Selection and integration of high temperature catalysts into a stove

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22 Workshop: Wood Stoves 22 - Towards high

1 Selection and integration of high temperature catalysts into a stove Thomas Brunner, Christoph Mandl, Ingwald Obernberger Project ERA-NET Bioenergy Stove 22 Workshop: Wood Stoves 22 - Towards high efficiency and low emissions Stockholm (Sweden), 13 th of June 217

2 Contents Background and objectives Catalysts for wood stoves Methodology High temperature catalysts applied Description of the chimney stove and the test stand Test run procedure Results of the test runs performed Metal based catalyst Foam ceramic catalyst Conclusions and recommendations 2

3 Background and objectives (I) In the recent 15 years biomass based room heating systems became more and more popular and the development towards low emission appliances is progressing. In particular, a further development and optimisation of stoves is necessary in order to achieve low emissions of atmospheric pollutants and particularly to meet stricter emission limits. Secondary measures like oxidation catalysts are already applied for emission reduction of wood stoves. As these catalysts are usually installed in the flue gas duct downstream the stove the emission reduction potential is limited due to: The comparably low temperatures at stove outlet The expected slow heat-up of the catalyst at this position. Almost no emission reduction during start-up where typically the highest emissions occur 3

4 Background and objectives (II) Therefore, a catalyst implementation into a stove may have several advantages: Light-off temperature of catalyst can be reached in short time High operation temperatures of the catalysts may support tar and soot reduction At high operation temperatures a better VOC reduction is expected Reduced risk of tar and soot deposits However, suitable materials for a high temperature application are needed as well as a higher pressure drop has to be considered. As usually primary measures are primarily applied as a tool to reduce emissions, a combination of primary and secondary measures may be a suitable approach for low emission wood stoves. Based on this approach different high temperature catalysts have been integrated into a new low emission stove concept at different positions and their basic suitability has been evaluated. 4

Catalysts for wood stoves (I) The most common

catalyst differs from that of the reactants:

structure of solid catalysts consists of

the structure solid catalysts for emission

5 Catalysts for wood stoves (I) The most common catalytic procedure to reduce emissions from stoves is the heterogeneous catalysis. At this type of catalysis the phase of the catalyst differs from that of the reactants: catalyst solid reactants gaseous The basic structure of solid catalysts consists of metals (most common is iron alloy) or ceramics (e.g. aluminium oxide, zirconium oxide) Regarding the structure solid catalysts for emission reduction can be divided into: Packed beds Monoliths (honeycomb or foam structure) Networks/ wire meshes

Catalysts for wood stoves (II) Components of solid catalysts: Substrate: Carrier material

The structure of the catalyst is defined by the material and production process of the

Washcoat: To increase the surface of the catalyst a washcoat (powder suspension of metal

surface is impregnated/coated with catalytically active components.

6 Catalysts for wood stoves (II) Components of solid catalysts: Substrate: Carrier material for the washcoat and the active metal. The structure of the catalyst is defined by the material and production process of the substrate. Washcoat: To increase the surface of the catalyst a washcoat (powder suspension of metal oxides) is spread and dried on the substrate. Substrate Washcoat Active metal Active metal: The surface is impregnated/coated with catalytically active components. Thereby the following main activities of the metals occur: Rh > Pd > Pt oxidation of CO Pt > Rh > Pd oxidation of VOC Rh > Pd > Pt reduction of NO At high operation temperatures also metals like Ni, Cu and Mg can achieve considerable conversion rates.

Methodology (I) Description of high temperature catalysts applied Based on an evaluation of catalysts available on the market and the experiences of test runs already

ceramics Active metal: Pt The catalysts applied have been tested at different positions of the low emission stove: Metal based honeycomb catalysts installed at the

7 Methodology (I) Description of high temperature catalysts applied Based on an evaluation of catalysts available on the market and the experiences of test runs already performed two different types of high temperature catalysts have been investigated: Metal based honeycomb catalysts Active metals: Pt, Pd Catalytically coated foam ceramics Active metal: Pt The catalysts applied have been tested at different positions of the low emission stove: Metal based honeycomb catalysts installed at the outlet of the post combustion chamber mounting position I Foam ceramics with and without catalyst installed at the outlet of the main combustion chamber mounting position II 7

Methodology (II) Description of the chimney stove applied Specially adapted low emission logwood chimney stove with 2 flue gas pathways downstream the post combustion chamber Flue gas fan

8 Methodology (II) Description of the chimney stove applied Specially adapted low emission logwood chimney stove with 2 flue gas pathways downstream the post combustion chamber Flue gas fan Window purge air Steel plate Main combustion chamber Primary air Post combustion chamber mounting position II foam ceramics mounting position I honeycomb catalysts Air box Catalyst Dummy 8

