METHOD FOR THE CATALYTIC REMOVAL OF SULPHUR DIOXIDE FROM WASTE GASES

Abstract

The present invention relates to a method for the catalytic removal of sulfur dioxide from waste gases in two reactors, wherein the first reactor is charged with an activated carbon catalyst. The method comprises: a. provision of a waste gas with a water content of less than 1 g H.sub.2O/Nm.sup.3 and an SO.sub.2 content of at least 5 ppm, b. introduction of the waste gases into a first reactor, c. catalytic conversion of the SO.sub.2 into gaseous SO.sub.3 in the first reactor by the activated carbon catalyst, wherein catalytic conversion on the activated carbon catalyst proceeds at a temperature of below 100° C., d. introduction of the prepurified waste gases from the first reactor into a second reactor, e. conversion of the SO.sub.3 with water into H.sub.2SO.sub.4 in the second reactor.

Claims

1-13. (canceled)

14. A method for the catalytic removal of sulfur dioxide from waste gases in two reactors, the first reactor being charged with an activated carbon catalyst, comprising the following steps: a. providing a waste gas with a water content of less than 1 g H.sub.2O/Nm.sup.3 and an SO.sub.2 content of at least 5 ppm, b. introducing the waste gases into a first reactor, c. catalytic converting the SO.sub.2 into gaseous SO.sub.3 in the first reactor by the activated carbon catalyst, wherein the catalytic conversion on the activated carbon catalyst proceeds at a temperature of below 100° C., d. introducing of the prepurified waste gases from the first reactor into a second reactor, e. converting of the SO.sub.3 with water into H.sub.2SO.sub.4 in the second reactor.

15. The method according to claim 14, wherein the waste gases to be treated contain at most 0.8 g water per Nm.sup.3 waste gas.

16. The method according to claim 15, wherein the waste gases to be treated contain at most 0.7 g water per Nm.sup.3 waste gas.

17. The method according to claim 15, wherein the waste gases to be treated contain at most 0.4 g water per Nm.sup.3 waste gas.

18. The method according to claim 14, wherein the SO.sub.2 content of the waste gases amounts to at most 180,000 ppm.

19. The method according to claim 18, wherein the SO.sub.2 content of the waste gases amounts to at most 130,000 ppm.

20. The method according to claim 18, wherein the SO.sub.2 content of the waste gases amounts to at most 110,000 ppm.

21. The method according to claim 14, wherein the inlet temperature of the waste gases is between ambient temperature and 150° C.

22. the method according to claim 14, wherein the gas pressure of the waste gases at the inlet to the first reactor is between 800 and 1400 mbar.

23. The method according to claim 14, wherein at least 60 vol. % of the SO.sub.2 present in the waste gases is converted.

24. The method according to claim 23, wherein at least 75 vol. % of the SO.sub.2 present in the waste gases is converted.

25. The method according to claim 23, wherein at least 90 vol. % of the SO.sub.2 present in the waste gases is converted.

26. The method according to claim 23, wherein at least 98 vol. % of the SO.sub.2 present in the waste gases is converted.

27. The method according to claim 14, wherein the O.sub.2 content of the waste gases amounts to at least 2 vol. %, preferably at least 5 vol. %, particularly preferably at least 8 vol. %, and in particular at least 10 vol. %.

28. The method according to claim 27, wherein the O.sub.2 content of the waste gases amounts to at least 5 vol. %.

29. The method according to claim 27, wherein the O.sub.2 content of the waste gases amounts to at least 8 vol. %.

30. The method according to claim 27, wherein the O.sub.2 content of the waste gases amounts to at least 10 vol. %

31. The method according to claim 14, wherein the O.sub.2 content is more than 8 times higher than the SO.sub.2 content.

32. The method according to claim 14, wherein the activated carbon catalyst is a natural peat activated carbon catalyst or an extruded wood activated carbon catalyst.

33. The method according to claim 14, wherein an H.sub.2SO.sub.4 acid of at least 10 wt. % is discharged.

34. The method according to claim 33, wherein an H.sub.2SO.sub.4 acid of at least 50 wt. % is discharged.

35. The method according to claim 33, wherein an H.sub.2SO.sub.4 acid of at least 70 wt. % is discharged.

36. The method according to claim 33, wherein an H.sub.2SO.sub.4 acid of at least 96 wt. % is discharged.

37. The method according to claim 14, wherein the method is carried out in a first reactor which comprises an activated carbon catalyst bed.

