Study of transport processes and reaction kinetics in coal devolatilization under very high heating rate conditions.

摘要

A novel technique using a CO{dollar}sb2{dollar} laser capable of heating single carbonaceous particles in the 60-120 {dollar}mu{dollar}m size range to a temperature in the 1200-2000 K range at a heating rate in excess of 10{dollar}sp4{dollar} K/s magnitude was developed. The evolved products were trapped by an automatic vapor-sampling inlet, separated by a gas chromatography column and analyzed by a mass spectrometer. The temperature history of the heated particles was recorded using a home-built dual-wavelength pyrometer. Recorded temperature histories were validated by a transient heat transport model. The heat transport model was used to estimate intraparticle temperature gradients. The evolved product profiles were used to construct the yield curves. To investigate the effect of porosity on product release rates, polystyrene, doped in porous Spherocarb particles and coated on nonporous Glassy Carbon particles (both 80 {dollar}mu{dollar}m diameter spherical carbonaceous particles), was thermally degraded by the CO{dollar}sb2{dollar} laser (by heating to a temperature in the 1400-1600 K range at 10{dollar}sp5{dollar} K/s). The styrene yield was compared with predictions from a 1{dollar}sp{lcub}rm st{rcub}{dollar} order decomposition kinetics model. Although the model predicted the styrene yields from polystyrene/Glassy Carbon successfully, it predicted five times faster styrene release rates from polystyrene/Spherocarb, Investigation of secondary pyrolysis products of polystyrene shows that higher yields of these products were observed from polystyrene/Spherocarb when compared to those from polystyrene/Glassy Carbon. Both of these results point toward longer residence time of products in Spherocarb, indicating the presence of pore diffusion limited evolution rates.; Three aerodynamic size classified coal types, namely, Pittsburgh # 8, Illinois # 6 and Lower Wilcox with size range of 90-110 {dollar}mu{dollar}m, were heated to a temperature in the 1500-2000 K range at an initial heating rate of 10{dollar}sp5{dollar} K/s approximately. The product yield profiles constructed were compared to tar yield predictions of the Functional Group-Depolymerization Vaporization Crosslinking (FG-DVC) and the Chemical Percolation Devolatilization (CPD) model. The models show faster tar yield rates than observed. The slower observed rates may be a result of transport limited evolution processes at the high heating rates and particle sizes used in the experiments.