FILTRATION 



305 



the cakes to be discharged and the cloths to be washed. As in the Kelly 

 press, only one joint is to be made. The filtering elements are formed of 

 wire frames covered with cloth. It also is widely used in American beet 

 sugar practice. The advantages of the two presses lie in their labour-saving 

 opportunities. They do not add. any new principle to the art of nitration. 



Sand Filters. Of the various types of sand filter, that due to Abraham 

 (patent 27629 of 1902), shown in Fig. 181, has been most used in the cane 

 sugar industry. The filtering elements consist of a number of conical iron 

 rings, a, piled vertically on one another and concentric with an upright 

 vertical cylinder, b. The sand fills the spaces between the rings and around 

 the cylinder. The material to be filtered enters at c, passes through the 

 sand and is withdrawn at d. The sand when 

 foul is discharged through a door and washed 

 in running water, which carries off the in- 

 tercepted matter. 



Bagasse Filters. A bagasse filter usually 

 consists of a vertical cylinder, through which 

 the juice flows from below upwards. The 

 bagasse used is generally that from the second 

 mill, that from the others being either too 

 coarse or too fine. Bagasse filters have the 

 advantage of eliminating washing, since the 

 bagasse when foul is merely thrown on to 

 the bagasse carrier of the mill and crushed 

 with the rest of the material. 



Wire Gauze Filters. The appliance usually 

 used consists of a cylindrical rotating screen, 

 set about 10 degrees from the horizontal. 

 The juice is introduced at the higher end and 

 escapes through the perforations. The fine 

 suspended matter is caught and carried for- 

 ward by the rotation of the cylinder. The 

 gauze used contains about 10,000 perfora- 

 tions per square inch, each being about o 005 

 inch in diameter. FlG - lSl 



Manipulation of Filter-Presses. Filter-presses for scums and first car- 

 bonated juices are usually worked at a pressure of about 40 Ibs. per sq. in., 

 the pressure being obtained from a montjus or pump. The montjus, Fig. 

 182, which is a French invention introduced in 1819, consists of a cylindrical 

 vertical or horizontal tank, a. It is filled with the material to be filtered 

 through the funnel, b, and steam or compressed air passing through the valve 

 c is allowed to act on the surface of the liquid, causing the material to ascend 

 through the pipe d. The pumps employed may be plunger or centrifugal 

 pumps. The former are often fitted with an appliance whereby the steam 

 is throttled when the pressure exceeds a certain limit. A very convenient 

 arrangement is as follows. The dirty juice is delivered from one centrifugal 

 pump to a tank, in which is maintained a pressure of 20 Ibs. per sq. in. 

 The presses are filled from this tank. A second pump draws from this tank, 



Y 



