GB1445140A - Method and apparatus for recovering phase components from a mixture of solids and liquid - Google Patents

Abstract

1445140 Settling crystallised solids; centrifugal separators; crystal separation USS ENGS & CONSULTANTS Inc 12 Sept 1973 [12 Sept 1972] 42921/73 Headings B1D, BIG and B2P [Also in Division C1] A solids-liquids mixture, e.g. crystals and another liquor, is separated by passing the mixture to a separating zone, which may comprise a settling tank, a centrifuge or a dewatering screen, to separate the mixture into a predominantly liquid first region and a predominantly solids second region; withdrawing a stream of liquids and solids from the second region; and introducing a vapour of the same chemical nature as the liquid into the stream at a point downstream of the withdrawal to condense therein and thereby retard liquids flow from the separation zone and concentrate solids in the withdrawal stream. The mass in the second region must be sufficient to permit withdrawal of the solids against the pressure caused by the introduction of the vapour. Suitably, the withdrawal stream is led from the separation zone through a first generally vertical flow passage and then into a communicating generally horizontal flow passage into which the vapour is introduced. The horizontal passage should contain baffles to maintain the pressure of the introduced vapour therein whilst allowing solids flow, e.g. partitions having openings in their lower portions. The resulting solids fraction may be further dried by centrifuging or heating. The introduced vapour has the effect of forming pressure, density and temperature differentials within the separating zone which has a classifying effect with the largest particles becoming concentrated in the solids region and, in the case of a crystallised salt, and the growth of larger crystals of uniform size in the solids region whilst maintaining the suspension of very fine crystals in the liquid. Figure 2 shows a settling tank 20 having inlet 21, feeding into the interior of circular baffle 23, an overflow outlet and a conical lower portion, defining the solids region and leading to the solids outlet. The outlet communicates with a first vertical pipe 30 and a second horizontal pipe 31 into which the vapour is introduced 40. Pipes 32 remove the solids fraction for further drying, e.g. by centrifuging. The method of the invention may be used for the separation of crystallised soluble oxygen, nitrogen, sulphur and/or halide-containing inorganic salts, e.g. ammonium sulphates, phosphotos or nitrates, metallic oxides, crystallised organic material, e.g. naphthalene, or siliceous material from sludge or the flue from stack washing treatments. The Example relates to the separation of ammonium sulphate crystals from a mother liquor solution using steam as the introduced vapour.