Abstract
The conditions of heat source and heat sink in a geothermal ORC system may frequently vary due to variations in geological conditions, ambient temperature and actual operation. In this study, an off-design performance prediction model for geothermal ORC systems is developed according to special designs of critical components, and an optimal control strategy which regards the turbine guide vane angle, the refrigerant pump rotational speed and the cooling water mass flow rate as control variables is proposed to maximize the net power output. Off-design performances of both subcritical and supercritical ORCs are analyzed. The results indicate that, under the optimal control strategy, the net power output of both ORCs increase with greater geothermal water mass flow rate, higher geothermal water inlet temperature and lower cooling water inlet temperature, which is mainly due to a greater working fluid mass flow rate, higher turbine inlet pressure and lower condensing pressure, respectively. The net power output of supercritical ORC is always greater than that of subcritical ORC within the range of this study, but the difference tends to decrease when supercritical ORC activates the geothermal water reinjection temperature restriction.
Highlights
Due to the rapid growth of the world economy, the global energy consumption continues to increase significantly, which leads to excessive consumption of fossil fuels and serious environmental deterioration
Plate heat exchanger (PHE) has been increasingly used in various industries owing to its high heat heat exchanger (PHE) has been increasingly used in less various industries owing to its high transferPlate coefficient, simple maintenance, compact structure and fouling
Is always smaller than that of supercritical Organic Rankine Cycle (ORC), the the difference between them presents a decrease trend as Tcw drops, which is owing to the difference between them presents a decrease trend as Tcw drops, which is owing to the reduction in reduction in mwf of supercritical ORC
Summary
Due to the rapid growth of the world economy, the global energy consumption continues to increase significantly, which leads to excessive consumption of fossil fuels and serious environmental deterioration. It turned out that higher temperature and greater flow rate of heat source led to increases in both net power output and thermal efficiency They only considered the off-design performance of the preheater. A sink auxiliary control optimization was performed to provide maximum part-load operation of air cooled and cooling water tower-based geothermal ORC systems installed power output at off-design conditions by changing the fan speed of cooling tower, air cooled condenser at different geographical locations. The turbine inlet pressure, the temperature condensingORCs pressure the mass flow rate of heat working fluid low temperature and high withand varying conditions of the source and following heat weresink, regulated to meet cycle requirements at off-design conditions. 5–6: The subcooled liquid is pumped to a high pressure in the refrigerant pump
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