Patent GB-824517-A (GB)
Title: Improvements in or relating to the separation and recovery of vaporous and gaseous oxides from gases
IPC: C01B25/12
Filed: 1957-12-10
Abstract: <PICT:0824517/III/1> Gaseous oxides, which can occur in various stages of oxidation, such as those of sulphur, nitrogen and phosphorus, are removed from industrial gases by bringing them together with some free oxygen, about 0.5 to 2%, into contact with a solid adsorption medium containing carbon particles, of preferably 3-10 mm., which is initially of low surface activity and which converts the oxides to a higher oxidation stage for which the adsorption medium has a greater adsorbing power than at the lower oxidation stage. Desorption of the adsorbed gaseous oxides is effected by raising the temperature of the adsorption medium to 300 DEG  C. or upwards when the carbon of the adsorption media effects reduction to a lower oxidation stage and the gases are recovered whereupon the medium is cooled and returned for further adsorption. Materials which may be employed are charcoal, peat coke, semi-coke made from coal or lignite and similar residues from the carbonization or organic substances without chemical or thermal activation before it is first brought into contact with the gas to be treated. Catalytically active substances which aid oxidation may be added to the adsorption agent while desorption may be aided by means of a scavenging gas.  The desorbed concentrated oxide may be recovered from the scavenging gas by washing with a solvent and/or adsorption upon a solid substance.  An adsorption shaft 1 is fitted with oblique plates 1a, over which the fresh and reactivated adsorption medium, which is fed in from a distributer device at the top, slides downwards and finally leaves the shaft at the bottom when charged with oxides while the gas to be purified enters the shaft at the bottom and leaves the shaft in a purified condition at the top.  A conveyer 2 transfers the charged adsorption medium to the top of desorption apparatus 3, consisting of a vertical shaft through which heating pipes 3a pass hot flue gas from an oil burner 4.  A waste heat section 5 is located in the bottom part of the desorption shaft, pipes 5a filled with boiler feed water enabling excess heat from the adsorption agent to produce steam.  About halfway up the waste heat section purified waste gas is introduced for scavenging, and this drives upwards the gas mixture produced during the desorption.  The adsorption agent, after it has been cooled down to a suitable temperature, leaves the desorption shaft 3 by a discharge device 6, passes through a vibratory screen 7, where dust, fines and ash are separated, and then is transferred by a further bucket conveyer 9 back to the adsorption shaft 1.  At the point 8, part of the circulating adsorption agent is tapped off for use elsewhere, for example for the removal of gumming agents from coke oven gas.  The gas mixture produced in the desorption phase and the scavenging gas added to it rise together in the desorption shaft and are taken to a washer 11, where the oxide or oxides are washed out, e.g. with water. The aqueous oxide solution passes through a heat exchanger 12 to column still 13, which is heated by means of steam from the waste heat utilizer, and the stripped liquid leaving the bottom of the column passes through the heat exchanger 12 and a cooler 14 once again to the washer 11.  The almost pure oxide leaving by the top of the column still 13 is then passed on for use or processing, for example to a sulphuric acid factory.