Automatic slurry supply method and system for desulfurized limestone slurry

Abstract

The invention discloses an automatic slurry supply method and system for desulfurized limestone slurry, which adopts a PID (Proportion Integration Differentiation) control strategy under a pH value condition, and performs variable-frequency slurry supply by changing a slurry supply flow and a variable-frequency dilution water flow. The calculation formula of the slurry supply flow V1 is as follows: the slurry supply flow V1 = X * A * 10 <-5 > * coal consumption or actual boiler load * SO2 concentration at an original flue gas inlet; the calculation formula of the variable-frequency dilution water flow is as follows: the variable-frequency dilution water flow = the set value-the slurry supply flow V1; at least two pH meters used for detecting the pH value of the slurry are arranged, and the pH detection feedback value is the average value of the pH meters. The method has the advantages of few input conditions, high accuracy of the input conditions, small relative error of calculation, high control precision and capability of realizing accurate automatic slurry supply which is easy to adjust and control.

Description

Technical Field

[0001] The present invention relates to the technical field of desulfurization, and in particular to an automatic slurry supply method and system for desulfurized limestone slurry. Background Art

[0002] The supply of desulfurization limestone slurry for the unit is determined by two data. One is the original slurry supply, which is the real-time required limestone slurry quantity automatically calculated by the DCS system based on the real-time total boiler air volume, SO2 concentration at the absorption tower inlet, etc. The other is the limestone slurry quantity obtained after pH correction calculation in the absorption tower. The corrected quantity is sent by PID control to the limestone slurry supply pump inverter to complete the automatic control of slurry supply and keep the pH in the absorption tower within a reasonable range. Calculate the amount of limestone liquid required to remove the SO2 content entering the absorption tower in real time, and then use the pH value of the absorption tower as a correction coefficient to obtain the final required limestone slurry volume. Use PID control to give the frequency conversion instruction of the limestone slurry pump to complete the automatic adjustment of the slurry supply. Theoretically, the SO2 content of the flue gas is proportional to the slurry supply volume. This control method is sufficient to achieve automatic adjustment of the slurry supply. However, the desulfurization process is affected by many factors such as the slurry pH value, calcium-sulfur ratio, liquid-gas ratio, and limestone and flue gas parameters. The desulfurization process cannot be in a theoretical state, especially under the influence of deep peak regulation and changes in coal types. The flue gas flow rate and inlet SO2 concentration often fluctuate greatly. The original control method cannot respond quickly to parameter changes, resulting in frequent exceeds of the outlet SO2 concentration. This not only increases the operation workload of the operating personnel, but also easily causes the operating personnel to fail to operate in a timely manner, resulting in the hourly average SO2 emission exceeding the standard.

[0003] Some automatic slurry supply adjustment methods disclosed in the prior art are difficult to adjust and control in actual application, involve many adjustment factors, and have large accumulated errors, which affect the implementation of automatic control. For example, the invention patent with patent publication number CN112999857A discloses a control method and control system for a wide-load limestone slurry supply system. This method avoids pipeline wear and slurry deposition caused by excessively fast or slow slurry flow rates, and achieves stable control of the pH value and SO2 emission concentration of the desulfurization system. However, it does not provide an automatic adjustment calculation method for dilution water. When the amount of dilution water changes, the slurry supply amount will also change accordingly, affecting the implementation of automatic control. In addition, its slurry amount calculation needs to be based on the flue gas volume, sulfur dioxide concentration, pH value, limestone slurry density, etc., resulting in a large accumulated error. The invention patent with patent publication number CN115970476A discloses an automatic slurry supply control method for a desulfurization island based on a DCS control system, which realizes online optimization adjustment of pH value and slurry supply flow, and realizes precise control of SO2 concentration in clean flue gas. It adopts the method of controlling the total flow of actual slurry supply and is provided with a return pipeline. However, no calculation method is provided for the return flow of the return pipeline, which affects accurate control. In addition, the calculation of the limestone slurry volume requires flue gas volume, sulfur dioxide concentration, limestone slurry density and solid content, etc. The cumulative error of the slurry supply volume is easy to exceed the adjustment range. Summary of the Invention

[0004] The object of the present invention is to provide a method and system for automatically supplying limestone slurry, which can realize automatic slurry supply accurately and easily adjusted and controlled.

