GB995207A - Improvements in or relating to the purification of gas mixtures - Google Patents

Abstract

<PICT:0995207/C1/1> In the process of the parent Specification for decreasing the concentration of nitric oxide in a gas mixture at least to a level at or below which any nitric oxide remaining is not deleterious for the use to which the treated gas mixture is to be put, the chlorine dioxide used to oxidize the nitric oxide to nitrogen dioxide is prepared by reacting an aqueous solution of sodium chlorite with an aqueous solution of another substance which will react with sodium chlorite to form chlorine dioxide but which does not contain free chlorine and does not liberate free chlorine on reaction with sodium chloride or with chlorine dioxide. The second aqueous solution may be of an acid, e.g. sulphuric acid, hydrochloric acid, an acid salt, e.g. sodium dihydrogen phosphate NaH2PO4, a reducing agent, e.g. ferrous sulphate or an oxidizing agent, e.g. potassium permanganate. In the apparatus of Fig. 2, 2b is a device for measuring the quantity of incoming gas mixture, 27 measures its effective pressure, 28 is a gas analysis with, e.g. a photo-electrically operating colorimeter for detecting nitric oxide and 29 is a computer for continuous calculation of the quantity of nitric oxide to be removed. The computer results are applied to the operation of a regulator 30 which controls the speed of motor 3. Motor 3 drives metering pumps 1 and 2 which continuously supply the two aqueous solutions from containers 5 and 6 to the head of wash column 7, where the washing liquid dripping through treble cap plates 8 flows counter to a stream of nitrogen carrier gas fed in at 9, and metering pumps 18, 19, pump 19 being used to spray or washing solution, e.g. of sodium thiosulphate in a solution of sodium hydroxide, carbonate or bicarbonate through nozzle 22 into the gas mixture to be purified. In the apparatus of Fig. 1 (not shown), the equipment for automatic supply of the reactant solutions, and also the washing arrangements 19-22 are omitted.ALSO:In the process of the parent Specification for decreasing the concentration of nitric oxide present in a gas mixture such as town gas, illuminating gas, producer gas, coke oven gas, coal gas, converter gas or flue gas at least to a level at which any nitric oxide remaining is not deleterious for the use to which the treated gas mixture is to be put, the chlorine dioxide used to oxidize the nitric oxide to nitrogen dioxide is prepared by reacting an aqueous solution of sodium chlorite with an aqueous solution of another substance e.g. an acid or acid salt, a reducing agent or an oxidizing agent which will react with sodium chlorite to form chlorine dioxide but which does not contain free chlorine and will not liberate free chlorine on reaction with sodium chloride or chlorine dioxide. A continuous process is described wherein the rate of supply of the aqueous solutions is continously controlled by means sensitive to the nitric oxide content of the incoming gas mixture.