H82

PLD: Heat Exchanger Network

Synthesis

Group number 31

Group Member

Adnaan Malak (012117)

Chumley Fernando (011493)

Santhosh Ganesan (009074)

Lecturer

Dr. Denny K. S. Ng

1. IntroductionIn industrial plants these days, one of the major problems that have been identified is the huge amount consumption of energy for production

purposes. This is found to be a reason that contributes to increase in operational and production cost of industries. At a specific level, energy is consumed and rejected at another level. Most of the industrial processes involve the heat transfer from a stream to another stream or from a utility to a stream. In order to overcome this highly rated problem, pinch analysis is used which is known to be successful for investigation of this matter and efficient design of heat exchangers networks. Pinch analysis basically is used to analyse the heat flow of a process based on the fundamentals of thermodynamics. It has the tools known as the hot and cold composite curves which are the overall heat demand release of an industrial process. This are used to identify the possible heat recovery which would lower the energy cost of industrial plants.

2. DiscussionGrand Composite Curves (GCC) is plotted based on the initial heat integration case and the proposed heat integration case. The assumption made in order to plot this curve is that the heat capacity is not affected by the change in temperature.

2.1Heat Integration1) Initial heat integration case

For the initial case, the plant has no pinch to divide the process into divisions for instance a region above the pinch and a region below the pinch. And this is known as the threshold problem. Figure 1 shows us the GCC for the initial heat integration case as observed. As the observation, there is no heat recovery pocket that has been identified in this curve.

0.00 20.00 40.00 60.00 80.00 100.00 120.00-100

0

100

200

300

400

500

600

700 GCC

GCC

Heat Flow(kW)

SH IF T

TE M PE R AT U RE (₀ C)

Graph 1: GCC of Initial Heat Integration case

2) Proposed heat integration case

It is interesting to note that threshold problems are very common in practice and although they do not have a process pinch, pinches are introduced into the design when multiple utilities are added. In our case we introduced a cold utility from 30◦ C -450◦ C to generate steam. As it can be seen from figure 2 that huge energy pocket is obtained on the graph

that represents that all the energy lost by hot stream is recovered by cold stream.

Graph 2: GCC curve for proposed case

Based on the above figure it is known that the required heat and cold utility is visible. As all the energy of hot utility is recovered there is no necessary need of adding an external utility. With that proposed alternative integration offers a new process configuration, and the simulation study for this design was performed via Microsoft Visio.

Energy Recovery Pocket

QHmin

QCmin

2.2UTILITY SAVINGS:The following table provide an overview of the utility savings predicted based on:-

1. Base Case – Without Heat Integration2. Initial Heat Integration3. Proposed Alternative integration

Table1: Estimated Utility Savings

Base Case(Based on task 2)

Initial Heat Integration

Proposed Alternative Integration

Hot utility (kW) 420555.6 - 8688.7Cold utility (kW) 530555.6 109400.56 8688.7Total utility (kW) 951111.2 109400.56 17377.4

Utility saving compared to base

case (%)- 88.5 98.2

It is obvious from table 1 that the proposed alternative offers a great deal of utility savings. The base case requires 951111.2kW of utility while the initial and proposed cases stand at 1009400.56kW and 17377.4kW respectively. Therefore, the utility savings for the proposed alternative is 98.2%, which 88.5% more than the initial integration.

3. ConclusionThe problem that is encountered the most by almost all of the industrial plant is the huge amount consumption of energy. This problem can be solved by introducing pinch analysis. This technology has been really efficient by reducing the amount of energy consumed and at the same time managed to reduce the capital cost as well of many industrial plants. This is though proven in the proposed case where huge amount of energy was saved using this solution. Through the use of this very efficient technology, energy was conversed, heat recovery was maximized, energy consumption was reduced and the reduction of capital cost.

