Design Study of Part Flow Evaporative Gas Turbine Cycles: Performance and Equipment Sizing: Part 2 — Industrial Core

Abstract

This is part two of a 2-part paper and presents calculation results of a part flow EvGT cycle based on gas turbine data for the ABB GTX100 (modified for intercooling). The evaporative gas turbine cycle is a new high efficiency cycle that has reached the pilot testing stage. This paper presents calculation results of a new humidification strategy based on part flow humidification. This strategy involves using only a fraction of the compressed air for humidification. Thermodynamically, it can be shown that not all the air needs to be passed through the humidification system to attain the intrinsic good flue gas heat recovery of an EvGT cycle. The presented system also includes live steam production and superheating, by heat from the hottest flue gas region, for injection. The humidifier then only uses the lower temperature levels, where it is best suited. The analyzed system is based on data for the ABB GTX100.gas turbine in intercooled mode. Part 1 of this 2-part paper presents the results based on data for the aeroderovative Rolls Royce Trent. Simulation results include electric efficiency and other process data as function of degree of part flow. A detailed model of the humidifier is used, which produces sizing results both for column height and diameter. Paper 1 includes detailed description of the modelling. For the GTX100-system, full flow humidification generates an electric efficiency of 52.6% (simple cycle 36.2%). The efficiency is virtually unaffected if the air portion to humidification is cut to 60% of accessible compressor air (represents 48% of compressor intake). If 30% of air from the compressor after cooling bleed (24% of intake)is led to the humidifier, the efficiency is reduced to 52.2%. On the other hand is the total heat exchanger area reduced by 20% and column volume by 50%. This calls for a recommendation not to use all the compressed air for humidification. It is recommended to use 15-30% of compressor intake air. The exact economic optimum depends on local fuel prices, CO2-taxes, interest rates et c.