A method for online control of the oxidation state of a desulfurization slurry by controlling the Ca2+ concentration and pH of the slurry.

Abstract

Ca in desulfurization slurry 2+ A method for controlling the oxidation state of a slurry online by concentration and pH, comprising: 2+ The step of acquiring the concentration and pH value, and calculating the oxidation air excess coefficient (α) and the pH value of the slurry by the oxidation air excess coefficient (α)-pH-SO3 under the oxidation air amount. 2- Enter the concentration model and calculate the SO3 in the desulfurization slurry. 2- Then, the real-time concentration of SO3 in the desulfurization slurry is obtained. 2- and the real-time concentration of SO3 when CaSO3 precipitates. 2- Calculating a CaSO3 precipitation index pi based on the critical concentration of CaSO3; and controlling the amount of oxidation air based on the CaSO3 precipitation index pi to remove Ca from the desulfurization slurry. 2+ and controlling the oxidation state of the slurry online by concentration and pH.

Description

【Technical Field】 【0001】 This disclosure belongs to the technical field of chemistry and relates to a method for on-line controlling the oxidation state of slurry by the Ca concentration and pH in desulfurization slurry. 2+ It relates to a method for on-line controlling the oxidation state of the slurry by the Ca concentration and pH in the desulfurization slurry. 【0002】 This application is filed based on a Chinese patent application with the application number 202210827492.6 and the filing date of July 14, 2022, and claims the priority of the Chinese patent application. All the contents of the Chinese patent application are incorporated herein by reference. 【Background Art】 【0003】 Currently, in coal-fired power units, the wet desulfurization process mainly using limestone-gypsum is mainly used to remove SO2 from flue gas. SO2 in the flue gas is collected in the slurry. After entering the slurry tank, it exists as a reduced +4-valent sulfur substance (H2SO3, HSO3 - , SO3 2- ), and is oxidized by an oxidation fan, combines with Ca 2+ and precipitates to become by-product gypsum (CaSO4·2H2O). When the slurry is in a state of insufficient oxidation, +4-valent sulfur substances such as H2SO3, HSO3 - , SO3 2- etc. are generated, and the pH of the desulfurization slurry is mostly controlled at 4-6. At this time, the content of H2SO3 can also be ignored. The oxidation degree of the desulfurization slurry in the absorption tower can be evaluated by the sulfite content in the slurry. By controlling the oxidation state of the slurry in real time and precisely adjusting the oxidation air volume, it contributes to the safe and energy-saving operation and automatic control of the desulfurization system. 【0004】 For the analysis of the sulfite content in the desulfurization slurry, mainly manual sampling and laboratory detection methods are adopted. Since sulfite itself is easily oxidized, the oxidation state of the slurry tested by this method is significantly delayed compared with the actual situation. Therefore, the detection results in the laboratory deviate greatly from the actual situation of the slurry, and the quality of gypsum cannot be ensured. 【Summary of the Invention】 【Problems to be Solved by the Invention】 【0005】 An object of the present disclosure is to provide a method for online controlling the oxidation state of slurry by the Ca 2+ concentration and pH in the desulfurization slurry. 【Means for Solving the Problems】 【0006】 To achieve the above object, a method for online controlling the oxidation state of slurry by the Ca 2+ concentration and pH in the desulfurization slurry described in the present disclosure includes: a step of obtaining the Ca 2+ concentration and pH value in the slurry; inputting the oxidation air excess coefficient (α) and the pH value of the slurry into an oxidation air excess coefficient (α)-pH-SO3 2- concentration model under the amount of oxidation air to obtain the real-time concentration of SO3 2- in the desulfurization slurry, and then calculating a CaSO3 precipitation index pi based on the real-time concentration of SO3 2- in the desulfurization slurry and the critical concentration of SO3 2- when CaSO3 precipitates; controlling the amount of oxidation air based on the CaSO3 precipitation index pi, and online controlling the oxidation state of the slurry by the Ca 2+ concentration and pH in the desulfurization slurry. 【0007】 In some embodiments, the Ca 2+ concentration in the slurry is measured in real time by a calcium ion meter, and the pH value of the slurry is measured in real time by a pH meter. 【0008】 In some embodiments, the method includes: a step of establishing an oxidation air excess coefficient (α)-pH-SO3 2- concentration model under various amounts of oxidation air; SO3 when CaSO3 precipitates 2- The process further includes the step of determining the critical concentration of . 