Moderate-Temperature Pyrolysis Characteristics of Lump Coal Under Varying Coal Particle Sizes

Yuanpei Luo, Luxuan Liu, Liangguo Lv, Shengping Zhang, Fei Dai (), Hongguang Jin and Jun Sui
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Yuanpei Luo: State Key Laboratory of Multiphase Flow in Power Engineering, Xi’an Jiaotong University, Xi’an 710049, China
Luxuan Liu: Laboratory of Distributed Energy System and Renewable Energy, Institute of Engineering Thermophysics, Chinese Academy of Sciences, Beijing 100190, China
Liangguo Lv: Laboratory of Distributed Energy System and Renewable Energy, Institute of Engineering Thermophysics, Chinese Academy of Sciences, Beijing 100190, China
Shengping Zhang: Laboratory of Distributed Energy System and Renewable Energy, Institute of Engineering Thermophysics, Chinese Academy of Sciences, Beijing 100190, China
Fei Dai: Laboratory of Distributed Energy System and Renewable Energy, Institute of Engineering Thermophysics, Chinese Academy of Sciences, Beijing 100190, China
Hongguang Jin: Laboratory of Distributed Energy System and Renewable Energy, Institute of Engineering Thermophysics, Chinese Academy of Sciences, Beijing 100190, China
Jun Sui: Laboratory of Distributed Energy System and Renewable Energy, Institute of Engineering Thermophysics, Chinese Academy of Sciences, Beijing 100190, China

Energies, 2025, vol. 18, issue 12, 1-18

Abstract: Pyrolysis is an important methodology for achieving efficient and clean utilization of coal. Lump coal pyrolysis demonstrates distinct advantages over pulverized coal processing, particularly in enhanced gas yield and superior coke quality. As a critical parameter in lump coal pyrolysis, particle size significantly influences heat transfer and mass transfer during pyrolysis, yet its governing mechanisms remain insufficiently explored. This research systematically investigates pyrolysis characteristics of the low-rank coal from Ordos, Inner Mongolia, across graded particle sizes (2–5 mm, 5–10 mm, 10–20 mm, and 20–30 mm) through pyrolysis experiments. Real-time central temperature monitoring of coal bed coupled with advanced characterization techniques—including X-ray diffraction (XRD), Raman spectroscopy, Brunauer–Emmett–Teller (BET) analysis, scanning electron microscopy (SEM), gas chromatography (GC), and GC–mass spectrometry (GC-MS)—reveals particle-size-dependent pyrolysis mechanisms. Key findings demonstrate that the larger particles enhance bed-scale convective heat transfer, accelerating temperature propagation from reactor walls to the coal center. However, excessive sizes cause significant intra-particle thermal gradients, impeding core pyrolysis. The 10–20 mm group emerges as optimal—balancing these effects to achieve uniform thermal attainment, evidenced by 20.99 vol% peak hydrogen yield and maximum char graphitization. Tar yield first demonstrates a tendency to rise and then decline, peaking at 14.66 wt.% for 5–10 mm particles. This behavior reflects competing mechanisms: enlarging particle size can improve bed permeability (reducing tar residence time and secondary reactions), but it can also inhibit volatile release and intensify thermal cracking of tar in oversized coal blocks. The BET analysis result reveals elevated specific surface area and pore volume with increasing particle size, except for the 10–20 mm group, showing abrupt porosity reduction—attributed to pore collapse caused by intense polycondensation reactions. Contrasting previous studies predominantly focused on less than 2 mm pulverized coal, this research selects large-size (from 2 mm to 30 mm) lump coal to clarify the effect of particle size on coal pyrolysis, providing critical guidance for industrial-scale lump coal pyrolysis optimization.

Keywords: low-rank coal pyrolysis; wide particle size; lump coal (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2025
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