Burning of Fuel Oil Mixed With Biofuel Derived From Lauan
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Transcript of Burning of Fuel Oil Mixed With Biofuel Derived From Lauan
Burning of Fuel Oil Mixed with Biofuels Derived from
Lauan Wood
Fakhrur M. Rizal1, Ta-Hui Lin
2*, Tzu-Yueh Yang
3, Hou-Peng Wan
3, Hom-Ti Lee
3
1Department of Mechanical Engineering, National Cheng Kung University
2 Research Center for Energy Technology and Strategy, National Cheng Kung University
3 Industrial Technology Research Institute, Green Energy and Environment Research
Laboratories, New Energy Technology Division
*e-mail: [email protected] (corresponding author)
Abstract
Vaporization characteristics of a single droplet of pyrolysis biofuels (PB) and fuel oil
emulsified were examined by using a suspended-droplet heating device. The tested biofuels
were produced from the pyrolysis process of lauan (shorea) wood. The heating temperature
and the mixing ratio of fuel oil and biofuels were varied in the experiment. Variations of drop
images in the vaporization process were recorded using a high speed camera. The d2-law was
applied to determine the behavior of the heated drop in the vaporization process. Results
showed that microexplosion and random behavior occurred for all cases of biofuels and fuel
oil emulsified and also pure biofuels. Random behavior of microexplosion occurred was
caused by the biofuels are being composed of many chemical compositions with various of
boiling points and also high contents of water. The evaporation rate of the drop identified by
the slope of d2-law line increased with heating temperature. Microexplosion and random
behavior of drop occurred more often at high temperatures and also ignition was found for
several cases at 500 OC.
Keywords: vaporization, single droplet, pyrolysis biofuels
1. Introduction
Currently, fossil fuels are still the main options as energy source for the world. However,
the availability of fuel is becoming less for each passing year. Research shows that within 40-
50 years, fossil fuels will become scarce and hard to find. And not only that, fossil fuels has
been proven responsible for the environment adversities such as global warming, acid rain,
urban smog, etc. due to the level of pollutant emissions produced [1]. Therefore, it is
necessary to find environmental-friendly alternative fuels that can be produced steadily.
Biofuels has emerged as the alternative fuels that can replace fossil fuels. There are
several reasons why biofuels become good alternative fuels, which include lower emissions
of greenhouse gases and pollutants such as sulfur (virtually none) and soot, as well as
polycyclic aromatic hydrocarbon (PAH) and nitrited PAH (regarded as carcinogens),
reduction of deforestation, increased lubricity for long-life utilization, and a higher flash point
for safer storage and management [2]. In addition, biofuels can be produced from various
types of plants such as rapeseed [3, 4], sun flower [4], cassava [5], sugarcane [6], etc. And
they can also be produced from wood [7], and fish oil [8].
Pyrolysis is an applicable method that can be used to convert energy from biomass into
biofuels by thermochemical conversion technology [9]. It involves the heating of organic
materials in the absence of reagents, especially oxygen, to achieve decomposition. Pyrolysis
biofuels (PB) is black-brownish liquids obtained by the condensation of vapors during the
pyrolysis of wood and other vegetable biomasses. The efficiency of the production process is
very high, typically we can generate around 70% of PB in weight from the raw material [10].
Pyrolysis biofuels are multi-component mixtures of different chemical compounds
derived from depolymerization and fragmentation of cellulose, hemicellulose and lignin.
Therefore, the elemental composition of PB and petroleum derived fuel is different [11, 12].
Consequently, the chemical and physical properties of fast pyrolysis bio-oil adversely affect
their combustion properties and result in difficulties in storage and handling. Biofuels is
characterised by high viscosity, acidity and electrical conductivity, presence of water and
various oxygenated compounds, ash and other solid impurities [13]. Biofuels has low heating
value, and does not ignite readily. Bio-oil is shown to be unstable when subjected to
relatively high temperature for long periods. A characteristic of this unstable oil is its self-
polymerization [14].
Many projects were conducted about pollutant emissions and performances of engines
or power plants using biofuels as fuel [1, 15]. On the other hand, only few fundamental
studies were conducted about the vaporization and combustion characteristics of biofuels
droplets. Such studies could provide the necessary basic data to characterise the mechanisms
responsible for deposit formation during biofuels combustion. Wornat et al. [16] have
performed single droplet experiments with two biomass oils, produced from the pyrolysis of
oak and pine. Liquid-phase polymerization and pyrolysis of the oxygenate-rich biomass oils
lead to the formation of carbonaceous cenospheres. The vaporization mechanisms of waste
vegetable oils droplets were investigated by Li et al.[17]. Results show that the biodiesel
droplet has higher burning rate, and that biodiesel in general has a lower propensity to soot
because its molecular oxygen content promotes the oxidation of the soot precursors. Calabria
et al. [18]investigated the combustion fundamentals of pyrolysis-oil-based fuels. The
microexplosion mechanism inside the droplets was observed and was found more important,
with biofuels droplets than with diesel fuel. According to the chemical composition of
biofuels and their esters, the residue formation is more or less important [4].
