Evaluation of the Influence of Different Conditions on the Na/Cl Release and Characteristics of High-Alkali Coal Pyrolysis Products by Orthogonal and Single-Factor Experiments

Abstract

During the thermal utilization of high-chlorine and high-sodium coal, significant Na and Cl release leads to equipment scaling and corrosion, limiting industrial applications. Pyrolysis, a key pretreatment process, aims to remove these elements before combustion to prevent high-temperature corrosion. This study identified optimal pyrolysis conditions (500 °C, 0.45 - 0.90 mm coal particle size, 400 L/h gas flow, CO atmosphere) through orthogonal experiments and grey correlation analysis. Under these conditions, char with high reactivity (R=0.55457) and yield (Y=71.05%) was obtained, along with significant Na and Cl release ratios (8.08% for Na and 77.10% for Cl). The influence of temperature and atmosphere on the char characteristics and the distribution of Na and Cl forms was further studied by single factor experiments. Temperature significantly influenced Na and Cl distribution and char characteristics. Compared to N2, non-inert atmospheres (CO and CH4) altered char's structure, reactivity, and ash melting point. Both experimental and molecular dynamics results demonstrate that CO and CH4 atmospheres enhanced Na release by reacting with insoluble sodium components, while maintaining high Cl release. This research provides insights to reduce corrosion, extend equipment lifespan, and improve high-chlorine and high-sodium coal utilization efficiency in industrial processes.

Keywords: High sodium and high chlorine coal, pyrolysis, migration of sodium and chlorine, grey correlation analysis, molecular dynamics