Emissions and properties of Bio-oil and Natural Gas Co-combustion in aPilot Stabilised Swirl Burner
by
Dylan Kowalewski
A thesis submitted in conformity with the requirementsfor the degree of Master of Applied Science
Graduate Department of Mechanical and Industrial EngineeringUniversity of Toronto
c© Copyright 2015 by Dylan Kowalewski
Abstract
Emissions and properties of Bio-oil and Natural Gas Co-combustion in a Pilot Stabilised Swirl Burner
Dylan Kowalewski
Master of Applied Science
Graduate Department of Mechanical and Industrial Engineering
University of Toronto
2015
Fast pyrolysis oil, or bio-oil, has been investigated to replace traditional fossil fuels in industrial burners.
However, flame stability is a challenge due to its high water content. In order to address its instability,
bio-oil was co-fired with natural gas in a lab scale 10kW swirl burner at energy ratios from 0% bio-oil to
80% bio-oil. To evaluate the combustion, flame shape, exhaust and particulate emissions, temperatures,
as well as infrared emission were monitored. As the bio-oil energy fraction increased, NO emissions
increased due to the nitrogen content of bio-oil. CO and particulate emissions increased likely due to
carbonaceous residue exiting the combustion zone. Unburnt Hydrocarbon (UHC) emissions increased
rapidly as combustion became poor at 60-80% bio-oil energy. The temperature and infrared output
decreased with more bio-oil energy. The natural gas proved to be effective at anchoring the bio-oil flame
to the nozzle, decreasing instances of extinction or blowout.
ii
Dedication
For Marianne, without whom this would not have happened
iii
Acknowledgements
I would like to acknowledge Prof. M. J. Thomson and Prof. H. Tran for their guidance and support.
I would like to thank Y. Afarin, S. Zadmajid and V. Sookrah for their assistance in running these
experiments. I would like to thank the Surface Ontario Lab for providing the photomicroscope to
examine the particles contained in the bio-oil. Financial support for this work was provided by NSERC
and BioFuelNet Canada. Finally, I would not have been able to complete this without the support of
my friends and family.
iv
Contents
1 Introduction 1
1.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Objective . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2 Literature Review 3
2.1 Bio-Oil Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.2 Bio-Oil Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.3 Bio-Oil Upgrading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.3.1 Physical Bio-Oil Upgrading Methods . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.3.2 Chemical Bio-Oil Upgrading Methods . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.4 Bio-Oil as a Fossil Fuel Replacement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.5 Bio-Oil Combustion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3 Apparatus Design 8
3.1 Burner Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.2 Energy Throughput . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.3 Variable Swirl Generator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.4 Fuel Atomizing Nozzle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.4.1 Natural Gas System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.5 Pilot Flame System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.5.1 Pilot Flame Alignment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
4 Experimental Methodology 13
4.1 Experimental Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
4.2 Fuel Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
4.2.1 Bio-Oil - Natural Gas Mixtures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
4.2.2 Bio-Oil Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
4.2.2.1 Thermogravimetric Analysis . . . . . . . . . . . . . . . . . . . . . . . . . 14
4.2.2.2 Photomicroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
4.2.3 Bio-Oil Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
4.2.4 Natural Gas Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
4.3 Gas Phase Emission Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
4.3.1 Unburnt Hydrocarbon Emissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
4.3.2 Detailed Exhaust Gas Composition . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
v
4.3.3 Equivalence Ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
4.4 Flame Visualization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
4.5 Flame Infrared Emission Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
4.5.1 Infrared Background Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
4.6 Burner Temperatures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
4.7 Particulate Measurement and Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
4.7.1 Isokinetic Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
4.7.2 Particulate Sampling System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
4.7.3 Particulate Sample Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
4.8 Test Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
4.8.1 Burner Start-up and Shutdown . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
4.8.2 Gas Phase Emissions Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
4.8.3 Particulate Emissions Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
4.8.4 Infrared Emissions Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
4.8.5 Flame Imaging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
5 Results and Discussion 23
5.1 Fuel Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
5.2 Base Point Operation and Repeatability . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
5.3 Reaction Zone Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
5.4 Flame Images . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
5.5 Particulate and Gas Phase Emissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
5.5.1 Exhaust Composition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
5.5.2 Particulate Emissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
5.6 Near Infrared Emissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
5.7 Effect of Natural Gas on Bio-Oil Combustion . . . . . . . . . . . . . . . . . . . . . . . . . 34
6 Conclusions and Recommendations 36
6.1 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
6.2 Implications for Industrial Burners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
6.3 Recommendations and Future Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
6.3.1 Burner Modifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
6.3.2 Experimental Methodology Improvements . . . . . . . . . . . . . . . . . . . . . . . 38
6.3.3 Future Bio-Oil Combustion Research . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Bibliography 39
Appendix A Fuel Flow Rate Calculation 43
Appendix B Peristaltic Pump Flow Rate Calibration 44
vi
Chapter 1
Introduction
1.1 Motivation
There are many industrial processes that require heat that currently derive this heat with fossil fuels.
However, due to liquid fuel prices and environmental considerations, there is an interest to replace a
portion of these fossil fuels with biofuels. Biomass is an important fuel world wide, making up 12% of
the worlds energy[1]. However, for many applications, a solid fuel is inappropriate, either due to storage
or incompatibility. A biomass derived liquid fuel could act as a drop in replacement for fossil fuels.
Biomass can be converted to liquid through the fast pyrolysis process[2]. The biomass is first finely
ground, then heated in the absence of oxygen at a high temperature. The vapours that come off the
biomass are then condensed, yielding fast pyrolysis liquid, or bio-oil. Bio-oil holds many advantages over
raw biomass, which is often used in residential heaters[3]. Primarily, due to being liquid, bio-oil is more
energy dense and is easier to transport and store. Furthermore, bio-oil can be produced using the waste
wood produced in the forestry and pulp and paper industries. Because of this, compared to other crop
based biofuels such as ethanol, the biomass used in bio-oil production does not need to be grown on land
that could otherwise be used for food agriculture[4].
To show how bio-oil can be used in furnaces and burners in industry, previous work has examined its
performance when blended with ethanol[5]. However, for industries in most parts of the world, ethanol is
too expensive to be used in heating applications[6]. However, in these studies, the ethanol was found to
improve combustion due to its low viscosity and ease of ignition[7]. A more viable solution would utilise
bio-oil as-is as a partial replacement for a fossil fuel. In this way, the fossil fuel provides the ignition
energy required to stabilise the bio-oil combustion. However, it is important to understand what effect
the change in fuel will have on the combustion.
Specifically, lime kilns in the pulp and paper industry offer a unique opportunity for the use of bio-oil.
Capable of burning a wide variety of fuels from natural gas to crushed petcoke, lime kilns are the only
part of the pulp production process that uses fossil fuels. Natural gas use in lime kilns has increased
recently as the fuel cost has decreased. Replacing some of this natural gas with bio-oil can help pulp
mills run more carbon neutral and have less impact on global warming. Furthermore, because pulp
mills often have waste wood on site, producing bio-oil at the mill eliminates the need to transport large
amounts of fuel, adding to the appeal.
1
1.2 Objective
The overall objective of this study is to investigate the combustion properties of bio-oil when it is
co-fired with natural gas. To achieve this, a 10 kW swirl burner is used and modified to atomize the
bio-oil with natural gas. The total energy of the system is kept constant and is run with different ratios
of bio-oil and natural gas to evaluate how combustion changes as more bio-oil is used. The combustion is
evaluated by looking at the gaseous (NOx, CO, unburnt hydrocarbons) and particulate emissions as well
as the near infrared heat output, flame images and temperatures. These measurements will be related
to the properties of bio-oil and the physical phenomena observed in the burner. The observations made
in this study will provide insight to how bio-oil and natural gas can be used in industrial burners to
reduce their use of fossil fuels.
2
Chapter 2
Literature Review
2.1 Bio-Oil Production
Bio-oil is produced in a fast pyrolysis process by burning biomass at high temperature in the absence
of oxygen[2]. As the biomass breaks down and thermally cracks, vapours are given off that can be
condensed into a liquid fuel. The process is run at high temperature to maintain a low vapour residence
time to prevent decomposition of the hydrocarbons so the remain condensable[2]. In addition to bio-
oil, char and non-condensable gases are also produced which can provide the energy needed to dry the
biomass as well as run the pyrolysis process[8]. By using these excess products to run the plant, there
are very few waste products in bio-oil production and the need for energy input from fossil fuels can be
minimized. Figure 2.1 shows a typical fast pyrolysis process schematic.
Figure 2.1: Fast pyrolysis plant schematic[8]
3
Chapter 2. Literature Review 4
The process used to produce bio-oil can be controlled to improve the quality of the fuel produced.
Firstly, by drying the feedstock as much as possible, the water content of the produced bio-oil can be
minimized [2]. However, it is important to note that the water contained in bio-oil reduces its viscosity,
making it easier to pump[5]. Secondly, the char that is produced in the pyrolysis process acts as a
catalyst for thermal cracking[9]. If the char is not separated from the bio-oil quickly, this cracking can
increase the amount of non-condensable gases produced, reducing conversion efficiency. Furthermore,
char remaining in the final product increases fuel aging caused by polymerization, introducing storage
challenges[10]. Typical bio-oil production systems can convert up to 70 wt% of the biomass to bio-oil.
2.2 Bio-Oil Properties
Table 2.1 shows the typical properties of bio-oil from literature as well as the requirements according
to the ASTM D7544 standards. It is important to note that the properties of bio-oil vary based on the
feedstock used for its production. For example, the ash content of a bio-oil made with only core wood
will be lower than that of a bio-oil that is made using bark.
Table 2.1: Typical range and ASTM D7544 standard properties of bio-oil [11, 12, 13, 14, 15, 16]
Parameter Units Typical Range ASTM D7544 Grade GWater Content wt% 15-30 30
Viscosity cSt@40◦C 10-100 125Acidity pH 2-3 ReportDensity kg/L 1.2 1.1-1.3
Solids Content wt% 0.2-1 2.5Ash Content wt% 0-0.3 0.25
Carbon Content wt% 50-60 -Hydrogen Content wt% 5-7 -Nitrogen Content wt% 0-0.3 -
Sulfur Content wt% 0-0.5 0.05Oxygen Content wt% 35-40 -
LHV MJ/kg 13-18 15Flash Point ◦C 60-100 45Pour Point ◦C -40-3 -9
The typical chemical composition of bio-oil influences its combustion emissions. Because it is made
from biomass, there is a significant amount of nitrogen contained in the fuel will result in increased NOx
emissions. However, because there is typically very little sulfur in bio-oil, it does not suffer from SOx
emissions like many petroleum based fuels.
