Device and method for treating ammonium sulfate wastewater by calcium method

Abstract

The invention discloses a device and a method for treating ammonium sulfate wastewater by a calcium method. The device comprises a lime feeding bin, a first reaction kettle, a calcium sulfate sedimentation tank, a carbonate feeding bin, a second reaction kettle and a calcium carbonate sedimentation tank, an upper feed port of the first reaction kettle is connected with upstream ammonium sulfate wastewater generation equipment, the top of the first reaction kettle is connected with a lime feeding bin, and a bottom outlet of the first reaction kettle is connected with a calcium sulfate sedimentation tank through a pipeline; a calcium sulfate extraction pipeline is arranged at the bottom of the calcium sulfate sedimentation tank, a lower liquid outlet is connected with a second reaction kettle, a top feeding hole of the second reaction kettle is connected with a carbonate feeding bin, and a bottom outlet of the second reaction kettle is connected with the calcium carbonate sedimentation tank; a calcium carbonate precipitation extraction pipeline is arranged at the bottom of the calcium carbonate precipitation tank. The device disclosed by the invention adopts a two-time precipitation method, wastewater treated by calcium salt is subjected to carbonate precipitation, the conversion rate of ammonium ions in the wastewater is increased, and the device has the advantages of cost saving, good wastewater treatment effect, high ammonia recovery rate, no environmental pollution and the like.

Description

Technical Field

[0001] This invention belongs to the field of ammonium sulfate wastewater treatment technology, and mainly relates to the lime-based ammonia removal process for high-concentration ammonium sulfate wastewater. Background Technology

[0002] In the context of environmental protection and sustainable development, higher requirements are placed on the treatment of ammonia nitrogen wastewater, which must not only meet wastewater treatment standards but also achieve nitrogen resource recovery and utilization. Currently, there are many methods for treating ammonium sulfate wastewater. Some methods involve using MVR (Medium-Vacuum Reduction) evaporation to crystallize the ammonium sulfate in the wastewater; others involve neutralizing the wastewater with lime and then directly pumping the neutralized liquid into a steam deammoniation tower to remove ammonia, yielding ammonia water; still others involve adding excess potassium hydroxide to the wastewater to react with sulfate ions in the solution to form potassium sulfate precipitate, and the filtered filtrate is also pumped into a steam deammoniation tower to remove ammonia and other volatile substances. Of the above treatment methods, MVR evaporation is suitable for wastewater with high ammonium sulfate concentration and low levels of other impurities. In the lime method, calcium hydroxide is poorly soluble in water. With the addition of calcium hydroxide, the pH of the wastewater becomes alkaline. At this time, hydroxide ions cannot completely dissociate in water, and some hydroxide ions react with calcium ions to form calcium hydroxide precipitate, which cannot participate in the conversion of ammonium ions. Therefore, even if an excessive amount of potassium hydroxide is added, the ammonium ions cannot be completely converted. This method is not suitable for wastewater treatment with high requirements. Potassium hydroxide and potassium oxide treatment agents are relatively more expensive than lime, resulting in higher treatment costs. Summary of the Invention

[0003] In view of the above-mentioned technical problems existing in the prior art, the purpose of the present invention is to provide an apparatus and method for treating ammonium sulfate wastewater by calcium method, which can reduce the treatment cost of ammonium sulfate wastewater, improve the treatment effect of ammonium sulfate wastewater, and realize the diversified utilization of ammonium sulfate wastewater.

[0004] The technical solution adopted in this invention is as follows:

[0005] An apparatus for treating ammonium sulfate wastewater using the calcium process includes a lime feeding silo, a first reaction vessel, a calcium sulfate precipitation tank, a carbonate feeding silo, a second reaction vessel, and a calcium carbonate precipitation tank.

[0006] The upper inlet of the first reactor is connected to the upstream ammonium sulfate wastewater generating equipment, its top is connected to the lime feeding silo, and its bottom outlet is connected to the calcium sulfate precipitation tank by a pipeline.

[0007] A calcium sulfate collection pipeline is installed at the bottom of the calcium sulfate precipitation tank. The lower outlet is connected to the second reactor. The top inlet of the second reactor is connected to the carbonate feeding silo. The bottom outlet of the second reactor is connected to the calcium carbonate precipitation tank.

