Multi objective optimization of using the surplus low pressure steam from natural gas refinery in the thermal desalination process

Abstract

Abstract The production of a large amount of wastewater in the process of natural gas refining, which cannot even be released into the environment in many cases, has become the major problem of the natural gas refineries. However, the existence of rich waste heat sources in gas refineries allows the use of thermal methods to desalinate the refinery wastewater. In this paper, the feasibility of using the surplus low pressure steam from Khangiran refinery to turn wastewater into drinking water was studied. In the first step, the changes in the important parameters of the thermal vapor compression section of the multi effect desalination system were examined and the Pareto method, as a multi-objective optimization technique, was employed to optimize the operating conditions of the thermal vapor compressor. As a result, the optimum values for the output steam pressure of thermal vapor compressor and the flow rate ejected from the final effect of the multi effect desalination unit were obtained 712.7 kPa and 0.1 kg/s, respectively. In the second step, the Pareto front for top effect temperature was calculated 82.73 °C, based on the exergy efficiency and useful exergy of multi effect desalination system. Finally, the optimal number of effects and the flow rate of the desalinated water were nine effects and 38.5 kg/s, respectively.