Safety assessment method for heating surface of coal-fired unit boiler based on field control signal

Abstract

The invention discloses a safety assessment method for a heating surface of a coal-fired unit boiler based on a field control signal. The method comprises the following steps: S1, collecting a monitoring signal through a field control end; s2, modifying the monitoring signal to obtain a fault monitoring signal under a simulation condition; s3, establishing a simulation structure model and a reaction model, and obtaining working condition data under simulation conditions; and S4, calculating the predicted residual life of the heating surface under the simulation condition. According to the method, by monitoring the control signal of the control end and combining simulation means for simulation analysis, the problem that monitoring cannot be carried out without a measuring point position in a conventional method can be avoided, and system danger can be early warned as soon as possible by utilizing signal analysis of the control end; the method is high in repeatability and safer to implement, can qualitatively analyze the working state of the boiler system under the abnormal field control signals, does not need to actually adjust parameter tests in the boiler system or collect signals of fixed measuring points at the rear end for safety evaluation, and is relatively low in cost.

Description

Technical Field

[0001] The present invention relates to the technical field of safety assessment, and in particular to a method for assessing the safety of a heating surface of a boiler of a coal-fired unit based on a field control signal. Background Art

[0002] Among the equipment in conventional power plants, boiler equipment is a relatively high-risk equipment. In recent years, boiler accidents have accounted for a high proportion of special equipment accidents nationwide, and accounted for a very high proportion of power plant accidents. Therefore, boiler safety assessment under abnormal field control signals is a very important method to prevent boiler accidents.

[0003] Among them, abnormal signals from the field control end may cause the boiler's combustion, water supply, slag discharge and other key process control disorders, resulting in reduced combustion efficiency, steam pressure fluctuations, inaccurate temperature control and other problems, affecting the stable operation of the boiler, and even further causing the boiler to operate at overpressure, overtemperature and overload. This long-term operation state will accelerate the wear of the boiler equipment and may even damage the boiler's heating surface, such as valves, pipes and other components. It will increase the safety risk during the operation of the boiler, leading to economic losses and the possibility of accidents.

[0004] At present, the main heating surface temperature detection method for the boiler system is: through the monitoring system installed on the boiler, the temperature, pressure, flow and other parameters of the heating surface are monitored in real time to determine its operating status. However, in the boiler, there are still some heating surfaces that cannot be installed with sensors for monitoring, such as the working surfaces of components such as superheaters. Therefore, it is necessary to use simulation methods to obtain the above working parameters and evaluate the overall safety. For example, Chinese patent application CN109635341A discloses a method for predicting the life of pressure parts of a rear three-flue secondary reheat boiler, which establishes a dynamic model of the steam-water system of the rear three-flue secondary reheat boiler; by accessing the DCS measurement point data as input parameters, the real-time parameters of the remaining pressure parts without measurement points installed in the model are calculated; according to the pressure part parameters output by the dynamic model, the life loss of the pressure parts is calculated. This technical solution can continuously predict the life of the pressure parts of the secondary reheat boiler, and can judge the service life of each component of the equipment in real time. Although this technical solution can evaluate the safety in real time through online detection, it has high calculation pressure and occupies a lot of resources.

[0005] In summary, it is also necessary to study a safety assessment method for the heating surface of the boiler system that occupies less resources and has a faster judgment speed. Summary of the invention

[0006] The present invention provides a method for evaluating the safety of the heating surface of a boiler of a coal-fired unit based on a field control signal to solve the above-mentioned problem.

[0007] The present invention adopts the following technical solutions to solve the above technical problems:

[0008] The present invention provides a method for safety assessment of a heating surface of a boiler of a coal-fired unit based on a field control signal, the steps comprising:

[0009] S1. Collect monitoring signals through the field control terminal;

[0010] S2. Based on the signal simulation modification method, modify the monitoring signal and obtain a fault monitoring signal under simulated conditions;

[0011] S3. Establish a simulation structure model of the coal-fired unit boiler;

[0012] Establishing a reaction model based on the simulation structure model, and bringing in the fault monitoring signal under the simulation conditions to obtain the working condition data under the simulation conditions;

[0013] S4, calculating the stress distribution and equivalent temperature of the heated surface under the simulation conditions based on the working condition data under the simulation conditions;

[0014] The remaining life of the heated surface is predicted under the stress distribution and equivalent temperature calculation simulation conditions.

