Control Analysis of Alternative Design Configurations for Bioethanol

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Control Analysis of Alternative Design Configurations for Bioethanol Purification Damla Gizem Arslan, and Devrim B. Kaymak Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.6b04145 • Publication Date (Web): 15 Feb 2017 Downloaded from http://pubs.acs.org on February 18, 2017

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Industrial & Engineering Chemistry Research

Paper submitted to Industrial & Engineering Chemistry Research

Control Analysis of Alternative Design Configurations for Bioethanol Purification

Damla G. Arslan Devrim B. Kaymak*

Department of Chemical Engineering Istanbul Technical University 34469, Maslak, Istanbul, Turkey

*

To whom correspondence should be addressed: [email protected]; Phone: +90-212-285-3539; Fax: +90-212-285-2925

October 25, 2016 Revised January 18, 2017

ACS Paragon Plus Environment


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ABSTRACT

This study presents a control analysis of different design configurations for the separation of bioethanol. Starting from a four-column configuration, a three-column configuration with a liquid recycle and a two-column configuration with a side stream vapor recycle are considered as design cases. For each configuration, the designed control structures including inferential temperature control loops are evaluated based on their step responses against two different types of disturbances. The results indicate that stable control is obtained for all configurations. In addition to the lower capital and energy costs, the dynamic performance of the two-column configuration is found competitive in terms of transient deviations and ultimate steady-state values when compared to other configurations.

1. INTRODUCTION

Economic and environmental concerns such as shortage of fossil fuels, increase in their price and global warming as a result of greenhouse gases force the industry to focus on alternative renewable energy sources. Bioethanol is considered as one of the most promising sustainable biofuel alternative. According to the current international standards, there is a maximum allowed water content for bioethanol. However, the ethanol-water mixture forms a minimum-boiling azeotrope of 89.4 mole % ethanol at atmospheric pressure. This binary azeotrope of ethanolwater mixture limits the maximum ethanol purity achievable with the traditional separation techniques.

There is a review paper in the literature surveying the present-day methods to break the azeotrope and purify the bioethanol1. There are studies on the design of well-known examples of


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alternative processes such as distillation and pervaporation2, pressure swing distillation3, dividing-wall distillation4 and reverse osmosis membrane pretreatment5.

On the other hand, extractive distillation process is the most widely used method to overcome the binary azeotrope problem in case of large scale production. In general, a typical extractive distillation process for dehydration of ethanol consist of two columns; an extractive distillation column in which the azeotropic mixture and solvent are fed to purify the ethanol, and a recovery column in which the solvent is purified to be reused6-9. Glycol10, glycerol11 and ionic liquids12 are the solvents usually used in extractive distillation process for dehydration of ethanol.

In 2013, Li and Bai observed that vapor-liquid equilibrium curves of ethanol-water system with solvent show contrary properties compared to the system without solvent at different concentrations of ethanol. Although the relative volatility with solvent is lower than that the system without solvent when the concentration of ethanol is below 21 mole %, the opposite is valid for the case where the concentration of ethanol is more than 21 mole %. Thus, they presented a new configuration including three distillation columns for separation of ethanolwater mixture. In this flowsheet, the bottoms of the extractive distillation column contains 21 mole % ethanol, and the third column is used to separate water and azeotropic mixture which is recycled back to the extractive distillation column13.

In the case of bioethanol process, the ethanol-water mixture comes from the fermentation unit, and the ethanol content of this mixture is more dilute (~5 mole % ethanol – 95 mole % water) compared to the azeotropic mixture. In such a case, a pre-concentration column should be added in front of the extractive distillation column to remove the water in excess from the bottoms and to form a concentrated distillate stream with a composition close to the azeotropic mixture14.



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Errico et al. compared steady-state performances of different design configurations for the separation of bioethanol in terms of energy demands and annualized capital costs. They used a four-column flowsheet as their base case by integrating the pre-concentrator column and the configuration proposed by Li and Bai. Then, a set of alternative configurations were developed using reduced number of columns by process intensification, different combinations of total or partial condensers, types of recycles (liquid or vapor) and thermally coupled sequences15,16.

