Method for preparing high-purity calcium sulfate dihydrate by wet desulphurization of trace manganese ion modified calcium hydroxide absorbent

Abstract

The invention discloses a method for preparing high-purity calcium sulfate dihydrate by wet desulfurization of a trace manganese ion modified calcium hydroxide absorbent, which comprises the following steps: introducing flue gas containing sulfur dioxide and oxygen into a desulfurization tower from the bottom of the desulfurization tower, and discharging the flue gas from the top of the desulfurization tower; inputting the manganese ion modified calcium hydroxide desulfurizer slurry into a third-stage circulating tank, pumping the manganese ion modified calcium hydroxide desulfurizer slurry into a desulfurizing tower for spraying, carrying out countercurrent contact reaction on the manganese ion modified calcium hydroxide desulfurizer slurry and flue gas, and circulating the reacted slurry back to the third-stage circulating tank; inputting the slurry in the third-stage circulating tank into a second-stage circulating tank, pumping the slurry into a desulfurizing tower for spraying, carrying out countercurrent contact reaction on the slurry and the flue gas, and circulating the reacted slurry back to the second-stage circulating tank; inputting the slurry in the second-stage circulating tank into a first-stage circulating tank, pumping the slurry into a desulfurizing tower for spraying, carrying out countercurrent contact reaction on the slurry and flue gas, and circulating the reacted slurry back to the first-stage circulating tank to obtain calcium sulfate dihydrate; the sulfur dioxide removal efficiency is high, and the method is simple and efficient and has remarkable economical efficiency.

Description

Technical Field

[0001] The present invention belongs to the field of treatment of air pollutants and resource utilization of solid waste, and particularly relates to a method for preparing high-purity calcium sulfate dihydrate by wet desulfurization with a calcium hydroxide absorbent modified by trace manganese ions. Background Art

[0002] The calcium hydroxide wet desulfurization technology is a widely used flue gas desulfurization technology. Specifically, calcium hydroxide is mixed with water to form a slurry, which is fully contacted with the flue gas through a spray tower, so that sulfur dioxide reacts with calcium hydroxide to form calcium sulfite, and then is further converted into calcium sulfate dihydrate under oxidation conditions. The calcium sulfate dihydrate (gypsum) generated by the desulfurization reaction can be used as building materials, etc., and has certain economic value. However, due to the presence of calcium sulfite and partial calcium hydroxide in the desulfurization reaction process, the desulfurization product calcium sulfate dihydrate is impure, which limits its downstream application. At present, the industrial treatment method is mainly to inject a large amount of air into the desulfurization system to make calcium sulfite fully contact with oxygen to promote its oxidation into calcium sulfate dihydrate, and continue to add sulfuric acid to the desulfurization product to force the oxidation of calcium sulfite into calcium sulfate dihydrate. Although this method obtains relatively pure calcium sulfate dihydrate, it converts high-value sulfuric acid into calcium sulfate dihydrate, greatly increasing the desulfurization cost.

[0003] Therefore, how to provide a simple and low-cost method to promote the conversion of calcium sulfite into high-purity calcium sulfate dihydrate during the calcium hydroxide desulfurization process is of great significance. Summary of the Invention

[0004] To solve the above technical problems, the present invention proposes a method for preparing high-purity calcium sulfate dihydrate by wet desulfurization with a calcium hydroxide absorbent modified by trace manganese ions.

[0005] The technical solution of the present invention is as follows:

[0006] A method for preparing high-purity calcium sulfate dihydrate by wet desulfurization with a calcium hydroxide absorbent modified by trace manganese ions, comprising the following steps:

[0007] Introduce the flue gas containing sulfur dioxide and oxygen into the desulfurization tower from the bottom of the desulfurization tower and discharge it from the top of the desulfurization tower;

[0008] Input the slurry of the calcium hydroxide desulfurizer modified by manganese ions into a three-stage circulation tank for stirring, and input the slurry of the calcium hydroxide desulfurizer modified by manganese ions into the desulfurization tower through a three-stage circulation pump for spraying with spray head III, and contact and react with the flue gas in a countercurrent manner. The reacted slurry is circulated back to the three-stage circulation tank;

[0009] Input the slurry in the three-stage circulation tank into the two-stage circulation tank, and input the slurry into the desulfurization tower through a two-stage circulation pump for spraying with spray head II, and contact and react with the flue gas in a countercurrent manner. The reacted slurry is circulated back to the two-stage circulation tank;

[0010] The slurry in the secondary circulation tank is input into the primary circulation tank. The slurry is input into the desulfurization tower through the primary circulation pump and sprayed by spray head I, and reacts with the flue gas in countercurrent contact. The reacted slurry is circulated back to the primary circulation tank. The primary circulation tank is located at the bottom of the desulfurization tower, and calcium sulfate dihydrate is obtained in the primary circulation tank.

