Development of Scroll Expander for Utilization of Waste Geothermal Heat Through Organic Rankine Cycle

The demand for energy is increasing rapidly and the need for energy resources is in demand. The increase in energy generation and consumption has led to the production of large amounts of waste heat. This waste heat, while holding enormous potential as an energy source, is simply rejected into the atmosphere, contributing to the inefficiency of energy generation processes as well as thermal pollution on the environment. As a solution to this, the Organic Rankine Cycle (ORC) is an environmentally-friendly approach to power generation by utilizing waste heat energy from geothermal power plants. Among waste heat sources, geothermal heat holds the most potential because of the stability and abundance of its source. By being directly installed in locally existing plants in the Philippines, the ORC can increase their working efficiency by enabling them to capture heat energy at low temperatures, which conventional steam power cycles cannot otherwise utilize, while further minimizing thermal impact. The study covers the development of a low-cost, small-scale ORC system simulating the heat capture from geothermal plants, at a temperature range of 80-85 °C. The mechanical design, control system, and software interface are all included in the construction of the system. A scroll expander converted from a scroll compressor is chosen as the type of power generator. The researchers conducted three trials to characterize the effectiveness of the converted scroll expander with the ORC test bench. A Carnot efficiency ranging from 11.8-13.2% was achieved by the system. Using R-134a as the working fluid, the expander reached an isentropic efficiency of 48-50%. Though the isentropic efficiency attained was quite low compared to other previous studies of similar nature, the ORC system managed to achieve a maximum power efficiency of 10.25%, with an average overall power efficiency ranging from 3.8- 7.3%, presenting the viability of the ORC for utilizing low-temperature waste heat as energy.