Evolution Overview

The 1997 case describes on a high pressure, direct-fired fluidized bed gasifier utilizing hot particulate removal. Th e system is coupled to a combined cycle power system based on the Westinghouse 251B12 gas turbine with a firm g temperature of 1,150°C (2,100°F) and pressure ratio of 15.3. This turbine is available with multi-annular swirl burners (for NOx control) designed for natural gas or low heating value synthesis gas. The overall process efficiency for thi s system is reported as 38.3% in DeLong [1]. The EPRI BIOPOWER model [4] reports the efficiency as 36.0%; however, it was not possible to precisely duplicate all aspects of the system in the BIOPOWER model.

The "power island" (gas turbine and steam cycle) utilized in the base case through the 2010 case is mature , commercially available technology, although minor technical improvements are expected to occur over this time frame. Of particular note are the improvements that will occur in the gasification and hot gas cleanup portions of the plant . The size range of the gas turbines used are available and have been widely demonstrated on natural gas and synthesi s gas derived from gasification of coal, residual oil, and petroleum coke. For gas turbine applications, these latter fuel s are all more problematic than biomass from a contaminant standpoint. Additionally, an unmodified small gas turbin e has been operated directly on fuel gas from the Battelle Columbus Laboratory process development scale gasifier with no difficulties.

Further improvements occur in the 2020 and 2030 cases when ATS-based turbines are employed. These will resul t from efforts such as DOE's Advanced Turbine Systems Program (ATS) and the industry-lead Collaborative Advanced Gas Turbine (CAGT) development program. These turbines are assumed to have firing temperatures in excess o f 1,250°C (2,282°F) and, for the purposes of this study, utilize steam injection for power generation. Such turbines ar e expected to be available for natural gas use around 2005, thus allowing an additional 15 years for any required research and demonstration of any combustor modifications or turbine "ruggedization" that may be required for synthesis ga s use. It should be noted that research on technology required for use of these turbines with coal and biomass is a n integral part of the turbine development programs.

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