METHOD AND DEVICE FOR PRODUCING SULFURIC ACID

Abstract

In a production mode a process for preparing sulfuric acid may involve oxidizing sulfur to sulfur dioxide in a first oxidation stage, and catalytically oxidizing the sulfur dioxide to sulfur trioxide in a second oxidation stage. The sulfur trioxide may be absorbed in at least one absorption stage. In the production mode, process gases from a last of the at least one absorption stage with respect to a flow direction are discharged. In a standby mode of the process, at least one heating stage for heating the process gases is connected. The process gases exiting from the at least one absorption stage are conveyed to the heating stage, and the process gases are circulated via the heating stage, the second oxidation stage, and the absorption stage.

Claims

1.-10. (canceled)

11. A process for preparing sulfuric acid, wherein in a production mode the process comprises: oxidizing sulfur to sulfur dioxide in a first oxidation stage; catalytically oxidizing the sulfur dioxide to sulfur trioxide in a second oxidation stage; and introducing the sulfur trioxide into at least one absorption stage for absorption of the sulfur trioxide, wherein process gases are discharged from the at least one absorption stage in a flow direction, wherein in a standby mode the process comprises: heating the process gases in a heating stage disposed upstream of the second oxidation stage with respect to the flow direction of the process gases, wherein the process gases exiting from the at least one absorption stage are fed or recirculated to the heating stage and the process gases are circulated via the heating stage, the second oxidation stage, and the at least one absorption stage.

12. The process of claim 11 wherein in the production mode the process comprises feeding sulfur and air for the oxidation to the first oxidation stage, wherein in the standby mode the process comprises stopping the feeding of sulfur and at least throttling back on the feeding of air.

13. The process of claim 11 wherein in the standby mode the process comprises conveying the process gases from the at least one absorption stage, bypassing the first oxidation stage, to the heating stage and from the heating stage to the second oxidation stage.

14. The process of claim 11 wherein the process gases are, after passing through a first part of the second oxidation stage, discharged from the second oxidation stage and in the production mode of the process, conveyed through an intermediate absorption stage of the at least one absorption stage and subsequently recirculated to the second oxidation stage where the process gases pass through a second part of the second oxidation stage, and in the standby mode of the process, recirculated via a closeable bypass conduit to the second oxidation stage, bypassing the intermediate absorption stage.

15. The process of claim 14 wherein after the process gases pass through the second part of the second oxidation stage, both the production and standby modes of the process comprise introducing the process gases into the at least one absorption stage or a final absorption stage of the at least one absorption stage.

16. The process of claim 14 wherein the standby mode of the process comprises at least throttling back a discharge of the process gases from the absorption stage in the flow direction and introducing the process gases into the heating stage.

17. An apparatus for preparing sulfuric acid, the apparatus comprising: a first oxidation facility for producing sulfur dioxide; a second oxidation facility connected to the first oxidation facility for oxidation of the sulfur dioxide to sulfur trioxide; and at least one absorption apparatus that is connected to the second oxidation facility for absorbing the sulfur trioxide, wherein a last absorption apparatus of the at least one absorption apparatus with respect to a flow direction of the process gas discharged from the at least one absorption apparatus includes a closeable discharge conduit and a closeable process gas conduit, wherein the closeable discharge conduit is open and the closeable process gas conduit is closed in a production mode of the apparatus and the closeable discharge conduit is closed and the closeable process gas conduit is open for circulation of the process gases in a standby mode of the apparatus, wherein the process gas conduit is connected to a heating device for heating the process gases, with the heating device being connected via a connecting line to the second oxidation facility so that heated process gases from the heating device are introducible into the second oxidation facility in the standby mode of the apparatus.

18. The apparatus of claim 17 comprising a blower, wherein in the production mode oxygen or air for oxidation of the sulfur is introducible into the first oxidation facility by way of the blower, wherein in the standby mode process gases are conveyable by way of the blower from the closeable process gas conduit to the heating device.

19. The apparatus of claim 17 wherein the second oxidation facility is configured as a multistage converter, wherein each converter stage of the multistage converter comprises a catalyst tray, wherein a first converter stage of the multistage converter is connected via a process gas discharge conduit to an intermediate absorption apparatus, wherein the intermediate absorption apparatus is connected via at least one process gas feed conduit to a second convertor stage of the multistage converter so that process gases from the first convertor stage are introducible via the intermediate absorption apparatus into the second convertor stage in the production mode.

20. The apparatus of claim 19 wherein the closeable process gas discharge conduit and the closeable process gas feed conduit are connected via a closeable bypass conduit, with the closeable bypass conduit being open in the standby mode of the apparatus so that process gas from the first convertor stage is introducible via the closeable bypass conduit, bypassing the intermediate absorption apparatus, into the second convertor stage.

Description

[0019] The invention will be illustrated below with the aid of a drawing which depicts merely one working example. The figures schematically show:

[0020] FIG. 1 a flow diagram of an apparatus according to the invention for carrying out the process of the invention and

[0021] FIG. 2 the subject matter of FIG. 1 in a modified embodiment.

[0022] The figures schematically show a flow diagram of an apparatus according to the invention for carrying out a process for preparing sulfuric acid. In the following, the apparatus according to the invention will firstly be illustrated with reference to the embodiment of FIG. 1.

