performance of a pinch analysis for the process of recovery of ethanol from fermentation

Research Article

Performance of a Pinch Analysis for theProcess of Recovery of Ethanol fromFermentation

The objectives of the project reported here were to perform an energy analysis forthe process of the recovery of ethanol from fermentation broths by catalytic con-version to gasoline and to conduct a pinch analysis to obtain a new heat exchan-ger network, and thus, reduce the utility costs. A minimum temperature differ-ence of 10 °C was used. A temperature interval diagram and cascade diagram weredrawn to identify the pinch points and four such points were observed. New heatexchanger networks were formulated from this information. The least number ofheat exchangers for the different networks created was 19, whereas the originalprocess had 9. The cost of utilities was the same for both systems. Therefore, itwas concluded that the implementation of this system in the Caribbean could beexpensive since in the first instance, ethanol is not particularly plentiful. Secondly,electricity and water costs are expensive in the Caribbean compared to othercountries in America, such that any effort in reducing CO2 emissions by usingethanol would not be feasible.

Keywords: Ethanol, Pinch technology, Utilities, Energy consumption, Optimization, Heatexchanger networks

Received: May 21, 2007; revised: July 12, 2007; accepted: July 13, 2007

DOI: 10.1002/ceat.200700183

1 Introduction

The demand for petroleum is increasing every year due to in-creasing energy consumption. As such, more research has fo-cused on creating cleaner, renewable sources of energy madefrom non-petroleum materials. One possible alternative energysource is the use of biomass. Biomass represents the only reple-nishable, environmentally acceptable energy resource, whichcould be developed and become available as a near to midtermoption.

The first step in this process entails the production of ethanolfrom biomass. This process can be carried out in three steps:I. Pentosan hydrolysis of cellulose to fermentable sugars (glu-

cose),II. Fermentation of pentosans and hexosans to alcohol, andIII. Recovery of alcohol from the fermentor broth.

Most of the energy is consumed in the last step, primarilybecause the ethanol is produced in small concentrations (typi-cally 8–10 wt %) in the fermentor broth and because of theexistence of an azeotrope in the ethanol-water system at an

ethanol concentration of ca. 95 wt %. Thus, from a purely eco-nomic point of view, the use of biomass-based ethanol as a fuelbecomes unattractive as compared to gasoline. Whitcraft [1]determined that it was technically feasible to convert 90 %aqueous ethanol solutions to gasoline, and this process formsthe focus of this report.

Aldridge [2] investigated the relationship between the ener-gy requirement for distillation of a 10 wt % feed mixture andthe overhead product composition from the distillation col-umn. For their investigation, the reflux ratio was 1.2 (the mini-mum reflux ratio), the feed was at its saturation temperature,and there was 99 % ethanol recovery in the distillate. The rela-tionship that the authors found in shown in Fig. 1. From thefigure it is seen that as the purity of the overhead product in-creases, the energy requirements also increase. This is to be ex-pected since if a greater purity is desired, more energy must beinputted to the separation of the ethanol and water. The plothas an exponential shape and the incremental energy expendi-ture for producing the overhead product increases rapidly forconcentrations greater than ca. 75 %. The minimum energy re-quirement exists at an overhead product composition of 60 %ethanol. According to the authors, this optimum value existsbecause the amount of energy required for the distillation (asthe overhead composition is lowered) decreases at a rate lower

© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim http://www.cet-journal.com

Salisha Khan1

Carmen Riverol1

1 Chemical EngineeeringDepartment, University ofWest Indies, Republic ofTrinidad and Tobago.

–Correspondence: C. Riverol ([email protected]), University of WestIndies, Trinidad, Republic of Trinidad and Tobago.

1328 Chem. Eng. Technol. 2007, 30, No. 10, 1328–1339

than the rate of increase of the energy required to drive thecompressors. The energy for the compressors increases due tothe increased amount of water vapor in the various streams.As a result, this optimum distillate concentration of 60 wt %ethanol was used for the current analysis.

2 Process Description

The output from the fermentor was used as the feed for theprocess and the feed was assumed to contain 10 % ethanol, seeFig. 2 [2]. This composition was chosen since 10 % alcoholfeedstocks are the highest concentration levels produced eco-nomically by conventional fermentation techniques. The liquidfeed was heated to its saturation temperature by three stages of

heat recovery in heat exchangers H-1, H-2, and H-3 (seeFig. 2). H-1 was the overhead condenser for the distillationcolumn, E-1. In H-2, the feed exchanged heat with the bottomproduct of E-1 and in H-3, the feed was heated by exchangewith the final product from the separation chamber, E-2.

