Method for calibrating and measuring density of limestone slurry of desulfurizing tower based on differential pressure method

Abstract

The invention relates to the technical field of density measurement, in particular to the field of G01N9 / 26, and more particularly relates to a method for calibrating and measuring the density of limestone slurry of a desulfurizing tower based on a differential pressure method. According to the invention, the industrial standard water is extracted into the measuring cylinder before the slurry is periodically extracted, and the measured density is compared with the density of the industrial standard water, so that whether the differential pressure transmitter has zero drift or not is judged, and the density deviation is compensated to the slurry density measurement, so that the accuracy and scientificity of the slurry density measurement are improved.

Description

Technical Field

[0001] The present invention relates to the field of density measurement technology, in particular to the field of G01N9 / 26, and more specifically to a method for calibrating and measuring the density of limestone slurry in a desulfurization tower based on a differential pressure method. Background Art

[0002] Wet flue gas desulfurization refers to the process of removing SO2 from flue gas by using alkaline aqueous solution or slurry as absorbent to react chemically with SO2 in flue gas to generate compounds such as sulfate or sulfite. It is mainly based on the principle of acid-base neutralization reaction, and neutralizes the acidic SO2 in flue gas by the alkalinity of the absorbent. The desulfurization tower, also known as the absorption tower, is the core device of wet flue gas desulfurization. Its main function is to reduce environmental pollution by absorbing and decomposing SO2 in flue gas. The structural design of the desulfurization tower usually includes air inlet, spray layer, absorption liquid layer, demister, air outlet and other parts to ensure that the flue gas and absorbent are fully in contact and chemically react. With the continuous improvement of environmental protection requirements, higher requirements are put forward for wet flue gas desulfurization systems, and the density and pH control of desulfurization tower slurry are more stringent. The density of desulfurization tower slurry is an important control parameter in the desulfurization system, which directly affects the desulfurization efficiency of the desulfurization system and the quality of the final product gypsum.

[0003] At present, there are many methods for density measurement, among which mass flow meter measurement, differential pressure method measurement, and radiographic method measurement are the most widely used. Mass flow meter can directly measure the density of the medium based on the Coriolis force measurement principle, which belongs to the direct measurement method. However, due to its high price and easy wear of the measuring tube, its application in desulfurization system is gradually reduced. The radiographic method uses the radionuclides to emit radiation through the slurry attenuation, and measures the density by analyzing the attenuation degree. Its procedures are cumbersome and harmful to the human body, and its application is also gradually decreasing.

[0004] The differential pressure method uses the pressure difference of the measured slurry to calculate the density. The principle is simple and the measurement is convenient. For example, the prior art CN102759494A discloses a source device method for measuring the density of the desulfurization tower slurry. It mainly uses the differential pressure method and can effectively measure the density of the desulfurization tower slurry without the need for power equipment. However, in the actual measurement process, since the differential pressure method is an indirect measurement, there are many places where errors are introduced in the process. For example, if the differential pressure transmitter has a zero point offset, it is easy to cause a large measurement deviation. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a method for calibrating and measuring the density of limestone slurry in a desulfurization tower based on a differential pressure method, comprising:

[0006] S1. First open the drain door 4, then open the flush door 3, then close the drain door 4, and then close the flush door 3; fill the measuring tube 1 with cleaning water, let it stand, take the pressure values ​​of the pressure port 5 on the positive pressure side of the differential pressure transmitter and the pressure port 6 on the negative pressure side of the differential pressure transmitter, calculate the pressure difference measurement value ΔP1, compare the pressure difference measurement value ΔP1 with the differential pressure value of standard water, determine whether the differential pressure transmitter drifts, and calculate the differential pressure drift value as Δ;

[0007] S2. Open the slurry feed door 2, use the slurry pressure in the desulfurization tower to fill the measuring tube 1 with slurry, then close the slurry feed door 2, take the pressure values ​​of the pressure port 5 on the positive pressure side of the differential pressure transmitter and the pressure port 6 on the negative pressure side of the differential pressure transmitter at this time, and calculate the pressure difference measurement value ΔP2; then open the emptying door 4 to discharge the slurry, then open the flushing door 3, and finally close the emptying door 4 and flushing door 3, and refill the measuring tube 1 with cleaning water; wait for the next cycle measurement; the final displayed measurement value is ΔP2±Δ, and finally the slurry density is calculated by the formula P=ρgh.

