| Summary: | 碩士 === 國立臺灣大學 === 化學工程學研究所 === 94 === Reactive distillation combines reaction and separation in a single unit, which provides substantial economic incentives for some chemical reaction systems. However, the multifunctional nature of the reactive distillation complicates already very nonlinear nature of either reaction or separation. Thus, the dynamics and control of reactive distillation are less obvious as compared to its single functional unit counterparts. The objective of this work is to explore the nonlinear dynamics of reactive distillation. The interaction between reaction and separation leads to possible “sign reversal” in the steady-state gains between the product compositions and typical manipulated inputs. In terms of process control, this implies the existence of right-half-plane (RHP) zeros, a non-minimum-phase (NMP) behavior. This is typically true as a near-optimal reactive distillation column design and, in many cases, the RHP zeros vary from zero to two in a small operating range. The situation worsens as the control structure grows larger, e.g., from 2x2 to 3x3 systems. Thus, the control structure design becomes important for this multifunctional unit. First, the stiochiometric of chemical reaction indicates that the “partial control” is an ideal candidate for reactive distillation control. Subsequently, the problem becomes the selection of controlled and manipulated variables. A systematic approach is proposed to select the most appropriate control structure. We analyze the process charaterictics of system - dynamic characteristic (NMP), nonlinearity measure, deviations of uncontrolled composition under setpoint and load changes. The methyl acetate example is used to illustrate the control structure design. The results clearly show that reasonable control performance can be achieved using partial control, provided with a careful control structure selection.
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