Ammonia nitrogen online detection system and method

Abstract

The invention relates to the technical field of ammonia nitrogen detection, in particular to an ammonia nitrogen online detection system and method.The ammonia nitrogen online detection system comprises a pretreatment unit, an ammonia gas sensitive electrode measuring unit and a control unit which are sequentially communicated, and the pretreatment unit is used for conducting physicochemical treatment on to-be-detected liquid containing high calcium and magnesium ions and high suspended matter; interference substances are removed; the ammonia gas sensitive electrode measuring unit is used for receiving the clear liquid treated by the pretreatment unit and detecting an ammonia nitrogen concentration signal in the clear liquid; the control unit is electrically connected with the pretreatment unit and the ammonia gas sensitive electrode measuring unit respectively and is used for controlling the operation of the pretreatment unit and treating a detection signal from the ammonia gas sensitive electrode measuring unit so as to obtain an ammonia nitrogen concentration value. By means of the integrated design, physicochemical pretreatment can be conducted on to-be-detected liquid (such as desulfurization slurry) containing high calcium and magnesium ions and high suspended matter, interferents are effectively removed, detection is conducted in combination with an ammonia gas sensitive electrode, and automatic operation and signal processing are achieved through a control unit.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ammonia nitrogen detection, and in particular to an ammonia nitrogen online detection system and method. BACKGROUND

[0002] With the widespread use of selective catalytic reduction (SCR) flue gas denitrification process in coal-fired power plants, ammonia escape phenomenon inevitably exists, which leads to the escaped ammonia entering the desulfurization system with the flue gas and gradually accumulating in the desulfurization slurry to form ammonium sulfate, forming a high ammonia nitrogen concentration (usually up to 100-500 mg / L). The excessively high ammonia nitrogen concentration not only easily causes equipment fouling and corrosion, reduces the desulfurization efficiency, but also increases the wastewater treatment cost. Therefore, continuous and accurate online monitoring of the ammonia nitrogen concentration in the desulfurization slurry is the key to realizing energy saving and stable operation of the power plant.

[0003] For ammonia nitrogen online monitoring, the existing technology mainly includes two types of mainstream schemes: one type is a detection system based on spectrophotometry, which measures the absorbance after filtering, adding a masking agent (such as potassium sodium tartrate), diluting, and developing color (such as Nash reagent); the other type is a detection method based on an ammonia gas sensitive electrode, usually assisted by an ion strength regulator (such as ISA containing EDTA) and temperature control to improve measurement accuracy. In addition, there are also some composite electrode schemes integrating pH and temperature sensors. However, the above existing technologies are mainly designed for general water quality (such as reclaimed water, aquaculture water), or only focus on the detection link itself.

[0004] However, in the existing detection means, the comprehensive interference caused by the complex working conditions such as high calcium and magnesium, high suspended solids and temperature fluctuations in the desulfurization slurry to the measurement leads to low precision, poor stability, frequent maintenance or environmental pollution risk. SUMMARY

[0005] The purpose of the present application is to provide an ammonia nitrogen online detection system and method to solve the technical problem that in the prior art, the comprehensive interference caused by the complex working conditions such as high calcium and magnesium, high suspended solids and temperature fluctuations in the desulfurization slurry to the measurement leads to low precision, poor stability, frequent maintenance or environmental pollution risk during ammonia nitrogen detection.

[0006] In a first aspect, the present application provides an ammonia nitrogen online detection system, comprising, in sequence, a pretreatment unit for performing physicochemical treatment on a to-be-measured liquid containing high calcium and magnesium ions and high suspended solids to remove interfering substances; an ammonia gas sensitive electrode measurement unit for receiving the clear liquid treated by the pretreatment unit and detecting the ammonia nitrogen concentration signal therein; an ammonia gas sensitive electrode measurement unit for receiving the clear liquid treated by the pretreatment unit and detecting the ammonia nitrogen concentration signal therein; A control unit is electrically connected with the pretreatment unit and the ammonia-sensitive electrode measurement unit respectively, for controlling the operation of the pretreatment unit and processing the detection signal from the ammonia-sensitive electrode measurement unit to obtain the ammonia nitrogen concentration value.

