Recycling method of ammonia-containing waste gas

Abstract

The invention belongs to the technical field of waste gas treatment, and discloses a recycling method of ammonia-containing waste gas. The preparation method comprises the following steps: (1) uniformly mixing a phosphoric acid solution, a magnesium salt / calcium salt solution and a hypochlorous acid solution according to the molar ratio of phosphoric acid to magnesium salt / calcium salt to hypochlorous acid being 1: (0.8-1): (0.8-1.2) to obtain a medicament; (2) continuously introducing the ammonia-containing waste gas into the medicament, reacting at room temperature, and continuously monitoring the pH value of the reaction liquid on line in real time until the pH value gt of the reaction liquid; 7, stopping introducing the ammonia-containing waste gas; and (3) adding nitrite bacteria into the reaction liquid obtained in the step (2) according to the molar-mass ratio of the magnesium salt / calcium salt to the nitrite bacteria in the step (1) of 0.41 mol: (0.1-1) g, mixing and reacting at 25-30 DEG C for 4-12 hours to obtain a solid-containing liquid-phase product, and directly using the solid-containing liquid-phase product as a liquid compound fertilizer for further use. The whole process is simple to operate and easy to industrialize, the used raw materials are common chemical raw materials, the cost is low, the fixing efficiency of ammonia gas is high, and the resource utilization rate is high.

Description

Technical Field

[0001] The present invention belongs to the technical field of waste gas treatment, and in particular relates to a method for recycling ammonia-containing waste gas. Background Art

[0002] Ammonia, as an important chemical raw material, is widely used in agriculture, industry, and environmental protection. It is primarily used in the production of nitrogen fertilizers such as urea and ammonium nitrate, synthetic fibers, plastics, and refrigerants, as well as in flue gas denitrification, reducing nitrogen oxide emissions and improving air quality. Despite its significant economic value, ammonia is generated in large quantities during many agricultural and industrial processes, resulting in significant waste of resources and serious negative environmental impacts. The impacts of ammonia emissions on the environment and human health primarily include air pollution, water contamination, and soil degradation. Currently, common technologies for treating ammonia-containing waste gas primarily include physical adsorption and chemical absorption, but these methods have shortcomings. While commonly used adsorbent materials for physical adsorption, such as activated carbon and zeolite, have high adsorption capacities, they are difficult to regenerate, and the ammonia retention after adsorption is unstable. Chemical absorption, which absorbs ammonia through alkaline solutions, has high absorption efficiency, but the product is difficult to handle and is costly. Given the shortcomings of existing ammonia-containing waste gas treatment technologies, the development of efficient, economical, and environmentally friendly ammonia recovery and utilization technologies is crucial. Summary of the Invention

[0003] In order to overcome the shortcomings of existing ammonia-containing waste gas treatment technologies, such as unstable effects and difficult product treatment, the present invention aims to provide a method for recycling ammonia-containing waste gas.

[0004] To achieve the above object, the technical solution adopted by the present invention is as follows: A method for recycling ammonia-containing waste gas comprises the following steps: (1) Phosphoric acid solution, magnesium salt / calcium salt solution and hypochlorous acid solution are uniformly mixed in a molar ratio of phosphoric acid, magnesium salt / calcium salt and hypochlorous acid = 1: (0.8-1): (0.8-1.2) to obtain a reagent; (2) continuously passing the ammonia-containing waste gas into the reagent obtained in step (1), reacting at room temperature and continuously monitoring the pH of the reaction solution online in real time until the pH of the reaction solution is greater than 7, then stopping the passing of the ammonia-containing waste gas; (3) Adding nitrosobacteria to the reaction solution obtained in step (2) according to the molar-mass ratio of magnesium salt / calcium salt: nitrosobacteria = 0.41 mol: (0.1-1) g in step (1), and mixing and reacting at 25-30° C. for 4-12 hours, thereby obtaining a liquid product containing solids, which is directly used as a liquid compound fertilizer; In the above molar ratio and molar-mass ratio, the magnesium salt / calcium salt is measured based on the magnesium ions or calcium ions it provides.

[0005] Preferably, the concentration of the phosphoric acid solution is 0.4-0.6 mol / L, the magnesium / calcium ion concentration of the magnesium salt / calcium salt solution is 0.2-0.6 mol / L, and the molar concentration of the hypochlorous acid solution is 0.48-0.6 mol / L.

[0006] Preferably, the magnesium salt is MgSO4·7H2O or MgCl2·6H2O, and the calcium salt is CaCl2·2H2O.

[0007] Preferably, in step (3), the nitrosating bacteria are added directly in the form of powder or in the form of an aqueous solution.

[0008] Preferably, the concentration of the nitrosobacteria aqueous solution is 0.2-0.4 g / mL.

