Compressed air is used throughout industrial manufacturing, often for applications that cannot be replaced by electricity. The drive to reduce energy consumption and costs creates a dilemma for manufacturing facilities with regard to compressed air treatment. Manufacturers often identify the compressed air system as a place to realize savings. However, when it comes to purification equipment, such as compressed air dryers, choosing a model based on the lowest energy consumption can directly impact air quality.
Most of today’s manufacturers use an air quality specification, typically based around the ISO 8573-1 air purity classifications, as a benchmark for the selection of their compressed air treatment equipment. While this should be the primary criteria used for product selection, energy reduction is often given higher priority. These two factors can offset each other, resulting in air purity below the desired classification.
Here, we will discuss several alternative air dryer technologies and their impact on the balance between energy consumption and air quality to help users identify the technology that best suits their facility.
There are several types of adsorption — or desiccant — dryers available. These are preferred for applications with particular sensitivity to moisture, like instrumentation and where external temperatures may have an impact. While the principle used to dry the compressed air is identical, the way they regenerate the desiccant material is different.
Low-energy adsorption dryers
The simplest way to regenerate the desiccant material also uses the most energy. Dry process air (purge air) is used to regenerate the off-line desiccant bed. This type of dryer, referred to as heatless, is most common. However, for higher compressed air flows, there are more energy-efficient alternatives available. Types of heatless dryers include:
- Blower dryers
- Heat of compression (HOC) dryers
- Vacuum regeneration dryers
While blower dryers do not use any purge air for regeneration, they do use dry process air to remove heat from the desiccant material. The amount of cooling air is typically expressed as 1~2% of the dryer’s flow. However, this is an average over the drying cycle, and during the cooling period, air consumption can be as high as 10~20%, significantly increasing overall energy consumption.
To reduce energy consumption, some blower dryers use ambient air for cooling. This practice can add up to 77°F (25°C) to the ambient air temperature, leading to inefficient cooling and directly impacting the delivered air quality (outlet dewpoint).
Heat of compression (HOC) dryers
HOC Dryers, often installed with oil-free compressors, use the heat generated from air compression to regenerate the adsorbent material. This process does not include a cooldown of the adsorbent material, the lack of which has a negative impact on the air quality (outlet dewpoint) delivered by the dryer. During periods of low air demand, insufficient heat can be available for full regeneration, further impacting outlet dewpoint.
As the dewpoint delivered by this type of dryer can fluctuate greatly, they are typically classified as dewpoint suppression dryers and will not provide an outlet air purity consistently in accordance with the ISO8573-1 classifications.
Vacuum regeneration dryers
The operation of a vacuum regeneration dryer is similar to a blower dryer. Instead of using a blower to “push” heated ambient air over the off-line desiccant bed, they use a vacuum pump to “pull” heated ambient air over the material. The desiccant material can regenerate more efficiently under vacuum, saving more energy. No process air is required for cooling (the desiccant is not impacted by heat generated by the vacuum pump,) providing significant energy savings without a negative impact on the outlet air quality (dewpoint).
An optimal solution
A successful example of vacuum regeneration technology is the WVM Series Generation 5 Vacuum Regeneration Dryers. The WVM Generation 5 is a low energy consumption adsorption dryer that does not require any process air for either the regeneration of the desiccant material or for cool down purpose after regeneration.
WVM Generation 5 dryers deliver outlet dewpoints in accordance with ISO 8573-1 Classes 1, 2 or 3 (-70, -40 or -20 respectively). They are equipped with a dew-point controlled energy management system, which ensures energy consumption is matched to the incoming water vapor loading — helping to prevent negative impact on the outlet dew-point.
Each model has a 7 inch, IP65 touchscreen HMI linked to an advanced PLC control system. IIOT (MQTT or OPC UA) connectivity, Modbus RTU via 2 wire RS485 & Modbus TCP/IP via Ethernet RJ45 are standard features, with Profinet/Profibus protocols and cloud connectivity available as options.
Additional energy savings can also be realized by replacing the electric heater, fitted as standard to WVM Generation 5 dryers, with an alternative heat source. If the manufacturing facility has steam on-site, the electric heater can be replaced with a steam heat exchanger, or a dual steam and electric configuration, which offers optimum conservation of energy and the peace of mind offered by a redundant system.
This article was contributed by Mark White, compressed air treatment applications manager, Parker Gas Separation and Filtration Division EMEA