Integrated optimisation of organic Rankine cycle systems considering dynamic responses

The organic Rankine cycle (ORC) has emerged as a promising and attractive technology for power generation from low- and medium-temperature heat sources. While a considerable amount of research effort has been devoted to the optimisation of ORC system under steady operating conditions, dynamic responses to various fluctuations in the heat source conditions are generally ignored; such transients in the heat source, however, may lead to safety issues and significant performance losses. In this paper, an optimisation method integrated with system dynamic responses is proposed to achieve optimal operating parameters for ORC systems. This method is implemented to obtain the best thermodynamic performance, as well as a secure and safe operation of the ORC system, and to maintain the working fluid in a saturated or superheated state during the expansion process. The effects of different design constraints (i.e., evaporation pressure, condensation pressure, pinch-point temperature differences, and degree of superheat) on the system's dynamic response are investigated, in order to choose appropriate design constraints corresponding to different heat-source variations. Thermodynamic optimisation is implemented for an ORC system exploiting a heat source with different condition variations, and results of the system's dynamic responses are compared with those obtained without such considerations. It is found that the dynamic responses of ORC systems to heat-source fluctuations need to be carefully considered in the design stage of such systems, in order to ensure safe and efficient operation.