38. The method according to claim 14, wherein the method is carried out in a first reactor which comprises a plurality of activated carbon catalyst beds connected in parallel.

39. The method according to claim 14, wherein the method is carried out in a first reactor which comprises a plurality of activated carbon catalyst beds connected in series.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0043] Further details and advantages of the invention may be inferred from the following detailed description of various possible embodiments of the invention made with reference to the appended figures, in which:

[0044] FIG. 1 is a schematic diagram of a first test arrangement,

[0045] FIG. 2 is a schematic diagram of a second test arrangement,

[0046] FIG. 3 is a schematic diagram of a third test arrangement,

[0047] FIG. 4 is a schematic diagram of a fourth test arrangement,

[0048] FIG. 5 and FIG. 6 are graphs showing the values, measured during testing, for the SO.sub.2 content of the waste gases on entering and leaving the reactor.

DESCRIPTION OF AN EMBODIMENT OF THE INVENTION

[0049] The first test arrangement shown in FIG. 1 to illustrate the invention comprises a fixed-bed reactor 10, into the lower part of which is supplied an SO.sub.2-containing waste gas via an inlet 12. The waste gas is passed from the bottom upwards through a fixed bed 14 with an activated carbon catalyst and is passed out of the upper part of the reactor 10 through an outlet 16 via a line 18 into an absorber 20.

[0050] In the fixed-bed reactor 10, the gaseous SO.sub.2 is converted into gaseous SO.sub.3 with the assistance of the activated carbon catalyst. In contrast with known methods, the SO.sub.3 is not adsorbed onto the activated carbon catalyst and converted into H.sub.2SO.sub.4, but is instead released again in gaseous form after the reaction. The SO.sub.2 is converted virtually 1:1, thus approximately 100%, into SO.sub.3, i.e. SO.sub.2 (almost) completely disappears from the waste gases and is replaced by the same quantity of SO.sub.3.

[0051] A heating/cooling coil 22 is mounted in the fixed bed 14 in order to control the temperature in the fixed bed 14. Care is taken to ensure that the temperature in the fixed bed 14 does not exceed 100° C., in order to be gentle on the activated carbon catalyst and not unnecessarily shorten the service life thereof.

[0052] After leaving the fixed-bed reactor 10, the prepurified waste gases are passed into an absorber 20 where they are passed through a washing solution of 30-98% H.sub.2SO.sub.4. Preferably, 96% sulfuric acid is used. The prepurified waste gases are introduced via the line 18 into the lower region of the absorber 20 and rise through the liquid sulfuric acid and are then withdrawn as pure gas through an outlet 24 at the top of the absorber 20.

[0053] The gaseous SO.sub.3 accordingly dissolves in the liquid sulfuric acid. As a result, disulfuric acid H.sub.2S.sub.2O.sub.7 is quickly formed which reacts with the water present in the sulfuric acid to form H.sub.2SO.sub.4. This is a conventional method for converting SO.sub.3 into H.sub.2SO.sub.4.

[0054] Liquid, dilute sulfuric acid from a tank 26 is introduced into the top region of the absorber 20 via a pump 28 and through a line 30. The sulfuric acid is discharged from the bottom 32 of the absorber 20 and flows via an outlet 34 and a line 36 back into the tank 26.

[0055] The sulfuric acid obtained may be pumped out of the tank 26 via a further line 38 with a pump 40. In this method, the sulfuric acid is thus concentrated because the water dissolved in the sulfuric acid is gradually consumed in order to convert SO.sub.3 into H.sub.2SO.sub.4. Once the sulfuric acid in the tank 26 has reached the desired concentration, some of it is pumped out and appropriately replaced by water/dilute sulfuric acid.

[0056] The test arrangements shown in FIGS. 2 and 3 differ from the test arrangement of FIG. 1 in that the absorber 20, as a second reactor, is replaced by a separator 42 (FIG. 2) or by a SULFACID reactor 44 (FIG. 3). Both reactors 42, 44 are filled with solids. The separator 42 of FIG. 2 contains a fixed bed of plastic packing 48 (example: VFF Acidur® special stoneware) while the SULFACID reactor 44 contains a fixed bed of activated carbon 50.