[0015] Optionally, also include:

[0016] S5. Establishing a mapping relationship between each fault monitoring signal under simulation conditions and the predicted remaining life of the heating surface obtained by corresponding solution;

[0017] When the duration of the fault monitoring signal is lower than a threshold, the system modifies the fault detection signal of the field control terminal based on a reverse regulation method;

[0018] When the duration of the fault monitoring signal is greater than or equal to the threshold, the system issues a prompt message; and when the predicted remaining life of the heating surface is less than the expected remaining life or the time margin before overhaul, the system issues a low safety alarm and corrects the design life based on the damage factor accumulation method:

[0019] The correction formula of the design life is:

[0020]

[0021] Where, L CS is the modified design life, L S is the initial design life, D i is the influence of the i-th damage factor, D i0 is the maximum allowable value of the ith damage factor, and n is the number of damage factors.

[0022] Optionally, the signal simulation modification method includes:

[0023] The deviation value of the monitoring signal under the fault condition and the monitoring signal under the normal condition is collected, and the deviation value is added to the monitoring signal to obtain the fault monitoring signal under the simulated condition.

[0024] Optionally, the reaction model includes a turbulent flow model, a radiation heat transfer calculation model, a gas phase combustion reaction model and a solid phase combustion process model.

[0025] Optionally, the turbulent flow model is a k-ε model with swirl correction.

[0026] Optionally, the radiation heat transfer calculation model is a P-1 radiation model.

[0027] Optionally, the gas phase combustion reaction model is a non-premixed gas phase combustion model.

[0028] Optionally, the solid phase combustion process model includes a volatile matter precipitation process equation and a combustion equation.

[0029] Optionally, the heating surface is a working surface inside a pipeline;

[0030] The calculation formula for the stress distribution is:

[0031] σ eq =P(D0-S) / (2S);

[0032] In the formula, σ eq is the hoop stress, P is the stress distribution calculation function, D0 is the outer diameter of the pipe, and S is the wall thickness of the pipe;

[0033] The calculation formula of the equivalent temperature is:

[0034] T = <a / [b+lgt-2lg(0.4678x)]>-273.15;

[0035] Where T is the equivalent temperature of the pipeline metal, t is the operation time of the pipeline, x is the thickness of the oxide film on the inner wall of the pipeline, and a and b are both material constants.

[0036] Optionally, the calculation process of the predicted remaining life of the heating surface includes:

[0037] Calculate the pipeline rupture time, the formula is:

[0038] P(σ)=T(22+lgt τ );

[0039] Where, t τ is the pipeline rupture time;

[0040] The predicted remaining life of the heating surface is calculated based on the pipeline material life curve and the pipeline rupture time.

[0041] ​Compared with the prior art, the present invention adopts the above technical solution and has the following technical effects:

[0042] The method of the present invention is different from the prior art. It can avoid the problem of being unable to monitor the location of the measuring point in the common back-end detection and analysis by monitoring the control signal of the control end and combining it with simulation analysis, and the use of the control signal of the control end is conducive to early warning of system dangers; the method has high repeatability and is safer to implement. It can qualitatively analyze the working state of the boiler system under abnormal field control signals, and there is no need to actually adjust the parameters in the boiler system for testing or collect signals from fixed measuring points at the back end for safety assessment, and the cost is relatively low. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0044] Figure 1 is a flow chart of a method in a specific embodiment of the present invention;

[0045] Figure 2 It is a schematic diagram of structural modeling in a specific embodiment of the present invention;

[0046] Figure 3 It is a simulation analysis display diagram in a specific embodiment of the present invention;

[0047] Figure 4 It is a curve diagram of pipeline material life in a specific embodiment of the present invention. DETAILED DESCRIPTION

[0048] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are 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.

