Control method for prolonging service life of milling part in variable-speed operation of medium-speed coal mill

Abstract

The invention discloses a control method for prolonging the service life of a milling part during variable-speed operation of a medium-speed coal mill. The control method comprises the following steps: step 1, acquiring the coal quantity of a coal feeder through operation parameters of the coal feeder; step 2, for the same coal type, carrying out coal mill maximum output tests at different rotating speeds to obtain coal mill maximum outputs at different rotating speeds; 3, on the basis of the step 2, pulverized coal fineness testing and analysis are conducted on the same coal type under different coal quantities and rotating speeds, and the optimal variable-speed operation mode of the medium-speed coal mill is obtained; step 4, adjusting the frequency of the variable-frequency control unit 5 through the change of the coal feeding amount according to the interval of the coal feeding amount and the frequency of the variable-frequency control unit 5, and operating at the optimal rotating speed calculated in the step 3; 5, on the basis of the step 4, the rotating speed of a motor 4 corresponding to the coal mill 3 is controlled through a frequency conversion control unit 5, and the coal mill is driven to operate at different rotating speeds; the abrasion loss of the grinding roller of the coal mill is reduced, and the purpose of prolonging the service life of the medium-speed coal mill is achieved.

Description

Technical Field

[0001] The invention belongs to the field of coal mill control, and in particular relates to a control method for a medium-speed coal mill to prolong the service life of grinding parts by variable speed operation. Background Art

[0002] Currently, large coal-fired power plants widely use direct-fired medium-speed coal mill systems. The service life of grinding components, such as the grinding rollers and guard plates, is currently 10 to 12 months (6,000 to 8,000 hours). This life is even shorter if the coal quality is poor. Coal mills are critical auxiliary equipment for thermal power plants. Increased wear of the grinding rollers can lead to poor performance, reduced output, and substandard coal fineness at the outlet. This can affect the unit's load capacity and negatively impact its safe, stable, and economical operation.

[0003] In order to reduce the wear of grinding parts such as grinding rollers and guard plates of coal mills and extend the service life of coal mills, power plant boiler technicians have made a lot of efforts and work. For example, the use of new wear-resistant materials can reduce the wear of grinding rollers of coal mills to a certain extent. However, as the quality of coal burned in boilers deteriorates, it cannot fundamentally solve the problem of wear of grinding rollers of coal mills.

[0004] The present invention analyzes and studies the operating characteristics of the medium-speed coal mill after speed-changing modification, and proposes a speed control method for the coal mill that is different from the fixed-speed operation method, that is, adjusting the coal mill speed according to the coal feed rate signal of the medium-speed coal mill. For example, during the low-load operation of the unit, when the coal feed rate of the pulverizing system is relatively low, by reducing the speed of the variable-speed coal mill, the wear of the coal mill roller is reduced while ensuring stable combustion of the boiler, thereby achieving the purpose of extending the service life of the medium-speed coal mill.

[0005] In the existing technology, there has been research on installing a frequency converter on the coal mill motor to improve the coal mill output by increasing the coal mill motor speed; however, there is still no relevant research on the changing rules of speed change and the fineness of coal powder in the coal mill and the service life of grinding parts. Summary of the Invention

[0006] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a control method for extending the service life of grinding components based on the variable speed operation of a medium speed coal mill.

[0007] This control method for extending the service life of grinding components based on variable speed operation of a medium-speed coal mill comprises the following steps:

[0008] Step 1: Obtain the coal quantity of the coal feeder through the operating parameters of the coal feeder;

[0009] Step 2: Under the same boundary conditions, the pulverizing system conducts a maximum output test of the coal mill at different speeds for the same type of coal to obtain the maximum output of the coal mill at different speeds;

[0010] Step 3: On the basis of Step 2, under the condition of consistent boundary conditions, for the same coal type, conduct pulverized coal fineness tests and analyses at different coal quantities and rotational speeds, and obtain the optimal mode of variable-speed operation of the medium-speed coal mill.

[0011] Step 4: According to the interval where the coal feeding quantity is located and the frequency of the frequency conversion control unit 5, adjust the frequency of the frequency conversion control unit 5 by changing the coal feeding quantity, operate at the optimal rotational speed calculated in Step 3, reduce and minimize the wear of the grinding components of the coal mill, and extend the service life of the coal mill; and add a first-order inertia to the change in the coal feeding quantity.

[0012] Step 5: On the basis of Step 4, control the rotational speed of the motor 4 corresponding to the coal mill 3 through the frequency conversion control unit 5 to drive the coal mill to operate at different rotational speeds.

[0013] Step 6: Select a conventional coal mill (the conventional coal mill has a fixed rotational speed), operate it under the same working conditions as the variable-speed coal mill for about 6000 h, and compare the wear amount of the main grinding components of the coal mill, which is mainly the wear amount of the grinding rollers.