[0057] In the case of these reactors 42, 44, the prepurified waste gas from the first reactor 10 is passed into the top region of reactors 42, 44. In this case too, the dilute sulfuric acid from tank 26 is introduced via a pump 28 through a line 30 into the top region of the separator 42 or of the SULFACID reactor 44. In these two embodiments, a spray device 46 is mounted in the top region of the separator 42 or of the SULFACID reactor 44, by means of which a uniform distribution of the dilute sulfuric acid onto the plastic packing 48 of the separator 42 or onto the activated carbon 50 of the SULFACID reactor 44 is achieved.

[0058] Unlike in FIG. 1, the prepurified waste gas is brought not countercurrently but instead cocurrently into contact with the dilute sulfuric acid. The prepurified waste gas is accordingly introduced via a line 18 into the top region of the separator 42 or of the SULFACID reactor 44 and, after the reaction, drawn off as pure gas through an outlet 52 in the lower region of the separator 42 or of the SULFACID reactor 44.

[0059] In these reactors 42, 44, the gaseous SO.sub.3 is again dissolved in the liquid sulfuric acid. As a result, disulf uric acid H.sub.2S.sub.2O.sub.7 is quickly formed which reacts with the water present in the sulfuric acid to form H.sub.2SO.sub.4.

[0060] FIG. 4 now shows a somewhat more complex test setup in which the reactor 10 corresponds to the reactors 10 in the previous figures. In this test arrangement, the SO.sub.2-containing waste gases are dried in a drying tower 54 before being introduced into the reactor 10.

[0061] The structure of the drying tower 54 broadly corresponds to that of the absorber 20 of FIG. 1. Said drying tower 54 is, however, located upstream of the reactor 10 and serves to remove water from the SO.sub.2-containing waste gases before they arrive in the reactor 10.

[0062] The SO.sub.2-containing waste gases are accordingly introduced into the lower region of the drying tower 54 where they are dried countercurrently with sulfuric acid. The sulfuric acid with a concentration of 30 wt. % to 98 wt. % from the tank 26 is introduced into the top region of the drying tower 54 via a line 56, a pump 58 and spray devices 60.

[0063] Once the sulfuric acid has removed the water from the SO.sub.2-containing waste gases, it is passed via a line 64 from the bottom of the drying tower 54 through an outlet 62 back into the tank 26.

[0064] The SO.sub.2-containing waste gases dried in the drying tower 54 are drawn off from the top region of the drying tower 54 and introduced via a blower 66 and a line 68 through the inlet 12 into the lower region of the reactor 10.

[0065] In the fixed-bed reactor 10, the gaseous SO.sub.2 is converted into gaseous SO.sub.3 with the assistance of the activated carbon catalyst. A heating/cooling coil 22 is mounted in the fixed bed 14 of the reactor 10 in order to control the temperature in the fixed bed 14.

[0066] After leaving the fixed-bed reactor 14, the prepurified waste gases i.e. SO.sub.3-containing waste gases are introduced into the top region of a reactor 70 where they are passed cocurrently through a washing solution of 30-98% H.sub.2SO.sub.4. Preferably, 96% sulfuric acid is used. After the reaction, the cleaned waste gas is drawn off as clean gas from the reactor 70 through an outlet 52 in the lower region.

[0067] The reactor 70 here comprises two zones one on top of the other, a SULFACID reactor 44 being arranged in the upper zone and a separator 42 in the lower zone. The two zones are separated from one another by a drop catcher 72.

[0068] Sulfuric acid from the tank 26 is passed through a line via a pump 28 to a spray device 74 which is located above the SULFACID reactor, whereby the sulfuric acid trickles through the activated carbon bed of the SULFACID reactor and absorbs the SO.sub.3 dissolved in the waste gas and converts it into sulfuric acid. The concentrated sulfuric acid collects on the drop catcher 72 from where it is passed back into the tank 26.

[0069] Furthermore, sulfuric acid from the tank 26 is sprayed via the same pump 28 and the same line 30 beneath the droplet separator onto the separator bed through a further spray device 76. The remaining SO.sub.3 present in the waste gas is then absorbed within the separator by the sulfuric acid and converted into sulfuric acid by reaction with the water dissolved in the sulfuric acid. The sulfuric acid is then passed through the outlet 34 in the bottom of the reactor 70 through the line 36 back into the tank 26.

[0070] Once the sulfuric acid in the tank 36 has reached the desired concentration, some of it is pumped out of the tank via the line 38 and the pump 40 and appropriately replaced by water/dilute sulfuric acid which is supplied by the line 76.

