Heat Integration and Control of a Triple-Column Pressure-Swing

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Heat Integration and Control of a TripleColumn Pressure-Swing Distillation Process Zhaoyou Zhu, Dongfang Xu, Hui Jia, Yongteng Zhao, and Yinglong Wang Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.6b04118 • Publication Date (Web): 30 Jan 2017 Downloaded from http://pubs.acs.org on February 2, 2017

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Industrial & Engineering Chemistry Research

Heat Integration and Control of a Triple-Column Pressure-Swing Distillation Process Zhaoyou Zhu, Dongfang Xu, Hui Jia, Yongteng Zhao, and Yinglong Wang * College of Chemical Engineering, Qingdao University of Science and Technology, Qingdao 266042, China ABSTRACT: Heat integration and dynamic characteristics are critical for the triple-column pressure-swing distillation (TCPSD) processes that are used to separate ternary or multicomponent systems. In this study, rigorous steady-state simulations of heat-integrated TCPSD processes are optimized using Aspen Plus, and dynamic strategies for the different TCPSD processes are explored using Aspen Dynamics. When ±20 % feed flow rates and composition disturbances are introduced, the CSB control structure, which uses stage 19 as the temperature sensitive stage in the second column, exhibits better controllability than the CSA, which uses stage 4 as the temperature sensitive stage. Three cases of partial heat integration are studied, and the first case, which uses an auxiliary condenser, is the most economic. The dynamic control strategies of the first and second cases handle ±10 % feed disturbances well; however, the CSE can attain good controllability when ±20 % feed disturbances are introduced. For the fully heat-integrated TCPSD process, the CSG exhibits good controllability for ±20 % feed disturbances. The time that the control structures require to reach new steady states varies greatly for different heat-integrated processes. Keywords: Pressure-swing distillation; Ternary azeotrope; Heat integration; Dynamic control

1

ACS Paragon Plus Environment


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1. INTRODUCTION Special distillations such as extractive distillation1-4, batch distillation5-8, azeotropic distillation9, 10

, reactive distillation11,

12

, and pressure-swing distillation (PSD)13-17 have made tremendous

contributions to the separation of binary azeotropes. However, some ternary or multicomponent mixtures in the pharmaceutical and chemical industries contain complex azeotropes. A recent study18 presented a triple-column pressure-swing distillation (TCPSD) method for separating the complex ternary system of acetonitrile/methanol/benzene, and another study19 reported the ability to control the TCPSD process without heat integration. The objective of this paper is to study the heat-integrated process and to analyze the control characteristics of the TCPSD process. For binary azeotrope mixtures, some studies on heat integration have improved the efficiency of the distillation process13,

15, 16, 20-22

. PSD changes the azeotropic composition using pressure

changes and uses different temperatures in each column for heat integration23,

24

. In the

heat-integrated process, the heat of the condenser from the high-pressure tower can be transferred to the reboiler of the low-pressure tower to provide heat. For a partially heat-integrated process, an auxiliary reboiler or condenser, should be added according to the energy requirements. Fulgueras et al.25 studied the separation of water and ethylenediamine using an auxiliary reboiler for a low/high-pressure column configuration and using an auxiliary condenser for the reverse configuration. Li et al.21 reported that the partially heat-integrated PSD process reduced energy consumption by up to 19.79 % compared with PSD without heat integration. Rigorous steady-state simulations for partially and fully heat-integrated PSD processes were implemented by Wang et al.26, 27 using Aspen Plus, and the results demonstrated that heat integration could efficiently improve the economics of the process. All the above studies further developed heat integration and presented energy savings. Controlling the PSD process in binary systems has been studied and discussed by many researchers in recent years13-15, 22, 28-34. For example, Zhang et al.29 investigated a heat-integrated PSD process for separating methyl acetate-methanol and proposed control structures for the feed flow rates and composition disturbances. Luyben22,

30

obtained pure products from the

maximum-boiling methanol/trimethoxysilane azeotrope using PSD and developed a control scheme for a flow controller to effectively handle large disturbances. Luo et al.31 discussed two control structures using extractive distillation and fully heat-integrated PSD for separating 2


