Kinetic model for calcium sulfate decomposition at high temperature

Calculation and Verification for the Thermodynamic Data of 3CaO·3Al2O3·CaSO4

In this paper, the influences of combustion atmosphere on the desulfurization characteristics such as SO2 emission, Content of f-CaO, desulfurization degree and mneralogical composition by means of flue gas analysis, chemical analylsis and X-ray diffraction(XRD). The results show that calcium sulphoaluminate gradually increase as the temperature and reached a maximum at 1300°C. However, during the process of coal combustion, the generation quanlity of calcium sulphoaluminate is not much. This is because the material composition of the coal complex, such as Fe2S, SiO2 and other substances have more influence on calcium sulphoaluminate formation. And oxidizing atmosphere promotes the ability of desulfurization at high temperature combustion, and the reducing atmosphere is contrary. The oxidizing atmosphere reduces the SO2 emissions, improves the burnability of raw materials, promotes the formation of calcium sulphoaluminate and thus increases the desulfurization degdree. Whereas, the reducing atmosphere promotes the decomposition of CaSO4, increasing the SO2 emissions and f-CaO contents, reduces the formation of calclium desulfurization degree greatly, and then decreases the desulfurization degree. Introduction

The Influence of the Combustion Atmosphere on the Desulfurization Characteristics

Thermodynamic data calculation for iron phases in sulfoaluminate cementitious materials prepared using solid wastes

Mineral contents in two Zhundong coals and PRB coal were determined by XRF (X-ray fluorescence), XRD (X-ray diffraction) and TG-DSC (thermo gravimetry–differential scanning calorimetry). Effect of ashing temperature was assessed by comparing ash element compositions and mineral patterns at three temperature levels. Element compositions of the ashes showed that Zhundong coals have higher slagging and fouling tendency than PRB coal. It was also found that quartz and kaolinite are main mineral patterns in Zhundong coals and PRB coal. Quartz barely changes with ashing temperature because of its high reaction and melting temperature. Kaolinite begins to dehydrate at ~673 K and then decomposes as temperature further increases. The mineral patterns strongly depend on ashing temperature because of the different reactions among minerals. Based on the mineral pattern and transformation analyses using TG-DSC, calcite was the main form of calcium in one Zhundong coal, while anhydrate was the main form of calcium in the other Zhundong coal and PRB coal.

Mineral Matters in High-AAEM Zhundong Coal—In Comparison with High-calcium PRB Coal

Activity of coal combustion solid residues is relevant closely to calcic minerals composition and reactions. In this paper, the solid residues were analyzed by X-ray powder diffraction when firing coal and additives in a single burner furnace, moreover, the computer package F*A*C*T was used to predict the products composition of the multi-component system containing coal and additives. The mineral composition of solid residues under different conditions has been well investigated. The results indicate that there are two types of reactions with respect to calcic minerals: desulfurization and solid state reaction. The calcic minerals generating from solid state reactions include CaO-SiO2, CaO-Al2O3, CaO-Fe2O3 and CaO-SiO2-Al2O3 group minerals. When increasing CaO content in ash, the primary mineral in the products varied following the route of mullite→anorthite→gehlenite→dicalcium silicate. Desulfurization is prior to solid state reaction when CaSO4 is stable. Due to the decomposition or further reactions of CaSO4 at high temperature, most calcium enters in silicate minerals and complicated S-containing minerals such as calcium aluminosulfate and calcium silicosulfate can be obtained.

Zhang Xiao-ping

Papers

Transportation and heterogeneous reactions of calcium containing minerals in coal combustion solid residues