Wood fuel quality requirement and impact on emissions

Transcription

1 VTT TECHNICAL RESEARCH CENTRE OF FINLAND LTD Wood fuel quality requirement and impact on emissions European Federation of Chimney-Sweeps 25 August 2017, Peurunka, Finland Eija Alakangas, principal scientist, VTT

2 Firewood quality

3 Quality requirements for firewood International firewood standard: EN ISO :2014 Quality classes A1 (first class firewood) A2 (second class firewood) B (third class firewood, mainly for boilers) Normative (mandatory) quality requirements Origin and source (e.g Stem wood) Wood species (e.g. beech, birch, spruce, pine) Diameter, D (thickness), (e.g. D15, 5 D 15 cm) Length, L (e.g. L25, 25 cm ± 2 cm) Moisture, M (e.g. M20, 20 w-%, wet basic) Volume or weight (e.g. 2 loose m 3 or 400 kg) 28/08/2017 3

4 EN ISO Diameter (Classes A1, A2) Diameter, D (A1 and A2) D2; 2 cm D5; 2 cm D 5 cm D15; 5 cm D 15 cm D15+; D > 15 cm (actual value to be informed) 85% of the firewood should be kept in specified diameter property class. Stoves/fireplaces; recommended D15. Cookers and ignition wood: recommended D2 and D5. 28/08/ Photo: VTT (D2, D5, D10, D15)

5 EN ISO Diameter (Class B) Diameter, L (class B) D15; 5 cm D 15 cm D15+; D > 35 cm 85% of the firewood should be kept in specified diameter property class Class B is used mainly in log wood boilers. Photo: VTT (D2, D5, D10, D15) 28/08/2017 5

6 EN ISO Length Length, L (Classes A1 and A2) L20; 20 cm ± 2 cm L25; 25 cm ± 2 cm L33; 33 cm ± 2 cm L50; 50 cm ± 4 cm L ± 5 cm Length, L (Class B) L30; 20 cm ± 2 cm L33; 33 cm ± 2 cm L40; 40 cm ± 2 cm L50; 50 cm ± 4 cm L ± 5 cm It is allowed to have 15% firewood shorter than requested length including the limit value. 28/08/ Photo: VTT (L20, L25 and L33)

7 EN ISO Moisture Moisture, (wet basis), M Classes A1 and A2: to be selected M20 or M25 Class B: to be selected M20, M25 or M35 Moisture (dry basis), U Voluntary Class A1 and A2: select U25 or U33 Class B: select U33 or U54 Moisture (M) should not be less than 12 w-% and not higher than 25 w-%, because dust emissions increase. Recommended moisture M20. Moisture,U (dry basis), % Optimum moisture w-% boilers w-% stoves OPTIMAL w-% Moisture, M (wet basis) % Photos: VTT 28/08/2017 7

8 EN ISO Volume or weight stacked m 3 loose m 3 Stacked m3 3 loose m 3 equals to 2 stacked m 3. Drawing: VTT Weighting firewood sack before delivery. Photo: Forestry Centre, Finland 28/08/2017 8

9 EN ISO Informative (voluntary) Energy content, E kwh/loose m 3 kwh/stacked m 3 kwh/kg Drying Natural seasoning Artificial drying (hot or cold air) Decay and mould (A1 No visible decay) Proportion of split volume (A1 90% split of pieces) Splitting and cutting firewood Photo: Ari Erkkilä Cut-off surface, left A2 and B, right: A1 class, Photo: VTT The cut-off surface (A1 even and smooth, cut by a chainsaw or a circular saw) 28/08/2017 9

10 How to use classification Stove and boiler manufacturer can select the firewood quality class (A1, A2 and B) Classification can be marked in the product Product declaration Stove Heat retaining stove EN Firewood Oven ready firewood EN ISO (A1) If firewood is packed information can be market in the package. Loose firewood: use a product declaration 28/08/

