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.

Pick The Perfect Industrial Air Compressor

Industrial air compressors have improved in many ways in the last several decades.  Over the years, compressor OEMs have integrated a multitude of features to increase efficiency, improve serviceability and enhance user interface with compressed air equipment.

However, in spite of these improvements, the primary technologies utilized for air compression have remained mostly the same since the late 1960s.  A few key types of industrial air compressor technologies dominate the marketplace, and each have characteristics that make them ideal for certain applications and environments.

Before purchasing a new industrial air compressor, end users should become familiar with these technologies and their respective benefits.  By educating themselves before making a final purchase decision, they can be sure to select a compressor capable of reliably and efficiently meeting their needs for years to come.

 

Industrial air compressors can be divided into two primary types based on their theory of operation:

Positive Displacement compressors trap air molecules in a confined space (known as a compression chamber), then mechanically reduce the volume of the space.  When volume is decreased, pressure is increased.  Many types of industrial air compressors employ the principle of positive displacement.

Dynamic compressors increase air pressure in a different way.  These machines use high speed impellers to accelerate air molecules to rapid velocity.  The direction of the fast-moving air stream is then quickly changed in a device called a diffuser.  This rapid change in direction causes the air molecules to bunch together – increasing pressure in the industrial air compressor.

Positive Displacement Compression

Reciprocating Compressors

Reciprocating compressors have been a staple of small commercial and industrial air compressor systems for decades.  This old and familiar technology uses pistons and cylinders to create a compression chamber for positive displacement.  The steady thumping sound of reciprocating compressors can be heard in small manufacturing and automotive repair shops around the world.

Despite their familiar technology and relatively low cost, reciprocating compressors are naturally limited in a few important areas.  For example, reciprocating compressors are not widely available in sizes above 30hp (100cfm).  Therefore, applications requiring larger capacities often require rotary screw or centrifugal compressor technology.  Moreover, the cylinders and pistons in reciprocating compressors are subject to heavy wear – causing decreased capacity and increased oil carryover over time.  The noisy operation of reciprocating compressor is also a limiting factor, as end users must install them away from offices or other spaces where high noise is disruptive.

In spite of these limitations, reciprocating compressors can be a good fit for many light or intermittent compressed air applications.  Talk to your local compressed air expert to determine if a reciprocating compressor makes sense for your facility.

 

Rotary Screw Compressors

Rotary screw compressors have been widely used in commercial and industrial applications since the 1960s.  They are robust and durable machines that can be deployed in a variety of applications and environments.   Because of their versatility, rotary screw compressors are some of the most common in the market today.

Rotary screw compressors are positive displacement machines.  Their compression chamber contains two rotors (or “screws”) that each have several lobes.  When the two rotors are turned, their lobes interlock to create air pockets.  The volume of these air pockets is progressively decreased as they travel through the compression chamber – causing pressure to increase.

Rotary screw compressors are known for smooth, reliable operation in almost any application or environment.  They are available in a wide range of capacities (5-600hp+) and deliver a steady supply of compressed air that is free from pulsation.  Additionally, rotary screw compressors are designed for high duty cycles at full load capacity.  They can operate at their maximum discharge capacity for long periods of time without risk of excess wear or damage.

Rotary screw compressors can be equipped with several control options to enhance efficiency at part load.  Additionally, they are available in oil-flooded or oil-free configurations.

The incredible versatility of rotary screw compressors makes them an easy choice for many industrial compressed air applications.  If you think a rotary screw compressor might be a good fit for your next project, call your trusted compressed air specialist for a professional recommendation.

Scroll Compressors

Scroll compressors are a relative newcomer to the commercial compressor landscape.  However, their quiet operation and oil-free compression technology has made them increasingly popular for laboratories and medical applications.

Scroll technology has been widely used in refrigeration systems for years.  These positive displacement machines contain two interlocking scrolls.  The orbiting scroll rotates around the fixed scroll in a circular motion.  In this way, progressively shrinking pockets of air are carried through the compression chamber – increasing pressure along the way.  The air is then discharged at final pressure into the system of the industrial air compressor.

Scroll compressors are limited in size, so larger machines usually contain several scroll pumps combined into a single unit.  However, despite their comparatively small capacities, scroll compressors emit very low operating noise.  The average scroll compressor is as quiet as a common household refrigerator.  Because of this, these machines are a great solution for labs and office spaces where noisy industrial machines are not practical.

Additionally, scroll compressors contain no lubricant in their compression chamber.  This oil-free design makes them a safe choice for medical and lab projects where compressed air quality is critical.

 

Dynamic Compressors

Centrifugal Compressors

Centrifugal compressors are capable of delivering extremely large volumes of oil-free compressed air.  This particular dynamic industrial air compressor uses one or more sets of impellers to impart velocity to incoming air molecules.  The high-velocity air stream is then passed through a diffuser, which quickly changes the direction of travel – causing the air molecules to bunch together, thus increasing pressure.

Centrifugal compressors are used primarily in applications where air demand is extremely high.  Major automotive plants, refineries, beverage bottle production and large-scale manufacturing facilities often use centrifugal compressors to supply their compressed air needs.

Because of their large drivers (up to 10,000hp+), high rotational speeds and dynamic compression technology, centrifugal compressors carry a different set of considerations than positive displacement machines.  Careful planning and engineering must be conducted when selecting a new centrifugal industrial air compressor. However, in applications where large and steady volumes of compressed air are required, centrifugal compressors are often the most efficient and practical long-term solution.

