404 



CHAPTER XIX 



air into the magma, and so will form an emulsion with the molasses. This 

 emulsion will be so light that it will float on the wall of sugar in the centri- 

 fugals. Similarly, when a crystallizer is being emptied the stirring gear 

 should be stopped. 



The temperature at which low grades should be dried is about 105 to 

 110 F. If allowed to cool below this limit the molasses becomes so viscous 

 that any gain in sugar deposited is counterbalanced by the increased quan- 

 tity of water required to wash the sugar in the basket. 



Crystallizing Tanks. The receptacles in which the massecuites are 

 received in order to be cooled in motion are either cylindrical or U-shaped. 

 More capacity in a given floor area is obtained with the latter. A shaft 

 located along the longitudinal axis of the vessel carries the stirring gear, 

 which usually takes the form of a double helix, as seen in Fig. 251. Motion 



FIG. 251 



is usually transmitted to the shaft by a worm and wheel drive. The power 

 absorbed is about I h.p. per 1,000 cu. ft. of massecuite. The tanks are made 

 plain or jacketed. In the latter case water or steam may be admitted to the 

 jacket so as to control the rate of cooling. In cane sugar houses this control 

 is very uncommon, and excellent results may be obtained with an uncontrolled 

 rate of cooling. 



In the beet sugar industry rapid cooling tanks are sometimes installed 

 by the use of which the massecuite is cooled and ready to dry in nine hours. 

 Two forms due to Ragout and Tourneur and to Huch are shown in Figs. 

 252 and 253. The cooling surface of the former is a rotating helix, and in 

 the latter a system of stationary tubes. In both patterns hot or cold water 

 circulates through the tube system. The Huch pattern is also made as a 

 vacuum crystallizer, permitting of the removal of water during cooling. 

 Neither of these types has come into use in the cane sugar industry and 

 possibly the v scosity of low cane products might prevent the deposit of 

 sugar keeping pace with the fall in temperature. 



Caleulatien of Crystallizer Capacity. The calculations given on page 395 

 show that the capacity depends on the gravity solids, on the purity as 

 variables, and n the time considered necessary for cooling as a constant. 



