SE417700B - PROCEDURE FOR PRODUCING SULFURIC ACID - Google Patents

Abstract

The present invention relates to a contact process for producing sulfuric acid from gases containing more than 10% by volume SO2 and which gives a maximum amount of surplus heat in an economical manner and is utilized for an increase in the concentration of dilute sulfuric acids. This improved process comprises the following steps: (a) combining the production of sulfuric acid with an increase of the concentration of dilute sulfuric acid; (b) adding oxygen-containing gases to a partial stream of SO2-containing gases at such a rate that the gas mixture can be reacted at least in a first contacting tray until the reaction has proceeded to an equilibrium below or at the highest temperature which is permissible for the catalyst; (c) heating said resulting gas mixture to the operating temperature of said first contacting tray by subjecting it to heat exchange with hot sulphur trioxidecontaining gases flowing between contacting trays; (d) adding the remaining SO2-containing gas to the sulphur trioxide-containing gas from at least the first contacting tray of the first catalytic reaction stage; (e) controlling the rate at which the partial stream of SO2-containing gases is fed to, the first contacting tray so that SO3 is produced in step (b) at such a rate that the ratio of SO2:SO3 in the mixture produced in step (d) is such that the reaction in the following contacting trays can proceed to an equilibrium below or at the highest temperature which is permissible for the catalyst; (f) removing SO3 from the catalytically reacted gases by interstage and final absorption at operating temperatures of 100-200.degree.C; (g) conducting the catalytic reaction in the second catalytic reaction stage in at least two contacting trays and cooling the gases between the contacting trays; (h) expelling water from the dilute sulfuric acids by directly contacting the acids with hot gases consisting of the contact process exhaust gases which have been subjected to final absorption or of inert gases having a low water content, or a mixture thereof; (i) heating the expelling gases with at least part of the heat which becomes available in the final heat exchanger, which follows the second catalytic reaction stage; (j) heating the expelling gases with at least part of the heat which becomes available during the cooling of the catalytically reacted gases in step (g) or with at least part of the heat which becomes available in the second cooling stage which follows the first catalytic reaction stage and precedes the interstage absorption, or both and (k) using the heat energy derived from the acids which are circulated through at least one of the devices in the group comprising the dryer, the interstage absorber and the final absorber so as to increase the concentration of or to preheat the dilute sulfuric acid, or both.