E-1 produced an overhead product vapor which contained60 % ethanol. This overhead product vapor was the feed to thereactor, E-4. Before it was fed to the reactor, the gas was com-pressed by C-1 to the reactor operating pressure of 8 atm andit was heated to the reactor temperature of 300 °C by H-5 andH-7. In the reactor, the ethanol vapor was dehydrated and iso-thermally converted to gasoline vapor using the zeolite cata-lyst, ZSM-5. The reactor was kept under isothermal conditionsby cooling with heat transfer oil, XCELTHERM®600. The oilrecovered the exothermic heat released by the reactor and partof this energy was used to supply heat to the reboiler of thedistillation column, and also to preheat the reactor feed. Thevapor product from the reactor was then partially condensedby H-4 and the heat removed was used to heat a portion of theboil-up for the distillation column.

This partially condensed stream was then separated in E-2.The gaseous fraction was primarily composed of C1–C4 hydro-carbon gases and this was compressed by C-2 to a pressure of8 atm. The compressed gas was then recycled back to the reac-tor for conversion to the higher hydrocarbons of which gaso-line is comprised. Thus, the liquid product from E-2 containedonly gasoline and water. This product was cooled in H-3 andH-9, and then separated by decantation, since gasoline andwater are immiscible. Stream data for the process flow diagramcan be found in Appendix A.1.


0.950.90.850.80.750.70.650.6

6000

4000

2000

0

Mass fraction of ethanol in overhead productBTU

per

pound o

f eth

anol pro

duced

Figure 1. Energy required for various distillate compositionsfrom 10 wt % ethanol feed (Aldridge [2]).

H-1 H-2 H -3

321 E-14

7

C -16

5

8

11

H-5

H -7

18

19

Steam

E-4H -4

22

20

E-2

23

C -2

25

21

26

H-9

27

E-3

28

30

29

10 12

24

17

H-8

13

15

14

16

34

E-5

35

H-8

31

H -10

3233

CW

CW

Oil

9

Figure 2. Process flow diagram for the recovery of ethanol by catalytic conversion to hydrocarbons in the gasoline boiling range.

Chem. Eng. Technol. 2007, 30, No. 10, 1328–1339 Pinch technology 1329

3 Current Optimal Heat ExchangerNetwork

The current optimal heat exchanger network presented by theauthors is shown in the process flow diagram, Fig. 2. This pro-cess had steam inputted at H-7 to provide the final preheatingof the reactor feed mixture and the energy supplied was693,125 kJ/h. An additional energy requirement of the processwas the electrical energy required to operate the compressors.The total energy requirement for the compressors was454,518 kJ/h. Hence, the total energy supplied to the processwas 1.148 · 106 kJ/h. Cooling water was supplied at H-9 andH-10 and the total energy removed by the cooling water was813,559 kJ/h. The energy recovery calculation is summarizedas follows:– Total energy recovered = 7,288,229 kJ/h– Total process energy requirements =

Energy recovered + Energy supplied by steam +Electrical energy = 8,435,872 kJ/h

– Percentage energy recovery = 86.4 %The overall objectives of this project were to perform an en-

ergy analysis for the process of the recovery of ethanol fromfermentation broths by catalytic conversion to gasoline, and toevaluate and compare the cost of utilities for the current andproposed heat exchanger networks.

4 Definition of Pinch Technology

Energy conservation is important for a company because it is akey operational factor, particularly when faced with low mar-gins, increasing fuel and utility costs, and greater competitionwithin the marketplace. Hence, one of the important ways acompany can reduce its costs is by optimizing heat exchangernetworks, thus reducing utility costs [3]. This can be achievedusing pinch technology. The term “pinch technology” was in-troduced by Linnhoff and Vredeveld to represent a new set ofthermodynamically based methods that guarantee minimumenergy levels in the design of heat exchanger networks. Pinchtechnology tracks the heat flow for all process streams in a sys-tem, from an entire plant to a unit operation. With pinch tech-nology, managers and engineers can:– Target minimum energy consumption.– Identify process modifications that further reduce energy

targets.– Design or redesign the process to meet these energy targets.– Design optimum heat and power systems to supply process

needs.Pinch technology provides a simple methodology for sys-

tematically analyzing chemical processes and the surroundingutility systems, using the first and second laws of thermody-namics [4]. The first law of thermodynamics states that energycannot be created or destroyed only converted from one formto another. It is from this law that the equation for calculatingthe enthalpy changes is obtained. The second law of thermody-namics states that for any physical or chemical process, the en-tropy of the universe tends to increase. In essence, this meansthat heat will not flow by itself from a low temperature point

to a high temperature point and this concept shall be appliedlater on in the cascade diagram.