[0009] The method of the present invention is particularly suitable for the recovery and utilization of ammonia in agricultural waste treatment, sewage treatment and other industrial processes that generate ammonia emissions.

[0010] In the present invention, the main functions of hypochlorous acid are: (1) inhibiting side reactions and organic pollution: hypochlorous acid can oxidatively decompose organic matter in the reaction system (such as humic acid in agricultural waste and pathogens and viruses carried in exhaust gas), preventing them from interfering with the struvite crystallization process (generated by the reaction of phosphoric acid, magnesium salt / calcium salt and ammonia), and improving the purity of crystallization; (2) preventing ammonia from volatilizing again: hypochlorous acid can regulate pH value (weakly acidic environment) and oxidize free ammonia (NH3→NH2Cl and other chloramine stable compounds. In the present invention, the amount of hypochlorous acid used is small, so this reaction is a side reaction. The main reaction is to convert ammonia into struvite through phosphoric acid + magnesium salt / calcium salt. NH2Cl can also be converted into NO2 by nitrosating bacteria in the later stage. - / NO3 - ), with phosphoric acid + magnesium salt / calcium salt to play a dual role in inhibiting ammonia escape; (3) Synergistic sterilization: hypochlorous acid's broad-spectrum killing effect on microorganisms can pre-eliminate miscellaneous bacteria in the system, providing a clean environment for the subsequent introduction of specific functional microorganisms (Nitrosomonas), avoiding biofilm pollution problems; the main functions of nitrite bacteria are: (1) In situ degradation and resource regeneration: NH4 in struvite + Can be gradually released by nitrosating bacteria and converted into NO2 - / NO3 - (nitrification), this process breaks through the limitation of traditional struvite fixation technology that only achieves "temporary sealing"; (2) Multifunctional treatment: Nitrosifying bacteria can not only degrade NH4 +, and can also simultaneously degrade organic pollutants (such as COD in sewage); the main functions of struvite are: (1) fixing ammonia; (2) struvite uses its lattice structure to provide a microenvironment (such as pH buffer and ion exchange sites) for nitrite bacteria, significantly improving the activity and tolerance of nitrite bacteria, and solving the problem of easy inactivation of free bacteria. In summary, the present invention can effectively convert ammonia into a stable solid form - struvite (MgNH4PO4·6H2O) or similar compounds through the synergistic effect of phosphoric acid, magnesium salt / calcium salt and hypochlorous acid, significantly improving the solidification efficiency of ammonia, avoiding the re-volatilization of ammonia, and reducing environmental pollution; on the basis of forming struvite or similar compounds, nitrite bacteria are introduced to convert struvite or similar compounds into fertilizers useful for crops, thereby improving the resource utilization rate of ammonia.

[0011] Beneficial effects: The entire process of the present invention is simple to operate and easy to industrialize; the raw materials used are all common chemical raw materials, the cost is low, the ammonia fixation efficiency is high, and the resource utilization rate is high. DETAILED DESCRIPTION

[0012] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described below in conjunction with specific embodiments. It should be understood that the described embodiments are only a portion of the embodiments of the present invention, rather than all of them. Based on the described embodiments, all other embodiments derived by those skilled in the art without requiring creative effort are intended to fall within the scope of protection of the present invention.

[0013] Example 1

[0014] A method for recycling ammonia-containing waste gas comprises the following steps: (1) Mix 0.5 mol / L phosphoric acid solution, 0.5 mol / L magnesium sulfate heptahydrate (MgSO4·7H2O) solution and 0.5 mol / L hypochlorous acid solution in a molar ratio of 1:1:1 of phosphoric acid, magnesium salt and hypochlorous acid to form a reagent; (2) continuously introducing ammonia-containing waste gas into the reagent obtained in step (1) and reacting at room temperature. During the reaction, the pH of the reaction solution is continuously monitored online using an online pH detector. When the pH of the reaction solution reaches > 7, the introduction of ammonia-containing waste gas is stopped. (3) Add nitrosating bacteria to the reaction solution obtained in step (2) according to the molar-mass ratio of magnesium sulfate heptahydrate to nitrosating bacteria = 0.41 mol to 0.5 g in step (1), and mix and react at 28 ° C. At this time, start timing, take samples every 2 hours in the early stage, and take samples every 8 hours after 16 hours to measure the total residual ammonium salt content and NH4 + Conversion rate (NH4 + Converted into NO2 - / NO3 - percentage) and NO2 - +NO3 - Accumulation amount.

[0015] Determination of total residual ammonium salt content: The sample to be tested after step (3) (which can be the filtered filter cake or the unfiltered mixed solution) is subjected to strong acid digestion (such as Kjeldahl nitrogen determination method or potassium persulfate oxidation method) to convert all forms of nitrogen (organic nitrogen, ammonium nitrogen, nitrite nitrogen, nitrate nitrogen) into ammonium salts, and then the ammonium ion (NH4 + ), which includes all ammonium in solid struvite or similar compounds and in the dissolved phase.

