FISH MEAL AND OIL 



479 



Air-Lift Drier. There are two types of air-lift driers: vertical and horizontal. 

 While both operate on the same principle, they are constructed differently. Both 

 are highly efficient and are able to produce a dried product of a high grade since 

 the temperature can be kept low, thus eliminating the likelihood of scorching. 

 They also reduce the discharge of objectionable odors into the air. 



One type is designed in the form of a vertical tower, the height and diameter 

 of which is controlled by the quantity of the material to be handled. Heat is gen- 

 erated in a furnace or by a bank of steam coils, and introduced at the bottom. 

 A high-velocity blower, situated at the top of the tower, pulls a sufficiently large 

 volume of air upward and holds in suspension the particles of wet material fed in 

 near the bottom. As the particles lose moisture, they become lighter and finally 

 float out through the blower and are caught in a cyclone separator. 



The horizontal-type drier is composed of an outside stationary cylinder and two 



3team lNi.eT- 



{Courtesy Edw. Renneburg and Sons Co.) 



deodorizing tower for drying fishmeal. 



inside rotating cylinders, one inside the other. These cylinders are arranged in the 

 form of baffles. The material travels three times the length of the drier before 

 being discharged in a cyclone-separating arrangement at the dry end. A furnace is 

 the source of heat, and a blower pulls a high-velocity stream of air through the 

 drier. The wet material is fed into the inner cylinder, and as it dries is carried 

 through by the air current. The rotation of the cylinders prevents the wet mate- 

 rial from sticking to the sides and forming a cake. It is claimed that this drier has 

 the capacity to evaporate 6 to 8 thousand pounds of water per hour. 



Vacuum Drier. The equipment for drying under a vacuum is almost identical 

 with that described under the "dry -reduction process." The wet material is loaded 

 into the drier, and the moisture evaporates under reduced pressure of approxi- 

 mately 29 inches of mercury. Heat is produced by the low-pressure steam in the 

 jacket of the drier. The meal produced under these conditions is of a high quality 

 because of the low temperature of the drying. The costs of meal production by this 

 method are slightly higher than the others previously mentioned. 



Handling Odors. As a general rule fish-meal plants are seriously troubled with 

 odors. In many instances the plants have been declared a nuisance and have had 

 legal difficulty until the odors were controlled. The gases from the drier, regard- 

 less of the type, may be recirculated and passed through the furnace, where 

 the heat of the combustion destroys the odors. Another common method for 



