How does a heatless dryer work?

A typical heatless dryer includes two towers filled with desiccant, activated alumina, or molecular sieve. One tower, the initial tower, dries the air while the other tower, is re-generated. As the air flows through the initial tower, the desiccant absorbs moisture, its pores capture and hold moisture, and the dried air flows out of that tower. When the initial tower is saturated, the towers switch roles.

A portion of the dry air, called the purge air, is depressurized to near atmospheric pressure. It then flows through the saturated tower and re-generates its desiccant. The wet purge air is then discharged to atmosphere through a silencer or muffler.

A typical dryer has a 10 minute cycle time – 5 minute/tower drying, 4 minutes/tower of re-generation and 30 seconds of re-pressurization to line inlet pressure. The re-pressurization prevents the shocking and erosion of the desiccant. After 5 minutes, the inlet air flow switches automatically from the left tower to the right tower.

To minimize purge air loss, Pioneer offers dew point demand cycle controls. This reduces purge air use in proportion to air usage. For example, a Pioneer Model PHL1000, capacity of 1000 scfm, has a purge air use of 15% or 150 scfm. If the average air usage is 500 scfm, the dew point demand cycle reduces the purge air use to 75 scfm or by 50%.

A typical drying system includes, at the minimum, a coalescing pre-filter and a particulate after-filter. The pre-filter prevents condensed fluids – oil and moisture – from entering the desiccant tower and prematurely damaging the desiccant. The after-filter prevents desiccant fines from flowing downstream into clean and dry piping systems.

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