A method for ammonia removal and recovery from ammonia-containing wastewater based on stripping absorption coupling

Abstract

The application discloses a kind of ammonia-containing wastewater deamination and recovery method based on stripping absorption coupling, belong to industrial wastewater treatment and resource recovery field, including the calcium load reduction treatment to the calcium-containing low ammonia-containing wastewater from hydrogen-based shaft furnace gas cooling washing process, make calcium source that easy to form scale deposition under subsequent alkalization stripping conditions be transferred to separable solid phase in advance, and low calcium clear wastewater is obtained by solid-liquid separation;Through calcium load reduction, stripping absorption coupling, evaporation concentration and evaporation water vapor return stripping linkage processing, so that hydrogen-based shaft furnace calcium-containing low ammonia-containing wastewater realizes the continuous removal of low-concentration ammonia and stable recovery of ammonium sulfate while avoiding alkalization scale formation, thereby solving the problem that existing process cannot simultaneously prevent scale continuous operation and low ammonia resource recovery.

Description

Technical Field

[0001] This invention relates to the field of industrial wastewater treatment and resource recovery technology, and more specifically, to a method for ammonia removal and recovery of ammonia-containing wastewater based on stripping absorption coupling. Background Technology

[0002] In the direct reduction process of hydrogen-based vertical shaft furnace, the circulating gas in the furnace usually needs to undergo cooling, washing and circulation purification. Ammonia substances are easily introduced into the process circulating water during the cooling and washing process, causing the circulating water discharge to form ammonia-containing wastewater. At the same time, due to the influence of the pellet ore, coating agent and washing water circulation process, this type of wastewater may also contain high concentrations of calcium ions and calcium salt precursors, making the wastewater have the combined characteristics of calcium-containing and low-ammonia-containing water.

[0003] Existing methods for treating ammonia-containing wastewater typically include alkali stripping, air stripping, acid absorption, or evaporation concentration. Alkali stripping combined with acid absorption can convert ammonia in the wastewater into ammonium salts for recovery. However, when these conventional processes are directly applied to calcium-containing, low-ammonia wastewater from hydrogen-based vertical shaft furnaces, several problems arise. First, high-calcium wastewater is prone to calcium salt deposition after alkali addition, leading to scaling and blockage in the alkali mixer, conveying pipelines, or stripping channels, affecting continuous operation. Second, due to the low ammonia nitrogen concentration in the wastewater, the amount of ammonia released during stripping is limited, and the acid absorption liquid is diluted by secondary steam condensate during circulation, easily causing slow ammonium sulfate solution enrichment and unstable recovery concentration. Summary of the Invention

[0004] To address the problems mentioned in the background section, the present invention provides the following technical solution: A method for ammonia removal and recovery from ammonia-containing wastewater based on stripping absorption coupling includes the following steps: The calcium load of the calcium-containing, low-ammonia wastewater from the gas cooling and washing process of a hydrogen-based vertical furnace is reduced. The ammonia nitrogen concentration of the calcium-containing, low-ammonia wastewater is not higher than 600 mg / L. This allows the calcium source, which is prone to forming scale deposits under subsequent alkaline stripping conditions, to be pre-transferred to a separable solid phase, and then cleared low-calcium wastewater is obtained through solid-liquid separation. After adjusting the low-calcium clarified wastewater to an alkaline state that can promote the conversion of ammonium nitrogen to free ammonia, the alkalized wastewater is introduced into the stripping deammoniation zone, and the alkalized wastewater is made to come into countercurrent contact with saturated steam from the hydrogen-based vertical furnace in the stripping deammoniation zone. At the same time, the ammonia-containing steam in the stripping deammoniation zone is circulated and disturbed, so that the ammonia in the wastewater is released with the secondary steam. The released ammonia-containing secondary vapor is introduced into the acidic absorption area, and the ammonia-containing secondary vapor is brought into contact with the circulating sulfuric acid absorption liquid to react and generate an ammonium sulfate solution. When the ammonium sulfate solution experiences a rise in liquid level or a concentration below the recovery requirement due to the accumulation of condensate during absorption, the ammonium sulfate solution is introduced into an evaporation and concentration zone for evaporation and concentration, so that the water in it evaporates and the concentration of ammonium sulfate increases, resulting in a concentrated ammonium sulfate solution. The water vapor generated in the evaporation and concentration zone is returned to the stripping and ammonia removal zone by circulating air, so that the returned water vapor and the saturated steam from the hydrogen-based vertical furnace participate together in the wastewater ammonia removal process. The wastewater after stripping and ammonia removal is discharged after its acidity is adjusted. The ammonia-containing water vapor generated from the volatilization of the cooling washing water circulation area of ​​the hydrogen-based vertical furnace is collected and sent to the acidic absorption area, so that the ammonia in the ammonia-containing water vapor is incorporated into the formation process of the ammonium sulfate solution. Furthermore, the calcium load reduction treatment includes adding coagulants and coagulant aids to calcium-containing, low-ammonia-content wastewater, so that calcium ions and calcium salt precursors in the wastewater are converted into precipitated particles, and the precipitated particles are aggregated into settleable flocs under the action of coagulants and coagulant aids, and then the settleable flocs are discharged as calcium-containing sludge.

[0005] Furthermore, the coagulant includes polyferric chloride, and the coagulant aid includes polyacrylamide. During the addition of the coagulant and coagulant aid, the pH value, turbidity value, and calcium ion concentration of the wastewater are detected, and the dosage of the coagulant and coagulant aid is adjusted according to the pH value, turbidity value, and calcium ion concentration to ensure that the calcium load of the low-calcium clarified wastewater before entering the alkalization stripping process is within a range that will not cause blockage of the alkali mixing unit and its subsequent conveying pipelines.

[0006] Furthermore, before adjusting the low-calcium clarified wastewater to an alkaline state, it exchanges heat with the stripped and deammonized wastewater to raise the temperature of the low-calcium clarified wastewater and lower the temperature of the stripped and deammonized wastewater; then, liquid alkali is added to the heated low-calcium clarified wastewater to adjust the pH value of the low-calcium clarified wastewater to 10 to 12.5.

[0007] Furthermore, the alkalized wastewater enters from the upper part of the stripping and ammonia removal zone and flows downwards, while the saturated steam from the hydrogen-based vertical furnace enters from the lower part of the stripping and ammonia removal zone and flows upwards. During the stripping and ammonia removal process, the ammonia-containing steam in the stripping and ammonia removal zone is circulated and disturbed by a circulating air conveying method, so that the ammonia-containing steam forms a circulating flow between the stripping and ammonia removal zone and the acidic absorption zone, thereby improving the ammonia release efficiency in the low-ammonia-content wastewater.

[0008] Furthermore, the acidic absorption zone uses dilute sulfuric acid or ammonium sulfate circulating liquid as the sulfuric acid absorption liquid. After the sulfuric acid absorption liquid comes into contact with ammonia-containing secondary steam, it forms an ammonium sulfate solution. The ammonium sulfate solution is collected by reflux and then sent back to the acidic absorption zone, so that the ammonium sulfate solution is gradually enriched during the circulating absorption process.

[0009] Furthermore, when the level of the ammonium sulfate solution rises to a preset level, or when the concentration of the ammonium sulfate solution is lower than a preset recovery concentration, the ammonium sulfate solution is sent to the evaporation and concentration zone. Saturated steam from the hydrogen-based vertical furnace is used as the heat medium to perform heat exchange evaporation on the ammonium sulfate solution. The water vapor generated by evaporation is returned to the stripping and ammonia removal zone by circulating air, and together with the saturated steam from the hydrogen-based vertical furnace, it participates in the stripping and ammonia removal of the alkalized wastewater.

