FINE PARTICULATE EMISSIONS FROM STATE-OF-THE-ART SMALL-SCALE AUSTRIAN PELLET FURNACES CHARACTERISATION, FORMATION AND POSSIBILITIES OF REDUCTION

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1 F PR FR -F-H-R - R P FR HRR, FR D P F RD homas runner, Georg ärnthaler, ngwald bernberger nstitute for Resource fficient and ustainable ystems.: +43 (316) 4813; FX: +43 (316) : thomas.brunner@tugraz.at HPG:

2 g a ontents R G H nstitute for Resource fficient and ustainable ystems ntention of the project presented Definitions Formation of fine particulate emissions during small-scale biomass combustion ethodology applied Results from measurements onclusions and outlook 2

3 g a ntention of the project () R G H nstitute for Resource fficient and ustainable ystems During the last years fine particulate air pollution (P 1 ) has become a topic of broad public awareness since it is well known that small particulates can cause severe health effects. he directive 1999/3/ limits P 1 concentrations in the ambient air. n many uropean regions these P 1 limits of 5 µg/m³ (daily mean value) are more often exceeded than the 35 times per year allowed. Domestic heating is one main P 1 emission source besides traffic and industry. herefore, fine particulate emissions of small-scale biomass combustion plants have to be investigated, evaluated and minimised. 3

4 g a ntention of the project () R G H nstitute for Resource fficient and ustainable ystems n order to gain more comprehensive information about fine particulate emissions from small-scale biomass combustion plants, a joint project of the ustrian ioenergy entre, Graz, and the nstitute for Resource fficient and ustainable ystems, has been started. he project is performed in close cooperation with 9 ustrian small-scale biomass furnace and boiler manufacturers. 4

5 g a Definitions classification of atmospheric aerosols () R G H nstitute for Resource fficient and ustainable ystems P 1 P 2.5 Δm/Δlog D P 1 nuclei mode accumulation mode Diameter [µm] fine mode particles coarse mode particles 5 ource: Wilson and uh, 1977

6 g a P emissions from biomass combustion plants R G H nstitute for Resource fficient and ustainable ystems xample: dm/dlog(dp) [mg/m³] Results from test runs at a grate-fired combustion plant (nominal boiler capacity: 44 kw th ) wood chips bark waste wood aerosols P 1 coarse fly ashes ,. dp [µm ae.d.]

7 g a erosol formation in small-scale biomass furnaces R G H nstitute for Resource fficient and ustainable ystems coarse fly ashes l, 2 4, 2 3 etc. 2, H 2,, x H y aerosols small amounts of coarse fly ashes are emitted Gas phase reactions (l, 2 4, Zn etc.) ooling of the flue gas Gas phase burn-out ( 2, H 2,, x H y ) condensation coagulation coarse fly ashes are entrained from the fuel bed, transported with the flue gas and partly precipitated in the furnace and the boiler 7, a,, l, Zn, Pb, d, x H y, H 2, etc bottom ash nucleation release of primary particles, soot formation

8 g a ethodology applied R G H nstitute for Resource fficient and ustainable ystems est runs at small-scale pellet furnaces test stand field tests easurement and determination of total fly ash emissions particle size distribution and concentration of aerosols - low pressure impactor (P) - electrical low pressure impactor (P) flue gas composition ( 2,,, x ) operation mode of the furnace (furnace temperature, load, flue gas temperature) 8

9 g a ystems tested R G H nstitute for Resource fficient and ustainable ystems state-of-the-art ustrian pellet combustion technologies nominal boiler capacity: 15 to 2 kw all furnaces were equipped with automatic ignition systems staged combustion automatic boiler cleaning systems automatic de-ashing systems different combustion technologies (underfeed stoker, overfed burner, horizontally fed burner) equipped with water cooled or insulated combustion chambers fully automated process control including λ-sensors or temperature sensors 9

10 g a easurements performed R G H nstitute for Resource fficient and ustainable ystems Furnace 1: test stand measurements at different load conditions Furnace 2: test stand measurements at different load conditions Furnace 3: field measurements at full and partial load Furnace 4: field measurements at full load Furnace 5: test stand measurements at different load conditions Furnace 6: test stand measurements at different load conditions 1

11 g a Results total fly ash emissions R G H nstitute for Resource fficient and ustainable ystems P emissions [mg/m³] full load partial load furnace 1 furnace 2 furnace 3 furnace 4 furnace 5 furnace 6 xplanations: measurements performed with the total dust measurement equipment; partial load: 5% of the nominal load all results related to dry flue gas and 13 vol% 2 ; mean values and standard deviations of at least 3 measurements 11

12 g a Results total fly ash, P 2 and P 1 emissions at full load R G H nstitute for Resource fficient and ustainable ystems P emissions [mg/m³] otal F P 2 P 1 furnace 1 furnace 2 furnace 3 furnace 4 furnace 5 furnace 6 xplanations: measurements performed with the P; all results related to dry flue gas and 13 vol% 2 ; 12 mean values and standard deviations of at least 5 measurements

