DEPOSITS AND EMISSIONS DURING THE COCOMBUSTION OF BIODIESEL RESIDUE WITH COAL AND BIOMASS IN A CFB PILOT Nevalainen H., Leino T., Tourunen A., Hiltunen M. Coda Zabetta E. 9th International Conference on Circulating Fluidized Beds Hamburg, May 2008 VTT TECHNICAL RESEARCH CENTRE OF FINLAND Contents FTIR sampling port Gas analysator • Introduction • Experimental Bag filter Deposit probe port Gas cooling Observation port To stack Sampling port Secondary cyclone • Results Zone 4 Primary cyclone Sampling port FTIR sampling port Sampling port • Temperature profiles Zone 3 Sampling port Sampling port • Emissions Zone 2 Sampling port • Deposit formation • Bed behaviour • Conclusions Zone 1 Fuel container 1 and 2 Secondary air Additive container Nitrogen M Primary gas heating PC control and data logging system Sampling port 2 Air VTT TECHNICAL RESEARCH CENTRE OF FINLAND Introduction • CO2 reduction → Ratio of biomass is increasing in heat and power production → Sets challenges for boiler availability, emission performance and efficiency • Production of biodiesel is increasing and use of bio-based residues should be exploited • E.g. rapeseed expeller from rapeseed biodiesel process • Combusting rapeseed expeller solves waste problem in biodiesel production through waste-to-energy technology • Reduces CO2 emissions of the boiler 3 VTT TECHNICAL RESEARCH CENTRE OF FINLAND Experimental FTIR sampling port Gas analysator Bag filter Deposit probe port Gas cooling Observation port To stack Sampling port Secondary cyclone Moisture (w-%) Rapeseed expeller Bituminous coal Wood chips 11.1 4.1 34.5 Proximate analysis, w-% on dry basis Zone 4 Primary cyclone Sampling port FTIR sampling port Sampling port Zone 3 Ash, 815 °C 6.5 12.5 0.8 Volatile content, Lower heating value, dry (kJ/kg) 75.7 29.7 84.6 19780 Fuels 27980Mixture ratio 18590 in energy basis % Sampling port Ultimate analysis, w-% on dry basis Sampling port 1 Zone 2 H Sampling port 2 Zone 1 Fuel container 1 and 2 C Secondary air Additive container N S 3 O (calc.) Nitrogen Cl 4 M 5 Primary gas heating Air 6 PC control and data logging system Sampling port 7 Rapeseed expeller 49.9 Polish coal 6.5 Rapeseed expeller 7.15 Polish coal 0.74 Rapeseed expeller 29.2coal Polish 0.020expeller Rapeseed Wood chips Rapeseed expeller Wood chips Rapeseed expeller Wood chips Rapeseed expeller 72.4 13 / 87 50.6 4.3 6.1 1.32 22 / 78 0.23 0.75 <0.02 8.6 33 / 67 >42.2 0.130 0.008 11 / 89 19 / 81 38 / 62 100 4 VTT TECHNICAL RESEARCH CENTRE OF FINLAND Temperature profiles • Bed temperature on the same level with additional cooling • Increase of biomass assosiated with increase in combustion after sec. air. 1000 950 o Temperature [ C] • To avoid ash melting external cooling was used for • Expeller 38% + wood • Expeller 100% Rapeseed 13%, Coal Rapeseed 22%, Coal Rapeseed 33%, Coal Rapeseed 11%, Wood Chips Rapeseed 19%, Wood Chips Rapeseed 38%, Wood Chips Rapeseed 100% Secondary air 900 850 800 750 0 1 2 3 4 5 6 7 8 Distance from the grid [m] 5 VTT TECHNICAL RESEARCH CENTRE OF FINLAND Emissions 12.0 H2O NO N2O SO2 700 with Wood chips 600 with Coal 10.0 H2O [%] • Used air stagging not optimal in biomass combustion for NO reduction • Meaurements show effect of - large S content of expeller - large N content of expeller 500 8.0 400 6.0 300 4.0 200 2.0 100 0.0 0 13 % 22 % 33 % 11 % 19 % 38 % Proportion of Rapeseed expeller 6 100 % N2O, NO, SO2 [ppm] • CO decreased with decreasing ratio of coal • CO spikes appeared • at long intevals in coal - expeller tests • continuosly in wood - expeller tests 14.0 → possible fuel feed mixing problems VTT TECHNICAL RESEARCH CENTRE OF FINLAND Deposit