A method for regulating sulfur dioxide content in bromine production absorption process

Abstract

The present invention relates to the technical field of bromine production, and in particular, provides a method for adjusting the sulfur dioxide content in a bromine production absorption process. The method comprises analyzing the sulfur dioxide content through a sulfur dioxide online detection device to obtain the test results of the sulfur dioxide content; obtaining the chromaticity values ​​of waste liquid at different stages according to the test results of the sulfur dioxide content, and uploading the chromaticity values ​​of the waste liquid at different stages to a distributed control system DCS; using the chromaticity values ​​of the waste liquid at different stages, adjusting the frequency of the sulfur feeder inverter through the DCS and a predictive control algorithm to adjust the sulfur dioxide content, and when chlorine and sulfur dioxide exist at the same time, the method can obtain the sulfur dioxide content, improve the accuracy of the sulfur dioxide addition amount, avoid sulfur waste, and reduce sulfur ton consumption.

Description

Technical Field

[0001] The invention relates to the technical field of bromine production, and in particular to a method for adjusting sulfur dioxide content in a bromine production absorption process. Background Art

[0002] At present, the commonly used processes in the bromine production industry are air blowing and steam distillation to produce bromine, among which the air blowing method is the main process technology currently adopted by the bromine production industry. The amount of sulfur dioxide added directly affects the quality of the bromine production process. If the sulfur dioxide is introduced less, the blown-out elemental bromine cannot be fully absorbed; if the sulfur dioxide is introduced more, the cost of burning sulfur will increase, and the bromine oxidized in the previous process will be reduced to bromide ions. Insufficient or excessive sulfur dioxide will reduce the extraction rate of bromine and reduce production efficiency.

[0003] Existing detection technology solution 1: In actual production, on-site workers currently use visual inspection methods. Workers usually judge the amount of sulfur dioxide introduced based on experience, and use the color change of the blown waste liquid as the basis for adjusting sulfur dioxide. The transparent and clear color of the blown waste liquid indicates excessive sulfur dioxide, and the slightly yellow color of the blown waste liquid indicates insufficient sulfur dioxide. Sulfur dioxide is often greatly affected by chlorine, so it is difficult to make an accurate judgment on the supply of sulfur dioxide manually. This method is greatly affected by environmental and personnel differences, and it is impossible to judge how much excess there is. Therefore, this method can only be used as an auxiliary method in production for rough judgment. Inaccurate sulfur dioxide control will directly affect the extraction rate of bromine. Existing detection technology solution 2: In the air blowing bromine production process, excess chlorine should be added in the oxidation process to fully oxidize bromide ions into bromine elements, and excess sulfur dioxide should be introduced in the subsequent absorption process to reduce the elements. The remaining sulfur dioxide enters the absorption through circulation, bringing some unreacted chlorine. Chlorine is oxidizing and sulfur dioxide is reducing. When the two meet, redox reactions will occur. In the traditional bromine extraction process, chemical titration is often used to detect sulfur dioxide, but sulfur dioxide is often greatly affected by chlorine. Due to the complex composition of the blown waste liquid in bromine production and the chemical reactions between them, it is difficult to accurately detect sulfur dioxide and chlorine at the same time, so it is difficult to use the iodine method to determine the sulfur dioxide content in the blown waste liquid. According to the manual observation of color changes, the amount of sulfur added is manually adjusted, or a simple control with hysteresis is used. There is a strong hysteresis and the amount of sulfur added cannot be accurately controlled, resulting in sulfur waste and high sulfur consumption per ton. Summary of the invention

[0004] In view of this, the present invention provides a method for adjusting the sulfur dioxide content in a bromine production absorption process, so as to obtain the sulfur dioxide content when chlorine and sulfur dioxide exist at the same time, improve the accuracy of sulfur dioxide addition, avoid sulfur waste, and reduce sulfur consumption.

[0005] In a first aspect, the present invention provides a method for adjusting sulfur dioxide content in a bromine production absorption process, the method comprising:

[0006] Step 1: Analyze the sulfur dioxide content through the sulfur dioxide online monitoring equipment to obtain the test results of the sulfur dioxide content;

[0007] Step 2: According to the test results of sulfur dioxide content, the chromaticity values ​​of the waste liquid at different stages are obtained, and the chromaticity values ​​of the waste liquid at different stages are uploaded to the distributed control system DCS;

[0008] Step 3: Using the chromaticity values ​​of the waste liquid at different stages, the frequency of the sulphur feeder inverter is adjusted through DCS and predictive control algorithm to regulate the sulphur dioxide content.

