Ammonia-based desulfurization system and method based on zoning control

Abstract

This invention discloses an ammonia-based desulfurization system and method based on zoned control, comprising a desulfurization tower, an absorption circulation tank, an ammonia water tank, a washing tank, and a process water tank. The desulfurization tower, from top to bottom, has a flue gas outlet, a demisting section, a second-stage absorption layer, a first-stage absorption layer, and a concentration section. The absorption circulation tank is divided into an upper oxidation tank and a lower absorption circulation section by a partition. The recovered liquid from the first-stage absorption is connected to the absorption circulation section of the absorption circulation tank via a pipeline; the oxidation tank has an aeration pipe connected to the spray inlet of the second-stage absorption via a pipeline; the lower concentration section of the desulfurization tower is connected to the oxidation tank via a liquid delivery pipeline. The washing tank supplies water to the demisting section and the absorption circulation tank; the ammonia water tank replenishes ammonia water to the oxidation tank, the first-stage absorption layer, and the absorption circulation section of the absorption circulation tank. This invention eliminates coupling interference between absorption and oxidation by dividing the tank into zones within the same tank; combined with two-stage absorption and demisting recovery, it effectively controls ammonia escape while ensuring efficient sulfur dioxide removal.

Description

Technical Field

[0001] This invention relates to the field of flue gas treatment technology, and in particular to an ammonia desulfurization system and method based on zoned control. Background Technology

[0002] Ammonia desulfurization technology, as a typical resource-based flue gas purification process, is widely used in flue gas treatment in coal-fired boilers, industrial kilns and other fields due to its advantages such as high desulfurization efficiency and the recyclability of by-product ammonium sulfate.

[0003] Existing conventional ammonia desulfurization processes often employ separate configurations for the absorption tower and oxidation tank, or, although placed within the same container, their functional zones are not clearly defined. This design leads to high mixing of the absorbent and oxidizing solutions within the system, creating a conflict between the optimal process environments required for the two key reaction stages: the absorption process requires a weakly alkaline environment to maintain the high absorption activity of ammonium sulfite, while the oxidation process requires an acidic environment to promote the efficient oxidation of ammonium bisulfite. In traditional processes, due to the lack of effective physical isolation or flow field control, oxidizing air can easily enter the absorption zone prematurely, partially oxidizing the key absorbent medium, ammonium sulfite, thereby reducing its effective concentration and absorption capacity. Conversely, if a large amount of alkaline substances from the absorption zone enters the oxidation zone, it will inhibit the oxidation reaction rate, leading to the accumulation of ammonium bisulfite and incomplete oxidation. This mutual constraint and interference between the absorption and oxidation environments makes it difficult for the system to simultaneously maintain high desulfurization efficiency and high oxidation rate, becoming a key factor limiting the performance improvement of traditional ammonia desulfurization processes.

[0004] In terms of emission control, existing technologies face severe challenges related to ammonia slip and aerosol problems. In localized areas within the absorber, especially when pH control is poor or mixing is uneven, gaseous ammonia and SO2 readily undergo gas-to-gas reactions to generate ammonium sulfite / ammonium sulfate aerosols. These submicron-sized aerosols are difficult to effectively capture by conventional demisters (such as baffles and wire mesh demisters). While some patents have improved demister structures, they lack specificity for chemically formed aerosols, resulting in ammonia slip concentrations often exceeding 5 mg / Nm³ and easily forming "blue smoke" visual pollution, failing to meet current ultra-low ammonia slip control requirements. Furthermore, to achieve stricter particulate matter emission standards, simply increasing demister density or the number of stages significantly increases system resistance, leading to higher operating energy consumption.

[0005] Therefore, overcoming the coupling interference between absorption and oxidation processes, optimizing the reaction environment separately, and addressing the insufficient control of ammonia slip and aerosols, making it difficult to simultaneously meet ultra-low limits for SO2, particulate matter, and ammonia slip; as well as improving system energy consumption, operational stability, and adaptive control capabilities, are the technical problems that urgently need to be solved in the current ammonia desulfurization technology field. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide an ammonia desulfurization system and method based on zone control.