 

End users should consult their trusted compressed air expert for a detailed system analysis before purchasing a new air compressor.  Each technology offers unique characteristics that can benefit specific applications.  However, with a proper planning and a little knowledge, buyers can be sure they make the right choice.

5 Signs An Industrial Air Compressor Needs Maintenance or Service

Man repairing

It is important for compressed air users to be familiar with their industrial air compressor maintenance needs.  Knowledge of machine performance, operating characteristics and service requirements enables the user to recognize when a specific machine requires attention. An air compressor that is operating below its design capabilities can be inefficient, costly and even dangerous.  Fortunately, most potential or impending issues show early warning signs that are easy to spot by a knowledgeable compressed air user. Air compressor operators should be on the lookout for any of the following potential warning signs, and be ready to take immediate action to limit potential failures, downtime and repair costs:

  1. High Operating Temperature

All air compressors fight a constant battle against heat.  The physical act of compressing air molecules produces huge amounts of it (known as the “heat of compression”), and effective dissipation of this heat is critical for safe and reliable compressor operation.  A sudden or unexplained rise in compressor operating temperature is a strong indicator that a problem is imminent.  Regular cleaning of a compressor’s coolers should be incorporated into any maintenance program.  Additionally, the condition of a compressor’s lubricant can greatly affect the machine’s ability to operate at a safe temperature.  Closely monitoring lubricant condition through a formal oil sampling program is a good strategy for preventing compressor failure and downtime.

  1. Increased Noise

Many industrial air compressors – especially older models – emit high operating noise.  While improving technology has enabled many compressor OEMs to reduce the overall operating noise of newer models, end users of compressed air should be familiar with the typical operating noise of their compressors during normal conditions.  Any change in operating noise should be investigated immediately.  Bearing noise should always be addressed right away, and any unexplained clicks, rattles or rumbles can forewarn a larger problem on the horizon.  If a specific noise cannot be identified or corrected, call a professional service company for troubleshooting and repair.

A vibration analysis program is highly recommended from the start on all equipment as this sets the base line vibration, then you can trend from there. This service improves the early detection of irregular vibration due to misalignment, or failing bearings etc. Also, you can check vibration on the motor same as the air end, detects early vibration issues, misalignments, soft foot, etc. worth the investment. ~ George Saez, Service Manager Sullair of Houston

  1. Motor overload or tripped breakers

Most industrial air compressors are equipped with a safety shutdown that will stop the unit automatically in the event motor amperage exceeds the acceptable range.  If a compressor shuts down due to this fault, the root cause should be investigated immediately.  Sometimes the issue can be resolved quickly with a minor adjustment by an authorized professional.  However, a motor overload or tripped breaker can often be indicative of more serious problems – such as deficiencies in a facilities’ electrical system or increased mechanical friction in the air compressor.  Regardless of the potential cause, an electrical overload should always be taken seriously and addressed immediately for the sake of safety.

  1. Low Flow or Pressure

A properly designed compressed air system should supply sufficient air flow and pressure to support the needs of the application.  If a compressed air system suddenly or inexplicably is unable to maintain adequate pressure, the results can be catastrophic to a company’s bottom line.  Poor product quality, facility downtime, and reduced safety can all eat into a company’s profits.  For these reasons, users of compressed air should be constantly aware of system performance to minimize the impact of insufficient compressed air supply.

The potential causes of reduced pressure or flow are varied – and can manifest in both the compressor room or in a facility’s air piping.  Leaking pipes, open valves and stuck drains can all cause pressure to fall.  However, sometimes the control system of the air compressor can be the culprit.  If the cause of sudden pressure loss cannot be identified immediately, call a trusted compressed air technician for assistance.

You are always going to look at your gauges or your indicators and ask ‘Are your temperatures within range? Is amperage correct? What kind of differential pressure over the separator do I have?’ Then you are going to know something is wrong and you troubleshoot it from there. ~Brad Bonnecaze, VP/COO, Sullair of Houston

  1. Increased or Excess Moisture

All compressed air systems produce liquid condensation.  This natural byproduct of the compression process is simply a fact of life for users of compressed air.  However, the presence of liquid water in a facility’s compressed air supply can be detrimental to quality, productivity and reliability.  For this reason, most end users utilize air treatment equipment such as dryers, filters and mist eliminators to remove condensation from their air systems.  If the amount of condensation in a compressed air system suddenly increases, an air treatment issue is often to blame.

“When troubleshooting this problem, start at the source and move forward.  Is the compressor’s aftercooler clean and functioning properly?  Is the compressor’s moisture separator draining?  These components are often overlooked as potential root causes, while dryers and filters get most of the attention.  However, if a dryer is being fed hot air and liquid water at its inlet, it doesn’t stand a chance.”  – Steve Mahaffey, Sullair of Houston   

Bottom Line

Over the course of time, you can expect your air compressor to experience the normal wear and tear of an industrial setting. In order to keep your system functioning effectively, having the knowledge to identify issues and perform routine maintenance can go a long way in prolonging the life of your compressor. If you notice any of these warning signs or a combination of these symptoms, have a technician evaluate your compressor as soon as possible. Prompt inspection and repair can save you money in the long run, since it prevents more costly problems and ensures that a faulty air compressor won’t slow your business down.