Conversion of biomass and biomass-coal mixtures:: Gasification, hot gas cleaning and gas turbine combustion

Air-blown fluidized bed biomass gasification integrated with a gas- and steam-turbine combined cycle (BIGCC) is a potentially attractive way to convert biomass into electricity and heat with a high efficiency. A number of technical uncertainties with regard to this option have to be understood better and in more detail before industrial-scale systems can be designed, optimized, controlled and assessed with regard to technical feasibility and costs. Some design choices that cannot be made convincingly on the basis of current knowledge are atmospheric versus pressurized gasification, bubbling versus circulating fluidized bed, dry versus wet gas cleaning, in-bed or ex-bed tar removal and required gas turbine modifications. All of these choices have an impact on operational issues like the fate of nitrogen components, tar, alkalies, trace components, gas turbine combustion, dynamic behaviour and control. To be able to predict the influence of the system choices on these issues, validated, reliable and possibly mechanistic models, simulating the relevant processes, are needed. A 1.5 MWth Process Development Unit which contains the main 'active' components of a BIGCC, is used to obtain experimental data which are needed to develop and validate models. The PDU basically consists of a dedicated compressed air-supply system, three independently controled solids feed systems, a pressurized bubbling fluidized bed gasifier, a high-temperature ceramic filter and a gas turbine combustion section equipped with a pressurized heated air supply system, simulating compressor air. In the current configuration the hot pressurized gas coming from the hot ceramic filter is directly entering the gas turbine combustor. Experimental results with regard to the fate of different components during their passage through the complete system will be presented and discussed.