4.1 Advantages of Pinch Technology

The application of pinch technology to a process can havemany benefits for a company [5, 6]. The ability of pinch tech-nology to target energy consumption and capital costs beforedetailed design ensures the proper balance between operatingand investment costs when major design decisions are made.Pinch analysis also clearly identifies energy usage throughoutthe entire process, and hence, its design procedures systemati-cally optimize the process. These features are not available withtraditional design methods. Pinch offers other advantages overtraditional design methods. These include:I. Cost Savings – Pinch technology recommendations result

in energy savings of approximately 25–40 %, although sav-ings achieved are specific to the process. For new facilitydesigns, energy savings are often accompanied by signifi-cant reductions in capital costs [5].

II. Reduced Emissions – Implementing pinch technology re-commendations reduces the amount of energy consumedand fuel burned, reducing emission levels. Plants wantingto increase capacity can maintain the total discharge vol-ume at or below permitted levels [4].

III. Increased Capacity – When heat and power systems limitprocess capacity, pinch technology recommendations helpease the strain of the current systems. As pinch optimizesprocess heat recovery, the heat and power systems can beused at a higher capacity.

4.2 Constraints of Using Pinch Technology

There are also constraint factors which need to be consideredwhen pinch technology is being applied to a system [5]. Theseinclude:I. Type of System – Pinch technology is ideal for large, com-

plex processes, often with multiple unit operations. Con-tinuous operations are the easiest applications. However, apinch analysis may be economical for any system in whichutility costs are a significant portion of the overall operat-ing costs. Simple systems, in which design assumptionsconcerning heat sources and sinks are straightforward,may not need pinch analysis.

II. Modification Constraints – An effective pinch analysis mustdefine and factor in constraints, i.e., parts of the systemthat cannot be modified, at the beginning of the analysis.Constraints include: Process constraints – critical factors af-fecting product quality, fixed operating parameters includ-ing temperature and pressure, space requirements, equip-ment operability, etc.; and Safety constraints – placementand operating conditions of volatile process streams.

III. Economic constraints – maximum modification costs andpayback periods.


1330 S. Khan et al. Chem. Eng. Technol. 2007, 30, No. 10, 1328–1339

5 Method of Pinch Analysis

A central part of data extraction is the identification of theheating and cooling requirements in the process. The necessarydata for each process stream are the identification of the hot,cold and utility streams in the process as well as the thermaldata extraction for process and utility streams.

The energy requirement for each hot and cold stream wasfound using Eq. (1):

Q = mCp(Ts – Tt) (1)

If there is a phase change, the latent heat of vaporizationwould be added to the Q value.

I. Selection of the minimum temperature difference, DTmin.In a heat exchanger, the heat transfer area required to transfera specified heat load is inversely proportional to the tempera-ture difference between the two streams. This means that thevalue chosen for DTmin will determine the size of the heat ex-changers in a network. A reduction in DTmin would increasethe heat recovery, thus decreasing the utility consumption andcost [6], but at the expense of an increase in the heat exchangersize and capital costs.

II. Construction of the temperature interval diagram.The temperature interval diagram contains all the source andtarget temperatures of the hot and cold streams, where the axesare shifted by the minimum approach temperature. The pro-cess streams are represented by arrows and each interval is la-beled alphabetically. This temperature interval diagram showsall the streams that have a temperature change in that interval,and thus, the net energy change for that interval can be calcu-lated by using Eq. (1) for each stream and then summing theenergy values.

III. Construction of the cascade diagram.The cascade diagram shows the net amount of energy in eachinterval. The basic concept of the cascade diagram is that ifthere is excess energy in a temperature interval, it can be trans-ferred or “cascaded” down. However, energy cannot be trans-ferred up. When a point is reached where no more energy canbe transferred down (the net energy value becomes negative)then utilities must be used. This temperature interval thencontains a pinch point. Energy is cascaded down through thepinch and rejected to the cold utility. If heat is transferredacross the pinch, the net result will be that more heat will haveto be added from the hot utility and rejected to the cold utility.Consequently, to minimize the hot and cold utility require-ments, energy should not be transferred across the pinch. Also,hot utilities should not be used below the pinch and cold utili-ties should not be used above the pinch.

