The purpose of this paper is to analyze the technical features of two different arrangements of supplying fresh air to the boilers in fully fired combined cycles for continuous boiler operation using a forced draft fan when the gas turbine is out of service. The first case is the conventional stand-by forced draft fan and the second is the supercharged fan arrangement. Two methods of separating the cycles are reviewed in detail: a) Cold start-up of system. b) While operating in the combined cycle mode, the gas turbine trips. c) While operating the boiler with fresh air firing the gas turbine is started for combined cycle operation. d) Normal shut down of the gas turbine. e) While operating in the combined cycle mode, the boiler trips. This paper presents the results of a study of a 350-MW combined cycle power plant for Alsands Energy Ltd., of Calgary, Alberta, Canada.

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