A method for judging the detection signal of the water level of a power station boiler drum

Abstract

The present invention belongs to the field of thermal detection signal detection of power station boilers, and discloses a method for judging the detection signal of a water level in a steam drum of a power station boiler, comprising the following steps: performing reliability judgment on each differential pressure water level detection signal; performing deviation judgment on three differential pressure steam drum water level signals according to the reliability judgment result; and shielding false water level signals. The present invention sets reliability judgment and deviation judgment methods for two ways of false water level, designs a false water level shielding scheme, realizes rate discrimination and reliability judgment of steam drum water level signals, avoids false water level signals causing false operation of boiler monitoring, alarm and safety interlock protection, and ensures safe operation of boilers.

Description

Technical Field

[0001] The invention belongs to the field of thermal detection signal detection of power station boilers, and in particular relates to a method for determining a detection signal of a steam drum water level of a power station boiler. Background Art

[0002] A boiler is an energy conversion device. A power station boiler uses coal gas as fuel and uses the heat energy released by the combustion of the fuel to transfer the heat energy to the water in the container, converting the water into superheated steam that reaches the required temperature or a certain pressure.

[0003] In a steam boiler, the steam drum is one of the main components of the boiler. It is an important connecting hub for the three process steps of heating, evaporation and superheating in the boiler. The steam drum is connected to the downcomer and the water-cooled wall to form a natural circulation loop of boiler water. During the flow of the circulation loop, the water receives heat energy from the combustion of fuel in the furnace. The water is heated into saturated water in the steam drum and further vaporized into saturated steam. Therefore, a certain amount of water and steam is stored in the steam drum.

[0004] The boiler drum water level is an important thermal parameter for the safe operation of power station boilers and steam turbines. If the drum water level is too high, it will affect the effect of the steam-water separation device, increase the humidity and salt content of the saturated steam, cause scaling of the superheater and steam turbine steam passage, cause superheater tube wall overheating or even tube bursting, reduce turbine efficiency, and increase axial thrust. It directly threatens the safe and economical operation of the steam turbine. If the drum water level is too low, it will affect the water circulation safety of the natural circulation boiler, cause the water-cooled wall tube circulation to stagnate, and thus cause local overheating or even tube bursting.

[0005] There are several main ways to measure the water level of a boiler drum: electric contact water level gauge, two-color mica water level gauge, and differential pressure water level gauge. The electric contact water level gauge uses the difference in the electrical conductivity of water and steam to detect water level changes, and the two-color mica water level gauge uses the different refractive indices of water and steam to detect water level. The characteristics of these two methods are that the water level detection signal is discontinuous and inaccurate, and can only be used as a monitoring reference and supplement to the measurement signal of the differential pressure water level gauge.

[0006] The differential pressure water level gauge measures the static pressure difference between the variable water level and the constant water level according to the principle of liquid statics, and then converts the static pressure difference into a standard electrical signal that changes continuously with the water level through the differential pressure transmitter. The signal is received by the automatic control equipment such as the acquisition module of the DCS computer system for monitoring. Medium-pressure and low-pressure power station steam boilers generally install two differential pressure water level gauges on the left and right sides of the steam drum, and high-pressure and above steam boilers generally install three differential pressure water level gauges on the left, middle and right positions of the steam drum to ensure the accuracy of boiler water level detection.

[0007] The boiler drum water level is measured using these three detection instruments at the same time. The differential pressure water level gauge detects the boiler static pressure difference and converts it into a 4-20mA standard signal to access the computer control system. It serves as the adjustment object for boiler water level parameter monitoring and alarm, safety interlock protection and water level three-impulse cascade automatic control. The electric contact water level gauge and mica water level gauge are used as auxiliary reference objects for the boiler differential pressure water level because of their simple structure and intuitive and clear observation.