In this work, experimental results concerning the vaporization and droplet behavior of
mixed diesel and biofuels droplets are presented. The vaporization and droplet behavior have
been determined for mixed fuel oil (diesel oil, heavy oil) and biofuels at a variety of mixing
ratios and temperatures under atmospheric pressure. The results are compared with those
using pure fuel oil and pure biofuels at the same variety temperature.
2. Experimental setup
A schematic of the experiment apparatus used in the study of suspended drop is shown in
figure 1. The experiment was conducted by placing a single droplet of fuel on the moving
thermocouple which simultaneously measured the temperature of the fuel drop and another
thermocouple was used to measure the temperature between the heating plates. Both of the
thermocouples we used were K-type thermocouples. Two heating plates kept the temperature
at a stable value during the test. The temperature between heating plates was controlled by
the temperature controller [19]. One camera shooting was conducted after the droplet was
hung on the thermocouple to determine the initial size of the droplet before the heating
experiment began.
The biofuels was produced from pyrolysis of lauan (shorea) wood. The basic data of
the biofuels are shown in Table 1. The experiments were conducted at different temperatures
with a variety of mixing ratio (pure fuel oil, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%,
80%, 90%, 100% of biofuels). Two kinds of fuel oil were chosen: diesel oil and heavy oil.
The average initial diameter of the drop diameter was around 1 mm. Because of the thickness
of the suspension fiber and its thickened end because of the joining process, it is somewhat
difficult to suspend a droplet much smaller than 1 mm in diameter, which is much larger than
typical droplet sizes within sprays. This should not be of serious concern if the size-
dependence of the phenomenon of interest is known. However, the shape of the suspension
fiber (thermocouple) that also gave an effect in the process of evaporation, particularly
towards the end of the droplet lifetime. This is because the size of the droplet at that time was
close to the size of the joining suspension fiber [20].
Table 1. Chemical properties of the pyrolysis biofuels of lauan wood
Fig 1. Experimental apparatus
The experiment began with the movement of the first thermocouple to the heating plates
by turning on the motor. When the moving arm touched the switch (trigger), the
thermocouple was in the right position. The phenomenon was captured and recorded using a
high speed camera. There was a delay circuit to set the delay time before the high speed
camera was turned on. The delay was conducted because of the limitation of the high speed
camera, which could only record the pictures for just a few seconds. High speed camera was
turned on before the lights to synchronize the time between the images with the data in the
computer. The images were measured and then the droplet size variation was plotted against
time according to the D2 law [21, 22].
Figure 2 shows some of the phenomena that may occur during the suspended drop
experiment. Line A-B-C-D shows the temperature of the droplet. Line a-b-c-d-e indicates the
diameter-squared of the drop. A-B is a phenomenon where the droplet absorbs heat from the
surrounding temperature. In this stage, the droplet starts to react with the heat treatment, such
as in a-b which microexplosion occurred early in the experiment and then followed by
evaporation in line b-c. c-d is the expansion phenomenon and ends with the stable state
condition shown in d-e where the droplet is at a stable size for a while. Plot B-C is the
ignition event and the droplet burned in this time interval. After ignition occurs, the
temperature becomes stable as shown in C-D. The results obtained were not all like figure 3.
It depends on the parameters imposed on the experiment.
Fig 2. Single droplet burning phenomenon
3. Results and discussion
Vaporization experiments for diesel/biofuels emulsified droplets, heavy oil/biofuels
emulsified and pure biofuels have been conducted in air at different temperatures and under
atmospheric pressure with a variety of mixing ratios.
3.1 Combustion of pure pyrolysis biofuels
The evolution of the droplet diameter was plotted versus the normalized time. Figures 3
and 4 show the experimental results for pure biofuels. In figure 3 at T = 300 OC, we can see
that microexplosion and random behavior occurs during the test as shown by the squared-
diameter of the droplet fluctuated which changes quite violently from t = 0 s to t = 5 s and
also can be seen at the images sequences at t = 0.263 s, 1.472 s, 1.731 s. Random behavior is
the condition where the size of the droplet kept changing and unpredictably. Random
behavior and micro explosion occurs because of bubbling. The bubbling phase is
characterized by the formation of small bubbles that move toward the surface of the droplet
where they explode producing small fragments, see images sequences at t = 1.47 s. The
biofuels used was a multi-component fuel in which there were many types of compounds
contained within. High percentage of water contents inside the biofuels also become the
major factors of the occurrence of bubbling phase. Droplet diameter changes cannot be
predicted when the microexplosion and random behaviors occurs. Ignition can not be found
in all cases with T = 300 OC because the temperature was not high enough to ignite the
droplet.
