Created on:2021-07-17 10:30

Boiler hydraulic fault diagnosis and maintenance_ Characteristics and operation of coal mill

Boiler hydraulic fault diagnosis and maintenance_ Characteristics and operation of coal mill

(1) Characteristics of rp-1003 coal mill

The characteristics of this kind of coal mill are: low power consumption, less auxiliary power; Compact structure, less metal consumption; It has strong adaptability to high moisture coal; The one-time investment is small, which is 35% - 45% lower than the negative pressure system; Quick response to load change; There is no powder deposit, and it is not easy to deflagration; Hydraulic loading is adopted, which can adapt to the variety of coal; The layout of pulverized coal pipeline is free; Sensitive to three pieces (stone, iron and wood); The maintenance technology of coal mill is required to be high; Since it is a positive pressure system, a sealed air system is added to prevent the oil system from entering pulverized coal and the leakage of pulverized coal.

(2) Operation of coal mill

Whether the operation condition of coal mill in direct fired pulverizing system is stable or not directly affects the boiler load, and then affects the operation of steam turbine and generator. For example, in terms of load, five mills are operating with a total load of 600 MW, with an average load of 120 MW for each mill. If one mill is shut down during operation, it is equivalent to shutting down a 125 MW unit in the power grid. It can be seen that the correct grasp of the operating characteristics of the coal mill is particularly important to improve the reliability of the coal mill and ensure the stable operation of the power grid.

The main indexes to evaluate the operation characteristics of coal mill include: coal mill output, the relationship between coal mill load and primary air volume, pulverized coal fineness, operating temperature of coal mill, etc.

① The grinding capacity of rp-1003 medium speed mill is quite sensitive to the grindability index (HGI) of coal. The lower the grindability coefficient is, the greater the variation range of output is. When the coal quality changes, the grindability coefficient changes and the output also changes. If the ash content of a bituminous coal is 25.28% (more than 20%), the recycle of raw coal in the mill will increase, thus reducing the output of the mill. The hot air in the mill has little drying effect on the pulverized coal before grinding, so the water content of the coal will affect the grinding efficiency. The larger the water content is, the smaller the output is. Moreover, the excessive water content will lead to the coalescence of coal and pulverized coal and affect the safe operation. With the coarsening of the pulverized coal, the output of the coal mill increases. Therefore, when the peak load requires a higher output of the coal mill, the RX value can be reduced to increase the output. The influence of the oil pressure of the hydraulic loading system on the output of the coal mill is shown in Fig. J.

JK.jpg

② The relationship between mill load and primary air volume when the pulverizing system is started and before the coal feeder is started, the oil pressure provided by the hydraulic pump is greater than 2.3mpa. Considering the stability of the powder feeding system, the minimum ventilation rate of the system must be maintained at not less than 70% of the total air volume. The relationship between mill load rate and primary air volume is shown in Figure K.

③ Because there is a linear relationship between the load rate of the coal mill and the primary air volume, when the load of the coal mill decreases, the absolute value of the air volume decreases, the air velocity at the air ring, in the coal mill and in the space of the separator decreases, the ability to take away the pulverized coal decreases, and the pulverized coal becomes finer; On the contrary, the primary air volume is large, the ability of carrying pulverized coal is strong, and the pulverized coal becomes coarse. In addition, the opening of the folding door is large, the resistance of the air powder mixture is small, and the pulverized coal becomes coarse. When the handle is in the "0" position, the blade opening of the folding door is the largest and the pulverized coal is the coarsest; When the handle is in "10" position, the blade opening of the folding door is the smallest, and the pulverized coal is the smallest. After the gap between the grinding roller and the grinding bowl is adjusted, it usually does not move. In this case, the pressure is large, the grinding ability of the grinding roller is strong, and the pulverized coal becomes fine; vice versa. Figure L shows the test results of pulverized coal fineness of rp-1003 coal mill under different hydraulic pressure. It can be seen from the figure that when the load of coal mill remains unchanged, the hydraulic pressure increases and the pulverized coal becomes fine; When the hydraulic pressure is constant, with the increase of load, the pulverized coal becomes coarse. The influence of the change of hydraulic loading force on the fineness of pulverized coal is more significant with the increase of load. Therefore, in low load operation, reducing the hydraulic pressure is conducive to reducing the vibration, and will not have too much impact on the fineness of pulverized coal.

④ The higher the temperature of the gas powder mixture at the outlet of the pulverizer, the more conducive to the drying process of pulverized coal, but the temperature should not exceed the safety limit. If the outlet temperature exceeds the specified value, the possibility of pulverized coal ignition will be increased; If the outlet temperature is too low, because the pulverized coal can not be dried in time, the pulverized coal will be absorbed in the inside of the pulverizer and in the pulverized coal pipe, which will block the pulverized coal pipe and cause the pulverizer and pulverized coal pipe to catch fire. The normal operating temperature of rp-1003 coal pulverizer is 75-82 ℃, and the maximum design outlet temperature is 93 ℃. Therefore, the operating temperature should not exceed 93 ℃, otherwise, the ignition will be caused by the escape of volatile matter in coal; However, the minimum temperature at the outlet of the mill should not be lower than 60 ℃, at least 10 ℃ higher than the dew point to avoid coal caking.

⑤ The operating temperature of the coal mill and the outlet temperature of the coal mill are controlled by adjusting the opening of the baffle to adjust the proportion of cold and hot air in the inlet air.

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