【0009】 In some examples, the excess oxidizing air coefficient α is the ratio of the amount of oxidizing air actually supplied by the absorption tower to the theoretical amount of oxidizing air required to completely oxidize the SO2 collected by the absorption tower, under conditions where the flue gas is considered capable of spontaneously oxidizing 10% of the SO2; that is, The values ​​of Q and S are calculated using JPEG0007875973000001.jpg2154, where Q is the amount of oxidizing air actually supplied by the absorption tower and S is the amount of SO2 collected by the absorption tower. Both Q and S values ​​are obtained in real time by the DCS system. 【0010】 In some embodiments, when CaSO3 precipitates, SO3 2- The critical concentration of is Ca 2+ and SO3 2- Solubility product constant K sp From the formula Determined by JPEG0007875973000002.jpg1730. 【0011】 In some examples, the excess oxidizing air coefficient (α)-pH-SO3 under various amounts of oxidizing air. 2- In the process of establishing a concentration model, specifically, 1) By adjusting the SO2 processing rate of the absorption tower by changing the load of the unit or adjusting the opening of the bypass valve while keeping the amount of oxidizing air constant, the excess coefficient of oxidizing air α also changes accordingly when the SO2 processing rate of the absorption tower changes, and the +4 valent sulfur substances H2SO3 and HSO3 under various SO2 processing conditions can be determined by chemical analysis using iodine titration. - and SO3 2- The total concentration is obtained, and further, the excess oxidation coefficient α under the amount of oxidizing air and the +4 valent sulfur substances H2SO3, HSO3 - and SO3 2- Obtaining the relationship with the total concentration, 2) Adjust the amount of oxidizing air and repeat step 1) so that the range of oxidizing air amounts includes the low, medium, and high SO2 processing amounts of the absorption tower, and the excess oxidizing air coefficient α and the +4 valent sulfur substances H2SO3, HSO3 under various oxidizing air amounts. - and SO3 2- Obtaining the relationship with the total concentration, 3) The excess oxidizing air coefficient α and the +4 valent sulfur substances H2SO3, HSO3 under various amounts of oxidizing air obtained in step 2). - and SO3 2- The relationship with the total concentration is fitted, and a fitting equation is obtained. 4) H2SO3, HSO3 - and SO3 2- The effect of pH on the concentration distribution relationship is introduced into the fitting equation, and the excess oxidizing air coefficient (α)-pH-SO3 under various oxidizing air amounts is obtained. 2- Establish a concentration model. 【0012】 In some examples, the excess oxidative air coefficient (α)-pH-SO3 2- SO3 in slurry during the process of establishing a concentration model 2- In the process of determining the concentration, First, chemical analysis by iodine titration identified the +4 valent sulfur substances H2SO3 and HSO3 in the slurry. - and SO3 2- The total concentration of H2SO3 is obtained, and then H2SO3 at various pH levels. - and SO3 2- SO3 in slurry according to the dissociation equilibrium relationship 2- If the concentration is calculated and the pH value of the slurry is controlled between 4 and 6, the H2SO3 content can be ignored. 【0013】 In some embodiments, the CaSO3 precipitation index pi is the SO3 in the slurry. 2- Real-time concentration and SO3 2- This is the ratio to the critical concentration. 【0014】 In some examples, when 0.8 ≤ pi ≤ 1, the system is well oxidized and maintains the amount of oxidized air; when pi < 0.8, the system is in a peroxidized state and the amount of oxidized air decreases; and when pi > 1, the system is in an under-oxidized state and the amount of oxidized air increases. [Brief explanation of the drawing] 【0015】 [Figure 1] This diagram shows the relationship between the excess oxidative air coefficient α and the total concentration of +4 valent sulfur substances H2SO3, HSO3-, and SO32-, as well as a schematic representation of the proportion of sulfites at various pH values. [Figure 2] This is a three-dimensional diagram of the excess oxidizing air coefficient (α)-pH-SO3 2-concentration model under various oxidizing air levels. [Figure 3] This is a logic diagram of online control designed based on the CaSO3 precipitation index (pi). [Modes for carrying out the invention] 【0016】 To enable those skilled in the art to better understand aspects of this disclosure, the technical solutions in the embodiments of this disclosure will be described clearly and completely below with reference to the drawings in the embodiments of this disclosure. However, it is clear that the embodiments described are only a selection of embodiments of this disclosure, not all embodiments, and do not limit the scope of this disclosure. Furthermore, in the following description, descriptions of known configurations and technologies will be omitted to avoid unnecessary confusion of concepts disclosed in this disclosure. All other embodiments that a person skilled in the art could obtain without creative work based on the embodiments of this disclosure should fall within the scope of this disclosure. 