[0014] Preferably, Step 2 specifically includes the following steps:

[0015] Step 2.1: For a coal mill with a designed rotational speed of n, a designed coal quantity of Q, a rated current of the motor frequency converter of I, a hydraulic loading method, and the pulverized coal fineness adjusted by the rotational speed of the dynamic separator, control the outlet temperature of the coal mill by the cold air regulating valve at the inlet of the coal mill and set it at 75°C; control the primary air volume at the inlet of the coal mill by the hot air regulating valve at the inlet of the coal mill; control the pulverized coal fineness of the coal mill according to the hydraulic loading force of the coal mill and the rotational speed of the dynamic separator at the outlet of the coal mill. The hydraulic loading force of the coal mill refers to the hydraulic loading curve of the mill, and set the rotational speed of the dynamic separator at the outlet of the coal mill at a fixed speed.

[0016] Step 2.2: After the adjustment in Step 2.1, for the same coal type, conduct the maximum output test of the coal mill at different rotational speeds, and take samples from the pulverized coal pipe 11 at the outlet of the coal mill for pulverized coal fineness testing.

[0017] Step 2.2.1: Under each working condition, the method for judging that the coal mill reaches the maximum output: the coal mill does not get blocked and the current of the coal mill motor does not exceed the rated value I.

[0018] Step 2.2.2, Determine whether the coal mill 3 is blocked: Monitor the relevant operating parameters of the coal pulverizing system. The relevant operating parameters are the primary air volume q at the inlet of the coal mill, the baffle opening of the cold primary air regulating valve 7 or the hot primary air regulating valve 8, the outlet temperature t2 of the coal mill, and the differential pressure across the coal mill bowl. If the primary air volume q at the inlet of the coal mill does not decrease slowly or the decreased value does not exceed the set value, the coal mill 3 is not blocked; otherwise, the coal mill 3 is blocked. If the baffle opening of the cold primary air regulating valve 5 or the hot primary air regulating valve 6 does not reach the set value, the coal mill 3 is not blocked; otherwise, the coal mill 3 is blocked. If the decreasing rate of the outlet temperature t2 of the coal mill is 0 or the decreasing rate does not reach the set value, the coal mill 3 is not blocked; otherwise, the coal mill 3 is blocked. If the differential pressure across the coal mill bowl does not increase slowly beyond the alarm value, the coal mill 3 is not blocked; otherwise, the coal mill 3 is blocked.

[0019] Step 2.2.3, For the same coal type, at five speeds of 0.75n, 0.9n, 1.0n, 1.1n, and 1.25n respectively, after the coal mill reaches the maximum output and the operating parameters of the coal pulverizing system are stable for more than 30 minutes, conduct a test for at least 2 hours, where n is the design speed. Sequentially take coal powder samples at the coal powder sampling hole 11 of the outlet powder pipe of the coal mill and then conduct coal powder fineness tests. Calculate the weighted coal powder fineness (R90) under this operating condition and record the operating parameters of the coal pulverizing system during this period through the DCS or PI system.

[0020] Preferably, Step 3 specifically includes the following steps:

[0021] Step 3.1, (Same as Step 2.1)

[0022] Step 3.2, After the adjustment in Step 3.1, for the same coal type, measure the coal powder fineness and conduct calculation and analysis.

[0023] Step 3.2.1, Under each operating condition, if the operating parameters of the coal pulverizing system are within the normal range for more than 30 minutes, record the relevant operating parameters of the coal pulverizing system during the test period through the DCS system and the PI system during the stable operation test time.

[0024] Step 3.2.2, Under different operating conditions, after the operating parameters of the coal pulverizing system are stable with the same coal quantity, conduct a test for at least 2 hours at five speeds of 0.70n, 0.80n, 0.90n, 1.00n, and 1.10n respectively, where n is the design speed. Sequentially take coal powder samples at the coal powder sampling hole 11 of the outlet powder pipe of the coal mill and then conduct coal powder fineness tests. Calculate the weighted coal powder fineness (R90) under this operating condition and record the operating parameters of the coal pulverizing system during this period.

[0025] Step 3.3. Analyze the test results of Step 3.2.2 to determine the optimal control method for the variable-speed operation of the medium-speed coal mill.

[0026] Preferably, the operating parameters of the coal feeder in Step 1 include current and coal feeding amount, and the coal feeding amount is regularly calibrated.

[0027] Preferably, the boundary conditions in Step 2 are the coal mill outlet temperature, hydraulic loading force, dynamic separator speed, and the coal mill outlet air volume and temperature control method described in Step 2.1.

[0028] Preferably, the optimal method for the variable-speed operation of the medium-speed coal mill in Step 3 is to minimize the variable-speed adjustment of the coal mill motor to drive the coal mill speed on the premise of ensuring that the fineness of the pulverized coal at the coal mill outlet varies within a suitable range (the fineness of the pulverized coal R90 is between 18% and 28%).

[0029] Preferably, the implementation method of adding a first-order inertia to the change in coal feeding amount in Step 4 is: adding a pulse to the change in coal feeding amount to prevent the speed of the coal mill motor from fluctuating back and forth at the critical coal amount.

[0030] Preferably, when controlling the primary air volume at the inlet of the coal mill in Step 2.1, refer to the air-coal ratio curve of the coal mill, and no offset is set for the primary air volume at the inlet of the coal mill.

