Measurement and modeling of individual carbonaceous particle temperature profiles during fast CO 2 laser heating : Part 1. Model char

Abstract

To investigate the chemical kinetics of coal pyrolysis under pulverized coal combustion conditions (coal particles of up to 100 μm diameter heated in excess of 10 5 K/s to 1500–2000 K), it is imperative to characterize the time–temperature profile and intraparticle temperature gradients during the heating phase. A CO 2 laser pyrolysis system with two-color micropyrometry system was developed to heat single particles in the 50–120 μm range to 1400–1800 K in 50 ms and measure the time–temperature profile. Before attempting to investigate coal particles, inert spherical carbonaceous particles (i.e. Spherocarb) were selected to investigate system performance and reliability. Part 1 of the article details the experiments on Spherocarb. Spherocarb particles of 80, 100 and 120 μm diameter, respectively, were irradiated with 10.6 μm wavelength, 30 ms duration CO 2 laser pulses, at two different intensity levels and their temperature histories were measured with a specially built two-color micropyrometry system. A heat transport model was used to predict the particle surface temperature histories. The density of the porous Spherocarb particles (one value used for all the cases), as well as the total laser flux absorbed, were used as fitting parameters, thus allowing numerical extraction of absorbed laser power values as a function of particle size. These parameters can be used to model the temperature histories of similar size coal particles. Moreover, this analysis can also help to evaluate the reliability of the two-color micropyrometer system. Based upon the modeling results an estimation of intraparticle temperature gradients were made.