Combustion Strategies for Syngas and High-Hydrogen Fuel

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6.0.2
6.0.2 Combustion Strategies for Syngas and High-
Hydrogen Fuel
The technical challenges surrounding syngas and
hydrogen fuel combustion have been outlined in
section 3.1. Given the issues presented there,
various options can be considered for combustor
design and operation. First, it is critical to define
the type of combustion system that will be used.
There are two broad categories: diffusion flame
combustors, and premixed combustors. These are
described below, but before discussing the
combustion strategies, it is useful to review how
NOx pollutants are formed.
NOx formation
There are several routes to form NOx
pollutants and these may be broadly catalogued as
thermally-generated, flame-generated, or fuel-
bound NOx. Different authors use different names
to catalogue these mechanisms and there is still
continuing research to understand the most
prominent mechanisms at ultra-low NOx
conditions. For example, in hydrogen fueled
systems, the prominence of H radicals may
contribute to NOx in a manner that is different than
in systems fueled by natural gas [1].
Thermal NOx is formed by oxidation of
nitrogen in air and requires sufficient temperature
and time to produce NOx. A rule of thumb is that
below approximately 1700K, the residence time in
typical gas turbine combustors is not long enough to
produce significant thermal NOx. Where
temperatures higher than 1700K cannot be avoided,
it is necessary to limit residence time to control NOx
formation, which favors very short combustor
designs. Thermal NOx production also increases
with the square root of operating pressure, making it
more difficult to reduce in higher-pressure
aeroderivative gas turbines.