A method for preventing and monitoring fouling of an exhaust gas treatment device

Abstract

The application discloses a method for preventing tail gas treatment device from scaling and scaling monitoring. The application monitors scaling conditions by using changes of pressures of different parts and changes of pump currents, and slows down or eliminates scaling by adjusting pH values of relevant points; the application controls pH values of weak acids of absorption and washing tower bottom circulating slurry modules and filtering modules, so that scaling phenomena of tail gas desulfurization and denitrification device system pipelines and tower inner devices are prevented, and equipment corrosion is avoided; when tail gas is discharged, indexes of NOx and SO2 can be better controlled within design ranges.

Description

Technical Field

[0001] This invention relates to methods for treating and monitoring scale buildup, specifically to a method for preventing scale buildup in exhaust gas treatment devices and for monitoring scale buildup, belonging to the field of exhaust gas treatment technology. Background Technology

[0002] Desulfurization and denitrification units effectively control SO2 and NOx emissions, ensuring they remain within environmental standards. Therefore, the long-term stable operation of these units is crucial. In tail gas desulfurization and denitrification, scaling and blockage frequently occur in related equipment. Scaling in pipelines and nozzles within the desulfurization and denitrification system directly affects absorption efficiency, impacting long-term operation and ultimately hindering SO2 and NOx emission compliance. Equipment scaling and blockage have become critical issues for long-term, normal operation. Therefore, it is essential to first understand the mechanism of scaling and the factors influencing scaling and blockage, and then address these issues specifically through process design, equipment structure, and operational control.

[0003] Some devices that require exhaust emissions are equipped with exhaust gas treatment devices (generally called scrubbing towers; some have desulfurization and denitrification functions, while others do not). For example, catalytic cracking units, sulfur recovery units, and thermal power units in oil refineries are all equipped with exhaust gas treatment devices.

[0004] Exhaust gas emissions typically contain dust, as well as sulfur-containing compounds such as H2S, SO2, mercaptans, thioethers, cyclic thioethers, thiophenols, and thiophene. During the reaction process, some sulfur-containing compounds are converted into hydrogen sulfide and thiophene, which exist in the reactants. Some sulfur is burned to produce sulfur oxides (SOx). Finally, the exhaust gas enters the exhaust gas purification system for desulfurization and denitrification before being discharged in compliance with emission standards.

[0005] The characteristics of exhaust gas are:

[0006] (1) The concentrations of SOx and NOx in the exhaust gas fluctuate greatly, with SOx concentrations generally ranging from 700 to 4500 mg / m³. 3 NOx concentration is between 50 and 400 mg / m³ 3 ;

[0007] (2) The concentration of particulate matter in the exhaust gas fluctuates greatly, with a normal concentration of 150–200 mg / m³. 3 .

[0008] The exhaust gas treatment device mainly consists of three parts: the lower section is mainly used for washing exhaust gas dust, cooling, acidification and neutralization; the middle section is a filter module, which is mainly used for desulfurization, denitrification, dust removal and neutralization; and the upper section is an exhaust gas separator.

[0009] The exhaust gas enters the treatment unit, where, under the strong oxidizing effect of ozone (ozone is used in units with denitrification function, but not in units without), some SO2 and NO react to form SO3 and NO2. The circulating slurry at the bottom of the scrubbing tower reacts with SOx and NOx in the exhaust gas through atomizing nozzles to form H2SOx and HNOx, lowering the pH and removing most of the dust. Alkali injection maintains the slurry's pH between 6 and 9. The exhaust gas then enters the middle filtration module for further removal of SOx and NOx, as well as any remaining fine dust. The purified exhaust gas passes through a cyclone separator at the top of the tower and is then discharged into the atmosphere through a steel chimney.

[0010] The exhaust gas enters the quench unit of the scrubbing system horizontally. The exhaust gas passes through a high-density water curtain containing atomized water droplets and cross-flowing, where it is quenched and saturated, and the resulting water flow simultaneously and evenly washes the inner wall.

[0011] An "empty" unit is reserved inside the cooling absorption tower. Its specific function is to form a reaction zone for ozone and nitrogen oxides, where the contact between exhaust gas and liquid is minimized.

[0012] In the reaction zone, reactions (1) to (3) occur. Ozone (O3) preferentially converts NO... x (NO and NO2) are oxidized to N2O5. N2O5 then combines with water vapor in the exhaust gas to form nitric acid (HNO3).

