Lingxue Kong

Effect of Na2O on mineral transformation of coal ash under high temperature gasification condition

Abstract In order to reveal the mechanism of Na 2 O influence on ash fusion temperatures (AFTs), effect of Na 2 O on mineral transformation of two coal ashes with different SiO 2 +Al 2 O 3 levels were investigated by XRD and FT-IR under reducing atmosphere at high temperature. Thermodynamic software package FactSage was used to calculate the Δ G of reactions between minerals to reveal the mechanism of Na 2 O influence on mineral transformation. It is found that the effect of Na 2 O on mineral compositions depends on SiO 2 +Al 2 O 3 levels of coal ash. For ash with 82.89% SiO 2 +Al 2 O 3 while Na 2 O content is 5%–20%, albite and nepheline are formed, leading to a decrease of AFTs. However, only nepheline is formed when Na 2 O content is higher than 20%. For ash with 47.85% SiO 2 +Al 2 O 3 , when Na 2 O content is less than 10%, no Na-containing mineral is observed. When Na 2 O content is higher than 10%, Na-containing minerals such as combeite, lazurite and sodium aluminium oxide are formed, resulting in a decrease of AFTs. Furthermore, FactSage results reveal that Na-containing mineral is easily formed at high temperature due to low Δ G of the reactions.

Effect of lime addition on slag fluidity of coal ash

Abstract The ash fusibility temperature (AFT) and slag fluidity of three different coal ash samples through addition of CaO with different amounts were studied. Especially the variation of temperature at critical viscosity was examined at different viscosities. The results show that the fusibility temperatures of coal ashes decrease and then increase with increasing addition amount of CaO, which is consistent with the change of liquids temperature with CaO content calculated by FACTsage. Slag viscosity also decreases with increasing amount of CaO addition above the temperature of critical viscosity ( T cv ). The temperature of critical viscosity firstly decreases with increasing addition of CaO, and then reaches a minimum value when the content of CaO is around 15%. FCATsage was employed to calculate the liquid composition at the temperature of critical viscosity. It indicates that high content of FeO of liquid leads to the low temperature of critical viscosity.

Transformation of minerals in direct coal liquefaction residue under gasification atmosphere at high temperatures

Abstract The transformation behavior of mineral matters in direct coal liquefaction residue from Shenhua Corporation under gasification atmosphere at high temperatures was examined by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). Mossbauer spectroscopy was also applied to investigate the iron-bearing minerals and the valence distribution of iron in ash at different temperatures. The results show that the major minerals in coal liquefaction residue are quartz, calcium sulfate, millosevichite, pyrrhotite, kaolinite, and calcite. At high temperatures, they become anorthite, gehlenite, maghemite and magnetite. Due to the formation of anorthite, gehlenite eutectic, ash of coal liquefaction residue exhibits low fusion temperature. The iron-bearing minerals characterized in ash include maghemite, magnetite, fayalite, and the vitreous matter. The content of iron in vitreous matter increases with increasing temperature. Meanwhile, Fe 2+ /Fe 3+ significantly increases from 1.08 to 2.39 as temperature increases from 1100 to 1200°C for the reduction of maghemite, and it is not obviously changed above 1200°C. Furthermore, the liquid phase in ash calculated by FactSage increases with temperature owing to the increase of iron in vitreous phase. In hence, high content of iron in ash from coal liquefaction residue is the major reason for its low ash fusion temperatures.

Regulation of high temperature flow properties of ash containing V and Ni

Abstract Three ashes containing V and Ni were preparation for the study. CaO addition and coal ash blending were chosen for regulation of high temperature flow properties. The regulation mechanism was explored by XRD, SEM-EDX and ternary phase diagram analysis. The results show that karelianite and Ni are main refractory matters in petroleum coke ash at high temperature. CaO addition and coal ash blending decrease the liquid temperatures of ash components except V and Ni, which reduces the ash fusion temperatures. When the contents of V and Ni are fewer than 30% in ash, CaO can obviously decrease the fusion temperature of ash, and the viscosity-temperature property becomes crystal type. When the contents of V and Ni are higher than 30% in ash, coal ash blending is an effective method to decrease the fusion temperature. In this condition, 5% of coal ash blending ratio is required, and its viscosity-temperature property is suitable for slag tapping, but when the coal ash proportion is 10% the viscosity-temperature property of ash becomes crystal type for the precipitation of vanadium-rich spinel, which cannot meet the requirement of slag tapping.