How to optimize and adjust the air coal ratio of t

How to optimize and adjust the air coal ratio of medium speed coal mill

too large and too small air coal ratio will also affect the normal combustion of pulverized coal in the boiler. A reasonable air coal ratio can provide guarantee for the safe and stable operation of the boiler. The determination of air coal ratio should comprehensively consider the type of coal mill, the type of rolled coal, the safety of pulverizing system, the full combustion of pulverized coal in the boiler and other aspects

the restriction of the lowest wind speed of the powder feeding pipe on the air volume at low coal volume. For the pulverizing system, in order to make the air have a certain ability to carry pulverized coal, the lowest medium flow rate is limited to ensure that there is no pulverized coal accumulation in the powder feeding pipe and avoid the spontaneous combustion of pulverized coal when the mill is stopped. The medium flow rate in the pulverized coal feeding pipe of the direct blowing pulverized coal system is recommended to be 22-28 M/s

2. The requirements of coal type on the air volume in the pulverized coal feeding pipe

the reasonable primary air speed should realize the optimal combustion of pulverized coal in the furnace on the basis of ensuring the safety of pulverized coal transportation and burner, so that there is a reasonable temperature field and velocity field in the furnace. The primary air in the pulverized coal flow is mainly used to burn the volatile matter released after the pulverized coal is heated. In recent years, the company's deeds have increased rapidly, and the remaining coke particles are burned out by the oxygen provided by the secondary air. For different types of coal, there are certain differences in the air volume in the powder feeding pipe required to complete the combustion of volatile matter. For commonly used coal, in order to ensure the full combustion of pulverized coal in the early stage, Ensure that the air coal ratio is about 1.8

the minimum ventilation volume and minimum output of the coal mill recommended by the data. Considering that the low wind speed may cause the deposition of pulverized coal in the powder feeding pipe and the reduction of the wind speed of the air ring of the coal mill, resulting in the sudden increase of the emission of pebble coal, the minimum ventilation volume is mostly specified as about 70% of the rated ventilation volume, and the shape can be divided into sizes. The composition of materials, and the minimum output of various coal mills is specified as 40% - 50% of the rated value. When the output is lower than the minimum output, because the coal seam on the grinding plate is too thin, it will cause direct contact with the grinding parts, resulting in strong wear and vibration. The coal mill has an air coal ratio suitable for combustion under the rated output and corresponding ventilation. When the output of the coal mill decreases to 50%, and the ventilation ratio needs to be maintained at 70% of the rated value, then the air coal ratio will increase a lot and the pulverized coal concentration will decrease. At low load, the furnace temperature level has been reduced, and the air coal ratio is too large, which will be more beneficial to the ignition and stable combustion of pulverized coal

3. Requirements for the air volume at the inlet of the pulverizer when the pulverizer has a large output

in order to ensure the safe and reliable operation of the pulverizer under a large output (drying output, grinding pressure difference, pebble coal emission, mill outlet temperature and other parameters meet the requirements), the pulverized coal rolled can meet the requirements of boiler combustion, meet the requirements of boiler operation output during the overhaul cycle, and ensure a sufficient air volume into the mill. For ZGM 95g coal pulverizer, the recommended air coal ratio is generally about 1.8 when it operates at an appropriate output. Therefore, when the output is 40 t/h, the air volume at the inlet of the mill should not be less than 70 t/h

the requirements of the setting of thermal control on the air coal ratio of the pulverizer and the setting of air coal ratio are limited in the process of thermal control. If the load is certain, the total air volume is determined, and only minor adjustments can be made according to the change of coal quality. When the coal quality is poor (low volatile), a small primary air rate should be adopted to reduce the ignition energy. Ignition under the condition of low temperature in the furnace can ensure the stable combustion of pulverized coal in the furnace. At the same time, the secondary air rate should be increased for the later burnout of pulverized coal; When the coal quality is good (high volatile), a larger primary air rate should be adopted to let the pulverized coal catch fire far away from the burner to prevent coking near the burner and burning of the burner, and the corresponding secondary air rate should be reduced to better organize the combustion in the furnace. The traditional air coal ratio curve of the coal mill is a straight line, and the thermal regulation configures the air volume according to this curve, which is lack of adaptability to the change of coal quality. Therefore, a better air coal ratio relationship can better adapt to the changes of coal quality

4. Factors affecting the emission of pebble coal from the coal mill

in order to reduce the emission of pebble coal from the coal mill, the operator usually adopts the way of increasing the air volume at the inlet of the coal mill. The test and theoretical analysis show that this operation mode is not desirable. The test shows that the larger air volume during operation reduces the emission of pebble coal from the coal mill, but the effect is not obvious. Due to the large clearance of the air ring of the coal mill, the actual flow area of the primary air increases, and a large part of the primary air flows out from this clearance, which does not participate in the role of floating pulverized coal, resulting in the reduction of the primary air flow through the nozzle and the reduction of the wind speed of the air ring; At the same time, the primary air flowing through the air ring gap has a horizontal downward flow direction, which has a certain disturbance effect on the normal flow direction of the wind powder mixture and hinders the normal upward flow state of the wind powder mixture. At the same time, due to the serious wear of the outer part of the grinding roller, the force exerted on the raw coal is greatly reduced, so that the raw coal cannot be fully broken here, that is, it is pushed to the outside of the air ring and enters the gravel coal discharge box. Therefore, the larger air ring clearance and the serious wear of the grinding roller are the main reasons for the increase in the emission of pebble coal. The maintenance personnel of the power plant unit should try to reduce the air ring clearance during the maintenance of the coal mill. The air ring clearance after maintenance is about 5 mm. If the grinding roller is seriously worn, it is recommended to turn the grinding roller over for use or replace it with a new one

5. Impact of excessive air volume at the inlet of the coal mill on combustion we often encounter more or less displacement of the tension machine

excessive air volume makes the wind speed of the pulverized coal conveying pipe higher, the ignition of pulverized coal is delayed, and the combustibles of fly ash are increased. At the same time, it will raise the flue gas temperature at the outlet of the furnace, affect the economy of boiler combustion and the safety of superheaters and reheaters, and in serious cases, it will cause difficulty in pulverized coal ignition and unstable combustion flame, Affect the safe and stable operation of the boiler. When the air volume at the inlet of the pulverizer is too large, the air coal ratio seriously deviates from the ideal value due to the large primary air volume, which worsens the combustion condition in the furnace. Especially in the case of poor coal quality, the output of single mill increases, and the large air volume operation mode adopted to reduce the emission of pebble coal will seriously affect the stability of boiler operation, which may lead to unstable combustion and the occurrence of boiler fire-fighting accidents. In daily operation, strengthen the maintenance of coal mills and control the emission of pebble coal within a reasonable range. Large air ring clearance and serious wear of grinding rollers are the main reasons for the increase of stone coal emissions. Excessive primary air volume at the inlet of the coal mill will increase the wind speed of the pulverized coal conveying pipe, and the air coal ratio will seriously deviate from the design value, making the combustion unstable and affecting the safe operation of the boiler. Combined with the respective characteristics of the power plant, the air coal ratio of the coal mill is optimized according to the analysis in this paper, so as to provide a guarantee for the stable operation of the boiler