[0007] Further, the pretreatment unit at least comprises: A hardness removal reaction unit configured to add an alkaline reagent to the liquid to be measured to reduce the concentration of calcium and magnesium ions in the liquid to be measured by chemical precipitation; A temperature adjustment unit configured to adjust and stabilize the temperature of the liquid to be measured in a preset room temperature measurement range; A solid-liquid separation unit configured to settle and filter the liquid to be measured after hardness removal and temperature adjustment to obtain clear liquid meeting the turbidity requirement.

[0008] Further, the hardness removal reaction unit comprises: A reagent storage tank for storing a mixed reagent containing sodium hydroxide and sodium carbonate; A quantitative reagent feeding pump connected with the reagent storage tank and the control unit, for accurately adding the mixed reagent to the liquid to be measured according to the instruction of the control unit.

[0009] Further, the temperature adjustment unit is a semiconductor cooler which cools the liquid to be measured through a cooling coil and a water circulation system, and is integrated with a temperature sensor to form a closed-loop temperature control circuit.

[0010] Further, the solid-liquid separation unit comprises: A sedimentation tank for containing the liquid to be measured after hardness removal and cooling to allow the precipitate to settle naturally; A multi-stage filtration assembly in communication with the supernatant outlet of the sedimentation tank, the multi-stage filtration assembly at least comprising a microporous membrane filter and an ultrafiltration membrane filter connected in series.

[0011] Further, the multi-stage filtration assembly further comprises a PP cotton filter arranged before the microporous membrane filter, and a ceramic membrane filter arranged between the microporous membrane filter and the ultrafiltration membrane filter.

[0012] Further, the ammonia-sensitive electrode measurement unit comprises: A measurement flow cell; An ammonia-sensitive electrode obliquely installed in the measurement flow cell; A pH sensor and a temperature sensor arranged in the measurement flow cell for real-time monitoring of the pH value and temperature of the clear liquid; The control unit is configured to control whether to add alkali agent according to the signal of the pH sensor to make the pH value greater than 11, and to calculate the ammonia nitrogen concentration value by Nernst equation through temperature compensation according to the output potential of the ammonia gas sensitive electrode and the signal of the temperature sensor.

[0013] Further, a shell is further included, the shell is provided with an air conditioning device therein, which is used to keep the ambient temperature in the shell constant at 20-25℃, and the pretreatment unit, the ammonia gas sensitive electrode measuring unit and the control unit are all arranged in the shell.

[0014] In the second aspect, the application further provides an ammonia nitrogen online detection method using the ammonia nitrogen online detection system, which comprises the following steps: S1: obtaining a desulfurization slurry to be measured; S2: performing double-alkali method hardness removal treatment on the liquid to be measured to reduce the concentration of calcium and magnesium ions; S3: cooling the liquid to be measured to a preset room temperature measurement interval; S4: performing static settling on the cooled liquid to be measured to separate supernatant; S5: performing multi-stage filtration on the supernatant to obtain clear liquid with a turbidity less than 1 NTU; S6: performing ammonia gas sensitive electrode detection on the clear liquid to obtain an ammonia nitrogen concentration signal, and combining the pH and temperature signals to perform compensation calculation to obtain the final ammonia nitrogen concentration.

[0015] Further, in the step S2, a mixed solution of sodium hydroxide and sodium carbonate is added to the liquid to be measured in proportion, wherein the sodium hydroxide is used to precipitate magnesium ions, and the sodium carbonate is used to precipitate calcium ions, and the addition amount is such that the total hardness of the slurry after hardness removal is reduced to below 500 mg / L; in the step S3, the semiconductor cooling technology is used to cool the liquid to be measured at 30-50℃ to 20-25℃, and the temperature fluctuation is controlled to be less than ±0.5℃.