[0010] Furthermore, the concentrated ammonium sulfate solution after evaporation and concentration is returned to the ammonium sulfate product collection area through a liquid seal or pressure balancing method to maintain stable liquid level and temperature during the evaporation and concentration process, and to limit the escape of evaporated water vapor from the concentrated liquid return path.

[0011] Furthermore, the hydrogen-based vertical furnace cooling and washing water circulation area includes at least one of a direct cooling collection tank, a hot water well, a vortex grit chamber, a sludge conditioning tank, and a sedimentation tank; the ammonia-containing water vapor generated by the volatilization of the cooling and washing water circulation area is collected and sent to the acidic absorption area, where it is absorbed by the sulfuric acid absorption liquid and then circulated into the ammonium sulfate solution.

[0012] Furthermore, during operation, the ammonia nitrogen value of the wastewater after stripping and ammonia removal, the temperature and steam pressure of the stripping and ammonia removal zone, the acidity of the acidic absorption zone, the concentration of ammonium sulfate solution, and the pressure of the stripping and ammonia removal zone are monitored. When the ammonia nitrogen value of the wastewater after stripping and ammonia removal exceeds the discharge requirements, the degree of alkalization of the wastewater is increased, the steam supply intensity is increased, sulfuric acid absorbent is added, or the stripping and ammonia removal zone is cleaned according to the monitoring results to restore the ammonia removal effect and the ammonium sulfate absorption effect.

[0013] In summary, the present invention has the following beneficial effects: By linking calcium load reduction, stripping absorption coupling, evaporation concentration, and steam return stripping, the calcium-containing and low-ammonia-containing wastewater from the hydrogen-based vertical furnace can achieve continuous removal of low-concentration ammonia and stable recovery of ammonium sulfate while avoiding alkalization and scaling. This solves the problem that existing processes cannot simultaneously achieve scale prevention and continuous operation and low-ammonia resource recovery. Attached Figure Description

[0014] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 This is a schematic diagram of the overall process flow of the present invention; Figure 2 This is a schematic diagram of the calcium load reduction and stripping absorption coupling structure of the present invention; Figure 3 This is a schematic diagram of the evaporation concentration and steam return process of the present invention; Figure 4 This is a schematic diagram of the ammonia-containing water vapor collection and operation regulation of the present invention. Detailed Implementation

[0016] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example 1

[0017] The following is in conjunction with the appendix Figure 1-4 The present invention will be described in further detail below.

[0018] This invention provides a technical solution: a method for ammonia removal and recovery from ammonia-containing wastewater based on stripping absorption coupling, comprising the following steps: The calcium load of the calcium-containing and low-ammonia wastewater from the gas cooling and washing process of the hydrogen-based vertical furnace is reduced. The ammonia nitrogen concentration of the calcium-containing and low-ammonia wastewater is not higher than 600 mg / L. This allows the calcium source, which is prone to forming scale deposits under subsequent alkaline stripping conditions, to be pre-transferred to a separable solid phase and then separated into low-calcium clarified wastewater through solid-liquid separation. After adjusting the low-calcium clarified wastewater to an alkaline state that can promote the conversion of ammonium nitrogen to free ammonia, the alkalized wastewater is introduced into the stripping and deammoniation zone. The alkalized wastewater is then brought into countercurrent contact with saturated steam from the hydrogen-based vertical furnace in the stripping and deammoniation zone. At the same time, the ammonia-containing steam in the stripping and deammoniation zone is circulated and disturbed, so that the ammonia in the wastewater is released with the secondary steam. The released ammonia-containing secondary vapor is introduced into the acidic absorption area, and the ammonia-containing secondary vapor is brought into contact with the circulating sulfuric acid absorption liquid to react and generate ammonium sulfate solution. When the ammonium sulfate solution experiences a rise in liquid level or a concentration below the recovery requirement due to the accumulation of condensate during absorption, the ammonium sulfate solution is introduced into the evaporation and concentration zone for evaporation and concentration, causing the water in the solution to evaporate and increasing the concentration of ammonium sulfate to obtain a concentrated ammonium sulfate solution. The water vapor generated in the evaporation and concentration zone is returned to the stripping and ammonia removal zone via a circulating air conveyor, so that the returned water vapor and the saturated steam from the hydrogen-based vertical furnace can participate together in the wastewater ammonia removal process. The wastewater after stripping and ammonia removal is discharged after its acidity is adjusted. The ammonia-containing water vapor generated from the volatilization of the cooling washing water circulation area of ​​the hydrogen-based vertical furnace is collected and sent to the acid absorption area, so that the ammonia in the ammonia-containing water vapor is incorporated into the formation of the ammonium sulfate solution. Before adjusting the low-calcium clarified wastewater to an alkaline state, it exchanges heat with the stripped and deammonified wastewater to raise the temperature of the low-calcium clarified wastewater and lower the temperature of the stripped and deammonified wastewater. Then, liquid alkali is added to the heated low-calcium clarified wastewater to adjust the pH value of the low-calcium clarified wastewater to 10 to 12.5. In this embodiment, the calcium-containing and low-ammonia-containing wastewater generated during the gas cooling and washing process of the hydrogen-based vertical furnace is used as the treatment object. The calcium-containing and low-ammonia-containing wastewater is taken from the circulating drain outlet of the cooling and washing water of the hydrogen-based vertical furnace. After continuous sampling for 3 days, the pH value of the wastewater was measured to be 6.86 to 7.24, the water temperature was 62.8℃ to 67.4℃, the ammonia nitrogen concentration was 536mg / L to 589mg / L, and the calcium ion concentration was 402mg / L to 471mg / L. The wastewater contains both low concentration of ammonia nitrogen and high calcium load, which is the type of wastewater that is prone to calcium salt deposition under subsequent high pH alkaline stripping conditions. During treatment, calcium-containing and low-ammonia-containing wastewater is introduced into the calcium load reduction treatment section at a flow rate of 4.7 t / h to 5.3 t / h. The pH value of the reaction zone is first adjusted to 8.4 to 8.9, and then polyferric chloride and polyacrylamide are added to the wastewater. The dosage of polyferric chloride is controlled at 220 mg / L to 285 mg / L, and the dosage of polyacrylamide is controlled at 2.2 mg / L to 4.1 mg / L. The mixture is stirred at 95 r / min to 125 r / min for 8 min to 12 min, and then at 25 r / min to 45 r / min for 12 min to 18 min. After that, it is allowed to stand and settle for 35 min to 50 min, so that the calcium ions and calcium salt precursors in the wastewater form precipitate particles and further coagulate into settleable flocs. The calcium-containing sludge after settling is discharged from the bottom, and the supernatant is used as low-calcium clarified wastewater for subsequent treatment. Testing revealed that the calcium ion concentration in the low-calcium clarified wastewater decreased to 86 mg / L to 138 mg / L, and the turbidity decreased to 10.4 NTU to 22.8 NTU. Subsequently, the low-calcium clarified wastewater was sent to a heat exchanger to exchange heat with the high-temperature wastewater after stripping and ammonia removal, raising the temperature of the low-calcium clarified wastewater to 86.5℃ to 92.8℃, while lowering the temperature of the wastewater after stripping and ammonia removal to 71.6℃ to 79.3℃. The low-calcium clarified wastewater after heat exchange was mixed with 30% liquid alkali to adjust the pH of the wastewater entering the tower to 11.8 to 12.4. The alkalized wastewater is introduced from the upper part of the stripping ammonia removal zone, allowing it to flow downwards along the trays. Simultaneously, saturated steam from the hydrogen-based vertical shaft furnace is introduced from the lower part of the stripping ammonia removal zone, causing the saturated steam to come into counter-current contact with the downward-flowing alkalized wastewater. The saturated steam pressure is controlled at 0.39 MPa to 0.47 MPa, the temperature in the upper part of the stripping ammonia removal zone is controlled at 84.9℃ to 89.6℃, the temperature in the middle part is controlled at 95.1℃ to 99.8℃, and the temperature in the lower part is controlled at 99.4℃ to 102.6℃, and the pressure in the stripping ammonia removal zone is controlled at 6.8 kPa to 13.6 kPa. During the stripping ammonia removal process, the circulating air is activated to create circulating disturbances in the ammonia-containing steam within the stripping ammonia removal zone, promoting the conversion of ammonium nitrogen in the wastewater into free ammonia, and releasing the free ammonia with the secondary steam. The released ammonia-containing secondary vapor enters the acidic absorption zone and comes into contact with the circulating sulfuric acid absorbent. The sulfuric acid absorbent consists of dilute sulfuric acid and ammonium sulfate circulating liquid, and the pH value of the absorbent is controlled between 3.1 and 4.3. The ammonia in the ammonia-containing secondary vapor is absorbed by the sulfuric acid absorbent to generate an ammonium sulfate solution. The ammonium sulfate solution is returned to the ammonium sulfate circulation tank through the purification tower section, and then sent back to the acidic absorption zone by the circulation pump, so that the ammonium sulfate solution is gradually enriched during the circulation absorption process. During continuous operation, the condensate from the secondary steam in the acid absorption zone enters the ammonium sulfate circulating liquid, raising the level of the ammonium sulfate circulating tank and diluting the ammonium sulfate solution. When the level of the ammonium sulfate circulating tank rises to 1.75m to 1.85m, or when the mass concentration of the ammonium sulfate solution is lower than 24.5%, the ammonium sulfate solution is sent to the evaporation and concentration zone, where saturated steam from the hydrogen-based vertical furnace is used as the heat medium for heat exchange and evaporation, so that the mass concentration of the concentrated ammonium sulfate solution reaches 28.9% to 30.6%. Batches with a mass concentration lower than 29.5% are recycled for further concentration, while batches with a mass concentration that meets the recovery requirements enter the ammonium sulfate finished product collection zone. The water vapor generated in the evaporation and concentration zone is returned to the lower part of the stripping and ammonia removal zone via a circulating air conveyor, so that the returned water vapor and the saturated steam from the hydrogen-based vertical furnace participate together in the wastewater ammonia removal process; the evaporated concentrated ammonium sulfate solution is returned to the ammonium sulfate product collection area through a liquid-sealed reflux structure. The liquid-sealed reflux structure is used to maintain the stability of the liquid level and temperature in the evaporation and concentration zone, and to reduce the escape of evaporated water vapor from the concentrated liquid reflux path; After stripping and ammonia removal, the wastewater is cooled by a heat exchanger and then enters the acidity adjustment section. Dilute sulfuric acid is added to the section for two-stage adjustment to adjust the pH of the discharged wastewater to 7.05 to 7.92. At the same time, the ammonia-containing water vapor generated from the direct cooling collection tank, hot water well, cyclone grit chamber, sludge conditioning tank and sedimentation tank in the hydrogen-based vertical furnace cooling washing water circulation area is collected by a deodorizing fan and sent to the acid absorption area, so that the ammonia in the ammonia-containing water vapor is incorporated into the formation of ammonium sulfate solution. This embodiment operated continuously for 168 hours. During operation, the temperature, steam pressure, pressure, effluent ammonia nitrogen concentration, and ammonium sulfate solution concentration in the stripping and ammonia removal zone were recorded every 2 hours. The influent ammonia nitrogen concentration, effluent ammonia nitrogen concentration, and effluent pH were sampled and tested every 12 hours. The calcium ion concentration, pressure difference before and after the alkali addition mixer, and ammonia concentration at the collection point in the cooling and washing water circulation area were measured every 24 hours. During continuous operation, the pressure difference of the alkali addition mixer increased slowly but no blockage requiring shutdown and cleaning occurred. The pressure in the stripping and ammonia removal zone fluctuated slightly but did not show a continuous abnormal pressure increase. The ammonia nitrogen concentration in the discharged wastewater remained below the set control limit, and the mass concentration of the ammonium sulfate finished solution met the requirements for subsequent recovery. Table 1: Detection Results of Closed-Loop Processing Continuous Operation in Example 1