[0007] A zone-controlled ammonia desulfurization system includes a desulfurization tower, an absorption circulation tank, an ammonia water tank, a water washing tank, and a process water tank. The desulfurization tower is arranged from top to bottom as follows: a flue gas outlet, a demister section, a second-stage absorption section, a first-stage absorption section, and a concentration section. A flue gas inlet is provided at the concentration section. The process water tank is used to provide flushing demineralized water or pure process water to the demister section.

[0008] The absorption circulation tank is equipped with a partition, which divides the absorption circulation tank into an upper oxidation tank and a lower absorption circulation section.

[0009] The oxidation tank is equipped with an aeration pipe;

[0010] The oxidation tank is connected to the spray inlet of the two-stage absorption system via a pipeline.

[0011] The lower concentration section of the desulfurization tower is connected to an external ammonium sulfate crystallization separation and drying post-treatment equipment via a pipeline;

[0012] The washing tank is used to provide rinsing desalinated water to the demisting section and to replenish water to the absorption circulation section of the absorption circulation tank.

[0013] The ammonia tank is used to supply ammonia to the oxidation tank, the first-stage absorption tank, and the absorption circulation section of the absorption circulation tank, respectively.

[0014] The recovered liquid in the demisting section is connected to the water washing tank via a pipeline;

[0015] The recovered liquid from the first absorption section is connected to the absorption circulation section of the absorption circulation tank via a pipeline.

[0016] The recovered liquid from the second-stage absorption is connected to the oxidation tank via a pipeline.

[0017] As a preferred embodiment of the present invention, a two-stage absorption and ammonia addition regulating valve is provided on the liquid supply pipeline from the ammonia tank to the oxidation tank.

[0018] As a preferred embodiment of the present invention, a micro-adjustment ammonia addition regulating valve is provided on the ammonia water tank to the absorption liquid supply pipeline.

[0019] As a preferred embodiment of the present invention, a main control ammonia addition regulating valve is provided on the liquid supply pipeline from the ammonia tank to the absorption circulation section of the absorption circulation tank.

[0020] As a preferred embodiment of the present invention, a pH meter is installed on the connecting pipe between the oxidation tank and the second-stage absorption.

[0021] As a preferred embodiment of the present invention, an ammonia flow meter is provided at the outlet of the ammonia tank.

[0022] As a preferred embodiment of the present invention, a flue gas inlet CEMS is provided at the flue gas inlet, and a flue gas outlet CEMS is provided at the flue gas outlet.

[0023] As a preferred embodiment of the present invention, the first stage of absorption is provided with two to five spray layers, one of which may be a combination of a spray layer and a high specific area filler layer; the second stage of absorption is provided with one to three spray layers; the single-layer coverage of each spray layer is ≥300%.

[0024] As a preferred embodiment of the present invention, the absorption circulation section of the absorption circulation tank is equipped with a pH monitoring and control unit for controlling the pH value of the absorption liquid at 5.5 to 7.0; the upper oxidation tank is equipped with an independent pH monitoring and control unit for controlling the pH value of the oxidation liquid at 3.5 to 5.5.

[0025] Meanwhile, the present invention also provides an ammonia desulfurization method based on zone control, which employs the system described above; the method is as follows:

[0026] Sulfur-containing flue gas enters the desulfurization tower through the flue gas inlet, and passes through the concentration section, the first absorption section and the second absorption section in sequence to fully absorb the sulfur dioxide in the flue gas and achieve the desulfurization effect.

[0027] In the absorption circulation section, after absorbing SO2, the mixed liquid flows into the absorption circulation tank by gravity. Part of the absorbent is then pressurized by the absorption pump and sent to the first absorption section of the desulfurization tower to continue circulating and spraying countercurrently to absorb SO2. Another part of the absorbent overflows into the oxidation tank under the action of pressure difference. As the absorption process proceeds, (NH4)2SO3 absorbs SO2 to form NH4HSO3. The continuously replenished absorbent, NH3, causes NH4HSO3 to be converted back into (NH4)2SO3.

