Air Dryer Desiccant: Types & Desiccants

Description:

Air Dryer Desiccant
Source: https://www.pneumatictips.com
An ‘Air Dryer Desiccant’ is a device that compresses air that is drawn in and which contains some water vapor in it. The process of compressing air at around 100 psi increases the air’s temperature.

The presence of excessive water in these systems causes problems like corrosion and bacterial growth that in-turn leads to some kind of damage and breakage of components of the device.

In a normal system, airflow takes place from the compressor to the aftercooler that helps to lower the temperature. This helps improve condensation and removes water from the system.

Certain filters like coalescing filters are installed to remove any form of additional water. If you need even more further treatment, then air dryers are highly recommended. They remove almost 90% of air present in the components and other parts of the device.

Desiccant air dryers absorb moisture (water vapor) from the air around it using a reversible process on its desiccant material. They produce low dew points that help usage in freezing weather conditions or when the processes undergone by the devices are in extremely dry air with around 5% moisture content.

Desiccant dryers are divided into two major categories: Heatless Desiccant Dryers and Heated Desiccant Dryers

Heatless Desiccant Dryers

These devices have a desiccant material in two large tanks that are placed adjacent to each other and are called the ‘Drying Tower’ and ‘Regenerating Tower’ respectively. Air containing water vapor flows into the drying tower where it gets compressed and it passes over it and gets attached to the desiccant material which is generally porous in appearance.

The extremely dry air of extremely low temperatures ranging between -40° F to – 100° F.As the air with moisture is absorbed by the desiccant material, a large amount of heat is released which leads to the increase in the air temperature up to 20° F.
 

 
To remove water further from the air, about 15% of dry air from the first tower is transported to the regenerating tower. In the regenerating tower, the compressed air is dry and expands according to the atmospheric pressure as it passes through the desiccant and pulls water out of it.

Moist air is then discharged completely from the system. The dryer tries to cycle between the ‘drying’ and ‘regenerating’ towers simultaneously. In either way, one of the towers tries to dry the air alternatively.

Heated Desiccant Dryers

As the name says it all, the ‘Heated Desiccant Dryers’ have an in-built heater present along the internal circuit. Same as the ‘heatless’ one, this too has two towers where one of the towers removes moisture from the inflowing air.

The pressure range points vary from very cold temperatures ranging from -40° F to – 100° F. The spent desiccant is regenerated using the second tower also called ‘Regenerating Tower’. The air passing over the drying tower passes over the heater and then passes over a desiccant in the present in the regenerating tower. The dry air is finally exerted out using a muffler.

These types of air dryer desiccants require a lot of electricity and therefore, to make the bills minimal, it is necessary to identify the specifics of the application and needs of the project to save costs wisely. Heat-of-compression of a dryer is a type of desiccant dryer.
 

 
These are special-versions of dryers that use oil-free air compressions and their heat produced as they are highly energy-efficient. In these dryers, high-pressure air that is released from the compressor is sent to the second (regeneration) tower and the moisture from the desiccant is released to the maximum extent.

Now the released air is made to flow via an aftercooler, that reduces the temperature to around 100° F.This cool air flows through the drying tower to leave the entire system at -40° F. When these HOC dryers are combined with oil-free compressors, they help generate high-quality compressed air that is exclusively free of any form of water and oil content.

HOC dryers are way more expensive than normal refrigerant or conventional desiccant dryers. The operational costs of them are low, however.

Desiccant Material

The desiccant generally is a microporous mineral that and the moisture is taken in from the air by the process of adsorption, which is not a chemical phenomenon. These substances are rigid, porous, and have sponge-like granules that provide a large active internal surface in attracting and maintaining fluid molecules of random substances.
 

 
This adsorption phenomenon was studied by many scientists including Stephen Brunauer and Paul Emmett. The physical attraction between its molecules was a result of van der Waal forces and electrostatic forces.

Later on, certain researchers like Johann Dietrich van der Waal and Linus Carl Pauling said that it included polar attractions, London forces, and gravitational dispersion forces altogether. They also devised the B.E.T method for measuring the internal surface area accurately for these adsorbent molecules.