Optimization Waste Heat Recovery and power generation for industrial sustainability: A comparative study of supercritical CO2 Brayton, organic Rankine, and inverted Brayton cycles with Synthesis Natural Gas as heat source

Generated waste heat in industrial processes, which is not applied in any functional work, is discharged into the environment by conduction, convection, and radiation from industrial products, processes, and equipment. Harnessing the waste heat carries significant attention because of its potential to decrease fossil fuel consumption and deterring of atmospheric pollutants. This study aims to provide an alternative for natural gas and reduce air pollution, serving the waste heat from the synthesis natural gas (SNG) production as the heat source for the cycles namely CO2 Brayton cycle, organic Rankine cycle, and Inverted Brayton cycles-organic Rankine cycle to the calculation of generated power, efficiencies, and total product unit cost of distinct layouts. By doing so, a comparison of the cost of synthetic natural gas between the two states can be made. Power output is analyzed concerning temperature and pressure, while exergy destruction calculations highlight the synthesis natural gas production process as the major contributor. Cost balance equations are applied to compute the cost of synthesized natural gas and total product unit cost. Objective functions encompass net power output, first law efficiency, and total product unit cost. Optimization employs the genetic algorithm method in MATLAB software. Results reveal that supercritical CO2 Brayton cycle achieves 17100kW power output, 0.8894 first law efficiency, and 26.32 $GJ total product unit cost. Conversely, with the inverted Brayton cycle-organic Rankine cycle, the outcomes are slightly lower, yielding 15430 kW power output, 0.879 first law efficiency, and 25.41 $GJ total product unit cost.