The present work focuses on the investigation of part-load operating strategies of a large-scale industrial recuperative Waste Heat Recovery Organic Rankine Cycle (WHR-ORC) equipped with an air-cooled condenser (ACC). The WHR-ORC includes an intermediate heat transfer oil (HTO) loop that is used for recovering thermal energy from the high-temperature exhaust gases and supplying it to the working fluid of the ORC (cyclopentane). The modelling approach is based on an iterative solver considering the off-design variation of the heat transfer coefficient of the heat exchangers, the turbine sliding constant and isentropic efficiency as well as the pump motor, turbine generator and ACC fan motor efficiencies. The part-load model can be used for predicting the electric power output and thermal efficiency of the ORC under variable heat transfer oil (HTO) mass flow rates, temperatures and ambient temperatures. Two main operating strategies are considered based on: a) constant superheating degree and variable turbine inlet temperature and b) variable superheating degree and constant turbine inlet temperature. In each case, the air mass flow rate in the ACC is optimized in order to maximize the net power output of the plant, while also taking into account the electricity consumed by the ACC fan motor. The operating strategy based on variable superheating and constant turbine inlet temperature (OS1) results in higher overall electric efficiencies compared to an operating strategy based on constant superheating degree and variable turbine inlet temperature (OS2) at lower HTO flow rates. This happens because OS1 is associated with higher superheating which promotes the beneficial effect of the recuperator. However, for the same heat transfer fluid flow rate, OS2 results in higher net power output than OS1 because it is associated with higher heat recovery in the ORC evaporator. Meanwhile, the part-load model was used to calculate the optimal condensation pressure of the ORC that corresponds to different combinations of HTO flow rates and ambient temperatures. For each ambient temperature, there is a threshold HTO flow rate under which the optimal air flow rate in the ACC is maximized. For lower HTO flow rates, the optimal air flow rate varies in an approximately linear way with the HTO flow rate. The threshold HTO flow rate is lower for lower ambient temperatures, for which the tradeoff between the cycle thermal efficiency and ACC fan power consumption favors the former, contrary to higher ambient temperatures, for which the higher air flow rates have a less positive effect on the net power output because of the increased negative influence of the ACC fan power consumption.     «

The present work focuses on the investigation of part-load operating strategies of a large-scale industrial recuperative Waste Heat Recovery Organic Rankine Cycle (WHR-ORC) equipped with an air-cooled condenser (ACC). The WHR-ORC includes an intermediate heat transfer oil (HTO) loop that is used for recovering thermal energy from the high-temperature exhaust gases and supplying it to the working fluid of the ORC (cyclopentane). The modelling approach is based on an iterative solver consideri...     »