A multi-objective genetic algorithm with quadratic programming(MOGA-QP)was proposed to optimize the liquid-nitrogen washing process in large fertilizer plants based on the simulation by using Aspen Plus software. According to the superstructure method

the flowsheet of liquid-nitrogen washing process was constructed by adding a throttle valve and a separator. The proposed algorithm MOGA-QP was employed to solve the superstructure of the liquid-nitrogen washing process. The results of the case study show that the optimization of the liquid-nitrogen washing process reduced the inlet flow rate of liquid-nitrogen and the CO volume fraction at the exit to 0.131 2 kmol/s and 0.25×10

-6

respectively. Moreover

the inlet flow rate of liquid nitrogen and the exergy loss decreased by 1.7% and 15.7%

respectively. It appears that the improved process is much better and the MOGA-QP algorithm is effective.