Chemical Engineering May 2012 - 54

26
HP
Cover Story
TECHNOLOGY
KNOW-HOW
The most important strategies
for reducing water consumption
and wastewater discharge
in large refining and chemical
companies can be categorized
as follows: 1) better
water management; 2) process
change and integration; and
(3) regeneration, recycle, reuse
and replacement (the four Rs).
By focusing on the practical
aspects of managing water use,
applying proven technologies,
and fostering corporate buyin,
plants can significantly cut
down water use and wastewater
discharge. Readers should
check Ref. [5] for further technology
details.
steam
180
10
4
60
Turbine
Deaerator
Furnace
material
loss
Conversion
25
Material
loss
35
180
10
MP
steam
16
38
7
31
70
65
26
4
38
25
HX
Stripping
CDU,VDU
Reaction
regeneration
Reboiler
HX
Stripping
Pipeline
and
equipment
Turbine
#1
FCC
25
2
12
11
8
Improved water
management
The success of any water-saving
project depends to the greatest
extent on effective and efficient
water management, and less
on water-saving technology. In
fact, the experience of the project
teams suggests that 70% of
the success of a water-saving project
derives from management improvement,
and only 30% comes from applications
of water-saving technology.
In particular, much of the unaccounted
water loss revealed by water-balance
diagrams (which list water inputs and
outputs) and monthly water auditing
of a chemical plant results from leakage
from underground water pipelines.
For example, in one ethylene plant, we
observed underground water leakage
as high as 100 ton/h. It is essential to
regularly use a modern pipeline leak
detection system, and electronic listening
and leak detection devices to identify
water leakage and repair failing
water pipelines.
Improving water management requires
an accurate monthly auditing
of water consumption for each manufacturing
plant. So for each refinery,
the project team compiled a monthly
accounting spreadsheet that included
the following information:
* Crude oil refined (ton/mo.)
* Total freshwater (industrial water)
consumed (ton/mo.)
15
6
Deaerator
1 #FCC
Deaerator
2 #FCC
Deaerator
2 #FCC
2
Deaerator
3 #FCC
Deaerator
chemical
water
station
13
1
5
35
2
5
2
5
18 18
Sour
water
stripper
19
55
Desalter
55
Wastewater
treatment
plant
(WWTP)
FIGURE 2. An example of a water-balance diagram for a reinery
Clean effluent
pH: 8.5-9.0
COD: 41-480 mg/L
K+: 2.2 mg/L
Turbidity: 22-77 mg/L
Hardness: 8-39 mg/L
S2-: 7.8-22.0 mg/L
Cl-: 13-64 mg/L
SO2-
4 : 67-74 mg/L
NH4+: 55-67 mg/L
Dissolved O2: N.D.
Steam stripping clean effluent 50 ton/h
Wastewater treatment
IW 20 ton/h
Desalter
SW 10 ton/h
Hydrotreating
unit
Washing column
IW 10 ton/h
Residue
SW 10 ton/h
hydrotreating
Industrial water (IW)
pH: 7.5-8.5
Hardness: 340 mg/L
Cl-: 100 mg/L
SO4-: 250 mg/L
Softened water (SW)
pH: 7.5-8.5
Hardness: 40 mg/L
Cl-: 50 mg/L
Residue: 2 mg/L
SO4-: 1,000 mg/L
Dissolved O2: < 0.05 mg/L
FIGURE 3. Clean effluent from the steam stripping of sour water can be used as
makeup water for desalters, quench towers, washing columns, hyrdotreating units
and others
* Freshwater consumed per ton of
crude oil refined (tons)
* Wastewater discharged per ton of
crude oil refined (tons)
* Freshwater reuse percentage
* Concentration ratio of cooling-tower
recirculating water
36 CHEMICAL ENGINEERING WWW.CHE.COM MAY 2012
* Freshwater consumption for the following:
cooling tower makeup water;
for producing high-purity boiler
makeup water (chemically treated
water); the freshwater equivalent of
externally purchased steam; freshwater
to processing units; water
10
Cooling
1
20
8
Direct
cooling 2
Washing
2
8
10
20
HP water
injection
Condensate
16
62
26
4
5
33
96
Condensate
pump
96
20
Pure
water
44
14
71
240
30
Soft
water
Pump
seal
2
Pump
seal
Pump
seal 1
Direct
cooling 1
Washing
1
62
85
284
30
20
16
22
7
8
29
70
39
65
12
12
10
61
69
Air
cooling
Washing
LP gas
Water
washing
10
Deaerator
3 #FCC
68
Softened
water
25
20
57
3
66
29
55
107
HRSG
#2 FCC
HRSG
#3 FCC
50
45
48
MP
steam
CCR
MP
steam
#1 H2
MP
steam
#2 H2
HRSG
#1 FCC
25
1
24
1
43
2
2
52
110
3
7
32
CT1
18
114
36
30
CT3
20
114
CT4
36
11
15
CT AK
4
150
50
CT2
150
50
Oil-water
separation
Industrial
water
http://WWW.CHE.COM
Chemical Engineering May 2012

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