PRILLING

摘要

1389821 Prilling FISONS Ltd 10 April 1972 [8 May 1971] 13893/71 Heading B5A A prilling head distributor plate has a plurality of bores the interior surface of which are of epoxy resin. Either the bores are coated with epoxy resin, or the plate is made thereof. Preferably, the plate is of mild or stainless steel with tubes of these materials, either integral or removable, forming the bores, the tubes being coated internally with epoxy resin and, preferably, coated externally with material which will not readily be wetted by the material being prilled. The external coating may be, e.g. a fluorocarbon, a mixture of ceramic and fluorocarbon, or a silicone rubber and may also be applied to the plate surface between the tubes. Alternatively, the plate may be of polytetrafluoroethylene in which case it need not be coated. Preferably, the tubes taper to a sharp nozzle rim (Fig. 2, not shown), and project below the plate. Suitable dimensions for all components are given. The epoxy resin coating is obtained by applying a prepolymer and curing in situ by catalyst and/or hardener of which examples are given. The epoxy resin prepolymer is preferably derived from epichlorhydrin and a bisphenol such as diphenylol methane, diphenylol propane or di-(dichlorophenylol)propane, a formula for the preferred type of bisphenol being given. The construction of a heated prilling head embodying such a distributor plate (Fig. 1, not shown), is described together with its use for prilling melts of ammonium nitrate, urea, ammonium nitrate/ammonium phosphate; mixtures of urea and potassium chloride or of ammonium nitrate and ammonium sulphate. The prilling tower may have a flexible lining of p.v.c. coated nylon or canvas or of p.v.c. or polyethylene sheeting. The molten material may have pressure waves induced in it by providing a transverse plate just above the distributor and reciprocating the former at 50 to 120 c.p.s. The droplets may fall through an upward stream of gas which may contain dust of the material being prilled, or of another fertilizer, or of some other material of which a large number of examples is given. A second fluidized bed of larger solid particles may be formed below this dust zone; these particles being of the same or different materials and formed either in the same or a separate gas stream.