A urea ammonia wastewater pH self-adjusting method and application

Abstract

The application discloses a urea ammonia wastewater pH self-adjusting method and application. The application does not need real-time feedback adjustment, only needs to add acid in a fixed amount and at a fixed time after calculating the acid amount, is especially suitable for small water intermittent operation scenes, and reduces equipment investment and maintenance cost; CO2 bubbles generated in situ by chemical reaction are used to realize full-tank mixing, mechanical agitators or circulating pumps are not needed, and power consumption is saved; a double-phase buffer system formed can resist the sharp change of pH in the denitrification reaction process, stabilizes the reaction condition, and improves the treatment effect; macroscopic circulation flow generated by the bubbles makes the acid liquid quickly and uniformly dispersed, and eliminates the local strong acid area problem of traditional single-point acid addition.

Description

Technical Field

[0001] This invention relates to the field of urea ammonia production wastewater treatment technology, and in particular to a method for self-adjusting the pH of urea ammonia production wastewater and its application. Background Technology

[0002] Wastewater from urea hydrolysis to ammonia production is typically strongly alkaline, with a pH value usually ranging from 9.0 to 11.5. This alkalinity primarily originates from the ammonia (NH3) produced during urea hydrolysis, which dissolves in water to form NH3·H2O and ionizes to release OH-. - In many advanced wastewater treatment processes (such as chemical reduction denitrification, Fenton oxidation, and metal precipitation), the reaction needs to be carried out under weakly acidic (pH 5.5–6.5) or near-neutral (pH 6.0–7.0) conditions to achieve optimal treatment efficiency. The conventional approach involves directly adding inorganic acids (such as sulfuric acid or hydrochloric acid) to the wastewater and automatically adjusting the pH using online pH meters and dosing pumps.

[0003] However, for wastewater from urea-ammonia production in thermal power plants, which is discharged in small volumes (0.5-1 ton per week) and intermittently, conventional acid adjustment methods have the following technical drawbacks: Relatively high equipment investment: Industrial pH meters, corrosion-resistant acid metering pumps, acid storage tanks, and associated safety protection facilities are required, resulting in excessively high equipment amortization costs per unit volume for small-scale water treatment; pH control lag and over-adjustment: Due to the small wastewater volume and irregular discharge times, pH meters require frequent calibration during intermittent operation, and the lag in response can easily lead to excessive or insufficient acid addition, causing large pH fluctuations and affecting the stability of subsequent denitrification reactions; Uneven mixing: Conventional acid addition ports are often single-point additions, requiring mechanical stirring or hydraulic circulation to mix the acid with the wastewater; otherwise, localized strong acid zones can easily form, damaging the microbial activity or effectiveness of chemical agents in subsequent treatment units; Lack of pH buffering capacity: Wastewater after simple acid neutralization has almost no buffering capacity, which can lead to excessive pH fluctuations when H2O is generated during subsequent denitrification reactions. + (e.g., Fe) 0 H is produced during the reduction of nitrates + ) or OH - When the pH of the system deviates rapidly from the optimal range, the processing efficiency will decrease; additional energy consumption: in order to achieve uniform mixing, it is often necessary to configure a stirrer or a circulating pump, which increases power consumption. Summary of the Invention

[0004] The present invention aims to at least partially solve one of the technical problems in the related art.

[0005] Therefore, embodiments of the present invention propose a method for self-adjusting the pH of urea-to-ammonia wastewater and its application. The present invention involves adding a certain amount of inorganic acid to the wastewater, causing it to react with free ammonia and carbonates in the wastewater, generating CO2 bubbles in situ. This utilizes the agitation effect of the bubbles to achieve self-stirring, and also utilizes the NH3 / NH4 ratio in the wastewater after the reaction. + and HCO3 - The two-component buffer system composed of CO2 automatically stabilizes the pH within the target range (5.5~6.5), eliminating the need for an online pH meter and external stirring equipment, thus greatly simplifying the process and control requirements.

[0006] In a first aspect, the present invention proposes a method for self-adjusting the pH of urea-to-ammonia wastewater, comprising the following steps:

[0007] (a) Calculate the amount of acid to be added according to formula (1). (1), Among them, V acid The required acid volume is expressed in L; Alk is the total alkalinity of the wastewater, expressed in mol / L, expressed as H₂. + Calculate; V ω The volume of wastewater is expressed in liters (L); C acid The concentration of the acid solution is expressed in mol / L; n represents the H+ ions ionized from the acid molecule. + Quantity; pH0 is the initial pH value; pH T The target pH value; (b) The acid solution is added by pressurized jet injection based on the amount of acid added obtained in step (a).

