Simulation And Optimization Of Methanol To Olefins Products Separation

Important low carbon olefins such as ethylene and propylene mainly rely on the method of naphtha pyrolysis. With the scarcity of oil resources, the transformation of methanol to olefins(MTO) with coal or natural gas gradually attracts the attention of academy and industry.In this paper, the separation process of methanol to olefins products is simulated and optimized by the Aspen Plus. Through Aspen Split, the minimum energy consumption distribution table of three different kinds of separate process:sequential separation process, front-end de-ethanizer process and front-end de-propanizer process have been acquired. The front-end de-propanizer process was chosen as the optimal separation process. In the de-methanizer column, the process of "pre-cutting oil absorption de-methanation" has been applied. In order to run design calculation and simulation, DSTWU and RadFrac distillation module in Aspen Plus has been used and thermodynamic model of RKS-BM has been selected. NSTAGE, feed stage, reflux ratio, operating temperature, operating pressure, and other module parameters of every column have been optimized. In addition, the dosage and temperature of dimethyl methane, selected as absorbent, have been confirmed. The rest of C4 olefins can be treated with the method of cracking and the products reentered into the olefin separation unit, just to get purity ethylene and propylene. Finally,99.95% ethylene and 99.98% propylene are obtained.Sulzer Mellapak Structured 250Y type packing has been selected as the distillation packing, height equivalent to a theoretical plate has been settled as 0.35 meters, through pack sizing and pack rating for the rectification process design, the column diameter, maximum capacity factor, maximum stage liquid holdup, maximum liquid superficial velocity and other simulation results have been obtained. Heat pump system also used to optimize energy consumption of propylene tower and ethylene tower. Under the circumstance of the same handling capacity, at least 72% cost of energy consumption can be reserved compared with normal distillation.