Chp 3 Pinch Tech

CHAPTER 3

3 UTILITIES AND HEAT INTEGRATION

3.1 Level 5 Decision: Heat Exchanger Network

3.1.1 Pinch Technology

The objective of pinch technology is to develop a heat exchanger network

(HEN) in a plant to optimize the use of energy, thus minimizing the operating cost.

The concepts behind pinch technology that should be abided when performing pinch

design are:

i. Common values for ∆ T min in the industry:

a. Oil refining = 20 – 40 ˚C

b. Petrochemical = 10 – 20 ˚C

c. Chemical = 10 – 20 ˚C

d. Low temperature processes = 3 – 5 ˚C

ii. The minimum heating requirement, QHmin and minimum cooling

requirement, QCmin and the pinch temperature are determined from the

cascade diagram.

iii. When performing pinch design, there are two pinches known as above

pinch and below pinch. When pairing up streams in above pinch, the

C p ,cold should always be greater than or equivalent to C p ,hot. Do the

same vice-versa for below pinch design. The stream pairing should

always start with the biggest C pvalue.

iv. Comparison of utility consumption before and after minimum energy

requirement (MER) is done to determine the MER efficiency.

The stream tables and heat exchangers involved in the HEN integration are

defined in Table 4.1.

Table 4.1: Summary of hot and cold streams.

Stream Tsource, K Ttarget, K CP, kW/K

ΔH, kW Comment

1 690.826 973.15 4.2196 1191.30 Cold fluid2 307.011 303.15 64.7668 -250 Hot fluid3 739.595 303.15 7.3402 -3203.63 Hot fluid4 303.15 973.15 4.4584 2987.12 Cold fluid5 973.15 303.15 9.8282 -6584.9 Hot fluid

where the stream identifications are:

i. Stream 1 : Inlet S-2 (Carbon dioxide gas)

ii. Stream 2 : Inlet S-6 (DEA liquid)

iii. Stream 3 : Inlet S-9 (Natural gas)

iv. Stream 4 : Inlet S-11 (Methane gas)

v. Stream 5 : Inlet S-12 (Mixture of H2, CO, CH4 and CO2)

3.1.1.1 Stream Characteristics

The streams were constructed on a cascade diagram as shown in Table 4.2 to

determine the minimum energy required for heating and cooling streams. The

following are the summary of the information obtained from the heat exchanger

network.

Minimum temperature, ∆ T min = 10 K

The pinch temperature, T pinch = 968.15 K

Hot pinch temperature, T pinch−hot = 973.15 K

Cold pinch temperature, T pinch−cold = 963.15 K

The minimum heating requirement, QHmin = 86.78 kW

The minimum cooling requirement, QCmin = 5946.94 kW

Table 4.2: Summary of Cascade Diagram

∆ H i(kW ) Residual (kW) 978.15 K 86.78

86.78968.15 K 0

-268.63 734.60 K 268.63

-329.17 695.83 K 569.80

-4927.39 308.15 K 5525.20

-105.40 302.01 K 5630.59

-316.35 298.15 K 5946.94

0.00

HEAT FLOW

Figure 4.1: Grand composite curve.

Figure 4.1 shows the grand composite curve. The x-axis is the cascaded heat

(heat flow). Cascaded heat is the amount of heat available from the hot streams and

the amount required by the cold stream when moving from higher to lower

temperature region. Form the Figure 4.1, it clearly illustrates that the heating utilities

requirement is become insignificant compared to cooling utilities requirement under

pinch analysis method.

3.1.1.2 Maximum Energy Recovery (MER)

The pinch design analysis was performed on below pinch since the pinch

temperature was determined between 963.15 K and 973.15 K. Since the pinch

temperature is considered quite high, the above pinch design analysis is negligible as

all temperatures are equivalent to the pinch temperature.

From the analysed information of grand composite curve, a summary table

about grid diagram of stream pairings (Appendix C) with the purpose of Maximum

Energy Recovery (MER) has been constructed as Table 4.3 follow. The summary of

the calculations can be referred at Appendix C.

Table 4.3: Summary table of grid diagram.

Paired

Stream

Equipment Heat Duty of heat

exchanger, kW

Tsource, K Ttarget, K Comment

1E-101 1149.10

690.826 963.15 Cold fluid

5 973.15 735.20 Hot fluid

4E-102 2942.54

303.15 963.15 Cold fluid

5 973.15 384.60 Hot fluid

Although the pinch analysis indeed to maximize the management and usage of

heat energy between streams, there are some residue heat requirement in particular

sections that need to be fulfilled by addition of extra heat exchangers with utilities in

order to achieve the targeted temperature of the streams in the end. Table 4.4 shows

the addition of heaters and coolers for the achievement of targeted temperature of

relater streams. Table 4.5 summarizes the result obtained from the final pinch design

analysis after performing stream pairing.

