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

Chapter 4
CHAPTER 4
EXPERIMENTAL AND NUMERICAL LAMINAR SYNGAS
COMBUSTION
Syngas obtained from gasification of biomass is considered to be an attractive new
fuel, especially for stationary power generation.
tel-00623090, version 1 - 13 Sep 2011
As reported in chapter 2 there is considerable variation in the composition of syngas
due to various sources and processing methods. Continuous variation in the
composition of the generated syngas from a given gasification source is another
challenge in designing efficient end use applications such as burners and combustion
chambers to suit changes in fuel composition. Designing such combustion appliances
needs fundamental understanding of the implications of syngas composition for its
combustion characteristics, such as laminar burning velocity and flammability limits.
Laminar burning velocity for single component fuels such as methane (Hassan et al.,
1998; Gu et al., 2000); and hydrogen (Aung et al., 1997; Bradley et al., 2007) are
abundantly available in the literature for various operating conditions. Burning velocity
studies on H 2 –O 2 –inert (such as N 2 , CO 2 , Ar, and He) are also available (Aung et al.,
1998; Lamoureux et al., 2003). Some studies on burning velocities are also available
for binary fuel mixtures such as H 2 –CH 4 (Halter et al., 2005; Coppens et al., 2007), and
H 2 –CO (Vagelopoulos and Egolfopoulos, 1994; Sun et al., 2007). Vagelopoulos and
Egolfopoulos, (1994) measured burning velocities of H 2 –CO mixtures using a counter
flow flame technique and reported that addition of 6% or more hydrogen to H 2 –CO
made the response of the H 2 –CO mixture more similar to the kinetics of hydrogen than
to that of CO. McLean et al., (1994) measured unstretched laminar burning velocities
for 5%H 2 – 95%CO and 50%H 2 – 50%CO mixtures using constant-pressure outwardly
propagating spherical flames to evaluate the rate of the CO + OH reaction. Brown et
al., (1996) reported flame stretch effects on burning velocities of H 2 –air, 50%H 2 –
50%CO–air and 5%H 2 –95%CO–air mixtures under atmospheric condition. Values of
Markstein length for 50%H 2 –50%CO–air mixtures were found to be very similar to
those of pure H 2 –air mixtures. It was concluded that H 2 was the dominant species and
governed the Markstein length behavior for the 50% H 2 – 50% CO–air mixture. Hassan
et al., (1997) reported the effects of positive stretch rate on burning velocities of H 2 –CO
mixtures under different mixture conditions by varying the H 2 fraction in the fuel from 3
to 50% by volume using constant-pressure outwardly propagating spherical flames.
85