A control method for a coal mill burning high-volatile raw coal

Abstract

The present invention relates to the technical field of coal mills, and proposes a new control method for coal mills burning blended high-volatile raw coal. A control method for a coal mill burning blended high-volatile raw coal. By adjusting the internal equipment parameters and operating process parameters of the coal mill, the present invention strictly controls the inlet temperature and outlet temperature of the coal mill to reduce the risk of deflagration of the coal mill burning blended high-volatile raw coal, ensure the safe and stable operation of the coal mill, and adjust the grinding roll force of the coal mill according to different coal types to reduce the friction between the grinding roll and the lining plate, extend the service life of the grinding roll and the lining plate, and solve the problem of large vibration.

Description

Technical Field

[0001] The invention belongs to the technical field of coal mills, and in particular relates to a method for controlling a coal mill for blending and burning high-volatile raw coal. Background Art

[0002] In order to cope with the changes in supply and demand in the domestic coal market, save fuel costs, expand coal supply channels, and ensure that the supply of fuel is not passive due to market fluctuations; my country's coastal cities, taking advantage of their ports, have imported a large amount of high-volatile Indonesian coal (including low-calorific value Indonesian lignite). The characteristics of high-volatile coal are quite different from the original design coal for most domestic power plant boilers. In order to ensure the stable combustion of boilers and the safe operation of equipment, in recent years, based on the continuous exploration and summary of the actual operation of power plant boilers, a control method for the safe operation of power plant boiler pulverizers has been formed.

[0003] The existing coal mill is designed and operated according to the characteristics of domestic raw coal (low calorific value 5361kCal / kg, volatile matter Vad25%, ash content Aad20%, total water Mar10%, ash melting point 1300℃). When the existing coal mill is converted from normal coal to imported Indonesian coal (including low calorific value Indonesian lignite), it is controlled according to the original design coal type, which has the risk of deflagration and requires a more precise control method.

[0004] However, the existing traditional operation method of the coal mill causes great wear on the mill. At present, the hydraulic system of the three-phase coal mill is in operation with the following problems: a. There is no standard for adjusting the loading force, which is basically stable at about 10MPa. In most cases, the loading force is too large, causing large vibrations of the hydraulic pull rod and its base. If the hydraulic cylinder ages, the problem of large vibrations will be more obvious; b. When Indonesian lignite is mixed and burned, especially at low coal volume, the coal mill vibrates greatly; c. The buffer pressure of the nitrogen buffer tank for the three grinding rollers of the coal mill is not adjusted properly, resulting in deviations in the gaps between the three grinding rollers and vibrations of the coal mill. This invention aims to improve these technical problems. Summary of the invention

[0005] To achieve the above object, the present invention is achieved as follows:

[0006] A method for controlling a coal mill for blending and burning high-volatile raw coal comprises the following steps:

[0007] S1. First warm up the coal mill. After the coal mill warms up, close the coal mill hot air regulating door to reduce the coal mill inlet temperature to 150℃. Preset the coal mill outlet temperature according to the required coal type to ensure that the coal mill outlet temperature is kept below 70℃ when high volatile coal is used; when normal coal is used, the coal mill outlet temperature is reduced to below 50℃.

[0008] S2. Feed coal into the coal mill through the coal feeder, and at the same time start the coal mill. Adjust and control the outlet temperature of the coal mill in real time according to the volatile content Vad of the coal. When the volatile content Vad of the coal < 40%, the outlet temperature of the coal mill = [(82 - Vad) * 5 / 3 ± 5] °C; when the volatile content Vad of the coal ≥ 40%, the outlet temperature of the coal mill is 60 - 70 °C. At the same time, adjust the loading force of the hydraulic system of the coal mill according to the volatile content and coal quantity of the fed coal.

[0009] S3. When the coal mill is operating normally, coal addition of different coal types needs to be carried out through the coal feeder according to the combustion situation of the coal in the coal mill. Adjust the inlet temperature and outlet temperature of the coal mill according to the different added coal types to ensure that the inlet temperature of the coal mill does not exceed 300 °C and the outlet temperature is stable within the limit values in step S2.

