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The flame length is a factor to consider the firing effect of rotary kiln, which has an important impact on the production quality of products. Therefore, it is very important to control the flame length in operation. The main factors affecting the flame length are as follows.
1. Secondary air temperature: the temperature increases, the combustion speed is fast, and the flame is short.
2. Fineness of pulverized coal: the finer the pulverized coal is, the faster the combustion speed is; the finer the pulverized coal is, the larger the surface area of pulverized coal is, and the contact area between coal and oxygen in the air is increased, so the combustion speed is accelerated and the flame length is shortened.
3. The form of coal injection nozzle: the form of coal nozzle affects the mixing of air and coal. The more uniform the air coal mixture is, the faster the combustion speed is.
The influence of volatile matter of coal on flame length: bituminous coal with high volatile content can be ignited near the nozzle, and the flame is longer, but the coal with low volatile content is on the contrary (as the ignition temperature decreases with the increase of volatile matter, the distance between ignition point and nozzle is different due to different volatile content, high volatile content, early ignition, and continuous heating process of coal Long distance, so the flame is long. For coal with low volatile matter, most of the heat energy can be released in a short distance, so that the flame is concentrated and the flame is short, sometimes local high temperature phenomenon occurs.
4. Influence of gas velocity on flame length in rotary kiln
The faster the flow rate is, the longer the flame is, and the gas velocity is affected by the primary wind speed and the exhaust air at the kiln tail. On the one hand, the increase of primary wind speed can increase the effective range of pulverized coal and lengthen the flame; on the other hand, it can make the air and coal mix evenly, so that the combustion speed is fast and the flame is short, which are two opposite effects. At the same time, in order to prevent "tempering", the velocity of ejecting should be higher than that of flame diffusion. The spray velocity is related to the diameter of the kiln. The large diameter rotary kiln requires a higher spraying speed, and the smaller one should be taken as a small value, which can create good conditions for heat exchange between flame and material. The increase of exhaust air at the kiln tail will increase the negative pressure at the kiln tail and the secondary air, which will increase the gas velocity outside the flame, so as to lengthen the flame. In normal production, we usually change the exhaust air at the kiln tail or reduce the tertiary air to increase the negative pressure at the kiln tail to change the flame length.
Knowing these factors that affect the flame length, we should pay attention to the operation of the rotary kiln, master the skills and control the length, so that the kiln can work smoothly and improve the product quality.