The use of gas turbine and combined cycle power plants for thermal and electric power generation is, nowadays, a consolidated technology. Moreover, the employment of combined heat and power production, especially for low power requirements, is constantly increasing. In this scenario, below ambient pressure discharge gas turbine (BAGT) is an innovative and interesting application; the hot gases discharged from a gas turbine may be expanded below ambient pressure to obtain an increase in electric power generation. The gases are then cooled to supply heat to the thermal utility and finally recompressed to the ambient pressure. The power plant cogenerative performance depends on the heat and electric demand that usually varies during the year (for residential heating the heat to electric power ratio may range from 0.3 to 9). In this paper, the thermal load variation influence on the BAGT performance will be investigated and compared with those of gas turbine and combined cycle power plants.
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