Investigation on pyrolysis mechanism and emission characteristics of CO2, NOx and SO2 during co-pyrolysis of coal gangue and sodium alginate/sodium carboxymethylcellulose/chitosan/guar gum

Biomass materials are potential to promote coal gangue pyrolysis process. This study investigates the effects of four biomass materials derived from different sources, namely sodium alginate (SA), sodium carboxymethyl cellulose (CMC), chitosan (CS), and guar gum (GG), on the pyrolysis of coal gangue (CG) in a nitrogen atmosphere. Thermal gravimetric analysis coupled with mass spectrometry (TG-MS) was used to analyze the thermal behaviors and emission characteristics of CO2, NOx, and SO2 during the co-pyrolysis process of CG and the four different biomaterial blends, which were mixed in varying ratios. The study investigated that the interactions between the various biomaterials and CG by calculating and comparing pyrolysis parameters, such as the comprehensive pyrolysis index (CPI) of CG and the blends. Additionally, a kinetic analysis using the KissingerAkahira-Sunose (KAS) method was conducted to reveal the co-pyrolysis mechanism. The thermal gravity analysis results illustrated that SA, CMC, CS and GG were all conducive to enhancing CG pyrolysis. As the biomass content in the blends increases, the sample experiences greater mass loss, while the initial pyrolysis temperature and residual mass ratio decrease. This suggests the presence of biomass enables more complete pyrolysis reactions of CG. Among the four biomass materials, GG had the most positive effect on promoting CG pyrolysis, followed by CS and SA, with CMC having the least effect. The kinetic analysis showed that the primary step of each blend sample generally conformed to the first-order kinetic model. The calculated activation energies of blends groups were lower than that of CG pyrolysis, verifying the positive effects of the four biomaterials on CG pyrolysis. However, the interaction mechanism varied in different pyrolysis stages for each type of biomass material. Gas emission analysis indicated that the emission of CO2, NOx and SO2 in blends groups were significantly lower than that of CG pyrolysis. This implies that the addition of the four biomaterials could effectively control the emission of carbon dioxide and pollutants during CG pyrolysis.