IV. Determination of the minimum number of heat exchangers.A separate analysis must be performed for above and belowthe pinch. Boxes are drawn to represent energy in the hot andcold process streams and utilities. The transfer of energy fromthe hot stream or utility to the cold stream or utility is shownby a line (with the amount of energy). Each line indicates a

heat exchanger that is required. However, for analysis abovethe pinch, the following rule must be applied:

mCp, hot ≤ mCp, cold (2)

For analysis below the pinch, the rule which must be fol-lowed is that:

mCp, hot ≥ mCp, cold (3)

In some cases, the streams may need to be divided into sub-streams so that the above criteria can be met, as splitting thestream reduces the mass flow rate.

V. Design of the heat exchanger network.The heat exchanger network is drawn where each exchanger isrepresented by two circles connected by a line. Each circle rep-resents a side of the heat exchanger. The heat exchanger net-work must be designed so that there are no temperature cross-overs, i.e., the DTmin criterion is met.

5.1 Methodology

The methodology employed in the pinch analysis is summa-rized as follows:I. Mass and energy balances were performed to determine

all missing information for the streams.II. A minimum temperature difference of 10 °C was chosen

and all heat exchangers which did not match this criter-ion were ignored and not included in the pinch analysis.

III. All hot and cold streams were identified and the enthalpychange for each stream was calculated using Eq. (1).

IV. The temperature interval diagram was drawn and the en-ergy of each interval was calculated using Eq. (1).

V. A cascade diagram was drawn and the pinch points wereidentified.

VI. An arrangement for the minimum number of heat ex-changers was designed, ensuring that the appropriate cri-teria for the heat capacities were met.

VII. The heat exchanger network was designed, ensuring thatthere were no temperature crossovers, see Eqs. (2) and (3).

VIII. The above steps were repeated until three possible heatexchanger networks were obtained, see Eq. (2).

6 Results

A summary of the stream data for the pinch analysis is given inTab. 1. Fig. 3 shows the temperature interval diagram for thepinch analysis of this process. Details of the calculation of theenergy value for each interval can be found in Appendix A.2.A cascade diagram for the pinch analysis is shown in Fig. 4.

For other arrangements of Figs. 5–8, the above heat ex-changer networks would remain the same. The only changewould be in the arrangements for below pinch 4, detailed inthe next section.

Figs. 9–12 describe the different arrangements obtainedusing different distributions of the energy above and below the



pinch. The algorithm offers the flexibility of modifying the dis-tribution of energy by taking Eqs. (1) and (2) into account.The arrangement that offer the least number of heat exchan-gers or reduces the consumption of utilities can be consideredas optimal.

7 Discussion

For the original process flow diagram (PFD) shown in Fig. 2,heat exchangers H-3, H-4, and H-8 were not considered in the

pinch analysis, since the change in temperature across theseheat exchangers was less than the minimum temperature dif-ference, DTmin, of 10 °C.

After the pinch analysis was completed, an optimal heat ex-changer network had to be developed and three of these ar-rangements were constructed. For all three networks, the ar-rangement of the heat exchangers for above pinch 1, abovepinch 2, above pinch 3 and above pinch 4 were the same dueto the presence, in most cases, of only the hot utility and onestream. A summary of the heat exchangers at each point of thepinch analysis is shown in Tab. 2.

The only difference in the heat exchanger networks was inthe analysis for below pinch 4. Arrangements 1, 2, and 3 had16, 11, and 10 heat, respectively, for the analysis below pinch4. Thus, arrangement 3 was the optimal heat exchanger net-work since it had the least number of heat exchangers and thenew process flow diagram shown in Fig. 12 was based on this.

However, there were limitations when developing the heatexchanger networks, such as:


Table 1. Stream data for the pinch analysis.

