Catalytic combustion of gasified biomass for gas turbine applications

Abstract: Catalytic combustion is an ultra-low emission technology forgas turbines. In parallel to the ongoing development andcommercialization of catalytic combustors fired by naturalgas,an increasing interest is aimed towards renewables, such asgasified biomass. Gasified biomass is a low-heating value (LHV)fuel, rich in hydrogen and carbon monoxide, with apotentiallyhigh level of ammonia. Consequently, specialconsiderations must be taken in the development of catalyticgas turbine combustors with gasified biomass as fuel.The first part of the present thesis reports onfundamental phenomena related to catalyticcombustion ofgasified biomass for gas turbine applications. Successfuldevelopment of the catalyst involves knowledge of both gasturbine technology and gasification of biomass.Therefore, basicconsiderations applied to integration of gasification and gasturbinetechnology are discussed. Moreover, formation ofnitrogen oxide emissions in combustion isdiscussed and asummary of the appended papers is given. Finally, recentdevelopments incatalytic combustion in gas turbines arereviewed in Paper I in the present thesis.The second part of the present thesis, Papers II-VIII,concerns preparation and testing ofpotential combustioncatalysts. The objectives of this work have been focused onpreparationmethods and development of thermally stable andactive hexaaluminate-based catalysts (Papers II, IV-VII),ignition of the LHV-gas (Papers III-VII), conversion offuel-bound nitrogen(Papers III, V-VI) and deactivation bythermal treatment and sulphur poisoning (PapersVI-VII).Moreover, enhancing catalytic activity for totaloxidation of methane through doping ofceria has been studied(Paper VIII). The experimental investigation included activitytesting inbench-scale monolithic, single-channel annular andfixed bed reactors, and characterisationsuch as BET, XRD, SEM,EDX, XPS and SIMS.In conclusion, lanthanum hexaaluminate impregnated with lowloading of palladiumignites the LHV-fuel at temperaturesbetween 200-250°C. At even lower palladium loading highconversion rates of carbon monoxide and hydrogen were stillobtained, while methaneconversion decreased substantially.Thermal stability and sulphur resistance of thepalladiumcatalyst exceeds those of similar platinum andtransition metal catalysts, with respect toignition of carbonmonoxide and hydrogen. Modification of the hexaaluminate phase,i.e. byion-substitution with manganese or iron, increasescatalytic activity and stability of the crystalphase, althoughsurface areas were equal to or smaller than those forunsubstituted samples.The conversion of ammonia to nitrogenoxides or molecular nitrogen (N2) was influenced by the inlettemperature and the catalyst composition. A high selectivity toN2 was observed in certain temperature regimes; higher overcatalysts based on manganese than on palladiumKEYWORDS:Catalytic combustion, gasified biomass, gasturbines, low-heating value, methanefuel-nitrogen,hexaaluminate, Pd, Pt, base metals, CeO2, deactivation, sulphurpoisoning,