Synergistic effects and mechanism of the ternary flux system Fe2O3-CaO-MgO on the coal ash slag fluidity.

• Synergistic effects of Fe 2 O 3 -CaO-MgO ternary flux system were revealed. • Flow temperature and T CV varied in V-shape as Fe 2 O 3 /(CaO + MgO) ratio decreased. • The formation and eutectic of ferroan spinel led to low flow temperature. • The presence of Fe and a CaO/MgO ratio of 4:6 could limit slag crystallization. • Adjusting the Fe 2 O 3 /(CaO + MgO) ratio to 1 is beneficial for gasifier slagging. Basic oxides are usually widespread in low-rank coals and cause many ash-related problems in gasification applications. In this paper, the synergistic effects of the ternary flux system of Fe 2 O 3 -CaO-MgO in lowering the ash fusion temperature and improving the viscosity-temperature characteristics were verified by testing the properties of samples with different Fe 2 O 3 /(CaO + MgO) ratios. The flow temperatures and temperatures of the critical viscosity decreased and then increased with the decrease of Fe 2 O 3 /(CaO + MgO) ratio and reached the lowest point when the iron oxide and alkaline earth metal oxide (CaO, MgO) contents were close to each other. From the perspective of mineral transformation, the formation of low melting point ferroan spinel and the eutectic between anorthite and ferroan spinel are the main mechanisms of synergism. No severe crystallization was observed in the iron-rich slags because Fe2+ could reduce the crystallization tendency. As CaO and MgO dominated the basic oxides, a CaO/MgO ratio of 4:6 effectively limited the crystallization and lower the temperature of critical viscosity (T CV). Thus, when regulating the coal ash fluidity, the content of iron oxide and the ratio between CaO and MgO should be consciously balanced to meet the requirements of the gasifier for slag removal. [ABSTRACT FROM AUTHOR]