A method for measuring and controlling the virtual liquid level in a wet desulfurization system
By dynamically calculating the average density of the slurry and using PID control, the problem of inaccurate measurement of the false liquid level in the absorption tower is solved, achieving accurate calculation and automatic control of the false liquid level, avoiding overflow and increased energy consumption, and protecting the equipment.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- ZHEJIANG TIANDI ENVIRONMENTAL PROTECTION TECH CO LTD
- Filing Date
- 2026-03-31
- Publication Date
- 2026-06-30
AI Technical Summary
Existing technology cannot accurately measure the false liquid level in the absorber slurry, resulting in delayed alarms in the DCS system, high risk of overflow, and the foam layer hinders flue gas flow, increasing energy consumption and corroding induced draft fan components.
By acquiring real-time data and dynamically calculating the average density of the slurry, and combining the principles of hydrostatics to calculate the virtual liquid level, automatic interlocking control is achieved using PID control theory. Alarm thresholds and dosing logic are set to eliminate the foam layer.
Accurately measure the virtual liquid level to prevent overflow, reduce energy consumption, protect equipment, and improve the system's ability to cope with abnormal foaming.
Smart Images
Figure CN122308479A_ABST
Abstract
Description
Technical Field
[0001] This patent relates to a virtual liquid level measurement and control method for a wet desulfurization system, specifically belonging to the technical field of automatic liquid level control technology in wet desulfurization processes. Background Technology
[0002] Limestone-gypsum wet desulfurization technology is currently the most widely used flue gas desulfurization technology in coal-fired power plants. During the operation of a limestone-gypsum wet desulfurization system, the formation of a foam layer is unavoidable. When the generation and bursting of foam are out of balance, and the bursting rate is much lower than the generation rate, the foam height in the slurry rises rapidly, the foam layer thickens continuously, forming a "virtual level" significantly higher than the actual slurry level, and even overflow may occur. Abnormal foaming of the slurry is the result of multiple factors, including flue gas composition, insufficient oxidation air volume, process water quality, and the composition of limestone powder.
[0003] Abnormal foaming of the absorber slurry can also lead to errors in the DCS system's judgment of the absorber slurry level. Traditional absorber level measurement commonly uses the differential pressure transmitter method, which is based on the hydrostatic formula ΔP = ρgh. It calculates the level height (h) by measuring the pressure difference (ΔP) between two points with a fixed height difference (Δh). However, this method has a fundamental flaw: the slurry density (ρ) used in the calculation is usually a constant value set based on clear or ideal slurry. In reality, due to the presence of foam and dissolved oxidizing air, the average density of the slurry will be significantly lower than this set value. This results in a severely underestimated level calculated by traditional methods, completely failing to reflect the true height of the illusory level including the foam layer. Therefore, the illusory level height including the foam layer is often ignored, leading to incorrect alarm judgments by the DCS system. When the error between the illusory level and the slurry level without the foam layer is too large, foamy slurry overflow may even occur.
[0004] Furthermore, an excessively large foam layer inside the absorption tower can obstruct the flow of flue gas into the flue. The upward path of the gas is blocked by the foam layer, resulting in poor gas flow. The induced draft fan requires greater power to maintain normal airflow, which increases energy consumption and may lead to overloading of the fan. Additionally, the flue gas may carry acidic and alkaline absorbent liquids into the induced draft fan, causing wear and corrosion to the fan blades and other metal components.
[0005] Therefore, there is an urgent need to establish a virtual liquid level measurement and control method for wet desulfurization systems, so as to more accurately calculate the virtual liquid level of the absorber slurry and implement control measures in a timely manner, providing a scientific basis for the design and safety control of similar projects. Summary of the Invention
[0006] To address the problem that existing differential pressure transmitter methods cannot accurately measure the illusory liquid level of the foam-containing slurry in the absorber tower, leading to delayed early warning and high risk of overflow, this patent provides a method for measuring and controlling the illusory liquid level in a wet desulfurization system. This method aims to achieve accurate calculation of the "illusory liquid level" by dynamically back-calculating the actual average density of the slurry, and to construct an over-limit alarm and automatic interlock control logic based on this, fundamentally improving the desulfurization system's ability to cope with abnormal foaming conditions. The core of this invention's technical solution includes the following innovations: (1) introducing the average density of the absorber tower slurry to back-calculate the illusory liquid level of the absorber tower slurry; (2) adding a visual display and alarm for the illusory liquid level.