[0019] As shown in Table 1, under the conditions that the influent ammonia nitrogen concentration is not higher than 600 mg / L and the calcium ion concentration is relatively high, this embodiment reduces the calcium ion concentration in the wastewater from an average of 439 mg / L to an average of 112 mg / L through calcium load reduction treatment. After the low-calcium clarified wastewater enters the high-pH alkalization stripping process, the pressure difference of the alkali addition mixer increases from 0.018 MPa to 0.024 MPa within 168 hours of continuous operation. Although there is a slight increase, no blockage phenomenon requiring shutdown and cleaning occurs, indicating that calcium load reduction treatment can reduce the scaling risk of the subsequent alkali addition mixer and its subsequent conveying pipeline. Meanwhile, the ammonia-containing steam in the stripping and ammonia removal zone is circulated and agitated by the circulating air. The steam generated in the evaporation and concentration zone returns to the stripping and ammonia removal zone and participates in the wastewater ammonia removal process together with the saturated steam from the hydrogen-based vertical furnace. This maintains the effluent ammonia nitrogen concentration in the range of 31.8 mg / L to 48.6 mg / L, and the ammonium sulfate finished product concentration reaches 28.9% to 30.6%. The external saturated steam consumption is 0.27 t / h to 0.33 t / h. This indicates that under low ammonia wastewater conditions, evaporation and concentration not only increase the concentration of ammonium sulfate solution, but the returned evaporated steam can also participate in the stripping and ammonia removal process, thereby maintaining the ammonia removal and ammonia recovery effect of low ammonia wastewater. Furthermore, after the ammonia-containing water vapor generated from the cooling washing water circulation area is collected and sent to the acid absorption area, the ammonia concentration at the collection point decreases from 15.6 mg / m³ to 22.4 mg / m³ to 2.8 mg / m³ to 5.9 mg / m³, and the total ammonia recovery rate is 87.4% to 92.1%. This indicates that incorporating the ammonia-containing water vapor into the ammonium sulfate solution generation process can reduce ammonia escape from the cooling washing water circulation area and increase the ammonia resource recovery rate. Example 2

[0020] like Figure 1-4As shown, the calcium load reduction treatment includes adding coagulants and coagulant aids to calcium-containing, low-ammonia wastewater. This causes calcium ions and calcium salt precursors in the wastewater to transform into precipitate particles, which are then coagulated into settleable flocs under the action of the coagulants and coagulant aids. The settleable flocs are then discharged as calcium-containing sludge. The coagulant includes polyferric chloride, and the coagulant aid includes polyacrylamide. During the addition of coagulants and coagulant aids, the pH, turbidity, and calcium ion concentration of the wastewater are monitored. The dosage of coagulants and coagulant aids is adjusted according to these parameters to ensure that the calcium load of the low-calcium clarified wastewater before entering the alkalization stripping process is within a range that does not cause blockage of the alkali mixing unit and its subsequent delivery pipelines.

