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7/30/2019 Chemical Plant Cooling Systems
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Filename and location14/03/2006 1
Cooling Systems
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Purpose of Cooling Systems
Prevention of over-heating of process equipment
Prevention of product damage
Ensure desired performance of process equipment
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Cooling Systems
Generally, the types of cooling available offshore are- Closed Circuit Cooling Water (CCCW)
Direct seawater
Air cooling
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Typical Cooling Loads
Process cooling - Crude oil ~ 0.6-0.7 kW/(m3/h.oC)
Condensate ~ 0.3-0.4 kW/(m3/h.oC)
Gas (no condensation) ~ 500-800 kW/(m3/h.oC)
Produced water cooling ~ 1.2 kW/(m3/h.oC)
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Utility Cooling - Instrument/plant air after cooling ~ 350 kW/(106Sm3/h.oC)
Turbine lube oil / seal oil cooling ~ 10% of driver rating(kW)
Compressor lube oil / seal oil cooling ~ 10% of driver rating
Pump motor cooling ~ 10% of motor rating
Diving facilities ~ 200kW
Air conditioning - small ~ 150kW
medium ~ 300kW
large ~ 500kW
Typical Cooling Loads
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Schematic of a Typical CCCW System
SEA WATERSUPPLY
OPEN
DRAINS
GLYCOLMAKE-UP
WATERMAKE-UP
LP FLARE
SEAWATER
RETURNTC
TCV
CCCW CIRCULATINGPUMPS
FC
TURBINE
GENERATOR
COOLERS
FCV
CRUDE OILLOADING
COOLERS
COMPRESSIONCOOLERS
PLATE HEATEXCHANGERS
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Closed Circuit Cooling Water
(CCCW) Systems
Utilises a closed circuit of glycol and water mixture which
is cooled by exchange with sea water
Type of glycol used is dependent on glycol that is used on
the platform, i.e. TEG or MEG. Typical glycol concentration is 30 - 40% w/w
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Corrosion inhibitors are injected into the cooling medium
Permits use of carbon steel piping
Use of CCCW is limited to situations where contamination
by seawater of the cooled stream is to be avoided I.e. compressor seal / lube oil cooler, crude shipping pump coolers
Closed Circuit Cooling Water
(CCCW) Systems
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CCCW System Design
To determine total cooling loads, Q, summate allcoincident loads and add an allowance for run-up of
largest spare machine.
To determine flowrate, m, use inlet and outlet
temperatures, T and specific heats, CP of glycol solution
i.e.
TmCQ P=
Pump design capacity is approximately 1.25*calculated
total load flowrate as a safety margin
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CCCW System Design
Header sizing is based on pressure drop and velocity offluid
Non-boiling liquid should be approximately 15oC below bubble
point
The sea water circulating pumps should have a flat head
characteristic in order to avoid excessive design pressureon the plate heat exchangers
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CCCW System Design
Heat Exchangers - For initial sizing of heat exchangers use -
CCCW 32oC in and 18oC out
Seawater 15oC in and 27oC out
Header Tanks -
Size based on thermal expansion and the design pressure of the
system to cater for tube rupture on the heat exchangers
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Direct Seawater Cooling System
TO SEAWATER
DUMP HEADER
FROM SEAWATER
FILTER PACKAGE
INLET GAS
COOLER
TEST
SEPARATOR
COOLER
FLASH GAS
AFTER
COOLERDEW
POINT
COOLER
CRUDE OIL
COOLER
PIPELINE COMPRESSOR
AFTER COOLER
FLASH GAS
COOLERS
BOOSTER
COMPRESSOR
COOLER
PLATFORM
TOILETS
SEWAGE
TREATMENT
UNIT
HVACSYSTEM
DESALINATION
PACKAGE
SEAWATER
CCCW
EXCHANGER
EQUIPMENT
OVERFLOWS
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Direct Seawater Cooling Systems
- Advantages
Results in a lower overall system weight and space
compared to CCCW
Due to lower operating temperature and hence larger temperature
difference and elimination of the seawater/CCCW heat exchangers
Process outlet temperatures down to 18oC are possible
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Corrosion resistant (more expensive) materials needed for
construction
E.g. cupro-nickel
Colder skin temperatures may cause hydrate or waxing
problems in exchangers
Higher maintenance / downtime
Seawater to be used must be treated with hypochlorite and
filtered to 80 - 120m
Flow rates may be high due to lower return temperaturelimitations
Direct Seawater Cooling Systems
- Disadvantages
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Air Cooling Systems - Advantages
Can still be used in the event of CCCW failure Ideal for emergency and life support equipment
Low power requirement
Only occasionally are air coolers considered for offshore
cooling duties
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Large in size and weight occupying a lot of space
Expensive to operate
Required temperatures lower than ~ 65oC are not possible
Low efficiency
Variable cooling rates difficult to achieve
Air Cooling Systems - Disadvantages