Externally fired gas turbine technology: A review

•High temperature heat exchanger technology is the key element to the EFGT success.•Closed cycle EFGT plants were operated successfully for more than half a century.•Closed cycle EFGT is expected to play a major role in HTR nuclear power plants.•Biomass fueled EFGT-CHP is a promising candidate for distributed generation.•Solar hybrid gas turbine is an upgrade for lower carbon-footprint gas turbine. Externally fired heat engines were used widely since helium the industrial revolution using dirty solid fuels for example coal, due to the lack of refined fuels. However, with the availability of clean fuels, external firing mode was abandoned, except for steam power plants. Lately, with the global trend moving towards green power production, the idea of the external fired system has captured the attention again especially externally fired gas turbine (EFGT) due to its wider range of power generation and the potential of using environment friendly renewable energy sources like biomass. In this paper, a wide range of thermal power sources utilizing EFGT such as concentrated solar power (CSP), fossil, nuclear and biomass fuels are reviewed. Gas turbine as the main component of EFGT is investigated from micro scale below 1MWe to the large scale central power generation. Moreover, the different high temperature heat exchanger (HTHE) materials and designs are reviewed. Finally, the methods of improving cycle efficiency such as the externally fired combined cycle (EFCC), humidified air turbine (HAT), EFGT with fuel cells and other cycles are reviewed thoroughly.