396 CHAPTER XIX 



In the case of the two-massecuite system, column i gives the syrup 

 purity, column 2 the quantity of 75 purity massecuite boiled in the pans, 

 column 3 the quantity of the same material delivered to the centrifugals, 

 including the 40 per cent, of wet sugar derived from the 55 purity massecuite, 

 and column 4 the quantity of 55 purity massecuite, all expressed as dry 

 matter per i part of gravity solids in the juice. 



The basis of computation of the three-massecuite system is as follows. 

 The massecuite is reduced to 80 purity by the addition of 50 purity molasses ; 

 a footing of 80 purity massecuite is left in the pan and reduced to 70 

 purity also by the addition of 50 purity molasses. The 70 purity masse- 

 cuite on drying affords 40 purity molasses, which is used to reduce a footing 

 of 70 purity massecuite to 55 purity : the 40 per cent, of wet sugar recovered 

 from this massecuite is considered as returned to the 80 purity strike. 

 Column I gives the purities of the syrup , columns 2 and 3 and 4 the quantity 

 of 80, 70 and 55 purity massecuite as boiled in the pan ; column 5 gives 

 the quantity of 80 purity massecuite delivered to the centrifugals, including 

 that returned as wet sugar from the 55 purity strikes ; and column 6 gives 

 the quantity of 70 purity massecuite delivered to the centrifugals. The 

 quantity of 55 purity massecuite made and dried in the centrifugals is the 

 same as in the two-massecuite process. 



Inspection of these tables shows how very great is the variation in material 

 to be handled as affected not only by the gravity solids in the juice, but also 

 by the purity. In the design of a sugar factory allowance must be made 

 for the most adverse circumstances. Decrease in purity implies more crystal- 

 lizer capacity, but fortunately low purity is usually correlated mth low 

 gravity solids. On the other hand, high purity and high gravity solids 

 generally occur together, so that an excessive capacity at stations affected 

 by these causes is necessary. 



Computation of Pan Capacity. — Generally pan capacity is designed on a 

 basis of heating surface and quantity of water to be evaporated, some flat 

 rate of evaporation per sq. ft. and per hour being accepted. This basis 

 does not appeal to the writer, since a pan, as shown in another section, 

 operates at a very variable rate. The method he uses is based on a knowledge 

 of what pans actually do under working conditions, a method really not 

 different from the process indicated as the usual wa\^ since the heat trans- 

 mission coefficients there used are based also on observation. As an example, 

 suppose a design is required for a house to work up 100 tons of juice at 

 15 per cent, gravity solids and 80 purity. Referring to the table on 

 page 395 for a two-massecuite process there will be produced in the pans 



1-167 '^-^ =■- 1-032 part of 75 purit}' massecuite, and 0-405 part of 



55 purity massecuite per part of gravity solids in the juice ; in all 1-437 

 part. For the selected quantity this in 24 hours will amount to 1-437 X 100 

 X 24 X 0-15 =517 tons ; allowing 23-5 cu. ft. at "93'' Brix " per ton of 

 gravity solids there will be 12,149 cu. ft. This quantity will have to be dis- 

 charged by the pan in 24 hours. Let the design call for four pans of equal 

 size ; then each pan will discharge 3,037 cu. ft. per da}^ of 24 hours. 



The tim^e required for the cycle of a pan strike varies with the steam 

 pressure, the heating surface in the pan, and a number of other causes, 

 amongst which are some obscure factors connected with the nature of the 

 syrup. Also a certain minimum time must be allowed, since the rate at 



