JP5223506B2 - Crushing mill life evaluation method - Google Patents

Description

  The present invention relates to a method for evaluating the life of a pulverizing mill that finely pulverizes coal, and more particularly to a method for evaluating the life of a pulverizing mill that can evaluate the life in consideration of the operation of the pulverizing mill.

  In coal-fired boiler facilities and the like, a pulverized coal mill is used to finely pulverize coal raw materials into pulverized coal.

  As shown in FIG. 8, the pulverized coal mill 81 includes a rotary table 83 that is rotationally driven by a driving device 82, and a pulverizing roller 84 that pulverizes the raw material (coal) supplied onto the rotary table 83. The rotary table 83 and the crushing roller 84 are covered with a casing 85, and the crushing roller 84 is fixed to the casing 85 via a roller pivot 86.

  In the pulverized coal mill 81, the raw material is supplied onto the rotary table 83 from a coal supply pipe 87 provided above the rotary table, and the raw material is pulverized by pressing the pulverizing roller 84 against the rotary table 83. The raw material pulverized to a predetermined particle size is blown up by air supplied from an air supply pipe 88 provided at the lower portion of the casing 85 and moved to the upper separator 89.

  The separator 89 is rotationally driven by a separator driving device 90. The pulverized raw material is classified here, and only pulverized coal is discharged from a pulverized coal pipe 91 provided on the upper portion of the casing 85, and the rest is a rotary table. It is returned to 83 and pulverized again.

  In a pulverizing mill such as the pulverized coal mill 81, the casing 85 vibrates at a specific frequency by the rotation of the rotary table 83 and the separator 89, while the pulverizing roller 84 vibrates randomly by pulverizing the raw material. . For this reason, fatigue cracks are generated by repeatedly applying stress in a portion where stress is concentrated in shape.

  The occurrence of fatigue cracks at the stress concentration part (critical point) is inevitable. Since these are exchanged in advance, a life evaluation method capable of predicting the life of the grinding mill is desired.

  In this regard, although it is not a method for evaluating the life of the crushing mill, as a method for evaluating the life of other structures, a method of measuring the load state of the structure using a fatigue sensor or strain gauge and estimating the life based on the result (For example, refer to Patent Documents 1 to 5).

  In this method, a fatigue sensor or strain gauge is attached to the stress concentration part of the structure, the stress is measured, a stress-frequency histogram is created based on the measurement result, and a fatigue strength diagram at the stress concentration part ( SN diagram) is created, the damage degree per unit time is calculated using these, and the lifetime of the structure is estimated from the calculated damage degree.

JP 2006-329837 A JP 2004-191340 A Japanese Patent Laid-Open No. 10-185854 Japanese Patent Laid-Open No. 2003-4599 Japanese Patent Laid-Open No. 6-323962

  However, there is a problem that this life evaluation method cannot be directly applied to a grinding mill.

  That is, in the crushing mill, the separator 89, the rotary table 83, the crushing roller 84, and the like serve as vibration sources, and the vibration changes depending on the raw material supply amount (coal supply amount), and the generated stress level also changes depending on the operation time. Therefore, the lifetime cannot be evaluated in the same manner as a structure to which stress is applied under substantially constant conditions.

  In the conventional crushing mill life evaluation, design drawings are used and a fatigue strength diagram is created using the material strength of the stress-concentrated part and the design fatigue strength diagram is compared with past damage records. This was only used for life evaluation.

  However, for example, a pulverizing mill with a small number of start and stop times may cause fatigue damage (fatigue cracks) earlier than a pulverizing mill with a large number of start and stop times, and this phenomenon cannot be explained by conventional methods. It was.

  As a result of intensive studies on this cause, the present inventor has found that in the pulverization mill, the pulverization roller 84 is worn when the operation time is long, and the vibration level of the random vibration is increased due to the wear of the pulverization roller 84. I found it.