[0028] The second-stage absorption liquid is taken from the oxidation tank. The unoxidized ammonium sulfite in the oxidation tank is used to further absorb the residual SO2 in the flue gas. By using the residual free ammonia or adding ammonia water in the second-stage absorption reflux, NH4HSO3 is converted back to (NH4)2SO, which increases the absorption rate and oxidation rate while reducing ammonia escape. The absorption liquid is returned to the oxidation tank near the top of the aeration pipe for oxidation treatment.

[0029] The oxidation tank is designed with reasonable residence time, aeration intensity, aeration height, and pH value controlled between 3.5 and 5.5 to ensure sufficient oxidation of nitrite. The pH value of the absorption circulation section of the absorption circulation tank is controlled between 5.5 and 7.0. The absorption circulation tank is divided into two sections by a partition, with the bottom being the absorption zone and the upper part being the oxidation zone. The absorption and oxidation processes do not interfere with each other, ensuring that the absorbent in one section is not oxidized, thereby improving absorption efficiency and reducing ammonia escape.

[0030] After passing through two absorption stages, the flue gas is treated to remove ammonia in a combined demister section before being discharged.

[0031] The above technical solution has the following advantages:

[0032] This application employs a zoned absorption and oxidation design. On one hand, the zoned design optimizes the pH environment from the reaction source, effectively suppressing aerosol formation. Combined with the terminal three-stage gradient depth capture, this significantly reduces and stably controls the ammonia escape concentration below 2.0 mg / Nm³, while ensuring that the particulate matter concentration in the outlet flue gas is below 1.5 mg / Nm³, completely solving the visual pollution problem of "blue smoke." On the other hand, this design allows the absorption and oxidation reactions to proceed independently under their respective optimal conditions. This not only eliminates process coupling interference and ensures the sulfur dioxide removal efficiency, keeping its emission concentration consistently below the ultra-low standard of 10 mg / Nm³, but also significantly improves the oxidation rate of sulfites, thereby enhancing the quality and resource utilization rate of the by-product ammonium sulfate, achieving a dual improvement in environmental and economic benefits. Attached Figure Description

[0033] Figure 1 This is a flowchart of one embodiment of the present invention;

[0034] In the picture:

[0035] 1-1. Flue gas inlet; 1-2. Desulfurization tower; 1-3. Concentration section; 1-4. Primary absorption stage; 1-5. Secondary absorption stage; 1-6. Demisting section; 1-7. Flue gas outlet; 1-8. Demineralized water (also known as process water); 1-9. Oxidation tank (hereinafter also known as oxidation zone); 1-10. Absorption circulation tank; 1-11. Aeration pipe; 1-12. Ammonia water tank; 1-13. Washing tank; 1-14. Process water tank; 1-15. Absorption circulation section (hereinafter also known as absorption zone);

[0036] 2-1. Flue gas inlet CEMS; 2-2. Flue gas outlet CEMS; 2-3. Main control ammonia addition regulating valve; 2-4. Micro-control ammonia addition regulating valve; 2-5. Second-stage absorption ammonia addition regulating valve; 2-6. Ammonia flow meter; 2-7. pH meter. Detailed Implementation

[0037] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings. It should be noted that these descriptions are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0038] Example 1

[0039] As attached Figure 1 As shown, an ammonia desulfurization system based on zoned control includes a desulfurization tower 1-2, an absorption circulation tank 1-10, an ammonia water tank 1-12, a water washing tank 1-13, and a process water tank 1-14. The desulfurization tower 1-2 is sequentially arranged from top to bottom as a flue gas outlet 1-7, a demister section 1-6, a second-stage absorption section 1-5, a first-stage absorption section 1-4, and a concentration section 1-3. A flue gas inlet 1-1 is located at the concentration section 1-3. The process water tank 1-14 is used to provide flushing demineralized water or pure process water 1-8 to the demister section 1-6.

