A desulfurization slurry blind area closing degree determination method based on pH value feedback

Abstract

The present application relates to the technical field of industrial flue gas desulfurization treatment, and aims to provide a desulfurization slurry blind area closure degree determination method based on pH value callback. The method comprises the following steps: sampling from a limestone-gypsum wet desulfurization device, and dividing the sample into two original slurry; adding acid to one of the two original slurry to adjust the pH value to 5.0, and recording the time T1 used for adjusting the pH value to 5.5; adding strong alkali to the other original slurry to remove the blind area, and then adding acid to adjust the pH value to 5.0, and recording the time T0 used for adjusting the pH value to 5.5; calculating the desulfurization slurry blind area closure degree ω=(1-T0 / T1)×100%, and determining the degree of obstruction of limestone dissolution in the blind area slurry according to the numerical value. The method directly studies the limestone closure characteristics in the blind area slurry, and is more intuitive and more comparable compared with the indirect method; the method is simple and effective in operation, the strong alkali is used to remove the interference, the time change in the pH value callback interval is used to reflect the limestone dissolution rate, and the key influence of the blind area of the desulfurization slurry on the obstruction of limestone dissolution can be directly reflected.

Description

Technical Field

[0001] This invention relates to a method for determining the degree of closure of the blind zone of desulfurization slurry based on pH value adjustment, belonging to the field of industrial flue gas desulfurization technology. Background Technology

[0002] The limestone-gypsum wet desulfurization process for coal-fired flue gas is widely used in large coal-fired power generating units and steel enterprises. Its main advantages are mature technology, strong adaptability to coal type load, and potential for deep desulfurization. However, due to significant fluctuations in coal market prices, the quality of coal delivered to the plant often deviates considerably from the design specifications. This can lead to abnormal operating conditions in some desulfurization systems, where limestone in the slurry enters the reaction blind zone. When the desulfurization slurry enters the reaction blind zone, the dissolution reaction of the limestone (CaCO3) introduced into the system is hindered, and its activity decreases. Furthermore, increasing the slurry supply not only fails to raise the pH value quickly but can even cause a continuous decrease in the pH of the desulfurization slurry. This results in a decrease in the desulfurization efficiency of the production unit and, in severe cases, can lead to excessive SO2 emissions from the flue gas.

[0003] In current desulfurization processes, aluminum fluoride blinding is the main cause of abnormal blind zones in the desulfurization slurry. High dust or heavy metal content in the flue gas after electrostatic precipitator treatment can form stable compounds, such as AlF, within the absorber slurry. n (n is generally 2-4). This compound, after adhering to the surface of limestone particles, directly affects the dissolution and reaction of the limestone particles. Once aluminum fluoride blinding occurs, the limestone slurry supply will fail to regulate the pH value, at which point only a large amount of slurry can be replaced, which is time-consuming and laborious. Since there is no reliable evaluation basis for the replacement effect and the recovery of slurry activity in existing studies, it is common for untimely replacement to lead to the instantaneous value of SO2 concentration at the desulfurization outlet exceeding the standard, and for excessive replacement to lead to a significant decrease in the economic efficiency of the desulfurization system.

[0004] Current research lacks a direct and effective evaluation method for the sealing degree of blind zones in limestone wet desulfurization slurry. In practice, blind zones in desulfurization slurry are often handled entirely based on experience. Indirect methods for evaluating slurry blind zones (such as comparing the relationship between the desulfurization limestone slurry supply and the pH value of the slurry) suffer from poor accuracy and comparability due to differences in the operating conditions of different desulfurization systems. Therefore, this greatly limits the safety and economy of wet desulfurization systems. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a method for determining the degree of closure of the blind zone of desulfurization slurry based on pH value adjustment.

[0006] To solve the technical problem, the solution of the present invention is:

[0007] A method for determining the degree of closure of desulfurization slurry blind zone based on pH value adjustment is provided, including the following steps:

[0008] (1) Obtain desulfurization slurry samples from limestone-gypsum wet desulfurization unit, divide them into two equal portions, and use them as the original slurry;

[0009] (2) Under the conditions of stirring and real-time pH measurement, acid solution was added to one of the original slurries to adjust the pH value to the lower limit of the pullback interval, 5.0, and the timing was started; as the limestone in the slurry dissolved naturally, the pH value gradually increased, and when it reached the upper limit of the pullback interval, 5.5, the time taken for the pullback process was recorded as T1.

[0010] (3) Under the conditions of stirring and real-time pH measurement, a strong alkali was added to another original slurry and the pH was adjusted to above 10.0; then acid was added for neutralization to obtain the deblinded slurry;

[0011] Then, following the procedure in step (2), the slurry after blinding was measured, and the time taken for the same callback process was T0.

