Role of multiplicity in reactive distillation control system design

Kumar, M. V. Pavan; Kaistha, Nitin

doi:10.1016/j.jprocont.2007.12.001

Cited by 29 publications

(13 citation statements)

References 43 publications

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“…Stable closed-loop responses without any form of control structure failures such as wrong control action [17,26] or closedloop steady-state transition [17] are obtained (data not shown). These results suggest that two-point temperature inferential control with fixed reflux ratio provides an effective regulatory control of the endothermic quaternary ideal RD system studied here.…”

Section: Control Structuresmentioning

confidence: 99%

“…The column operates in the kinetically controlled regime [22,26] where the catalyst holdup on the reactive trays is not large enough for reaction equilibrium to be attained on the trays. If the catalyst loading is increased to an extent where reaction equilibrium is attained on the trays, then for a given reactive zone temperature, the composition of the vapor and liquid streams leaving the reactive zone would remain constant, regardless of throughput.…”

Section: Increased Catalyst Loading Per Traymentioning

confidence: 99%

“…Different decentralized temperature inferential control structures were proposed and tested for their ability to reject the disturbances with tightly controlled product purities [20]. The impact of steady-state multiplicity on the performance of decentralized control structures for this system was demonstrated by Kumar and Kaistha [26]. It has been used as a control test-bed problem by several researchers [17,[26][27][28][29].…”

Section: Introductionmentioning

confidence: 99%

“…The impact of steady-state multiplicity on the performance of decentralized control structures for this system was demonstrated by Kumar and Kaistha [26]. It has been used as a control test-bed problem by several researchers [17,[26][27][28][29]. Its endothermic counterpart, on the other hand, has received much less attention in the open literature.…”

Section: Introductionmentioning

confidence: 99%

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Control of Quaternary Ideal Endothermic Reactive Distillation with and without Internal Heat Integration

2016

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Decentralized control system design is evaluated for a basic and an internally heat-integrated generic, ideal, double-feed, two-product reactive distillation system. The internally heat-integrated reactive distillation column (HiRDC) is obtained via catalyst redistribution into the rectifying zone and feed tray relocation. For basic regulatory control, three two-point control structures with a fixed reflux rate or a fixed reflux ratio operation policy are synthesized and evaluated for their closed-loop disturbance rejection characteristics using rigorous dynamic simulations. To eliminate the purity offsets for on-target product purities, product purity composition controllers manipulating the reflux ratio and stripping tray temperature set point are implemented. Reactive tray section composition control is necessary for on-target product purity operation of HiRDC.

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Section: Control Structuresmentioning

confidence: 99%

Section: Increased Catalyst Loading Per Traymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Control of Quaternary Ideal Endothermic Reactive Distillation with and without Internal Heat Integration

2016

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“…Output multiplicity (multiple outputs for given input) is also observed in the T 32 M - S IO relation. Although output multiplicity is not an issue as a feedback controller with the appropriate set point and action (reverse/direct) would stabilize T 32 M at the desired value, input multiplicity in T 32 M and T 39 M can potentially result in control system failure due to set point infeasibility or “wrong” control action. , In both IO relations, since the slope at the crossover point marked with the asterisk (∗) has the same sign as the base-case, the “wrong” control action can lead to a closed loop steady state transition for sufficiently large disturbances.…”

Section: Introductionmentioning

confidence: 99%

Role of Nonlinear Effects in Benzene–Toluene–Xylene Dividing Wall Column Control System Design

Gupta

Kaistha

2015

Ind. Eng. Chem. Res.

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Steady-state bifurcation analysis is applied to a ternary benzene−toluene−xylene (BTX) dividing wall column (DWC) to synthesize robust temperature inferential controlled variables (CVs). The coupling between the prefractionator and the main column causes steady-state multiplicity in conventional tray temperature CV loops. Using physical insights into the DWC behavior, differential tray temperature across the side-draw and double differential temperature control across the prefractionator rectification section are shown to significantly mitigate the steady-state multiplicity. Control system variants (with and without prefractionator liquid split manipulation) with alternative temperature-based CVs exhibit nonlinear dynamic phenomena of seeking an infeasible temperature/purity set point and input multiplicity induced "wrong" control action leading to a low purity steady-state transition under closed loop operation. These nonlinear dynamic phenomena correlate with the bifurcation analysis results. The recommended control structure with robust temperature inferential CVs is shown to effectively reject very large feed composition changes, including for on-target product purity operation via temperature inferential CV update. The work brings out the importance of robust CV design for effective control of the highly coupled and nonlinear ternary DWC process. ■ INTRODUCTIONThe ternary dividing wall column (DWC) emulating the Petlyuk sequence 1 in a single column shell has been known to be significantly more energy efficient and cheaper than the conventional light/heavy-out-first distillation sequence. For a ternary mixture of components A (light), B (intermediate), and C (heavy), the feed side of the dividing wall (see Figure 1) acts as the prefractionator (TS1 and TS2) and does the easy AC split. The tray sections above and below the side-draw (TS4 and TS5) prevent, respectively, light A and heavy C leakage in the side-draw. The main column rectifying (TS3) and stripping (TS6) sections prevent B leakage up the top and down the bottoms, respectively. With the prefractionator performing the easy AC split, the intermediate boiler B distributes evenly in the prefractionator top and bottom mitigating its remixing and thus inherent thermodynamic irreversibility, compared to a conventional two-column sequence. Consequently, significant energy saving in the range of 20−40% can be achieved. 2−5 Despite its high energy efficiency, reports of industrial DWC applications have only recently appeared in the literature, BASF being the industry pioneer. 6 More recently, extractive DWC distillation 7 and multiple DWCs 8 have been reported in the literature. The reluctance on part of the industry to adopt DWC technology is due to the control system design being significantly more complex compared to conventional simple distillation. Specifically, the highly nonlinear interaction between the prefractionator and the main column makes tight quality control on the intermediate boiler (B) side-draw stream around a stringent target (e.g., >99%...

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Reaction‐separation interaction on the control of ideal two‐feed, two‐product exothermic reactive distillation columns

Kumar

Mathew

2016

Can J Chem Eng

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In this paper, the interaction of reaction and separation in an optimal design of an ideal, hypothetical, exothermic, quaternary (A + B↔C + D) reactive distillation (RD) system is explored. The relative volatilities of the components are αC:αA:αB:αD = 8:4:2:1. The closed loop dynamics of the column are evaluated for five different decentralized control structures. The prevention of the accumulation of light reactant A is crucial for successful control. A drastic improvement in the controllability is observed for a modified design of the RD system having a greater number of reactive trays as the accumulation of A is effectively prevented. The controllability improvement is observed to be control structure specific. A comprehensive understanding of the interaction of reaction and separation is very helpful for the design of RD columns of improved controllability. Application of the plant‐wide control principles in the control of RD columns is highlighted.

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Role of multiplicity in reactive distillation control system design

Cited by 29 publications

References 43 publications

Control of Quaternary Ideal Endothermic Reactive Distillation with and without Internal Heat Integration

Control of Quaternary Ideal Endothermic Reactive Distillation with and without Internal Heat Integration

Role of Nonlinear Effects in Benzene–Toluene–Xylene Dividing Wall Column Control System Design

Reaction‐separation interaction on the control of ideal two‐feed, two‐product exothermic reactive distillation columns

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