[0010] S4. When the coal mill stops operating after work, the purging time of the coal mill must be > 10 minutes. Each powder pipe is purged separately for more than 90 s with an air volume of more than 40 t / h. Judge and confirm whether it has been purged clean through the outlet pressure, and strengthen the monitoring of the outlet temperature of the coal mill before and after shutdown and the differential pressure between the grinding bowl of the coal mill.

[0011] As a further solution of the present invention, when adjusting the loading force of the hydraulic system of the coal mill in step S2, when the volatile content Vad of the coal < 36%, the loading force P of the hydraulic system of the coal mill = acting force P1 - reaction force P2; when the coal feeding amount is 0 - 16 t / h, the acting force P1 is stable at 4.2 MPa and the reaction force P2 is stable at 3.0 MPa; when the coal feeding amount is 16 - 63 t / h, the acting force P1 = 4.2 + (A - 16) * 6.8 / 47; the reaction force P2 = 3 - (A - 16) * 1 / 47; A is the coal feeding amount.

[0012] When the volatile content Vad of the coal ≥ 36% and the coal feeding amount is 40 - 45 t / h, the loading force P of the hydraulic system of the coal mill is reduced by 0.5 - 1 MPa relative to the acting force P1 of the normal coal type.

[0013] As a further solution of the present invention, when the impact sound of the reaction force nitrogen buffer tank increases, the reaction force P is increased by 0.2 - 0.3 MPa relative to the calculated value to increase the grinding roll clearance and slow down the impact of the loading force.

[0014] As a further solution of the present invention, in step S2, when the fed coal type is blended coal, it should be set and operated according to the outlet temperature limit value of the coal mill reduced by 5 °C.

[0015] As a further solution of the present invention, when feeding coal through the coal feeder in step S2, when the fed coal type has a total moisture content ≥ 30%, the primary air volume of the coal mill is positively offset to increase the outlet temperature by 4 - 6 °C to dry the coal type.

[0016] As a further solution of the present invention, in step S3, the inlet and outlet temperatures of the coal mill during operation are automatically adjusted by introducing hot and cold air.

[0017] As a further solution of the present invention, in step S3, when the volatile matter content Vad of the added coal type ≤ 36%, the outlet temperature limit of the coal mill is 69 - 85 °C; when the volatile matter content Vad of the added coal type ≥ 36%, the outlet temperature limit of the coal mill is 56 - 68 °C.

[0018] As a further solution of the present invention, in step S3, after the coal mill starts running, the inerting steam system for coal mill deflagration is kept in standby state, with the temperature set at 150 - 180 °C and the pressure set at 0.5 MPa.

[0019] As a further solution of the present invention, during the operation of the S3 coal mill, when changing from the normal coal type to adding high - volatile coal, according to the changing trend of the outlet temperature of the coal mill, the set value of the outlet temperature of the coal mill should be gradually reduced and ensure that the inlet temperature ≯ 300 °C, and at the same time, the co - firing of Indonesian coal should be promptly carried out; when changing from high - volatile coal to adding normal coal, according to the changing trend of the inlet and outlet temperatures of the coal mill, the set value of the outlet temperature of the coal mill should be gradually increased.

[0020] As a further solution of the present invention, during the operation of the S3 coal mill, in case of unit outage or planned maintenance of the coal mill for more than 5 days, the raw coal bin filled with high - volatile coal needs to be emptied or replaced with normal coal; or, during the operation of the S3 coal mill, in case of forced outage of the coal - pulverizing system, the temperature around the raw coal bin should be measured at least every 8 hours and the highest temperature should be written into the duty log, and the inspection work on the upper part of the raw coal bin should be done well. In case of any abnormality, it should be reported immediately, and carbon dioxide should be injected into the coal bin for fire extinguishing.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] 1. It improves the original control method of the coal mill, solves the problem of temperature control limits in the traditional coal mill control method when co - firing different volatile coal types, and prevents the risk of deflagration.

[0023] 2. During the operation of the coal mill, the inlet temperature and outlet temperature of the coal mill are strictly controlled. By using "co - firing of Indonesian coal", an alarm is given in time when the inlet temperature and outlet temperature of the coal mill exceed the limit, reducing the accumulated heat energy inside the coal mill and lowering the risk of coal mill deflagration.

