PROCESSING UNIT FOR A WASHING MEDIUM CONTAMINATED WITH SULPHUR OXIDES AND/OR NITROGEN OXIDES

Abstract

A processing unit for a liquid washing medium contaminated with sulphur oxides and/or nitrogen oxides, has an evaporation stage for concentrating the active components of the washing medium by an evaporator and/or by a heat exchanger, and has a collecting tank connected to the evaporator and/or to the heat exchanger. The collecting tank is configured as a crystallizer for removing sulfur oxides from the washing medium by crystallization of a sulphate, in particular of potassium sulphate. A separating device for carbon dioxide has a corresponding processing unit, and a method for processing a washing medium contaminated with sulphur oxides and/or nitrogen oxides uses a corresponding processing unit.

Claims

1.-26. (canceled)

27. A processing unit for a liquid scrubbing medium contaminated with sulphur oxides and/or nitrogen oxides, comprising an evaporation stage for concentrating the active component of the scrubbing medium having an evaporator and/or having a heat exchanger, having a collecting tank that is connected to the evaporator and/or to the heat exchanger, wherein the collecting tank is connected via an outlet to a separation unit, wherein the collecting tank is constructed as a crystallizer for removing sulphur oxides from the scrubbing medium by crystallization of a sulphate, and wherein an outlet of the separation unit is connected to an additional crystallizer for recovery of the active component of the scrubbing medium.

28. The processing unit as claimed in claim 27, wherein the separation unit is constructed as a hydro cyclone.

29. The processing unit as claimed in claim 27, wherein the collecting tank comprises a classifying appliance for separating the crystallized sulphate particles according to the particle size thereof.

30. The processing unit as claimed in claim 29, wherein the classifying appliance is constructed in the form of a classifying zone having a first classifying region and a second classifying region within the crystallizer, wherein the first classifying region is connected via a first outlet of the collecting tank to an inlet of the separation unit.

31. The processing unit as claimed in claim 27, wherein an outlet of the separation unit is connected to an inlet of the evaporator.

32. The processing unit as claimed in claim 27, wherein the collecting tank is connected via an outlet to an inlet of the collecting tank.

33. The processing unit as claimed in claim 27, wherein an outlet of the separation unit is connected to an inlet of the collecting tank.

34. The processing unit as claimed in claim 27, wherein an outlet of the separation unit is connected to an inlet of an absorber unit of a carbon dioxide separation device.

35. The processing unit as claimed in claim 27, further comprising a metering device for adjusting an alkali metal concentration in the scrubbing medium, which metering device is connected to the collecting tank.

36. The processing unit as claimed in claim 30, wherein the second classifying region is connected via an outlet of the collecting tank to a reclamation appliance for the precipitated sulphate.

37. The processing unit as claimed in claim 27, wherein an amino acid salt is used as active component of the scrubbing medium.

38. A carbon dioxide separation device, comprising an absorber unit for separating off carbon dioxide from a flue gas by means of a scrubbing medium, and also a desorber unit that is flow-connected downstream of the absorber unit and is for separating off the carbon dioxide from the scrubbing medium, and a processing unit as claimed in claim 27, which is flow-connected downstream of the desorber unit.

39. A method for processing a scrubbing medium contaminated with sulphur oxides and/or nitrogen oxides, the method comprising: feeding the scrubbing medium, to concentrate an active component thereof, to an evaporation stage having an evaporator and/or having a heat exchanger, and also having a collecting tank that is flow-connected to the evaporator and/or to the heat exchanger, wherein sulphur oxides present in the scrubbing medium are crystallized out in the collecting tank as sulfate particles that are fed to a separation unit from the collecting tank, and feeding a first substream of an overflow of the separation unit to an additional crystallizer for recovery of the active component of the scrubbing medium.

40. The method as claimed in claim 39, further comprising: separating the sulphate particles in a classifying appliance of the collecting tank according to their particle size.

41. The method as claimed in claim 39, wherein a heat exchanger is comprised by the evaporator stage, wherein a second sub stream is fed from the collecting tank to the heat exchanger.

42. The method as claimed in claim 41, further comprising: recirculating the second sub stream, after it passes through the heat exchanger, to the collecting tank.

43. The method as claimed in claim 40, further comprising: feeding a second sub stream of an overflow of the separation unit to the evaporator.

44. The method as claimed in claim 40, further comprising: feeding a second sub stream of an overflow of the separation unit to the collecting tank.

45. The method as claimed in claim 40, feeding a third sub stream of an overflow of the separation unit to an absorber unit of a separation device.

46. The method as claimed in claim 39, further comprising: adjusting an alkali metal concentration in the scrubbing medium via a metering device connected to the collecting tank.

47. The method as claimed in claim 39, further comprising: feeding a second sub stream that is enriched with sulphate particles having substantially large sulphate particles from the collecting tank to a reclamation appliance.

