The organic Rankine cycle (ORC) is a mature technology for the conversion of waste heat to electricity. Although many energy intensive industries could benefit significantly from the integration of ORC technology, its current adoption rate is limited. One important reason for this arises from the difficulty of prospective investors and end-users to recognize and, ultimately, realise the potential energy savings from such deployment. In recent years, electric arc furnaces (EAF) have been identified as particularly interesting candidates for the implementation of waste heat recovery projects. Therefore, in this work, the integration of an ORC system into a 100 MWe EAF is investigated. The effect of evaluations based on averaged heat profiles, a steam buffer and optimized ORC architectures is investigated. The results show that it is crucial to take into account the heat profile variations for the typical batch process of an EAF. An optimized subcritical ORC system is found capable of generating a net electrical output of 752 kWe with a steam buffer working at 25 bar. If combined heating is considered, the ORC system can be optimized to generate 521 kWe of electricity, while also delivering 4.52 MW of heat. Finally, an increased power output (by 26% with combined heating, and by 39% without combined heating) can be achieved by using high temperature thermal oil for buffering instead of a steam loop; however, the use of thermal oil in these applications has been until now typically discouraged due to flammability concerns.

b s t r a c tA detailed experimental investigation of a small-scale low-temperature organic Rankine cycle (ORC) with R-404A is presented. The tests are first conducted at laboratory conditions for detailed evaluation of the main components at both design and off-design conditions, for variable heat input up to 48 kW th and hot water temperature in the range of 65e100 C. A scroll compressor in reverse operation is used as expansion machine and a dedicated helical coil heat exchanger is installed, suitable for high-pressure and temperature operation. The ORC pump is a diaphragm pump coupled with an induction motor. The rotational speeds of both the expander and pump are regulated with frequency inverters, in order to have the full control of the engine operation. The ORC has been then connected with concentrating PV/ thermal collectors, which produce electricity and heat and provide it to the ORC. These field tests are also presented with the overall focus on the performance of the whole ORC unit and its power contribution to the solar field. The tests have revealed that such low-temperature ORC unit can have adequate efficiency and that its coupling with a solar field is feasible, increasing the power production of the whole system.

Worldwide interest in low grade heat valorization using organic Rankine cycle (ORC) technologies has increased significantly. A new small-scale ORC with a net capacity of 3 kW was efficiently integrated with a concentrated solar power technology for electricity generation. The excess heat source from Photovoltaic (PV) collectors with a maximum temperature of 100˝C was utilized through a supercritical heat exchanger that uses R-404A as working medium. By ensuring supercritical heat transfer leads to a better thermal match in the heat exchanger and improved overall cycle efficiency. A helical coil heat exchanger was designed by using heat transfer correlations from the literature. These heat transfer correlations were derived for different conditions than ORCs and their estimated uncertainty is~20%. In order to account for the heat transfer correlation uncertainties this component was oversized by 20%. Next, a prototype was built and installed in an integrated concentrated photovoltaic/thermal (CPV/T)/Rankine system. The results from the measurements show that for better estimation of the sizing of the heat exchanger a more accurate correlation is required in order to design an optimal configuration and thus employ cheaper components.

solar collectors, evaporators, condensers and relevant energy storage schemes during thermal charging and discharging. A brief overview of some energy storage options are also presented to motivate the inclusion of thermal energy storage into direct steam generation systems.