[0013] (1) NO + O3 → NO2 + O2

[0014] (2) 2NO₂ + O₃ → N₂O₅ + O₂

[0015] (3) N2O5 + H2O → 2HNO3

[0016] Above the reaction zone, HNO3 is washed and absorbed from the vertical unit of the cooling absorption tower of the spray bed. The pH of the washing liquid is maintained at 7.0. As shown in reaction (4), nitric acid is effectively removed due to the strong contact between the tail gas and the liquid.

[0017] (4) HNO3 + NaOH → NaNO3 + H2O

[0018] In addition, the strong contact between exhaust gas and liquid effectively removes coarse particles and performs desulfurization. The water after spraying flows down the four walls to the bottom of the tower and then into the internal recirculation tank.

[0019] Any excess O3 in the cooling absorption tower will convert bisulfite and sulfite into sulfate. However, the cooling absorption tower recirculation loop needs to maintain a minimum of 3000 ppm of sulfite and bisulfite to minimize the drop in O3 from the chimney. If necessary, bisulfite can be added to maintain this minimum level.

[0020] The scrubbing tower requires fresh water as a makeup water. The calcium ions in the fresh water will continuously concentrate and accumulate. Some calcium ions exist in the form of Ca(OH)2, which leads to an increase in pH value. Ca(OH)2 reacts with CO2 and SO2 in the exhaust gas to produce CaCO3 and CaSO4. Calcium carbonate, calcium sulfate, etc., mix with dust and adhere to the equipment, forming dense scale, which can cause problems such as nozzle blockage, pump impeller scaling, and pipeline blockage.

[0021] The following reactions occur during the dual-alkali desulfurization process:

[0022] 1) SOx absorption process

[0023] (1) Na2SO3 + SO2 + H2O → 2NaHSO3 (when pH = 5-9)

[0024] (2) 2NaOH + SO2 → Na2SO3 + H2O (when pH > 9)

[0025] (3) 2NaOH + SO3 → Na2SO4 + H2O

[0026] Among them, equation (1) is the main reaction equation during operation; equations (2) and (3) are the main reaction equations when the pH of the regenerated liquid is high.

[0027] 2) Regeneration process

[0028] (4)2NaHSO3+Ca(OH)2→Na2SO3+CaSO31 / 2H2O+3 / 2H2O

[0029] (5)2NaHSO3+Ca(OH)2+H2O→4NaOH+2CaSO31 / 2H2O

[0030] (6)Na2SO4+Ca(OH)2+2H2O→2NaOH+2CaSO42H2O

[0031] Since the solubility of CaSO4 in water is much greater than that of CaSO3, the reaction in equation (6) is not easily carried out in the regeneration stage and requires Ca in the solution. 2+ This can only occur when the concentration is kept at a high level.

[0032] Scaling and clogging in the equipment within the scrubbing tower can cause scaling and clogging in the absorption tower, nozzles, demisters, and heat exchangers. This is because oxygen in the exhaust gas oxidizes CaSO3 into CaSO4 (gypsum), saturating the gypsum and causing it to precipitate and adhere to pipelines and components within the scrubbing tower, thus affecting the absorption efficiency of NOx and SO2.

[0033] Because the exhaust gas contains sulfur-containing compounds such as H2S, SO2, and mercaptans, it is easy to form acidic substances in a wet environment. Generally, the equipment selected for exhaust gas treatment devices should be made of corrosion-resistant materials, such as high-grade stainless steel like 304 and 316. In order to reduce corrosion, the design institute requires that the pH value of the slurry in the scrubbing tower of the exhaust gas treatment device be controlled between 7 and 9. However, this brings a problem: salt is generated in the slurry in a weakly alkaline environment, causing scale to form on the equipment of the exhaust gas treatment device, which affects the long-term operation of the device.

