Optimization of the integrated ORC and carbon capture units coupled to the refinery furnace with the RSM-BBD method

Abstract

To recover waste heat and reduce the CO2 emissions into the atmosphere, an integrated system of organic Rankine cycle and post-combustion carbon capture unit coupled with furnaces of a refinery located in Tabriz, East Azerbaijan, Iran has been presented. To assess the performances of the proposed system, thermodynamic and economic analyses are performed. The organic Rankine cycle was optimized by selecting the suitable working fluid with optimal operating conditions among the primary considered ones through multi-objective optimization. Then, the response surface methodology combined with the Box-Behnken design was employed to evaluate the effects of decision variables and their interaction on the CO2 capture cost and attain the optimal conditions. The results indicate that the R-245fa is the best working fluids among the selected ones. According to the results, the flue gas inlet temperature into the absorber and lean loading are the terms of the model that have a significant impact on the output response. In the optimum setting of the decision variables, the CO2 capture cost equals 81.60 $/tCO2 and 81.90 $/tCO2 for ORC+CC and DCC+CC processes, respectively. Furthermore, due to the absence of a turbine in the DCC+CC system, its equivalent work is 28 % higher than the ORC+CC system. Also, the amine regeneration energy is responsible for 91.47 % and 86.15 % of the variable operating cost of the optimal ORC+CC and optimal DCC+CC, respectively.