[0005] To achieve the above object, the technical solution provided by the present invention is:

[0006] The first aspect of the present application provides a method for automatically supplying desulfurized limestone slurry, which adopts a PID control strategy under pH conditions to automatically supply slurry by changing the slurry supply flow rate and the frequency conversion dilution water flow rate;

[0007] The calculation formula of slurry flow rate V1 is as follows:

[0008] Slurry flow rate V1 = X*A*10 -5 *Coal consumption or actual boiler load*SO2 concentration in original flue gas inlet

[0009] Where X represents the automatic adjustment value of PID control, and the pH value of the slurry under PID control is controlled within the required condition range by changing the X value; A represents the correction parameter, which is pre-set based on the coal quality parameters and error parameters, including slurry density or slurry limestone concentration, limestone purity, and instrument error correction value;

[0010] The calculation formula for variable frequency dilution water flow is as follows:

[0011] Frequency conversion dilution water flow = set value - slurry flow V1

[0012] The set value represents the set value of the flow rate corresponding to the pipeline flow velocity.

[0013] To optimize the above technical solutions, specific measures / limitations adopted also include:

[0014] The unit of slurry flow rate V1 is m 3 / h, the unit of coal consumption is t / h, the unit of actual boiler load is MW / h, and the unit of SO2 concentration in the original flue gas inlet is mg / Nm 3 ; The correction parameter A has a value range of 1 to 10; the pipeline flow rate value is >1.2m / s.

[0015] The pH value of the slurry under PID control is controlled within the required condition range, so that the pH of the slurry reaches the pH allowable range of 5.0 to 5.8.

[0016] The slurry pump frequency is set by setting the SP value of PID control to control the automatic slurry supply flow rate; the SP value of PID control is determined by the input amount of limestone slurry.

[0017] The conditions for the normal input of limestone slurry are as follows: the liquid level of the limestone slurry tank is higher than the low liquid level limit; at least two pH meters are set to detect the pH value of the slurry, the pH detection feedback value is the average value of each pH meter, the slurry pH measured by each pH meter is within the pH allowable range of 5.0 to 5.8, and the pH value difference between different pH meters is not greater than 0.05; the actual limestone slurry flow rate V is normal; the SO2 concentration at the desulfurization outlet is within the normal range of SO2 concentration of 5 to 25 mg / Nm 3 The unit load is above the load setting threshold; if all the above conditions are met, the limestone slurry will be put into the machine normally; if any one of the conditions is not met, the automatic slurry supply will be stopped.

[0018] After the limestone slurry is put in and automatic slurry supply begins, the limestone slurry supply amount is adjusted according to the pH target setting value; when the actual limestone slurry flow rate V is less than the slurry supply flow rate V1, the limestone slurry supply amount is automatically adjusted according to the pH value change trend, the flow rate of the limestone slurry flow rate V is determined, and the actual limestone slurry flow rate V reaches the slurry supply flow rate V1 by changing the slurry supply pump frequency; similarly, when the actual limestone slurry flow rate V is greater than V1, the limestone slurry supply amount is automatically adjusted according to the pH value change trend, the flow rate of the limestone slurry flow rate V is determined, and the actual limestone slurry flow rate V reaches the slurry supply flow rate V1 by changing the slurry supply pump frequency.

[0019] Furthermore, in order to adapt to the desulfurization chemical reaction with a long reaction time, the pH adjustment method adopts variable integral control. When the deviation between the actual pH value and the pH target setting value is less than 0.1, a relatively large integral time is used to extend the change interval of the slurry pump inverter and slow down the impact of the slow desulfurization chemical reaction. When the deviation between the actual pH value and the pH target setting value is greater than 0.1, a relatively small integral time is used to shorten the change interval of the slurry pump inverter and speed up the pH change adjustment. The output frequency conversion adjustment step and time interval of the slurry pump inverter are determined according to the time interval after the actual limestone slurry flow rate V changes to cause the pH or outlet SO2 concentration to change.

[0020] Furthermore, the adjustment of the slurry pH is linked to the desulfurization outlet SO2 to form an automatic adjustment of the pH target setting value; when the desulfurization outlet SO2 concentration is relatively low, the slurry pH target setting value is lowered to avoid the desulfurization outlet SO2 concentration being zero; when the desulfurization outlet SO2 concentration is relatively high, the slurry pH target setting value is increased to improve the desulfurization efficiency.

