International Journal of Thermofluids (May 2023)
A comprehensive review and evaluation of heat recovery methods from gas turbine exhaust systems
Abstract
Globally, over 60% of generated electricity is derived from fossil fuels. In the Gulf Cooperation Council (GCC) region, most of electrical power is generated from fossil fuel fired thermal power stations, which are operated either in simple cycle (SC) or combined cycle (CC). The combined cycle is applied in industry to maximize the waste heat recovery. However, 70% of the thermal power plants are in SC configuration in GCC countries, while only 30% are in CC. In the United States, the SC to CC ratio is 54–46%. Considering the large number of SC power plants, exhaust heat recovery upgrades options are of particular interest. This paper aims to investigate and evaluate the potential of incorporating cost-effective new developed heat recovery methods.In this work, the utilization of extracted heat is categorized into three implementation zones: within the gas turbine flange-to-flange section, auxiliary systems and outside the gas turbine system in the power plant. Moreover, a new methodology has been established to enable qualitative and comparative analyses of the system performance of nine recently developed heat extraction methods according to well identified criteria including safety and risk, complexity of implementation, effectiveness, scale of modifications and the potential market opportunity. The developed methodology is used to advise further system modifications and improvements on the studied inventions for the purpose of enhancing the plant efficiency.Based on the conducted analysis, no single design out of the investigated in this paper was able to full achieve the established criteria, a summarized comparison and scoring table was constructed to provide direct comparison between the recent heat recovery patents, among each other, as well as typical waste heat recovery units that are commonly used in the gas turbine industry. It was concluded that each of the presented designs has particular benefits and can be selected for implementation according to the objective, the length of downtime and monetary capital available to the owner of the power station.Based on the results obtained from the comparative scoring tables, a new design of integrated heat recovery system was proposed. The new system incorporated a circular duct heat exchanger to extract the heat from the exhaust stack and deliver the intermediary heat transfer fluid to a separate fuel gas exchanger. This system showed superiority in improving the thermodynamic cycle efficiency, while mitigating safety risks and avoiding undesired exhaust system pressure drop.
