Effect of potassium-containing sulfates on high-temperature mineral transformation and coal ash fusibility

ABSTRACT

Potassium-containing sulfates are important species that aggravates fouling and slagging in coal and biomass co-combustion plants. K₂SO₄, K₂S₂O₇, and K₃Fe(SO₄)₃ were added to coal ash to study the effects of potassium-containing sulfates on coal ash fusibility and mineral transformation at high temperature. Ash Fusion Temperatures (AFTs) of ash samples were tested. Mineral transformation was analyzed by X-Ray Diffraction (XRD) spectra and was simulated by thermodynamic equilibrium calculation. AFTs test results showed that when potassium-containing sulfate content increased by 5%, AFTs dropped by 10°C approximately. XRD analyses illustrated that at 1000°C-1200°C, potassium-containing sulfates reacted with quartz, corundum to form aluminosilicate. K was firstly present in microcline and transformed into leucite kalsilite as K content increased. Thermodynamic simulations showed that when K₂SO₄ content increased, microcline and leucite content increased rapidly while quartz, corundum, and kyanite content gradually decreased. The low melting temperature and eutectic effect of potassium-containing minerals lead to a significant decrease in AFTs. This work can provide guidance for coal and biomass co-combustion plants to regulate blended ratio of biomass so as to prevent fouling and slagging resulted from potassium-containing sulfates.

Graphical abstract

This graphical abstract clearly summarizes the research results of the paper and shows minerals transformation of coal ash added with potassium-containing sulfates with increasing temperature.

KEYWORDS:

• Potassium-containing sulfate
• ash fusibility
• XRD
• thermodynamic simulation
• mineral transformation

Highlights

• When potassium-containing sulfate content increased by 5%, Zhijin Xingwang (ZJXW) Ash Fusion Temperatures (AFTs) fell by nearly 10°C.

• Specific transformation paths of major minerals in ash fusion process are concluded in a figure.

• For ZJXW coal ash, AFTs corresponds to a temperature range of 10%-20% crystalline phases.

• Effect of Na and K-containing sulfates on ash fusibility and mineral transformation path are different though Na and K have similar property.

Acknowledgments

The authors gratefully acknowledge the financial support of the National Natural Science Foundation of China (No. 51206047).

Declaration of interest statement

The authors declare no declaration of interests.

Additional information

Funding

This work was supported by the National Natural Science Foundation of China [51206047].