CPE614 - Assignment (Energy Optimal Integration Solution) [Dimethyl Ether Process Plant] (2019) PDF

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FACULTY OF CHEMICAL ENGINEERING UNIVERSITI TEKNOLOGI MARA ASSIGNMENT: ENERGY OPTIMAL INTEGRATION SOLUTIONS PRODUCTION OF DIMETHYL ETHER (DME) PREPARED BY: EH2206I 1 NURUL NAJIHA BINTI SURANI 2017632166 2 QURRATUAINI BINTI MD ALI 2017632078 3 SITI NUR AISHAH BINTI MOHAMAD FAUDZI 2017632136 4 NURLINA ...

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CPE614 - Assignment (Energy Optimal Integration Solution) [Dimethyl Ether Process Plant] (2019) Nurlina Syahiirah

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FACULTY OF CHEMICAL ENGINEERING UNIVERSITI TEKNOLOGI MARA

ASSIGNMENT: ENERGY OPTIMAL INTEGRATION SOLUTIONS PRODUCTION OF DIMETHYL ETHER (DME) PREPARED BY: EH2206I 1

NURUL NAJIHA BINTI SURANI

2017632166

2

QURRATUAINI BINTI MD ALI

2017632078

3

SITI NUR AISHAH BINTI MOHAMAD FAUDZI

2017632136

4

NURLINA SYAHIIRAH BINTI MD TAHIR

2017632214

DATE OF SUBMISSION: 24th MAY 2019

NAME OF LECTURER: DR. NOR HAZELAH BINTI KASMURI

0

TABLE OF CONTENT

1.0

INTRODUCTION ……………………………………………………………

2.0

PROCESS FLOW DIAGRAM FOR DIMETHYL ETHER (DME) PRODUCTION PLANT …………………………………………………….

2

4

3.0

PROBLEM TABLE CASCADE (PTA) …………………………………….

6

4.0

HEAT EXCHANGER NETWORK (HEN) …………………………………

11

5.0

FEASIBILITY STUDY ………………………………………………………

13

6.0

GRAND COMPOSITE CURVE (GCC) ……………………………………..

14

7.0

ESTIMATION OF UTILITIES COST ……………………………………….

16

8.0

CONCLUSION ………………………………………………………………

19

9.0

REFERENCES ……………………………………………………………….

20

APPENDICES ………………………………………………………………………..

21

1

1.0

INTRODUCTION

For our project process integration, the process that might conceivable to undergoes integration is Dimethyl Ether (DME) production, Unit 200. According to (Turton, Bailie, Whiting, Shaeiwitz, & Bhattacharya, 2012), DME is used primarily as an aerosol propellent. It is miscible with most organic solvents, has high solubility in water and miscible in water and 6% ethanol. Furthermore, engineers invented that DME also can be as additive for diesel engines because of its high volatility and high cetane number. Due to its easy compression, condensation, vaporization, Freon is traded for DME as refrigerant as well (Bai, Ma, Zhang, Ying, & Fang, 2013). They continued DME can develop downstream products and cultivate new consumption market. DME can be produced by direct synthesis of DME from syngas or dehydration of methanol. Hence, in this scheme we will used dehydration of methanol to produce DME. The compositions of reactions DME by syngas are much complex than methanol dehydration process. Methanol dehydration process by using solid acid catalyst in an adiabatic fixed-bed reactor has been proven more commercial. It is also method which comes with various advantages including fewer byproducts, high selectivity and high purity. The production of DME is via the catalytic dehydration of methanol over an acid zeolite catalyst. The main reaction is as shown in equation 1 below. Under normal temperature range, there will be no significant of side reactions (Turton, Bailie, Whiting, Shaeiwitz, & Bhattacharya, 2012). 𝟐𝐂𝐇𝟑 𝐎𝐇 → (𝐂𝐇𝟑 )𝟐 𝐎𝐇 + 𝐇𝟐 𝐎 Equation 1

In this worksheet, we will integrate energy using the heat exchanger network to optimizes the energy usage in the plant. The ∆Tmin used is 20ºC and 10 ºC. Based on (Smith,

n.d), ∆Tmin is very important to sets the relative location of the hot and cold stream in this

two-stream problem and the amount of heat recovery. The pinch temperature can be determined by sketching the composite curve or by calculating the problem table algorithm (PTA). Thus, we would solve pinch temperature using PTA method in this scheme. Although composite curve can be used to set energy target, they are inconvenient way since they are based on graphical construction. Therefore, researcher came out with method of calculating targets directly without necessity of graphical construction. The process is first divided into temperature intervals. It is not possible to recover all of the heat in each temperature interval