[0049] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0050] It should be noted that the methods used in the present invention are all conventional methods unless otherwise specified; the raw materials and devices used are all conventional commercially available products unless otherwise specified.

[0051] This embodiment provides a method for evaluating the safety of the heating surface of a coal-fired boiler based on a field control signal. Figure 1 As shown, the main steps include:

[0052] S1. Collect monitoring signals through the field control end. First, connect to the field control end and collect corresponding monitoring signals. The detection signals collected from the field control end are control signals of the boiler system. This design is different from the prior art of collecting measurement point signals on the boiler system. It can avoid blind spots in the measurement point settings and is more conducive to early detection of problems starting from the control end. This embodiment is described by taking air volume control as an example, so the collected signals come from the signals of the corresponding air volume control module.

[0053] In the DCS (distributed control system), determine the corresponding air volume control damper or valve, access the information module at that point, and determine the actual monitoring signal value in the Hardware. For example, for a secondary air damper opening of 0-100, it is a 4mA-20mA current signal.

[0054] S2. Based on the signal simulation modification method, the monitoring signal is modified, and the actual value of the air volume control module signal collected in the previous step is modified according to its signal type; the signal simulation modification method of this embodiment is to pre-collect the deviation value of the monitoring signal under fault conditions and the monitoring signal under normal conditions, and add the deviation value to the monitoring signal to obtain the fault monitoring signal under simulated conditions, such as: assuming that the collected monitoring signal is a 5mA current signal, and the deviation value under a real fault condition is 1mA, then the monitoring signal is modified to 6mA to realize the simulation of the changes in the on-site boiler combustion air volume field control signal caused by faults and other reasons, thereby completing the modification process of the field control terminal signal and obtaining the fault monitoring signal under simulated conditions.

[0055] S3. Establish a simulation structure model of the coal-fired unit boiler; specifically, Figure 2 As shown, the boiler is modeled 1:1 in the Ansys Fluent simulation wind and smoke system;

[0056] Afterwards, a reaction model is established based on the simulation structure model. In the process of building the reaction model, the selection of a suitable model can improve the accuracy and performance of the simulation, which has a vital impact on the simulation results. The reaction model of this embodiment includes a turbulent flow model, a radiation heat transfer calculation model, a gas phase combustion reaction model and a solid phase combustion process model. Among them, in the selection of the turbulent flow model, it is necessary to comprehensively consider the flow characteristics of the calculation object and the applicability of each turbulence model. Therefore, this embodiment selects a k-ε model with swirl correction, that is, a Realizable k-ε model, which is similar to the RNG The k-ε model is similar, but has better performance for swirl, strong adverse pressure gradient boundary layer flow and secondary flow; in the selection of radiation heat transfer models, there is a P-1 model with the advantages of small calculation amount and consideration of the scattering effect of radiation, so this embodiment selects the P-1 model as the radiation heat transfer model for calculation and solution; in the selection of gas phase combustion reaction model, this embodiment selects a non-premixed model for simulation calculation, and the transport equation of the mixture components is more efficient in solving; in the selection of solid phase combustion process model, since the process of volatile precipitation is very complicated, two equation models are selected to connect for calculation, specifically including the volatile precipitation process equation and the combustion equation. The two-equation model divides the volatile precipitation process into two parts according to the temperature. In low temperature environment, the volatile precipitation process equation plays a major control role, and in high temperature environment, the combustion equation plays a major control role.

[0057] Using the above model, the operating data under simulated conditions (i.e., the wind and smoke data of this embodiment) obtained by simulation analysis and calculation of the fault monitoring signal under simulated conditions is introduced, such as Figure 3 shown.

[0058] S4. Calculate the stress distribution and equivalent temperature of the heated surface under the simulated conditions based on the wind and smoke data under the simulated conditions;

[0059] The heating surface of this embodiment is the inner working surface of the superheater pipe;

[0060] Therefore, the calculation formula for stress distribution is:

[0061] σ eq =P(D0-S) / (2S);

[0062] In the formula, σ eq is the hoop stress, P is the stress distribution calculation function, D0 is the outer diameter of the pipe, and S is the wall thickness of the pipe;

[0063] The calculation formula for equivalent temperature is:

[0064] T = <a / [b+lgt-2lg(0.4678x)]>-273.15;

[0065] ​Where T is the equivalent temperature of the pipeline metal, t is the operation time of the pipeline, x is the thickness of the oxide film on the inner wall of the pipeline, and a and b are both material constants.