On the other hand, there are only a handful of papers discussing the dynamic behavior and control of extractive distillation processes for ethanol dehydration system. Maciel and Brito evaluated the dynamic behavior of an extractive column for dehydration of aqueous ethanol mixture to recommend the best manipulated variables17. Gil et al. studied controllability of a conventional two-column extractive distillation process, where the feed stream is close to the azeotropic composition. Suggested control structures including temperature controller shows stable operations against large feed disturbances and holds the purity specifications18. Errico et al. compared the controllability of alternative design configurations. However, they only used control structures including composition controllers (LV type), but they did not develop any control structures including temperature controllers, ratio control etc. In addition, they analyzed the closed-loop performances only by applying set point changes to product compositions, but they never use any disturbances such as throughput changes and impurities in feed streams to check the ability of control structures against disturbance rejections19-21.

The purpose of this study is comparing the controllability of three different configurations of extractive distillation process proposed by Errico et al. used for bioethanol dehydration. In the next section, the details of three selected configurations including four, three and two columns,


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respectively, are given. Then, control structures are developed for each design configuration, and they are tested against two different types of disturbances. At the end, the results are discussed and conclusion remarks are done.

2. CONFIGURATIONS STUDIED In this study, three process configurations proposed by Errico et al.15,16 are considered. The first one is a four-column distillation sequence, the second configuration is a three-column system, called conventional separation sequences with liquid recycle (CLR), and the last one is a twocolumn system, called SSVR (side stream vapor recycle).

For all configurations, a fermentation broth is used as the feed stream. A flowrate of 1700 kmol/h including 5 mole % ethanol and 95 mole % water is fed to the pre-concentrator column. The composition and the physical properties of the feed stream are reported in Table 1. Ethylene glycol has been used as solvent due to its low volatility and low boiling point. All the simulations have been performed by the process simulator Aspen Plus. The NRTL method has been applied to evaluate the activity coefficients. For all columns, “the strongly non-ideal convergence method” is selected.

First configuration given in Figure 1 includes four columns: the pre-concentrator column, the extractive distillation column, the solvent recovery column, and the concentrator column. In preconcentrator column, fermentation broth is separated until a purity close to the azeotropic mixture. The excess of the water is taken from the bottoms of the column, while the nearly azeotropic mixture, containing 85 mole % ethanol and 15 mole % water, is removed from the distillate stream and sent to the extractive distillation column. The other fed to the extractive



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distillation column is ethylene glycol with a solvent to feed ratio of 1. Pure bioethanol is obtained from the distillate stream, while a ternary mixture containing ethanol with a molar proportion of 0.21 (excluding solvent) left the column from the bottoms and sent to the solvent recovery column. Ethylene glycol is recovered with a high purity from the bottoms of the solvent recovery column and recycled back to the extractive distillation column. A solvent make-up is also fed to the extractive distillation column to compensate the loss of the solvent in the process as impurity. On the other hand, the distillate of the solvent recovery column is fed to the concentrator column to separate the binary mixture as water and azeotropic mixture. The azetropic mixture removed from the top is recycled back to the extractive distillation column. The steady-state design results for the base case configuration are given in Table 2.

Second configuration including three distillation columns is shown in Figure 2. In this flowsheet, the fermentation broth is fed into the pre-concentrator column to obtain a binary mixture at the ethanol concentration of 85 mole %. The almost azeotropic mixture in vapor form is taken from the top of the first column, and fed to the extractive distillation column. The main product bioethanol is obtained from the distillate, while the ternary mixture is removed from the bottoms of second column, and introduced into the solvent recovery column. Ethylene glycol is recovered from the bottoms of the third column and is recycled to the extractive distillation column. In this process, the concentrator column of the first configuration is integrated with the pre-concentrator column. Thus, the distillate of the recovery column is fed to the pre-concentrator column to separate the excess of water. The steady-state design results for the three-column configuration are given in Table 3.


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The final configuration is a two-column process and given in Figure 3. The pre-concentrator column of this flowsheet is similar with that of the second configuration. On the other hand, extractive distillation column and solvent recovery column are combined into a single column with a side stream. Purified bioethanol is removed from the distillate of this column, while ethylene glycol leaves the column from bottoms, and is recycled back to same column after mixed with solvent make-up stream. The vapor side stream includes a mixture of water and ethanol, and is recycled to the pre-concentrator column. The steady-state design results of the two-column configuration are given in Table 4.