[0008] As an important parameter of boiler feed water automatic control system and boiler interlock safety protection, water level is affected by the complexity of drum water level object, the inherent characteristics of water level gauge measurement principle, the quality and performance of measuring equipment, etc. In actual measurement, there are many uncertain factors and large measurement errors that affect its detection accuracy and authenticity. For example, when the pressure of boiler drum rises suddenly, the heat used to evaporate boiler water is reduced accordingly, the amount of bubbles in boiler water is reduced, the volume of steam-water mixture shrinks, and the water level detection value drops rapidly on the basis of the real water level unchanged, forming a false water level. In addition, when the unstable fuel in the boiler causes the heat load to increase or decrease suddenly, the specific volume of water will also increase or decrease, and a false water level will also be formed. In addition, sudden changes in boiler load, fire extinguishing, safety valve action, differential pressure transmitter failure, etc. will all produce false water levels, which will cause operators and computer control systems to make misjudgments, lead to wrong operating instructions, and cause serious consequences that endanger boiler operation and personal safety accidents.

[0009] The reasons for the false water level of the boiler are, on the one hand, sudden changes in process objects such as boiler fuel and steam load, sudden movements of equipment such as safety valves and vent valves, and blockage or leakage of differential pressure water level measurement components such as balance containers, pulse pipelines, and differential pressure transmitters, which results in a rapid rise or fall in the water level measurement signal, characterized by a continuous and large change in parameters. On the other hand, differential pressure transmitter failure, disconnection of the signal cable that transmits the standard electrical signal from the differential pressure transmitter to the computer control system, and failure of the acquisition module that receives the standard electrical signal from the computer control system will also cause the drum water level signal to suddenly change to form a false signal, resulting in the water level measurement signal returning to zero instantly, characterized by a step-like and large change in parameters. Therefore, it is necessary to provide a method for determining the detection signal of the drum water level of a power station boiler, and to achieve rate discrimination and reliability determination of the drum water level signal according to the change characteristics of the false water level measurement signal, so as to avoid false water level signals causing false operation of the boiler monitoring, alarm, and safety interlock protection, and ensure safe operation of the boiler. Summary of the invention

[0010] In order to overcome the defects of the above-mentioned prior art, the purpose of the present invention is to provide a method for judging the water level detection signal of the steam drum of a power station boiler. By analyzing the changing characteristics of the false water level measurement signal, software programming is performed in the boiler computer automatic control system to realize the rate discrimination and reliability judgment of the steam drum water level signal, thereby avoiding malfunction of the boiler monitoring, alarm and safety interlock protection caused by false water level signals, and ensuring the safe operation of the boiler.

[0011] To achieve the above object, the present invention provides the following technical solutions:

[0012] A method for determining a detection signal of a water level of a power station boiler drum, comprising the following steps:

[0013] Conduct reliability judgment on each differential pressure water level detection signal;

[0014] According to the reliability judgment results, the deviation of three differential pressure drum water level signals is judged;

[0015] Shield false water level signals.

[0016] Furthermore, the reliability judgment of each differential pressure water level detection signal includes:

[0017] Determine the rate of change of the standard 4-20mA signal of the drum water level;

[0018] Determine whether the drum water level signal exceeds the range limit in engineering units;

[0019] The standard 4-20mA signal of the drum water level is judged to have exceeded the amplitude range.

[0020] Furthermore, the rate of change of the standard 4-20 mA signal of the drum water level is determined, including:

[0021] The signal of the current scanning cycle of the differential pressure water level gauge is compared with the maximum signal value and / or the minimum signal value of the previous scanning cycle segment. If the signal increase or decrease amplitude of the current scanning cycle exceeds the preset value, the drum water level output signal is maintained at the signal value of the previous scanning cycle where the rate change exceeds the limit, and an over-limit alarm is issued. If the signal increase or decrease amplitude of the current scanning cycle does not exceed the preset value, the water level signal value of the current scanning cycle is output.

[0022] Furthermore, the drum water level signal is judged to be out of range in engineering units, including:

[0023] The water level signal of the current scanning cycle is compared with the upper limit and / or lower limit of the normal range of the water level signal. If the water level signal of the current scanning cycle exceeds the normal range of the water level signal, the drum water level output signal is maintained at the signal value of the scanning cycle before the limit is exceeded, and an over-limit alarm is issued. If the signal of the current scanning cycle does not exceed the normal range of the water level signal, the water level signal value of the current scanning cycle is output.