The high water content of bio-oil results in poor ignition and can cause instability during its burning.
This is compounded with the fact that a large portion of the fuel is non-volatile. For this reason, many
previous studies have used blends of bio-oil and ethanol, which adds a volatile fraction to the fuel [5].
However, in a low grade heating application, ethanol blending may be too expensive. For this reason,
using natural gas, which is often used in such applications, can help with ignition and stability[7].
Ash contained in the bio-oil results in higher particulate matter (PM) emissions during combustion.
In many applications, this may not be ideal and can cause clogging of equipment [17].
The acidity must be taken into account when designing the fuel delivery system for bio-oil. While
it will not immediately corrode steel, using stainless steel for all surfaces that come into contact with
Chapter 2. Literature Review 5
liquid bio-oil would greatly increase the life of the system.
2.3 Bio-Oil Upgrading
Because bio-oil contains many compounds such as water and ash that make it difficult to use as a
direct fossil fuel replacement, there is often a desire to upgrade it[18]. These methods can be broken
down into physical upgrading and chemical upgrading.
2.3.1 Physical Bio-Oil Upgrading Methods
Physical methods of upgrading bio-oil attempt to remove specific undesirable properties without
changing the chemical composition of the fuel. Typical methods of physical upgrading include filtering
the solids out of the bio-oil to slow down fuel aging [10] through hot gas filtration. Additionally, adding
solvents can reduce its viscosity to improve spray characteristics. Lastly, distillation can remove the
water from the bio-oil improving its heating value.
Cyclonic separation is a common method of filtration; however because cyclonic separation is not
very efficient at removing 5-10 micron particles, char remains in bio-oil filtered this way [19]. If hot
gas filtration is performed bio-oil after cyclonic separation, the remaining particles can be removed [20].
The result is a very low solids and ash bio-oil that ages more slowly [21]. It has been shown that aging
can greatly affect the combustion quality and emissions when burned at the same conditions [10]. The
drawback of hot gas filtration is that because the filter is heated from 350 ◦C to 400 ◦C, the residence
time in the reactor is increased, resulting in further thermal cracking [21][22]. While the quality of the
bio-oil produced is increased, only 40-50 wt% of the biomass is converted to bio-oil[22]. While this loss
to non-condensable gases can be recovered to run the process and dry the feedstock, if the fuel is more
expensive, it may not be viable for use in industry.
Adding a solvent to the bio-oil can help with fuel flow and improve spray characteristics. Adding
methanol has been observed to greatly decrease the rate of aging when 10 wt% is blended with bio-
oil [23]. Furthermore, the decreased fuel viscosity achieved with solvent blending improves the spray
characteristics of the fuel, improving combustion stability [5]. The main drawback of solvent blending is
the cost associated with methanol and ethanol. While methanol is produced in paper pulp production,
water and impurities must be removed [24]. Ethanol, while in some areas of the world, such as Brazil,
can be produced in large enough quantities to be used as fuel, it is typically reserved for transportation
fuel and not as an alternative to fuel oil [25]. The most viable solution would be to utilize bio-oil in an
unblended form.
Removing the water contained in bio-oil would be useful to maximize its specific heating value.
However, if the water is simply boiled off, the bio-oil will rapidly polymerize [26]. By reducing the
pressure, the temperature at which the water can be boiled off is reduced, thus minimizing the effect of
of polymerization during the distillation [27]. Vacuum distillation is often used when a solution contains
compounds that are sensitive to temperature [27]. However, the water that is contained in the bio-oil
aids in its use by reducing its viscosity. A dewatered bio-oil is very viscous and may be difficult to pump
in a burner, possibly requiring the use of a solvent. As previously discussed, this study is focused on
utilizing bio-oil without the need for solvents.
Chapter 2. Literature Review 6
2.3.2 Chemical Bio-Oil Upgrading Methods
Bio-oil can be chemically upgraded to produce a fuel that is more similar to the fuels that it is replac-
ing. The two main methods of upgrading bio-oil chemically are catalytic cracking and hydrotreating.
Catalytic cracking is a method of using a catalyst and heat to break apart high molecular weight
hydrocarbons to produce a fuel made of lower molecular weight hydrocarbons. In addition, the oxygen
contained in the fuel is removed and released as CO and CO2 [28]. The result is the removal of the water,
which contains most of the oxygen in the bio-oil. While the result is a transportation grade fuel, there
are some significant drawbacks to catalytic cracking. Because the zeolite catalyst requires a temperature
of 450 ◦C, the polymerization of the bio-oil can deactivate the catalyst over time [28]. Furthermore,
carbon released in the deoxygenation means that the conversion rate is typically poor (20-30%) [29].
Hydrotreating, or hydrodeoxygenation, addresses some of the issues with catalytic cracking. Using a
catalyst at high temperatures and pressures in a hydrogen rich environment, the oxygen is removed as
water [29]. Similar to catalytic cracking, the high molecular weight hydrocarbons are also broken down
to produce a higher grade fuel. Because the oxygen isn’t released as CO or CO2, there is a much higher
yield compared to catalytic cracking (up to 60%) [29].
These catalytic methods however both suffer from the same issues. Catalysts are typically expensive,
so chemically upgrading bio-oil is not currently the best solution to broadening its appeal. Furthermore,
this study is focused on the use of bio-oil as a replacement in low grade applications. The fuels produced
with these upgrading methods would be more suited as a replacement for transportation fuels.
2.4 Bio-Oil as a Fossil Fuel Replacement
Due to the impurities contained in bio-oil, it is not directly suitable for a replacement for transporta-
tion fuels like gasoline or diesel. This study is focused on evaluating its potential for use as a replacement
for heavy fuel oil, often used in low grade heat applications. For example, in the pulp and paper industry,
many different fuels can be used to power the lime kiln used to convert calcium carbonate (CaCO3) into
lime (CaO) [30]. There are many reasons that lime kilns are a good candidate for bio-oil use, primarily
due to other types of fuels typically used, the combustion environment and the availability of feedstock.
Rotary lime kilns are very simple combustion devices that are used to produce lime in the pulp
and paper and cement industries. Because of this simplicity, a wide variety of fuels can be used, from
natural gas to fuel oils to petroleum coke [30]. The versatility of these systems lends itself well to
adapting to different fuels as long as they can be burned via spray combustion. Furthermore, due to the
environment inside the lime kiln, the ash content of the bio-oil is not as important as it would be inside
an internal combustion engine or other combustion devices with moving parts that can get clogged with
the ash left on the walls. In a lime kiln, the mass of the ash from the bio-oil is small relative to the
inorganics contained in the lime and would therefore not impact coking inside the burner [31]. Lastly,
as with all biofuels, feedstock availability is always a concern. By using waste wood and implementing
a bio-oil reactor as part of the pulp and paper plant, not only is access to feedstock improved, but
the cost of transporting the fuel can be minimized [32]. Previous research has shown that utilizing
bio-oil in lime kilns is possible, however the heat release compared to natural gas was shown to be lower
[33]. However, this study did not investigate the synergistic effect of co-firing natural gas and bio-oil to
improve combustion.
Chapter 2. Literature Review 7
2.5 Bio-Oil Combustion
The overall combustion phenomena occurring within the spray combustion of bio-oil can be explained
by knowing what happens during the combustion of a single droplet. As the droplet of bio-oil is exposed
to the hot combustion environment, the low molecular weight volatile fraction begins burning. During
this phase of combustion, the higher molecular weight compounds at the surface of the droplet experience
polymerization [34]. As the surface of the droplet polymerizes, the pressure inside the droplet increases
due to water and volatiles boiling. The result is that the volatiles force their way out of the skin, leaving
a hollow cenosphere behind which then burns out [35]. This process is very important to understand
what occurs inside a lab scale burner. Because there is solid char remaining after the volatiles have
burned, the combustion only occurs on the surface of the char particles, so the reaction is much slower.
The most important parameter for bio-oil combustion is droplet size. While in any spray, there is
a distribution of droplet diameters, the Sauter Mean Diameter, or SMD, describes the diameter of the
droplets if they all had the same volume to surface area ratio [36]. For practical devices, this parameter
can be estimated using a variety of empirical equations, and one for air blast nozzles has been selected
for this study, shown in Equation 2.1[36], while Table 2.2 describes the variables in this equation.
SMD = 0.95[(σmL)33
ρ0.37L ρ0.30A UR](1 +
mL
mA)1.70 + 0.13(
µ2LdoσρL
)(1 +mL
mA)1.70 (2.1)
Table 2.2: Variables in SMD calculation
Variable Parameterσ Surface tensionmL Liquid mass flow ratemL Air mass flow rateρL Liquid densityρA Air densityUR Air-liquid relative velocityµL Dynamic viscositydo Discharge orifice diameter
In order to keep the bio-oil combustion the same in each test, the atomizing gas flow rate is adjusted
to keep a constant SMD. Taking the nozzle capabilities into account, an SMD of 100 µm was selected.
By keeping the droplet size constant, the size of the droplet will not influence the results.
Chapter 3
Apparatus Design
3.1 Burner Design
The apparatus used in this study is a 10 kW pilot stabilised spray burner. The burner consists of
a swirl generator, fuel nozzle, pilot flame, and the main burner section and its overall configuration is
shown in 3.1.
Figure 3.1: Overall burner configuration [5]
8
Chapter 3. Apparatus Design 9
The burner is constructed from 3.2 mm thick 316 stainless steel to prevent corrosion that may occur
if liquid bio-oil collects on the walls. The overall size of the burner is 1.2m in length and a 221 mm inner
diameter at its widest point. The nozzle is mounted such that the fuel is sprayed vertically downward.
The swirl generator is mounted to the top of the main burner section and is constructed from aluminium
and mild steel. There was no need to construct the swirl generator from stainless steel because its
components do not come into contact with the bio-oil.