[0034] Therefore, researching anti-scaling methods for exhaust gas treatment devices is of great significance. Currently, there are no methods in industry that address both anti-scaling and monitoring; often, a single method or a random mixture of several methods is chosen, which fails to effectively combine different scale inhibition techniques, thus making it difficult to achieve the desired treatment effect. Furthermore, inappropriate scale inhibition methods can also cause damage to pipeline equipment. Summary of the Invention

[0035] Purpose of the Invention: The purpose of this invention is to address the shortcomings of existing technologies by providing a method for preventing and monitoring scaling in exhaust gas treatment devices. This method is used to prevent scaling and monitor the scaling status of equipment, components, and pipelines within the exhaust gas treatment device system. This invention monitors the changes in circulating slurry concentration and scaling status by measuring the outlet current (A) of the slurry circulation pump, the pump outlet pressure (B), the quench nozzle pressure (C), and the filter module nozzle pressure (D). Scaling is mitigated or eliminated by adjusting the pH value at relevant points. By controlling the slightly acidic pH of the circulating slurry module and filter module at the bottom of the absorption and scrubbing tower, scaling is prevented in the pipelines and internal components of the exhaust gas desulfurization and denitrification device system, thus avoiding equipment corrosion. During exhaust gas emissions, NOx and SO2 levels can be better controlled within the design range.

[0036] Technical solution: The objective of this invention is achieved through the following technical solution:

[0037] This invention provides a method for preventing and monitoring scaling in exhaust gas treatment devices, comprising the following steps: sulfide-containing exhaust gas enters horizontally through a flue into the quenching unit and the middle filtration module unit of an absorption scrubbing tower; the pH value of the circulating slurry at the bottom of the tower is controlled at 6.5–7.0, and the pH value of the filtration module is controlled at 6.0–6.5; the circulating slurry at the bottom of the tower is circulated by a pump, and is cooled and saturated by counter-current contact with the exhaust gas entering the absorption scrubbing tower; the filtration module is arranged in a ring shape in the upper part of the spray tower of the quenching unit; in the spray box at the top of the filtration module, high-density spraying from nozzles is used for filtration to remove water mist and fine dust; the slurry containing dust and sodium sulfite is discharged from the outlet of the bottom slurry circulation pump of the absorption tower.

[0038] By monitoring changes in the slurry circulation pump outlet current (A), pump outlet pressure (B), quench nozzle pressure (C), and filter module nozzle pressure (D), the scaling condition of the system is monitored, and the pH value of each unit is adjusted accordingly to prevent scaling.

[0039] Preferably, to ensure absorption efficiency, the inlet temperature of the flue is 180–250°C. To avoid dew point corrosion, the flue gas temperature is controlled above the dew point temperature. The bottom operating temperature of the absorption scrubbing tower is 50–70°C, which is higher than the crystallization temperature of the slurry.

[0040] Preferably, the present invention specifically includes the following steps:

[0041] (1) The exhaust gas enters the scrubber of the rapid cooling unit of the absorption scrubbing tower horizontally through the flue. One or more nozzles are used to spray water or slurry at a flow rate that can achieve atomization to rapidly cool the exhaust gas and evenly wash the inner wall to ensure that the exhaust gas temperature is ≤65℃.

[0042] (2) Set up multiple levels of spray in the spray tower area of ​​the scrubber, with one or more nozzles in each level to remove SO2 in stages; each level of nozzle sprays circulating slurry at a flow rate that can achieve atomization, so that the gas / liquid are in close contact, ensuring sufficient absorption of dust and reaction, and the pH value of the circulating slurry at the bottom of the tower is maintained at 6.5 to 7.0.

[0043] (3) After the exhaust gas passes through the spray tower area, it is distributed to multiple filter modules. The filter modules are arranged in a ring in the upper part of the spray tower of the quench unit. In the spray box at the top of the filter module, the high-density spray generated by the nozzle is used for filtration to remove water mist and fine dust. The pH value of the filter module is controlled at 6.0 to 6.5 to achieve the purpose of thoroughly washing the fine dust in the exhaust gas.

[0044] (4) After passing through the filtration module, the exhaust gas enters several water droplet separators; the separators are set around the chimney to remove free water droplets in the gas;

[0045] (5) The absorption scrubbing tower is fed with fresh water by a water pump to the tail gas desulfurization to control the circulating slurry concentration to 30% to 40%;

[0046] (6) In order to control the slurry concentration, the slurry containing dust and sodium sulfite is discharged from the outlet of the slurry circulation pump of the absorption washing tower to ensure that the slurry concentration is controlled at 30% to 40%.

[0047] (7) By monitoring the outlet current A of the slurry circulation pump, the outlet pressure B of the pump, the pressure of the quench nozzle C, and the nozzle pressure D of the filter module, the changes in the concentration of the circulating slurry and the scaling of the system can be determined.

