The effect on ash deposition by blending high‐calcium Zhundong coal with vermiculite: Focusing on minerals transformations

Abstract

To solve the ash deposition problem caused by burning high‐calcium Zhundong coal (ZDC), the addition of vermiculite is a promising solution. However, complete mechanisms of vermiculite addition reducing ash deposition are still unknown. In this paper, the effect of vermiculite on sodium emission, ash fusion characteristics, and mineral transformation is investigated. The results show that although vermiculite, with limited Na capture capacity, lowers the ash fusion temperatures (AFTs), it can greatly reduce ash deposition. In the combustion of ZDC, calcium‐bearing minerals will react with clay minerals and then convert to molten glassy phase. Those molten minerals will take high melting point minerals, Ca2Al2SiO7 and CaMgSi2O6, as bone, showing slagging phenomenon with high AFTs. When vermiculite is introduced, the main reaction products are Ca2MgSi2O7 and Mg2SiO4 and that reduces the extent of molten minerals formation. The main ash product transforming from Ca2Al2SiO7 to Ca2MgSi2O7 leads to the decrease of AFTs. The initial ash deposition with Ca2Al2SiO7 still happens; however, vermiculite addition makes it hard for ash to grow on the existing ash deposit. The results of FactSage software agree with the experimental ones, and the proportion of slag decreases by 36% with vermiculite at 1250°C.

Correlation between the Flow Temperature and Mineral Factor for Coal Ashes Based on FactSage Calculation

“…The accuracy of these correlations is relatively less because the AFT at a given condition is determined by mineral species and its content. , However, determination of the mineral composition of ash at a certain condition is complex and time-consuming. Fortunately, FactSage software provides a simple method to calculate the ash mineral composition and its variation with increasing temperature. , Although the prediction of AFT has been explored recently from different perspectives (e.g., liquid slag fraction or the temperature corresponding to a certain liquid fraction, , thermomechanical analysis, rule-based intelligent system model, liquid-phase content stage and its variation trend, and the diffraction intensity ratio of refractory minerals and fluxing minerals), the papers on the quantitative correlation between AFT and mineral compositions are relatively lacking, especially for the mineral composition calculated based on FactSage software. Thus, the aims of the paper are to establish the quantitative correlation between the FT and mineral composition (including liquid slag content) at a certain condition and to provide a simple way to predict the FT using FactSage software according to ash oxide composition in a reducing atmosphere and atmospheric pressure.…”

Effect of steel slag bed material on ash deposition and Na migration in circulating fluidised bed during Zhundong lignite combustion

“…1 Coal from this field has merits of low ash and sulfur contents as well as high reactivity for combustion. 2,3 However, Na content in Zhundong lignite ash is as high as 10%, which has induced severe ash deposition during combustion. 4 Circulating fluidised bed (CFB) combustion could be one of the promising means for its clean and efficient utilisation.…”

“…Zhundong coalfield in Northwest China has an estimated reserve of 390 Gt and is currently the largest integrated coalfield in China 1 . Coal from this field has merits of low ash and sulfur contents as well as high reactivity for combustion 2,3 . However, Na content in Zhundong lignite ash is as high as 10%, which has induced severe ash deposition during combustion 4 .…”