GB589241A - Improvements in and relating to the manufacture of oleum - Google Patents

Abstract

Oleum is produced by absorbing sulphur trioxide from converter or like gas in weak oleum which in dispersed condition and in contact with a horizontally disposed heat exchange surface contacts the gas, the temperature of a cooling medium which is circulated in indirect heat exchange with the oleum past the heat exchange surface being controlled at a predetermined figure by passing relatively cold water in heat exchange with the cooling-medium. The gases containing sulphur trioxide are forced by a blower 2 through a chamber 3 and projecting inlets 4 up through a tower 1 and escape through outlet 7. Oleum of absorption strength is circulated in a closed circuit comprising the tower 1 and a reservoir 8. Weak acid enters the reservoir 8 by a pipe 19 and is mixed with the effluent from the tower 1 prior to being elevated by pump 9 to the top of tower 1, whence it is distributed as a film over cooling elements 10 by a distributor 11, and returned by way of pipe 6, de-gassing unit 12, and pressure equaliser 13, and pipe 14 to a pipe 15 at the bottom of the reservoir from which a proportion of the product-acid (i.e. oleum produced) is conducted via pipe 16 which forms a hydrostatic column 17, to storage and the remainder escapes through an annular outlet 15a to the acid in the reservoir. An automatic analyzer 18 actuates a control valve 19a to increase or decrease the flow of weak oleum according as the product acid is too strong or too weak. Continuous circulation of cooling medium is maintained by a pump 22 which causes the cooling medium to flow, prefer ably <PICT:0589241/III/1> upwardly, through the cooling elements 10 and out through pipe 23 into receiver 24, from which it is withdrawn to the intake of pump 22 where it mingles with cold water pumped from a suitable source. An automatic temperature-responsive controller, situated at 30, actuates a control valve 31 to increase or decrease the amount of surface water introduced into the cooling circuit. Gas that collects in the top of the degassifier 12 is returned to the bottom 3 of the absorption tower, and the oleum withdrawn from the unit 12 passes into the element 13, which is a hydrostatic column for equalizing the pressures, where any sulphur trioxide liberated is returned through pipe 38 to the reservoir 8. This continuous process is suitable for the production of oleum of various strengths, and consequently the ratio by weight of the weak acid fed to the system and the acid circulated to the tower may vary between the preferred limits of 3 : 1 and 8 : 1.