2 CIRCULAR 443, U. S. DEPARTMENT OF AGRICULTURE 



possibilities of leaf shattering in handling and of leaching due to 

 weathering in the field. 



TYPES OF DRIERS 



The artificial drying of forage crops has been practiced to a limited 

 extent in some localities in the United States for many years. Avail- 

 able information does not indicate the exact date of the first hay drier 

 in this country. However, about 1909 an experimental drier was 

 constructed and used in Missouri for alfalfa. Also, a machine was 

 constructed for drying native grasses in Louisiana as early as 1910. 

 Since that date many attempts have been made by commercial, State, 



Air from fan I mixed 

 with hot gases from furnace 



Discharge 



/ Am 



Air to 



Air return Air from fan 2 mixed 



to fan 2 with hot gases from furnace 2 

 V 



Feed 



D 



Figure 1.— Apron-conveyor type of forage drier. 



and Federal agencies to develop satisfactory forage driers, but few 

 were developed beyond the experimental stage. 



The design of many of the early machines indicated a radical 

 departure from established practices in the utilization of heat for 

 evaporating moisture from damp or wet materials. In other cases 

 slight changes in design and alterations were made of equipment 

 typical of that used for drying materials other than hay. The most 

 common types were those generally known as apron-conveyor and 

 revolving-drum driers. An apron-conveyor drier of the type corn- 



Feed 



Figure 2.— Revolving-drum type of forage drier, single-drum design. 



monly used for hay is diagrammatically illustrated in figure 1, and 

 drum driers in figures 2 and 3. 



The principles involved in these machines are not new, but the 

 direct exposure of material to be dried to the furnace gases is a practice 

 that has been closely associated with the development of hay driers 

 of various types in the United States. Previously steam was com- 

 monly used, the material to be dried being brought into direct contact 

 with or exposed to air heated by steam radiators. Higher efficiency 

 in the utilization of heat and elimination of the expense and trouble 

 commonly associated with steam boilers are factors frequently cited 

 in favor of direct application of furnace gases. 



In the apron-conveyor type (fig. 1) the green forage is loaded on an 

 endless screen-wire apron and conveyed through the drying chamber 



