Patent GB-759821-A (GB)
Title: Improvements in or relating to a method of calcining barium carbonate
IPC: C01F11/06
Filed: 1953-03-19
Abstract: <PICT:0759821/III/1> Barium carbonate granules of particle size greater than 80 mesh (Tyler) are calcined in a fluidized bed, generally at 800-1100 DEG C., although 1200 DEG C. and even higher temperatures can be used.  An inert fluidizing gas, preferably nitrogen, is used; carbon monoxide may be used at temperatures above 1050 DEG C.  At least 6 per cent of carbon by weight of the barium carbonate, and depending on the purpose for which the product is required, up to 20 per cent may be used.  Excess carbon remaining after calcination can be removed by heating in the presence of an inert gas and less than 20 per cent by volume of oxygen as disclosed in Specification 759,765.  In a modification a hydrocarbon gaseous at the calcination temperature, preferably methane but including ethane, ethylene, propane, propylene, butanes, butylenes, benzene and petroleum naphtha, may partially or wholly replace the inert gas, some or all of the carbon then being dispensed with, if desired, due to carbon formation in situ by cracking: e.g. 1-4 per cent carbon may be used.  Examples use methane/nitrogen mixtures. Oxygen water and carbon monoxide should not be present in inert fluidizing gases to an extent greater than about 1/2 per cent each, but may be removed by heating the gases in the presence of a hydrocarbon, or carbon (e.g. as a fluidized bed), before passing to the reactor.  The granules are generally prepared by mixing barium carbonate ground to minus 100 mesh and carbon (e.g. carbon black or petroleum coke) with a binder which forms carbon or carbon monoxide on calcination, such as a wheat-, corn- or rice-starch paste, or glue, sugar, syrup or molasses, and water, extruding or otherwise forming the mixture, drying at a low temperature, e.g. 100-150 DEG C., lightly crushing and screening. Alternatively granules prepared with little or no carbon may be penetrated with methane at cracking temperatures, e.g. 400-800 DEG C. to deposit carbon thereupon.  The fluidized bed is preferably established by first forming a bed of calcined barium oxide particles heating to calcination temperature and then introducing the barium carbonate granules: the bed should preferably contain at least 50 per cent and preferably 90 per cent by weight of barium oxide as disclosed in Specification 759,766, to minimize fusion.  Heat is supplied by heating the reactor walls and/or by preheating the gases: it may be augmented by the addition of hot barium oxide granules or by preheating the barium carbonate granules. In the apparatus shown, furnace 14 preheats the nitrogen, which is passed through tube 12 thereby fluidizing a bed of carbon (e.g. graphite) granules (or coarse inert materials) supplied from hopper 32, and is provided with heaters, e.g. gas burners: the calciner 22, 24 is similarly constructed.  The barium carbonate granules in a bin 52 are conveyed into the reactor 22 by the preheated gas and there calcined under fluidized conditions, the product being discharged at 60.  Examples are given in which the reactor (22) is slightly tapered downwardly.