13 g a Results particle size distributions during full load operation R G H nstitute for Resource fficient and ustainable ystems Particle mass size distributions Particle number size distributions dm/dlog(dp) furnace 1 furnace 2 furnace 3 furnace 4 furnace 5 furnace 6 dn*1 13 /dlog(dp) furnace 1 furnace 2 furnace 3 furnace 4 furnace 5 furnace dp [µm ae.d.] dp [µm ae.d.] xplanations: measurements performed with the P (mass) and the P (number); all results related to dry flue gas and 13 vol% 2 ; ae.d.: aerodynamic particle diameter; 13 mean values of at least 5 measurements

14 g a Results unstable load conditions: start up R G H nstitute for Resource fficient and ustainable ystems P1 [mg/m³] [mg/m³] , 3, 2, 1, 1:45 11: 11:15 1:45 11: 11: [mg/m³] xplanations: P data from P measurements; F furnace temperature; 2 related to dry flue gas; P 1, and related to dry flue gas and 13 vol% 2 ; 2 [vol%], P [kw] P F :45 11: 11: F [ ]

15 g a Results unstable load conditions: load changes R G H nstitute for Resource fficient and ustainable ystems P1 7,5 5, 2, [mg/m³] [mg/m³] (vol%) P1 [mg/m³] xplanations: Results of a 5h measurement period with several load changes; P data from P measurements; 2 related to dry flue gas; P 1, and related to dry flue gas and 13 vol% 2 ; (vol%)

16 g a Results chemical composition of the P 1 fraction inorganic part R G H nstitute for Resource fficient and ustainable ystems 8 [wt% (d.b.)] full load partial load a l Zn xplanations: mean values and standard deviations of at least 3 analyses per furnace investigated; partial load: 5% of the nominal load values normalised to 1% without and 16

17 g a Results structure and chemical composition of fine particulates R G H nstitute for Resource fficient and ustainable ystems xplanations: DX-scan from area marked in the -image; particle sampling during full load operation with a 3-stage impactor; 17 i originates from the filter material; picture width: 2 µm

18 g a onclusions () R G H nstitute for Resource fficient and ustainable ystems verage total dust emissions during stable full and partial load operation: <2 mg/m³ (dry flue gas and 13 vol% 2 ) respectively <13.3 mg/j V he average number concentration of small particulate emissions (particles <1µm) is in the range of 1 13 particles/m³ ore than 95% of the total dust emissions are P1 ompared with literature data available for older pellet furnace technologies (emissions up to 1 mg/m³), a considerable reduction of particulate emissions due to improved combustion conditions and therefore a considerable reduction of organic aerosols has been observed. 18

19 g a onclusions () R G H nstitute for Resource fficient and ustainable ystems o significant differences concerning the particulate emissions with respect to full load and partial load operation different furnace technologies applied test runs at the test stand and field measurements During start-up as well as during load changes (change from partial to full load), operation conditions with insufficient gas phase burnout and therefore, with increased particle formation occur. 19

20 g a onclusions () R G H nstitute for Resource fficient and ustainable ystems t stable operation conditions and sufficient gas phase burnout: aerosols formed mainly consist of, a,, l as well as Zn and show only minor concentrations of organic. concerning these operation conditions, mainly the chemical composition of the fuel influences the mass of aerosols formed. onsequently, the combustion of fuels with low concentrations of aerosol forming species (e.g. clean wood pellets) causes considerably lower particulate emissions than the combustion of alkaline, and l rich fuels (e.g.: herbaceous fuels). 2

21 g a onclusions (V) R G H nstitute for Resource fficient and ustainable ystems During unstable operation conditions causing insufficient gas phase burnout: fine particle emissions significantly increase for short operation periods. the concentration of the organic carbon content in the fine particulates significantly increases. onsequently, advanced process control technologies and appropriate furnace designs should be developed and applied in order to keep operation periods at insufficient gas phase burnout conditions as short as possible. 21

22 g a Recommendations R G H nstitute for Resource fficient and ustainable ystems wo relevant primary measures for particulate emission reduction in small-scale pellet boilers can therefore be recommended. 22 tilisation of fuels with low concentrations of inorganic aerosol forming species (e.g. softwood pellets). pplication of advanced furnace designs and process control systems. he substitution of old wood furnaces by state-of-the-art pellet combustion technologies should be enforced and maybe even subsidised by the state respectively regional governments. For a further reduction of particulate emissions below the range of about 15 mg/m³ secondary measures (e.g. small-scale P systems or scrubbers) are needed which are currently under development but not yet sufficiently tested.

23 g a WDG R G H nstitute for Resource fficient and ustainable ystems he financial support of the ustrian plus program and Zukunftsfonds of the tyrian state government is gratefully acknowledged 23