A method for online monitoring of the activity of desulfurization slurry and controlling the circulation volume

Abstract

The present application discloses a method for online monitoring of the activity of desulfurization slurry and controlling the circulation volume in the technical field of limestone-gypsum wet desulfurization. The original flue gas SO2 and flue gas volume data are collected by the original flue gas CEMS monitoring instrument at the desulfurization inlet flue, and the clean flue gas SO2 and flue gas volume data are collected by the clean flue gas CEMS monitoring instrument at the desulfurization outlet flue. The slurry circulation pump transports the slurry to the spray layer, and the DCS system collects the data of the original flue gas CEMS monitoring instrument and the clean flue gas CEMS monitoring instrument for activity calculation, controls the start and stop of the slurry circulation pump or adjusts its power; a method for online characterizing and monitoring the activity of the slurry and predicting and adjusting the slurry circulation volume based on the slurry activity provides guiding significance for the refined control and energy conservation and consumption reduction of desulfurization.

Description

Technical Field

[0001] This application relates to the technical field of limestone-gypsum wet flue gas desulfurization, and in particular to a method for online monitoring of the activity of desulfurization slurry and controlling the circulation volume. Background Art

[0002] Limestone-gypsum wet flue gas desulfurization technology is commonly used in desulfurization systems of coal-fired power plants to control pollutants in flue gas.

[0003] In order to respond to the requirements of environmental protection policies, domestic coal-fired power plants have generally carried out efficiency improvement transformations on desulfurization systems, controlling pollutant emission levels at a relatively low level, with SO2 controlled below 35 mg / m 3 Below, coal-fired power plants have higher requirements for the slurry quality and equipment operation control of desulfurization systems. While the desulfurization efficiency is improved, there are also higher requirements for the activity quality of the slurry. A decrease in slurry activity will directly cause a decrease in the absorption capacity of the slurry for SO2, and then lead to a decrease in desulfurization efficiency. Slurry activity is an important indicator for judging slurry reactivity. Currently, only the activity of limestone slurry can be used to judge slurry activity. However, limestone only accounts for a small part in the absorption tower slurry, usually less than 5%, and cannot reflect the overall activity state of the slurry under operating conditions. In addition, the measurement of limestone activity relies on offline laboratory analysis, making it difficult to timely guide the regulation of desulfurization operation.

[0004] Currently, there is no conclusive definition for the activity of desulfurization absorption tower slurry, and there are few reports on the measurement methods for slurry activity. The standard DL / T 943-2015 "Determination of the Reaction Rate of Limestone for Wet Flue Gas Desulfurization" defines the activity of limestone as the reaction time when 80% of the carbonate in limestone powder reacts with acid at a pH of 5.5. To a certain extent, slurry activity can refer to the standard of limestone. There are many factors affecting slurry activity, and ultimately it affects the absorption degree of the slurry for SO2. By correlating the two and referring to the limestone activity, the activity of the slurry can be defined and measured according to the absorption capacity of the slurry for SO2. However, under the operating conditions of the unit, there is a large delay and lag from sampling to laboratory testing, and the risk brought by the deterioration of slurry quality cannot be timely prevented.

[0005] At the same time, the slurry circulation volume of the desulfurization system is mainly adjusted according to the raw flue gas volume and SO2 concentration, mostly only considering that the environmental protection indicators meet the emission requirements, and ignoring the problems of energy consumption and operation caused by excessive circulation volume.

[0006] The prior art (patent application number 202111103001.5) characterized the activity of the slurry and provided a method for measuring the activity of gypsum slurry, that is, by introducing a standard SO2 gas into the slurry, and characterizing the activity of the slurry with the SO2 concentration in the tail gas, the pH value of the gypsum slurry before and after absorbing SO2, and the difference in sulfite content, so as to realize the characterization of the quality of gypsum slurry with digital indicators. However, the related technology has a complex structure, poor operability, requires new equipment, and the realization of continuous monitoring cannot make full use of the existing facilities. At the same time, the relationship between slurry activity and the operation regulation of slurry circulation volume has not been established, which cannot meet the requirements of refined desulfurization control.