[0011] Spray head III, turbulator III, spray head II, turbulator II, spray head I, and turbulator I are arranged from top to bottom in the desulfurization tower. Turbulator III and turbulator II are inclined, and the lower end of turbulator III is connected to the tertiary circulation tank, and the lower end of turbulator II is connected to the secondary circulation tank.

[0012] The slurry of the manganese ion-modified calcium hydroxide desulfurizer is prepared by mixing a manganese ion source, calcium hydroxide, and water, where the mass concentration of calcium hydroxide is 20%-60%, and the concentration of manganese ions is 0.2 g / L-20 g / L; the manganese ion source is soluble manganese sulfate salt, wastewater containing manganese ions in industrial production, etc.

[0013] In the present invention, desulfurization is carried out by preparing a desulfurizer by mixing a trace amount of manganese ion source, calcium hydroxide, and water, and the sulfur dioxide in the flue gas is washed three times. The sulfur dioxide concentration in the flue gas at the outlet of the desulfurization tower is controlled to be lower than 35 mg / Nm 3 through the third-stage washing, and the content of calcium sulfate dihydrate in the slurry discharged from the primary circulation tank is controlled to be higher than 98% through the first-stage washing.

[0014] The present invention is simple to operate, low in cost, economically feasible, and is generally applicable to the removal of sulfur dioxide in coal-fired flue gas. Compared with the traditional method of preparing calcium sulfate dihydrate by strong oxidation of calcium sulfite, it can effectively reduce the investment and operation costs. Description of the Drawings

[0015] Figure 1 It is a schematic structural diagram of the device in Example 1;

[0016] Figure 2 It is an X-ray diagram of the solid in the slurry discharged from the primary circulation tank in Example 2 and Comparative Example 1. Detailed Embodiments

[0017] The technical solution of the present invention will be clearly and completely described below in conjunction with specific embodiments and drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0018] Example 1

[0019] An apparatus for preparing high-purity calcium sulfate dihydrate by wet desulfurization with a trace manganese ion-modified calcium hydroxide absorbent is as follows Figure 1 shown, including a desulfurization tower. Inside the desulfurization tower, spray head III, turbulator III, spray head II, turbulator II, spray head I, and turbulator I are arranged from top to bottom. Turbulator III and turbulator II are inclined, and the lower end of turbulator III is connected to a tertiary circulation tank. The lower end of turbulator II is connected to a secondary circulation tank. The tertiary circulation tank is filled with a manganese ion-modified calcium hydroxide desulfurization agent slurry. The tertiary circulation tank is respectively connected to a tertiary circulation pump and the secondary circulation tank. The tertiary circulation pump is connected to spray head III. The secondary circulation tank is respectively connected to a secondary circulation pump and a primary circulation tank. The secondary circulation pump is connected to spray head II. The primary circulation tank is respectively connected to a primary circulation pump and the bottom of the desulfurization tower. The primary circulation pump is connected to spray head I. A flue gas inlet is arranged on the side of the lower part of the desulfurization tower, and the flue gas inlet is located below turbulator I.

[0020] Example 2

[0021] A method for preparing high-purity calcium sulfate dihydrate by wet desulfurization with a trace manganese ion-modified calcium hydroxide absorbent, using the apparatus of Example 1, includes the following steps:

[0022] Flue gas containing 2500 mg / Nm 3 sulfur dioxide and 6% oxygen is introduced into the desulfurization tower from the flue gas inlet at the lower part of the desulfurization tower; a desulfurization agent slurry is prepared by mixing a manganese ion source, calcium hydroxide, and water, where the mass concentration of calcium hydroxide is 40%, the concentration of manganese ions is 1 mg / L, and the manganese ion source is manganese sulfate;

[0023] The manganese ion-modified calcium hydroxide desulfurization agent slurry is input into the tertiary circulation tank for stirring, and the manganese ion-modified calcium hydroxide desulfurization agent slurry is input into the desulfurization tower through the tertiary circulation pump and sprayed by spray head III for countercurrent contact reaction with the flue gas. The reacted slurry is recycled back to the tertiary circulation tank;

[0024] The slurry in the tertiary circulation tank is input into the secondary circulation tank, and the slurry is input into the desulfurization tower through the secondary circulation pump and sprayed by spray head II for countercurrent contact reaction with the flue gas. The reacted slurry is recycled back to the secondary circulation tank;

[0025] The slurry in the secondary circulation tank is input into the primary circulation tank, and the slurry is input into the desulfurization tower through the primary circulation pump and sprayed by spray head I for countercurrent contact reaction with the flue gas. The reacted slurry is recycled back to the primary circulation tank. The primary circulation tank is located at the bottom of the desulfurization tower, and calcium sulfate dihydrate is obtained in the primary circulation tank;

[0026] The flue gas is discharged from the top of the desulfurization tower.