[0040] The absorption circulation tank 1-10 is equipped with a baffle (not shown in the figure), which divides the upper part of the absorption circulation tank 1-10 into an upper oxidation tank 1-9 and a lower absorption circulation section 1-15. The baffle preferably adopts computer flow field simulation opening to ensure uniform liquid distribution in the tank and ensure sufficient oxidation of sulfite. The baffle is made of corrosion-resistant alloy material or lined with glass flake resin. It uses the liquid level difference to realize the directional and orderly flow of slurry from the lower absorption zone to the upper oxidation zone, effectively preventing oxidation air from flowing back into the absorption zone. The lower part is the absorption zone with the pH value maintained at 5.5-6.0, and the upper part is the forced oxidation tank. This structure allows the absorption and oxidation processes to take place in an optimal reaction environment without interference, which not only greatly improves the absorption efficiency and oxidation rate of ammonium sulfite for SO2, but also inhibits the direct formation of aerosols from gaseous ammonia and SO2 from the reaction mechanism, realizing source control of ammonia escape.

[0041] The oxidation tank 1-9 is equipped with aeration pipes 1-11. The aeration pipes 1-11 are microporous aeration coils or perforated pipe arrays, arranged at the bottom of the oxidation tank 1-9. The pore diameter is 10mm and the porosity is ≥15%. They are used in conjunction with Roots blowers or magnetic levitation blowers to provide oxidation air, so that the dissolved oxygen concentration in the oxidation zone is maintained at 4.0-8.0mg / L, which promotes the efficient conversion of ammonium sulfite into ammonium sulfate in an acidic environment with a pH of 3.5-5.5.

[0042] The oxidation tank 1-9 is connected to the spray inlet of the second-stage absorption 1-5 through a pipeline. The connecting pipeline transports the oxidation liquid containing unoxidized ammonium sulfite to the second-stage absorption 1-5 for deep purification. By adding ammonia in the second-stage absorption reflux, NH4HSO3 is converted into (NH4)2SO absorbent and SO2 is further removed. At the same time, this loop is a key means of controlling the pH value of the oxidation zone.

[0043] The lower concentration section of the desulfurization tower 1-2 is connected to the oxidation tank 1-9 through a liquid conveying pipeline. This pipeline serves as a channel for the oxidation tank 1-9 to naturally overflow and replenish the lower concentration section of the desulfurization tower.

[0044] Meanwhile, the lower concentration section 1-3 of the desulfurization tower 1-2 is connected to an external ammonium sulfate crystallization separation and drying post-treatment equipment via a pipeline.

[0045] The washing tank 1-13 is used to provide rinsing demineralized water to the demisting section 1-6 and replenish water to the absorption circulation section 1-15 of the absorption circulation tank 1-10, respectively. As the second-level buffer unit for system water balance, its volume is designed to be 1.5-2.0 times the system's hourly water consumption. It automatically receives the recovered liquid from the demisting section 1-6 and replenishes water to the absorption circulation section 1-15 through liquid level interlocking to maintain the system's material balance.

[0046] The ammonia tank 1-12 is used to supply ammonia water to the oxidation tank 1-9, the first-stage absorption 1-4 and the absorption circulation section 1-15 of the absorption circulation tank 1-10 respectively. The ammonia tank 1-12 can be equipped with a stirrer to prevent the ammonia water from separating, and precise control can be achieved through a distributed ammonia addition strategy.

[0047] The recovered liquid from the demisting section 1-6 is connected to the washing tank 1-13 via a pipeline. The recovered liquid enters the washing tank 1-13 to realize the in-situ recovery of ammonia resources and the recycling of water resources.

[0048] The recovered liquid from the first absorption section 1-4 is connected to the absorption circulation section 1-15 of the absorption circulation tank 1-10 through a pipeline to form the main absorption circulation loop. The pH value of the slurry in this loop is independently controlled within the range of 5.0-7.0 to maintain the high-activity absorption state of ammonium sulfite.

[0049] The recovered liquid from the second-stage absorbers 1-5 is connected to the oxidation tanks 1-9 via pipelines to form an oxidation circulation loop, ensuring the acidic environment and sufficient residence time required for the oxidation reaction.

[0050] As a preferred technical solution in this embodiment, a two-stage absorption ammonia addition regulating valve 2-5 is provided on the liquid supply pipeline from the ammonia tank 1-12 to the oxidation tank 1-9. This valve is preferably a pneumatic diaphragm regulating valve with a response time of ≤5 seconds. The ammonia addition amount is finely adjusted according to the feedback signal from the pH meter 2-7 of the oxidation tank 1-9 to accurately maintain the pH value of the oxidation zone in the optimal oxidation range, preventing equipment corrosion caused by excessively high pH inhibiting oxidation or excessively low pH.