[0008] A calcium carbonate precipitation and extraction pipeline is installed at the bottom of the calcium carbonate precipitation tank.

[0009] Furthermore, the top of the first reactor is equipped with an ammonia outlet and connected to an ammonia absorption tower.

[0010] Furthermore, it also includes a stripping tower. The lower outlet of the calcium carbonate precipitation tank is connected to the stripping ammonia removal tower via a pipeline. The gas outlet at the top of the stripping ammonia removal tower is connected to the ammonia absorption tower, and the outlet of the tower bottom is connected to the pipeline for the treated and qualified products.

[0011] The method for treating ammonium sulfate wastewater using the calcium process according to the apparatus of the present invention includes the following steps:

[0012] Step 1: Ammonium sulfate wastewater is fed into the first reactor. Quicklime or hydrated lime precipitant is added to the first reactor through the lime feeding hopper. The ammonium sulfate wastewater reacts chemically with the quicklime or hydrated lime precipitant to generate calcium sulfate precipitate and ammonia water. A large amount of heat is released during the reaction, causing some ammonia gas to escape and be sent to the ammonia absorption tower through the gas phase outlet at the top of the first reactor.

[0013] Step 2: After the reaction in Step 1 is completed, the liquid-solid mixture enters the calcium sulfate precipitation tank from the bottom outlet of the first reaction vessel for precipitation, and the calcium sulfate precipitate is collected.

[0014] Step 3: The supernatant after precipitation in Step 2 enters the second reaction vessel. Carbonate is added to the second reaction vessel through the carbonate feeding hopper. The carbonate reacts with the calcium hydroxide dissolved in the supernatant solution to generate calcium carbonate precipitate and sodium hydroxide. The generated sodium hydroxide further reacts with the incompletely converted ammonium ions in the solution.

[0015] Step 4: After the reaction in Step 3 is completed, the liquid-solid mixture enters the calcium carbonate precipitation tank from the bottom outlet of the second reaction vessel for precipitation, and the calcium carbonate precipitate is collected.

[0016] Furthermore, the supernatant obtained after sedimentation in step 4 is sent to the stripping tower. During the stripping process, ammonia is continuously extracted from the wastewater. The ammonia is collected from the top of the stripping tower and enters the ammonia absorption tower. The wastewater that has been stripped is collected from the bottom of the stripping tower.

[0017] Furthermore, in step 3, the carbonate in the carbonate feeding hopper is sodium carbonate or potassium carbonate.

[0018] Furthermore, in step 1, the pH at which the chemical reaction is complete is greater than 7, preferably pH = 11 to 13.

[0019] Furthermore, the amount of precipitant added in step 1 is based on the Ca content in the precipitant. 2+ SO4 in wastewater 2- The molar ratio is 1:1. In actual production, Ca... 2+ With SO4 2-The molar ratio can be appropriately increased to between 1 and 1.3:1.

[0020] Furthermore, the amount of carbonate added in step 3 is based on the CO3 content in the carbonate precipitant. 2- With dissolved Ca in the supernatant 2+ The molar ratio was controlled at 1-1.05:1, and the pH of the system was adjusted to 11.5-12.5 during the reaction.

[0021] In the device provided by the present invention, the interconnection between pipelines and equipment, as well as between each piece of equipment, can be set according to the specific engineering case requirements. The connection position and connection method between each piece of equipment and pipeline are not limited to the methods described above.

[0022] In the device structure of the present invention, the top of the second reactor does not have a gas phase outlet connected to the ammonia absorption tower.

[0023] The method described in this invention is for treating industrial wastewater containing ammonium sulfate, which can come from the production of dyes, enzymes, catalysts, etc., and there are no particular limitations on the source of the ammonium sulfate wastewater.

[0024] The raw material in the lime feeding silo of this invention is not limited to quicklime, but can be any substance that can react with sulfate ions to form a precipitate. The raw material in the carbonate feeding silo is not limited to sodium carbonate, but can be any substance that can react with calcium ions to form a precipitate. The selection of reaction raw materials can be arbitrary, and those skilled in the art can determine it according to the actual situation.

