A method of increasing the reliability of boiler feed water regulating valve regulation

Abstract

The application discloses a method for increasing the regulation reliability of a boiler feed water regulating valve, comprising the following steps: determining the input of a selector according to the running speed of a feed water pump, the inlet flow and the outlet pressure of the feed water pump; selecting the minimum input by using a manual setting constant block in combination with the selector, and taking the minimum input as the deviation input of a PID controller; outputting a control instruction by the PID controller through linear combination of the deviation input; and controlling the feed water regulating valve according to the control instruction to achieve the effect of temperature reduction. The method can increase the boiler feed water by regulating the regulating valve, improve the throttling loss without affecting the safe operation of the reheater temperature reducing water, avoid the frequent opening and closing of the feed water regulating valve caused by load fluctuation during low load, and reduce the loss of the valve equipment and the energy consumption of the steam-driven feed water pump.

Description

Technical Field

[0001] This invention relates to the technical field of boiler feedwater, and more particularly to a method for increasing the reliability of boiler feedwater regulating valves. Background Technology

[0002] Currently, the feedwater regulating valves for boilers No. 1 and No. 2 at Shidongkou No. 2 Power Plant are an important component of the feedwater system. Feedwater pumped from the boiler feedwater pump sequentially enters the No. 6, 7, and 8 high-pressure heaters via the three-way valve FW003, then the No. 8 high-pressure heater outlet valve FW005, and finally the main boiler feedwater valve FW006. After FW006, a superheater spray desuperheating branch is connected, and finally, the feedwater enters the boiler economizer via the feedwater regulating valve FW004. The function of the feedwater regulating valve is to maintain the feedwater pressure at a level greater than the main steam pressure by 2.5 MPa, ensuring a sufficient pressure difference between the first and second stage superheater desuperheating water and the superheated steam, allowing it to be sprayed into the superheater for desuperheating. During operation, the feedwater regulating valve often exhibits a defect of intermittent loss of feedback signal, where the valve opening suddenly drops to 0 and then quickly recovers to its original value. If the feedwater regulating valve is frequently closed to a small opening during adjustment, it is relatively easy to cause wear or scoring of the valve's copper slip threads and valve stem threads. Summary of the Invention

[0003] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0004] In view of the aforementioned existing problems, the present invention is proposed.

[0005] Therefore, the technical problem solved by the present invention is that the existing water supply regulating valves are often closed to a small opening during adjustment, causing wear and scratching of the local copper lubricating threads and valve stem threads, resulting in high equipment losses.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution, including:

[0007] The input of the small selector is determined based on the operating speed, inlet flow rate, and outlet pressure of the water pump.

[0008] The minimum input is selected by manually setting a constant block in combination with a small selector, and the minimum input is used as the deviation input of the PID controller;

[0009] The PID controller outputs control commands by linearly combining the deviation input;

[0010] Controlling the water supply regulating valve according to the control command to achieve a cooling effect; controlling the water supply regulating valve according to the control command includes:

[0011] When the boiler output decreases and the feedwater pump speed and feedwater flow rate decrease, the pressure difference between the feedwater pump outlet and the main steam will gradually decrease. The PID controller controls the pressure difference between the feedwater pump outlet pressure and the main steam pressure to 1.5 MPa, controls the regulating water valve, keeps the feedwater regulating valve at a large opening, reduces wear and scratches caused by frequent valve closing and closing, and increases valve reliability.

[0012] The cooling of the superheater includes:

[0013] When the feedwater regulating valve of the unit is kept at a pressure 1.5 MPa higher than the main steam pressure, and the feedwater regulating valve is kept fully open at any load section under the unit's coordinated operation mode, the superheater and reheater can still operate safely and achieve the desuperheating effect. The reduction in the desuperheating water volume also reduces the steam volume and the energy consumption of the first steam-driven feedwater pump and the second steam-driven feedwater pump.

[0014] As a preferred embodiment of the method for increasing the reliability of boiler feedwater regulating valve as described in this invention, the feedwater pump includes: a first steam-driven feedwater pump, a second steam-driven feedwater pump, and an electric feedwater pump.

[0015] As a preferred embodiment of the method for increasing the reliability of boiler feedwater regulating valve as described in this invention, the input of the feedwater pump outlet pressure determination selector includes: the pressure difference between the feedwater pump outlet pressure and the main steam pressure +2.5MPa obtained by weighted summation of the difference between the feedwater pump outlet pressure and the main steam pressure +2.5MPa by an adder and a manually set constant block, which serves as the first input of the selector.

