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

Experimental and numerical laminar syngas combustion
Similar curves are obtained for all syngas compositions under study being shifted by a
value around 0.06 m/s in average between downdraft and updraft compositions and
about 0.1 m/s between fluidized and updraft syngas. These results could be endorsed
to:
tel-00623090, version 1 - 13 Sep 2011
- the heat value of the syngas compositions. This value varies from 5.4 (fluidized
bed syngas) to 5.7 MJ/m 3 (downdraft syngas), which is in agreement, however
not proportional to the burning velocities.
- the amount of H 2 , due to its high reactivity, is a very important parameter to be
considered. As shown in the Table 3.1 the amount of H 2 of fluidized bed syngas
(9% by volume) is very close to the updraft syngas (11% by volume) and about
half of the downdraft syngas (17% by volume). This explains the lowest burning
velocity of the fluidized bed syngas and the highest shift when compared to
downdraft syngas. However, the close amount of H 2 between fluidized bed and
updraft syngas is not reflected in the burning velocity values shown in the Fig.
4.19.
- and the amount of dilution by N 2 and CO 2 in the fuel gases H 2 -CO-CH 4 that
compose the typical syngas mixtures. Again, fluidized bed syngas is he highest
diluted syngas (70% by volume), being updraft and downdraft less diluted with
61% and 62% by volume, respectively. Therefore, the highest shift in burning
velocity of fluidized bed syngas could be explained by its highest dilution.
Based on the experimental data the correlations of unstretched laminar burning
velocities as function of equivalence ratio can be fitted as follows:
S =− 0.8125φ + 1.6375φ
− 0.5725 (Updraft) (4.10)
0 2
u
S =− 0.7313φ + 1.5428φ
− 0.4924 (Downdraft) (4.11)
0 2
u
S =− 0.7500φ + 1.5450φ
− 0.6210 (Fluidized) (4.12)
0 2
u
for updraft, downdraft and fluidized bed syngas–air mixture combustion, respectively.
Information for fluidized syngas is limited due to ignition difficulties of this mixture.
Formula (4.12) was fitted for equivalence ratios between 0.8 and 1.0.
4.1.1.5 Karlovitz and Markstein numbers
Figures 4.20-4.22 illustrates the evolution of the normalized laminar burning velocity,
S u /S 0 u, as a function of the normalized stretch rate, the Karlovitz number for typical
syngas compositions at various equivalence ratios. From Fig. 4.20 one can see that the
106