Process and apparatus for drying liquid-borne solid material

摘要

A method and apparatus are disclosed for continuously drying, preferably with agglomeration and/or coating and sizing, and separating a solid product from a liquid feed material, especially bauxite slurry which passes through a very sticky phase during drying, without significant encrustation of the equipment used. The apparatus comprises a drying vessel (1, 101) having a lower inlet (2, 102) for a drying gas and an upper outlet (7, 107) for a mixture of the drying gas and entrained dried particles of solid material, an upwardly directed spray nozzle (5, 105) for the liquid bearing solid material positioned within the lower inlet (2, 102) for the drying gas but spaced from the walls thereof, means (8, 10, 108, 110) for separating the entrained dried particles from their mixture with the drying gas, means (17, 117) for returning the separated dried particles to the drying vessel (1, 101), wherein the lower portion of the drying vessel (1, 101) is shaped to guide descending particles of the solid material being dried by the drying gas and those being returned by the separating means (17, 117) back towards the drying gas inlet (2, 102), and an outlet (21, 121) for the dried particles, characterised in that the apparatus includes means for continuously removing the dried particles positioned with their outlet (21, 121) below the spray nozzle (5, 105) and in that the drying gas inlet (2, 102) is arranged to supply the drying gas into the drying vessel (1, 101) past the spray nozzle (5, 105) in substantially parallel flow leaving a lower moving boundary layer adjacent the walls of the drying gas inlet (2, 102) through which dried particles can fall under gravity towards their outlet (21, 121), when the apparatus is in use. Average particle sizes for the dried particles of at least 0.5 mm, and preferably from 2 to 15 mm, are attainable. IMAGE