[0021] In this embodiment, the impact of calcium load reduction treatment on the continuous operation stability of the subsequent alkalization stripping process is illustrated. The treated wastewater is taken from the circulating drain of the gas cooling washing water of the hydrogen-based vertical furnace. During continuous sampling, the wastewater pH value is 6.82 to 7.31, the ammonia nitrogen concentration is 528 mg / L to 592 mg / L, the calcium ion concentration is 396 mg / L to 486 mg / L, and the turbidity is 46 NTU to 82 NTU. The wastewater contains fine suspended particles, carbonate alkalinity, and calcium salt precursors that are prone to precipitate in high pH environments. During treatment, the calcium-containing and low-ammonia-containing wastewater is introduced into a two-stage flocculation and clarification treatment section. The first flocculation reaction zone is used to receive the raw wastewater and complete rapid mixing, while the second flocculation reaction zone is used for reagent replenishment and slow flocculation. pH detection probes, turbidity detection probes, and calcium ion detection probes are respectively installed in the first and second flocculation reaction zones. The detection data is updated every 5 minutes and used to adjust the dosage of polyferric chloride and polyacrylamide. In this embodiment, the pH value of the first flocculation reaction zone is first controlled at 8.3 to 8.9, so that some calcium ions and calcium salt precursors in the wastewater form fine precipitate particles under the action of carbonate alkalinity; then, polyferric chloride is added as a coagulant and polyacrylamide is added as a coagulant aid, so that the fine precipitate particles and suspended particles form settleable flocs; the dosage of polyferric chloride is adjusted between 205 mg / L and 330 mg / L according to the changes in calcium ion concentration and turbidity of the influent, and the dosage of polyacrylamide is adjusted between 2.1 mg / L and 4.6 mg / L; The specific adjustment method is as follows: when the influent calcium ion concentration is higher than 450 mg / L or the turbidity is higher than 70 NTU, the dosage of polyferric chloride is increased to 280 mg / L to 330 mg / L, and the dosage of polyacrylamide is increased to 3.8 mg / L to 4.6 mg / L; when the influent calcium ion concentration is 400 mg / L to 450 mg / L and the turbidity is 50 NTU to 70 NTU, the dosage of polyferric chloride is controlled at 235 mg / L to 280 mg / L, and the dosage of polyacrylamide is controlled at 2.8 mg / L to 3.8 mg / L; when the influent calcium ion concentration is lower than 400 mg / L and the turbidity is lower than 50 NTU, the dosage of polyferric chloride is controlled at 205 mg / L to 235 mg / L, and the dosage of polyacrylamide is controlled at 2.1 mg / L to 2.8 mg / L. After the reagents are added, the wastewater is first stirred at 100 to 130 rpm for 6 to 10 minutes, then stirred at 28 to 45 rpm for 12 to 20 minutes, and then allowed to settle in the settling zone for 35 to 55 minutes. The calcium-containing sludge formed during settling is discharged intermittently from the bottom outlet, with a sludge discharge cycle of 40 to 70 minutes. The supernatant is then fed into the subsequent heat exchange and alkali stripping steps through the overflow outlet. To verify the impact of calcium load reduction treatment on the subsequent alkali addition and mixing pathway, this embodiment sets up three operating modes for comparison. Operating mode A is to directly add alkali to the original wastewater to a pH value of 12.0 to 12.4 without calcium load reduction treatment before it enters the stripping and deammoniation zone; operating mode B is to use fixed dosage for calcium load reduction treatment, wherein the dosage of polyferric chloride is fixed at 240 mg / L and the dosage of polyacrylamide is fixed at 3.0 mg / L; operating mode C is to use the online detection and linkage dosing method of this embodiment for calcium load reduction treatment. Table 2: Water quality test results after calcium load reduction treatment

[0022] Wastewater treated by the three operating modes was fed into an alkali addition mixer of the same specification to adjust the pH value of the wastewater to 12.0 to 12.4, and a 72-hour continuous operation test was conducted under the same steam pressure and the same influent flow rate. During the operation, the pressure difference before and after the alkali addition mixer was recorded, and the bypass short section was opened after the operation to check the deposit adhesion. Table 3: Comparison Results of Continuous Operation of Alkali Addition Mixing Path

[0023] As shown in Tables 2 and 3, in operation mode A without calcium load reduction treatment, after the wastewater was adjusted to a high pH state by adding alkali, the pressure difference of the alkali mixer increased from 0.019 MPa to 0.083 MPa, and scale deposits requiring manual cleaning appeared after 68 hours of operation. This indicates that for calcium-containing and low-ammonia wastewater from hydrogen-based vertical furnaces, if alkali stripping is carried out directly, calcium ions and calcium salt precursors in the wastewater are prone to deposit in the alkali mixing area and subsequent conveying pipelines. Operating mode B, which uses a fixed dosage, can reduce the calcium load. However, due to fluctuations in the influent calcium ion concentration and turbidity, the calcium ion concentration after treatment still varies between 142 mg / L and 213 mg / L. The pressure difference of the alkali mixer rises to 0.041 MPa after 72 hours, and local sedimentation still exists. This result indicates that using a fixed dosage alone is insufficient to adapt to the fluctuations in the water quality of hydrogen-based vertical furnace cooling and washing wastewater. In operation mode C, which employs online detection and linkage dosing, the dosage of polyferric chloride and polyacrylamide is adjusted according to pH value, turbidity value, and calcium ion concentration, so that the calcium ion concentration after pre-decalcification is reduced to 82 mg / L to 146 mg / L, and the turbidity is reduced to 9.6 NTU to 24.1 NTU. After continuous operation for 72 hours of subsequent alkali stripping, the pressure difference of the alkali mixer only increased from 0.018 MPa to 0.026 MPa, and no blockage requiring shutdown for cleaning was observed. Therefore, the calcium load reduction treatment in this embodiment is not simply aimed at reducing hardness, but rather at reducing the scale-forming calcium load of the wastewater before it enters the high-pH alkalization stripping process by online detection of the wastewater's pH value, turbidity value, and calcium ion concentration, and dynamically adjusting the dosage of coagulant and coagulant aid. This reduces the scale-forming calcium load of the wastewater to a range that is unlikely to cause blockage of the alkali mixing unit and subsequent conveying pipelines, thereby providing stable influent conditions for the continuous stripping and ammonia removal of low-ammonia wastewater. Example 3

