Multi-objective optimisation of a geothermal-liquefied natural gas combined organic Rankine cycle system under different distribution pressures

Multi-objective optimisation is drawing more and more attention in the organic Rankine cycle research field due to its comprehensiveness in demonstrating optimum results from multiple perspectives. For this reason, a comparative two-objective optimisation is performed on a combined organic Rankine cycle system liquefied with geothermal among three typical distribution pressures: 1 MPa, 4 MPa and 7 MPa. Eight operational parameters, 11 working fluids, and 16 possible configurations are included during optimisation. The optimisation result is divided and analysed on the basis of the thermodynamic weight (W 1 ). The results reveal that the recuperative organic Rankine cycle configuration is preferred when W 1 is higher, while the basic organic Rankine cycle configuration is preferred when W 1 is lower. Two typical cases are further analysed in detail: the balanced case (W 1 = 0.5) and the maximum case (W 1 = 1). The system is able to yield the maximum energy efficiency of 32.78% with the working fluid Propane under the maximum case with a distribution pressure of 1 MPa. Compared to the maximum case, the balanced case is capable of achieving considerable economic benefits while incurring minimal thermodynamic losses. When the distribution pressure is 7 MPa, the balanced case can achieve as much as 82.94% of the energy efficiency compared to the maximum case, requiring only 44.17% of the electricity production cost. • A two-objective optimisation under three distribution pressures is conducted. • Techno-economic performances are the optimisation goals. • Eight operational parameters are included as optimisation variables. • Eleven working fluids and sixteen system configurations are optimised. • Two cases are analysed and compared from thermodynamic and economic viewpoints.