Table 4.4: Summary of heaters and coolers.

Stream Equipment Tinlet, K Toutlet K ΔH (kW) Comment

1 E-103 963.1 973.15 42.407 Heater

4 E-104 963.1 973.15 44.807 Heater

2 E-105 307.011 303.15 250.065 Cooler

3 E-106 739.595 303.15 3203.63 Cooler

5 E-107 E-108

735.20384.60

303.15303.15

2086407.5

Cooler

Table 4.5: Summary of heat equipment duties before and after MER

Heat Before MER After MER

Heating Duty Cooling Duty Heating Duty Cooling Duty

E-101 1191.29 - - -E-102 2987.13 - - -E-103 42.407 - 42.407 -E-104 44.807 - 44.807 -E-105 - 250.065 - 250.065E-106 - 3203.63 - 3203.63E-107 - 6584.894 - 2086E-108 - - - 407.5Total 4265.634 10125.615 87.214 5947.195

The net heat between the heating duty and the cooling duty after MER is

5859.981 kW same as before MER. Thus, the pinch design is balanced. Subsequently,

shows that, 76 % of utility energy usage can be saved after performing MER as shown

in Table 4.6.

Table 4.6: Summary of amount of energy usage

Specification Before MER After MER SavingCold utility consumptions (kW)

10125.615 5947.195 41.27%

Hot utility consumption (kW)

4265.634 87.214 97.96%

Total consumption (kW)

14391.249 6034.409 58.07%

3.1.2 Utilities

The word “utilities” is now generally used for the ancillary services needed in

the operation of any production process. These services normally be supplied from a

central site facility; and will include electricity, steam (for process heating and

cooling), water for general use, demineralized water, compressed air, inert-gas

supplied and effluent disposal facilities (Sinnott, 2005). However, this section will

discuss in detail about the utilities requirement that are related to chemical

engineering field. It consists of steam and power consumption in this proposed plant.

3.1.2.1 Steam Consumption

Steam is majorly used in the plant to aid the hydrolysis reaction and also as a

source of heating. Generally, the steam can be produced by using either watertube or

firetube boilers. In this section, a comparison between watertube and firetube boiler

would be discussed and subsequently propose a suitable solution to the DMR case.

Watertube and firetube boilers are essentially the opposite in design. In a

watertube boiler, water travels through tubes which are surrounded by the by-products

of combustion, or flue gas. In a firetube boiler, the flue gas travels through the tubes,

which are surrounded by hot water. Firetube boilers are typically designed with either

three or four sets of tubes (three- or four-pass boilers). Every set of tubes that the flue

gas travels through is considered a “pass”. Boilers designed for three-passes have the

stack at the rear, and boilers designed for four-passes have the stack at the front. A

boiler with more passes has a higher heat extraction rate and is more efficient than

one with less passes.

Watertube boilers are safer by design and generally can operate many years

longer than firetube boilers. Watertube boilers are available in larger capacities and

recover faster than firetube boilers. Watertube boilers can also handle higher pressures

(up to 350 atm), and have the ability to reach very high temperatures with the use of

superheaters. Firetube boilers are not suitable for pressures above 25 atm and actual

operating steam output of firetube boilers are less than the stated nameplate.

Watertube boilers are rated at actual operating conditions (Nagiar, Maneski &

Milosevic-Mitic, 2014).

From a maintenance standpoint, firetube boilers are typically have lower

operating costs comparable to a similarly sized watertube boiler. Firetube boilers have

easy access to the boiler’s firesides and tubes can easily be replaced without

additional repair of the boiler. Although firetube boilers are smaller in design, they

have a larger water volume than similar size watertube boilers, causing them to take

longer to bring up to operating temperature from a cold start. Once a firetube boiler is

started up and is operating at its desired pressure, a firetube boiler can handle a

sudden upward load surge better than a watertube boiler because of the large steam

disengaging area. The drawback to this feature is once the pressure of a firetube is

dropped, it takes longer to catch back up. With less water volume, a watertube boiler

has the ability to follow load swings more precisely and generally has better turndown

than a firetube boiler (Johnson, 1995).

Since the applied pressure across the whole plant is approximately to 60 atm,

the watertube boiler is more suitable to generate the steam instead of fire tube boiler.