In order to connect the components of the burner, flange connections are used to make maintenance
and upgrading easier. The flanges are sealed with silicone rubber gaskets rated for 260 ◦C in lower
temperature areas and with compressible graphite gaskets rated for 450 ◦C in higher temperature areas,
such as near the flame. The components of the burner are described in more detail below.
3.2 Energy Throughput
The burner is designed for a 10 kW input energy. While this is significantly lower than the typical
input energy for a lime kiln or other industrial burner, it allows for the combustion properties of bio-oil
to be studied in a lab setting without needing to store huge amounts of fuel. Furthermore, there are
currently few producers that make bio-oil in large quantities. However, by using a smaller burner, it is
possible to have custom bio-oils made to investigate the ideal properties that a bio-oil should have to be
best suited for an industrial burner.
To ensure each test run is comparable with each other, the overall input energy is kept at a constant
10 kW. So, for each test, the input energy is divided between bio-oil and natural gas by energy using the
Lower Heating Value (LHV) of each fuel. For example, in the case where 80% of the input energy comes
from bio-oil, the flow rate of the two fuels is set so that 8 kW is input from bio-oil and the remaining
2 kW is input from natural gas.
3.3 Variable Swirl Generator
At the top of the burner, the primary combustion air enters through a variable swirl generator as
shown in figure 3.2.
Chapter 3. Apparatus Design 10
Figure 3.2: Variable Swirl Generator Design
The swirl generator guides the heated primary combustion air entering the burner to impart a degree
of angular momentum, the amount of which is determined by the position of the movable blocks. Previous
research on this burner has shown the effects the degree of primary air swirl has on bio-oil combustion, so
these effects are not investigated in this study. Instead, the swirl number is set to the maximum value of
5.41, which is estimated using Equation 3.1. This value was chosen because it has been shown to produce
the most stable flames[5]. The value of the swirl produced depends on the physical characteristics of the
swirl generator which are provided in Table 3.1
S ≈ 2π
nξmsinα
cosα[1 + tanα tan(ξ/2)](ξ/ξm)
{1− [1− cosα(1 + tanα tan(ξ/2))]ξξm}2R
2B
[1− (
Rh
R)2]
(3.1)
Table 3.1: Geometric parameters for movable block type swirl generator
Parameter Description Design Valuen Number of swirl blocks 8R Swirl generator exit radius 76.2 mmRh Swirl generator inner radius 9.53 mmB Depth of swirl blocks 38.1 mmα Fixed swirl block angle 60◦
ξ Adjustable swirl block angle -ξm Maximum opening angle 12◦
By giving the primary air swirl, as it enters the main burner section, the flow expands outward
reducing the pressure in front of the nozzle, producing a recirculation zone as shown in Figure 3.3. This
recirculation improves combustion stability by bringing hot combustion products back toward the nozzle,
increasing the residence time of fuel gases and droplets as well as greatly improves mixing.
Chapter 3. Apparatus Design 11
Figure 3.3: Recirculation zone formed in a swirling flow[37]
3.4 Fuel Atomizing Nozzle
The burner uses an internal-mix air blast atomizing nozzle (BEX Engineering: model 1/4” JX6BPL11
with a 152 mm long extension tube and 2X2JPL back-connect body, a JPG60 air cap and JPL40100
liquid cap) to atomize the fuel. All components are made from 316 stainless steel to prevent corrosion
due to the acidic nature of the fuel. The overall configuration of the nozzle is shown in Figure 3.4.
Figure 3.4: Burner nozzle assembly[38]
The bio-oil enters the nozzle through the central 1.0 mm diameter orifice in the liquid cap. The liquid
fuel is then forced through six 0.89 mm orifices in the air cap. The spray pattern that is produced is six
equally spaced jets around a 65◦ hollow cone. This spray pattern was selected due to its compatibility
Chapter 3. Apparatus Design 12
with the central recirculation zone. That is, the spray does not introduce enough axial momentum to
penetrate the entire recirculation zone the way a single axial fuel jet would. The recirculation zone is
then able to form in the hollow cone between the fuel jets, improving flame stability [5].
3.4.1 Natural Gas System
In previous studies using this burner, the atomizing gas was compressed air. For this experiment
however, it was necessary to burn both bio-oil and natural gas together. The atomizing gas was changed
by replacing the air input with a tee connected to natural gas and nitrogen cylinders. By using nitrogen
as a balance gas, the atomizing flow rate can be adjusted to provide adequate atomization for all natural
gas energy flow rates. Furthermore, by using nitrogen, the gas mixture inside the tube is non-flammable
for safer operation.
3.5 Pilot Flame System
The flame is stabilised by a oxygen-natural gas pilot flame (Hoke model No. 110-406) which is run
for the duration of each test to prevent any extinguishing of the flame. The nozzle tip is a 1.2 mm orifice
with a hexagonal ”rosebud” pattern. This nozzle pattern produces a wider flame than a single orifice
nozzle, which is more stable in the turbulent environment inside the burner. The torch is mounted to
the burner with a 1/4” bore-through compression fitting such that only 5 mm of the tip is inside the
burner. This reduces the impact the pilot flame has on the air flow of the burner. The flow rate of
natural gas through the nozzle is set to 0.95 SLPM to achieve 0.5 kW pilot flame energy. The energy
from the pilot flame is not part of the 10 kW burner energy.
3.5.1 Pilot Flame Alignment
It is important for the pilot flame to be properly aligned relative to the nozzle jets to achieve good
combustion. While the pilot flame port is stationary, the fuel atomizing nozzle can be rotated in its
mounting collar. While burning pure ethanol, the fuel atomizing nozzle is rotated until the pilot flame
is in a good position between two fuel jets as shown in Figure 3.5.
(a) Good pilot alignment (b) Poor pilot alignment
Figure 3.5: Pilot flame alignment quality [5]
Chapter 4
Experimental Methodology
4.1 Experimental Setup
Figure 4.1 shows an outline of how the overall burner system and analysis equipment are connected.
Figure 4.1: Overall burner setup schematic
The bio-oil is pumped to the nozzle using peristaltic pumps through Teflon tubing connected with
316 stainless steel Swagelok fittings to prevent the bio-oil from corroding the materials. Two peristaltic
pumps are used in parallel to reduce the intermittent flow that was observed when using only one pump,
especially at low flow rates. The pumps are set to an rpm that is calibrated to the desired flow rate in
mL/min. This calibration method is shown in Appendix B. A pressure relief valve is installed between
the pumps and the nozzle to prevent any issues that may arise if the nozzle becomes clogged. To prepare
the burner for bio-oil combustion, it is first heated up with ethanol. By switching to bio-oil after the
burner is up to temperature, the occurrence of bio-oil droplets hitting the walls and forming char deposits
13
Chapter 4. Experimental Methodology 14
is greatly reduced.
Primary combustion air is pulled through the burner through the two stack fans downstream of the
burner with its flow rate monitored with a flow meter and is adjustable with variable voltage transformers.
This maintains a negative pressure of approximately 150 Pa inside the combustion region of the burner.
The main benefit of this compared to pushing air through the burner is that the negative pressure ensures
that no gases leak out of the burner. The primary air is heated with a 1.5 kW air heater controlled with a
variable voltage transformer to preheat the combustion air to 230 ◦C to 250 ◦C. Heating the combustion
air also helps in atomization by warming up the bio-oil as it enters the fuel nozzle, reducing its viscosity.
The exhaust stream is tapped at two locations for analysis. First, for the isokinetic particulate
matter sampling system and second for the gas phase sampling systems. The isokinetic particulate
matter sampling system is used to collect particulates on filters for gravimetric analysis. For the gas
phase sampling system, the exhaust is transported with a 1/4” heated sampling line at 190 ◦C to 195 ◦C to
prevent condensation of water or hydrocarbons. The exhaust is then passed through a heated glass/Teflon
filter to remove particulates before the gas composition is measured. The unsampled exhaust is passed
through a heat exchanger and condenser to reduce the temperature of the gas going through the stack
fan and remove as much moisture as possible.
4.2 Fuel Analysis
4.2.1 Bio-Oil - Natural Gas Mixtures
In this study, two fuels is co-fired with natural gas. It has been observed that 100% bio-oil will
not ignite in the burner, likely due to the lack of low molecular weight volatile hydrocarbon content.
By atomizing with natural gas, the initial energy for bio-oil combustion is provided and the flame is
”anchored” to the nozzle. Mixtures of 20%, 40%, 60% and 80% were selected to be compared against a
pure natural gas flame to determine how the combustion behaves.
4.2.2 Bio-Oil Analysis
4.2.2.1 Thermogravimetric Analysis
Thermogravimetric Analysis (TGA) is a method of determining the volatilization properties of a fuel
[39]. A small sample around 50 mg is heated at a constant rate up to 700 ◦C while nitrogen is passed
over the sample at a rate of 100 mL/min to carry away vapours and prevent the fuel from oxidizing.
These samples are taken from a larger bottle of bio-oil which has been thoroughly blended. The weight
change of the sample is measured throughout the test. This test provides a detailed description of how
much of the fuel evaporates, as well as what the rate of devolatilisation with respect to temperature.
For this analysis, a Texas Instruments Q50 TGA was is used at SAPL.
4.2.2.2 Photomicroscopy
A common issue with the burner used for this study in its current configuration, is the diameter
of the nozzle orifices. The 0.89 mm holes in the air cap can become blocked due to the solid particles
contained in the bio-oil. In order to evaluate the chance of a blockage occurring, the bio-oil is inspected
using a Leica EZ4D photomicroscope at a magnification of 35x to measure the size of the particles.
Chapter 4. Experimental Methodology 15
The bio-oil used for this study is a low solids, filtered bio-oil selected specifically to reduce the risk of
blockage. This analysis is performed at the Surface Interface Ontario Lab.
4.2.3 Bio-Oil Properties
The bio-oil was provided from a commercial supplier with an analysis certificate. These values were
validated by sending the bio-oil to Alberta Innovates Technology Futures for independent evaluation.
4.2.4 Natural Gas Properties
The natural gas used in this study is Linde Gas Methane Grade 1.3 (Natural Gas). The only
composition data Linde provides for this product is that it is 93% methane. The balance is considered
inert for this study so that the heating value of the fuel by volume is 93% that of pure methane.
