Remixing Control for Divided-Wall Columns - Industrial & Engineering

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Remixing Control for Divided-Wall Columns Hao Ling,*,† Zhi Cai,‡ Hao Wu,† Jun Wang,‡ and Benxian Shen† † ‡

State Key Laboratory of Chemical Engineering, East China University of Science and Technology, Shanghai 200237, China Sinopec Jiujiang Company, Jiujiang, Jiangxi 332004, China ABSTRACT: The divided-wall column is an energy-saving promising technology for the separation of ternary mixtures, but control is difficult because of its complexity structure and interactions of control loops. Although a few control methods have been reported, the general control method for all ternary mixtures is still pending because of the difference of relative volatilities. In this work, we explore a new control structure by control the remixing of the intermediate at the top trays in the prefractionator section for the separation of benzene, toluene, and o-xylene. It is found that avoiding the remixing of toluene helps the divided-wall column work very close to the optimal conditions. The remixing of toluene is studied at steady state first. Then, a remixing control structure with one remixing control loop and three composition control loops is presented. Minimized energy consumption is achieved by avoiding the remixing of toluene at the top of the prefractionator. Disturbances in feed flow rate and feed compositions are used to demonstrate the effectiveness of the proposed control structure. Remixing profile analysis of intermediate compounds gives an easy and new way to design and control the divided-wall column at energy saving conditions.

1. INTRODUCTION Process intensification is nowadays commonly mentioned as one of the most promising development paths for the chemical process industry and the chemical engineering research.1 The divided-wall column (DWC) is an important example of process intensification. It leads to substantially cheaper processes in terms of energy consumption, capital cost, land use area, etc. In 1985, DWC was found the first industrial application in BASF. More than 60 DWCs have been implemented in industry within BASF today.2 Uhde, a German plant construction company, reported that more than 100 DWCs had been used around the world. Most of them are used for separating benzene/toluene/xylene (BTX) ternary mixtures obtained from reformats and coke oven light oils.3 Another leading company is Montz; its detailed structure of DWC is very interesting and attractive.4 Ternary mixtures include three components: A, B, and C, with A being the lightest, B the intermediate, and C the heaviest. In the conventional direct sequence, A is removed first as distillate with B and C going out as bottom. It is unavoidable that the concentration of B reaches a maximum somewhere in the first tower. The maximum B concentration tray is often located close to the bottom but necessarily must be lower in the bottom. The remixing of intermediate component represents a thermodynamic loss that is unavoidable in the sequential distillation scheme.5 10 One way to solve this is using DWC. DWC reduces the remixing of intermediate component and thus saves energy. The reason for the high thermal efficiency of DWC is to avoid the remixing of the intermediate component, but it should work at optimal conditions for the best energyefficient separation. A few authors discussed the remixing of the intermediate compound in DWC. Hernandez and his co-workers compared the behavior of conventional and coupled indirect distillation columns. Their results showed the significant reduction of remixing.6 Kim discussed the remixing for different designs. His method could eliminate tedious iteration encountered in the DWC design.7 In a recent paper, Ho, Ward, and Yu r 2011 American Chemical Society

developed new quantitative relationships between the degree of remixing and the vapor saving. They checked some real mixture examples often seen in the published literatures, and examined the performance of the minimum vapor demand analytical expression. Their predictions are very close to the actual values.10 Finding a suitable control structure is vital for the application of DWC. Wolff and Skogestad pointed out that DWC has four control degrees of freedom: reflux R, vapor boil up V, side stream S, liquid split βL, and vapor split βV, while βV is often fixed at design stage. The solution surface to variations in βL and βV looks like a valley in steady state. There is a quite flat region/vapor boil up at the bottom of the valley.11,12 It is not very difficult to find optimal conditions in steady state. However, the practical problem of keeping DWC operating at optimal points is not easy in the face of disturbance of feed flow rate and feed composition. It becomes a dynamic or control difficulty. In the cases of lower energy efficiency, DWC often works away from optimal conditions, and then, thermodynamic energy efficiency drops. The dynamic control and optimization of DWC has been explored only in a few papers by now.13 23 However, only very few control structures have the function of control product purities and also minimize energy consumption. Ling and Luyben proposed a 4 4 control structure in 2009. The structure is capable of simultaneously controlling product compositions and minimizing energy consumption in a practical way. The essential idea is to control the heavy composition at the top of the prefractionator by manipulating the liquid split.21,22 In a very recent paper, Kiss and Rewagad reported several conventional control structures were enhanced by adding an extra loop controlling the heavy component composition in the top of the prefractionator, using the liquid split as an additional manipulated variable, thus implicitly achieving Received: July 26, 2011 Accepted: October 12, 2011 Revised: September 15, 2011 Published: October 13, 2011 12694

dx.doi.org/10.1021/ie201610g | Ind. Eng. Chem. Res. 2011, 50, 12694–12705

Industrial & Engineering Chemistry Research

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Figure 1. BTX separation divided-wall column and conventional flowsheets.

