GB1040809A - Improvements in or relating to the manufacture of a non-oxidizing gas - Google Patents

Abstract

<PICT:1040809/C1/1> A non-oxidizing gas mixture containing at least 80% by volume of nitrogen is produced by (a) burning a hydrocarbon in air (b) decomposing gaseous ammonia by heat using part of the heat produced in (a), (c) mixing the gases obtained at the end of steps (a) and (b) and eliminating free oxygen from the mixture by reaction of the oxygen with hydrogen present in the mixture in the presence of a catalyst. The hydrocarbon may be burned in the presence of 1 to 3% excess air. The gas may contain hydrogen and/or carbon monoxide and/or methane. The hydrocarbon may be propane. Air is compressed in blower 2 and passed through flowmeter 4 to burner 5. Propane supplied at 8 is fed through coil 9 of vaporizer 10, through pressure regulating device 12, through flowmeter 6 into burner 5. From burner 5 the combustion gases are discharged into chamber 14 lined with refractory material which contains ammonia cracking device 16. The combustion gases pass into vaporizer 10 where they heat the water serving as heating fluid for the vaporizer coils and are themselves cooled, into coil 17 of water cooler 18 and into gasometer 20. Water trap 24 permits condensed water to be removed. Liquid ammonia introduced at 26 is vaporized in coil 27 of vaporizer 10, expanded in pressure regulating device 28, fed through flowmeter 30 and sent to ammonia cracking device 16 wherein ammonia is decomposed into hydrogen and nitrogen in the presence of a catalyst say based on iron or nickel by the heat produced in burning propane. The gas leaving the cracking device is mixed at 32 with the combustion gases leaving coil 17. The gas mixture is compressed in compressor 34 and passed to column 36 which is lined with rings over which trickles water supplied by pump 38. The water absorbs CO2 and leaves the column at 40. The gas mixture then enters apparatus 42 which contains a platinum group metal catalyst, e.g. a palladium catalyst which causes oxygen and hydrogen in the gas mixture to react. The catalyst may be heated to 300 DEG C. The gas mixture then passes through coil 43 of cooler 18 at the outlet of which an automatic purifier 44 discharges condensed water, and fed to adsorber 50 or 52 filled with say artificial zeolite to remove residual carbon dioxide and water. One of the adsorbers may be for purifying while the other is being regenerated. Regeneration may be effected by lowering the pressure by connecting the adsorber to the gasometer and flushing with a current of gas to be purified. Gases of the following composition may be obtained: 90% N2 + 10% H2; 98% N2 + 2% H2; 96% N2 4% CO; 96% N2 + 2% CO + 2% CH4. The carbon dioxide content may be less than 0.10%, and the dewpoint - 70 DEG C. A tank of solid caustic soda at the outlet of the adsorber or finishing the regeneration of the adsorbers in vacuo lowers the CO2 content further. Mixtures containing CO2 may be obtained by stopping the cracking of the ammonia and the operation of the adsorbers and by moderating or preventing the introduction of water into column 36. The gases may be used in metallurgical reactions such as bright annealing and cementation.