[0016] NH4 + Conversion rate (%) = { (initial dissolved NH4 + -Current dissolved NH4 + ]) / initial dissolved NH4 +}×100%; among which, dissolved NH4 + , directly determined by HPLC.

[0017] NO2 - / NO3 - Method for determining accumulation amount: ion chromatography (IC) method.

[0018] The experimental results are shown in Table 1. The results show that when the dosage of nitrite bacteria is 0.5g / 0.41mol magnesium salt, NH4 + The conversion rate can reach 75%, but if it is shorter than 4 hours, struvite dissolves slowly (the total ammonium salt residual rate is >85%); at 12 hours, NO2 - +NO3 - The accumulation reaches a peak value, and if it exceeds 12 hours, it is easy to cause denitrification (NO2 - / NO3 - →N2), reducing the nitrogen fertilizer efficiency. Therefore, after adding nitrite-depleting bacteria, the optimal mixing reaction time is 4 to 12 hours.

[0019]

[0020] Example 2

[0021] A method for recycling ammonia-containing waste gas comprises the following steps: (1) Mix 0.4 mol / L phosphoric acid solution, 0.32 mol / L calcium chloride dihydrate (CaCl2·2H2O) solution and 0.48 mol / L hypochlorous acid solution in a molar ratio of phosphoric acid, calcium chloride and hypochlorous acid = 1:0.8:1.2 to form a reagent; (2) continuously introducing ammonia-containing waste gas into the reagent obtained in step (1) and reacting at room temperature. During the reaction, the pH of the reaction solution is continuously monitored online using an online pH detector. When the pH of the reaction solution reaches > 7, the introduction of ammonia-containing waste gas is stopped. (3) Add nitrosating bacteria to the reaction solution obtained in step (2) at a molar-mass ratio of calcium chloride dihydrate to nitrosating bacteria = 0.41 mol to 0.9 g in step (1), and mix and react at 25°C for 10 hours. At this time, a liquid product containing solids is obtained, which can be directly used as a liquid compound fertilizer.

[0022] Example 3

[0023] A method for recycling ammonia-containing waste gas comprises the following steps: (1) Mix 0.6 mol / L phosphoric acid solution, 0.6 mol / L magnesium chloride hexahydrate (MgCl2·6H2O) solution and 0.6 mol / L hypochlorous acid solution in a molar ratio of phosphoric acid, magnesium chloride hexahydrate and hypochlorous acid = 1:1:0.8 to form a reagent; (2) continuously introducing ammonia-containing waste gas into the reagent obtained in step (1) and reacting at room temperature. During the reaction, the pH of the reaction solution is continuously monitored online using an online pH detector. When the pH of the reaction solution reaches > 7, the introduction of ammonia-containing waste gas is stopped. (3) To the reaction solution obtained in step (2), nitrosobacteria are added according to the molar-mass ratio of magnesium chloride hexahydrate to nitrosobacteria = 0.41 mol to 0.4 g in step (1), and the mixture is mixed and reacted at 30° C. for 4 h. At this time, a liquid product containing solids is obtained, which can be directly used as a liquid compound fertilizer.

[0024] Comparative Example 1 The difference from Example 1 is that no hypochlorous acid is added in step (1); the rest is the same as Example 1.

[0025] Comparative Example 2 The difference from Example 1 is that step (3) is omitted, that is, no nitrosating bacteria are added, and the product obtained after step (2) is the final product; the rest is the same as Example 1.

[0026] Determination of ammonia fixation rate The ammonia fixation rate, ammonia fixation time and total nitrogen content of the final product of Example 1 and Comparative Examples 1 to 3 were measured respectively.

[0027] The ammonia fixation rate (η) represents the percentage of ammonia converted into struvite or similar compounds in the total input ammonia. The calculation formula is: η=M 固定 / M0×100%; Among them, M 固定 : mass of ammonia fixed by struvite (g); M0: total mass of ammonia introduced into the ammonia-containing waste gas (g); Determination of M0: According to M0=C NH3 ×Q×t×M NH3 Calculation, C NH3 : ammonia concentration in ammonia-containing waste gas (mol / L); Q: gas flow rate (L / min); t: reaction time (min); M NH3 : molar mass of ammonia (17 g / mol); M 固定 Determination of: At the end of step (2) of the reaction (stop introducing ammonia-containing waste gas), take a small amount of sample, weigh the mass of the generated struvite or similar compound, and calculate the amount of bound ammonia according to its chemical formula (MgNH4PO4·6H2O) (1 mol MgNH4PO4·6H2O binds to 1 mol ammonia); then convert the M in the entire reaction solution according to the mass ratio of the sample amount to the total reaction solution. 固定 .