[0024] Furthermore, the standard 4-20 mA signal of the drum water level is judged to be out of range, including:

[0025] The amplitude of the water level signal in the current scanning cycle is compared with the upper limit of 20mA and the lower limit of 4mA. If the amplitude of the water level signal in the current scanning cycle exceeds 20mA or is lower than 4mA, the drum water level output signal is maintained at the signal value of the scanning cycle before the limit is exceeded, and an over-limit alarm is issued. If the amplitude of the water level signal in the current scanning cycle does not exceed the upper limit of 20mA and the lower limit of 4mA, the water level signal value of the current scanning cycle is output.

[0026] Furthermore, the three differential pressure drum water level signals are subjected to deviation judgment according to the reliability judgment result, including:

[0027] The normal drum water level signals of the three water level differential pressure gauges of the same boiler after reliability judgment are compared with each other. If the deviations of the three water level signals are all within the preset limit value range, the middle value of the three water level signals is taken as the total water level signal. If the deviations of two water level signals are within the preset limit value range, the average value of the two water level signals is taken as the total water level signal. If the deviations of multiple water level signals exceed the preset limit value range, the total water level signal remains at the total water level signal of the scanning cycle before the limit is exceeded and an over-limit alarm is issued.

[0028] Furthermore, false water level signals are shielded, including:

[0029] The over-limit total water level signal is shielded according to the result of the deviation judgment.

[0030] Furthermore, shielding false water level signals also includes:

[0031] During the operation of the safety valve and the air vent valve equipment, the boiler drum water level signal is shielded.

[0032] Furthermore, during the operation of the safety valve and the air exhaust valve equipment, the boiler drum water level signal is shielded, including:

[0033] The control signal shielding time is 60 seconds.

[0034] Furthermore, during the operation of the safety valve and the air exhaust valve, the boiler drum water level signal is shielded, and the method further includes:

[0035] The output total water level signal is maintained at the total water level signal of the previous scanning cycle for the operation of the safety valve and the air exhaust valve equipment, and an alarm prompt is issued.

[0036] Technical effects and advantages of the present invention:

[0037] The present invention sets reliability judgment and deviation judgment methods according to two ways of false water level occurrence, designs a false water level shielding scheme, realizes the identification of the change rate and reliability judgment of the drum water level signal, avoids malfunction of boiler monitoring, alarm and safety interlock protection caused by false water level signals, and ensures the safe operation of the boiler.

[0038] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures pointed out in the description, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a flow chart of a method for determining a detection signal of a power station boiler drum water level according to the present invention;

[0040] Figure 2 A flow chart of judging the rate of change of a water level signal according to the present invention;

[0041] Figure 3 This is a flow chart of water level signal reliability judgment of the present invention. DETAILED DESCRIPTION

[0042] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0043] Figure 1 The following is a flow chart of a method for judging the detection signal of the steam drum water level of a power station boiler. Figure 1 As shown, the present invention provides a method for determining a detection signal of a water level of a power station boiler drum, comprising:

[0044] Conduct reliability judgment on each differential pressure water level detection signal;

[0045] According to the reliability judgment results, the deviation of three differential pressure drum water level signals is judged;

[0046] Shield false water level signals.

[0047] The specific steps for determining the reliability of each differential pressure water level detection signal are as follows:

[0048] ⑴ Figure 2 This is a flow chart of judging the rate of change of the water level signal of the present invention, as shown in FIG. Figure 2 As shown, the change rate of the standard 4-20mA signal of the drum water level is judged, that is, after the data acquisition module of the computer automatic control system receives the water level signal, the signal of the current scanning cycle is compared with the maximum (or minimum) signal of the previous scanning cycle segment. If the increase or decrease amplitude of the signal of the current scanning cycle exceeds a calculated set value, it is judged that the change amount of the signal exceeds the normal value. At this time, the drum water level signal remains at the signal value of the previous scanning cycle where the rate change exceeds the limit, and the monitoring system issues an alarm prompt for the drum water level signal to indicate that the rate change exceeds the limit.

