COMPARTMENT DRYERS 



With compartment dryers the regime is the reverse of that in pro- 

 gressive dryers. In the compartment system the temperature is varied 

 without movement of the material. A compartment dryer, as the name 

 indicates, consists of a number of compartments or rooms. These are 

 provided with heat either by steam pipes in the room itself, or from a 

 heater outside. Ventilation and renewal of the air may be either by 

 chimney draught or by the action of fans. Moisture for restraining the 

 too rapid action of dry heat is provided by water spray or steam jets, 

 and also by re-circulating a part of the warm, wet air from the dryer. 



As the whole of the room is, or should be, at one even temperature, 

 the only circulation that is possible by thermal means is by chimney 

 draught. The contents of the compartment being warmer than the 

 outside air, there would be a natural flow outwards through the chimney, 

 replaced by an inward flow of cold air at floor level. The intensity of this 

 action depends on the height of the chimney and the difference in tempera- 

 ture between the interior and the outside air. The circulation thus varies 

 with the amount of heat, and can only be controlled negatively, that 

 is to say, by shutting dampers in the chimneys. Makers of thermal 

 compartment dryers usually provide either steam coils in the chimneys 

 to accelerate the draught, or steam jet ejectors. Both of these prove 

 somewhat inefficient, and consequently for all compartment dryers there 

 is much to be said in favour of fan circulation. 



With fan-operated compartment dryers the heating is effected by 

 means of hot air blown into the drying rooms by centrifugal fans. The 

 air is heated by contact with steam-pipe heaters placed outside the rooms, 

 and the necessary humidity is obtained by exhausting part of the used 

 warm moist air from the dryer and re -circulating it. When greater 

 humidity is needed, steam vapour is admitted. The temperature and 

 humidity of the air injected can thus be varied quite independently of 

 the circulation, which is in itself under control. 



With the first fan-operated dryers this held good only when there was 

 a single compartment. With two or more chambers working with one 

 fan and one heater it was only possible to alter the temperatures in 

 individual rooms by reducing or increasing the amount of air admitted, 

 as otherwise the conditions in the remaining compartments would be 

 interfered with. 



The Sturtevant triple duct dryer, however, as has been said before, 



401 2D 



