To substantially reduce a condensation tendency of water by controlling the inlet temperature of compression air in one of a plurality of compression stages continuous to a first stage to a value for preventing excess of saturated steam pressure in pressure and a temperature achieved at a compressor stage in which partial pressure of steam in compression air is continued to a following stage.
For example, in a two-stage type compressor 10, when the temperature of compression gas delivered from a first compressor stage 10a is a temperature and less for preventing excess of saturation steam pressure in pressure and a temperature achieved at a second compressor stage 10b in which partial pressure of steam in compression gas is continued to a following stage, all compression gas directly flows to the second compressor stage 10b without passing an intercooler 16 while changing the direction even in a part thereof. Only when the temperature is such temperature or more, compression gas flows through the intercooler 16 by deviating a part thereof. A three way valve 30 and a control device 36 are used in such a constitution that cooling and non-cooling compression gas or mixture are selectively passed comply at need, in order to hold compression gas which flows into the second compressor stage 10b at a prescribed target temperature.
GOETTEL WALTER E
WAGNER DANIEL G
DRUMMOND ROGER