3. CONTROL STRUCTURES OF CONFIGURATIONS

Before the flowsheets are exported to Aspen Dynamics, sizing of the reflux drum and the column base is done using commonly used heuristics. For all configurations in this study, decentralized multi-loop control systems using several single-input, single-output (SISO) feedback controllers are considered. All level control loops are proportional-only controllers with a controller gain of 2. Pressure controllers are proportional-integral with KC = 20 and τI = 12 min. Since the temperature loops have dynamic lags, a dead time of 60 sec is added to these loops, and they are tuned using the relay-feedback method. Controller parameters of these loops are calculated by Tyreus-Luyben settings. For the cooler temperature control loop, an open loop test following the IMC-PI tuning rules is performed to determine the controller parameters. It should also be noticed that all the valves are half open at steady-state conditions.

Control structure of the four-column configuration is given in Figure 4. The fresh feed to the preconcentrator column is flow controlled and used as the production rate handle. The reflux drum levels of all columns are controlled by manipulating distillate flowrates. The base levels of pre-



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concentrator column, extractive distillation column and concentrator column are controlled by manipulating bottoms flowrates. The base level of recovery column is controlled by manipulating make-up flowrate. The reflux ratios are held constant in each column at their nominal values. This is set in Aspen Dynamics by using a multiplier block. The first input of the block is the mass flowrate of the distillate stream, while the output is the mass flowrate of the reflux. Nominal R/D ratio is the second input of the block and used as set value. The operating pressures of all columns are controlled by manipulating the corresponding condenser duties. The entrainer flowrate is rationed to the azeotropic feed and the ratio is controlled by manipulating bottoms flowrate of the recovery column. The entrainer feed temperature is controlled by manipulating cooler duty. The reboiler duty of each column is manipulated to control the temperature in a particular tray of the corresponding column. Selection of the tray location for temperature control is done using the steady-state temperature profiles of the columns. The tray with the highest slope is selected as the controlled variable. For the four-column configuration, tray 36, tray 24, tray 5 and tray 22 are selected as controlled variables for pre-concentrator column, extractive distillation column, recovery column and concentrator column, respectively.

Figure 5 shows the control structure of the three-column process. In this configuration, the preconcentrator has a partial condenser, and the controllability might be more complicated due to the connection between pressure, reflux drum level and tray temperature control loops22. Thus, three alternative control structures are studied, and the best one is presented here. The reflux drum level of pre-concentrator column is controlled by manipulating the reflux flowrate, and the distillate flowrate is rationed to the reflux flowrate. The reflux drum levels of extractive distillation and solvent recovery columns are controlled by manipulating the distillate flowrates. The reflux ratios are fixed in these columns. The base levels of pre-concentrator and extractive


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distillation columns are controlled by manipulating bottoms flowrate, while the base level of solvent recovery column is controlled by manipulating the make-up flowrate. The condenser duties are manipulated to control the corresponding column pressures in all columns. Similar to the four-column configuration, the entrainer flowrate is rationed to the azeotropic feed and the ratio is controlled by manipulating bottoms flowrate of the recovery column. The entrainer feed temperature is controlled by manipulating cooler duty. Temperatures of particular trays are controlled in each column by manipulating the corresponding reboiler duties. The selected trays are 38, 27 and 12 for pre-concentrator, extractive distillation and solvent recovery columns, respectively. The fresh feed to the pre-concentrator column is flow controlled and used as the production rate handle.

The control structure of the two-column configuration is illustrated in Figure 6. The fresh feed to the pre-concentrator column is flow controlled and used as the production rate handle. The reflux drum level of the pre-concentrator column is controlled by manipulating the corresponding reflux flowrate, while the reflux drum level of the extractive distillation column is controlled by manipulating the corresponding distillate flowrate. The base level of the pre-concentrator and extractive distillation columns are controlled by manipulating bottoms flowrate of the first column and make-up flowrate, respectively. The distillate flowrate is rationed to the reflux flowrate in pre-concentrator column, while reflux ratio is fixed in extractive distillation column. Operating pressures of both columns are controlled by manipulating the corresponding condenser duties. The entrainer flowrate is rationed to the azeotropic feed and the ratio is controlled by manipulating bottoms flowrate of the extractive distillation column. The entrainer feed temperature is controlled by manipulating cooler duty. Temperatures of tray 35 in preconcentrator column and tray 37 in extractive distillation column are controlled by manipulating



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the corresponding reboiler duties. The temperature of tray 26 in extractive distillation column is controlled by manipulating the flowrate of the side-stream.

