Combustion Characteristics of Carbon:  Dependence of the Zone I−Zone II Transition Temperature (T_c) on Particle Radius

Abstract

Reformulation of the standard equations governing internal reaction of carbon, used to predict the Zone I−Zone II transition temperature, T c, shows that T c is, primarily, an inverse function of particle radius (a). The expression obtained has the form: log(a) ∝ (1/T c). This result is supported by the (limited) experimental data available. The numerical values also show that, for particles of pulverized coal size, the values of T c are in the flame temperature range, thus possibly allowing a discontinuous drop in reaction rate toward the end of a flame; this has relevance to increased LOI due to staging for NOX control. The results also permit evaluation of the internal diffusion coefficient indicating that internal reaction most probably involves only the macropores, and total internal surface area measurements are probably irrelevant in determining reaction rates.

A semi-detailed kinetic model of char combustion with consideration of thermal annealing

“…This is reflected by the larger value of the particle effectiveness factor which approaches values of g ffi 0.4. This feature is consistent with the observation of Regime I transition in the late stage of particle burn off discussed by Essenhigh and coworkers [34] and Hurt and coworkers [6], a feature which is, in turn, closely associated with the particle near-extinction phenomenon that has been frequently observed in entrained flow combustion [6,33] and to the change in apparent reaction order with respect to oxygen concentration [35,36].…”

Effect of different fuel NO models on the prediction of NO formation/reduction characteristics in a pulverized coal combustion field

“…Cases investigated in this study. [45] Modified TDP model [43] Combined model of kinetics and eddy dissipation [46] Field et al [47] Essenhigh et al [48] Lagrangian Stochastic [49]…”

Simulation Study on the Reaction-Diffusion Coupling in Simple Pore Structures

“…To study the reaction-diffusion processes within the complicated porous media, previous models have mostly based on dimensionless groups, such as Damköhler number, Thiele modulus, and the corresponding external/internal effectiveness factors, − which were defined based on Fick’s diffusion law using empirical effective diffusion coefficients and idealized pellet shapes. As gas diffusion in complicated pores does not follow Fick’s law, and actual pore microstructures are not considered directly, , these models and indexes, though helpful, are often used on a phenomenological and qualitative basis. , …”

“…As gas diffusion in complicated pores does not follow Fick's law, 17 and actual pore microstructures are not considered directly, 23,24 these models and indexes, though helpful, are often used on a phenomenological and qualitative basis. 26,27 Since the pore structure in actual porous media is too complicated to be described integrally and elaborately, it is meaningful to first focus on some typical structures at microscale and try to characterize the coupling of reaction and diffusion in a more quantitative way. For this purpose, molecular dynamics (MD) simulation can be used as a powerful tool in that the complicated diffusion and reaction processes are reproduced by the basic motion of the microscopic elements, rather than numerically computed from their material properties or statistical correlations, which are hard to obtain at this scale.…”