48. The method as claimed in claim 39, wherein an amino acid salt is used as active component of the scrubbing medium.

49. The processing unit as claimed in claim 27, wherein the sulphate comprises potassium sulphate.

50. The processing unit as claimed in claim 35, wherein the alkali metal concentration comprises a potassium concentration.

51. The processing unit as claimed in claim 36, wherein the precipitated sulphate comprises potassium sulphate.

52. The processing unit as claimed in claim 37, wherein the amino acid salt comprises a potassium-containing amino acid salt.

53. The method as claimed in claim 39, wherein the sulfate particles comprise potassium sulphate particles.

54. The method as claimed in claim 40, further comprising: feeding a first substream having substantially small and medium sulphate particles from the collecting tank to the separation unit.

55. The method as claimed in claim 54, wherein the substantially small and medium sulphate particles comprise substantially small and medium potassium sulphate particles.

56. The method as claimed in claim 46, wherein the alkali metal concentration comprises a potassium concentration.

57. The method as claimed in claim 48, wherein the amino acid salt comprises a potassium-containing amino acid salt.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Hereinafter, exemplary embodiments of the invention are explained in more detail with reference to a drawing. In the drawings:

[0063] FIG. 1 shows a processing unit for a scrubbing medium contaminated with sulfur oxides and/or nitrogen oxides and having an evaporator and a collecting tank connected thereto, and also

[0064] FIG. 2 shows a carbon dioxide separation device having a processing unit according to FIG. 1.

DETAILED DESCRIPTION OF INVENTION

[0065] In FIG. 1, a processing unit 1 for a scrubbing medium contaminated with sulfur oxides and/or nitrogen oxides is shown. The processing unit 1 comprises an evaporation stage 2 having an evaporator 3 constructed as a thin-film evaporator for concentrating contaminated scrubbing medium by concentrating the active component of the scrubbing medium, and also having a collecting tank 7 connected to the evaporator 3.

[0066] Such a collecting tank 7 is in principle used in the processing of scrubbing medium in an NO.sub.x reclaimer, in which it serves as receiver tank or as pump receiver for the scrubbing medium feedable to a crystallizer of the NO.sub.x reclaimer.

[0067] In contrast thereto, the collecting tank 7 of the processing unit 1 is constructed as a crystallizer 9 for removing sulfur oxides from the scrubbing medium by crystallization of potassium sulfate. The crystallizer 9 is dimensioned so as to be larger in comparison with collecting tanks used to date, and, optionally, but not obligatorily, equipped with an agitator 10.

[0068] The feed of the scrubbing medium in the collecting tank 7 constructed as a crystallizer 9 proceeds starting from a carbon dioxide separation device desorption unit, which is not shown. Starting from the desorption unit, a sulfate-rich input stream 11 having approximately 30% by weight of an amino acid salt used as active component of the scrubbing medium is conducted into the collecting tank 7 and there mixed with thickened scrubbing medium (approximately 60% by weight) of the amino acid salt from the evaporator 3. The input stream 11 has an entry temperature between 30 C. and 40 C., whereas the temperature in the collecting tank 7 is between 60 C. and 65 C. Despite the temperature rise, the solubility of the potassium sulfate decreases sharply within the scrubbing medium and the scrubbing medium becomes supersaturated.

[0069] Supersaturation of the scrubbing medium then decreases owing to the crystallization of potassium sulfate in the crystallizer 9. For this purpose, the crystallizer 9 is constructed having a crystallization chamber 12.

[0070] In addition, the crystallizer 9 comprises a classifying appliance 13 that permits separation according to their particle size of potassium sulfate particles that have crystallized out in the crystallization chamber 12. The classifying appliance 13 is constructed in the form of a classifying zone 14 having a first classifying region 15 and a second classifying region 16 within the crystallizer 9. In the first classifying region 15, substantially potassium sulfate particles of medium and small size collect, wherein, in the second classifying region 16, the large potassium sulfate particles collect. The collecting tank 7 and the evaporator 3 are therefore an evaporating crystallizer having an internal classifying function.

[0071] After the potassium sulfate particles have been separated according to the particle size thereof, a first substream 17 of the scrubbing medium is fed by means of a pump 19 from the collecting tank 7 to a separation unit 21 constructed as a hydrocyclone. For this purpose the first classifying region 15 is coupled via the outlet 22 of the collecting tank 7 to an inlet 23 of the separation unit 21. The first substream 17 substantially comprises the medium and small potassium sulfate particles that have been separated off from the heavy particles in the classifying zone 15 of the crystallizer 9.

[0072] In addition, via an outlet 24 of the collecting tank 7, a second substream 25 enriched with potassium sulfate particles is fed from the second classifying region 16 by means of a pump 27 constructed as a sump pump from the collecting tank 7 to a reclamation appliance 29. The suspension ejected in this case, that is to say second substream 25, has a potassium sulfate fraction between 3% by weight and 10% by weight, wherein the solids fraction can be adjusted via the discharge rate of the sump pump 27.

