Physico-chemical structure and combustion properties of chars derived from co-pyrolysis of lignite with direct coal liquefaction residue

Co-pyrolysis of lignite with direct coal liquefaction residue (DCLR) is a promising method in the field of clean coal technology. To investigate the influence of DCLR fraction on the physico-chemical structure and combustion reactivity of the co-pyrolysis chars, char samples with different mass fraction of lignite and DCLR were prepared in a quartz tube fixed-bed reactor at 550 °C. Then the physico-chemical structure and combustion properties of co-pyrolysis chars were characterized by Microscope, Scaning electron microscope, Raman Spectrometer, Fourier Transform Infrared Spectrometer, automatic gas sorption analyzer and thermogravimetric analyzer. Results showed that there was interaction of the co-pyrolysis of lignite and DCLR, both on char yield and on char's structure and combustion reactivity. And such interaction became obvious with the increase of DCLR fraction. Compared with lignite char, the addition of DCLR resulted in high aromaticity and ordered structure of co-pyrolysis chars, while the pore structure of chars from co-pyrolysis became less developed. The combustion reactivity of chars decreased with the increase of DCLR fraction. The chars produced during co-pyrolysis were of special structure, which were different from lignite and DCLR chars pyrolyzed individually, and that was the reason for their different combustion behavior and reactivity. With the increase of DCLR dosage, the combustion reactivity of components corresponding to lignite char in co-pyrolysis chars reduced while components to DCLR char were enhanced. In addition, the combustion reactivity of pyrolysis chars showed good correlations with Raman/FTIR parameters.