Chrome-free Basic Refractories for Burning Zone of Cement Rotary Kiln

Based on the relevant phase diagrams of ternary system in MgO - CaO - ZrO2 - SiO2 quarternary systems, the phase diagram of Fe - O system and the condensed phase stability area diagram of iron oxides, the corrosion resistance of MgO - CaO - ZrO2 refractories to silicate cement, and the forming conditions and prepar- ing measures of hercynite are analyzed.

Corrosion of Disposing Urban Domestic Wastes on Refractories for Cement Rotary Kilns

Corrosion of burning urban domestic wastes to alkali-resistant bricks and spalling-resistant high alumina bricks was researched by static crucible method and SEM in order to choose refractories for cement rotary kilns for collaboratively disposing wastes. The result indicates that the main corrosion mechanism is slag permeation and corrosion ; the emitted high temperature gases containing alkali, sulfur and chlorine during burning the wastes re- act with refractories forming low melting point sulfate, chloride and compound salts, which metamorphose the refractories, and the loose metamorphic layer is easy to spall under thermal stress. So, corrosion resistance and spaUing resistance shall be taken into account when choosing refractories for cement rotary kilns for collaboratively disposing wastes. It is suggested that decomposition furnaces should adopt spaUing resistant high alumina bricks and anti-coating SiC castables, and preheating equipment should adopt high strength alkali-resistant bricks and castables.

Damage Mechanism of Silicon Carbidemullite Bricks for Transition Zone of Cement Rotary Kilns

In order to improve the service performance and explore the damage mechanism of silicon carbide-mullite bricks for the transition zone of cement rotary kilns,the phase composition and the microstructure of a used brick in the transition zone of a cement rotary kiln were analyzed by XRD,SEM and EDS.The results show that the liquid and alkali vapor phases generated by the reaction between cement materials and the silicon carbide-mullite brick mostly enter the silicon carbide-mullite brick through the pores;meanwhile,Ca+and K+in the cement penetrate through the liquid maintaining a high chemical potential energy to dissolve Al2O3 and SiO2 at the top of the liquid phase thus enhancing the phase penetration;with the decreasing temperature,crystals such as gehlenite,potassium feldspar and potassium chloride are precipitated,which destroy the original structure and increase the difference of thermal expansion coefficient between the high temperature dense end and the metamorphic layer thus resulting in cracks,spalling,and rupture.

Predictive Model for Cement Clinker Quality Parameters

Managers of cement plants are gradually becoming aware of the need for soft sensors in product quality assessment. Cement clinker quality parameters are mostly measured by offline laboratory analysis or by the use of online analyzers. The measurement delay and cost, associated with these methods, are a concern in the cement industry. In this study, a regression-based model was developed to predict the clinker quality parameters as a function of the raw meal quality and the kiln operating variables. This model has mean squared error, coefficient of determination, worst case relative error and variance account for (in external data) given as 8.96 × 10–7, 0.9999, 2.17% and above 97%, respectively. Thus, it is concluded that the developed model can provide real time estimates of the clinker quality parameters and capture wider ranges of real plant operating conditions from first principle-based cement rotary kiln models. Also, the model developed can be utilized online as soft sensor since they contain only variables that are easily measured online.

Adherence Characteristics of Cement Clinker on Basic Bricks

Based on the sandwich test, adherence mechanisms of cement clinker on various basic bricks were tackled by microstructural observations with help of cathodolumi-nescence technique. Doloma based bricks offer sufficient lime to react with clinker, forming C3S rich layer and initializing superior adherence. However, clinker with low silica ratio leads to MgO agglomeration at the interface of doloma bricks, which reduces adherence strength. On magnesia spinel bricks , fine, crystalline spinel easily reacts with lime containing phases from clinker to form low-melting phases and belite zone, which shows high adherence performance. Lack of fine spinel in magnesia spinel bricks results in poor adherence.

Properties of Magnesia-Hercynite Brick

Properties of magnesia-hercynite brick were studied. The coatability, thermal shock resistance, corrosion resistance to cement clinker and thermal conductivity were compared with those of magnesia-chrome brick and magnesia-spinel brick used widely in sintering zone of cement rotary kiln. The result shows that magnesia-hercynite brick is better than magnesia-chrome brick in thermal chock resistance and corrosion resistance to cement clinker, is similar to magnesia-chrome brick and is better than magnesia-spinel brick in coatability and thermal conductivity.