EVAPORATION 



337 



but excellent entrainment traps also are provided, with economy in the use 

 of injection water. 



Effect of Initial Density of Juice on the Steam Consumption. — In making 

 an estimate of the steam consumption, it is at once evident that this will 

 vary with the initial percentage of solids in the juice, with the percentage of 

 solids to which this juice is evaporated before the graining at single effect 

 takes place, and the equivalent percentage of solids to which the final con- 

 centration is carried, if done in one process. Let Bj, Bg and B,„ be the 

 percentage of solids in the juice, sj^rup, and massecuite, and let there be a 

 multiple effect of n effects operated without separation of steam : then 

 the total consumption of steam in the multiple effect or pans is 

 B—Bj , B„-Bj B.-Bj 

 B, 



nB, 



nB„ 



B„ 

 B,- 



which reduces^to 



n B, Bj+ B,„ B—B.„ B, 



If 



n B,., B, 

 the consumption of steam is constant, when Bj changes to Bj, 

 n B„, Bi - n B, B — n B,„ Bj = n B,„ B, -nB,Bj-n B,„ Bj 



whence n = — ^^-^-• 



£5,,, — Bg 



Accordingly when B,,, and B, are constant, the consumption of steam is 

 constant for one particular value of n, and independent of change in the 

 value of B,. Taking 5,„ to refer to the first and subsequent boilings, its 

 value may be approximated at 96 ; then, when B, has the values below, 



the values of n or 



With syrup at 65° Brix, and with triple effect evaporation, there wiU be 

 a nearly constant consumption of steam. When, however, the steam is 

 used more economically, a lower consiunption Mill be found as the 

 degree Brix of the juice or value of B; decreases. Actually, however, 

 within such Umits as occur, the total consumption of steam does not vary 

 much when expressed as a percentage on the same weight of juice ; its 

 distribution between evaporators and pans, however, varies very largely. 



Heat Losses in Evaporators and in the Sugar Houses generaUy. — As 



regards steam pipes, the following table prepared by the John Manville Co., 

 referred to external air at 72° F., may be taken as in accord with inde- 

 pendent observations : — 



Heat transmitted B.T.U. per hour, per sq. ft., at the Stated Pressures 



IN LBS. per sq. in. 



2A 



