Understanding Different Types of Air Compressor Dryers

Last updated on: June 3rd, 2020 at: 02:30 pm

In the world of manufacturing, three utilities are essential to most processes: water, electricity and natural gas. That said, there is one utility considered nearly as important as these: compressed air. 

Many consider compressed air to be the fourth utility in manufacturing, due to the number of businesses and industries that rely on it for daily operations. The four primary types of air compressor dryers are:

  1. Refrigerated dryers
  2. Desiccant dryers
  3. Chemical dryers 
  4. Membrane air dryers

The main difference between each dryer type is the agent placed inside the machine to dry the incoming air.

What Is a Compressor Air Dryer?

Moisture can enter your air and air compressing machine in several different ways. You might be using an undersized — and, by extension, an overworked — air compressor or your air compressor could have malfunctioning parts, which is causing it to absorb more moisture from the air around you. The operating environment in which a compressor is used also makes a difference. For example, high-humidity atmospheres are capable of holding a lot more moisture than non-humid atmospheres. When the air reaches a temperature conducive to moisture saturation and condensation, it is known as the “dew point.” 

Although some level of moisture will always be present, too much of it can cause rust, corrosion and contaminate the quality of your compressed air. Poor quality compressed air can damage your final product or end-use. To reduce the amount of moisture in your compressed air — and to prolong the life of your machine — a compressed air dryer is critical.

A compressed air dryer is a machine designed to reduce the amount of moisture in compressed air significantly. In addition to creating a safer, more sanitary workplace for employees, air dryers promote high-quality products and minimize compressed air contamination. In some cases, such as particularly humid work environments, an air dryer can mean the difference between stalling operations or moving forward with production. 

Before you learn how to choose a compressed air dryer, you need to know the following information about your air compressor and your business:

  • The specific uses of your compressed air
  • Your desired pressure dew point
  • The required temperature of the air
  • How often the compressed air will be used
  • What kind of environment the air compressor is operated in

Please keep in mind that your business may require multiple different types of air compressors, and, as a result, multiple types of air compressor dryers. 

Compressed Air Dryer Types

Though it’s often assumed that dehumidifiers and air compressors are mostly needed for large operations, smaller businesses can also benefit from the sanitation and power such machinery provides. Even if you run an operation that consists of fewer than 10 employees, a compressed air drying system could help boost your production volume. If you need a guide for choosing an air dryer or want to see which methods are most effective for you, there are four dryer types to consider:

1. Refrigerated Dryers

Out of all the compressed air dryers, the refrigerated dryer is the most popular and widespread type. True to its name, the refrigerated air dryer functions in a similar manner to home refrigerators in that a cooling process is employed that prevents moisture. The main difference is the objects or elements being cooled. While a kitchen refrigerator cools and preserves perishable foods and beverages, a refrigerated air dryer maintains the quality of air in manufacturing plants.

In a refrigerated dryer, compressed air is cooled to around 35 degrees Fahrenheit. After the air has passed through the inlet valve, the moisture is extracted and drained, and the newly dried air is reheated by incoming air. At the end of each cycle, the outgoing compressed air has a dew point in the range of 35 to 40 degrees Fahrenheit. Overall, the process of the refrigerated dryer creates a more sanitary working environment that is also far more conducive for manufacturing.

Advantages and Disadvantages of Refrigerant Dryers

Refrigerant dryers are widely used because they offer several benefits, such as:

  • Refrigerant dryers are generally very inexpensive to set up, compared to other air drying systems.
  • Operation and ongoing maintenance costs are lower with refrigerated systems.
  • Refrigerated systems are resistant to airborne oil particles.

Although refrigerant dryers are an excellent choice for many industries and businesses, there are a few considerations to keep in mind, including:

Non-Cycling Refrigerant Dryers

In a non-cycling refrigerated dryer, the refrigerant perpetually circulates within the machine. This allows for quick responses to changes in the load, be it low or high densities of moisture within the incoming air. As such, factory environments with steamy engines can be de-moisturized in much the same way as low-moisture environments. The flow of the refrigerant is regulated with a bypass or unloader valve. In most units, the refrigerant is condensed by a heat exchanger after the compression process has completed a cycle.

CFC refrigerants like R12 and R22 were used in vintage refrigerant air dryers, though times have changed regarding the acceptability of such gases due to concerns over their impact on the environment. Therefore, in newer refrigerant dryers, a different range of chlorine-free refrigerants are used, such as the eco-friendlier R134A and R410A. The change was brought about by the Montreal Protocol, an international, anti-ozone-depletion treaty that was implemented in 1989.