[0031] Preferably, the operating parameters of the coal pulverizing system include the average values of coal feeding amount, coal mill current, frequency converter current, primary air volume, and coal mill outlet temperature; among them, the stable operation test time is not less than 2h.

[0032] Preferably, the coal pulverizing system is equipped with a frequency converter, and a remote control signal interface is provided on the frequency converter; the frequency conversion control unit 5 controls the frequency converter, the frequency converter drives the coal mill motor, the coal mill motor drives the coal mill to rotate, and the coal pulverizing system changes the coal mill speed according to the coal feeding amount through the frequency conversion control unit of the coal mill motor.

[0033] Preferably, the coal pulverizing system includes: a coal bunker, a coal feeder, a coal mill, a coal mill motor, a frequency conversion control unit, a dynamic separator, a cold primary air regulating valve, a hot primary air regulating valve, a coal mill outlet powder pipe, and a boiler; a coal powder sampling hole is provided on the coal mill outlet powder pipe; the frequency conversion control unit is electrically connected to the coal mill motor, and the coal mill motor is electrically connected to the coal mill; the coal bunker is connected to the coal feeder, and the coal feeder is connected to the coal mill; a dynamic separator is provided at the outlet of the coal mill, the dynamic separator is connected to the coal mill outlet powder pipe, and the coal mill outlet powder pipe is connected to the boiler; a cold primary air regulating valve and a hot primary air regulating valve are also provided on the coal mill.

[0034] Preferably, adding a first-order inertia to the change in coal feeding amount in Step 4 specifically means:

[0035] When the coal feeding amount is in the range of (0, 30) t / h, the rotational speed of the coal mill is 0.7n r / min; add a first-order inertia to the change of the coal feeding amount;

[0036] When the coal feeding amount is in the range of [30, 40) t / h, the rotational speed of the coal mill is 0.8n r / min; add a first-order inertia to the change of the coal feeding amount;

[0037] When the coal feeding amount is in the range of [40, 48) t / h, the rotational speed of the coal mill is 0.9n r / min; add a first-order inertia to the change of the coal feeding amount;

[0038] When the coal feeding amount is in the range of [48, 55) t / h, the rotational speed of the coal mill is 1.0n r / min; add a first-order inertia to the change of the coal feeding amount;

[0039] When the coal feeding amount is in the range of [50, 70) t / h, the rotational speed of the coal mill is 1.1n r / min; add a first-order inertia to the change of the coal feeding amount.

[0040] Preferably, the conventional coal mill described in steps 6 and 7 is an asynchronous motor constant-speed coal mill, and the rotational speed of the coal mill is n.

[0041] Preferably, the same operating conditions described in steps 6 and 7 mean that the constant-speed coal mill and the variable-speed coal mill operate under the condition that the coal type, coal feeding amount, primary air volume, outlet temperature, and dynamic separator rotational speed are the same. For comparison, the grinding components such as the grinding rollers of the two coal mills are all brand new.

[0042] The beneficial effect of the present invention is that the present invention proposes a control method for prolonging the service life of the grinding components based on the variable-speed operation of the medium-speed coal mill: according to the coal feeding amount signal of the medium-speed coal mill, adjust the rotational speed of the coal mill. For example, during the low-load operation of the unit, when the coal feeding amount of the coal pulverizing system is relatively low, by reducing the rotational speed of the variable-speed coal mill, on the premise of ensuring the stable combustion of the boiler, reduce the wear amount of the grinding rollers of the coal mill, and achieve the purpose of prolonging the service life of the medium-speed coal mill. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 It is a schematic diagram of the operation of the coal pulverizing system;

[0044] Figure 2 It is a schematic diagram of sampling at the powder pipe outlet of the coal mill;

[0045] Figure 3 It is a broken line graph of the maximum output and coal powder fineness of the coal mill at different rotational speeds;

[0046] Figure 4 It is the operation strategy for the variable-speed regulation of the coal mill motor to make the grinding components of the coal mill have the lightest wear within the full output range;

[0047] Figure 5Schematic diagram of the variable speed adjustment control strategy of the coal mill motor according to the coal feeding amount

[0048] In the figure: 1. Coal bunker; 2. Coal feeder; 3. Coal mill; 4. Variable speed coal mill motor; 5. Frequency conversion control unit; 6. Dynamic separator; 7. Cold primary air regulating valve; 8. Hot primary air regulating valve; 9. Coal powder pipe at the outlet of the coal mill; 10. Boiler; 11. Coal powder sampling hole in the coal powder pipe at the outlet of the coal mill. Specific implementation mode

[0049] The present invention will be further described below in conjunction with embodiments. The description of the following embodiments is only used to help understand the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0050] Embodiment 1

[0051] Embodiment 1 of the present application provides a method for extending the service life of the grinding components of a medium-speed coal mill based on the variable speed adjustment of the coal mill motor:

[0052] Step 1: Obtain the coal amount of the coal feeder through the operating parameters of the coal feeder.

