Off-design performance comparison of an organic Rankine cycle under different control strategies

Abstract

This paper presents the off-design performance analysis of an organic Rankine cycle system in the view of control strategies. Variable inlet guide vanes and evaporating pressure are considered as control variables to adapt the system to the variable geothermal fluid mass flow rate and temperature. The optimal control strategy is studied to maximize the net power under the given geothermal source conditions. The constant pressure operation, the sliding pressure operation and the optimal control strategy are compared in order to analyze their differences. The results indicate that the constant pressure operation with variable inlet guide vanes generates more net power than the sliding pressure operation when the geothermal fluid mass flow rate is relative low. The optimal control strategy is determined by the off-design performance of evaporator and turbine. With fixed geothermal fluid temperature and variable geothermal fluid mass flow rate, the potential increase of the net power under the optimal operation can reach 4.7% and 11.0% for the constant and sliding pressure operation, respectively. When the geothermal fluid temperature decreases, the curve of net power tends to shift to the direction of larger geothermal fluid mass flow rate in all control strategies.