[0008] Furthermore, the pH T It ranges from 5.5 to 6.5.

[0009] Furthermore, the acid solution includes dilute sulfuric acid or dilute hydrochloric acid.

[0010] Furthermore, the concentration of the dilute sulfuric acid is 5% to 20%.

[0011] Furthermore, in step (b), the acid solution is injected into the wastewater at high speed through a nozzle.

[0012] Furthermore, the nozzle has an orifice diameter of 0.5~2mm and a jet velocity of 10 m / s or higher.

[0013] Furthermore, the acid solution is added over a period of 0.5 to 5 minutes.

[0014] Furthermore, after the acid solution is added in step (b), the acid solution reacts with the carbonates or bicarbonates in the wastewater to generate CO2 microbubbles, which form aeration and stirring.

[0015] Furthermore, after the acid solution is added and reacted in step (b), the remaining NH3 / NH4 in the wastewater + and HCO3 - / CO2 together form a two-component buffer system.

[0016] Secondly, the present invention proposes the application of the method proposed in the first aspect in the denitrification process, wherein the pH self-adjustment method for urea ammonia production wastewater is carried out as an independent pretreatment unit or simultaneously with the denitrification process in the same reactor.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention does not require real-time feedback adjustment; it only requires calculating the amount of acid to be added and then adding it at regular intervals and in precise quantities. It is particularly suitable for intermittent operation scenarios with small water volumes, reducing equipment investment and maintenance costs. It utilizes CO2 bubbles generated in situ by the chemical reaction to achieve mixing throughout the tank, eliminating the need for mechanical stirrers or circulating pumps and saving power. The resulting two-phase buffer system can resist drastic pH changes during the denitrification reaction, stabilizing reaction conditions and improving treatment efficiency. The macroscopic circulation flow generated by the bubbles ensures rapid and uniform dispersion of the acid solution, eliminating the problem of localized strong acid zones associated with traditional single-point acid addition. Attached Figure Description

[0018] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein: Figure 1 This is a schematic diagram of the flow field distribution and bubble stirring effect inside the reactor after acid injection according to the present invention. Figure 2 This is a schematic diagram of the pH self-regulation method in some embodiments of the present invention. Detailed Implementation

[0019] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0020] The following description, in conjunction with the accompanying drawings, illustrates the pH self-adjustment method for urea-to-ammonia wastewater proposed in this invention and its application.

[0021] The pH self-adjustment method for urea-to-ammonia wastewater of the present invention includes the following steps: (a) Calculate the amount of acid to be added according to formula (1). (1), Among them, V acid The required acid volume is expressed in L; Alk is the total alkalinity of the wastewater, expressed in mol / L, expressed as H₂.+ Calculate; V ω The volume of wastewater is expressed in liters (L); C acid The concentration of the acid solution is expressed in mol / L; n represents the H+ ions ionized from the acid molecule. + Quantity; pH0 is the initial pH value; pH T The target pH value; (b) The acid solution is added by pressurized jet injection based on the amount of acid added obtained in step (a).

[0022] Step (a) involves calculating the amount of acid to be added, which is done using equation (1). (1), Among them, V acid The required acid volume is expressed in L; Alk is the total alkalinity of the wastewater, expressed in mol / L, expressed as H₂. + Calculate; V ω The volume of wastewater is expressed in liters (L); C acid The concentration of the acid solution is expressed in mol / L; n represents the H+ ions ionized from the acid molecule. + Quantities, for example, 2 parts sulfuric acid and 1 part hydrochloric acid; pH0 is the initial pH value; pH T The target pH value is [value to be filled in]. In practice, the optimal amount of acid added can be determined through small-batch trials. For urea-to-ammonia wastewater, approximately 0.5–1.0 mmol of H₂O is required to lower the pH by one unit (from 10 to 9). + / L.

[0023] The main alkaline substances in the wastewater from urea hydrolysis to ammonia production are: free ammonia (NH3) and its conjugate acid NH4. + This constitutes an ammonia buffer system; bicarbonate (HCO3-) is generated from urea hydrolysis and dissolved CO2 in the air. - ) and carbonate (CO3²) - Total alkalinity (Alk) is typically 10–60 mmol / L, with ammonia alkalinity accounting for approximately 70%–90% and carbonate alkalinity accounting for approximately 10%–30%.

[0024] Target pH value T The target pH value is determined based on the subsequent coupled chemical reduction denitrification process (such as zero-valent iron reduction of nitrate), with an optimal pH range of 5.5–6.5. Within this pH range: Fe 0 The corrosion rate is moderate, providing sufficient electron donors without generating excessive H2 due to rapid corrosion; the nitrate reduction reaction proceeds relatively thoroughly; heavy metal ions (such as Cu) 2+ Zn 2+ It will not dissolve at too low a pH, nor will it form a hydroxide precipitate to encapsulate Fe at too high a pH. 0Particles.