[0009] Optionally, step 1 includes:

[0010] The sulfur dioxide content is analyzed by using the color change characteristics of methyl red through the sulfur dioxide online monitoring equipment. The test results of the sulfur dioxide content are obtained according to the depth of the color of the reaction between the waste liquid and methyl red. The reaction formula is as follows:

[0011] SO2+H2O+Br2→Br - +SO4 2- +H + ;

[0012] SO2+H2O+CLO - →Cl - + SO4 2- +H + .

[0013] Optionally, the test results include:

[0014] When the reaction color of the waste liquid and methyl red is transparent, the sulfur dioxide content ranges from 0 to 10 ppm;

[0015] When the reaction color of the waste liquid and methyl red is light red, the sulfur dioxide content ranges from 10ppm to 18ppm;

[0016] When the waste liquid reacts with methyl red to produce a red color, the sulfur dioxide content ranges from 18ppm to 25ppm;

[0017] When the reaction color of the waste liquid and methyl red is dark red, the sulfur dioxide content is greater than 25 ppm.

[0018] Optionally, the step 2 includes:

[0019] By converting the RGB model to the HSI model, the RGB-HSI conversion model is obtained, and the chromaticity values ​​of the waste liquid at different stages are output to solve the color difference and color distortion detection under different environments; the conversion model is expressed as:

[0020] ;

[0021] ;

[0022] ,

[0023] or ,like , ;

[0024] in, H , S , I Three parameters describe color characteristics, H Hue is used to represent the wavelength of color; S Saturation is used to indicate the depth of color; I Indicates intensity or brightness; R , G , B Respectively represents the three primary colors of red, green and blue.

[0025] Optionally, the predictive control algorithm in step 3 includes:

[0026] Step 31, determining the chromaticity range of the sulfur dioxide content, firstly determining the chromaticity range of the current sulfur dioxide content value through actual on-site testing;

[0027] Step 32: Construct the state equation. The chromaticity value of sulfur dioxide content in the next state is , then the state equation is constructed as: , Indicates the chromaticity value of the current sulfur dioxide content; Indicates the frequency control variable of the sulfur inverter, , is the matrix equation of the current state;

[0028] Step 33: Use the forward Euler method to discretize the state equation, which is expressed as follows:

[0029] ;

[0030] ;

[0031] ;

[0032] in, k Indicates the current state;k +1 indicates the next state; t indicates the sampling period; express The conjugate matrix of ; express The conjugate matrix of ; I Indicates intensity or brightness;

[0033] Step 34: predict the chromaticity value of sulfur dioxide content in the future state, define p as the prediction time domain, and record the predicted chromaticity value of sulfur dioxide in the future p control cycles X k , whose expression is:

[0034] ;

[0035] Prediction of control quantity in the time domain U k , whose expression is:

[0036] ;

[0037] Step 35, obtain the reference value of the state equation, and output the sulfur conversion frequency reference coefficient U according to the current sulfur dioxide content chromaticity value; first give the reference value when the sulfur dioxide is just in the state in the prediction time domain, and obtain the reference value sequence in p time domains R k , whose expression is:

[0038] ;

[0039] Among them, the content range of sulfur dioxide is 18ppm-25ppm;

[0040] Step 36: Optimize and solve the control quantity U k , define the optimization objective function using the cumulative error between the predicted chromaticity value and the reference value, and establish an optimization function with constraints J ( U k ), whose expression is:

[0041] ;

[0042] in Q is a diagonal matrix;

[0043] Solved J ( U k ) to obtain the minimum value of the sulfur inverter frequency in the predicted time domain u value, thereby adjusting the frequency of sulfur addition and thus adjusting the sulfur dioxide content.

