around 9ppm. But we also know that these
requirements are typically enacted gradually.
Switching to operating at 9 ppm NOx now
for regulations that might not come into
effect for 5 or 10 years means incurring a
lot of unnecessary operating costs in the
meantime. At the same time, many old
burners need to be replaced -- and if
you’re going to replace one, shouldn’t
you replace it with an ultra-low NOx
model so that you’re not facing another
replacement in a few years when regulations change?
The way out of this conundrum is the
latest breed of low-NOx burners that offer
configurable NOx emissions concentrations.
These now exist in both FGR and lean premix forms. In the case of the FGR configurable burners, the amount of flue gas that
gets recirculated is programmable over a
wide range, and down to the lowest theoretically possible levels. In the case of the
lean premix configurable burners, that fuel-to-air ratio is configurable, from super lean
to very rich. These configurable systems are
the best option for areas that don’t yet face
the strictest NOx standards. By switching
to one of these burners, NOx emissions can
be set to exactly meet current NOx regulations, while maximizing efficiency. When
and if these standards change in the future,
the burner can be simply reconfigured to
meet the new requirements.
RETROFITTING FOR
BIOFUEL: THE NEW
FRONTIER OF LIQUID
WOOD
Along with a trend towards lower NOx
emissions, there is a trend toward lower
carbon footprints and the use of renewable
biofuels. Until recently, the only viable op-
tion for boilers was solid-mass biofuels -- in
particular, wood pellets or chips.
The wood for these fuels can be sustain-
ably sourced from tree farms, and replanting
the trees used to produce the fuel can mostly
offset the carbon emitted from burning
them. What has limited their widespread
adoption, however, are the significant costs
of switching to such a system. An entirely
new boiler is generally required to enable
burning solid chunks of fuel as opposed to
burning liquid or gas. The solid biomass
fuel will need to be burned over a grate or
in a fluidized bed boiler, which is signifi-
cantly different from a standard firetube or
watertube boiler. Additionally, burning solid
biomass produces much more ash, and the
burner has to be equipped so that this can
be regularly removed from the boiler. All
of this means that switching to solid
biomass fuels can easily exceed $20M in
upfront investment. That type of investment
is generally only made sense for institutions
with very strict carbon or renewable com-
mitments (for example, universities which
adopted strict carbon commitments under
the American College & University Presi-
dents’ Climate Commitment).
However, it is now possible to retrofit
for biofuel because liquid wood, (
renewable fuel oil or bio-oil) has become viable
for use in existing gas or oil boilers for the
first time. Liquid wood is produced by
heating wood in the absence of oxygen, in
excess of 500º Celsius. Because there is no
oxygen, the wood does not combust: it first
becomes charcoal, and then further decomposes into gas and liquid. When heated
above 700º C, pyrolysis occurs very quickly
and the yield will be around 60% bio-oil,
20% char, and 20% “syngas.”
From the perspective of the boiler, this
bio-oil is essentially the same as traditional fuel oils or natural gas. Burning the