[0024] 3. Adjust the hydraulic system loading force of the coal mill as needed to better apply the force of the grinding roller, reduce the friction between the grinding roller and the liner, extend the life of the grinding roller and liner, and solve the problems of large vibration of the coal mill when burning Indonesian lignite, especially at low coal volume, and the nitrogen buffer tank buffer pressure of the three grinding rollers of the coal mill is not adjusted properly, resulting in deviation in the gap between the three grinding rollers and vibration of the coal mill. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A method flow chart of a coal mill control method for blending and burning high-volatile raw coal provided by the present invention;

[0026] Figure 2 The present invention provides a curve diagram of the hydraulic loading force P changing with the coal feed amount. DETAILED DESCRIPTION

[0027] 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 only part of the embodiments of the present invention, rather than all the embodiments; based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0028] The invention provides a new control method for a coal mill for burning high-volatile raw coal, improves and adjusts the internal equipment parameters and operation process parameters of the coal mill, reduces the risk of deflagration of the coal mill for burning high-volatile raw coal, and ensures the safe and stable operation of the coal mill.

[0029] Indonesian coal (including Indonesian lignite with low calorific value) is a high-volatile coal that is very prone to spontaneous combustion. The transportation process of Indonesian coal must be controlled at the source, and coal that has spontaneously combusted or is about to spontaneously combust should be reliably handled before it can be loaded on board.

[0030] After arriving at the power plant, the stacking and use of coal should be arranged reasonably. In principle, it should be stacked separately and not mixed at will to prevent spontaneous combustion due to mixing, untimely consumption, etc. When spontaneous combustion occurs, it should be eliminated by turning the pile over, compacting, etc. It is strictly forbidden to add coal with sparks into the raw coal bin to prevent explosion. It is strictly forbidden to add raw coal after spraying water directly to the bin to prevent accidents such as blockage of the pulverizing system, vibration of the coal mill, and boiler fire extinguishing.

[0031] The process of blending and burning ground coal specifically includes the following steps:

[0032] S1. First, warm up the coal mill. After the warm-up of the coal mill is completed, first close the hot air regulating valve of the coal mill slightly to reduce the inlet temperature of the coal mill to 150 °C. According to different coal types required, preset the outlet temperature of the coal mill in advance to ensure that when high-volatile coal types are input, the outlet temperature of the coal mill remains below 70 °C; when normal coal types are used, the outlet temperature of the coal mill is reduced to below 50 °C.

[0033] S2. Feed the coal type into the coal mill through the coal feeder, and at the same time start the operation of the coal mill. Adjust and control the outlet temperature after the operation of the coal mill in real time according to the volatile content Vdaf of the coal type. When the volatile content Vad of the coal type < 40%, the outlet temperature of the coal mill = [(82 - Vad) * 5 / 3 ± 5] °C; when the volatile content Vad of the coal type ≥ 40%, the outlet temperature of the coal mill is 60 - 70 °C; at the same time, adjust the loading force P of the hydraulic system of the coal mill according to the volatile content and coal quantity of the fed coal type.

[0034] Specifically, the volatile content of the coal types in the current coal storage and coal addition list is usually reported as Vad on an air-dried basis. According to the calculation formula: Aad = Ad × (100 - Mad) / 100;

[0035] Vdaf = Vad × 100 / (100 - Mad - Aad)

[0036] Moisture on an air-dried basis (Mad), Ash on an air-dried basis (Aad)

[0037] Taking the normal coal type (Vad) ≤ 36% and the high-volatile coal type (Vad) ≥ 36% as the calculation conditions, the outlet temperature table of the coal mill is calculated by combining the above formulas, as shown in Table 1:

[0038] Table 1 Outlet Temperature Table of Coal Mill

[0039]

[0040] Outlet temperature limit of coal mill:

[0041] Volatile content (Vad) ≤ 36%, outlet temperature limit of coal mill is 69 - 85 °C;

[0042] Volatile content (Vad) ≥ 36%, outlet temperature limit of coal mill is 56 - 68 °C;

[0043] When the coal type burned is blended coal (such as India-Australia blend), to prevent uneven blending of the blended coal, it should be operated 5 °C lower according to the above table.

[0044] When the coal type burned has a total moisture (Mt) ≥ 30%, the primary air volume of the coal mill should be positively offset, increasing the outlet temperature by 4 - 6 °C. At the same time, prevent problems such as poor pulverized coal fluidity, unstable combustion, and boiler flameout caused by low outlet temperature. However, pay attention to the thin coal bed, low current, and large vibration of the coal mill caused by the increased air volume.

