Co-Gasification Performance of Low-Quality Lignite with Woody Wastes Using Greenhouse Gas CO2—A TG–MS Study

Abstract

The carbon dioxide gasification performance of low-quality lignite-agroindustrial/forest waste blends was investigated in terms of reactivity, conversion, cold gas efficiency, product gas composition and heating value. The experiments were conducted in a fixed bed unit and a thermal analysis mass spectrometer system. Raw materials, chars, liquids and gases were quantitatively analyzed and their energy content was determined. Synergetic effects and the role of minerals were examined, the latter through chemical and fusibility analyses of the ashes. Ahlada lignite (AL) was of low quality, with a calorific value of 8.9 MJ/kg. The biomass materials, ginning cotton waste (GCW) and pine needles (PN) had calorific values 16.6 MJ/kg and 20.1 MJ/kg, respectively. The slagging/fouling propensity of AL ash was low, whereas that of biomass wastes was medium to high. Thermal treatment of the samples and their blends prior to gasification produced upgraded fuels. A Boudourd reaction occurred above 750 °C. Gasification reactivity followed the order: GCW > PN > AL. AL/PN mixtures presented additivity effects; however, AL/GCW mixtures presented synergy effects. When the lignite was blended with the biochars studied, its conversion increased from 90% to 94.5% and its cold gas efficiency from 31.8% to 35%. Generated gas attained a heating value of about 12 MJ/m3.