Drying for Rotary Kiln Lining with Low Cement Castables Refractory

July 13, 2018

Generally speaking, the lining of shaped refractory products has been fully roasted due to manufactured, the drying kiln time can be shortened properly. When unshaped refractory castable as the lining,it’s made of bulk material and mixing with water. Because the refractory material is not fully prefired, it’s not stable at low temperature and water content is relatively large.If the speed is too fast, it will cause the inner lining cracked due to rapid discharge of water, and drying time should be extended properly.

Determine of heating rate according to different lining material

The lining made by unshaped refractory materials is mainly subjected to a series of dehydration changes at low temperature during the heating process. Because of close combination of the low cement castable refractory, and adding ultrafine powder (particle size less than 5 mic) filling the gap of the castables refractory, make the lining has high density, low porosity and poor permeability. The moisture in the lining materials is mainly discharged as a gas. If the temperature rises too fast, the vaporization speed of water will increase, so do the gas discharge and the volume.Once the pressure generated by the expansion of gas exceeds the max than the lining can bear, it will cause cracks, peeled or peeling off. Therefore, the heating rate of the low cement castable refractory should be lower than other types of castable refractory. Especially when the lining temperature is below 600℃, the longer heating time should be maintained so that the water is fully discharged.

In addition, due to the addition of active SiO2 in the low cement castable, when lining temperature is higher than 900℃,the mullite reaction occurs between Al2O3 and SiO2 in the lining raw material to form mullite, forming the volume effect of mullite, counteracting the partial volume shrinkage of the refractory castable and promotes increased strength of the liner. The process of mullite is the key process affecting the high temperature performance of the cement castable. Therefore, the lower temperature of the kiln should be controlled at the end of the process,and the heat preservation time is relatively long, so that the reaction of the mullite is fully carried out.

Determine the heating time according to the specification and shape of industrial furnace

When the kiln volume is small and the flue gas flow is short, the heating time can be shortened properly because of kiln temperature is uniform and balanced. For some large thermal equipment such as rotary kiln, it’s difficult to achieve the balance of temperature at a certain period of time. Therefore, the heating time should be longer to reduce the temperature differently in each part of the lining and avoid the cracks in the non uniform shrinkage of the lining.

Determine the drying system according to the lining construction method and the lining conditions

The lining construction method and the maintenance conditions are different, so the drying kiln system should be different. The lining with long curing time, exhaust hole and small thickness of lining heating time can be fast. The curing time is short, in winter, lining body high dense,, the thickness is large, high water content or the lining of the furnace quality is not ideal. The heating time should be longer. After low cement refractory castable lining is finished, it should be maintained at 15~25℃ for not less than 7 days. In winter,lining insulation measures should be also taken. In the construction of castables, in addition to ensuring the mixing time,vibration time and vibration strength of the castable, it should be every 150~150mm in the lining, and a depth of about 1/3~2/3 of the lining is fixed, and the diameter of the exhaust hole is about 4mm.

Determine the kiln control temperature according to the lining temperature in the high temperature working area

During drying process, the temperature control parameter should be the temperature of the lining. For large furnace with temperature ladder, since the lining temperature of each part can not be simultaneously heated, the surface temperature of the lining should be controlled in the direct contact area with the flame. The lining in this area is generally located in the high temperature working area, which is the most vulnerable part of the kiln lining, and the most sensitive part of the flame temperature change. The heating rate and temperature rise of the lining in this area can reflect whether the temperature rise of the entire lining of the kiln is reasonable.

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