[0045] S3. The coal mill operates normally. According to the combustion situation of the coal type in the coal mill, coal type addition needs to be carried out through the coal feeder. According to different added coal types, the inlet temperature and outlet temperature of the coal mill are adjusted to ensure that the inlet temperature of the coal mill does not exceed 300 °C, and the outlet temperature is stable within the limit values calculated in step S2.

[0046] The inlet and outlet temperatures of the operating coal mill can be automatically adjusted by introducing hot and cold air through the automatic hot and cold air regulating valve.

[0047] During the operation of the coal mill, strictly control the inlet temperature and outlet temperature of the coal mill. The inerting steam system of the coal mill remains in standby state, with the temperature set at 150 - 180 °C and the pressure set at 0.5 MPa. When co-firing high volatile coal types, Indonesian coal should be added for co-firing. When the temperature rise rate of the outlet temperature of the coal mill is greater than 1.5 °C / 1.5 s, it is determined that the inerting steam is automatically put into use.

[0048] During the operation of the coal mill, when the added coal type is changed from the normal coal type (Vad < 36%) to the high volatile coal type (Vad ≥ 36%), since the high volatile coal type contains a relatively large amount of moisture, when burning to the high volatile coal type, the outlet temperature of the coal mill drops significantly. According to the coal storage volume and addition volume in the coal bunker, the time point of burning to the high volatile coal type is judged. During this process, in the "automatic" state of the cold and hot air of the coal mill, gradually reduce the set value of the outlet temperature of the coal mill and ensure that the inlet temperature ≯ 300 °C. At the same time, promptly add Indonesian coal for co-firing. The purpose of using the "Indonesian coal co-firing" link is to increase the alarm of the inlet and outlet temperatures of the coal mill to monitor the operation status of the high volatile coal type in the coal mill and prevent deflagration.

[0049] During the operation of the coal mill, when the added coal type is changed from the high volatile coal type (Vad ≥ 36%) to the normal coal type (Vad < 36%), similarly, according to the coal storage volume and addition volume in the coal bunker, the time point when the high volatile coal type has been burned out is judged. In the "automatic" state of the cold and hot air of the coal mill, gradually increase the set value of the outlet temperature of the coal mill, but the false appearance of low inlet temperature and high outlet temperature of the high volatile coal type caused by the dry climate in autumn and winter should be prevented, and the outlet temperature should be strictly controlled according to the limit values.

[0050] During the period of co-firing high volatile coal, on-site patrol inspections should be strengthened. Pay attention to checking the operation of the pebble coal hopper, pebble coal belt, vibration of the coal mill, and the air chamber scraper to prevent the pebble coal hopper or the belt from catching fire. Especially pay attention to checking the paint color of the coal mill body, outlet powder pipe, etc. and the smooth discharge of pebble coal. During each inspection, measure the temperature of the coal mill powder pipe at the inlet of the burner to prevent spontaneous combustion due to powder accumulation in the powder pipe.

[0051] S4. When the coal mill stops operating after work, the purging time of the coal mill must be > 10 minutes. Each powder pipe is purged individually for more than 90 s with an air volume of more than 40 t / h maintained. It is judged and confirmed to be purged clean through the outlet pressure, and the outlet temperature of the coal mill and the differential pressure of the coal mill grinding bowl before and after shutdown are closely monitored.

[0052] During the operation of the coal mill in S3, it is necessary to reasonably arrange the maintenance plan of the coal mill and the calibration plan of the coal feeder belt. In case of unit outage or the planned maintenance of the coal mill for more than 5 days, the raw coal bunker filled with high-volatile coal needs to be emptied or replaced with normal coal. Or, if it is not emptied before the outage or the coal pulverizing system fails and is forced to stop operating, the temperature around the raw coal bunker is measured at least every 8 hours and the highest temperature is written into the duty log. Patrol work on the upper part of the raw coal bunker is done well. Any abnormality should be reported immediately, and carbon dioxide is injected into the coal bunker for fire extinguishing. And as soon as possible, organize personnel to speed up the defect elimination progress and put the coal pulverizing system into operation as soon as possible. If necessary, close cooperation should be carried out, and the raw coal in the coal bunker is taken out by special methods such as manual transportation.

