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Session: Poster Session and Sponsors Exhibition
Session starts: Thursday 22 September, 14:00

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Shengjun Zhang (Tianjin University)
Huaixin Wang (Tianjin University)
Tao Guo (Tianjin University)

Abstract:
Kalina cycle, sub- and trans-critical ORC are three promising cycles to use low-temperature (i.e. 80-100°C) geothermal sources. However, little studies were published on the economic performance comparison of the three systems under their optimized operation parameters. The objective of this study is to provide favorable cycle and fluids as well as the corresponding optimum operation conditions for low-temperature (i.e. 80-100°C) geothermal ORC power system. And the minimum cost of geothermal power plant should be the determining factor of both choices. The LECplant value of the geothermal power plant can be divided into LECsystem and LECfield. The exploration, transmission, drilling, piping, control system, land use costs, etc, which almost const for a specific geothermal source, are indicated by LECfield. And the costs of refrigerant pump, turbine and heat exchangers are revealed by LECsystem and almost the same by our previous study [1] for both cycles when the optimum working fluids and parameters were used. So the fluids with maximum power output will be favored in this study. The power output of the system is used the objective function. The simulation is performed by using a program written in Matlab referred to our previous study [1]. The inlet temperature of the heat source and sink is 90oC and 20oC, respectively. The pinch temperature difference is 5oC and flow rate of the heat source is 1kg/s. And saturated vapor was assumed at the turbine inlet in subcritical ORC system. Aside from the 16 different working fluids considered in our previous study [1], the mixtures of ammonia/water with four solutions (Ammonia/Water mole fraction: 0.78/0.22, 0.82/0.18, 0.92/0.08, 0.98/0.02) are included. The results indicate that the R227ea exhibits the highest power output in subcritical ORC and the R218 is the excellent fluid by the highest power output of 12.3kW in transcritical ORC. The power output of Kalina cycle increases with the increasing of ammonia concentration in the mixture. The power output of the R218 is 30.2% larger than that of R227ea and 5% larger than that of ammonia/water (mole fraction: 0.98/0.02) mixture in Kalina cycle. In conclusion, the transcritical power cycle with R218 as the working fluid is a cost effective approach for the low-temperature geothermal ORC system. REFERENCES [1] Zhang Shengjun, Wang Huaixin, Guo Tao. Performance comparison and parametric optimization of subcritical Organic Rankine Cycle (ORC) and transcritical power cycle system for low-temperature geothermal power generation. Appl Energy 2011, 88, 2740-2754