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isopropyl alcohol/diisopropyl ether. Their results showed that fully heat-integrated PSD had better controllability for the feed composition disturbances, whereas extractive distillation better maintained the product purities during feed flow rate disturbances. Hosgor et al.32 proposed a pressure-compensated temperature control structure to control the pressure. In addition, studies on dynamic control for extractive distillation31, 35-43, reactive distillation20, 44, 45, batch distillation46, 47, and other separation methods48-52 have received increasing attention; until now, there have been few reports on the dynamic control of TCPSD19. Due to the relatively high number of operating parameters and the interactions within multicomponent systems, designing the required control structure is difficult and complex. Based on the study by Zhu et al.18, Luyben19 studied the plantwide dynamic controllability of a TCPSD process without heat integration. An effective control structure using temperature controllers and pressure compensation was proposed to avoid using a composition controller. However, the methanol purity decreased slightly (from 99.91 % to 99.83 %) when a +20 % feed disturbance was introduced. In this paper, rigorous TCPSD separation processes with no, partial, and full heat integration for separating acetonitrile/methanol/benzene are analyzed using the minimal total annual cost (TAC). Control structures are explored for the three TCPSD processes, and optimal control strategies using composition control structures are determined using Aspen Dynamics.

2. HEAT-INTEGRATED PROCESS DESIGN The azeotropic compositions and azeotropic temperatures of the methanol/acetonitrile/benzene system around the vapor-liquid equilibrium (VLE) were provided in a previous reference18. In that reference, the flowsheet processes to separate a ternary azeotropic system composed of 70.0 wt% methanol, 20.0 wt% acetonitrile, and 10.0 wt% benzene were optimized via steady-state TCPSD with four different separation configurations.

2.1. PARTIAL HEAT INTEGRATION In a steady-state TCPSD process, the temperature difference between the first column (C1) and second column (C2) or between C2 and the third column (C3) makes heat integration possible. Based on processes without heat integration, the distillates of C1 or C3 are used to provide energy to the reboiler of C2 to achieve heat integration. For the first type of partially heat-integrated TCPSD, the heat duty in the condenser of C1 (1087.36 kW) is larger than that of the reboiler of 3



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C2 (732.13 kW); therefore, an auxiliary condenser in C1 is required to remove the excess heat. In the second type, the heat of the condenser in C3 is transferred to the reboiler of C2 to provide partial heat, and the makeup heat is provided by an auxiliary reboiler. In the third type, when the heat from the condensers in C1 and C3 (573.75 and 158.38 kW, respectively) are transferred to the reboiler of C2, the excess heat is removed by an auxiliary condenser. Thus, heat integration among the three columns is achieved. Based on the TCPSD process without heat integration18, the parameters and economics of the partially heat-integrated TCPSD processes are shown in Table 1, and the three flowsheets for the optimal process with partial heat integration are shown in Figs. 1(a), 1(b), and 1(c).

2.2. FULL HEAT INTEGRATION The design of the fully heat-integrated TCPSD process is implemented by adjusting the reflux ratio of C1 to make the condenser duty of C1 equal to the reboiler duty of C2 in Aspen Plus. To minimize the TAC, some operating parameters, such as the number of stages (NT1, NT2, and NT3), reflux ratios (RR2 and RR3), the feed locations (NF1, NF2, and NF3), and the recycle location (NREC) are optimized using the sequential iterative optimization procedure of the TCPSD process18, and the optimal operating parameters are shown in Table 1. The flowsheet of the optimized TCPSD process with full heat integration is shown in Fig. 2.

3. CONTROL STRUCTURE DESIGN Dynamic control structures are investigated for the steady-state heat-integrated TCPSD processes. When the vessels are half full, the volumes of the reflux drums and sumps are specified to provide 5 min of liquid holdup, and the height-to-diameter ratio is set to 2. A sufficient pressure drop is provided by adding pumps and valves to handle the changes in the flow rate. In each column, the specified product purity is 99.9 wt%.