[0021] Set the PID control automatic cut-off conditions. When at least one of the following conditions is met, the PID control is automatically cut off: set the slurry tank low liquid level, and the limestone slurry tank level is below the low liquid level; set the actual slurry minimum flow threshold, when the actual limestone slurry flow V is less than the actual slurry minimum flow threshold, and continues for more than the set time; set the alarm pH, when the actual pH value is greater than the alarm pH, and exceeds the alarm time limit; set the SO2 alarm setting value, when the desulfurization outlet SO2 exceeds the SO2 alarm setting value; set the load setting threshold, when the unit load is below the load setting threshold; after the PID control is automatically cut off, the valve and pipeline are flushed and the water pump is turned off, and manual control adjustment is switched to, and the system alarm is at the same time.

[0022] The second aspect of the present application provides an automatic limestone slurry supply system, including a variable frequency slurry supply pump, a variable frequency dilution water pump, a pH meter and a PID control device; the variable frequency slurry supply pump is used to provide slurry according to the needs of the slurry supply flow rate V1; the variable frequency dilution water pump is used to provide dilution water according to the needs of the variable frequency dilution water flow rate; the pH meter is used to detect the pH value of the slurry after dilution with dilution water; the PID control device is used to achieve automatic control; wherein, the slurry supply flow rate V1 and the variable frequency dilution water flow rate are calculated using the above-mentioned calculation formula.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The present invention provides a method and system for accurately controlling the automatic supply of limestone slurry. The formula of the present invention requires only two measured values ​​to derive a highly accurate supply quantity. The power generation load is calculated using measured values, namely the power generation load or boiler load and the sulfur dioxide concentration. The present invention has few input conditions, high accuracy of the input conditions, small relative calculation error, and high control precision, fully meeting the requirements of automatic control.

[0025] The present invention also associates the automatic slurry supply with the outlet SO2 concentration, automatically adjusts the pH target setting value to stabilize the outlet SO2 concentration, and improves the use stability of the automatic slurry supply system. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 : Schematic diagram of the automatic slurry supply strategy for desulfurized limestone slurry of the present invention. DETAILED DESCRIPTION

[0027] The above contents of the present invention are further described in detail below in the form of embodiments, but this should not be understood as the scope of the above subject matter of the present invention being limited to the following embodiments. All technologies implemented based on the above contents of the present invention fall within the scope of the present invention.

[0028] The present invention proposes a method for automatically supplying desulfurized limestone slurry, such as Figure 1 As shown, the PID control strategy under pH conditions is adopted to automatically perform variable frequency slurry supply by changing the slurry supply flow rate and variable frequency dilution water flow rate;

[0029] In one embodiment, the coal consumption method is used, and the calculation formula for the slurry flow rate V1 is as follows:

[0030] Slurry flow rate V1 = X*A*10 -5 *Coal consumption*SO2 concentration in original flue gas inlet

[0031] In another embodiment, the power generation load calculation method is adopted, and the calculation formula of the slurry flow rate V1 is as follows:

[0032] Slurry flow rate V1 = X*A*10 -5 *Actual boiler load*SO2 concentration in original flue gas inlet

[0033] Where X represents the automatic adjustment value of PID control, and the pH value of the slurry (after dilution) under PID control is controlled within the required condition range by changing the X value; A represents the correction parameter, which is pre-set based on the coal quality parameters and error parameters, including slurry density or slurry limestone concentration, limestone purity, and instrument error correction value;

[0034] The calculation formula for variable frequency dilution water flow is as follows:

[0035] Frequency conversion dilution water flow = set value - slurry flow V1

[0036] Among them, the set value represents the set value of the flow rate corresponding to the pipeline flow velocity;

[0037] At least two pH meters are provided for detecting the pH value of the slurry, and the pH detection feedback value is the average value of each pH meter.

[0038] In the embodiment of the present invention, the unit of the slurry flow rate V1 is m 3 / h, the unit of coal consumption is t / h, the unit of actual boiler load is MW / h, and the unit of SO2 concentration in the original flue gas inlet is mg / Nm 3 ; The value range of correction parameter A is 1 to 10; the pipeline flow velocity value is greater than 1.2m / s.

