Techno-economic and multi-objective optimization of a hydrogen liquefaction plant based on RBC integrated with ORC for waste heat recovery

To comply with the trend of emission reduction and energy-saving in the industrial sector, a novel integration of the hydrogen liquefaction process based on reversed Brayton cycle (RBC) with the organic Rankine cycle (ORC), for waste heat recovery is proposed. The high temperature gas in the compressor outlet of RBC, which is typically wasted in air-coolers, is recovered in ORC and used as the heat source for power generation for the hydrogen liquefaction process. Thermodynamic analysis showed that compared to the conventional system COP increased by 17.95% from 0.11 to 0.14 and specific energy consumption (SEC) decreased by 16.33% from 10.84 to 9.07 kWh/kg LH2. Parametric analysis was conducted to evaluate the impact of pressure ratio, evaporator temperature and minimum temperature difference (M Delta T) in heat exchangers, on system performance. Changes in these variables affect the system performance and heat transfer area in opposite directions, thus multi-objective optimization by the genetic algorithm was performed to determine the optimum operating conditions. The SEC and the net present value (NPV) were selected as objective functions and were optimized simultaneously. Results from the optimization process indicate that the SEC and NPV were found to be 9.165 kWh/kgH2 and 1.55 million dollars with the optimal evaporator temperature of 365 K, pressure ratio of 2.85, and the M Delta T of 7.79.