[0016] Compared with the prior art, the ammonia nitrogen online detection system provided by the application comprises a pretreatment unit, an ammonia gas sensitive electrode measurement unit and a control unit which are sequentially in fluid communication: the pretreatment unit is used for subjecting the to-be-detected liquid containing high calcium and magnesium ions and high suspended solids to physicochemical treatment to remove interfering substances; the ammonia gas sensitive electrode measurement unit is used for receiving the clear liquid treated by the pretreatment unit and detecting the ammonia nitrogen concentration signal therein; and the control unit is electrically connected with the pretreatment unit and the ammonia gas sensitive electrode measurement unit respectively, is used for controlling the operation of the pretreatment unit and processing the detection signal from the ammonia gas sensitive electrode measurement unit to obtain the ammonia nitrogen concentration value; through the integrated "pretreatment-measurement-control" integrated architecture, the key defects existing in the prior art are fundamentally solved. The system removes the interfering substances of the specific to-be-detected liquid (such as desulfurization slurry), combines the precise ammonia gas sensitive electrode detection and automatic control, and thus can effectively overcome the comprehensive interference caused by complex working conditions such as high calcium and magnesium ions, high suspended solids and temperature fluctuation. The direct beneficial effect is that the ammonia nitrogen concentration in the high-interference characteristic slurry can be continuously, stably and precisely monitored online, the environmental pollution risk caused by the dependence on mercury-containing reagents is avoided, and the reliability and environmental friendliness of the system are significantly improved. BRIEF DESCRIPTION OF DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the specific embodiments or the prior art, the drawings needed to be used in the specific embodiments or the prior art description will be briefly introduced. Obviously, the drawings in the following description are some embodiments of the application, and other drawings can be obtained by those skilled in the art without any creative effort.

[0018] Figure 1 The structural schematic diagram of the ammonia nitrogen online detection system provided by the embodiments of the application; Figure 2 The process flow chart of the ammonia nitrogen online detection method provided by the embodiments of the application.

[0019] Reference signs: 10, desulfurization tower; 110, medicine storage tank; 120, quantitative dosing pump 220, cooling coil; 310, sedimentation tank; 320, multi-stage filtration assembly; 321, microporous membrane filter; 322, ultrafiltration membrane filter; 323, PP cotton filter; 324, ceramic membrane filter; 410, measurement flow tank; 420, ammonia gas sensitive electrode; 430, pH sensor. DETAILED DESCRIPTION

[0020] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some but not all of the embodiments of the present application. The components of the embodiments of the present application described and shown in the drawings can be arranged and designed in various different configurations.

[0021] Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the claimed application, but merely represents selected embodiments of the application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of protection of the present application.

[0022] It should be noted that: similar reference numerals and letters represent similar items in the following drawings, therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0023] In the description of the present application, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship commonly placed when the product of the application is used, and are only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the indicated device or element must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application. In addition, the terms "first", "second", "third" and the like are only used for differentiation in description and cannot be understood as indicating or implying relative importance.

[0024] In addition, the terms "horizontal", "vertical", "overhanging" and the like do not mean that the components must be absolutely horizontal or overhanging, but can be slightly inclined. For example, "horizontal" only means that its direction is relatively more horizontal than "vertical", and does not mean that the structure must be completely horizontal, but can be slightly inclined.

[0025] In the description of the present application, it should also be noted that, unless otherwise explicitly specified and limited, the terms "arrangement", "installation", "connection", "connection" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium; it can be the communication inside two elements. For those of ordinary skill in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0026] Some embodiments of the present application will be described in detail with reference to the drawings. The following embodiments and features described below can be combined with each other in the case of no conflict.

[0027] Embodiment one: an ammonia nitrogen online detection system The present embodiment provides an ammonia nitrogen online detection system, the overall structure diagram of which can be seen from Figure 1 . The system is particularly used for continuously monitoring the ammonia nitrogen concentration in desulfurization slurry taken from a desulfurization tower 10 (such as the outlet pipeline of a slurry circulating pump of a wet desulfurization system) of a thermal power plant. The system particularly comprises a pretreatment unit, an ammonia gas sensitive electrode measurement unit and a control unit which are sequentially fluidly connected and integrated on an overall cabinet or platform to form a compact online analysis instrument.