【0017】 The drawings show schematic diagrams of the structures of the embodiments disclosed herein. These drawings are not drawn to scale, and some details may be enlarged or omitted for clarity. The shapes of the various regions and layers shown in the drawings, and their relative sizes and positions, are illustrative and may vary in practice due to manufacturing tolerances or technical constraints. Those skilled in the art may design regions / layers with different shapes, sizes, and relative positions as needed. 【0018】 As shown in Figures 1, 2, and 3, Ca in the desulfurization slurry described herein 2+ A method for online control of the oxidation state of a slurry by concentration and pH involves controlling the Ca in the slurry. 2+ This includes monitoring of concentration and pH values, determination of the CaSO3 precipitation index pi, and online oxidation control. 【0019】 Ca in the desulfurization slurry according to this disclosure 2+ A method for online control of the oxidation state of a slurry by concentration and pH involves controlling the Ca in the slurry. 2+ Steps include obtaining the concentration and pH value, and calculating the excess oxidizing air coefficient (α) and the pH value of the slurry under the amount of oxidizing air: excess oxidizing air coefficient (α)-pH-SO3 2- Input into the concentration model, SO3 in desulfurization slurry 2- The real-time concentration of SO3 in the desulfurization slurry is obtained, and then the SO3 in the desulfurization slurry is obtained. 2- Real-time concentration and SO3 when CaSO3 precipitates 2- The steps involve calculating the CaSO3 precipitation index pi based on the critical concentration of CaSO3, and controlling the amount of oxidizing air based on the CaSO3 precipitation index pi to control the amount of Ca in the desulfurization slurry. 2+ The method includes the step of controlling the oxidation state of the slurry online by concentration and pH. 【0020】 In some embodiments, Ca in the slurry 2+ The concentration was measured in real time using a calcium ion meter, and the pH value of the slurry was measured in real time using a pH meter. 【0021】 In the process of determining the CaSO3 precipitation index pi, 1) the excess oxidizing air coefficient (α)-pH-SO3 under various amounts of oxidizing air 2- Establish a concentration model, and 2) SO3 when CaSO3 precipitates 2- Determine the critical concentration and calculate the CaSO3 precipitation index pi. 【0022】 The aforementioned excess oxidizing air coefficient α is the ratio of the amount of oxidizing air actually supplied by the absorption tower to the theoretical amount of oxidizing air required to completely oxidize the SO2 collected by the absorption tower, under conditions where the flue gas is considered capable of naturally oxidizing 10% SO2. JPEG0007875973000003.jpg2154 The calculation is performed by , where Q is the amount of oxidized air actually supplied by the absorption tower, and S is the amount of SO2 collected by the absorption tower. Both the Q and S values ​​are obtained as real-time data by the DCS system. 【0023】 The SO3 2- In the process of determining the concentration, first, chemical analysis by iodine titration is performed to determine the +4 valent sulfur substances H2SO3 and HSO3 in the slurry. - and SO3 2- The total concentration of H2SO3 is obtained, and then H2SO3 at various pH levels. - and SO3 2- SO3 2- If the concentration is calculated and the pH value of the desulfurization slurry is controlled between 4 and 6, the H2SO3 content can be ignored. 【0024】 Oxidation excess coefficient (α)-pH-SO3 under various oxidizing air amounts 2- The concentration model was obtained through testing, specifically, 1) By changing the load on the unit or adjusting the opening of the bypass valve while keeping the amount of oxidizing air constant, the SO2 processing rate of the absorption tower is adjusted. As the SO2 processing rate of the absorption tower changes, the excess oxidizing air coefficient α also changes accordingly. Chemical analysis by iodine titration was performed to determine the +4 valent sulfur substances H2SO3 and HSO3 under various SO2 processing rate conditions (steady state conditions). - and SO3 2- The total concentration is obtained, and further, the excess oxidation coefficient α under the amount of oxidizing air and the +4 valent sulfur substances H2SO3, HSO3 - and SO3 2- Obtaining the relationship with the total concentration, 2) Adjust the amount of oxidizing air and repeat step 1) so that the range of oxidizing air amounts includes the low, medium, and high SO2 processing amounts of the absorption tower, and the excess oxidizing air coefficient α and the +4 valent sulfur substances H2SO3, HSO3 under various oxidizing air amounts. - and SO3 2- Obtaining the relationship with the total concentration, 3) The excess oxidizing air coefficient α and the +4 valent sulfur substances H2SO3, HSO3 under various amounts of oxidizing air obtained in step 2). - and SO3 2- The relationship with the total concentration is fitted, and a fitting equation is obtained. 