[0053] Once a deflagration occurs in the coal pulverizing system (whether inside the coal mill or in the outlet powder pipe), the inlet pressure of the air of the coal mill suddenly rises and the explosion-proof door of the air acts. The coal feeder should be stopped immediately and the coal gate should be closed. If the deflagration causes the high temperature protection of the coal mill outlet to act, all its inlet cold air damper doors and regulating doors, inlet hot air damper doors and regulating doors, and sealing damper doors should be closed, and the coal mill outlet door, the pebble coal discharge door, etc. should be closed for suffocation fire extinguishing. After 30 minutes of confirming that there is no combustion, make preparations for starting the coal mill. With the coal mill outlet door closed, start the coal mill to discharge the stored coal in the coal mill through the pebble coal discharge port to the pebble coal hopper and confirm that the discharge is clean. The temperature of the powder pipe and the coal mill body of the deflagrated coal mill is measured on-site with a thermometer. Wait until the temperature of each powder pipe and the coal mill body no longer rises and all drop below 70 °C. Confirm that the pebble coal outlet discharge door of the coal mill is closed, and then open the coal mill outlet door to naturally discharge the internal gas through the furnace negative pressure for more than 10 minutes, and then open the cold air door for thorough ventilation and purging for more than 30 minutes. Then notify the maintenance to conduct internal inspections of the powder pipe, the coal mill, etc. During the purging process, the change of the outlet temperature of the coal mill should also be noted. When the temperature rises abnormally, it is handled according to the situation of the coal mill catching fire. If the temperature still cannot be lowered and open fire leakage is found on-site, the fire duty should be notified immediately and the method of external water spraying for cooling should be adopted.

[0054] The present invention further specifically explains the relevant loading force P of the hydraulic system in S2:

[0055] Loading force: The grinding force required for grinding materials (grinding force = component gravity + loading force) is provided by the hydraulic system. This system includes a hydraulic station, three hydraulically actuated cylinders working in parallel, and accumulators installed on the hydraulically actuated cylinders. The loading force is a function of the pressure difference between the acting pressure formed by the hydraulic system in the annular area of the rod chamber of the hydraulically actuated cylinder and the reaction pressure formed by the rodless chamber of the hydraulically actuated cylinder.

[0056] Control the acting force and the reaction force according to the size of the coal flow rate of the coal mill, that is, the signal of the coal feeder speed or the signal of the belt scale.

[0057] However, the existing traditional operation method for the coal mill causes great wear on the grinding rollers. Currently, in the operation of the coal mill in the third phase, the problems existing in the hydraulic system are as follows: a. There is no standard for adjusting the loading force, which is basically stable at about 10 MPa. In most cases, the loading force is too large, resulting in relatively large vibrations of the hydraulic pull rod and its base. If the hydraulic cylinder ages, the problem of large vibrations becomes more obvious; b. When co-firing Indonesian lignite, especially at low coal volumes, the coal mill vibrates greatly; c. The buffer pressure of the nitrogen buffer tank for the acting forces of the three grinding rollers of the coal mill (the nitrogen buffer tank is a device for stabilizing the acting force and the reaction force by buffering the pressure) is not adjusted properly, resulting in deviations in the gaps between the three grinding rollers and vibrations of the coal mill. This invention aims to improve these technical problems.

[0058] Therefore, when the output of the coal mill is stable and the requirements for pulverized coal combustion are met, within a certain range of changes in the hydraulic loading force P of the coal mill, the influence on the fineness of the pulverized coal is not significant; in order to reduce the wear and vibration of the coal mill, extend the service life, and reduce the unit coal grinding consumption, when the output of the coal mill permits, it is necessary to adjust the hydraulic loading force P during the operation of the coal mill and try to reduce the operation of the hydraulic loading force P under the same coal grinding effect.

[0059] During the operation of the coal mill, the magnitudes of the acting force P1 and the reaction force P2 act on the grinding rollers according to the coal feed rate;

[0060] When the coal mill is operating, the optimal loading force is obtained based on experience and the results of multiple experiments:

[0061] When the coal feed rate is 0 - 16 t / h, the acting force P1 is stable at 4.2 MPa, and the reaction force P2 is stable at 3.0 MPa; the values before and after the fixed values do not affect the operation results of the coal mill.

