Page 4 of catalogue Diaphragm Compressors of Andreas Hofer Hochdrucktechnik GmbH

Hofer Diaphragm compressors

page 4 of 20

Introduction Nearly all chemical processes as well as process engineering involve the requirement of compressing gas from a lower to a higher pressure level. Selection of the type of compressor is done depending on the parameter of the process (type of gas, capacity, pressure difference to be overcome). For higher pressure differences (approx. 40 bar upward) only reciprocating Compressors can be used (Fig. 1) [1].

Fig. 1: Present applications of different compressor types [1]

The classic piston compressor has been and will be oil-lubricated, and thus will have the inherent disadvantage of this type of compressor design, which is that lube oil enters and appears in the different compression stages. This lube oil has to be drained again from the gas, separated and suitably removed downstream the last compressor stage. These washed-out lube oil may admittedly not be too great a problem for compressors for air, nitrogen or hydrogen, but positively these residual oils are difficult to be handled from e.g. sour-Gas compressors and require a considerable extent of treatment and cleaning. The availability of new modern synthetics, being sufficiently heat- and chemical resistant and having perfect sliding properties made it possible to design a non-lubricated type of piston compressor. This type of compressor needs no lubrication of the cylinder space, but, sure, has other disadvantages. The quantity of leak gas which escapes to the atmosphere via the (non-lubricated) piston rod seal is by far larger than it is at oil-lubricated Machines. Furthermore, even with only low requirements to maintain purity of the gas, filter systems have to be installed downstream the compressor, because abrasive particles originating from the Piston rings and rod seal will penetrate into the gas. Finally, the efficiency of non-lubricated compressors is considerably lower, because the oil-film, which helps with the sealing, is missing and consequently the inner leakage increases [2].