs 100 – 1000 mm Cutting with sharp tools
Whole wood >500 mm Cutt ing with sharp tools Small straw bales Big straw bales Round straw bales 0.1 m3 3.7 m3 2.1 m3 Compressed and bound to squares Compressed and bound to squares Compressed and bound to cylinders Bundle Varying Lengthways oriented & bound Bark Varying Debarking residue from trees Can be shredded or unshredded Chopped straw 10 – 200 mm Ch opped during harvesting Grain or seed Varying No preparation or drying Shells and fruit stones 5 – 15 mm No preparation
Fiber cake Varying Prepared from fibrous waste by dewatering
The specifications of proper ties of these different form s are given in the annex.



### 8.2.3 Revision of EN14961:2005

Currently the EN14961 is under revision. The revised standard will not only define the specification of properties of solid bio-fuels, but al so include definite properties such as threshold values for different quality classes. The main intention of this step is to simplify the acquisition of appropriate fu els for end users. To cover al l kinds of solid biomass fuels as well as industrial fuels with lower quality requirements, a general section (part 1 of the revised EN14961) will be included in the revised st andard. The structure of prEN 14961-part 1 is very similar to the fi rst version of the standard from 2005 (see chapter 8.1):106 

### European Biomass Fuel Requirements

EN14961-1: Scope and general requ irements of solid bio-fuels Parts 2 – 6 of the new standard will define fuel quality classes and specifications explicitly for non-industrial bio-fuels:

• EN14961-2: Fuel quality classes and specifications of wood pellets

• EN14961-3: Fuel quality classes and sp ecifications of wood briquettes

• EN14961-4: Fuel quality classes and specifications of wood chips

• EN14961-5: Fuel quality classes an d specifications for firewood

• EN14961-6: Fuel quality classes and sp ecifications of non-woody pellets The current proposal prEN 14961 (statu s summer 2009) is show n in the annex.



## 8.3 European countries with national pellet standards

As previously mentioned, some European co untries developed nation al quality standards for solid bio-fuels – mainly for wood pellet s – long before a European standard was available. Some of these nation al standards do not only regu late the declaration of solid bio-fuels as the existing Euro pean standard EN14961:2005, but set definite specifications of properties (e.g. threshold values for contaminants) for high quality fuels. If the revised European Standard for solid bio-fuels is implemented, the national standards will be discarded.



### 8.3.1 Austria

In Austria, three standards referring to pe llets product quality, logistic quality and storage quality are available:

• OeNORM M 7135 - Compressed wood in natura l state or bark in natural state – pellets and briquettes - requirements and test specifications

• OeNORM M 7136 - Compressed wood in natural state - Wood pellets quality assurance in the field of logi stics of transport and storage

• OeNORM M 7137 - Compressed wood in natural state - Wood pellets – Requirements on pellets st orage at the end-consumer

8.3.1.1 OeNORM M 7135

This product standard covers wood pellets as well as briquettes. Pellets or briquettes must be made of virgin wood; up to 2 % of natural binding agents are allowed. Physical and chemical property requirements for the hi ghest quality class are listed in Table 8-3. The process of quality management includes internal and external audits. Manufacturers must perform internal quality assurance continuously, at least once a week by testing abrasion, water content, unit density and pressi ng aids. External audits include an initial inspection of the production plant and the sampling for labora tory tests, the control of the internal quality assurance system as well as the control of the labeling. Periodic, unannounced supervision is done once a year.107 

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8.3.1.2 OeNORM M 7136

In order to assure the qua lity of wood pellets produced according to OeNORM M 7135 during transport and storage, certain requ irements are specified under the OeNORM M 7136. Specifications encompass transp ortation and temporary storag e. These specifications are intended to assist pellet manufacturers, ha ulers and traders in avoiding mistakes to ensure customer satisfaction along the logistic chain.

8.3.1.3 OeNORM M 7137

This standard refers to the storage of w ood pellets produced according to OeNORM M 7135. It defines specifications and requirements of wood pell et storage for the end user. The standard addresses the end users of wood pellets as we ll as the manufacturers of pellets storage units.