[0048] To further prevent the tendency of the device to scale, by monitoring the outlet pressure and current changes of the slurry circulation pump at the bottom of the absorption scrubbing tower and the circulation pump of the filtration module, the change in the concentration of the circulating slurry and the scaling situation of the system can be understood in a timely manner. An increase in concentration will lead to an increase in the current of the slurry circulation pump and the pump outlet pressure, resulting in an increase in the pressure of the quench nozzles at the bottom of the tower and the nozzles of the filtration module, nozzle blockage, and an increased risk of scaling; if there is scaling in the pipeline, the pressure of the quench nozzles of the circulating slurry and the nozzles of the filtration module will decrease. During the operation, monitor the outlet current A of the slurry circulation pump, the pump outlet pressure B, the quench nozzle pressure C, and the filtration module nozzle pressure D. When it is found that the outlet current of the circulating slurry pump > A, the pump outlet pressure > B, the quench nozzle pressure > C, and the filtration module nozzle pressure > D, it is determined that the concentration has increased. The concentration of the circulating slurry in the absorption scrubbing tower can be diluted by increasing the amount of discharged saline wastewater and increasing the amount of fresh water replenishment to achieve the purpose of preventing scaling. If the quench nozzle pressure < C and the filtration module nozzle pressure < D, it is determined that there is scaling in the pipeline, and the scaling can be dissolved by reducing the system pH value to achieve the purpose of dissolving the scale.

[0049] Further preferably, for the tail gas treatment device with desulfurization and denitrification functions, ozone is injected at the inlet of the quench unit of the absorption tower to oxidize sulfur dioxide in the tail gas into sulfur trioxide and nitric oxide into nitrogen dioxide.

[0050] Further, in the step (3), each filtration module is provided with one nozzle or multiple nozzles, and the sprayed liquid is discharged into the circulation tank; the nozzles are arranged above the filtration module.

[0051] Even further, in the step (3), reverse spray nozzles are added to the filtration module, and one nozzle is correspondingly added to the inlet of each filtration module to enhance the dust removal effect of the filtration module.

[0052] Further, the present invention further includes the following steps: separating water through a dedicated pipeline, discharging the water from the bottom of the water droplet separator into the circulation tank; the tail gas without water droplets flows into the bottom of the chimney; a drain pipe is provided at the bottom of the chimney to collect the water droplets discharged from the gas flow and condensed water vapor and discharge them into the circulation tank through a pipeline.

[0053] Preferably, the present invention further includes the following steps: injecting air into the slurry at the bottom of the absorption tower to oxidize the sulfite in the desulfurized wastewater, and maintaining the pH value of the oxidized effluent at 6.5 - 7.0; or pumping out the slurry at the bottom of the tower and entering a separately arranged oxidation facility for oxidation to achieve the pH value of the effluent maintained at 6.5 - 7.0.

[0054] Further, the present invention specifically includes the following steps: [[ID=第十九]]

[0055] (1) The supernatant of the slurry buffer tank is pumped into the oxidation tower, and air is blown in to oxidize the sulfite in the desulfurization wastewater to reduce the pseudo COD. After the wastewater is oxidized in the oxidation tank, the pH value of the slurry decreases. The pH value of the effluent from the oxidation tank is monitored by an online pH analyzer. The amount of alkali added is controlled by the regulating valve on the alkali pipeline to maintain the pH value of the effluent at 6.5 to 7.0.

[0056] (2) After the treated wastewater is oxidized in the oxidation tank, it flows by gravity to the discharge tank after the pH and COD meet the standards, and is then discharged to the sewage treatment plant by the discharge pump.

[0057] (3) The sludge discharged from the bottom of the clarifier to the filter box is further concentrated and dried in the filter box, and then the sludge is transported off-site for treatment. The wastewater filtered out by the filter box is returned to the slurry buffer tank.

[0058] Preferably, the pH values ​​of the circulating slurry at the bottom of the tower, the filtration module, and the effluent after oxidation are adjusted by controlling the amount of aqueous caustic alkali solution used; the caustic alkali solution is NaOH solution, Ca(OH)2 solution, or ammonia water.

