Reefer Cargo Brine Circulation System

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Reefer Cargo Brine Circulation
systems
Carriage of refrigerated cargo
• Refrigerated cargo can be carried in
1. Specialised “Reefer Ships”
2. Refrigerated containers.
Reefer Ships
• Reefer ships are effectively large refrigerators, heavily
insulated with modern glass fibre or similarly
efficient insulation , shuttered with bright metal that
prevents taint and is easy to clean. They are ships
that tend to be divided into many more spaces than
conventional dry cargo ships, with several
’tweendecks spaces, so that different commodities
can be separated and carried, if required, at different
temperatures. Cleanliness and the maintenance of
optimum temperatures are the pre-requisites.
• The main features of a modern,
450,000 ft3 reefer vessel are as
follows.
• Four holds with 4 or 5 cargo
decks, each with the same clear
head of 2.2m to minimize lost
load space when storing standard
pallets (1.2m long x 1.0 m wide x
2.1 m high maximum). These
decks are arranged usually in
eight air tight temperature zones,
with the air coolers placed along
the bulk-heads serving one or
sometimes two decks. Variable
speed fans are placed above the
coolers forcing air through, under
the grating then vertically from
bottom to top through the cargo
and back to the coolers.
• Four fast cranes able to handle a 40 ft
container laden, for example, with frozen
meat.
• Space for eighty or more integral containers
on the weather deck, and space for fork lift
trucks and pallet cages.
Air circulation and refreshing
• Between 90 and 120 air changes of the net volume
per hour is usually provided in holds. Such volume
flow guarantees good and uniform cooling rate of
palletized and bulk cargo and allows for imperfect
storage. This air rate will be reduced on completion
of cooling down and when frozen cargo is carried.
• Air refreshing rates to remove carbon dioxide,
ethylene and other volatiles, can be two or three air
changes per hour.
Brine battery and air
• In this system, brine instead of primary refrigerant is
circulated through the batteries. Air is cooled in a
brine cooling system and cold air ducted to the
cargo spaces.
• Brine is relatively easy to regulate. The system
shown is arranged with three separate refrigeration
and brine circuits with connections from both brine
systems to the air cooler batteries (or grids). Brine is
inexpensive, being made with calcium chloride and
fresh water to a gravity of about 1.25. Sodium
dichromate or lime may be added to maintain the
brine in an alkaline condition.
Calcium Chloride Brine
CALCIUM CHLORIDE / BRINE
Specific
Gravity
Hydrometer Reading
Freezing Point of Solution
(Twaddell)
°C
°F
1·20
40
-21
-6
1·21
42
-23
-9 5
1·22
44
-25
-13
1·23
46
-27
-17
1·24
48
-30
-21.5
1·25
50
-32
-26
1·26
52
-35
-31
1·27
54
-38
-37
1·28
50
-42
-44
1·29
58
-51
-60
Single Space Single
Evaporator
Expansion tank
Freon/Ammonia inlet
Freon/Ammonia outlet
Evaporator
Cold
Air to
space
Battery
pump
Five Spaces Single
Evaporator
Expansion tank
Freon/Ammonia inlet
Evaporator
Return Header
pump
Delivery/supply
Header
Five Spaces Double
Evaporator
Expansion tank
Freon/Ammonia inlet
Evaporator
Return Header
Evaporator
pump
Delivery/
supply
Header
Five Spaces Double
Evaporator 1 brine
Freon/Ammonia inlet heater, 1 injection
Expansion tank
Evaporator
Return Header
Evaporator
Bypass valve
Brine heater
pumps
Delivery/
supply
Header
Showing third pair of headers served by a brine heater and third pump, so that any
battery can be individually defrosted by circulating the warm brine. Also
introduced is a brine "injection cross connection from the delivery of pump No. 1
to the suction of' pump No. 2. Brine injection is used so that evaporator No. 1 can
assist evaporator No. 2 when No. 1 is set to deliver brine at a lower temperature
than No. 2. A further refinement of this injection is the by-pass arranged across the
inlet and outlet of evaporator No. 2 so that the cooling, of the brine circulating in
No. 2 system can be achieved entirely by injection if desired.
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