EVAPORATION 333 



104 (2 X 15 4) 12 5 2 8 , 

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



o 

 per cent, on cane. 



4. Pre-evaporator supplying first heater, quadruple effect and syrup 

 at 65 Brix. 



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



4 



5. As in 4, but with double effect pre-evaporator. 



Consumption of steam is, -f 35 3 =53 ' 6 per cent, on cane. 



4 



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

 quadruple effect supplying steam for graining from first cell. 



Consumption of steam is, - ' + 35 ' 3 = 53 ' 7 per 



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 very much greater than that which 

 generally obtains. The total consumption of steam for any system 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 

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

 of the sugar in the cane, with 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 supply 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 Ibs. steam per I.H.P.-hour 

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

 figures, based on trials made by the writer and on textbook statements, 

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

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

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

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

 unless heating surfaces of exaggerated dimensions be 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 will have to be done with steam at single effect in a separate 

 heater. 



It may 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. 



