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

Abstract

This is Part II of a two-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 I of this two-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 I includes detailed description of the modeling. 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, etc.

Design Point Performance and Optimization of Humid Air Turbine Power Plants

“…from a recuperator that recovers the high-quality-i.e., high-temperature waste heat from the exhaust gases before streaming the humid air into the combustion chamber. An additional bypass is also present between the high-pressure compressor exit and the inlet of the recuperator, as suggested by Agren and Westermark [8,9], so that a certain fraction of dry air can bypass the humidification process and is mixed with the rest of the humid air between the saturator and the recuperator inlet. The amount of air that bypasses the humidifier is represented by the parameter , which represents the ratio of air flowing through the aftercooler and saturator to the inlet mass flow.…”

“…The pinch point temperature difference is defined as the minimum temperature difference between the operating line of the water and the saturated air enthalpy line across the saturator [28]. For this modelling process, the air-vapor mixture is treated as an ideal mixture of ideal gases, while the air at the outlet of the saturator is assumed to be fully saturated [9]. From the conservation of the dry air and water mass as well as conservation of energy two invariants of the system, (M + , H + ) can be defined as:…”