[0008] Preferably, the differential pressure transmitter is a diaphragm differential pressure transmitter mounted with a capillary flange.

[0009] The diaphragm of the diaphragm differential pressure transmitter with capillary flange is in direct contact with the slurry to be measured, which effectively isolates the slurry in the pipeline from the sensor components inside the transmitter, preventing direct damage to the sensor by corrosive, high-viscosity or high-temperature media; the transmitter and the diaphragm are connected by a capillary filled with fluid, which not only transmits the pressure signal but also prevents the medium from directly entering the transmitter, protecting the measuring element; in addition, the diaphragm differential pressure transmitter uses sensing technology and signal processing algorithms, which can provide high-precision pressure measurement results. Since the fluid in the capillary can quickly transmit pressure signals, this type of transmitter has a faster response speed and can reflect the changes in the slurry to be measured in real time.

[0010] Preferably, in the step S1, the flushing door is opened 10 to 30 seconds after the draining door is opened.

[0011] Preferably, in the step S1, the drain door is closed 10 to 30 seconds after the flush door is opened.

[0012] Preferably, in the step S1, the flushing door is closed 10 to 30 seconds after the emptying door is closed.

[0013] The main function of the vent door is to control the entry or exit of gas to adjust the air pressure and vacuum degree in the system. Before density calibration, opening the vent door can exhaust the residual gas or impurities in the system to create a clean and stable environment for the subsequent calibration process. In density measurement, bubbles are a common interference factor that will affect the accuracy of pressure measurement. By opening the vent door, bubbles in the system can be minimized to reduce their impact on the calibration results.

[0014] The flush door is usually used to introduce cleaning water to clean and prepare the measuring device. During the density calibration process, opening the flush door can introduce an appropriate amount of cleaning water to flush and wet the measuring device to ensure the accuracy of the measurement.

[0015] First, open the drain door to quickly discharge the residual gas and impurities in the system, creating a good environment for the subsequent calibration process; open the flush door after a delay to ensure that the drain door has fully discharged the gas and impurities in the system. At this time, introduce the cleaning water for flushing, which can more effectively reduce bubbles and other interference factors; keep the drain door closed during the flushing process to prevent the cleaning water from leaking out and ensure the effective flushing process. At the same time, closing the drain door also helps to maintain the air pressure in the system. After the flushing is completed, the flushing door is closed with a delay to ensure that the cleaning water has fully acted on the measuring device and reached a stable state. At this time, closing the flushing door can fix the measurement state and prepare for subsequent calibration measurements.

[0016] Preferably, the opening time of the slurry feed gate in the step S2 is 10 to 30 seconds.

[0017] Preferably, in the step S2, the discharge door is opened 5 to 20 seconds after the slurry feed door is closed.

[0018] Preferably, in the step S2, the flushing door is opened 10 to 30 seconds after the emptying door is opened.

[0019] Preferably, in the step S2, the drain door is closed 5 to 20 seconds after the flush door is opened.

[0020] Preferably, in the step S2, the flushing door is closed 30 to 60 seconds after the emptying door is closed.

[0021] Currently, the most direct way to test the density of desulfurization tower slurry in the existing technology is to use a mass flow meter for measurement. However, the slurry to be measured can easily cause serious wear of the mass flow meter's measuring elbow and a short lifespan. At the same time, the mass flow meter is expensive, resulting in high cost of use. The indirect measurement method includes installing the differential pressure transmitter directly on the desulfurization tower, but it is easy to cause the pressure taking pipe to be blocked, the measured data does not change, and the monitoring function is lost. At the same time, there is also interference caused by stirring, oxidation fan blowing air, etc., which makes the measurement produce a large deviation; based on the differential pressure method, the slurry is continuously measured using a measuring tube. Because of dynamic measurement, it is affected by dynamic pressure and the measurement data will have deviations; and the present invention is mainly based on the differential pressure method to periodically extract the slurry and measure it using a measuring tube, which can avoid the influence of continuous measurement of dynamic pressure. However, when the slurry is periodically extracted and measured using a measuring tube, the differential pressure transmitter may produce zero drift during the measurement process, and the measurement error caused by this cannot be discovered in time; therefore, in the actual measurement, the present invention performs a zero drift correction operation on the differential pressure transmitter and performs reasonable differential pressure compensation when measuring the differential pressure, which can further reduce the measurement error caused by zero drift in periodic measurement and ensure the accuracy of the slurry density measurement result.