[0053] Step 2: Under the condition that the boundary conditions of the coal pulverizing system are the same, for the same coal type, conduct the maximum output test of the coal mill at different speeds to obtain the maximum output of the coal mill at different speeds.

[0054] Step 2.1: For a coal mill with a designed speed of n, a designed coal amount of Q, a rated current of I for the coal mill motor frequency converter, a hydraulic loading method, and the fineness of coal powder adjusted by the speed of the dynamic separator, control the outlet temperature of the coal mill by the cold primary air regulating valve at the inlet of the coal mill and set it at 75 °C; control the primary air volume at the inlet of the coal mill by the hot primary air regulating valve at the inlet of the coal mill; control the fineness of coal powder in the coal mill according to the hydraulic loading force of the coal mill and the speed of the dynamic separator at the outlet of the coal mill. The hydraulic loading force of the coal mill refers to the hydraulic loading curve of the mill, and set the speed of the dynamic separator at the outlet of the coal mill at a fixed speed.

[0055] Step 2.2: After the adjustment in Step 2.1, for the same coal type, conduct the maximum output test of the coal mill at different speeds, and take samples at the coal powder sampling hole 11 in the coal powder pipe at the outlet of the coal mill for coal powder fineness testing.

[0056] Step 2.2.1: The method for judging whether the coal mill reaches the maximum output under each working condition: The coal mill does not have coal blockage and the current of the coal mill motor does not exceed the rated value I.

[0057] Step 2.2.2, Determine whether the coal mill 3 is blocked: Monitor the relevant operating parameters of the coal pulverizing system. The relevant operating parameters are the primary air volume q at the inlet of the coal mill, the damper opening of the cold primary air regulating valve 7 or the hot primary air regulating valve 8, the outlet temperature t2 of the coal mill, and the differential pressure of the coal mill grinding bowl. If the primary air volume q at the inlet of the coal mill does not decrease slowly or the decreased value does not exceed the set value, the coal mill 3 is not blocked; otherwise, the coal mill 3 is blocked. If the damper opening of the cold primary air regulating valve 5 or the hot primary air regulating valve 6 does not reach the set value, the coal mill 3 is not blocked; otherwise, the coal mill 3 is blocked. If the decreasing rate of the outlet temperature t2 of the coal mill is 0 or the decreasing rate does not reach the set value, the coal mill 3 is not blocked; otherwise, the coal mill 3 is blocked. If the differential pressure of the coal mill grinding bowl does not increase slowly beyond the alarm value, the coal mill 3 is not blocked; otherwise, the coal mill 3 is blocked;

[0058] Step 2.2.3, For the same coal type, at five speeds of 0.75n, 0.9n, 1.0n, 1.1n, and 1.25n respectively, after the coal mill reaches the maximum output and the operating parameters of the coal pulverizing system are stable for more than 30 minutes, conduct a test for not less than 2 hours, where n is the design speed; successively take coal powder samples at the coal powder sampling hole 11 of the outlet powder pipe of the coal mill and then conduct coal powder fineness tests, and calculate the coal powder fineness (R90) under this condition by weighted calculation, and record the operating parameters of the coal pulverizing system during this period through the DCS or PI system.

[0059] Step 3, On the basis of Step 2, under the condition of consistent boundary conditions, for the same coal type, conduct coal powder fineness tests and analyses at different coal amounts and speeds, and obtain the best way to adjust the operation of the coal mill by the variable speed of the coal mill motor;

[0060] Step 3.1, (Same as Step 2.1)

[0061] Step 3.2, After the adjustment in Step 3.1, for the same coal type, measure the coal powder fineness and conduct calculation and analysis;

[0062] Step 3.2.1, Under each working condition, if the operating parameters of the coal pulverizing system are within the normal range for more than 30 minutes, record the relevant operating parameters of the coal pulverizing system during the test period through the DCS system and the PI system during the stable operation test time;

[0063] Step 3.2.2, Under different working conditions, after the operating parameters of the coal pulverizing system are stable at the same coal amount, conduct a test for not less than 2 hours at five speeds of 0.70n, 0.80n, 0.90n, 1.00n, and 1.10n respectively, where n is the design speed; successively take coal powder samples at the coal powder sampling hole 11 of the outlet powder pipe of the coal mill and then conduct coal powder fineness tests, and calculate the coal powder fineness (R90) under this condition by weighted calculation, and record the operating parameters of the coal pulverizing system during this period;

[0064] Step 3.3. Analyze the test results of Step 3.2.2 to determine the optimal way to adjust the operation of the coal mill by varying the speed of the coal mill motor.

[0065] Step 4. Based on the interval where the coal feeding amount is located and the frequency of the variable frequency control unit 5, adjust the frequency of the variable frequency control unit 5 by changing the coal feeding amount, and operate at the optimal rotational speed calculated in Step 3 to reduce and minimize the wear of the grinding components of the coal mill and extend the service life of the coal mill; and add a first-order inertia to the change in the coal feeding amount.

[0066] Step 5. On the basis of Step 4, control the rotational speed of the coal mill motor 4 corresponding to the coal mill 3 through the variable frequency control unit 5 to drive the coal mill to operate at different rotational speeds.

