METHOD AND DEVICE FOR PRODUCING SULFURIC ACID

Abstract

A process for preparing sulfuric acid may involve melting elemental sulfur in a melting stage to give molten sulfur. Sulfuric acid is subsequently produced from the molten sulfur. Further, sulfur-containing offgases formed in the melting stage may be subjected to oxidation in a supplementary oxidation stage in which sulfur-containing components of the offgases are oxidized to sulfur dioxide. The process may further involve processing the sulfur dioxide to give at least one reaction product. The melting stage may be operated without emissions by processing all of the offgases from the melting stage. An apparatus may be employed for carrying out such a process.

Claims

1.-16. (canceled)

17. A process for preparing sulfuric acid, the process comprising: melting elemental sulfur in a melting stage to give molten sulfur; producing sulfuric acid from the molten sulfur; and subjecting offgases formed in the melting stage to oxidation in a supplementary oxidation stage in which sulfur-containing components of the offgases are oxidized to sulfur dioxide and the sulfur dioxide is processed to give a reaction product.

18. The process of claim 17 wherein the melting stage is operated without emissions by processing all offgases from the melting stage, wherein the offgases that are subjected to oxidation in the supplementary oxidation stage form at least a portion of all offgases from the melting stage.

19. The process of claim 17 wherein the melting stage is operated in a gastight manner.

20. The process of claim 17 comprising at least partly processing the sulfur dioxide in the offgases to give sulfuric acid.

21. The process of claim 17 comprising oxidizing the molten sulfur to sulfur dioxide in a first oxidation stage, oxidizing the sulfur dioxide from the first oxidation stage to sulfur trioxide in a second oxidation stage, and converting the sulfur trioxide into sulfuric acid in an absorption stage.

22. The process of claim 21 comprising introducing the sulfur dioxide from the offgases into the second oxidation stage to be oxidized to sulfur trioxide, wherein the sulfur trioxide is then converted into sulfuric acid in the absorption stage.

23. The process of claim 21 comprising: introducing the offgases after oxidation of the sulfur-containing offgas components together with process gas from the second oxidation stage into an intermediate absorption stage; and feeding sulfur dioxide from the offgases or from the process gas from the intermediate absorption stage into the second oxidation stage.

24. The process of claim 23 comprising conveying the offgases and the process gas from the second oxidation stage countercurrent to sulfuric acid in the intermediate absorption stage so that sulfur trioxide is absorbed from the process gas by the sulfuric acid.

25. The process of claim 17 comprising recovering thermal energy carried by the offgases after the oxidation in a heat recovery device.

26. An apparatus for preparing sulfuric acid, the apparatus comprising: a melting oven for melting elemental sulfur; a first oxidation facility that is connected to the melting oven, wherein the first oxidation facility is configured to oxidize molten sulfur to sulfur dioxide; a second oxidation facility configured to oxidize the sulfur dioxide from the first oxidation facility to sulfur trioxide; and a supplementary oxidation facility connected to the melting oven, wherein offgases formed while melting the elemental sulfur are configured to be taken off from the melting oven and at least partly fed to the supplementary oxidation facility, wherein the supplementary oxidation facility is configured to oxidize sulfur-containing components of the offgases to sulfur dioxide, wherein the second oxidation facility is configured to oxidize the sulfur dioxide from the supplementary oxidation facility to sulfur trioxide.

27. The apparatus of claim 26 wherein the melting oven is emission-free.

28. The apparatus of claim 26 comprising an intermediate absorption tower, which forms an intermediate absorption stage, connected to the supplementary oxidation facility, wherein the sulfur dioxide-containing offgases from the supplementary oxidation facility together with the process gas from the second oxidation facility are introduced into the intermediate absorption tower.

29. The apparatus of claim 28 comprising a heat recovery device connected to the intermediate absorption tower, wherein the heat recovery device recovers thermal and chemical energy from the offgases.

30. The apparatus of claim 28 wherein the second oxidation facility is configured as a multistage converter, with a first converter stage of the multistage converter being connected to the intermediate absorption tower such that process gas, after flowing through the first converter stage, is introduced together with the sulfur dioxide-containing offgases from the supplementary oxidation facility into the intermediate absorption tower.

31. The apparatus of claim 30 wherein a second multistage converter of the multistage converter is connected to the intermediate absorption tower such that offgases and process gas from the intermediate absorption tower is introduced into the second converter stage.

32. The apparatus of claim 26 wherein an absorption stage configured as an absorption tower is connected to the second oxidation facility, wherein sulfur trioxide coming from the second oxidation facility is absorbed in the absorption tower.

Description

DESCRIPTION OF THE FIGURES

[0015] The invention is illustrated below with the aid of a drawing which merely depicts one working example.

DETAILED DESCRIPTION OF THE FIGURE

[0016] The single figure schematically shows the flow diagram of an apparatus for carrying out the process of the invention for preparing sulfuric acid. The apparatus has a melting oven 1 for melting elemental sulfur (melting stage). In a particularly preferred embodiment of the invention, this melting oven 1 is made emission-free or emission-tight. This means, in particular, that, apart from the offtake described below of the offgases from the melting oven 1, no emissions or offgases are released into the surroundings. The melting in the melting oven 1 is advantageously carried out with exclusion of air. The sulfur to be melted is preferably supplied (arrow in the figure) to the melting oven 1 via a lock device which is preferably configured as a star feeder 6 as is shown in the working example.

