Instrument and Operating Air

Instrument and operating air can in most of the cases described here be obtained by way of the air compressor in the air separation unit. The instrument air is dried in switchable gel dryers at pressures between 6 and 8 bar to a water dew point (referred to atmospheric pressure) which is clearly lower than for the lowest local temperatures, in order to prevent steam condensation in piping, instruments and control valves. Sufficient air to shut down the plant in case of malfunction is stored in an air receiver of appropriate capacity. The air compressor of the air separation unit is almost in all cases supplemented by a stand-by instrument air compressor which normally produces only the air rate required to start up the plant. 

Operating air can simply be taken from the air compressm in the air separation unit It need not be dried nor stored. 

A grass roots plant needs a whole lot of other offsites in addition to the utility production or conditioning units described in this chapter some of these offsites form part of the infrastructure, others are associated with administration, safety and maintenance. The list below can no doubt be enlarged in specific cases  

Construction and operation of these facilities normally make a considerable contribution to the total investment and in some cases have an influence on energy demand as well. They, too, need therefore to be appropriately considered at the design stage. 

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