### 8.3.2 Germany

In Germany there exist two standards, DIN 51731 for common pellets and briquettes and Din plus with higher requirements, especially for the use in automatically stoked pellet boilers.

8.3.2.1 DIN 51731

The German standard defines the physical and chemical property re quirements such as shape, unit density and the chemical composition of wood pellets. Specifications of the highest pellet quality class according to DIN 51731 are listed in Table 8-3.

8.3.2.2 DIN plus Standard

The DIN plus certification programme is used for high quality pellets intended for use in small scale household appliances. The specifications are mainly based on the Austrian standard OeNORM M7135, extended by the th reshold requirements for minor elements from the DIN 51731. External auditing is pe rformed once a year and is unannounced. Specifications of the DIN plus pellet quality label are listed in Table 8-3.

8.3.2.3 Certification of pellet logistics

“DIN-Gepruefter Fachbetrieb – Pelletlogistik” (DIN tested qualified enterprise pellet logistics) monitors the transport to the en d-costumer. The test criteria for suppliers include specifications for the storage depot, employees, internal and external monitoring and transport vehicles. The requirements ar e very similar to th e Austrian standard OeNORM M 7136.108 

### European Biomass Fuel Requirements

DIN CERTCO developed a new standard for the storage of pellets for end consumers based on the Austrian standa rd OeNORM M7137: “DIN gepr uefte Pelletlagerung” (“DIN certified pellet storage”).



### 8.3.3 Sweden

The Swedish standard SS187120: “Bio-fuels an d peat—Fuel pellets—C lassification” for wood pellets specifies properties and thresh old values for three different wood pellet quality classes. Specifications are listed in Table 8-3.



### 8.3.4 Italy

The Italian standard for solid bio-fuel CT I - R 04/5 was published in March 2004 and specifies the requirements for biopellets fo r energetic purposes and is related to the technical specification define d by CEN/TC335 (EN14961:2005). This standard classifies 4 catego ries of pellets and includes the origin of the raw material. Categories A1 and A2 (with / without additive s) determine the fuel quality classes and specifications for pellets originating from virgin wood, by-products and residues from the wood processing industry as well as chemic ally untreated used wood. Categories B and C encompass non-woody pellets produced from herbaceous biomass, fruit biomass and biomass blends and mixtures. Specifications of the CTI - R 04/5 are listed in Table 8-3.



### 8.3.5 United Kingdom

The Department of Trade and Industry of the UK published “Codes of Good Practice” for Bio-fuel pellets. These codes we re adopted by British BioGen members as a standard for products and services. The Codes of good prac tice will be supersed ed by the European standards for solid bio-fuels once they are pu blished. Specifications of the British code are listed in Table 8-3.



## 8.4 Additional environmental or quality labels

In addition to the official national standards, additional environmenta l or quality labels for pellets have been published. In some countries these quality labels act as a substitute for the lack of a national standard, while in ot hers they function as a supplement to the national standard indicating the best available product quality or special ecological products. Figure 8-1 shows logos of environmental and quality labels for solid bio-fuels.109 

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Figure 8-1: Environmental labels for solid bio-fuels
Austria – “Umweltzeichen (Environmental Label)”: The Federal Ministry for the Environment has devised a special environmen t label for biomass fuels, where only raw materials from natural wood are allowed. Nordic Ecolabelling – “Nordic Swan”: The Swan-labelling of pelle ts includes requirements on manufacturing methods, transportation an d storage. The aim is to identify the topgrade quality from an environmental perspect ive. The quality of the pellets shall mean that they are easy to use and thus meet th e end-users’ wishes wh en converting to a renewable energy source that reduces the emi ssion of greenhouse gases. In addition, the energy required to manufacture the pellets is limited to en sure the energy efficiency. Finally, the combustion shall not entail a health or environmental risk. Specifications of “Swan labeled” pellets are summarized in Table 8-3. Italy – “Pellet Gold” ( Pelletgold 2009 ): is the highest Italian wood fuel quality standard. The certification system is based on clear operation rules to determine that the product satisfies the requirement indicate d in the reference documents. The requirements of Pellet Gold are base d on CEN/TS 14961, DINplus, OeNORM M 7135 and the limits introduced by the American Pellet Fuels Institute (PFI).
An additional element in the Pellet Gold standard which is not present in other European certification systems was introduced by AIEL (Associazione Italiana Energie Agroforestali): the Formaldehyde content (H CHO) which is fundamental to verify the presence of health hazardou s materials such as glue an d varnish (see Table 8-3).110European BiomassFuel Requirements8.5Summary of European and national property specifications for bio-fuelsTable 8-3 Comparison of European and national woodpellet/briquette standardsand environmental labelsAUSTRIAEU GERMANYGREATBRITAINITALYSWEDEN

