The coproduction of electrical, thermal and refrigerating power is a well-known strategy which can sig- nificantly improve the efficiency of energy systems. Often in such tri-generation systems the refrigerating power is obtained by means of absorption cycles. This paper deals with the potential use of ejector-powered refrigerating cycles for heat recovery from a micro-gas turbine. At first, ejector performance is analyzed by a one-dimensional flow model using a cubic equation of state to describe the thermo-volumetric properties of the working fluid. The calculated maximum ejectorÕs efficiency, in the considered conditions, is about 25% and is considerably affected by the molecular complexity of the working fluid. The thermodynamic performance of the mentioned refrigerant cycles is also considered. Water, ammonia and HFC-134a are the selected working fluids for the analysis. The cooling coefficients of performance achievable, with a con- densation temperature of about 40 °C, are about 0.30. Finally, assuming a micro-gas turbine of 30 kWe as a reference, three examples of heat recovery are investigated: (1) the complete recovery of the available heat; (2) the generation of refrigerating thermal power together with the production of sanitary water; (3) the partial recovery of heat in order to cool air before gas turbine intake. In the first and in the second case the considered micro-gas turbine provides an electrical power of about 25kWe (with an assumed ambient temperature of 35 °C, a typical value in summer-time); the refrigeration power is about 20 kWth for the com- plete recovery of the available heat (case (1)) and about 16 kWth in the case (2). In this case 15 kWth are also available as hot water at about 50°C. The partial recovery of the heat strictly necessary for cooling air before gas turbine intake from 35 to 15 °C (case (3)) allows a very small ejector, despite the relatively high assumed condensation temperature (50°C), making it suitable for the integration into typical micro-gas turbine.
Heat recovery from a micro-gas turbine by vapour jet refrigeration systems
INVERNIZZI, Costante Mario;IORA, Paolo Giulio
2005-01-01
Abstract
The coproduction of electrical, thermal and refrigerating power is a well-known strategy which can sig- nificantly improve the efficiency of energy systems. Often in such tri-generation systems the refrigerating power is obtained by means of absorption cycles. This paper deals with the potential use of ejector-powered refrigerating cycles for heat recovery from a micro-gas turbine. At first, ejector performance is analyzed by a one-dimensional flow model using a cubic equation of state to describe the thermo-volumetric properties of the working fluid. The calculated maximum ejectorÕs efficiency, in the considered conditions, is about 25% and is considerably affected by the molecular complexity of the working fluid. The thermodynamic performance of the mentioned refrigerant cycles is also considered. Water, ammonia and HFC-134a are the selected working fluids for the analysis. The cooling coefficients of performance achievable, with a con- densation temperature of about 40 °C, are about 0.30. Finally, assuming a micro-gas turbine of 30 kWe as a reference, three examples of heat recovery are investigated: (1) the complete recovery of the available heat; (2) the generation of refrigerating thermal power together with the production of sanitary water; (3) the partial recovery of heat in order to cool air before gas turbine intake. In the first and in the second case the considered micro-gas turbine provides an electrical power of about 25kWe (with an assumed ambient temperature of 35 °C, a typical value in summer-time); the refrigeration power is about 20 kWth for the com- plete recovery of the available heat (case (1)) and about 16 kWth in the case (2). In this case 15 kWth are also available as hot water at about 50°C. The partial recovery of the heat strictly necessary for cooling air before gas turbine intake from 35 to 15 °C (case (3)) allows a very small ejector, despite the relatively high assumed condensation temperature (50°C), making it suitable for the integration into typical micro-gas turbine.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
