System and method for desulfurization and denitrification of alumina calcination flue gas, and use

Abstract

Disclosed are a system and a method for desulfurization and denitrification of an alumina calcination flue gas, and a use. The system comprises an ozone generator, a red mud pre-impregnation slurry scrubbing tower, and a red mud pre-impregnation tank and a red mud pre-impregnation clear liquid scrubbing tower. NO.sub.x in a flue gas is oxidized into a high valence oxynitride by ozone, and with the red mud as an absorbent, the synergistic absorption of SO.sub.2 and NO.sub.x in the flue gas is achieved, while the dealkalization of the red mud is achieved. By means of the synergistic catalytic oxidation of metal ions such as Fe.sup.3+ in a red mud slurry and ozone, the synergistic absorption of sulfur and oxynitride is prompted; and the use of a structure of staged absorption in two towers overcomes the problem of the difficulty in absorbing NO.sub.2 with a low O.sub.3/NO.sub.x molar ratio.

Claims

1. A system for desulfurization and denitrification of alumina calcination flue gas, comprising: an ozone generator, a red mud pre-impregnation slurry scrubbing tower, a red mud pre-impregnation tank and a red mud pre-impregnation clear liquid scrubbing tower; wherein the red mud pre-impregnation slurry scrubbing tower is provided with a spray layer at a upper part, and a flue gas inlet disposed on a tower wall below the spray layer and connected to an alumina calcination flue gas pipeline; the red mud pre-impregnation clear liquid scrubbing tower is provided with a spray layer at a upper part, and a flue gas inlet disposed on a tower wall below the spray layer; a gas outlet at the top of the red mud pre-impregnation slurry scrubbing tower is connected to the flue gas inlet of the red mud pre-impregnation clear liquid scrubbing tower through a pipeline; the red mud pre-impregnation tank is provided with a clear liquid outlet at an upper part and a slurry outlet at a lower part, wherein the clear liquid outlet is connected to a spray liquid inlet of the spray layer in the red mud pre-impregnation clear liquid scrubbing tower, and the slurry outlet is connected to a spray liquid inlet of the spray layer in the red mud pre-impregnation slurry scrubbing tower; and a gas outlet of the ozone generator is connected to the alumina calcination flue gas pipeline and to the pipeline between the gas outlet at the top of the red mud pre-impregnation slurry scrubbing tower and the flue gas inlet of the red mud pre-impregnation clear liquid scrubbing tower, separately.

2. The system of claim 1, comprising: a first ozone homogenizer and a second ozone homogenizer, wherein the first ozone homogenizer is disposed on the alumina calcination flue gas pipeline, the second ozone homogenizer is disposed on the pipeline between the gas outlet at the top of the red mud pre-impregnation slurry scrubbing tower and the flue gas inlet of the red mud pre-impregnation clear liquid scrubbing tower, the gas outlet of the ozone generator is connected to the first ozone homogenizer and the second ozone homogenizer, separately, and ozone is homogenized in pipelines by the first ozone homogenizer and the second ozone homogenizer.

3. The system of claim 1, comprising: a demister and a chimney, wherein a flue gas outlet at the top of the red mud pre-impregnation clear liquid scrubbing tower is connected to the demister and the chimney in sequence.

4. The system of claim 1, wherein a red mud pre-impregnation slurry pond is disposed between the slurry outlet of the red mud pre-impregnation tank and the spray liquid inlet of the spray layer in the red mud pre-impregnation slurry scrubbing tower.

5. The system of claim 1, wherein the red mud pre-impregnation slurry scrubbing tower is provided with a bottom liquid outlet connected to the spray liquid inlet of the spray layer in the red mud pre-impregnation slurry scrubbing tower.

6. The system of claim 1, wherein a red mud pre-impregnation clear liquid pond is disposed between the clear liquid outlet of the red mud pre-impregnation tank and the spray liquid inlet of the spray layer in the red mud pre-impregnation clear liquid scrubbing tower.

7. The system of claim 1, wherein the spray liquid inlet of the spray layer in the red mud pre-impregnation slurry scrubbing tower is connected to a process water pipeline.

8. The system of claim 1, wherein the bottom liquid outlet of the red mud pre-impregnation slurry scrubbing tower is connected to a material inlet of the red mud pre-impregnation tank.