[0044] In the technical solution provided by the present invention, the method comprises analyzing the sulfur dioxide content by means of sulfur dioxide online monitoring equipment to obtain the test results of the sulfur dioxide content; obtaining the chromaticity values ​​of the waste liquid at different stages according to the test results of the sulfur dioxide content, and uploading the chromaticity values ​​of the waste liquid at different stages to the distributed control system DCS; using the chromaticity values ​​of the waste liquid at different stages, adjusting the frequency of the frequency converter of the sulfur feeder through the DCS and the predictive control algorithm to adjust the sulfur dioxide content. When chlorine and sulfur dioxide exist at the same time, the method can obtain the sulfur dioxide content, improve the accuracy of the sulfur dioxide addition amount, avoid the waste of sulfur, and reduce the sulfur ton consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0046] Figure 1 A flow chart of a method for adjusting sulfur dioxide content provided by an embodiment of the present invention;

[0047] Figure 2 A schematic diagram of an online sulfur dioxide monitoring device provided by an embodiment of the present invention;

[0048] Figure 3 A schematic diagram of a bromine production absorption process provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0049] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0050] It should be clear that the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0051] The terms used in the embodiments of the present invention are only for the purpose of describing specific embodiments, and are not intended to limit the present invention. The singular forms "a", "said" and "the" used in the embodiments of the present invention are also intended to include plural forms, unless the context clearly indicates other meanings.

[0052] It should be understood that the term "and / or" used in this article is only a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0053] The word "if" as used herein may be interpreted as "at the time of" or "when" or "in response to determining" or "in response to detecting", depending on the context. Similarly, the phrases "if it is determined" or "if (stated condition or event) is detected" may be interpreted as "when it is determined" or "in response to determining" or "when detecting (stated condition or event)" or "in response to detecting (stated condition or event)", depending on the context.

[0054] Figure 1 A flow chart of a method for adjusting sulfur dioxide content provided by an embodiment of the present invention, such as Figure 1 As shown, the method includes:

[0055] Step 1: Analyze the sulfur dioxide content through the sulfur dioxide online monitoring equipment to obtain the test results of the sulfur dioxide content.

[0056] In the embodiment of the present invention, step 1 includes:

[0057] In addition to waste acid, the waste liquid discharged from the blow-out tower may also contain excess free chlorine, free bromine, or sulfurous acid formed by the dissolution of sulfur dioxide. Methyl red is a dye whose azo bond is easily oxidized and broken. It will definitely fade after the azo bond breaks, and the chlorine gas introduced into the blow-out tower has strong oxidizing properties, which can cause methyl red to be oxidized and fade. The color change range of methyl red is pH 4.4~6.2, where it is red when the pH value is ≤4.4, orange when the pH value is in the range of 4.4~6.2, and yellow when the pH value is ≥6.2. The pH value of the waste liquid is around 3, and the addition of methyl red to the waste liquid should show red, but the free chlorine in the waste liquid will cause methyl red to fade, and the degree of fading is related to the content of free chlorine.

[0058] The sulfur dioxide content is analyzed by using the color change characteristics of methyl red through the sulfur dioxide online monitoring equipment. The test results of the sulfur dioxide content are obtained according to the depth of the color of the reaction between the waste liquid and methyl red. The reaction formula is as follows:

[0059] SO2+H2O+Br2→Br- +SO4 2- +H + ;

[0060] SO2+H2O+CLO - →Cl - + SO4 2- +H + .

[0061] In the embodiment of the present invention, the test results include:

[0062] When the reaction color of the waste liquid and methyl red is transparent, the content of sulfur dioxide ranges from 0 to 10ppm, which indicates that the content of sulfur dioxide is seriously insufficient; when the reaction color of the waste liquid and methyl red is light red, the content of sulfur dioxide ranges from 10ppm to 18ppm, which indicates that the content of sulfur dioxide is insufficient; when the reaction color of the waste liquid and methyl red is red, the content of sulfur dioxide ranges from 18ppm to 25ppm, which indicates that the content of sulfur dioxide is just right; when the reaction color of the waste liquid and methyl red is dark red, the content of sulfur dioxide is greater than 25ppm, which indicates that the content of sulfur dioxide is excessive.