  That is, the longer the operation time is, the more the grinding roller 84 wears, and the wear increases the vibration level of random vibration due to raw material grinding, and the generated stress level at the stress concentration portion due to the random vibration rises. This is thought to have an effect on the life (generation of fatigue cracks).

  In the conventional life evaluation method, since the increase in the generated stress level due to wear of the crushing roller 84 is not taken into consideration, the life of the crushing mill cannot be accurately evaluated. Therefore, a life evaluation method that takes into account an increase in stress level due to wear of the grinding roller 84 is desired.

  Accordingly, an object of the present invention is to provide a life evaluation method for a crushing mill in which the accuracy of life evaluation is improved in consideration of an increase in generated stress level due to wear of the crushing roller.

  The present invention has been devised to achieve the above object, and the invention of claim 1 is a rotary table rotatably provided in a casing, and is rotatably supported on the rotary table. In the life evaluation method of a crushing mill that evaluates the life of a crushing mill equipped with a crushing roller that crushes the raw material supplied on the table, a sensor is installed at the stress concentration part of the new crushing mill and the old crushing mill that has been operated for a predetermined time Attaching and measuring strain from starting to stopping of these crushing mills as one cycle, creating a stress-frequency histogram for each, and creating a stress-frequency histogram for each raw material supply amount, on the other hand, stress concentration of crushing mill The fatigue strength diagram of the part is set from the past damage results, and the equivalent vibration stress is obtained from the fatigue strength diagram and the stress-frequency histogram, Determine the damage level in one cycle of the new crushing roller and the old crushing roller from the equivalent vibration stress, and set the relationship between the damage level in 1 cycle and the operation time, Based on the past operation results, the degree of damage in one cycle of the crushing mill can be estimated, and a stress-frequency histogram can be created for any operation time from the degree of damage in that one cycle. This is a crushing mill life evaluation method for calculating the cumulative damage degree by accumulating the damage degree up to an arbitrary operation time and predicting the life based on the cumulative damage degree.

  According to a second aspect of the present invention, the stress-frequency histogram of the new pulverization mill and the old pulverization mill is created for each operation pattern at startup, normal operation, and stop. This is a life evaluation method.

  According to the invention of claim 3, stress-frequency histograms of the new pulverizing mill and the old pulverizing mill are created for each raw material supply amount and for each operation pattern, and the respective equivalent vibration stresses are obtained based on the histograms. It is the lifetime evaluation method of the crushing mill of Claim 2.

  According to a fourth aspect of the present invention, the degree of damage is obtained from the equivalent vibration stress of each operation pattern at the time of start-up, normal operation, and stop, and these are added together to obtain the degree of damage in one cycle. This is a method for evaluating the life of a crushing mill described in the above.

  In the invention of claim 5, the degree of damage in one cycle of the new pulverizing mill and the old pulverizing mill is determined under the same raw material supply amount, and the old pulverizing mill is operated from the new pulverizing mill. It is a crushing mill life evaluation method according to any one of claims 1 to 4, wherein the relationship between the damage degree in one cycle and the operation time is set on a time scale.

  In the invention of claim 6, the degree of damage in one cycle of the new crushing mill and the old crushing mill is obtained by taking into account the equivalent vibration stress of the stress-frequency histogram corresponding to the amount of raw material supplied. It is the lifetime evaluation method of the grinding | pulverization mill in any one.

  In the invention according to claim 7, the cumulative damage degree is obtained by calculating an equivalent vibration stress from the stress-frequency histogram at the arbitrary operation time, calculating the damage degree from the equivalent vibration stress, and accumulating the damage degree. It is the lifetime evaluation method of the grinding | pulverization mill in any one of Claims 1-6 calculated | required.

  In the invention according to claim 8, the cumulative damage degree is created based on the stress-frequency histogram in the total operation time by creating a stress-frequency histogram in the total operation time from the stress-frequency histogram in the arbitrary operation time. It is the lifetime evaluation method of the grinding | pulverization mill in any one of Claims 1-6 calculated by these.

