Genetic algorithm (GA) is used as the optimizer, and the progress of the optimization towards reaching the maximum reduction of GHG emissions is illustrated in Figure . The mean objective value is the average objective value of populations at every iteration. In the initial generations, the mean objective value is negative, which indicates CCU can even cause more GHG emissions than the reference system. We terminate the optimizer after 50 iterations, where the mean objective value is closed to the best objective. Herein, we approximate the found values for decision variables as the optimal operating condition, as shown in Table .