2

since temperature driving forces are not feasible throughout the interval. Some of heat is possible, but all of the heat cannot be recovered. This problem can be overcome if, purely for the purposes of construction, the hot composite is shifted to be ∆Tmin /2 colder than it is in practice and that the cold composite is

shifted to be ∆Tmin /2 hotter than it is in practice. Carrying out heat balance between the shifted

composite curves within a shifted temperature interval shows that heat transfer is feasible throughout each shifted temperature interval, since hot streams in practice are actually ∆Tmin /2 hotter and cold streams ∆Tmin /2 colder. Within each shifted interval, the hot streams are in reality hotter than the cold streams by ∆Tmin. The shift simply removes the problem of ensuring temperature feasibility within temperature intervals. Concisely, this shifting technique can be used to develop strategy to calculate the energy target without having to construct composite curve (Smith, n.d).

3

2.0 V-201 Feed Vessel

PROCESS FLOW DIAGRAM FOR DIMETHYL ETHER (DME) PRODUCTION PLANT E-201 Methanol Preheater

E-203 DME Cooler

T-201 DME Tower

E-204 DME Reboiler

E-205 DME Condenser

V-202 DME Reflux Drum

P202A/B DME Reflux Pumps

E-206 Methanol Reboiler

T-202 Methanol Tower

E-207 Methanol Condenser

V-203 Methanol Reflux Drum

P203A/B Methanol Pumps

E-208 Wastewater Cooler

P201A/B Feed Pump

E-202 Reactor Cooler

R-201 Reactor

Figure 1 - Dimethyl Ether Production Plant Process Flow Diagram

4

Table 1 - Stream Table for Production of Dimethyl Ether Stream Number

1

2

3

4

5

6

7

8

9

10

11

12

13

14

16

17

Temperature (°C)

25

25

45

154

250

364

278

100

89

46

153

139

121

167

46

121

Pressure (bar)

1.0

15.5

15.2

15.1

14.7

13.9

13.8

13.4

10.4

11.4

10.5

7.4

15.5

7.6

11.4

7.3

Vapor fraction

0.0

0.0

0.0

1.0

1.0

1.0

1.0

0.0798 0.148

0.0

0.0

0.04

0.0

0.0

0.0

0.0

Mass flow (tonne/h)

8.37

8.37

10.49 10.49 10.49 10.49 10.49

10.49

10.49

5.97

4.52

4.52

2.13

2.39

2.17

3.62

Mole flow (kmol/h)

262.2 262.2 328.3 328.3 328.3 328.3 328.3

328.3

328.3 129.7 198.6 198.6

66.3

132.3

47.1 113.0

130.5 130.5

130.5

130.5 129.1

1.4

1.4

1.4

0.0

46.9

2.4

64.9

64.9

64.9

64.9

0.6

64.3

64.3

63.6

0.7

0.2

108.4

132.9 132.9

132.9

132.9

0.0

132.9 132.9

1.3

131.6

0.0

2.2

Component flowrates (kmol/h) Dimethyl ether Methanol Water

0.0

0.0

1.5

1.5

1.5

259.7 259.7 323.0 323.0 323.0 2.5

2.5

3.8

3.8

3.8

5

3.0

PROBLEM TABLE CASCADE (PTA)

In order to optimize the energy utilization and reducing the cost for additional utilities, the required minimum heat utilities and the possible heat recovered need to be determine. Thus, Problem Table Cascade Method is used since this method is more accurate compared to composite curve as composite curve is more complicated and difficult to get accurate point for pinch temperature, and the minimum heat utilities. Table 2 - Stream Data Extracted From PFD Dimethyl Ethyl Production Plant, ∆𝑻𝒎𝒊𝒏 = 𝟐𝟎℃ Stream

Supply Target Type Temperature, Temperature, TS (⁰C) TT (⁰C)

7→8

Hot

278.00

100.00

6→7

Hot

364.00

3→4

Cold

E – 204

Heat Temperature Heat Shifted Shifted Mass Capacity, Difference, Capacity Enthalpy, Supply Target Flowrate, Cp Flowrate, Temperature, Temperature, 𝜟H (kW) 𝜟𝑻 (⁰C) m (kg) (kJ/kg.⁰C) CP (kJ/⁰C) TS (⁰C) TT (⁰C) 6.6516