Stream mCp (kJ/hr °C) Ts (°C) Tt (°C) Condition Q (kJ/hr)

7 1,160 88.9 67.6 Hot 545,595

10 31,685 98.9 44.9 Hot 1,710,990

27 5,133 74.2 20.0 Hot 278,209

32 5,375 129.6 30.0 Hot 535,350

34 5,375 289.6 268.0 Hot 116,393

1 36,373 25.0 40.0 Cold –545,595

2 36,404 40.0 87.0 Cold –1,710,990

18 10,300 238.7 250.0 Cold –116,393

19 12,466 250.0 305.6 Cold –693,125

Total 120,434

Stream 7 10 27 32 34 1 2 18 19

mCp 1160 31685 5133 5375 5375 36373 36404 10300 12466

Temp (ºC) Temp(ºC) Q(kJ/hr)

315.6 305.6

289.6 A 279.6 -324,116

268 B 258 -153,520

260 C 250 -99,105

248.7 D 238.7 -116,390

129.6 E 119.6 0

98.9 F 88.9 165,013

97 G 87 70,414

88.9 H 78.9 5,314

74.2 I 64.2 547,597

67.6 J 57.6 45,863

50 K 40 101,886

44.9 L 34.9 29,682

35 M 25 -256,064

30 N 20 52,540

20 O 10 51,330

120,444

Figure 3. Temperature Interval Diagram for the pinch analysis.

Table 2. Summary of the heat at each point of the pinch analysis.

No. of Heat Exchangers

Above Pinch 1: 1

Above Pinch 2: 2

Above Pinch 3: 1

Above Pinch 4: 1

Below Pinch 4: 10



A

-324,116

B

-153,520

Pinch 1

HU

324,116

C

-99,105

Pinch 2

HU

153,520

D

-116,390

Pinch 3

HU

99,105

E

0

Pinch 4

F

165,013

G

70,414

0

165,013

H

5,314

235,427

I

547,597

240,741

HU

116,390

788,338

J

45,863

K

101,886

834,201

L

29,682

936,087

M

-256,064

965,769

N

52,540

709,705

O

51,330

762,245

CU

813,575

813,575

Figure 4. Cascade diagram for the pinch analysis.

19

1 HU

Q = 324,116 kJ/hr

305.6

279.6

Figure 5. HEN above pinch 1.

34 19

289.6

2

268

2 267.3

258

1 279.6

267.3 HU

Q = 153,520 kJ/hr

Q = 116,393 kJ/hr


19

1 258

250

HU

Q = 99,105 kJ/hr


18

1 250

238.7

HU

Q = 116,390 kJ/hr




7 10 27 32 1a 1b 1c 1d 1e 1f 1g 1h 1i 1j 2a 2b

1 1

98.9

51.9

87

40

Q = 1,488,960 kJ/h

2 2

Q = 80,625 kJ/h51.9

49.4

40

25

3 49.4

44.9

CU

4 74.2

59.2

4

Q = 141,405 kJ/h

Q = 76,995 kJ/h 40

25

5 59.2

44.2

5

Q = 76,995 kJ/h 40

25

6

44.2

20

CU

Q = 124,235 kJ/h

7 10 27 32 1a 1b 1c 1d 1e 1f 1g 1h 1i 1j 2a 2b

7

129.6

88.3

7

87

40

Q = 222,030 kJ/h

8

88.3

73.3

8

40

25

Q = 80,625 kJ/h

9

73.3

58.3

9

40

25

Q = 80,625 kJ/h

10

58.3

43.3

10

40

25

Q = 80,625 kJ/h

11

43.3

30

Q = 71,445 kJ/h

CU

7 10 27 32 1a 1b 1c 1d 1e 1f 1g 1h 1i 1j 2a 2b

12

88.9

88.9

12

40

25

Q = 17,400 kJ/h

13

88.9

88.9

13

40

25

Q = 17,400 kJ/h

14

88.9

88.9

14

Q = 17,400 kJ/h 40

25

15

88.9

88.9

15

Q = 16,905 kJ/h 40

25

16

88.9

67.6

CU

Q = 476,490 kJ/h

Figure 9. HEN Arrangement 1.



7 10 1b 1c 1d 1e 1f 2a 2b

1

129.6

88.3

1

Q = 221,795 kJ/hr

2

87

40

88.3

73.3

2

40

25

Q = 80,625 kJ/hr

3

73.3

58.3

3

40

25

Q = 80,625 kJ/hr

4

58.3

43.3

4

40

25

Q = 80,625 kJ/hr

5

43.3

30

CU

Q = 71,680 kJ/hr

27 32 1a

6

74.2

59.2

6

40

25

Q = 76,995 kJ/hr

7

59.2

20

CU

Q = 201,230 kJ/hr

8

98.9

51.9

8

87

40

Q = 1,489,195 kJ/hr

9

51.9

44.9

9

40

25

Q = 221,795 kJ/hr

10

88.9

88.9

10

Q = 4930 kJ/hr 40

25

11

88.9

67.6

CU

Q = 540,665 kJ/hr

7 10 1b 1c 1d 1e 1f 2a 2b27 32 1a



I. Stream 7 was initially at a temperature of 88 °C and had afinal temperature of 67.6 °C but stream 2 had a final tem-perature of 87 °C. Hence, these two streams could not beconnected since a temperature cross would occur.

