Influence of plastic co-feeding on oxygen utilization pathways in high-temperature coal gasification

Coal gasification is a mature technology for producing synthesis gas (syngas), while managing end-of-life plastics remains a growing environmental challenge. Co-gasification of coal and plastics offers a promising approach to both valorize plastic waste and expand feedstock flexibility in existing systems. However, interactions between plastic-derived volatiles and coal, particularly regarding oxygen competition and syngas composition, are not well understood. This study investigates coal/HDPE co-gasification using a laminar entrained-flow reactor at 1300–1400°C. Pulverized bituminous coal was blended with high-density polyethylene (HDPE) at 5–30% mass fractions and gasified with oxygen at a stoichiometric ratio of 0.5. Effects of temperature, particle size, plastic loading, and residence time were evaluated. Coal carbon conversion ranged from 65% to 78%, increasing with higher temperature, smaller particles, and longer residence time. Adding HDPE resulted in only modest gains in coal conversion (1–3 percentage points) but significantly increased the CO/CO 2 ratio by up to 45% at higher temperatures and rose consistently with plastic content. Results indicate that most oxygen is consumed by volatile combustion, limiting availability for char reactions. Because HDPE volatilizes at low temperatures, it intensifies oxygen competition but does not significantly reduce coal conversion. Instead, partial oxidation of plastic volatiles under oxygen-limited conditions favors CO production, improving syngas quality. These findings demonstrate that coal–plastic co-gasification can enhance syngas composition while providing a viable pathway for plastic waste utilization. • Addition of plastic to coal gasification creates competition for O 2 • Higher temperatures, smaller particle sizes and longer residence times improved conversion • Addition of up to 30% plastic had minimal influence on coal carbon conversion • Co-gasifying plastic with coal increases the CO/CO 2 ratio of the product gas