ETHYL ALCOHOL, FROM WOOD WASTE. 65 



DIGESTERS. 



The digesters should be of the rotating kind, and may be spherical 

 or in the form of a short cylindrical section with dished ends. If 

 they are of the latter type, the diameter should be double the length 

 of the cylindrical section in order that the digester may be filled as 

 nearly full as possible. A number of satisfactory acid-proof linings 

 are now obtainable. During the cooking the mass shrinks in volume 

 and settles, the final volume being only about two- thirds the original 

 volume. There is, therefore, ample room for thorough mixing during 

 the cooking. 



The size of the digesters will be governed by the daily capacity of 

 the plant, the heating period, and the time of the complete cycle for 

 each digester. If the heating period is 15 minutes out of a total of 

 1 hour for each cook, four digesters or multiples of four should be 

 used; whereas if the heating period is 20 minutes out of a total of 1 

 hour, only three or multiples of three should be used. In this way 

 the steam load on the boilers will be made as uniform as possible. 

 The boiler capacity will be largely determined by this load, since 

 that for power and distillation purposes will usually be constant. 

 In addition, the hogging, shredding, and digester capacity of the 

 plant should be sufficient to give enough digested sawdust in 18 or 20 

 hours to run the rest of the plant 24 hours, thereby allowing time 

 for breakdowns and repairs. 



By the rotation of the digester the cooked sawdust is discharged and 

 falls into a large bin, which receives this material from all the diges- 

 ters. From this bin it goes by mechanical conveyor to the different 

 cells of the diffusion battery. 



DIFFUSION BATTERY. 



Closed cells similar to those used for the extraction of sugar beets 

 or dyewood chips maybe used. These should be lined and made 

 acid-resistant like the digesters, and are usually fitted with bronze 

 and copper. The top and bottom should be so arranged that charg- 

 ing and discharging may be readily accomplished. Cells of this type 

 may be obtained from which the extracted material will empty itself 

 when the bottom of the cell is released. 



The temperature of the extracting water will rise 30° to 50° F. 

 during extraction because of the hot dust. In cold weather it would 

 be advisable to warm the water before it is used. If the acid juice 

 comes from the battery with a temperature between 125° and 150° 

 F., a good extraction will be obtained, and the large volumes of water 

 that would be required to cool hotter juice will not be necessary. 



The size and number of cells in the battery and the amount of 

 water in each cell will be governed by the size of the plant and the 

 54976°— 22— Bull. 983 5 



