GB474191A - Improvements in the cooling of gases - Google Patents

Abstract

Hot gases or vapours are cooled by injecting a liquid of a different chemical nature, preferably water, in a finely distributed state at a temperature which is (a) equal to or above its boiling point at the pressure of the gases to be cooled, and (b) below the temperature of the said gases. The complete evaporation of the injected water thus ensured is useful in processes, such as the obtaining of gases by roasting pyrites, where the presence of liquid water is deleterious to the constructional materials of the apparatus. The water, heated directly or indirectly, may be forced through atomizing nozzles arranged in known manner. The superheated pressure water may be obtained from the feed water for a boiler. Preferably the temperature of the liquid under pressure should be at least 5 DEG C. above its boiling point at the gas pressure. The invention is applicable to exothermic catalytic reactions in which the main part of the gases involved is converted by means of a first contact layer, the final conversion being effected by means of a second contact layer and the gases being cooled between the two stages. Such processes are used, for example, for producing hydrogen and carbon monoxide from hydrocarbons and steam, or for oxidizing sulphur dioxide, in the synthesis of ammonia from nitrogen and hydrogen, liquefied ammonia being preferably injected in this case between the contact layers for cooling the gas, or in the synthesis of hydrocarbons from carbon monoxide and hydrogen, superheated hydrocarbons being preferably injected between two or more contact layers. The invention is also useful when products formed are to be prevented from decomposing by cooling them rapidly, as in the production of oxides of nitrogen by combustion of ammonia in the production of unsaturated hydrocarbons by thermal decomposition. A quantitative example is given to illustrate the application to the cooling of sulphur-containing gases obtained by the Claus process. These gases having a temperature of 400 DEG C. are cooled down to 150 DEG C. by the injection of finely atomized water at a temperature of 125 DEG C., the whole of the sulphur being condensed into the liquid phase. One third of the sulphur precipitates as a liquid in the vaporizer sump and is continuously withdrawn by means of a heated overflow pipe; the bulk of the sulphur is separated on an electrofilter arranged behind the cooler.