[0007] In view of the above related technologies, the present application provides a method for on-line monitoring the activity of desulfurization slurry and controlling the circulation volume. Summary of the Invention

[0008] The purpose of the present application is to overcome the above problems existing in the prior art, and provide a method for on-line characterizing and monitoring the activity of slurry by using the existing desulfurization system facilities, and predicting and adjusting the slurry circulation volume according to the slurry activity, which provides guiding significance for the refined control and energy conservation and consumption reduction of desulfurization.

[0009] The present application provides a method for on-line monitoring the activity of desulfurization slurry and controlling the circulation volume, and adopts the following technical solutions: including the following specific steps:

[0010] It is carried out in the absorber body and the corresponding system. The data of the SO2 and flue gas volume of the raw flue gas are collected by the raw flue gas CEMS monitoring instrument at the desulfurization inlet flue, and the data of the SO2 and flue gas volume of the clean flue gas are collected by the clean flue gas CEMS monitoring instrument at the desulfurization outlet flue. The slurry circulation pump conveys the slurry to the spray layer, and the DCS system collects the data of the raw flue gas CEMS monitoring instrument and the clean flue gas CEMS monitoring instrument for activity calculation, and controls the start and stop of the slurry circulation pump or adjusts its power;

[0011] The circulation volume before starting the slurry circulation pump is the actual minimum circulation volume that meets the requirements, and the circulation volume after starting the slurry circulation pump is the maximum circulation volume of the slurry under this activity. The theoretical circulation volume under the actual working conditions is calculated from the SO2 and flue gas volume of the raw flue gas. The theoretical circulation volume L is calculated by the following formula:

[0012]

[0013] Wherein, the theoretical circulation volume L under the actual working conditions, the volume of the raw flue gas V, the SO2 concentration is C, the SO2 concentration of the raw flue gas under the design working conditions is C0, the flue gas volume V0, and the circulation volume L0;

[0014] The activity of the slurry is defined as follows: under the condition that the load of the unit is 50% to 100% of the rated load and the SO2 concentration in the raw flue gas is lower than or equal to the design value, when the output of the slurry circulation pump increases by a certain degree of 5% - 25% from 40% - 80% of the corresponding condition, the SO2 concentration detected by the CEMS monitoring instrument in the desulfurized clean flue gas decreases from the original controlled maximum concentration of 20 - 35 mg / m 3 to a concentration ≤ 10 mg / m 3 The required time is represented by 1 / t;

[0015] Select the activity of a normally operating slurry as the benchmark, corresponding to a minimum benchmark circulation volume and a maximum benchmark circulation volume respectively. Through data collection by the DCS system, draw the curves of slurry activity with respect to the minimum and maximum benchmark circulation volumes, and based on this, the adjustment range of the slurry circulation volume under different slurry activity conditions can be determined.

[0016] Optionally, there is more than one slurry circulation pump, which can be fixed - frequency or variable - frequency. For fixed - frequency, the power is adjusted by the number of slurry circulation pumps started and stopped; for variable - frequency, the power of each slurry circulation pump can be adjusted.

[0017] Optionally, define the ratio of the minimum circulation volume to the theoretical circulation volume as the minimum circulation ratio, and the ratio of the maximum circulation volume to the theoretical circulation volume as the maximum circulation ratio. The actual operating circulation ratio should be controlled between the minimum circulation ratio and the maximum circulation ratio. Exceeding the maximum circulation ratio will increase energy consumption and resistance, and cause blockage of the spray layer during long - term operation. Falling below the minimum circulation ratio will result in problems such as exceeding the environmental protection emission standard.

[0018] Optionally, when the activity changes, the corresponding minimum circulation volume and maximum circulation volume also change, the minimum circulation ratio and the maximum circulation ratio also change, and the adjustment of the circulation volume also changes accordingly, but the theoretical circulation volume L remains unchanged.

[0019] Optionally, the time 1 / t does not include the response time of the slurry circulation pump and the data acquisition time. During the test, ensure that the SO2 concentrations and loads of the raw flue gas and the clean flue gas are relatively stable, the slurry circulation pump operates normally, and there is no obvious damage to the spray layer.

[0020] Optionally, the absorber body is a wet desulfurization absorber with a spray layer, and the absorber body is a spray tower for limestone - gypsum wet desulfurization or a liquid column tower for limestone - gypsum wet desulfurization or a double - alkali method desulfurization absorber.