Two significant advantages of a non-cycling refrigerant dryer are the consistent dew point and its capability for continual operation. Because of this continual operation, however, non-cycling dryers do not conserve energy during periods of low airflow.

Cycling Refrigerant Dryers

Refrigerant dryers of the cycling variety use refrigerant to cool down a glycol or aluminum mass, which surrounds the air passage. The compressed air is then cooled by a thermostat-controlled heat sink. Unlike a non-cycling refrigerant dryer, a cycling system works to conserve energy during periods of low airflow. The dew point, however, is variable. Cycling refrigerant dryers are also a high overhead cost, partly due to their size and weight.

2. Desiccant Dryers

Some dryers use desiccant agents to dry compressed air, in a process known as adsorption. These are known as desiccant type dryers

Adsorption is a distinct process from absorption: 

  • Adsorption: In adsorption, moisture attaches itself to the desiccant without being dissolved.
  • Absorption: In absorption, moisture gets absorbed by a drying agent.

What Is a Desiccant Dryer?

In terms of dryers, the word “desiccant” refers to not just one dryer type, but to a select category of dryers that are alternately referred to as adsorption dryers and regenerative dryers. Desiccant dryers get their name from the hygroscopic drying agent contained within.

Basically, a desiccant dryer works as follows:

  1. Compressed air is sent through a vessel that contains a pair of towers, both of which are filled with a specific drying agent, such as silica gel or activated alumina.
  2. The drying agent sucks moisture from the compressed air through the process of adsorption. As this continues, the desiccant agent becomes saturated.
  3. The drying process switches from one tower to the other, and compressed air within the system blows the desiccant material dry.

Desiccant dryers can be either heatless, heated internally or heated externally. In regenerative desiccant dryers of the heatless variety, heaters aren’t present internally or externally. At 100 psig, such a dryer will usually have a dew point rating of minus 40 degrees Fahrenheit, though sometimes the dew point can drop as low as minus 100 degrees. In heat reactivated desiccant dryers, a heater might be part of the system, either internally or externally. With an internal heater, less purge air is needed for the regenerative process. In desiccant dryers that use external heaters, the heated purge air accounts for up to 10 percent of the dryer’s airflow. A coalescing filter is often needed to safeguard the desiccant agent from oil contamination.

Desiccant dryers are important in a vast range of industrial applications, where the drying process is needed to maintain the integrity of operations and also to maintain the quality of products. In short, desiccant dryers make it possible to maintain controlled humidity environments. In some of the most sensitive environments, refrigerant dehumidifiers are incapable of providing the right drying levels, and would actually have the effect of being too blunt or insufficient.

Desiccant dryers are often considered stronger than refrigerant-based dehumidifiers because the latter perform at a level that is somewhat determined by the temperature of the surrounding air on a given day. As such, refrigerant dehumidifiers work best in warmer temperatures, whereas desiccant dryers operate at their highest efficiency in cooler ambient environments.

Common Industry Applications for Desiccant Dryers

Desiccant dryers are commonly used in the following applications:

  • Material processing: Any given material has its own processing requirements, which need to be met without deviation for things to materialize as planned. Desiccant air dryers help make this possible.
  • Mold prevention: When left to evaporate into surfaces, moisture turns to mold, which reduces sanitation in any working environment. With a compressed-air drying system in place, factories are spared of mold.

The following industries, in particular, reap tremendous benefits from the utilization of desiccant drying systems:

  • Health care: In environments where patients are treated and medications are prescribed and administered, air sanitation is of utmost importance. To that end, desiccant dryers deliver.
  • Flood relief: Desiccant dryers are a common feature in flood-relief scenarios because once a flood has passed through an area, properties must be dried as quickly as possible to prevent floodwaters from evaporating and causing mold in wood and furnishings.
  • Food drying: Moisture can rot food before it leaves the factory if the ambient air is not dehumidified and stripped of water particulates by a desiccant dryer.
  • Fabric production: Airborne moisture can shrink and damage the surfaces of fabrics in pressing plants that lack sufficient means to control the quality of ambient air.
  • Ice rinks: To maintain a solid bed of ice, a rink must keep ambient warmth and moisture to a minimum at all times, which makes desiccant drying systems essential at such establishments.

