| Reactive distillation is a typical process intensification technology, because the reaction and separation couples in one operation unit, the design of control structures and the combination of control loops unique characteristics. Reactive distillation process usually needs to be more strictly、sensitive and reliable controlled than ordinary distillation process in order to maintain the stability of the system operation, which makes the design of the control structure of the reactive distillation process more complex. In this paper, the reactive distillation column control structure of ethylene glycol monobutyl ether synthesized by ethylene oxide and n-butyl alcohol are designed, aiming at providing some theoretical foundation for dynamic operation and operation control. The main work and the results obtained involve the following aspects:(1) Raising the control requirement of EGMBE reactive distillation column based on steady state simulation results:Maintain the normal operation of column; Regain stability after having disturbance happened; Keep the reactant conversion rate above90%, the target product selectivity is more than95%, the bottom product mole purity is above90%, the product purity fit the requirement after disturbance happened. Determine the control variables and manipulated variables; using temperature as indirect quality and the temperature sensitive trays are the tray6in reactive section and the tray11in stripping section. The main variables are respectively EO flow rate, n-Butanol flow rate, reflux flow rate, product flow rate, Reboiler heat medium flow and condenser cool medium flow rate.(2) Take a steady state relative gain array analysis on the reactive distillation column and obtain the temperature control loop:FEO-T6, QR-T11。Other control loops for use according to the experience to determine:Fprod-LB,Freflux-LD,QC-P and control itself. The result simulated by Aspen Dynamic when Fn-Butanoi have ±10%step disturbance on control structure I show that n-Butanol feed flow rate decreases by10%will lead to product selectivity lower close to5%, n-Butanol conversion rate increase less than1%, the bottom EGMBE mole composition decreases5%and continues to drop in80h. EGMBE mole composition, n-Butanol conversion and EGMBE selectivity change less than1%when n-Butanol feed flow rate increase10%and the system can maintain the stable operating. Control structure I can not achieve control requirements in case of n-Butanol feed flow rate decrease, and can do in case of increase.(3) The dynamic relative gain array analysis method on control loops ’pairing and control structure design is proposed aiming at the steady relative gain array cannot estimate dynamic process variable relation ships. Dynamic relative gain array analysis gets all the control loops:FEO-T6, QR-T11, Fprod-LB, Fn-BUtan0l-LD, QC-P and Freflux control itself. Aspen Dynamic simulation results show that when EO feed flow rate decrease-10%of step disturbance the system can regain operation stability in3h. DEGMBE mole fraction changes less than1%. Regardless of EO feed flow rate increases or decreases, the selectivity of EGMBE changes less than1%.Control structure Ⅱ designed by dynamic relative gain array analysis make the system restore stability in a relatively short time so as to meet requirements. Dynamic relative gain array can estimate all variables of reactive distillation column the coupling relationship at the same time and get the whole control loops. Aspen Dynamic simulation results show that the dynamic relative gain array can be used to the design of control structure of reactive distillation column. The research expands the range of relative gain array application. |
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