[0067] Step 6. Select a conventional coal mill and conduct pulverized coal fineness test experiments at different coal amounts for the same coal type under the same boundary conditions as the coal pulverizing system with variable-speed coal mill motor.

[0068] Step 7. Select a conventional coal mill and compare the wear amount of the main grinding components, i.e., the grinding rollers, after operating for about 6000 h under the same working conditions as the coal mill with variable-speed coal mill motor.

[0069] The coal pulverizing system is equipped with an inverter, and a remote control signal interface is provided on the inverter; the variable frequency control unit 5 controls the inverter, the inverter drives the coal mill motor 4, the coal mill motor 4 drives the coal mill 3 to rotate, and the coal pulverizing system changes the rotational speed of the coal mill according to the coal feeding amount through the variable frequency control unit 5 of the coal mill motor.

[0070] The coal pulverizing system includes: coal bunker 1, coal feeder 2, coal mill 3, coal mill motor 4, variable frequency control unit 5, static separator 6, cold primary air regulating valve 7, hot primary air regulating valve 8, coal mill outlet powder pipe 9, and boiler 10; a coal mill outlet powder pipe coal powder sampling hole 11 is provided on the coal mill outlet powder pipe 9; the variable frequency control unit 5 is electrically connected to the coal mill motor 4, and the coal mill motor 4 is electrically connected to the coal mill 3; the coal bunker 1 is connected to the coal feeder 2, and the coal feeder 2 is connected to the coal mill 3; a static separator 6 is provided at the outlet of the coal mill 3, the static separator 6 is connected to the coal mill outlet powder pipe 9, and the coal mill outlet powder pipe 9 is connected to the boiler 10; cold primary air regulating valve 7 and hot primary air regulating valve 8 are also provided on the coal mill 3.

[0071] Embodiment 2

[0072] On the basis of Embodiment 1, Embodiment 2 of the present application provides the application of the method for extending the service life of the grinding components of a medium-speed coal mill based on variable-speed regulation of the coal mill motor in Embodiment 1 to a certain coal mill in a certain power plant:

[0073] The designed rotational speed of this coal mill is 30.8 r / min, and the designed minimum coal output is 15.18 t / h. Specific coal mill parameters are shown in Table 1 below:

[0074] Table 1 Coal Mill Parameter Table

[0075]

[0076] Parameters of the variable-speed coal mill motor used are shown in Table 2 below:

[0077] Table 2 Variable-speed Coal Mill Motor Parameter Table

[0078]

[0079] To obtain a method for extending the service life of the grinding components of the medium-speed coal mill in a variable-speed coal mill. For a coal mill with a designed rotational speed of n and a designed coal output of Q, when using the same coal type, maximum coal output and pulverized coal fineness tests were carried out at different rotational speeds, with a total of 6 test conditions.

[0080] As Figure 1 shown, when the coal preparation system is in operation, raw coal enters the feeder 2 from the coal bunker 1, and enters the coal mill 3 through the feeder downcomer. The coal mill 3 is driven to rotate by the coal mill motor 4 and the frequency conversion control unit 5. After grinding the raw coal particles into pulverized coal, it is separated by the deflector baffle of the static separator 6. The pulverized coal with suitable fineness enters the boiler 10, and the pulverized coal with slightly coarser fineness re-enters the coal mill 3 for grinding. The power for the pulverized coal to enter the boiler 10 mainly comes from the primary air at the inlet of the coal mill. The primary air not only enables the pulverized coal to enter the boiler 10, but also plays a role in heating the pulverized coal, which helps the pulverized coal to ignite and burn after entering the boiler 10.

[0081] Step 101: Obtain the coal feeding amount parameter through the operating parameters of the feeder. The feeder can control the coal feeding amount by the belt speed, and the coal feeding amount is regularly calibrated; if a larger coal feeding amount is required, a faster belt speed is needed.

[0082] Step 102: Control the outlet temperature of the coal mill and the inlet primary air volume through the cold and hot air dampers at the inlet of the coal mill. Among them, the cold air adjustment door controls the outlet temperature of the coal mill by the opening degree. When the cold air adjustment door opens wider, the temperature decreases; the hot air adjustment door controls the inlet primary air volume of the coal mill by the damper baffle opening degree; the cold air adjustment door at the inlet of the coal mill adjusts the temperature, and the hot air door adjusts the primary air volume. In this embodiment, the inlet primary air volume of the coal mill is adjusted by changing the damper baffle opening degree through setting an offset on the control panel of the hot air adjustment door at the inlet of the coal mill based on the air-coal ratio control logic, and the outlet temperature of the coal mill is automatically adjusted to maintain at 75°C by the opening degrees of the cold and hot air damper baffles at the inlet of the coal mill.

