Cause analysis and prevention measures of ring formation in active lime rotary kiln Henan Hongxing

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Cause analysis and prevention measures of ring formation in active lime rotary kiln

Ring formation is a common phenomenon in the operation of rotary kiln, Active lime rotary kiln In the process of calcining lime, because the soil and powder on the surface of limestone are not sieved out, the limestone enters the kiln and reacts with Cao under the action of high temperature flame, which is the main reason for the ring formation of metallurgical lime rotary kiln. For a long time, rotary kiln manufacturers have taken many measures to eliminate the adverse effect of ring formation on the production of rotary kiln, but they have not been successful. The following paper analyzes the location and causes of rotary kiln ring formation, and takes corresponding preventive measures. The following is a detailed introduction.

 Active lime rotary kiln

Distribution and composition analysis of ring forming position in rotary kiln

1. Distribution of ring forming position in rotary kiln

After stopping the kiln, it was observed that the location of ring formation was mainly about 15 m away from the end face of kiln head cylinder, and the thickness of serious ring formation was up to 1000 mm. The position of the front end of the aluminum cylinder is also the location of the flame.

2、 Composition analysis of ring material in rotary kiln

The color of the binder is different, the yellow one is loose, and the black one is slightly stronger, but the layered structure of the two materials is obvious, and the pores formed by the condensation of the internal liquid phase are clearly visible.

Cause analysis of rotary kiln

1. Influence of impurities in limestone

It can be seen from the composition analysis results of lime and ring binder that the content of SiO2 and MgO in the ring binder is obviously higher than that in the lime. After analyzing the production process and thermal system, it is considered that the high content of SiO2 is mainly brought in by limestone, while the high content of MgO is mainly caused by the pulverization of high magnesium limestone after calcination.

Therefore, it is determined that the fuel in the coke oven is mainly limestone. The production practice has also proved that when the circle formation is serious from May to October every year, the residue (≤ 10 mm) under the limestone screen is reduced by more than 50% compared with that without ring formation. Therefore, it is concluded that due to the adhesion of rainwater to soil, SiO2 can not be sieved out on the limestone surface and enters the rotary kiln, forming a ring at higher temperature.

In addition, the content of MgO in the ring material is also high, mainly because the limestone contains high magnesium limestone, the MgO content can reach 7% ~ 11%. At the same calcination temperature, the high magnesium limestone is easy to crack during the calcination process, and more powder is produced. When this part of powder is combined with the liquid with low melting point, the ring forming becomes more and more serious.

2. Influence of calcination temperature

The calcination temperature of limestone used in rotary kiln is 1050 ~ 1150 ℃, and the activity of calcined lime can reach more than 360ml and Cao can reach about 90%. If the calcination temperature is increased, these indexes will decrease and may even form over burning. When coke oven gas is used in rotary kiln, the temperature exceeds 1500 ℃ when the thermal parameters or flame shape are not adjusted properly, and the excessive temperature aggravates the formation of ring formation.

3. Poor ventilation in the kiln

Many factors, such as insufficient suction of main exhaust fan, too thick material layer in kiln and too much powder material, will lead to poor ventilation in the kiln, resulting in dust can not be discharged in time and always circulates in the kiln, resulting in ring formation. In addition, if the negative pressure is too small, the heat can not be transferred to the kiln tail in time, which makes the high temperature area of the flame head in the kiln too concentrated, and the liquid phase is produced locally, which leads to ring formation.

Prevention measures for rotary kiln

1. Increase limestone in kiln

Rotary kiln does not have limestone washing process, so other methods should be adopted to reduce excessive soil and powder brought into the kiln by limestone. Open up a temporary stockyard. Once the limestone ore is too wet, this batch of materials can be placed in the temporary stockyard to be used after air drying. After controlling the wet limestone, it is necessary to ensure that the screen screen of raw material vibrating screen is not blocked by soil, and it is necessary to clean it at any time. It is forbidden to use the vibrating screen that has not been cleaned up. The production practice shows that no or less use of wet limestone and ensuring the screening efficiency of limestone play an important role in reducing ring formation. When the above measures are not adopted, sometimes the screening material is only about 30% of the normal production, and a large amount of soil and crushed materials are brought into the kiln. After taking the above measures, the fluctuation of the proportion of limestone screen discharge is very small, and the amount of soil and powder into the kiln is reduced.

2. Reduce the flame temperature

The existing combustion system uses normal temperature gas, which has the ability to cool the burner itself. Therefore, the function of primary air should be mainly focused on adjusting the flame shape. In view of this, reducing the proportion of primary air and increasing the proportion of secondary air, at the same time, using the preheated secondary air as much as possible can effectively reduce the gas volume, thus making the flame thinner and reducing the flame temperature. By reducing the swirl and direct inflow of primary air, the outflow air is increased and the flame is lengthened.

After the above measures are taken, the flame temperature is reduced from 1450 ℃ to 1250 ~ 1350 ° C, which can not only ensure the calcination of high-quality lime, but also create conditions for avoiding ring formation.

3. Ensure smooth ventilation in kiln

By adjusting the exhaust gas speed, the negative pressure in the rotary kiln is increased to ensure that there is a large negative pressure from the preheater to the rotary kiln, so that the dust in the kiln can be discharged in time. In addition, sufficient negative pressure will make the high temperature zone move backward, give full play to the preheating effect of preheater, make the waste gas better preheat limestone, reduce the decomposition pressure of lime in calcination zone, so as to reduce the gas consumption, reduce the probability of liquid phase, and implement the kiln head negative pressure standard in case of conflict with the three before and after adjustment.

After the above measures are taken, there is no ring formation in the production and operation of the rotary kiln all year round, which improves the operation rate of the rotary kiln, reduces the times of kiln shutdown, reduces the labor intensity, avoids the environmental pollution caused by the discharge of the ring materials, and creates conditions for the normal production of steel-making and sintering.

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