9. The system of claim 1, wherein a dewatering pond is disposed between the bottom liquid outlet of the red mud pre-impregnation slurry scrubbing tower and the material inlet of the red mud pre-impregnation tank, and a clear liquid outlet at an upper part of the dewatering pond is connected to the material inlet of the red mud pre-impregnation tank.

10. The system of claim 1, wherein the red mud pre-impregnation clear liquid scrubbing tower is provided with a bottom liquid outlet connected to the spray liquid inlet of the spray layer in the red mud pre-impregnation clear liquid scrubbing tower.

11. The system of claim 1, wherein preferably, the bottom liquid outlet of the red mud pre-impregnation clear liquid scrubbing tower is connected to a liquid inlet of the red mud pre-impregnation clear liquid pond.

12. A method for desulfurization and denitrification of alumina calcination flue gas, comprising: (a) transporting the alumina calcination flue gas mixed with ozone to a red mud pre-impregnation slurry scrubbing tower for reverse spraying with a slurry obtained after red mud pre-impregnation, so as to obtain a flue gas after a primary treatment and a red mud slurry after the spraying; and (b) mixing the flue gas after the first treatment in step (a) with ozone before transporting to a red mud pre-impregnation clear liquid scrubbing tower for reverse spraying with a clear liquid obtained after the red mud pre-impregnation, so as to obtain a treated flue gas and a red mud clear liquid after the spraying.

13. The method of claim 12, wherein the method is performed by the system for desulfurization and denitrification of alumina calcination flue gas of claim 1.

14. The method of claim 12, wherein a molar ratio of the ozone to remaining NO.sub.x in the flue gas after the primary treatment in step (b) is (0.1-1.0):1.

15. The method of claim 12 wherein a molar ratio of the ozone to NO.sub.x in the alumina calcination flue gas in step (a) is (0.4-1.5):1.

16. The method of claim 12 wherein the red mud pre-impregnation in step (a) comprises: pre-impregnating and layering a red mud generated in an alumina calcination process in a red mud pre-impregnation tank, wherein the slurry is obtained at a lower layer, and the clear liquid is obtained at an upper layer.

17. The method of claim 12 wherein no additives are added during the red mud pre-impregnation.

18. The method of claim 12 wherein a pH of the clear liquid obtained after the red mud pre-impregnation in step (b) is 7-12.

19. The method of claim 12 wherein the red mud clear liquid after the spraying in step (b) is returned to a spray layer in the red mud pre-impregnation clear liquid scrubbing tower as spray water to be recycled.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic structural view of a system for desulfurization and denitrification of alumina calcination flue gas according to Embodiment 1 of the present disclosure.

(2) In the FIGURE, 1—ozone generator, 2—first ozone homogenizer, 3—red mud pre-impregnation slurry scrubbing tower, 4—second ozone homogenizer, 5—red mud pre-impregnation tank, 6—red mud pre-impregnation slurry pond, 7—process water pipeline, 8—dewatering pond, 9—red mud pre-impregnation clear liquid pond, 10—red mud pre-impregnation clear liquid scrubbing tower, 11—demister and 12—chimney.

DETAILED DESCRIPTION

(3) To better illustrate the present disclosure and to facilitate the understanding of the solutions of the present disclosure, the present disclosure is further described in detail below. Embodiments set forth below are merely simple examples of the present disclosure, and are not intended to represent or limit the protection scope of the present disclosure. The protection scope of the present disclosure is defined by the claims.

(4) A system and a method for desulfurization and denitrification of alumina calcination flue gas are provided in the detailed description of the present disclosure. The system includes an ozone generator 1, a red mud pre-impregnation slurry scrubbing tower 3, a red mud pre-impregnation tank 5 and a red mud pre-impregnation clear liquid scrubbing tower 10. The red mud pre-impregnation slurry scrubbing tower 3 is provided with a spray layer at an upper part, and a flue gas inlet disposed on a tower wall below the spray layer and connected to an alumina calcination flue gas pipeline. The red mud pre-impregnation clear liquid scrubbing tower 10 is provided with a spray layer at an upper part, and a flue gas inlet disposed on a tower wall below the spray layer. A gas outlet at the top of the red mud pre-impregnation slurry scrubbing tower 3 is connected to the flue gas inlet of the red mud pre-impregnation clear liquid scrubbing tower 10 through a pipeline. The red mud pre-impregnation tank 5 is provided with a clear liquid outlet at an upper part and a slurry outlet at a lower part, where the clear liquid outlet is connected to a spray liquid inlet of the spray layer in the red mud pre-impregnation clear liquid scrubbing tower 10, and the slurry outlet is connected to a spray liquid inlet of the spray layer in the red mud pre-impregnation slurry scrubbing tower 3. A gas outlet of the ozone generator 1 is connected to the alumina calcination flue gas pipeline and to the pipeline between the gas outlet at the top of the red mud pre-impregnation slurry scrubbing tower 3 and the flue gas inlet of the red mud pre-impregnation clear liquid scrubbing tower 10, separately.

