Biomass-derived fast pyrolysis liquid,
also called bio-oil (FPBO),
can replace petroleum fuels in thermal devices, but several undesirable
properties hinder its widespread application. This paper aims to improve
these properties and quantify their effect on its combustion performance.
In this study, higher quality bio-oil having similar viscosity and
surface tension as FPBO was obtained through the thermo-catalytic
reforming bio-oil (TCRBO) process. The effect of fuel chemical composition,
thermogravimetric analysis (TGA) residue, fuel volatility, heating
value, water content, solid content, and ash content was examined
in a 10 kW spray burner. Gas phase emissions and particulate matter
(PM) were also measured and compared to its operation on fuel oil
#2 for which diesel was used. TCRBO ignited irrespective of the primary
air preheat temperature, and its evaporation characteristics (i.e.,
TGA residue of less than 3%) were more like diesel. TCRBO does not
display any flash atomization. Both FPBO and TCRBO displayed coking
potential; however, for TCRBO, no coking was observed if the primary
air was heated above 110 °C. FPBO droplets were larger in size
(∼100 μm) and could not achieve complete burnout due
to increasing emissions. TCRBO exhibits lower emissions than FPBO
at any given operating point, primarily due to better atomization
achieved due to its higher fuel heating value, which reduced the fuel
flow rate by almost 40%. FPBO resulted in the highest PM emissions,
which can be attributed to the formation of secondary char particles.
Higher fuel ash content also contributed to the PM emissions. The
reduction in fuel water content (i.e., ∼2 wt %) made the TCRBO
flame less susceptible to blow out, and a stable flame was observed
without the pilot flame. Swirl and pilot were necessary to stabilize
the FPBO flame. The TCRBO’s higher fuel nitrogen content significantly
increased its NO
x
emissions. Overall,
thermo-catalytic reforming significantly improved the combustion characteristics
of pyrolysis bio-oil. Although TCRBO was obtained from lower quality
feedstock (e.g., sewage sludge), its superior combustion performance
is attributed to the ability of the TCR process to produce higher
quality liquid fuels from various biomass sources.