Rotary kiln is the main equipment of cement production. The raw meal powder is fed into the kiln tube from the high end of kiln tail cylinder. Due to the tilt and slow rotation of kiln cylinder, the material produces a compound movement that is tumbling along the circumferential direction and moving from the high temperature to the low end along the axis. The raw meal in the kiln through decomposition, firing and other processes, the cement clinker is unloaded from the bottom of kiln cylinder and into the cooling machine. The fuel is injected into the kiln head and burns in the kiln, and the heat emitted heats the raw meal and calcinates the raw meal into clinker. The hot air formed in the process of exchanging with the material, the feed end of kiln enters the kiln system, and finally it is discharged into the atmosphere through the chimney.
2 Calcination Technology of Cement Rotary Kiln Clinker
2.1 The function of increasing primary air volume and ejecting air speed is to provide volatile combustion of pulverized coal, which is divided into high-speed axial flow wind, swirl wind and a small amount of low-speed central air to transport pulverized coal into the kiln to form a powerful "willow leaf" flame in the kiln. If the primary air volume is reduced, the amount of high temperature secondary air can be increased naturally. At present, the total amount of coal supply air and primary clean air in the kiln mostly accounts for about 10%-15% of the total combustion air in the kiln, which can also be considered to be the actual level that can be achieved at present. The unique structure of coal wind on the inside of the cyclone is adopted to form a flame with moderate intensity and reasonable thermal distribution in the length direction, which is convenient for timely adjustment and control in production. When used in the kiln system with high efficiency grate cooler, the primary air ratio can be basically controlled at about 8%. When used in the kiln system with single cooler, the primary air ratio is increased to 14% 18% before the kiln system enters a good condition. Therefore, we emphasize that the temperature of the whole kiln increases with the increase of firing zone temperature, which is very beneficial to the pre-firing of pre-tropical raw meal.
2.2 Negative pressure control and airflow velocity analysis in the kiln is critical. A negative pressure measuring point is installed at the end of the cement rotary kiln, and the negative pressure generated at the end of the kiln will be directly displayed by the transmitter on the operating instrument of the kiln head. The change of negative pressure also indicates the corresponding change of air flow velocity in the kiln. If the air flow velocity in the cement rotary kiln is controlled stably, the calcination condition of the kiln will be very good, so the control of the air flow speed is also the key factor of the kiln calcination. In the operation process of the cement rotary kiln, if the flow rate is relatively fast, it is easy to send the fuel injected into the kiln to the end of the kiln or the smoke room before it is fully burned. when the temperature of the firing zone is low, it will have a corresponding impact on the normal thermal system of the kiln, and lose a lot of heat, resulting in the reduction of clinker quality and output. Those who are familiar with the calcination process of cement rotary kiln will know that when the temperature of the smoke room is too high, it will also affect the structure of the smoke room, threaten the firmness of the building, and in serious cases, the vault of the smoke chamber will collapse.
2.3 When the coal ring and kiln mouth brick are calcined in the cement rotary kiln, the coal ring in the burning zone will be very difficult to form, and the calcination environment in the kiln is very good, which will be relatively high yield. More attention should be paid to the formation and shedding of the kiln skin in the firing zone, to prevent the influence caused by carelessness, and to pay attention to that the coal ring in the kiln should not be too thick, and it is necessary to sort out the cooked material when it is more difficult to pass through the coal ring, otherwise it will have an impact. According to the analysis of the actual calcination experience, the ring is also beneficial, if the thickness of the ring is relatively moderate, it will also be helpful to the calcination of the rotary kiln. When the pulverized coal in the rotary kiln burns from the air duct into the firing zone, the coal ring will be the flame to be fully burned and a higher flame temperature will be obtained. The burning of the flame will proceed more smoothly because the coal ring is blocked by the cold air at the head of the rotary kiln and the water vapor from the bleaching machine. At the same time, we also need to increase the height of the kiln mouth brick of the rotary kiln, thicken the material layer of the cooling zone and increase the residence time of the clinker in the high temperature zone. In this way, the temperature of the kiln mouth of the rotary kiln will be raised, which can help the combustion of pulverized coal into the kiln and speed up the combustion speed. First, the distance from the end of the burner to the kiln mouth is 100-200cm. The more it extends into the kiln, the higher the temperature point moves backward, and the cooling zone increases, which shortens the kiln length and increases the tail temperature.
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