formation • To simulate the superheater area windward temperature set to 480°C • Ash appearence -coal + expeller: the gray, loose, easily removable -wood chips + expeller: the ash was compact and close to white -100% expeller: granular and dence • The deposition rate calculated based on the weights of the deposit sleeves before and after each test. • With wood deposition rate larger the for 100% expeller eventhough, wood lowers the ash flow in the reactor After 78/22% coal/rapeseed expeller test After 100% rapeseed expeller test 7 VTT TECHNICAL RESEARCH CENTRE OF FINLAND Expeller 100% • Enrichment of clorine in the deposits → indicates increased risk of chlorine induced hot corrosion at least when fired alone or with wood Wood/expeller 62/38% • Elemental mapping from SEM-EDX: • Potassium and phosphorous similarly distributed • Presense of K and P minor in coal cofiring • K and P increase with increasing share of expeller in wood co-firing Coal/expeller 67/33% Composition of deposits 8 VTT TECHNICAL RESEARCH CENTRE OF FINLAND Slagging • Reactor was examined after the tests • Co-firing with coal did not cause problems • With wood ships severe slagging occured over the sec. air feed -Slag formation started with 38%/62% -mixture but increased significantly with 100% expeller coal / rapeseed expeller wood / rapeseed expeller 9 VTT TECHNICAL RESEARCH CENTRE OF FINLAND Bed agglomeration • For expeller clear agglomeration effect with wood and alone • No signs of agglomeration with coal co-firing • Elemental mapping by SEM-EDX: - Ca, P and S similar distribution • Low melting point of potassium phosphate could explain observed slagging and bed agglomeration. • Whether P and K reacted to phosphates, can not be confirmed based on SEM analysis Coal / Expeller 67/33% Wood / Expeller 62/38% Expeller 100% 10 VTT TECHNICAL RESEARCH CENTRE OF FINLAND Conclusions 1/2 • Temperature above secondary inlet was more difficult to control in co-combustion with wood chips, due to higher amount of volatiles • Decrease of CO from coal by rapeseed expeller suggests an effective option to reduce CO from coal • NOx emissions increase with increasing share of expeller • In full scale increase on NOx and SOx would likely to be reduced with air stagging (NOx, temperature) and in-furnace capture with limestone (SOx) 11 VTT TECHNICAL RESEARCH CENTRE OF FINLAND Conclusions 2/2 • Increse of rapeseed expeller increased the fouling rate with both coal and wood chips • The enrichment of the chlorine, typical also for other biomass fuels indicates a slightly inreased risk of chlorine-induced hot corrosion • Expeller was found to have clear agglomeration effect over the bed material when fired alone or with wood chips, but no agglomeration was found with coal • Potassium and phosphorous content in the deposit incresed consistently with the ratio of expeller in the biomass co-firing cases Coal co-firing favourable technology of firing rapeseed residues into energy 12 VTT TECHNICAL RESEARCH CENTRE OF FINLAND Thank you for your attention! 13 VTT TECHNICAL RESEARCH CENTRE OF FINLAND Moisture (w-%) Rapeseed expeller Bituminous coal Wood chips 11.1 4.1 34.5 Proximate analysis, w-% on dry basis Ash, 815 °C 6.5 12.5 0.8 Volatile content, Lower heating value, dry (kJ/kg) 75.7 29.7 84.6 19780 27980 18590 Ultimate analysis, w-% on dry basis C 49.9 72.4 50.6 H 6.5 4.3 6.1 N 7.15 1.32 0.23 S 0.74 0.75 <0.02 29.2 8.6 >42.2 0.020 0.130 0.008 O (calc.) Cl Ash composition, (ashing at 550 °C), w-% in ash Na 0 1.1 0.3 K 18.9 2.3 11.1 Ca 10.7 3.8 29.9 Mg 5.4 1.1 3.3 Al 0 13.5 0.2 Fe 0.2 4.5 0.5 Si 0 18.7 0.4 P 17.9 0.5 1.9 Ti 0 0.7 0 S 3 5.1 1.7 Cl 0.3 0 0 14