[0024] like Figure 1-4 As shown, the alkalized wastewater enters from the upper part of the stripping ammonia removal zone and flows downwards, while the saturated steam from the hydrogen-based vertical furnace enters from the lower part of the stripping ammonia removal zone and flows upwards. During the stripping ammonia removal process, the ammonia-containing steam in the stripping ammonia removal zone is circulated and disturbed by a circulating air conveying method, so that the ammonia-containing steam forms a circulating flow between the stripping ammonia removal zone and the acid absorption zone, thereby improving the ammonia release efficiency in the low-ammonia-content wastewater. The acid absorption zone uses dilute sulfuric acid or ammonium sulfate circulating liquid as sulfuric acid absorption liquid. After the sulfuric acid absorption liquid comes into contact with ammonia-containing secondary vapor, it forms an ammonium sulfate solution. The ammonium sulfate solution is collected by reflux and then sent back to the acid absorption zone, so that the ammonium sulfate solution is gradually enriched during the circulating absorption process. When the level of the ammonium sulfate solution rises to the preset level, or the concentration of the ammonium sulfate solution is lower than the preset recovery concentration, the ammonium sulfate solution is sent to the evaporation and concentration zone. Saturated steam from the hydrogen-based vertical furnace is used as the heat medium to heat exchange and evaporate the ammonium sulfate solution. The water vapor generated by evaporation is returned to the stripping and ammonia removal zone through a circulating air conveyor, and together with the saturated steam from the hydrogen-based vertical furnace, it participates in the stripping and ammonia removal of the alkalized wastewater. In this embodiment, we will illustrate the effect of steam circulation between the stripping deammoniation zone, the acid absorption zone, and the evaporation concentration zone on the deammoniation effect and the enrichment effect of ammonium sulfate solution in low-ammonia wastewater. The wastewater to be treated is taken from the gas cooling washing water circulation drain of the hydrogen-based vertical furnace. Before entering this embodiment, the calcium load reduction treatment has been completed according to the method of Example 2. The ammonia nitrogen concentration in the pre-decalcified low-calcium clarified wastewater is 542 mg / L to 584 mg / L, the calcium ion concentration is 91 mg / L to 135 mg / L, and the water temperature is 64.1℃ to 68.2℃. The low-calcium clarified wastewater is heated by heat exchange and then mixed with 30% liquid alkali to control the pH value of the wastewater entering the stripping ammonia removal zone at 11.9 to 12.4 and the influent flow rate at 4.8 t / h to 5.2 t / h. The stripping ammonia removal zone uses vertical furnace saturated steam as the main stripping medium. The saturated steam enters from the bottom of the stripping ammonia removal zone, and the alkalized wastewater enters from the top of the stripping ammonia removal zone, so that the two form a counter-contact between the trays. During the stripping ammonia removal process, the temperature in the upper part of the stripping ammonia removal zone is controlled at 85.2℃ to 89.4℃, the temperature in the middle part at 95.4℃ to 99.6℃, and the temperature in the lower part at 99.6℃ to 102.4℃. The pressure in the stripping ammonia removal zone is controlled at 7.2 kPa to 13.1 kPa, and the circulating air volume is controlled at 820 m³ / h to 1080 m³ / h. The circulating air is used to generate circulating disturbance in the ammonia-containing water vapor in the stripping ammonia removal zone and to send some of the ammonia-containing secondary steam into the acid absorption zone. A sulfuric acid absorbent solution is circulated within the acidic absorption zone. The absorbent solution consists of dilute sulfuric acid and ammonium sulfate circulating solution. The pH value of the absorbent solution is controlled between 3.1 and 4.0, the temperature of the circulating solution is controlled between 42℃ and 51℃, and the circulation flow rate is controlled between 18 m³ / h and 24 m³ / h. After ammonia-containing secondary vapor enters the acidic absorption zone, it comes into contact with the sulfuric acid absorbent solution. The ammonia is absorbed and converted into an ammonium sulfate solution. The ammonium sulfate solution is collected by reflux and then re-enters the acidic absorption zone for absorption. As the operating time increases, the moisture in the ammonia-containing secondary steam condenses in the acidic absorption zone, causing the ammonium sulfate circulating liquid level to rise and the concentration increase rate to decrease. When the mass concentration of the ammonium sulfate circulating liquid is below 24.5% and the liquid level in the ammonium sulfate circulating tank reaches 1.76m to 1.84m, part of the ammonium sulfate circulating liquid is sent to the evaporation and concentration zone for heat exchange and evaporation. The heating medium in the evaporation and concentration zone is saturated steam from the hydrogen-based vertical furnace. After evaporation, an ammonium sulfate solution with a mass concentration of 28.7% to 30.4% is obtained. The water vapor generated in the evaporation and concentration zone is treated to remove liquid mist and then returned to the lower part of the stripping and ammonia removal zone via a circulating air conveyor. It then enters the stripping and ammonia removal zone together with the saturated steam from the hydrogen-based vertical furnace. The temperature of the returned water vapor is 93.5℃ to 98.8℃, and the return flow rate is converted to 0.055t / h to 0.086t / h. After entering the stripping and ammonia removal zone, it participates in the vapor-liquid contact process to replenish the amount of water vapor and reduce the intensity of circulation disturbance in the stripping and ammonia removal zone. To verify the effect of steam return on ammonia removal and ammonium sulfate enrichment in low-ammonia wastewater, this embodiment sets up three operating modes for comparison. Operating mode A uses only vertical furnace saturated steam stripping and sulfuric acid absorption, without returning steam to the stripping ammonia removal area; operating mode B returns steam to the stripping ammonia removal area, but does not perform circulating air disturbance, relying only on the natural rising airflow in the tower to participate in stripping; operating mode C uses the circulating air conveying method of this embodiment, returning steam to the stripping ammonia removal area and participating in stripping ammonia removal together with the vertical furnace saturated steam.

[0025] Table 4: Operational data of ammonia stripping under different steam circulation modes

[0026] Table 5: Ammonium sulfate enrichment data under different steam circulation methods

[0027] As shown in Table 4, under the condition that the influent ammonia nitrogen concentration is not higher than 600 mg / L, Operation Mode A relies solely on the saturated steam of the vertical furnace for stripping. Although some ammonia can be released with the secondary steam, the effluent ammonia nitrogen concentration fluctuates between 44.6 mg / L and 63.8 mg / L, with some periods exceeding 50 mg / L. Operation Mode B returns the evaporated steam to the stripping and ammonia removal area, which reduces the external saturated steam consumption. However, due to the lack of circulating air disturbance, the distribution of the returned steam in the stripping and ammonia removal area is not uniform, and the effluent ammonia nitrogen still shows periods of high levels. Operating mode C uses a circulating pneumatic conveying method to return the evaporated water vapor to the stripping and ammonia removal zone, allowing the returned water vapor to participate in the steam-liquid contact process together with the saturated steam of the vertical furnace. This reduces the ammonia nitrogen concentration in the effluent to 31.5 mg / L to 48.9 mg / L, and the external saturated steam consumption to an average of 0.30 t / h. This result indicates that under low ammonia wastewater conditions, the return of evaporated water vapor is not simply a heat recovery process, but rather participates in the steam-liquid contact process within the stripping and ammonia removal zone through circulating pneumatic conveying, thereby improving the release effect of low-concentration ammonia. As shown in Table 5, in operation mode A, the ammonium sulfate circulating liquid is diluted by condensate during acid absorption, and its concentration before entering the evaporation and concentration is 19.8% to 23.2%, requiring a concentration time of 6.5h to 7.4h to reach 29.5%. In operation mode C, after the evaporated water vapor returns to the stripping and ammonia removal area and is circulated and disturbed, the concentration and flow state of the ammonia-containing secondary steam entering the acid absorption area are more stable, the concentration of the ammonium sulfate circulating liquid increases to 21.7% to 24.8%, and the concentration time required to reach 29.5% is shortened to 4.8h to 5.6h. Therefore, this embodiment illustrates that in the treatment of calcium-containing and low-ammonia-content wastewater in a hydrogen-based vertical shaft furnace, the steam circulation formed between the stripping ammonia removal zone, the acid absorption zone, and the evaporation and concentration zone can simultaneously affect the ammonia release efficiency, the external saturated steam consumption, and the enrichment rate of the ammonium sulfate solution in the low-ammonia-content wastewater. Among these methods, returning the evaporated steam to the stripping ammonia removal zone through a circulating air conveying system, and having it participate in the stripping ammonia removal together with the saturated steam of the vertical shaft furnace, is more suitable for the continuous ammonia removal and ammonia recovery of low-ammonia-content wastewater compared to separate stripping absorption or simple steam return methods. Example 4