[0025] This part of the technology should be understood as follows: the process for treating ammonium sulfate wastewater in this invention mainly involves adding calcium ions to extract sulfate ions from the solution in the form of a precipitate, while simultaneously converting ammonium ions into ammonia water, facilitating subsequent resource utilization. Furthermore, the reaction in this step is exothermic, causing the temperature in the reactor to rise, and some ammonia gas to escape from the solution; this ammonia gas can then be recovered and reused.

[0026] This technique should be understood as follows: with the addition of calcium hydroxide, the solution becomes alkaline, and some hydroxide ions cannot completely dissociate in water. Hydroxide ions and calcium ions exist in the solution as precipitates, so some unconverted ammonium ions also exist in the solution. At this point, adding carbonates such as sodium carbonate to the solution causes them to react with calcium hydroxide to form calcium carbonate precipitate and sodium hydroxide. The generated sodium hydroxide continues to react with ammonium ions, promoting the conversion of ammonium ions into ammonia.

[0027] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0028] (1) In this invention, calcium hydroxide or calcium oxide is used as the main precipitant, which reduces the wastewater treatment cost compared with directly adding sodium hydroxide or magnesium hydroxide.

[0029] (2) In this invention, carbonate is used as a supplementary precipitant. Excessive use can avoid incomplete reaction caused by solubility and other issues when using calcium hydroxide as a single precipitant, thus preventing the wastewater treatment from failing to meet standards.

[0030] (3) In this invention, by adding carbonate, excess calcium ions in the solution are removed, thus avoiding the consequences of calcium ions causing blockage of the stripping tower in the subsequent stripping process.

[0031] (4) In this invention, an ammonia outlet is provided at the top of the first reactor and connected to the ammonia absorption tower, which can improve the ammonia recovery rate and reduce the recovery cost. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the structure of a novel ammonium sulfate wastewater calcium process treatment device according to the present invention.

[0033] In the diagram: 1. Lime feeding silo; 2. First reaction vessel; 3. Calcium sulfate precipitation tank; 4. Carbonate feeding silo; 5. Second reaction vessel; 6. Calcium carbonate precipitation tank; 7. Stripping tower. Detailed Implementation

[0034] The technical solution of the present invention will now be clearly and completely described, and examples of the embodiments are shown in the accompanying drawings. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. All other embodiments based on the embodiments of the present invention, with adjustments or improvements made by those skilled in the art, are within the protection scope of the present invention.

[0035] Example 1:

[0036] A device for treating ammonium sulfate wastewater using the calcium process, comparison Figure 1 It includes a lime feeding silo 1, a first reaction vessel 2, a calcium sulfate precipitation tank 3, a carbonate feeding silo 4, a second reaction vessel 5, a calcium carbonate precipitation tank 6, and a stripping tower 7.

[0037] The upper inlet of the first reactor 2 is connected to the upstream ammonium sulfate wastewater generating equipment, its top is connected to the lime feeding silo 1, and its bottom outlet is connected to the calcium sulfate precipitation tank 3 by a pipeline. The top of the first reactor 2 is equipped with an ammonia outlet and is connected to an ammonia absorption tower.

[0038] A calcium sulfate precipitation tank 3 has a calcium sulfate collection pipeline at its bottom, with its lower outlet connected to a second reactor 5. The top inlet of the second reactor 5 is connected to a carbonate feeding silo 4, and its bottom outlet is connected to a calcium carbonate precipitation tank 6. A calcium carbonate precipitation collection pipeline is also installed at the bottom of the calcium carbonate precipitation tank 6. The lower outlet of the calcium carbonate precipitation tank 6 is connected to a stripping ammonia removal tower 7 via a pipeline. The top gas outlet of the stripping ammonia removal tower 7 is connected to an ammonia absorption tower, and the bottom outlet of the tower is connected to a pipeline for the treated, compliant product.

[0039] The present invention is explained using the treatment of ammonium sulfate wastewater from a dye factory as an example. The factory's ammonium sulfate wastewater treatment capacity is 1200 kg / h, with an ammonia nitrogen content of 22 g / L and SO4 content of [missing information]. 2- The content was 0.72 mol / L.