3.1. CONTROL OF THE NON-HEAT-INTEGRATED TCPSD PROCESS The temperatures and slope profiles of the non-heat-integrated process within three columns are shown in Fig. 3(a). According to the slope criterion53, there is one peak in the slope profiles of C1 and C3, and their corresponding stages (i.e., stages 38 and 7, respectively) are selected as the temperature sensitive stages. However, the slope profile of C2 has two peaks (i.e., stages 4 and 19). Next, the dynamic performances of the different temperature control stages are evaluated for the control structure using basic controllers. The basic controllers are listed as follows: 4


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(1) The feed is flow controlled. (2) The pressures in the three columns are controlled by manipulating the condenser duties of the three columns. (3) The reflux drum levels in the three columns are controlled by manipulating the distillate flow rates. (4) The sump levels in the three columns are controlled by manipulating the bottoms flow rates. (5) The reflux ratios of the three columns are kept constant. (6) The temperature in stage 38 of C1 is controlled by manipulating the reboiler heat input in C1. (7) The temperature in stage 7 of C3 is controlled by manipulating the reboiler heat input in C3. The

flow,

level,

and

pressure

controllers

are

implemented

using

conventional

proportional-integral (PI) controllers in the dynamic simulation control process. The PI settings of the feed flow controller are set with a gain (KC) of 0.5 and an integral time (τI) of 0.3 min; for the pressure controllers, KC = 20 and τI = 12 min. All the level loops are set as proportion controllers with KC = 2 and τI = 9999 min. A dead time of 1 min is used in the temperature control systems; then, relay-feedback tests are run, and the ultimate gains (KU) and periods (PU) are calculated using Tyreus-Luyben tuning53. Based on the basic control structure, a temperature controller with stage 4 as a temperature sensitive stage is added by manipulating the heat duty of the reboiler in C2. However, this structure is unable to return the purities of the three products back to the specified values by introducing ±20 % feed flow rates and composition disturbances. An improved control structure was explored based on the temperature control structure. The reboiler duty of C1 is proportional to the feed flow rate, and a multiplier QR1/F control structure is added. One of the input signals for the QR1/F control structure is the ratio that is controlled by the temperature controller from stage 38 in C1, and the other is the feed mole flow rate. The variables KU and PU are obtained through Tyreus-Luyben tuning after relay-feedback tests. The online composition measurement is investigated to maintain the product mass fraction at the bottom of each column. Fig. 4 shows the improved composition/temperature control structure with stage 4 in C2 as the temperature sensitive stage (CSA) when the temperature controllers are on “cascade”. The dead times of the composition control structures are set to 3 min, and Table 2 gives the ultimate data for the 5



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temperature control and composition control after tuning. Fig. 5 shows the dynamic responses after the feed flow rate increases to 1200 kg/h and decreases to 800 kg/h. The composition mass fraction for the +20 % feed composition disturbance for methanol consists of 84 % methanol, 10.7 % acetonitrile, and 5.3 % benzene, whereas that for the -20 % disturbance consists of 56 % methanol, 29.3 % acetonitrile, and 14.7 % benzene. The disturbances are introduced at 2 h, and the termination time is set to 40 h. The three product purities are able to return to their specified values, as shown in Fig. 5, indicating that the three columns are well controlled. For the condition of using stage 19 in C2 as the temperature control location, the QR/F and composition control structures exhibit the same effects as the TCPSD process when using temperature control tray 4 in C2. The data for the temperature controllers, such as the transmitter ranges, tuning parameters, and controller output ranges, are listed in Table 3. A composition/temperature cascade control structure (CSB), which is similar to CSA, is also analyzed, and the corresponding dynamic performance is shown in Fig. 6. The CSB has a strong resistance to flow disturbances.

3.2.

