A Combined Cycle Power Plant Based on Pressurized Fluid Bed Gasification and Combustion
Publication Date: 2012-Jun-06
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A COMBINED CYCLE POWER PLANT BASED ON
PRESSURIZED CIRCULATING FLUID BED
GASIFICATION AND COMBUSTION
W. M. CAMPBELL AND J. J. O'DONNELL
The M. W. Kellogg Company,Three Greenway Plaza, Houston,TX 77046
This paper presents results of a study, funded by the Department of Energy, Morgantown Energy Technology Center, to develop and evaluate a new concept in pressurized fluid bed combustion. The concept involves the use of a pressurized fluid bed combustor integrated with a fluid bed gasifier in a combined cycle plant to generate power more efficiently than a modern, conventional power plant. The prime objectives of the study were to achieve approximately 45% overall thermal efficiency as well as a 20% lower cost o f electricity (compared to conventional plants) with a reasonable yet flexible design,based on what is soon to be commercial gas turbinetechnology. A second,and important, objectivewas to incorporate into the design features which would reduce gaseous and particulate emissions to well below the New Source Performance Standards for fossil
0 fuel fired power plants.
The final design is a 551 MW power plant. This size is basically dictated by the gas handling capability of the gas turbine selected. For this study,the final choice was a United TechnologiesV84.4 gas turbine. This machine,which becomes available in 1993, can operate at turbine inlet temperatures approaching 2500OF and represents the latest,most advanced turbine technology.
The design concept combines a fluid bed gasifier with a fluid bed combustorto produce fuel gas and hot flue gas feed for a gas turbine. The gasifier is designed to convert only a fraction of the feed coal, and the resultant char product from the gasifier is burned completely in the combustor. This arrangement takes advantage of the relativemerits of both the gasifier and the combustor. In the gasifier,the devolatilization o f
the coal and the initial gasification reactions are relatively easy to carry out. As the gasification continues, however, the char becomes more refractory and gasification becomes progressively more difficult. On the other hand,the char from the gasifier can be easily burned in the combustor sincethe combustion reactions are quite rapid. By combining partial gasification of coal with combustion of char,an integrated, complementary system,referred to as the hybrid, results. Fuel gas from the gasifier i s combined with flue gas from the combustor and air from the gas turbine compressor and is burned in the turbine silo combustorto produce hot gas which is expanded in the turbine to produce power. Additional power is generated by transfero f heat from the turbine exhaust gas to a steam cycle.
To limit sulfuremissions from these gases, limestone sorbent is added with the coal and flows through the gasifier and combustor. Sufficient removal of H2S and SO2 occurs such that no further removal is required downstream of the reactor systems.
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