Polyethylene gasification in a bubbling fluidized bed: Operating-parameter effects on syngas, tar and soot formation

Plastic gasification offers a route to recover polymer carbon as synthesis gas; changes in operating conditions affect both syngas properties and the partitioning of carbon among gaseous, condensable, and solid products. This study investigates these effects during polyethylene gasification in an electrically heated lab-scale bubbling fluidized bed. Experimental series varied temperature (750–850 °C), equivalence ratio (ER; 0.20–0.30), and steam-to-carbon ratio (S/C; 0.25–0.75), with additional tests assessing the influence of feed rate and oxygen enrichment. Raising temperature increased H 2 and CO yields, doubled gas yield from 0.90 to 1.74 Nm 3 /kg daf , and raised carbon conversion efficiency to 93%, while shifting condensables from aliphatics toward aromatics/PAHs. Increasing ER to 0.30 lowered condenser-collected tar but increased soot sixfold and produced less favourable methanol-relevant stoichiometry, showing a trade-off between tar reduction, soot formation, and syngas quality. Steam addition suppressed soot by almost one order of magnitude, but H 2 , CO, and gas yields peaked at S/C = 0.50, with limited further conversion benefit at higher S/C. Oxygen enrichment from 30% to 72%, with additional steam moderating bed temperature, maintained gas-phase carbon conversion with only a minor reduction in cold-gas efficiency. Paired in-reactor and downstream sampling tracked gas evolution through the freeboard, showing continued olefin conversion and H 2 formation consistent with kinetic-model predictions at an imposed 850 °C. C 2 H 4 in the product gas accounted for 25–35% of feed carbon under all conditions. Further hydrocarbon conversion, contaminant removal, and H 2 adjustment would therefore be required before the syngas could be used for methanol synthesis.