[0027] The sulfur dioxide content in the flue gas discharged from the top of the desulfurization tower is 30 mg / Nm 3 , and the content of calcium sulfate dihydrate in the solid discharged from the primary circulation tank is higher than 98.2%.

[0028] Example 2

[0029] A method for preparing high-purity calcium sulfate dihydrate by wet desulfurization with a trace manganese ion-modified calcium hydroxide absorbent. Using the device of Example 1, it includes the following steps:

[0030] The flue gas containing 2000 mg / Nm 3 of sulfur dioxide and 6% oxygen is introduced into the desulfurization tower from the flue gas inlet at the lower part of the desulfurization tower; a desulfurization agent slurry is prepared by mixing a manganese ion source, calcium hydroxide and water, wherein the mass concentration of calcium hydroxide is 50%, the concentration of manganese ions is 3 mg / L, and the manganese ion source is manganese sulfate;

[0031] The manganese ion-modified calcium hydroxide desulfurization agent slurry is input into a three-stage circulation tank for stirring, and the manganese ion-modified calcium hydroxide desulfurization agent slurry is input into the desulfurization tower by a three-stage circulation pump and sprayed by spray head Ⅲ for countercurrent contact reaction with the flue gas, and the reacted slurry is circulated back to the three-stage circulation tank;

[0032] The slurry in the three-stage circulation tank is input into the two-stage circulation tank, and the slurry is input into the desulfurization tower by a two-stage circulation pump and sprayed by spray head Ⅱ for countercurrent contact reaction with the flue gas, and the reacted slurry is circulated back to the two-stage circulation tank;

[0033] The slurry in the two-stage circulation tank is input into the one-stage circulation tank, and the slurry is input into the desulfurization tower by a one-stage circulation pump and sprayed by spray head Ⅰ for countercurrent contact reaction with the flue gas, and the reacted slurry is circulated back to the one-stage circulation tank. The one-stage circulation tank is located at the bottom of the desulfurization tower, and calcium sulfate dihydrate is obtained in the one-stage circulation tank;

[0034] The flue gas is discharged from the top of the desulfurization tower.

[0035] The sulfur dioxide content in the flue gas discharged from the top of the desulfurization tower is 25 mg / Nm 3 , and the content of calcium sulfate dihydrate in the solid discharged from the one-stage circulation tank is higher than 98.6%.

[0036] Example 3

[0037] A method for preparing high-purity calcium sulfate dihydrate by wet desulfurization with a trace manganese ion-modified calcium hydroxide absorbent. Using the device of Example 1, it includes the following steps:

[0038] The flue gas containing 1500 mg / Nm 3 of sulfur dioxide and 6% oxygen is introduced into the desulfurization tower from the flue gas inlet at the lower part of the desulfurization tower; a desulfurization agent slurry is prepared by mixing a manganese ion source, calcium hydroxide and water, wherein the mass concentration of calcium hydroxide is 60%, the concentration of manganese ions is 20 mg / L, and the manganese ion-containing wastewater in industrial production (yellow phosphorus production wastewater);

[0039] The slurry of manganese ion-modified calcium hydroxide desulfurizer is input into the three-stage circulation tank for stirring, and the slurry of manganese ion-modified calcium hydroxide desulfurizer is input into the desulfurization tower through the three-stage circulation pump and sprayed by spray head Ⅲ, and reacts with the flue gas in countercurrent contact. The reacted slurry is circulated back to the three-stage circulation tank;

[0040] The slurry in the three-stage circulation tank is input into the two-stage circulation tank, and the slurry is input into the desulfurization tower through the two-stage circulation pump and sprayed by spray head Ⅱ, and reacts with the flue gas in countercurrent contact. The reacted slurry is circulated back to the two-stage circulation tank;

[0041] The slurry in the two-stage circulation tank is input into the one-stage circulation tank, and the slurry is input into the desulfurization tower through the one-stage circulation pump and sprayed by spray head Ⅰ, and reacts with the flue gas in countercurrent contact. The reacted slurry is circulated back to the one-stage circulation tank. The one-stage circulation tank is located at the bottom of the desulfurization tower, and calcium sulfate dihydrate is obtained in the one-stage circulation tank;

[0042] The flue gas is discharged from the top of the desulfurization tower.

[0043] The sulfur dioxide content in the flue gas discharged from the top of the desulfurization tower is 25mg / Nm 3 , and the content of calcium sulfate dihydrate in the solid discharged from the one-stage circulation tank is higher than 99.2%.

[0044] Comparative Example 1

[0045] The difference between Comparative Example 1 and Example 2 is that the desulfurizer does not contain manganese ions, and the rest of the process steps and parameters are the same as those in Example 2. It is detected that the sulfur dioxide content in the flue gas discharged from the top of the desulfurization tower is 25mg / Nm 3 , but the content of calcium sulfate dihydrate in the solid discharged from the one-stage circulation tank is only 89%.

