Intelligent Compressed Air: Refrigerant Dryers

When we talk with customers about their EXAIR Products, we also discuss the quality of their compressed air. Many of our products have no moving parts and are considered maintenance-free when supplied with clean, moisture free compressed air. One of the most critical aspects of a compressed air distribution system is the dryer.

No matter where you are in the world, the atmospheric air will contain water vapor. Even in the driest place in the world, McMurdo Dry Valley in Antarctica, there is some moisture in the air. As this air cools to the saturation point, also known as dew point, the vapor will condense into liquid water. The amount of this moisture will vary depending on both the ambient temperature and the relative humidity. According to the Compressed Air Challenge, a general rule of thumb is that the amount of moisture air can hold at a saturated condition will double for every increase of 20°F. In regions or periods of warmer temperatures, this poses an even greater problem. Some problems that can be associated with moisture-laden compressed air include:

  • Increased wear of moving parts due to removal of lubrication
  • Formation of rust in piping and equipment
  • Can affect the color, adherence, and finish of paint that is applied using compressed air
  • Jeopardizes processes that are dependent upon pneumatic controls. A malfunction due to rust, scale, or clogged orifices can damage product or cause costly shutdowns
  • In colder temperatures, the moisture can freeze in the control lines

In order to remove moisture from the air after compression, a dryer must be installed at the outlet of the compressor. It is recommended to dry the compressed air to a dew point at least 18°F below the lowest ambient temperature to which the distribution system or end use is exposed. A dew point of 35-38°F is often sufficient and can be achieved by a refrigerated dryer (Best Practices for Compressed Air Systems). This makes the refrigerant dryer the most commonly used type in the industry.

A refrigerant dryer works by cooling the warm air that comes out of the compressor to 35-40°F. As the temperature decreases, moisture condenses and is removed from the compressed air supply. It’s then reheated to around ambient air temperatures (this helps to prevent condensation on the outside of distribution piping) and sent out to the distribution system.

With your air clean and dry at the point of use, you’re making sure you get the most out of EXAIR’s Intelligent Compressed Air Products without adhering to pesky maintenance procedures.

Tyler Daniel
Application Engineer
E-mail: TylerDaniel@EXAIR.com
Twitter: @EXAIR_TD

Compressor image courtesy of Tampere Hacklab via Flickr Creative Commons License

Intelligent Compressed Air: What is an Air Compressor?

One thing that is found in virtually every industrial environment is an air compressor. Some uses for the compressed air generated are: powering pneumatic tools, packaging, automation equipment, conveyors, controls systems, and various others. Pneumatic tools are favored because they tend to be smaller and more lightweight than electric tools, offer infinitely variable speed and torque, and can be safer than the hazards associated with electrical devices. In order to power these devices, compressed air must be generated.

There are two main categories of air compressors: positive-displacement and dynamic. In a positive-displacement type, a given quantity of air is trapped in a compression chamber. The volume of which it occupies is mechanically reduced (squished), causing a corresponding rise in pressure. In a dynamic compressor, velocity energy is imparted to continuously flowing air by a means of impellers rotating at a very high speed. The velocity energy is then converted into pressure energy.

Of the positive-displacement variety they are broken down further into two more categories: reciprocating and rotary. A reciprocating compressor works like a bicycle pump. A piston reduces the volume occupied by the air or gas, compressing it into a higher pressure. There are two types of reciprocating compressors, single or double-acting. Single-acting compressors are the most common and are available up to 30HP at 200 psig. Their small size and weight allow them to be installed near the point of use and avoid lengthy piping runs. These are the types of compressors that would be commonly found in your garage. The double-acting reciprocating compressor is much like its single-acting brethren, only it uses both sides of the piston and cylinder for air compression. This doubles the capacity of the compressor for a given cylinder size. They are much more efficient than single-acting compressors, but are more expensive and do require a more specialized installation and maintenance.

Rotary compressors are available in lubricant-injected or lubricant-free varieties. These types of compressors use two inter-meshing rotors that have an inlet port at one end and a discharge port at the other. Air flows through the inlet port and is trapped between the lobes and the stator. As the rotation continues, the point intermeshing begins to move along the length of the rotors. This reduces the space that is occupied by the air, resulting in an increase in pressure. In the lubricant-injected compressors, the compression chamber is lubricated between the intermeshing rotors and bearings. This takes away the heat of compression and also acts as a seal. In the lubricant-free varieties, the intermeshing rotors have very tight tolerances and are not allowed to touch. Since there is no fluid to remove the heat of compression, they typically have two stages of compression with an intercooler between and an after cooler after the second stage. Lubricant-free compressors are beneficial as they supply clean, oil-free compressed air. They are, however, more expensive and less efficient to operate than the lubricant-injected variety.

On the other side of the coin, we have the dynamic compressors. These are comprised of two main categories: axial and centrifugal. These types of compressors raise the pressure of air or gas by imparting velocity energy and converting it to pressure energy. In a centrifugal air compressor, air continuously flows and is accelerated by an impeller. This impeller can rotate at speeds that exceed 50,000 rpm. Centrifugal air compressors are generally much larger and can accommodate flow ranges of 500-100,000 CFM. They also provide lubricant-free air.

Axial compressors are used for situations that require lower pressure but high flow rates. They do not change the direction of the gas, it enters and exits the compressor in an axial direction. It is accelerated and then diffused which creates the increase in pressure. A common application that would be served by this type of compressor is to compress the air intake of gas turbines. They have a relatively high peak efficiency, however their large overall size and weight as well as the high starting power requirements pose some disadvantages.