II. Stream 27 was initially at a temperature of 74.2 °C butstream 2 had a final temperature of 87 °C. The hot streamcannot heat stream 2 to a temperature higher than thetemperature at which the hot stream enters, and therefore,these streams could not be connected since this would re-sult in a temperature cross.

III. Stream 7 had a very low mCp value of 1160 kJ/°C com-pared to the mCp values of the cold streams, and therefore,care had to be taken when connecting it to the streams inorder to meet the objective of using the minimum numberof heat exchangers possible.

A comparison of the actual process flow diagram and thatdetermined from the pinch analysis showed that the originaldiagram had less heat exchangers and streams than the sug-gested alternative. The original PFD had a total of 9 heat ex-changers whereas the new PFD had 19 heat exchangers. Fromthis result, it can be concluded that if the new alternative fromthe pinch analysis were to be installed, there would be a signifi-cant capital cost due to the purchase of new heat exchangerssince there would be twice the number of heat exchangers re-quired. There would also be a cost for the installation of newpipelines due to the increased number of streams since manyof the streams have to split under the new heat exchanger net-work. However, the new PFD guarantees the total reuse of theenergy in the process.

The amount of energy to be supplied as heat to the systemby the hot utilities was the same for both process flow dia-


7 10 27 32 1a 1b 1c 1d 1e 2a 2b

1

88.9

67.6

CU

Q = 545,595 kJ/hr

2

98.9

52.9

2

87

40

Q = 1,458,365 kJ/hr

3

52.9

44.9

3

40

25

Q = 252,625 kJ/hr

4

74.2

64.2

4

40

25

Q = 51,095 kJ/hr

5

64.2

20

CU Q = 227,130 kJ/hr

6

129.6

82.6

6

87

40

Q = 252,625 kJ/hr

7

82.6

67.6

7

40

25

Q = 80,625 kJ/hr

8

67.6

52.6

8

40

25

Q = 80,625 kJ/hr

9

52.6

37.6

9

40

25

Q = 80,625 kJ/hr

10

37.6

30

CU

Q = 40,850 kJ/hr

7 10 27 32 1a 1b 1c 1d 1e 2a 2b



grams, at a value of 693,131 kJ/h. Similarly, the amount of en-ergy removed by the cold utilities was the same for both dia-grams, at a value of 813,575 kJ/h. Electricity costs for workdone by the compressors were also the same. As a result, thecost of the utilities for both PFDs would be equivalent. For thealternative PFD, the possibilities for the utilities to be recycledwere considered, i.e., where the output conditions of the cool-ing water could be used as the source of heat for heaters or viceversa. However, due to the high temperatures (greater than307 °C) at which the steam must be supplied, it would be ex-tremely difficult to get the cooling water (assumed to be enter-ing at 30 °C) to be heated to these temperatures solely by ab-sorption of heat from the process streams.

8 Conclusions

I. The pinch analysis could be repeated for different values ofthe minimum temperature difference, DTmin. A reductionin DTmin would increase the heat recovery, thus decreasingthe utility consumption and cost, but at the expense of anincrease in the heat exchanger size and capital cost.

II. The pinch analysis could be performed using Total SiteAnalysis. This pinch analysis just focused on the part ofthe plant that converted the ethanol/water feed to gasolineso the pinch analysis could be made to include the hydro-lysis and fermentation part of the process that generatedthe ethanol/water mixture.

III. A Top Level Analysis could be performed on the process.Top level analysis is a bottom-up procedure in which onefirst determines the utilities "worth saving" and how muchof the existing utility system can be saved within the con-text of the constraints. This can be determined by formu-lating a MINLP model of the entire utility system includ-ing steam distribution headers, back-pressure andcondensing turbines, and steam generation facilities, to-gether with the constraints on the system such as maxi-mum and minimum flow rates. Optimization of the modelto minimize operational costs for theoretical steam savingsin each header shows the extent of savings.

IV. In order to look for other ways in which the utility costscould be reduced, a Water Pinch Analysis could be per-formed on the process. Water pinch is a systematic tech-nique for analyzing water networks and reducing watercosts for processes. It uses advanced algorithms to identifyand optimize the best water reuse, regeneration, and efflu-ent treatment opportunities. This could also help to reducelosses of both feedstock and valuable products in the efflu-ent streams.