[0083] Step 103: Adjust the fineness of pulverized coal by adjusting the rotational speed of the dynamic separator at the outlet of the coal mill. Among them, the adjustment range of the rotational speed of the dynamic separator is 0 r / min to 800 r / min°. The higher the rotational speed of the dynamic separator, the smaller the fineness of the pulverized coal; the lower the rotational speed of the dynamic separator, the larger the fineness of the pulverized coal. Here, a large fineness means large particle size of the pulverized coal particles, and a small fineness means small particle size of the pulverized coal particles. In this embodiment, the rotational speed of the dynamic separator at the outlet of the coal mill is maintained at 650 r / min without change.

[0084] Step 104: For the hydraulic loading force of the coal mill grinding rollers, when the coal feeding amount is in the range of [0, 20] t / h, the magnitude of the hydraulic loading force of the coal mill grinding rollers is 4 MPa; when the coal feeding amount is in the range of (20, 60] t / h, the magnitude of the hydraulic loading force of the coal mill grinding rollers is y = 0.3x - 2 (MPa); when the coal feeding amount is in the range of (60, 70] t / h, the magnitude of the hydraulic loading force of the coal mill grinding rollers is 16 MPa, where x represents the coal feeding amount and Y represents the hydraulic loading force.

[0085] Step 105: Control the rotational speed of the coal mill motor through the speed / frequency adjustment unit, thereby driving the coal mill grinding rollers to operate at different rotational speeds. In this embodiment, the maximum output tests of the coal mill are carried out at five rotational speeds of 0.70n, 0.80n, 0.90n, 1.00n, and 1.10n respectively.

[0086] Step 106: The maximum output of the coal pulverizing system is that under the boundary conditions of Steps 102, 103, and 104, the coal mill does not get blocked with coal and the current of the coal mill motor does not exceed the rated value I.

[0087] As described in Step 101 above, under the boundary conditions of Step 102, Step 103, and Step 104, the judgment condition for the coal mill not getting blocked with coal is: monitor the relevant operating parameters of the coal pulverizing system, such as the primary air volume does not decrease slowly or the slow decrease does not exceed 5 t / h, the damper opening degrees of the cold primary air adjustment valve 7 and the hot primary air adjustment valve 8 are less than 80%, the outlet temperature of the coal mill does not decrease slowly or the slow decrease within ten minutes does not exceed 5 °C, and the differential pressure of the coal mill grinding bowl does not slowly increase beyond the alarm value, etc.

[0088] Step 107: Under each working condition, after the coal mill reaches the maximum output and the operating parameters are stable for more than 30 minutes, conduct a test on the fineness of the pulverized coal. At the same time, record the relevant operating parameters during the test through the DCS and PI systems, including the time-averaged values of the coal feeding amount, the current of the coal mill, the primary air volume, the outlet temperature of the coal mill, and the discharge amount of the reject coal. Among them, the test time after stabilization is not less than 2 h.

[0089] As Figure 2 shown is the sampling schematic diagram of the pulverized coal pipe at the outlet of the coal mill in this embodiment. Under different working conditions, the fineness of the pulverized coal is tested successively on 6 pulverized coal pipes at the outlet of the coal mill, and the fineness of the pulverized coal R90 under this working condition is obtained by weighted average.

[0090] According to Steps 106 and 107, the maximum output and pulverized coal fineness broken line graphs of the coal mill at different rotational speeds as shown in Figure 3 are obtained.

[0091] Step 108: According to Figure 3 the maximum output and pulverized coal fineness broken line graphs of the coal mill at different rotational speeds as shown in Figure 4 the following shown, formulate an operation strategy for the coal mill motor to adjust the speed so that the grinding components of the coal mill have the least wear within the full output range.

[0092] Step 109: Select a conventional coal mill with a rated speed of n in the same unit. Under the condition that the boundary conditions of the coal mill motor variable speed coal pulverizing system are the same, for the same coal type, conduct pulverized coal fineness test experiments at different coal amounts. The results are shown in Table 3 below.

[0093] Table 3 Pulverized Coal Fineness Test Results of Variable Speed Coal Mill and Conventional Coal Mill at Different Coal Amounts under the Same Coal Type

[0094]

[0095] Step 110: The grinding rolls and other grinding components of both coal mills are brand new. Keep the coal type, coal feeding amount, primary air volume, outlet temperature, and dynamic separator speed of the two coal mills the same and run them together for about 6000 h, and record the wear amount of the main grinding components of the coal mill, which are mainly the grinding rolls. As shown in Table 4 below.

[0096] Table 4 Wear Amount of Grinding Components after 6000 h of Operation under the Condition that the Operating Conditions of the Variable Speed Coal Mill and the Conventional Coal Mill are the Same

[0097]

[0098] The results of this embodiment show that: 1) When the rotational speed of the variable speed coal mill decreases, the maximum output decreases; 2) For the same coal type, at the same coal amount, when the variable speed coal mill operates below the rated speed, the change in pulverized coal fineness R90 is not significant, and it has basically no impact on the combustion economy of the boiler; 3) When the variable speed coal mill operates at the optimal speed according to the change in coal amount, the pulverized coal fineness changes within a reasonable range, which has little impact on the boiler economy, but the wear of the grinding components of the coal mill is significantly reduced, and the service life of the grinding components of the coal mill increases.

