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DOMNICK HUNTER DESICCANT AIR DRYERS
What is adsorption drying?
Drying compressed air through adsorption represents a purely physical process in which water vapor (adsorbate) is bound to the drying medium (adsorbent) through binding forces of molecular adhesion. Adsorbents are solids in spherical and granular form which are permeated by an array of pores. The water vapor is deposited onto the internal and external surface of the adsorption medium, without the formation of chemical compounds taking place, therefore the adsorption medium does not have to be replenished but only periodically regenerated.
Types of adsorption desiccant air dryers:
Heatless desiccant air dryers
The layout of desiccant air dryers with heatless regeneration is clear and simple. Compared with other desiccant air dryers, pressure dewpoints down to -100oF (-70oC) can be achieved without additional effort.
Use in the higher pressure ranges and at low inlet temperatures causes the quantity of air needed for desorption to be reduced to an economical value.
At low operating pressure the demand for already dried compressed air for purposes of regeneration is increased. This increase causes a large proportion of the prepared compressed air to be no longer available for productive purposes.
Depending on the cycle, the quantity of air enclosed in the adsorber expands upon release at regular intervals with an emission noise level of about 90 - 95 dB(A). Given suitable noise attenuation measures, a reduction of the noise emission level to the region of 10 - 15 dB(A) can be accomplished.
The use of desiccant air dryers with heatless regeneration is preferred in the following applications:
Externally heated desiccant air dryers
With their external and autonomous regeneration equipments, externally heated desiccant air dryers are independent of compressor operation. Widely differing regeneration energy sources as heat carriers result in flexible, economical utilization also in explosion proof areas. Pressure dewpoints down to -100oF (-70oC) can be achieved with continuous operation. Pressure release and expansion during switch-over occurs only once within the 4-hour half-cycle and can be programmed to occur in a delayed manner, thus achieving reduced noise emission levels. Without proper pre-filtration, the regeneration air can be polluted by solids and this may influence not only the adsorber but also its adsorbing material. Increasing differential pressure inside the adsorber impairs the flow of regeneration air, resulting in a proportionally longer heating time. High inlet temperature accompanied by low operating pressure to reduce the capacity of the drying medium considerably, at the same time increasing the heat of reaction up to the lower range of regeneration temperatures, so that reliable adsorption is no longer assured throughout the entire cycle.
Externally heated regeneration desiccant air dryers are used:
Blower purge desiccant air dryers
Desiccant air dryers with external heat regeneration and an ambient blower system require only small quantities of processed and treated compressed air for purging and for building up pressure. The quantity of air required for regeneration is blown in, or drawn in from the surrounding atmosphere by means of a blower. A desiccant air dryer with vacuum regeneration forms a logical and consistent further development. These is a growing tendency for using such system also in tower performance ranges thanks to the efficiencies that can be realized. Operating by blower regeneration offers a wide ranging freedom for adaptation to problematic marginal conditions. The regeneration system, consisting of a blower and a heater, is selected from a wide range of choices. Using different materials, customer specific requirements can be met.