Optimization Of Distillation System For Butene Alkylation Combined Process

C₄ is the main by-product of refinery industries,and mainly composed of butadiene,isobutylene,n-butene,isobutane and butane.Butadiene is mainly used as raw material in the polymer polymerization industry.Isobutylene is used to produce MTBE and butyl rubber.N-butene can be converted into isobutylene or isobutane to form isooctane.Isobutane can also be dehydrogenated to form isobutylene with high purity.Nevertheless,the utilization of n-butane is still at a very low level.The comprehensive C4 utilization technology of He Yun Group has established an alkylation process to convert isobutane and butene into isooctane.As the low content of isobutane in the C4 raw materials,a new isomerization unit is to be built to convert n-butane into isobutene.In this paper,Aspen Plus software with Wilson-RK equation is used to simulate the rectification system of the combined process.And based on the original design,two optimization solutions are proposed and the effect on the process is analyzed.The refrigeration unit,fractionation unit and isomerization unit were simulated by chemical process simulation software.The total feed was 50993 kg/h.The total production and the yield were 50329 kg/h and 98.7%,respectively.Comparing the simulation data of the refrigeration unit and the fractionation unit with the actual data,the error of the simulation result is relatively small,the temperature error is less than 2°C,and the purity error is less than 2.5%,suggesting that the selected model is appropriate.Two optimization solutions were also proposed,First,the isooctane fractionation unit and the isomerization product unit were combined.The butane separation tower and the de-weighting tower of the isomerization unit were eliminated,and the mixing butane at the tower bottom was directly sent into the isobutane column.Second,the purity of the key intermediate product isobutane was reduced to 85%.The optimization of the distillation system is simulated in chapter 3.The mixing butane was used as new feedstock to deisobutane column C201.The feed position was at the 28th tray,and the feed temperature was 56°C.The reflux ratio droped to 0.96,and the reboiler energy consumption was 68.31 GJ/h,the energy consumption increased by 4.99 GJ/h.The feed position of the de-n-butane column C202 was changed to the 12th tray.The reflux ratio was reduced to 1.3,and the energy consumption of the reboiler increased 2.95 GJ/h to 10.85GJ/h.The operating pressure of stabilization tower C301 was set at 2.1 MPaG,and return flow was 20 t/h.The reboiler energy consumption increased 0.22 GJ/h to 6.74 GJ/h.The butane separation column C302 and the de-weighting tower C303 were cancelled,and the total energy consumption was decreased by 4.64 GJ/h.As the decrease of 5%in isobutane purity,the load of recycled isobutane and the refrigeration unit increased by 4.0%and 2.5%,respectively,and the deisobutane reflux decreased to 0.66,and the energy consumption decreased to 61 GJ/h,and the energy consumption decreased by 7.31.GJ/h,and there was little effect on the other systems except for aforementioned changes.Optimizing the feed position of the de-isobutane column and the de-n-butane column simplified the rectification system,reduced the operation purity,reduced the operation difficulty,and decreased investment.The heavy component by-products are converted into the main product isooctane.The market value of the two products is comparable,and there is little effect on the flow of the remaining raw materials and products.Meanwhile,two optimizations were carried out.The total process energy consumption decreased by 10%from111.8 GJ/h to 100.7 GJ/h through two optimizations,and the annual cost was decreased by7.02 million RMB.