Energy Conservation and Optimization of Condensate Splitter
Plant
Eid M. Al-Mutairi* and Husamelden Elkawad
Department of Chemical Engineering
King Fahd University of Petroleum and Minerals
Dhahran31261, Saudi Arabia
mutairi@kfupm.edu.sa
Abstract
In this work, energy integration of a heat exchanger network (HEN) of the Plant Refinery was carried out using the
Pinch Analysis Technology through (heat-int) software. From the operating data, the HEN data was extracted, then
the heat exchanger network data were analyzed through varying the pinch temperature and the amount of hot and
cold utilities were observed. Also the effects of pinch temperature on the area of heat exchangers were done. The
percentages of changing in hot and cold utilizes beside the area of heat exchangers were investigated and the
percentages of utilities and area changing with pinch temperature were done. The main problem of the exiting heat
exchanger network came from cross pinch temperature, seven heat exchangers with total energy of
183099704.2BTU\hr crosses the pinch point that’s violated the pinch rules. Cross pinch point with different pinch
temperature was found to occur, so attention must be taken with these temperatures.
The area efficiency of the current heat exchangers is 0.4 comparing with the ideal area with the same amount of hot
utility. Retrofitting of the current heat exchangers was done by replacing some heat exchangers and adding new
units. The reduced in hot and cold utilities were 6.79% and 27.9 % respectively with 10.53% decreases in the area.
1.0Introduction
Pinch technology is a methodology derived from simple scientific principles, by which it is possible to design new
plants with optimum energy and capital costs. Also it’s used with existing processes to improve the performance.
The condensate splitter plant produced high quality ofnaphtha,stabilized naphtha, LPG, heavy naphtha, kerosene,
light and heavy diesel and atmospheric gas oil (AGO) for domestic uses and exportation.
In this work we are going to extract and analyze the information data to find the quantities of hot and cold utilities
required for the crude distillation unit (CDU)and theninvestigate the effects of changing the pinch temperature on the
current heat exchanger network (HEN) using HEAT-INT software.
2.0Literature Review
The pinch analysis technique has been used globally to target hot and cold energy requirement for crude distillation
units CDU specifically and for any distillation column generally as mentioned in many several articles [1,2,3,4,5,6].
Riyami(2001) studied the effects of changing the pinch temperature of a fluid catalytic cracking plant on the hot and
cold utilizes and the area of the heat exchanger networks [2] .Ajao(2009) investigated the energy integration of the
crude pre heat train of kaduna refinery, from the study he found the optimum pinch temperature for the pre-heat train
using pinch analysis techniques [6].Salomeh(2008) used the Hint software which is based on methods of pinch
technology to design, optimize and improve the integrated heat exchanger network of crude oil preheating Process in
distillation unit in Arak refinery , also he reduced the load of the furnace[7].
The above hard work has proven that using the pinch analysis technique is very helpful and powerful in optimization
not only of distillation units, but also in general chemical and petrochemical industries.
3.0 Process Description
The process consisting from desalting units, stabilized feed and the crude distillation units as shown in the block
diagram in figure (1).
Condensate
Fraction Overhead& CDU Overhead
Final Products
Crude distillation
unit
Desalting unit
Stabilizer
Unit
LPG & Light Naphtha
Figure (1): The Process Block Diagram
The splitter plant Refinery of the crude condensate produced a high quality ofNaphtha, stabilizedNaphtha, Liquefied
Petroleum Gas (LPG), HeavyNaphtha, Kerosene, Light and Heavy dieseland atmospheric Gas Oil (AGO) for
domestic uses and exporting.
First, the condensate crude from storage is preheated by the resulting products from the Crude Distillation Unit
(CDU), thecrudeenters the desalting unit to remove the dissolved salts. Then it’s entering the first distillation column
(Flash Column). The bottom product from the flash columnis heated in two furnaces using flue fuel gases then enters
a second distillation column (CDU) .Thetop product is routed as feed to the condensate fractionator, while medium
naphtha sent to the fractionator top and light naphtha is routed to the fractionator’s overhead/cold condensate
exchanger.The distillations products are then used to pre-heat the feedstock beforestoring in the tanks or sends to
exporting ports.