V. The implementation of this system in the Caribbean couldbe expensive because ethanol is not plentiful. The use ofpetroleum is still the first option. On the other hand, thecost of electricity is expensive in the Caribbean with re-spect to other countries in America, so it may be viable toimplement the system at a future date.


H-1

1

1a

H-2

H-3

1b

H-4

1d

1c

H-5

1e

1a-h

1b-h

1c-h

1e-h

1d-h

H-6

H-7

2

2b

2a

2a-h

2b-h

H-8

3

E-1

4

H-9

7

8

C-1

6

5

H-10

12

9

17

14

H-11

18

Steam

H-12

19a

Steam

H-13

19b

H-14

19c

Steam

H-15

19d

E-4

20

CW

H-16

22

E-2

23

C-2

24

25

21

15

13

16

26

27a

H-18

27b

CW

E-3

28

29Gasoline

30Water

10a

10b

11

Reject

34 35

Oil

31

H-10

32a

32b

32c

32d

H-17

32e

33

CW

E-5

Figure 12. New process flow diagram according to pinch analysis.


Appendix A

A.1 Stream Data for the Original Process FlowDiagram as Shown in Fig. 1

COMPONENT Stream 1 Stream 2 Stream 3 Stream 4 Stream 5

Ethanol (kmol/h) 19.69 19.69 19.69 19.69 24.31

Water (kmol/h) 453.59 453.59 453.59 453.59 41.48

C2H4(kmol/h) 0.00 0.00 0.00 0.00 0.00

C5H12 (kmol/h) 0.00 0.00 0.00 0.00 0.00

C6H14 (kmol/h) 0.00 0.00 0.00 0.00 0.00

C7H16 (kmol/h) 0.00 0.00 0.00 0.00 0.00

C8H18 (kmol/h) 0.00 0.00 0.00 0.00 0.00

C6H5-CH3

(kmol/h)0.00 0.00 0.00 0.00 0.00

C6H4-(CH3)2

(kmol/h)0.00 0.00 0.00 0.00 0.00

Total Molar FlowRate (kmol/h)

473.28 473.28 473.28 473.28 65.79

Pressure (psia) 14.7 14.7 14.7 14.7 14.7

Temperature (°C) 25.0 40.0 87.0 92.0 88.9


Ethanol (kmol/h) 19.49 4.81 4.81 0.25 0.20

Water (kmol/h) 33.26 8.22 8.22 523.42 420.33

C2H4(kmol/h) 0.00 0.00 0.00 0.00 0.00

C5H12 (kmol/h) 0.00 0.00 0.00 0.00 0.00

C6H14 (kmol/h) 0.00 0.00 0.00 0.00 0.00

C7H16 (kmol/h) 0.00 0.00 0.00 0.00 0.00

C8H18 (kmol/h) 0.00 0.00 0.00 0.00 0.00

C6H5-CH3

(kmol/h)0.00 0.00 0.00 0.00 0.00

C6H4-(CH3)2

(kmol/h)0.00 0.00 0.00 0.00 0.00

Total Molar FlowRate (kmol/h)

52.76 13.03 13.03 523.67 420.53

Pressure (psia) 14.7 14.7 14.7 14.7 14.7

Temperature (°C) 88.9 88.9 67.6 98.9 98.9


Ethanol(kmol/h)

0.20 0.05 0.00887 0.0143 0.041

Water (kmol/h) 420.33 103.09 18.27 29.45 84.82

C2H4(kmol/h) 0.00 0.00 0.00 0.00 0.00

C5H12 (kmol/h) 0.00 0.00 0.00 0.00 0.00

C6H14 (kmol/h) 0.00 0.00 0.00 0.00 0.00

C7H16 (kmol/h) 0.00 0.00 0.00 0.00 0.00

C8H18 (kmol/h) 0.00 0.00 0.00 0.00 0.00

C6H5-CH3

(kmol/h)0.00 0.00 0.00 0.00 0.00

C6H4-(CH3)2

(kmol/h)0.00 0.00 0.00 0.00 0.00

Total MolarFlow Rate(kmol/h)

420.53 103.14 18.28 29.46 84.86

Pressure (psia) 14.7 14.7 14.7 14.7 14.7

Temperature(°C)

44.9 98.9 98.9 98.9 98.9


Ethanol(kmol/h)

