Lignite-Fired Combined Cycle Power Plant With ACPFBC: Concept and Thermodynamic Calculations

A 200 kWth test plant was constructed by BTU Cottbus for the purpose of developing a special variant of coal conversion based on 2nd generation PFBC. This concept, primarily to be used for generating power from lignite, employs a circulating type fluidized bed and is characterized by a design that combines the two air-blown steps “partial gasification” and “residual char combustion” in a single component. The subject of this paper is to develop an overall power plant concept based on this process, and to perform the associated thermodynamic calculations. In addition to the base concept with one large heavy-duty Siemens gas turbine V94.3A fired with Lausitz dried lignite (19% H2O), further versions with variation of Siemens gas turbine model (V94.3A and V64.3A), the water content of the fuel fired (raw lignite with more than 52% H2O or dried lignite) as well as the method of drying the coal were investigated. Common assumptions for all versions were ISO conditions for the ambient air and a condenser pressure of 0.05 bar. As expected, the calculations yielded very attractive net efficiencies of almost 50% (LHV based) for a variant with the small V64.3A gas turbine and up to more than 55% for the large plants with the V94.3A gas turbine. It was further demonstrated that thermodynamic integration of an advanced, innovative coal drying process (e.g. fluidized-bed drying with waste heat utilization) causes an additional gain in net efficiency of about three percentage points compared with the variant of firing lignite that was first dried externally. In addition to the basic function of the coal conversion system, it was necessary to also assume preconditions such as complete carbon conversion, reliable hot gas cleaning facilities and fuel gas properties that are acceptable for combustion in the gas turbine. Put abstract text here.