Watertube boiler consists of mainly two drums, one is upper drum called steam drum

other is lower drum called mud drum. These upper drum and lower drum are

connected with two tubes namely down-comer and riser tubes. Water in the lower

drum and in the riser connected to it, is heated and steam is produced in them which

comes to the upper drums naturally. In the upper drum the steam is separated from

water naturally and stored above the water surface. The colder water is fed from feed

water inlet at upper drum and as this water is heavier than the hotter water of lower

drum and that in the riser, the colder water push the hotter water upwards through the

riser. So there is one convectional flow of water in the boiler system. Subsequently,

more and more steam is produced the pressure of the closed system increases which

obstructs this convectional flow of water and hence rate production of steam becomes

slower proportionately. If the steam is taken trough steam outlet, the pressure inside

the system falls and consequently the convectional flow of water becomes faster

which result in faster steam production rate. In this way the watertube boiler can

control its own pressure. Hence this type of boiler is referred as self-controlled

machine (Electuical4u.com, 2015)

The steam from watertube boiler will be supplied to heat up heat exchanger E-

103 to E-108. While heat requirement of R-100 will be supplied by the fuel gas

instead of steam.

3.1.2.2 Power Consumption

Development of industrial process is one of the main driving force towards

Malaysia on the path to become an advanced country in the future. Relatively, a high

consumption in electrical energy would became an issue due to majority of

manufacturer comply a high tech equipment and unit plant to operate and increase

their production. Therefore, the sources of electrical energy in Malaysia is provided

by Tenaga Nasional Berhad (TNB) with cooperation by Malaysia government, which

provide a suitable power quality needed by the customer so that equipment can be

operated and get some production. Tenaga Nasional Berhad (TNB) is the monopoly

generator and supplier of electrical power in Peninsular Malaysia. While in East

Malaysia, the Sabah Electricity Sdn. Bhd. (SESB) and the Sarawak Electricity Supply

Corporation (SESCO) provide power to the States of Sabah and Sarawak respectively.

The power supply from TNB trough the grid line (Transmission line) into the

industrial building is at 500kV, 275kV and 132kV. While to distribute the power

among the section needed in the plant are called distribution line which at voltages

33kV, 11kV and 400/230 volts. The power is distributed from high voltage to low

voltage of equipment used and each part to lower down the voltage is done by

transformer. Usually most of the equipment used in Malaysia required 240V voltage

with a frequency of 50 hertz. The electricity from the TNB is usually for start-up and

outage process (plant maintenance). Tenaga Nasional Berhad (TNB) is the main

electricity power generator and supplier in Peninsular Malaysia. New electricity tariff

rates which effective from 1 Jan 2014 are shown as Table 4.8 follow:-

Electricity consumption in our plant consists mainly of electric motors, pump,

lighting, ventilation, compressor, boilers and collecting equipment. To simplify the

prospects of our utility consumption we consider pump and compressor in our utility

energy requirements. Table 4.7 shows the equipment and corresponding power

requirement in operating.

Table 4.7: Power consumption of equipment.

Equipment Power Consumption (kW)

Pump P-101 A/B 243.73

Compressor C-101 A/B 1400.88

Compressor C-102 A/B 3203.60

Total electricity consumption 4848.21

Table 4.7: Pricing and Tariff of industrial in Malaysia.

3.1.3 Level 5 Decision: Heat Exchanger Network

3.1.3.1 Heat exchanger cost

After carrying out HEN, it was concluded that the dry methane reforming plant requires a total of 8 heat exchangers for the heating and cooling process carried out in the plant. Stated below is the summary table of each reactor cost, Table 4.8. The detailed cost calculations of each heat exchanger could be refer to Appendix C.

Table 4.8: Installation cost of heat exchanger according to area.Equipment Area (m2) Installation Cost (RM)

E-101 17.96 318,492.45E-102 57.092 572,218.36E-103 0.56 516,106.57E-104 0.59 622,254.08E-105 3.29 470,567.48E-106 57.83 574,220.60E-107 38.84 443,732.73E-108 5.374 381,788.35

Total Installation Cost (RM) 3,899,380.62

Total installation cost of heat exchangers

Cinst = RM 3,899,380.62 x 2.0

= RM 7,798,761.24

1 2 3 4 5 6 7 8 9 100

100000000

200000000

300000000

400000000

500000000

600000000

700000000

800000000

900000000

1000000000

Conversion, X

EP (R

M/y

r)

Figure 4.1: EP versus conversion

As the result of the calculation, from the graph EP (RM/yr) versus conversion

in Figure 4.2, the profit can be obtained as the conversion increases to 1.0. The lowest

profit is obtained as RM 498,370,998/yr when the conversion, x = 0.1 whereas for

conversion, x =1.0 the maximum of RM 930,502,821/yr.

