Industrial Refrigeration

Ammonia is the Future
The Past
Ammonia has been an established, pre-eminent industrial refrigerant for over 125 years. Ammonia has been used in industrial refrigeration applications such as food production. CFCs, such as Freon, became popular in the 1930s due to their low toxicity. The chlorine in the refrigerant was found to have caused a hole in the ozone layer. Therefore, they have now been phased out. Non-chlorine, low toxicity, HFCs were developed to replace the CFCs. HFCs, however, have a high global warming potential, so they too are being phased down to 21% by 2030

The Future
Between now and 2030 ammonia will become increasingly popular in non-industrial applications, such as, the cooling of data centres and the air conditioning of buildings. Systems with a low refrigerant charge are now being developed, so the application of cooling a small office with ammonia is now realistic. New ammonia chillers are simpler in design, therefore competitive in price to HFC chillers. The higher initial cost is paid back in electricity savings within 2 years- then they become cheaper. They use less electricity because ammonia has a latent heat bubble 5 times bigger than other refrigerants, more refrigeration effect and less gas. The range of smaller, non-industrial applications will spiral during the HFC phase down

Toxicity
There are no concerns now-a-days with the toxicity of the refrigerant. The low charge refrigeration plant shuts down in the event of a leak. It brings a fan on which disperses the small amount of ammonia into air

Industrial Refrigeration Compressors

A popular compressor type is the Screw compressor, right and below, which has two rotors running together. The Reciprocating compressor, in the above video, is another popular Ammonia compressor. NH3 compressors are open drive.

Grasso Screw Compressor
NH3 Compressor
NH3 Compressor

                                                              Rotors

Bearings

Pipework used for Industrial Refrigeration

Ammonia corrodes various metals and alloys. Steel, however, works well with ammonia. The use of steel makes the maintenance different as opposed to HFC chillers. HFC chillers are prone to leaks on the copper pipework. On the condenser, the copper expands and contracts- eventually rubbing through against the steel frame. Vibration related leaks are also common. With ammonia systems, the thing to pay the utmost attention to is rust. Lagging, used for insulation, that is in place and in good condition should not be removed to inspect the pipework. The main cause for concern is exposed steel that is freezing then thawing on defrost or off cycles. This freezing and thawing creates rapid rust formation and can lead to catastrophic failure of the pipework. Exposed steel that is permanently frozen creates slow rust formation as the ice slows the oxidisation process

Grasso compressor being lifted out
Grasso compressor being lifted out

Oil Harvesting

Oil used to lubricate the compressor and ammonia are non-miscible. That is to say: the refrigerant does not carry the oil round the system and back to the compressor. Oil return is achieved by:

Eductors
These work the same way a paint gun works that is used in a car body shop. High pressure discharge gas is blown across the low-pressure oil. The oil, which tends to accumulate in the bottom of the evaporator, is picked up then carried back to the compressor down an oil return line

Oil Pot
Accumulating oil collects in the oil pot at the bottom of the low-pressure receiver and is returned via a solenoid through an oil return line

Oil Separator
This vessel is the first vessel after the compressor. Put simply: it makes it as hard as possible for a liquid to pass through, while as easy as possible for a gas to pass through. The discharge gas enters the vessel towards the bottom and is swirled around the edge. The oil drops down and the remaining gas and oil go up through several layers of mesh getting finer and finer. The oil sticks to the mesh, runs down and back to the low side of the screw

Manual oil recovery
Despite the above, the engineer has to work out where oil is not returning from and use his experience to resolve the issue. Otherwise, the machine will experience low oil return problems

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