The causes and solutions for the unstable negative pressure at the kiln head of the rotary kiln!
During the production process of the rotary kiln, the negative pressure at the kiln head is an important parameter reflecting the ventilation condition and the calcination process inside the kiln. The magnitude and stability of the negative pressure directly affect the shape of the flame, combustion efficiency, thermal system, and production. Therefore, mastering the changing pattern of the kiln head negative pressure and taking timely countermeasures are of vital importance for ensuring the stable operation of the system.
I. Analysis of the Causes of Unstable Negative Pressure at the Kiln Head
1.The reasons for the increase in negative pressure
(1) When the cooling air volume is out of balance with the exhaust air volume, if the secondary air volume extracted by the kiln system is greater than the cooling air volume provided by the grate cooler, the balance of the system air volume is disrupted, resulting in a large negative pressure at the kiln head. For example, if one of the fans of the grate cooler stops running, the cooling air volume drops sharply, and the negative pressure at the kiln head subsequently increases.
(2) Insufficient layer thickness leads to changes in air volume When the material layer in the rotary cooler is too thin, the resistance for the cooling air to penetrate is reduced, resulting in an increase in air volume. At the same time, the temperature of the residual air changes from high to low, and the gas density increases. With the fan damper remaining unchanged, the actual air volume increases, disrupting the air volume balance between the kiln system and the cooling system, causing the negative pressure at the kiln head to rise.
(3) Excessive material layer thickness leads to ventilation obstruction. When the material layer in the rotary kiln suddenly thickens, the ventilation resistance significantly increases. The cooling air is unable to effectively penetrate the material layer, resulting in a decrease in cooling air volume, insufficient air supply in the kiln, and a decline in the overall system air volume. Consequently, the negative pressure at the kiln head rises.
2. The reasons for the reduction in negative pressure
(1) Collapse of materials in the kiln When the preheater or decomposition furnace experiences material collapse, a large amount of raw materials suddenly enter the kiln through the sealing ring, and within a short period of time, they reach the firing zone. This process will sharply increase the system resistance, disrupt normal ventilation, and cause the negative pressure at the kiln head and kiln tail to decrease simultaneously. If not handled promptly, it is prone to cause incomplete firing, flame spitting outwards, and even lead to accidents.
(2) Poor calcination leading to raw material leakage or agglomeration If the raw materials are not adequately calcined, "raw material leakage" or the formation of large lumps may occur, resulting in an increase in the kiln exit clinker temperature, a rapid rise in the residual air temperature in the rotary kiln, an expansion of the gas volume, an increase in the air volume, and a decrease in the kiln head negative pressure. In severe cases, positive pressure may occur and the flame may overflow.
(3) The large lump balls approaching the kiln opening interfere with ventilation. When large lump balls form in the kiln and move close to the kiln opening, they will severely obstruct the air flow channels within the kiln, affecting the flame extension and combustion stability, resulting in a decrease in negative pressure at the kiln head and even causing violent fluctuations.
II. Countermeasures for the fluctuation of negative pressure at the kiln head
The handling method when negative pressure increases
(1) Timely increase the cooling air volume by adjusting the air valves of other operating fans or starting backup fans to replenish the cooling air volume, restore the air volume balance between the kiln system and the cooling system, and gradually stabilize the negative pressure at the kiln head. At the same time, quickly identify and troubleshoot equipment failures (such as fan shutdowns), and resume operation as soon as possible.
(2) Dynamically adjust the cooling air volume according to the system's operating trend. Reasonably adjust the air volume of each air chamber in the rotary kiln to avoid excessive or insufficient air volume, and keep the negative pressure at the kiln head within a reasonable range.
(3) Optimize the material layer control by appropriately increasing the rotation speed of the grate bed, accelerating the movement speed of the materials, reducing the thickness of the material layer, minimizing the ventilation resistance, restoring the balance of system air volume, and stabilizing the negative pressure at the kiln head.
2. Handling method when negative pressure decreases
(1) In case of blockage, once it occurs, the feeding volume, air volume and coal quantity should be adjusted promptly according to the scale of the blockage to avoid large disturbances caused by minor fluctuations. If necessary, the feeding can be temporarily reduced to stabilize the thermal system.
(2) To improve the cooling effect, appropriately reduce the bed speed, extend the material residence time, increase the cooling air volume, enhance the cooling efficiency, lower the kiln exit clinker temperature, and prevent excessive residual air temperature from causing a decrease in negative pressure.
(3) Monitor the calcination process, prevent the formation of large lumps, and observe the flames and material movement inside the kiln. Timely adjust parameters such as the position of the burners and the ratio of air to coal to prevent local over-burning or under-burning, avoid the formation of large lumps, and ensure smooth ventilation inside the kiln.
III. Summary
The stability of the negative pressure at the kiln head is an important manifestation of the thermal balance of the rotary kiln system. Abnormal negative pressure often results from imbalance in air volume, abnormal materials, or equipment failures. Operators should closely monitor the changes in key parameters such as negative pressure at the kiln head, negative pressure at the kiln tail, air volume, and temperature. Based on the actual situation on site, they should promptly adjust the operating parameters to achieve "early detection, early judgment, and early adjustment", ensuring the stable and effective operation of the kiln system.
Regular equipment maintenance, optimization of operation procedures, and improvement of automation monitoring levels are the key guarantees for preventing negative pressure fluctuations and achieving stable and high production.
