Effect of reaction conditions on the evolution of surface functional groups in O2/H2O combustion process of demineralized coal char

O-2/H2O combustion is now regarded as a novel and promising technology of coal utilization for next-generation oxy-fuel combustion. The combustion reaction mainly occurs in the mixture of O-2 and H2O instead of recycled flue gas (mainly CO2). The purpose of this research is to clarify the evolution characteristics of O/N-containing complexes (C(O)/C(N)) during O-2/H2O combustion. Fourier transform infrared spectroscopy (FT-IR), temperature programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS) were employed in this study. The addition of H2O in the atmosphere promoted the generation of NO and HCN in char combustion. There was a good linear relationship between the C(O) amount and char reactivity, as well as the NO conversion ratio, during the O-2/H2O combustion process. Moreover, trace amounts of the precursors of CO2 with low thermal stability remained on the particle surface in the O-2/H2O combustion. The enhancement of the reaction temperature revealed positive effects on inhibiting NO emissions in the O-2/H2O combustion. The relative amount of pyrrole (N-5), which was the precursor of HCN, increased apparently at the expense of pyridine (N-6) and quaternary nitrogen (N-Q) in the early reaction stage. VVhen the char conversion degree exceeded 50%, N-Q and N-6 became the dominant forms of C(N).