Gas Compressors Ltd is capable of taking on projects in many specialised gas boosting and compression applications. The following applications outline our major areas of competence.

Fuel Gas Boosting
The gas network operated by your local distribution company, is subdivided into four pressure bands: low pressure, medium pressure, intermediate pressure and high pressure. In practice this means that the main that runs past your door, can be at a pressure of anywhere between about 50 mbar/20" WC and 50 bar/725 psi.

On many applications, such as direct boiler firing, and electricity generation using reciprocating gas engines and gas turbines, project engineers will find that there is insufficient gas pressure available direct from the supply network.

The most favoured solution normally is to negotiate with the distribution company, in order to obtain the required pressure, however this may not be possible economically, and also it may not be possible within a suitable project time frame. In this case engineers need to look at booster compressors, in order to solve their problem.

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Digester Mixing
During the sewage and aqueous industrial waste treatment process, it is often environmentally advantageous to treat sludges in large tanks known as digesters. Sludge is held in these air tight tanks for typically two to three weeks, while they are broken down by anaerobic bacteria. The result of this break down is a reduction in sludge volume, together with the liberation of large volumes of gas.

Digester gas is completely saturated with water, and although of variable quality usually has constituents of about 50% methane, 30% carbon dioxide, 20% nitrogen and significant trace quantities of hydrogen sulphide.

In order to promote digestion at optimum efficiency, it is necessary to keep the digester at an elevated temperature, and to keep it thoroughly mixed. Using a compressor to draw off gas from the top of the digester, and to reinject it back at the base is a very efficient way of doing this - it also has the advantage that the heat of compression is passed into the sludge, helping to keep it up to temperature. Other advantages of gas mixing over mechanical mixing are a lower initial capital cost, simpler installation, higher gas production, and a reduced tendency to be fouled by detritus.

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Digester Gas Boosting
Whether sludge digesters are mixed with mechanical paddles or with small compressors, they will still be creating a surplus of gas all the time. This gas may be stored, flared off or utilised in some way.

Depending on the size of the installation, the uses would normally be either direct burning in order to help keep the digesters up to temperature, or burning in reciprocating gas engines or gas turbines.

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Landfill Gas Extraction and Boosting
Mankind has for centuries disposed of unwanted objects by burying them. With the growth of the industrial age, the volumes of waste that have been disposed of in this way have increased to huge levels.

Organic components of municipal landfill refuse gradually decay, degrading to produce amongst other things landfill gas, which has a similar molecular makeup to digester gas.

Although environmental policy is now starting to curtail the development of new landfills, landfill gas will continue to be produced for many years to come.

The gas must be gathered and either flared or utilised, otherwise it migrates along the ground and can cause dangerous gas build up, in for example sewers or under buildings.

Low pressure centrifugal blowers are used for gas gathering, and higher pressure boosting is achieved with rotary positive displacement machines.

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Wellhead Vapour Recovery
When crude oil is drilled and commercially exploited, it carries with it a certain percentage of dissolved low molecular weight gases, which tend to come out of solution at the wellhead.

For many years it has been accepted practice to flare off this gas, as it was considered uneconomic to utilise this resource.

Environmental and public opinion considerations have lead engineers to challenge this concept. New affordable technologies have become available to enable this gas to be used. The gas can be re-compressed and used as a fuel in either microturbines or should sufficient be available, in conventional turbines.

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Refinery Service
After the initial refining process is complete, many of the resulting products are then utilised as feedstocks in order to further manufacture petrochemicals. Often the driving forces to these processes are compressors. Large turbocompressors are used for most high flow processes, whilst smaller rotary and reciprocating machines are used for sidestreams.

With many complicated and potentially dangerous reactions and processes running simultaneously, it is necessary for safety reasons to have a system in place, that will take away any quantities of gas that can be suddenly produced or emitted when a reaction goes slightly out of control. These gases are typically flared at a single central facilty. As above these gases can also be recompressed and either re-injected into another process stream, or used as fuel for the fractional distillation columns.

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Pyrolysis of Municipal Waste
Pyrolysis is where a substance is heated very strongly in the absence of oxygen. Under these conditions organic matter such as food waste, packaging and fibres tend to break down quickly into ash and a mixture of gases.

Great steps are being made at the moment in perfecting this technology. At present this gas mixture, which contains methane and hydogen is usually burned to fuel the process.

With the drive to use the environmentally friendly gas hydrogen at the top of the agenda, it will soon be economic to remove the hydrogen from the pyrolysis gas stream. Recent advances with membrane gas separation technology, together with robust compression equipment, will make this next step successful in the near future.

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Process Vacuum
Many industrial processes call for the removal of contaminated air or gas: this could take the form, for example, of solvents from metal cleaning or dust particles from a painting line.

In automated production lines, vacuum is often used to hold items while they are worked upon, and also to transfer them from place to place.

Many glass containers such as bottles and glasses are manufactured by being drawn over a mould by vacuum. Lower than atmospheric suction conditions are also found in landfill gas extraction, natural gas extraction and the extraction of dissolved gases from liquids.

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Aeration
The processing of aqueous waste streams and some industrial operations, calls for the introduction of air into various sludges or slurries, in order to maximise the oxygen transfer into the system.

When air is injected into the bottom of a tank, the pressure required is directly proportional to the depth of the liquid, and a further factor is the viscosity of the liquid.

For most municipal sewage aeration projects, the injection pressure does not exceed 1 bar/15 psi, and so we offer positive displacement or centrifugal blowers.

Where deep tank aeration is preferred, and along with it higher pressures, rotary vane compressors are the preferred technology.

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Pneumatic Conveying
Bulk powdered or granulated solids such as cement, plastics and feedstuffs can be easily and cheaply moved or unloaded by pneumatic conveying. This is where dry solid particles are entrained in a gas stream, which is normally air.

Lean phase pneumatic conveying is where a comparatively small volume of solid is entrained into large volumes of low pressure air. Typical equipment used for this type of process would be rotary lobe or centrifugal blowers discharging at up to 1 bar/15 psi. This is the preferred solution for larger granulated solids such as wheat or polyethylene.

Conversely dense phase pneumatic conveying is where a comparatively large volume of solid is entrained into smaller volumes of higher pressure air. Typical equipment used for this type of process would be screw blowers or rotary vane compressors discharging at up to 3 bar/45 psi. This is the preferred solution for powdered solids such as cement or chalk.

The positioning of the blower or compressor at either the source end of the line or the receiving end, makes the difference between whether the powder is sucked by vacuum or thrust by pressure. Cyclone separators are used to disentrain the powder or granulate on arrival at its destination. Care must be taken when sucking the product, to ensure that no solid is carried over into the blower or compressor, as this will damage it.

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