[0016] As a preferred embodiment of the method for increasing the reliability of boiler feedwater regulating valve as described in this invention, the inputs of the selector during normal unit operation include: the difference between the flow rate value on the maximum flow curve corresponding to the current speed of the first steam-driven feedwater pump and the actual inlet flow rate value is the second input of the selector; the difference between the flow rate value on the maximum flow curve corresponding to the current speed of the second steam-driven feedwater pump and the actual inlet flow rate value is the third input of the selector; the electric feedwater pump is only used during accident handling or unit startup, and does not operate during normal operation.

[0017] As a preferred embodiment of the method for increasing the reliability of boiler feedwater regulating valve as described in this invention, wherein: when the electric feedwater pump is not running, the input of the small selector is determined by: when the electric feedwater pump is not running, a fixed constant is input as the fourth input of the small selector.

[0018] As a preferred embodiment of the method for increasing the reliability of boiler feedwater regulating valves according to the present invention, selecting the minimum input includes:

[0019] In actual operation, the difference between the flow rate value on the maximum flow curve corresponding to the first steam-driven feedwater pump and the second steam-driven feedwater pump and the actual inlet flow rate value is greater than 100. During normal operation, without considering the electric feedwater pump, the input constant is 100. The manual constant block of the first input is set to 1, and the minimum input is the sum of the pump outlet pressure minus the main steam pressure and 2.5MPa.

[0020] As a preferred embodiment of the method for increasing the reliability of boiler feedwater regulating valve regulation according to the present invention, the PID controller outputs control commands by linearly combining the deviation input, including:

[0021] The PID controller combines the proportional (P), integral (I), and derivative (D) values ​​of the deviation input into a linear combination to form a control quantity, and outputs a control command to control the water regulating valve.

[0022] As a preferred embodiment of the method for increasing the reliability of boiler feedwater regulating valves according to the present invention, the control commands include:

[0023] When the boiler is running at low load, control the pressure difference between the feedwater pump outlet pressure and the main steam pressure to 1.5 MPa.

[0024] The beneficial effects of the present invention are as follows: The method of the present invention increases boiler feedwater by adjusting the regulating valve, which improves the throttling loss without affecting the safe operation of the reheater desuperheating water. At the same time, it avoids the frequent opening and closing of the feedwater regulating valve caused by load fluctuations during low load periods, and reduces the wear and tear of valve equipment and the energy consumption of steam-driven feedwater pumps. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments 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. Wherein:

[0026] Figure 1 This is a control logic diagram of a method for increasing the reliability of boiler feedwater regulating valve according to an embodiment of the present invention;

[0027] Figure 2 This is a conventional control logic diagram of a method for increasing the reliability of boiler feedwater regulating valve regulation according to an embodiment of the present invention. Detailed Implementation

[0028] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the protection scope of the present invention.

[0029] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0030] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0031] This invention is described in detail with reference to the schematic diagrams. When detailing the embodiments of this invention, for ease of explanation, the cross-sectional views illustrating the device structure may be partially enlarged, not adhering to the usual scale. Furthermore, the schematic diagrams are merely examples and should not be construed as limiting the scope of protection of this invention. In actual fabrication, the three-dimensional spatial dimensions of length, width, and depth should be included.

[0032] Furthermore, in the description of this invention, it should be noted that the terms "upper," "lower," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are used solely for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. In addition, the terms "first," "second," or "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0033] Unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" in this invention should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; similarly, they can refer to mechanical connections, electrical connections, or direct connections, or indirect connections through an intermediate medium, or internal connections between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0034] Example 1

[0035] Reference Figure 1This is the first embodiment of the present invention, which provides a method for increasing the reliability of boiler feedwater regulating valve regulation, comprising:

[0036] S1: Determine the input of the small selector based on the operating speed, inlet flow rate, and outlet pressure of the water pump;

[0037] Furthermore, the water pumps include: a first steam-driven water pump, a second steam-driven water pump, and an electric water pump.

[0038] Furthermore, the inputs to the feedwater pump outlet pressure determination selector include: the pressure difference between the feedwater pump outlet pressure and the main steam pressure +2.5MPa, obtained by weighted summation of the difference between the feedwater pump outlet pressure and the main steam pressure and the manually set constant block, which serves as the first input to the selector.

