1. Desiccant Dryers
Kaeser has been manufacturing compressor/dryer packages for some time now and this has become a popular option for customers.
They save floor space and the dryer is properly sized for the compressor output capacity. This pretty much eliminates the possibility of the dryer being under sized and eliminates quite a few problems related to under sizing.
These type of dryers are know as a non-cycling dryers.
There are 2 modes of operation for the dryer, Continuous and Timer.
Continuous – In this mode the dryer runs continuously, even if the compressor is shut down (no system demand). This is the default mode set at the factory.
The advantage to this mode is a constant dew point. The disadvantage is of course, more power consumption.
Timer – In this mode the dryer is turned on when the compressor is running and turned off when the compressor is shut down. This is an energy saving feature.
The advantage to this mode is energy savings when the compressor is not running. The disadvantage to this mode is a brief increase in dew point when the compressor restarts.
It is ultimately up to the customer which mode they prefer.
Let’s look inside and see what makes these dryers tick.

2. Desiccant Fundamentals
Lets look at Kaeser’s line of cycling refrigerated dryers in detail now.
Since you know how the refrigeration cycle works now, we will just be focusing on specific components of each type of dryer that are different than we have seen already and go through the wiring diagram of each and point out anything that doesn’t look familiar.
Let’s start with the smallest line, the TX Series.

3. Desiccant Beads 1/8” Activated alumina Large surface area
High crush strength
Highly abrasive
All Kaeser desiccant dryers use 3mm (1/8”) spherical activated alumina desiccant beads.
Activated alumina is made of aluminum oxide which is basically the same chemical compound that makes up sapphires and rubies but does not contain the impurities that give those gems their color.
- Looking at the magnified section of the desiccant bead, you can see that there are numerous chasms and peaks on each bead instead of having a smooth surface.
These chasms and peaks add an incredible amount of surface area to each bead which is why they are so good for our application. The more surface area, the more moisture they hold.
To give you a rough idea of how much surface area, imagine a 1 square inch cube filled with desiccant beads. This small amount of desiccant has the same area as a football field.
- These beads also have a high crush strength. It takes 30 psi to crush a bead. One bead on the floor by itself doesn’t pose much of a threat. However, just 10 beads together means the crush strength just multiplied to 300 psi.
Be extremely careful when changing desiccant, if there is a bunch on the floor, don’t step on it because you will more than likely go for a ride.
- Desiccant is also very abrasive and creates large amounts of dust when replacing old desiccant or doing an initial fill. We recommend wearing a dust mask and having plenty of drinking water on hand when doing this job.

4. Adsorption Process Stage 1:
Water vapor moves from areas of higher concentration to areas of lower concentration
The compressed air stream is saturated with water vapor when it leaves the air compressor and passes through the piping system.
As you can see in the picture, the air stream is the high concentration area, the desiccant bead is the lower concentration area.

5. Adsorption Process Stage 2:
Water vapor molecules come in contact with the surface of the bead and are adsorbed
As the air stream moves across the desiccant bead and comes in contact with the peaks and chasms that create the large surface area, the water molecules adsorb onto the surface.
In other words, the molecules cling to the rough areas of the bead. The air molecules continue on and are dry after depositing their water vapor onto the bead.

6. Adsorption Process Stage 3:
Water vapor builds up on surfaces, eventually becoming dense enough to change states into a liquid
As more air flows across the bead, water vapor continues to build on the surface of the bead. Eventually, the vapor becomes dense enough to change from a vapor to liquid water.
Think of it like raindrops on your windshield. When it first starts raining, the drops are small. When they hit your windshield they stay in one spot for a while. As more and more of these small drops gather, they gain mass and form to make larger drops.

7. Adsorption Process Stage 4:
Heat is released as water is adsorbed (1250 BTU’s per pound of water)
As more and more water is adsorbed, heat is released. This heat is used to regenerate the desiccant (dry the desiccant in the offline tower).
1250 BTU’s are produced per pound of water adsorbed.
A British Thermal Unit (BTU) is the amount of heat energy needed to raise the temperature of one pound of water by one degree F.
This is the standard measurement used to state the amount of output of any heat generating device.
You might be able to imagine it this way. Take one gallon (8 pounds) of water and put it on your stove. If the water it 60 degrees F. and you want to bring it to a boil (212 degrees F.) then you will need about 1,200 BTUs to do this.