Basically, any product that could perish, attract mold or easily become damaged should only be manufactured in environments where compressed air dryers are employed at all times.

Advantages and Disadvantages of Desiccant Dryers

The advantages of a regenerative desiccant dryer are as follows:

  • Regenerative desiccant dryers have low dew points.
  • These dryers operate at a reasonable operating cost.
  • Desiccant dryers are employable in remote and hazardous environments.

Some qualities of regenerative desiccant dryers to keep in mind are:

  • Initial set up costs for a desiccant system can be high.
  • The desiccant bed in these dryers must be replaced every three to five years.
  • Airborne oil particulates can degrade the desiccant agent without proper filtration.
  • Desiccant dryers often need purge air.

Desiccant Air Dryer vs. Refrigerated Air Dryers

Despite their mechanical differences, refrigerant and desiccant dryers have more similarities than differences because both serve the purpose of ridding nearby ambient air of moisture. Therefore, the debate between the two dryer types is not so much about which is better, but which is better suited to the needs of a given environment. In some cases, refrigerant and desiccant dryer systems work best in combination with each other, because one dryer’s strengths compensate for the other’s weaknesses, and vice versa.

In any case, the concerns most often raised by manufacturers include the following:

  • High-temperature environments: In high-temperature environments, refrigerated dryers are more economical than desiccant dehumidifiers. Refrigerated dryers are rarely used in lower temperatures because colder environments would necessitate a lowering of the coil temperature, which would ultimately cause the coil to freeze. There’s no real way around this since the solutions that do exist — defrost cycles, brine solutions, etc. — are difficult to implement.
  • Low-temperature environments: In low-temperature environments, where moisture levels are also bound to be lower, desiccant systems are the more affordable drying option. As such, desiccant dryers are optimized for and utilized within environments of 40 degrees and under. In most desiccant systems, the inlet will be mounted with a cooling coil or DX. This creates a double-cooling effect, whereby air is reduced of heat and airborne water particulates upon entering the dryer, and then further cooled and de-moisturized within the system.
  • Thermal energy costs: In environments where the cost of thermal energy is higher than that of electricity, desiccant dryers are the more cost-effective system. Contrastingly, refrigerated dryers are the more cost-effective option in places where electrical costs outweigh those of steam or gas. Therefore, energy costs could be a determining factor in whether to go for one system over the other. Ideally, however, this would only determine which type of dryer would be more optimal during most applications without ruling the other out completely.

The applications that are most likely to favor a predominantly desiccant method of drying over refrigerants are in the industries of food processing, medicine production, auto assembly and marine storage.

In the majority of applications where temperatures exceed the desiccant threshold by double-digit degrees, refrigerant dryers are the more effective and financially sensible option. However, even in hotter locations, the occasional use of a desiccant dryer can still help lower costs over the span of a year when utilized at the right times, such as in the colder weeks of winter. For example, the cooling costs of an HVAC-equipped building can be lowered by treating the air with a desiccant system, which can help reduce the energy consumption of fans and pumps and also reduce deep coils and pressure drops.

3. Chemical Air Dryers

Chemical dryers use a process of passing compressed air over a bed of deliquescent chemicals until these chemicals are saturated with the excess moisture from the air. The chemicals used in this process are those with a natural capacity for water attraction, such as sodium, calcium chloride and lithium. 

As these chemicals attract and collect the moisture, they are disposed of, along with the water they have collected. For this reason, having a high-quality filtration system in place is crucial for successful chemical dryer operation. Otherwise, you risk these chemicals building up over time and causing performance problems for your compressor and quality issues with your compressed air.

In summary, the advantages of a chemical dryer system are:

  • Operation of these dryers is relatively straightforward and requires little ongoing monitoring.
  • There are no moving parts to maintain.
  • Aside from the ongoing cost of chemical replacement, initial set-up is usually inexpensive.

The primary disadvantages of chemical dryers include:

  • Replacing chemicals can get costly, especially if you use your dryer frequently.
  • They depend on high-quality filtration systems to operate efficiently.
  • Disposal of the saturated chemicals can be complicated and expensive.

4. Membrane Air Dryers

Membrane dryers are often used for dehumidification and for applications that require gas separation, including food production. When compressed air enters a membrane air dryer, it moves across bundles of semi-permeable membrane fibers. These fibers allow certain materials, such as oxygen, to pass through the membrane, separating it from the desired gas. These dryers are typically sized for smaller projects and single points-of-use.