Property class Unit OeNORM M 7135 EN 14961:2005 Best pellet categories prEN 14961-2 A1-class DIN 51731 DIN plus BioGen - Code of good practice CTI – R 04/5 Pellet Gold SS 187120 Nordic Ecolabelling – Swan LabelDiameter, D andLength, Lin0.16≤D≤0.39D06 0.24± 0.02D06 0.24± 0.040.16≤D≤0.390.16≤D≤0.39D 0.16 –0.79D 0.24 –0.31-D -L≤4D0.24 ±0.02Moisture, Mas received,w-%≤10 M10≤10 M10≤10≤12≤10≤10≤10≤10≤10≤10Ash, a w-% dry≤0.5A0.7≤0.7A0.5≤0.5A0.7≤0.7≤1.5≤0.5≤1.0≤0.7≤1.0≤0.7≤0.5Mechanicaldurability, DU orabrasion (100 –DU)as received,w-%≥97.7DU97.5≥97.5DU97.5≥97.5-≥97.7 -≥97.7≥97.7 -≥97.5Fines at factorygate in bulktransportw-% -F1.0≤1,0F1.0≤1,0- -≤0,5 - -≤0,8≤1,0111ReportAUSTRIAEU GERMANYGREATBRITAINITALYSWEDENFines in smallbags at factorygate (at packing)Fines in smallbags (at deliveryto end-user)F0.5≤0,5F1.0≤1,0Additives w-%≤2Type andamountto bestatedType andamountto bestatednone≤2 - none≤2Type andamountto bestated-Net calorificvalue, Qas received,MBtu/lb≥7.74 -Q16.5≥7.107.53 –8.39≥7.74≥7.27≥7.27≥7.27≥7.27≥7.35Gross density lb/oz≥0.073 - -0.065 –0.091≥0.073 - -≥0.075 - -Bulk density, BD 103·lb/oz - -BD600≥39.0- -≥39.040.3-746.8≥39.0≥39.0D6: 39.0-45.5D8: 45.5-50.7Nitrogen, N w-% dry≤0.3N0.3≤0.3N0.3≤0.3≤0.3≤0.3 -≤0.3≤0.3 -≤0.3Sulphur , S w-% dry≤0.04 -S0.05≤0.05≤0.08≤0.04≤0.03≤0.05≤0.05≤0.08≤0.04Chlorine, Cl w-% dry≤0.02Cl0.03≤0.03Cl0.02≤0.02≤0.03≤0.02≤0.08≤0.03≤0.03≤0.03≤0.02112European BiomassFuel RequirementsAUSTRIAEU GERMANYGREATBRITAINITALYSWEDENArsenic, As mg/kg dry - -≤1≤0.8≤0.8 - -≤0.8 - -Cadmium, Cd mg/kg dry - -≤0.5≤0.5≤0.5 - -≤0.5 - -Chromium, Cr mg/kg dry - -≤10≤8≤8 - -≤8 - -Copper, Cu mg/kg dry - -≤10≤5≤5 - -≤5 - -Lead, Pb mg/kg dry - -≤10≤10≤10 - -≤10 - -Mercury, Hg mg/kg dry - -≤0.1≤0.05≤0.05 - -≤0.05 - -Nickel, Ni mg/kg dry - -≤10 - - - -- -Zinc, Zn mg/kg dry - -≤100≤100≤100 - -≤100 - -Sodium; Na w-% dry - - - - - - -≤0.03 - -EOX (extract.org. halogens)mg/kg dry - - -≤3≤3 -≤1 - - -Formaldehyde mg/100g dry - - - - - - -≤1.5 - -Ash meltingbehavior, DToF - -DT1200>2190- - -Temperature to bestatedIT≥2370HT≥2550113 