[0039] It should be noted that the input of manually setting constant block and the pressure difference between the feedwater pump and the main steam pressure +2.5MPa is added, and the weighted summation by the adder is used as the first input of the small selector in the feedwater regulating valve control logic to control the pressure difference between the feedwater pump outlet pressure and the main steam pressure to 1.5MPa.

[0040] Furthermore, during normal unit operation, the inputs of the selector include: the difference between the flow rate value on the maximum flow curve corresponding to the current speed of the first steam-driven feedwater pump and the actual inlet flow rate value is the second input of the selector; the difference between the flow rate value on the maximum flow curve corresponding to the current speed of the second steam-driven feedwater pump and the actual inlet flow rate value is the third input of the selector; the electric feedwater pump is only used during accident handling or unit startup, and does not operate during normal operation.

[0041] Furthermore, when the electric water pump is not running, the inputs to the selector are determined as follows: when the electric water pump is not running, a fixed constant is input as the fourth input to the selector.

[0042] S2: Use the manual setting constant block combined with the small selector to select the minimum input, and use the minimum input as the deviation input of the PID controller;

[0043] Furthermore, selecting the minimum input includes:

[0044] In actual operation, the difference between the flow rate value on the maximum flow curve corresponding to the first steam-driven feedwater pump and the second steam-driven feedwater pump and the actual inlet flow rate value is greater than 100. During normal operation, without considering the electric feedwater pump, the input constant is 100. The manual constant block of the first input is set to 1, and the minimum input is the sum of the pump outlet pressure minus the main steam pressure and 2.5MPa.

[0045] It should be noted that the maximum flow rate curves of the first / second steam-driven feedwater pumps are as follows: 2500 rpm corresponds to 660 t / h; 3000 rpm corresponds to 800 t / h; 3500 rpm corresponds to 945 t / h; 4000 rpm corresponds to 1085 t / h; 5000 rpm corresponds to 1380 t / h; and 5640 rpm corresponds to 1560 t / h. However, in actual operation, the actual inlet flow rates of the first / second steam-driven feedwater pumps at the above speeds are 255 t / h, 500 t / h, 510 t / h, 610 t / h, 900 t / h, and 1100 t / h, respectively. Obviously, the difference between the flow rate corresponding to the curve and the actual inlet flow rate is quite large.

[0046] The maximum flow rate curves of the electric water supply pump are as follows: 1500 rpm corresponds to 260 t / h; 2500 rpm corresponds to 380 t / h; 3500 rpm corresponds to 570 t / h; 4500 rpm corresponds to 770 t / h; 5000 rpm corresponds to 870 t / h; 5780 rpm corresponds to 1000 t / h. Since the electric pump does not run during normal operation, these parameters can be disregarded.

[0047] During normal operation, the first steam-driven feedwater pump and the second steam-driven feedwater pump are in operation. The electric feedwater pump is only used during emergency handling or unit startup. When both steam-driven feedwater pumps are operating normally, they run in parallel with the same speed, output, and output pressure. If the first steam-driven feedwater pump fails, the outlet pressure will be the same when the second steam-driven feedwater pump and one electric feedwater pump are running during emergency handling.

[0048] S3: The PID controller outputs control commands by linearly combining the deviation input;

[0049] Furthermore, the PID controller outputs control commands through a linear combination of the deviation input, including:

[0050] The PID controller combines the proportional (P), integral (I), and derivative (D) values ​​of the deviation input into a linear combination to form a control quantity, and outputs a control command to control the water regulating valve.

[0051] It should be noted that when the water supply regulating valve is put into automatic control, the output of the PID controller is the opening command of the water supply regulating valve.

[0052] S4: Controls the water supply regulating valve according to the control command to achieve the effect of reducing temperature;

[0053] Furthermore, the control commands include: when the boiler is running at low load, controlling the pressure difference between the feedwater pump outlet pressure and the main steam pressure to 1.5 MPa.

[0054] It should be noted that when the boiler output begins to decrease, as the feedwater speed and feedwater flow rate decrease, the pressure difference between the feedwater pump outlet and the main steam will gradually decrease. Consequently, the deviation input of the PID controller will gradually change from positive to negative. As a result, the output of the PID controller, i.e., the opening setting value of the boiler feedwater regulating valve, will decrease, and the feedwater regulating valve will close, controlling the pressure difference between the feedwater pump outlet pressure and the main steam pressure to 1.5 MPa. When the boiler is running at low load, this ensures that the feedwater regulating valve will not frequently close.