[0099] Combined with the results of this embodiment, optimize the adjustment method of the rotational speed of the variable speed coal mill with the change in coal amount:

[0100] Adding a first-order inertia to the change in coal feeding amount is specifically:

[0101] When the coal feeding amount is in the range of (0, 30) t / h, the rotational speed of the coal mill is 21.56 r / min; add a first-order inertia to the change in coal feeding amount;

[0102] When the coal feeding rate is in the range of [30, 40) t / h, the rotational speed of the coal mill is 24.64 r / min; add a first-order inertia to the change of the coal feeding rate;

[0103] When the coal feeding rate is in the range of [40, 48) t / h, the rotational speed of the coal mill is 27.72 r / min; add a first-order inertia to the change of the coal feeding rate;

[0104] When the coal feeding rate is in the range of [48, 55) t / h, the rotational speed of the coal mill is 30.80 r / min; add a first-order inertia to the change of the coal feeding rate;

[0105] When the coal feeding rate is in the range of [50, 70) t / h, the rotational speed of the coal mill is 33.88 r / min; add a first-order inertia to the change of the coal feeding rate.

[0106] As Figure 4 shown is the schematic diagram of the optimized rotational speed and coal quantity control curve.

[0107] Through the above optimization, as the coal feeding rate of the variable-speed coal mill changes, the rotational speed of the coal mill is changed to control the fineness of the pulverized coal at the outlet of the coal mill to vary within a reasonable range. On the premise of ensuring the stable and economic combustion of the boiler, the wear of the grinding components of the coal mill is effectively reduced and decreased, the service life of the coal mill is extended, and the operation safety stability and economy of the unit are improved.

Claims

1. A control method for extending the service life of grinding components during variable-speed operation of a medium-speed coal mill, characterized in that, It includes the following steps Step 1: Obtain the coal quantity of the coal feeder based on the operating parameters of the coal feeder; Step 2: Under the condition of consistent boundary conditions, for the same coal type, conduct the maximum output test of the coal mill at different speeds in the coal pulverizing system to obtain the maximum output of the coal mill at different speeds; Step 3: On the basis of Step 2, under the condition of consistent boundary conditions, for the same coal type, conduct the pulverized coal fineness test and analysis at different coal quantities and speeds in the coal pulverizing system to obtain the best operation mode of the medium-speed coal mill under variable speed operation; Step 4: According to the interval where the coal feeding quantity is located and the frequency of the frequency conversion control unit, adjust the frequency of the frequency conversion control unit by the change of the coal feeding quantity, operate at the best speed calculated in Step 3, and add a first-order inertia to the change of the coal feeding quantity; Step 5: On the basis of Step 4, control the speed of the motor corresponding to the coal mill through the frequency conversion control unit to drive the coal mill to operate at different speeds; Step 6: Select another fixed-speed coal mill, after operating for the same time under the same working conditions, compare the wear amounts of the grinding parts of the two coal mills.

2. The control method for prolonging the service life of grinding components during variable-speed operation of a medium-speed coal mill according to claim 1, wherein The coal pulverizing system includes: coal bunker (1), coal feeder (2), coal mill (3), coal mill motor (4), frequency conversion control unit (5), dynamic separator (6), cold primary air regulating valve (7), hot primary air regulating valve (8), coal mill outlet powder pipe (9) and boiler (10); a coal mill outlet powder pipe coal powder sampling hole (11) is provided on the coal mill outlet powder pipe (9); the frequency conversion control unit (5) is electrically connected to the coal mill motor (4), and the coal mill motor (4) is connected to the coal mill (3); the coal bunker (1) is connected to the coal feeder (2), and the coal feeder (2) is connected to the coal mill (3); a dynamic separator (6) is provided at the outlet of the coal mill (3), the dynamic separator (6) is connected to the coal mill outlet powder pipe (9), and the coal mill outlet powder pipe (9) is connected to the boiler (10); a cold primary air regulating valve (7) and a hot primary air regulating valve (8) are also provided on the coal mill (3).