8. Adsorption Process Stage 5:
The desiccant adsorbs water until the concentration of water vapor equals that of the compressed air stream
As more and more water is adsorbed, heat is released. This heat is used to regenerate the desiccant (dry the desiccant in the offline tower).
1250 BTU’s are produced per pound of water adsorbed.
A British Thermal Unit (BTU) is the amount of heat energy needed to raise the temperature of one pound of water by one degree F.
This is the standard measurement used to state the amount of output of any heat generating device.
You might be able to imagine it this way. Take one gallon (8 pounds) of water and put it on your stove. If the water it 60 degrees F. and you want to bring it to a boil (212 degrees F.) then you will need about 1,200 BTUs to do this.

9. Operating Principles
Compressed air passes through a vessel filled with desiccant
Water vapor is captured on the surface of the desiccant by the process called adsorption
Dry air exits the dryer
There are 2 towers (tanks) filled with desiccant on the dryer. One tower is used for drying the compressed air while the other is regenerating. A controller switches towers based on criteria entered so each has time to dry air and regenerate the desiccant when not drying. As the dryer operates, it switches towers based on the cycle time.
All Kaeser dryers are up-flow design meaning the air flows in from the bottom of the tank and exits at the top. This increases air contact time with the desiccant beads. Also we can use gravity to help as water is heavier than air and tends to drain downward.
Water vapor is adsorbed on the surface of the desiccant beads.
As the beads adsorb the moisture from the air stream, the air continues to flow upward through the remaining beads and the dry air exits the dryer and out into the customer’s plant.

10. Heatless Desiccant Dryers
The first dryer we are going to look at in this section is the KAD Heatless or Pressure Swing Desiccant Dryer.
This and the other 2 types of desiccant dryer presentations will be very short and will briefly cover dryer operation, components and their location.
Once we get through the presentation, we will spend a fair amount of time going through the KAD Series instruction manual dated 11/05.
Each of you has a copy of this manual in your Student Guide that is yours to keep. This will come in handy when you have to go to a customer who has one of these types of dryers and they have no clue where the manual that came with the dryer is located.
As we go through the manual, I will be pointing out what I have found to be the most important and most useful items when installing and servicing the dryers. It will be very beneficial to you to hi-lite the items in the manual I specifically point out.
Once we finish this, we will go to the warehouse and put this information to use in some hands-on activities designed to get you familiar with dryer set up and operation.
Let’s get started.

11. Left Tower Drying
Compressed air enters inlet through shuttle valve (3)
Air dries in tower (4A)
Dry air flows through shuttle valve (5) to outlet
Small portion of air branches from main air stream for purge
Adjustable purge valve (6) and purge orifices (7) control purge rate
Dryer operation always begins with the left tower drying and the right tower regenerating.
Compressed air flows through inlet shuttle valve (3) to tower (4A) where the air is dried.
After the air is dried, it flows through the outlet shuttle valve (5) and then to the dryer outlet.
A portion of the dry air (15% for this style dryer), the purge stream, branches off from the main air stream prior to the outlet.
The purge flow rate is controlled by the adjustable purge rate valve (6) and the two purge orifices (7)
That is the whole left tower drying process.
Tower 4A Drying
Tower 4B Regenerating

12. Right Tower Regenerating
Purge flow directed to tower (4B)
Purge flow passes through desiccant to remove water vapor from desiccant beads
Purge air passes through purge and re-pressurization valve (9B)
Purge air exits through purge muffler (10B) to atmosphere
Purge and re-pressurization valve (9B) closes, tower (4B) re-pressurizes
The purge flow, which has been throttled to near atmospheric pressure, is directed to tower (4B).
As the purge flow passes over the desiccant in tower (4B), it removes the water vapor which was deposited there while the tower was online drying.
This is where the 1250 BTU’s per pound of water comes into play. This heat is used along with the purge air flow to dry (regenerate) the desiccant.
The purge air then passes through purge and re-pressurization valve (9B) (Normally Closed) and purge muffler (10B) to atmosphere.
After regeneration, purge and re-pressurization valve (9B) (Normally Closed) closes, allowing tower (4B) to re-pressurize slowly.
Tower 4A Drying
Tower 4B Regenerating

