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Leitungs- und Instrumentendiagramm (P&ID) und Stromleitungsdiagramm
The non-condensable gases (NC's) are collected and released to the atmosphere
by a special blow-off metering valve.
Operating sequence
Typically the ammonia liquid receiver or separate line, is at a pressure of around
13 Bar(a) corresponding with a saturation temperature of close to 34°C. The gas
mixture (ammonia + NC's) that rises from liquid receiver to the ammonia heat
exchanger will be cooled down to min. around -30°C.
The cooling of the gas mixture is done with a small cooler unit (the heart of the
NC-purger) that is started by the clock timer signal being high, but only if the
pressure in the ammonia part of the heat exchanger (= refrigeration plant con-
denser pressure) ánd the NC-purger's evaporator pressure are above their mini-
mum starting set point.
If there's a significant amount of non-condensable (NC-) gas present (and thus
no ammonia left to be condensed) in the ammonia compartment of the ammonia/
R290 heat exchanger, there's far less heat to keep the R290-evaporator at the
pressure at which ammonia condensates.
As a result the pressure in the R290 evaporator part of the ammonia/R290 heat
exchanger, or more specifically, in the complete low pressure part of the R290-
cooling circuit will drop. This pressure drop is the input to determine the presence
of NC's and when to stop cooling. If NC-gas is indeed present, it is released to
the atmosphere; which is done by opening a solenoid valve if the pressure has
dropped below the opening set point. As soon as the pressure has reached the
set point for closing the solenoid valve; it is closed again.
If the both the pressures (in the ammonia (NH
tor part) are still/again above their minimum starting set point while the clock
timer signal is still high, the cooling-purging cycle is repeated. The cycle is repea-
ted until the pressure in the ammonia (NH
ped below the setpoint at which the volume of non-condensables is at a minimi-
zed level (as long as the clock timer allows to do so).
After completing one or more of cycles and the clock timer signal becoming low,
the NC-urger is completely stopped. As soon as the clock timer became low it
started counting down again to the next allowed starting point of the NC-purger.
The control unit also is equipped with several operating-safety measures, such as
a pressure switch to shut down the NC-purger if the R290-discharge pressure
becomes too high (apart from an electro-mechanical safety pressure switch) as
well as measures to prevent purging ammonia in case of malfunction of the ther-
mostatic expansion valve.
1.5
Leitungs- und Instrumentendiagramm (P&ID) und Stromleitungsdiagramm
1.5.1
Piping & Instrumentation Diagram (P&ID)
12
) compartment and R290 evapora-
3
) part of the heat exchanger has drop-
3
0089393_imm_purger_Propane_german_5
01.11.2021
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