Release characteristics of organic pollutants during co-firing coal liquefaction residue in a circulating fluidized bed boiler

Abstract

Coal liquefaction residue (CLR) is usually categorized as hazardous waste, which is inevitably generated during the coal-liquefaction process. Studies show that CLR has a high calorific value and can be used to decrease coal consumption during the co-firing process. In this regard, field tests were carried out to study the emission and environmental risks of organic pollutants during co-firing CLR in a circulating fluidized bed (CFB) boiler. In the present study, the effects of co-firing CLR on the operating conditions of the boiler and the concentrations of 16 polycyclic aromatic hydrocarbons (PAHs), hexachlorobenzene (HCB), dioxins, dioxin-like polychlorinated biphenyls (dl-PCBs), volatile organic compounds (VOCs), and total organic carbons (TOCs) in the flue gas, fly ash, and bottom ash were investigated. It is found that burning the fuel consisting of 85 % coal and 15 % CLR by mass decreases the coal consumption by 2–3 t/h while the combustion parameters almost remain intact. The performed analyses reveal that co-firing the CLR does not increase the emission of PAHs compared to pure coal combustion. Meanwhile, it is found that fly ash has a high concentration of PAHs while the concentration is relatively low in the bottom ash. Doped with m-dichlorobenzene as an organic marker, the destruction removal efficiency (DRE) exceeds 99.99 %. The releases of organic pollutants during the co-firing process are lower than the specified limit in relevant environmental standards.