A STUDY OF THE OFF-DESIGN PERFORMANCE OF INTEGRATED COAL GASIFICATION COMBINED-CYCLE POWER PLANTS

An Integrated Coal Gasification Combined-Cycle (IGCC) plant is a combined-cycle plant fueled by coal. A combined-cycle plant consists of one or more gas turbines with a Rankine (i.e., steam) bottoming cycle. The coal is first gasified to produce a synfuel which can be combusted in a gas turbine after particles and sulfur compounds are removed. The exhaust from the gas turbine is then used to raise steam for the Rankine bottoming cycle.; A computer simulation model for the steady-state operation of an IGCC plant has been developed. The model uses the ASPEN advanced flowsheet simulation software package as a framework. ASPEN's built-in unit operation models were augmented by six component models developed for this study including a numerical finite differencing scheme which used the diffusion approximation to evaluate the radiant heat transfer in the syngas coolers, the Stanford Turbine Evaluation Program (STEP) which extended the algorithms of General Electric for steam turbine performance analysis, and a heat exchanger model which used Kays and London's methodology and data.; The effect of ambient air temperature and part-load operation on a commercial scale IGCC plant was investigated and strategies to mitigate off-design performance penalties were examined. The results showed the plant generation capacity would drop 21.5% as air temperature increased from 20(DEGREES) to 100(DEGREES)F. This drop could be reduced to only 10.0% if supplemental firing was used to increase the temperature of the exhaust gases which energize the steam cycle.; Further calculations showed the heat rate would increase to 239% of design as the plant load was reduced from 100% to 16.7%. However, very large improvements in part-load performance were identified when a unit turndown strategy was used for the gas turbines in which one or more of the gas turbines was shut off completely allowing the others to run nearer to full-load.; With the use of supplemental firing and unit turndown it was predicted that the IGCC plant could operate from 106.2 to 22.0% of design power at 59(DEGREES)F ambient temperature with the heat rate ranging from 9,100 to 11,000 Btu/kWh.