Effect of Sodium-Containing Sulfates on Ash Fusibility

Abstract

Various amounts of Na2SO4, Na2S2O7, and Na3Fe­(SO4)3 were added to two kinds of coal ash to study the effects of sodium-containing sulfates on ash fusibility. Ash fusion temperature (AFT) tests and X-ray diffraction (XRD) were applied to measure the ash fusibility and detect mineral compositions. Thermodynamic calculations were used to analyze mineral transformations of ash samples. It was found that the AFTs decreased with increasing sodium-containing sulfate contents. The primary sodium-containing minerals in ash mixed with Na2SO4 were nepheline, nosean, and albite, which all had low melting points and easily formed low-temperature co-melts. Labradorite appeared when the ash was mixed with Na2S2O7 and Na3Fe­(SO4)3, leading to lower AFTs when compared to ash mixed with Na2SO4. The trend of liquidus temperatures from thermodynamic calculations was consistent with the AFT tests. The calculations also indicated that sodium-containing minerals were easily formed because of low-reaction ΔG values.

Co-Firing Zhundong Coal with Its Gangue: Combustion Performance, Sodium Retention and Ash Fusion Behaviors

“…Extensive efforts have been made to elucidate the mechanism and the possible solutions to alleviate the ash-related problems (slagging and fouling) [15,[19][20][21][22]. Based on the previous literatures, Na easily sublimates into the gas phase during combustion [17,23], while Cl and S in the coal combined with gaseous Na and forms NaCl or Na 2 SO 4 at high temperatures [24,25]. The Na-containing compounds promote the formation of a sticky inner layer, which is closely related to the ash-fouling problems [26].…”