Figure 4.3: Final process flow diagram.

APPENDIX C

C.1 Pinch Technology

C.1.1 Grid Diagram (Pinch Analysis)

where E-101 and E-102 are heat exchangers; H3 and H4 are heaters; C5 and C6 are coolers.

C.1.1.1 Heat exchanger (E-101)

t1 : Inlet temperature of cooling/heating mediumt2 : Outlet temperature of cooling/heating mediumT1: Inlet temperature of process streamT2: Outlet temperature of process stream

For Stream 1,Q = CP(T 2−T1 ¿ = (4.2196)(963.15 - 690.826 ) = 1149.1 kW

For Stream 5,Q = CP(t 1−t 2¿

1149.1 = (9.8282)(973.15 - t 2 )t 2 = 735.2 K

Thus,

Heat Exchanger, E-101


t1 : Inlet temperature of cooling/heating mediumt2 : Outlet temperature of cooling/heating mediumT1: Inlet temperature of process streamT2: Outlet temperature of process streamFor Stream 4,Q = CP(T 2−T1 ¿ = (4.4584)(963.15 – 303.15 ) = 2942.54 kW


2942.54 = (9.8282)(973.15 - t 2 )t 2 = 384.6 K

Thus,



For downstream part of Stream 1 after E-101,Q = CP(T 2−T1 ¿

= (4.2196)(973.15 – 963.15 )= 42.407 kW

For Stream Hot Steam Utilities, Q = CP(t 1−t 2¿

42.407 = (2.48)( 1000 – t 2) t 2= 982.9 K

Thus,



For downstream part of Stream 4 after E-102,Q = CP(T 2−T1 ¿

= (4.4584)(973.15 – 963.15 )= 44.8069 kW

For Stream Hot Steam Utilities, Q = CP(t 1−t 2¿

44.8069 = (2.48)( 1000 – t 2) t 2= 981.93 K

Thus,




= (64.766)( 307.01 – 303.15 )= 250.065 kW

For Stream Cooling Water Utilities, Q = CP(T 2−T1 ¿

250.065 = (3.75)( T 2 – 288.15) t 2= 300.15 K

Thus,




= (7.34)( 739.595 – 303.15 )= 3203.63 kW


3203.63 = (3.75)( T 2 – 288.15) t 2= 450.15 K

Thus,



For downstream part of Stream 5 after E-101,Q = CP(t 1−t 2¿

= (9.8282)( 735.2 – 303.15 )= 2086 kW


2086 = (3.75)( T 2 – 288.15) t 2= 450.15 K

Thus,



For downstream part of Stream 5 after E-102,Q = CP(t 1−t 2¿

= (9.8282)( 384.60 – 303.15 )= 407.5 kW


407.5 = (3.75)( T 2 – 288.15) t 2= 350.15 K

Thus,


C.1.2 Heat Exchanger Cost


Purchase cost, Cp

The purchase cost, Cp follows the following equation:

Log10Cop = K1 + K2 log10(A) + K3[log10(A)2] where

K1 = 4.3247

K2 = - 0.303

K3 = 0.1634

A (m2) = 17.96

The following values were adapted from Table A.1 Part A (Turton et al., 2009)

Thus, Cp = $ 159,911.82

Pressure factor, Fp

The equation in order to determine the pressure factor is as follows:

Log10Fp = C1 + C2 log10 P + C3 (log10 P)2 where;

C1 = 0.03881

C2 = -0.11272

C3 = 0.08183

P =29.3843barg

Fp = 1.121

The following values were adapted from Table A.2 (Turton et al., 2009)

Bare module cost, CBM (2001)

The bare module cost for this equipment is given by the following equation;

CBM = Cop(B1 + B2FMFP) where

B1 = 1.63

B2 = 1.66

FM = 1.4

CBM = $ 67,389.80

The following values were adapted from Table A.4 Part A and Table A.2 Part C

(Turton et al., 1998; Turton et al., 2009)


I2001 = 394.3

I2014 = 564.7

CBM (2014 )=C2001( I 2014

I 2001)

