Catalytic Co-gasification of Lignites Blended with a Forest Residue under the Carbon Dioxide Stream

The present study investigated the co-gasification of two different lignites blended with the forest residue collected from the land restoration activity sites of open-pit mines located in the region of the Ptolemais basin in North Greece performed under the carbon dioxide stream. All samples were devolatilized in a fixed bed unit prior to the gasification evaluations. The gasification evaluations were performed using a thermal analysis system (TG/DTG) operated at temperatures of up to 1000 °C. The reactivity, conversion, cold gas efficiency, and influence of the external catalysts CaO and K2CO3 were assessed in the evaluations. The reaction rate of the forest residue was 2–3 folds higher than that of the lignites, with the conversion of the former reaching a value of 96.4% (dry basis), while the conversion of the lignites varied between 43.4% and 51.6%. The peak inflection temperature was in the range of 859–939 °C. The reactivity of the lignite/biomass blends was higher than that of the lignites, and the final conversion was increased by approximately 30%. When individual biochars were impregnated with 30% CaO or K2CO3, the process occurred at lower temperatures, and the conversion of the lignites increased by 35%–40% while that of the forest residue reached a value of 100%. The CaO catalyst performed better. Finally, a blend of equal amounts of Kardia lignite or Ahlada lignite and the forest residue with 30% CaO was formulated, which resulted in an 89.6% or 71.7% conversion to carbon monoxide gas, respectively.