Analysis of the causes of burning of refractory bricks in double-chamber kilns
The physical and chemical indicators of the original mullite brick layer and the residual brick layer were tested. The refractoriness of the original mullite brick layer reached 1780℃, the load softening temperature was 1531℃, and the chemical composition also met the requirements of the corresponding technical standards. Under normal use, it can fully meet the use requirements.
The refractoriness of the mullite residual brick layer is only 1390℃, indicating that there are more low-melting point substances in the brick layer. Through the research and analysis of mullite residual brick samples, it is believed that the low-melting substances formed by alkali metals (such as K₂O, Na₂O, etc.) are the main cause of high-temperature melting of mullite bricks.
The K₂O and Na₂O components in the raw material dolomite are only 0.01%. The ash content of the mixed coal is about 12%. The ash content was tested and analyzed. The physical and chemical test of the slag on the back of the insulation layer mullite brick was listed. The results of the chemical analysis of the remaining ash after the pulverized coal used in the Wuxuan double-chamber kiln of Liugang were listed.
It can be seen that the K₂O content in the ash is 2.25%, and the Na₂O content is 2.08%. Therefore, the ash of the pulverized coal is the main source of the introduction of alkali metal elements.
According to the on-site inspection, it is speculated that there is a tilt during the use of the spray gun, which causes the ash after the pulverized coal is completely burned to adhere to the surface of the mullite brick. The low melting point phase in the ash melts and softens at high temperature, and continuously penetrates into the interior through the pores on the surface of the mullite brick, eventually causing the damage of the mullite brick and the redness of the furnace shell. The remaining mullite refractory bricks were inspected, and no abnormalities were found in the load softening temperature, linear change rate, chemical composition and other indicators.
It was found on site that the No. 1 and No. 2 spray guns were tilted, indicating that the spray guns were crooked and the flames directly eroded the refractory materials, causing the refractory materials to burn. The investigation found that other flux bases of Liugang had also had "pit" shapes in the kiln refractory materials due to the spray guns being installed too close, indicating that the refractory materials were eroded.
The coal powder conveying fan is not a variable frequency fan, and the wind pressure is higher than that of the lime kilns of other flux bases of Liugang, which aggravates the wear of the coal powder guide pipe of the spray gun and causes the burning of this part. From the above situation, it can be seen that the improper installation of the coal powder spray gun and the direct erosion of the flame against the furnace wall are the direct causes of the burning of the refractory materials.
The coal powder conveying fan is not a variable frequency fan, the wind pressure is high, and the flow rate is too fast, causing the coal powder guide pipe to wear in less than 1 month, and increasing the coal powder delivery of the spray gun, which is another reason for aggravating the burning of the refractory materials.
03. The effect of rectification requires the construction party to strictly follow the drawings to ensure that the spray gun is vertically parallel and downward, and to ensure the distance between the spray gun and the furnace wall, so as to reduce the burning of refractory materials. At the same time, by installing frequency conversion modification on the coal powder conveying fan and updating the fan operation program, that is, reducing the fan operation frequency during the reversing period, and adjusting the fan speed according to the kiln conditions during the combustion period, so as to ensure the coal powder transportation while reducing power consumption. The double-chamber kiln after rectification has a good operation effect, and no corresponding refractory material burning phenomenon occurs.
04. After the inspection and maintenance of the refractory bricks of the double C structure kiln and the frequency conversion modification of the conveying fan, the entire kiln has no refractory material burning phenomenon, which fully proves that the rectification effect is good.
(1) The abnormal damage of the furnace wall in the high-temperature section of the lime kiln caused the furnace shell to turn red. The main reason is that the mullite bricks in the working layer are eroded and melted at high temperature during the production process.
(2) Alkali metals such as K₂O and Na₂O react with mullite bricks at high temperatures to form low-melting products such as feldspar, which continuously corrode mullite bricks. The furnace wall becomes thinner after melting, which causes the furnace shell to turn red at high temperature.
(3) The source of alkali metal oxides in the lime kiln is mainly the ash of the mixed coal. Due to the characteristics of the double C structure of the kiln, abnormal installation of the spray gun will also cause the ash to adhere near the end wall and corrode the furnace wall.
(4) The frequency conversion transformation of the conveying fan is conducive to reducing power consumption, stabilizing the kiln condition, reducing the erosion of the coal powder guide pipe, and increasing its service life.