[0059] In this invention, the exhaust gas horizontally enters the quenching unit and the middle filtration module unit of the absorption scrubbing tower. The circulating slurry at the bottom of the tower cools and saturates the exhaust gas, allowing for strong contact between the exhaust gas and the liquid, effectively removing coarse particles and performing desulfurization. The filtration modules are arranged in a ring shape at the top of the quenching unit's spray tower. Within the venturi section of each filtration module, the expansion of saturated gas causes a water film to condense and coalesce on the fine dust. At the spray box at the top of the filtration module, high-density spraying from each nozzle removes water mist and fine dust. The slurry containing dust and sodium sulfite is discharged from the outlet of the absorption scrubbing tower's slurry circulation pump. Oxygen in the exhaust gas oxidizes CaSO3 to CaSO4 (gypsum), saturating the gypsum and causing precipitation, resulting in scaling on pipelines and nozzles in the absorption section, thus reducing absorption efficiency. By controlling the pH value of the circulating slurry module and the filtration module in the absorption scrubbing tower to be weakly acidic, the CaSO4 (gypsum) is quickly dissolved, preventing scaling.

[0060] To prevent scaling on the desulfurization and denitrification system pipelines and the nozzles of the absorption scrubbing tower, the pH value of the circulating slurry at the bottom of the absorption scrubbing tower is controlled at 6.5–7.0, and the pH value of the upper filtration module is controlled at 6.0–6.5 to ensure a certain degree of weak acidity and reduce the possibility of scaling. The circulating slurry module at the bottom of the tower and the filtration module are maintained at a pH value of 6.5–7.0 and a pH value of 6.0–6.5 by injecting an aqueous caustic alkali solution.

[0061] Dust entrained in exhaust gas contains Ca 2+The substance will exist in the form of Ca(OH)2. In addition to reacting with SO2 in the exhaust gas, it will also undergo a recarbonization reaction with CO2 in the exhaust gas, regenerating CaCO3 deposits. Ca(OH)2 reacts with SO2 to form soft scale CaSO3¹ / ²H2O, which will then be oxidized to form CaSO4²H2O. CaSO4²H2O has very low solubility and easily crystallizes out of the solution, forming hard scale that is difficult to remove on the pipe walls and device surfaces.

[0062] Because the lower the pH value, the greater the dissolution rate of CaCO3 and CaSO42H2O. By adopting the anti-scaling method of this invention, the pH value of the circulating slurry at the bottom of the absorption and washing tower is controlled to be slightly acidic, thereby preventing scaling in the pipelines and internal components of the tail gas desulfurization and denitrification device system. During tail gas emission, the NOx and SO2 levels can be better controlled within the design range.

[0063] Beneficial effects:

[0064] This invention monitors the degree of scaling by controlling pressure changes in different parts and current changes in pumps. By adjusting the pH value to a slightly acidic level by controlling the amount of water-based caustic alkali solution injected into the bottom circulating slurry module and the filtration module, scaling of pipelines and devices can be effectively prevented, reducing operational complexity and equipment reinvestment. At the same time, it can also reduce the emissions of NOx, SO2 and dust in the exhaust gas of the scrubbing tower, so that environmental emissions meet standards. Attached Figure Description

[0065] Figure 1 A process flow diagram for preventing scaling in exhaust gas treatment devices.

[0066] Attached reference numerals: 1. Quenching zone; 2. Exhaust gas; 3. Scrubber; 4. Quenching zone inlet; 5. Ozone; 6. Spray tower area; 7. Filter module; 8. Water droplet separator; 9. Pipeline; 10. Drain pipe; 11. Make-up water pump; 12. Slurry circulation pump; 13. Flocculant; 14. Slurry clarification tank; 15. Filtration tank; 16. Oxidation tower; 18. Control valve; 20. Drain pump; 21. Slurry buffer tank; 22. Circulation tank. Detailed Implementation

[0067] The technical solution of the present invention will be described in detail below through specific embodiments, but the scope of protection of the present invention is not limited to the embodiments described.

[0068] Example 1: Desulfurization and denitrification unit of a catalytic cracking unit in an oil refinery.

[0069] See Figure 1 The process flow diagram for preventing scaling in the exhaust gas treatment device shown illustrates a method for preventing and monitoring scaling in the exhaust gas treatment device. The process is as follows:

[0070] (1) In the rapid cooling zone 1, the generated exhaust gas 2 enters the scrubber 3 horizontally through the flue. A nozzle is used to spray circulating slurry at a flow rate that can achieve atomization to rapidly cool the exhaust gas 2. The gas passes through a high-density water curtain, and the atomized water droplets move in a cross-flow manner, covering the entire cross-section of the gas flow and uniformly washing the entire inner wall to ensure that the exhaust gas temperature is ≤65℃;

[0071] (2) By injecting ozone 5 into the inlet 4 of the quench zone, the sulfur dioxide in the exhaust gas 2 is oxidized into sulfur trioxide and the nitric oxide is oxidized into nitrogen dioxide.

