Microwave co-pyrolysis of lignite with direct coal liquefaction residue: Synergistic effects and product combustion characteristics

Abstract

To effectively and cleanly handle the direct coal liquefaction residue (DCLR), a two-phase microwave reaction system was designed based on poly-generation lignite technology, that performed both individual pyrolysis and co-pyrolysis, to investigate the effect of microwave co-pyrolysis of lignite with different addition of DCLR on the pyrolysis products characteristics. The experimental results demonstrated the presence of synergism during microwave co-pyrolysis, which enhanced the condensation reaction of different free radicals, and thus increased the char (upgraded lignite, UL) yield by 6.14–10.42%. The DCLR showed excellent catalytic effects as consumable absorbents in terms of heating rate, and char and gas yields, and it eventually converted into high value-added combustible gases (CO, CH4, and H2). Furthermore, when compared to the individual pyrolysis sample and lignite, the co-pyrolysis samples’ chemical structures were progressively aromatized, and exhibited significantly lower O/C ratios, re-adsorption moisture content, and reactive groups and available sites. Moreover, the pore structures on the surface for the co-pyrolysis samples were dominated by cracks, blowholes, and open-ended fissures, which gradually decreased as DCLR contents increased. Combustion behavior and kinetic analysis confirmed that microwave co-pyrolysis changed activation energy (Ea) distribution of ULs and thus improving their combustion performance. Therefore, microwave co-pyrolysis of lignite with DCLR was an effective and economical approach for clean utilization DCLR and obtaining high-quality lignite fuel.