[0012] (4) Calculate the degree of sealing of the desulfurization slurry blind zone ω=(1-T0 / T1)×100%, and determine the degree of limestone dissolution inhibition in the blind zone slurry according to the following method:

[0013] (a) If the slurry blind zone closure value ω≥30%, it indicates that the slurry reaction in the limestone-gypsum wet desulfurization unit has entered the blind zone, and the limestone dissolution rate has decreased significantly.

[0014] (b) If the slurry blind zone closure value ω < 30%, it indicates that the slurry reaction blind zone in the limestone-gypsum wet desulfurization unit is not obvious and the limestone dissolution rate is normal.

[0015] As a preferred embodiment of the present invention, in steps (2) to (3), an online pH meter is used to measure the pH value in real time; the online pH meter has a resolution of 0.01 and a sensitivity of ±0.1.

[0016] As a preferred embodiment of the present invention, in steps (2) to (3), the stirring speed is controlled to be 250 r / min.

[0017] As a preferred embodiment of the present invention, in step (3), the amount of strong alkali used should be sufficient to adjust the pH value of the original slurry to above 10.0.

[0018] As a preferred embodiment of the present invention, in step (3), when adding acid for neutralization, the amount of acid added is controlled to be equal to the amount of strong alkali used in step (3) to prevent aluminum ions from re-hydrolyzing and encapsulating limestone, causing blindness again.

[0019] As a preferred embodiment of the present invention, the strong alkali is a NaOH solution with a concentration of 0.1 mol / L.

[0020] As a preferred embodiment of the present invention, the acid solution is a hydrochloric acid solution with a concentration of 0.1 mol / L.

[0021] Description of the invention principle:

[0022] In limestone wet desulfurization processes, AlF n The formation and stability of the complex are directly related to the pH value of the slurry. During normal desulfurization operation, the pH value is between 5.0 and 6.0, at which point the generated AlF... n The complex will coat the limestone, reducing its dissolution rate and causing the slurry reaction to enter a dead zone. This is because AlF... n All complexes will be destroyed. During the deblinding process, an equal amount of acid is added to neutralize the strong alkali, so the pH of the slurry sample will not be too low. At this time, Al will react as AlF₂. n Hydrolyzed complexes in the form of Al(OH)3 exist stably in the slurry and are not destroyed by strong acids. Therefore, the Al in the slurry will not hydrolyze and encapsulate the limestone again as it dissolves, thus restoring the activity of the limestone and completing the deblinding process.

[0023] The pH correction of slurry in the blind zone refers to the phenomenon where the pH value of a slurry decreases after adding a certain amount of hydrochloric acid to the slurry sample. However, as the limestone in the slurry dissolves naturally, the pH value gradually increases again. This invention refers to this process as pH correction.

[0024] After the desulfurization slurry enters the reaction blind zone, the limestone dissolution rate decreases significantly. The degree of decrease in the limestone dissolution rate in the blind zone slurry is the degree of blind zone closure of the desulfurization slurry as described in this invention. Further research revealed that by comparing the time it takes for the pH value of the slurry to adjust back before and after desulfurization, the difference in limestone dissolution rate can be determined, and this time can then be used to evaluate the degree of blind zone closure of the desulfurization slurry.

[0025] The method of the present invention can determine the degree of sealing of the desulfurization slurry blind zone in a timely manner, provide early warning of desulfurization slurry blind zone anomalies, and guide the efficient replacement of abnormal desulfurization slurry, thereby reducing the number of times the SO2 concentration at the unit outlet exceeds the standard and greatly improving the economic efficiency of handling desulfurization slurry blind zone anomalies.

[0026] Compared with the prior art, the present invention has the following advantages:

[0027] 1. This method directly studies the sealing characteristics of limestone in the slurry of the blind zone, which is more intuitive and comparable than the indirect method;

[0028] 2. This method is simple and effective to operate and can be completed by personnel with basic chemical instrument operation skills. It does not require extensive experience in desulfurization operation or complex logical judgment.

[0029] 3. This method uses strong alkali for deblinding, and the components such as F and CaCO3 in the slurry samples before and after deblinding are not affected. Therefore, this method can eliminate related interference.

[0030] 4. Using the pH value adjustment range within a certain time frame to reflect the limestone dissolution rate can directly reflect the key impact of the desulfurization slurry blind zone on the limestone dissolution rate. Attached Figure Description

[0031] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0032] The present invention will be further described below through specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0033] The #1 desulfurization blind zone slurry, #2 desulfurization blind zone slurry, and #3 desulfurization normal slurry in the various embodiments and comparative examples of this invention were all taken from the limestone-gypsum wet desulfurization unit for coal-fired flue gas at Zhejiang Energy Changxing Power Plant.

