GB429267A - Process of and apparatus for the recovery of sulphuric acid by condensation - Google Patents

Abstract

<PICT:0429267/III/1> In recovering sulphuric acid by condensation from dilute gases containing sulphur trioxide and at least sufficient water vapour for the conversion of the sulphur trioxide into sulphuric acid, a reduced rate of cooling is maintained which prevents any quenching of the gases between the dew point and 140 DEG C. while effecting the condensation within the inner of two concentric tubes separated by an intermediate space which preferably contains a filling composition, the outer tube being constructed of a strong material such as iron, the inner tube being constructed of a material of high chemical resistance and low heat conductivity such as ceramic material, ferrosilicon or high silicon steel, and the combination of concentric tubes being externally cooled. Gases or a liquid, such as oil, boiling water or water under pressure at a temperature above 100 DEG C., may be employed as a cooling medium. The temperature of the cooling water may rise to 150 DEG C. thus generating steam under a pressure of 4 atmospheres. The gases may enter the condenser at a temperature at or slightly above the dew point, say 340 DEG C., the condensation taking place at temperatures down to 140 DEG C. Preferably, the gases enter the bottom of the column and issue at the top, the condensate flowing downwards in counter-flow. In this way 94 per cent acid may be recovered. As shown, the condenser consists of an outer shell a and tubes b inserted therein. Each tube b comprises an outer tube c exposed to the cooling medium and made of a material such as iron and an inner tube d exposed to the acid and made of ceramic material. The space between the tubes is preferably filled by a filling material c, such as lead-antimony or the like acid resisting alloys, acid resisting cement or powders such as powdered metals or fine sand. The gases enter through a tube g and leave by a stack k while the sulphuric acid collects in a chamber h and is withdrawn through a syphon i. The tubes may be provided with fillers. The Specification as open to inspection under Sect. 91 is not restricted to the maintenance of the reduced rate of cooling by operating in a condenser of the kind described above. It also describes the production of highly concentrated sulphuric acid in the presence of excess of water vapour by fractional condensation. The condensation may also be effected with the gases and condensate passing in parallel flow. The condenser may be irrigated with sulphuric acid. The examples describe the conversion of gases containing sulphur-dioxide and water vapour into sulphur trioxide by the action, at 450 DEG C., of a catalyst comprising silica, potassium oxide and vanadium oxide, the resulting gases being first cooled down to 340 DEG C. by heat exchange with the gases to be converted and then being uniformly cooled down to 150 DEG C. in a tower in periods of from 0,2 to 2 seconds. According to one example, the speed of flow of the gases through the condenser tube is sufficient to produce a strong turbulence. This subject-matter does not appear in the Specification as accepted.