[0028] As shown in Figure 1 , the pretreatment unit is the core for purifying high-interference desulfurization slurry, which sequentially comprises a hardness removal reaction unit, a temperature adjustment unit and a solid-liquid separation unit. The three sub-units work cooperatively to remove the substances in the slurry which interfere with the ammonia gas sensitive electrode measurement in steps and thoroughly.

[0029] Firstly, the hardness removal reaction unit is used to remove high-concentration calcium and magnesium ions in the slurry. Specifically, the unit comprises a reagent storage tank 110 and a quantitative reagent feeding pump 120. The reagent storage tank 110 stores a mixed solution of sodium hydroxide (NaOH) and sodium carbonate (Na2CO3) (i.e. “double alkali method” reagent) which is configured in advance. The control unit sends an instruction to the quantitative reagent feeding pump 120 according to a preset program or an initial hardness signal of the slurry received. The pump pumps a quantitative mixed reagent into the starting reaction area (for example, a mixing tank with stirring or the inlet pipeline of a subsequent sedimentation tank) of the pretreatment process with high precision (such as ±1%). Sodium hydroxide reacts with magnesium ions (Mg² + ) in the slurry to generate magnesium hydroxide (Mg(OH)2) precipitate with extremely small solubility, and sodium carbonate reacts with calcium ions (Ca² + ) to generate calcium carbonate (CaCO3) precipitate. By accurately controlling the dosage, the total hardness of the slurry can be effectively reduced from the original 3000-4000 mg / L (calculated as CaCO3) to below 500 mg / L, and the removal rate of calcium and magnesium ions is more than 90%, which fundamentally solves the problem of adsorption and interference of calcium and magnesium ions on the electrode gas permeable membrane, and is superior to the limited effect of traditional masking agents (such as potassium sodium tartrate or EDTA) under high hardness.

[0030] Secondly, the temperature control unit is responsible for stabilizing the desulfurization slurry from the process temperature (typically 30-50℃) to room temperature (20-25℃), consistent with the calibration temperature of the ammonia-sensitive electrode. This unit preferably uses a semiconductor cooler (TEC) as the cold source, which exchanges heat with the slurry through cooling coil 220. An integrated temperature sensor (such as Pt100) monitors the slurry temperature in real time and feeds the signal back to the control unit. The control unit dynamically adjusts the power of the semiconductor cooler accordingly, forming a closed-loop temperature control circuit. This design can precisely control the slurry temperature within ±0.5℃ of the target value. Compared to existing technologies that only heat samples at room temperature or rely solely on software temperature compensation, this active cooling method more effectively eliminates the influence of temperature changes on ammonia solubility and electrode response slope (conforming to the Nernst equation), reducing temperature-induced measurement errors to below 1%.

[0031] Then, the solid-liquid separation unit is used to thoroughly physically separate the precipitates and original suspended solids generated in the slurry after hardening and cooling. This unit includes a sedimentation tank 310 and a multi-stage filtration assembly 320. The mixed and reacted slurry enters the sedimentation tank 310 and is allowed to stand under gravity for a sufficient time (e.g., 30 minutes) to allow the generated CaCO3, Mg(OH)2 precipitates, and some large gypsum particles and other suspended solids to settle to the bottom of the tank. The sedimentation tank 310 is usually designed with a conical bottom structure to facilitate the collection and periodic discharge of precipitates. The supernatant after standing is pumped into the multi-stage filtration assembly 320. Figure 1 As shown, the assembly includes at least a microporous membrane filter 321 (e.g., a polypropylene microporous membrane with a pore size of 0.45 μm) and an ultrafiltration membrane filter 322 (with a pore size of 0.001 μm or smaller) connected in series. To further protect the precision filter membrane and extend its lifespan, a PP cotton filter 323 can be added before the microporous membrane filter 321 as a coarse filter, and a ceramic membrane filter 324 (with a pore size of 0.1 μm) can be added between the two as a fine filter. This combination of "sedimentation + multi-stage gradient filtration" ensures that the turbidity of the final product water entering the measurement unit is consistently less than 1 NTU, effectively preventing tiny suspended solids from clogging subsequent flow paths or contaminating electrode membranes, and solving the problem of traditional single-stage filtration easily failing under high turbidity conditions of desulfurization slurry.