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# 9 Heat storage (accumulator tank)

9.1 Introduction

Function An accumulator tank is a heat-insulated steel tank in which a heat carrier (mostly water) circulates when it is loaded. Temperature stra tification results from the density difference between cold and hot water (cold water has a higher density than hot water). Hot water from the boiler is introduced into the buffer accumulator at the top. The design of the inlet ensures that turbulence is low and that the temperature stratification is not destroyed. High flow temperatures result in good temperature stratification and high heat storage capacity.

Types Different types of buffer accumulators are av ailable depending on th e use of the buffer accumulators as heat storage devices with or without integrated hot service water storage and/or integration of a dditional heating sour ces, e. g. solar energy (Figure 9-1).

Figure 9-1 Different types of bu ffer (adapted from FNR I 2007)
The capacity of the hydraulic installations can be reduced wh en using a combined storage unit for heating and hot water. Major drawback s are however the reduction of the volume of the buffer accumulator and energy losses in summer, when only hot water is needed.

Application area Although modern solid wood bo ilers are able to modulate their operation load from 100 to 50%, the use of heat storage is strong ly recommended by manufacturers of the boilers, by R&D institutions and authorities.114 

### Heat storage (accumulator tank)

Pellet and wood chip boilers can even modu late their operation load from 100 to 30%. Nonetheless, some manufacturers recommend the integration of accumulator tanks in these heating systems as well in order to incr ease the annual effici encies of the heating systems. The research field on annual efficiencies in residential homes is quite young in Europe; there are however some ongoing research ac tivities. BE 2020+ for example is currently working on the development of a test stand method for th e determination of system efficiency and emi ssion factors of small-scale biomass combustion systems.



## 9.2 Dimensioning

9.2.1 General aspects

The necessary volume of the accumulator ta nk is influenced by several factors:

• range of capacity of the boiler (only full load of variable heat load)

• volume of the fuel stor age in the boiler (for manually stoked boilers)

• nominal heat load of the boiler

• Calorific value and ener gy density of fuel

• effective temperature difference in the heat storage

• demand for convenience

In Table 9-1 the benefits and disadvantages of large and sm all heat storage vessels are summarised. Table 9-1 benefits and drawbacks of large and small heat storages (adapted from FNR III 2007) benefits disadvantagelarge heat storage(one fuel charge canbe accumulated) o boiler can always be operated at full load (low emission operation)

o reduction of combustion

intervals

o one combustion period with

maximum fuel charge covers heat demand for a couple of days in spring/autumn o high investments costs for large heat storage

o heat losses by accumulator tank

(even if tank is well insulated)small heatstorage o low investment costs o boiler will be operated in part load (which means high er emissions)

o emergency shut-downs may occur

if heat load of boiler is larger than heat demand (which results in very high emissions for a short time)

o reduction of boiler durability115 

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In general, the dimensioning of the accumula tor tank is an optimisation function of investment costs and boiler performance.



### 9.2.2 Sizing guidelines

For the sizing of heat storage vessel for solid wood boilers, many guidelines can be found in literature. These guidelines are related to the nominal heat load of the boiler and vary from approximately 10 to 30 l/MBtu/h and 340 to 1010 fl oz/MBtu/h respectively (FNR II 2007, Struschka et al. 2004...). Struschka et al. 2004 analysed the emissions of solid wood boilers with heat loads of 100 MBtu/h which were operated with and without accumulator tanks in field tests. Table 9-2 and Figure 9-2 show the majo r results of this study. Table 9-2 average annual CO emission fact ors for solid wood boilers (adapted from Struschka et al. 2004) control concept: modulated nominal load only volume of heat storage average annual CO emissions in mg/MBtu 0 l 0 fl gal 4 384 4 384 750 l 200 fl gal 1 431 1 444 1 500 l 400 fl gal 1 110 1 003