[0072] (3) Five spray levels are set up in spray tower area 6 to remove SO2 in stages; each level is equipped with a nozzle to spray circulating slurry (excluding the amount flowing to quench zone 1) at an atomized flow rate in the scrubbing tower, so that the gas / liquid come into close contact, thereby effectively removing coarse dust and performing desulfurization. The pH value of the circulating slurry at the bottom of the tower is maintained at 6.5-7.0. The sprayed liquid flows down the wall to the bottom of the tower.

[0073] (4) After passing through the spray tower area 6, the exhaust gas 2 is distributed to 21 filter modules 7. These filter modules are arranged in a ring in the upper part of the quench unit spray tower; within the cross-section of each filter module, due to the expansion of saturated gas, a water film condenses on the fine dust, causing agglomeration. In the spray box at the top of the filter module 7, filtration is performed by high-density spraying generated by each nozzle, thereby removing water mist and fine dust; the pH value of the filter module is controlled at 6.0 to 6.5 to achieve the purpose of thoroughly washing the fine dust in the exhaust gas;

[0074] (5) Each filter module 7 is equipped with an independent nozzle on its upper part. The sprayed liquid is discharged into the circulation tank 22. The nozzle is located above the filter module 7. In the early stage, a back-spray nozzle is added to the filter module 7. One back-spray nozzle is added to the inlet of each filter module 7 to enhance the dust removal effect of the filter module.

[0075] (6) After passing through the filter module 7, the exhaust gas 2 enters the water droplet separator 8; the water droplet separator processes a portion of the flue gas, removing free water droplets from the exhaust gas through centrifugal force. The rough blades at the inlet of each water droplet separator force the gas to rotate. Water droplets are collected on the wall, and the treated exhaust gas is discharged to a weir that allows water droplets-free exhaust gas to pass through. The collected water continues to clean the water droplet separator and is recycled in the process.

[0076] (7) Water is separated through a dedicated pipeline 9 and discharged from the bottom of the water droplet separator 8 to the circulation tank 22. The pipeline 9 discharges below the liquid surface, forming a seal to prevent gas from bypassing the water droplet separator 8. The exhaust gas, free of water droplets, flows into the bottom of the chimney after being processed. The flue gas velocity is low (chimney effect, the flue gas rises at a low velocity, not enough to carry a large amount of condensate), so that the condensate flows downward back into the scrubber. A drain pipe 10 is installed at the bottom of the chimney to collect water droplets discharged from the gas flow and condensate vapor. This water is discharged to the circulation tank 22 through a pipe. This pipe also has a liquid seal to prevent gas from bypassing the water droplet separator 8.

[0077] (8) Fresh water is added to the absorption scrubbing tower through the water supply pump 11 to the tail gas desulfurization to control the circulating slurry concentration to 30% to 40%.

[0078] (9) The slurry containing dust and sodium sulfite discharged from the outlet of the slurry circulation pump 12 of the absorption washing tower is mixed with flocculant 13 from the flocculant pump and sent to the slurry clarification tank 14. In the clarification tank, the slurry settles and separates, with the lower catalyst slurry entering the filtrate tank 15 and the upper brine flowing by gravity into the oxidation tower 16. To enhance the sedimentation effect, a metering pump is used to add flocculant, and solid or liquid flocculant is selected according to the actual situation.

[0079] (10) By monitoring the outlet current A of the slurry circulation pump, the pump outlet pressure B, the quench nozzle pressure C, and the filter module nozzle pressure D, the changes in the circulating slurry concentration and the scaling situation of the system can be determined. (Since the power and head of the selected pumps are different, the current and outlet pressure are different. The current and pressure at the time of commissioning are monitored as the initial current and pressure, and then compared with the initial pressure and current during later operation.)

[0080] (11) Air is blown in by an oxidation blower to oxidize the sulfites in the desulfurization wastewater, thereby reducing the pseudo COD. After the wastewater is oxidized in the oxidation tank, the pH value of the slurry decreases. The pH value of the effluent from oxidation tank 16 is monitored by an online pH analyzer. The amount of 30% NaOH solution is controlled by regulating valve 18 on the alkaline solution pipeline to maintain the pH value of the effluent at 6.5-7.0.

