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Hybrid Plants for Coal and Natural Gas Firing

AUTHOR: Rohan Fernando
DATE: December 2000

The operation of hybrid plant, which can fire both coal and natural gas, has become increasingly more commonplace in recent years. There are several advantages for a power plant to be able to fire both coal and gas including greater fuel flexibility, less environmental emissions and increasing both the capability and efficiency of the plant. Natural gas reburn has been installed on several full-scale plant and there are considerable operational data on its applicability. Variations of reburn such as advanced reburn, which combines reburn with SNCR, and fuel lean gas reburn, which is a simpler variation of reburn without overfire air, have also been tested. Several coal-fired plant have been converted to fully fire on coal or natural gas. Full scale plant which combine conventional coal fired boilers and gas turbines are in operation and have provied to be very versatile. In addition, designs combining the best features of coal gasification and pressurised fluidised bed combustion, which can also utilise natural gas, have been proposed and promise high efficiencies and low environmental emissions.

This report describes a range of plant which demonstrate hybrid technologies utilising coal and natural gas. It presents, results at major reburn trials in the US at Hennepin, Lakeside and Cherokee plants and at the Longannet plant in Scotland. The testing of advanced reburn at the Greenidge plant, fuel lean gas reburn at Riverbend, Elmara and Joliet plants and amine-enhanced fuel lean gas reburn at Pleasant Prairie and Mercer plants are described. The technical issues that need to be considered when fully converting a coal-fired plant to natural gas/coal firing are discussed and the practical steps taken at Didcot "A" power station are described. The design and the construction of the multifuel Avedore 2 plant are described as is the design and operation of the Altback-Deizisau parallel powered combined cycle plant. The proposed design of a first and second generation PCFB project originally to be sited at the Lakeland McIntosh plant are also discussed.