in-bed limestone for sulfur capture is proposed, but hot gas desulfurization is also being considered. Because of the relatively long residence times and limitation on reactor diameter, moving fixed-bed units have lower coal throughput than is achieved with fluidized-bed units. Commercial moving bed gasifiers have capacities in the 800 to 1,000 tons/day range.

The Shell, Destec, and Texaco high-temperature entrained-flow gasifiers have a single-train capacity, resulting from the small coal particle size and high operating temperature, of up to 2,000 tons of coal/day, corresponding to about 265 MW of electricity. The high-temperature Winkler circulating fluidized-bed system planned for the European KoBra demonstration after the year 2000 has a planned capacity of about 300 MW using brown coal. To date, Lurgi fixed-bed units have a lower capacity than do entrained-flow units. This difference in capacity is subject to change with further development.

Gasification Technology and IGCC Performance

The first-generation U.S. IGCC systems are scheduled for demonstration in the ongoing CCT program (see Chapters 7 and 8) using the Destec and Texaco entrained-flow gasifiers with design power generation efficiencies of 38 and 40 percent, respectively. Demonstration of the Shell gasifier as part of an IGCC system is under way in the Netherlands, and a Prenflo system demonstration is under way in Spain. Another IGCC demonstration project based on the moving bed British Gas/Lurgi slagging gasifier is included in DOE's CCT program but has not yet been contracted for. Also in the CCT program, a 100-MW IGCC system with a KRW fluidized-bed gasifier has been designed with an efficiency of 40.7 percent. Since all these systems make use of state-of-the-art 1300 °C (2350 °F) gas turbines, increases in efficiency to the 45 percent level projected for second-generation systems depend on the use of hot gas cleanup systems plus improvements in gasifier performance and optimized systems integration.

In addition to the method of contacting coal and oxidant (entrained-flow, fluidized-bed, or moving fixed-bed), important gasification choices include the use of air or oxygen, and hot or cold gas cleanup. Table 6-2 presents results of a study of the effects of these variables on efficiency using Illinois No. 6 coal in two gasifiers still in the development stage, namely, the KRW fluidized-bed system and the Asea Brown Boveri (ABB)/Combustion Engineering (CE) air-blown entrained-flow system, both using a General Electric MS7001 (1300 °C [2350 °F]) turbine (Gilbert/Commonwealth, Inc., 1994).2 Both are scheduled for demonstration in the DOE CCT program.

2  

The KRW air-blown in situ desulfurization version of the KRW process is scheduled for demonstration under CCT-IV at the Sierra Pacific Power Company. For this process, using Western coal, the ash is sintered and removed as agglomerate. The ABB/CE process is scheduled for demonstration at City Water, Light and Power in Springfield, Illinois, with CCT cost sharing. The first stage of the



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement