In the process of calcining clinker in the rotary kiln, the uniform and reasonable distribution of the kiln skin can not only protect the kiln tube, reduce the erosion, wear and high temperature damage of the kiln lining by the flame, and prolong the service life of the refractory bricks in the kiln; it can also reduce the heat dissipation of the kiln tube. , stabilize the thermal system of the system and improve the comprehensive thermal efficiency. The long and thick kiln skin in the kiln is a common process problem in the industry, which often affects the ventilation in the kiln, resulting in large fluctuations in the incoming materials in the kiln, and it is difficult to stabilize the thermal system of the system, which directly affects the improvement of the production quality of the rotary kiln and the safe operation of the equipment. Combined with the actual production process, this paper analyzes the causes of such process problems, and summarizes the treatment measures and precautions in process adjustment.
1. Analysis of the cause of the problem
Generally speaking, the inducing factors that affect the change of kiln skin are complex, such as the change of the chemical composition of the raw material leading to the change of the liquid phase content and viscosity of the liquid phase in the material; The flame shape and calcination temperature lead to incomplete combustion of pulverized coal; the unreasonable matching of wind, coal, material, and kiln speed and the abundance of harmful components will affect the structural distribution of the kiln skin.
1.1 Influence of chemical composition and rate value of raw meal
Since the kiln skin is a process of liquid phase solidification to the surface of the kiln lining, the liquid phase content and liquid phase viscosity directly affect the formation and distribution of the kiln skin, and the change in the chemical composition of the raw material directly affects the liquid phase amount and liquid phase viscosity. Only by reasonably configuring the three-rate value of the raw materials, the kiln skin can be smooth, dense and firm. Generally speaking, it is recommended that the raw material composition when combined with the kiln skin is consistent with normal production.
According to the production practice experience, the raw material has low KH content and high iron oxide content, which leads to excessive liquid phase in the calcination process and early formation. Especially in the calcination process of calcined high-magnesium clinker, the high-magnesium raw material has poor refractoriness, and the central control operation is adjusted frequently. The high-temperature liquid is easy to form in advance, and it is easy to bond with the surface of the refractory brick or the surface of the kiln skin, and the kiln skin will become long and thick and even form a circle. The ventilation conditions of the rotary kiln are deteriorated, and the thermal system of the system is not easy to be stabilized, resulting in a series of process problems such as poor clinker granulation, more core and yellow core materials, and low clinker strength.
1.2 Influence of pulverized coal quality and flame shape
fineness of coal powder. Excessive moisture and unmatched air in the kiln system lead to the reducing atmosphere in the kiln, the coal powder in the kiln is not completely burned, and the unburned coke particles continue to burn after sedimentation, so that Feo is reduced to Feo in the reducing atmosphere, forming low melting point minerals. Lead to the problem of thick kiln skin. The unbalance of the content ratio of alkali and Cl.SO in the raw fuel has a great influence on the time and position of the liquid phase in the kiln material. If the material contains too many harmful substances, the melting point will be lowered, increasing the possibility of thick kiln skin.
Since the shape of the flame determines the quality of the kiln skin, it is necessary to maintain the stability of the shape of the flame during production and adjust the ideal flame for the shape of the kiln. In order to avoid the occurrence of abnormal kiln skin. In the early stage of production, with the gradual recovery of the output, in order to extend the kiln skin from the front of the kiln to the inside of the kiln, the use and adjustment of the burner, due to the improper matching of internal and external air volumes, the shape of the flame is too fine, resulting in the inconsistency of the high temperature area of the flame, although calcination The temperature is OK, but it is easy to form thick kiln skin, uneven clinker particles, and poor quality.
1.3 Influence of operation and thermal regime
(1) The amount of coal fed to the kiln head is too large, and the system is windy. The proportion of coal is unbalanced, resulting in incomplete chemical combustion and recovery of the flame; due to the large amount of CO generated in the combustion zone, some iron oxides in the material are reduced to ferrous oxides, forming FeO·SiO compounds with low melting point. Make the liquid phase appear in the combustion zone ahead of time and gather the unmelted material together, resulting in thick kiln skin and even circles.
(2) In the process of resuming production, the kiln body is slow for a long time, which leads to the excessive filling rate of materials in the kiln. It is easy to form thick kiln skin or uneven distribution of the kiln skin when the pulverized coal settles and wraps in the material. The kiln current is high but the amplitude is large. However, the kiln skin is not firmly attached, and it is easy to collapse due to fluctuations in the thermal system during the adjustment process. The central control operation is adjusted frequently and is not easy to stabilize.