Of course, any of these types of compressors can be used to supply air to your engineered Intelligent Compressed Air Products. If you have an application in your facility that could benefit from an engineered solution, give us a call. An Application Engineer would be happy to discuss your options with you and see to it that you’re getting the most out of your compressed air!

Tyler Daniel
Application Engineer
E-mail: TylerDaniel@exair.com
Twitter: @EXAIR_TD

Image courtesy of Compressor1 via Creative Commons License

Top Factors for Air Compressor & System Maintenance

Performing regular maintenance on your compressor system helps to keep everything operating in peak condition and ensures you’re not wasting unnecessary energy. Just as you perform regular routine maintenance on your vehicles, a compressed air system also needs a little TLC to keep things running smoothly. Neglected maintenance items can lead to increased energy costs, high operating temperatures, and coolant carryover. Much of these issues can be eliminated simply by performing routine maintenance on the components of the system.

According to the Best Practices for Compressed Air Systems by the Compressed Air Challenge (1), components within the system that need maintained include: the compressor, heat exchanger surfaces, lubricant, lubricant filter, air inlet filter, motors, belts, and air/oil separators.  

The compressor and all surfaces of the heat exchanger need to be kept clean and free of contaminants. When these components are dirty, compressor efficiency is greatly reduced. Any fans and water pumps should also be regularly inspected to ensure that they’re functioning properly. The air inlet filter and piping should also be cleaned. The quality of the air in the facility will impact the frequency, refer to the manufacturer’s specifications for ideal intervals for performing scheduled maintenance.

The lubricant and lubricant filter must also be changed per manufacturer’s specifications. Old coolant can become corrosive, impacting useful life and damaging other components while reducing efficiency. While synthetic lubricants are available that have an extended life compared to standard coolants, this does not extend the life of the lubricant filter itself.

Belts should be routinely checked for tension (every 400 hours is reasonable) to alleviate bearing wear. Belts will stretch and wear under normal operation and must be adjusted periodically. It’s a good practice to keep some spares on hand in the event of a failure.

End use filters, regulators, and lubricators should also be periodically inspected and filter elements replaced as needed. If left unchecked, a clogged filter will increase pressure drop. This can cause both a reduction of pressure at the point of use or an increase in the pressure supplied by the compressor, leading to increased energy costs.

Another often overlooked maintenance item is leak detection and repair. Leaks contribute to unnecessary air usage, pressure drop, and increased energy costs. EXAIR offers an Ultrasonic Leak Detector that can be used to identify the leaks in your system and allow you to make the necessary repairs.

EXAIR Ultrasonic Leak Detector

In order to keep your system running in peak condition, regular maintenance is critical. By paying close attention to the manufacture’s recommendations, and implementing a regular maintenance schedule, you can ensure you’re getting the most out of your system components.

Tyler Daniel
Application Engineer
E-mail: TylerDaniel@EXAIR.com
Twitter: @EXAIR_TD

(1) Scales, W. (2021). Best Practices for Compressed Air Systems : Second Edition (2nd ed.). The Compressed Air Challenge,.

Compressor system image courtesy of Compressor1 via Flickr Creative Commons License

Determining Leakage Rate and Cost of Compressed Air Leaks

The electricity costs associated with the generation of compressed air make it the most expensive utility within an industrial environment. In a   poorly maintained compressor system, up to 30% of the total operational costs can be attributed simply to compressed air leaks. While this wasted energy is much like throwing money into the air, it can also cause your compressed air system to lose pressure. This can reduce the ability of the end use products to function properly, negatively impacting production rates and overall quality. Luckily, it’s quite easy to estimate the leakage rate and is something that you should be including in your regular PM schedule.

According to the Compressed Air Challenge, a well-maintained system should have a leakage rate of less than 5-10% of the average system demand. To estimate what your leakage rate is across the facility, first start by shutting off all of the point of use compressed air products so that there’s no demand on the system. Then, start the compressor and record the average time it takes for the compressor to cycle on/off. The compressor will load and unload as the air leaks cause a pressure drop from air escaping. The percentage of total leakage can be calculated using the following formula:

Leakage % = [(T x 100) / (T + t)]

Where:

T = loaded time (seconds)

T = unloaded time (seconds)

The leakage rate will be given in a percentage of total compressor capacity lost. This value should be less than 10% for a well-maintained system. It is not uncommon within a poorly maintained system to experience losses as high as 20-40% of the total capacity and power.

A leak that is equivalent to the size of a 1/16” diameter hole will consume roughly 3.8 SCFM at a line pressure of 80 PSIG. If you don’t know your company’s air cost, a reasonable average is $0.25 per 1,000 SCF. Let’s calculate what the cost would be for a plant operating 24hrs a day, 7 days a week.

3.8 SCFM x 60 minutes x $0.25/1,000 SCFM =

$0.06/hour

$0.06 x 24 hours =

$1.44/ day

$1.44 x 7 days x 52 weeks =

$524.16 per year

A small leak of just 3.8 SCFM would end up costing $524.16. This is just ONE small leak! Odds are there’s several throughout the facility, quickly escalating your operating costs. If you can hear a leak, it’s a pretty severe one. Most leaks aren’t detectable by the human ear and require a special instrument to convert the ultrasonic sound created into something that we can pick up. For that, EXAIR has our Model 9061 Ultrasonic Leak Detector.

ULD_Pr
Model 9061 ULD w/ parabola attachment checking for compressed air leaks

Implementing a regular procedure to determine your leakage rate in the facility as well as a compressed air audit to locate, tag, and fix any known leaks should be a priority. The savings that you can experience can be quite dramatic, especially if it’s not something that has ever been done before!

Tyler Daniel
Application Engineer
E-mail: TylerDaniel@exair.com
Twitter: @EXAIR_TD