13. Tower Switchover Tower (4B) fully re-pressurizes
Re-pressurization valve (9A) opens
Inlet and outlet shuttle valves switch positions
Tower (4B) now dries air and tower (4A) begins regeneration
Sequence is repeated at end of cycle time
Adequate re-pressurization time is allowed so that tower (4B) is fully re-pressurized before tower switchover.
After a controlled time period, purge and re-pressurization valve (9A) (Normally Closed) open.
This causes the inlet shuttle valve (3) and outlet shuttle valve (5) to shift, directing the air flow through tower (4B).
Tower (4B) is now drying the air and tower (4A) is in the regeneration phase.
This continues until the cycle time has elapsed at which time tower switchover occurs again and the process is repeated.
Tower 4A Drying
Tower 4B Regenerating

14. Shuttle Valve
The inlet and outlet shuttle valves replace the old style inlet switching valves.
These valves only have one moving part which is the shuttle assembly. These valves have been tested to over 1 million cycles in heavy desiccant dust conditions with almost no failure.
There is no maintenance requirement on these valves.

15. RIGHT CHAMBER PRESSURE
Pressure Gauges and Moisture Indicator
LEFT CHAMBER PRESSURE
RIGHT CHAMBER PRESSURE
INLET PRESSURE
OUTLET PRESSURE
The gauges are labeled to tell you exactly what each is for.
The upper right hand gauge is the Right Tower pressure gauge. It indicates the pressure inside the right tower.
The outlet pressure gauge displays the pressure at the air outlet of the dryer.
The upper left hand gauge on the panel is the Left Tower pressure gauge. It indicates the pressure in the left tower.
The lower left hand gauge is the Inlet Pressure Gauge. It displays the inlet air pressure to the dryer.
The thing in the middle of the gauge panel is the Color Change Moisture Indicator. The crystals inside are yellow if moisture is present. As moisture is removed from the air, the crystals turn green indicating the air is dry.

16. Controller(s) HHE HHL (Level 1) HHS (Level 2)
There are 3 KAD models to choose from:
-"KAD E" models are equipped with a basic fixed cycle timer perfectly suited for consistent air usage at or near the dryer’s capacity.
The KAD E dryer has no monitoring or diagnostic capability, has power-on LED, tower drying LED's and is the least expensive of the heatless dryers.
- KAD models feature the Level 1 controller.
This controller includes LED's for user programmable routine filter and dryer maintenance intervals, a switching failure alarm, a common alarm LED, tower drying and tower regenerating LED's, an RS-232 communications port, remote start/stop contacts and four (4) user selectable cycle times for outlet dew points of -40°F, -4°F,
+38°F or -100°F. An On/Off switch with Power On LED is also provided.
A diagnostic mode allows the user to step through the operational sequence to confirm proper operation of components.
The Level 1 controller also has limited purge saving capability via the Purge Economizer Switches. These switches allow the open-time of the purge valve to be reduced when a known and continuing, reduced load condition exists. Purge valve open time can be reduced in increments of 10% of the full load open-time down to 30% of the full load open-time.
- KAD PS models feature the Level 2 controller.
This controller includes all of the same features as the Level 1 controller, except for the Purge Economizer Switches, as the Level 2 controller provides fully automatic purge savings.
The Level 2 controller automatically adjusts purge consumption to match the load on the dryer. The system employs thermistors, for their ruggedness and repeatability, that monitor desiccant bed temperatures.
Temperature differentials, over time at each measurement point, determine the duration of the drying cycle and the need for regeneration. Since the temperature differentials analyzed are those of each individual thermistor, and not comparing the measurement of one thermistor to another, the system never requires calibration.
HHS (Level 2)