4. RESULTS

The performance of the control structures for different design configurations are tested using two types of disturbances: step changes in the production rate handles and the feed compositions. All the results are denoted as deviations of variables from their nominal values with respect to time.

Figure 7A gives the results for ±20% step changes in production rate handle of the four-column configuration. It is seen that the control structure provides a stable base-level regulatory control. The controlled tray temperatures settles down to their set points in less than 4 h. The ethanol product purity of the extractive distillation column is held fairly close to its specification with small transient deviations. Although its exact recovery time exceeds 10 h against the positive step change, it settles down quite fast against the negative step change, but with an acceptable offset. The results show that the purity of the ethylene glycol in the bottoms of the recovery column and the water in the bottoms of the concentrator column are also held fairly close to their set points with short settling times and transient deviations.

Results for feed composition disturbances are given in Figure 7B. The responses are quite similar to those found for production rate disturbances. The temperatures recover back into their set points in less than 4 h. The product purities are maintained close to their specifications. In addition, no large transient deviations are observed for any of the product purities, although the exact settling time is a little long for some of the purities.


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Figure 8A shows the performance of the proposed control structure against ±20% step changes in the production rate handle of the three-column configuration. Results demonstrate that all controlled temperatures settle down into their steady-state values in ~4 hours. It is seen that the purity of ethanol in extractive distillation column is recovered back close to its nominal value in 4 hours without having big transient deviations. However, in case of comparison of transient deviation and offset in the ethanol purity, three-column process shows worse performance than the four-column configuration, especially against the negative production rate handle change. In addition, ethylene glycol and water purities in the bottoms of recovery and pre-concentrator columns, respectively, are also held close to their set points with short settling times. However, the transient deviations of these components are bigger compared to the four-column configuration. This is especially true for the maximum transient deviation of water in the preconcentrator column of three-column configuration in the case of positive production rate handle change.

Results for feed composition disturbances are given in Figure 8B. The responses are similar with the responses of production rate disturbances. Controlled temperatures recover back into their set points in less than 4 h, while product purities settle down into new steady-states in close vicinity of nominal values. Although settling time is quite fast for both temperatures and compositions, transient deviations of these quantities are bigger than those of four-column configuration.

The performance of the proposed control structure to ±20% step changes in the production rate handle of the two-column configuration is demonstrated by Figure 9A. It is observed that a stable base-level regulatory control is provided by this control structure. Results show that the tray temperatures settles down to their set points in less than 4 h. The purity of ethanol is held very



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close to its steady-state value with a small transient deviation in less than 5 h. It is seen that the two-column configuration has a better performance than the four- and three-column configurations in terms of transient and ultimate deviations of ethanol specification. Although the compositions of ethylene glycol and water in the side-stream of extractive and bottoms of pre-concentrator columns are also kept fairly close to their specifications with short settling times, a high maximum transient deviation is observed for water in pre-concentrator column.

Figure 9B gives the results for feed composition disturbances in two-column configuration. It is seen that the temperatures recover back into their set points in short time period. The product purities are also maintained close to their specifications with small settling times. In addition, no large transient deviations are observed for any of the product purities.

5. CONCLUSIONS

In this study, an investigation on the dynamic controllability of three alternative design configurations for the purification of bioethanol is presented. The configurations are four-, threeand two-column sequences including an extractive distillation column. Results indicate that stable base-level regulatory control is possible for all design configurations using inferential temperature control. Ethanol purity could be held close to the design specification against both types of disturbances studied without having big offset. Among the configurations, the twocolumn configuration including a side stream vapor recycle shows a better performance compared to other configuration in terms of transient deviations and ultimate steady-state values. In pairing with advantages of capital and energy cost reductions, the two-column configuration with a side-stream has been found as a good alternative to the conventional four-column configuration.