(5) The method includes the following steps.

(6) (a) The alumina calcination flue gas mixed with ozone was transported to the red mud pre-impregnation slurry scrubbing tower 3 for reverse spraying with a slurry obtained after red mud pre-impregnation so that a flue gas after a primary treatment and a red mud slurry after the spraying were obtained.

(7) (b) The flue gas after the primary treatment in step (a) was mixed with the ozone and then transported to the red mud pre-impregnation clear liquid scrubbing tower 10 for reverse spraying with a clear liquid obtained after the red mud pre-impregnation, so that a treated flue gas and a red mud clear liquid after the spraying were obtained.

(8) Typical but non-limiting embodiments of the present disclosure are described below.

Embodiment 1

(9) This embodiment provides a system for desulfurization and denitrification of alumina calcination flue gas. As shown in FIG. 1, the system includes an ozone generator 1, a first ozone homogenizer 2, a red mud pre-impregnation slurry scrubbing tower 3, a second ozone homogenizer 4, a red mud pre-impregnation tank 5, a red mud pre-impregnation slurry pond 6, a process water pipeline 7, a dewatering pond 8, a red mud pre-impregnation clear liquid pond 9, a red mud pre-impregnation clear liquid scrubbing tower 10, a demister 11 and a chimney 12.

(10) The red mud pre-impregnation slurry scrubbing tower 3 is provided with a spray layer at a upper part, and a flue gas inlet disposed on a tower wall below the spray layer and connected to an alumina calcination flue gas pipeline provided with the first ozone homogenizer 2. The red mud pre-impregnation clear liquid scrubbing tower 10 is provided with a spray layer at a upper part, and a flue gas inlet disposed on a tower wall below the spray layer. A gas outlet at the top of the red mud pre-impregnation slurry scrubbing tower 3 is connected to the flue gas inlet of the red mud pre-impregnation clear liquid scrubbing tower 10 through a pipeline provided with the second ozone homogenizer 4. The red mud pre-impregnation tank 5 is provided with a clear liquid outlet at an upper part and a slurry outlet at a lower part, where the clear liquid outlet is connected to a spray liquid inlet of the spray layer in the red mud pre-impregnation clear liquid scrubbing tower 10 through the red mud pre-impregnation clear liquid pond 9, and the slurry outlet is connected to a spray liquid inlet of the spray layer in the red mud pre-impregnation slurry scrubbing tower 3 through the red mud pre-impregnation slurry pond 6. A gas outlet of the ozone generator 1 is connected to the first ozone homogenizer 2 and the second ozone homogenizer 4, separately. A flue gas outlet at the top of the red mud pre-impregnation clear liquid scrubbing tower 10 is connected to the demister 11 and the chimney 12 in sequence. The red mud pre-impregnation slurry scrubbing tower 3 is provided with a bottom liquid outlet, where the bottom liquid outlet is connected to the spray liquid inlet of the spray layer in the red mud pre-impregnation slurry scrubbing tower 3 and to the dewatering pond 8, separately. A clear liquid outlet at an upper part of the dewatering pond 8 is connected to a material inlet of the red mud pre-impregnation tank 5. The red mud pre-impregnation clear liquid scrubbing tower 10 is provided with a bottom liquid outlet, where the bottom liquid outlet is connected to the spray liquid inlet of the spray layer in the red mud pre-impregnation clear liquid scrubbing tower 10 through the red mud pre-impregnation clear liquid pond 9.

