CANE SUGAR. 



i.e., 91 91 per cent, of that required with conventional triple effect 

 evaporation. Results of similar calculations are tabulated below : 



Relative 



Consumption 



of Steam. 



Conventional triple evaporation 100 -00 



Conventional quadruple evaporation 87 '28 



Triple evaporation and extra steam to pan 91 '91 



Pre-evaporator to pan, and triple 91*91 



Triple evaporation and extra steam to heater 91*62 



Pre-evaporator to heater, and triple 91 '62 



Triple evaporation and extra steam to pan and heater . . 83*46 



Pre-evaporator to pan and heater, and triple 83*46 



Quadruple evaporation and extra steam to pan 81*32 



Pre-evaporator to pan, and quadruple 81*32 



Quadruple evaporation and extra steam to heater . . . . 80*52 



Pre-evaporator to heater, and quadruple ...... ... 80*52 



Quadruple evaporation and extra steam to pan and heater. . 75*00 



Pre-evaporator to pan and heater and quadruple 75*00 



In addition combinations of the pre-evaporator with extra steam from 

 the multiple can be devised. 



The Picard System. This method has never, the writer believes, 

 been applied in any sugar factory, although it has been working in other 

 manufacturing processes since 1878. In this scheme part of the vapours given 

 off from the first vessel are drawn off into a compressor and raised to a high 

 pressure ; their temperature is thereby increased, and on again being introduced 

 into the calandria of the effect are capable of evaporating a further quantity of 

 water. This scheme can of course be worked to its best advantage where 

 power, as from a fall of water, is available to drive the compressor. This 

 method was described in 1880 by P. 0. Whitehead, 11 and its mathematics 

 have been discussed in detail by Svorcik, 12 who as a final result lays down that 

 in a triple with this scheme one part of steam will evaporate altogether 4*248 

 parts of water. His idea of the regeneration of vapours has been made 

 practical by Selwig and Lange, who have put into practice the scheme of 

 withdrawing part of the vapour from the penultimate vessel of a multiple by 

 the use of live steam injectors, and returning them either to an earlier vessel 

 -or utilizing them in heating or in the pans. 



Calculation of Heating Surfaces. When the amount of heat 

 necessary to be transmitted, the difference of temperature between the juice 

 to be heated or juice to be evaporated, and heating steam are known, the 

 requisite surface can be calculated by means of the coefficients of transmission 

 -already quoted. 



320 



