Experimental Investigations of Lean Stability Limits of a Prototype Syngas Burner for Low Calorific Value Gases

The lean stability limit of a prototype syngas burner is
investigated. The burner is a three sector system, consisting
of a separate igniter, stabilizer and Main burner. The
ignition sector, Rich-Pilot-Lean (RPL), can be operated with
both rich or lean equivalence values, and serves to ignite the
Pilot sector which stabilizes the Main combustion sector.
The RPL and Main sectors are fully premixed, while the
Pilot sector is partially premixed. The complexity of this
burner design, especially the ability to vary equivalence
ratios in all three sectors, allows for the burner to be
adapted to various gases and achieve optimal combustion.
The gases examined are methane and a high H2 model
syngas (10% CH4, 22.5% CO, 67.5% H2). Both gases are
combusted at their original compositions and the syngas
was also diluted with N2 to a low calorific value fuel with a
Wobbe index of 15 MJ/m3. The syngas is a typical product of
gasification of biomass or coal. Gasification of biomass can
be considered to be CO2 neutral. The lean stability limit is
localized by lowering the equivalence ratio from stable
combustion until the limit is reached. To get a comparable
blowout definition the CO emissions is measured using a
non-dispersive infrared sensor analyzer. The stability limit is
defined when the measured CO emissions exceed 200 ppm. The stability limit is measured for the 3 gas mixtures at
atmospheric pressure. The RPL equivalence ratio is varied
to investigate how this affected the lean blowout limit. A
small decrease in stability limit can be observed when
increasing the RPL equivalence ratio. The experimental
values are compared with values from a perfectly stirred
reactor modeled (PSR), under burner conditions, using the
GRI 3.0 kinetic mechanism for methane and the San Diego
mechanism for the syngas fuels.