Devolatilization Characteristics of Coal Particles Heated with a CO_2 Laser Controlled by Double Shutters: A Simulation Investigation

摘要

An empirical model was established based on measurements of devolatilization characteristics of coal particles (18.7%, 32.7%, and 43.0% VM; 0.14, 0.20, and 0.30 mm, respectively) heated at a heating rate of 10~3- 10~4 K/s by a well-controlled CO_2 laser with double shutters and a high-accuracy two-color pyrometer. The conclusions obtained are as follows: (1) particle temperature (T_p), volatile yield (V), heating rate (HR), and in situ energy density flux (F_(cd)) during devolatilization can be well-predicted by solving an energy conservation equation and a devolatilization rate equation with two competing reaction rates; (2) the pre-exponential factor and activation energy of the two reactions are A, = (1.7249-1.8936) × 10~2 s~(-1), E_1 = (2.6248-3.5447)× 10~4 J/mol, A_2 = 2.6× 10~6 s~(-1), and E_2 = 1.6740× 10~5 J/mol, respectively, which are obtained by fitting our experiment data; (3) the final volatile yield (V_f) is dependent on the laser intensity (Q_L), the particle size (D_n), and the proximate volatile matter content ( V_o), and it can be well-predicted by a regressive equation of V_f with Q_L, D_n, and V_o; (4) a modified Merrick's heat capacity correlation can be used to predict the temperature history of coal particles heated at a rate of 10~3-10~4 K/s with excellent agreement; (5) the heats of devolatilization, which are given as -0.5244, -0.6629, and - 0.7348 MJ/kg for the three coals used in this study, are suitable values for predictions; (6) the sum of the heat of devolatilization (ΔH_d) and energy loss per unit mass volatile yield (ΔH_(vl)), which can be represented as ΔH_d + Δ_H_(vl) = -0.01046 MJ/kg, is a suitable value for predicting particle temperatures and volatile yields for all three coals; (7) the measured histories of weight loss are imperative for predicting the temperature and the devolatilization kinetics of coal particles heated at a high heating rate; and (8) the swelling-shrinking ratios, absorptivity, emissivity, thermal capacity, and heat of devolatilization of coal particles at high heating rates should be measured for better predictions.