Drying Supply Side Air With Heat of Compression Dryers

The supply side of a compressed air system has many critical parts that factor in to how well the system operates and how easily it can be maintained.   Dryers for the compressed air play a key role within the supply side are available in many form factors and fitments.  Today we will discuss heat of compression-type dryers.

Heat of compression-type dryer- Twin Tower Version

Heat of compression-type dryers are a regenerative desiccant dryer that take the heat from the act of compression to regenerate the desiccant.  By using this cycle they are grouped as a heat reactivated dryer rather than membrane technology, deliquescent type, or refrigerant type dryers.   They are also manufactured into two separate types.

The single vessel-type heat of compression-type dryer offers a no cycling action in order to provide continuous drying of throughput air.  The drying process is performed within a single pressure vessel with a rotating desiccant drum.  The vessel is divided into two air streams, one is a portion of air taken straight off the hot air exhaust from the air compressor which is used to provide the heat to dry the desiccant. The second air stream is the remainder of the air compressor output after it has been processed through the after-cooler. This same air stream passes through the drying section within the rotating desiccant drum where the air is then dried.  The hot air stream that was used for regeneration passes through a cooler just before it gets reintroduced to the main air stream all before entering the desiccant bed.  The air exits from the desiccant bed and is passed on to the next point in the supply side before distribution to the demand side of the system.

The  twin tower heat of compression-type dryer operates on the same theory and has a slightly different process.  This system divides the air process into two separate towers.  There is a saturated tower (vessel) that holds all of the desiccant.  This desiccant is regenerated by all of the hot air leaving the compressor discharge.  The total flow of compressed air then flows through an after-cooler before entering the second tower (vessel) which dries the air and then passes the air flow to the next stage within the supply side to then be distributed to the demand side of the system.

The heat of compression-type dryers do require a large amount of heat and escalated temperatures in order to successfully perform the regeneration of the desiccant.  Due to this they are mainly observed being used on systems which are based on a lubricant-free rotary screw compressor or a centrifugal compressor.

No matter the type of dryer your system has in place, EXAIR still recommends to place a redundant point of use filter on the demand side of the system.  This helps to reduce contamination from piping, collection during dryer down time, and acts as a fail safe to protect your process.  If you would like to discuss supply side or demand side factors of your compressed air system please contact us.

Brian Farno
Application Engineer
BrianFarno@EXAIR.com
@EXAIR_BF

Heat of compression image: Compressed Air Challenge: Drive down your energy costs with heat of compression recovery: https://www.plantservices.com/articles/2013/03-heat-of-compression-recovery/

About Dual Acting Reciprocating Compressors

When it comes to generating compressed air there are many types of compressors to utilize within a facility.  One of those types is a dual acting reciprocating compressor.  This is a type of positive displacement compressor that takes advantage of a piston style action and actually compresses air on both directions of the stroke.  Below you can see a video from a company that showcases how a dual acting compressor works and gives a good representation of how it is compressing the air on both directions of travel.

Dual_Recip
Click on this image for video

The reciprocating type of air compressor uses a motor that turns a crank which pushes a piston inside a cylinder; like the engine in your car.  In a basic cycle, an intake valve opens to allow the ambient air into the cylinder, the gas gets trapped, and once it is compressed by the piston, the exhaust valve opens to discharge the compressed volume into a tank.  This method of compression happens for both the single and double acting reciprocating compressors.

With a single acting compressor, the air is compressed only on the up-stroke of the piston inside the cylinder.  The double acting compressor compresses the air on both the up-stroke and the down-stroke of the piston, doubling the capacity of a given cylinder size.  This “double” compression cycle is what makes this type of air compressor very efficient.  A single acting compressor will have an operating efficiency between 100 cfm / 23 kW of air while the double acting compressor has an operating efficiency between 100 cfm 15.5 kW .  Therefore, electricity cost is less with a double-acting reciprocating air compressor to make the same amount of compressed air.

These compressors are ruggedly designed to be driven 100% of the time and to essentially be a Clydesdale of compressors.  They are commonly used with applications or systems requiring higher pressures and come in lubricated or non-lubricated models.

If you would like to discuss air compressors or how to efficiently utilize the air that your system is producing so that you aren’t giving your compressor an artificial load that isn’t needed, contact us.

Brian Farno
Application Engineer
BrianFarno@EXAIR.com
@EXAIR_BF