4. Reference:

1. Smith, R. (2005). Chemical Process Design and Integration. New York: John Wiley & Sons

2. Polley, G.T. and Hegg, P.J. (1999). Don’t let the Pinch pinch you. ABI/INFORM Trade & Industry.

3. Pinch Technology Basic for Engineers; article

5. Appendix– Pinch AnalysisInitial case

1) Extraction of data:From the given process flow diagram, the following data are extracted.No. Stream Supply

TemperatureTarget Temperature

Heat Duty Heat Capacity flowrate

oC oC kJ/h MW MW/Oc1 7--8 635.50 160.00 -3E+08 -77.72 0.163452 14--15 137.50 210.00 4E+07 12.11 0.167053 16--17 326.30 34.98 -2E+08 -47.28 0.162294 25--27 30.02 110.00 1E+07 3.47 0.043385 39--41 220.00 10.02 -7E+07 -20.25 0.096446 22--23 139.90 110.00 -6E+05 -0.17 0.005727 36--37 30.87 240.90 5E+07 14.59 0.069458 46--48 10.06 200.00 2E+07 5.02 0.026439 50--51 54.30 75.00 7E+05 0.18 0.0087310 67--68 164.80 215.00 5E+05 0.15 0.0030411 53--54 53.23 94.16 8E+06 2.22 0.0541812 60--61 93.97 93.13 -1E+06 -0.39 0.4695813 57--58 52.75 141.00 1E+06 0.29 0.0032714 70-1--71 132.20 240.90 4E+05 0.10 0.0009315 74-BDO--

74S250.60 35.00 -4E+06 -1.24 0.00575

16 63PM--63 104.10 30.00 -2E+06 -0.47 0.00638FIGURE 1: Stream Data Table

2) Analysis of data: For a ΔTmin= 30 °C

No. Stream Type Supply Shift Target Shift

oC oC

1 7--8 hot 620.50 145.00

2 14--15 cold 152.50 225.00

3 16--17 hot 311.30 19.98

4 25--27 cold 45.02 125.00

5 39--41 hot 205.00 -4.98

6 22--23 hot 124.90 95.00

7 36--37 cold 45.87 255.90

8 46--48 cold 25.06 215.00

9 50--51 cold 69.30 90.00

10 67--68 cold 179.80 230.00

11 53--54 cold 68.23 109.16

12 60--61 hot 78.97 78.13

13 57--58 cold 67.75 156.00

14 70-1--71 cold 147.20 255.90

15 74-BDO--74S hot 235.60 20.00

16 63PM--63 hot 89.10 15.00

FIGURE 2: Table for Shift temperatures

3) Targeting and Heat Cascade Shift

Temperature Interval T(i+1)-Ti mCpnet dH Infeasible Cascade Feasible Cascade°C °C kW/K kW Hot Pinch 635.5 °C

620.5 PINCH ▼ 0 ▼ 0 Cold Pinch 605.5 °C1 309.2 163.5 50539.8762 surplus 50539.88 50539.88

311.3 ▼ 50539.88 ▼ 50539.88 Min Hot Utility 0.0 kW2 55.4 325.7 18046.0959 surplus 18046.1 18046.1 Min Cold Utility109400.56 kW

255.9 ▼ 68585.97 ▼ 68585.973 20.3 255.4 5183.8139 surplus 5183.814 5183.814 SINGLE PINCH PROBLEM

235.6 ▼ 73769.79 ▼ 73769.794 5.6 261.1 1462.2182 surplus 1462.218 1462.218 THRESHOLD PROBLEM