[0028] like Figure 1-4 As shown, the concentrated ammonium sulfate solution after evaporation and concentration is returned to the ammonium sulfate product collection area through a liquid seal or pressure balancing method to maintain stable liquid level and temperature during the evaporation and concentration process, and to limit the escape of evaporated water vapor from the concentrated liquid return path. The cooling and washing water circulation area of ​​the hydrogen-based vertical furnace includes at least one of the following: direct cooling collection tank, hot water well, cyclone grit chamber, sludge conditioning tank and sedimentation tank; the ammonia-containing water vapor generated by the volatilization in the cooling and washing water circulation area is collected and sent to the acid absorption area, where it is absorbed by the sulfuric acid absorption liquid and then circulated into the ammonium sulfate solution. During operation, the ammonia nitrogen value of the wastewater after stripping and ammonia removal, the temperature of the stripping and ammonia removal zone, the steam pressure, the acidity of the acid absorption zone, the concentration of ammonium sulfate solution, and the pressure of the stripping and ammonia removal zone are monitored. When the ammonia nitrogen value of the wastewater after stripping and ammonia removal exceeds the discharge requirements, the degree of alkalization of the wastewater is increased, the steam supply intensity is increased, sulfuric acid absorbent is added, or the stripping and ammonia removal zone is cleaned to restore the ammonia removal effect and the ammonium sulfate absorption effect. In this embodiment, based on the continuous treatment process of Example 1, the effects of the reflux method of the concentrated ammonium sulfate solution after evaporation and concentration, the collection method of ammonia-containing water vapor in the cooling washing water circulation area, and the correction method of operating parameters on the stability of continuous treatment are further investigated. The influent flow rate of the calcium-containing and low-ammonia-containing wastewater treated in this embodiment is 4.8 t / h to 5.2 t / h, the influent ammonia nitrogen concentration is 541 mg / L to 586 mg / L, the calcium ion concentration after pre-decalcification is 89 mg / L to 132 mg / L, and the pH value of the wastewater entering the tower is 11.9 to 12.4. During the evaporation and concentration process, the ammonium sulfate circulating liquid formed by the reflux of the acid absorption zone is sent to the evaporation and concentration zone. The evaporation and concentration zone uses saturated steam from the hydrogen-based vertical furnace as the heat medium. The saturated steam pressure is controlled at 0.40 MPa to 0.46 MPa. The mass concentration of the ammonium sulfate circulating liquid before entering the evaporation and concentration zone is 21.9% to 24.7%, and the evaporation and concentration temperature is controlled at 98.5℃ to 103.2℃. The concentrated ammonium sulfate solution after evaporation and concentration is returned to the ammonium sulfate finished product collection area through the liquid seal reflux structure. The liquid seal height of the liquid seal reflux structure is controlled at 0.42m to 0.58m, and a pressure balance bypass pipe is set up to keep the liquid level and temperature in the evaporation and concentration zone within the allowable fluctuation range during the return of the concentrated liquid. To observe the effect of the liquid seal reflux structure, this embodiment compared two reflux methods. Operation mode A involved ordinary gravity reflux of the concentrated ammonium sulfate solution, without liquid seal or pressure balance in the reflux path. Operation mode B involved reflux of the concentrated ammonium sulfate solution to the ammonium sulfate finished product collection area via the liquid seal reflux structure and the pressure balance bypass pipe. Both operation modes were continuously operated for 24 hours under the same inlet concentration, the same steam pressure, and the same inlet flow rate. The test results are shown in Table 6.

[0029] Table 6: Results of Reflux Stability Test for Concentrated Ammonium Sulfate Solution

[0030] As shown in Table 6, in operating mode A without liquid seal and pressure balance, there is a certain pulsation during the concentrate reflux process, with the liquid level fluctuation in the evaporation and concentration area reaching ±0.18m to ±0.26m, and the ammonium sulfate concentration after evaporation and concentration fluctuating within a wide range. After adopting operating mode B, the liquid level fluctuation is reduced to ±0.05m to ±0.10m, and the ammonium sulfate mass concentration after evaporation and concentration remains at 29.1% to 30.6%. This indicates that liquid seal and pressure balance reflux can reduce the disturbance of the liquid level and temperature in the evaporation and concentration area caused by the concentrate reflux, and reduce the backflow of evaporated water vapor from the concentrate reflux path. During the ammonia-containing water vapor collection process, the direct cooling collection tank, hot water well, cyclone grit chamber, sludge equalization tank, and sedimentation tank in the cooling and washing water circulation area of ​​the hydrogen-based vertical furnace are selected as the collection targets. A gas collection hood or negative pressure collection branch pipe is installed above each collection point. The collection air volume is allocated according to the opening area of ​​each collection point and the ammonia detection value. The collection air volume at a single point is controlled at 260 m³ / h to 620 m³ / h. The collected ammonia-containing water vapor is sent to the acidic absorption area by a deodorizing fan and is absorbed by contact with the sulfuric acid absorption liquid. The pH value of the absorption liquid in the acidic absorption area is controlled at 3.2 to 4.1, and the circulation flow rate of the absorption liquid is controlled at 18 m³ / h to 24 m³ / h. In this embodiment, the ammonia concentration near each collection point was detected before and after the ammonia-containing water vapor was collected. The average range was taken after three consecutive tests at each detection point. The test results are shown in Table 7. Table 7: Results of Ammonia Vapor Collection and Detection in Cooling Washing Water Circulation Area

[0031] As shown in Table 7, after the ammonia-containing water vapor in the cooling washing water circulation area was collected and sent to the acidic absorption area, the ammonia concentration near each detection point decreased. Specifically, the ammonia concentration above the direct cooling collection tank decreased from 17.8 mg / m³ to 25.6 mg / m³ to 4.1 mg / m³ to 7.3 mg / m³, and the ammonia concentration above the hot water well decreased from 14.6 mg / m³ to 21.2 mg / m³ to 3.5 mg / m³ to 6.4 mg / m³. At the same time, the equivalent increase of ammonium sulfate in the acidic absorption area was 13.8 kg / d to 21.6 kg / d. This indicates that incorporating the ammonia-containing water vapor volatilized from the cooling washing water circulation area into the acidic absorption area not only reduces ammonia escape in the area but also allows this low-concentration ammonia source to enter the ammonium sulfate solution generation process. During continuous operation, the ammonia nitrogen value of the wastewater after stripping and ammonia removal, the temperature of the stripping and ammonia removal zone, the steam pressure, the acidity of the acid absorption zone, the concentration of ammonium sulfate solution, and the pressure of the stripping and ammonia removal zone were further monitored. When the above parameters deviated from the control range, corresponding adjustments were made according to the cause of the deviation. In this embodiment, four typical operating fluctuations were selected and recorded, and the results are shown in Table 8. Table 8: Record of Operating Parameter Fluctuations and Corrections in Example 4

[0032] As shown in Table 8, when the ammonia nitrogen in the effluent increases, the conversion of ammonium nitrogen to free ammonia and the stripping release can be restored to the set level by increasing the degree of wastewater alkalization and restoring the steam pressure. When the pH value in the acidic absorption zone increases, the absorption effect of ammonia-containing secondary steam can be restored by supplementing sulfuric acid absorbent and increasing the circulating absorption rate. When the concentration of ammonium sulfate circulating liquid is low and the liquid level in the circulating tank increases, the concentration of ammonium sulfate finished liquid can be restored by increasing the evaporation concentration treatment ratio and maintaining the return of evaporated water vapor. When the pressure in the stripping and ammonia removal zone increases and the pressure difference in the alkali addition mixer increases, the pressure can be prevented from continuously increasing by reducing the influent load, increasing the pre-decalcification sludge discharge frequency, and online flushing. Therefore, this embodiment illustrates that using liquid sealing or pressure balancing to reflux the concentrated ammonium sulfate solution can improve the stability of liquid level and temperature during the evaporation and concentration process; the ammonia-containing water vapor generated by the evaporation of the cooling washing water circulation area is collected and sent to the acid absorption area, which can reduce the escape of low-concentration ammonia sources and increase the amount of ammonium sulfate generated; at the same time, the operation is modified according to the ammonia nitrogen in the effluent, the temperature of the stripping and ammonia removal area, the steam pressure, the acidity of the acid absorption area, the concentration of the ammonium sulfate solution, and the pressure of the stripping and ammonia removal area, so that the treatment method can maintain continuous ammonia removal and ammonia recovery effect under fluctuations in influent water quality and operating load.

