Selection and analysis of the main components of a 10 kW CHP ORC system powered by waste heat from the food drying process

The paper discusses issues related to the selection of the basic components for a newly designed ORC system with an electrical output of 10 kW. The system was designed to recover waste heat from the food drying process, which would otherwise be released into the atmosphere as exhaust gases at a temperature of 280 °C. To maintain the purity of food production and ensure the safety of service personnel, the ORC system utilised the non-flammable and non-toxic working fluid HFE-7100. Additionally, an intermediate thermal oil circuit was implemented to prevent local overheating of the low-boiling medium and enhance operational safety. The selection of components for the CHP ORC system was made together with the study of operating parameters of the low-boiling medium circuit and auxiliary circuits (heating and cooling), as well as with a detailed analysis of the operating conditions of each component. Based on the results of the conducted studies and a review of market solutions, models of heat exchangers, pumps, and valves used for controlling the circuits were selected. The basic operating parameters of the expansion device were also determined, which were suitable for using a single-stage microturbine in this case. The article also presents the results of laboratory tests on the microturbine turbogenerator and the preliminary tests of the entire ORC system under real operating conditions. Tests conducted at partial heat source power showed that, with the pressure and temperature of the working fluid at the inlet to the blade system at 6 bar and 146 °C, respectively, the rotational speed and internal power of the microturbine were 17,700 rpm and 1.74 kW. At these parameters, the isentropic efficiency of the microturbine and the actual electrical power supplied to the grid were approximately 44 % and 0.8 kW, respectively.