228 



FISHERY INDUSTRIAL PRODUCTS 



rapid heating but does not prevent oxidation of the oil in scrap. It merely 

 delays its onset and probably stretches out the time necessary for essen- 

 tially complete oxidation. 



Recent evidence indicates that among the many factors involved in 

 excessive heating of the scrap, a high initial temperature of the scrap in 

 the first pile as it comes from the dryer may have the most detrimental 

 influence. The critical temperature seems to be about 140 to 135°F; above 

 this point pile temperatures build up, below it the temperature of the pile 

 holds and gradually falls'. 



Solids fo dryer 



Press liquor 



1 



Horizontal 

 centrifuge 



Centrifugal 



separation 



Gravity 



separation *] 0'' settling tank 



Centrifuge 



Series 

 of tanks 



-Stear 



Tank car to consumer 



Figure 16.4. Flow' diagram of production of fish oil from press 

 liquor. (U.S. Fish and Wildlife Service.) 



Several ways have been found in practice at various plants to reduce 

 initial pile temperatures. Among the best are: 



1. Using high ceiling conveyors to give the scrap a maximum drop and 

 air exposure while it is hottest 



2. Piling initially in 5 or 6 piles rather than building just one, then 

 another, pile up to conveyor height — this gives more meal a long fall 

 and the more slowly forming piles trap less heat 



3. Making the first drop into a moving floor conveyor that then carries 

 the scrap to an elevator and a second drop in another floor area 



4. Using large blowers to give high air flow through the dryer and to 

 move the hot scrap to the curing shed. 