0.041 0.043 19.49 19.49 19.49

Water (kmol/h) 84.82 88.67 33.26 33.26 33.26

C2H4(kmol/h) 0.00 0.00 0.00 0.00 0.00

C5H12 (kmol/h) 0.00 0.00 0.00 0.00 0.00

C6H14 (kmol/h) 0.00 0.00 0.00 0.00 0.00

C7H16 (kmol/h) 0.00 0.00 0.00 0.00 0.00

C8H18 (kmol/h) 0.00 0.00 0.00 0.00 0.00

C6H5-CH3 (km-ol/h)

0.00 0.00 0.00 0.00 0.00

C6H4-(CH3)2

(kmol/h)0.00 0.00 0.00 0.00 0.00


84.86 88.72 52.76 52.76 52.76

Pressure (psia) 14.7 14.7 125.0 125.0 125.0

Temperature(°C)

98.9 98.9 238.7 250.0 305.6




Ethanol(kmol/h)

19.49 0.00 0.00 0.00 0.00

Water (kmol/h) 34.37 53.88 53.88 1.11 1.11

C2H4(kmol/h) 4.88 4.88 4.88 4.88 4.88

C5H12 (kmol/h) 0.16 1.59 1.59 0.16 0.16

C6H14 (kmol/h) 0.06 1.32 1.32 0.06 0.06

C7H16 (kmol/h) 0.01 0.62 0.62 0.01 0.01

C8H18 (kmol/h) 0.01 1.40 1.40 0.01 0.01

C6H5-CH3

(kmol/h)0.01 0.51 0.51 0.01 0.01

C6H4-(CH3)2

(kmol/h)0.00 0.66 0.66 0.00 0.00


58.99 64.86 64.86 6.24 6.24

Pressure (psia) 110.0 110.0 110.0 105.0 117.6

Temperature(°C)

300.0 300.0 110.0 110.0 117.2


Ethanol(kmol/h)

0.00 0.00 0.00 0.00 0.00

Water (kmol/h) 52.77 52.77 52.77 0.00 52.77

C2H4(kmol/h) 0.00 0.00 0.00 0.00 0.00

C5H12 (kmol/h) 1.44 1.44 1.44 1.44 0.00

C6H14 (kmol/h) 1.27 1.27 1.27 1.27 0.00

C7H16 (kmol/h) 0.60 0.60 0.60 0.60 0.00

C8H18 (kmol/h) 1.38 1.38 1.38 1.38 0.00

C6H5-CH3

(kmol/h)0.50 0.50 0.50 0.50 0.00

C6H4-(CH3)2

(kmol/h)0.66 0.66 0.66 0.66 0.00


58.62 58.62 58.62 5.85 52.77

Pressure (psia) 105.0 105.0 105.0 100 100

Temperature(°C)

110.0 74.2 20.0 20.0 20.0

COMPONENT Stream 31Stream 32Stream 33Stream 34Stream 35

Oil (kg/h) 2150 2150 2150 2150 2150

Total Molar FlowRate (kg/h)

2150 2150 2150 2150 2150

Pressure (psia) 14.7 14.7 14.7 14.7 14.7

Temperature (°C) 268.0 129.6 30.0 289.6 268.0

A.2 Energy Values of Each Interval in the IntervalDiagram

Interval Q (kJ/kmol)

A –324,116

B –153,520

C –99,105

D –116,390

E 0

F 165,013

G 70,414

H 5,314

I 547,597

J 45,863

K 101,886

L 29,682

M –256,064

N 52,540

O 51,330

Total 120,444

Symbols used

m [kmol/h] mass flow rateCp [kJ/kg°C] specific heat capacityDHvap [kJ/kmol] heat of vaporization for streams

with a phase changeTs [°C] supply temperatureTt [°C] target temperature

References

[1] D. R. Whitcraft, Ind. Eng. Chem. 1983, 22, 452.[2] G. A Aldridge, X. E. Verykios, R. Mutharasan, Ind. Eng.

Chem. 1984, 23, 733.[3] W. D. Seider, J. D. Seader, D. R. Lewin, Process Design Princi-

ples – Synthesis, Analysis and Evaluation, John Wiley & Sons,New York 2005.

[4] R. Smith, Chemical Process Design, McGraw-Hill, New York1995.

[5] Pinch TechnologyTechnical Commentary, EPRI Process Indus-try Coordination Office, 1988, 1 (3), 1.

[6] G. Ricci, C. Bealing, Hydrocarbon Process. 2003, 12, 76.



performance of a pinch analysis for the process of recovery of ethanol from fermentation

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