CANE SUGAR. 



Witcowitz Heater. In Fig. 172 is shown in section the radiating 

 heater of "Witcowitz. It consists of a forged steel body, aa, through which 

 pass at right angles to each other a series of tubes, bb. The juice circulates 

 through these tubes, the heating steam being without the tubes and within 

 the steel body ; the condensed water and heavier gases are drawn off at c, the 

 lighter ammonia cal gas at d. A very rapid circulation is claimed for this 

 design ; it is usually applied to the horizontal form of evaporator described 

 above, and is also used as a heater in saturation and defecating tanks, and is 

 capable of application to the vertical form of evaporator. 



Express System. 5 Another modification of the heating surface, 

 known as the 'Express' system, is shown in section in Fig. 178. It consists 

 of a belt, aa, in which are arranged the tubes which form the heating 

 surface ; as in the Witcowitz heater above described, the juice circulates 

 through the tubes b, steam entering 

 the collector box at c, and the con- 

 densed water passing away at d. 

 The collector box is set at an angle 

 following the slope of the saucer 

 of the effect, usually at an angle 

 of about 30 from the horizontal; 

 the tubes are about 18 inches long. 

 In an effect entirely on this system 

 there will be a second calandria 

 above the one shown and placed in 

 regard to it as a mirror image to 

 the object. This design can be 

 readily applied to effects with the 

 ordinary vertical tube calandria, a 

 belt being added to the effect below Fm - I72t 



the existing calandria in which the additional heating surface is placed. 



The ' Express ' system has been further developed by placing within the 

 shell of a vessel an inner shell of the same diameter as the calandria and 

 leaving a space of some inches between the two walls ; a colder and heavier 

 liquor collects here, which tends to descend and thus to form an induced 

 circulation. 



Incondensible Gases. In the process of evaporation a certain 

 quantity of incondensible gas is formed, and in addition some air enters with 

 the steam and through leaks in the apparatus. These gases have a corroding 

 effect on the apparatus, and if allowed to accumulate seriously diminish the 

 efficiency of the heating surface. In the first vessel they may be removed by 

 a cock opening into the atmosphere, but as steam also will pass out, this 

 process is uneconomical, and it is preferable to pass the gases successively 



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