4.3 Gas Phase Emission Measurement
4.3.1 Unburnt Hydrocarbon Emissions
A California Analytical Instruments model 600 Flame Ionization Detector (FID) is used to measure
the UHC in the exhaust. By passing the exhaust through a hydrogen flame, a current proportional
to the number of carbons in the exhaust is produced [40]. Exhaust is sampled at a rate of 1.5 SLPM
controlled by the built in sampling pump and is transferred with heated lines at 190 ◦C to 195 ◦C to
prevent condensation of water or hydrocarbons. The FID is calibrated using dry air as the zero gas and
a mixture of 90 parts per million (ppm) methane in nitrogen as the span gas. The FID uses these two
points provide a linear range from 0 to 300 ppm CH4 with an uncertainty of ±3 ppm. It is important
to note that the output does not take into account the actual composition of the UHC contained in the
exhaust.
4.3.2 Detailed Exhaust Gas Composition
A Nicolet 380 Fourier transform infrared spectrometer (FTIR) is used to determine a more detailed
composition of the gas phase emissions. Specifically, the concentrations of CO2, CO, H2O and NO are
measured. The FTIR is fitted with a gas cell with a 2 m path length and a volume of 0.19 l. The gas
is sampled with 24 scans over 1 minute with a wave number resolution of 1 cm-1. The samples are then
compared to the mid infrared (500 to 4000 cm-1) absorption spectra of known gas compositions.
The FTIR is calibrated using a partial least squares model. Software is used to randomly generate
an array of combinations of the gases that are to be measured that covers the full range of the desired
detection limits. These mixtures are then manually input to the gas cell to generate spectra for each.
While collecting a spectrum during a test, the exhaust is drawn through the gas cell at a rate to
keep the pressure at 86.3 kPa. Similar to all the transfer lines, the gas cell is heated to 120 ◦C to prevent
water from condensing. By passing the exhaust through the gas cell constantly while collecting the
spectrum, a time averaged gas composition is measured. At each test condition, five spectra are taken
consecutively and are averaged arithmetically.
Chapter 4. Experimental Methodology 16
4.3.3 Equivalence Ratio
The %O2 in the exhaust is measured using a Zirconia (ZrO2) oxygen sensor (Engine Control and
Monitoring, model OXY6200). The sensor produces a 0 to 5 VDC signal which is linearly proportional
to %O2. Using room air supplied with a vacuum pump at 1.8 SLPM, the sensor is calibrated to 21%
O2. The O2 sensor raises the temperature of the gas, which may oxidize the hydrocarbons and other
gas species. To prevent affecting the measurements of the FID and FTIR, the O2 sensor is not in-line
with the rest of the gas phase sampling system as shown in Figure 4.1. The output of the oxygen sensor
is used to determine the equivalence ratio using the composition of the fuels and assuming complete
combustion.
4.4 Flame Visualization
A 4 mm Lennox Instruments Co. borescope with a 90◦ mirror tube is used to visually evaluate the
flame. The borescope is inserted in the burner as shown in Figure 3.1 and provides an axial view towards
the nozzle. The borescope can also be connected to a camera (Kodak Z1012S) to take photographs and
video of the flame. A detailed setup for how the borescope is inserted into the burner is shown in Figure
4.2.
Figure 4.2: Borescope insertion into burner
The borescope is inserted into the burner through a 9.5 mm tube with a connection to compressed
air which flows at 250 SLPM to cool the borescope as well as prevent fuel droplets or PM from settling
on the mirror. The camera is attached to the end of the borescope and is set up on a rail which allows
for the rapid insertion of the camera. By minimizing the time the borescope is inside the burner, there
is less chance particles coming to rest on the mirror. The camera is therefore set up with maximum
zoom, an aperture of f=5.0 and a shutter speed of 1/6s. These settings are kept constant for all pictures
so that the relative luminosity of the flames is reflected in the photographs. By setting up the camera
Chapter 4. Experimental Methodology 17
before insertion, the borescope only needs to be in the burner for 5-10s to take a photo, at which point
it is removed and the borescope port is immediately capped.
4.5 Flame Infrared Emission Measurement
In addition to visible light measurements, the borescope allows for infrared light measurements using
an adapter to connect to an optical fibre. An Edmund Optics InGas Near Infrared (NIR) spectrometer
(model BTC261E-512) is used for these measurements. The principle for these measurements is the
same as for taking photographs; the borescope is briefly inserted to take a spectrum looking up at the
flame. For each test, 5 spectra are taken and averaged together to take into account any fluctuations
in the flame. Using these spectra and integrating over all wavelengths, a relative value for how much
infrared light each flame emits is obtained.
4.5.1 Infrared Background Measurement
In early tests, it was noted that the walls of the burner emit infrared light and affect the results. To
investigate the effect the walls have on the NIR spectra, two successive spectra were obtained: one with
the flame on, and one immediately after extinguishing the flame. These spectra are shown in Figure 4.3.
Figure 4.3: NIR background spectrum test
The spectrum with no flame was then observed over time as the walls cooled and it was noted that
the shape remains the same, but the magnitude decreased. Furthermore, the spectrum with no flame
closely matches the smooth part of the spectrum with the flame, indicating that the flame is represented
by the part of the spectrum that deviates from this line. So for analysis, the background was subtracted
from each spectrum to get a measure of the NIR emission solely from the flame.
Chapter 4. Experimental Methodology 18
It is important to note that the output from the spectrometer is a non-dimensional, relative measure-
ment. The results are therefore reported as normalized values relative to the NIR emission of a flame
consisting of 100% natural gas.
4.6 Burner Temperatures
Several thermocouples are placed around the burner to provide real time monitoring of key temper-
atures of the burner. The exact location of these thermocouples is shown in Figure 4.4.
Figure 4.4: Thermocouple placement for burner monitoring
The intake air and nozzle sheath temperatures are measured with exposed bead J-Type thermocou-
ples. The intake air is heated with an electric heater that is controlled with a variable voltage power
supply. The voltage is tuned so that the temperature of the air is 230 ◦C to 260 ◦C as it enters the
Chapter 4. Experimental Methodology 19
combustion region. To ensure the burner has reached steady state, another J-Type thermocouple is
installed on the outer wall of the burner. This temperature is continuously monitored during operation
and measurements are only taken once the wall temperature is no longer increasing.
To evaluate the quality of the combustion, an exposed bead sheathed K-Type thermocouple is inserted
into the thermocouple insertion port shown in Figure 4.4. The thermocouple is inserted 11 cm until the
bead is located along the centreline of the burner. The thermocouple is left in position for 30s until
it reaches an equilibrium temperature. Due to the turbulent nature of the combustion region, this is
not considered the flame temperature, rather the average temperature of the combustion gases. This
temperature provides insight to the conditions just after the flame that helps explain exhaust composition
measurements. However, due to losses from radiation, conduction along the thermocouple sheath as well
as cool room air leaking in from the insertion port, these measurements should be considered relative
[41].
4.7 Particulate Measurement and Analysis
4.7.1 Isokinetic Sampling
To sample the particulates contained in the exhaust stream, it is important to sample isokinetically,
that is, to sample the gas without changing its velocity [42]. By keeping the velocity constant at the
sampling probe, the sampled gas will contain a representative quantity of particles [43]. By measuring the
pressure difference between the exhaust stream and sampling probe inlet, isokinetic sampling happens
when the pressure difference is zero.
4.7.2 Particulate Sampling System
The particulate sampling system is shown in Figure 4.5. A flow straightener is located at the exit of
the burner to eliminate any angular momentum that may remain. The flow straightener is made from
0.25 mm stainless steel in a checkerboard pattern. This ensures that in the particulate sampling system,
there is only axial flow with a uniform particulate distribution. A detailed description of the design of
the particulate sampling system can be found elsewhere [5].
There are two taps for pressure measurement, one in the main exhaust stream and another in the
sampling probe. These are connected to a manometer so the flow rate through the sampling probe can
be adjusted with a needle valve until the pressure difference is zero. The pressure tap is calibrated to
measure the pressure at the centreline of the exhaust stream. To achieve this, the sampling probe is
offset from the pressure tap 12.7 mm [5]. A 47 mm Pall Life Sciences Tissuquartz filter (model 7202) is
placed in the filter holder to collect PM during the tests. The filters are made out of borosilicate glass
and are able to sustain very high temperatures (up to 1100 ◦C) and have a very low air resistance. They
retain 99.9% of aerosols at 0.3 micron.
The filter temperature is monitored during each test using a J-Type thermocouple to ensure water will
not condense on the filter. While the filters do not absorb water due to humidity, it has been observed
that because they do not contain a binder, moisture causes them to break down. The particulate
sampling system is heated up with heating tape to 120 ◦C to 140 ◦C before taking any data to make sure
condensation does not become an issue.
Chapter 4. Experimental Methodology 20
Figure 4.5: Overall particulate sampling system [5]
4.7.3 Particulate Sample Measurement
During particulate collection, a dummy filter is used to run exhaust through the system to heat all
the components to 120 ◦C to 140 ◦C. Once this is done, a second dummy filter is placed in the filter
holder to adjust the sampling pressure to achieve isokinetic conditions (zero pressure difference between
the sampling probe and exhaust line). Once the system is set up, the first test filter is placed in the
filter holder and the exhaust is run through it for 3 minutes. The filter is then placed in a petri dish to
prevent any contamination and the process is repeated with 4 subsequent filters.
The collected particulate samples are weighed with a Scientech SM-128D Microbalance to determine
the total amount of particulates in the exhaust stream. The filters are weighed after resting in ambient
conditions for 24 hours. The filters are then placed in a Thermo Scientific Thermolyne oven at 640 ◦C for
1 hour to burn off all the carbonaceous residue (CR). The samples are then weighed again to determine
the organic/inorganic composition of the particles.
After each test, it was observed that significant amounts of ash were left on the walls, especially on
the horizontal surfaces in front of the viewports. In order to avoid misrepresenting the particulate mea-
Chapter 4. Experimental Methodology 21
surements, the data is presented as a value relative to the largest value obtained. While the magnitude
of the particulates in the exhaust stream is likely underestimated, due to the consistent measurement
procedure across all tests, the trend is retained.
4.8 Test Procedure
For all tests, one batch of bio-oil was used. The bio-oil was received in a large bucket that was then
thoroughly mixed and distributed into 2 l bottles which were then kept in a refrigerator to fuel aging. By
dividing the bio-oil into smaller bottles immediately after mixing, there is less chance that the properties
of the bio-oil change from test to test. The following sections outline the procedure that was carried
out to collect each set of data. Table 4.1 shows the fuel and nitrogen flow rates as well as the %O2 in
the exaust measured at each test points. The procedure for calculating the fuel flow rates is shown in
Appendix A.