11 FIREWOOD PRODUCT DECLARATION BASED ON STANDARD EN ISO :2014 Producer: Eijan Laatupilke Oy Contact information: Ketunleipä 10, Jyväskylä, puh Delivery amount:. loose m 3 or. kg Production date: Delivery date:.. Raw material origin (EN ISO ). Quality class (EN ISO ): A1 A2 B Wood spiecies: birch, alder, spruce,pine, mixed Length: L cm Diameter: D.cm Moisture, wet basis: (M) w-% Amount of split wood: A1 > 90 %, A2 > 50 %, B % piecies Cut-off surface: even and smoot uneven Mould: A1 no visible mould and decay, A2 < 5 % piecies, B % piecies Energy content:. kwh/kg Whole delivery lot, total... kwh Drying: natural seasoning, cold air drying, warm air drying 28/08/

12 Firewood quality impact on emission 12

13 Total PM emission Moisture content and dust emissions (PM) Particle size distribution 90 mg/nm 80 3 (13 % O 2 ) Staubemission >10µm 2,5-10µm 1-2,5µm <1µm 50 1 % 1 % 4 % 94 % 43 1 % 2 % 4 % 93 % 57 1 % 1 % 4 % 94 % 57 1 % 1 % 4 % 94 % PM emissions and particle size distribution from a tiled stove insert (7 kw) studied by TFZ If moisture is lower than 12 w-% or higher than 20 w-% PM emissions increase n=4 12 % n=2 18 % n=2 23 % n=2 30 % Fuel moisture Wassergehalt content (M) Source: TFZ-Report No. 22 download: 28/08/

14 Particle emission Gaseous emission Fuel moisture (M) impact of beech wood 10,000 CO OGC mg/nm³ 8,000 (13 % O 2 ) 1,500 Undiluted flue gas Diluted flue gas 6,000 mg/nm³ (13 1,200 % O 2 ) 4,000 2, % 45 Fuel moisture content % 45 Fuel moisture content test fuel shape 8 kw stove Hartmann Schön Source: TFZ-Report No. 36 download: 14

15 Particle emission Fuel moisture (M) impact of spruce & beech wood 300 mg/nm³ 250 (13 % O 2 ) Beech Spruce Undiluted flue gas rain % 30 Fuel moisture content 8 kw stove Source: TFZ-Report No. 36 download: Hartmann Schön, TFZ 15

16 Particle emission Log size impact on total PM emission 300 mg/nm³ ( % O 2 ) Stove 1 Stove 2 Stove 3 Undiluted flue gas Stove 1 Stove 2 Stove 3 0 n=3 5x5 cm n=3 7x7 cm Log size n=3 9x9 cm Source: TFZ-Report No. 36 download: Schön Hartmann 16

17 Particle emission Fuel load impact on total PM emission 1,000 mg/nm³ 800 (13 % O 2 ) 600 Stove 1 Stove 2 Stove 3 Stove 1 Stove 2 Stove 3 Undiluted flue gas Hartmann Schön Low load Nominal Overload n=3 7x7x1 Low load n=3 7x7x3 Nominal load Fuel load 161 n=3 7x7x5 Overload 112 Source: TFZ-Report No. 36 download: 17

18 Total PM emissions with top-down & bottom-up ignition top-down bottom-up top-down bottom-up Roomheater A Roomheater B top-down bottom-up Source: Bioenergy 2020 & TFZ (from bereal-project ) Reichert Schön Hartmann 18

19 Cumulated CO-emission CO emission during stove ignition: top-down versus bottom-up 160 g bottom-up ignition "top-down" ignition :00 0:10 0:20 0:30 0:40 0:50 h 1:00 Burning time Source: Hans Hartman All trials were performed with 8 kw chimney stove with grate, results are mean values of three replications, all were started from cold stage 19

20 Wood chip quality

21 21 Wood chip standard EN ISO Classes A1, A2, B1 and B2 For domestic boilers class A1 is recommended Classes A1 and A2 for clean virgin wood (1.1, 1.2.1) No short rotation wood (class e.g. willow), if fertilized by sewage sludge (belongs class B1) Normative (mandatory) quality requirements Origin and source (e.g. stem wood 1.1.3) Particle size, P (e.g. P31) Moisture, M (wet basis), % (e.g. M30) Ash, A (dry basis), % (e.g. A1.0) Bulk density, BD (e.g. 250 kg/m 3 ) Informative (voluntary) quality requirements Net calorific value (wet basis), Q, MJ/kg or kwh/kg (e.g. 3,5 kwh/kg) Alternatively energy density, E, kwh/loose m 3 (e.g. 850 kwh/loose m 3 ) 28/08/

