Coal char-CO2 gasification reactivity and kinetics characteristics for varying char particle sizes

Abstract

Research on the reactivity and kinetics of the gasification reaction between coal char and CO₂ is fundamental for designing and optimizing gasification reactors. This paper focuses on investigating the low rank coal char-CO₂ gasification performance and the dynamic evolution of char’s physical and chemical structures for various char particle sizes (0.8–1, 2–2.5, and 4–10 mm), during the char samples were prepared through the Ordos coal pyrolysis under 1123 K. The smaller the coal char particle size, the higher the initial gasification reaction rate and carbon conversion rate, while the coal char gasification reaction speed with big particle size exhibits the trend that was initially ascending and then descending. The dimension of the coal char particles affects the mass and heat transfer between CO₂ molecule and solid surface of char. Subsequently, combined characterization approaches, including X-ray diffraction (XRD), Raman spectroscopy, N₂ isothermal adsorption, and Scanning electron microscopy (SEM), are employed to analyze the morphological variations of the coal char carbon matrix under various gasification reaction times. The graphene-like structure in the coal char is gradually strengthened as the size of the char decreases. The reason is that the amorphous carbon in the small-sized coal char structure is rapidly consumed and causes the stacking and fusion of aromatic layers, which enlarging the graphite stacking height and forming a more orderly structure. In addition, this paper also studies the coal char-CO₂ gasification reaction kinetic based on four distinct models, the mixture model (MM) could relatively well predict the characteristics of Ordos coal-CO₂ gasification reaction for a broad range of particle sizes. This investigation offers support for the application of the coal char-CO₂ gasification technology.