[0033] Comparative Example 1 The difference between this comparative example and Example 1 is that the calcium load reduction treatment is not performed on the calcium-containing and low-ammonia-content wastewater. Instead, 30% liquid alkali is directly added to the original wastewater after heat exchange and heating to adjust the pH value of the wastewater entering the tower to 11.9 to 12.4. Then, it enters the stripping and ammonia removal zone for stripping and ammonia removal. The ammonia-containing secondary steam still enters the acidic absorption zone and contacts the sulfuric acid absorbent to generate ammonium sulfate solution. The ammonium sulfate solution still enters the evaporation and concentration zone for concentration. The evaporated water vapor is still returned to the stripping and ammonia removal zone by circulating air. During continuous operation of this comparative example, the pressure difference across the alkali mixer gradually increased with operating time. After 48 hours of operation, the pressure difference rose from 0.019 MPa to 0.066 MPa, and after 61 hours, it rose to 0.079 MPa, accompanied by flow fluctuations at the outlet section and subsequent bends of the alkali mixer. After 64 hours of operation, an inspection of the outlet section of the alkali mixer revealed grayish-white hard deposits on the inner wall. The deposits were mainly attached to the mixing zone after the liquid alkali entered and at the downstream bend. The machine needed to be shut down for flushing and manual cleaning before it could continue to operate.

[0034] Comparative Example 2 The difference between this comparative example and Example 1 is that the calcium load reduction treatment, alkalization stripping, acid absorption and evaporation concentration steps are retained, but the water vapor generated in the evaporation concentration area is not returned to the stripping and ammonia removal area, but is discharged after condensation or enters the condensate collection section; the stripping and ammonia removal area only uses saturated steam from the hydrogen-based vertical furnace as the stripping medium, and the circulating air conveying is only used for gas conveying at the front end of the acid absorption area and does not undertake the function of returning evaporated water vapor; This comparative example operated continuously for 168 hours. After pre-decalcification, the calcium ion concentration ranged from 88 mg / L to 147 mg / L. No significant alkali addition mixer blockage was observed. However, the external saturated steam consumption increased compared to Example 1, and the effluent ammonia nitrogen concentration approached or exceeded 50 mg / L at certain times. Meanwhile, due to the limited amount of ammonia released from the low-ammonia wastewater, the concentration of ammonium sulfate circulating liquid in the acidic absorption zone increased slowly. After being diluted by the secondary steam condensate, the ammonium sulfate circulating liquid required a long concentration time to reach the finished product recovery concentration.

[0035] Comparative Example 3 The difference between this comparative example and Example 1 is that the steps of calcium load reduction treatment, alkalization stripping, acid absorption, evaporation concentration and return of evaporated water vapor to the stripping deammoniation zone are retained, but the ammonia-containing water vapor generated by volatilization in the direct cooling collection tank, hot water well, cyclone grit chamber, sludge conditioning tank and sedimentation tank in the hydrogen-based vertical furnace cooling washing water circulation zone is not collected in a centralized manner, nor is this part of the ammonia-containing water vapor sent to the acid absorption zone. This comparative example operated continuously for 168 hours. The main stripping and ammonia removal process was able to maintain operation, and the ammonia nitrogen concentration in the effluent was kept within the set control range. However, there was still an intermittent ammonia odor near the cooling and washing water circulation area. The ammonia concentration above the direct cooling collection tank, hot water well, and sludge equalization tank fluctuated with the water temperature and stirring status. Since this part of the low-concentration ammonia-containing water vapor was not incorporated into the acid absorption area, the ammonium sulfate recovery amount was lower than that in Example 1, and the total ammonia recovery rate was also reduced accordingly.

[0036] Table 9: Comparison of Results between Comparative Example and Example 1

[0037] As shown in Table 9, in Comparative Example 1, without calcium load reduction treatment, the pressure difference of the alkali mixer rapidly increased from 0.019 MPa to 0.066 MPa under high-pH alkali stripping conditions, and required shutdown for cleaning after 64 hours of operation due to the adhesion of hard deposits. In contrast, after calcium load reduction treatment, the pressure difference of the alkali mixer in Example 1 only increased to 0.024 MPa after 168 hours of operation, and no blockage requiring shutdown for cleaning occurred. This result indicates that for calcium-containing and low-ammonia wastewater from hydrogen-based vertical furnaces, calcium load reduction treatment is not a normal water softening step, but a pretreatment step to ensure the continuous operation of subsequent high-pH alkali stripping. Although Comparative Example 2 underwent calcium load reduction treatment and stripping absorption, the water vapor generated in the evaporation and concentration zone was not returned to the stripping and ammonia removal zone. This resulted in an increase in the external saturated steam consumption to 0.35 t / h to 0.40 t / h, and the effluent ammonia nitrogen concentration fluctuated between 43.6 mg / L and 61.4 mg / L. Furthermore, the concentration time required for the ammonium sulfate product solution to reach a concentration of 29.5% was extended to 6.6 h to 7.8 h. Compared with Example 1, these results indicate that returning the evaporated water vapor to the stripping and ammonia removal zone is not simply a heat recovery process, but rather it can participate in the stripping and ammonia removal process of low-ammonia wastewater together with the saturated steam from the vertical shaft furnace, thereby improving the ammonia removal and ammonium sulfate enrichment effects under low-ammonia conditions. In Comparative Example 3, where ammonia-containing water vapor from the cooling washing water circulation area was not collected, although the main process could still complete stripping and ammonia removal and ammonium sulfate concentration, the ammonia concentration near each collection point remained between 14.2 mg / m³ and 24.8 mg / m³, with a total ammonia recovery rate of 78.9% to 84.6%. In Example 1, after incorporating this portion of ammonia-containing water vapor into the acidic absorption area, the ammonia concentration at the collection points decreased to between 2.8 mg / m³ and 5.9 mg / m³, and the total ammonia recovery rate increased to between 87.4% and 92.1%. These results indicate that incorporating ammonia-containing water vapor from the cooling washing water circulation area into the acidic absorption area not only reduces ammonia escape but also allows low-concentration ammonia sources to enter the ammonium sulfate generation process. Therefore, by comparing Example 1 with Comparative Examples 1 to 3, it can be seen that the calcium load reduction treatment, the return of evaporated water vapor to the stripping and ammonia removal area, and the incorporation of ammonia-containing water vapor from the cooling and washing water circulation area into the acid absorption area are not simply parallel processes. The calcium load reduction treatment ensures the continuous operation of subsequent alkalization stripping, the return of evaporated water vapor improves the stripping and ammonia removal efficiency and ammonium sulfate concentration efficiency of low-ammonia wastewater, and the incorporation of ammonia-containing water vapor into the acid absorption area increases the ammonia recovery rate of the entire process.