[0025] The acid solution includes dilute sulfuric acid or dilute hydrochloric acid, wherein the concentration of the dilute sulfuric acid is 5% to 20%, preferably 10%. Sulfuric acid is preferred because it is inexpensive, non-volatile, and has good effects on subsequent Fe... 0 The reaction has no adverse effects; however, hydrochloric acid may cause Cl... - Corrosion resistant, therefore, suitable for Cl- resistant - Corrosion scenario; because nitric acid has strong oxidizing properties, it will react with Fe. 0 The reaction is direct, and the introduction of additional nitrate nitrogen increases the total nitrogen load. Nitric acid is avoided in this invention.

[0026] Step (b) is the acid addition process. Based on the amount of acid added obtained in step (a), the acid is added by pressurized jet injection. Specifically, the acid is injected at high speed into the wastewater collection tank or pipeline through a nozzle. The nozzle has an orifice diameter of 0.5~2mm and a jet velocity of more than 10 m / s, so that the acid is sheared and dispersed into tiny droplets the instant it comes into contact with the wastewater.

[0027] After the acid solution is added, it reacts with carbonates or bicarbonates in the wastewater to generate CO2 microbubbles, forming aeration and stirring. Specifically, after the acid solution is added to the wastewater, the following reaction first occurs: , When acidic solutions come into contact with carbonates or bicarbonates in water, they react violently to produce CO2 gas. Because CO2 has low solubility in alkaline wastewater (Henry's constant is approximately 3.4 × 10⁻⁶), it is difficult to obtain CO2 gas. - ² mol / (L·atm)), after the gas is supersaturated, it rapidly precipitates from the liquid phase, forming a large number of microbubbles (0.1~2 mm in diameter).

[0028] Then, the generated CO2 bubbles grow, merge, and burst as they rise, creating strong local turbulence, similar to aeration and mixing. The bubbles also carry some liquid upwards; after bursting at the surface, the liquid falls back to the bottom of the tank, forming an overall macroscopic circulation. This pneumatic self-mixing requires no mechanical stirring equipment or additional gas compressor; it achieves efficient mixing solely using the gas generated in situ during the acid-base reaction. The flow field distribution and bubble mixing effect inside the reactor after acid injection are shown below. Figure 1 As shown.

[0029] To control the amount of bubbles generated, the acid addition rate needs to be controlled. Slow addition prolongs the bubble generation time, resulting in continuous and gentle stirring; rapid addition generates a large number of bubbles instantly, causing violent disturbance. Depending on the reactor size and mixing requirements, the acid addition time should be controlled between 0.5 and 5 minutes. Furthermore, higher acid concentrations lead to more vigorous local reactions and more concentrated bubble generation; lower concentrations result in a gentler reaction.

[0030] After the acid solution is added and reacted, the remaining NH3 / NH4 in the wastewater + and HCO3 - / CO2 together form a two-component buffer system.

[0031]

[0032] When the target pH is between 5.5 and 6.5, the dominant buffer pair is H2CO3 / HCO3. - (pKa1=6.35), because within this pH range, HCO3 - It is the main form in which it exists, and dissolved CO2 in the solution (gas-liquid equilibrium) forms H2CO3.

[0033] Since the CO2 generated in the reaction exists in the form of supersaturated bubbles, some of the CO2 dissolves in water to form H2CO3. When subsequent denitrification reactions consume H2... + Or generate OH - At that time, dissolved CO2 can respond rapidly through the following equilibrium: if the reaction consumes H2... + (e.g., Fe) 0 Restore NO3 - Time: Fe 0 +NO3 - + 2H + →Fe 2+ + NO2 - + H2O), then the equilibrium HCO3 - + H + H₂CO₃ moves to the right, and H₂CO₃ dissociates to replenish H₂. + This inhibits the increase in pH; if the reaction produces OH... - Then H2CO3 provides H in a timely manner + Neutralize.

[0034] In addition, the gaseous CO2 in the bubbles reacts with the H2CO3 / HCO3 in the liquid phase. - Maintaining dynamic equilibrium (Henry's Law), when the liquid phase H + When consumed, the gaseous CO2 dissolves into the water to replenish it, forming a huge gas buffer that greatly enhances the system's resistance to interference.

