Study on the Occurrence Morphology and Combustion Characteristics of Carbon and Ash in Coal Gasification Coarse Slag with Different Granularity

Abstract

To investigate the morphological occurrence of carbon and ash in coal gasification coarse slag (CS) and their impacts on resource utilization, this study focused on Jinhua CS after grinding for 40 s. Samples with progressively decreasing particle sizes, ranging from CS60 (coarse fraction) to CS200 (fine fraction), were obtained through sieving. Combined with proximate analysis, LOI, XRF, FTIR, XRD, SEM-EDS, Raman, BET, and TG-DTG, the physicochemical properties of the samples were systematically analyzed. Results indicated that the particle size distribution was predominantly composed of intermediate fractions (CS60–200), with a total yield exceeding 90%. As the particle size decreased, the ash content reduced from 95.79% (CS60) to 82.72% (CS200), while the fixed carbon content correspondingly increased from 2.29 to 14.71%, illustrating the distribution pattern of ″residual carbon enrichment in fine fractions and inorganic mineral dominance in coarse fractions.″ CS200 exhibited a greater diversity of crystalline phases, with carbon and ash primarily existing as ″ash-encapsulated carbon,″ ″carbon-encapsulated ash,″ and cross-linked structures. This fraction demonstrated a surface carbon content of 54.74%, predominantly comprising stable C–C/C–H bonds (68.00%), along with a high specific surface area (104.35 m2/g), well-developed mesopores, abundant carbon defect sites, and excellent combustion activity (DTGmax = −4.69%·min–1), making it suitable for preparing adsorbent materials or energy recovery as fuel. Conversely, CS60 was characterized by discrete and ″carbon-encapsulated ash″ distributions of carbon and ash, enriched with inorganic elements such as O, Si, and Al, exhibiting low combustion activity, and could be utilized for the preparation of geopolymers, construction aggregates, etc.