[0073] In the separation unit 21, the medium and small particles of potassium sulfate present in the first substream 17 are separated off from the scrubbing medium. The underflow 30 which is formed in solid-liquid separation contains the potassium sulfate particles separated off from the scrubbing medium which are then fed back to the crystallization process as crystal nuclei via a coupling of the outlet 31 of the separation unit 21 to an inlet 32 of the collecting tank 7.

[0074] A first substream 33 of the overflow 34 formed in this solid-liquid separation, that is to say low-particle clear run, is then fed by means of a pump 36 to an additional crystallizer 37 for recovery of the active component of the scrubbing medium. The crystallizer 37 is constructed as a crystallizer for the NO.sub.x reclaiming process.

[0075] In addition, the separation unit 21 is coupled to the evaporator 3. The coupling proceeds via the outlet 35 of the separation unit to an inlet 38 of the evaporator 3. A second substream 39 of the overflow 34, the main stream, can in this manner be recirculated to the evaporator 3 and there, for the purpose of concentrating the active component of the scrubbing medium, can eject water therefrom.

[0076] A third substream 41 of the overflow 34 of the separation unit 21 is fed by means of a pump 43 to an absorber unit which is not shown of a carbon dioxide separation device. For this purpose, the outlet 35 of the separation unit 21 is coupled to the inlet 44 of the absorber unit, which is shown in FIG. 2. Such a recirculation is suggested when, for the ejection of the potassium sulfate, more scrubbing medium must be treated than would be economically necessary for the regeneration of the scrubbing medium associated with losses of the scrubbing medium.

[0077] To adjust the potassium concentration in the scrubbing medium, a metering device 45 is connected to the collecting tank 7 constructed as crystallizer 9. The metering device 45 comprises two pumps 47, 49, by means of which additional reactants can be fed to the system, in order in this manner to prevent an unwanted concentration of potassium, for example in gas-fueled power plant applications, or alternatively an unwanted depletion of potassium, for example in coal-fired power plant applications.

[0078] In FIG. 2, a further processing unit 51 for a scrubbing medium contaminated with sulfur oxides and/or nitrogen oxides may be seen illustrated. The processing unit 51 comprises an evaporation stage 52 having a heat exchanger 53, and also a collecting tank 7 connected to the heat exchanger 53. This combination of heat exchanger 53 and collecting tank 7 is known as a forced circulation (FC) crystallizer.

[0079] In contrast to the evaporation stage 2 according to FIG. 1, in the present case a second substream 55 is withdrawn from the collecting tank 7 via a second outlet 54. The second substream 55 is fed to the heat exchanger 53 by means of a pump 56. In the heat exchanger 53, the second substream 55 passes through heating tubes and is correspondingly heated. After passage through the heat exchanger 53, the heated second substream 55 is fed to the collecting tank 7 via an inlet 57 thereof.

[0080] In the collecting tank 7, a reduced pressure of about 100 mbar prevails, as a result of which water evaporates with heat removal at the boundary surfaces of the collecting tank 7. Via a takeoff of the water, or of the steam, supersaturation results, and the particles grow in the scrubbing medium.

[0081] Since the processing unit 51, or the evaporation stage 52, in contrast to the processing unit 1 according to FIG. 1, comprises the heat exchanger 53 instead of an evaporator, the second substream 39 withdrawn from the outlet 35 of the separation unit 21 is fed to the overflow 34 of the collecting tank 7. For this purpose, the outlet 35 of the separation unit 21 is connected to an inlet 58 of the collecting tank 7.

[0082] With respect to the description of the function of the further components of the processing unit 51, at this point, reference is made to the detailed description of the processing unit 1 according to FIG. 1.

[0083] In FIG. 3, a carbon dioxide separation device 61 having a processing unit 1 according to FIG. 1 is shown. The separation device 61 comprises an absorber unit 63 and a desorber unit 65 that is flow-coupled thereto. The processing unit 1 is flow-connected downstream of the processing unit.

[0084] In the absorber unit 63 a flue gas stream is contacted with the scrubbing medium, a potassium-containing amino acid salt, and the carbon dioxide present in the scrubbing medium is absorbed in the scrubbing medium. At the same time, sulfur oxides and nitrogen oxides present in the flue gas are co-introduced into absorber unit 63 and absorbed in the scrubbing medium. The loaded scrubbing medium is then, via heat exchangers that are not shown, conducted into the desorber unit 65, where the absorbed carbon dioxide is removed from the scrubbing medium by thermal desorbtion.

[0085] The nitrogen oxides (NO.sub.x) and sulfur oxides (SO.sub.x) remaining in the scrubbing medium are then removed from the scrubbing medium in the processing unit 1 flow-connected downstream in the desorber unit 65 and said scrubbing medium is correspondingly regenerated for renewed use in the course of the absorption-desoption process. For this purpose, the scrubbing medium is introduced as input stream 11 in the collecting tank 7 of the processing unit 1. The corresponding processing of the scrubbing medium is described in detail in FIG. 1, to which reference is made at this point.

[0086] Of course, the processing unit 51 shown in FIG. 2 can also be used in a separation device 61.