Chemistry of pulp and paper making . ompany have recently proposed to caustidzeand wash the Ume mud ia a continuous operation by machinerysimilar to that used in metallurgical work. The lime is crushedand continuously mixed in definite proportions with a sodaash solution; the mixture then passes through three reactionagitators which are furnished with steam coils and then goesto the first thickener. The clear liquor overflowing from thisgoes to the storage tank for cooking liquor, while the sludge ispumped to the second thickener where it is mixed with theoverflow from a third thickener. The c
Chemistry of pulp and paper making . ompany have recently proposed to caustidzeand wash the Ume mud ia a continuous operation by machinerysimilar to that used in metallurgical work. The lime is crushedand continuously mixed in definite proportions with a sodaash solution; the mixture then passes through three reactionagitators which are furnished with steam coils and then goesto the first thickener. The clear liquor overflowing from thisgoes to the storage tank for cooking liquor, while the sludge ispumped to the second thickener where it is mixed with theoverflow from a third thickener. The clear liquor from thesecond thickener flows to the reaction agitators, while the sludgegoes to the third thickener and thence to waste or to a recoveryplant for Ume. A causticizing plant of this type is shown inplan in Fig. 9. A plant operated in this manner has been inoperation for some time and is said to be giving good satisfac-tion. It seems doubtful if it is very much superior to a carefullysupervised plant of the ordinary hi o g oU (lOl) I02 THE SODA PROCESS The lime mud produced in causticizing is generally a wasteproduct, though there is sometimes a small local demand foragricultural purposes. Attempts have been made to reburnthe mud and use the Hme over again and a number of plantsare now operating with rotary kilns similar to those used in thecement industry. The lime mud is freed from water as muchas possible by mechanical means and then enters the kiln,through which it passes in a direction opposite to the combus-tion gases. It is first dried and then heated to such a tempera-ture that the carbon dioxide is driven off and the materialdelivered as burned Ume. A kiln 7 ft. in diameter and 120 wiU bum 35 to 40 tons of hme per day, while for capacitiesbetween 20 and 30 tons a kiln 6 ft. by 100 ft. is sufficient. Ifthe mud enters at 55 per cent dry, the fuel requirements willbe about 9500 cu. ft. of natural gas or 675 lbs. of coal per tonof lime burned. In
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