Industrial Air Compressor Treatment Basics

Air Treatment Basics

In previous installments of this blog, we have discussed not only industrial air compressor basics and their application, but also sizing and upkeep in industrial settings. While this subject is of great importance, and will be continually covered in future articles, consideration should also be given to other components of the air system that affect the usefulness of compressed air as an industrial energy source.

All industrial air compressors have the same basic principle of operation – they draw in ambient air and increase pressure by reducing the empty space between molecules. By doing this, the compressor not only increases air pressure, but also increases the concentration of any other substances that are present. Foreign materials that are drawn in with the ambient air (like water vapor, dust, fumes or aerosols) are concentrated at higher levels when the air is compressed and often can be detrimental to pneumatic processes and machinery.

For this reason, many industrial compressed air systems are equipped with dedicated equipment to clean and dry the compressed air stream. This equipment ensures that compressed air quality is suitable for its end use. Compressed air dryers, filters and condensate management systems all perform this function, and are often as important to an air system as the compressor itself. Equipment of this type is commonly referred to as “Air Treatment.”

Types of Contamination

There are three primary types of compressed air contaminants as described by the International Standards Organization in their specification ISO 8573.1. These contaminant types are: water (or water vapor), solid particulate and oil. In this article, we will discuss the presence of water in compressed air systems, and the equipment that is commonly used to remove it.

Water

Water is a contaminant that is always present in compressed air systems. The concentration of ambient humidity during the compression process, combined with a sharp rise in temperature due to the heat of compression, causes all industrial compressors to discharge air at 100% saturation. The water vapor in compressed air will begin condensing into liquid as it travels through the pipe and cools. Because liquid water can corrode metal components and damage expensive industrial equipment, it is often removed from compressed air immediately after it leaves the compressor to protect the rest of the air system from its harmful effects.

Liquid water can be removed by moisture separators that utilize centrifugal motion to separate water droplets from the air stream. This liquid is then expelled from the system using a drain valve. However, water vapor cannot be removed by a moisture separator. Water vapor is often considered a contaminant in compressed air, because it has the potential to condense into liquid in the future. In order to effectively remove water vapor, a dedicated compressed air dryer must be utilized. Several
dryer technologies are used throughout the industry for this purpose – each with its own advantages and limitations. The most common types are Refrigerated Dryers and Regenerative Dryers.

Refrigerated Dryers

Refrigerated Dryers are commonly used in industrial and commercial settings, and often provide an affordable and effective solution for removing water from a compressed air system. They operate as their name suggests – by using a refrigeration circuit to decrease the temperature of the compressed air. When air temperature is decreased, its capacity to hold water vapor is also decreased. Thus, when air passes through a refrigerated dryer, a significant portion of its laden water vapor is condensed into liquid. This liquid water is then collected in a moisture separator, and expelled through a drain valve.

These dryers are commonly used because they provide an adequate solution for many industrial facilities at relatively low cost. However, there are some limitations to the application of refrigerated dryers. For example, refrigerated dryers cool the air in order to remove moisture. Therefore, their lowest pressure dewpoint is limited by the temperature at which water will freeze. Accordingly, refrigerated dryers are generally rated to produce pressure dewpoints around +38°F to avoid freezing. Similarly, the performance of refrigerated dryers can be greatly affected by ambient conditions. High ambient heat and poor ventilation exert a heavier workload on refrigeration systems, and cause the performance of refrigerated dryers to decline. These limitations must be accounted for when refrigerated dryers are sized and selected for a given application.

Regenerative Dryers

Regenerative Dryers pass compressed air through a media bed to remove water vapor. These units employ the properties of certain chemicals that have a high affinity to attract water molecules. Common chemicals used in regenerative dryer media beds are activated alumina, molecular sieve and silica gel. Regenerative dryers are capable of drying air much more thoroughly than refrigerated dryers, and can produce pressure dewpoints as low as -100°F.

These units are often used in applications where compressed air quality is of the utmost importance. Chemical manufacturing, oil & gas refining, medical applications and power plant systems often include regenerative air dryers. Additionally, regenerative air dryers are commonly used in outdoor applications where extremely high or low temperatures are possible, as they are less sensitive to ambient conditions than refrigerated dryers.

While regenerative dryers produce lower pressure dewpoints than refrigerated dryers, and are generally more robust, they come with a unique set of considerations. First, regenerative dryers are more expensive to own and operate than refrigerated dryers. They not only carry a higher initial purchase price, but also reduce the overall capacity and efficiency of the systems in which they are installed.

Normally, regenerative dryers are configured with two media beds. At any given time, one bed is drying, while the other bed is regenerating (or purging the moisture that has been picked up during the drying process.) During regeneration, the dryer actually consumes compressed air. For this reason, regenerative dryers must be selected carefully, as to not under supply a given application. Additionally, regenerative dryers decrease overall system efficiency by using compressed air for purging.

In Conclusion

Various technologies can be utilized to reduce the amount of air that these dryers use for regeneration (such as external heaters or blowers). However, each added feature will increase the initial purchase price of the dryer, so end users often employ these technologies only when the long-term efficiency gains outweigh the increase in initial cost.

In future articles, we will explore how additional air treatment equipment is used to combat the other forms of compressed air system contamination (particulate and oil). Additionally, we will cover the basics of air treatment sizing and selection.

