THE CONCENTRATION OF THE SYRUP TO MASSECUITE. 



heating surface is not in use. As a rule, modern pans have a capacity of 

 about 70 Ibs. of massecuite per square foot of heating surface ; these data are 

 sufficient to calculate the size of pans for the concentration of any given 

 quantity of syrup. 



The effect of a low vacuum in the single effect pan is not so noticeable as 

 affecting the temperature difference as in the multiple effect ; if in the example 

 worked above, a 27-inch vacuum be assumed, the mean pressure of the vapour 

 at the moment of its formation is found to be 3-86 Ibs. per square inch, corres- 

 ponding to a temperature of 152F., and giving a temperature difference of 

 107F. as compared with 97 F. or roughly 10 per cent. ; for the triple effect 

 considered in the previous chapter the same final vacua altered the tempera- 

 ture difference to the extent of 30 per cent. 



Relation of Heating Sur- 

 face to Capacity. In a standard 

 type of coil pan there will be per cubic 

 foot of capacity from 1*2 to T6 square 

 feet heating surface ; in a vertical tube 

 pan from 2 to 2*2 square feet; in a 

 lyre coil pan from 2-5 to 3 square 

 feet, and in a Welner-Jelinek pan from 

 2' 8 to 3 square feet. 



Kind of Steam used. In 



general, in modern factories, and always 

 unless the engines are large steam con- 

 sumers, all the exhaust steam is used up 

 by the juice heater and multiple effect 

 apparatus, and none remains for the pans. 

 The majority of sugar manufacturers 

 object with considerable reason to the 

 use of high pressure steam in the pans, 

 and consequently the main steam is 

 reduced before entering the coils to a pressure generally lying between the 

 limits of 10 Ibs. and 20 Ibs. per square inch. The objection to the use of high 

 pressure steam is the tendency towards local overheating and caramelization of 

 the sugar. This danger is not so great if the circulation is kept very rapid, 

 and the use of high pressure steam adds very considerably to the capacity of a 

 pan, the passage of heat being proportional to the difference in temperature 

 between the exterior and interior of the coils; pans are now constructed, 

 especially by United States firms, to work with steam pressures of 50 Ibs. per 

 square inch or even more, but it is really doubtful if the use of high pressure 

 steam is to be advised. 



FIG. 193. 



349 