  According to the present invention, the life of the crushing mill can be accurately evaluated by performing the life evaluation in consideration of an increase in the generated stress level due to wear of the crushing roller.

  Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.

  The present invention is a life evaluation method for predicting the occurrence of fatigue cracks in the stress concentration part of a pulverizing mill such as the pulverized coal mill described in FIG.

  The conventional life evaluation method using only the fatigue strength diagram has a problem that the life of the grinding mill cannot be accurately evaluated.

  Therefore, the present inventor has conducted intensive studies on this cause, and as a result, has found that the generated stress level increases due to wear of the crushing roller, which affects the life evaluation of the crushing mill.

  As shown in FIG. 2, when the generated stress level in the stress concentration part of the old product crushing mill (shown by the broken line in the figure) and the new product crushing mill (shown by the solid line in the figure) operated for a predetermined time as one cycle from start to stop is compared, When starting and stopping, the old product crushing mill has a lower stress level than the new crushing mill, but during normal operation, the old product crushing mill has a higher stress level than the new crushing mill. I understood.

  The reason why the generated stress level of the old crushing mill is higher than that of the new crushing mill during normal operation is considered to be due to the wear of the crushing roller. The wear level of the crushing roller increases the vibration level of random vibration. Therefore, the generated stress level is considered to have increased.

  In FIG. 2, the generated stress level increases at the time of start and stop, because the raw material is not supplied or the raw material supply amount is small, so that the pulverizing roller is in direct contact with the rotary table, resulting in a large generated stress level. This is because of this.

  From the above results, the present inventor has conducted research on a life evaluation method capable of evaluating the life of a grinding mill in consideration of an increase in vibration stress level due to wear of the grinding roller, and has reached the present invention.

  Now, FIG. 1 is a flowchart of the crushing mill life evaluation method according to the present embodiment.

  As shown in FIG. 1, the crushing mill life evaluation method according to the present embodiment is performed in one cycle of a new crushing mill (operation time: 0 hour) and an old crushing mill (operation time: x hours) operated for a predetermined time. The life evaluation is performed by using the relationship between the degree of damage and the operation time in one cycle (steps S1 to S7) and the relationship between the degree of damage and the operation time in one cycle. The cumulative damage degree of the crushing mill that performs the process is calculated and the life is evaluated (steps S8 to S9).

  First, the process (steps S1 to S7) of obtaining the damage degree in one cycle of the new crushing mill and the old article crushing mill and obtaining the relationship between the damage degree in one cycle and the operation time from the damage degree will be described.

  The new crushing mill and the old crushing mill used in step S1 are of the same type as the crushing mill for performing life evaluation. In this embodiment, an old product grinding mill that has been operating for 26000 hours was used.

  In step S1, a new crushing mill (or an old crushing mill, or a crushing mill for performing life evaluation) is subjected to natural vibration analysis (FEM), and a stress concentration portion (critical point) for fatigue crack generation is extracted. In the present embodiment, the stress concentration portion is extracted from the low-order three-mode modal stress distribution. The extracted stress concentration portion is, for example, a roller pivot or a connection portion between the air supply pipe and the casing.

  In step S2, sensors such as fatigue sensors and strain gauges are affixed to the stress concentration portion extracted in step S1, and the new pulverizing mill and the old pulverizing mill are started, normally operated, and stopped in each operation pattern. Measure the load condition (strain fluctuation). During normal operation, the load state is measured for each raw material supply amount. An example of the waveform of the strain fluctuation measured by the sensor is shown in FIG.

  In step S3, the stress waveform of each operation pattern in the stress concentration portion obtained in step S2 is subjected to stress frequency analysis, and a stress-frequency histogram in each operation pattern of the new product crushing mill and the old product crushing mill is created. For example, a rain flow method may be used as the stress frequency analysis method. An example of the stress-frequency histogram created is shown in FIG.