[0034] Example 1:

[0035] According to GB / T 5762-2012 "Chemical Analysis Methods for Limestone, Quicklime and Hydrated Lime for Building Materials", the CaCO3 content in the #1 desulfurization blind zone slurry was measured to be 20.45%.

[0036] Simultaneously, measure two 50 mL aliquots of the slurry sample, accurate to 0.1 mL, and place each in a 250 mL beaker. Add deionized water to bring the volume of both slurry samples to 250 mL. Set the magnetic stirring speed to 250 rpm at room temperature. -1 .

[0037] An online pH meter with a resolution of 0.01 and a sensitivity of ±0.1 was inserted into one of the slurry samples to display the current pH value of the slurry sample in real time. 5 mL of 0.1 mol / L hydrochloric acid was added to the sample using a burette. Timing started when the pH value of the slurry reached 5.0, and the timing was 13.25 seconds when the pH value of the slurry returned to 5.5.

[0038] After cleaning the online pH meter, insert it into another slurry sample to display the current pH value of the slurry sample in real time. Add 5 mL of 0.1 mol / L NaOH solution to the sample using a burette to adjust the pH value to 10.3, stabilize for 5 minutes, then add 5 mL of 0.1 mol / L hydrochloric acid to the sample for neutralization. Continue adding 5 mL of 0.1 mol / L hydrochloric acid to the sample using a burette, and start timing when the slurry pH value reaches 5.0. Start timing for 6 seconds when the slurry pH value returns to 5.5.

[0039] With the upper limit of the pH value adjustment range set at 5.5, the slurry sealing degree of the #1 desulfurization blind zone is calculated to be 54.72%.

[0040] Example 2:

[0041] According to GB / T 5762-2012 "Chemical Analysis Methods for Limestone, Quicklime and Hydrated Lime for Building Materials", the CaCO3 content in the #2 desulfurization blind zone slurry was measured to be 9.28%.

[0042] Simultaneously, measure two 50 mL aliquots of the slurry sample, accurate to 0.1 mL, and place each in a 250 mL beaker. Add deionized water to bring the volume of both slurry samples to 250 mL. Set the magnetic stirring speed to 250 rpm at room temperature. -1 An online pH meter with a resolution of 0.01 and a sensitivity of ±0.1 was inserted into one of the slurry samples to display the current pH value of the slurry sample in real time. 5 mL of 0.1 mol / L hydrochloric acid was added to the sample using a burette. Timing began when the slurry pH reached 5.0, and was continued for 46.5 seconds when the pH returned to 5.5, and for 145 seconds when the pH returned to 6.0.

[0043] After cleaning the online pH meter, another slurry sample was inserted to display the current pH value of the slurry sample in real time. 5 mL of 0.1 mol / L NaOH solution was added to the sample using a burette to adjust the pH to 10.5, and the solution was allowed to stabilize for 5 minutes. Then, 5 mL of 0.1 mol / L hydrochloric acid was added to the sample using a burette for neutralization. Another 5 mL of 0.1 mol / L hydrochloric acid was added to the sample using a burette. Timing began when the slurry pH reached 5.0, and 28.5 seconds were recorded when the pH returned to 5.5.

[0044] When the upper limit of the pH value adjustment range is set to 5.5, the slurry sealing degree of the #2 desulfurization blind zone is calculated to be 38.71%.

[0045] Comparative Example 1:

[0046] According to GB / T 5762-2012 "Chemical Analysis Methods for Limestone, Quicklime and Hydrated Lime for Building Materials", the CaCO3 content in the #3 desulfurization normal slurry was measured to be 10%.

[0047] Simultaneously, measure two 50 mL aliquots of the slurry sample, accurate to 0.1 mL, and place each in a 250 mL beaker. Add deionized water to bring the volume of both slurry samples to 250 mL. Set the magnetic stirring speed to 250 rpm at room temperature. -1An online pH meter with a resolution of 0.01 and a sensitivity of ±0.1 was inserted into one of the slurry samples to display the current pH value of the slurry sample in real time. 5 mL of 0.1 mol / L hydrochloric acid was added to the sample using a burette. Timing began when the slurry pH reached 5.0, and continued for 19 seconds when the pH returned to 5.5.

[0048] After cleaning the online pH meter, another slurry sample was inserted to display the current pH value of the slurry sample in real time. 5 mL of 0.1 mol / L NaOH solution was added to the sample using a burette to adjust the pH to 11.0, and the solution was allowed to stabilize for 5 minutes. Then, 5 mL of 0.1 mol / L hydrochloric acid was added to the sample using a burette for neutralization. Another 5 mL of 0.1 mol / L hydrochloric acid was added to the sample using a burette, and timing began when the slurry pH reached 5.0. Timing was continued for 15 seconds when the slurry pH returned to 5.5.