[0035] By controlling the amount of acid added, the pH after the reaction is kept within the range of 5.5 to 6.5. Furthermore, due to the aforementioned buffering mechanism, even if subjected to external disturbances (such as an acid addition error of ±10%), the final pH will not deviate significantly from the target range (fluctuation range <0.5 pH units). This is equivalent to achieving "tolerance" for the amount of acid added, eliminating the need for high-precision measurement.

[0036] The pH self-adjustment method for urea-to-ammonia wastewater of the present invention can be carried out as an independent pretreatment unit or simultaneously with the denitrification process within the same reactor. When the pH self-adjustment method for urea-to-ammonia wastewater is used as an independent pretreatment unit, acid is first added to the wastewater collection tank / adjustment tank to self-adjust the pH to 5.5-6.5 according to the above method. Then, the adjusted wastewater is pumped into the subsequent denitrification reactor (such as a zero-valent iron fixed bed, biological denitrification filter, etc.). This scheme is suitable for batch treatment. Figure 2 As shown, dilute sulfuric acid is stored in an acid storage tank. Dilute sulfuric acid is added to the wastewater tank through a nozzle, and the adjusted wastewater is pumped into a subsequent zero-valent iron fixed bed for denitrification reaction.

[0037] When the pH self-adjustment method for urea-to-ammonia wastewater is carried out simultaneously with the denitrification process, an acid injection point is set on the circulation pipeline of the denitrification reactor (such as a fixed-bed reactor with a circulation system). Acid addition is controlled online by ORP or by timed control to maintain the overall pH within the reactor within the target range. This scheme utilizes the circulating liquid flow to drive bubble agitation, requiring no additional setup.

[0038] When the pH self-regulation method for urea-to-ammonia wastewater is coupled with the denitrification process, the generation of CO2 bubbles and the stirring effect after acid addition are basically completed within 5 to 10 minutes, at which point the pH has stabilized; the denitrification reaction lasts for 1 to 3 hours, during which the pH fluctuation is <0.5; the temperature range is 15 to 35℃, and no heating is required; the CO2 bubbles have a certain air-lifting effect on the system, which can remove some dissolved oxygen, which is beneficial to the subsequent anoxic denitrification reaction.

[0039] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms may refer to different embodiments or examples. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0040] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0041] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A method for self-adjusting the pH of urea-to-ammonia wastewater, characterized in that, Includes the following steps: (a) Calculate the amount of acid to be added according to formula (1). （1）， Among them, V acid The required acid volume is expressed in L; Alk is the total alkalinity of the wastewater, expressed in mol / L, expressed as H₂. + Calculate; V ω The volume of wastewater is expressed in liters (L); C acid The concentration of the acid solution is expressed in mol / L; n represents the H+ ions ionized from the acid molecule. + Quantity; pH0 is the initial pH value; pH T The target pH value; (b) The acid solution is added by pressurized jet injection based on the amount of acid added obtained in step (a).

2. The method for self-adjusting pH of urea-to-ammonia wastewater as described in claim 1, characterized in that, The pH T It ranges from 5.5 to 6.

5.

3. The method for self-adjusting pH of urea-to-ammonia wastewater as described in claim 1, characterized in that, The acid solution includes dilute sulfuric acid or dilute hydrochloric acid.

4. The method for self-adjusting pH of urea-to-ammonia wastewater as described in claim 3, characterized in that, The concentration of the dilute sulfuric acid is 5% to 20%.

5. The method for self-adjusting pH of urea-to-ammonia wastewater as described in claim 1, characterized in that, In step (b), the acid solution is injected into the wastewater at high speed through a nozzle.

6. The method for self-adjusting pH of urea-to-ammonia wastewater as described in claim 5, characterized in that, The nozzle has an orifice diameter of 0.5~2mm and a jet velocity of 10 m / s or higher.

7. The method for self-adjusting pH of urea-to-ammonia wastewater as described in claim 1, characterized in that, The acid solution is added over a period of 0.5 to 5 minutes.

8. The method for self-adjusting pH of urea-to-ammonia wastewater as described in claim 1, characterized in that, In step (b), after the acid solution is added, the acid solution reacts with the carbonates or bicarbonates in the wastewater to generate CO2 microbubbles, which form an aeration and stirring effect.

9. The method for self-adjusting pH of urea-to-ammonia wastewater as described in claim 1, characterized in that, After the acid solution is added and reacted in step (b), the remaining NH3 / NH4 in the wastewater + and HCO3 - / CO2 together form a two-component buffer system.

10. The application of the pH self-adjustment method for urea-to-ammonia wastewater according to any one of claims 1 to 9 in a nitrogen removal process, characterized in that, The pH self-adjustment method for urea-to-ammonia wastewater can be carried out as an independent pretreatment unit or simultaneously with the denitrification process in the same reactor.

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