[0007] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a method for measuring and controlling the virtual liquid level in a wet desulfurization system, used to calculate and control the actual liquid level of the absorber slurry after foaming in the wet desulfurization process, including the following steps: S1: Real-time data acquisition and processing: Real-time acquisition of pressure values from at least two pressure measurement points installed at different heights on the side wall of the absorption tower; the pressure value output from the pressure measurement point located at the bottom is recorded as the bottom pressure value. The pressure value output from a pressure measuring point located at the top is recorded as the high-level pressure value. Simultaneously, the pressure value at the flue gas inlet of the absorption tower is acquired in real time and recorded as the flue gas inlet pressure. ; S2: Dynamic average density back calculation: Based on the principle of hydrostatics, according to the bottom pressure value. High pressure value and the known fixed vertical distance between the two pressure measurement points Dynamically calculate the actual average density of the slurry inside the absorption tower. ; S3: Virtual Liquid Level Calculation and Display: Calculate the actual average density obtained in step S2. High pressure value and the pressure at the smoke inlet Calculate the virtual liquid level of the absorber slurry. And add the display of this liquid level on the DCS system screen; S4: Alarm and control based on virtual liquid level: specifically including: a. Set the false liquid level alarm threshold ; b. In a DCS system, based on proportional-integral-derivative (PID) control theory, the following is defined: To control the output, the PID algorithm for absorber level control can be expressed by the following formula:
[0008] in, For proportional gain parameters, For integral gain parameters, The differential gain parameter, This is the current time; in, The error signal is calculated using the following formula:
[0009] in, For the input setpoint of the PID control system, This is the output value of the PID control system.
[0010] Will Set as the input setpoint for the PID level control system The virtual liquid level will be calculated in real time. As a process variable output value Real-time virtual liquid level With alarm threshold Compare and determine the generated error signal Size; c. When the error signal e(t) ≥ 0, a bubble alarm is triggered, and the predetermined DCS system automatic interlock control logic is started to eliminate the bubble.
[0011] Furthermore, the aforementioned and It is obtained by selecting the median or calculating the average of the measured values from multiple pressure transmitters installed at the same horizontal height.
[0012] Furthermore, in step S2, based on the hydrostatic formula:
[0013] In conjunction with the above measurements , The pressure value was used to calculate the average density of the absorber slurry.
[0014] in , and These are the height values of the pressure measurement points at the top and bottom, respectively. This is the acceleration due to gravity.
[0015] Furthermore, in step S3, the illusory liquid level of the absorber slurry... The calculation formula is as follows:
[0016] in, For the pressure measurement point at the flue gas inlet of the absorption tower, The slurry level was calculated using a differential pressure transmitter when the absorption tower overflowed, as obtained during system instance debugging.
[0017] Furthermore, in step S4, This is a dummy liquid level bubbling alarm value set by the pressure transmitter and inlet pressure parameters of the absorber tower under the condition of overflow during commissioning. The specific calculation formula is as follows:
[0018] in, The value of the high-pressure transmitter under the overflow condition of the absorption tower. The value is the pressure measurement point at the flue gas inlet under overflow conditions of the absorber tower. This is the average density of the slurry calculated under the overflow condition of the absorption tower.
[0019] Furthermore, the automatic interlocking control logic includes: triggering a sequential control program to automatically add defoamer into the absorption tower, controlling the opening and closing of the defoamer dosing valve, and automatically starting a pipeline flushing program after the dosing is completed.
[0020] Furthermore, step S4 also includes: after the automatic control logic is executed, continuously recalculating the virtual liquid level value of the absorption tower by using the updated upper and lower liquid level pressure values from the measuring element pressure transmitter. The value is then returned to the output value of the PID control system to update the error signal. When the error signal e(t) < 0 and continues for a preset time, the bubbling alarm is automatically reset and the desulfurization system returns to normal operation.
[0021] Furthermore, in step S4, a first delay T1 is set from the error signal e(t) ≥ 0 to the triggering of the bubble alarm; a second delay T2 is set from the triggering of the alarm to the initiation of the first action in the automatic interlock control logic.
[0022] Furthermore, the first delay T1 is 20 seconds, and the second delay T2 is 10 seconds. That is, when the error signal of the PID system is greater than or equal to 0, a foaming alarm is triggered after a 20-second delay, which then triggers the interlocking control logic of the absorber DCS system. After a 10-second delay, the automatic dosing sequential control logic is triggered, and after a 10-second delay, the valve from the dosing device to the absorber is opened and closed. After a 10-second delay, the flushing sequential control logic of the absorber dosing device inlet pipe is triggered.
[0023] The beneficial effects of this invention are as follows: 1. This invention avoids the drawback of the traditional differential pressure transmitter method, which results in a calculated liquid level that is lower than the virtual liquid level including the foam layer, due to the constant density of the absorber slurry. The average density obtained by back-calculation can be used to calculate the liquid level rise caused by air foam and oxidizing air mixed in the slurry, thereby obtaining a more accurate virtual liquid level value of the absorber slurry.