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REFERENCES 1. Frolkova, A. K.; Raeva, V. M. Bioethanol Dehydration: State of the Art. Theor. Found. Chem. Eng., 2010, 44, 545. 2. Hoch, P. M.; Espinosa, J. Conceptual Design and Simulation Tools Applied to the Evolutionary Optimization of a Bioethanol Purification Plant, Ind. Eng. Chem. Res. 2008, 47, 7381. 3. Mulia-Soto, J. F.; Flores-Tlacuahuac, A. Modeling, Simulation and Control of an Internally Heat Integrated Pressure-Swing Distillation Process for Bioethanol Separation, Comput. Chem. Eng. 2011, 35, 1532. 4. Kiss, A. A.; Ignat, R. M. Innovative Single Step Bioethanol Dehydration in an Extractive Dividing-Wall Column, Sep. Purif. Technol, 2012, 98, 290. 5. Kanchanalai, P.; Lively, R. P.; Realff, M. J.; Kawajiri, Y. Cost and Energy Savings Using an Optimal Design of Reverse Osmosis Membrane Pretreatment for Dilute Bioethanol Purification, Ind. Eng. Chem. Res. 2013, 52, 11132. 6. Knight, J. R.; Doherty, M. F. Optimal Design and Synthesis of Homogeneous Azeotropic Distillation Sequences. Ind. Eng. Chem. Res. 1989, 28, 564. 7. Meirelles, A.; Weiss, S.; Herfurth, H. Ethanol Dehydration by Extractive Distillation. J. Chem. Technol. Biotechnol. 1992, 53, 181. 8. Taylor, M.; Wankat, P. C. Increasing the Energy Efficiency of Extractive Distillation. Sep. Sci. Technol. 2004, 39, 1. 9. Garcia-Herreros, P.; Gomez, J. M.; Gil, I. D.; Rodriguez, G. Optimization of the Design and Operation of an Extractive Distillation System for the Production of Fuel Grade Ethanol Using Glycerol as Entrainer. Ind. Eng. Chem. Res. 2011, 50, 3977.



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10. Benyahia, K.; Benyounes, H.; Shen, W. Energy Evaluation of Ethanol Dehydration with Glycol Mixture as Entrainer, Chem. Eng. Tech. 2014, 37,987. 11. Gu, Y.; Jerome, F. Glycerol as a Sustainable Solvent for Green Chemistry, Green Chem. 2010, 12, 1127. 12. Chavez-Islas, L. M.; Vasquez-Medrano, R.; Flores-Tlacuahuac, A. Optimal Synthesis of a High Purity Bioethanol Distillation Column Using Ionic Liquids. Ind. Eng. Chem. Res. 2011, 50, 5175. 13. Li, G.; Bai, P. New Operation Strategy for Separation of Ethanol−Water by Extractive Distillation. Ind. Eng. Chem. Res. 2012, 51, 2723−2729. 14. Doherty, M. F.; Caldarola, G. A. Design and Synthesis of Homogeneous Azeotropic Distillations. 3. The Sequencing of Columns for Azeotropic and Extractive Distillations. Ind. Eng. Chem. Fundam. 1985, 24, 474. 15. Errico, M.; Rong, B. G.; Tola, G.; Spano, M. Optimal Synthesis of Distillation Systems for Bioethanol Separation: Part 1. Extractive Distillation with Simple Columns. Ind. Eng. Chem. Res. 2013, 52, 1612. 16. Errico, M.; Rong, B. G.; Tola, G.; Spano, M. Optimal Synthesis of Distillation Systems for Bioethanol Separation: Part 2. Extractive Distillation with Complex Columns. Ind. Eng. Chem. Res. 2013, 52, 1620. 17. Maciel, N. R. W.; Brito, R. P. Evaluation of the Dynamic Behavior of an Extractive Distillation Column for Dehydration of Aqueous-Ethanol Mixtures. Comput. Chem. Eng. 1995, 19, S405. 18. Gil, I. D.; Gómez, J. M.; Rodríguez, G. Control of an Extractive Distillation Process to Dehydrate Ethanol Using Glycerol as Entrainer. Comput. Chem. Eng. 2012, 39, 129.


