Etude de la combustion de gaz de synthèse issus d'un processus de ...

Experimental and numerical laminar syngas combustion
Tendency observed on the unstretched burning velocity is in agreement with the heat
of reaction of the syngas composition. The higher heat value is associated with the
higher amount of H 2 and lower dilution by N 2 and CO 2 in the syngas composition. The
incomplete combustion and ignition difficulty of the typical fluidized bed syngas
composition makes it a less candidate to stationary power applications without addition
of another fuel. Markstein numbers shows that syngas-air flames are generally
unstable. Karlovitz numbers indicates that syngas-air flames are little influenced by
stretch rate. Based on the experimental data a formula for calculating the laminar
burning velocities of syngas–air flames is proposed.
tel-00623090, version 1 - 13 Sep 2011
The laminar burning velocity of typical syngas compositions is not dissimilar to that of
methane especially the downdraft syngas case, although somewhat slower than
propane. This could be due to the syngas stoichiometric air–fuel ratio that is ten times
lower than the methane air-fuel ratio and more than twenty times in the case of
propane. Thus, the energy content per unit quantity of mixture (air + fuel) inducted to
the chamber is only marginally lower when using syngas, compared with the
corresponding common gas fuels. The values of laminar burning velocity reported for
syngas (28H 2 -25CO-47N 2 ) can be seen to be higher than those obtained for the
syngas in the current study; this is associated with the lower H 2 content, greater N 2
content and the presence of CO 2 in the typical syngas compositions. The simulated
syngas mixture that better matches the magnitude of laminar burning velocity for the
typical syngas compositions is the mixture comprising 5%H 2 /95%CO.
Base on the experimental data some empirical formulations of the burning velocities
have been establish for pressure range 0.75-20 bar and temperature range 293K-
450K.
The numerical simulation code of the laminar spherical combustion allows the pressure
and wall heat flux reproduction under a various conditions of pressure, equivalence
ratio and fuel. Quenching distance correlations for typical syngas-air flames were
developed tanks to this code. One can conclude that quenching distance decreases
with the increase of pressure and is higher for lower heating value mixtures.
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