[0028] Method for determining the ammonia fixation time (min): in step (2), the real-time cumulative time from the start of the introduction of the ammonia-containing waste gas to the time when the online pH detector displays pH>7 is accurate to 0.1 min.

[0029] Method for determining the total nitrogen content (g / L) of the final product: take the solid and liquid phase products after the reaction in step (3), centrifuge to separate the bacteria (10000rpm, 10min), take the supernatant and determine the total nitrogen (including NO2 - 、NO3 - and trace amounts of dissolved NH4 + ).

[0030] The results of the comparative experiment are shown in Table 2. As can be seen from Table 2: Example 1, due to the addition of hypochlorous acid, reducing impurities (such as H2S and organic matter) in the exhaust gas can be removed, the oxidation environment of the reaction liquid can be maintained, and the phosphoric acid-magnesium salt / calcium salt can be efficiently precipitated to form struvite or similar compounds. Therefore, the addition of hypochlorous acid significantly optimizes the reaction conditions (oxidation of interfering substances, maintaining pH stability), making the ammonia fixation efficiency close to complete, η=98%; Comparative Example 1, due to the lack of hypochlorous acid, leads to two problems: (i) the reaction time is extended by 36% (50min→68min), which is because the addition of hypochlorous acid can inhibit the dissolution of acidic gases (such as CO2) and maintain the pH of the reaction liquid >5.0 (the optimal pH for precipitation of struvite or similar compounds is 8~10), which can shorten the precipitation time; (ii) η=95%, which is reduced by about 3%, because, in the absence of hypochlorous acid, impurities consume part of the phosphoric acid and magnesium salt / calcium salt (generating by-products such as MgS), resulting in about 5% NH3 is not fixed (escapes or forms soluble ammonium); in Comparative Example 2, the addition of nitrosating bacteria does not affect ammonia fixation, and its chemical fixation stage (containing hypochlorous acid) is consistent with that of Example 1, so η is slightly higher, η=99%. In addition, in Example 1, struvite or similar compounds are converted into NO2 by nitrosating bacteria. - / NO3 - (water-soluble nitrogen, directly absorbed by plants), the total nitrogen content is relatively high; however, in Comparative Example 1, due to a 3% decrease in η (impurity competition), the initial fixed nitrogen is reduced, resulting in a slightly lower total nitrogen content in the final product than in Example 1; in Comparative Example 2, struvite or similar compounds experience ammonia volatilization loss during storage (reaction: MgNH4PO4→MgHPO4+NH3↑), resulting in a lower total nitrogen content in the product of Comparative Example 2, resulting in low agricultural value of the product and low plant absorption efficiency.

[0031]

Claims

1. A method for recycling ammonia-containing waste gas, characterized in that: Here are the steps: (1) Phosphoric acid solution, magnesium salt / calcium salt solution and hypochlorous acid solution are uniformly mixed in a molar ratio of phosphoric acid, magnesium salt / calcium salt and hypochlorous acid = 1: (0.8-1): (0.8-1.2) to obtain a reagent; (2) continuously passing the ammonia-containing waste gas into the reagent obtained in step (1), reacting at room temperature and continuously monitoring the pH of the reaction solution online in real time until the pH of the reaction solution is greater than 7, then stopping the passing of the ammonia-containing waste gas; (3) Adding nitrosobacteria to the reaction solution obtained in step (2) according to the molar-mass ratio of magnesium salt / calcium salt: nitrosobacteria = 0.41 mol: (0.1-1) g in step (1), and mixing and reacting at 25-30° C. for 4-12 hours, thereby obtaining a liquid product containing solids, which is directly used as a liquid compound fertilizer; In the above molar ratio and molar-mass ratio, the magnesium salt / calcium salt is measured based on the magnesium ions or calcium ions it provides.

2. The method for recycling ammonia-containing waste gas according to claim 1, wherein: The concentration of the phosphoric acid solution is 0.4-0.6 mol / L, the magnesium / calcium ion concentration of the magnesium salt / calcium salt solution is 0.2-0.6 mol / L, and the molar concentration of the hypochlorous acid solution is 0.48-0.6 mol / L.

3. The method for recycling ammonia-containing waste gas according to claim 1 or 2, characterized in that: The magnesium salt is MgSO4·7H2O or MgCl2·6H2O, and the calcium salt is CaCl2·2H2O.

4. The method for recycling ammonia-containing waste gas according to claim 1, wherein: In step (3), the nitrosating bacteria are directly added in the form of powder or in the form of an aqueous solution.

5. The method for recycling ammonia-containing waste gas according to claim 4, characterized in that: The concentration of the nitrite-containing aqueous solution is 0.2~0.4g / mL.

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