minimization of energy requirements. The results of the dynamic simulations show relatively short settling times and low overshooting, especially for the DB/LSV and LB/DSV control structures.23 This paper attempts to propose an alternative control structure based on the remixing analysis of the intermediate compound. The numerical example is the BTX ternary mixture. A remixing control structure with one remixing control loop and three composition control loops is presented and studied.

2. STEADY-STATE ANALYSIS OF INTERMEDIATE COMPOUND REMIXING Figure 1 gives the steady-state design of the DWC and conventional two columns flowsheets studied in this work. The ternary

separation of benzene, toluene, and o-xylene (BTX) is used as a numerical example. Their normal boiling points are 353, 385, and 419 K, respectively, and their relative volatilities are about 7.1/2.2/1. The feed conditions are a flow rate of 1 kmol/s, a composition of 30/30/40 mol % B/T/X, and a temperature of 358 K. Product purities are all 99 mol %. All simulations use rigorous distillation column models in Aspen Plus with Chao-Seader physical properties. The optimum economic design of the DWC is given in a previous paper.21 In the Aspen Plus simulations, the “Design Spec/Vary” functions are used for specifying the desired impurity levels for the three products. The reflux ratio is varied to control distillate impurity, the side-streamflow rate is varied to control sidestream impurity, and the reboiler heat input is varied to control bottom impurity. With all 12695

dx.doi.org/10.1021/ie201610g |Ind. Eng. Chem. Res. 2011, 50, 12694–12705


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Figure 2. Composition profiles in BTX direct sequence distillation columns.

Figure 3. Composition profiles in divided-wall column.

Figure 4. Effect of βL on the remixing of toluene and benzene. 12696



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Figure 5. Effect of βV on the remixing of toluene and benzene.

Figure 6. Effect of βL on the remixing and energy consumption with different βV.

products being held at their specified values, the liquid split ratio is varied over a range of values to find the optimal βL, which gives the

minimum energy consumption. The “Sensitivity” function in “Model Analysis Tools” is used for finding the optimal βL and βV. 12697



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Figure 7. Effect of βL on remixing of toluene and energy consumption for changes in benzene feed composition.

Figure 8. Effect of βL on remixing of toluene and energy consumption for changes in toluene feed composition.

In the conventional direct separation sequence, the remixing of intermediate compound is unavoidable. Figure 2 shows the liquid mole fraction profiles. In the first column, left figure in Figure 2, toluene reaches a maximum value at stage 26. Then, the

toluene mole fraction gradually drops with the increase of stage number. The remixing of toluene represents a thermodynamic loss. In the second column, no remixing was found because only two compounds were separated. If we put this in an indirect 12698



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Figure 9. Effect of βL on remixing of toluene and energy consumption for changes in benzene feed composition.

separation sequence, the remixing of the intermediate compound is also unavoidable, and the maximum value of the intermediate compound could be found close to the top tray. The maximum value location depends on the relative volatility and feed composition of the ternary mixture. In DWC, remixing of intermediate compound is mostly avoided at optimal operation conditions; see Figure 3. Line xP,T in the prefractionator and line xM,T in the main column show no toluene remixing exists. The xP,T line goes up in two directions and then merges into the xM,T line to form a loop. Benzene and o-xylene do not remix either. Benzene composition climbs up from bottom to top all the way. o-Xylene drops directly down to the bottom. More, benzene composition in the prefractionator is higher that that of the main column at the same trays. For example, xBenzene, P15 is about 0.25, while xBenzene, M15 is close to zero. DWC forces all three compounds to run in no remixing ways at optimal conditions. The split liquid to prefrationator side works for preventing the heavy compound from going out of the top of the wall, and the split vapor avoids the light compound dropping out of the bottom of the wall. The split vapor in the main column pushes the intermediate compound up and rectifies the light compound out of the top of the wall, and the split liquid in the side cools down the intermediate compound and drives heavy compound out of the divided wall. No remixing of intermediate compound only appears close to the optimal operation conditions. However, the remixing tends to appear when βL or βV is away from the optimal conditions. “Sensitivity” function in “Model Analysis Tools” is used for observing the remixing change at various conditions. It is found that the remixing of toluene appears when βL or βV is away from the optimal values, shown in Figure 4. The left top graph in