230 ▼ 75232 ▼ 752325 5 258.1 1290.3378 surplus 1290.338 1290.338

225 ▼ 76522.34 ▼ 76522.346 10 91.0 910.1776 surplus 910.1776 910.1776

215 ▼ 77432.52 ▼ 77432.527 10 64.6 645.9128 surplus 645.9128 645.9128

205 ▼ 78078.43 ▼ 78078.438 25.2 161.0 4057.9651 surplus 4057.965 4057.965

179.8 ▼ 82136.4 ▼ 82136.49 23.8 164.1 3904.9419 surplus 3904.942 3904.942

156 ▼ 86041.34 ▼ 86041.3410 3.5 160.8 562.8098 surplus 562.8098 562.8098

152.5 ▼ 86604.15 ▼ 86604.1511 5.3 327.9 1737.6189 surplus 1737.619 1737.619

147.2 ▼ 88341.77 ▼ 88341.7712 2.2 328.8 723.33 surplus 723.33 723.33

145 ▼ 89065.1 ▼ 89065.113 20 165.3 3306.6541 surplus 3306.654 3306.654

125 ▼ 92371.75 ▼ 92371.7514 0.1 122.0 12.1954 surplus 12.19538 12.19538

124.9 ▼ 92383.95 ▼ 92383.9515 15.74 127.7 2009.5125 surplus 2009.512 2009.512

109.16 ▼ 94393.46 ▼ 94393.4616 14.16 73.5 1040.5405 surplus 1040.541 1040.541

95 ▼ 95434 ▼ 9543417 5 67.8 338.8458 surplus 338.8458 338.8458

90 ▼ 95772.85 ▼ 95772.85

18 0.9 59.0 53.1311 surplus 53.13113 53.1311389.1 ▼ 95825.98 ▼ 95825.98

19 10.13 65.4 662.6525 surplus 662.6525 662.652578.97 ▼ 96488.63 ▼ 96488.63

20 0.84 535.0 449.3929 surplus 449.3929 449.392978.13 ▼ 96938.02 ▼ 96938.02

21 8.83 65.4 577.6132 surplus 577.6132 577.613269.3 ▼ 97515.64 ▼ 97515.64

22 1.07 74.1 79.3399 surplus 79.33988 79.3398868.23 ▼ 97594.98 ▼ 97594.98

23 0.48 128.3 61.6004 surplus 61.60035 61.6003567.75 ▼ 97656.58 ▼ 97656.58

24 21.88 131.6 2879.5054 surplus 2879.505 2879.50545.87 ▼ 100536.1 ▼ 100536.1

25 0.85 201.1 170.8944 surplus 170.8944 170.894445.02 ▼ 100707 ▼ 100707

26 19.96 244.4 4878.8448 surplus 4878.845 4878.84525.06 ▼ 105585.8 ▼ 105585.8

27 5.06 270.9 1370.5393 surplus 1370.539 1370.53920 ▼ 106956.4 ▼ 106956.4

28 0.02 265.1 5.3021 surplus 5.302149 5.30214919.98 ▼ 106961.7 ▼ 106961.7

29 4.98 102.8 512.0403 surplus 512.0403 512.040315 ▼ 107473.7 ▼ 107473.7

30 19.98 96.4 1926.8528 surplus 1926.853 1926.853-4.98 ▼ 109400.6 ▼ 109400.6

FIGURE 3: Problem Table Algorithm (PTA) for initial case

4) Utility Selection-Grand Composite Curve (GCC)

0.00 20.00 40.00 60.00 80.00 100.00 120.00-100

0

100

200

300

400

500

600

700GCC

GCC

Heat Flow(kW)

SH IF T

TE M PE R AT U RE (₀ C)

The heat recovery pocket is merely visible in the GCC.

5) Grid DesignStream NameHeat Flow (kW)mCp (kW/ K) Stream Type T(oC) T(oC)

12 394 469.05 HOT 93.97 93.13 12

1 77722.2 163.45 HOT 635.00 160.00 157335.5KW

3 47277.8 162.30 HOT 326.30 34.98 332961.7KW

5 20250.3 96.40 HOT 220.00 10.02 718032.5 kW

16 472.8 6.38 HOT 104.10 30.00 16184.2 kW

6 170.9 5.72 HOT 139.90 110.00 518.2KW

15 1239.7 5.75 HOT 250.60 35.00 151138.2KW

2 12111.1 166.90 COLD 210.00 137.50 2394 kW 11717.1 kW

7 14586.1 69.45 COLD 240.90 30.87 614586.1KW

11 2220 54.18 COLD 94.16 53.23 11. 2217.8KW

4 3469.4 43.39 COLD 110.00 30.02 43469.4KW

8 5019.4 26.43 COLD 200.00 10.06 85019.4 kW

9 180.8 8.73 COLD 75.00 54.30 9180.8 kW

13 288.6 3.27 COLD 141.00 52.75 13288.6 kW

10 152.7 3.04 COLD 164.80 215.00 10152.7KW

14 101.5 0.93 COLD 240.90 132.20 14101.5KW

C

C

C

C

C

C

FIGURE 4: Grid Diagram for initial case

From the grid, there are 16 heat exchangers in the system.Total cold utility= 32961.7+184.2+1138.2+57335.5+18032.5+18.2 = 109,670.3 kW

6) Number of Heat Exchanger Units

Minimum number of heat exchanger in a HEN, Nunits= (SAbove Pinch-1)+(SBelow Pinch-1)= 16

Proposed Case

1) Extraction of data: No. Stream Sup.

