314 THE SPRAY PROCESS 



of the product. But even in the case of quite granular powders 

 a very appreciable portion leaves the desiccating chamber. Again, 

 efforts have been made to prevent this escape of milk powder by 

 extending the length of the desiccating chamber, thereby augment- 

 ing the distance between the intake and exit of the hot air. This 

 arrangement subjects the dried particles over a longer distance to 

 the gravity force, their opportunity to drop to and deposit on the 

 bottom of the desiccating chamber before being caught in the out- 

 going air current is augmented, and the tendency for escape is 

 diminished. In other cases, see Gray patent, the intake and dis- 

 charge of the air and the direction of the particles of milk are so 

 arranged that the moisture-laden air escapes in the center while the 

 milk spray moves tangentially toward the periphery, tbus making 

 for minimum escape and maximum recovery of the powder. 



At best, however, there is need of provisions to recover milk 

 powder carried off in the air currents escaping from the desiccating 

 chamber, and diverse contrivances have been designed and are in use 

 in milk powder factories for this purpose. 



These arrangements for the purpose of reclaiming or recover- 

 ing the milk powder are known as "dust collectors." They are 

 similar in principle to those used in flower mills. Some of these 

 dust collectors now in commercial use are guaranteed to accom- 

 plish 99.9 per cent recovery of such products as corn starch, wheat 

 flour and the like. 



They chiefly consist of vaults or drums or other containers 

 into which the suction fan, located at the air exit end of the dry- 

 ing chamber, discharges the outgoing air. These vaults are 

 equipped with a series of canvas screens or bags on which the par- 

 ticles of milk powder floating in the outgoing air, are deposited, 

 and from which by mechanical shaking or otherwise, the escaping 

 milk powder is reclaimed and recovered. 



In some factories a part of the recovery equipment consists 

 of a so-called cyclone. This is usually a cylindrical receptacle 

 with cone-shaped bottom. The air escaping from the drying cham- 

 ber is blown into this cyclone with great force and, being thrown 

 against its walls, drops at least a portion of the fine, dust-like milk 

 powder it contains. 