4.0 Data Extraction
The source temperature (Ts), target temperature (Tt), flow –rate and heatcapacity and of each streams in the heat
exchangers network were extracted. Also the areas of each heat exchanger in the network were extracted. The
physical properties of the products from the crude distillation unit are shown in the table (1) below.
Table (1): The Physical Properties of the Crude Distillation Unit Products
Viscosity CP
Specific
gravity
60
oF/60oF
No.
Stream name
Type
Density
lb/ft3
1.
Fractionators overhead
Cold
0.41
0.01
-
2.
Heavy naphtha
Cold
39
0.18
0.78
3.
Kerosene
Cold
38
0.17
0.81
4.
Light diesel
Cold
42
0.24
0.83
5.
Heavy diesel
Cold
42
0.24
0.85
6.
Fraction bottom
Cold
42
0.3
0.88
7.
Dirty wash oil
Cold
40
0.21
0.87
8.
Fractional feed
Hot
0.66/40
-
0.87
9.
Pre flash column overhead
Cold
0.63
0.01
-
10
Hot crude
Hot
40
0.2
0.78
11.
Crude (tank)
Hot
48
0.84
0.78
5.0 Cost Data
There are two types of cost data, the operating cost for utilities and the capital cost for heat exchangers. These cost
data are need in the compression between different values of pinch temperatures and in retrofitting. The cost data
annualized base on 86000 hours per year, a payback period of 10 years with interest rate of 8%.
5.1 Operating Cost
The currently used cooling utilities are air and sea water, while the heating utilities are 150-Psig and flue gas. The
cost of these utilities are shown in the table (3) below
Table (3): Cost Data of Hot and Cold Utilities
No.
1
2
4
5
Stream
Air Cooling
Type
Cold
Cost
6407SR (Btu /year)
Cooling Water
Cold
6407 SR (Btu /year)
150-Psig
Hot
36120SR (Btu /year)
Flue Gas
Hot
1.161SR (Btu /year)
5.2 Capital Cost Data
The capital cost is represented by the following relation
Capital Cost = A + B(area of heat exchangers)C
Where A represents the fixed cost of installation independent of area , B and C represents the cost of area per unit
and they depends on the material of constructions of heat exchanger.Here we assume that the same equation is
used for all types of heat exchangers in the network, process to process and utilities exchangers.
6.Existing Heat Exchangers Network
The process includes 128 streams with cold streams and hot streams. Also it’s includes process to process heat
exchangers and hot and cold utilities heat exchangers. The hot exchanger’s utility usessteam and flue gases and the
cold utilities heat exchangers uses sea water and air as coolants.The energy consumptions of the exiting process are
shown on the grand composite curve in figure (2).
Figure (2): The Current Heat Exchanger Network Grand Composite Curve
From the diagram, the pinch temperature of the network is 28.85 0F, the amounts of the hot and cold utilities are
329000000 BTU\hr and 429834000 BTU\hr respectively, the processes to processes heat exchanges is 893209000
BTU\hr. The percentage of the energy consumptions are as shown in Table (4)
Table (4): The Current Heat Exchanger Network Data
Hot utilities
Flue Gases
99.998%
Cold utilities
Air Cooling
99.82 %
150 Psig
0.001 %
Sea Water
0.178%
Table (4): Existing Utilities Percentages
6.1Capital, Utilities and Total Costs of the Existing Network
The costs and the area of the existing network are shown in table (4) per year below.
Hot Utility Cost
4.44E+03
SR/year
Cold Utility Cost
3.20E+07
SR /year
Total Utility Cost
3.20E+07
SR /year
Capital Cost
8.39E+06
SR /year
Total Network Cost
7.24E+07
SR /year
Total area
432000
ft2
Process area
290408.36
ft2
Utility area
141591.63
ft2
6.2Analyzing of Exiting Heat Exchanger Network
The existing network consists from 64 heat exchangers (process to process s heat exchangers , 2 furnaces , 3
utilities and air fans cooling heat exchangers).Through analyzing the network to determine the inappropriate uses of
energy consumption, either through crossing the pinch temperature or inappropriate using for utilities. Table (5)
shows the heat exchangers that violated the pinch rule.
Table (5): The Current Heat Exchanger Cross Pinch Energy
1.
2.