[0049] For example, In1 is the water level parameter value currently scanned, RL is the change per second, and the previous scanning cycle segment n is set to 10 seconds, then K1, K2, K3...Kn are the water level parameter values ​​within 10 seconds. When |In1-max(Ki)|>RL or |In1-min(Ki)|>RL (note: 1≤i≤n), the computer control system programming logic determines that the signal change rate exceeds the limit.

[0050] ⑵ The drum water level signal is judged to be out of range in engineering units (mm), including comparing the water level signal received in each scanning cycle with the upper and lower limits of the normal measuring range of the water level signal. If it exceeds the upper or lower limit of the measuring range, the signal is judged to be out of range. At this time, the drum water level signal remains at the signal value of the scanning cycle before the over-limit, and the monitoring system issues an over-limit alarm prompt.

[0051] ⑶ Judge whether the amplitude range of the standard 4~20mA signal of the drum water level is out of limit, that is, the standard 4~20mA signal received by the data acquisition module of the computer automatic control system in each scanning cycle is compared with the upper limit of 20mA and the lower limit of 4mA. If it exceeds the upper limit or is lower than the lower limit, the signal state is judged to be the amplitude out-of-limit state. At this time, the drum water level signal maintains the signal value of the scanning cycle before the over-limit, and the monitoring system issues an over-limit alarm prompt.

[0052] The specific steps for judging the deviation of the three differential pressure drum water level signals according to the reliability judgment results are as follows:

[0053] The normal drum water level signals of the three water level differential pressure gauges of the same boiler after reliability judgment are compared with each other. If the deviations of the three water level signals are all within the preset limit value range, the middle value of the three water level signals is taken as the total water level signal. If the deviations of two water level signals are within the preset limit value range, the average value of the two water level signals is taken as the total water level signal. If the deviations of multiple water level signals exceed the preset limit value range, the total water level signal remains at the total water level signal of the scanning cycle before the limit is exceeded and an over-limit alarm is issued, thereby avoiding the situation where individual differential pressure gauges among multiple water level differential pressure gauges are inaccurately detected.

[0054] Shielding false water level signals, including:

[0055] The over-limit total water level signal is shielded based on the result of deviation judgment. In addition, during the operation of equipment such as the safety valve and the air exhaust valve, the false water level generated at this time cannot be used as the adjustment object of the automatic adjustment of the boiler feed water and the judgment basis of the boiler safety interlock protection due to the great changes in the steam drum pressure and steam load. The boiler steam drum water level signal is shielded for 60 seconds, so that the total steam drum water level parameter is maintained at the total water level parameter value of the previous scanning cycle of the equipment operation for 60 seconds and an alarm prompt is issued.

[0056] The reasons for causing false water level in boilers include, on the one hand, sudden changes in process objects such as boiler fuel and steam load, sudden movements of equipment such as safety valves and vent valves, and blockage or leakage of differential pressure water level measurement components such as balance containers, pulse pipelines, and differential pressure transmitters, which results in a rapid rise or fall in the water level measurement signal, characterized by a continuous and substantial change in the parameter change. On the other hand, differential pressure transmitter failure, disconnection of the signal cable that transmits the standard electrical signal from the differential pressure transmitter to the computer control system, and failure of the acquisition module that receives the standard electrical signal from the computer control system will also cause the drum water level signal to suddenly change to form a false signal, resulting in the water level measurement signal returning to zero instantly, characterized by a step-like and substantial change in the parameter change. The present invention aims at the change characteristics of the false water level measurement signal, and by performing reliability judgment and deviation judgment on the water level measurement signal, in conjunction with a false water level shielding scheme, realizes the identification of the change rate and reliability judgment of the drum water level signal, avoids the false water level signal causing the boiler's monitoring, alarm, and safety interlock protection to malfunction, and ensures the safe operation of the boiler.