[0063] In the embodiment of the present invention, Figure 2 As shown, the sulfur dioxide online monitoring equipment consists of a water suction pump, a metering pump, an injection pump, a waste pump, a controller, a visual inspection device, a stirrer, and a reaction dish. The water suction pump is used to extract pure water, the metering pump is used to meter the titration solution, and the injection pump is used to inject the sample to be tested. The stirring device is used to provide stirring power to the reaction dish to speed up the reaction; the controller is used to control the overall operation of the entire system to ensure that the system executes according to logic; the visual inspection device is used to detect the color change of the reaction dish and output the chromaticity value of the current color. The reaction dish is used to mix and react with samples, titration solutions, pure water and other liquids. The measurement principle of the sulfur dioxide online monitoring equipment is: the controller controls the injection pump to quantitatively extract samples, the metering pump to quantitatively extract titration solutions, the stirring device starts to work and stir, and waits for the reaction. After the reaction is completed, the visual inspection device calls a high-performance visual recognition algorithm to identify color changes and output the chromaticity value, which is the qualitative value of the current sulfur dioxide content. At the same time, it can determine whether the current sulfur dioxide is excessive, insufficient or seriously insufficient.

[0064] Step 2: According to the test results of the sulfur dioxide content, the color values ​​of the waste liquid at different stages are obtained, and the color values ​​of the waste liquid at different stages are uploaded to the Distributed Control System (DCS).

[0065] In the embodiment of the present invention, step 2 includes:

[0066] When the model of the collected image is the RGB model, the three quantities interact with each other to produce color difference or color distortion, which leads to system misjudgment. It is converted into an HSI model and the current chromaticity value is output. The above algorithm model conversion can solve the color difference and color distortion detection problems in different environments.

[0067] By converting the RGB model to the HSI model, the RGB-HSI conversion model is obtained, and the chromaticity values ​​of the waste liquid at different stages are output to solve the color difference and color distortion detection under different environments; the conversion model is expressed as:

[0068] ;

[0069] ;

[0070] ,

[0071] or ,like , ;

[0072] in, H , S , I Three parameters describe color characteristics, H Hue is used to represent the wavelength of color; S Saturation is used to indicate the depth of color; I Indicates intensity or brightness; R , G , B Respectively represents the three primary colors of red, green and blue.

[0073] Step 3: Using the chromaticity values ​​of the waste liquid at different stages, the frequency of the sulphur feeder inverter is adjusted through DCS and predictive control algorithm to regulate the sulphur dioxide content.

[0074] In the embodiment of the present invention, the predictive control algorithm in step 3 includes:

[0075] Step 31, determining the chromaticity range of the sulfur dioxide content, firstly determining the chromaticity range of the current sulfur dioxide content value through actual on-site testing;

[0076] In the embodiment of the present invention, as shown in Table 1, when L1≤chromaticity value A≤H1, it indicates that the current state of sulfur dioxide is seriously insufficient; when L2≤chromaticity value B≤H2, it indicates that the current state of sulfur dioxide is insufficient; when L3≤chromaticity value C≤H3, it indicates that the current state of sulfur dioxide is just right; when L4≤chromaticity value D≤H4, it indicates that the current state of sulfur dioxide is excessive;

[0077] Table 1

[0078] .

[0079] In a possible implementation, L1 takes a value of 50 and H1 takes a value of 100, at which time 50≤chromaticity value≤100, indicating that the current state of sulfur dioxide is seriously insufficient; L2 takes a value of 150 and H2 takes a value of 200, at which time 150≤chromaticity value≤200, indicating that the current state of sulfur dioxide is insufficient; L3 takes a value of 210 and H3 takes a value of 260, at which time 210≤chromaticity value≤260, indicating that the current state of sulfur dioxide is just right; L4 takes a value of 300 and H4 takes a value of 350, at which time 300≤chromaticity value≤350, indicating that the current state of sulfur dioxide is excessive.

[0080] Step 32: Construct the state equation. The chromaticity value of sulfur dioxide content in the next state is , then the state equation is constructed as: , Indicates the chromaticity value of the current sulfur dioxide content; Indicates the frequency control variable of the sulfur inverter, , is the matrix equation of the current state;

[0081] Step 33: Use the forward Euler method to discretize the state equation, which is expressed as follows:

[0082] ;

[0083] ;

[0084] ;

[0085] in, k Indicates the current state; k +1 indicates the next state; t indicates the sampling period; express The conjugate matrix of ; express The conjugate matrix of ; I Indicates intensity or brightness;

[0086] Step 34: predict the chromaticity value of sulfur dioxide content in the future state, define p as the prediction time domain, and record the predicted chromaticity value of sulfur dioxide in the future p control cycles X k , whose expression is:

[0087] ;

[0088] Prediction of control quantity in the time domain U k , whose expression is:

[0089] ;

[0090] Step 35, obtain the reference value of the state equation, and output the sulfur conversion frequency reference coefficient U according to the current sulfur dioxide content chromaticity value; first give the reference value when the sulfur dioxide is just in the state in the prediction time domain, and obtain the reference value sequence in p time domains R k , whose expression is:

[0091] ;

[0092] In the embodiment of the present invention, the content range of sulfur dioxide in the just state is 18ppm-25ppm; the reference value of sulfur dioxide in the just state needs to be obtained by bringing it into the state equation through actual on-site testing, and this value requires a large amount of on-site data to obtain the reference value of the state equation.