Table 4.1: Fuel flow rates for each burner test
Bio-oil EnergyFraction
Bio-oil FlowRate (mL/min)
Natural GasFlow Rate(L/min)
Nitrogen FlowRate (L/min)
Oxygen inExhaust (%)
0% 0 18.29 6.70 7.0620% 5.85 14.63 10.37 6.4840% 11.70 10.97 14.02 6.5360% 17.54 7.31 17.68 5.8980% 23.38 3.66 21.34 5.59
To ensure the SMD in each test is approximately the same, nitrogen is added to the natural gas to
control the overall atomizing gas flow rate. The empirical relation in Equation 2.1 is used as a starting
point so the SMD is 100µm. However, it was found in preliminary tests that combustion fluctuations
became large at low bio-oil flow rates. At 20% bio-oil energy especially, carbonaceous residue built up
on the nozzle and partially clogged the fuel jets. To remedy this, in each test, the nitrogen was varied to
achieve the lowest CO emissions possible. By doing this, the optimal atomization is achieved with the
minimal amount of flame lift off.
4.8.1 Burner Start-up and Shutdown
The burner is first warmed up on ethanol with air atomization before running bio-oil through the
system. The warm-up period lasts for 15-20 minutes sets up the burner so that there are no extinction
issues when bio-oil is introduced. Once the burner wall temperature has reached 425 ◦C to 450 ◦C, the
fuel is switched to bio-oil with the appropriate flow rate, and the atomizing air is switched to the natural
gas and nitrogen mixture required for the test. At the end of each test, the bio-oil is switched back to
ethanol and the atomization gas is switched back to air. This shutdown procedure ensures that bio-oil
does not remain inside the hot nozzle, which would cause polymerization and clogging. The operating
conditions used for each of the tests is shown in Table 4.2.
Chapter 4. Experimental Methodology 22
Table 4.2: Operating condition of burner variables for each test point
Parameter ValuePrimary Air Flow (SLPM) 250
Equivalence Ratio 0.66Pilot Methane (SLPM) 0.88Pilot Oxygen (SLPM) 2.3
Primary Air Preheat (◦C) 240-260Energy Throughput 10 kW
4.8.2 Gas Phase Emissions Tests
After switching to the bio-oil, the burner is allowed to run for another 15-20 minutes to allow the
burner to reach steady state. While this is happening, the FID is calibrated and the FTIR gas cell is
purged with nitrogen. The FID and FTIR measurements are carried out in succession. A valve controls
the flow selection to either the FID or FTIR. Once the FTIR spectra are collected, the gas cell shut off
from the exhaust, evacuated and purged with nitrogen to limit its exposure to the exhaust.
4.8.3 Particulate Emissions Tests
Before the test has begun, 5 filters are weighed and placed in individual petri dishes to prevent
contamination. After the gas phase measurements are taken, the particulate sampling system is heated
up. Dummy filters are placed in the test and bypass filter holders, and exhaust is pulled through the
system while the flow rate is adjusted to reach isokinetic flow. Once the filter holder has reached 120 ◦C
to 140 ◦C, the first test filter is placed in the test filter holder while the exhaust passes through the
bypass filter. The bypass valve is then closed and the valve to the test filter is opened. After 2 minutes
of sampling, the gas flow is switched back to bypass and the test filter is removed and placed back in its
petri dish. This procedure is then repeated with the remaining test filters.
4.8.4 Infrared Emissions Tests
Once the emission testing is done, the borescope is set up for NIR emission testing. After taking
a dark scan (NIR scan of the ambient conditions in the lab), the borescope is inserted into the burner
and 5 successive spectra are obtained. Between each test, the borescope is removed to prevent it from
getting too hot or contaminating the mirror. The borescope tube is marked to ensure the each spectra
is taken at the same depth.
4.8.5 Flame Imaging
To ensure the photographs of the flames are all taken with the same conditions, the photos of all test
points were taken during a separate test. After heating up on ethanol, the fuel was switched to 100%
natural gas and photos were taken. The fuel flow rates were then changed to run through tests with
20%, 40%, 60% and 80% bio-oil. The burner was then flushed with ethanol in the same way as the other
tests.
Chapter 5
Results and Discussion
5.1 Fuel Analysis
The properties of the two fuels used in this study are provided in Table 5.1. For the bio-oil, the
properties were provided by the manufacturer, and the testing methods are listed. The natural gas
properties are calculated based on a purity of 93% by volume methane provided by Linde Canada, and
assuming the remaining 7% is inert.
Table 5.1: Bio-oil and natural gas properties [44]
Parameter Test MethodBio-Oil
Manufacturer DataBio-Oil
Lab TestNatural Gas
Water Content, wt% as is* ASTM E203 25.1% - -Viscosity 25 ◦C, cSt ASTM D445 93.7 - -Viscosity 40 ◦C, cSt ASTM D445 35.4 - -Viscosity 60 ◦C, cSt ASTM D445 13.3 mm - -
Solids Content, wt% as is ASTM D7579 0.05% - -Ash Content, wt% as is EN 055 0.17% - -
Density 20 ◦C, kg/L EN 064 1.22 - 0.000 656Carbon Content, wt% as is ASTM D5291 42.4% 41.45 -
Hydrogen Content, wt% as is ASTM D5291 7.59% 7.2 -Nitrogen Content, wt% as is ASTM D5291 0.13% 0.13 -
Sulfur Content, wt% as is ASTM D5453 0.01% - -Oxygen Content, wt% as is Difference 49.71% 40.54 -
HHV, MJ/kg as is ASTM D240 17.1 - -LHV, MJ/kg as is Calculated 15.12 - 46.5
*Included in the hydrogen and oxygen content
23
Chapter 5. Results and Discussion 24
There is a very clear contrast between the two fuels used in this study. While natural gas has a high
LHV and does not contain any undesirable compounds for combustion, bio-oil has several properties
that pose a challenge for its use as a fuel. Bio-oil is liquid and it has a low LHV, typically around half
that of Diesel, or Number 2 Fuel Oil. Combined with its high water content, bio-oil combustion suffers
by requiring a high ignition energy. Its low volatility therefore can cause difficulties with ignition and
extinction. The volatility curve produced from the TGA is shown in Figure 5.1.
Figure 5.1: Bio-oil TGA curve
The TGA curve shows that there is a significant portion of the total mass that evaporates at around
100 ◦C. This is mainly the water as well as the low molecular weight hydrocarbons and acids contained
in the bio-oil. The peaks and fluctuations that are shown in this area signify the polymerization that
bio-oil goes through at high temperatures. As the temperature increases, a skin forms on the surface of
the bio-oil which then bursts as the water boils [45]. Fuel polymerization poses a clogging threat to the
fuel delivery system, so the fuel line is water-cooled as it enters the nozzle. Once the test is complete,
approximately 17 wt% of the original mass remains as solid char. The majority of the remaining char
is carbon, so nearly half of the carbon in the bio-oil (42.4 wt%) is not volatile. This has been shown in
a previous study to increase the particulate emissions [46]. Because there is no oxygen available to the
bio-oil during the TGA test, there is no char oxidation, so the only mass lost is due to evaporation. In
a combustion application, this char forms particles which react much slower than vaporised fuel. These
organic particles may remain in the exhaust stream if the residence time or temperature too low.
The solids content of bio-oil also presents a challenge for the use of bio-oil, especially for a small,
lab-scale burner. To investigate the risk of nozzle clogging due to particle accumulation, the size of the
Chapter 5. Results and Discussion 25
particles was examined with an optical photomicroscope, shown in Figure 5.2.
Chapter 5. Results and Discussion 26
Figure 5.2: Typical solid particles contained in this bio-oil
It is important to note that the bio-oil used in this study was specially designed for use in the
burner. That is, that it was filtered to remove potentially problematic particles. The solids content
varies significantly between bio-oils based on feedstock and processing, so while one bio-oil may not
cause clogging, another may. Measuring the particles contained in the bio-oil used in this study yielded
an average particle size of about 100µm. Also shown is a larger particle, around 250 µm long, which
demonstrates the variability in particle size in the bio-oil. However, because the bio-oil has been filtered,
the few large particles left in the bio-oil do not pose a clogging risk. The nozzle opening diameter is
1 mm, much larger than the largest particles in the bio-oil.
5.2 Base Point Operation and Repeatability
During each test, the burner is allowed to heat up on ethanol for 30 minutes before switching to
the bio-oil and natural gas. Once the fuel is switched, the burner is allowed to run for an additional
30 minutes to ensure it is running at steady state before taking any measurements. To ensure steady
state operation, and that the exhaust composition is stable during each test, a test was performed at
60% bio-oil energy. After heating up using the same method, the exhaust composition was measured
five times over the course of an hour. The results of this test are shown in Table 5.2.
Chapter 5. Results and Discussion 27
Table 5.2: Exhaust composition repeatability at 60% bio-oil energy
Species Average Value (ppm) Average Deviation (ppm) Percent DeviationCO 653.2 49.1 7.5%NO 108.6 2.5 2.3%
5.3 Reaction Zone Temperature
The temperature in the reaction zone is a very important measurement to determine what is occur-
ring in the combustion reaction and helps to explain other measurements. Figure 5.3 shows how the
temperature changes with respect to bio-oil input energy.
Figure 5.3: Temperature vs bio-oil input energy percent
It is important to note that this is not the peak temperature inside the burner, but more of an average
temperature within the turbulently mixed recirculation zone. Because the exhaust temperature at the
burner exit, as shown in Figure 4.4 remains relatively constant in all tests, around 250 ◦C to 300 ◦C due
to the heat losses to the walls, the temperature of the reaction zone will greatly affect how effectively the
combustion products convert to CO2 and water. The temperature after the flame region drops quickly,
so the combustion reaction does not continue further down in the burner. It is important to note that the
temperature only 10 cm below the nozzle is significantly lower than the adiabatic flame temperature of
approximately 1930 ◦C of methane [44]. This shows that the heat loss to the walls introduces a significant
Chapter 5. Results and Discussion 28
temperature gradient in the burner. While this would not be the case in a lime kiln or industrial burner,
the heat loss will exaggerate the effects that bio-oil has on combustion.