[0051] As a preferred technical solution in this embodiment, a micro-adjustment ammonia addition regulating valve 2-4 is installed on the liquid supply pipeline from the ammonia tank 1-12 to the absorption section 1-4. This valve, together with the inlet flue gas SO2 concentration feedforward signal and the outlet SO2 concentration feedback signal, forms a cascade control loop to achieve millisecond-level rapid response, dynamically compensate for ammonia consumption changes caused by load fluctuations, and ensure stable desulfurization efficiency and minimized ammonia consumption.

[0052] As a preferred technical solution in this embodiment, a main control ammonia addition regulating valve 2-3 is provided on the liquid supply pipeline from the ammonia tank 1-12 to the absorption circulation section 1-15. This valve is used to maintain the overall alkalinity balance of the absorption circulation section 1-15 of the absorption circulation tank 1-10. The valve opening is automatically calculated by the DCS system based on the ammonia addition amount based on the flue gas inlet CEMS and outlet SO2 control values ​​to add ammonia water to the absorption circulation section 1-15 of the absorption circulation tank 1-10, preventing the explosive generation of aerosols due to local over-alkaliness.

[0053] As a preferred technical solution in this embodiment, a pH meter 2-7 is installed on the connecting pipe between the oxidation tank 1-9 and the second-stage absorption 1-5. The pH meter 2-7 is an online insertable electrode that is resistant to erosion. It monitors the acidity and alkalinity of the oxidation solution in real time and serves as the core feedback parameter for controlling the addition of ammonia in the oxidation zone, ensuring that the kinetic conditions of the oxidation reaction are optimal.

[0054] As a preferred technical solution in this embodiment, an ammonia flow meter is installed at the outlet of the ammonia tank 1-12. The flow meter is an electromagnetic ammonia flow meter or a mass ammonia flow meter. It is used to cumulatively measure the ammonia consumption of each branch, provide data support for system energy efficiency analysis and cost accounting, and can also serve as a redundancy verification signal for the ammonia control system.

[0055] As a preferred technical solution in this embodiment, a flue gas inlet CEMS2-1 is installed at the flue gas inlet 1-1 to monitor the flow rate, temperature, SO2, NOx, and particulate matter concentration of the inlet flue gas in real time, serving as the feedforward input variables for the control system. A flue gas outlet CEMS2-2 is installed at the flue gas outlet 1-7 to monitor the SO2, particulate matter, ammonia slip concentration, and oxygen content of the outlet flue gas in real time. Ammonia slip monitoring preferably employs TDLAS (Diverterless Laser Light Spectroscopy) to ensure the accuracy and reliability of emission data and compliance with ultra-low emission standards. All monitoring data is uploaded to the DCS system in the central control room to achieve intelligent closed-loop control throughout the entire process. The flue gas inlet CEMS2-1 and flue gas outlet CEMS2-2 refer to CEMS (Online Flue Gas Monitoring Systems) that measure flue gas by means of electrochemical or photoelectric sensors directly inserted into the flue or pipe and installed at the probe tip, or by emitting a beam of light through the flue or pipe. The first-stage absorber 1-4 is provided with two to five spray layers, one of which can be a combination of a spray layer and a high specific area filler layer; the second-stage absorber 1-5 is provided with one to three spray layers; the single-layer coverage of each spray layer is ≥300%.

[0056] Example 2

[0057] A zone-controlled ammonia desulfurization method employs the system described in Example 1; the method is as follows:

[0058] This technology was applied in a domestic project where a single tower could treat 643,200 Nm³ of flue gas. 3 / h (standard conditions, wet basis, actual oxygen), SO2 at the desulfurization tower inlet is 3300 mg / Nm³. 3 After desulfurization, the SO2 content in the clean flue gas is ≤10mg / Nm³. 3 Dust ≤1.5mg / Nm 3 (Standard condition, dry basis, 6% oxygen, inlet dust content ≤20mg / Nm³) 3 (At that time), ammonia escape concentration ≤2mg / Nm 3 The specific process is as follows: sulfur-containing flue gas enters desulfurization tower 1-2 through the flue gas inlet, and sequentially passes through concentration section 1-3, primary absorption section 1-4, and secondary absorption section 1-5. Primary absorption section 1-4 is equipped with one layer of empty tower spray and one layer of packed spray, using high specific area packing to increase the contact area and contact time between the absorbent and the flue gas. After two stages of absorption, sulfur dioxide in the flue gas is fully absorbed, achieving the desulfurization effect. The empty tower spray coverage rate is ≥300%.