Figure 4 plots the changes of xToluene, P10 (the top tray in the prefractionator section), xToluene, P11, and xToluene, P12 when βL changes from 0.346 to 0.41 while holding βV at 0.627. Results clearly disclose that xToluene, P10 moves up slower than xToluene, P11 and xToluene, P12. A remixing point of xToluene, P10 and xToluene, P11 appears at βL of 0.365. When βL is increased, xToluene, P10 will meet xToluene, P12 when βL is 0.391. The right top figure in Figure 4 shows that the intersection of xBenzene, P11 and xBenzene, P12 also appears when βL is 0.41, but it is far away from the optimal point. The two bottom figures in Figure 4 are the change of yP10, Xylene and reboiler duty. It could be found that the energy consumptions are close to the bottom values before the first remixing point of toluene turns up. Figure 5 varies βV while fixing the liquid split ratio at 0.353. Although βV could not change in an industrial or designed application, we want to find whether the remixing happens when βV is changed. The left top graph in Figure 5 does not give any remixing point of toluene. However, the right top figure shows remixing of benzene when βV changes from the optimal point to 0.597. The calculation shows that the vapor split ratio should not be much higher than the optimal value. The excessive vapor split in the prefractionator side leads to a heavier compound going out of the top of the wall, which seriously affects the purity of sidestream. DWC has many optimal energy consumption solutions. Different optimal conditions have different optimal βV and βL. We extend the case of Figure 4 to two close βV value cases. Figure 6 shows the remixing of toluene, and the change of energy consumption is the same as that in Figure 4. These cases show that the differences of xToluene, P10 and xToluene, P11 are all about 1% at optimal conditions. The energy consumption increases linearly when there is an increase in βL from the optimal point. 12699



Figure 10. Effect of βL on remixing of toluene and energy consumption for (10% changes in toluene feed composition.

The difference of xToluene, P10 and xToluene, P11 decreases with increasing βL because of the overflux on the top of the prefractionator. This decreasing trend of the difference becomes serious, even reaching negative values. At such conditions, the thermodynamic energy efficiency of DWC drops. The conclusion is reached that the remixing of toluene is a common feature when βL is away from the optimal values. Figures 4 and 6 show that the difference of xToluene, P10 and xToluene, P11 is about 1% when DWC works at the optimal conditions. Overreflux or increasing the liquid split ratio leads to the decrease of the difference, which is a thermodynamic loss. Prevention the remixing of intermediate compound at the top two trays of the prefractionator could make the DWC work very close to the optimal energy consumption point. In a practical DWC, βL should change in the face of feed composition changes if energy is to be minimized, while βV is always set in design and manufacture stages. The remixing of toluene is a common feature when DWC is working away from the optimal point. We ask whether it is a valuable selection as a feedback variable for keeping DWC close to optimal in a “self-optimizing” control scheme. Figure 7 shows how the remixing of toluene varies with βL in the face of benzene composition disturbances in the feed. The (20% change means that the benzene is changed from 30 to 36 (+20%) or 24 ( 20%) mol %. The other two feed compositions

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are changed and kept in the same ratio of 30/40 to make the total add to 100. There is an optimum liquid split for each case that minimizes energy. Figure 7 shows how xToluene, P10, xToluene, P11, and xToluene, P12 vary with βL. Three conclusions could be made: (1) a 1% mole fraction difference point of xToluene, P10 and xToluene, P11 is very close to the optimal energy consumption point; (2) remixing of toluene shows when liquid split is away from the optimal point; (3) the xToluene, P11 line meets the xToluene, P10 line first, and the xToluene, P12 line meets the line xToluene, P10 second. Figure 8 gives results for changes in the toluene feed composition. Figure 9 gives results for changes in o-xylene feed composition. The above conclusion (1) is suitable for all cases. This means that controlling toluene composition differences could prevent the remixing of toluene and implicitly minimize energy consumption of DWC. Conclusions (2) and (3) above could apply to all cases except the case of 20% toluene. No remixing of toluene is found in the case of 20% toluene. The reason is that toluene in feed is low. It is not common because toluene composition is about 40% in the refinery reformats. A 20% mole fraction decrease of toluene has rarely happened. Figure 10 compares the change of xToluene, P10 and xToluene, P11 when toluene in feed changes (10%. Figures 8 and 10 indicate that high toluene composition in the feed (+10% and +20%) is easy to remix, while low toluene composition ( 10% and 20%) is not. The 20% case shows that no remixing of toluene happens when the liquid split ratio varies from 0.357 to 0.41. The +20% case plots that the remixing point is about 0.35 when the liquid split ratio changes from 0.337. DWC with high intermediate composition in the feed often has high thermodynamic energy efficiency compared with the two column separation sequence. The reason is that DWC could prevent the remixing of the intermediate, which happed in the first column of the two columns separation sequence. The more intermediate compound in the feed, the higher could be the achieved thermodynamic efficiency of DWC. In the condition of low intermediate in a ternary feed, control of the remixing of the intermediate still works but not as good as high intermediate cases.

