Greenhouse gas emission and exergy assessments of an integrated organic Rankine cycle with a biomass combustor for combined cooling, heating and power production

In this study, greenhouse gas emission and exergy assessments of an integrated organic Rankine cycle (ORC) with a biomass combustor for combined cooling, heating, and power production as a trigeneration system are conducted. This trigeneration system consists of a biomass combustor, an ORC, a single-effect absorption chiller, and a heat exchanger. Four special cases are considered in this comprehensive study, namely, electrical power, cooling-cogeneration, heating-cogeneration, and trigeneration cases. Various exergetic and environmental output performance parameters, namely, exergy efficiency, exergy destruction rate, and greenhouse gas emissions, are examined under varying ORC evaporator pinch point temperature, pump inlet temperature, and turbine inlet pressure. This study shows that using trigeneration considerably increases both energy and exergy efficiencies and decreases the greenhouse gas emissions as compared to the electrical power case. This study reveals that the heating-cogeneration and trigeneration cases are less sensitive to the considered temperature and pressure variations as compared with the electrical power and cooling-cogeneration cases. In addition, the results show that when the trigeneration case is used, the exergy efficiency increases significantly to 27% as compared with the exergy efficiency of the electrical power case, which is around 11%. It is also found that the main two sources of exergy destruction are the biomass combustor and ORC evaporator. Moreover, this study shows that the emissions of CO₂ in kg/MWh are significantly high for the electrical power case while for the trigeneration case, the emissions per MWh of trigeneration drop significantly to relatively low level. Specifically, the emissions drop to around one seventh per MWh produced when trigeneration is used as compared with only electrical power production case.