CONTROL OF THE

PARTIALLY HEAT-INTEGRATED

TCPSD

PROCESS Based on the steady-state simulation, the dynamic controls of the partially heat-integrated TCPSD processes are studied using an auxiliary condenser and implemented using the “flowsheet equations” function in Aspen Dynamics. The overall heat transfer coefficient is set to 0.0020448 GJ/hm2℃54. The condenser of C1 provides 732.13 kW of heat to the reboiler of C2; thus, the heat removal of the auxiliary condenser is 355.23 kW, and the area of the heat exchanger is 28.12 m2. As shown in Fig. 7(a), two flowsheet equations are used to calculate the reboiler duty of C2 and the heat removal rate. The reflux ratio in C2 is controlled by adjusting the temperature in stage 4 or 19; however, the control process cannot run after the composition/temperature cascade control structure is added. Therefore, the output signal of the composition controller CC2 is equal to the value of RR2, and CC2 is used to achieve a high purity methanol product. Not all structures can handle the ±20 % feed flow rate and feed composition disturbances well due to their degrees of freedom. Therefore, the disturbances are reduced to ±10 % feed disturbances, and the corresponding dynamic responses of the improved composition/temperature cascade control structure (CSC) are shown in Fig. 8. The CSC experiences narrow transient deviations, and the 6


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purity of the three products returns to 99.9 wt% although oscillations appear. This structure can be kept constant after 25 h for the feed flow rate disturbances and 15 h for the feed composition disturbances. For the second case, the condenser of C3 provides 158.38 kW heat to the reboiler of C2, and the heat duty in the auxiliary reboiler is 573.77 kW; hence, the area of the heat exchanger is 6.02 m2. Fig. 7(b) gives the flowsheet equations for implementing the partially heat-integrated process with the auxiliary reboiler. The response results (Fig. 9) prove that strong controllability is possible using the control structure (CSD) that is shown in Fig. 10; however, the CSD experiences large transient deviations and some oscillations. The third case of the TCPSD process with partial heat integration is also studied; the condenser duty of C1, the reboiler duty of C2 and the heat removal rate are calculated using three flowsheet equations, as shown in Fig. 7(c). The areas of the two heat exchangers are 6.01 and 22.08 m2. An improved control scheme (CSE) is explored for the partially heat-integrated process shown in Fig. 11. The relevant responses for the ±20 % feed flow rate and the feed composition disturbances are shown in Fig. 12. The pressures in C1 and C3 are set as free variables, and the pressures shift with added disturbances to maintain the product content. The CSE structure achieves good product quality and handles the disturbances well.

3.3. CONTROL OF THE FULLY HEAT-INTEGRATED TCPSD PROCESS The dynamic performance of the fully heat-integrated TCPSD process was implemented using the “flowsheet equations” function. As shown in Fig. 7(d), the first equation is used to calculate the reboiler duty of C2, and the second is used to specify that the condenser duty of C1 is equal to the negative reboiler duty of C2. The control scheme of the fully heat-integrated TCPSD process is the same as that of the partially heat-integrated TCPSD process; however, the product purities cannot be maintained under this scheme due to the large oscillations. A control structure (CSF) is added that includes the QR1/F and composition/temperature cascade control structure. The dynamic responses of this scheme to the 20 % feed disturbances are shown in Fig. 13. The CSF can maintain the purity at the specified value; however, obvious oscillations occur when the feed composition disturbances are introduced, and approximately 30 h are required to reach a new steady state. A pressure-compensated temperature control structure27,

32, 55

7


is used to improve the


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anti-disturbance performance of a fully heat-integrated TCPSD process. The bubble point temperatures of stage 36 (as shown in Fig. 3(b), according to the slope criterion) in C1 are investigated in the pressure range of 5-7 atm. The pressure of stage 36 is 6.24 atm with a composition of 11.56 wt% methanol, 73.84 wt% acetonitrile, and 14.60 wt% benzene; the bubble point temperatures are 407.52 K at 6.24 atm and 412.58 K at 7 atm. The slope is 6.57, and the corresponding equation is shown in Fig. 7(d). This equation is used to calculate the signals fed to the deadtime element, which is then used as the process variable (PV) signal for the temperature controller. The pressure-compensated temperature control structure (CSG) of the TCPSD and the corresponding dynamic responses are provided in Figs. 14 and 15, respectively. The CSG exhibited good controllability, and the responses returned to the constant values at approximately 30 h for ±20 % feed disturbances.