[0038] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," 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 invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0039] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the present invention. Various changes and modifications can be made to the present invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed.

Claims

1. A method for ammonia removal and recovery from ammonia-containing wastewater based on stripping absorption coupling, characterized in that, Includes the following steps: The calcium load of the calcium-containing, low-ammonia wastewater from the gas cooling and washing process of a hydrogen-based vertical furnace is reduced. The ammonia nitrogen concentration of the calcium-containing, low-ammonia wastewater is not higher than 600 mg / L. This allows the calcium source, which is prone to forming scale deposits under subsequent alkaline stripping conditions, to be pre-transferred to a separable solid phase, and then cleared low-calcium wastewater is obtained through solid-liquid separation. After adjusting the low-calcium clarified wastewater to an alkaline state that can promote the conversion of ammonium nitrogen to free ammonia, the alkalized wastewater is introduced into the stripping deammoniation zone, and the alkalized wastewater is made to come into countercurrent contact with saturated steam from the hydrogen-based vertical furnace in the stripping deammoniation zone. At the same time, the ammonia-containing steam in the stripping deammoniation zone is circulated and disturbed, so that the ammonia in the wastewater is released with the secondary steam. The released ammonia-containing secondary vapor is introduced into the acidic absorption area, and the ammonia-containing secondary vapor is brought into contact with the circulating sulfuric acid absorption liquid to react and generate an ammonium sulfate solution. When the ammonium sulfate solution experiences a rise in liquid level or a concentration below the recovery requirement due to the accumulation of condensate during absorption, the ammonium sulfate solution is introduced into an evaporation and concentration zone for evaporation and concentration, so that the water in it evaporates and the concentration of ammonium sulfate increases, resulting in a concentrated ammonium sulfate solution. The water vapor generated in the evaporation and concentration zone is returned to the stripping and ammonia removal zone by circulating air, so that the returned water vapor and the saturated steam from the hydrogen-based vertical furnace participate together in the wastewater ammonia removal process. The wastewater after stripping and ammonia removal is discharged after its acidity is adjusted. The ammonia-containing water vapor generated from the volatilization of the cooling washing water circulation area of ​​the hydrogen-based vertical furnace is collected and sent to the acidic absorption area, so that the ammonia in the ammonia-containing water vapor is incorporated into the formation of the ammonium sulfate solution.

2. The method for ammonia removal and recovery from ammonia-containing wastewater based on stripping absorption coupling according to claim 1, characterized in that, The calcium load reduction treatment includes adding coagulants and coagulant aids to calcium-containing, low-ammonia-content wastewater, so that calcium ions and calcium salt precursors in the wastewater are converted into precipitated particles, and the precipitated particles are aggregated into settleable flocs under the action of coagulants and coagulant aids, and then the settleable flocs are discharged as calcium-containing sludge.

3. The method for ammonia removal and recovery from ammonia-containing wastewater based on stripping absorption coupling according to claim 1, characterized in that, The coagulant includes polyferric chloride, and the coagulant aid includes polyacrylamide; During the addition of coagulants and coagulant aids, the pH value, turbidity value, and calcium ion concentration of the wastewater are monitored, and the dosage of coagulants and coagulant aids is adjusted according to the pH value, turbidity value, and calcium ion concentration to ensure that the calcium load of the low-calcium clarified wastewater before entering the alkalization stripping process is within a range that will not cause blockage of the alkali addition mixer and its subsequent conveying pipelines.

4. The method for ammonia removal and recovery from ammonia-containing wastewater based on stripping absorption coupling according to claim 1, characterized in that, Before being adjusted to an alkaline state, the low-calcium clarified wastewater is heat-exchanged with the stripped ammonia-removed wastewater to raise the temperature of the low-calcium clarified wastewater and lower the temperature of the stripped ammonia-removed wastewater. Subsequently, liquid alkali was added to the heated low-calcium clarified wastewater to adjust its pH value to 10 to 12.

5.

5. The method for ammonia removal and recovery from ammonia-containing wastewater based on stripping absorption coupling according to claim 1, characterized in that, The alkalized wastewater enters from the upper part of the stripping and ammonia removal zone and flows downward, while the saturated steam from the hydrogen-based vertical furnace enters from the lower part of the stripping and ammonia removal zone and flows upward. During the stripping and ammonia removal process, the ammonia-containing steam in the stripping and ammonia removal area is circulated and disturbed by a circulating air conveying method, so that the ammonia-containing steam forms a circulating flow between the stripping and ammonia removal area and the acidic absorption area, thereby improving the ammonia release efficiency in low-ammonia wastewater.

6. The method for ammonia removal and recovery from ammonia-containing wastewater based on stripping absorption coupling according to claim 1, characterized in that, The acidic absorption zone uses dilute sulfuric acid or ammonium sulfate circulating solution as the sulfuric acid absorption liquid. After the sulfuric acid absorption liquid comes into contact with ammonia-containing secondary steam, it forms an ammonium sulfate solution. The ammonium sulfate solution is collected by reflux and then sent back to the acidic absorption zone, so that the ammonium sulfate solution is gradually enriched during the circulating absorption process.

7. The method for ammonia removal and recovery from ammonia-containing wastewater based on stripping absorption coupling according to claim 1, characterized in that, When the level of the ammonium sulfate solution rises to a preset level, or when the concentration of the ammonium sulfate solution is lower than a preset recovery concentration, the ammonium sulfate solution is sent to the evaporation and concentration zone. Saturated steam from the hydrogen-based vertical furnace is used as the heat medium to heat exchange and evaporate the ammonium sulfate solution. The water vapor generated by evaporation is returned to the stripping and ammonia removal zone by circulating air, and together with the saturated steam from the hydrogen-based vertical furnace, it participates in the stripping and ammonia removal of the alkalized wastewater.

8. The method for ammonia removal and recovery from ammonia-containing wastewater based on stripping absorption coupling according to claim 7, characterized in that, The concentrated ammonium sulfate solution after evaporation and concentration is returned to the ammonium sulfate product collection area through a liquid seal or pressure balancing method to maintain stable liquid level and temperature during the evaporation and concentration process, and to limit the escape of evaporated water vapor from the concentrated liquid return path.

9. The method for ammonia removal and recovery from ammonia-containing wastewater based on stripping absorption coupling according to claim 1, characterized in that, The hydrogen-based vertical furnace cooling and washing water circulation area includes at least one of the following: a direct cooling collection tank, a hot water well, a vortex grit chamber, a sludge conditioning tank, and a sedimentation tank; The ammonia-containing water vapor generated by the evaporation of the cooling washing water circulation area is collected and sent to the acid absorption area, where it is absorbed by the sulfuric acid absorption liquid and then circulated into the ammonium sulfate solution.

10. The method for ammonia removal and recovery from ammonia-containing wastewater based on stripping absorption coupling according to claim 1, characterized in that, During operation, the ammonia nitrogen value of the wastewater after stripping and ammonia removal, the temperature and steam pressure of the stripping and ammonia removal zone, the acidity of the acid absorption zone, the concentration of ammonium sulfate solution, and the pressure of the stripping and ammonia removal zone are monitored. When the ammonia nitrogen value of the wastewater after stripping and ammonia removal is higher than the discharge requirements, the degree of alkalization of the wastewater, the intensity of steam supply, the addition of sulfuric acid absorbent, or the cleaning of the stripping and ammonia removal area can be increased according to the test results to restore the ammonia removal effect and ammonium sulfate absorption effect of the wastewater.

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