| |
|
|
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 civils 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 civils 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 multistage 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 refueling.
- 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. Multistage 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 civils 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.
|
|
|
|
|
|
|
