Cement rotary kilns require high performing refractories able to withstand very high temperatures, high thermo-mechanical stresses, and chemical attack from hot or liquid clinker. Consequently the lining of the upper transition, burning and lower transition zones consists very often in magnesia spinel bricks. Magnesia can withstand high temperature, the incorporation of spinel grains is known to improve capability to resist to high thermo-mechanical solicitations such as thermal cycling or geometrical deformation during operation. However, there are sections where bricks cannot be installed easily; mainly due to strong shell geometrical deformation; or do not perform as expected due strong lining deformation during operation. This is typically the case for the tires areas. It is also more and more the case that magnesia-spinel bricks suffer from strong chemical attack resulting from penetration of alkali salts or sulfurs and chlorides coming from intensive use of alternative fuels. In the upper cases of difficulty for brick installation, high shell and lining deformation during operation and strong chemical attack, monolithic refractories could be an advantageous solution. Refractory castables can be installed on any geometry, can accommodate thermal cycling and hot deformation during operation, and can as well exhibit totally different pores size and capillary structure than bricks, resulting in different behavior in front of salts attack. In particular magnesia based castables could be valuable candidates. The present paper describes in a first part how formulation design of dense, cement free, magnesia based castables has been optimized in terms of thermal-cycling resistance and macro crack propagation resistance when submitted to deformation. In particular it has been investigated how the mentioned optimizations can be achieved by incorporation of compounds such as alumina, AM spinel or Zirconia, exhibiting either thermal expansion mismatch versus magnesia matrix, or phase transformations, that results in micro-cracks formation during first lining heating up or first cooling down. In a second part, properties of such optimized castables are compared to standard magnesia-spinel bricks, both in terms of thermo-mechanical behavior and in terms of resistance to clinker, alkali, sulfurs and chlorides contact.
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