Mineralogical Characterization of Gasification Ash with Different Particle Sizes from Lurgi Gasifier in the Coal-to-Synthetic Natural Gas Plant.

The Lurgi gasifier in China is one of the most suitable technologies to produce synthetic natural gas (SNG) from coal; however, a large amount of byproduct ash is discharged during the Lurgi gasification process, causing many environmental problems. Based on ash samples collected from a commercial Lurgi gasifier in a Chinese coal-to-SNG plant, this paper studied the mineral composition and microscopic appearance of gasification ash with different particle sizes. The typical minerals were identified and investigated by comparing them with the ash from a laboratory fixed-bed reactor. The results showed that the main high-temperature minerals in the Lurgi gasification ash with different particle sizes under the gasification condition of 4 MPa and 1100 °C were anorthite (CaAlSiO), augite (CaFeSiO), hematite (FeO), and gehlenite (CaAlSiO). As the particle size of the Lurgi gasification ash increased, the quartz content increased but the residual carbon content decreased. Additionally, the high-temperature minerals were more likely to agglomerate with fine particles of the ash. The FactSage modeling showed that calcium-bearing minerals were formed earlier than iron-bearing minerals. The high FeO content in ash hindered the transformation of calcium-bearing minerals into the high-melting-point mullite, resulting in a low ash flow temperature. Additionally, the fine ash had a relatively high content of calcium-bearing minerals which was not conducive to its utilization as an additive in cement and concrete.