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In situ laser measurements of CO and CH 4 close to the surface of a burning single fuel particle

2002; IOP Publishing; Volume: 13; Issue: 10 Linguagem: Inglês

10.1088/0957-0233/13/10/306

1361-6501

Maximilian Lackner, Gerhard Totschnig, Franz Winter, M. Maiorov, D Z Garbuzov, J.C. Connolly,

Atmospheric chemistry and aerosols

The combustion behaviour of three different fuels, bituminous coal, beech wood and fir wood, was investigated by monitoring the concentrations of CO, CH4, CO2 and O2 during devolatilization and char combustion. Single fuel particles (4–6 mm diameter, 55 mm in length) were positioned in the freeboard of a laboratory-scale fluidized bed combustor. The superficial velocity was 0.3 m s−1. Tunable diode laser absorption spectroscopy was used to investigate in situ the concentration histories of the evolving species CO and CH4. An InGaAsSb/AlGaAsSb diode laser was frequency tuned around 2.3 µm at 300 Hz and traversed the reactor directly above the particle. This enabled for the first time, to the knowledge of the authors, the accurate measurement of species concentrations close to the surface of a burning particle. The influence of the oxygen partial pressure (5, 10, 15, 21 kPa), the bed temperature (700, 800, 900oC), the distance of the laser beam from the particle (4, 10, 21, 31 mm) and hence the residence time (12, 30, 60, 90 ms), the particle size (4, 6 mm diameter) and the fuel type were investigated by independently changing these governing parameters. Conventional methods were deployed to determine CO, CO2 and O2 in the exhaust gas. The evolving CO could be tracked down to 12 ms after its generation. Biomass was found to produce four times as much CO as coal. The CO/CO2 ratio was found to be about five times higher for beech wood (a typical hardwood) than for fir wood (a typical softwood). The comparison of the in situ results with conventionally measured concentrations showed that the CO is normally underestimated during devolatilization and overestimated during char combustion. The discrepancy was attributed to more efficient degradation mechanisms for CO during devolatilization.