CBM = $ 96,512.86 = RM 318,492.45


Purchase cost, Cp



K1 = 4.3247

K2 = - 0.303

K3 = 0.1634

A (m2) = 57.092


Thus, Cp = $19,798.74

Pressure factor, Fp



C1 = 0.03881

C2 = -0.00627

C3 = 0.08183

P = 59.7818barg

Fp = 1.93





B1 = 1.63

B2 = 1.66

FM = 1.4

CBM = $ 121,075.66




I2001 = 394.3

I2014 = 564.7

CBM (2014 )=C2001( I 2014

I 2001)

CBM = $ 173,399.50 = RM 572,218.36


Purchase cost, Cp



K1 = 4.3247

K2 = - 0.303

K3 = 0.1634

A (m2) = 0.56


Thus, Cp = $ 25,784.58

Pressure factor, Fp



C1 = 0.03881

C2 = -0.11272

C3 = 0.08183

P = 29.3843barg

Fp = 1.121





B1 = 1.63

B2 = 1.66

FM = 1.4

CBM = $ 109,202.97




I2001 = 394.3

I2014 = 564.7

CBM (2014 )=C2001( I 2014

I 2001)

CBM = $ 156,395.93 = RM 516,106.57


Purchase cost, Cp



K1 = 4.3247

K2 = - 0.303

K3 = 0.1634

A (m2) = 0.59


Thus, Cp = $ 25,276.20

Pressure factor, Fp



C1 = 0.03881

C2 = -0.00627

C3 = 0.08183

P =24.318barg

Fp = 1.54





B1 = 1.63

B2 = 1.66

FM = 1.4

CBM = $ 131,662.71




I2001 = 394.3

I2014 = 564.7

CBM (2014 )=C2001( I 2014

I 2001)

CBM = $ 188,561.84 = RM 622,254.08


Purchase cost, Cp



K1 = 4.3247

K2 = - 0.303

K3 = 0.1634

A (m2) = 3.29


Thus, Cp = $ 16,281.63

Pressure factor, Fp



C1 = 0.03881

C2 = -0.00627

C3 = 0.08183

P = 59.7818barg

Fp = 1.93





B1 = 1.63

B2 = 1.66

FM = 1.4

CBM = $ 99,567.35




I2001 = 394.3

I2014 = 564.7

CBM (2014 )=C2001( I 2014

I 2001)

CBM = $ 142,596.21 = RM 470,567.48


Purchase cost, Cp



K1 = 4.3247

K2 = - 0.303

K3 = 0.1634

A (m2) = 57.83


Thus, Cp = $ 19,868.02

Pressure factor, Fp



C1 = 0.03881

C2 = -0.00627

C3 = 0.08183

P = 59.7818barg

Fp = 1.93





B1 = 1.63

B2 = 1.66

FM = 1.4

CBM = $ 121,499.31




I2001 = 394.3

I2014 = 564.7

CBM (2014 )=C2001( I 2014

I 2001)

CBM = $ 174,006.24 = RM 574,220.60


Purchase cost, Cp



K1 = 4.3247

K2 = - 0.303

K3 = 0.1634

A (m2) = 38.84


Thus, Cp = $ 18,024.59

Pressure factor, Fp



C1 = 0.03881

C2 = -0.00627

C3 = 0.08183

P = 24.318barg

Fp = 1.54





B1 = 1.63

B2 = 1.66

FM = 1.4

CBM = $ 93,889.39




I2001 = 394.3

I2014 = 564.7

CBM (2014 )=C2001( I 2014

I 2001)

CBM = $ 134,464.47 = RM 443,732.73


Purchase cost, Cp



K1 = 4.3247

K2 = - 0.303

K3 = 0.1634

A (m2) = 5.374


Thus, Cp = $ 15,508.39

Pressure factor, Fp



C1 = 0.03881

C2 = -0.00627

C3 = 0.08183

P = 24.318barg

Fp = 1.54





B1 = 1.63

B2 = 1.66

FM = 1.4

CBM = $ 80,782.58




I2001 = 394.3

I2014 = 564.7

CBM (2014 )=C2001( I 2014

I 2001)

CBM = $ 115,693.44 = RM 381,788.35

REFERENCES Nagiar, H., Maneski, T., Milosevic-Mitic, V., Gacesa, B., & Andjelic, N. (2014).

Modeling of the buckstay system of membrane-walls in watertube boiler

construction. THERM SCI, 18(suppl.1), 59-72. doi:10.2298/tsci120204174n

Electrical4u.com,. (2015). Water Tube Boiler | Operation and Types of Water

Tube Boiler | Electrical4u. Retrieved 28 March 2015, from

http://electrical4u.com/water-tube-boiler-operation-and-types-of-water-tube-

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Chp 3 Pinch Tech