As shown in Figure 5.3, as the fraction of the total energy input from bio-oil increases, there is a
decrease in reaction zone temperature. The pure natural gas flame burns very quickly and releases its
energy very high up in the burner, resulting in a higher temperature in the reaction zone. However,
as bio-oil is added, more time is required for complete combustion due to the water content and char
formation of the bio-oil. So, the same amount of energy will be released over a larger volume inside the
burner, resulting in a lower average temperature. Furthermore, if the solid char left over after the volatile
compounds in the bio-oil evaporate (about 17 wt%) exits the hot reaction zone too quickly, it may not
oxidize. The energy in these particles will not release their energy, further contributing to the decrease
in temperature (Discussed further in Section 5.5.2). The longer flame seen as the bio-oil energy fraction
increases indicates that bio-oil has a longer burnout time than natural gas which will be proportional to
the CO and UHC in the exhaust.
A decrease in reaction zone temperature also has implications for incomplete combustion products.
If the temperature inside the burner decreases too quickly, there will be increased CO emissions simply
because the temperature is too low to convert the CO to CO2[44]. These effects are discussed further in
Section 5.5.1.
5.4 Flame Images
Figure 5.4 shows the images captured using the borescope looking axially toward the nozzle.
Chapter 5. Results and Discussion 29
(a) 0% bio-oil energy (b) 20% bio-oil energy
(c) 40% bio-oil energy (d) 60% bio-oil energy
(e) 80% bio-oil energy
Figure 5.4: Flame images viewing axially towards the nozzle
The images of the flames provide a way to evaluate the flames qualitatively. Figure 5.4a shows the
clean burning flame characteristic of natural gas. Because the fuel is quickly mixed with the air in
the recirculation zone, there is no soot to produce light. Furthermore, the natural gas flame does not
propagate far down the burner due to its relatively rapid combustion [44]. Because there is a smaller
volume heated by the natural gas flame, the average temperature of the gas in this case is increased as
discussed in Section 5.3. In the remaining four tests, there are two different regimes that are visible.
In the 20% and 40% bio-oil input energy cases, shown in Figure 5.4b and Figure 5.4c respectively,
the flame structure is dominated by the natural gas that comprises the majority of the flame energy.
In these tests, there are fewer droplets (assuming a constant average droplet diameter), and the natural
gas anchors the flame to the nozzle, preventing extinction. However, it is clear that the flame continues
further down in the burner, shown by the increased curvature of the fuel jets. Because the air in the
burner is swirling as it travels through the burner, fuel jet curvature is an indicator of vertical distance
travelled.
Chapter 5. Results and Discussion 30
In the 60% and 80% bio-oil input energy cases, shown in Figure 5.4d and Figure 5.4e respectively,
the flame has become dimmer, with more of the flame composed of burning droplets. During these tests,
there was a significant increase in fluctuations, likely caused by the decrease in anchoring provided by
the natural gas. In these cases, the flame length grew long enough to be visible in the viewport, shown
in Figure 3.1. In these cases, significantly more air is being heated by the flame compared to the natural
gas case, contributing to the trend seen in the average reaction zone temperature in Section 5.3.
Whereas the natural gas flame is nearly invisible, the bio-oil flames are very luminous with an orange
colour. This is due to the char particles formed in the flame heating up and emitting light. It is
important to note that because bio-oil is a heavily oxygenated fuel, the orange colour is not a product
of soot formation in the fuel [47]. The volatile components of the bio-oil evaporate until all that is left
is the char as was shown in the TGA test [48]. The light emission increases heat transfer to the wall,
which due to the burner design (non-refractory lined) results in increased heat loss. The light emission
therefore contributes to the lower reaction zone temperature. Furthermore, char particles are more likely
to travel further from the nozzle where the burner is much cooler. The flame volume is therefore larger
in the tests with more bio-oil energy.
5.5 Particulate and Gas Phase Emissions
5.5.1 Exhaust Composition
As more of the total input energy is replaced with bio-oil, significant changes occur in the combustion
region that are reflected in the exhaust composition. Figure 5.5 shows the amount of CO and NO and
Figure 5.6 shows the UHC in the exhaust as more of the input energy comes from bio-oil.
Figure 5.5: CO and NO concentration in exhaust with respect to bio-oil input energy
Chapter 5. Results and Discussion 31
Figure 5.6: UHC concentration in exhaust with respect to bio-oil input energy
The NO produced in the combustion increases linearly as more energy comes from bio-oil. This
corresponds to the nitrogen content of the bio-oil being the source of the nitrogen oxides formed in the
combustion. Due to the high swirl number in each test, the recirculation zone effectively acts as exhaust
gas recirculation, helping to limit the thermal NOx produced in the burner[49]. However, previous
research has been done with this burner to investigate the effect of swirl number on NOx formation and
found that increasing the swirl number yielded no change in NOx, indicating that the NOx formed in
the burner is generally not produced thermally[5]. The increase in NOx therefore is due to the nitrogen
content of the bio-oil.
The UHC content in the exhaust increases as more bio-oil is input to the burner. Due to the
low volatility of the bio-oil and the decreased temperature of the gas inside the burner, not all of the
hydrocarbons in the combustion region will ignite. Furthermore, due to the heat lost to the walls, the gas
downstream of the flame quickly becomes too cool to allow the UHC to oxidize. However, the increase in
UHC is not linear as bio-oil input is increased. Significantly more UHC is produced when the majority
of energy is bio-oil. During these tests, there were significantly more fluctuations in flame stability,
likely due to the lack of natural gas providing the energy for ignition. These instabilities result in the
flame locally extinguishing, allowing unburnt fuel to exit the reaction zone. Because the temperature
downstream is too low, this results in a greater increase in UHC emission when there is more extinction.
This is also reflected in the flame images shown in Section 5.4 where at 60% and 80% bio-oil energy, the
flame appears to be made up of mostly burning fuel droplets, rather than at 20% and 40% where the
burning droplets are contained in a turbulent gaseous flame.
The trend in CO emissions further demonstrates the requirements needed to burn bio-oil. As the
bio-oil energy percentage increases, there is a significant increase in CO concentration in the exhaust,
Chapter 5. Results and Discussion 32
indicating that combustion is not as complete. There are two sources of this CO. First, due to the
decreased temperature in the reaction region, CO that exits the hot reaction zone, or quenches on
the wall, is not exposed to a high enough temperature to oxidize to CO2, as discussed in Section 5.3.
Secondly, the char particles that exit the recirculation zone quickly cool down and are similarly unable
to convert to CO2, but are still hot enough to slowly release CO. Examining the carbon input into
the burner and calculating the amount of that carbon that exits as CO, it is found that approximately
96% of that carbon is being converted to CO2 in the worst case. Considering the UHC, which in the
worst case is 300ppm CH4, the vast majority of the carbon is being converted to CO2, indicating that
it is likely the recirculation maintains the combustion products at a high enough temperature and the
majority of the CO is being released by char particles further away from the flame. The reaction rate
from solid carbon to CO2 is much slower, and these particles do not experience a high temperature for
very long. The measurement of these particles is discussed in more detail in Section 5.5.2.
5.5.2 Particulate Emissions
The collected particulate emission of each test is shown in Figure 5.7. Due to the design of the
burner, significant amounts of particulates deposit on the walls and on horizontal surfaces inside the
burner. However, the linear trend seen in the ash indicates a constant percentage loss in each test.
Figure 5.7: Relative particulate emission
As more bio-oil energy is used, there is a larger amount of fuel that has the potential to form
particulates. Natural gas is very clean burning and does not produce any particulates, shown visually
by its dim, blue flame. However, when bio-oil burns, once the volatile compounds evaporate, there is a
solid char particle that is left over. These particles oxidize at a much slower rate simply because they
Chapter 5. Results and Discussion 33
are solid and there is less surface area available to react. These particles give the flame a bright orange
colour, however, they also allow heat to radiate to the walls more efficiently. Because the walls are not
well insulated, there is a large heat loss to the walls, which reduces the temperature of the gas inside
the burner.
In order to examine why there is a large increase in particulates between 0% and 20% and then a
subsequent linear increase, the organic component of each particulate sample was burnt off. Figure 5.8a
shows what a typical filter looks like with particulates immediately after sampling, while Figure 5.8b
shows a filter after the carbon has been burned off. The resulting filter mass provides the mass of the
inorganic ash component of the particulates, shown in Figure 5.7.
(a) Filter with particulates as collectedfrom the burner
(b) Filter after carbon burn off in ovenat 640 ◦C for 1 hour
Figure 5.8: Particulates collected on a quartz filter before and after carbon burn off
There is no ash produced in a natural gas flame, so any ash produced in the flame comes from the
bio-oil. The ash weight percentage of the bio-oil is shown in Table 5.1, allowing the expected mass of
ash per kilogram of fuel to be calculated. Due to particulates coming to rest on horizontal surfaces in
the burner, only approximately 20% of the total ash input from the bio-oil has been captured. However,
because the loss is relatively constant, the linear trend that is expected is captured with the correct
slope.
Once the ash is subtracted from the total mass of the particles, the mass of the total char is deter-
mined. There is a relatively flat relation between bio-oil energy fraction and char particulates collected
on the filter. This is in contrast with the ash, which increases linearly. This indicates that with even a
small amount of bio-oil a significant amount of char escapes the reaction zone. A test was run at 10%
bio-oil energy to validate the trend between 0% and 20% bio-oil energy. However, the nozzle became
clogged due to char build up approximately 15 minutes after switching from ethanol. It is likely that
the elevated char mass seen in 5.7 at 0% and 20% is due to the nozzle not operating at its design liquid
flow rate.
5.6 Near Infrared Emissions
The near infrared emission measurements reflected what was seen in all other measurements. The
quality of the combustion is poorer and less complete in tests with higher bio-oil energy input. These
Chapter 5. Results and Discussion 34
measurements are shown in Figure 5.9
Figure 5.9: NIR emission vs bio-oil input energy
The trend observed in these NIR measurements is mirrored in the reaction zone temperature data
shown in Figure 5.3. While the natural gas flame is very dim, it is very hot, and the CO2 and H2O
produced in the flame are good at transmitting in the infrared. Despite the bio-oil containing flames
being much brighter and emitting more light in the visible spectrum, in the near infrared, there is less
measured radiation due to the decrease in temperature. It has previously been noted that in lightly
sooting flames, the infrared radiation due to the effect of soot is not as important as the effect of
temperature [44]. Bio-oil is generally not considered a highly sooting flame because of its oxygen content
[44]. The temperature is therefore the determining factor for the magnitude of the infrared emission
for bio-oil and natural gas co-combustion. Further investigation should be done with a refractory lined
burner to eliminate heat loss to the walls.