4. COMPARISON This section compares the economics and dynamic performances of the TCPSD processes with no, partial, and full heat integration. As shown in Table 1, the TAC of the partially heat-integrated TCPSD process with an auxiliary condenser is 6.63×105 $/y, which is 19.54 % less than the value of 8.24×105 $/y for the TCPSD process without heat integration. The TACs of the second and third cases are 4.25 % and 4.00 % less than that of the non-heat-integrated process. The fully heat-integrated TCPSD process, with a TAC of 6.41×105 $/y, exhibits the best economic efficiency compared to the TCPSD processes with no and partial heat integration. The CSA and CSB cascade control structures maintain the purities of the three products well while controlling the TCPSD process without heat integration. The CSB takes 10 h to reach steady state, while the CSA takes 20 h. The CSA requires a longer time to reach a new state while maintaining the purity of methanol compared with the CSB. The three partially heat-integrated TCPSD processes produce oscillations after feed flow rate disturbances are introduced. Compared with the CSB control structure, the CSE takes a similar amount of time to reach a new steady state; however, the product purities using the CSE have larger transient deviations than those of the CSB process. For the fully heat-integrated TCPSD process with feed composition disturbances, the CSG process can reduce oscillations and arrive at a new steady state faster than the CSF. However, the benzene purity of the fully heat-integrated TCPSD process experiences larger transient deviations than that of the non-heat-integrated TCPSD process, and the dynamic control of the 8


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fully heat-integrated process takes longer than that of the non-heat-integrated process to reach a new steady state under +20 % feed composition disturbances.

5. CONCLUSION TCPSD processes for separating a complex ternary system of acetonitrile, methanol, and benzene with no, partial, and full heat integration are explored using the Aspen Plus platform. Based on the minimal TAC, the fully heat-integrated TCPSD process is more economical than the processes with no and partial heat integration. The dynamic performances of the different heat-integrated TCPSD processes are investigated using Aspen Dynamics after introducing feed flow rate and composition disturbances. The improved control structures for the three TCPSD processes show good controllability. There are three cases for partial heat integration. In the first case, the condenser duty of C1 provides energy to the reboiler of C2, and excess steam heat is transferred by the auxiliary condenser. In the second case, an auxiliary reboiler is required, and the condenser of C3 sends all of its energy to the reboiler of C2. In the third case, the reboiler of C2 is heated by the top vapor of C3; additional heat is provided by the top vapor of C1; and an auxiliary condenser is needed to cool the remaining top vapor of C1. The TAC of the first case is less than that of the others, whereas the dynamic response of the first case is inferior to that of the third case. Unlike the non-heat-integrated TCPSD process, the partially and fully heat-integrated TCPSD processes generated oscillations . The different strategies for the three processes require different times to reach new steady states because of the interactions of several operating parameters in the three columns. The fully heat-integrated TCPSD process shows better economy than that the other two TCPSD processes; however, the dynamic control of the fully heat-integrated TCPSD process is inferior to that of the non-heat-integrated TCPSD process. These studies contribute to the development of the heat integration and controllability of PSD processes for separating ternary or multicomponent azeotropic mixtures. AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] Notes The authors declare no competing financial interests.

ACKNOWLEDGEMENT 9



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Financial support from the National Natural Science Foundation of China (Projects 21676152 and 21306093) is gratefully acknowledged.

NOTATION B

bottom flow rate [kg/h]

C

distillation column

CS

control structure

CC

composition controller of the columns

D

distillate flow rate [kg/h]

Feed

feed flow rate [kg/h]

ID

column diameter [m]

KC

gain of the controller

KU

ultimate gain

NF

number of feed locations

NREC

number of recycle locations

NT

number of stages

P

pressure [atm]

PC

pressure controller of the columns

PI

proportional-integral controller

PU

ultimate period [min]

QR/F

reboiler duty / molar flow rate of the feed

REC

recycle flow rate [kg/h]

R/F

reflux ratio/ molar flow rate of the feed

RR

reflux ratio

TAC

total annual cost [$/y]

TC

temperature controller of the columns

τI

integral time of the controller [min]

