INSTITUTE OF PHYSICS PUBLISHING MEASUREMENT SCIENCE AND TECHNOLOGY Meas. Sci. Technol. 13 (2002) 1545–1551 PII: S0957-0233(02)36475-0 In situ laser measurements of CO and CH 4 close to the surface of a burning single fuel particle M Lackner 1,3 , G Totschnig 1 , F Winter 1 , M A Maiorov 2 , D Z Garbuzov 2 and J C Connolly 2 1 Institute of Chemical Engineering, Vienna University of Technology, Getreidemarkt 9/166, A-1060 Vienna, Austria 2 Princeton Lightwave, Inc., 2601 US Rte 130 South, Cranbury, NJ 08512, USA E-mail: lackner@mail.zserv.tuwien.ac.at Received 1 May 2002, in final form 13 June 2002, accepted for publication 24 July 2002 Published 4 September 2002 Online at stacks.iop.org/MST/13/1545 Abstract The combustion behaviour of three different fuels, bituminous coal, beech wood and fir wood, was investigated by monitoring the concentrations of CO, CH 4 , CO 2 and O 2 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 CH 4 . 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, 900 ◦ C), 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, CO 2 and O 2 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/CO 2 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. Keywords: coal, biomass, in situ laser spectroscopy, concentration measurements, devolatilization, char combustion, carbon monoxide, methane 1. Introduction Rapid and accurate in situ species concentration measurements are a competitive tool compared to traditional methods of capturing and externally analysing the interesting species. 3 Author to whom any correspondence should be addressed. With respect to in situ determinations, the use of extractive probes in conjunction with non-dispersive infrared analysers yields increasingly deviating, faulty concentration values with rising temperature. The discrepancy in the values for sampled and directly determined CO has been found to reach one order of magnitude for different designs and conditions comparable 0957-0233/02/101545+07$30.00 © 2002 IOP Publishing Ltd Printed in the UK 1545