[0039] In a preferred embodiment, the pipeline flow velocity is 2.6 m / s.

[0040] The pH value of the slurry under PID control is controlled within the required condition range, so that the pH of the slurry reaches the pH allowable range of 5.0 to 5.8.

[0041] In a preferred embodiment, the pH value of the slurry is controlled at 5.5.

[0042] By setting the SP value of PID control, the slurry pump frequency is set to control the automatic slurry supply flow rate; the SP value of PID control is determined by the input amount of limestone slurry.

[0043] The conditions for normal input of limestone slurry are:

[0044] The liquid level in the limestone slurry tank is above the low level limit;

[0045] The slurry pH measured by each pH meter is within the pH allowable range of 5.0 to 5.8, and the difference in pH values ​​between different pH meters is no more than 0.05;

[0046] The actual limestone slurry flow rate V is displayed as normal;

[0047] The SO2 concentration at the desulfurization outlet is within the normal range of SO2 concentration values; in a preferred embodiment, the SO2 concentration is within the normal range of values.

[0048] The unit load is above a load setting threshold; in a preferred embodiment, the load setting threshold is set to 210MW.

[0049] If all the above conditions are met, the limestone slurry will be put into the slurry normally. If any one of the conditions is not met, the slurry supply will be stopped.

[0050] After the limestone slurry is put in and automatic slurry supply begins, the limestone slurry supply amount is adjusted according to the pH target setting value; when the actual limestone slurry flow rate V is less than the slurry supply flow rate V1, the limestone slurry supply amount is automatically adjusted according to the pH value change trend, the flow rate of the limestone slurry flow rate V is determined, and the actual limestone slurry flow rate V reaches the slurry supply flow rate V1 by changing the slurry supply pump frequency; similarly, when the actual limestone slurry flow rate V is greater than V1, the limestone slurry supply amount is automatically adjusted according to the pH value change trend, the flow rate of the limestone slurry flow rate V is determined, and the actual limestone slurry flow rate V reaches the slurry supply flow rate V1 by changing the slurry supply pump frequency.

[0051] In order to adapt to the desulfurization chemical reaction with a long reaction time, the pH adjustment method adopts variable integral control. When the deviation between the actual pH value and the pH target setting value is less than 0.1, a relatively large integral time is used to extend the change interval of the slurry pump inverter and slow down the impact of the slow desulfurization chemical reaction. When the deviation between the actual pH value and the pH target setting value is greater than 0.1, a relatively small integral time is used to shorten the change interval of the slurry pump inverter and speed up the pH change adjustment. The output frequency conversion adjustment step and time interval of the slurry pump inverter are determined according to the time interval after the actual limestone slurry flow rate V changes to cause the pH or outlet SO2 concentration to change.

[0052] The adjustment of the slurry pH is linked to the SO2 at the desulfurization outlet to form an automatic adjustment of the pH target setting value; when the SO2 concentration at the desulfurization outlet is relatively low, the pH target setting value of the slurry is lowered to avoid the SO2 concentration at the desulfurization outlet being zero or negative; when the SO2 concentration at the desulfurization outlet is relatively high, the pH target setting value of the slurry is increased to improve the desulfurization efficiency.

[0053] Set the PID control automatic cut-off conditions. When at least one of the following conditions is met, the PID control automatically cuts off:

[0054] Set the slurry tank low liquid level, and the limestone slurry tank liquid level is below the low liquid level;

[0055] Set the actual slurry minimum flow threshold value. When the actual limestone slurry flow rate V is less than the actual slurry minimum flow threshold value and lasts for more than the set time; in a preferred embodiment, the actual slurry minimum flow threshold value is set to 27.5m 3 / h, the set time is 30s, the slurry flow rate is less than 27.5m 3 / h and the duration is greater than 30s; PID control is automatically cut off;

[0056] Set an alarm pH value. When the actual pH value is greater than the alarm pH value and exceeds the alarm time limit; in a preferred embodiment, the alarm pH value is set to 6.1 and the alarm time limit is delayed for 2 minutes;

[0057] Set the SO2 alarm setting value. When the SO2 at the desulfurization outlet exceeds the SO2 alarm setting value;

