GB580991A - Improvement in a process of and system for the softening of water - Google Patents

Abstract

580,991. Softening water. TRIGGS, W. W. (Dorr Co.). Sept. 8, 1944, No. 17193. [Class 46] A water-softening process producing a sludge containing suspended particles of calcium carbonate and magnesium hydroxide includes the step of subjecting the sludge to centrifugal forces so as to cause segregation of the sludge into a cake consisting substantially of calcium carbonate particles and into an effluent the suspension in which contains a substantial portion of the magnesium hydroxide particles. The cake is calcined to convert the calcium carbonate into lime suitable for use in the process. In the arrangement shown, water is fed to a mixer 1 and treated with soda ash and lime. The liquid with precipitates is then conveyed to a flocculating tank 2 containing slow-moving paddles. Afterwards the liquid is led to a sedimentation tank 3 where calcium carbonate and magnesium hydroxide settle out. The effluent passes to a tank 4 where it is treated with carbon dioxide. The resulting calcium carbonate is carried with the liquid to a flocculation tank 5 thence to a settling tank 6. The effluent from the tank 6 is softened water. The sludge from the two settling tanks 3, 6 is conveyed by pipe 26 to a centrifuge 7, where the main portion of the calcium carbonate is separated in the form of.a cake from most of the magnesium hydroxide which flows away with the effluent. The cake is delivered to a kiln 8 where it is calcined, the carbon dioxide being utilized in the tank 4 and the lime being conveyed to a slaker 9. The slaked lime is conveyed to the mixer 1. If the water to be softened contained soluble iron and aluminium compounds these are removed in the form of hydroxides, with the magnesium hydroxide.