[0081] (12) After the wastewater is oxidized by oxidation tank 16, it is discharged to the company’s wastewater treatment plant by drainage pump 20 after the pH and COD meet the standards.

[0082] (13) The sludge discharged from the bottom of the slurry clarification tank 14 to the filtrate tank 15 is further concentrated and dried in the filtrate tank, and then the sludge is transported off-site for treatment. The wastewater filtered out of the filtrate tank 15 is returned to the slurry buffer tank 21.

[0083] Specifically in this embodiment, please refer to Figure 1, the dashed part in the figure is the optimized control scheme for anti-scaling this time. The pH value of the circulating slurry module at the bottom of the absorption washing tower is controlled at 6.5 - 7.0, the pH value of the filtration module is controlled at 6.0 - 6.5, and the pH value at the oxidation tank is controlled at 6.5 - 7.0. Through the bottom slurry circulation, the working temperature at the bottom of the absorption washing tower is 55°C, and the flue gas inlet temperature is 230°C.

[0084] When the tail gas passes through the absorption washing tower, it is necessary to detect the outlet pressure and current of the on-site slurry circulation pump 12 and the washing liquid pump of the filtration module to judge whether there is scaling in the system. At the same time, it can also check the amount of dust entrained in the tail gas to better ensure the safe operation of the device. When it is found that the outlet current of the slurry circulation pump > A, the pump outlet pressure > B, the quench nozzle pressure > C, and the filtration module nozzle pressure > D, it is determined that the concentration has increased. The concentration of the circulating slurry in the absorption washing tower can be diluted by increasing the amount of discharged salty wastewater and increasing the amount of fresh water replenishment to achieve the purpose of anti-scaling. If the quench nozzle pressure < C and the filtration module nozzle pressure < D, it is determined that there is scaling in the pipeline, and the scaling can be dissolved by reducing the system pH value to achieve the purpose of dissolving the scaling.

[0085] The high-salt water is sent from the self-draining liquid pool to the sewage treatment workshop. The COD content and pH value need to be controlled at 6.5 - 7.0, which can ensure that no hard scale will form and block in this pipeline. Under weak acid conditions, the soft scale formed by the reaction of Ca(OH)2 and SO2 to generate CaSO3·1 / 2H2O can be better dissolved to achieve the purpose of anti-scaling.

[0086] In this invention, within the range of maintaining a suitable pH value, aqueous caustic soda solution is reasonably used, and at the same time, the pH value of the discharged high-salt water containing dust and sulfite can meet the emission index requirements, reducing the usage amount of the caustic soda solution; no additional investment is required, and no modification to the process is needed. Only by controlling the pH values of the slurry circulation module and the filtration module of the absorption washing tower can the purpose of anti-scaling of the desulfurization and denitrification device components and pipelines be achieved, and the long-term operation of the device can also be realized.

[0087] In this invention, for the existing equipment status, a series of reactions that occur when the tail gas passes through the absorption washing tower and calcium ions contained in the tail gas cannot be changed. However, through this invention, the scaling of the desulfurization and denitrification device components and pipelines can be greatly reduced.

[0088] As described above, although the present invention has been shown and described with reference to specific preferred embodiments, it should not be construed as a limitation of the present invention itself. Various changes can be made in its form and details without departing from the spirit and scope of the present invention defined by the appended claims.