TempTar. Temp Heat Duty Heat Capacity

flowrateoC oC kW kW/K

1 7--8 635.50 160.00 77722.2222 163.453672 14--15 137.50 210.00 12111.1111 -167.049813 16--17 326.30 34.98 47277.7778 162.288134 25--27 30.02 110.00 3469.4444 -43.378905 39--41 220.00 10.02 20250.2778 96.439086 22--23 139.90 110.00 170.8889 5.715357 36--37 30.87 240.90 14586.1111 -69.447758 46--48 10.06 200.00 5019.4444 -26.426479 50--51 54.30 75.00 180.8056 -8.7345710 67--68 164.80 215.00 152.75 -3.0428311 53--54 53.23 94.16 2217.7778 -54.1846512 60--61 93.97 93.13 394.4444 469.5767213 57--58 52.75 141.00 288.6111 -3.2703814 70-1--71 132.20 240.90 101.5 -0.9337615 74-BDO--

74S250.60 35.00 1239.7222 5.75010

16 63PM--63 104.10 30.00 472.7778 6.3802717 cold utility 30.00 450.00 109400.56 -260.47752

FIGURE 5: Stream Data Table

2) Analysis of data:

For a ΔTmin= 30 °CNo. Stream Type Sup. Shift Tar.

Shift°C °C

1 7--8 HOT 620.50 175.002 14--15 COLD 152.50 225.003 16--17 HOT 311.30 49.984 25--27 COLD 45.02 125.005 39--41 HOT 205.00 25.026 22--23 HOT 124.90 125.007 36--37 COLD 45.87 255.908 46--48 COLD 25.06 215.009 50--51 COLD 69.30 90.0010 67--68 COLD 179.80 230.0011 53--54 COLD 68.23 109.1612 60--61 HOT 78.97 108.1313 57--58 COLD 67.75 156.0014 70-1--71 COLD 147.20 255.9015 74-BDO--74S HOT 235.60 50.0016 63PM--63 HOT 89.10 45.0017 cold utility COLD 45.00 465.00

FIGURE 6: Table for Shift temperatures

3) Targeting and Heat Cascade

FIGURE 7: Problem Table Algorithm (PTA) for proposed case

4) Utility Selection-Grand Composite Curve (GCC)

0 5000 10000 15000 20000 25000 30000 35000 400000

100

200

300

400

500

600

700GCC

GCC

Heat Load(kW)

Shift

Tem

pera

ture

(oC)

The heat recovery pocket is obvious in the GCC.

5) Grid Design PINCH

Stream Name Heat Flow (kW) mCp (kW/K) Stream Type T(oc)

1 77722.22 163.45 HOT 635.50 160

6 170.89 5.72 HOT 139.00 110

12 394.44 469.57 HOT 93.97 933531.6KW

3 473 162.29 HOT 326.30 60 354822KW

5 20250.28 96.44 HOT 220.00 60 10143.75KW

15 1239.72 5.75 HOT 250.60 60 35335.1KW

16 472.78 6.38 HOT 104.10 60 30

101.5KW14 101.5 0.93 COLD 240.90 132

2 12111.11 167.05 COLD 210.00 138394.4KW 11588.17KW128.54KW

4 3469.44 43.38 COLD 110.00 30170.89KW 2454.15KW

7 14586.11 69.45 COLD 240.90 3114586.11KW

9 180.8 8.73 COLD 75.00 54180.81KW

10 152.75 3.04 COLD 215.00 165152.75KW

11 2217.78 54.18 COLD 94.16 531095.95KW 1170.6KW

13 288.61 3.27 COLD 141.00 53288.61KW

8 5019.44 26.43 COLD 200.00 30 104211.74KW 281.36KW 525.9kW

17 106955.75 260.47 COLD 450.00 3077722.2KW31678.34KW

H

H

H

H

H

H

H

H

C

C

C

C

FIGURE 7: Grid Diagram for proposed case

ABOVE PINCH BELOW PINCH

From the grid, there are 22 heat exchangers in the system.Total cold utility= 3531.6+4822+ 143.75+335.1 = 8688.7 kW

Total hot utility = 101.5+128.54+2454.15+180.81+152.75+ 1170.6+288.61+4211.74 = 8688.7 kW

6) Number of Heat Exchanger Units

Minimum number of heat exchanger in a HEN, Nunits= (SAbove Pinch-1)+(SBelow Pinch-1)= 22