1. Too large particle size: the calcination speed of limestone depends on the material size of lime and the temperature of limestone surface. However, at a certain temperature, the calcination speed of limestone depends on the particle size of limestone. The larger the material content, the slower the calcination speed. Here, because the thermal conductivity of lime is less than that of lime calcination, the thickness of lime layer gradually increases, the more difficult it is for heat to enter the stone, and the calcination speed is also slow. Therefore, there is often a sandwich in large limestone, which is the first reason for quicklime. In recent years, Henan Kelan Cement Co., Ltd. has specially designed a small-sized limestone kiln with a particle size of 40-150mm, which can also save the cost for ordinary limestone kilns with a special capacity of 40-150mm.

2. Small proportion of fuel or low calorific value of fuel. The proportion of fuel used in the mixed firing kiln is related to the technical performance of the kiln. The energy-saving and environment-friendly mixed firing lime kiln designed by Zhengzhou Bulang Machinery Technology Co., Ltd. has introduced advanced technology from Japan and Germany. The kiln shape design is more scientific and the relative coal ratio is very low. At present, some advanced kiln types have exceeded 125 kg per ton of lime, and the calorific value of coal used in the mixed firing kiln is generally required to be more than 5500 kcal. The particle size of fuel shall be controlled to a certain extent, and appropriate water shall be added when using end coal.

3. The air supply is unreasonable. The stones in the lime kiln are heated and calcined by fuel combustion, while the fuel is burned by oxygen (air). The combustion of any fuel must meet three conditions, including fuel, oxygen and fire. In addition, the wind and fire are uniform, and the air supply is reasonable except that there is a certain proportion of fuel. Some parts of the section in the kiln have large air volume and others have small air volume, The place with strong wind is burned, but the place with small wind naturally appears raw burning. The kiln type designed by Zhengzhou Bulang Machinery Technology Co., Ltd. pays special attention to the design of air supply. In order to make the air supply reasonable, in addition to the air supply at a certain height, the computer simulation hood which can supply air evenly in the kiln is specially studied and manufactured. It can make the air pressure and volume equalizing drum on the section of the whole kiln and make the fuel burn evenly. In order to improve the productivity of shaft furnace lime kiln and the activity of lime produced by the company, The two-dimensional mathematical model is used to simulate the shaft furnace lime kiln. The results show that the low productivity of the shaft furnace lime kiln and the low activity of the produced lime are caused by the unreasonable air distribution in the furnace, and the unreasonable air distribution reflects the structural defects of the original computer simulation hood of the shaft furnace lime kiln. In view of this problem, the company has reformed the hood structure of the shaft furnace lime kiln in combination with several domestic experts, The measure adopted is to set up a special air duct at the top of the hood to open up the central air flow, in order to eliminate or inhibit the raw burning phenomenon caused by the central entrainment of the shaft furnace lime kiln. After the transformation of the hood structure, the air flow distribution in the lime kiln is greatly improved, and the activity of the lime produced is more than 15 higher than that of the lime produced by the same type of lime kiln without the transformation of the hood structure.

4. The quality of quick lime depends on the content of calcium oxide and magnesium oxide and the rate of quick lime burning. Quick burning means that part of the limestone is not completely decomposed, while over burning is the transition of limestone calcination to make the quick lime dense, also known as overheated lime or dead burned lime. This part of quicklime has low activity and is difficult to differentiate in later production,

For ordinary limestone, the normal combustion temperature is 1000-1200 ℃, and the over burnt ash is usually a shell with high combustion temperature, long time, cracks or glass on the surface, obvious volume shrinkage, black color and increased block volume. Naturally, it is over burnt. Of course, the treatment of overburning should first consider whether the fuel ratio is too large and should be adjusted to a reasonable proportioning. Of course, the coal blending amount should fully consider the quality of coal, and adjust the air supply to adapt to it. The main method to control the coal ratio and make the fuel evenly arranged in the furnace is to reasonably use the rotary distributor. The multi-point rotary distributor designed by Zhengzhou Bulang Machinery Technology Co., Ltd. fully absorbs the distribution principle of blast furnace, The designed and manufactured rotary distributor can realize single point, multi-point, forward and reverse distribution operations. In particular, the designed distribution spreader in the furnace can control the material flow and quantity like the planter in agriculture, so that the fuel material layer is thin and uniform, the fuel and raw materials are fully mixed, the distribution is uniform and the combustion is sufficient.

key words：Main problems in lime kiln production