Study On Magnesia-hercynite Refractory For Burning Zone Of The Cement Kiln

Refractories for the burning zone of cement rotary kilns are important for the safeoperation of kilns. The refractories should be resistant to chemical attack and be able totolerate heat stress induced damage. Because of their excellent performance, refractoriesfor the burning zone of dry-method cement rotary kilns have primarily used magnesiachrome bricks in the past. However, due to the formation of water-soluble andcarcinogenic Cr6+during the production of cement, which severely contaminates waterand soil, the use of magnesia chrome bricks is prohibited worldwide. Currently,chrome-free refractories are primarily composed of magnesite dolomite bricks,magnesia alumina spinel bricks, and magnesia-calcia-zirconia bricks. Unfortunately, theproperties of these substitutes are inferior to those of magnesia chrome bricks.Therefore, there have been many studies exploring chrome-free substitutes for magnesiachrome brick.The magnesia-hercynite refractories have better coating adhering performance toresistance the chemical attack of the cement clinker, and Fe2+giving rises to a materialwith good structure flexibility. Thus, magnesia-hercynite has become a promisingcandidate material for the burning zone of rotary kilns. This paper aims at the requestproperties of the bricks for cement kiln, magnesia-hercynite samples were prepared withhigh purity magnesia and fused hercynite as starting materials in the laboratory, thestability of hercynite under high temperature and the properties change laws ofmagnesia-hercynite refractories under different condition were investigated. The resultsindicate that:1. The stability of hercynite at different calcining temperatures and atmospheresare quiet different. Hercynite has been oxidized to hematite and corundum at800℃inair, the higher firing temperature, the more complete oxidation. Control firingatmosphere can protect the stability of hercynite at high temperature, calcining in Aratmosphere, immerged carbon powders, adding a certain amount of metal Al powder orSi powder can protect hercynite cannot be oxidized.2. With the different of addition and adding way of hercynite, sinteringtemperatures, the properties of magnesia-hercynite samples showed regular change.With increasing the contents of hercynite, the strength, thermal expansion coefficient and elasticity modulus decreased. The magnesia-hercynite bricks with hercynite areintroduced in the form of powder has higher strength, elasticity modulus than themagnesia-hercynite bricks with hercynite is introduced in the form of particles. Adding2%hercynite can significantly improve the thermal shock resistance of magnesiaproducts, the magnesia-hercynite bricks with hercynite are introduced in the form ofparticles have better thermal shock resistance than the magnesia-hercynite bricks withhercynite is introduced in the form of powder. When the magnesia-hercyniterrefractories sintered at high temperature, the hercynite particles oxidized and forms thesolution of spinel and hercynite around hercynite particles, and inside the particlesremain hercynite; whereas hercynite powder react with magnesite matrix to form thesolution of spinel and hercynite in the periclase.3. Sintering immerged carbon powders and adding metal Al powder benefit toimprove the thermal shock resistance of the magnesia-hercynite samples. Sinteringimmerged carbon powders can significantly improve the thermal shock resistance of themagnesia-hercynite samples with hercynite are introduced in the form of particles, buthave little effect on the magnesia-hercynite bricks with hercynite are introduced in theform of powder. The thermal shock resistance of magnesia-hercynite bricks could bedeveloped by adding metal Al powder.