Scale buildup and blockage in the kiln tail riser flue of a rotary kiln are common problems in the production of new dry-process cement kilns. After scale buildup, the ventilation area of ​​the kiln tail riser flue in a lime rotary kiln decreases. In severe cases, the actual ventilation cross-sectional area of ​​the riser flue is only about one-quarter of the normal area. The gas control damper in the kiln tail riser flue fails to regulate the airflow in the kiln’s tertiary air duct, significantly increasing the kiln tail resistance loss. This leads to poor ventilation within the kiln, inhibiting the kiln head’s heating capacity, causing a sharp drop in temperature of over 200 degrees Celsius in the kiln head calcination zone, failing to meet the requirements for clinker calcination. Severe raw material leakage occurs within the lime rotary kiln, potentially extinguishing the flame. Incomplete combustion of pulverized coal further exacerbates the reducing atmosphere in the riser flue, accelerating the scale buildup rate. Therefore, scale buildup and blockage in the riser flue can cause kiln system malfunctions, making it difficult to adjust various control parameters.

As the temperature in the burning zone gradually decreases from normal to low, the flame color darkens and the shadow shifts, requiring timely addition of coal. When the amount of coal increases, the flame shortens, and the rear of the burning zone darkens, necessitating early addition of coal. As the amount of pulverized coal increases, the primary air should also be increased to ensure thorough coal-air mixing and rapid, complete combustion. At this stage, the flame in the burning zone is slightly shorter but more powerful, with a larger flame color than normal. The clinker exiting the cooler is greenish-gray and has many small holes when broken open.

If the temperature does not stabilize and continues to decrease, the engine should be started at a low speed early, and the exhaust air should be appropriately reduced to maintain a constant tail temperature and a concentrated flame. Otherwise, the temperature will continue to drop, the flame color will change from pink to red, the fine powder in the clinker will increase, tumbling will be poor, the dark green clinker will have a loose structure, many small holes when broken open, and the weight gain will be around 1200g. If this occurs, the kiln must be started at a low speed with reduced exhaust ventilation to raise the temperature. Otherwise, the temperature will drop even lower, and the clinker will lose its tumbling properties like sand, sliding down the kiln walls and resulting in waste. In such a situation, the kiln must be shut down. This is a special measure taken only as a last resort; shutting down the kiln is strictly prohibited under normal circumstances.

Low temperatures inside the cement rotary kiln, aside from insufficient coal supply and mechanical shutdowns, are mostly caused by improper handling by the kiln operator. To prevent this, the main focus should be on strengthening the operator’s skills, mastering fundamental techniques, and achieving technical proficiency.