3.
4.
5.
6.
7.
Heat exchanger no.
E 231
E 101
E 201
E222
E350
E211
E 241
Total Energy
Amount of Energy (BTU/hr)
1697015.12
47909491
9270976
22430081
27256375
14436456
12189819.08
183099704.2
6.3Heat Exchanger Network Area versusDifferent Pinch Temperatures
The areas counter current and 1-2 shell and tube heat exchangers networks changes with pinch temperatures. Figure
(4) shows the variation of network areas with different values of temperatures.
4.00E+05
3.00E+05
2.00E+05
1.00E+05
0.00E+00
0
5
10
15
20
1-2 shell and tube heat exchangers area
25
30
35
40
45
counter current heat exchanger area
Figure (4): Heat Exchanger Area versus Pinch Temperature
The area of process to process heat exchangers increaseswhen temperature decreases, that’s will decrease the
amount energy consumption for the networks.
6.4Heat Exchanger Network Annualized Costsversus Different Pinch Temperatures
The total annualized cost versus different approach temperatures are shown in figure (5&6) below for counter current
and 1-2 shell and tube heat exchangers. From the graph we could select the optimum approach temperature with
minimum total cost.
3.20E+10
3.00E+10
2.80E+10
2.60E+10
0
5
10
15
20
25
30
35
40
45
35
40
45
total cost
Figure (5): The Total Heat Exchanger Network Cost perYear (counter current)
3.20E+10
3.00E+10
2.80E+10
2.60E+10
0
5
10
15
20
25
30
total cost
Figure (6): The Total Heat Exchanger Network Cost per Year (1-2shell & tube)
The area of heat exchangers decreases from190100 ft2 to 134400ft2, when the pinch temperature increases from
100F to400F, that’s will increases the cost from 8394026.42 SR/year to6369165.69 SR/year for counter current heat
exchangers.For 1-2 shell and tube heat excanghers the area of heat exchangers decreases from237900 ft2 to
173200 ft2, when the pinch temperature increases from 10 0F to 40 0F, that’s will increases the cost from
10036970.24 SR/year to 7794045.78 SR/year.
The cost of the cold and the hot utilities increases within the increases of the pinch temperatures as shown in figures
(7). The cost increases from 29170673.10 SR/year to 33090083.20 SR/year, when the pinch temperature increases
from 100F to 400F.
3.20E+10
3.00E+10
2.80E+10
2.60E+10
0
5
10
15
20
25
30
35
40
45
utility cost
Figure (7): The Utilities Cost per Year for the Heat Exchanger Network
6.5Analyzing the Heat Exchangers Network at Different Pinch Temperature
When applying different pinch temperatures for the exitingheat exchangers’ network, some heat exchangers violated
one of the pinch rules, heat transfer across pinch. The table (6) below showed the numbers of heat exchangers that’s
violated this rule and the amount of heat transfer through the pinch. Figure (8) shows the loss of energy due to cross
pinchtemperaturedecreases as the pinch temperature increases.
Table (6): The Current Heat Exchanger Cross Pinch Energy
Pinch temperature 10 0F
Pinch temperature 15 0F
Pinch temperature 20 0F
Heat exchanger no.
Heat transferred BTU/hr
Heat transferred BTU/hr
Heat transferred BTU/hr
E 101
32266000
12798600
16144440
E 241
18917780
16923040
14949020
E 211
4320570
3336710
2352840
E 231
19755600
18178200
16600700
E 222
7476810
7476810
7476810
E 350
17931940
14033700
10135440
E 202
2939480
2351600
1763694
103608180
84142500
69433000
150000000
100000000
50000000
0
0
5
10
15
20
25
30
35
40
45
cross pinch energy
Figure (8): The Cross Pinch Temperature Energy vs different Pinch Temperatures
BTU/hr
6.7 Effects of Changing the Current Pinch Temperature on both Utilities and Area of Heat Exchangers
The current heat exchanger network is working at specific pinch temperature. Figure (9) below showed the
percentages effects of changing the current pinch temperature on hot and cold utilities beside the area of the heat
exchangers.
