422 CHAPTER XX 



Capacity of Machines. This term is used to refer to the volume as defined 

 by the shell, the lip and a perpendicular dropped from the inner edge of the 

 lip to meet the bottom of the basket. This volume forms the maximum 

 volume occupied by the dried charge. The volume of the charge delivered 

 to the machine will be less than this, and the capacity in cubic feet over a 

 stated period will depend mainly on the purity of the massecuite, the skill 

 used in boiling, and the power available for driving. Referred to a 75 

 purity massecuite, as obtained in a two-massecuite process, the capacities 

 given below may be taken as conservative. These may be diminished or 

 increased 10 per cent, when referred to a 70 purity and 80 per cent, purity 

 massecuite produced in a three-massecuite process. The actual volumes 

 will, of course, vary from maker to maker. 



Machine, Capacity Charge Cu. ft. of 75 purity 



inches. cu. ft. cu. ft. massecuite per hour. 

 42x24 87 80 



42x20 6-75 5-75 67 



40x24 7-5 6-5 75 



40 x 20 6 -25 5 -25 62 



3 6 Xi8 4-5 3-75 45 



3Xi8 3-75 3 34 



Determination of Centrifugals required. In Chapter XIX the quantity 

 of massecuite produced per ton of gravity solids in the juice has been cal- 

 culated both for a two-massecuite and for a three-massecuite process. It 

 was also shown there how these quantities varied with the purity of juice. 

 Referring to the table in that chapter it will be seen that when there is a low 

 purity originally, say 75, for every ton of gravity solids there is produced 

 0-524 ton of 55 purity massecuite, and 1-035 ton 75 purity massecuite, 

 including here the low sugar obtained from the 55 purity material. With a 

 high purity of 90 these figures become o 167 ton and I 572 ton respectively. 

 In the course of a crop the gravity solids in the juice and consequently also 

 per ton of cane are constantly varying, as is also the purity. Accordingly, 

 at one period of the crop there may be an excess capacity in the centrifugals, 

 and later on in the season the capacity may be too small. In addition, the 

 proper distribution of the centrifugals as between high grade and low grade 

 machines will be constantly changing. 



To illustrate this point a concrete example may be taken : An installa- 

 tion is required to treat the massecuite resulting from 100 tons of juice per 

 hour, the extreme composition being 77 purity and 15 per cent, gravity 

 solids and 85 purity and 18 per cent, gravity solids. 



A two-massecuite process is to be used at purities of 75 and 55. From 

 the table in Chapter XIX it follows that there result 



Ibs. 



77 purity gravity solids per hour in 75 purity massecuite . . . . ; >.'.!,- 32,970 

 ., 55 ,. I4.3i> 



85 ., 75 _ " 49,672 



,, ,, ,, ,, ,, 55 ,, ,, ...... 10,296 



In a preceding section a 4O-in. X 24-in. machine was given as handling 

 80 cu. ft., or 7,200 Ibs. containing 6,800 Ibs. gravity solids per hour, at 75 * 

 purity. A 36-in. x i8-in. machine may be expected to handle 850 Ibs. of 

 gravity solids per hour at 55 to 60 purity. 