[0058] In a preferred embodiment, the SO2 concentration at the desulfurization outlet is set at 5-25 mg / Nm 3 If the pH value fluctuates within the range, if it is lower or higher than the range, the pH target setting value will be automatically increased or decreased, and the setting value change is 0.1 (adjustable according to the situation). If it continues to rise or fall within 3 minutes after the change, the pH target setting value will be automatically increased or decreased again. 3 When the alarm is sounded, the automatic pulp supply will be stopped;

[0059] Set the load setting threshold. When the unit load is below the load setting threshold;

[0060] After the PID control is automatically cut off, the valve flushes the pipeline and then shuts down the water pump, switches to manual control and adjustment, and the system alarms at the same time.

[0061] The present invention also proposes an automatic limestone slurry supply system, including a variable frequency slurry supply pump, a variable frequency dilution water pump, and a PID control device; the variable frequency slurry supply pump is used to provide slurry according to the needs of the slurry supply flow rate V1; the variable frequency dilution water pump is used to provide dilution water according to the needs of the variable frequency dilution water flow rate; the PID control device is used to achieve automatic control; wherein, the slurry supply flow rate V1 and the variable frequency dilution water flow rate are calculated using the above-mentioned calculation formula.

[0062] The formula of the present invention only requires two measured values ​​to obtain a high-precision slurry supply amount; the power generation load calculation method is used to measure the power generation load (or boiler load) and sulfur dioxide concentration, and the relative error of the power generation load is ±0.2%, and the relative error of the sulfur dioxide concentration detection instrument is ±15%; the coal consumption method is used to measure the coal consumption and sulfur dioxide concentration, and the relative error of the coal consumption is ±0.2%, and the relative error of the sulfur dioxide concentration detection instrument is ±15%. The main error is the sulfur dioxide concentration error. According to national standards, the drift error of a 24-hour sulfur dioxide detection instrument is ±2.5%. The control of the present invention is actually calculated in seconds. A correction coefficient is set in the calculation method, and the control accuracy can be guaranteed to be within ±3 to ±5%, which fully meets the requirements of automatic control.

[0063] The above are only preferred embodiments of the present invention and do not constitute any form of limitation to the present invention. Any simple modification, equivalent replacement and improvement made by any technician familiar with the profession to the above embodiments without departing from the scope of the technical solution of the present invention and based on the technical essence of the present invention shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for automatically supplying desulfurized limestone slurry, characterized by: Adopting PID control strategy under pH conditions, automatic variable frequency slurry supply is achieved by changing the slurry supply flow rate and variable frequency dilution water flow rate; The calculation formula of slurry flow rate V1 is as follows: Slurry flow rate V1 = X*A*10 -5 *Coal consumption or actual boiler load*SO2 concentration in original flue gas inlet Where X represents the automatic adjustment value of PID control, and the pH value of the slurry under PID control is controlled within the required condition range by changing the X value; A represents the correction parameter, which is pre-set based on the coal quality parameters and error parameters, including slurry density or slurry limestone concentration, limestone purity, and instrument error correction value; The calculation formula for variable frequency dilution water flow is as follows: Frequency conversion dilution water flow = set value - slurry flow V1 The set value represents the flow rate set value corresponding to the pipeline flow velocity.

2. The automatic slurry supply method for desulfurized limestone according to claim 1, characterized in that: The unit of slurry flow rate V1 is m 3 / h, the unit of coal consumption is t / h, the unit of actual boiler load is MW / h, and the unit of SO2 concentration in the original flue gas inlet is mg / Nm 3 ; The correction parameter A has a value range of 1 to 10; the pipeline flow rate value is >1.2m / s.

3. The automatic slurry supply method for desulfurized limestone according to claim 1, characterized in that: The pH value of the slurry under PID control is controlled within the required condition range so that the pH of the slurry reaches the pH allowable range of 5.0 to 5.8; at least two pH meters are set to detect the pH value of the slurry, and the pH detection feedback value is the average value of each pH meter; if there are 3 or more pH meters, the values ​​of the two pH meters closest to the average value are selected in each sampling cycle, and then the average value of the values ​​of these two pH meters is taken as the control value.