CO with modulation CO without modulation OGC with modulation OGC without modulation

volume of heat storage in l Figure 9-2 development of CO and OGC em issions depending on the volume of the heat storage Heat storage vessels with larger dimensions give rise to lower annual emission factors and solid wood boilers, which are operated solely at nominal load, emit less than modulated boilers. The characte ristics of the curve in Figure 9-2 shows that significant reductions of emissions will be reached for storage volumes between 0 to 2,500 l (650 fl gal).116 

### Heat storage (accumulator tank)

The authors of this study iden tify 2,250 l (600 fl gal) to be the optimum volume for the heat storage vessel, which corresponds to 20 l/MBtu/h and 750 fl oz /MBtu/h respectively. In spite of these common guidelines, FN R III 2007 recommends to dimension the heat storage vessel according to the volume of th e fuel storage of the boiler and not according to the heat load of the boiler due to the fact that the volume of the fuel storage vessel determines the amount of heat which is produced during a combustion cycle, and not the nominal heat load of the boiler.



### 9.2.3 EN 303-5

The EN 303-5 requests manufacturers for boilers with manual stoking to specify how the amount of heat generated can be dissipated. The most probable solution is to install a heat storage vessel. For the sizing of a heat storage vessel for ma nual fed boilers, the following equation is given:



### ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛

− ⋅ ⋅ ⋅ = min 

### 3

. 0 1 5

. 4 Q Q Q T V H N B AT

V AT Accumulator tank capacity l Q N Nominal heat output MBtu/h T B Burning period h Q H Heating load of the premises MBtu/h Q min Minimum heat output MBtu/h

In order to convert the volume of the heat storage vessel from liter to gallons, a factor of 0.264 must be multiplied with V AT .117 

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# 10 Energy from non-Woody Biomass Fuels

10.1 Emissions and efficiencies of solid non wood biomasses

Carvalho et al. 2007 summarized the main cha llenges of using agri cultural fuels in residential boilers as follows: “... agricultural fuels have, in general, certai n physical and chemical properties that may induce problems during combustion. In addition to their low heating value, on average 5% to 10% lower than wood, they have higher ash contents, lower melting points of the ash and higher concentrations of nitrogen, su lphur and chlorine than typical wooden fuels (Werther et al. 2000). Large ash quantities in connection with low as h melting points can cause disturbances by the formation of depo sits or slags in combustion systems not prepared for agricultural fuels. High concen trations of sulphur, nitrogen and chlorine, intensify the emissions of SO 2 , NO x and chlorine compounds respectively (Werther et al. 2000). Chlorine and sulphur, besides promotin g the formation of deposits, are also involved in corrosion reactions of metals (Bryers 1996, van Loo, Koppejan 2002).” In extensive tests, combustion behavior of diverse agricultural pe lletized biomasses was analyzed by the BE 2020+. Results of these tests are discussed afterwards.



### 10.1.1 Fuels & fuel properties

For the analysis of the combustion behavior of agricultural pellets, most relevant biomasses for the Austrian market were ch osen. Altogether, 6 different fuels – hay, maize, miscanthus, straw, vineyard pruning and wheat bran – were considered. In Table 10-1 the fuels and their mo st relevant properties with regard to combustion are shown as well as average pr operties of wood fuels. Table 10-1 fuel properties of the investigated pellets and av erage values for wood fuel (Wopienka et al. 2007)fueldiameter(in)GCV d.b(MBtu/lb)water(%)ash(%) d.b.volatilematter(%) d.b.nitrogen(%) d.b.sulfur(%) d.b.softeningtemperature(°F)

wood (spruce) 8.6 0.20 0.10 0.04 2480 hay 0.236 7.5 7.5 7.40 73.1 1.08 0.13 2085 maize (whole crop) 0.236 8. 2 8.7 3.39 80.2 0.89 0.09 1670 miscanthus 0.236 8.2 8.7 3.26 82.9 0.24 0.03 1850 straw 0.236 8.0 7.9 5.71 74.8 0.66 0.10 1470 vineyard pruning 0.236 9.0 8.4 2.70 - 0.39 - 1465 wheat bran 0.315 8.3 13.7 5.70 76.8 3.04 0.24 1780118 