[0021] In summary, the present application includes at least one of the following beneficial effects:

[0022] 1. It can on - line monitor the activity quality of the slurry and give the adjustment range of the circulation volume.

[0023] 2. Utilize the existing process system of the desulfurization system without adding new equipment and systems, with strong economic efficiency and reliability.

[0024] 3. The measurement of the slurry activity varies with the start-stop and power changes of different pumps. However, under the same slurry activity, the smaller the measured activity when increasing the same power, the smaller the pump output. Based on this, the output of several pumps can be judged.

[0025] 4. Compared with the original desulfurization, on the one hand, it can avoid unnecessary power loss of the slurry circulation pump to save energy and reduce consumption. On the other hand, it can automatically start the pump or increase the pump power through activity monitoring, thus preventing the SO2 index from exceeding the standard.

[0026] 5. The change of the slurry activity is slow and almost remains constant in a short time. Under the conditions of the change of the SO2 concentration at the desulfurization inlet and the load command, the required circulation volume can be predicted and adjusted to prevent the SO2 concentration from exceeding the standard. Description of the Drawings

[0027] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0028] Figure 1 It is a schematic structural diagram of the present application.

[0029] Description of the reference numerals in the drawings: 1. Absorption tower body; 2. Desulfurization inlet flue; 3. DCS system; 4. Original flue gas CEMS monitoring instrument; 5. Clean flue gas CEMS monitoring instrument; 6. Desulfurization outlet flue; 7. Spray layer; 8. Slurry circulation pump. Detailed Embodiments

[0030] The following will further describe the present application in detail Figure 1 in conjunction with the attached

[0031] Referring to Figure 1 , the present application discloses a method for online monitoring the activity of desulfurization slurry and controlling the circulation volume, including the following specific steps:

[0032] The activity of the slurry, under the condition of online monitoring, can be defined as under a certain load condition (50% to 100% load rate) and the original flue gas SO2 concentration (lower than or equal to the design value), when the output of the slurry circulation pump increases by a certain degree (5% - 25%) from the corresponding condition (40% - 80%), the SO2 concentration detected by the clean flue gas CEMS monitoring instrument 5 decreases from the original controlled maximum concentration (20 - 35mg / m 3 ) to a lower concentration (≤10mg / m3 ) The required time is represented by 1 / t. This time does not include the response time of the slurry circulation pump 8 and the data acquisition time. During the test, it is necessary to ensure that the SO2 concentration and load of the original flue gas and the clean flue gas are relatively stable, the slurry circulation pump 8 operates normally, and there is no obvious damage to the spray layer 7, so as to ensure that the slurry activity data can be more accurate. The test process is carried out in the absorber body 1 and the corresponding system. The original flue gas SO2 and flue gas volume data are collected by the original flue gas CEMS monitoring instrument 4 at the desulfurization inlet flue 2, and the clean flue gas SO2 and flue gas volume data are collected by the clean flue gas CEMS monitoring instrument 5 at the desulfurization outlet flue 6. The slurry circulation pump 8 transports the slurry to the spray layer 7, and its start-stop and power adjustment are controlled by the DCS system 3. The number of slurry circulation pumps 8 is not one, and in Figure 1 it represents all pumps.

[0033] Under the active test conditions, the circulation volume before starting the slurry circulation pump 8 is the actual minimum circulation volume that meets the requirements, and the circulation volume after starting the slurry circulation pump 8 is the maximum circulation volume of the slurry at this activity. The theoretical circulation volume under the actual working conditions is calculated from the original flue gas volume and SO2. Define the ratio of the minimum circulation volume to the theoretical circulation volume as the minimum circulation ratio, and the ratio of the maximum circulation volume to the theoretical circulation volume as the maximum circulation ratio. The actual operation should be between the minimum circulation ratios. Exceeding the maximum circulation ratio will increase energy consumption and resistance, and long-term operation will also cause blockage of the spray layer 7. Below the minimum circulation ratio, there will be problems with exceeding environmental protection emissions. The theoretical circulation volume L under the actual working conditions, the original flue gas volume V, the SO2 concentration C, the original flue gas SO2 concentration C0, the flue gas volume V0, the circulation volume L0, and the theoretical circulation volume L are calculated by the following formula:

