Question: My dual bed desiccant bead dryer will not attain a -40˚ dew point. What should I check?
Most dual bed dryers are a closed loop air system so check all hoses, gaskets, and clamps for air leaks. Air could also be entering the dryer through a vacuum loader. Do not let the Gaylord get empty and suck air into the vacuum loader. Keep the wand in the material at all times when filling the hopper.
If you have a microprocessor-controlled dryer, verify that the regeneration temperatures are set properly for your model dryer. If your dryer is controlled by a cam timer, check that the cam lobes are set properly and that you are getting an output to the regeneration heaters.
Do amperage readings on the regeneration heater elements to check for bad elements. (See print for spec.)
Check the valve assembly on small dual bed dryers (up to 50 lb./hr.) for broken cotter pins, broken springs, bad solenoid, and bad gaskets on the disks.
On a large dual bed dryer (100 lb./hr. & up) check the lower valve seal for air blow by. The gasket material sealing the valve may be bad. A good way to check this is to see if the regeneration blower is turning backwards when the dryer is in static cooling.
Check the air lines to the sensor and make sure that they are not clogged. DO NOT BLOW AIR TOWARD THE SENSOR.
If you have a microprocessor-controlled dryer you can check the dew point circuit in the CPU by unplugging the dew point sensor. Depending on the type of sensor you are using the display will read the lowest range. When you jump out the sensor the display will read the highest reading.
Example: Hygro sensor will read –40 to +10. If you don’t know the range of your sensor call the manufacturer to verify the range.
Crush test – Take some desiccant that has been dried out through the regeneration cycle and try to crush it with your fingertips. If the desiccant crushes it needs to be replaced.
Water test – Take some desiccant that has been dried out through the regeneration cycle and a half cup of water at room temperature. Mix the two together, letting the water cover the desiccant. There should be a chemical reaction that will increase the water temperature by about 30˚F. If there isn’t a temperature rise the desiccant should be replaced.
The color should be an off white. The desiccant touching the heater elements on small dryers units may be brown in color due to the heat from the elements. If it is black, it is contaminated and should be replaced.
Airflow is also an important aspect of drying and dew point may suffer if airflow is restricted or compromised.
Clean filter elements or replace them if damaged.
Tighten all hose connections
Clear obstructions from air hoses and make sure linings are not collapsed
Replace any crimped hoses
Jeff Rodway: Technical Service Manager, Novatec, Inc.
Question: Why am I getting temperature fluctuations in my dual bed dryer?
Response: It depends, if those fluctuations occur:
At bed change - this may be a normal heat spike at changeover
When the regeneration heaters are on - you may have worn wiper seals
When the hopper is loading – probably air is being drawn out of the hopper by the vacuum conveying system. This could be caused by a missing or damaged grommet on bottom of vacuum receiver. It can also be caused by a stuck/damaged relay on the microprocessor or a stuck / damaged heater contactor.
Jeff Rodway: Technical Service manager, Novatec, Inc.