### Energy from nonWoody Biomass Fuels

The ash content of agricultural pellets is 10 to 20 times higher than the ash content of wood pellets, the nitrogen content is 5 to 10 times and the sulfur co ntent is even 10 to 30 times higher. In comparison to average wood fuels, the soft ening temperature of agricultural fuels is 550 to 1100 °F lower. These differences clearly influence the comb ustion process and therefore emissions and efficiencies.



### 10.1.2 Emissions

In Figure 10-1 the average CO emissions and their deviations are shown for the analyzed bio-fuels and Figure 10-2 exhi bits the average dust emissi ons including deviations for these fuels.

0 50 100 150 200 250 300 350

123456CO-emissions in mg/MJ

Miscanthus Maize Vineyard pruning Wheat bran Straw Hay

Figure 10-1 average CO emissions including their deviation of th e investigated fuels (1 mg/MJ ≈ 1.5 mg/m2 at 12% O 2 )(Wopienka et al. 2007)

0 20 40 60 80 100 120 140 160

Hay Maize (whole crop) Miscanthus Straw Vineyard pruning Wheat branParticle emissions in mg/MJ

Figure 10-2 average dust emissions including their deviation of the investigated fuels; 1 mg/MJ = 0.0023 lb/MMBtu (Wopienka et al. 2007)119 

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The emission values of Figure 10-1 and Figu re 10-2 show a week correlation of CO and dust emissions. If CO emissi ons are low, dust emissions will also be rather low. Miscanthus and vineyard pruning, which have a quite low ash content (Table 10-1), reach the lowest dust and CO emissi ons. Hay exhibits the highest ash content. It reaches the highest CO emissions, but its dust emissions are relatively low. A simple and reliable correlation of fuel properties and CO- and dust emissions co uld not be found. Figure 10-3 exhibits the NO X and SO 2 -Emissions of the considered bio-fuels depending on the nitrogen respectively su lfur content of the fuels.

Figure 10-3 NO X

and SO 2 emissions depending on the nitrogen respective sulphur content of the investigated bi omasses (Wopienka et al. 2007) In this case, quite clear correla tions can be found: if the nitrogen respectively the sulphur content is low, NO X and SO 2 emissions will be low as well and the other way round.



### 10.1.3 Efficiencies

In Figure 10-4 the CO-excess air ratio characteristic of the in vestigated fuels for the test boiler is shown. The CO-excess air ratio char acteristic shows at wh ich range of excess air the minimum CO emissions are reached in the test boiler.

m a

i z e

m i s ca n t h u s W h e a t b r a n h a y

V

i n e y d

. p r

.

s t r a w

Figure 10-4 correlation of CO emissions an d excess air ratio for the considered fuels ((Wopienka et al. 2007)120 

### Energy from nonWoody Biomass Fuels

The optimum excess air ratio varies from a pproximately 1.5 for maize to approximately 1.9 for wheat bran. Straw shows a very broad characteristic. If the fuels are burnt at opti mum conditions (low CO), di fferent excess air ratios are needed. The higher the excess air ratio, the lower the efficiency of the boiler, because more combustion air is sucked through the boiler and heat losses in the flue gas are increased therefore. Hence, the boiler will reach higher effici encies with maize than with wheat bran, if it is operated at optimum combustion conditions.



### 10.1.4 Slagging & Corrosion

If non wood bio-fuels are used for combustion , the slagging behavior of these bio-fuels has to be considered. Otherwise molten ash or slag can lead to an emergency shutdown of the combustion unit and cause severe da mage in the primary combustion chamber (grate, lining...).

Figure 10-5 ash (left) and ash lumps (right) from combustion of agricultural fuels In Figure 10-6 the slagging te ndency of the considered fuel s (except for hay) is shown. In order to evaluate the slagging tendency, a mash analysis of the ash was carried out to determine the fraction of all particles in the ash with a diameter > 5.6 mm (0.22 in).

