Reactions and transformations of mineral matters during entrained flow coal gasification using oxygen-enriched air

Abstract

Clarification of the reactions and transformations mechanisms of mineral matters during entrained flow gasification using oxygen-enriched air is necessary for the reliability of the gasifier. To explore the impacts of different gasification temperatures (1000 and 1200 °C) and oxygen concentrations (21, 50, 100 vol % O2 in N2) on the mineral behaviors, the gasified chars obtained from a pilot-scale gasifier were characterized by the means of ICP-OES, XRD, PSD, SEM-EDX, and AFT methods. Results indicated that gasification with oxygen-enriched air not only promoted the retention of inorganic elements in the solid phase but also changed the mineral types and contents. The main components of gasified chars were SiO2 and Ca-bearing minerals, and the increase in gasification temperature and oxygen concentration would promote the transformation of CaCO3 and CaSO4 to CaO, CaS, and Ca2Al2SiO7. With increasing oxygen concentration under 1000 °C gasification, the average particle size of gasified chars was getting smaller and the high-melting mineral Al6Si2O13 was likely to form, leading to the increase in the fusion temperature. However, when the gasification temperature rose to 1200 °C, the re-carbonation of CaCO3 was largely promoted with the increase of oxygen concentration due to the more abundant CO2 in the reaction atmosphere. Meanwhile, the morphologies of apparent agglomerate and sintering began to appear in the 1200 °C gasified chars, leading to a significant increase in particle size. It is deduced that the enrichment of Ca and Fe in the 1200 °C gasified chars would accelerate the formation of low-temperature eutectic mixtures, thus reducing the ash fusion temperatures of 1200 °C samples. Overall, the ash fusion temperatures of the gasified chars are closely linked to mineral composition, particle size distribution, and agglomeration behavior during the gasification process.