Hydrocarbon Processing - March 2022 - 86

Water Management
changers E-5 and E-6 that are located at a higher elevation than
the rest lowers the cooling water demand for the Base Case hydraulic
balance by ~12%, from 27,284,921 kg/hr (TABLE 1) to
23,982,989 kg/hr (TABLE 2). After segregating exchangers E-5
and E-6, the next limiting constraints for determining the supply
pressure are exchangers E-7 and E-8.
Two alternate schematic representations of the network
summarized in TABLE 2 are depicted in FIGS. 4 and 5. While both
networks require the same amount of cooling water, a considerable
difference exists in energy consumption and, consequently,
OPEX. The auxiliary pump network (FIG. 5) saves approximately
500 kW (14%) over the pressure controlled network
(FIG. 4). The initially higher CAPEX required for the auxiliary
TABLE 3. Cascaded cooling water balance
Item No.
Primary header,
kh/hr**
CWS from BL
E-1
E-2
E-3
E-4
E-5
E-6
E-7
E-8
E-9
E-10
E-11
E-12
E-13
E-14
E-15
E-16
E-17
E-18
E-19
E-20
E-21
E-22
E-23
E-24
E-25
E-26
E-27
E-28
E-29
Bypass flow
CWR to BL
12,823,726
-2,413,657
-2,410,918
-2,407,427
-2,407,988
-1,383,548
-989,450
-55,684
-10,713
-61,622
-224,562
-55,304
-322,758
-75,588
-4,507
-98,655
-37,423
-12,378
-24,453
-467,518
-632,708
-2,642,339
-2,869,597
-2,869,597
-750,952
-750,952
-43,698
-138,722
-632,931
-41,065
Cascaded header,
kg/hr**
2,413,657
2,410,918
2,407,427
2,407,988
1,383,548
989,450
55,684
10,713
61,622
224,562
55,304
322,758
75,588
4,507
98,655
37,423
12,378
24,453
467,518
632,708
2,642,339
2,869,597
2,869,597
750,952
750,952
43,698
138,722
632,931
41,065
-12,823,726
Negative values (-) represent outflow, while positive values represent inflow.
86 MARCH 2022 | HydrocarbonProcessing.com
Return header,
kg/hr**
pump network can usually be offset by the lower OPEX within
a short period of time.
Cascaded network. A cascaded cooling water network
(FIG. 3) comprises primary and cascaded headers. The primary
header receives cooling water at the battery limit supply temperature,
while the cascaded header is supplied by the primary
cooling water that has already been used in selected heat exchangers.
The choice between which services are supplied by
the primary header and which are supplied by the cascaded
header is usually clear cut. Primary users typically have a relatively
low rise (< 4°C) in cooling water temperature and therefore
a high cooling water demand.
TABLE 4. Cascaded cooling water balance with auxiliary pump
Item No.
Primary header,
kh/hr**
CWS from BL
E-1
E-2
E-3
E-4
E-5
E-6
E-7
E-8
E-9
E-10
E-11
E-12
E-13
E-14
E-15
E-16
E-17
E-18
E-19
E-20
E-21
E-22
E-23
E-24
E-25
E-26
E-27
E-28
E-29
Bypass flow
CWR to BL
11,358,460
-1,931,807
-1,930,831
-1,928,320
-1,928,829
-1,188,100
-113,000
-51,900
-9,929
-52,667
-246,480
-55,494
-299,110
-69,161
-4,558
-10,832
-35,414
-11,761
-23,121
-1,063,385
-484,889
1,063,385
484,889
-2,369,575
-2,775,973
-2,775,973
-714,046
-714,046
-77,955
-167,585
-257,516
-36,681
-485,683
2,369,575
2,775,973
2,775,973
714,046
714,046
77,955
167,585
257,516
36,681
485,683
-11,358,460
Negative values (-) represent outflow, while positive values represent inflow.
Cascaded header,
kg/hr**
1,931,807
1,930,831
1,928,320
1,928,829
1,188,100
113,000
51,900
9,929
52,667
246,480
55,494
299,110
69,161
4,558
10,832
35,414
11,761
23,121
Return header,
kg/hr**
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Hydrocarbon Processing - March 2022

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