Embodiment 2

(11) This embodiment provides a method for desulfurization and denitrification of alumina calcination flue gas. The method is performed by using the system for desulfurization and denitrification of alumina calcination flue gas in embodiment 1, so as to conduct the desulfurization and denitrification on an alumina calciner of 500,000 tons/year, where a concentration of SO.sub.2 in the flue gas is 250 mg/m.sup.3, and a concentration of NO.sub.x in the flue gas is 500 mg/m.sup.3.

(12) The method specifically includes the following steps.

(13) (a) Ozone generated by the ozone generator 1 was mixed with the alumina calcination flue gas through the first ozone homogenizer 2, where a molar ratio of the ozone to NO.sub.x in the alumina calcination flue gas was 0.4:1, the alumina calcination flue gas mixed with the ozone was transported to the red mud pre-impregnation slurry scrubbing tower 3 for reverse spraying with a slurry of pH 4 which was obtained after red mud pre-impregnation in the red mud pre-impregnation tank 5, so that a flue gas after a primary treatment and a red mud slurry after the spraying were obtained, where a part of the red mud slurry after the spraying was dewatered in the dewatering pond 8 to obtain a clear liquid which was returned to the red mud pre-impregnation tank 5 for the red mud pre-impregnation to be recycled, and the other part of the red mud slurry after the spraying was returned to the spray layer in the red mud pre-impregnation slurry scrubbing tower 3 as spray water to be recycled.

(14) (b) The ozone generated by the ozone generator 1 was mixed with the flue gas after the primary treatment in step (a) through the second ozone homogenizer 4, where a molar ratio of the ozone to remaining NO.sub.x in the flue gas after the primary treatment was 0.1:1, the flue gas mixed with the ozone was transported to the red mud pre-impregnation clear liquid scrubbing tower 10 for reverse spraying with a clear liquid pf pH 7 which was obtained after the red mud pre-impregnation in the red mud pre-impregnation tank 5, so that a treated flue gas and a red mud clear liquid after the spraying were obtained, where the red mud clear liquid after the spraying was returned to the spray layer in the red mud pre-impregnation clear liquid scrubbing tower 10 as spray water to be recycled, and the treated flue gas was demisted to obtain purified flue gas.

(15) In this embodiment, the concentration of SO.sub.2 in the purified flue gas was 8 mg/m.sup.3, and the concentration of NO.sub.x in the purified flue gas was 90 mg/m.sup.3.

Embodiment 3

(16) This embodiment provides a method for desulfurization and denitrification of alumina calcination flue gas. The method is performed by using the system for desulfurization and denitrification of alumina calcination flue gas in embodiment 1. The treatment method is similar to that in embodiment 2 except for differences that the molar ratio of the ozone to NO.sub.x in the alumina calcination flue gas was 0.8:1 and a pH of the slurry obtained after the red mud pre-impregnation was 5 in step (a), and the molar ratio of the ozone to the remaining NO.sub.x in the flue gas after the primary treatment was 0.4:1, and a pH of the clear liquid obtained after the red mud pre-impregnation was 9 in step (b).

(17) In this embodiment, the concentration of SO.sub.2 in the purified flue gas was 6 mg/m.sup.3, and the concentration of NO.sub.x in the purified flue gas was 60 mg/m.sup.3.

Embodiment 4

(18) This embodiment provides a method for desulfurization and denitrification of alumina calcination flue gas. The method is performed by using the system for desulfurization and denitrification of alumina calcination flue gas in embodiment 1. The treatment method is similar to that in embodiment 2 except for differences that the molar ratio of the ozone to NO.sub.x in the alumina calcination flue gas was 1:1 and a pH of the slurry obtained after the red mud pre-impregnation was 6 in step (a), and the molar ratio of the ozone to the remaining NO.sub.x in the flue gas after the primary treatment was 0.6:1, and a pH of the clear liquid obtained after the red mud pre-impregnation was 10 in step (b).

(19) In this embodiment, the concentration of SO.sub.2 in the purified flue gas was 5 mg/m.sup.3, and the concentration of NO.sub.x in the purified flue gas was 50 mg/m.sup.3.

Embodiment 5

(20) This embodiment provides a method for desulfurization and denitrification of alumina calcination flue gas. The method is performed by using the system for desulfurization and denitrification of alumina calcination flue gas in embodiment 1. The treatment method is similar to that in embodiment 2 except for differences that the molar ratio of the ozone to NO.sub.x in the alumina calcination flue gas was 1.5:1 and a pH of the slurry obtained after the red mud pre-impregnation was 7 in step (a), and the molar ratio of the ozone to the remaining NO.sub.x in the flue gas after the primary treatment was 1:1, and a pH of the clear liquid obtained after the red mud pre-impregnation was 12 in step (b).