3. DYNAMIC REMIXING CONTROL RESULTS In this section, we will explore the remixing control method. Halvorsen and Skogestad pointed out that the feedback from the impurity of the heavy key in the top of the prefractionator probably required one or two composition measurements.11,12 Our previous work illustrated the effectiveness of controlling a xylene composition at the top of the prefractionator side of BTX DWC by manipulating the liquid split.21,22 Remixing control is an alternative choice for control DWC working close to optimal conditions. This structure needs two composition measurements for measuring the remixing degree of the intermediate. The intermediate remixing control also prevents the heavy compound from going out of the top of the prefractionator side of DWC. The remixing control structure has four control loops, including a remixing control loop and three product purity control loops. The remixing control loop is installed at the top of the prefractionator. Two liquid compositions, xToluene, P10 and xToluene, P11, were selected, and their difference was calculated for control of the remixing of the intermediate component toluene. Steady-state analysis shows that 1% difference of xToluene, P10 and xToluene, P11 is almost the same as the values that minimize energy consumption for all feed composition cases, so this value was 12700



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Figure 11. Aspen Dynamics implementation.

Table 1. Remixing Control Structure Controller Tuning Parameters control

controlled

loops

variable

manipulated controller controller integral variable

gain KC

time τI (min)

xDT xSX

R S

0.11 0.21

71 51

CC3

xBT

QR

0.07

71

CC4

xP10, T xP11, T

βL

0.13

44

CC1 CC2

selected as a feedback variable for control of the liquid split ratio. This control loop has two functions. One is preventing the remixing of toluene. The other is avoiding o-xylene from going out the top of the wall. Three product purity control loops include (1) control of the toluene impurity in the distillate at xDT = 0.01, (2)

control of the toluene impurity in the bottoms at xBT = 0.01, and (3) control of the o-xylene impurity of xSX = 0.009 for sidestream. These three controlled variables require three manipulated variables. Reflux is selected for control of the distillate composition. The sidestream flow rate is selected for control of the sidestream purity. The bottom composition is controlled by vapor boil up. The remixing control loop requires two composition measurements instead of one, which is a disadvantage compared with our previous control structure. Two composition measurements double the measurement errors. However, the 1% mole fraction difference of xToluene, P10 and xToluene, P11 is larger than the heavy composition at the top of the prefractionator side of the wall. This advantage could be used when the heavy compound at the top of prefractionator is too small to be measured. For example, a 99.9% purity of toluene sidestream is specified in industrial BTX applications. In this case, heavy compound is difficult to be 12701



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Figure 12. 20% Feed flow rate disturbances for divided-wall column.

Figure 13. 20% Benzene disturbances for divided-wall column.

measured because of the limitation of the composition online analyzer, but it is not a problem to measure the toluene remixing degree. Figure 11 gives the Aspen Dynamic implementation. The four control loops each have a 5 min dead time. They were tuned using a sequential method. The xBT/QR loop was tuned first with the other three controllers on manual. Relay-feedback testing was

used to find the ultimate gain and period. Tyreus-Luyben tuning rules were used. Next, the xDT/R loop was tuned using the same procedure with the xBT/QR loop on automatic. Then, the xSX loop was tuned with the two loops on automatic. Finally, the remixing control loop was tuned with the other three loops on automatic. Table 1 gives controller tuning results for all four loops. More, QR/F and an R/F ratio control feedforward loops 12702



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Figure 14. Comparison of different control methods; benzene feed composition disturbances.