178

2.91

19.38

3450.00

268.00

90.00

278.00

2.2502

86

2.91

6.56

563.89

354.00

268.00

45.00

154.00

12.5939

109

2.91

36.70

4000.00

55.00

164.00

Cold

153.00

901.05

2.6418

748.05

0.35

0.92

691.67

163.00

911.05

4→5

Cold

154.00

250.00

2.0158

96

2.91

5.87

563.89

164.00

260.00

E – 206

Cold

167.00

918.61

2.6418

751.61

0.81

2.13

1608.33

177.00

928.61

Shifting Rule, Hot Stream = −

Cold Stream = +

∆Tmin 20℃ = − = −10℃ 2 2

20℃ ∆Tmin = + = +10℃ 2 2

6

Table 3 - Problem Table Cascade, ∆𝑻𝒎𝒊𝒏 = 𝟐𝟎℃ ∆T

Temperature (⁰C)

(⁰C) 928.61 911.05

0.92

268

163

36.70

19.38

164

5.87

260 177

2.13

6.56

354

90

Utilities (kJ/h) ∑ 𝐂𝐏𝐂 − 𝐂𝐏𝐇 (kJ/h.⁰C)

∆𝐇

(kJ/h)

Deficit /

1st Try

2nd Try

0.00

2839.16

-37.40

2801.76

-1736.41

1102.75

-1434.55

1404.61

-1303.91

1535.25

-435.73

2403.43

-272.06

2567.10

-290.30

2548.86

-1554.66

1284.50

-2839.16

0.00

Surplus

17.56

2.13

37.40

Surplus

557.05

3.05

1699.00

Surplus

86.00

-3.51

-301.86

Surplus

8.00

-16.33

-130.64

Surplus

83.00

-10.46

-868.18

Surplus

13.00

-12.59

-163.67

Surplus

1.00

18.24

18.24

Deficit

73.00

17.32

1264.36

Deficit

35.00

36.70

1284.50

Deficit

55

The pinch temperature

= 55⁰C

The minimum hot utilities, Qh,min

= 2839.16 kW

The hot pinch temperature

= 65⁰C

The minimum cold utilities, Qc,min

= 0.00 kW

The cold pinch temperature = 45⁰C

7

Table 4 - Stream Data Extracted From PFD Dimethyl Ethyl Production Plant, ∆𝑻𝒎𝒊𝒏 = 𝟏𝟎℃ Stream

Supply Target Type Temperature, Temperature, TS (⁰C) TT (⁰C)

7→8

Hot

278.00

100.00

6→7

Hot

364.00

3→4

Cold

E – 204

Heat Temperature Heat Shifted Shifted Mass Capacity, Difference, Capacity Enthalpy, Supply Target Flowrate, Cp Flowrate, 𝜟H (kW) Temperature, Temperature, 𝜟𝑻 (⁰C) m (kg) (kJ/kg.⁰C) CP (kJ/⁰C) TS (⁰C) TT (⁰C) 6.6516

178

2.91

19.38

3450.00

273.00

95.00

278.00

2.2502

86

2.91

6.56

563.89

359.00

273.00

45.00

154.00

12.5939

109

2.91

36.70

4000.00

50.00

159.00

Cold

153.00

901.05

2.6418

748.05

0.35

0.92

691.67

158.00

906.05

4→5

Cold

154.00

250.00

2.0158

96

2.91

5.87

563.89

159.00

255.00

E – 206

Cold

167.00

918.61

2.6418

751.61

0.81

2.13

1608.33

172.00

923.61

Shifting Rule, Hot Stream = −

Cold Stream = +

∆Tmin 10℃ = − = −5℃ 2 2

∆Tmin 10℃ = + = +5℃ 2 2

8

Table 5 - Problem Table Cascade, ∆𝑻𝒎𝒊𝒏 = 𝟏𝟎℃ ∆T

Temperature (⁰C)

(⁰C) 923.61 906.05

0.92

273

158

36.70

19.38

159

5.87

255 172

2.13

6.56

359

95

Utilities (kJ/h) ∑ 𝐂𝐏𝐂 − 𝐂𝐏𝐇 (kJ/h.⁰C)

∆𝐇

(kJ/h)