[0034]

[0035] When the activity changes, the corresponding minimum and maximum circulation volumes also change, but the theoretical circulation volume L remains unchanged, and the minimum and maximum circulation ratios also change, and the circulation volume adjustment also changes accordingly. Select a normally operating slurry activity as the benchmark, corresponding to a minimum benchmark circulation volume and a maximum benchmark circulation volume respectively. Through the data collection of the DCS system 3, make a curve of the slurry activity with respect to the minimum and maximum benchmark circulation volumes, and based on this, the adjustment range of the slurry circulation volume under different slurry activity conditions can be determined. The DCS system 3 collects the data of the original flue gas CEMS monitoring instrument 4 and the clean flue gas CEMS monitoring instrument 5 for activity calculation, and controls the start-stop of the slurry circulation pump 8 or adjusts its power.

[0036] Example 1

[0037] For a 300WM unit of a coal-fired power plant, the desulfurization system is a spray tower, with 5 identical fixed-frequency slurry circulation pumps 8, and the designed original flue gas SO2 concentration C a , and the designed flue gas volume is Va , the SO2 concentration in the clean flue gas is controlled at ≤ 35 mg / m³ in accordance with environmental protection requirements 3 . The unit operates stably for a long time under the condition of half load of 150 MW, and the SO2 concentration in the original flue gas of desulfurization is stable at 0.8C a . When two slurry circulation pumps are started for 8 hours, the SO2 concentration in the desulfurized clean flue gas can be stabilized at 35 mg / m³ 3 . According to the actual conditions, the slurry activity is defined as the time required for the SO2 concentration detected by the CEMS instrument in the desulfurized clean flue gas to decrease from 35 mg / m³ to 10 mg / m³ when the number of slurry circulation pumps increases from 2 to 3 (the circulation volume increases by 20%) under the condition of 150 MW. It is expressed by 1 / t 3 under the condition of 150 MW. The corresponding minimum circulation volume is the volume of two pumps, and the maximum circulation volume is the circulation volume of three pumps. Through the data accumulation of the DCS system 3, the relationship curve between the slurry activity 1 / t and the circulation volume is established. Since the adjustment of the circulation volume is related to the start and stop of the pumps at this time, the established curve is discontinuous. When the slurry activity increases, starting two pumps with the minimum circulation volume under the original slurry activity can meet the requirements; when the slurry activity decreases, starting two pumps with the minimum circulation volume under the original slurry activity cannot meet the requirements. According to the established corresponding relationship, three or more pumps are required to meet the requirements 3 a

[0038] Example 2

[0039] For a 660 WM unit of a coal-fired power plant, the desulfurization system is a spray tower with 5 identical variable-frequency slurry circulation pumps, whose power can be adjusted. The designed SO2 concentration C in the original flue gas b , and the designed flue gas volume is V b . According to the operation requirements, the SO2 concentration in the clean flue gas is controlled at ≤ 30 mg / m³ 3 . The unit operates stably for a long time under the condition of 600 MW load, and the SO2 concentration in the original flue gas of desulfurization is stable at 0.7C b . When four slurry circulation pumps are started, with three fully started and one half started, the SO2 concentration in the desulfurized clean flue gas can be stabilized at 30 mg / m³ 3 . According to the actual conditions, the slurry activity is defined as the time required for the SO2 concentration detected by the CEMS instrument in the desulfurized clean flue gas to decrease from 30 mg / m³ to 10 mg / m³ when the power of the slurry circulation pumps increases from 70% to 80% (all four pumps are fully started) under the condition of 600 MW. It is expressed by 1 / t 3 3 b . When the activity remains unchanged and the load decreases to 480 MW, with little change in the SO2 concentration in the original flue gas, the total power of the circulation pumps can be reduced to 0.8 times the original. Under variable-frequency conditions, through the data accumulation of the DCS system 3, the established relationship curve between the slurry activity 1 / t and the circulation volume is continuous​​​​

[0040] The above are all preferred embodiments of the present application, and do not limit the protection scope of the present application accordingly. Therefore, any equivalent changes made according to the structure, shape, and principle of the present application shall be covered within the protection scope of the present application.

