Steady-State Design And Dynamic Control Of Rectification Separation Of Mixed Alcohol By Using DWC

As a kind of important chemical products and alternative fuels,higher alcohols have great potential.Higher alcohol synthesis from syngas is is one of the important ways for indirect coal liquefaction.The separation of the following products is an important step to realize industrialization.This paper is based on the pilot scale product of the preliminary study of our research group.The feed composition is as flow: methanol(265kg/h),ethanol(255.8kg/h),n-propanol(197.4kg/h),n-butanol(110.3kg/h).This paper utilized the technology in which dehydration and separation were conducted sequentially to obtain mono alcohols,used a normal distillation to get methanol and a dividing wall column(DWC)for separation of mixed alcohol and with the simulation software Aspen Plus and Aspen Dynamics,comprehensively studied the steady-state process design and dynamic control structure.The optimal operating parameters of the DWC were obtained by the software self-function and the Total Annual Cost(TAC),and the optimum thermal integration method and operating pressure were found.On the basis of steady-state operation,constant disturbance of ± 5% of fluctuations in discharge was added,and dynamic response effects of 4 kinds of control structures were investigated.The main conclusions were as follows:(1)The steady state process of the separation of the DWC is calculated and optimized by the software self-function,and the process parameters are optimized when the separation requirements are satisfied.The result shows there are 4 parameters have the best value: The optimum range of LR is 0.38-0.42,the optimum range of VR is 0.6-0.63,the optimum value of NI/N2 is 0.33,the optimum value of NO/N1 is 0.5.In the case of 4 aboveparameter being fixed,by means of TAC method,we get the following values: the optimum value of N1 is 54;the optimum value of N2 is 27;the optimum value of NS is 27;the optimum value of NS is 12;the reflux ratio of DWC is 2.17;the annual total cost is $174478.(2)In terms of saving energy,we studied different thermal integration methods and found the optimum method is counter-flow and the optimum operating pressure is low pressure(0.3atm)-atmospheric pressure(1.0atm).The whole process of energy consumption is 265.2kW and the energy efficiency is 51.4% compared to traditional process.(3)There are 4 control modes with QC to control the level of reflux tank and considering the hysteresis effect of stage: LQR/DSB,LB/DSQR,DB/LSQR,DQR/LSB.In the case of ignoring LL,the control effect is not good.In the case of adding QC to control the pressure of primary distillation column,the optimum control mode is DB/LSQR.And the setting time and the maximum deviation could be further shortened by temperaturecomposition cascade control.