[0023] The apparatus comprises a first oxidation facility 1 for the oxidation or combustion of sulfur to form sulfur dioxide. For this purpose, an air feed apparatus 2 and a sulfur feed conduit 3 for the introduction of air and sulfur are connected to the first oxidation facility 1. It is within the scope of the invention for the first oxidation facility 1 and the air feed apparatus 2 and the sulfur feed conduit 3 to be active only in the production mode of the apparatus. The air fed in by means of the air feed apparatus 2 is, in the production mode, introduced via the air feed conduit 25 and the opened air feed valve 19 into the air drying device 24 and conveyed from there with the aid of the blower 23 to the first oxidation facility 1. The air drying device 24 is configured as an air drying tower in the working example.

[0024] In the production mode, the sulfur dioxide formed in the first oxidation facility 1 is introduced into the second oxidation facility 4 which is configured as a convertor having catalyst trays 5, with the sulfur dioxide being catalytically oxidized to sulfur trioxide (SO.sub.3) in this convertor. The second oxidation facility 4 or the convertor preferably comprises, and as shown in the working example, two convertor stages 6, 7. In the working example, the sulfur dioxide is firstly conveyed through the first convertor stage 6, which here comprises three catalyst trays 5. After flowing through the first convertor stage 6, the process gas is, in the production mode, preferably and in the working example, introduced via a process gas discharge conduit 8 into the intermediate absorption apparatus 9. In the working example, the SO.sub.3-containing process gas is here conveyed in countercurrent to dilute sulfuric acid, so that sulfur trioxide is absorbed by the sulfuric acid and the sulfuric acid is at the same time concentrated as a result. The remaining process gas is then advantageously, and as shown in the working example, reintroduced via the process gas feed conduit 10 into the second oxidation facility 4, in fact into the second convertor stage 7 thereof. After flowing through this second convertor stage 7, in which remaining sulfur dioxide is oxidized to sulfur trioxide, the process gas is then, as is recommended and shown in the working example, introduced via the connecting conduit 11 into the final absorption apparatus 12. Here too, the process gas is advantageously conveyed in countercurrent to dilute sulfuric acid, so that sulfur trioxide is absorbed by the sulfuric acid. The remaining process gas is preferably, and as shown in the working example, discharged at the upper end of the final absorption apparatus 12, in the production mode discharged from the process or from the apparatus via a closeable discharge conduit 13.

[0025] To implement the standby mode according to the invention, the final absorption apparatus 12 is connected via a process gas conduit 14 to the heating device 15 for heating the process gas. The heating device 15 is in turn connected via a connecting conduit 16 to the second oxidation facility 4 or to the first convertor stage 6 of the second oxidation facility 4, preferably and as shown in the working example, the process gas discharge conduit 8 is, to implement the standby mode, short-circuited to the process gas feed conduit 10 upstream of the intermediate absorption apparatus 9 by means of a closeable bypass conduit 17. The bypass conduit 17 is closeable by means of the bypass valve 18.

[0026] To switch over from the production mode to the standby mode, the air feed valve 19 for introduction of air into the first oxidation facility 1 is firstly closed. In addition, the discharge conduit 13 is closed by means of the discharge valve 20. Instead, the process gas conduit valve 21 is opened so that process gas can be conveyed from the final absorption apparatus 12 via the conduit 22 to the heating device 15. To assist this process gas route, the blower 23 provided in the production mode for the introduction of air is preferably activated, as also shown in the working example. In the heating device 15, the process gas is, for example, heated to a temperature of about 500 C. The process gas which has been heated in this way is then fed via the connecting conduit 16 to the second oxidation facility 4 or to the first convertor stage 6 of the second oxidation facility 4. Here, the process gas flows through the first convertor stage 6 and is then conveyed via the process gas discharge conduit 8 out of the second oxidation facility 4. In the standby mode, the bypass valve 18 of the bypass conduit 17 is opened and the process gas thus flows from the process gas discharge conduit 8 via the bypass conduit 17 into the process gas feed conduit 10, bypassing the intermediate absorption apparatus 9. By means of this process gas feed conduit 10, the process gas is again fed to the second oxidation facility 4 or the second convertor stage 7 of this second oxidation facility 4. After flowing through the second convertor stage 7, the process gas goes via the connecting conduit 11 into the final absorption apparatus 12. Here, residues of sulfur trioxide and water remaining in the process gas are absorbed. In contrast to the production mode, the process gas is then recirculated with the discharge valve 20 closed via the process gas conduit 14 with the process gas conduit valve 21 opened via the blower 23 to the heating device 15 and in this way continues to flow in the circuit. It is within the scope of the invention for the process gas to be gradually replaced by nitrogen.

[0027] The apparatus in the embodiment shown in FIG. 2 in principle operates like the apparatus in FIG. 1. The important difference compared to the working example of FIG. 1 is the connection of the process gas conduit 14 connected to the final absorption apparatus 12. In this embodiment, too, in order to switch over from the production mode into the standby mode, the air feed valve 19 for the introduction of air into the first oxidation facility 1 is firstly closed and the discharge conduit 13 is closed by means of the discharge valve 20. Here too, the process gas conduit valve 21 is opened so that process gas can be conveyed from the final absorption apparatus 12 via the conduit 22 to the heating device 15. However, the process gas is, in the standby mode of the embodiment shown in FIG. 2, introduced via the process gas conduit 14 with the process gas conduit valve 21 open into the air feed conduit 25 arranged upstream of the air drying device 24. In this embodiment, the blower 23 is also arranged upstream of the air drying device 24 in flow direction. With the air feed valve 19 closed, the process gas is conveyed by means of the blower 23 through the air drying device 24 and from there is conveyed further via the conduit 22 to the heating device 15.