25
20
15
10
5
0
Hot Utility
Cold Utility
Heat Exchangesr Area
∆T %
Figure (9): Percentage Change in Pinch Temperature versus HEN Area andUtilities
6.8Determination of area efficiency for Retrofit Design
In retrofit design the area efficiency measures the performance of the exiting heat exchangers network with the ideal
network. The closer the exiting heat exchangers area to the curve, best performance is given by the installed heat
exchangers area.As shown in figure (10), the efficiency of exiting heat exchangers area is 0.4397, where the exiting
and target areas for the energy recovery were 432100.15 and190022 ft 2 respectively.
4.00E+05
exiting HEA
3.00E+05
2.00E+05
1.00E+05
0.00E+00
2.50E+08
2.70E+08
2.90E+08
3.10E+08
3.30E+08
3.50E+08
1-2 shell and tube heat exchangers
Figure (10): Energy Area Plot of the CDU Heat Exchangers Area vs. EnergyRecovery
6.9Adjusting the Current Heat Exchangers Network
When pinch analysis was applied to the current heat exchangers network, seven heat exchangers (E221, E241,
E231, E101, E211, E222, E 350 and E202) crossed the pinch temperature as shown in table (7). In order to avoid this
situation, some arrangement for the network design is suggested as shown in figure (11) in general manners. The
solutions steps are:-

Determine the heat exchangers that cross the pinch temperature.

Find out which streams violet the pinch rule.

Move the exiting heat exchanger either below or above the pinch point, calculate the new area needed.

Calculate the area for heat exchanger for the remaining energy recovery.

After these steps, the expected energy saving are 6.79 and 27.9 for hot and cold respectively.
Table (1): Heat Exchangers Cross Pinch Temperature
Amount of energy transfer(Btu/hr)
Heat
exchanger
Stream
cross
temperature
pinch
Hot stream
Cold stream
1.
E 101
hot
42833477.45
2.
E 241
hot + cold
17372603.07
10744787.2
3.
E 211
hot + cold
3362687.261
9622843.575
4.
E 231
hot
10863454.11
5.
E 222
hot
4032883.301
6.
E 350
hot
41243273.4
7.
E 201
hot
456147.175
In this procedure, the old heat exchangers that violated the pinch rules will be replaced by efficient heat exchangers.
By this way the area will be reduced by 10.5% , as shown in the table (8) below.
Table (8): Heat Exchangers retrofit of current network
HE
old area ft2
new area ft2
E101
5500.9
6010.134
E201
4311.83
3681.059
E231
5144.35
4081.736
E222
3621
3637.812
E241
9208
3077.186
E350
4880
10133.26
E211
7398.44
5220.855
Diff
Diff %
Total area
4.01E+04
3.58E+04
4.22E+03
10.5392
Capital cost
2.44E+06
2.24E+06
2.05E+05
8.401942
Solution
Pinch temp.
Pinch temp.
Figure (11): Suggested Solution for the Current Heat Exchangers Network
7.0 Conclusion
In conclusion, the heat integration of the heat exchanger network (HEN) of The Plant Refinery was carried out using
the Pinch Analysis Technology by Heat-int software. Moreover, merits of integrated network are shown compared to
the base case design.
8.0 References
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(2010) 9534-9541.
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a fluid catalytic cracking plant. Applied Thermal Engineering 21 (2001) 1449–1487.
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columns: A review. National Institute of Advanced Industerial Science & Technology, Japan. And Institute of
Industerial Technology, Japan.
4- K. Liebmann and V. R. Dhole.Integrated crude distillation design.Computers Chemical Engineering. Vol. 19 (1995)
119–124.
5- Patipat Promvitak, Kitipat Siemanond, Somporn Bunluesriruang, and Voratai Raghareutai. Retrofit Design of Heat
Exchanger Networks of Crude Distillation Unit. Process Integration and Energy Optimization Conference. Florence,
Italy (2011).
6- K.R. Ajao and H. F. Akande. Energy Integration Of Crude Distillation Unit Using Pinch Analysis. Researcher, 1(2),
(2009) 54–66.
7- Salomeh Chegini , Reza Dargahi , Afshin Mahdavi , Modification of Preheating Heat Exchanger Network in Crude
Distillation Unit of Arak Refinery Based on Pinch Technology, WCECS 2008, October 22 - 24, 2008, San Francisco,
USA