Industrial Refrigeration Compressors
Vapour compression in ammonia refrigeration used for industrial refrigeration is achieved by a Screw compressor, as above, which has two rotors running together. It is also achieved by a Reciprocating compressor- in the above video. Ammonia compressors are open drive because the refrigerant would rot the windings if they where semi-hermetic
Oil Harvesting
Oil used to lubricate the compressor and ammonia used for industrial refrigeration 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 solonoid 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 and runs down
Despite this, oil still collects over time. It needs to be harvested and disposed of during the maintenance. The harvested oil is replaced by new oil. Oil changes are carried out periodically
Ammonia Refrigerant Recovery
Vessels
We work on industrial refrigeration systems that have 1000kg of ammonia or more. We can recover and dispose of any amount of ammonia during the decommissioning of the refrigeration plant. Recovery can be made into containerised recovery tanks that come on articulated trucks, in 530kg cylinders or small 56kg cylinders
Equipment
We have state of the art ammonia liquid pumps. We use these to connect to a part of the system which contains ammonia in its liquid phase. The pump discharges into the recovery cylinder. Our fast pump-out unit is connected to suck ammonia vapour from the top of the recovery cylinder. The pump-out unit condenses the vapour into liquid, then puts this small amount of liquid back into the ammonia refrigeration system. This process we call ‘push pull’ Steel braided lines are carried by our engineers and can be connected together to get from the plant to the containerised recovery tank
Pipework used for Industrial Refrigeration
Ammonia corrodes various metals and alloys. Steel, however, works well in ammonia refrigeration. 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. On pipework used for industrial refrigeration, 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. During maintenance on an industrial refrigeration plant, the pipework is inspected and a quote submitted for the replacement of the pipework, valves or components
Our Safety Equipment used for Industrial Refrigeration
We have state of the art ammonia refrigeration equipment. Each engineer attends site with an NH3 kit-bag. Escape masks are provided, tested, certificated and fit tested to the individual engineer. Our engineers wear full length overalls to protect exposed skin against ammonia splashes. Nitrile gloves and fit tested goggles are worn routinely. Each engineer has a Dräger Pac 7000 NH3 detector which alarms above the 35 parts per million level, this warns the engineer he has 15 minutes exposure time. Chemical suits are provided as part of the kit. Ammonia warning signs are provided to hang on the entrance and exit to the machine room; this is to warn other authorised engineers that the industrial refrigeration plant is being worked on
Ammonia Refrigeration is the Future
The Passed
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 getting more and more realistic. The range of smaller, non-industrial applications will spiral during the HFC phase down
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