Effect of flue gas recirculation technology on soot and NO formation in the biomass pyrolysis-combustion system

Pyrolysis of biomass followed by combustion of pyrolytic vapors to replace fossil fuels is an economic low-carbon solution.However,the polycyclic aromatic hydrocarbons and N-containing species in biomass pyrolysis vapors result in the soot and NO emissions.The flue gas recirculation(FGR)technology,having the potential to reduce the soot and NO emissions,was introduced to the biomass pyrolysis-combustion system.In addition,it was numerically studied by simulating the biomass pyrolysis vapors based co-flow diffusion flames with CO_(2)addition.Both the experimental and simulated results showed that the FGR had significant suppression effects on the soot formation.When the FGR ratio(i.e.,CO_(2)addition ratio)increased from 0%to 15%,the experimental and simulated soot volume fraction respectively decreased by 32%and 21%,which verified the models used in this study.The decrease in OH concentration caused by the CO_(2)addition was responsible for the decrease in the decomposition rate of A2(A2+OH=A2–+H_(2)O).Hence,more benzo(ghi)fluoranthene(BGHIF)was generated through A1C_(2)H–+A2→BGHIF+H_(2)+H,leading to the increase in inception rate.The decrease in benzo(a)pyrene(BAPYR)concentration was the major factor in the decrease in soot condensation rate.Moreover,the decrease in the C_(2)H_(2) and OH concentrations was responsible for the decrease in the HACA surface growth rate.Furthermore,the simulated results showed that the NO concentration decreased by 0.4%when the content of CO_(2)was increased by 1 vol.%.The decrease in OH concentration suppressed the NO formation via decreasing reaction rates of N+OH=NO+H and HNO+OH=NO+H_(2)O and enhanced the NO consumption via increasing reaction rate of HO_(2)+NO=NO_(2)+OH.