Steady-state multiplicity, flashback, and control issues in CH4 radiant burners

Abstract

Methane is widely employed as a source of energy in combustion systems. Among the currently available technologies, radiant heaters offer high thermal efficiency and low environmental impact in comparison with atmospheric burners. The present work deals with the modeling of methane combustion in a noncatalytic metal fiber burner, represented by means of one-dimensional transient equations. The model accounts for a detailed reaction mechanism, radiation within the porous medium, longitudinal heat and mass transfer. After its validation, the model was employed to analyze a typical stability problem that affects these systems: under given operating conditions (low specific power inputs and excess of air) the occurrence of flashback may in fact preclude the safe operation of the system. As a consequence of energy radiation in the upstream direction, the burner upstream surface and the plenum chamber might become hot enough to heat in turn the gas feedstock, thus eventually determining flashback. In this paper, the mechanism of flashback is numerically investigated as a function of the burner structure and operating conditions by means of a model analysis so as to single out regions of flashback occurrence and a criterion for safe operation. Finally, some guidelines are outlined for a cheap and effective control of the system, paving the way for possible improvement of currently adopted control systems. © 2004 American Institute of Chemical Engineers AIChE J, 50: 2276–2286, 2004