  In step S4, a fatigue strength diagram of the stress concentration portion is created. In the present embodiment, the inclination of the fatigue strength diagram and the truncation limit (lower limit stress that does not cause fatigue damage) are set based on the past damage record. An example of the prepared fatigue strength diagram is shown in FIG.

  In step S5, using the stress-frequency histogram obtained in step S3 and the fatigue strength diagram obtained in step S4, equation (1) shown in equation (1)

Thus, the equivalent vibration stress σ _{v_eq} in each operation pattern of the new pulverization mill and the old pulverization mill is calculated.

Furthermore, from this equivalent vibration stress σ _{v_eq} , the equation (2) shown in the equation (2)

Thus, the damage degree D per unit time in each operation pattern of the new pulverization mill and the old pulverization mill is calculated.

  In step S6, from the damage degree D per unit time in each operation pattern obtained in step S5 and the operation time of each operation pattern in one cycle, the new crushing mill and the old crushing mill in one cycle. Determine the degree of damage.

Specifically, for example, assuming that the degree of damage per unit time at start-up is D ₁ and the start-up time within one cycle is t ₁ (h), the total degree of damage at start-up is obtained by D ₁ × t ₁ . It is done. When this is stopped and during normal operation (for each raw material supply amount when the raw material supply amount changes), the same calculation is performed, and when all of these are added, the degree of damage in one cycle can be obtained.

  The degree of damage in one cycle of the new crushing mill and the old crushing mill can be obtained by taking into account the equivalent vibration stress (damage per unit time) of the stress-frequency histogram corresponding to the raw material supply amount.

  In step S7, the operation of the new crushing mill (operation time: 0 hours) to the old crushing mill (operation time: 26000 hours) is determined based on the degree of damage in one cycle of the new crushing mill and the old crushing mill obtained in step S6. Set the relationship between the degree of damage in one cycle and the operation time on a time scale. An example of the relationship between the degree of damage in one cycle to be set and the operation time is shown in FIG.

  From the relationship between the damage degree in one cycle and the operation time, the damage degree in one cycle at an arbitrary operation time (total operation time) can be obtained.

  Next, the process (steps S8 to S9) for calculating the cumulative damage degree of the crushing mill for performing the life evaluation and performing the life evaluation using the relationship between the damage degree in one cycle and the operation time obtained as described above (steps S8 to S9) will be described. To do.

  In step S8, using the relationship between the degree of damage in one cycle and the operating time obtained in step S7, the degree of damage in one cycle at any operating time is obtained, and based on the degree of damage, A stress-frequency histogram of each operation pattern is created, and a stress-frequency histogram for each operation time in consideration of the operation of the crushing mill that evaluates the life can be taken out.

  Specifically, first, from the relationship between the degree of damage in one cycle obtained in step S7 and the operating time, the degree of damage in one cycle at an arbitrary operating time of the crushing mill for evaluating the life is estimated, The ratio between the degree of damage in one cycle and the degree of damage in one cycle of the new crushing mill (or old product crushing mill) obtained in step S2 is obtained, and the ratio is calculated as the new crushing mill (or old product crushing mill). By multiplying the stress-frequency histogram, it is possible to create a stress-frequency histogram of each operation pattern at an arbitrary operation time.

  When creating a stress-frequency histogram of each operation pattern at this arbitrary operation time, considering the past start and stop frequency and raw material supply amount pattern from the past performance of the grinding mill that performs life evaluation, A stress-frequency histogram is preferably created for each cycle. The future stress-frequency histogram should be created in consideration of the number of start / stops within the required life (design life) while estimating the operation pattern and raw material supply amount pattern from past operation results. . The same applies to the evaluation of the life of a new crushing mill.