5.7 Effect of Natural Gas on Bio-Oil Combustion
The trends seen in each set of data demonstrate the effect natural gas has on bio oil combustion. The
bio-oil flame is prone to lift off from the nozzle. This produces many undesirable effects. As the flame
lifts off, the chance of it extinguishing increases either locally or globally. When the fuel extinguishes,
unburned fuel does not fully oxidize and gives rise to the increased UHC measurements observed in the
60% and 80% bio-oil energy tests. With a larger energy percentage of the flame coming from natural
gas, the anchoring greatly improves, significantly reducing the UHC emissions.
With more bio-oil, the temperature inside the burner decreases due to the flame occupying a larger
volume. This decrease in temperature contributes to the poorer flame quality measurements observed.
Chapter 5. Results and Discussion 35
As the temperature decreases, not only does local extinction become more likely, but the oxidation from
fuel to complete combustion products becomes limited. This gives rise to the increased CO emissions
observed in the tests with higher bio-oil energy percentages. The decreased temperature also contributes
to the reduced near infrared emission, decreasing radiative heat transfer.
The increased NO emission as more bio-oil energy is utilized is due to the nitrogen content of the
bio-oil, rather than the lack of natural gas anchoring the flame. Similarly, the overall PM emission
increase is also primarily due to the increase in bio-oil entering the burner. This is demonstrated by the
linear increase in ash measured in the samples. The carbonaceous residue however did not change much
between 20% and 80% bio-oil energy. Observations during the tests determined this is primarily due to
the nozzle operating at a much lower liquid flow rate than it was designed for.
Chapter 6
Conclusions and Recommendations
6.1 Conclusions
As the bio-oil input energy was increased, there were many changes in the quality of the combustion.
First, the flame changed from a jet that quickly burned in a small, intense volume when only natural gas
was used, to longer, slower flame that burned in a larger volume and was affected more by the airflow in
the burner. This change had an effect on the average temperature in the area just after the flame, which
greatly affected the exhaust composition. This lower average temperature prevented the bio-oil from
fully oxidize, resulting in UHC emissions increasing from 10ppm in the natural gas flame to 300ppm at
80% bio-oil input energy. In addition to the fuel not oxidizing, the reduction of temperature reduces the
time at which exhaust products and char particles are above the CO to CO2 conversion temperature.
This resulted in a dramatic increase in CO emissions from 16ppm in the natural gas flame to 850ppm in
the 80% bio-oil input energy case. Finally, the NO emissions were mainly due to the nitrogen content of
the fuel, seeing a linear increase from 20ppm to 160ppm from the natural gas flame to the 80% bio-oil
input energy case, respectively.
Particulates increased as bio-oil energy was increased, with the ash component increasing proportion-
ately with the ash contained in the bio-oil. However, in each case, the char component of the particulates
was relatively constant. The organic component of the particulates contributes to the elevated CO levels
seen in higher bio-oil energy input tests as well as indicates that there is poorer energy conversion of the
fuel.
The infrared heat output of the flame as bio-oil input energy was increased followed the trend seen in
the average temperature inside the burner. The heat radiated by the particles in the flame therefore do
not compensate for the decrease in temperature that is seen. While the emission in the visible spectrum
because of the broadband emission of the char particles gives a very bright flame, the NIR emission of
the water and mathrmCO2 is more efficient at transferring heat by radiation. This result suggests that
if used in a full scale burner, the input energy would need to be increased compared to only natural gas
in order to achieve the same heat transfer.
36
Chapter 6. Conclusions and Recommendations 37
6.2 Implications for Industrial Burners
Co-combustion of natural gas and bio-oil allows for the utilization of a low grade biofuel that has
a low energy cost to produce. Natural gas is a fuel often used in industrial burners and by co-firing it
with bio-oil, the issues with bio-oil combustion can be minimized. Furthermore, the operator does not
need to fully rely on only bio-oil to provide heat. By showing that bio-oil combustion is more stable
without the need for chemical upgrading or ethanol blending, it becomes a more appealing biofuel to use
in industry. The measurements in this study suggest that using natural gas energy percentages as low
as 40% greatly improve flame stability by anchoring the flame to the nozzle. In an industrial setting,
it is important be sure that changing the fuel will not result in an expensive shut down. However, the
reduction in heat transfer shown in the NIR emission data suggests that the input energy may need to
be increased in order to achieve the same heat delivery.
Specifically for lime kilns in the pulp and paper industry, the char produced in the bio-oil flame may
be a concern. While the lime kilns have very long residence times, giving plenty of time for the fuel to
fully burn, if the char escapes the flame and ends up in the lime, it may work its way into the pulp.
The char may then appear on the finished paper as black dots, and may ruin a batch of paper. Careful
monitoring of the lime exiting the kiln can avoid this issue.
6.3 Recommendations and Future Work
6.3.1 Burner Modifications
In order to better examine the combustion of bio-oil, the burner should be modified to have refractory
lining to reduce heat losses. Heat losses limit the operating points that can be studied with the current
burner. For example, 100% bio-oil will not ignite, likely due to the heat lost to the walls that would
otherwise be available to ignite the bio-oil. By adding refractory lining to the current burner, it may be
possible to investigate how bio-oil burns without any need of ethanol or natural gas.
In addition, a new nozzle design can help improve combustion in the burner at all fuel fuel flow
rates. In cases with very little bio-oil flow (from 10% to 20% bio-oil energy input) there was difficulty
maintaining combustion throughout the full test. After running for an extended period, the nozzle
became clogged due to char build-up on the end of air cap. As shown in Figure ??, tests with low bio-oil
energy input showed an elevated carbonaceous PM output. This was likely due to the nozzle not being
specifically designed for these very low liquid flow rates. A new nozzle designed custom for the burner
can help in these cases, as well as be designed to more realistically resemble industrial burner nozzles.
In many tests, there were fluctuations caused by unsteady primary air intake due to the unstable fan
performance. These fluctuations could be reduced by replacing the current exhaust duct with a rigid
material. The current exhaust duct is made with flexible ducting that, while easy to route, changes
shape when the exhaust fans are turned on. This flexibility is likely contributing to these fluctuations.
By minimizing fluctuations, there will be much less chance for the flame to encounter a condition where
it will extinguish.
Chapter 6. Conclusions and Recommendations 38
6.3.2 Experimental Methodology Improvements
Improvements to the experimental methodology may reduce the variability in the measurements
observed in this study. The FID data was recorded manually on a data sheet for each test. It would be
best to use the FID’s data output capability to record the UHC data with LabVIEW. This could allow
a more thorough statistical analysis of this data set.
When the borescope is used to photograph the flame, a port in the wall must be opened. When the
borescope is inserted, there is not a leak proof seal around the tube, so air is able to enter through this
port. Because the primary air is pulled through the burner, any leak downstream of the main intake
reduces the air flow through the main primary air intake. This may change the shape of the flame
when photos are taken. By ensuring there is a good seal around the borescope, the photos can be more
representative of the flame.
6.3.3 Future Bio-Oil Combustion Research
Currently, the SMD of the bio-oil droplets is calculated with an empirical formula[36]. The droplet
size is a very important parameter for bio-oil combustion quality. Measuring the droplet size in situ
and determining its relationship with flame quality will provide insight for designing optimal nozzles
specifically for bio-oil. Furthermore, the experimental results of this study can inform modelling studies.
In some industrial settings, it may not be viable to use natural gas and bio-oil because of the handling
requirements for both gaseous and liquid fuels. However, there may be interest in examining the effect
of burning mixtures of bio-oil with number 2 fuel oil. These two fuels however are not soluble in each
other, so either a dual fuel nozzle could be tested or an emulsion would need to be prepared.
Bio-oil has a very complicated composition containing many different compounds. The carbonaceous
residue left at the end of the TGA testing was assumed to be pure carbon, however measuring the
chemical composition of fhis residue would add more understanding of bio-oils volatility.
Bibliography
[1] M. F. Demirbas, “Current technologies for biomass conversion into chemicals and fuels,” Energy
Sources, Part A: Recovery, Utilization, and Environmental Effects, vol. 28, pp. 1181–1188, October
1 2006 2006.
[2] A. V. Bridgwater, “Renewable fuels and chemicals by thermal processing of biomass,” Chemical
Engineering Journal, vol. 91, no. 2-3, pp. 87–102, 2003.
[3] I. Dincer, Progress in Sustainable Energy Technologies: Generating Renewable Energy. Cham:
Imprint: Springer, 2014. ID: 9899502 (UTL catalogue ckey).
[4] T. Koizumi, Biofuels and Food Security: Biofuel Impact on Food Security in Brazil, Asia and Major
Producing Countries. Cham: Imprint: Springer, 2014. ID: 9742106 (UTL catalogue ckey).
[5] T. Tzanetakis, Spray Combustion Characteristics and Emissions of a Wood Derived Fast Pyrolysis
Liquid-Ethanol Blend in a Pilot Stabilized Swirl Burner. PhD thesis, University of Toronto, Toronto,
2011.
[6] D. Auld, “The economics of ethanol, agriculture and food,” Journal of Sustainable Development,
vol. 5, pp. 136–143, 08 2012.
[7] S. Moloodi, T. Tzanetakis, B. Nguyen, M. Zarghami-Tehran, U. Khan, and M. J. Thomson, “Fuel
property effects on the combustion performance and emissions of hardwood-derived fast pyrolysis
liquid-ethanol blends in a swirl burner,” Energy & Fuels, vol. 26, no. 9, pp. 5452–5461, 2012.
[8] A. V. Bridgwater and G. V. C. Peacocke, “Fast pyrolysis processes for biomass,” Renewable and
Sustainable Energy Reviews, vol. 4, no. 1, pp. 1–73, 2000.
[9] O. D. Mante and F. A. Agblevor, “Storage stability of biocrude oils from fast pyrolysis of poultry
litter,” Waste Management, vol. 32, pp. 67–76, 201201 2012.
