Performance Analysis and Optimization of a Novel Combined Cooling, Heating and Power System Integrated Rankine Cycle and Brayton Cycle Utilizing the Liquified Natural Gas Cold Energy

For realizing efficient utilization of liquified natural gas cold energy and high-temperature flue gas waste heat, herein, a combined cooling, heating, and power system using Peng–Robinson property package in Aspen HYSYS software, which includes a three-stage parallel Rankine cycle (RC) in series with single-stage RC and a supercritical CO2 (S-CO2) Brayton cycle, is proposed. The system performance is evaluated using the first law of thermodynamics, second law of thermodynamics, specific energy costing method, and exergoenvironment analysis method. The influences of the pump 1 outlet pressure, turbine 3 inlet temperature, working fluid R23 mass flow rate, compressor 1 outlet pressure, CO2 liquefaction pressure, and ambient temperature on system performance are investigated. The nondominated sorting whale optimization algorithm and technique for order preference by similarity to ideal situation are applied to optimize the multiobjective system performance, and the payback periods of system before and after optimization are calculated. The analysis indicates that under the initial conditions, the thermal efficiency, exergy efficiency, total product unit cost, and sustainability index of the system are 41.68%, 48.50%, 112.293 $ GJ−1, and 1.75, respectively. After optimization, exergy efficiency increases by 2.4% and exergoeconomy decreases by 8.277 $ GJ−1.