Synergistic PM2.5 and PAHs suppression in biomass-coal briquettes for household combustion: multi-parameter optimization and mechanistic insights from ash chemistry to particulate morphology

Abstract

Biomass combustion represents a significant source of particulate matter, posing substantial risks to both human health and the environment. This study underscores bio-coal briquettes as a promising solid fuel for residential applications, with the potential to significantly curtail PM_2.5 emissions. The PM_2.5 emissions were quantified using URG cyclones and quartz-fiber filters. PAHs were analyzed via GC/MS, and PM morphology via SEM-EDS. The quantitative analysis particularly examines the influence of diverse furnace types, ignition modes, and biomass blending ratios on PM_2.5 emissions during bio-coal briquettes combustion. A quadratic function model is formulated to elucidate the correlations between the PM_2.5 emission factors and the volatile as well as ash content. Furthermore, the presence of ash in the samples exacerbates the production of polycyclic aromatic hydrocarbons (PAHs) in the flue gas during combustion. Optimal conditions (20 % straw, semi-gasifier, upper ignition) reduced PM_2.5 emissions to 4.9 mg/g (vs. 24.9 mg/g in conventional furnaces). Quadratic models linked volatile matter (R² ≥ 0.97) and ash content (R² ≥ 0.99) to PM_2.5. Under these parameters, the emission factors for 16 PAHs, including benzo[a]pyrene (BaP), as well as water-soluble cations and ions, are observed at their lowest levels, demonstrating superior emission reduction efficacy. Scanning electron microscopy revealed that the collected PM_2.5 exhibited a variety of morphologies and structures. Energy dispersive spectroscopy indicated that the primary constituents of PM_2.5 were C, O, Na, Zn, K, Al, Ti, Ca, Cl, Te and Hg. This strategy offers a viable pathway to mitigate household air pollution in rural regions.