17. Other Components Purge adjustment valve Desiccant fill ports
Desiccant drain ports
Lifting lugs
ASME pressure relief valve
Purge exhaust mufflers
Purge and re-pressurization valves
-The purge pressure adjustment valve is used to adjust the purge flow rate of the dryer.
The flow rate is set according to:
Maximum Operating Pressure (MOP) of the dryer
Air Pressure at inlet to the dryer
ISO Class cycle setting (Class 1, 2, 3, or 4). Note: For units with the Level 2 Controller and the Automatic Purge Saving System in the demand cycle mode, use ISO Class 2 (10 minute) purge pressure settings only.
Energy (purge) Savings % setting. This setting is applicable to the Level 1 Controller only.
-The desiccant fill ports are located at the top of each tower and allow each to be replenished with desiccant.
-The desiccant drain ports allow desiccant to be drained from each tower. When removing the plugs from these ports, make sure you have a way to control the flow of desiccant or you will have a big mess on your hands as well as a safety issue. Remember the crush strength of each bead is 30 psi.
-The lifting lugs must be used to position the dryer when moving it. These lugs are specifically designed to hold the weight of the dryer. Do not attempt to use the piping or valves to move the dryer. These items were not designed to hold the weight of the dryer and will crush under the weight.
The ASME pressure relief valve is required under ASME code regulations because the dryer is in fact a pressure vessel. It must be capable of venting the full rated capacity of the pressure vessel. It must also be mounted in a vertical position.
The purge exhaust mufflers reduce noise when the dryer is purging.
The purge and re-pressurization valves are normally closed valves that open when the tower they are attached to is in the purge phase of the drying cycle. This allows the purge air to flow out of the dryer.
This was just a brief overview to get you acquainted with the dryer. Take out your KAD manuals now and we will get into a lot more detail. On the installation, set-up and operation of the dryer. After we finish with this, we will go out to the dryer and do some hands-on activities as promised.

18. HPD Heated Purge Desiccant Dryers
The next dryer we will be looking at is the KED Heated Purge Desiccant dryer.
As the name indicates, this dryer uses a heater to heat the desiccant bed. A Purge Booster option is available as well to reduce purge air requirements. More on this later on.
This will be a very short presentation that will briefly cover dryer operation, components and their location.
Once we get through the presentation, we will spend a fair amount of time going through the KED Series instruction manual dated 9/05.
Each of you has a copy of this manual in your Student Guide that is yours to keep. This will come in handy when you have to go to a customer who has one of these types of dryers and they have no clue where the manual that came with the dryer is located.
As we go through the manual, I will be pointing out what I have found to be the most important and most useful items when installing and servicing the dryers. It will be very beneficial to you to hi-lite the items in the manual I specifically point out.
Once we finish this, we will go to the warehouse and put this information to use in some hands-on activities designed to get you familiar with dryer set up and operation.
Let’s get started

19. Left Tower Drying Valve A opens and compressed air enters the dryer
Air flows up through tower 1 and exits through outlet E
At the start of the left tower drying cycle, Left Inlet Valve A opens, Right Inlet Valve B closes to isolate the two towers.
Wet compressed air enters the dryer at the bottom, enters Tower 1 through valve A and flows upward through the left tower and is dried.
The dry air exits through the Left Outlet Check Valve (Valve E) into the customer’s piping to perform the desired function.
Next the Purge Supply Valve (F) is closed and the Right Purge Exhaust Valve (C) is opened. The right tower is slowly depressurized through the exhaust muffler.
Tower 2 closes valve B, then de-pressurizes through valve C and the muffler

20. Left Tower Drying
Two and a half minutes later, valve C closes and valves D and G open and the heater turns on
A portion of the dried compressed air (purge air) is diverted through orifice F and passes through the heater to regenerate tower 2
Two and a half minutes later, valve C closes and Valves D and G open.
The heater turns on and operates.

21. Left Tower Drying
Three hours later, the heater turns off and dry purge air continues to cool the desiccant bed
Fifty-eight minutes later, valve D closes and tower 2 is re-pressurized
Three hours later, the heater turns off based on a signal from the temperature sensor.
Dry air continues to cool the desiccant bed.
Fifty eight minutes later, Valve D closes and tower 2 re-pressurizes.
Two minutes later, Valve B opens, Valve A closes and Tower 2 begins drying and Tower 1 begins to regenerate.
Two minutes later, valve B opens, valve A closes and the sequence is repeated as tower 1 is regenerated

22. Purge Booster Option
Supplements 7% purge air with 7% ambient air
Supplies larger amount of air to heater to regenerate desiccant bed more thoroughly than standard exhaust purge dryers
Recommended for 24-hour operations where -40ºF dew point is critical
Reduces dried compressed air purge requirement to 7%
Instructor Note: Follow description and operation of Purge Booster on this and the following 2 slides.

