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Vapour Recovery

How to reduce wastage when it comes to LPG and refrigerant transfer.


Following the introduction of the revised F-Gas Regulation, (EU) No 517/2014 in 2015 which repealed the original F-Gas Regulation (EC) 842/2006, and it subsequent phased implementation through to 2030,users and manufacturers have been required to look at the containment, use, recovery and destruction of HFCs (Hydrofluorcarbons). Discharging fluorinated gas into the atmosphere causes environmental damage and is illegal, making its recovery essential to the refrigeration and air conditioning industry.

Far from being an onerous requirement, F-Gas Regulation does provide the opportunity for users to obtain financial credits through an incentive scheme for returned refrigerants. Once reclaimed product has been reprocessed and returned to an approved standard by a licensed reprocessing facility it can be resold for further use. Cleaning involves removing water oil and possible non-condensables. This turns the refrigerant to virgin refrigerant standard.
Gases with a medium to high Ozone depletion level and GWP Global Warming potential are being phased out and being replaced by new gases that are more environmentally acceptable, but they do contain chemicals that more highly flammable. Also vapour pressures are much higher. Together, this means that the process of transferring gases and liquids is even more critical in terms of safety and in recovering the optimum amount for recycling.
Harp International in Pontypridd is a leading supplier of high quality refrigerants for air conditioning and refrigeration plant and equipment both in the UK and overseas and takes in gas from companies all over the world. It follows therefore that Harp International has extensive environmental knowledge on FGas Regulation, and the recovery and destruction of HFCs.
The plant at Pontypridd is the largest stand alone refrigerant reclamation plant in the UK and operating under a waste management licence it has sufficient capacity to meet the total needs of the market. Analytical quality control ensures that all reprocessed material meets virgin quality specifications. Harp International is also actively involved in developing its own novel separation technology for a variety of halocarbon and other mixtures.
Central to the plant's operation is the management of systems for the collection, transportation, treatment and disposal with appropriate registration and licences. It is not untypical to have 20,000lt tankers delivering used gas for cleaning and once this has taken place it is stored for reuse. With regard to the operation and the value of the gas being so high, Harp International has always used the highest specification equipment for optimum reclamation. As a result there has been a smooth transformation following the introduction of the new FGas regulations.
In order to ensure safe handling and optimum product recovery, Hall International uses AxFlow vapour and liquid transfer systems for offloading tankers and for storage duties. It makes sound economic sense to make sure that any product that remains in a tanker or bulk container is extracted for recycling and storage for future use. Also, if a tanker is to be used for another product, it needs to be thoroughly cleaned to prevent cross-contamination it is essential that the tanker is completely free of any liquid and vapour before cleaning can commence. The element of safety and recovery also extends to process storage vessels when the contents need to be transferred or for large storage tanks when maintenance is required.
In a great many applications, liquefied gas is removed from the tanker or vessel using a centrifugal pump. However, this will not necessarily remove the entire contents of the tanker, leaving behind a potential y expensive product (the liquid heel). Because not all suppliers pay compensation for the gas remaining in tanks after emptying, it is important to recover the heel. Also, there is the fact that some liquefied gases boil very easily, so using a centrifugal pump to transfer these products can be a problem. The answer to this difficulty is to employ a single or two-stage compressor system.
Single stage compressor units for vapour recovery can attain very high temperatures which mean that not all the gas is recovered. This can overcome by using two- stage units. The two stage units are used for liquid recovery, but can also be used for vapour recovery. The two stage unit gives the user greater flexibility for reclaiming, vapour, gas and liquids. The new gases have higher vapour pressure and these, together with other factors are producing demand for recovery systems. The lower the GWP the higher the degree of flammability. The benefit of the AxFlow double stage unit is that it can switch between single and double stage operation as and when required.
The function of the system is to push the liquid from inside the tanker into the storage vessel using pressurised vapour from the storage vessel. Following this, the compressor connections are reversed using a 4-way valve to suck out any remaining vapour in the tanker and transfer it to the storage vessel.
Designed specifically for liquefied gas transfer duties, AxFlow's systems use Blackmer vertical piston compressors which come in single or two stage versions with air or water-cooling. The Blackmer single-stage reciprocating compressor creates a low-pressure area in the compression chamber, when the piston moves from the highest point of the stroke to the lowest point. The gaseous product (at a higher pressure in the tank) moves into the compression chamber whereupon this volume of gas is reduced as the piston moves to the top of the stroke with a corresponding increase in pressure.
AxFlow's units are available in stand-alone configurations and as packages engineered to meet customer's specific requirements, whether for continuous gas transfer, liquid transfer or gas evacuation down to pressures of 50 millibar absolute. They are suitable for displacements of up to 212 m3/h and system pressures up to 42 bar.
To meet the varying requirements for tanker emptying, AxFlow offers compressor and pump packages, both for fixed and transportable installations. For companies such as Hall International, transportable units enable them to be used at various locations around their plant. These skid-mounted systems take the gas from the container, compress it before condensing it into a liquid via a water-cooled plate heat exchanger and then pass it into the receiving container for onward storage. At the latter stages of vapour recovery the pressure in the container drops until it reaches atmospheric pressure and at this point the vacuum pump is started. This pre-boosts the compressor and pulls out the remaining vapour in to the receiving container as before. Thus, the combination of compressor and vacuum pump removes almost the entire residual product to give maximum product recovery.

Summary
Using a purpose-designed compressor unit to remove both liquid and vapour overcomes most of the limitations of using pumps, whilst the added flexibility of adding a vacuum pump enables removal of even more gas, increasing both safety and cost savings.

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