[0024] 2. By setting a more accurate false liquid level alarm value, this invention prevents the overflow of foamy slurry caused by excessive liquid level rise due to air foam and oxidizing air. It also prevents the foam layer from obstructing the upward path of flue gas entering the absorption tower and prevents the flue gas from entering the induced draft fan with the acidic and alkaline absorbent liquid in the foam layer, thus avoiding wear and corrosion of the blades and other metal parts of the induced draft fan. Attached Figure Description
[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0026] Figure 1 A flowchart of the calculation method provided for an example of the present invention; Figure 2 A schematic diagram showing the locations of the liquid level and pressure measuring points in the absorption tower, as provided in this embodiment of the invention. Figure 3 A control strategy logic diagram provided for an example of the present invention.
[0027] Explanation of the attached diagram labels: 1-Spray zone of the absorption tower; 2-Pressure transmitter at the top; 3-Pressure transmitter at the bottom; 4-Pressure measuring point at the flue gas inlet; 5-Actual liquid level of the slurry in the absorption tower. Detailed Implementation
[0028] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that, unless otherwise specified, the following embodiments and features described therein can be combined with each other.
[0029] Wet desulfurization, as the most commonly used desulfurization process in modern thermal power plants, has gained widespread industry recognition for its high efficiency and stability. However, this method still has certain shortcomings. The foam layer generated by the combined effects of multiple factors creates a false liquid level within the absorber tower. As the error between the true and false liquid levels increases, various equipment in the desulfurization system will be affected and wear will occur, potentially even leading to overflow in severe cases. Existing differential pressure transmitter methods cannot accurately reflect the height of the foam layer in the absorber tower slurry level, resulting in delayed alarm signals from the DCS system and making it difficult to take appropriate emergency measures in time to address the foaming of the slurry within the absorber tower.
[0030] This patent provides a method for measuring and controlling the virtual liquid level in a wet desulfurization system. To illustrate the effectiveness of the method proposed in this patent, the following detailed description of the above technical solution is provided through a specific embodiment. Figure 2 The diagram shown illustrates the locations of the slurry level and pressure measuring points in the absorption tower, as illustrated in the example. The specific implementation steps are as follows: like Figure 1 As shown, the bottom liquid level pressure value is first obtained by reading the values from three pressure transmitters A / B / C installed at the bottom of the absorption tower and three pressure transmitters A / B / C installed at the top of the absorption tower, and then taking the median value. and high liquid level pressure value Because the installation positions of the bottom pressure transmitter and the top pressure transmitter are fixed, their positions are as follows: Figure 2 As shown, we can therefore obtain the heights corresponding to the two pressure values. and ,in , .
[0031] Furthermore, the average density of the absorber slurry was calculated using hydrostatic formulas. Based on this density and the pressure measurement point at the inlet of the absorption tower, the virtual liquid level of the absorption tower is then calculated. This will also allow the liquid level to be displayed on the DCS system screen.
[0032]
[0033] The formula for calculating virtual liquid level includes The absorber slurry level was calculated using a differential pressure transmitter method when overflow occurred during the commissioning process, and the pressure value at the higher part of the slurry level during overflow was also considered. The average density of the slurry during overflow and inlet pressure value Calculate the virtual liquid level during overflow. And set an alarm for this false liquid level.
[0034] ; ; In a specific embodiment, such as Figure 3 As shown, the virtual liquid level is set under the overflow state of the absorber tower. As the input value of the PID control system for the absorber level Furthermore, according to the calculation expression for the error signal mentioned above, when When the absorption tower DCS system triggers a 20-second delay, an alarm will be triggered.
[0035]
[0036] In this case Therefore, the absorption tower did not trigger an alarm.
[0037] But in another case, when When the foaming alarm signal appears, the interlocking control logic of the absorption tower DCS system is triggered. After a 10-second delay, the automatic dosing sequential control logic is triggered. After a 10-second delay, the valve from the dosing device to the absorption tower is opened. After a 10-second delay, the valve from the dosing device to the absorption tower is closed. After a 10-second delay, the flushing sequential control logic of the liquid inlet pipe of the absorption tower dosing device is triggered.
[0038] Once the foam layer in the absorber is effectively eliminated, the virtual liquid level value of the absorber is recalculated by updating the high and low liquid level pressure values using the pressure transmitter of the measuring element. This value is then returned to the input of the PID control system to update the error signal. ,until When the alarm is triggered, the absorption tower bubbling alarm resets after a 20-second delay, the desulfurization system returns to normal operation, and the system resumes normal monitoring.
[0039] The method of this invention has a significantly lower virtual liquid level measurement error than the traditional method, which can completely avoid slurry overflow accidents, while effectively reducing the energy consumption and maintenance cost of the induced draft fan. It also has a fast alarm response speed and has significant technical advantages and practical value.
