20 CIRCULAR 4 4 3 ; U. S. DEPARTMENT OF AGRICULTURE 



electric power has the advantage. Where electric energy is available, 

 in most instances the rates are low enough for its profitable use. 



Examination of table 3 shows that the power requirements for the 

 experimental apron-conveyor drier ranged from 22 to 28.2 kilowatt- 

 hours per 1,000 pounds of water evaporated. The power requirements 

 are distributed approximately as follows : 



Percent 



Moving apron and auxiliary conveyors 11 



Moving drying gases 83 



Oil-burner operation 6 



For an experimental rotary drier the power requirements ranged 

 from 11 to 19 kilowatt-hours per 1,000 pounds, distributed roughly as 

 follows : 



Percent 

 Chopping forage 25 to 35 



Moving drying gases 45 to 60 



Oil-burner operation 4 to 8 



Rotating drum and conveying forage 10 to 15 



With these figures in mind it will be found that a drum drier capable 

 of evaporating 3,000 pounds of water per hour will need motive power 

 equivalent to 35 or 40 horsepower to run it. This would be divided 

 as follows: 



Horsepower 



Chopper 15 



Fan and drum 20 



Burner iy 2 



Conveying equipment 3 



Induction-type electric motors are widely used on drier equipment. 

 They should be enclosed to protect the windings from the fine dust 

 usually found in the air around the drying plant. 



OPERATION OF DRIERS 



Careful planning of a drying installation will effect economies 

 in all of the important items affecting the efficiency and cost of opera- 

 tion. The operation of a typical drum-drying plant may be described 

 as follows : Forage is cut, chopped, and blown into trucks or trailers 

 with a field chopper. It is then transported to and dumped into the 

 automatic feeder of the dehydrator. The feeder conveys the chopped 

 alfalfa to the drying-drum — from the drum the dried forage is con- 

 veyed through one or more cooling cyclones to a hammer mill— then 

 through one or more cyclones for further cooling and finally to a 

 sacker. The dried forage is conveyed by means of a system of pipes 

 and fans or conveyors to the cooling cyclones, hammer mill, and sacker. 

 When meal is pelleted, it is treated with steam or water spray as 

 required for a binding agent, then is run through a pellet machine. 

 Since the temperature of dried meal is raised in the pelleting process, 

 the meal is run through a cooling chamber. The pellets enter the top 

 of the cooling chamber and are drawn off the bottom in a continuous 

 stream. Any fine meal found with the pellets is usually screened out 

 and passed through the pellet machine. 