Claims

1. An online monitoring method for the activity of desulfurization slurry and controlling the circulation volume, characterized in that: It includes the following specific steps: It is carried out in the absorption tower body (1) and the corresponding system. The original flue gas SO2 and flue gas volume data are collected by the original flue gas CEMS monitoring instrument (4) at the desulfurization inlet flue (2), and the clean flue gas SO2 and flue gas volume data are collected by the clean flue gas CEMS monitoring instrument (5) at the desulfurization outlet flue (6). The slurry circulation pump (8) transports the slurry to the spray layer (7). The DCS system (3) collects the data of the original flue gas CEMS monitoring instrument (4) and the clean flue gas CEMS monitoring instrument (5) for activity calculation, and controls the start-stop or power adjustment of the slurry circulation pump (8); The circulation volume before starting the slurry circulation pump (8) is the actual minimum circulation volume that meets the requirements, and the circulation volume after starting the slurry circulation pump (8) is the maximum circulation volume of the slurry under this activity. The theoretical circulation volume under the actual working conditions is calculated from the original flue gas SO2 and flue gas volume. The theoretical circulation volume L is calculated by the following formula: Among them, the theoretical circulation volume L under the actual working conditions, the original flue gas volume V, the SO2 concentration is C, the original flue gas SO2 concentration under the design working conditions is C0, the flue gas volume V0, and the circulation volume L0; The activity of the slurry is defined as follows: under the condition that the load of the unit is 50% to 100% of the rated load and the SO2 concentration in the original flue gas is lower than or equal to the design value, when the output of the slurry circulation pump (8) increases by a certain degree of 5% - 25% from 40% - 80% under the corresponding condition, the SO2 concentration detected by the desulfurized clean flue gas CEMS monitoring instrument (5) decreases from the original controlled maximum concentration of 20 - 35 mg / m 3 to a concentration of ≤ 10 mg / m 3 The required time is expressed as 1 / t; Select the activity of a normally operating slurry as the benchmark, which respectively corresponds to a minimum benchmark circulation volume and a maximum benchmark circulation volume. Through the data collection of the DCS system (3), a curve of slurry activity versus the minimum and maximum benchmark circulation volumes is made, and based on this, the adjustment range of the slurry circulation volume under different slurry activity conditions can be determined; The slurry circulation pump (8) is more than one, and it is fixed-frequency or variable-frequency. The fixed-frequency adjusts the power by the number of starts and stops of the slurry circulation pump (8), and the variable-frequency can adjust the power of each slurry circulation pump (8).

2. The method for online monitoring of the activity of desulfurization slurry and controlling the circulation volume according to claim 1, characterized in that: Define the ratio of the minimum circulation volume to the theoretical circulation volume as the minimum circulation ratio, and the ratio of the maximum circulation volume to the theoretical circulation volume as the maximum circulation ratio. The actual operating circulation ratio should be controlled between the minimum circulation ratio and the maximum circulation ratio. Exceeding the maximum circulation ratio will increase energy consumption and resistance, and will also cause blockage of the spray layer (7) during long-term operation. Being lower than the minimum circulation ratio will result in environmental protection emission exceeding the standard problem.

3. The method for online monitoring the activity of desulfurization slurry and controlling the circulation volume according to claim 2, wherein: When the activity changes, the corresponding minimum circulation volume and maximum circulation volume also change, the minimum circulation ratio and the maximum circulation ratio also change, and the circulation volume adjustment also changes accordingly, but the theoretical circulation volume L remains unchanged.

4. The method for online monitoring of the activity of desulfurization slurry and controlling the circulation volume according to claim 1, characterized in that: The time of 1 / t does not include the response time of the slurry circulation pump (8) and the data acquisition time. During the test period, ensure that the SO2 concentration and load of the original flue gas and the clean flue gas are relatively stable, the slurry circulation pump (8) operates normally, and the spray layer (7) has no obvious damage.

5. The method for online monitoring of the activity of desulfurization slurry and controlling the circulation volume according to claim 1, wherein: The absorption tower body (1) is a wet desulfurization absorption tower with a spray layer (7). The absorption tower body (1) is a spray tower for limestone-gypsum wet desulfurization or a liquid column tower for limestone-gypsum wet desulfurization or a double-alkali method desulfurization absorption tower.

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