Claims

1. A method for preventing scaling in an exhaust gas absorption device and for monitoring scaling, characterized in that, Includes the following steps: (1) The exhaust gas generated in the rapid cooling zone enters the scrubber horizontally through the flue. A nozzle is used to spray circulating slurry at a flow rate that can reach the atomization state to rapidly cool the exhaust gas. The gas passes through a high-density water curtain and is atomized by water droplets moving in a cross-flow manner, covering the entire cross-section of the gas flow and uniformly washing the entire inner wall to ensure that the exhaust gas temperature is ≤65℃. (2) By injecting ozone into the inlet of the quench zone, sulfur dioxide in the exhaust gas is oxidized into sulfur trioxide and nitric oxide is oxidized into nitrogen dioxide. (3) Five levels of spraying are set in the spray tower area to remove SO2 in stages; each level is equipped with a nozzle to spray the circulating slurry in the scrubbing tower at a flow rate that reaches the atomization state, so that the gas / liquid are in close contact, thereby effectively removing coarse dust and performing desulfurization; the pH value of the circulating slurry at the bottom of the tower is maintained at 6.5 to 7.0; the sprayed liquid flows down the wall and to the bottom of the tower; (4) After passing through the spray tower area, the exhaust gas is distributed to 21 filter modules, which are arranged in a ring in the upper part of the quench unit spray tower. In the cross section of each filter module, due to the expansion of saturated gas, water film condenses on fine dust and agglomerates. In the spray box at the top of the filter module, the water mist and fine dust are removed by high-density spraying generated by each nozzle. The pH value of the filter module is controlled at 6.0 to 6.5 to achieve the purpose of thoroughly washing the fine dust in the exhaust gas. (5) Each filter module is equipped with an independent nozzle at the top, and the sprayed liquid is discharged into the circulation tank. The nozzle is above the filter module. In the early filter module, a back spray nozzle is added. A back spray nozzle is added to the inlet of each filter module to enhance the dust removal effect of the filter module. (6) After passing through the filtration module, the exhaust gas enters the water droplet separator; the water droplet separator processes a portion of the flue gas and removes free water droplets from the exhaust gas by centrifugal force; the rough blades at the inlet of each water droplet separator force the gas to rotate; the water droplets are collected on the wall, and the treated exhaust gas is discharged to the weir that allows exhaust gas without water droplets to pass through; the collected water continues to clean the water droplet separator and is recycled in the process; (7) Water is separated by a dedicated pipeline and discharged from the bottom of the water droplet separator to the circulation tank; the pipeline is discharged below the liquid surface, forming a seal to prevent gas from bypassing the water droplet separator; the exhaust gas without water droplets flows into the bottom of the chimney after being processed; the flue gas velocity is low so that the condensate flows down back into the scrubber; a drain pipe is installed at the bottom of the chimney to collect the water droplets discharged from the gas flow and condensate vapor; this water is discharged to the circulation tank through a pipe; the pipe also has a liquid seal to prevent gas from bypassing the water droplet separator; (8) Fresh water is added to the absorption scrubbing tower through a water supply pump to the tail gas desulfurization process to control the circulating slurry concentration to 30%~40%; The slurry containing dust and sodium sulfite discharged from the outlet of the slurry circulation pump of the absorption washing tower is mixed with the flocculant from the flocculant pump and then sent to the slurry clarifying tank. It is settled and separated in the clarifying tank. The lower catalyst slurry enters the filtrate tank, and the upper brine flows into the oxidation tower by gravity; (10) By monitoring the current A at the outlet of the slurry circulation pump, the pump outlet pressure B, the quench nozzle pressure C, and the filter module nozzle pressure D, the change of the circulating slurry concentration and the scaling situation of the system are judged; (11) Air is blown into the desulfurization wastewater by the oxidation fan to oxidize the sulfite in the wastewater to reduce the pseudo-COD therein. After the wastewater is oxidized in the oxidation tank, the pH value of the slurry decreases. The pH value of the effluent from the oxidation tank is monitored by an online pH analyzer. The amount of 30% NaOH solution is controlled through the regulating valve on the lye pipeline to keep the effluent pH value at 6.5 - 7.0; (12) After the treated wastewater is oxidized in the oxidation tank and the pH and COD meet the standards, it is discharged to the company's sewage treatment plant by the drain pump; (13) The sludge discharged from the bottom of the slurry clarifying tank to the filtrate tank is further concentrated and dried in the filtrate tank, and then the sludge is transported out for treatment. The wastewater filtered out by the filtrate tank returns to the slurry buffer tank; The pH value of the bottom circulation slurry module of the absorption washing tower is controlled at 6.5 - 7.0, the pH value of the filter module is controlled at 6.0 - 6.5, and the pH value at the oxidation tank is controlled at 6.5 - 7.0; Through the bottom slurry circulation, the bottom working temperature of the absorption washing tower is 55 °C, and the flue gas inlet temperature is 230 °C; When it is found that the current at the outlet of the slurry circulation pump > A, the pump outlet pressure > B, the quench nozzle pressure > C, and the filter module nozzle pressure > D, it is determined that the concentration has increased. The concentration of the circulating slurry in the absorption washing tower can be diluted by increasing the amount of discharged saline wastewater and increasing the amount of fresh water replenishment to achieve the purpose of preventing scaling; If the quench nozzle pressure < C and the filter module nozzle pressure < D, it is determined that there is a scaling phenomenon in the pipeline. The scaling can be dissolved by reducing the system pH value to achieve the purpose of dissolving the scaling.

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