[0059] After absorbing SO2, the absorbent in section 1-4 flows by gravity into absorption circulation section 1-15 of absorption circulation tank 1-10. Most of the absorbent is then pressurized by an absorption pump and sent to the absorption section of desulfurization tower 1-2 for continued countercurrent spraying and SO2 absorption. A small portion of the absorbent enters oxidation tank 1-9. As the absorption process proceeds, (NH4)2SO3 absorbs SO2 to form NH4HSO3. The continuously replenished absorbent—NH3—converts NH4HSO3 back into (NH4)2SO3, achieving low ammonia consumption and stable absorption. The ammonia water is replenished through ammonia water tank 1-12.

[0060] The second-stage absorber (1-5) takes liquid from the oxidation tank, and the residual SO2 in the flue gas is reabsorbed by the ammonium sulfite in the liquid in the oxidation tank, increasing the absorption rate and reducing ammonia slip. The absorbent is returned to the oxidation tank (1-9) near the aeration pipe (1-11) for further oxidation treatment.

[0061] The oxidation tanks 1-9 are designed with reasonable residence time, aeration intensity, aeration height, and pH value controlled between 3.5 and 5.5 to ensure sufficient oxidation of nitrite. The pH value in the absorption zone is controlled between 5.5 and 7.0. Based on the ammonia desulfurization reaction mechanism where nitrite plays a major absorption role, the absorption circulation tanks 1-10 are divided into partitions using the principle of potential difference. The bottom is the absorption zone, and the upper part is the oxidation zone. The absorption and oxidation processes do not interfere with each other, ensuring that the absorbent in the first absorption section 1-4 is not oxidized, thus improving absorption efficiency. By controlling different pH values ​​for oxidation and absorption, the optimal reaction environment is ensured.

[0062] After two stages of absorption, the flue gas undergoes ammonia removal treatment in the combined demister section 1-6 to achieve ultra-low emissions. The combined demister section 1-6 comprises three demister stages: the first stage is an absorption demister stage with a two-stage ridge demister; the second stage is an ammonia removal demister stage with a high-efficiency water-washing packing spray layer; and the third stage is a water mist removal demister stage with a three-stage ridge demister. Each demister is equipped with water flushing, which is replenished through process water tank 1-14. The flushing water circulates internally and does not affect the water balance of the desulfurization system. Another function of the combined demister system is for system water replenishment to maintain water balance. Flushing water from process water tank 1-14 replenishes water in washing tank 1-13, water in washing tank 1-13 replenishes water in absorption circulation section 1-15 of oxidation tank 1-10, and water in oxidation tank 1-9 replenishes water in concentration section 1-3 to maintain water balance within the system.

[0063] The automatic ammonia addition technology used in this application consists of three stages: main control, micro-control, and two-stage absorption control, as detailed below.

[0064] Main control: In the automatic control program, based on the emission target requirements, the target is assumed to be 10 mg / Nm³. 3 The outlet SO2 concentration control value is set at 9.8 mg / Nm³. 3Based on the SO2 concentration and flue gas flow data measured by the CEMS 2-1 at the flue gas inlet, an automatic calculation program is set in the DCS system. According to the total amount of SO2 to be removed from the flue gas, the theoretical amount of ammonia water with a concentration of 20% is calculated to be 5.61t / h. Ammonia is added through the main control ammonia addition regulating valve 2-3 and ammonia addition flow meter 2-6 in the first absorption 1-4 reflux pipe.

[0065] Micro-adjustment: Based on the actual SO2 concentration and its changing trend measured by the CEMS at the flue gas outlet, the DCS system automatically calculates and controls the ammonia addition regulating valves 2-4 to add ammonia at the inlet of the first-stage absorption pumps 1-4, controlling the outlet SO2 concentration to be between 7 and 10 mg / Nm³. 3 .

