Modelling and simulation analysis of an ORC-FPC waste heat recovery system for the stationary CNG-fuelled compressor

In this paper, an organic Rankine cycle-free piston compressor (ORC-FPC) system was employed to recover waste heat of exhaust gas produced by a stationary compressed natural gas (CNG) fuelled internal combustion compressor. FPC was used as the expander in ORC to assist in compressing natural gas, of which the working principle was investigated in detail. To verify the feasibility of the system, an ORC-FPC model was built up with GT-suite software and parameters of the key parts were selected based on the analytical data. Effects of ratio of the power piston area to the compression piston area (Sp/Sc) and output pressure of natural gas on the system were studied through GT-suite simulations. Results indicated that the feasibility of the system could be validated based on the present model. When Sp/Sc varied from 2.5 to 5.0, the effective efficiency of FPC (ηe,t) in five cycles decreased gradually, while the indicated efficiency of FPC (ηi,t) in five cycles firstly decreased and then increased. When Sp/Sc was 2.5, the model achieved the best performance (ηi,t of 50.7% and ηe,t of 23.7%). ηi,t and ηe,t decreased with the increase of output pressure of CNGwithin the range of 11-14 bar, and the best performance of the system was obtained at 11 bar (ηi,t of 53.2% and ηe,t of 26.5%).