Figure 15. Comparison of different control methods; toluene feed composition disturbances.

were installed with 30 min lag time. This method improved the control result and reduced the deviations in the product purity.21 Figures 12 and 13 give the responses of the divided-wall column in the face of throughput and benzene feed composition disturbances. Figure 12 shows that disturbances in the feed flow rate are made at time equal 2 h. Stable regulatory control is achieved

with product purities returned to their specifications in about 9 h. Notice that mole fraction difference and liquid split ratio also returned to the initial value. Figure 13 gives results when the benzene is changed (20 mol % in the feed. The left three figures in Figure 13 show that the purities of all three products are well controlled. The right three figures show that the paired control 12703



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Figure 16. Comparison of different control methods with 5% relative error noise; benzene feed composition disturbances.

variables change for obtaining desired products purity. The bottom two figures disclose that the value of the toluene difference returns to the initial value, while the liquid split changes. Similar results were observed for changes in the concentrations of toluene or xylene. These results clarify that control of the remixing degree of toluene is a suitable method to control DWC in the face of feed composition changes. Figures 14 and 15 compare the dynamic responses of the remixing control and our previous method.21 The blue solid line is the responses of the remixing control method, and the green dashed line is the result of the latter. The top three graphs in Figure 14 give results for 20% benzene disturbances. The deviations of the two control methods are very close. In the case of +20% benzene, the deviations of the remixing control are a little bit larger than that of the other control methods. Similar results were observed for changes of o-xylene. Figure 15 gives the results for the toluene disturbances. The bottom three graphs in Figure 15 show that the remixing control method reacts faster that the other control method. This occurs because the remixing control uses the toluene difference to control the liquid split ratio. The control effectiveness of the two methods is very close in the face of all feed composition disturbances. In order to observe the dynamic responses of the two methods when the signals contain measurement errors, each composition signal in the βL control loops was given a 5% relative error noise. Two measurement noise modules were installed in the remixing control loop because the loop has two composition detectors, while one noise module was added in the previous control method. Figure 16 compares the dynamic responses for 20% benzene disturbances. All cases could stabilize in 9 h after giving a 20% composition disturbance, but the product purity deviations of the remixing control are larger than that of the previous method.

Similar results were observed for changes of toluene and o-xylene. The main reason is that the values of the toluene compositions in remixing control are about 66% and 67%; see Figure 4. The 5% measurement error gives a range of (3.3% composition deviation. As the remixing control has two composition detectors and the measurement errors are when calculating the composition difference, the dynamic responses of the previous method do not change much. The main reason is that the o-xylene composition value for control βL is 0.39%. The measurement noise does not affect the value as much as that of the remixing control. This indicates that the previous method is not sensitive to the relative error noise, while remixing control gives more deviations.

4. CONCLUSION This paper discloses a remixing control structure for DWC. It controls the remixing of the intermediate at the top of prefractionator. The remixing of the intermediate toluene is prevented so that DWC works close to the optimal energy consumption states. The remixing control also avoids the heavy compound from going out the top of the wall, which ensures the purity of sidestream easily reaching to the specified value. Dynamic control results demonstrate that the new structure gives effective control for (20% disturbances. Control of the remixing of intermediate compound is essential for DWC to work close to the optimal conditions in the face of the change of throughput and the feed composition fluctuations. Up to now, we proposed two candidate control structures for DWC, and their effectiveness was proved by the dynamic simulation results. As the relative volatilities B/T and T/X are close, the effectiveness of these two structures still needs to be proved in other ternary mixtures. However, it could be imagined 12704


Industrial & Engineering Chemistry Research that the two structures should work if the liquid split ratio is sensitive to the remixing of the intermediate compound at the top of the prefractionator and the heavy compound coming out of the prefractionator. This sensitivity depends mainly on two factors. One is the relative volatilities of the ternary mixture, and the other is the feed composition. Future work will verify whether the two control structures work for separating two ternary mixtures. One is propane, n-butane, and isobutene. The other is n-butane, isobutene, and n-pentane.

’ AUTHOR INFORMATION Corresponding Author

*E-mail: [email protected]. Tel: 0086-2164252328. Fax: 86-2164252160.