[0062] When the coal feed rate is 16 - 63 t / h, the acting force P1 is 4.2 - 11 MPa, and the reaction force P2 is 3.0 - 2.0 MPa.

[0063] Such as Figure 2 , according to the experimental data, a graph is obtained, and the calculation formula for the most optimized loading force curve is obtained by fitting the function curve closest to the experimental data. That is, when the coal feed rate is 16 - 63 t / h, the calculation formula is:

[0064] The acting force P1 = 4.2 + (A - 16) * 6.8 / 47; the reaction force P2 = 3 - (A - 16) * 1 / 47;

[0065] The hydraulic system loading force P = the acting force P1 - the reaction force P2; A is the coal feed rate (t / h).

[0066] The Indonesian lignite fed into our factory has the following characteristics: low calorific value, high moisture content, and high volatile matter. Due to these characteristics, this coal type is fragile, flammable, and the outlet temperature of the coal mill is low. The lignite is easily compacted under the grinding roller. If the loading force is too large, the buffer force between the grinding table and the grinding roller decreases, resulting in increased wear of the grinding roller and the grinding table. In the case of low coal volume, the above situation will be aggravated. When co-firing lignite, in order to increase the outlet temperature of the coal mill and improve fluidity, it is necessary to increase the air flow rate. In addition, the lignite contains a relatively large amount of sand, which all accelerates the wear of the grinding roller.

[0067] During multiple working processes, it is found that when the coal feeding amount of coal with high volatile matter (Vad≥36%) is 40 - 45 t / h, the calculated value of the acting force P1 can be reduced by 0.5 - 1 MPa compared with that of normal coal types, thereby reducing the loading force P of the hydraulic system. Although this may increase the fineness of the pulverized coal, it is safer for co-firing lignite. Because Indonesian lignite is extremely flammable, if the pulverized coal is too fine, the flame at the burner outlet will be shorter, which is likely to cause wall sticking and coking, and is also prone to explosion.

[0068] In the case of low coal volume, since the coal seam between the grinding roller and the grinding table becomes thinner, if the loading is too large, the impact of the grinding roller on the coal seam and the grinding table will increase, and the vibration of the coal mill will increase. At this time, it will also impact the nitrogen buffer tank for the acting force and the reaction force. If the impact sound of the reaction force nitrogen buffer tank increases, the reaction force P can be increased by 0.2 - 0.3 MPa relative to the calculated value to increase the grinding roller gap, so as to slow down the impact of the loading force.

[0069] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation to the present invention.

[0070] The above are only embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. Any equivalent structure or equivalent process transformation made by using the content of the specification and drawings of the present invention, or directly or indirectly applied in other related technical fields, shall be included in the patent protection scope of the present invention by the same token.

Claims

1. A control method for a coal mill co-firing high-volatile raw coal, characterized in that, It includes the following steps: S1. First, warm up the coal mill. After the warm-up of the coal mill is completed, first close the hot air regulating valve of the coal mill to reduce the inlet temperature of the coal mill to 150 °C. According to different coal types required, preset the outlet temperature of the coal mill in advance to ensure that when high-volatile coal is put into use, the outlet temperature of the coal mill remains below 70 °C; when normal coal is used, the outlet temperature of the coal mill is reduced to below 50 °C; S2. Feed the coal type into the coal mill through the feeder, and at the same time start the operation of the coal mill. Adjust and control the outlet temperature after the operation of the coal mill in real time according to the volatile content Vad of the coal. When the volatile content Vad of the coal < 40%, the outlet temperature of the coal mill = [(82 - Vad) * 5 / 3 ± 5] °C; when the volatile content Vad of the coal ≥ 40%, the outlet temperature of the coal mill is 60 - 70 °C; at the same time, adjust the loading force of the hydraulic system of the coal mill according to the volatile content and coal quantity of the fed coal; S3. When the coal mill is running normally, coal addition of different coal types needs to be carried out through the feeder according to the combustion situation of the coal in the coal mill. Adjust the inlet temperature and outlet temperature of the coal mill according to different added coal types to ensure that the inlet temperature of the coal mill is not greater than 300 °C, and the outlet temperature is stable within the limit values in step S2; S4. When the coal mill stops running after work, the purging time of the coal mill must be > 10 minutes. Each pulverized coal pipe is purged separately for more than 90 s with an air volume of more than 40 t / h. Judge and confirm that it has been purged clean through the outlet pressure, and strengthen the monitoring of the outlet temperature of the coal mill before and after shutdown and the differential pressure between the grinding bowl of the coal mill.