23. Purge Booster Operation
Compressed Air Inlet
Hankison’s purge booster makes use of air amplifier technology:
Nozzle
Compressed air is forced through a nozzle which converts pressure energy to velocity energy
High Speed Air Flow
High Speed Air Flow
Ambient Air Inlet
High speed air flows across an ambient air inlet which creates a pressure drop at the ambient air inlet
Outlet

24. Purge Booster Operation
Nozzle
Ambient air rushes in behind the high speed air
High Speed Air Flow
Ambient Air “Chaser”
The combined air streams increase the total air supplied to regenerate the desiccant bed
Outlet

25. Depressurization Valve
Component Location
Air Outlet
Air Inlet
Purge Exhaust Valve
Inlet Valve
Outlet Check Valve
Purge Check Valve
Purge Orifice
Heater
Depressurization Valve
Depressurization Muffler
These are the basic components of the KED dryer.
Open your KED instruction manuals now and we will begin a more thorough explanation of the dryer.

26. HBP Blower Purge Desiccant Dryers
The next dryer we will be looking at is the KBD Blower Purge Heated Desiccant dryer.
As the name indicates, this dryer uses a blower to supply the purge air to regenerate the desiccant.
This will be a very short presentation that will briefly cover dryer operation, components and their location.
Once we get through the presentation, we will spend a fair amount of time going through the KED Series instruction manual dated 9/05.
Each of you has a copy of this manual in your Student Guide that is yours to keep. This will come in handy when you have to go to a customer who has one of these types of dryers and they have no clue where the manual that came with the dryer is located.
As we go through the manual, I will be pointing out what I have found to be the most important and most useful items when installing and servicing the dryers. It will be very beneficial to you to hi-lite the items in the manual I specifically point out.
Once we finish this, we will go to the warehouse and put this information to use in some hands-on activities designed to get you familiar with dryer set up and operation.
Let’s get started.

27. KBD Operation
Moisture laden compressed air enters dryer through open valve A
Air flows up through tower 1 and exits through air outlet
Wet compressed air enters Tower 1 through valve A.
Air flows up through the tower and exits through the outlet.
Valve B closes and Tower 2 de-pressurizes through Valve C and the muffler.
Tower 2 closes valve B, then de-pressurizes through valve C and the muffler

28. KBD Operation
Two and a half minutes later, valve C closes, valves D and F open, and heater turns on
Ambient air is drawn in through the blower and supplied to heater
Two and a half minutes later, Valve C closes, Valve D and F open and the heater turns on.
Ambient air is drawn in through the blower and is supplied to the heater.
Heated ambient air flows across the tower and regenerates the desiccant.
Heated ambient air flows across tower 2 and regenerates desiccant

29. KBD Operation
Fifty-eight minutes later, valve D closes and tower 2 is re-pressurized
Two minutes later, valve B opens, valve A closes and the sequence is repeated
If 2-stage regeneration mode is selected, blower turns off and dry compressed air is supplied to cool desiccant bed
Three hours later, heater turns off and blower continues to supply ambient air to cool desiccant bed
Three hours later, the heater turns off, and the blower continues to supply ambient air to cool the desiccant bed.
If 2-stage regeneration mode is selected, the blower turns off and dry compressed air is supplied to cool the desiccant bed.
Fifty eight minutes later, valve D closes and Tower 2 is re-pressurized
Two minutes later, Valve B opens, Valve A closes and the sequence is repeated.

30. Component Location Outlet Check Valve Air Outlet
Re-pressurization Valve
Re-Pressurization/Sweep Orifice
Re-Pressurization/Sweep Check Valve
Purge Check Valve
Pilot Air Shut-Off Valve
Pilot Air Filter
Pilot Air Regulator
Heater
Inlet Valve
Purge Valve
These are the basic components of the KBD dryer.
Open your KBD instruction manuals now and we will begin a more thorough explanation of the dryer.
Air Inlet
De-Pressurization Valve
De-Pressurization Muffler