Energy utilization of direct coal liquefaction residue via co-slurry with lignite: Slurryability, combustion characteristics, and their typical pollutant emissions

Abstract

Direct coal liquefaction residue (DCLR) as an auxiliary feed material with lignite to prepare coal water slurry (CWS), which is then used as combustion fuels, enables recycle resources of DCLR and diminishes its impact on the surrounding environment. This paper aims to study the slurryability, combustion characteristics, and typical pollutant emissions of the lignite water slurry (LWS), DCLR water slurry (DCLRWS), and lignite-DCLR water slurry (L-DWS). Results showed that the DCLR and lignite were complementary in physicochemical properties for preparing the L-DWSs. The maximum solid concentration (ωmax) of the DCLR was 73.19 wt% with poor static stability, whereas that of the LWS was 41.70 wt% with high pseudoplasticity. By contrast, the ωmax of the L-DWS-5 prepared from the lignite and DCLR at mass ratio of 5:5 was 53.91 wt% with lower pseudoplasticity and static stability. Meanwhile, combustion experiments confirmed that the introduced DCLR was effective in improving the ignition, burnout, and comprehensive combustion performance of the L-DWS. The Qnet, p of the slurrying samples increased from 6.70 MJ/Kg for the LWS to 14.41 MJ/Kg for the L-DWS-5. And the addition of the DCLR exhibited slight influences on the emissions of NOx and SO2, but significantly increased HCN and other organic compounds such as CnHm, CO, and NH3 emissions. Furthermore, except for Pb and Zn, more than 85% Cr, Cu, and Ni were intercepted in solid residues.