[0040] The present invention provides a novel ammonium sulfate wastewater calcium treatment device and process for removing ammonia nitrogen from the wastewater. The specific process is as follows: Figure 1 As shown:

[0041] (1) 1000L of ammonium sulfate wastewater (SO4) generated during dye production 2- The content of calcium oxide (0.72 mol / L) was directly fed into the first reactor 2, and 44.5 kg of calcium oxide (Ca) was added from the top of the first reactor 2. 2+ (Molar mass is 794.6 mol), controlling the Ca content in the precipitant. 2+ SO4 in wastewater 2- The molar ratio is 1.1:1 (SO4) 2- The total amount of substance is 0.72 mol / L × 1000 L = 720 mol, Ca 2+ The dosage was 794.6 mol (molar ratio 794.6:720 ≈ 1.1:1). During the reaction, the pH of the system was adjusted to 12-13. An ammonia outlet was installed at the top of the first reactor 2. Ammonium sulfate wastewater and calcium oxide reacted in the first reactor 2 to produce gas, which entered an ammonia recovery tower for recycling via the ammonia outlet at the top of the first reactor 2. After the reaction, the liquid-solid mixture entered a calcium sulfate precipitation tank 3 from the bottom outlet of the first reactor 2 for precipitation, and the calcium sulfate precipitate was collected. The supernatant after precipitation entered the second reactor 5. Testing showed that the conversion rate of ammonium ions in the wastewater after this step was approximately 92%, and SO42-... 2- Almost completely removed.

[0042] (2) After the supernatant from the precipitation process enters the second reaction vessel 5, the content of unreacted Ca(OH)2 in the supernatant is measured (converted to Ca). 2+ With a concentration of 0.07 mol / L (corresponding to 70 mol of Ca(OH)2), 7.5 kg of sodium carbonate was added from the top of the second reactor (reactor 5) to control the CO3 concentration in the precipitant.2- With dissolved Ca in the supernatant 2+ The molar ratio is 1:1 to ensure dissolved Ca 2+ The sodium carbonate is completely removed by precipitation. During the reaction, the pH of the system is adjusted to 11.5–12.5. Sodium carbonate reacts with calcium hydroxide dissolved in the supernatant: Na₂CO₃ + Ca(OH)₂ = CaCO₃↓ + 2NaOH. The generated sodium hydroxide can further react with incompletely converted ammonium ions in the solution. This process promotes the conversion of ammonium ions into ammonia water. After the reaction, the liquid-solid mixture enters the calcium carbonate precipitation tank 6 from the bottom outlet of the second reactor 5 for precipitation. Calcium carbonate precipitate is removed in the calcium carbonate precipitate, and the treated liquid enters the stripping tower. The second reactor 5 does not have a gas phase outlet connected to the ammonia absorption tower at the top. Through this step, the conversion rate of ammonium ions in the wastewater is increased from approximately 92% to 99%.

[0043] (3) The wastewater treated in step (2) enters the stripping tower. During the stripping process, ammonia gas is continuously extracted from the wastewater and enters the ammonia absorption tower from the top gas phase outlet. The top gas phase outlet of the stripping tower is connected to the ammonia absorption tower. The treated liquid is discharged from the bottom of the tower after meeting the standards.

[0044] The above describes an embodiment of the present invention. After step (1), the conversion rate of ammonium ions in the wastewater is approximately 92%. After step (2), the conversion rate of ammonium ions in the wastewater increases to 99%. At this point, after stripping in step (3), ammonia nitrogen can be essentially removed. The cost of the precipitant for each 1000L of wastewater treated using this method is approximately 68.7 yuan, while the cost of using the sodium hydroxide treatment method, which can achieve the same treatment effect, is approximately 146.4 yuan, representing a cost reduction of approximately 53.1%.

[0045] The embodiments described above are merely illustrative of the implementation methods of the present invention, but should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the protection scope of the present invention.