ACRONYMS PSD

pressure-swing distillation

TCPSD

triple column pressure-swing distillation

INDICES 10


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1, 2, 3

column index

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Process. 2016, 110, 160-171. (35) Wang, Q.; Yu, B.; Xu, C. Design and control of distillation system for methylal/methanol separation. Part 1: Extractive distillation using DMF as an entrainer. Ind. Eng. Chem. Res. 2012, 51, 1281-1292. (36) Luyben, W. L. Comparison of pressure-swing and extractive-distillation methods for methanol-recovery systems in the TAME reactive-distillation process. Ind. Eng. Chem. Res. 2005, 44, 5715-5725. (37) Dai, X.; Ye, Q.; Qin, J.; Yu, H.; Suo, X.; Li, R. Energy-saving dividing-wall column design and control for benzene extraction distillation via mixed entrainer. Chem. Eng. Process. 2016, 100, 49-64. (38) Chen, Y.; Li, K.; Chen, C.; Chien, I. L. Design and Control of a Hybrid Extraction–Distillation System for the Separation of Pyridine and Water. Ind. Eng. Chem. Res. 2015, 54, 7715-7727. (39) Yuan, S.; Zou, C.; Yin, H.; Chen, Z.; Yang, W. Study on the separation of binary azeotropic mixtures by continuous extractive distillation. Chem. Eng. Res. Des. 2015, 93, 113-119. (40) Wang, H.; Li, Y.; Su, W.; Zhang, Y.; Guo, J.; Li, C. Design and Control of Extractive Distillation Based on an Effective Relative Gain Array. Chem. Eng. Technol. 2016, 39, 1-10. (41) Luyben, W. L. Control comparison of conventional and thermally coupled ternary extractive distillation processes. Chem. Eng. Res. Des. 2016, 106, 253-262. (42) Benyounes, H.; Shen, W.; Gerbaud, V. Entropy Flow and Energy Efficiency Analysis of Extractive Distillation with a Heavy Entrainer. Ind. Eng. Chem. Res. 2014, 53, 4778-4791. (43) Hsu, K.; Hsiao, Y.; Chien, I. Design and control of dimethyl carbonate− methanol separation via extractive distillation in the dimethyl carbonate reactive-distillation process. Ind. Eng. Chem. Res. 2009, 49, 735-749. (44) Sharma, N.; Singh, K. Control of reactive distillation column: a review. Int. J. Chem. React. Eng. 2010, 8. (45) Prakash, K. J.; Patle, D. S.; Jana, A. K. Neuro-estimator based GMC control of a batch reactive distillation. ISA Trans 2011, 50, 357-63. (46) Diwekar, U. Batch distillation: simulation, optimal design, and control. CRC Press: 2011. (47) Zhu, Z.; Li, X.; Cao, Y.; Liu, X.; Wang, Y. Design and Control of a Middle Vessel Batch Distillation Process for Separating the Methyl Formate/Methanol/Water Ternary System. Ind. Eng. Chem. Res. 2016, 55, 2760-2768. (48) Karami, G.; Amidpour, M.; Sheibani, B. H.; Salehi, G. R. Distillation column controllability analysis through heat pump integration. Chem. Eng. Process. 2015, 97, 23-37. (49) TututiAvila, S.; JiménezGutiérrez, A.; Hahn, J. Control analysis of an extractive dividing-wall column used for ethanol dehydration. Chem. Eng. Process. 2014, 82, 88-100. (50) Kiss, A. A.; Suszwalak, D. J. P. C. Enhanced bioethanol dehydration by extractive and azeotropic distillation in dividing-wall columns. Sep. Purif. Technol. 2012, 86, 70-78. (51) AlcántaraAvila, J. R.; GómezCastro, F. I.; SegoviaHernández, J. G.; Sotowa, K.; Horikawa, T. Optimal design of cryogenic distillation columns with side heat pumps for the propylene/propane separation. Chem. Eng. Process. 2014, 82, 112-122. (52) Zhu, Z.; Liu, X.; Cao, Y.; Liang, S.; Wang, Y. Controllability of separate heat pump distillation for separating

isopropanol-chlorobenzene

mixture.

Korean

J.

Chem.

Eng.

2016.

DOI:

10.1007/s11814-016-0313-1. (53) Luyben, W. L.; Chien, I. Design and control of distillation systems for separating azeotropes. John Wiley & Sons: 2011.

