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.

Choosing the Right Industrial Air Compressor: Four Factors that Affect Compressor Sizing

For many Plant Managers and Engineers, selecting the right-sized industrial air compressor can be a challenging task.  Compressed air is an energy source that is rarely measured or tracked in existing industrial facilities, so reliable data on this subject is often unavailable.  Frequently, this information must be cobbled together from the stories and anecdotes of plant personnel.  While these observations are well-intentioned, they usually provide little benefit to an engineer that is sizing a new air compressor.

When designing and building a brand-new facility, selecting the right-sized industrial air compressor can be even more daunting.  Without an existing baseline from which to start, engineers must meticulously tally the air demand of every pneumatic component to be installed, apply a usage factor for the expected duty cycle, and hope the end result is an accurate representation of reality.

Both of these scenarios are fraught with uncertainty, and many engineers intentionally “pad” their estimates to avoid selecting a compressor that is too small.  This often leads to the installation of oversized and improperly selected air compressors.

It has been a huge problem in Texas where a business only needed 50hp, but someone says ‘ I’m just going to buy 100hp because it will be more than I need.’ But, that is a really bad idea because the machine will run at half-capacity all the time, so it is not the way it is designed to run and it is going to use more power than a 50 horsepower running at 100% capacity.

~ Brad Bonnecaze, Sullair of Houston

In spite of these uncertainties, there is good news for folks tasked with selecting and purchasing a new industrial air compressor.  By carefully considering the following questions, engineers can increase the likelihood they will choose the right-sized unit for their next project.

How will the compressed air be used?

As with any industrial system, the end-use application is the most important factor in determining air compressor sizing.  Each application is different, and carries a unique set of considerations.

Some applications require a steady, predictable supply of compressed air with little variation (e.g.- process air for chemical manufacturing).  In these scenarios, it is usually best to install a compressor with a full load capacity that closely matches actual air usage.  Little consideration for part load efficiency is needed, and extra capacity is not required.  The best strategy in this case is to achieve optimal performance at full load, and ensure the process is never under-supplied with compressed air.

By contrast, other applications require highly variant supplies of compressed air.  These processes need air compressors that can fully support the largest anticipated demand, but also operate efficiently in part load conditions.  For example, an industrial machine shop might have several machining centers that are used at different times.  Air usage will depend on which combination of machines is utilized for a particular job.  In these scenarios, compressors with efficient part-load operation are often beneficial.  In some cases, the installation of multiple compressors for staggered operation is a viable approach.

What are the expected ambient conditions?

Ambient conditions are always an important factor in industrial air compressor sizing and selection.  Not only do equipment sub-components need to be rated for operation in the expected conditions, but air compressor output capacity is also affected.  In high heat, ambient air is less dense because its molecules are farther apart from each other.  As such, an air compressor must work harder in order to deliver the same output as compared to colder temperatures.  Likewise, high humidity also reduces air compressor capacity.  Water molecules displace air molecules on humid days, so compressors must intake a greater volume of ambient air to produce the same output.

Consideration must be given to these factors when selecting a new compressor.  The full load capacity of an industrial air compressor can be reduced by 10% or more due to high heat and humidity.  Engineers must pay careful attention to ensure they size new compressors for the worst-case conditions expected at the site.

Are there any intermittent demands?

Applications that use compressed air are often divided into two primary categories.  Dynamic applications require a steady supply of compressed air at all times.   A common example of a dynamic application is a sandblast cabinet.  When the sandblast nozzle is engaged, an uninterrupted supply of compressed air is needed.  The only acceptable interruption of this flow occurs when the operator releases the nozzle trigger.

Conversely, intermittent applications require a fixed burst of compressed for a short time, with a break between cycles that allows the system to recover.  An example of an intermittent application is a pneumatic cylinder that actuates periodically.  A fixed volume of compressed air is required to push the piston through its stroke, but no other compressed air is needed until the next cycle.

When sizing a new air compressor, engineers should be aware of how each compressed air application fits into these categories.  Often, intermittent demands can be supplemented by installing air receiver tanks at the point-of-use.  This strategy can sometimes reduce the amount of required compressor horsepower.  Talk to a trusted and competent compressed air professional for more information on employing air receivers to supplement intermittent demands.

What is the compressed air quality requirement?

Some critical applications require the compressed air supply to be extremely dry and free of contaminants.  In these instances, regenerative dryers must be utilized to achieve ultra-low dew points in the compressed air stream.

While regenerative dryers are useful for this purpose, they reduce the overall volume of compressed air that is available for the application.  When sizing a new industrial air compressor, engineers must incorporate regenerative dryer purge losses into their demand estimates to ensure an adequate volume of air is supplied at the point-of-use.

When designing a compressed air system, start from the point-of-use and move backward from there.  First, determine the flow, pressure and air quality that is required at the application.  Many folks try to pick the air compressor first…but, the best strategy is to start at the end, then add up all of the variables (such as demand, dryer purge losses and leaks) before selecting an air compressor that can handle the job. 

~Steve Mahaffey, Sullair of Houston

Wrapping Up…

Though the general concepts of mechanically-compressed air have been around for hundreds of years, in the recent years, industrial air compressor technology has evolved rapidly in order to keep up with constantly changing demands and needs for compressed air.

Thus, searching for the right industrial air compressor system with the right size for your facility or your next job can be tricky. But now you’re equipped with the tools and knowledge necessary to make an educated decision on which compressor is a perfect fit your business.