[10] A. Oasmaa and E. Kuoppala, “Fast pyrolysis of forestry residue. 3. storage stability of liquid fuel,”
Energy & Fuels, vol. 17, no. 4, pp. 1075–1084, 2003.
[11] S. Czernik and A. V. Bridgwater, “Overview of applications of biomass fast pyrolysis oil,” Energy
& Fuels, vol. 18, no. 2, pp. 590–598, 2004.
[12] C. Shaddix and D. Hardesty, “Combustion properties of biomass flash pyrolysis oils: Final project
report,” Tech. Rep. SAND99-8238, Sandia National Laboratories, 1999.
39
Bibliography 40
[13] M. E. Boucher, A. Chaala, and C. Roy, “Bio-oils obtained by vacuum pyrolysis of softwood bark
as a liquid fuel for gas turbines. part i: Properties of bio-oil and its blends with methanol and a
pyrolytic aqueous phase,” Biomass and Bioenergy, vol. 19, no. 5, pp. 337–350, 2000.
[14] A. Oasmaa and S. Czernik, “Fuel oil quality of biomass pyrolysis oils-state of the art for the end
users,” Energy & Fuels, vol. 13, no. 4, pp. 914–921, 1999.
[15] E. A.V. Bridgwater, Fast pyrolysis of biomass : a handbook volume 3. Newbury: CPL Press, 2005.
[16] 2012 ASTM Standard D7544, “Standard specification for pyrolysis liquid biofuel,” West Con-
shohocken, PA: ASTM International, 2012, DOI:10.1520/D7544-12, www.astm.org.
[17] H. Naganuma, N. Ikeda, T. Ito, and H. Satake, “Control of ash deposition in solid fuel fired boiler,”
Fuel Processing Technology, vol. 105, p. 77, Jan 2013.
[18] A. V. Bridgwater and M. L. Cottam, “Opportunities for biomass pyrolysis liquids production and
upgrading,” Energy & Fuels, vol. 6, no. 2, pp. 113–120, 1992.
[19] F. A. Agblevor and S. Besler, “Inorganic compounds in biomass feedstocks. 1. effect on the quality
of fast pyrolysis oils,” Energy & Fuels, vol. 10, no. 2, pp. 293–298, 1996.
[20] A. V. Bridgwater, “Upgrading biomass fast pyrolysis liquids,” Environmental Progress & Sustainable
Energy, vol. 31, no. 2, pp. 261–268, 2012.
[21] J. Scahill, J. Diebold, and C. Feik, “Removal of residual char fines from pyrolysis vapors by
hot gas filtration,” in Developments in Thermochemical Biomass Conversion (A. Bridgwater and
D. Boocock, eds.), pp. 253–266, Springer Netherlands, 1997.
[22] J. Diebold, S. Czernik, J. Scahill, S. Phillips, and C. Feik, “Hot-gas filtration to remove char from
pyrolysis vapors produced in the vortex reactor at nrel,” in Biomass Pyrolysis Oil Properties and
Combustion Meeting, Proceedings, NREL CP-430-7215, pp. 90–109, 1994.
[23] F. Wenting, L. Ronghou, Z. Weiqi, and M. Yuanfei, “Influence of methanol additive on bio-oil
stability,” International Journal of Agricultural and Biological Engineering, vol. 7, p. 83, -06-01
2014.
[24] Y. Tao, C. Y. Wu, and D. W. Mazyck, “Removal of methanol from pulp and paper mills using
combined activated carbon adsorption and photocatalytic regeneration,” Chemosphere, vol. 65,
no. 1, pp. 35–42, 2006.
[25] S. S. da Silva, Biofuels in Brazil: Fundamental Aspects, Recent Developments, and Future Perspec-
tives. New York: Imprint: Springer, 2014.
[26] X. Hu, Y. Wang, D. Mourant, R. Gunawan, C. Lievens, W. Chaiwat, M. Gholizadeh, L. Wu, X. Li,
and C.-Z. Li, “Polymerization on heating up of bio-oil: A model compound study,” AIChE Journal,
vol. 59, no. 3, pp. 888–900, 2013.
[27] Y. Xu, X. Zheng, Y. Peng, and B. Li, “Upgrading the lubricity of bio-oil via homogeneous catalytic
esterification under vacuum distillation conditions,” Biomass and Bioenergy, vol. 80, pp. 1–9, Sept
2015.
Bibliography 41
[28] K. L. Hew, A. M. Tamidi, S. Yusup, K. T. Lee, and M. M. Ahmad, “Catalytic cracking of bio-oil
to organic liquid product (olp),” Bioresource technology, vol. 101, pp. 8855–8858, Nov 2010.
[29] P. M. Mortensen, J. D. Grunwaldt, P. A. Jensen, K. G. Knudsen, and A. D. Jensen, “A review
of catalytic upgrading of bio-oil to engine fuels,” Applied Catalysis A, General, vol. 407, pp. 1–19,
20111104 2011.
[30] S. Francey, H. Tran, and A. Jones, “Current status of alternative fuel use in lime kilns,” TAPPI
Journal, pp. 33–39, oct 2009.
[31] I. R. Dominguez, J. Gmez-Milln, M. Alvarez, S. D. Aza, L. Contreras, and A. H. D. Aza, “Build-
up formation and corrosion of monolithic refractories in cement kiln preheaters,” Journal of the
European Ceramic Society, vol. 30, pp. 1879–1885, Jul 2010.
[32] A. Demirbas, “Biofuels sources, biofuel policy, biofuel economy and global biofuel projections,”
Energy Conversion and Management, vol. 49, no. 8, pp. 2106–2116, 2008.
[33] Y. Li, A. Watkinson, and P. Barr, “Bio-oil as a fuel for the lime kiln,” in Science in Thermal and
Chemical Biomass Conversion (Bridgwater and Boocock, eds.), pp. 1491–1503, CPL Press, 2006.
[34] S.-S. Hou, F. M. Rizal, T.-H. Lin, and T.-Y. Yang, “Microexplosion and ignition of droplets of fuel
oil/bio-oil blends,” Fuel, vol. 113, p. 31, Nov 2013.
[35] R. Calabria, F. Chiariello, and P. Massoli, “Combustion fundamentals of pyrolysis oil based fuels,”
Experimental Thermal and Fluid Science, vol. 31, no. 5, pp. 413–420, 2007.
[36] A. H. Lefebvre, Atomization and sprays. New York: Hemisphere Pub. Corp., 1989.
[37] A. Gupta, D. Lilley, and N. Syred, Swirl Flows. England: Abacus Press, Tunbridge Wells, 1984.
[38] BEX Engineering Ltd., Mississauga, Ontario, Canada, Catalog No. JPL99C, JPL Series Air Atom-
izing Nozzles.
[39] Q. Lu, W.-Z. Li, and X.-F. Zhu, “Overview of fuel properties of biomass fast pyrolysis oils,” Energy
Conversion and Management, vol. 50, pp. 1376–1383, 200905 2009.
[40] K. Schofield, “The enigmatic mechanism of the flame ionization detector: Its overlooked implications
for fossil fuel combustion modeling,” Progress in Energy and Combustion Science, vol. 34, pp. 330–
350, 2008.
[41] R. S. Figliola, Theory and design for mechanical measurements. Hoboken, N.J.: John Wiley &
Sons, 4th ed. ed., 2006.
[42] R. Dennis, W. R. Samples, D. M. Anderson, and L. Silverman, “Isokinetic sampling probes,”
Industrial & Engineering Chemistry, vol. 49, no. 2, pp. 294–302, 1957.
[43] T. Allen, Particle size measurement. London: Chapman and Hall, 4th ed. – ed., 1990.
[44] I. Glassman, Combustion. Boston: Elsevier, 4th ed. ed., 2008.
Bibliography 42
[45] C. R. Shaddix and P. J. Tennison, “Effects of char content and simple additives on biomass pyrolysis
oil droplet combustion,” Symposium (International) on Combustion, vol. 27, no. 2, pp. 1907–1914,
1998.
[46] S. Moloodi, T. Tzanetakis, B. Nguyen, M. Zarghami-Tehran, U. Khan, and M. J. Thomson, “Fuel
property effects on the combustion performance and emissions of hardwood-derived fast pyrolysis
liquid-ethanol blends in a swirl burner,” Energy & Fuels, vol. 26, no. 9, pp. 5452–5461, 2012.
[47] H. Zhu, S. V. Bohac, K. Nakashima, L. M. Hagen, Z. Huang, and D. N. Assanis, “Effect of fuel oxy-
gen on the trade-offs between soot, {NOx} and combustion efficiency in premixed low-temperature
diesel engine combustion,” Fuel, vol. 112, pp. 459 – 465, 2013.
[48] T. Tzanetakis, S. Moloodi, N. Farra, B. Nguyen, and M. J. Thomson, “Spray combustion and
particulate matter emissions of a wood derived fast pyrolysis liquid-ethanol blend in a pilot stabilized
swirl burner,” Energy & Fuels, vol. 25, no. 4, pp. 1405–1422, 2011.
[49] K. P. Vanoverberghe, E. V. V. D. Bulck, and M. J. Tummers, “Confined annular swirling jet
combustion,” Combustion Science and Technology, vol. 175, pp. 545–578, March 2003.
Appendix A
Fuel Flow Rate Calculation
The fuel flow rates were calculated using the LHV of each fuel and the percentage of the total power
required from each fuel. The LHV for bio oil was provided as kJ/L and the LHV for natural gas was
provided in kJ/L. The flow rates, mL/min for bio-oil and L/min for natural gas, were calculated with
the following equations.
Vbio−oil = %bio−oil ∗10kW
LHVbio−oil∗ 60000 (A.1)
Vnaturalgas = (1−%bio−oil) ∗10kW
LHVnaturalgas∗ 60 (A.2)
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Appendix B
Peristaltic Pump Flow Rate
Calibration
To calibrate the peristaltic pumps, bio-oil was pumped at various pump RPMs to determine the
relationship between RPM and flow rate. These tests are summarised below.
Table B.1: pumpcal
RPM Flow Rate83 2790 29100 32
Using these points, a line was fit to calculate the RPM for any flow rate.
RPM = 3.1037 ∗ Vbio−oil (B.1)
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