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CHAPTER XV 



the gas cooled down to a temperature of 40° C. Various other forms of gas 

 washers are made ; in one, perforated plates take the place of the transverse 

 partitions described above. Any of the forms of jet condensers described in 

 connection with evaporation serve equally well as gas washers. 



In certain beet factories the gas evolved from the kiln is purified by being 

 passed through closely packed carbonate of soda or through a solution of this 

 substance ; the object of this procedure is to eliminate any sulphurous acid 

 which may be present, as the coke employed contains sulphur. 



Lime Kilns.— The carbon dioxide requisite for the carbonation process 

 is obtained by burning lime in kilns at the factory, which in this case makes 

 its own temper lime from crude limestone. Lime kilns are of two types, 

 continuous and intermittent, and the former, of course, is the type required foi 

 a sugar factory. They may also be classed as long flame and short flame kilns. 



In the former the fuel is burnt on a 



hearth, and the products of combustion 

 pass through the limestone in the kiln 

 proper. In the latter the fuel and lime 

 stone are mixed together and charged 

 into the kiln from above. Externally 

 fired kilns give a purer product, since no 

 contamination with the ash of the fuel 

 results. As, however, the ash of gas 

 coke, the fuel usually employed, is in- 

 soluble, this objection has for sugar 

 work little weight. The external-fired 

 kiln finds apphcation when wood or 

 lignite fuel is used. 



The early form of kiln consisted of a 

 truncated cone, as shown in Fig. 168, 

 of height up to 40 or 50 feet. The 

 limestone and fuel were charged into 

 the kiln from above and, as shown at 

 a, supplementary external furnaces 

 were sometimes provided. The burnt 

 hme was discharged through doors, h, 

 arranged around the base of the kiln, 

 the bottom of the kiln being built 

 sloping downwards and outwards. The 

 gas collected in the chambers, /, whence it passed by pipes g to the pumps. 



The present form of kiln is known as the Kern or Belgian kiln, and is 

 shown in Fig. 169. It consists of two opposed truncated cones, the upper one 

 being by far the longer. The mouth of the lower cone terminates about two 

 feet from the ground and immediately over a conical surface. The action 

 of the kiln is continuous, burnt lime gravitating on to the hearth, being 

 continuously removed as further charges are dumped into the kiln. 



The height of the Belgian or other form of kiln varies from a minimum 

 of 30 feet to a maximum of 70 feet. With less height decomposition of the 

 limestone is incomplete, and with a greater one the weight of the column of 

 limestone causes crushing of the lower strata. There is no limit, of course, 

 to the diameter. 



In American beet sugar houses, continuous rotary gas and oil-fired kilns 



Fig. I 68 



