FOERFARANDE FOER FRAMSTAELLNING AV SVAVELTRIOXID

1. Process for the preparation of sulphur trioxide by the contact process employing the fluidised bed technique, wherein SO2 -containing gases are reacted with oxygen-containing gases in a single-stage fluidised bed of catalyst material to give sulphur trioxide and the temperature of the catalyst mass is controlled by heat exchangers, characterised in that the height of the single-stage fluidised bed in the fluidised state is about 0,1 to 2 m, the average particle size of the catalyst mass is between about 0.4 and 2 mm, the gas velocity in the empty reactor chamber is between about 0.1 and 0.6 mN /sec, the velocity after the bottom of the inlet chamber has been reached and before contact with the catalyst particles is less than or equal to 9 mn /sec, wherein over 90% of the SO2 -containing gases, which have a temperature of about 20 degrees C to 700 degrees C and a content of sulphur dioxide of up to 66,7%, are converted into sulphur trioxide, the SO3 -containing reaction gases are fed to an intermediate absorption step and the gases freed from sulphur trioxide are reacted within a single stage or two stage catalyst and for the control of temperature steam from a constant pressure heat accumulator which is arranged separately from the reaction chamber and is filled with boiling water is forced, as the cooling medium, through the reaction chamber, in several sequences, is superheated therein and in each case subsequently recooled in the heat accumulator by indirect evaporation cooling, the steam being kept at a constant pressure in the heat accumulator by choosing the number of superheating and recooling sequences such that the ratio of the sum of enthalpy differences of the recooling stages to the enthalpy difference between the saturated steam and the feed water supplied is at least 1.1.