EVAPORATION 333 



„ ^. f ^ . 104 — (2 X 15-4) — 12-5 — 2-S 



Consumption of steam is, — ^ ^^^-—^ ^ h 35 ' 3 = 47 * i 



5 

 per cent, on cane. 



4. Pre-evaporator supplying first heater, quadruple effect and s\Tup 

 at 65° Brix. 



Consumption of steam is, — ^—^ + 35'3 = 57'4 per cent, on cane. 



4 



5. As in 4, but \\'ith double effect pre-evaporator. 



r- X- r . ■ 104— (2 X 15-4) , ^ 



Consumption of steam is, -— ^ — ^ ^^—^ + 35 • 3 =53 " 6 per cent, on cane. 



6. Pre-evaporator supplying heater and re-heater, syrup at 65° Brix, 

 quadruple effect supplying steam for graining from first cell. 



. r ■ 104 — 15-4 — 2-8 — 12-5 , 



Consumption of steam is, ■ — ^^^—^ -f 35"3 = 53"7 per 



4 

 cent, on cane. 



These different systems, as well as an isolated triple and quadruple 

 effect system are illustrated diagrammatically in Fig 186, those bodies 

 which receive virgin steam being indicated by a cross. 



In the computation given above the total amount of juice treated is 

 taken as 130 per cent, on cane, which is ver}' much greater than that which 

 generally obtains. The total consumption of steam for any s3-stem will be 

 roughly proportional to the actual quantity of juice, so that it is easy to pass 

 from the quantities above to any other assumed quantity of juice. The 

 wTiter adopted the data used as representing an extraction of 99 per cent, 

 of the sugar in the cane, ^^•ith the object of showing that even with only 

 II per cent, fibre in cane the bagasse can supply steam to operate the factory 

 when the steam is utilized at great economy. 



In the Chapter on Bagasse it is shown from experimental results that 

 each per cent, of fibre in the cane can supph'^ steam equal to 4-5 per cent, 

 on cane. In case 3 above, which may be taken as one of extreme economy, 

 the consumption was computed as 47-1 per cent, on cane ; that is to say, 

 with exceptionally low fibre and exceptionally high dilution extra fuel may 

 be necessary. With less economical schemes for steam utilization extra 

 fuel must be used or extraction sacrificed unless there is more fibre in the 

 cane. 



In the computation above a consumption of 30 lbs. steam per I. H. P. -hour 

 was accepted, of which 25 lbs. was taken as recoverable in exhaust. These 

 figures, based on trials made by the \\Titer and on textbook statements, 

 refer generally to engines not less efficient than a Corliss, to live steam 

 pressures of 90-100 lbs., and to exhaust pressures of 0-5 lbs. With 5 lbs. 

 steam pressure only, the first cell of a quadruple will boil at about atmospheric 

 pressure and steam at this pressure will have only a hmited application, 

 unless heating surfaces of exaggerated dimensions he installed in the heaters 

 and vacuum pans. Under such conditions steam may be separated from the 

 first cell to perform a portion of the heating of the juice, say to 180° -190° F., 

 and the balance \\\\\ have to be done with steam at single effect in a separate 

 heater. 



It ma}' happen, too^ that the engines are uneconomical and badly arranged, 

 the result being that so much exhaust is produced that difficulty is experi- 

 enced in its utilization. In this case economy is impossible without re- 

 arrangement of the power plant. 