4. The automatic slurry supply method for desulfurized limestone according to claim 1, characterized in that: The slurry pump frequency is set by setting the SP value of PID control to control the automatic slurry supply flow rate; the SP value of PID control is determined by the input amount of limestone slurry.

5. The automatic slurry supply method for desulfurized limestone according to claim 3, characterized in that: The conditions for the normal input of limestone slurry are as follows: the liquid level of the limestone slurry tank is higher than the low liquid level limit; the slurry pH measured by each pH meter is within the allowable pH range of 5.0 to 5.8, and the difference in pH values ​​between different pH meters is not greater than 0.05; the actual limestone slurry flow V is displayed normally; the SO2 concentration at the desulfurization outlet is within the normal range of SO2 concentration; the unit load is above the load setting threshold; if all the above conditions are met, the limestone slurry can be input normally; if one condition is not met, the automatic slurry supply will be stopped and manual control and adjustment will be implemented.

6. The automatic slurry supply method for desulfurized limestone according to claim 1, characterized in that: After the limestone slurry is put in and automatic slurry supply begins, the limestone slurry supply amount is adjusted according to the pH target setting value; when the actual limestone slurry flow rate V is less than the slurry supply flow rate V1, the limestone slurry supply amount is automatically adjusted according to the pH value change trend, the flow rate of the limestone slurry flow rate V is determined, and the actual limestone slurry flow rate V reaches the slurry supply flow rate V1 by changing the slurry supply pump frequency; similarly, when the actual limestone slurry flow rate V is greater than V1, the limestone slurry supply amount is automatically adjusted according to the pH value change trend, the flow rate of the limestone slurry flow rate V is determined, and the actual limestone slurry flow rate V reaches the slurry supply flow rate V1 by changing the slurry supply pump frequency.

7. The automatic slurry supply method for desulfurized limestone according to claim 1, characterized in that: The pH adjustment method adopts variable integral control. When the deviation between the actual pH value and the pH target setting value is less than 0.1, a relatively large integral time is used to extend the change interval of the slurry pump inverter; when the deviation between the actual pH value and the pH target setting value is greater than 0.1, a relatively small integral time is used to shorten the change interval of the slurry pump inverter and accelerate the pH change adjustment; the output frequency conversion adjustment step and time interval of the slurry pump inverter are determined according to the time interval after the actual limestone slurry flow rate V changes, which causes the pH or outlet SO2 concentration to change.

8. The automatic slurry supply method for desulfurized limestone according to claim 1, characterized in that: The adjustment of the slurry pH is linked to the SO2 at the desulfurization outlet to form an automatic adjustment of the pH target setting value; when the SO2 concentration at the desulfurization outlet is relatively low, the pH target setting value of the slurry is lowered to avoid the SO2 concentration at the desulfurization outlet being zero; when the SO2 concentration at the desulfurization outlet is relatively high, the pH target setting value of the slurry is increased to improve the desulfurization efficiency.

9. The automatic slurry supply method for desulfurized limestone according to claim 1, characterized in that: Set the PID control automatic cut-off conditions. When at least one of the following conditions is met, the PID control is automatically cut off: set the slurry tank low liquid level, and the limestone slurry tank level is below the low liquid level; set the actual slurry minimum flow threshold, when the actual limestone slurry flow V is less than the actual slurry minimum flow threshold, and continues for more than the set time; set the alarm pH, when the actual pH value is greater than the alarm pH, and exceeds the alarm time limit; set the SO2 alarm setting value, when the desulfurization outlet SO2 exceeds the SO2 alarm setting value; set the load setting threshold, when the unit load is below the load setting threshold; after the PID control is automatically cut off, the valve will flush the pipeline and then turn off the water pump, and switch to manual control adjustment, and the system will alarm at the same time.

10. An automatic limestone slurry supply system, characterized by: It includes a variable frequency slurry supply pump, a variable frequency dilution water pump, and a PID control device; the variable frequency slurry supply pump is used to provide slurry according to the needs of the slurry supply flow rate V1; the variable frequency dilution water pump is used to provide dilution water according to the needs of the variable frequency dilution water flow rate; the PID control device is used to realize automatic control; wherein, the slurry supply flow rate V1 and the variable frequency dilution water flow rate are calculated using the calculation formula in claim 1.

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