4) H2SO3, HSO3 - and SO3 2- The effect of pH on the concentration distribution relationship was introduced, and the excess oxidizing air coefficient (α)-pH-SO3 under various oxidizing air amounts was examined. 2- Establish a concentration model. 【0025】 SO3 when CaSO3 precipitates 2- In the process of determining the critical concentration, specifically, SO3 2- The critical concentration is Ca 2+ and SO3 2- Solubility product constant K sp From the formula 【0026】 Determined by JPEG0007875973000004.jpg1730, Ca 2+ The concentration is obtained in real time by a calcium ion meter. 【0027】 The aforementioned CaSO3 precipitation index pi is the SO3 in the slurry. 2- Real-time concentration and SO3 2- This is the ratio to the critical concentration, and SO3 in the desulfurization slurry. 2- The real-time concentration is the excess oxidative air coefficient (α)-pH-SO3 2- It is obtained by the model. 【0028】 In the aforementioned online oxidation control, the control logic is designed based on the CaSO3 precipitation index pi. When 0.8 ≤ pi ≤ 1, the system is in a state of good oxidation and maintains the amount of oxidizing air as is. When pi < 0.8, the system is in a state of peroxidation and the amount of oxidizing air is reduced. When pi > 1, the system is in a state of insufficient oxidation and the amount of oxidizing air is increased. 【0029】 The amount of oxidizing air can be adjusted by changing the number of oxidizing fans, the configuration of their combinations, or the frequency of the oxidizing fans. 【0030】 Ca in the desulfurization slurry described in the present invention 2+ When specifically implementing a method to control the oxidation state of a slurry online by concentration and pH, the Ca in the slurry 2+ Concentration, pH value, and excess oxidizing air coefficient (α)-pH-SO3 2- Using a concentration model, SO3 in desulfurization slurry 2- By determining the real-time concentration of [amount], calculating the CaSO3 precipitation index pi from this concentration, and finally controlling the amount of oxidizing air using this index, the oxidation state of the wet desulfurization slurry can be controlled in real time, thereby ensuring the quality of the gypsum, simplifying the process, providing accurate monitoring results, and making it highly practical. In this disclosure, terms such as "first," "second," etc., are for illustrative purposes only and should not be understood as indicating or implying relative importance. Also, in this disclosure, "plural" means two or more unless otherwise specified. 【0031】 A description of a process or method, whether in a flowchart or otherwise, may be understood to represent a module, fragment, or portion of code containing one or more executable instructions for implementing a particular logical function or step in a process. Furthermore, the scope of preferred embodiments of this disclosure includes other implementations, which, as those skilled in the art should understand, may involve functions being performed in an order other than those illustrated or discussed, such as substantially simultaneously or in reverse order, depending on the functions involved. 【0032】 In this specification, any reference to terms such as “one embodiment,” “several embodiments,” “example,” “specific example,” or “several examples” means that the specific features, structures, materials, or properties described with reference to that embodiment or example are included in at least one embodiment or example of this disclosure. In this specification, the general expressions of the above terms do not necessarily mean the same embodiment or example. Furthermore, the specific features, structures, materials, or properties described may be combined in an appropriate manner in any one or more embodiments or examples. 【0033】 While the above has provided a detailed description of the Disclosure using general descriptions and specific embodiments, it will be apparent to those skilled in the art that several modifications or improvements can be made based on the Disclosure. Accordingly, any such modifications or improvements made without departing from the spirit of the Disclosure will fall within the scope of the claims of the Disclosure.

