Screw compressors were invented at about the same time as centrifugal compressors - in 1908, a patent was registered, now owned by Svenska Rotor Maskiner AB (SRM). Currently, the patent has been purchased by more than 50 companies.
Structurally, screw compressors are rotary compressors. Compression of the medium is achieved using two rotors with helical teeth coupled together. A screw compressor consists of a housing and two spiral rotors (male and female) which are very closely meshed with each other.
Compressors show excellent energy savings, as well as reduced compressor maintenance costs. The payback period of a screw compressor can reach about 18 months. Reducing the energy consumption of screw compressors leads to cost savings.
TYPES OF SCREW COMPRESSORS
Screw compressors are oil-free and oil-flooded.
In oil-flooded screw compressors, as a rule, one rotor is the leading one (male). The screws mesh with each other, and the secondary rotor (female) rotates automatically when the leading rotor rotates. Oil, which is constantly injected into the casing, prevents metal contact between the rotors. In addition to lubricating the screw block, the oil performs two more important functions: it seals the gaps between the rotors, between the rotors and the compressor housing, and also removes heat.
In an oil-flooded screw compressor, oil is injected into the working compression space at a rate of 8-10 l/m3/min, which covers the process gaps and seals the compressor. To clean the compressed gas from oil, an oil separator is installed at the discharge of the screw compressor.
The key feature of screw compressors is that they provide a fixed compression ratio.
Rotary screw compressors are ideal for multi-stage compression ratios.
This type of compressor can be called transitional between positive displacement compression (piston) and dynamic compression (centrifugal), since there is a process of volumetric compression (before the gas reaches the outlet window), and external (dynamic).
PURPOSE
The main areas of application of screw compressors:
- Gas supply to gas turbines
- Natural and associated gas transfer
- Gas injection for underground gas storages
- Cooling and compression of gases (propane/butane)
- Compression of process gases
- Offshore platforms
- Synthetic fertilizer plants
- Synthetic rubber plants
ADVANTAGES
- High compression ratio
- Reliability in operation
- No special foundation required
- No valves or friction parts in the compression space, increasing reliability
- No mechanical converters
- Ability to compress process gases with different molar masses
- Ability to work with a medium containing liquid droplets
- High energy efficiency (at least 30%)
- Does not require large initial investments and small capital investments for repairs
- No vibration
- Compactness
- Low cost
- Easy to maintain
- Small dimensions and weight
DISADVANTAGES
- Oil contamination of compressed gas
- An oil system with cooling system is required
- With a low compressor load in the suction section, the efficiency is significantly reduced
WORKING RANGE
- Power range: 100 - 3500 kW
- Volume range: 300 - 12000 m³/h
- Pressure: 0.4 -6.3 MPa
- Speed: 500 - 3000 rpm
