De-oiling ammonia (NH3) refrigeration systems

De-oiling ammonia (NH3) refrigeration systems

Unlike HFC refrigerants, ammonia does not mix with oil. Since the density of the oil is higher than that of the ammonia, it settles in the apparatus at the lowest point and can be discharged there via a safety oil drain valve.

The fluidity of the oil decreases at lower temperatures. It must therefore be selected for ammonia plants oils that are still flowable at the existing evaporating temperatures in the plants. If this can not be ensured, the unit must be stopped for de-oiling and serviced until the temperature rises until the oil is free-flowing again.

Systems operating in the vacuum range (evaporation temperature <1 bar) receive a separate oil collector. In normal operation, the valves in the inlet and degassing lines are open, so that the oil can settle. Before de-oiling, the inlet valve is closed so that the refrigerant evaporates. The evaporation takes place with uninsulated container by heat radiation from the environment. For insulated containers, a thermostatically controlled electric heater is usually installed.

To drain the oil and the degassing valve is closed. The remaining refrigerant in the oil receiver is sufficient to cause a pressure increase that causes the oil to flow out when the safety oil drain valve opens.

Source:

IKET (ed.) 
Pohlmann Taschenbuch der Kältetechnik
Fundamentals, applications, worktables and regulations

21st, revised and expanded edition 2013 
ISBN 978-3-8007-3393-4

VDE VERLAG GmbH, Berlin - Offenbach