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(17) Adrian, T.; Schoenmakers, H.; Boll, M. Model predictive control of integrated unit operations: Control of a divided wall column. Chem. Eng. Process 2004, 43, 347–355. (18) Wang, S.; Wong, D. Controllability and energy efficiency of highpurity divided wall column. Chem. Eng. Sci. 2007, 62, 1010–1025. (19) Wang, S.; Lee, C.; Jang, S. Plant-wide design and control of acetic acid dehydration system via heterogeneous azeotropic distillation and divided wall distillation. J. Process Control 2008, 18, 45–60. (20) Woinaroschy, A.; Isopescu, R. Time-optimal control of dividingwall distillation columns. Ind. Eng. Chem. Res. 2010, 49, 9195–9208. (21) Ling, H.; Luyben, W. L. New control structure for divided-wall columns. Ind. Eng. Chem. Res. 2009, 48, 6034–6049. (22) Ling, H.; Luyben, W. L. Temperature control of the BTX divided-wall column. Ind. Eng. Chem. Res. 2010, 49, 189–203. (23) Kiss, A. A.; Rewagad, R. R. Energy efficient control of a BTX dividing-wall column. Comput. Chem. Eng. 2011, doi:10.1016/ j.cep.2011.04.002.

’ ACKNOWLEDGMENT We thank Professor William L. Luyben for the very helpful discussions. The financial support given by Sinopec Jiujiang Company and Ministry of Education of People’s Republic of China is also gratefully acknowledged. ’ REFERENCES (1) Stankiewicz, A.; Moulijn, J. A. Process intensification. Ind. Eng. Chem. Res. 2002, 41, 1920–1924. (2) Niggemann, G.; Hiller, C.; Fieg, G. Experimental and theoretical studies of a dividing-wall column used for the recovery of high-purity products. Ind. Eng. Chem. Res. 2010, 49, 6566–6577. (3) Book of ideas. http://www.uhde.eu/cgi-bin/byteserver.pl/archive/ upload/uhde_brochures_pdf_en_15000038.00.pdf, 2010. .; J€odecke, M.; Shilkin, A.; Schuch, G.; Kaibel, B. (4) Olujic, Z Equipment improvement trends in distillation. Chem. Eng. Process 2009, 48, 1089–1104. (5) Pendergast, J. G.; Vickery, D.; Au-Yeung, P.; Anderson, J. Consider Dividing Wall Columns. http://www.chemicalprocessing.com/articles/ 2008/245.html, 2008. (6) Hernandez, S.; Pereira-Pech, S.; Jimenez, A.; Rico-Ramírez, V. Energy Efficiency of an Indirect, Thermally Coupled Distillation Sequence. Can. J. Chem. Eng. 2003, 81, 1087–1091. (7) Lee, J. Y.; Kim, Y. H.; Hwang, K. S. Application of a fully thermally coupled distillation column for fractionation process in naphtha reforming plant. Chem. Eng. Process. 2004, 43, 495–501. (8) Triantafyllou, C.; Smith, R. The Design and Optimization of Fully Thermally Coupled Distillation-Columns. Chem. Eng. Res. Des. 1992, 70 (2), 118–132. (9) Hernandez, S.; Jimenez, A. Design of Energy-Efficient Petlyuk Systems. Comput. Chem. Eng. 1999, 23 (8), 1005–1010. (10) Ho, Y. C.; Ward, J. D.; Yu, C. C. Quantifying Potential Energy Savings of Divided Wall Columns Based on Degree of Remixing. Ind. Eng. Chem. Res. 2011, 50, 1473–1487. (11) Wolff, E. A.; Skogestad, S. Operation of integrated three-product (Petlyuk) distillation columns. Ind. Eng. Chem. Res. 1995, 34, 2094–2103. (12) Halvorsen, I. J.; Skogestad, S. Optimal operation of Petlyuk distillation: steady-state behavior. J. Process Control 1999, 9, 407–424. (13) Asprion, N.; Kaibel, G. Dividing wall columns: Fundamentals and recent advances. Chem. Eng. Process 2010, 49, 139–146. (14) Abdul Mutalib, M. I.; Smith, R. Operation and control of dividing wall columns Part 1: Degree of freedom and dynamic simulation. Trans. Inst. Chem. Eng., Part A 1998, 76, 308–318. (15) Abdul Mutalib, M. I.; Zeglam, A. O.; Smith, R. Operation and control of dividing wall columns Part 2: Simulation and pilot plant studies using temperature control. Trans. Inst. Chem. Eng., Part A 1998, 76, 319–334. (16) Serra, M.; Perrier, E. A.; Puigjaner, L. Analysis of different control possibilities for the divided wall column: feedback diagonal and dynamic matrix control. Comput. Chem. Eng. 2001, 25, 859–866. 12705


Remixing Control for Divided-Wall Columns - Industrial & Engineering

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