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19. Ramírez-Márquez, C.; Segovia-Hernández, J. G.; Hernández, S.; Errico, M.; Rong, B. G. Dynamic Behavior of Alternative Separation Processes for Ethanol Dehydration by Extractive Distillation. Ind. Eng. Chem. Res. 2013, 52, 17554. 20. Segovia-Hernandez, J. G.; Vázquez-Ojeda, M.; Gómez-Castro, F. I.; Ramírez-Márquez, C.; Errico, M.; Tronci, S.; Rong, B. G. Process Control Analysis for Intensified Bioethanol Separation Systems, Chem. Eng. Proc.: Proc. Int. 2014, 75, 119. 21. Errico, M.; Ramírez-Márquez, C.; Torres Ortega, C. E.; Rong, B. G.; Segovia-Hernandez, J. G. Design and Control of an Alternative Distillation Sequence for Bioethanol Purification, J. Chem. Technol. Biotechnol. 2015, 90, 2180. 22. Luyben, W. L. Alternative Control Structures for Distillation Columns with Partial Condensers, Ind. Eng. Chem. Res. 2004, 43, 6416.



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Table 1. Feed parameters Parameters feed mole flow (kmol/h)

value 1700

mole fraction ethanol mole fraction

0.05

water mole fraction

0.95

feed temperature (°C)

78.14

Solvent mole flow (kmol/hr)

100

solvent feed temperature (°C)

20

pressure (atm)

1

Table 2 Steady-State Design Results for Four-Column Configuration C1

C2

C3

C4

number of stages

44

25

12

25

feed stage

30

22

6

16

solvent feed stage

7

distillate rate (kmol/hr)

100

85

20

3.75

reflux ratio (molar)

2.42

0.23

0.5

3

column diameter (m)

1.36

0.80

0.53

0.31

condenser duty (W)

-3755.8

-1136.4

-348.0

-206.8

reboiler duty (W)

4863.4

1672.1

630.2

214.3

total condenser duty

-5447

total reboiler duty

7380


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Table 3. Steady-State Design Results for Three-Column Configuration C1

C2

C3

number of stages

44

28

17

feed stage

30

25

7

distillate feed stage

30

solvent feed stage

5


103.375

85

18.5


2.335

0.246

0.39

column diameter (m)

1.3747

0.8038

0.4885

condenser duty (W)

-2722.1

-1151.4

-294.1

reboiler duty (W)

4968.1

340.3

546.9


-4167.6

total reboiler duty

5855.3

Table 4. Steady-State Design Results for Two-Column Configuration C1

C2

number of stages

44

41

feed stage

30

25

distillate feed stage

31

solvent feed stage

5

side-stream stage

28


100.216

85


2.325

0.39

column diameter (m)

1.3558

0.8784

condenser duty (W)

-2650.6

-1457.7

reboiler duty (W)

4624.3

277.1


-4108.3

total reboiler duty

4901.4



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Figure Caption Figure 1 – Flowsheet of four-column configuration Figure 2 – Flowsheet of three-column configuration Figure 3 – Flowsheet of two-column configuration Figure 4 – Control structure of four-column configuration Figure 5 – Control structure of three -column configuration Figure 6 – Control structure of two-column configuration Figure 7 – Results of four-column configuration: Change (A) in feed flowrate, (B) in feed composition Figure 8 – Results of three-column configuration: Change (A) in feed flowrate, (B) in feed composition Figure 9 – Results of two-column configuration: Change (A) in feed flowrate, (B) in feed composition


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Solvent Makeup

Solvent Recycle

Ethanol

Az. Feed

Fermentation Broth

Water 2

Water 1 Distillate Recycle


Figure 2 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42


Solvent Makeup

Solvent Recycle

Ethanol

Az. Feed

Fermentation Broth

Distillate Recycle Water


Page 20 of 31

Page 21 of 31 Figure 3 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42


Solvent Makeup

Solvent Recycle

Ethanol

Az. Feed

Vapor side stream Fermentation Broth

Water


Figure 4 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42



Page 22 of 31

Page 23 of 31 Figure 5 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42



Figure 6 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42



Page 24 of 31

Page 25 of 31 Figure 7A 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42



Figure 7B 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42



Page 26 of 31

Page 27 of 31 Figure 8A 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42



Figure 8B 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42



Page 28 of 31

Page 29 of 31 Figure 9A 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42



Figure 9B 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42



Page 30 of 31

Page 31 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42


Solvent Recycle

Solvent Makeup

Fermentation Broth

Az. Feed

Ethanol

Water 2 Water 1 Distillate Recycle Solvent Recycle

Solvent Makeup Az. Feed

Ethanol

Fermentation Broth Water Vapor side stream


Control Analysis of Alternative Design Configurations for Bioethanol

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