[0022] Beneficial Effects

[0023] (1) The technical solution provided by the present invention overcomes many shortcomings of the traditional differential pressure density measuring device directly installed on the desulfurization tower, and avoids the influence of pressure tapping port being easily blocked, stirring and oxidizing air blowing on the differential pressure.

[0024] (2) The equipment involved in the method of calibrating and measuring the density of limestone slurry in a desulfurization tower based on the differential pressure method of the present invention is simple in structure and has low requirements on the design, management and control levels.

[0025] (3) The new technical solution provided by the present invention mainly determines whether the differential pressure transmitter has drifted by increasing the density of the measured industrial water, and compensates the slurry density measurement by the deviation in the measurement process to improve the accuracy of the slurry density measurement.

[0026] (4) The equipment involved in the present invention has a long service life and low initial investment cost, and the process is expected to be promoted on a large scale.

[0027] (5) The relevant process steps in the present invention mainly rely on automatic operation of the program, and the measurement cycle can be adjusted at any time according to needs, reducing the workload of process operators. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of the process for calibrating and measuring the density of limestone slurry in the desulfurization tower using the differential pressure method, where: 1- measuring cylinder; 2- slurry feed gate; 3- flushing water gate; 4- drain gate; 5- pressure tapping port on the positive pressure side of the differential pressure transmitter; 6- pressure tapping port on the negative pressure side of the differential pressure transmitter. DETAILED DESCRIPTION

[0029] Example 1

[0030] This example provides a method for calibrating and measuring the density of limestone slurry in a desulfurization tower based on the differential pressure method, including:

[0031] S1. First open the drain door 4, delay 20s and then open the flush door 3. After 20s, close the drain door 4 and delay 10s to close the flush door 3. Fill the measuring cylinder 1 with cleaning water and let it stand for 1min. Take the pressure values ​​of the pressure port 5 on the positive pressure side of the differential pressure transmitter and the pressure port 6 on the negative pressure side of the differential pressure transmitter at this time, calculate the pressure difference measurement value ΔP1, compare the pressure difference measurement value ΔP1 with the differential pressure value of industrial standard water, determine whether the differential pressure transmitter drifts, and calculate the differential pressure drift value as Δ;

[0032] S2, open the slurry feed gate 2, use the slurry pressure in the desulfurization tower to fill the measuring cylinder 1 with slurry, close the slurry feed gate 2 after 30 seconds, take the pressure values ​​of the pressure port 5 on the positive pressure side of the differential pressure transmitter and the pressure port 6 on the negative pressure side of the differential pressure transmitter after 5 seconds, and calculate the pressure difference measurement value ΔP2; then open the emptying gate 4 to discharge the slurry, open the flushing gate 3 after 30 seconds to flush, close the emptying gate 4 after 10 seconds, close the flushing gate 3 after 40 seconds, and refill the measuring cylinder 1 with cleaning water; finally, according to the set cycle, return to the step of comparing and judging with the industrial standard water measurement value; wait for the next cycle measurement. The final displayed measurement value is ΔP2±Δ, and finally the density of the limestone slurry in the desulfurization tower is calculated by P=ρgh.

[0033] In P=ρgh, P is ΔP2±Δ, h is the height difference between the pressure tapping port 5 on the positive pressure side of the differential pressure transmitter and the pressure tapping port 6 on the negative pressure side of the differential pressure transmitter, and g is the unit of gravity, g=9.8N / kg.

[0034] The differential pressure transmitter is a diaphragm differential pressure transmitter with a capillary flange.

[0035] The process flow chart of Example 1 is as follows Figure 1 shown.

[0036] According to the set 30-minute sampling cycle, the system was put into actual production operation, and one day's measurement data was obtained and compared with the manual sampling measurement data. The test data is shown in Table 1.

[0037] Table 1

[0038]

[0039] The calculated density value before compensation is the density value calculated according to the formula P=ρgh before compensation, wherein g is 9.8, and h is the height difference between the pressure tapping port 5 on the positive pressure side of the differential pressure transmitter and the pressure tapping port 6 on the negative pressure side of the differential pressure transmitter.