44,3

25,4

0,3 0,2 34,8

0 10 20 30 40 50 60

1Fraction of slag particles (> 5,6 mm) in %

Miscanthus Maize (whole crop) Vineyard pruning Wheat bran Straw 1470°F

1670°F

1850°F 1465°F 1240°F 5,7%

3,4%

3,3% 2,7% 5,7% Softening temp.

Ash content

Figure 10-6 Slagging tendency of the investigated fuels (Wopienka et al. 2007)121 

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Straw, wheat bran and maize sh owed a higher slag forming tendency than miscanthus or vineyard pruning pellets. From the combustion of hay almost no slag was found in the ash. Basically, fuels with higher ash conten t combined with lower softening temperature tend to from a bigger fraction of molten lumps. Next to the slagging phenomena also corrosion of the boiler (heat exchanger, ceramics, grate, combustion chamber) has to be cons idered when burning non wood bio-fuels. Chlorine and sulphur are involved in corrosion reactions, therefore the combustion conditions (temperature, atmosphere) have to be observed. Figure 10-7 shows two examples of corrosion attacks wh ile burning agricultural fuels.

Figure 10-7 corrosive attack of refractory materials after operat ion with grain (left) and corrosion of metal after straw combustion



## 10.2 Summary

Due to their high availability, non-wood biom asses are very attractive fuels. They may however have certain general physical and ch emical properties that may cause problems during combustion. In addition to the possible increase of NO X , HCl, SO 2 , and other emissions in comparison to wood biomass, hi gher ash contents combined with lower ash melting temperatures and corrosive effects negatively influence the failure rate and durability of the boilers.122 

### Literature



# Literature

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K ACHELOFENVERBAND 2007 Oesterreichischer Kachelofenverband, www.kachelofenverband.at , November 2007
K ALTSCHMITT , H ARTMANN 2001 Kaltschmitt M., Hartmann H. (Hrsg.): Energi e aus Biomasse, Grun dlagen, Technik, Verfahren; Springer Verlag; Berlin, 2001
K LIPPEL 2007 Klippel N., Nussbaumer Th.: Wirkung von Verbrennungspartikeln – Vergleich der Gesundheitsrelevanz von Holzfeuerung und Dieselmotoren, Bundesamt fuer Energie, Bern 2007
KWB 2007 KWB Kraft und Waerme aus Biomasse GmbH, www.kwb.at , November 2007
L EUCKEL , R OEMER 1979 Leuckel W., Roemer R.; Schadstoffe aus Verbrennungsprozessen; VDI-Bericht Nr. 346; VDI Verlag Duessel dorf; Duesseldorf, 1979
L OO , K OPPEJAN , 2002 Loo S. van, Koppejan J. (ed.): Handbook of Biomass Combustion and Co-Firing. Enschede, 2002
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### Annex



# Annex

1. European standards – preview

1.1. EN 12815

1.2. EN 13229

1.3. EN 13240

1.4. EN 15250

2. Test report for small scale appliance

2.1. Solid wood appliance

2.2. Pellet appliance

3. Commissioning report

4. Test details of biomass appliances

4.1. TOP 25% models – solid wood boilers

4.2. TOP 25% models – pellet boilers

4.3. TOP 25% models – wood chip boilers

4.4. All models – combined technology boilers

4.5. All models – pellet stoves

4.6. All models – solid wood stoves

5. Model list of German masonry- and room-heaters

5.1. EN 13229 certified prefabricated heaters

5.2. EN 13240 certified wood stoves

6. Manufacturers of biomass appliances

6.1. Manufacturers considered in creating TOP 25% list

6.2. Other manufacturers from Austria, Germany and Scandinavian countries

6.3. Manufacturers of medium and large scale biomass appliances from Austria, Germany and Scandinavian countries

6.4. Manufacturers considered in 5.1 and 5.2

7. Manufacturers of dust emission control technology for small scale appliances

8. Specifications of prop erties of biofuels

9. Revision of EN 14961