[0032] The clear, low-hardness, and temperature-controlled solution obtained after purification by the pretreatment unit is transported to the ammonia-sensitive electrode measurement unit. This unit includes a flow cell 410. Within the flow cell 410, key detection components are arranged in a specific manner: an ammonia-sensitive electrode 420 is installed at an angle of approximately 60° to the horizontal. This angle helps reduce the adhesion of air bubbles to the electrode's sensitive membrane surface during measurement, improving response stability. Simultaneously, the flow cell 410 also houses a pH sensor 430 and another temperature sensor for monitoring the real-time temperature of the solution. Figure 1The control unit reads the signal of the pH sensor 430 in real time, and if the pH value is lower than 11 (to ensure that the ammonium ions in the slurry are completely converted into gaseous ammonia NH3), a dosing pump (not shown in the figure) is controlled to inject a small amount of strong alkali solution (such as NaOH) into the flow cell, so that the pH value is stabilized above 11. The ammonia-sensitive electrode 420 detects the millivolt-level potential signal generated by the NH3 concentration and transmits it to the control unit together with the temperature sensor signal.

[0033] The control unit is the brain of the entire system, usually composed of programmable logic controllers (PLC), data acquisition modules, human-machine interfaces (HMI), and communication modules. It performs the following core functions: 1) automatically controls the start and stop and adjustment of various actuators (such as the quantitative dosing pump 120, the cooling unit, the filtration booster pump, the sedimentation tank sludge valve, etc.) according to the preset logic; 2) receives signals from the ammonia-sensitive electrode 420, the pH sensor 430, and various temperature sensors; 3) calculates the ammonia nitrogen concentration in the clear liquid using the Nernst equation (for example, E = -56.4 lgC_NH3 + 107.5) combined with real-time temperature slope compensation; 4) displays concentration, temperature, pH, and historical curves in real time through the touch screen, and uploads data to the power plant distributed control system (DCS) through the communication interface (such as supporting Modbus protocol); 5) issues an alarm when the ammonia nitrogen concentration exceeds the standard or the system itself operates abnormally.

[0034] In addition, in order to further improve the stability and environmental adaptability of the system during long-term operation, preferably, the core components of the above-mentioned pretreatment unit, ammonia-sensitive electrode measurement unit, and control unit are integrated and installed in a shell with insulation. The shell is equipped with air conditioning devices to keep the temperature inside the shell constant at 20-25°C throughout the year. This system-level environmental constant temperature control not only provides an optimal working environment for the ammonia-sensitive electrode and the pH sensor, reducing the performance drift caused by environmental temperature fluctuations, but also assists the operation of the semiconductor cooler, reducing its thermal load, and ensuring the temperature stability of the entire measurement link.

[0035] Example Two: An ammonia nitrogen online detection method This embodiment provides an ammonia nitrogen online detection method using the system of Example One, and the process flow chart can be seen in Figure 2 . This method is particularly suitable for continuous online monitoring of desulfurization slurry in thermal power plants, and specifically includes the following steps: S1: Obtain the desulfurization slurry to be tested. Through an automatic sampling valve (such as an electric flange ball valve) installed on the slurry circulation pipeline of the desulfurization tower, representative desulfurization slurry raw samples are obtained according to a set period (for example, once every 30 minutes) or continuously, and are transported to the inlet of the pretreatment unit of the system through a corrosion-resistant pipeline.

[0036] S2: Double-alkali method is used to remove hardness from the liquid to be tested. The obtained slurry is introduced into the reaction zone. The control unit drives the quantitative dosing pump, and according to the slurry flow or the preset program, a mixed solution of sodium hydroxide and sodium carbonate is added to the slurry in a precise proportion. The amount of addition is calculated and optimized, and the target is to reduce the total hardness of the slurry after the hardness removal reaction to below 500 mg / L (calculated as CaCO3). Sodium hydroxide mainly precipitates magnesium ions to form Mg(OH)2, and sodium carbonate mainly precipitates calcium ions to form CaCO3. Mechanical stirring is used to ensure that the reagents and the slurry are fully mixed and reacted.

