Model Based Control of Fluidized Bed Biomass Steam Gasification

Because of increased efforts to reduce CO2-emissions the energetic utilization of biomass got very important within the last decades. In most cases the biomass is combusted typically applied for residential heating as well as for combined production of heat and power in medium and large-scale applications. Parallel to the increase of practically implemented biomass combustion systems a strong focus of research and development was given to biomass gasification. Biomass gasification leads to a combustible product gas what gives high flexibility. By this technology not only heat and power can be produced, but also transportation fuels, chemicals or valuable gases. For large scale applications typically fluidized bed reactors are applied. Thereby, one very successful technology already realized at several real-scale plants is the dual fluidized bed steam gasification which allows the production of a nitrogen free producer gas of a high calorific value. This technology was demonstrated for the first time at an industrial sized plant in Güssing (Austria) in 2001 and got realized several times at other locations since then. Within the last years different improvements have been performed which mostly focussed on the process engineering and specific components but limited effort has been made on the control system up to now. However, the gasification system is rather complex with strong couplings and nonlinear correlations between the different process variables which are just partially considered by the control systems currently applied. The most reasonable approach for an improvement of the control strategy of such complex and strongly coupled and nonlinear systems are model based control strategies. They base on comparatively simple mathematical models especially describing the dynamic characteristic of the system to be controlled which are finally used for the control unit design. Thus, the aim of this project is to develop model based control strategies for different processes of the dual fluidized bed steam gasification in order to increase the stability of the entire process and improve the fuel flexibility as well the overall efficiency. Finally, the model based control strategy for selected processes should be implemented and validated at an industrial plant based on the dual fluidized bed steam gasification operated by the Stadtwerke Ulm (Germany) and engineered by REPOTEC the company partner of the project. In the field of biomass gasification as well as the downstream gas processing of the resulting gases there has been almost no preliminary work on advanced control strategies performed up to now. Thus, the planned work would lead to a completely new technology in these fields. Furthermore, the project would establish a new cooperation of control engineers with unique know-how and experience in the model based control of biomass combustion systems and one of the leading groups in large-scale biomass gasification.