[0055] Furthermore, the water supply regulating valve controlled according to control commands includes:

[0056] When the boiler output decreases and the feedwater pump speed and feedwater flow rate decrease, the pressure difference between the feedwater pump outlet and the main steam will gradually decrease. The PID controller controls the pressure difference between the feedwater pump outlet pressure and the main steam pressure to 1.5 MPa, controls the regulating water valve, keeps the feedwater regulating valve at a large opening, reduces wear and scratches caused by frequent valve closing and closing, and increases valve reliability.

[0057] Furthermore, the cooling of the superheater includes:

[0058] When the feedwater regulating valve of the unit is kept at a pressure 1.5 MPa higher than the main steam pressure, and the feedwater regulating valve is kept fully open at any load section under the unit's coordinated operation mode, the superheater and reheater can still operate safely and achieve the desuperheating effect. The reduction in the desuperheating water volume also reduces the steam volume and the energy consumption of the first steam-driven feedwater pump and the second steam-driven feedwater pump.

[0059] Example 2

[0060] Reference Figures 1-2 This is the second embodiment of the present invention. The beneficial effects are verified through comparative experiments.

[0061] Table 1 shows the relevant operating parameters when the water supply regulating valve is manually kept at 70% opening during a troubleshooting process:

[0062] Table 1 Operating parameters of water supply regulating valve at 70% opening

[0063]

[0064]

[0065] The relevant operating parameters for automatic operation of the water supply regulating valve after troubleshooting are shown in Table 2:

[0066] Table 2 Improved operating parameters

[0067]

[0068] Combining Tables 1 and 2, it can be seen that when the feedwater regulating valve is maintained at 70% opening during the low-load operation period (300MW and below), the pressure difference between the feedwater pump outlet and the main steam pressure is relatively smaller compared to when the feedwater regulating valve is in automatic operation. During low-load periods, the boiler's own heat load is relatively low, so increasing the feedwater regulating valve opening reduces the pressure difference between the feedwater pump outlet and the main steam pressure. Under the current coal type conditions in the experimental stage, this does not result in a significant difference in the superheater's primary and secondary desuperheating water.

[0069] Since the feedwater pressure offset test of Unit 1, the feedwater regulating valve has maintained the feedwater pump outlet pressure at 1.5 MPa higher than the main steam pressure. Feedwater regulating valve FW004 has remained fully open under any load segment in unit coordinated mode. We have been tracking and observing, and collecting relevant operating data. Traditional operating data is shown in Table 3.

[0070] Table 3 Traditional Operation Data

[0071]

[0072] Table 4 Improved Operational Data

[0073]

[0074] Theoretically, fully opening the feedwater regulating valve and reducing the feedwater pressure differential will directly affect the cooling effect of the superheater desuperheating water, and indirectly affect the reheater desuperheating water. A larger opening of the feedwater regulating valve will correspondingly decrease the pump speed. Based on actual operating data analysis, and referring to Tables 3 and 4, it can be seen that:

[0075] 1. After the feedwater pressure offset is set to 1, the feedwater regulating valve can remain fully open in any load segment under the unit coordination mode. Compared with the previous 300MW and below load segment, the feedwater regulating valve is usually closed to 35% thermal control limit, which significantly improves the throttling loss. At the same time, it avoids the frequent opening and closing of the feedwater regulating valve caused by load fluctuations during low load periods, reducing the wear and tear on valve equipment.

[0076] 2. By setting the feedwater pressure offset to 1 and opening the feedwater regulating valve, the pressure difference between the pump outlet and the main steam pressure is reduced to 1.5 MPa. This should have a direct impact on the superheater desuperheating water. However, based on the single-point data in the table, due to different coal types and boiler operating conditions, the amount of desuperheating water automatically controlled when the feedwater pressure offset is set to 1 is even less than the amount of desuperheating water before the test. Therefore, the impact of opening the feedwater regulating valve on the actual effect of the superheater desuperheating water is within a controllable range.

[0077] 3. With the feedwater pressure offset set to 1 and the feedwater regulating valve opened, the corresponding feed pump speed decreases. Based on empirical curves, when the feed pump speed differs by 100 RPM, the pressure of the reheater desuperheating water from the feed pump tap is affected by approximately 0.5 MPa. Comparing the single-point data in the table, the amount of reheater desuperheating water during operation with the feedwater regulating valve opened is still less than the data before the test. The reheater desuperheating water can still operate safely when the feedwater regulating valve is opened.

