Four key parameters, the 4 S’s, determine the technoeconomical performance of the steam bottoming cycle to a given gasturbine: [S1], the temperature of the heat Source, [S2], the temperature of the heat Sink, [S3] cycle Structure and [S4] component Specifications. The first two are given by the gasturbine exhaust gas temperature (TEX) and ambient water/air temperatures respectively; the last two are designer’s choice but depend on economics: how much can you afford to pay for an extra kW? (parity factor or differential capital outlay).

The paper analyses the effect of current trends in the first two S’s on the latter two: «S1», the higher TIT (turbine inlet temperature) of advanced GT’s generally leads to higher TEX, especially when coupled with Sequential Combustion; and [S2]«S2», the trend from fresh water cooling to cooling towers — and again from wet to dry types — due to environmental considerations and/or water shortages leads to higher condenser pressures. These trends change the economics of «S3», the structure (one-, two- or three-pressure, reheat, supercritical etc.); finally, macro-economical trends (fuel cost, cost of capital, more Independent Power Producers or IPP’s) determine «S4», equipment specifications (delta-T’s, delta-P’s, number of stages or exhaust flows etc.).

In this written paper the authors report on their technoeconomical analysis; at the conference they will present hands-on solutions, optimized for ABB’s Type GT24 (60Hz, 165 MW) and GT26 (50 Hz, 240 MW) gasturbines. (Note that throughout the paper definite figures are only given for ABB gasturbines and steam turbines, as the authors cannot vouch for information published by other manufacturers or third parties).

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