Analysis of Thermodynamic Simulation of Small-Scale Organic Rankine Cycle (ORC) Through Utilization of Low Grade Temperature Geothermal Plants

Nowadays, the low-temperature waste heat recovery in the water-dominated geothermal field using the Organic Rankine Cycle (ORC) principle has become an interesting topic. The existing geothermal field with a water-dominated type can be developed an additional power generation without spending the time and cost of exploration. Currently, there are still many types of research focusing on ORC plants to select effective utilization ways. This paper presents the thermodynamic simulation of a small-scale ORC testing facility. The facility mainly consists of a scroll expander integrated with an alternator to generate electric power, an electric heater with thermal oil for representing brine water as a heat source for heating working fluid up to 130 ^oC in an evaporator, an ORC pump that recirculates working fluid, and a condenser unit as cold sink water at 35 ^oC. The simulation was performed using the Engineering Equation Solver (EES) as well as the REFPROP external library of thermo-physical properties of working fluids. This study investigates 5 different working fluids of R245fa, R123, R1233zd, n-pentane, and R141b. The performance of the system using each working fluid has been evaluated in terms of thermal efficiency, maximum power output generation, as well as pressure ratio. The temperature of outlet working fluids in the evaporator is simulated in the range of 70^o – 130^oC with the increment of 5 ^oC, and the discharge temperature of a condenser is maintained at each temperature of 55 ^oC, 60 ^oC, and 65 ^oC. In terms of maximum power output, R245fa is the best value among other working fluids with a power output of 8.757kW. However, the highest thermal efficiency of 14.17% is achieved by n-Pentane. The highest value of power output doesn’t mean related to the performance of thermal efficiency, as a consequence of different characteristics for those properties i.e. density, molecular weight, critical temperature, and pressure. Furthermore, the pressure ratio of almost all working fluids is typically similar by 6.8, unless R1233zd is the lowest among others. Simulation work is examined to understand the effect of different characteristics of various working fluids on the main component's performance system before running at the testing facility. Thus, future works will provide some experiments small-scale test bench and then validate the simulation results.