ARTIFICIAL DRYING OF FORAGE CROPS 



When used for hay the drum drier may be classed as a high tem- 

 perature machine, necessitating a short period of exposure to prevent 

 charring or burning the hay. The temperature of the furnace gases 

 entering the machine is usually held at from 1,000° to 1,500° F. by 

 a combination of adjustments on the air inlet to the furnace and on 

 the quantity of fuel supplied to the burner. The material remains 

 in a drier of the drum type for approximately 1 to 3 minutes, or 

 even less, depending somewhat upon the initial moisture content of 

 the forage. However, as in the apron-conveyor type, the tempera- 

 ture of the hay is much below that of the drying gases. 



The chopping of the hay into short pieces enables it to dry quickly 

 and thereby makes possible the use of high temperatures in drum 

 driers. The use of air for moving the material through the drier 

 is helpful in preventing overdrying, since the light particles move 

 more rapidly than the stemmy material. 



The use of high temperatures and a short period of exposure in drum 

 driers makes possible a rather small, compact unit in comparison with 

 the apron-conveyor type. Single-drum driers are usually 35 to 40 

 feet in length and from 7 to 10 feet in diameter. Double- or triple- 

 drum driers may be somewhat shorter than single-drum units, as the 

 use of multiple drums increases the length of the drying zone with 

 reference to over- all length. 



In drum driers there seems to be a definite relation between the 

 temperature of the exhaust gases and the moisture content of the hay 

 as it is discharged from the machine. An exhaust-gas temperature of 

 about 225° to 325° F. is usually maintained by controlling the rate of 

 feed of undried hay. If the moisture content of the forage entering 

 the drier is high (65 to 80 percent) the exhaust temperature should 

 be kept at the high point of the range. When moisture content is 

 around 50 percent the exhaust temperature should be held at the lower 

 end of the range. The high exhaust temperature represents a consid- 

 erable loss of heat that tends to reduce the thermal efficiency of drum 

 driers. 



TESTS OF DRIERS 



Early investigational work by the United States Department of 

 Agriculture consisted of a study of the mechanics of artificial drying 

 of forage crops, the elements of cost, and the feeding value of artifi- 

 cially dried forage. Work of this type was done by the Department 

 as early as 1930. A small apron-conveyor drier of the type commonly 

 used in drying cotton linters was set up on the Iberia Livestock Experi- 

 ment Station at Jeanerette, La., for experimental use in drying crops 

 for feeding trials (fig. 5). This machine was approximately 46 feet 

 long, 11 feet wide, and 9 feet high. The drying chamber was approxi- 

 mately 8 by 36 feet, and the machine would usually evaporate from 

 500 to 1,000 pounds of water per hour under the conditions in which 

 it was operated. This drier was used for several seasons, but its capac- 

 ity was insufficient for drying the forage needed for feeding trials. 

 It was unsatisfactory also for drying coarse-stemmed crops such as 

 soybeans. 



