A waste heat recovery system extracts the thermal power from the exhaust gas of the industrial plant to feed the ORC module via the intermediate fluid. The intermediate fluid, which is usually oil, pressurized water or steam, transfers heat to the organic fluid in the ORC evaporator, where the organic fluid vaporizes. The vaporized fluid then passes to the turbine. Here the vapour expands causing the turbine to spin and creating electricity into the generator. The vaporized organic fluid then continues through the cycle to the condenser where once again becomes a liquid. It then passes through the pump before beginning the cycle again.
ORC WASTE HEAT RECOVERY VS. TRADITIONAL STEAM RANKINE CYCLE TECHNOLOGY: HOW TO CHOOSE?
Regardless of the heat source temperature, the ORC is generally the best solution for small power output. The simplicity and compactness of the system, the higher efficiency of the turbine, the optimal match with the heat release curve and the better operation at partial loads, ensure a higher system efficiency and a lower specific cost compared to conventional Rankine cycles. In certain cases, they become the only practical solution.
Conversely, at considerably high temperatures and large power output, traditional Rankine cycles using steam turbines prove to be the most suitable solution all round: in these conditions, the limited increase in performance for heat sources available over 350-400°C for a ORC implies lower conversion efficiency.
Of course, if water is not available, then the steam solution is not an option.