[0040] The calculated density value after compensation is the density value measured after compensation.

[0041] The manual sampling measurement value is the actual measurement value obtained by using a density meter after sampling on site.

[0042] The difference between the compensated density and the manually sampled density, that is, the difference between the compensated value measured by the differential pressure method and the manually compared density, can be seen to be significantly reduced compared to the value before compensation.

[0043] The density difference before compensation and the manual sampling density, that is, the difference between the value before compensation measured by the differential pressure method and the manually compared density.

[0044] Working principle: The present invention mainly extracts industrial standard water into the measuring cylinder before periodically extracting the slurry, and measures the density and industrial water density (ρ = 1.0 × 10 3 kg / m 3 ) to determine whether there is zero drift in the differential pressure transmitter, and compensate the density deviation in the limestone slurry density measurement in the desulfurization tower to improve the accuracy of the slurry density measurement.

Claims

1. A method for calibrating and measuring the density of limestone slurry in a desulfurization tower based on differential pressure method, characterized in that: include: S1, first open the drain door (4), then open the flush door (3), then close the drain door (4), and close the flush door (3); fill the measuring tube (1) with cleaning water, let it stand, take the pressure values ​​of the pressure port (5) on the positive pressure side of the differential pressure transmitter and the pressure port (6) on the negative pressure side of the differential pressure transmitter, calculate the pressure difference measurement value ΔP1, compare the pressure difference measurement value ΔP1 with the differential pressure value of standard water, determine whether the differential pressure transmitter drifts, and calculate the differential pressure drift value as Δ; S2, open the slurry feed door (2), use the slurry pressure in the desulfurization tower to fill the measuring tube (1) with slurry, then close the slurry feed door (2), take the pressure values ​​of the pressure port (5) on the positive pressure side of the differential pressure transmitter and the pressure port (6) on the negative pressure side of the differential pressure transmitter, and calculate the pressure difference measurement value ΔP2; then open the emptying door (4) to discharge the slurry, then open the flushing door (3), and finally close the emptying door (4) and the flushing door (3), and refill the measuring tube (1) with cleaning water; wait for the next periodic measurement; the final displayed measurement value is ΔP2±Δ, and finally the slurry density is calculated by the formula P=ρgh.

2. The method for calibrating and measuring the density of limestone slurry in a desulfurization tower based on differential pressure method according to claim 1, characterized in that: The differential pressure transmitter is a diaphragm differential pressure transmitter with a capillary flange.

3. The method for calibrating and measuring the density of limestone slurry in a desulfurization tower based on differential pressure method according to claim 1, characterized in that: In the step S1, the flushing door (3) is opened 10 to 30 seconds after the emptying door (4) is opened.

4. The method for calibrating and measuring the density of limestone slurry in a desulfurization tower based on differential pressure method according to claim 1, characterized in that: In the step S1, the flushing door (3) is opened and then the draining door (4) is closed 10 to 30 seconds later.

5. The method for calibrating and measuring the density of limestone slurry in a desulfurization tower based on differential pressure method according to claim 1, characterized in that: In the step S1, the flushing door (3) is closed 10 to 30 seconds after the emptying door (4) is closed.

6. The method for calibrating and measuring the density of limestone slurry in a desulfurization tower based on differential pressure method according to claim 1, characterized in that: In the step S2, the slurry feed gate (2) is opened for 10 to 30 seconds.

7. The method for calibrating and measuring the density of limestone slurry in a desulfurization tower based on differential pressure method according to claim 1, characterized in that: In the step S2, the slurry feed door (2) is closed and then the discharge door (4) is opened 5 to 20 seconds later.

8. The method for calibrating and measuring the density of limestone slurry in a desulfurization tower based on differential pressure method according to claim 1, characterized in that: In the step S2, the flushing door (3) is opened 10 to 30 seconds after the emptying door (4) is opened.

9. The method for calibrating and measuring the density of limestone slurry in a desulfurization tower based on differential pressure method according to claim 1, characterized in that: In the step S2, the flushing door (3) is opened and then the draining door (4) is closed 5 to 20 seconds later.

10. The method for calibrating and measuring the density of limestone slurry in a desulfurization tower based on differential pressure method according to claim 1, characterized in that: In the step S2, the flushing door (3) is closed 30 to 60 seconds after the emptying door (4) is closed.

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