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(54) Luyben, W. L. Distillation design and control using Aspen simulation. John Wiley & Sons: 2013. (55) Zhu, Z.; Wang, L.; Ma, Y.; Wang, W.; Wang, Y. Separating an azeotropic mixture of toluene and ethanol via heat integration pressure swing distillation. Comput. Chem. Eng. 2015, 76, 137-149.

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Table 1. The optimal parameters of different heat-integrated TCPSD processes. TCPSD processes Variables

Partial heat integration

No heat

Full heat

integration

First case

Second case

Third case

integration

NT1

46

46

46

46

43

NT2

50

50

50

50

43

NT3

15

15

15

15

13

NF1/NREC

37/28

37/28

37/28

37/28

33/24

NF2

18

18

18

18

19

NF3

4

4

4

4

2

RR1

2.13

2.13

2.13

2.13

1.51

RR2

3.19

3.19

3.19

3.19

3.37

RR3

0.01

0.01

0.01

0.01

0.01

ID1 (m)

0.66

0.66

0.66

0.66

0.63

ID2 (m)

0.69

0.69

0.69

0.69

0.79

ID3 (m)

0.32

0.32

0.32

0.32

0.36

REC (kg/h)

953

953

953

953

1214

1.64×106

1.65×106

1.61×106

1.66×106

1.60×106

4.97×105

3.33×105

4.97×105

4.60×105

3.21×105

8.24×105

6.63×105

7.89×105

7.91×105

6.41×105

Total Capital investment ($) Annual Operating cost ($/y) TAC ($/y)

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Table 2. Transmitter ranges, controller output ranges, and tuning parameters of the three temperature controllers in the non-heat-integrated TCPSD process, with stage 4 in C2 as a temperature control stage. TC1

TC2

TC3

Controlled variable

T1,38

T2,4

T3,7

Manipulated variable

QR1/F

QR2/F2

QR3/F3

Transmitter range (℃)

0-263.45

0-120.97

0-266.68

Controller output range (GJ/kmol)

0-0.30

0-0.12

0-0.07

KU

4.55

37.26

4.04

PU (min)

4.8

4.2

4.8

KC

1.42

11.65

1.26

τI (min)

10.56

8.24

10.56

CC1

CC2

CC3

X(C2H3N)1,47

X(CH4O)2,50

X(C6H6)3,15

Controlled variable Manipulated variable

T1,38

T2,4

T3,7

Transmitter range

0-2.00

0-2.00

0-2.00

Controller output range (℃)

0-263.45

0-120.97

0-266.68

KU

64.18

309.03

135.43

PU (min)

19.2

16.8

18

KC

20.06

96.57

42.32

τI (min)

42.24

36.96

39.6

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Table 3. Transmitter ranges, controller output ranges, and tuning parameters of the three temperature controllers in the non-heat-integrated TCPSD process, with stage 19 in C2 as a temperature control stage. TC1

TC2

TC3

Controlled variable

T1,38

T2,19

T3,7


QR1/F

QR2/F2

QR3/F3

Transmitter range (℃)

0-265.26

0-131.94

0-266.64

Controller output range (GJ/kmol)

0-0.30

0-0.12

0-0.07

KU

3.33

24.79

3.29

PU (min)

5.4

3.6

4.2

KC

1.04

7.75

1.03

τI (min)

11.88

7.92

9.24

CC1

CC2

CC3

X(C2H3N)1,47

X(CH4O)2,50

X(C6H6)3,15


T1,38

T2,19

T3,7

Transmitter range

0-2.00

0-2.00

0-2.00

Controller output range (℃)

0-265.26

0-132.00

0-266.64

KU

151.09

282.12

139.89

PU (min)

16.2

20.4

18

KC

47.22

88.16

43.72

τI (min)

35.64

44.88

39.60

Controlled variable

17



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Figure 1. Flowsheet of the TCPSD processes with partial heat integration: (a) first case, (b) second case, and (3) third case.

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Figure 2. Flowsheet of the TCPSD process with full heat integration.

