Abstract
This study investigates the utilization of low grade waste heat using a new cogeneration cycle for simultaneous production of heating and triple effect refrigeration. The proposed cogeneration cycle combines the low grade heat driven vapor absorption and ejector system for refrigeration and high grade energy driven cascaded system for producing heating and refrigeration. The LiBr-H2O absorption system is employed to ejector which uses R141b for cooling and the cascaded system which uses CO2 and N2O as a working fluid for cooling and heating. Combined first and second law approach is applied and a thermodynamic analysis is performed to investigate the effects of industrial waste heat temperature, refrigerant turbine inlet pressure, ejector evaporator temperature and compressor pressure ratio of cascaded cycle on energy and exergy efficiency of a waste heat driven cogeneration cycle. A maximum thermal efficiency of 32% and exergy efficiency of 10% are obtained at waste heat temperature of 160 degrees C (320 degrees F). A narrow range of 9.75% to 10.8% exergy efficiency and a wide range of 26.4% to 58% energy efficiency were achieved between the turbine inlet pressure of 0.9MPa (130.5 lb/in.(2)) to 1.7 MPa (246.56 lb/in.(2)). A close range of variation of both energy and exergy efficiency of (28.17% to 24%) and (10% to 9.37%) respectively were obtained between the ejector temperature ranges of [-1 degrees C (-33.8 degrees F) to -9 degrees C (-48.2 degrees F)]. Comprehensive second law analysis indicates that 87% of waste heat exergy is destroyed due to various irreversible processes of the cycle, around 10% is available as heating and refrigeration output, and 3% is lost via exhaust.