[0046] The solids in the slurry discharged from the one-stage circulation tank in Example 2 and Comparative Example 1 were analyzed by X-ray diffraction, and the results are as Figure 2 shown. It can be seen from the figure that in Example 2, the solid discharged from the one-stage circulation tank after desulfurization of the modified calcium hydroxide absorbent with trace manganese ions added is calcium sulfate dihydrate, and there is no obvious peak of calcium sulfite in the calcium sulfate dihydrate after desulfurization, indicating that it is converted into calcium sulfate dihydrate; in Comparative Example 1, calcium sulfite was significantly detected in the solid discharged from the one-stage circulation tank after desulfurization of the calcium hydroxide absorbent without adding trace manganese ions, indicating that the present invention has a significant effect on the preparation of high-purity calcium sulfate dihydrate.

[0047] Comparative Example 2

[0048] The difference between Comparative Example 2 and Example 2 is that the desulfurization tower has only one layer of spraying, that is, there are no supporting components such as a three-stage circulation pump, a three-stage circulation tank, a two-stage circulation pump, a two-stage circulation tank, spray head III, turbulator III, spray head II, turbulator II, etc. There are only spray head I, turbulator I, and a first-stage circulation tank. The remaining process steps and parameters are the same as those in Example 2. It is detected that if the sulfur dioxide content in the flue gas discharged from the top of the desulfurization tower is ensured to be less than 25 mg / Nm 3 , the content of calcium sulfate dihydrate in the solid discharged from the first-stage circulation tank is only 70%; if the content of calcium sulfate dihydrate in the solid discharged from the first-stage circulation tank is ensured to reach more than 95%, the sulfur dioxide content in the flue gas discharged from the top of the desulfurization tower is higher than 150 mg / Nm 3 , which cannot meet the requirements for flue gas pollutant emissions. It can be seen that the multi-stage circulation designed in the present invention can not only ensure that the sulfur dioxide content in the flue gas discharged from the top of the desulfurization tower meets the ultra-low emission requirements (i.e., the sulfur dioxide emission concentration is less than 35 mg / m 3 ), but also ensure the preparation of high-purity calcium sulfate dihydrate, having significant advantages.

[0049] The above is only the preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A method for preparing high-purity calcium sulfate dihydrate by wet desulfurization using a trace amount of manganese ion modified calcium hydroxide absorbent, characterized in that: The following steps are involved: The flue gas containing sulfur dioxide and oxygen is passed into the desulfurization tower from the bottom of the desulfurization tower and discharged from the top of the desulfurization tower; The manganese ion modified calcium hydroxide desulfurizer slurry is input into the tertiary circulation tank for stirring, and the manganese ion modified calcium hydroxide desulfurizer slurry is input into the desulfurization tower through the tertiary circulation pump for spraying with nozzle III, and reacts with the flue gas in countercurrent contact, and the slurry after the reaction is circulated back to the tertiary circulation tank; The slurry in the tertiary circulation tank is input into the secondary circulation tank, and the slurry is input into the desulfurization tower through the secondary circulation pump and sprayed by nozzle II, and reacts with the flue gas in countercurrent, and the slurry after the reaction is circulated back to the secondary circulation tank; The slurry in the secondary circulation tank is input into the primary circulation tank, and the slurry is input into the desulfurization tower through the primary circulation pump and sprayed by nozzle I, and reacts with the flue gas in countercurrent. The slurry after the reaction is circulated back to the primary circulation tank, which is located at the bottom of the desulfurization tower, and obtains high-purity calcium sulfate dihydrate.

2. The method for preparing high-purity calcium sulfate by wet desulfurization using trace manganese ion-modified calcium hydroxide absorbent according to claim 1, characterized in that: Nozzle III, turbulator III, nozzle II, turbulator II, nozzle I and turbulator I are arranged from top to bottom in the desulfurization tower. Turbulator III and turbulator II are arranged obliquely, and the lower end of turbulator III is connected to the tertiary circulation tank, and the lower end of turbulator II is connected to the secondary circulation tank.

3. The method for preparing high-purity calcium sulfate dihydrate by wet desulfurization using trace manganese ion modified calcium hydroxide absorbent according to claim 1, characterized in that: The manganese ion modified calcium hydroxide desulfurizer slurry is prepared by mixing a manganese ion source, calcium hydroxide and water, wherein the mass concentration of the calcium hydroxide is 20%-60%, and the concentration of the manganese ion is 0.2g / L-20g / L.

4. The method for preparing high-purity calcium sulfate dihydrate by wet desulfurization using trace manganese ion modified calcium hydroxide absorbent according to claim 1, characterized in that: The manganese ion source is soluble manganese sulfate salt and waste water containing manganese ions in industrial production.

Images