3. The control method for prolonging the service life of grinding components by variable-speed operation of a medium-speed coal mill according to claim 1, characterized in that, The specific steps of Step 2 are as follows: Step 2.1: For a coal mill with a designed speed of n, a designed coal quantity of Q, a rated current of I for the motor frequency converter, a hydraulic loading method, and the pulverized coal fineness adjusted by the speed of the dynamic separator, control the outlet temperature of the coal mill by the cold primary air regulating valve at the inlet of the coal mill and set it at 75 °C; control the primary air volume at the inlet of the coal mill by the hot primary air regulating valve at the inlet of the coal mill; control the pulverized coal fineness of the coal mill according to the hydraulic loading force of the coal mill and the speed of the dynamic separator at the outlet of the coal mill. The hydraulic loading force of the coal mill refers to the hydraulic loading curve of the coal mill, and set the speed of the dynamic separator at the outlet of the coal mill at a fixed speed; Step 2.2: After the adjustment in Step 2.1, for the same coal type, conduct the maximum output test of the coal mill at different speeds and take samples from the coal mill outlet powder pipe for pulverized coal fineness test; Step 2.2.1: Under each working condition, the method for judging that the coal mill reaches the maximum output: the coal mill does not get blocked with coal and the current of the coal mill motor does not exceed the rated value I; Step 2.2.2, Determine whether the coal mill is blocked: Monitor the relevant operating parameters of the coal pulverizing system. The relevant operating parameters are the primary air volume q at the inlet of the coal mill, the damper opening of the cold primary air regulating valve or the hot primary air regulating valve, the outlet temperature t2 of the coal mill, and the differential pressure of the coal mill grinding bowl. If the primary air volume q at the inlet of the coal mill does not decrease slowly or the decreased value does not exceed the set value, the coal mill is not blocked; otherwise, the coal mill is blocked. If the damper opening of the cold primary air regulating valve or the hot primary air regulating valve does not reach the set value, the coal mill is not blocked; otherwise, the coal mill is blocked. If the decreasing rate of the outlet temperature t2 of the coal mill is 0 or the decreasing rate does not reach the set value, the coal mill is not blocked; otherwise, the coal mill is blocked. If the differential pressure of the coal mill grinding bowl does not slowly rise beyond the alarm value, the coal mill is not blocked; otherwise, the coal mill is blocked. Step 2.2.3, For the same coal type, at five speeds of 0.75n, 0.9n, 1.0n, 1.1n, and 1.25n respectively, after the coal mill reaches the maximum output and the operating parameters of the coal pulverizing system are stable for more than 30 minutes, conduct a test for not less than 2 hours, where n is the design speed. Sequentially take coal powder samples at the coal powder sampling holes of the outlet powder pipe of the coal mill and conduct coal powder fineness tests, and calculate the coal powder fineness R90 under this condition by weighted calculation, and record the operating parameters of the coal pulverizing system during this period through the DCS or PI system.

4. The control method for prolonging the service life of grinding components during variable-speed operation of a medium-speed coal mill according to claim 3, characterized in that, The specific steps of step 3 are as follows: Step 3.1, Same as step 2.1; Step 3.2, After the adjustment in step 3.1, for the same coal type, measure the coal powder fineness and conduct calculation and analysis; Step 3.2.1, Under each working condition, if the operating parameters of the coal pulverizing system are within the normal range for more than 30 minutes, record the relevant operating parameters of the coal pulverizing system during the test through the DCS system and the PI system during the stable operation test time; Step 3.2.2, Under different working conditions, after the operating parameters of the coal pulverizing system are stable with the same coal quantity, conduct a test for not less than 2 hours at five speeds of 0.70n, 0.80n, 0.90n, 1.00n, and 1.10n respectively, where n is the design speed. Sequentially take coal powder samples at the coal powder sampling hole 11 of the outlet powder pipe of the coal mill and conduct coal powder fineness tests, and calculate the coal powder fineness R90 under this condition by weighted calculation, and record the operating parameters of the coal pulverizing system during this period; Step 3.3, Analyze the test results of step 3.2.2 to determine the best control method for the variable-speed operation of the medium-speed coal mill.

5. The control method for prolonging the service life of grinding components during variable-speed operation of a medium-speed coal mill according to claim 1, characterized in that, The operating parameters of the coal feeder in step 1 include current and coal feeding quantity, and the coal feeding quantity is calibrated regularly.

6. The control method for prolonging the service life of grinding components by variable-speed operation of a medium-speed coal mill according to claim 1, characterized in that, The boundary conditions in step 2 are the outlet temperature of the coal mill, the hydraulic loading force, the speed of the dynamic separator, and the outlet air volume and temperature control method of the coal mill described in step 2.

1.

7. The control method for prolonging the service life of grinding components during variable-speed operation of a medium-speed coal mill according to claim 1, characterized in that, The implementation method of adding a first-order inertia to the change of the coal feeding quantity in step 4 is: Add a pulse to the change of the coal feeding quantity to prevent the motor speed of the coal mill from fluctuating back and forth at the critical coal feeding quantity.

8. The control method for prolonging the service life of grinding components during variable-speed operation of a medium-speed coal mill according to claim 2, wherein, When controlling the primary air volume at the inlet of the coal mill in step 2.1, refer to the air-coal ratio curve of the coal mill, and no offset is set for the primary air volume at the inlet of the coal mill.

9. The control method for prolonging the service life of grinding components during variable-speed operation of the medium-speed coal mill according to claim 2, characterized in that The operating parameters of the coal pulverizing system include the time-averaged values of the coal feeding amount, the current of the coal mill, the current of the frequency converter, the primary air volume, and the outlet temperature of the coal mill.

10. The control method for prolonging the service life of grinding components during variable-speed operation of a medium-speed coal mill according to claim 9, characterized in that, The coal pulverizing system is equipped with a frequency converter, and a remote control signal interface is provided on the frequency converter; the frequency conversion control unit (5) controls the frequency converter, the frequency converter drives the coal mill motor (4), the coal mill motor (4) drives the coal mill (3) to rotate, and the coal pulverizing system changes the rotation speed of the coal mill according to the coal feeding amount through the frequency conversion control unit (5).

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