[0066] Two-stage absorption control: The outlet of pump 1-5 in the two-stage absorption is located on oxidation tank 1-9. It utilizes unreacted ammonium sulfite from the first-stage absorption 1-4 solution to circulate and absorb SO2 from the flue gas; and uses residual free ammonia to regenerate ammonium bisulfite in the absorption solution to generate the absorbent ammonium sulfite. When the free ammonia content in the oxidation solution is insufficient, pH meter 2-7 will interlock with the ammonia addition regulating valve 2-5 in the two-stage absorption, adding ammonia to the return pipe of the two-stage absorption 1-5 to maintain the pH value of oxidation tank 1-9 within the design range, creating a favorable oxidation environment and simultaneously improving the oxidation rate and absorption rate. An ammonia addition flow meter is installed on the main ammonia addition pipe to dynamically monitor the ammonia addition amount over a period of time. The DCS system integrates the time-SO2 function to obtain the actual SO2 removal amount over the corresponding period, achieving dynamic control. When the system detects significant changes in the flue gas volume and SO2 concentration at the inlet of the coal-fired boiler, it will automatically adjust the ammonia addition amount based on the SO2 removal amount at the outlet over a period of time and the corresponding ammonia addition amount.

[0067] After the above treatment, the sulfur dioxide content in the outlet flue gas is reduced to <10mg / Nm³, the dust content to <1.5mg / Nm³, and the ammonia slip to <2.0mg / Nm³.

[0068] The CEMS and DCS systems involved in this invention are all existing technologies, which can be fully implemented by those skilled in the art and need not be elaborated upon.

[0069] In the description of the above embodiments, for the sake of brevity and clarity, some components and their specific structural details that are not directly related to the core innovations of this invention have been omitted. These omitted parts all fall within the scope of existing technology, and those skilled in the art can fully implement the design and manufacture of these parts based on their professional knowledge and existing technical materials. Therefore, they will not be described in detail here.

[0070] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A zone-controlled ammonia desulfurization system, comprising a desulfurization tower (1-2), an absorption circulation tank (1-10), an ammonia water tank (1-12), a water washing tank (1-13), and a process water tank (1-14); the desulfurization tower (1-2) is provided with, from top to bottom, a flue gas outlet (1-7), a demister section (1-6), a second-stage absorption section (1-5), a first-stage absorption section (1-4), and a concentration section (1-3), wherein a flue gas inlet (1-1) is provided at the concentration section (1-3); the process water tank (1-14) is used to provide flushing demineralized water or pure process water (1-8) to the demister section (1-6); characterized in that: The absorption circulation tank (1-10) is provided with a partition, which divides the absorption circulation tank (1-10) into an upper oxidation tank (1-9) and a lower absorption circulation section (1-15). An aeration pipe (1-11) is installed inside the oxidation tank (1-9). The oxidation tank (1-9) is connected to the spray inlet of the second-stage absorption tank (1-5) via a pipe; The lower concentration section (1-3) of the desulfurization tower (1-2) is connected to an external ammonium sulfate crystallization separation and drying post-treatment equipment via a pipeline; The washing tank (1-13) is used to provide rinsing demineralized water to the demisting section (1-6) and to replenish water to the absorption circulation section (1-15) of the absorption circulation tank (1-10); The ammonia tank (1-12) is used to supply ammonia to the oxidation tank (1-9), the first-stage absorption tank (1-4), and the absorption circulation section (1-15) of the absorption circulation tank (1-10), respectively. The recovered liquid from the demisting section (1-6) is connected to the washing tank (1-13) via a pipeline; The recovered liquid from the first absorption section (1-4) is connected to the absorption circulation section (1-15) of the absorption circulation tank (1-10) via a pipeline; The recovered liquid from the two-stage absorption (1-5) is connected to the oxidation tank (1-9) via a pipeline.

2. The ammonia desulfurization system based on zone control according to claim 1, characterized in that: The ammonia tank (1-12) is equipped with a two-stage absorption and ammonia addition regulating valve (2-5) on the liquid supply pipeline from the ammonia tank (1-12) to the oxidation tank (1-9).

