How Does An Internal Heater Dryer Work?
A typical internal heater dryer includes two towers filled with desiccant, either activated alumina or molecular sieve media. One tower dries air while the other tower is regenerated. As the air flows through the initial tower, the desiccant, which has an affinity for moisture in its pores, adsorbs moisture and dry air flows out of that tower. When the initial tower is saturated, the towers switch roles.
Usually, 3% of the dried air is depressurized to near atmospheric pressure, heated to 350oF/177oC and directed to the right tower for desiccant regeneration. Wet purge air from the regenerating tower is discharged to atmosphere through a silencer or muffler.
Each tower has an internal heater element for a more efficient heating of desiccant. A typical dryer has an 8 hour cycle time: 4 hours of drying, 2.5 hours of heating, 1 hour and 25 minutes of desiccant cooling and 5 minutes of re-pressurizing to line pressure, per tower. The re-pressurization prevents the shocking of the desiccant causing erosion of the media. After 4 hours, the air flow switches from the one tower to the other tower and the process is repeated.
The Pioneer design includes instrumentation for monitoring temperature of purge air exiting the regenerating tower. An exit air temperature of over 250oF/121oC signals completion of the heating mode and switches the heater ‘off’ to save energy.
To minimize purge air loss, Pioneer offers the dew point demand cycle
control. 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.