22 Particle size of wood chips EN ISO Class Fines (< 3.15 mm), w-% Main fraction (min. 60 w-%) mm Coarse fraction, w-% (mm) Maximum length of longest particle, mm P16S <P < 16 <6% >31,5 mm < 45 mm < 2 P31S 10 3,15 <P< 31,5 <6% >45 mm <150 mm < 4 P45S 10 3,15 <P < 45 <10% >63 mm < 200 mm < 6 Max. cross sectional area of the coarse fraction, cm 2 Screen sizes used 3.15, 8,16, 31.5, 45, 63 and 100 mm. Usually not measured Classes P16S and P31S suitable for small boilers 28/08/

23 Particle size distribution - example Fraction Screen size Mass, w-% Measured (requirement) Class 1 Fine < 3,15 mm 6,9 6,9% ( 10%) P31S Main 3,15 8 mm 11, mm 28, % ( 60 %) P31S 16 31,5 mm 42,1 31,5 45 mm 10,8 P31S Coarse mm mm 0 < 100 mm 0 Max. cross sectional 3,4 cm 2 area of the coarse fraction 0.2% 45 mm, all less 63 mm (P31S, 6 % 45 mm and all less than 150 mm) P31S 1 The lowest possible class should be stated. Only one class shall be specified for wood chips Particle size of this delimbed stem wood chips is P31S according to EN ISO , because coarse fraction is more than 6%. For small boilers homogenous particle size is recommended. 28/08/

24 24 Bulk density BD (kg/m 3 ) A1-class: BD150; BD200; BD250; A2-class: BD150; BD200; BD250 BD300; Wood species and moisture affect BD Usually measured only for small district heating plants by 50 litre container for each load because trade is based on volume. 28/08/

25 25 Wood chip standard EN ISO Moisture (M) A1-class; M10 and M25, A2 class; M35, Measured each load (ten 3 litre samples) Ash (A) A1-class; A1.0, stemwood chips belongs to this class A2-class; A1.5 Net calorific value as received (Q) Important for wood chip trade when based on energy unit (e.g. /MWh) Net calorific value can be calculated from net calorific value on dry basis and moisture content. Net calorific value on dry basis can be found from literature, good average is 18.8 MJ/kg (5.2 kwh/kg) Net calorific value as received depend on moisture content and is for seasoned stem wood chips around 12.4 MJ/kg 3.5 kwh/kg, when moisture is 30%). 1 MWh = kwh 28/08/

26 Wood chip quality impact on emission 26

27 Wood chip quality effects Too dry wood chips Back fire problems Boiler will be burnt (damaged) In partical load difficult to keep smooth combustion Too wet wood chips Heat demand is not received Output of flue gas fan is not sufficient Can be suitable fuel for a partial load what about emissions? Unburn particles in ash Unhomogenous particle size Problems with fans Inregular combustion, some part burn good and some part badly Boiler efficiency is not optimal Fine particles can directly go to flue gas fan 28/08/

28 Influence of moisture content on flue gas emissions WG1 Wood chips, MC moisture content, TPM = total particle matter Source Schön et al. :Influence of wood chip quality on emission behaviour in small-scale wood chip boilers, Biomass Conv. Bioref., March /08/

29 Influence on full and part load to flue gas emissions WG1 Wood chips, MC moisture content, TPM = total particle matter Source Schön et al. :Influence of wood chip quality on emission behaviour in small-scale wood chip boilers, Biomass Conv. Bioref., March /08/

30 Additional information Alakangas, E., et al Properties of indigenous fuels in Finland, VTT Technology 272, 222 p.+ app. 23 p. Alakangas, E. et al Efficient and environmentally friendly biomass heating. Firewood production and use in fireplaces and stoves, _Fire_wood_production_and_use_in_stoves_VTT_1_ (2).pdf 28/08/

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