Claims

[Claim 1] Ca in slurry ２＋ Steps to obtain concentration and pH values, The oxidation air excess coefficient (α) and the pH value of the slurry are input into the oxidation air excess coefficient (α)-pH-SO ３ ２－ concentration model to obtain the real-time concentration of SO in the desulfurization slurry. Next, based on the real-time concentration of SO in the desulfurization slurry and the critical concentration of SO when CaSO ３ ２－ precipitates, the step of calculating the CaSO ３ ２－ precipitation index pi is carried out, and ３ when SO ３ ２－ precipitates, based on the critical concentration of SO, the CaSO ３ precipitation index pi is calculated, and CaSO ３ The amount of oxidizing air is controlled based on the precipitation index pi, and Ca in the desulfurization slurry ２＋ The process includes a step of controlling the oxidation state of the slurry online by concentration and pH, and a desulfurization slurry containing Ca ２＋ A method for online control of the oxidation state of a slurry by concentration and pH, This method involves determining the excess oxidizing air coefficient (α) - pH - SO2 under various amounts of oxidizing air. ３ ２－ Steps to establish a concentration model, CaSO ３ SO when precipitated ３ ２－ The process further includes the step of determining the critical concentration of, The aforementioned excess oxidation coefficient (α) is calculated assuming the exhaust gas contains 10% SO2. ２ Under conditions where spontaneous oxidation is considered possible, the amount of oxidizing air actually supplied by the absorption tower and the amount of SO collected by the absorption tower ２ This is the ratio to the theoretical amount of oxidizing air required to completely oxidize it, i.e., [Math 1] The calculation is performed by the formula, where Q is the amount of oxidizing air actually supplied by the absorption tower, and S is the amount of SO2 collected by the absorption tower. ２ These are quantities, and the values ​​of Q and S are both obtained as real-time data by the DCS system. CaSO ３ SO when precipitated ３ ２－ The critical concentration of is Ca ２＋ and SO ３ ２－ Solubility product constant K ｓｐ From the formula [Math 2] Determined by, Oxidation excess coefficient (α) - pH - SO2 under various oxidizing air levels ３ ２－ In the process of establishing a concentration model, specifically, 1) By changing the load on the unit or adjusting the opening of the bypass valve while keeping the amount of oxidizing air constant, the SO2 absorption tower can be reduced. ２ Adjust the processing rate and the SO2 absorption tower ２ When the processing rate changes, the excess oxidizing air coefficient α also changes accordingly, and various SO2s can be identified through chemical analysis by iodine titration. ２ +4 valent sulfur substance H under processing volume conditions ２ SO ３ HSO ３ － and SO ３ ２－ The total concentration is obtained, and further, the excess oxidation coefficient α under the amount of oxidizing air and the +4 valent sulfur substance H are obtained. ２ SO ３ HSO ３ － and SO ３ ２－ Obtaining the relationship with the total concentration, 2) Adjust the amount of oxidizing air and repeat step 1) to adjust the absorption tower's low, medium, and high SO levels within the range of oxidizing air amounts. ２ The processing amount is included, and the excess oxidation air coefficient α and the +4 valent sulfur substance H under various oxidation air amounts are measured. ２ SO ３ HSO ３ － and SO ３ ２－ Obtaining the relationship with the total concentration, 3) The excess oxidizing air coefficient α and the +4 valent sulfur substance H under various amounts of oxidizing air obtained in step 2) ２ SO ３ HSO ３ － and SO ３ ２－ The relationship with the total concentration is fitted, and a fitting equation is obtained. 4) H ２ SO ３ HSO ３ － and SO ３ ２－ The effect of pH on the concentration distribution relationship is introduced into the fitting equation, and the excess oxidizing air coefficient (α) - pH - SO₂ under various oxidizing air amounts is obtained. ３ ２－ We established a concentration model, The aforementioned CaSO ３ The precipitation index pi is the SO2 in slurry. ３ ２－ Real-time concentration and SO ３ ２－ The ratio of Ca in the desulfurization slurry to the critical concentration. ２＋ A method for online control of the oxidation state of a slurry based on its concentration and pH. [Claim 2] Ca in slurry ２＋ The concentration was measured in real time using a calcium ion meter, and the pH value of the slurry was measured in real time using a pH meter, according to claim 1, the Ca in the desulfurization slurry ２＋ A method for online control of the oxidation state of a slurry based on its concentration and pH. [Claim 3] SO in slurry ３ ２－ In the process of determining the concentration, First, the total concentration of tetravalent sulfur substances H ２ SO ３ , HSO ３ － and SO ３ ２－ in the slurry is obtained by chemical analysis using the iodine titration method. Next, according to the dissociation equilibrium relationships of H ２ SO ３ , HSO ３ － and SO ３ ２－ at various pH values, the concentration of SO ３ ２－ in the slurry is calculated. When the pH value of the slurry is controlled between 4 and 6, the content of H ２ SO ３ can be ignored. A method for online controlling the oxidation state of the desulfurization slurry according to the Ca ２＋ concentration and pH in Claim 1.

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