2. The coal mill control method for co-firing high-volatile raw coal according to claim 1, wherein When adjusting the loading force of the hydraulic system of the coal mill in step S2, When the volatile content Vad of the coal < 36%, the loading force P of the hydraulic system of the coal mill = acting force P1 - reaction force P2; when the coal feeding amount is 0 - 16 t / h, the acting force P1 is stable at 4.2 MPa, and the reaction force P2 is stable at 3.0 MPa; when the coal feeding amount is 16 - 63 t / h, the acting force P1 = 4.2 + (A - 16) * 6.8 / 47; the reaction force P2 = 3 - (A - 16) * 1 / 47; A is the coal feeding amount in t / h; When the volatile content Vad of the coal ≥ 36% and the coal feeding amount is 40 - 45 t / h, the loading force P of the hydraulic system of the coal mill is reduced by 0.5 - 1 MPa compared with the acting force P1 of normal coal.

3. The coal mill control method for co-firing high volatile bituminous coal according to claim 2, wherein, When the impact sound of the reaction force nitrogen buffer tank increases, the reaction force P increases by 0.2 - 0.3 MPa compared with the calculated value to increase the grinding roll gap to slow down the impact of the loading force.

4. A control method for a coal mill burning a high-volatile raw coal according to claim 1, characterized in that, In step S2, when the coal type put into use is blended coal, it should be set and operated according to a 5 °C reduction in the outlet temperature limit value of the coal mill.

5. A control method for a coal mill burning a high-volatile raw coal according to claim 1, characterized in that, In step S2, when the coal type fed through the feeder is a coal type with a total moisture content ≥ 30%, the primary air volume offset of the coal mill is positively offset to increase the outlet temperature by 4 - 6 °C to dry the coal type.

6. The control method of a coal mill for co-firing high-volatile raw coal according to claim 1, characterized in that, In step S3, the inlet and outlet temperatures of the running coal mill are automatically adjusted by introducing hot and cold air.

7. A control method for a coal mill burning high-volatile raw coal according to claim 1, characterized in that, In step S3, when the volatile content Vad of the added coal ≤ 36%, the outlet temperature limit value of the coal mill is 69 - 85 °C; when the volatile content Vad of the added coal ≥ 36%, the outlet temperature limit value of the coal mill is 56 - 68 °C.

8. A control method for a coal mill burning a high-volatile raw coal according to claim 1, characterized in that, In the step S3, after the coal mill starts running, keep the inerting steam system for coal mill deflagration in standby state, with the temperature set at 150 - 180 °C and the pressure set at 0.5 MPa.

9. A control method for a coal mill burning a high-volatile raw coal according to claim 1, characterized in that, During the operation of the coal mill in the S3, when changing from the normal coal type to adding coal of high volatile coal type, according to the changing trend of the outlet temperature of the coal mill, gradually reduce the set value of the outlet temperature of the coal mill and ensure that the inlet temperature ≤ 300 °C. At the same time, promptly input the blended combustion of Indonesian coal. When changing from adding coal of high volatile coal type to the normal coal type, gradually increase the set value of the outlet temperature of the coal mill according to the changing trend of the inlet and outlet temperatures of the coal mill.

10. A control method for a coal mill burning high-volatile raw coal as claimed in claim 1, characterized in that, During the operation of the coal mill in the S3, in case of unit outage or planned maintenance of the coal mill for more than 5 days, the raw coal bunker with high volatile coal added needs to be emptied or replaced with normal coal type. Or, during the operation of the coal mill in the S3, in case of forced outage of the coal pulverizing system, measure the temperature around the raw coal bunker at least every 8 hours and write the highest temperature into the duty log, do a good job in the inspection of the upper part of the raw coal bunker, report immediately in case of abnormality, and inject carbon dioxide for fire extinguishing into this coal bunker.

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