Saturday, August 2, 2008

screw compressors


In this, there are only two moving components, the rotors themselves. Timing gears
are also installed on the rotors and are primarily used for synchronisation. The gears synchronise the rotation of rotors and prevent contact of rotors between themselvesand with the casing.

This type of compressors are used for air and many process gas applications which do not allow contamination with oil. Suitable sealing arrangement is designed for each service.


Compression is accompanied by volume reduction and increase in temperature This increase in temperature puts limitation on compressor design. Temperature increase in certain gas mixtures poses problems like ‘polymerisation’, ‘gumming’ etc. Hence suitable liquids like water, benzol, other solvents etc are injected in the process gaswhich control the temperature rise by absorbing heat of compression.


The fundamental difference between the oil free and oil injected screw compressors is that in oil injected, lubricant is added to the gas being compressed and removed again after the compression is complete. It can be stated that the power absorbed in compressing a gas all appears as heat in the system. Normally the vast majority of this heat appears in the gas itself as increase in temperature, the remainder being absorbed in the compressor and its cooling systems. However, in an oil injected compressor, a large part of the mass flow going
through the compressor is made up of the injected oil and hence this absorbs the heat. The mass of oil is relatively large compared to the gas mass flow because the oil is in the liquid phase, but the volume of the oil relative to the gas is normally less than 1% and therefore, the effect of oil volume on the gas throughput of the compressor is negligible.

The addition of the appropriate quantity of oil to the compressor related to the
absorbed power therefore, controls the compressor discharge temperature regardless of the pressure ratio over which it is operating. As long as the cooling for the oil is designed to remove the heat absorbed by it, the system remains under accurate control with great flexibility.

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