[0066] Furthermore, the calculation process of the predicted remaining life of the heating surface includes:

[0067] Calculate the pipeline rupture time, the formula is:

[0068] P(σ)=T(22+lgt τ );

[0069] Where, t τ is the pipeline rupture time. It is known that pipeline rupture time = remaining life + service time (i.e., pipeline operation time t); therefore, based on the pipeline material life curve (such as Figure 4 As shown, it represents the initial design life under different working conditions), service time and pipeline rupture time to calculate the predicted remaining life of the heating surface.

[0070] On the above basis, simulations are performed for different fault types (fault monitoring signals under different simulation conditions), and the above steps are repeated to obtain the predicted remaining life of the heating surface corresponding to each fault monitoring signal under different simulation conditions;

[0071] Furthermore, in order to simplify the subsequent monitoring steps and calculation amount, the steps of this embodiment also include:

[0072] S5. Establish a mapping relationship between each fault monitoring signal under simulation conditions and the predicted remaining life of the heating surface obtained by the corresponding solution, and include the complete calculation process and formula in the mapping relationship; thereby, establish a corresponding database, in which the fault monitoring signal is a characteristic quantity, and the corresponding predicted remaining life of the heating surface is obtained by guiding the solution through the mapping relationship;

[0073] Afterwards, the system monitors the field control terminal signal online in real time. When the monitoring signal matches the stored fault monitoring signal, the system quickly calculates the predicted remaining life of the heating surface under the current abnormal working condition through the corresponding stored mapping relationship, and records the duration of the fault monitoring signal;

[0074] When the duration of the fault monitoring signal is lower than the initially set threshold, the abnormal control signal has not yet caused significant damage to the system due to the delay in the operation of the boiler system. On this basis, the field control system can modify the fault detection signal of the field control end based on the reverse adjustment method. For example, if the abnormal increase in the air valve switching amount is detected, the system reversely adjusts the air valve switching amount to reduce it. Of course, not all fault conditions can be solved by reverse adjustment. For example, if some execution units fail and are no longer controlled by the system, it is necessary to manually go to the fault point for troubleshooting, and continuous timing is required during this period.

[0075] When the duration of the fault monitoring signal is greater than or equal to the threshold, it indicates that the boiler system has received substantial damage, and the system used in this implementation issues a prompt message; and when the predicted remaining life of the aforementioned heating surface is less than the expected remaining life or the time margin before overhaul, the predicted remaining life of the heating surface is compared with the expected remaining life or the time margin before overhaul, and when the predicted remaining life of the heating surface is less than any of the above values, it indicates that it cannot operate safely until the time of maintenance or replacement, so the system issues a low safety alarm and corrects the design life based on the cumulative method of damage factors.

[0076] The reason for correcting the design life is that although the pipeline has not been broken, it has been damaged. If the initial design life is still used to calculate the remaining life in the subsequent process according to the above steps, there will be obvious deviations, resulting in the calculation time being longer than the actual rupture time. The pipeline does not need to be replaced for one abnormal situation, so the design life must be corrected for each abnormal situation so that it can be used next time. The correction formula for the design life is;

[0077]

[0078] Where, L CS is the modified design life, L S is the initial design life, D i is the influence of the i-th damage factor, D i0 is the maximum allowable value of the ith damage factor, and n is the number of damage factors.

[0079] On the above basis, except for the first abnormal situation after the pipeline is installed, the remaining life is calculated according to the initial design life, the remaining life calculations of subsequent abnormal situations are all based on the previously corrected design life. In this way, by adding the correction of cumulative damage, a more accurate calculation result can be obtained, thereby improving the accuracy of the method of this embodiment and the safety of the application scenario.