(3) The ventilation resistance of the system increases, and the process adjustment process unilaterally emphasizes the ventilation of the system, which leads to the high wind speed of the system, the high filling rate in the kiln, and the high negative pressure of the kiln tail and tertiary air. The material in the kiln tail smoke chamber is granulated in advance, and the kiln tail is poured.
2. Treatment measures
(1) Control of raw material batching and three-rate value; according to the production experience of clinker calcination for many years, it is of great significance to control the sinterability of raw materials in the kiln to improve the quality of clinker and stabilize the thermal system of the system. In the production process, considering the poor physical and chemical activity of the main silicon raw material sandstone in our factory, according to the three-rate plan specified by the laboratory, the sandstone ingredient ratio was reduced from 3% to 2.4%, and a high saturation ratio suitable for the current process conditions was gradually explored. Low silicon batching scheme. The clinker third rate range corresponding to the high saturation ratio raw material batching scheme is KH=0.93±0.02, SM=2.3±0.1, IM=1.3±0.1, and the average 3d strength of clinker can be guaranteed to be above 31MPa. According to the definition of the three rate value of cement clinker, the aluminum rate (IM) represents the proportional relationship between CA and CAF in the clinker flux minerals. The higher the aluminum ratio, the higher the liquid phase viscosity. Therefore, while ensuring the liquid content of clinker within a reasonable range, the Alo?o? control index in clinker was adjusted from 5.0% to over 4.8%. The indicator was adjusted to around 3.7%. In the practice process of calcining clinker with high-magnesium limestone, it can effectively reduce the problems of clinker agglomeration, core material and long thick kiln skin caused by excessive liquid viscosity.
Especially since the second half of 2020, the 3d strength and 28d strength of clinker have increased month by month, the clinker has uniform granulation, the qualified rate of free calcium has reached 95%, and the clinker has better grindability. While ensuring high production of clinker, it provides better conditions for cement grinding.
(2) The kiln air matching adjustment; in order to avoid the problem of poor ventilation in the kiln caused by the long and thick kiln skin, the gate valve of the tertiary air duct can be properly closed to strengthen the ventilation in the kiln. At the same time, closing the tertiary air gate valve can also change the shape and position of the tertiary air entering the calciner, thereby changing the flow field distribution of the materials in the calciner from the C4 spreading box, enhancing the vortex effect between the tertiary air and the calciner fuel, and improving the Insufficient combustion of tail coal causes the temperature of the calciner outlet and the C5 feeding pipe to hang upside down, and the early granulation of the smoke chamber also plays an important role.
(3) Quality control of pulverized coal; due to the coarse fineness, high ash content and high moisture content of pulverized coal, the burning speed of pulverized coal will be affected, the flame will be elongated, and the firing zone will move backward. The kiln skin is easy to elongate and knot. Effective control of the fineness and moisture of the pulverized coal can improve the combustion rate of the pulverized coal and reduce the sedimentation of the pulverized coal; but pay attention to the use of fuel in the kiln to avoid top burning and dead burning of mature materials, and form a reducing atmosphere in the kiln , to promote the premature appearance of the liquid phase, resulting in the problem of long and thick kiln skin formation.
(4) Adjust the flame shape and the position of the coal pipe; on the one hand, by adjusting the external air of the burner, the air-coal mixing efficiency is enhanced, and the combustion efficiency of pulverized coal is improved; at the same time, the rotation effect of the internal air is strengthened to form a rapid ignition cycle of fuel zone, which is conducive to the formation of short and stable flames. This can not only shorten the calcination range, but also strengthen the clinker calcination and stabilize the thermal system. In addition, according to the change of cylinder temperature, adjust the position of the burner in the kiln in time, change the high temperature point, and gradually burn the thick kiln skin. Care should be taken to strictly control the calcination temperature to avoid large-area damage to the kiln lining caused by excessive calcination temperature.
(5) When dealing with the problem of material dumping at the kiln tail, first of all, it is necessary to strengthen the cleaning of the slopes and shrinkage of the kiln tail smoke chamber to ensure normal ventilation at the kiln tail; only by appropriately reducing the amount of feed, can the filling of materials in the kiln be completely eliminated The problem of dumping caused by excessive amount.
In a word, a stable and reasonable thermal system is the fundamental task of the new dry process cement kiln, and it is also the basis of high quality, high output and high equipment operation rate. For the treatment of long and thick kiln skin process problems, the operation should be optimized. Combined with the monitoring data of on-site advanced instruments, scientifically and rationally adjust the wind, coal, materials and kiln speed to effectively avoid the occurrence of such process problems.