[0037] S3: The liquid to be tested is cooled to the preset room temperature measurement interval. The slurry after the hardness removal reaction is temperature adjusted. The semiconductor cooling technology is used to exchange heat between the cooling coil and the slurry, and the temperature is actively cooled from the original 30-50℃ to the room temperature measurement interval of 20-25℃. The temperature is monitored in real time by the temperature sensor during the process, and the temperature fluctuation is less than ±0.5℃ through closed-loop control.

[0038] S4: The cooled liquid to be tested is allowed to stand and settle. The cooled slurry is sent to the sedimentation tank and allowed to stand for a sufficient time (e.g., 30 minutes). During this process, a large amount of chemical precipitate (CaCO3, Mg(OH)2) produced in step S2 and part of the larger suspended matter (such as gypsum particles) originally in the slurry naturally settle to the bottom of the tank under the action of gravity, forming a sludge layer, and the liquid above becomes relatively clear supernatant.

[0039] S5: The supernatant is filtered by multiple stages. The supernatant in the sedimentation tank is extracted and passed through multiple-stage filtering devices from coarse to fine. For example, first pass through a PP cotton filter to remove residual large particles, then pass through a microporous membrane filter (0.45μm) and a ceramic membrane filter (0.1μm) for fine filtration, and finally pass through an ultrafiltration membrane filter (0.001μm) for deep purification. After this step, a clear and transparent test liquid with a turbidity of less than 1 NTU is obtained.

[0040] S6: Ammonia-sensitive electrode detection and calculation. The filtered clear liquid is injected into the measurement flow cell. First, the pH value of the clear liquid is detected by a pH sensor, and if it is lower than 11, an alkali agent (such as NaOH) is automatically added to adjust the pH value to above 11 to ensure that all ammonium nitrogen is completely converted into ammonia gas (NH3). Then, the NH3 concentration produces a potential signal which is detected by an inclined ammonia-sensitive electrode. The control unit synchronously collects the potential signal and the real-time temperature signal in the flow cell. Finally, the control unit calculates the ammonia nitrogen concentration value in the clear liquid according to the Nernst equation, using the standard curve (slope) of the electrode and combining real-time temperature compensation. This concentration value is the accurate result measured after removing interference, which can be directly used for display, recording, alarm and uploading.

[0041] At the end of each measurement cycle, the system can automatically perform a cleaning program: open the sludge discharge valve to discharge the sludge at the bottom of the sedimentation tank, and use pure water or cleaning liquid to backwash or clean the filter flow path and the measurement flow cell, so as to prepare for the next measurement, thereby realizing automatic, unattended continuous operation.

[0042] Through the detailed description of the system embodiments and method embodiments, those skilled in the art can clearly understand how the present application solves all the technical problems raised in the background art by integrating the technical chain of "dual-alkali method for hardness removal-semiconductor cooling-resting precipitation-multi-stage filtration-electrode detection and compensation", and realizes high-precision, high-stability, and environmentally friendly online monitoring of ammonia nitrogen in desulfurization slurry.

[0043] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. An online ammonia nitrogen detection system, characterized in that, Including those that are fluidly connected in sequence: The pretreatment unit is used to perform physicochemical treatment on the test solution containing high calcium and magnesium ions and high suspended matter to remove interfering substances; An ammonia-sensitive electrode measurement unit is used to receive the clear liquid after it has been treated by the pretreatment unit and to detect the ammonia nitrogen concentration signal therein. The control unit is electrically connected to both the pretreatment unit and the ammonia-sensitive electrode measurement unit, and is used to control the operation of the pretreatment unit and process the detection signal from the ammonia-sensitive electrode measurement unit to obtain the ammonia nitrogen concentration value.