9 Chimney Methodology (III) Description of the test stand TSP measurement Flue gas temperature measurement according to EN 1324 Chimney draught O 2, CO, CO 2, OGC, CH 4 O 2, CO, CO 2, OGC (Dummy) Temperature upstream foam ceramic Pressure drop over foam ceramic Temperature downstream foam ceramic O 2, CO, CO 2, OGC CH 4, (Catalyst) Temperature combustion chamber T before catalyst Pressure drop over catalyst mounting position II - foam ceramic mounting position I - honeycomb catalyst 9

10 Methodology (IV) Test run procedure Performance of test runs with different high temperature catalysts at a low-emission logwood stove Long-term (2 or 3 weeks) operation of the stove with each catalyst Performance of dedicated testing campaigns with emission measurements One operation day consists of 8 successive batches (5 full load + 3 partial load) General operation conditions Constant draught of 12 Pa over the stove Test fuel: hardwood (beech) without bark, moisture content: wt% w.b. Performance of gaseous and TSP emission measurements Gaseous emissions (CO, OGC, CH 4, O 2 ): continuous measurement from before ignition of batch 1 until the end of test run TSP emissions (according to VDI 266): over the whole batch (from closing the door until opening it again) 1

11 CO [mg/nm³] Reduction [%] CO [mg/nm³] Reduction [%] Results of test runs performed (I) Honeycomb catalyst mounting position 1 Trends of CO emissions and CO reduction at the 1 st day of operation 1, 8, 6, 4, 2, Batch 1 (ignition) Batch 2 Batch 3 Batch 4 Batch 5 Batch 6 PL Trends of CO emissions and CO reduction at the 11 th day of operation Batch 1 (ignition) Batch 2 Batch 3 Batch 4 Batch 5 Batch 6 (PL) Batch 7 PL Batch 7 (PL) Batch 8 PL 1:4 11:4 12:4 13:4 14:4 15:4 16:4 17:4 18:4 CO - Catalyst CO - Dummy CO - Reduction Batch 8 (PL) :45 11:45 12:45 13:45 14:45 15:45 16:45 17:45 18:45 CO - Catalyst CO - Dummy CO - Reduction Explanations: Emissions related to dry flue gas and 13 vol% O

12 Temperatures [ c] Temperatures [ C] Results of test runs performed (II) Honeycomb catalyst mounting position 1 Trends of flue gas temperatures at the 1 st day of operation Batch 1 (ignition) Batch 2 Batch 3 Batch 4 Batch 5 Batch 6 PL Batch 8 PL Batch 7 PL 9 T combustion chamber T catalyst inlet T flue gas :4 11:4 12:4 13:4 14:4 15:4 16:4 17:4 18:4 Trends of flue gas temperatures at the 11 th day of operation Batch 1 (ignition) Batch 2 Batch 3 Batch 4 Batch 5 Batch 6 (PL) Batch 7 (PL) Batch 8 (PL) 9 T combustion chamber T catalyst inlet T flue gas :45 11:45 12:45 13:45 14:45 15:45 16:45 17:45 18:45 12

13 Results of test runs performed (III) Honeycomb catalyst mounting position 1 Influence of CH 4 on OGC reduction Batch 3 Batch 4 Batch :4 13:1 13:4 14:1 14:4 15:1 15:4 16:1 OGC reduction [%] non-methane-ogc-reduction [%] CH4 in OGC [vol - %] CH 4 is hardly converted by the catalyst Explanations: Results of test run at day 1; OGC reduction (green), non-methane OGC reduction (blue); % CH 4 in OGC = (ppm CH 4 / ppm OGC) * 1 13

14 Results of test runs performed (IV) Honeycomb catalyst mounting position 1 2 O2 - Dummy [vol% d.b.] O2 - Catalyst [vol% d.b.] Press. drop cat. [Pa] ,5 1,25 1, Nominal load CO - Dummy [mg/mj] CO - Catalyst [mg/mj] CO reduction [%] 12 1,5 OGC - Dummy [mg/mj] OGC - Catalyst [mg/mj] OGC reduction [%] Day 1 Day 6 Day 11 Day , O2 - Dummy [vol% d.b.] O2 - Catalyst [vol% d.b.] Press. drop cat. [Pa] , Partial load CO - Dummy [mg/mj] CO - Catalyst [mg/mj] CO reduction [%] OGC - Dummy [mg/mj] OGC - Catalyst [mg/mj] OGC reduction [%] Day 1 Day 6 Day 11 Day Manual cleaning of the catalyst with compressed air after 11 th day of operation 14

Results of test runs performed (V) Honeycomb catalyst mounting position 1 Catalyst before the test runs

after 11 days of operation (view at inlet) Significant and partly very hard to remove fly ash deposits

analyses as well as SEM/EDX analyses clearly indicated that the catalyst has been de-activated by

15 Results of test runs performed (V) Honeycomb catalyst mounting position 1 Catalyst before the test runs (view at outlet) Catalyst after 11 days of operation (view at inlet) Catalyst after manual cleaning after 11 days of operation (view at inlet) Significant and partly very hard to remove fly ash deposits pressure drop increased Manual cleaning showed no effect on the emission reduction efficiencies Chemical analyses as well as SEM/EDX analyses clearly indicated that the catalyst has been de-activated by aerosol deposits (condensation of mainly K 2 SO 4 and KCl), which have blocked the active centre of the catalysts 15