[0040] The embodiments described above are merely preferred embodiments of this patent and are not intended to limit the scope of this patent. Any modifications and improvements made by those skilled in the art to the technical solutions of this patent without departing from the spirit of this patent should fall within the protection scope of this invention.
Claims
1. A method for measuring and controlling the virtual liquid level in a wet desulfurization system, characterized in that, Includes the following steps: S1: Real-time data acquisition and processing: Real-time acquisition of pressure values from at least two pressure measurement points installed at different heights on the side wall of the absorption tower; the pressure value output from the pressure measurement point located at the bottom is recorded as the bottom pressure value. The pressure value output from a pressure measuring point located at the top is recorded as the high-level pressure value. Simultaneously, the pressure value at the flue gas inlet of the absorption tower is acquired in real time and recorded as the flue gas inlet pressure. ; S2: Dynamic average density back calculation: Based on the principle of hydrostatics, according to the bottom pressure value. High pressure value and the known fixed vertical distance between the two pressure measurement points Dynamically calculate the actual average density of the slurry inside the absorption tower. ; S3: Virtual Liquid Level Calculation and Display: Calculate the actual average density obtained in step S2. High pressure value and the pressure at the smoke inlet Calculate the virtual liquid level of the absorber slurry. And add the display of this liquid level on the DCS system screen; S4: Alarm and control based on virtual liquid level: specifically including: a. Set the false liquid level alarm threshold ; b. In the DCS system, Set as the input setpoint for the PID level control system The virtual liquid level will be calculated in real time. As a process variable output value Define the error signal of the PID system. Real-time virtual liquid level With alarm threshold Compare and determine the generated error signal Size; c. When the error signal e(t) ≥ 0, a bubble alarm is triggered, and the predetermined DCS system automatic interlock control logic is started to eliminate the bubble.
2. The virtual liquid level measurement and control method for a wet desulfurization system according to claim 1, characterized in that, The and It is obtained by selecting the median or calculating the average of the measured values from multiple pressure transmitters installed at the same horizontal height.
3. The virtual liquid level measurement and control method for a wet desulfurization system according to claim 1, characterized in that, In step S2, based on the hydrostatic formula: ; In conjunction with the above measurements , The pressure value was used to calculate the average density of the absorber slurry. ; in , and These are the height values of the pressure measurement points at the top and bottom, respectively. This is the acceleration due to gravity.
4. The virtual liquid level measurement and control method for a wet desulfurization system according to claim 1, characterized in that, In step S3, the illusory liquid level of the absorber slurry... The calculation formula is as follows: ; in, For the pressure measurement point at the flue gas inlet of the absorption tower, The slurry level was calculated using a differential pressure transmitter when the absorption tower overflowed, as obtained during system instance debugging.
5. The virtual liquid level measurement and control method for a wet desulfurization system according to claim 4, characterized in that, In step S4, This is a dummy liquid level bubbling alarm value set by the pressure transmitter and inlet pressure parameters of the absorber tower under the condition of overflow during commissioning. The specific calculation formula is as follows: ; in, The value of the high-pressure transmitter under the overflow condition of the absorption tower. The value is the pressure measurement point at the flue gas inlet under overflow conditions of the absorber tower. This is the average density of the slurry calculated under the overflow condition of the absorption tower.
6. The method for measuring and controlling the virtual liquid level in a wet desulfurization system according to claim 1, characterized in that, The automatic interlock control logic includes: triggering a sequential control program to automatically add defoamer into the absorption tower, controlling the opening and closing of the defoamer dosing valve, and automatically starting a pipeline flushing program after the dosing is completed.
7. The method for measuring and controlling the virtual liquid level in a wet desulfurization system according to claim 6, characterized in that, Step S4 further includes: after the automatic control logic is executed, continuously recalculating the virtual liquid level value of the absorption tower by using the updated upper and lower liquid level pressure values from the measuring element pressure transmitter. The value is then returned to the input of the PID control system to update the error signal. When the error signal e(t) < 0 and continues for a preset time, the bubbling alarm is automatically reset and the desulfurization system returns to normal operation.
8. The method for measuring and controlling the virtual liquid level in a wet desulfurization system according to claim 6, characterized in that, In step S4, a first delay T1 is set from the error signal e(t) ≥ 0 to the triggering of the bubble alarm; a second delay T2 is set from the triggering of the alarm to the initiation of the first action in the automatic interlock control logic.
9. The method for measuring and controlling the virtual liquid level in a wet desulfurization system according to claim 8, characterized in that, The first delay T1 is 20 seconds, and the second delay T2 is 10 seconds.