2. The online ammonia nitrogen detection system according to claim 1, characterized in that, The preprocessing unit includes at least: Except for the hard reaction unit, it is configured to add alkaline reagents to the test solution to reduce the concentration of calcium and magnesium ions in the test solution through chemical precipitation; The temperature control unit is configured to adjust and stabilize the temperature of the liquid to be tested within a preset room temperature measurement range; The solid-liquid separation unit is configured to settle and filter the test liquid after hardening and temperature adjustment to obtain a clear liquid that meets the turbidity requirements.

3. The online ammonia nitrogen detection system according to claim 2, characterized in that, The hardening reaction unit includes: A storage tank for storing a mixture of sodium hydroxide and sodium carbonate. A metering pump, connected to the storage tank and the control unit, is used to precisely add the mixed reagent to the test solution according to the instructions of the control unit.

4. The online ammonia nitrogen detection system according to claim 2, characterized in that, The temperature regulation unit is a semiconductor cooler, which cools the test liquid through a cooling coil and a water circulation system, and integrates a temperature sensor to form a closed-loop temperature control circuit.

5. The online ammonia nitrogen detection system according to claim 2, characterized in that, The solid-liquid separation unit includes: A sedimentation tank is used to hold the test liquid after hardening and cooling, allowing the precipitate in it to settle naturally. A multi-stage filtration assembly is connected to the supernatant outlet of the sedimentation tank, and the multi-stage filtration assembly includes at least a microporous membrane filter and an ultrafiltration membrane filter connected in series.

6. The online ammonia nitrogen detection system according to claim 5, characterized in that, The multi-stage filtration assembly also includes a PP cotton filter disposed before the microporous membrane filter, and a ceramic membrane filter disposed between the microporous membrane filter and the ultrafiltration membrane filter.

7. The online ammonia nitrogen detection system according to any one of claims 1 to 6, characterized in that, The ammonia-sensitive electrode measurement unit includes: Measuring flow cell; An ammonia-sensitive electrode is installed at an angle inside the measuring flow cell; A pH sensor and a temperature sensor are installed in the measurement flow cell to monitor the pH value and temperature of the clear liquid in real time. The control unit is configured to: control whether to add an alkalizing agent based on the signal from the pH sensor to make the pH value greater than 11; and combine the output potential of the ammonia-sensitive electrode and the signal from the temperature sensor to perform temperature compensation calculations using the Nernst equation to obtain the ammonia nitrogen concentration value.

8. The online ammonia nitrogen detection system according to claim 1, characterized in that, It also includes a housing, inside which is an air conditioning device for maintaining the ambient temperature at 20-25°C. The pretreatment unit, the ammonia-sensitive electrode measuring unit, and the control unit are all located inside the housing.

9. A method for online detection of ammonia nitrogen, using an online ammonia nitrogen detection system as described in any one of claims 1 to 8, characterized in that, Includes the following steps: S1: Obtain the desulfurization slurry to be tested; S2: The test solution is subjected to a double alkali method to remove hardness and reduce the concentration of calcium and magnesium ions; S3: Cool the test liquid to the preset room temperature measurement range; S4: Allow the cooled test liquid to stand and settle, and separate the supernatant; S5: The supernatant is filtered through multiple stages to obtain a clear liquid with a turbidity of less than 1 NTU; S6: The clear liquid is subjected to ammonia-sensitive electrode detection to obtain the ammonia nitrogen concentration signal, and the final ammonia nitrogen concentration is obtained by compensation calculation in combination with pH and temperature signals.

10. The online ammonia nitrogen detection method according to claim 9, characterized in that, In step S2, a mixed solution of sodium hydroxide and sodium carbonate is added to the test solution in proportion, wherein sodium hydroxide is used to precipitate magnesium ions and sodium carbonate is used to precipitate calcium ions, and the amount added is such that the total hardness of the slurry after hardening is reduced to below 500 mg / L. In step S3, semiconductor cooling technology is used to cool the test liquid from 30-50°C to 20-25°C, and the temperature fluctuation is controlled to be less than ±0.5°C.

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