Claims

1. An apparatus for treating ammonium sulfate wastewater using the calcium method, characterized in that, It includes a lime feeding silo (1), a first reaction vessel (2), a calcium sulfate precipitation tank (3), a carbonate feeding silo (4), a second reaction vessel (5), and a calcium carbonate precipitation tank (6). The upper feed port of the first reactor (2) is connected to the upstream ammonium sulfate wastewater generating equipment, its top is connected to the lime feeding silo (1), and its bottom outlet is connected to the calcium sulfate precipitation tank (3) by a pipeline. A calcium sulfate collection pipeline is installed at the bottom of the calcium sulfate precipitation tank (3). The lower outlet is connected to the second reactor (5). The top inlet of the second reactor (5) is connected to the carbonate feeding bin (4). The bottom outlet of the second reactor (5) is connected to the calcium carbonate precipitation tank (6). A calcium carbonate precipitation collection pipeline is installed at the bottom of the calcium carbonate precipitation tank (6).

2. The apparatus for treating ammonium sulfate wastewater using the calcium method as described in claim 1, characterized in that, The first reactor (2) has an ammonia outlet at the top and is connected to an ammonia absorption tower.

3. The apparatus for treating ammonium sulfate wastewater using the calcium method as described in claim 1, characterized in that, It also includes a stripping tower (7), the lower outlet of the calcium carbonate precipitation tank (6) is connected to the stripping ammonia removal tower (7) through a pipeline, the top gas outlet of the stripping ammonia removal tower (7) is connected to the ammonia absorption tower, and the bottom outlet of the tower is connected to the pipeline for the treated and qualified products.

4. A method for treating ammonium sulfate wastewater using the calcium process based on the apparatus described in claim 1, characterized in that, Includes the following steps: Step 1: Ammonium sulfate wastewater is fed into the first reactor (2). Quicklime or hydrated lime precipitant is added into the first reactor (2) through the lime feeding bin (1). The ammonium sulfate wastewater reacts chemically with the quicklime or hydrated lime precipitant to generate calcium sulfate precipitate and ammonia water. A large amount of heat is released during the reaction, causing some ammonia gas to escape and be sent to the ammonia absorption tower through the gas phase outlet at the top of the first reactor (2). Step 2: After the reaction in Step 1 is completed, the liquid-solid mixture enters the calcium sulfate precipitation tank (3) from the bottom outlet of the first reaction vessel (2) for precipitation, and the calcium sulfate precipitate is collected. Step 3: The supernatant after precipitation in Step 2 enters the second reactor (5). Carbonate is fed into the second reactor (5) through the carbonate feeding bin (4). The carbonate reacts with the calcium hydroxide dissolved in the supernatant solution to generate calcium carbonate precipitate and sodium hydroxide. The generated sodium hydroxide further reacts with the incompletely converted ammonium ions in the solution. Step 4: After the reaction in Step 3 is completed, the liquid-solid mixture enters the calcium carbonate precipitation tank (6) from the bottom outlet of the second reaction vessel (5) for precipitation, and the calcium carbonate precipitate is collected.

5. The method as described in claim 4, characterized in that, Step 4: The supernatant after sedimentation is completed is sent to the stripping tower (7). During the stripping process, ammonia is continuously extracted from the wastewater. The ammonia is taken out from the top of the stripping tower and enters the ammonia absorption tower. The wastewater that has been stripped is taken out from the bottom of the stripping tower.

6. The method as described in claim 4, characterized in that, In step 3, the carbonate in the carbonate feeding bin (4) is sodium carbonate or potassium carbonate.

7. The method as described in claim 4, characterized in that, In step 1, the pH at which the chemical reaction is complete is greater than 7, preferably pH = 11~13.

8. The method as described in claim 4, characterized in that, The amount of precipitant added in step 1 is based on the Ca content in the precipitant. 2 + SO4 in wastewater 2- The molar ratio is controlled at 1~1.3:

1.

9. The method as described in claim 4, characterized in that, The amount of carbonate added in step 3 is based on the CO3 content in the carbonate precipitant. 2- With dissolved Ca in the supernatant 2+ The molar ratio was controlled at 1-1.05:1, and the pH of the system was adjusted to 11.5-12.5 during the reaction.

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