Factors to Consider when Choosing Compressed Air Systems

Related Vendors

Glatt Ingenieurtechnik GmbH

Italvacuum, Srl

TRM Filter d.o.o.

Devising dryers

Multiple dryer technologies exist. The most common dryer technology used for process applications is desiccant; however, not all desiccants are created equal. Desiccant dryers require regeneration of the drying media. The simplest design is a twin-tower heatless desiccant dryer and requires 15–18 percent purge of the rated compressed-air flow for regeneration.

An externally-heated twin-tower dryer may only require seven to eight percent purge, but needs energy for the heating element. An externally-heated dryer with blower purge may reduce the purge rate to two to three percent, but also requires energy for both the heater and the blower.

Trade-offs in flow and power consumption need to be determined for optimised system design. If compressor capacity exists for the additional purge, of the three dryers mentioned above, it may be best to purchase the simplest dryer design — which, in this case, is heatless. An assessment of first and operating cost will help determine the right dryer design as per your requirements. Heat-ofcompression drying uses the waste heat from the compressor to regenerate the drying media; therefore, no purge air is required and the total power required to run the dryer is equivalent to that used by a light bulb. Pressure dew points must be repeatable for pharmaceutical applications and some heatof- compression desiccant dryers fluctuate significantly with changes in load. The single vessel heat of compression-integrated dryers

at variable speeds cannot be recommended for constant dew point. Other heat-of-compression designs use twin-tower technology and offer no air loss, with relatively constant dew point. Heat-of-compression dryers are not available with oil-injected compressors, as too much of the heat is carried away by the synthetic oil. The chart above shows the trade-offs in initial cost, operating cost anddew points.

Focussing on filters

Coalescing filters are required after the discharge of oil-injected compressors. Standard particulate filters should be used after the dryer, to catch any desiccant fines.

Activated carbon can be used to remove odours created by oil-injected compressors. Sterile filters can be placed in the main supply or at point of use. Sterile filters are at point of use, as many air systems use the same generation system for both process air and instrument air. Once the stream is split for process, a check valve may be introduced with sterile filters downstream.

* The author is Category Manager, Configured Products (compressed

* air), Ingersoll Rand Company.

(ID:25805550)