[0057] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for determining a detection signal of a power station boiler drum water level, characterized in that: The method comprises the following steps: Conduct reliability judgment on each differential pressure water level detection signal; According to the reliability judgment results, the deviation of three differential pressure drum water level signals is judged; Shield false water level signals; The reliability judgment of each differential pressure water level detection signal includes: Determine the rate of change of the standard 4-20mA signal of the drum water level; Determine whether the drum water level signal exceeds the range limit in engineering units; Determine if the amplitude range of the standard 4-20mA signal of the drum water level exceeds the limit; The deviation judgment of the three differential pressure drum water level signals according to the reliability judgment result includes: The normal drum water level signals of the three water level differential pressure gauges of the same boiler after reliability judgment are compared with each other. If the deviations of the three water level signals are all within the preset limit value range, the middle value of the three water level signals is taken as the total water level signal. If the deviations of two water level signals are within the preset limit value range, the average value of the two water level signals is taken as the total water level signal. If the deviations of multiple water level signals exceed the preset limit value range, the total water level signal remains at the total water level signal of the scanning cycle before the limit is exceeded and an over-limit alarm is issued.

2. A method for determining a power station boiler drum water level detection signal according to claim 1, characterized in that: The determination of the rate of change of the standard 4-20 mA signal of the drum water level comprises: The signal of the current scanning cycle of the differential pressure water level gauge is compared with the maximum signal value and / or the minimum signal value of the previous scanning cycle segment. If the signal increase or decrease amplitude of the current scanning cycle exceeds the preset value, the drum water level output signal is maintained at the signal value of the previous scanning cycle where the rate change exceeds the limit, and an over-limit alarm is issued. If the signal increase or decrease amplitude of the current scanning cycle does not exceed the preset value, the water level signal value of the current scanning cycle is output.

3. A method for determining a power station boiler drum water level detection signal according to claim 1, characterized in that: The judgment of whether the drum water level signal exceeds the range limit in engineering units includes: The water level signal of the current scanning cycle is compared with the upper limit and / or lower limit of the normal range of the water level signal. If the water level signal of the current scanning cycle exceeds the normal range of the water level signal, the drum water level output signal is maintained at the signal value of the scanning cycle before the limit is exceeded, and an over-limit alarm is issued. If the signal of the current scanning cycle does not exceed the normal range of the water level signal, the water level signal value of the current scanning cycle is output.

4. A method for determining a power station boiler drum water level detection signal according to claim 1, characterized in that: The determination of whether the amplitude range of the standard 4-20 mA signal of the drum water level exceeds the limit includes: The amplitude of the water level signal in the current scanning cycle is compared with the upper limit of 20mA and the lower limit of 4mA. If the amplitude of the water level signal in the current scanning cycle exceeds 20mA or is lower than 4mA, the drum water level output signal is maintained at the signal value of the scanning cycle before the limit is exceeded, and an over-limit alarm is issued. If the amplitude of the water level signal in the current scanning cycle does not exceed the upper limit of 20mA and the lower limit of 4mA, the water level signal value of the current scanning cycle is output.

5. A method for determining a power station boiler drum water level detection signal according to claim 1, characterized in that: The shielding of false water level signals comprises: The over-limit total water level signal is shielded according to the result of the deviation judgment.

6. A method for determining a detection signal of a power station boiler drum water level according to claim 1, characterized in that: The method for shielding false water level signals further comprises: During the operation of the safety valve and the air vent valve equipment, the boiler drum water level signal is shielded.

7. A method for determining a detection signal of a power station boiler drum water level according to claim 6, characterized in that: The signal shielding of the boiler drum water level signal during the operation of the safety valve and the air exhaust valve equipment includes: The control signal shielding time is 60 seconds.

8. A method for determining a detection signal of a power station boiler drum water level according to claim 7, characterized in that: The method of shielding the boiler drum water level signal during the operation of the safety valve and the air exhaust valve equipment also includes: The output total water level signal is maintained at the total water level signal of the previous scanning cycle for the operation of the safety valve and the air exhaust valve equipment, and an alarm prompt is issued.

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