  In step S9, first, using the stress-frequency histogram of each operation pattern for each arbitrary operation time created in step S8, the equation (3) is expressed as described in steps S5 to S6 ( 1)

To calculate the equivalent vibration stress sigma _{V_eq} each driving pattern, shown from the equivalent vibration stress sigma _{V_eq} number (4) Formula (2)

To obtain the damage degree D per unit time in each operation pattern.

  The degree of damage D per unit time in each pattern is accumulated for each cycle, thereby calculating the degree of damage in one cycle at an arbitrary operation time (each cycle).

  After that, the cumulative damage degree is obtained by cumulatively calculating the damage degree in one cycle of each calculated operation time.

  When this cumulative damage level becomes equal to 1, fatigue cracks are generated. Therefore, the life of the grinding mill can be predicted from this cumulative damage degree.

  It is also possible to determine whether or not a fatigue crack will occur by cumulatively calculating the cumulative damage degree with respect to the total operating time of the required life (design life).

In this embodiment, in step S9, the equivalent vibration stress σ _{v — eq} and the damage degree D per unit time are obtained from the stress-frequency histogram of each operation pattern at an arbitrary time, and the damage degree in one cycle is obtained based on this. The cumulative damage degree is obtained by accumulating the damage degree in this one cycle, but the stress-frequency histogram with respect to the total operation time may be obtained, and the cumulative damage degree may be obtained from the simple sum.

  In this case, the stress-frequency histograms created at arbitrary times are added together for each operation pattern, and a stress-frequency histogram for the total operation time (operation time) is created for each operation pattern. Formula (3) shown in

Is used to determine the cumulative damage degree D 'in each operation pattern. If the cumulative damage degree D ′ in each operation pattern is added, the total cumulative damage degree can be obtained.

  Further, the creation of a stress-frequency histogram of each operation pattern at an arbitrary time in step S8 is omitted, and the relationship between the damage degree and the operation time in one cycle in FIG. The damage degree may be directly obtained, and the cumulative damage degree may be directly calculated based on data such as the number of start / stop times.

  In this case, since it is necessary to consider the raw material supply amount and the operation pattern, it is preferable to create a relationship between the damage degree in one cycle and the operation time in advance according to the raw material supply amount and each operation pattern.

  As described above, in the present invention, the strain of the stress concentration part of the old pulverization mill operated for a predetermined time with the new pulverization mill is measured, and based on this, a stress-frequency histogram is created for each raw material supply amount, On the other hand, the fatigue strength diagram of the stress concentration part of the crushing mill is set from past damage records, and the equivalent vibration stress is obtained from the fatigue strength diagram and the stress-frequency histogram, and the new product is crushed from the equivalent vibration stress. Find the degree of damage in one cycle of the roller and the old crushing roller, set the relationship between the degree of damage in one cycle and the operation time, and then from the past operation results of the crushing mill that performs life evaluation, The degree of damage in one cycle is obtained, and a stress-frequency histogram at any operation time can be created from the degree of damage in that one cycle. Cumulatively calculates the cumulative damage degree predicts the life by the accumulated degree of damage.

  As a result, it is possible to evaluate the fatigue strength in consideration of an increase in the generated stress level due to wear of the grinding roller, and the life of the grinding mill can be accurately evaluated.

  Furthermore, according to the present invention, it is possible to evaluate the fatigue strength that can explain the phenomenon that the fatigue damage occurs earlier by the method of the pulverization mill having the smaller number of start / stop times than the pulverization mill having the larger number of start / stop times, and the reliability of the pulverization mill can be improved. Can be improved.

  Here, a graph comparing the service life of the pulverizing mill predicted by the present invention and the service life when a fatigue crack actually occurs is shown in FIG.

  As shown in FIG. 7, the service life of the pulverization mill predicted by the present invention and the operation life of the actual machine are in good agreement, and according to the present invention, it can be seen that the service life of the pulverization mill can be evaluated with high accuracy.