[0093] Step 36: Optimize and solve the control quantity U k , define the optimization objective function using the cumulative error between the predicted chromaticity value and the reference value, and establish an optimization function with constraints J ( U k ), whose expression is:

[0094] ;

[0095] in Q is a diagonal matrix;

[0096] Solved J ( U k ) to obtain the minimum value of the sulfur inverter frequency in the predicted time domain u value, thereby adjusting the frequency of sulfur addition and thus adjusting the sulfur dioxide content.

[0097] In the embodiment of the present invention, the predictive control algorithm can realize accurate control of the amount of sulfur dioxide added in the absorption process, and maintain the sulfur dioxide gas content in the circulating tail gas of the absorption process stable at around 20 ppm.

[0098] In the embodiment of the present invention, in addition to the waste acid, the waste liquid of the blow-out tower may also contain excessive free chlorine, free bromine or sulfurous acid formed by the dissolution of sulfur dioxide. In order to complete the automatic sampling, automatic detection, automatic analysis and automatic control of the current bromine absorption process, a bromine absorption process measurement and control system is systematically proposed, such as Figure 3As shown, the bromine absorption process measurement and control system mainly includes detection instruments and predictive control algorithms. By installing sulfur dioxide online monitoring equipment at the exhaust port of the blow-out tower, the sulfur dioxide online monitoring equipment adopts titration analysis to comprehensively analyze the specific situation of insufficient sulfur dioxide and excessive chlorine in the waste liquid, and complete the automatic sampling and testing in the production process to obtain data. The value of the blown waste liquid fluctuates within the range with the change of the amount of chlorine and sulfur added, and can obviously reflect the situation of insufficient chlorine and excessive chlorine. The output is the chromaticity value of the blown waste liquid. The data is automatically uploaded to the DCS, which can be used as the basis for adjusting the frequency of the sulfur feeder inverter. Through the predictive control algorithm, the frequency of the sulfur feeder inverter is adjusted, and then the amount of sulfur dioxide added in the absorption process is adjusted, thereby improving the bromine extraction rate and reducing the sulfur ton consumption.

[0099] The present invention proposes a new sulfur dioxide content detection method for the simultaneous presence of chlorine and sulfur dioxide in the bromine production absorption process, using the color change property of the methyl red indicator to determine the sulfur dioxide content in the current blow-out tower wastewater by dropping the indicator; the present invention proposes a sulfur dioxide content visual titration detection method, using the different indicator colors of sample content at different stages, using a self-developed flow visual detection algorithm, analyzing and determining the titration endpoints at different stages, and outputting the chromaticity values ​​at different stages. The present invention proposes a sulfur dioxide content addition prediction control algorithm, using the chromaticity values ​​detected at different stages, so as to adjust the sulfur inverter frequency in advance, thereby adjusting the sulfur dioxide content value.

[0100] The present invention proposes a method for detecting sulfur dioxide content in the presence of chlorine and sulfur dioxide and a method for visual titration detection of sulfur dioxide content. The above two methods are combined with the structure of an analytical instrument to form a unique sulfur dioxide analysis instrument on the market. The innovation of the instrument is to solve the qualitative analysis of sulfur dioxide in the presence of chlorine (oxidizing) and sulfur dioxide (reducing) substances in the original solution, accurately locate the current sulfur dioxide reaction degree, and maintain the sulfur dioxide content within a certain range in the bromine production absorption process.

[0101] In the technical solution provided by the present invention, the method comprises analyzing the sulfur dioxide content by means of a sulfur dioxide online detection device to obtain the test result of the sulfur dioxide content; obtaining the chromaticity value of the waste liquid at different stages according to the test result of the sulfur dioxide content, and uploading the chromaticity value of the waste liquid at different stages to a distributed control system DCS; using the chromaticity value of the waste liquid at different stages, adjusting the frequency of the frequency converter of the sulfur feeder through the DCS and a predictive control algorithm to adjust the sulfur dioxide content. When chlorine and sulfur dioxide exist at the same time, the method can obtain the sulfur dioxide content, improve the accuracy of the sulfur dioxide addition amount, avoid the waste of sulfur, and reduce the sulfur consumption per ton.