3. The ammonia desulfurization system based on zone control according to claim 1 or 2, characterized in that: The ammonia tank (1-12) is equipped with a micro-adjustment ammonia addition regulating valve (2-4) on the liquid supply pipeline to the first absorption section (1-4).

4. The ammonia desulfurization system based on zone control according to claim 1 or 2, characterized in that: The ammonia tank (1-12) is equipped with a main control ammonia addition regulating valve (2-3) on the liquid supply pipeline to the absorption circulation section (1-15).

5. The ammonia desulfurization system based on zone control according to claim 1 or 2, characterized in that: A pH meter (2-7) is installed on the connecting pipe between the oxidation tank (1-9) and the second-stage absorption (1-5).

6. The ammonia desulfurization system based on zone control according to claim 1 or 2, characterized in that: An ammonia flow meter (2-6) is installed at the outlet of the ammonia tank (1-12).

7. The ammonia desulfurization system based on zone control according to claim 1 or 2, characterized in that: A flue gas inlet CEMS (2-1) is provided at the flue gas inlet (1-1), and a flue gas outlet CEMS (2-2) is provided at the flue gas outlet (1-7).

8. The ammonia desulfurization system based on zone control according to claim 1, characterized in that: The first-stage absorption (1-4) is provided with two to five spray layers, one of which can be a combination of a spray layer and a high specific area filler layer; the second-stage absorption (1-5) is provided with one to three spray layers; the single-layer coverage of each spray layer is ≥300%.

9. The ammonia desulfurization system based on zone control according to claim 1, characterized in that: The absorption circulation section (1-15) of the absorption circulation tank (1-10) is equipped with a pH monitoring and control unit to control the pH value of the absorption liquid at 5.5 to 7.0; the upper oxidation tank (1-9) is equipped with an independent pH monitoring and control unit to control the pH value of the oxidation liquid at 3.5 to 5.

5.

10. A method for ammonia desulfurization based on zoned control, characterized in that... The system described in any one of claims 1-9 is employed; the method is specifically as follows: Sulfur-containing flue gas enters the desulfurization tower (1-2) through the flue gas inlet, and passes through the concentration section (1-3), the first absorption section (1-4), and the second absorption section (1-5) in sequence to fully absorb sulfur dioxide in the flue gas and achieve the desulfurization effect; After absorbing SO2, the first absorption section (1-4) mixes and flows into the absorption circulation tank (1-10) in the absorption circulation section (1-15). A portion of the absorbent is then pressurized by the absorption pump and sent to the first absorption section of the desulfurization tower (1-2) to continue circulating and spraying countercurrently to absorb SO2. Another portion of the absorbent overflows into the oxidation tank (1-9) under the action of pressure difference. As the absorption process proceeds, (NH4)2SO3 absorbs SO2 to form NH4HSO3. The continuously replenished absorbent, NH3, causes NH4HSO3 to be converted back into (NH4)2SO3. The second-stage absorption (1-5) takes liquid from the oxidation tank and uses the unoxidized ammonium sulfite in the oxidation tank to further absorb the residual SO2 in the flue gas. By using the residual free ammonia or adding ammonia water in the second-stage absorption reflux, NH4HSO3 is converted back to (NH4)2SO, which increases the absorption rate and oxidation rate while reducing ammonia escape. The absorbent is returned to the oxidation tank (1-9) near the top of the aeration pipe (1-11) for oxidation treatment. The oxidation tank (1-9) is designed with reasonable residence time, aeration intensity, aeration height and pH value controlled at 3.5-5.5 to ensure sufficient oxidation of nitrite. The pH value of the absorption circulation section (1-15) of the absorption circulation tank (1-10) is controlled at 5.5-7.

0. The absorption circulation tank (1-10) is divided into two sections by the tank partition, with the bottom being the absorption zone and the upper part being the oxidation zone. The absorption and oxidation processes do not interfere with each other, ensuring that the absorbent liquid in the first absorption section (1-4) is not oxidized, thereby improving absorption efficiency and reducing ammonia escape. After passing through two absorption stages, the flue gas is discharged after ammonia removal treatment in a combined demister section (1-6).

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