THE CARBONATION PROCESS. 



Gas Washer. The carbon dioxide used in this process is, of course, 

 generated on the spot by burning limestone ; after being generated in the 

 kiln, the gas is passed through a gas washer, a form of which is shown in 

 Fig. 1JJ.9 ; it consists of an upright cylindrical vessel in which is placed a 

 series of transverse horizontal partitions e; in each of these, and projecting 

 a few inches, are fitted the funnels /; water is pumped into the vessel by 

 the pipe c and flows over the partitions, down through the funnels and out 

 through the pipe d. The gas from the kiln enters by the pipe a, the lower 

 end of which is perforated, and flows upwards in the direction indicated by 

 the arrows. In the passage of the gas the dust carried over is deposited and 

 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 for 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 

 limestone are mixed together and charged into the kiln from the top. It is 

 very general to use a combination of short and long flame burning. The latter 

 is more expensive as regards fuel, but gives a purer product, as in short flame 

 burning the lime is contaminated with the ash of the fuel. When using good 

 quality coke, with short flame burning, 2 per cent, of the product consists of 

 the ash of the fuel. When wood is used a rather larger percentage is 

 present. 



In Fig. 150 is shown a section of a continuous type of kiln very generally 

 used in beet factories, which can be employed as a long or short flame kiln, 

 or as a combination of both methods. The kiln consists of a tapering masonry 

 shaft of forty to fifty feet high ; the diameter at the base is fifteen feet, and 

 at the beginning of the curved portion twelve feet. Many kilns are built with 

 much narrower shafts a diameter of eight feet for a height of fifty feet not 

 being uncommon. The interior of the kiln is lined with fire-brick, d\ the 

 exterior being of common brick, e ; the whole is sometimes cased with iron 

 plates to prevent leakage of air through the masonry, and sometimes a layer 

 of non-conducting material is placed between the fire-brick and outer casing. 



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