Patent GB-1058261-A (GB)
Title: Process for the production of so, and/or sulphuric acid by the catalytic conversion of so-containing gases
IPC: C01B17/765
Filed: 1964-01-30
Abstract: <PICT:1058261/C1/1> In the conversion of gases containing at least 9% by volume SO2 to SO3 and/or sulphuric acid by passage of the gases through a multi-stage catalytic converter, the SO3 from the part-catalyzed gases is absorbed in acid in an intermediate dip absorber before the gases enter the final stage of the converter, and the SO3 from the gases leaving the final stage of the converter is absorbed in a final absorber. Excess heat resulting from the catalytic process is removed by heat exchange between gases containing SO3 and a cooling medium not introduced into the circulation system of the converter and is used to heat feed water or to produce low pressure steam.  At least a major portion of the incoming gases is preheated by heat exchange with gases containing SO3. The part-catalyzed gases are cooled before they enter the intermediate absorber by heat exchange in a first heat exchanger with outflowing gases from the intermediate absorber free from SO3, which gases are heated to a temperature sufficient to initiate conversion in the final catalytic stage, and in a second heat exchanger to a temperature which will result in the intermediate absorption taking place at a temperature between 170 DEG  and 250 DEG  C., preferably at 200 DEG  C.  Absorbing acid containing SO2 is preferably degasified of SO2 in the intermediate absorber, the degasified acid preferably being able to overflow into the final absorber.  In the embodiment illustrated in Figure 1, after passing through drying tower 2 and blower 5, the major part of the gases containing SO2 is preheated in second heat exchanger 8, further preheated in either of heat exchangers 12 and 15, passed through the first catalytic stage 18 of a multi-stage catalytic converter 19, mixed at 21 with the remainder of the starting gases, cooled by heat exchange with starting gases in heat exchanger 15, passed through second catalytic stage 25, cooled by heat exchange with starting gases in heat exchanger 12, passed through third catalytic stage 28, cooled in first and second heat exchangers 30 and 8 forming the intermediate heat exchanger 9, and passed into the dip tube 32 of intermediate absorber 33 where SO3 is removed.  After leaving this absorber, the gases are heated by heat exchange with the part-converted gases in first heat exchanger 30, passed through the final catalytic stage 36, cooled in economizer 38 by heat exchange with the medium not introduced into the circulation system of the converter, and passed to the final absorber 40 from which spent gases pass to atmosphere via pipe 42.  Acid may overflow from intermediate absorber 33 via pipe 43 to final absorber 40 from which acid is withdrawn via pump 46, cooler 47 and pipe 48.  Exchange or drying acid passes via pipe 49 to drier 2 from which it is withdrawn via pump 51, part passing to intermediate absorber 33 via pipe 52 and part returning via cooler 53 to drier 2 as spray acid.  Fig. 2 (not shown), illustrates a similar process in which second heat-exchanger 8 and economizer 38 are interchanged, the major part of the incoming gases being preheated by heat exchange with the gases leaving the final catalytic stage, and heat exchange in the second heat exchanger being with the cooling medium not introduced into the circulation system of the converter. The prior art is fully discussed in the Specification, numerous references being given.  Reference has been directed by the Comptroller to Specification 956,049.