Industrial driers have many applications for the drying of air and industrial gases in relatively large quantities on either continuous or intermittent duty cycles. Usually the requirements are such that two columns are needed, one to be in service while the other is being regenerated.

Calculation of Bed Size

Cooling a gas that is to be dried is an economical way to reduce its water load. A gas saturated at 100° F carries approximately three pounds of water per 1000 cubic feet. If this gas is cooled to 78° F, half of its water load is removed by condensation. This is more economical than drying by chemical means alone.
The size of a DRIERITE bed is usually calculated on the basis of the amount of water to be absorbed in the desired operating period. The water load is determined by the volume, temperature, pressure, and degree of saturation of the gas to be dried. Commercial grade DRIERITE has a design capacity of 5% and Du-Cal has a design capacity of 10% under most conditions. DRIERITE weighs approximately 65 pounds per cubic foot. From these constants, the weight and the volume in cubic feet of the desiccant are calculated. The pressure and the allowable resistance to flow through the desiccant bed are considered in determining the diameter and depth of the bed and the granule size of the desiccant.
In cases where the gas to be dried has a low water content and the volume of the gas is large, the rate of flow becomes the basis for the calculation of the quantity of desiccant and the size and the dimensions of the columns. The size of the unit in this type of application is larger in order to allow sufficient contact time of the gas with the DRIERITE. One pound of DRIERITE should be used for each 10 cubic feet per hour of actual flow rate for maximum efficiency.

Packing DRIERITE Beds

In placing the DRIERITE in the columns, care should be taken to obtain uniform distribution over the whole cross-section to avoid channeling. Pouring in from the top allows larger granules to roll out from the center and makes channeling probable. The desiccant should be lowered into the column in small containers or using a suitable funnel arrangement.

Regeneration of DRIERITE in Columns

Regeneration is usually accomplished by passing hot air through the drying column. A blower forces air through a heater where it is heated to 450° F and then downward through the DRIERITE bed. The moisture laden air is exhausted to the atmosphere. When a thermometer located in the bottom of the DRIERITE bed reads approximately 400° F, the regeneration is complete. The heat is turned off and the blower should continue until the top of the bed has cooled to about 274° F and then turned off to prevent absorption of moisture. When the bed has cooled to operating temperature, the column may be returned to service.
Approximately 250 to 300 BTU's are required to regenerate a pound of DRIERITE exclusive of heat loss. Any source of heat may be used that will provide clean air for the operation at the required temperature. If the tower has two inches of insulation, it will require about 25 scfm of air and 3 KW's of electric heat per 100 pounds of DRIERITE to regenerate it in four hours. The accumulation of dust, soot, resinous materials, etc., which may clog the pores of the granules, will bring about the gradual deterioration of the DRIERITE.