[0071] FIG. 5 shows results from a first test series in which a flue gas from a contact plant with a water content of less than 0.2 g H.sub.2O/Nm.sup.3 and an SO.sub.2 content of between 11000 and 12000 ppm SO.sub.2 was treated in a plant with two reactors as shown in FIG. 3.

[0072] In the first reactor made from a glass fibre reinforced plastic, which had a volume of 3 m.sup.3 and was provided with a fixed bed of 2 m.sup.3 of Norit-RST3, PK 2.5, Calgon Carbon—Centaur HSV, Jacobi-Ecosorb G-SWC80, VRX-Super, CPPE 25 or CPPE 30 activated carbon catalyst, the SO.sub.2 was completely converted into gaseous SO.sub.3.

[0073] These catalysts are activated carbon pellets or shaped carbon, with a grain size between 1 and 3 mm, between 2 and 4 mm or between 3 and 5 mm and were produced by steam activation. The following general properties are guaranteed by the manufacturer: iodine number 800; methylene blue adsorption 11 g/100 g; internal surface area (BET) 875 m.sup.2/g; bulk density 260 kg/m.sup.3; density after back-wash 230 kg/m.sup.3; uniformity factor 1.3; ash content 7 wt. %; pH alkaline; moisture (packed) 2 wt. %.

[0074] The temperature of the waste gases was between 20° C. and 30° C. at the inlet and between 20° C. and 30° C. at the outlet of the first reactor.

[0075] The waste gases treated in this manner were then passed into a second reactor. The second reactor was a SULFACID reactor which had a volume 2 m.sup.3 and was filled with 1 m.sup.3 of Norit-RST3, PK 2.5, Calgon Carbon—Centaur HSV, Jacobi-Ecosorb G-SWC80, VRX-Super, CPPE 25 or CPPE 30 brand activated carbon.

[0076] These catalysts are activated carbon pellets or shaped carbon with a grain size of between 1 and 3 mm, between 2 and 4 mm or between 3 and 5 mm and were produced by steam activation. The following general properties are guaranteed by the manufacturer: iodine number 800; methylene blue adsorption 11 g/100 g; internal surface area (BET) 875 m.sup.2/g; bulk density 260 kg/m.sup.3; density after back-wash 230 kg/m.sup.3; uniformity factor 1.3; ash content 7 wt. %; pH alkaline; moisture (packed) 2 wt. %

[0077] The activated carbon in the second reactor was sprayed every 15 minutes with 25 l of sulfuric acid of a concentration of 1000 g/l.

[0078] This test series lasted approximately 30 minutes and approximately 150 Nm.sup.3 of waste gases were treated.

[0079] FIG. 6 shows results from a second test series in the same plant as the first test series.

[0080] SO.sub.2-containing waste gases from the same contact plant as in the first test series were used in this test series. The SO.sub.2 content of the waste gases was, however, lower (between 4500 ppm and 2500 ppm).

[0081] The test lasted approximately 120 minutes and approximately 600 Nm.sup.3 of waste gases were treated.

[0082] Testo brand flue gas analysers were used in the tests. The analysers are of a recent generation (year of manufacture 2009) and were calibrated by the manufacturer. The analytical data from these flue gas analysers were moreover confirmed by wet chemical measurements carried out in parallel. The results for all the measurements were within admissible deviation tolerances.

[0083] These two tests revealed that the SO.sub.2 from the waste gases was (almost) completely converted into SO.sub.3 in the first reactor and the SO.sub.3 was (almost) completely converted into H.sub.2SO.sub.4 only in the second reactor.

[0084] Thanks to the rapid and complete conversion of gaseous SO.sub.2 into gaseous SO.sub.3 in the first reactor, the activated carbon catalyst in the first reactor was not saturated.

TABLE-US-00001 Key to drawings: 10 Reactor 12 Inlet 14 Fixed bed 16 Outlet 18 Line 20 Absorber 22 Heating/cooling coil 24 Outlet 26 Tank 28 Pump 30 Line 32 Bottom 34 Outlet 36 Line 38 Line 40 Pump 42 Separator 44 SULFACID reactor 46 Spray device 48 Plastic packing 50 Activated carbon 52 Outlet 54 Drying tower 56 Line 58 Pump 60 Spray devices 62 Outlet 64 Line 66 Blower 68 Line 70 Reactor 72 Drop catcher 74 Spray device 76 Spray device 78 Spray device