It is a flowchart of the lifetime evaluation method of the crushing mill of this invention. In this invention, it is a figure which compares the generated stress level of a new article crushing mill and an old article crushing mill. It is a figure which shows an example of the waveform of the distortion fluctuation | variation measured by this invention. It is a figure which shows an example of the stress-frequency histogram created by this invention. It is a figure which shows an example of the fatigue strength diagram created by this invention. It is a figure which shows an example of the relationship between the damage degree in 1 cycle created by this invention, and operation time. It is the graph which compared the lifetime of the grinding | pulverization mill estimated by this invention, and the operation lifetime when a fatigue crack actually generate | occur | produces. It is a schematic sectional drawing of a pulverized coal mill.

Explanation of symbols

81 pulverized coal mill 82 drive unit 83 rotary table 84 crushing roller 85 casing 86 roller pivot 87 coal supply pipe 88 air supply pipe 89 separator 90 separator drive unit 91 pulverized coal pipe

Claims (8)

Grinding for evaluating the life of a grinding mill comprising a rotary table rotatably provided in a casing, and a grinding roller that is rotatably supported on the rotary table and crushes the raw material supplied to the rotary table. In the mill life evaluation method,
A sensor is attached to the stress concentration part of the new crushing mill and the old crushing mill that has been operating for a predetermined time, and the strain is measured in one cycle from the start to the stop of the crushing mill. A stress-frequency histogram for each supply amount is created, and on the other hand, a fatigue strength diagram of the stress concentration part of the crushing mill is set from past damage records, and an equivalent vibration is calculated from the fatigue strength diagram and the stress-frequency histogram. In addition to obtaining the stress, the degree of damage in one cycle between the new grinding roller and the old grinding roller is obtained from the equivalent vibration stress, and the relationship between the degree of damage in one cycle and the operation time is set, and then the life evaluation The degree of damage in one cycle of the pulverizing mill is estimated from the past operation results of the pulverizing mill, and the stress at any operating time is calculated from the degree of damage in the one cycle. The life of a grinding mill is characterized by the fact that the degree of damage can be created and the degree of damage is calculated by accumulating the degree of damage up to an arbitrary operation time based on this, and the life is predicted by the accumulated degree of damage. Evaluation method.   2. The method for evaluating the life of a crushing mill according to claim 1, wherein stress-frequency histograms of the new crushing mill and the old crushing mill are created for each operation pattern at startup, normal operation, and stop.   The pulverization mill according to claim 2, wherein stress-frequency histograms of the new pulverization mill and the old pulverization mill are prepared for each raw material supply amount and for each operation pattern, and the equivalent vibration stress is obtained based on the histogram. Life evaluation method.   The pulverization mill according to any one of claims 1 to 3, wherein a damage degree is obtained from an equivalent vibration stress of each operation pattern at start-up, normal operation, and stop, and the damage degree in one cycle is obtained by adding the damage degrees. Life evaluation method.   The degree of damage in one cycle of the new pulverizing mill and the old pulverizing mill is determined under the same raw material supply amount, and the cycle time of the old pulverizing mill from the new pulverizing mill is one cycle. The lifetime evaluation method of the crushing mill in any one of Claims 1-4 which was made to set the relationship between the damage degree in this, and operation time.   The degree of damage in one cycle of the new product crushing mill and the old product crushing mill is determined by taking into account the equivalent vibration stress of a stress-frequency histogram corresponding to the amount of raw material supplied. Life evaluation method.   The cumulative damage degree is obtained by calculating an equivalent vibration stress from the stress-frequency histogram at the arbitrary operation time, calculating a damage degree from the equivalent vibration stress, and accumulating the damage degree. The life evaluation method of the grinding | pulverization mill in any one.   The cumulative damage level is calculated based on a stress-frequency histogram for a total operation time created from a stress-frequency histogram for the arbitrary operation time and a stress-frequency histogram for the total operation time. The life evaluation method of the grinding | pulverization mill in any one of -6.

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