[0017] The molten sulfur is conveyed from the melting oven 1 into a first oxidation facility 2 which is preferably configured as a burner, as shown in the working example. Here, the molten sulfur is oxidized or burnt with the aid of atmospheric oxygen so as to form sulfur dioxide (SO.sub.2). The air fed to the first oxidation facility 2 (arrow in the figure) is dried beforehand in a drying tower 7, for example with the aid of concentrated sulfuric acid.

[0018] The sulfur dioxide formed in the first oxidation facility 2 is subsequently introduced into the second oxidation facility 5 configured as a converter.

[0019] In the second oxidation facility 5 or in the converter, the sulfur dioxide is oxidized to sulfur trioxide (SO.sub.3) by means of a catalyst, preferably by means of vanadium pentoxide (V.sub.2O.sub.5). The sulfur dioxide preferably flows from the top downward through the converter, as shown in the working example. A plurality of catalyst trays 8 is provided here. From this second oxidation facility 5 or from this converter, the sulfur trioxide or the sulfur trioxide-containing process gas is fed to an absorption stage in the form of a final absorption tower 9. In this final absorption tower 9, sulfuric acid is formed from the sulfur trioxide. For this purpose, the sulfur trioxide-containing process gas is preferably, as depicted in the working example, conveyed in countercurrent to sulfuric acid or dilute sulfuric acid, in the working example 98.5% strength-99.5% strength sulfuric acid. As a result, the sulfur trioxide is absorbed in the sulfuric acid and the sulfuric acid is at the same time concentrated. This concentrated sulfuric acid is subsequently diluted again with water, depending on requirements and the desired dilution.

[0020] The converter forming the second oxidation facility 5 is preferably configured as two-stage converter, as shown in the working example. According to recommended measures and as shown in the working example, process gas is, after passing through the first converter stage 10 with the catalyst trays 8 arranged there, introduced as SO.sub.2- and SO.sub.3-containing process gas from the first converter stage 10 into the intermediate absorption stage configured as intermediate absorption tower 11. The process gas is preferably, as in the working example, introduced from below into the intermediate absorption tower 11 and conveyed in countercurrent to dilute sulfuric acid, for example 98.5% strength-99.5% strength sulfuric acid. In this way, sulfur trioxide is absorbed from the process gas into the sulfuric acid and the sulfuric acid is concentrated. At the upper end of the intermediate absorption tower 11, the process gas or the sulfur dioxide-containing process gas is advantageously recirculated into the converter, namely into the second converter stage 12 with its catalyst trays 8 arranged below the first converter stage 10 in the working example. The sulfur dioxide present in the process gas is catalytically oxidized to sulfur trioxide in the second converter stage 12 and the sulfur trioxide is then, as described above, taken off at the lower end of the converter and introduced into the final absorption tower 9.

[0021] According to the invention, the sulfur-containing offgases formed in the melting stage or in the melting oven 1 during melting are subjected to oxidation. For this purpose, these offgases are, in the working example, taken off via the offtake conduit 3 from the melting oven 1 and fed into the supplementary oxidation facility 4. The supplementary oxidation facility 4 preferably has, as shown in the working example, a burner which is supplied with fuel, e.g. natural gas, (arrow in the figure) and the elemental sulfur (S) present in the offgas and also the hydrogen sulfide (H.sub.2S) present in the offgas are oxidized to sulfur dioxide with the aid of atmospheric oxygen in this supplementary oxidation facility 4. In the working example as shown in the figure, a blower 13 by means of which the offgases can be fed to the supplementary oxidation facility 4 is provided. It is also possible for a sufficiently high pressure to be built up in the melting oven 1, especially as a result of the water vapor present in the offgas, so that such a blower 13 is not necessary. The water vapor present in the offgases arises particularly when, according to one variant, the sulfur introduced into the melting oven 1 has been moistened for safety reasons. The offgases leaving the melting oven 1 contain first and foremost sulfur dioxide (SO.sub.2), elemental sulfur (S), hydrogen sulfide (H.sub.2S) and water vapor (H.sub.2O). After oxidation of the sulfur-containing offgas components S and H.sub.2S in the supplementary oxidation facility 4, the offgases comprise essentially sulfur dioxide (SO.sub.2) and water (H.sub.2O) in addition to nitrogen and oxygen.

[0022] The sulfur dioxide-containing offgases exiting from the supplementary oxidation facility 4 are, according to recommended measures and as shown in the working example, introduced together with the process gas from the first converter stage 10 into the intermediate absorption tower 11. The sulfur dioxide-containing offgas is thus conveyed with the process gas in countercurrent to the abovementioned sulfuric acid. As a result, the water vapor present in the offgases is absorbed by the sulfuric acid, so that the concentrating effect of the sulfur trioxide on the sulfuric acid is partially compensated for by the water taken up. In this way, water required for dilution of the concentrated sulfuric acid collecting at the lower end of the intermediate absorption tower 11 can be saved.

[0023] A particular aspect of the process of the invention is the preferred recovery of the thermal and chemical energy arising in the process. For this purpose, a heat recovery device 14 is preferably, and as shown in the working example, connected to the lower end of the intermediate absorption tower. The hot concentrated sulfuric acid can be taken from the bottom of the intermediate absorption tower and fed to the heat recovery device 14 where heat can be transferred to water or steam, so that the thermal and chemical energy can preferably be conveyed and utilized further in the form of low-pressure steam.