Estimating the Performance of Gas Turbine Heat-Recovery Boilers Off-Design

Abstract

In installations where a gas turbine is coupled to a steam prime mover through an exhaust heat steam generator, the need may arise to estimate the behaviour of the latter away from its specified design conditions. For example, the performance of the steam generator when the gas turbine is operating away from its design conditions may be of fundamental importance in relation to the economics of a proposed coupled installation. In particular, it determines inter alia the extent to which supplementary firing may be required. A question closely related to that of the off-design performance of a given exhaust heat steam generator is that of evaluating the comparative merits as regards thermal performance of designs differing in the layout and configuration of the heat-transfer surfaces when tendered for the same specified duty. (The need for such assessments frequently arises in the examination of competitive tenders.) The paper discusses briefly procedures allowing the influences of the interrelated heat balances of the heat-transfer surfaces, of the heat-transfer surface geometry and of the steam and gas physical properties to be analysed separately and integrated into a computational procedure permitting their combined effect on performance to be determined with sufficient accuracy.