Gaseous Emissions from the Fluidized-Bed Incineration of Sewage SludgeM. Pohořelý, K. Svoboda, O. Trnka, D. Baxter, and M. Hartman Institute of Chemical Process Fundamentals, Academy of Sciences of the Czech Republic, CZ-165 02 Prague
E-mail: hartman@icpf.cas.cz Abstract: Combustion of dried sewage sludge has been studied in a bench-scale fluidized-bed combustor operated under steady-state conditions. The attention has been focused on the emissions of pollutant gases and on the unburned carbon in elutriated fines. Steady-state combustion experiments were carried out at different temperatures by feeding pre-dried sludge particles into an inert bed of ceramsite particles. The 9.4 cm i.d. combustor was operated at superficial gas velocities of 0.3—0.8 m s−1 and at different excesses of air. Very small amounts of unburned carbon in the fly ash separated by the cyclone (below 0.8 mass %) and generally very low levels of carbon monoxide in the exit flue gas (usually below 50 ppm) document very good combustion efficiency attained in a bubbling (dense) fluidized bed. Although conversions of the fuel nitrogen, measured under practical conditions, to NOx and N2O amounted to only about 10 % and 5 %, respectively, the resulting harmful emissions must be of serious concern. The measured content of NOx varied between approximately 600 ppm and 1100 ppm, in the case of N2O it was 150—400 ppm. The emissions of CO and NOx are closely interdependent and connected: the lower concentration of CO is in flue gas, the higher level of NOx measured. Higher operating temperatures, higher partial pressures of oxygen, and longer residence times in the combustor improved the combustion efficiency, according to the amount of unburned CO, CxHy, and carbon. Unfortunately, such process conditions inherently lead to unwanted higher conversions of the fuel-bound nitrogen-to-nitrogen oxides. Full paper in Portable Document Format: 596ba458.pdf
Chemical Papers 59 (6b) 458–463 (2005) |
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