The effects of the M-cycle on the performance of a gas turbine

Abstract

Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.

The M-Cycle represents one of the best heat recovery technologies known today. Technically, it can be incorporated into the Brayton cycle by replacing the heat recuperator with a recuperator-humidifier and directing high humidity compressed air into the combustion chamber. This provides a large increase in the cycle efficiency due to the reduction of the ambient temperature (from dry bulb to the dew point temperature), a reduction in compressor work, an increase in the volumetric flow, increase in combustion efficiency (increased fuel economy), and a large reduction in NOx.These combined improvements provide an improved Brayton cycle efficiency. By adding steam to the fuel gas stream in the combustion chamber of a Brayton cycle turbine the operating power will increase substantially. Experiments with innovative gas turbine cycles like Evaporative Gas Turbine (EvGT)[1], the Humid Air Turbines (HAT)[2], or the Cascade Humidified Advanced Turbine (CHAT) cycle[3], where instead of steam an equivalent amount of water vapor is created from waste heat from stack gases, and in some cases intercompressor coolers, have shown improvements in efficiency. Using reduced compressor power for the same mass flow rate causes the largest efficiency gain. However, efforts to commercialize these advanced turbine cycles have been stymied by the difficulty in maintaining the air to humidity ratio, and the added capital equipment cost such as the saturating tower, boilers and numerous heat exchangers. The development of the M-Cycle offers a cost-effective solution to these issues by presenting the opportunity to realize the thermodynamic advantages of these high performance cycles [4]. This paper analyzes the performance of the M-Cycle when operating with a Rolls-Royce 250 gas turbine and compares the output to the standard Brayton Cycle while varying the inlet humidity, temperature and air and fuel flow rates.