Kiln balls

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1- I read here (in this forum) several questions about the reasons of ball formation in kilns and most of the answers were “due to variation or high content of Mn2O3 or MgO”. My question is which value (%) in these two elements can be accepted as high? And what is the acceptable limit of variation in Mn2O3 or MgO?

Ans:

• Kiln balls can form in upper transition zone, and can be up to 1 m in diameter. They are made up of a combination of calcined material generated by stripping and balling up of old coating, agglomeration of clinker and salt melt, or a ring acting as a dam and retaining material for a long time. Chemically, they are usually made up of a relatively low melting point eutectic mixture. Desired limit of Mn2O3 is 1.5-2% and MgO is 0-2%.

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2- Whenever we have ball in our kiln we usually trying to demolish it by increasing or reducing the speed of the kiln but the funny thing is that some engineers believe increasing the speed of kiln will help in demolishing the ball before burning the material of ball while other group think reducing the speed of the kiln will increase the residence time of the ball in kiln and there will be more chance to be demolished before reaching to the nose ring and falling in the cooler. If you have experience about this subject which group do you support? And why?

Ans:

• Controlling liquid phase level and changing the kiln feed chemistry is better  proactive action or solution to control the ball formation. Reducing kiln speed will increase already formed ball size so it is not desirable.