16 CO [mg/nm³] OGC [mg/nm³] CO [mg/nm³] OGC [mg/nm³] Results of test runs performed (I) Foam ceramic mounting position 2 Trends of CO and OGC emissions at the 3 rd day of operation 5, Batch1 (ignition) Batch2 Batch3 Batch4 Batch5 Batch6 (PL) Batch7 (PL) Batch8 (PL) 5 4, 3, 2, 1, 8:3 9:3 1:3 11:3 12:3 13:3 14:3 15:3 CO flue gas [mg/nm³] OGC flue gas [mg/nm³] Trends of CO and OGC emissions at the 18 th day of operation Batch1 (ignition) Batch2 Batch3 Batch4 Batch5 Batch6 (PL) Batch7 (PL) Batch8 (PL) 5, 4, 3, 2, 1, 1: 11: 12: 13: 14: 15: 16: 17: 18: CO flue gas [mg/nm³] OGC flue gas [mg/nm³] Explanations: Emissions related to dry flue gas and 13 vol% O

17 flue gas temperature flue gas temperature Results of test runs performed (I) Foam ceramic mounting position 2 Trends of flue gas temperatures at the 3 rd day of operation 9 Batch1 (ignition) Batch2 Batch3 Batch4 Batch5 Batch6 (PL) Batch7 (PL) Batch8 (PL) 6 3 8:3 9:3 1:3 11:3 12:3 13:3 14:3 15:3 T upstream foam ceramic [ C] T downstream foam ceramic [ C] T flue gas [ C] Trends of flue gas temperatures at the 18 th day of operation 9 Batch1 (ignition) Batch2 Batch3 Batch4 Batch5 Batch6 (PL) Batch7 (PL) Batch8 (PL) 6 3 1: 11: 12: 13: 14: 15: 16: 17: 18: T upstream foam ceramic [ C] T downstream foam ceramic [ C] T flue gas [ C] 17

18 Results of test runs performed (II) Foam ceramic mounting position 2 35 O2 flue gas [vol% d.b.] Press. drop foam ceramic [Pa] , CO flue gas [mg/mj] CO reduction % Nominal load OGC flue gas [mg/mj] OGC reduction % Day 3 Day 11 Day 18 without foam ceramic TSP [mg/mj] Day 3 Day 11 Day 18 without foam ceramic 1 1, O2 flue gas [vol% d.b.] Press. drop foam ceramic [Pa] Partial load CO flue gas [mg/mj] CO reduction % OGC flue gas [mg/mj] OGC reduction % Day 3 Day 11 Day 18 without foam ceramic TSP [mg/mj] Day 3 Day 11 Day 18 without foam ceramic Manual cleaning of the catalyst with compressed air after 11 th day of operation 18

Results of test runs performed (III) Foam ceramic mounting position 2 Foam

ceramic after 18 days of operation Some fly ash deposits on the surface of the

fly ash deposits could be removed and the pressure drop over the foam ceramic

19 Results of test runs performed (III) Foam ceramic mounting position 2 Foam ceramic before the test runs Foam ceramic after 11 days of operation Foam ceramic after 18 days of operation Some fly ash deposits on the surface of the foam ceramic slight increase of pressure drop By manual cleaning most of the fly ash deposits could be removed and the pressure drop over the foam ceramic could be reduced again Manual cleaning showed no effect on the emission reduction efficiencies 19

20 Conclusions and recommendations (I) The implementation of a high temperature catalyst at the outlet of the post combustion chamber (temperature range of about 5 C) is not recommended as tests showed unstable reduction efficiencies. Decreasing reduction efficiencies over time can most likely be attributed to catalyst de-activation as a consequence of blocking of active centers caused by aerosol condensation. High temperature catalysts, which are mounted at the outlet of the main combustion chamber (temperature range 6-8 C) showed sufficiently high emission reduction efficiencies regarding CO (69 73%) and OGC (27 38%) and seem basically to be suitable for logwood stoves. However, the emission reduction efficiency decreased for the catalysts over the testing period of about 1 hours of operation and manual cleaning showed no positive effect 2

21 Conclusions and recommendations (II) Tests over a whole heating period would be needed to be able to evaluate the long-term performance of catalysts in wood stoves as well as the possible need of cleaning. Furthermore, catalysts need enough surface to achieve a sufficient reduction efficiency. This is usually provided by narrow channels which cause a certain pressure drop. The pressure drops are usually too high for an operation of the stove with natural draught only. Therefore, either a flue gas fan is needed if a catalyst should be integrated or the dimension of the catalyst needs to be increased. In general, the mounting position of integrated catalysts has to be carefully evaluated in terms of operating conditions (existing temperature), materials used and the availability to clean the catalyst. 21

22 Thank you for your attention Hedwig-Katschinka-Straße 4 A - 82 Graz, Tel.: mailto:mandl@bios-bioenergy.at

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