(21) In this embodiment, the concentration of SO.sub.2 in the purified flue gas was 3 mg/m.sup.3, and the concentration of NO.sub.x in the purified flue gas was 45 mg/m.sup.3.

COMPARATIVE EXAMPLE 1

(22) This comparative example provides a method for desulfurization and denitrification of alumina calcination flue gas. The method is similar to that in embodiment 2 except for that a red mud method in a purification system in an apparatus used was replaced with a limestone-gypsum method, that is, the spray liquid was a liquid obtained by the limestone-gypsum method.

(23) In this comparative example, the concentration of SO.sub.2 in purified flue gas was 25 mg/m.sup.3, and the concentration of NO.sub.x in the purified flue gas was 180 mg/m.sup.3. It can be seen that oxynitrides in the flue gas cannot be removed by using the liquid in the limestone-gypsum method as the spray liquid.

COMPARATIVE EXAMPLE 2

(24) This comparative example provides a method for desulfurization and denitrification of alumina calcination flue gas. The method is similar to that in embodiment 2 except for that neither the second ozone homogenizer was disposed in an apparatus used nor ozone was sprayed, that is, the flue gas after the primary treatment, without being mixed with the ozone, was directly transported to the red mud pre-impregnation clear liquid scrubbing tower 10 for the reverse spraying with the clear liquid obtained after the red mud pre-impregnation.

(25) In this comparative example, the concentration of SO.sub.2 in purified flue gas was 20 mg/m.sup.3, and the concentration of NO.sub.x in the purified flue gas was 150 mg/m.sup.3. It can be seen that oxynitrides in the flue gas after the primary treatment cannot be effectively removed.

COMPARATIVE EXAMPLE 3

(26) This comparative example provides a method for desulfurization and denitrification of alumina calcination flue gas. The method is similar to that in embodiment 2 except for that neither the first ozone homogenizer was disposed in an apparatus used nor ozone was sprayed, that is, the alumina calcination flue gas, without being mixed with the ozone, was directly transported to the red mud pre-impregnation slurry scrubbing tower 3 for the reverse spraying with the slurry obtained after the red mud pre-impregnation.

(27) In this comparative example, the concentration of SO.sub.2 in purified flue gas was 10 mg/m.sup.3, and the concentration of NO.sub.x in the purified flue gas was 180 mg/m.sup.3.

(28) It can be seen by summarizing the embodiments and comparative examples described above that the present disclosure conducts the desulfurization and denitrification of the alumina calcination flue gas by merely using red mud solid wastes generated in an alumina production process as an absorbent and in combination with a synergistic effect of ozone, making it possible to achieve simultaneous flue gas purification and red mud dealkalization without adding other additives (such as a magnesium additive), which, and achieving the utilization of the solid wastes.

(29) Moreover, the present disclosure achieves the synergistic absorption of sulfur and nitrate by utilizing a synergistic catalytic oxidation effect of metal ions such as Fe.sup.3+ in the red mud slurry and the ozone, with reduced material consumption for subsequent desulfurization and denitrification, a flue gas desulfurization efficiency of more than 96.8% and an oxynitride removal efficiency of more than 82%.

(30) With the use of a structure of double-tower staged absorption, the present disclosure overcomes the problem of a difficulty in absorbing NO.sub.2 at a low O.sub.3/NO.sub.x molar ratio and reduces ozone consumption and a risk of ozone escape through enhanced absorption by sodium alkali at a second stage, which has advantages of high purification efficiency, low operation costs, etc., and has high applicability to the alumina calcination flue gas.

(31) The applicant has stated that although the detailed process equipment and flows of the present disclosure are described through the embodiments described above, the present disclosure is not limited to the detailed process equipment and flows described above, which means that the implementation of the present disclosure does not necessarily depend on the detailed process equipment and flows described above. It should be apparent to those skilled in the art that any improvements made to the present disclosure, equivalent replacements of various raw materials, the addition of adjuvant ingredients, and the selection of specific manners, etc. in the present disclosure all fall within the protection scope and the scope of disclosure of the present disclosure.