Deficit /

1st Try

2nd Try

0.00

2839.16

-37.40

2801.76

-1705.91

1133.25

-1404.05

1435.11

-1110.11

1729.05

-241.93

2597.23

-78.26

2760.90

-96.50

2742.66

-1187.66

1651.50

-2839.16

0.00

Surplus

17.56

2.13

37.40

Surplus

547.05

3.05

1668.50

Surplus

86.00

-3.51

-301.86

Surplus

18.00

-16.33

-293.94

Surplus

83.00

-10.46

-868.18

Surplus

13.00

-12.59

-163.67

Surplus

1.00

18.24

18.24

Deficit

63.00

17.32

1091.16

Deficit

45.00

36.70

1651.50

Deficit

50

The pinch temperature

= 50⁰C

The minimum hot utilities, Qh,min

= 2839.16 kW

The hot pinch temperature

= 55⁰C

The minimum cold utilities, Qc,min

= 0.00 kW

The cold pinch temperature = 45⁰C

9

The Heat Load for Cold Stream, ∆HC ∆HC = 4000 kW + 691.67 kW + 563.89 kW + 1608.33 kW ∆HC = 6863.89 kW

The Heat Load for Hot Stream, ∆HH ∆HH = 3450 kW + 563.89 kW

∆HH = 4013.89 kW

The heat recovered from the process, Qrec Qrec = ∆HC − Qh,min

Qrec = 6863.89 kW − 2839.16 kW Qrec = 4024.73 kW

The heat recovered from the process, Qrec Qrec = ∆HH − Qc,min

Qrec = 4013.89 kW − 0.00 kW Qrec = 4013.89 kW

Therefore, Qrec ≅ 4000 kW.

For both ∆Tmin, the PTA resulting in threshold problem where the cold utilitize is fully utilized however the minimum hot utilities is still present. Thus, this shows that the process required additional heat utilities to be supplied for the process. Since the hot stream cannot satisfy the heat load required by the cold stream. Besides, since the recovered heat is still abundant there are possibilities for improvement for the dimethyl ether process plant. Therefore, heat exchanger network (HEN), is required to oversee the possibilities.

10

4.0

HEAT EXCHANGER NETWORK (HEN)

Heat exchanger network is designed for the process to achieve the optimal energy target by utilizing the heat released from the hot stream to the cold stream by ensuring the heat exchanger to be placed accordingly and consistent with the rules.

Figure 2 - Heat Exchanger Network (HEN) at ∆Tmin = 10⁰C

Figure 3 - Heat Exchanger Network (HEN) at ∆Tmin = 20⁰C

Based on the Heat Exchanger Network, for both ∆Tmin the number of heat exchanger than can be placed is the same since the amount of heat load transfer is the same.

11

The minimum number of heat exchanger units is, Nunits Nunits = (S − P)above pinch + (S − P)below pinch

Nunits = (6 − 1)above pinch + (0 − 1)below pinch Nunits = 4 units of Heat Exchanger

Therefore, the heat exchanger unit for the process plant excluding the condenser can be reduced from 6 units to 4 units from the heat exchanger network. However, there are no possibilities left to reduce further the number of heat exchanger unit as there are no loop that can be made from the Heat Exchanger Network (HEN). As for the condensers, E – 205 and E - 207, the temperature inlet and outlet is the same, thus showing that the presence of heat load is due to latent heat as the reflux changes phase from gas to liquid at the same temperature. Thus, the condenser need not be integrated with the rest of the process.

12

5.0

FEASIBILITY STUDY

1)

Heat Exchanger 1

Q = CP∆T 3449.64kW = 36.7kW/°C (T − 45°C) 𝐓 = 𝟏𝟑𝟗°𝐂

2)

Heat Exchanger 2

Q = CP∆T 550.66kW = 6.56kW/°C (T − 278°C) 𝐓 = 𝟑𝟔𝟏. 𝟗𝟒°𝐂

3)

Heat Exchanger 3

Q = CP∆T 13.5kW = 5.87kW/°C (T − 154°C) 𝐓 = 𝟏𝟓𝟔. 𝟑𝟎°𝐂

Heat Exchanger 1 and 2 is feasible since they follow the rule for above pinch where, the heat capacity flowrate for hot stream is smaller than cold stream CPH < CPC and the number of stream of the cold stream is higher than the hot stream. NH < NC. Heat Exchanger 3 however did not obey the CPH < CPC rule but still consider feasible as it did not violate the ∆Tmin and the p...