CANE SUGAK. 



It is however in the pan that the greatest change is made, for although 

 the amount of work done here is unaltered it is now done with steam, at say, 

 a temperature of 210 F. whereas previously the temperature may have heen 

 260 F ; taking an average temperature in the pan of 160 F. the temperature 

 differences are 100F. and 50 F., so that at least double the amount of pan 

 heating surface will be required. 



The Pre-evaporator. The very large heating surfaces required 

 with the use of extra steam have led to the introduction of the Pauly ' pre- 

 evaporator/ This consists of a vessel independent of the evaporator proper 

 and receiving steam at a pressure of about 30 Ibs. ; the juice is partly concen- 

 trated herein and the vapour given off which may be at a pressure of about 

 15 Ibs. per square inch goes to the heaters and pans ; the partly concentrated 

 juice passes on to the evaporator which is heated by exhaust steam from the 

 engines; in the pre-evaporator the transmission of heat is high and compara- 

 tively small heating surfaces are required. In beet factories it has been 

 established that no appreciable loss of sugar due to the high temperature 

 boiling need obtain. In this scheme there seems great opportunity for the 

 use of the ' Kestner ' as a pre-evaporator, as in this type the juices are the 

 minimum time under treatment. This scheme modified by Greiner and known 

 as the Pauly-Greiner is shown in Fig. 179 ; in this arrangement two sets of 

 boilers are used, one, a, supplying high pressure steam to the engine b, the 

 exhaust from which passes to the first vessel of the evaporator c ; the other 

 set of boilers a 1 supply steam at 30 Ibs. to the pre-evaporator d which in turn 

 supplies the pan e and heater /. Connections are usually established so that 

 the pre-heater and quadruple may, if desired at any time, work as a 

 quintuple. 



The relative economy of some of the different possible combinations is 

 calculated and tabulated below; in making these calculations the following 

 data are assumed : 100 parts of juice at 15 Brix, of temperature 82 F., of 

 specific heat *9, are heated to 212 F. ; this juice is evaporated to 55 Brix in 

 the multiple and finally to 96 Brix in the pans ; hence 72-72 per cent, of the 

 juice is removed in the multiple and 11 '65 per cent, in the pans. The con- 

 sumption of heat in the heater is 100 x (212 82) X '9 = 11,700 units, 

 and taking the latent heat of steam as 970 this is equivalent to the evapora- 

 tion at single effect of 12'06 parts of water. At triple effect the evaporation 

 is equivalent to the removal of 24 -24 parts water at single effect, so that the 

 number 12-06 -f 24'24 + 11 -65 = 47'95 is proportional to the heat or steam 

 consumption with this method of working. Now let all the steam required 

 for the pans be taken from the first vessel of the triple; then, as already 

 shown above, 32-01 parts of steam must be there delivered, and the total 

 consumption of heat or steam is proportional to 32*01 -|- 12-06 or 44*07, 



318 



