Modeling the Performance and Emissions of British Gas/Lurgi-Based Integrated Gasification Combined Cycle Systems

Abstract

To evaluate the risks and potential pay-offs of a new technology, a systematic approach for assessment must be developed. Characterization of the performance and emissions of the technology must be made comparable to conventional and other advanced alternatives. This study deals with the design and implementation of a performance and emission model for a gasification based power system fueled with municipal solid waste (MSW) and coal in ASPEN PLUS —C a chemical process simulation software package. The power system modeled is an integrated gasification combined cycle (IGCC) and has several advantages over conventional combustion plants including lower pollutant emissions; higher thermal efficiencies; and the ability to co-produce several products aside from electricity. The model was developed to analyze and quantify the expected benefits associated with MSW gasification. This research models a British Gas/Lurgi (BGL) Slagging gasifer-based IGCC power and methanol production facility firing coal and MSW. The ASPEN PLUS IGCC model consists of 153 unit operation blocks, 24 FORTRAN blocks and 32 design specifications. The performance model calculates mass and energy balances for the entire IGCC system. For validation, the model was calibrated to a design study by the Electric Power Research Institute (EPRI) of a BGL gasifier based IGCC system (Pechtl et al., 1992). First developed and calibrated for a coal fueled IGCC system, the model was then converted to process MSW. Three fuels are used in this study: a Pittsburgh No. 8 bituminous coal; a German waste blend; and an American 75/25 percent mixture of Refuse Derived Fuel (RDF) and Pittsburgh No. 8 Bituminous coal. Methanol plant sizes of 10,000, 20,000 and 40,000 lb methanol/hr, each with and without recycling the methanol plant purge gas to the gas turbine, were modeled for each fuel. Regardless of the type of fuel fired, all systems were more efficient when the purge gas from the methanol plant was recycled for combustion in the gas turbine. Another trend observed between the fuels is that as a system produces more methanol, the overall thermal efficiency of the plant decreases. Systems fueled with German waste performed most efficiently, followed by the Pittsburgh coal and American waste.Compared to conventional combustion power plants, Integrated Gasification Combined Cycles are relatively new technologies promising decreased pollutant emissions and increased thermal efficiencies. Additionally, IGCC systems can co-produce chemicals, further increasing the marketability of the plant. The ASPEN PLUS model can be used with several other analysis tools and techniques. The model can be used in conjunction with life cycle analysis to quantify the benefits associated with the avoided (prevented) emissions and avoided use of virgin feedstock. Probabilistic analysis can be utilized in the model to identify which model parameters most affect performance and to quantify the uncertainty and variability associated with the system.