GB730298A - Improvements in and relating to the manufacture of cyanamides - Google Patents

Abstract

In the production of alkali and alkaline earth metal cyanamides, particularly calcium cyanamide, by the reaction of the carbonate, with ammonia or the oxide with carbon dioxide or monoxide and ammonia at a selected reaction temperature above 600 DEG C., the ammonia is fed to the reaction chamber at a temperature at which decomposition thereof does not occur and which is below the selected reaction temperature and the oxide or carbonate is injected as a suspension in a carrier gas at a temperature lying sufficiently above the selected reaction temperature to supply the heat required to establish and maintain the selected temperature in the reaction chamber. Suitable temperatures are, for the ammonia, 400 DEG to 500 DEG C., for the lime, 1000 DEG C., and for the carbon mon- or dioxide, 400 DEG to 500 DEG C. A suitable apparatus is shown in Fig. 1 where a system A serves to convert calcium carbonate to lime and system B to convert the lime to calcium cyanamide. Calcium carbonate passes from hopper 1 to an injector 2 from which it is injected as a gaseous suspension into an externally-heated reactor 5, preferably as a helical flow along the heated walls. The lime after separation from the gases passes to a bunker 12. The gases drawn off by pipe 10 from separator 9 are passed through a cyclone separator 14 and a heat exchanger 17 where their heat is employed to preheat the ammonia gas entering at 18 and leaving at 19. The cooled waste gases leave at 20. The carbon monoxide or dioxide is preheated in regenerative heaters 52 and is fed to an injection device 23 (Fig. 2, described below). The lime/gas suspension is given a helical movement in entering reactor 46 through line 45 and ammonia is injected through lines 19 and at points 48 through openings in the reactor wall. The reaction products pass to a separator 53 from <PICT:0730298/III/1> <PICT:0730298/III/2> which solid calcium cyanamide is withdrawn at 54 and gases from pipe 55. The latter pass to a separator 56 and a cooler 58 in which water is deposited. The residual gases, still containing ammonia leave at 59 and may, after suitable enrichment be recycled to the cyanamide reactor. The injection device (Fig. 2) is fed with hot solids (i.e. lime in injector 23 or calcium carbonate in injector 2) through pipe 26, to pass through a conveyer worm 28 to a grinder 37. The solids pass between grinder members 37, 38 to an annular passage 39 to which several nozzles 40 open from lines 41 for the supply of carbon monoxide or dioxide. The suspension formed may be passed directly to the reactor. Specification 719,716, [Group II], is referred to.