[0049] When the upper limit of the pH value adjustment range is set to 5.5, the calculated sealing degree of the normal slurry for desulfurization #3 is 21.05%.

[0050] Results and Analytical Conclusions

[0051] Table 1 Test results of the examples and comparative examples

[0052]

[0053] As can be seen from Table 1:

[0054] In Examples 1 and 2, the pH value recovery time T1 of the slurry in the blind zone was 5.5, which was greater than the recovery time T0 of the slurry after deblinding in Examples 1 and 2, respectively. Based on this, the sealing degrees ω1 and ω2 of the slurry in blind zones #1 and #2 were calculated to be 54.72% and 38.71%, respectively. According to the judgment principle of the present invention, when ω ≥ 30%, the limestone dissolution reaction of the slurry has entered the blind zone. In contrast, in Comparative Example 1, the recovery time T0 of the normal slurry after deblinding differed from the recovery time T1 before deblinding by only 4 seconds, and the sealing degree ω was 21.05%. According to the judgment principle of the present invention, ω < 30%, at which point the limestone dissolution reaction of the slurry was normal. This shows that the method of using strong alkali to deblind the slurry and judging the sealing degree based on pH value recovery is effective.

[0055] Example of application method of the present invention:

[0056] After determining the degree of sealing of the desulfurization slurry blind zone, the following applications can be achieved based on the determination results:

[0057] 1. To address the issue of slurry entering the reaction blind zone and not being dealt with in a timely manner, resulting in the instantaneous SO2 concentration at the desulfurization outlet exceeding the standard.

[0058] This method can be used for early warning of slurry blind zones. By periodically and manually manipulating the slurry using this method, the degree of slurry closure (ω) is obtained. Combined with the method's judgment principle, a ω ≥ 30% indicates that the slurry has entered the reaction blind zone. Alternatively, by using automated sample analysis, real-time online monitoring and judgment can be achieved to determine whether the desulfurization slurry has entered the reaction blind zone. Early identification of slurry blind zones helps to accurately determine the cause of abnormal parameters, allowing for timely intervention and preventing the abnormality from escalating.

[0059] 2. To address the problem of excessive replacement leading to a significant decrease in the economic efficiency of the desulfurization system.

[0060] This method can also be used to guide economical operation during the fault recovery phase. During the disposal of slurry blind zones, large-scale slurry replacement results in significant energy consumption and difficult-to-treat desulfurization wastewater, greatly impacting the economical operation of the unit's desulfurization process. Early determination of whether the slurry has left the blind zone helps to promptly restore the unit's normal operating mode and improves the economic efficiency of the disposal process.

Claims

1. A method for determining the degree of sealing of desulfurization slurry blind zone based on pH value adjustment, characterized in that: Includes the following steps: (1) Obtain desulfurization slurry samples from limestone-gypsum wet desulfurization unit, divide them into two equal portions, and use them as the original slurry; (2) Under the conditions of stirring and real-time pH measurement, acid solution was added to one of the original slurries to adjust the pH value to the lower limit of the pullback interval, 5.0, and the timing was started; as the limestone in the slurry dissolved naturally, the pH value gradually increased, and when it reached the upper limit of the pullback interval, 5.5, the time taken for the pullback process was recorded as T1. (3) Under the conditions of stirring and real-time pH measurement, add strong alkali to another original slurry and adjust the pH value to above 10.0; then add hydrochloric acid solution for neutralization to obtain the deblinded slurry; control the amount of hydrochloric acid and strong alkali to be equal to prevent aluminum ions from re-hydrolyzing and encapsulating limestone to cause blindness again. Then, following the procedure in step (2), the slurry after blinding was measured, and the time taken for the same callback process was T0. (4) Calculate the degree of sealing of the desulfurization slurry blind zone ω=(1-T0 / T1)×100%, and determine the degree of limestone dissolution obstruction in the blind zone slurry according to the following method: (a) If the slurry blind zone closure value ω≥30%, it indicates that the slurry reaction in the limestone-gypsum wet desulfurization unit has entered the blind zone, and the limestone dissolution rate has decreased significantly. (b) If the slurry blind zone closure value ω < 30%, it indicates that the slurry reaction blind zone in the limestone-gypsum wet desulfurization unit is not obvious and the limestone dissolution rate is normal.

2. The method according to claim 1, characterized in that, In steps (2) to (3), an online pH meter is used to measure the pH value in real time; the online pH meter has a resolution of 0.01 and a sensitivity of ±0.

1.

3. The method according to claim 1, characterized in that, In steps (2) to (3), the stirring speed is controlled at 250 r / min.

4. The method according to claim 1, characterized in that, The strong base is a 0.1 mol / L NaOH solution.

5. The method according to claim 1, characterized in that, The concentration of the hydrochloric acid solution is 0.1 mol / L.

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