Cold Link Africa Cold Link AfricaOctober 2018_digital | Page 25

PROJECT
INCORPORATING COLD CHAIN
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airlock. The cooling tunnels were designed to
operate with a coil air off temperature of -1°C, the
chillers at an average air temperature of +2°C to
+4°C, and the airlock at +12°C.
Four high-stage reciprocating compressors
were designed to meet the facility load and
operate at saturated suction and condensing
temperatures of between -8°C and +34°C,
respectively. Three compressors were required
to run under peak conditions, with a fourth as
standby. The compressors operate at a fixed
speed of 1 450rpm.
Two evaporative condensers were installed
on strip plinths on top of the new plant room
roof and together, the condensers operate at a
saturated condensing temperature of +34°C. With
one condenser out of operation, the saturated
condensing temperature will rise to +37°C.
One horizontal -8°C accumulator vessel is
provided for the plant as well as one receiver
vessel.
CONTROLS
The refrigeration plant is equipped with an
automated control system to ensure that the
starting, stopping, and capacity control is fully
automated. The refrigeration plant isn’t manned,
and the control system therefore accommodates
this. In addition, the control system has the facility
to allow for plant monitoring, including all room
temperatures and cooling tunnel temperatures
from the client’s operations office.
The control system also accommodates data
logging for temperatures and pressures throughout
the refrigeration plant. This data is readily available
in the form of tabulated or graphical display.
The control system even sends text messages
via the cellular networks to select phone numbers
for plant alarm conditions.
The cooling tunnels make use of proportional
suction control valves to maintain temperatures
for export goods accurately. This control allows
for the fastest cool-down rate with least amount
1. Motors powering the Mycom N8M ammonia
compressors in the plant room.
2. The accumulator, gauge panel, and ammonia
liquid make-up line.
3. A Mycom N8M compressor. The Mycom
packages produced by MRE are fitted
with an internal relief valve (a SANS 10147
requirement). This is one of many robust safety
features on the compressors.
4. Proportional expansion valves are used on
the suction side of the valve station to control
evaporating pressure precisely.
5. Airlock valve station.
6. Walkway between the two large chillers. Valve
stations for the chiller to either side.
7. The airlock and additional rapid cooling
tunnels. Product ready to be loaded.
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COLD LINK AFRICA • October 2018
www.coldlinkafrica.co.za
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