An Industrial Air Compressor Maintenance Checklist: 5 Areas Your Technician Should Check

Industrial Air Compressor

In most industrial facilities, an industrial air compressor is an important utility.  It is used for power, process and control throughout all aspects of operation, and is essential for keeping production up and running.  However, unlike other utilities, compressed air is usually generated onsite with user-owned equipment.

While most companies do not produce their own electricity, heat or water, they often own and operate an on-site compressed air system.  Because this utility is vital to a facility’s operation, a thorough preventative maintenance program should be implemented to minimize unexpected downtime resulting from compressor failure.

Every industrial air compressor is configured with a few common components that must be checked and serviced regularly.  A working knowledge of the following five items will enable industrial compressed air users to better understand and maintain their equipment.

Filters

Filters are necessary components in all the mechanical systems of an industrial air compressor.  They are installed in the air circuit, lubricant circuit and control circuit to protect against contamination.   Each filter serves a unique and important purpose, and must be cleaned or replaced based on the manufacturer’s recommended intervals and environmental conditions.

Additionally, there are several filters that require regular attention when it comes to lubricated rotary screw compressors.

Air Inlet Filter:

Removes contaminants from inlet air before it enters the compressor.

Lubricant Filter:

Cleans the industrial air compressor’s lubricant – protecting precision metal parts from damage caused by solid contaminants in the oil circuit.

Air/Oil Separator:

Because lubricated rotary screw compressors operate with a flooded compression chamber, an air/oil mixture is discharged from the compressor airend.  Before usable compressed air can be discharged from the compressor package, the air and lubricant must be separated.  The air/oil separator serves this purpose, and is equipped with a replaceable coalescing filter element that should be changed regularly.

Control Line Filters: 

Many industrial air compressors are equipped with pneumatic lines for controlling and sensing various functions during unit operation.  Proper maintenance of control line filters helps to ensure the air compressor is responding appropriately to changes in system demand.

Coolers

Effective removal and dissipation of heat is an ongoing battle in every industrial air compressor.  The heat of compression must continually be expelled to prevent unsafe operating conditions and machine failure.  In light of this fact, compressor coolers must be regularly inspected and cleaned during routine maintenance.

Air-cooled rotary screw compressors are often equipped with a heat exchanger for the lubricant, and a separate exchanger (aftercooler) for the discharge air stream.  Over time, these coolers will become clogged with dust and other contaminants from the ambient environment.

Water-cooled compressors are usually configured similarly.  However, they use water as a cooling media instead of air.  Cleaning and maintaining water-cooled heat exchangers can be trickier than their air-cooled counterparts, as these units are more subject to corrosion, clogging and leaks.

Additionally, many centrifugal and multi-stage industrial air compressors include inter-stage coolers to reduce temperature between stages of compression.  These coolers must also be checked regularly to identify potential problem areas.

Lubricant

Air compressor lubricants serve a multitude of functions.  In oil-flooded compressors, lubricants are used to remove the heat of compression, seal clearances in the compression chamber, and lubricate bearings.  In compressor motors and gearboxes, separate lubricants are used to reduce friction between components for increased equipment longevity.

Regardless of their purpose, all industrial air compressor lubricants must be selected and maintained properly.  This is one of the most critical maintenance areas for operators of industrial compressed air systems.  Users that neglect to monitor and maintain the condition of their compressor lubricant can cause irreparable damage to their compressed air systems.

Regular oil sampling and analysis can turn a good compressor PM program into a great one.  By analyzing the chemical properties of a compressor’s lubricant, we can spot potential problems before they occur.  At Sullair of Houston, our standard oil sample report highlights many aspects of lubricant condition – like particle count, water content and total acid number.  This allows us to make informed and insightful recommendations to our customers about how to better maintain their equipment.  ~ George Saez, Service Manager Sullair of Houston

Controls

Controls are an often misunderstood and overlooked system in industrial air compressors.  However, their impact on the reliability, longevity and efficiency of industrial air systems cannot be understated.

In general, the controls of an industrial air compressor enable it to respond appropriately to changes in system demand.  For example, when system pressure drops, an air compressor should respond by increasing output to offset demand.  When pressure rises, an air compressor should respond by decreasing output to prevent over-pressuring the system.

There are many compressor control types available today – each with a unique set of characteristics and benefits.  However, regardless of type, all compressor control systems consist of several mechanical and electrical components that must be incorporated into the unit PM program.  Potential maintenance items include valves, solenoids, regulators, switches, transmitters, tubing, etc.   If one of these items requires service, the air compressor can operate unpredictably.

Call a trusted compressor service provider for help troubleshooting and repairing control problems.

Drains

Most industrial air compressor systems are equipped with several condensate drains.  Often, there are drains installed on compressors, filters, dryers and receiver tanks.  When functioning properly, these drain valves expel liquid water to protect downstream equipment from potential corrosion or damage.  However, if not regularly checked and maintained, a compressed air condensate drain can fail – having a detrimental impact on system performance and reliability.

A drain valve that is stuck in the open position can be a nuisance.  It creates an air leak that reduces system efficiency, or even causes overall pressure to sag.

A drain valve that is stuck in the closed position can often be more problematic – sending liquid slugs of water downstream to overwhelm dryers, filters and pneumatic equipment in the plant.

Many pneumatic control valves used in chemical process and refining applications cost thousands of dollars.  Even a small slug of water can ruin them, and replacement costs are very high.  Protecting these components from liquid water is critical – and a simple, inexpensive maintenance program for compressor condensate drains can help to prevent major failures down the road.  ~ Steve Mahaffey, Sullair of Houston