A Guide to Desiccant Air Dryers: Achieving Ultra-Dry Compressed Air

In critical manufacturing and industrial processes, standard compressed air just won’t do. It’s full of water vapour, which can lead to corrosion of pipework, contamination of products and expensive equipment breakdown. Standard refrigerated dryers are an excellent solution for many applications. Still, where you need nothing but the best air, like in pharmaceuticals, food and beverage and electronics, you need the best drying solution.

That solution is the desiccant air dryer. This specialised system is the key to producing ultra-dry compressed air, achieving exceptionally low pressure dew points (PDP) that are impossible with other technologies. At Compressive, we understand that for many businesses across Yorkshire and the East Midlands, moisture-free air is a necessity with no margin for error.

How Do Desiccant Dryers Work? The Power of Adsorption

The desiccant (also referred to as adsorption) dryer is a device that dries compressed air by passing it through a bed of hygroscopic material (commonly known as the “desiccant”). The most widely used desiccants in the air-drying process are activated alumina or silica gel. The material is composed of a porous surface that can adsorb water molecules.

Do not confuse the term adsorption with absorption. Absorption is when a substance is taken up by the volume of another (like a sponge absorbing water). At the same time, adsorption is a surface phenomenon in which molecules stick to the exterior of the adsorbent material. Adsorption is a highly effective and easily reversible process, making it ideal for continuous drying cycles.

The Twin-Tower Regeneration Cycle

To supply non-stop dry air, most industrial applications of desiccant dryers utilise a twin-tower configuration, which works like this:

1. Drying Phase (Tower 1): Wet compressed air from your compressor enters the first tower. As it flows through the desiccant bed, the water vapour is adsorbed, and ultra-dry air is discharged downstream to your facility.
2. Regeneration Phase (Tower 2): At the same time, the second tower, which is full of water from a previous cycle, enters regeneration, also known as “refresh”, or “purge”, whereby the water is removed from the desiccant so it can be used to dry air again.
3. Switchover: Once the first tower is full of water, an automated controller switches the airflow to the second, freshly regenerated tower, repeating the cycle to prevent dry air outages.

The type of regeneration system used, either a portion of the dry air itself (heatless) or compressed air heated by a blower (blower-purge), determines the type of dryer and the energy usage it will require.

Why Pressure Dew Point (PDP) is Critical

An air dryer’s performance is defined by its Pressure Dew Point (PDP). The PDP of compressed air is the temperature at which it will condense back into a liquid at a specific pressure. The smaller the dew point value, the drier the compressed air. It’s an essential specification for businesses with pipework exposed to the elements. In this guide to using air compressors in Humid UK Environments, an incorrect dew point may result in frozen and ruptured pipes during the winter months.

Dryer types are only specified when the application requires a PDP below 0°C. PDP is also the key specification in the international standard for compressed air purity classes (ISO 8573-1:2010). For critical compressed air applications, a particular class is a compliance requirement that cannot be compromised.

• Class 2 (-40°C PDP): Preventing microbial growth in food and beverage production and ensuring a high-quality finish for spray painting and abrasive blasting applications.
• Class 1 (-70°C PDP): Used in highly sensitive processes, particularly in electronics and pharmaceutical manufacturing processes, where even the tiniest quantity of moisture will cause defects or contamination.

To help you get up to speed on moisture removal options quickly, let’s explore what air compressor dryers are. Provides an introduction and then ranks the different types against each other.

A Guide to Desiccant Air Dryers

Common Problems Solved by Desiccant Drying

Protect your business from costly and persistent problems in your facility by selecting the right air treatment system today.

• Eliminates Moisture Damage: Ultra-dry air protects pipework and pneumatic tools from rust and corrosion, increasing the life of your assets and maximising system performance.
• Prevents Product Spoilage: Bacteria love moisture. If you work with food, beverage or pharmaceuticals, you’ll need a desiccant dryer with a -40°C PDP to protect your products and guarantee compliance.
• Avoids Winter Freezing: For systems with external air lines in Yorkshire and the East Midlands, desiccant drying is essential to prevent freezing and ensure production continuity.

The Modern Solution: Atlas Copco Cerades™

One problem with conventional desiccant beads is that they wear over time, forming a fine dust that contaminates downstream equipment and hinders performance. Atlas Copco, the global compressed air specialist, has put an end to that with its new Cerades™ structured desiccant. This solid ceramic material doesn’t break down, eliminating dusting, ensuring a consistent PDP, and extending service intervals.

Choosing the Right Desiccant Dryer with Compressive

As a Premier Distributor for Atlas Copco for over two decades, Compressive provides a market-leading range of desiccant dryers engineered for maximum efficiency and reliability. While general manufacturing can often rely on Refrigerant Air Dryers (which achieve a +3°C PDP), critical applications demand the superior performance of desiccant technology.

Our range of Advanced Air Drying and Filtration solutions includes:

• Heatless Desiccant Dryers (CD⁺): This is a proven design with an uncomplicated, very reliable unit that uses a small quantity of compressed air for regeneration.
• Blower-Purge Dryers (BD⁺): This is a highly efficient design that uses heated ambient air from a blower, which cuts energy consumption significantly.
• Heat-of-Compression Dryers (XD⁺): This is the most efficient of the highly efficient designs. It uses waste heat from the compressor for regeneration, with zero energy loss.
• Rotary Drum Dryers (MDG, MD, ND): Zero-purge units that provide the highest level of reliability, eliminating switching valves. The design is ideal for use with oil-free compressor installations.

Desiccant dryers are widely used in the pharmaceutical industry and other high-purity applications where the quality of the delivered air must meet the most stringent regulatory requirements.

Maintenance and Local Support

Choosing the right dryer is essential, but so is ongoing maintenance. The Compressive team can provide expert support to keep your dryer working efficiently and reliably. Operating from our depots in Leeds, Sheffield and Nottingham, we offer customised service plans to keep your equipment at the top of its game. We also offer preventative maintenance packages, including regular desiccant checks, filter inspection and performance monitoring, to avoid expensive downtime.

Frequently Asked Questions

What PDP do I need for my application?

For general industrial applications where the pipe-work is subject to freezing conditions, a PDP to -40°C (Class 2) is a safe minimum. Most critical applications (pharmaceutical, electronic, food production, etc.) require a -70°C (Class 1) to meet the high quality standards required in these industries.

What is the difference between a heatless and a heat-of-compression dryer?

A heatless dryer uses approximately 15-20% of the dried compressed air as purge air to remove moisture from the desiccant bed. A heat-of-compression dryer recycles the waste heat produced by your air compressor to regenerate the desiccant using practically no compressed air – resulting in substantial energy savings.

How often does the desiccant material need to be replaced?

In most cases, the desiccant media will last 2–3 years, depending on the hours of operation, air quality and ambient conditions. Atlas Copco’s Cerades™ structured desiccant is designed for a much longer service life.

Get Expert Advice for Your Compressed Air System

Selecting the correct desiccant dryer is a technical choice that will affect your product quality, operating cost and your profitability. Leave it to the experts.

With over 78 years of experience, the experts at Compressive (Search Air) are here to help. Call today to receive a free system audit. If you are located in Leeds, Sheffield, Nottingham or anywhere within Yorkshire and the East Midlands, we will steer you towards the right solution.