[0080] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for safety assessment of the heating surface of a coal-fired boiler based on field control signals, characterized in that the steps include: S1. Collect monitoring signals through the field control terminal; S2. Based on the signal simulation modification method, modify the monitoring signal and obtain a fault monitoring signal under simulated conditions; S3. Establish a simulation structure model of the coal-fired unit boiler; Establishing a reaction model based on the simulation structure model, and bringing in the fault monitoring signal under the simulation conditions to obtain the working condition data under the simulation conditions; S4, calculating the stress distribution and equivalent temperature of the heated surface under the simulation conditions based on the working condition data under the simulation conditions; The remaining life of the heated surface is predicted under the stress distribution and equivalent temperature calculation simulation conditions.

2. The method for safety assessment of the heating surface of a coal-fired unit boiler based on field control signals according to claim 1 is characterized in that: Also includes: S5. Establishing a mapping relationship between each fault monitoring signal under simulation conditions and the predicted remaining life of the heating surface obtained by corresponding solution; Online monitoring of field control terminal signals. When a fault monitoring signal appears, the predicted remaining life of the heating surface is obtained through mapping calculations; When the duration of the fault monitoring signal is lower than a threshold, the system modifies the fault detection signal of the field control terminal based on a reverse regulation method; When the duration of the fault monitoring signal is greater than or equal to the threshold, the system issues a prompt message; and when the predicted remaining life of the heating surface is less than the expected remaining life or the time margin before overhaul, the system issues a low safety alarm and corrects the design life based on the damage factor accumulation method: The correction formula of the design life is: Where, L CS is the modified design life, L S is the initial design life, D i is the influence of the i-th damage factor, D i0 is the maximum allowable value of the ith damage factor, and n is the number of damage factors.

3. The method for safety assessment of the heating surface of a coal-fired unit boiler based on field control signals according to claim 1 is characterized in that: The signal simulation modification method comprises: The deviation value of the monitoring signal under the fault condition and the monitoring signal under the normal condition is collected, and the deviation value is added to the monitoring signal to obtain the fault monitoring signal under the simulated condition.

4. The method for safety assessment of the heating surface of a coal-fired unit boiler based on field control signals according to claim 1 is characterized in that: The reaction model includes a turbulent flow model, a radiation heat transfer calculation model, a gas phase combustion reaction model and a solid phase combustion process model.

5. The method for safety assessment of heating surface of boiler of coal-fired unit based on field control signal according to claim 4 is characterized in that: The turbulent flow model is a k-ε model with swirl correction.

6. The method for safety assessment of heating surface of boiler of coal-fired unit based on field control signal according to claim 4 is characterized in that: The radiation heat transfer calculation model is a P-1 radiation model.

7. The method for safety assessment of heating surface of boiler of coal-fired unit based on field control signal according to claim 4 is characterized in that: The gas phase combustion reaction model is a non-premixed gas phase combustion model.

8. The method for safety assessment of the heating surface of a coal-fired unit boiler based on field control signals according to claim 4 is characterized in that: The solid phase combustion process model includes a volatile matter precipitation process equation and a combustion equation.

9. The method for safety assessment of heating surface of boiler of coal-fired unit based on field control signal according to claim 1, characterized in that: The heating surface is the working surface inside the pipeline; The calculation formula for the stress distribution is: s eq =P(D0-S) / (2S); In the formula, σ eq is the hoop stress, P is the stress distribution calculation function, D0 is the outer diameter of the pipe, and S is the wall thickness of the pipe; The calculation formula of the equivalent temperature is: T = <a / [b+lgt-2lg(0.4678x)]>-273.15; Where T is the equivalent temperature of the pipeline metal, t is the operation time of the pipeline, x is the thickness of the oxide film on the inner wall of the pipeline, and a and b are both material constants. The calculation process of the predicted remaining life of the heating surface includes:

10. The method for safety assessment of the heating surface of a coal-fired unit boiler based on field control signals according to claim 9, characterized in that: Calculate the pipeline rupture time, the formula is: The predicted remaining life of the heating surface is calculated based on the pipeline material life curve and the pipeline rupture time. P(σ)=T(22+lgt τ ); Where, t τ is the pipeline rupture time; ​

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