ReaxFF molecular dynamics study of co-combustion of waste tires with petroleum coke gasification residue: Combustion characteristics, gas evolution and micro mechanism

Abstract

Solid wastes such as waste tires (WT) and petroleum coke gasification residue (PCGR) could be used as fuels to realize the recovery of resources. The detailed composition of WT and PCGR was determined in this study through the proximate and ultimate analyses, FTIR, XPS, and 13C NMR characterization. Based on experimental characterization results, molecular models of WT (C557H802O16S4N3) and PCGR (C156H61O5S3N) were constructed. Then, the co-combustion characteristics of WT and PCGR were in-depth investigated via the reactive force field molecular dynamics (ReaxFF MD) simulations. The migration pathways of N/S during combustion in both O2 and O2/N2 atmospheres were also elucidated. Meanwhile, the evolution of specific products with oxygen concentration and temperature was investigated. The results indicated the oxidation process began with thermal decomposition to form small fragments, which were next attacked by O radicals to generate inorganics. Additionally, the blending combustion was promoted as the molar fraction of the WT increased. The PCGR decomposed and burnt faster in fuel-lean conditions. Besides, higher temperature could accelerate the combustion process. The pyrrole/pyridine was converted to HCN and NHx in the first step and then oxidized to NOx. The production of NOx was significantly higher in the O2/N2 atmosphere than that in the O2 atmosphere. The main product was NO, with a small amount of NO2. The conversion of thiol to HS and thiophene S to COS was also observed. The COS easily reacted with H atoms to form HxS. In O2/N2 environment, CNS and elemental sulfur were formed due to the N-rich atmosphere.