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Gas Compressors Ltd | Technologies

Gas Compressors Ltd is experienced in the design, packaging, installation and commissioning of the following types of compressors and blowers. When selecting a technology for a particular application, our engineers will weigh the advantages and disadvantages of the various generic types of machine available, in order to offer you the user, the best combination of reliability and economic benefits. As we are not tied to specific suppliers, you can be sure that the optimum solution will be designed and installed at your plant.

Rotary Vane Compressor
 
Principle
A single rotor is mounted offset in a cylindrical housing. Slots in the rotor contain vanes, which are thrown against the wall of the housing as it rotates. Oil is injected into the compression space to lubricate the bearings and vanes. As the rotor is offset, the segments that are created by the vanes vary in size through the cycle, causing the trapped gas to be compressed. Ports in the housing wall are positioned to let the gas in and out at the points of minimum and maximum pressure.
Typical Performance Envelope
  Imperial Metric
Minimum flow 10 cfm 17 m3/h
Maximum flow 6,000 cfm 10,000 m3/h
Maximum casing pressure 175 psi 12 bar
Maximum pressure ratio per stage 4  
Advantages

  • Slow speed of rotation means low wear.
  • Single rotor and vanes are only moving parts.
  • Once-through oil lubrication means no build up of aggressive contaminants. Film of oil protects internals from attack.
  • Vibration free operation.
  • High speed range, typically -50% +20% from standard, gives easy flow controllability through VSD operation.
  • No special foundation required, lowering civil costs.
  • Can usually be direct driven - doing away with belts or gearboxes.
  • Pulsation free gas discharge.
  • Valveless porting means no drop off in efficiency between overhauls, and no valves to maintain or break in service.
  • Very economic to purchase and maintain - vanes and bearings are only wear parts.
  • Simplicity: units are readily overhauled in the field without special tools.
Disadvantages

  • Intimate contact between lubrication oil and compressed gas.
  • Small quantities of lubrication oil need to be disposed of after use.
  • Low pressure capability as single stage unit.
Common Applications

  • Fuel gas boosting.
  • Digester mixing.
  • Landfill gas gathering and boosting.
  • Wellhead gas compression.
  • Flare gas recovery.

 

Oil Flooded Screw Compressor
 
Principle
Twin screw shaped meshing rotors are mounted in a figure of eight shaped housing, which has suction and discharge ports at either end. As the rotors turn they form a space that traps gas, the space travels down the length of the housing, and because of the profile of the screws is compressed as it goes. Oil is flood injected into the compression space to lubricate the bearings and screws, and to absorb the heat of compression. The oil and compressed gas mixture subsequently passes into a de-oiling vessel. The oil is then cooled and filtered and goes back round the cycle once again.
Typical Performance Envelope
  Imperial Metric
Minimum flow 500 cfm 850 m3/h
Maximum flow 5,000 cfm 8,500 m3/h
Maximum casing pressure 580 psi 40 bar
Maximum pressure ratio 40  
Minimum pressure ratio 3  
Advantages

  • Oil flooded lubrication system absorbs heat of compression, thereby allowing very high compression ratios. Film of oil protects internals from attack by aggressive constituents.
  • Pressure ratio controllable by slide valve, which lengthens discharge port in the direction of the suction port.
  • Flow controllable by slide valve on suction port.
  • Vibration free operation.
  • No special foundation required, lowering civil costs.
  • Pulsation free gas discharge.
  • Valveless porting means no drop off in efficiency between overhauls, and no valves to maintain or break in service.
Disadvantages

  • Intimate contact between lubrication oil and compressed gas.
  • Moderately high cost.
Common Applications

  •  Fuel gas boosting for gas turbines.
  •  Refinery service.

 

Reciprocating Compressor
 
Principle

Similar to an automotive combustion engine, except passive non return valves replace actuated valves. A piston travels up and down inside a cylinder, and is connected to a crank shaft by a connecting rod. On the down stroke, the discharge valves are forced shut, and gas is therefore sucked into the cylinder. On the up stroke the suction valves are forced shut, and gas is expelled into the discharge port. On multi-stage machines, the gas must be cooled before entering the next stage.
Typical Performance Envelope
  Imperial Metric
Minimum flow 10 cfm 17 m3/h
Maximum flow 1,000 cfm 1,700 m3/h
Maximum casing pressure 5800 psi 400 bar
Maximum pressure ratio 4  
Advantages

  • High efficiency when new and after overhauls.
  • Very high pressures possible.
Disadvantages

  • Expensive to purchase.
  • Expensive to maintain.
  • Fixed speed - not easy to control flow.
  • Out of balance forces mean a special foundation is required.
  • Noisy.
  • Pulsating gas at discharge may need damping.
  • Complicated - many moving parts.
  • Efficiency drops off between overhauls.
Common Applications

  • Fuel gas boosting.
  • Vehicle re-fueling.
  • Wellhead gas compression.
  • Natural gas distribution.
  • Plastic bottle blowing.

 

Positive Displacement Rotary Blower
 
Principle

Two profiled rotors turn in a figure of eight housing. They are geared together so that they almost , but do not quite, touch. There is no compression within the machine, it simply pushes gas into the system to which it is connected.
Typical Performance Envelope
  Imperial Metric
Minimum flow 50 cfm 185 m3/h
Maximum flow 3,000 cfm 5,000 m3/h
Maximum casing pressure 30 psi 2 bar
Maximum pressure ratio 2  
Advantages

  • High speed range, typically ±35% from standard, gives easy flow controllability through VSD operation.
  • Valveless porting means no drop off in efficiency between overhauls, and no valves to maintain or break in service.
  • Low purchase price.
  • High efficiency.
  • Oil free gas path.
Disadvantages

  • Noisy.
  • Pulsating gas discharge.
  • High speed of operation.
  • High maintenance requirement.
Common Applications

  • Waste water aeration.
  • Pneumatic conveying.
  • Fuel gas boosting for boilers.

 

Centrifugal Blower
 
Principle
An impeller is attached to a rotating shaft within a cylindrical housing. Gas drawn into the housing near the centre, is then thrown towards the perimeter. The imparted velocity of the gas causes a pressure rise and flow. Multi-stage machines direct the gas back to the centre of the next stage.
Typical Performance Envelope
  Imperial Metric
Minimum flow 300 cfm 500 m3/h
Maximum flow 60,000 cfm 100,000 m3/h
Maximum casing pressure 30 psi 2 bar
Maximum pressure ratio 2.2  
Advantages

  • Slow speed of rotation gives exceptional wear part life.
  • Single rotor is only moving part.
  • Oil free gas path.
  • Vibration free operation.
  • Flow control through inlet throttling.
  • No special foundation required, lowering civil costs.
  • Can usually be direct driven - doing away with belts or gearboxes.
  • Pulsation free gas discharge.
  • Valveless porting means no drop off in efficiency between overhauls, and no valves to maintain or break in service.
  • Simplicity: units are readily overhauled in the field without special tools.
  • Efficiency is good on the larger flow machines.
  • Quiet operation - often no sound attenuation is required.

Disadvantages

  • Lower efficiency on smaller flows.
  • More expensive than positive displacement blowers.
  • Low maximum casing pressure.
Common Applications

  • Landfill gas gathering and boosting.
  • Waste water aeration.
  • Vacuum cleaning.
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