19



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Figure 3. Temperature and temperature difference profiles for the three columns: (a) no heat integration and (b) full heat integration.

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Figure 4. CSA control structure with stage 4 in C2 as a temperature control stage for the TCPSD process without heat integration.

21



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Figure 5. Dynamic performances of the CSA control structure with stage 4 in C2 as a temperature control stage for the TCPSD process without heat integration.

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Figure 6. Dynamic performances of the CSB control structure with stage 19 in C2 as a temperature control stage for the TCPSD process without heat integration.

23



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Figure 7. Flowsheet equations of (a) the first case of the partially heat-integrated TCPSD process, (b) the second case of the partially heat-integrated TCPSD process, (c) the third case of the partially heat-integrated TCPSD process, (d) the fully heat-integrated TCPSD process, and (e) the fully heat-integrated TCPSD process using the CSG control structure.

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Figure 8. Dynamic performance of the CSC control structure for the TCPSD process with partial heat integration.

25



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Figure 9. Dynamic performance of the CSD control structure for the TCPSD process with partial heat integration.

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Figure 10. CSD control structure for the TCPSD process with partial heat integration.

27



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Figure 11. CSE control structure for the TCPSD process with partial heat integration.

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Figure 12. Dynamic performance of the CSE control structure for the TCPSD process with partial heat integration.

29



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Figure 13. Dynamic performance of the CSF control structure for the TCPSD process with full heat integration.

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Figure 14. CSG control structure for the TCPSD process with full heat integration.

.

31



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Figure 15. Dynamic performance of the control CSG structure for the TCPSD process with full heat integration.

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Figure 1. Flowsheet of the TCPSD processes with partial heat integration: (a) First case, (b) Second case, and (3) Third case. 197x277mm (200 x 200 DPI)



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 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 2. Flowsheet of the TCPSD process with full heat integration. 199x107mm (200 x 200 DPI)


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Figure 3. Temperature and temperature difference profiles for the three columns: (a) no heat integration and (b) full heat integration. 201x200mm (300 x 300 DPI)



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 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 4. CSA control structure with stage 4 in C2 as a temperature control stage for the TCPSD process without heat integration. 132x62mm (300 x 300 DPI)


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Figure 5. Dynamic performances of control structure CSA with stage 4 in C2 as a temperature control stage for the TCPSD process without heat integration. 247x404mm (300 x 300 DPI)



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Figure 6. Dynamic performances of control structure CSB with stage 19 in C2 as a temperature control stage for the TCPSD process without heat integration. 255x405mm (300 x 300 DPI)


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Figure 7. Flowsheet equations of the partially heat-integrated TCPSD processes: (a) First case, (b) Second case, and (c) Third case; (d) Flowsheet equations of the fully heat-integrated TCPSD process; (e) Flowsheet equations of the fully heat-integrated TCPSD process by using control structure CSG.process; (e) Flowsheet equations of the fully heat-integrated TCPSD process by using control structure CSG. 77x85mm (300 x 300 DPI)



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Figure 8. Dynamic performance of control structure CSC for the TCPSD process with partial heat integration. 249x408mm (300 x 300 DPI)


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Figure 9. Dynamic performance of control structure CSD for the TCPSD process with partial heat integration. 209x297mm (300 x 300 DPI)



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 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 10. CSD control structure for the TCPSD process with partial heat integration. 132x62mm (300 x 300 DPI)


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Figure 11. CSE control structure for the TCPSD process with partial heat integration. 131x62mm (300 x 300 DPI)



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Figure 12. Dynamic performance of control structure CSE for the TCPSD process with partial heat integration. 209x297mm (300 x 300 DPI)


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Figure 13. Dynamic performance of control structure CSF for the TCPSD process with full heat integration. 252x405mm (300 x 300 DPI)



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Figure 14. CSG control structure for the TCPSD process with full heat integration. 115x62mm (300 x 300 DPI)


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Figure 15. Dynamic performance of control structure CSG for the TCPSD process with full heat integration. 241x405mm (300 x 300 DPI)



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38x20mm (300 x 300 DPI)


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Heat Integration and Control of a Triple-Column Pressure-Swing

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