A few advantages of membrane air dryers include:

  • Membrane dryers require no electricity, making them ideal for remote operation.
  • Operation is quieter than with other dryers.
  • They are easy and affordable to maintain.

A few things to consider about these dryers are:

  • They require consistently clean air, free of oil and particulate.
  • They require a prefilter that needs to be changed often to avoid blockage.

Other Air Dryer Tips

Having an air dryer is a great step toward improving the quality and efficiency of your compressed air. To get the most out of your investment, follow these additional air dryer tips:

  • Improve the quality of your intake air: The less polluted your intake air, the less your air compressor and air dryer will have to work to purify it. Contaminants can be liquid, solid or gas, and can enter the air through before it’s processed by the machine, or inside the machine itself. Two steps you can take to minimize this contamination is promoting a clean workspace and introducing a filtration system to your compressed air cycle. If your industry requires heavily regulated air, you might also consider a lubrication-free compression system if possible. 
  • Use a compressed air storage system: Use a compressed air storage tank to store dried, filtered air once it has been compressed. This will help prevent additional moisture from re-entering the air, saving you time, energy and valuable resources.
  • Schedule preventive maintenance for your air compressor: An efficient air drying system means little if your compressed air machine is not working correctly. To avoid production setbacks, schedule regular preventive maintenance checkups for your compressor and air dryer systems. You should also create and implement a monitoring system that allows you to stay up-to-date on the status of your equipment and the quality of the air being produced. Taking preventive measures like these can alert you to possible concerns and have them adjusted before they turn into costly, more time-consuming repairs later. 

Find Refrigerated and Desiccant Air Dryers at Quincy Compressor

Nearly a century ago, Quincy Compressor began offering air compressors and pneumatic tools to manufacturers and craftsmen across a range of trades and industries. Since then, we have been at the forefront of technological innovation with air compressors, vacuum pumps and air-drying systems. With each passing decade, entities within the public and private sectors have immensely benefited from the machines offered in the Quincy catalog. 

From food processing to vehicle production, Quincy-brand machinery has played a vital role in turning raw products and materials into consumable goods and usable vehicles, furnishings and appliances. Throughout the world, Quincy’s reputation as a maker and supplier of air compressors, dehumidifiers, vacuum pumps and pneumatic tools is second to none. 

If you need a refrigerated air dryer for your business, Quincy offers the following industry-leading options:

  • The QPNC non-cycling dryer: The QPNC uses a two-stage heat exchanging configuration for consistent, high-quality performance with energy-saving benefits. This dryer is ideal for small applications that require constant air drying and can provide up to 230 psig pressures at volumes between 10 and 3,000 CFM. 
  • The QED cycling dryer: Our QED cycling dryers use a three-stage heat exchange configuration that allows the system to shut on and off as needed, conserving resources. These dryers also feature automatic adjustment depending on the operating environment, making them one of our most energy-efficient drying options.
  • The compact QRHT high-temperature dryer: At Quincy, we know that small spaces do not always mean small operations. The QRHT makes zero compromises in performance. It uses an air-cooled aftercooler, moisture separator, zero-loss drain and a coalescing filter, all packed into one space-saving machine. The QRHT can provide up to 232 psig and operate at volumes between 25 and 125 CFM.

We also offer a range of desiccant air dryers, including:

  • The QHD heatless dryer: The QHD series is an affordable solution for business owners looking for high-performance with minimal maintenance costs. They operate at 100 psig and deliver between 230 and 3,400 CFM of dry air.
  • The QHP heated dryer: QHP dryers require less than half the air that other models need and are designed to be compatible with the Quincy MicroBurst Regeneration (MBR) system, which allows you to minimize purge requirements and help you save more money over time. 
  • The QBP blow purge dryer: The QBP dryer combines heat with forced ambient air for truly efficient operation, and features some of our lowest operating and ongoing maintenance costs. It operates at 100 psig and produces between 210 and 3,400 CFM. 
  • The modular QMOD heatless dryer: Low on space? The QMOD heatless dryer is designed to be compact enough to fit into tight spots — both vertically and horizontally — without sacrificing optimal performance. The QMOD produces between eight and 365 CFM.

Visit Quincy Compressor online to learn more about the benefits and features of our desiccant and refrigerated air drying systems. If you have any questions or need help deciding which is right for your business, do not hesitate to contact our team of highly professional and knowledgable air experts.