[0102] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working processes of the systems, devices and units described above can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.

[0103] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for adjusting sulfur dioxide content in a bromine production absorption process, characterized in that: The method comprises: Step 1: Analyze the sulfur dioxide content through the sulfur dioxide online monitoring equipment to obtain the test results of the sulfur dioxide content; Step 2: According to the test results of sulfur dioxide content, the chromaticity values ​​of the waste liquid at different stages are obtained, and the chromaticity values ​​of the waste liquid at different stages are uploaded to the distributed control system DCS; Step 3: Using the chromaticity values ​​of the waste liquid at different stages, the frequency of the converter of the sulfur feeder is adjusted through the DCS and predictive control algorithm to adjust the sulfur dioxide content; The step 2 comprises: By converting the RGB model to the HSI model, the RGB-HSI conversion model is obtained, and the chromaticity values ​​of the waste liquid at different stages are output to solve the color difference and color distortion detection under different environments; the conversion model is expressed as: ； ； ， or ,like , ; in, H , S , I Three parameters describe color characteristics, H Hue is used to represent the wavelength of color; S Saturation is used to indicate the depth of color; I Indicates intensity or brightness; R , G , B Respectively represent the three primary colors of red, green and blue; The predictive control algorithm in step 3 includes: Step 31, determining the chromaticity range of sulfur dioxide content, firstly determining the chromaticity range of the current sulfur dioxide content value through actual on-site testing; Step 32: Construct the state equation. The chromaticity value of sulfur dioxide content in the next state is , then the state equation is constructed as: , Indicates the chromaticity value of the current sulfur dioxide content; Indicates the frequency control variable of the sulfur inverter, , is the matrix equation of the current state; Step 33: Use the forward Euler method to discretize the state equation, which is expressed as follows: ； ； ； in, k Indicates the current state; k +1 indicates the next state; t indicates the sampling period; express The conjugate matrix of ; express The conjugate matrix of ; I Indicates intensity or brightness; Step 34: predict the chromaticity value of sulfur dioxide content in the future state, define p as the prediction time domain, and record the predicted chromaticity value of sulfur dioxide in the future p control cycles X k , whose expression is: ； Prediction of control quantity in the time domain U k , whose expression is: ； Step 35, obtain the reference value of the state equation, and output the sulfur conversion frequency reference coefficient U according to the current sulfur dioxide content chromaticity value; first give the reference value when the sulfur dioxide is just in the state in the prediction time domain, and obtain the reference value sequence in p time domains R k , whose expression is: ； Among them, the content range of sulfur dioxide is 18ppm-25ppm; Step 36: Optimize and solve the control quantity U k , define the optimization objective function using the cumulative error between the predicted chromaticity value and the reference value, and establish an optimization function with constraints J ( U k ), whose expression is: ； in Q is a diagonal matrix; Solved J ( U k ) to obtain the minimum value of the sulfur inverter frequency in the predicted time domain u value, thereby adjusting the frequency of sulfur addition and thus adjusting the sulfur dioxide content.

2. The method according to claim 1, characterized in that The step 1 comprises: The sulfur dioxide content is analyzed by using the color change characteristics of methyl red through the sulfur dioxide online monitoring equipment. The test results of the sulfur dioxide content are obtained according to the depth of the color of the reaction between the waste liquid and methyl red. The reaction formula is as follows: SO2+H2O+Br2→Br - +SO4 2- +H + ; SO2+H2O+CLO - →Cl - + SO4 2- +H + 。 3. The method according to claim 2, characterized in that The test results include: When the reaction color of the waste liquid and methyl red is transparent, the sulfur dioxide content ranges from 0 to 10 ppm; When the reaction color of the waste liquid and methyl red is light red, the sulfur dioxide content ranges from 10ppm to 18ppm; When the waste liquid reacts with methyl red to produce a red color, the sulfur dioxide content ranges from 18ppm to 25ppm; When the reaction color of the waste liquid and methyl red is dark red, the sulfur dioxide content is greater than 25 ppm.

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