[0078] 4. Under low load, after the feedwater regulating valve is opened to the maximum, the feedwater pump speed will decrease by about 100-200 RPM within the rated safe operating speed range. This corresponds to a reduction in the amount of steam consumed by the feedwater pump at the fifth stage of extraction, thus reducing the energy consumption of the steam-driven feedwater pump.

[0079] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for increasing the reliability of boiler feedwater regulating valves, characterized in that, include: The input of the small selector is determined based on the operating speed, inlet flow rate, and outlet pressure of the water pump. The minimum input is selected by manually setting a constant block in combination with a small selector, and the minimum input is used as the deviation input of the PID controller; The PID controller outputs control commands by linearly combining the deviation input; The control command controls the water supply regulating valve to achieve a cooling effect. Controlling the water supply regulating valve according to the control command includes: When the boiler output decreases and the feedwater pump speed and feedwater flow rate decrease, the pressure difference between the feedwater pump outlet and the main steam will gradually decrease. The PID controller controls the pressure difference between the feedwater pump outlet pressure and the main steam pressure to 1.5 MPa, controls the regulating water valve, keeps the feedwater regulating valve at a large opening, reduces wear and scratches caused by frequent valve closing and closing, and increases valve reliability. The cooling of the superheater includes: When the feedwater regulating valve of the unit is kept at a pressure 1.5 MPa higher than the main steam pressure, and the feedwater regulating valve is kept fully open at any load section under the unit's coordinated operation mode, the superheater and reheater can still operate safely and achieve the desuperheating effect. The reduction in the desuperheating water volume also reduces the steam volume and the energy consumption of the first steam-driven feedwater pump and the second steam-driven feedwater pump.

2. The method for increasing the reliability of boiler feedwater regulating valve as described in claim 1, characterized in that, The water supply pump includes: First steam-driven water pump, second steam-driven water pump, and electric water pump.

3. The method for increasing the reliability of boiler feedwater regulating valve as described in claim 2, characterized in that, The inputs to the selector for determining the outlet pressure of the feedwater pump include: the pressure difference between the feedwater pump outlet pressure and the main steam pressure +2.5MPa, obtained by weighted summation of the difference between the feedwater pump outlet pressure and the main steam pressure and the manually set constant block, which serves as the first input to the selector.

4. The method for increasing the reliability of boiler feedwater regulating valve as described in claim 3, characterized in that, During normal operation of the unit, the inputs of the selector include: the difference between the flow rate value on the maximum flow curve corresponding to the current speed of the first steam-driven feedwater pump and the actual inlet flow rate value is the second input of the selector; the difference between the flow rate value on the maximum flow curve corresponding to the current speed of the second steam-driven feedwater pump and the actual inlet flow rate value is the third input of the selector; the electric feedwater pump is only used in emergency handling or unit startup, and does not run during normal operation.

5. A method for increasing the reliability of boiler feedwater regulating valve as described in claim 4, characterized in that, When the electric water pump is not running, the inputs of the small selector are determined as follows: when the electric water pump is not running, a fixed constant is input as the fourth input of the small selector.

6. The method for increasing the reliability of boiler feedwater regulating valve as described in claim 5, characterized in that, Selecting the minimum input includes: In actual operation, the difference between the flow rate value on the maximum flow curve corresponding to the first steam-driven feedwater pump and the second steam-driven feedwater pump and the actual inlet flow rate value is greater than 100. During normal operation, without considering the electric feedwater pump, the input constant is 100. The manual constant block of the first input is set to 1, and the minimum input is the sum of the pump outlet pressure minus the main steam pressure and 2.5MPa.

7. A method for increasing the reliability of boiler feedwater regulating valve as described in claim 6, characterized in that, The PID controller outputs control commands through a linear combination of the deviation input, including: The PID controller combines the proportional (P), integral (I), and derivative (D) values ​​of the deviation input into a linear combination to form a control quantity, and outputs a control command to control the water regulating valve.

8. A method for increasing the reliability of boiler feedwater regulating valve as described in claim 7, characterized in that, The control commands include: When the boiler is running at low load, control the pressure difference between the feedwater pump outlet pressure and the main steam pressure to 1.5 MPa.

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