Search

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 105 K/s to 1500–2000 K), it is imperative to characterize the time–temperature profile and intraparticle temperature gradients during the heating phase. A CO2 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 CO2 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. [Copyright &y& Elsevier]

In part 1, we discussed the temperature profiles of laser heated spherical carbonaceous particles along with the temperature modeling. In this paper, we perform the same set of experiments with selected coal particles. Coals of three different ranks (i.e. degree of coalification) represented by three different particle sizes (80, 100, and 120 μm), with and without aerodynamic size classification, were analyzed under the same set of experimental conditions. The temperature profiles were modeled using a heat transport model modified to include chemical kinetics (based on the FG-DVC model). Non-aerodynamically size-classified particles displayed better model prediction when laser heated in nitrogen atmosphere compared with heating in air. Best model predictions, however, were obtained in the case of aerodynamically size-classified particles heated under nitrogen atmosphere. [Copyright &y& Elsevier]