These dry kilns are usually operated as "Blower" kilns, the heating apparatus is generally located in a separate room or building adjacent to the main structure or drying rooms, and arranged so that the hot air discharged through the inlet duct (see illustration) is thoroughly distributed beneath a lattice floor upon which rests the material to be dried. Through this floor the air passes directly upward, between and around the stock, and finally returns to the fan or heating room.
This return air duct is so arranged that by means of dampers, leading from each drying room, the air may be returned in any quantity to the fan room where it is mixed with fresh air and again used. This is one of the main features of economy of the blower system of drying, as by the employment of this return air system, considerable saving may be made in the amount of steam required for drying.
[Illustration: Fig. 38. Exterior and Sectional View of a Battery of Tower Dry Kilns. This is a "Blower" or "Hot Blast" type, and shows the arrangement of the fan blower, engine, etc. This type of dry kin is used principally for the seasoning of small, loose material.]
The lattice floors in this type of dry kiln are built on an incline, which arrangement materially lessens the cost, and increases the convenience with which the dried stock may be removed from the bins or drying rooms.
In operation, the material is conveyed in cars or trucks on an overhead trestle--which is inclosed--from which the material to be dried is dumped directly into the drying rooms or bins, through hoppers arranged for that purpose thereby creating considerable saving in the handling of the material to be dried into the kiln. The entire arrangement thus secures the maximum capacity, with a minimum amount of floor space, with the least expense. Of course, the higher these kilns are built, the less relative cost for a given result in the amount of material dried.
In some instances, these kilns are built less in height and up against an embankment so that teamloads of material may be run directly onto the roof of the kilns, and dumped through the hoppers into the drying rooms or bins, thus again reducing to a minimum the cost of this handling.