Annular Shaft Lime Kiln

Taking the 500-ton annular shaft lime kiln as an example, the process flow is as follows:

The annular shaft lime kiln has upper and lower layers of burners, with 6 evenly distributed on each layer, and the distance between the center lines of the two layers of burners is 3.9 meters, with a difference of 30 degrees. The lower burner divides the annular shaft lime kiln into two calcination zones, namely the countercurrent calcination zone and the downstream calcination zone. The upper part is the countercurrent calcination zone and the lower part is the downstream calcination zone. The downstream calcination starts from the lower combustion chamber and ends at the inlet of the circulating gas.

Each combustion chamber of the annular shaft lime kiln has an arch bridge from the kiln shell to the lower inner sleeve made of refractory materials. After the gas is burned in the combustion chamber, the hot gas generated enters the material bed from the space under the arch bridge and is evenly distributed to the entire material bed.

The annular sleeve active lime kiln is composed of inner and outer cylinders. The inner cylinder and the outer cylinder are concentrically arranged to form an annular space, and the limestone is calcined in the annular area. The kiln body is divided into preheating zone, countercurrent calcination zone, cocurrent calcination zone and cooling zone from top to bottom.

In the co-current calcination zone, as the material flows downward, a CaO shell is gradually formed on the surface of the limestone, and its heat absorption becomes poor. However, at this time, the leaner fuel and air are contacted and burned, and the heat supply is relatively mild, so it will not overheat the CaO shell, but also make the raw core continue to decompose.

Annular active lime kiln is divided into upper and lower sleeves, the upper inner sleeve is suspended on the top of the kiln, and the lower inner sleeve is located in the middle and lower parts of the entire shaft kiln. The upper and lower inner cylinders are made of boiler steel plates, and there are two layers. An annular gap is formed between the two layers, and air is passed through the annular gap for forced cooling. The inner and outer sides of the inner cylinder are built with refractory materials.

Through the above design, the pressure, airflow and temperature in the annular lime kiln are evenly distributed in the annular section and the entire limestone layer, which ensures the uniformity of limestone calcination, improves the quality of the product, and reduces the unit consumption of the product at the same time. Compared with the traditional limestone kiln In comparison, the equipment is also more adaptable to raw materials.

The division of the three zones of the annular shaft lime kiln: the preheating zone is about 9 meters, and the temperature range is from the top temperature of 90-140°C to the junction of preheating and calcination at 850-900°C; the calcining zone is about 11 meters, and the temperature range is from preheating , calcination junction 850-900 ℃ to calcination, cooling junction 900-950 ℃, the cooling zone is about 7 meters, the temperature range is 900-950 to 80-130 ℃.

In the preheating zone, the limestone is heated to its calcination temperature (850-900°C). If gas fuel with low calorific value (such as converter gas) or limestone containing more than 90% CaCO3 is used, there will always be waste heat in the preheating zone, so the upper inner sleeve and heat exchanger are designed in the lime preheating zone of the annular shaft lime kiln, and the waste heat in the preheating zone enters the heat exchanger through the upper inner to make the loss as small as possible and the exhaust gas temperature is as low as possible. The heated driving air is sent to the six ejectors through the upper ring pipe.

In the calcination zone, all the calcination processes are carried out here, of which 70-80% of the calcination process is carried out in the counter-current calcination zone, and the other 20-30% of the calcination process is carried out in the downstream calcination zone. The temperature of the limestone entering the calcining zone is about 850-900°C, and the temperature of the limestone entering the cooling zone at the bottom of the downstream calcining zone is about 900-950°C.

In the cooling zone, the hot lime is exchanged with the cold air drawn from the bottom of the kiln, and the temperature is lowered and then discharged out of the kiln body. The temperature is about 80-130°C.