Thermodynamic analysis and comparison study of an Organic Rankine Cycle (ORC) and a Kalina cycle for waste heat recovery of compressor intercooling

The intercooling of multi-stage compressors contributes to reducing the power consumption of compressors and the waste heat is generally taken away by cooling water, which is a great waste of energy. This paper employs an organic Rankine cycle (ORC) or a Kalina cycle to recover the waste heat of compressor intercooling. The mathematical models of ORC and Kalina cycle are established by MATLAB software to simulate the ORC system and the Kalina cycle system under steady-state conditions. A parametric analysis is conducted to evaluate the effects of several key thermodynamic parameters on the system performance. In addition, a parametric optimization is carried out to find the optimum performance of waste heat recovery system from thermodynamic aspect. The results showed that, for the ORC system, there is an optimum value of turbine inlet pressure with the state of working fluid being saturated vapor that yields the minimum net power consumption of the system; whereas for the Kalina cycle system, in some ranges of accessible operation conditions, a higher turbine inlet pressure, a lower turbine inlet temperature and a lower ammonia mass fraction of basic solution could obtain a less net power consumption of the system. The optimization results indicated that the Kalina cycle system shows a better performance than the ORC system.