Fig 3. Suspended droplet results of pure biofuels at 300 OC
At higher temperatures as shown in figure 4 at T = 500 OC, Microexplosion and
random behavior occurs from t = 0 s to t = 2 s followed by expansion as can be seen in
images sequences at t = 3.648 s. during expansion periods, the droplets size did not change or
-4 0 4 8 12
Time (s)
0
400
800
1200
Tem
per
ature
(OC
)
0
1
2
3
(d/d
0)2
Pure biofuels
T = 300 OC
d0 = 1.12 mm
kept stable. Expansion corresponds to the heterogeneous combustion of cenospheres, i.e., the
carbonaceous particle formed by pyrolysis oils during the last stages of droplet combustion
[18]. Ignition can be observed in this case as shown by the changing of temperature curves at
t = 3.8 s to t = 5 s and also can be seen in the images sequences at t = 3.821 s where the flame
is appeared.
Fig 4. Suspended droplet results of pure biofuels at 500 OC
3.2 Combustion of emulsions of pyrolysis biofuels in diesel oil
Experiment using emulsions of pyrolysis biofuels in diesel oil were conducted for 5%
biofuels and each multiple of ten percent in the mixture. The experimental results shows that
more biofuels content in the mixtures, more unstable the emulsion, as already explained
above that the biofuels itself basically consists of many components. So, just a little biofuels
in the diesel can result in microexplosion and random behavior. More biofuels significantly
resulted in microexplosion and random behavior occurred frequently and more quickly.
At low percentages of biofuels in the diesel oil as shown in figure 5, diesel oil dominates
where in the experiment using pure diesel oil, random behavior and microexplosion can not
be found, only evaporation occurs followed by increasing the evaporation rate when the T
increases. In figure 5 we can see that microexplosion and randon behavior occurs in small
scales as shown in images sequences at t = 0.33 s where the droplets size changes a little bit.
Not much carbonaceous particles can be formed due to the amount of biofuels so that the
expansion almost can not be observed, but little bit amount of fuel left on the thermocouple
and finally ignition occurs as shown by the changing of temperature curves at t = 1.4 s to t =
2 s and appearance of flame in images sequences at t = 1.4 s.
-4 0 4 8 12
Time (s)
0
400
800
1200
Tem
per
ature
(OC
)
0
1
2
3
(d/d
0)2
5% Biofuels, 95% Diesel oil
T = 500 OC
d0 = 1.1 mm
Fig 5. Suspended droplet results of emulsions of biofuels in diesel oil at 500 OC
Increasing the amounts of biofuels will increase the emergence of microexplosion and
random behavior as shown in figure 6 squared-diameter of droplet and images sequences at t
= 1.296 s. Expansion can be observed in this case as shown in images sequences at t = 4.212 s
followed by ignition at t = 4.462 s. a lot of carbonaceous particles formed when the amounts
of biofuels increased so that the expansion can be observed more clearly.
Fig 5. Suspended droplet results of emulsions of 50% biofuels in diesel oil at 500 OC
3.3 Combustion of emulsions of pyrolysis biofuels in heavy oil
Suspended droplet experiments were also conducted for the cases of biofuels and heavy
oil. Random behavior, micro-explosion, bubbling, and expansion also can be found in these
cases but for ignition, only several cases in biofuels/heavy oil emulsions when biofuels
-4 0 4 8 12
Time (s)
0
400
800
1200
Tem
per
ature
(OC
)
0
1
2
3
(d/d
0)2
5% Biofuels, 95% Diesel oil
T = 500 OC
d0 = 1.1 mm
-4 0 4 8 12
Time (s)
0
400
800
1200
Tem
per
ature
(OC
)
0
1
2
3
(d/d
0)2
60% Biofuels, 40% Diesel oil
T = 500 OC
d0 = 0.96 mm
content is higher in the emulsions.
For biofuels/heavy oil emulsions, evaporation and bubbling occurs very slow but stronger
than biofuels/diesel oil cases. At low percentage of biofuels in heavy oil as seen in figure 6,
microexplosion occurs very strong. The droplets size increase up to 2 times of the initial size
before exploding as shown in squared-diameter curves at t = 2 s. compared with
biofuels/diesel oil emulsions which microexplosion occurs weaker but faster. That’s because
of heavy oil itself has higher boiling point than diesel oil, so that in the heavy oil cases, the
occurrence of evaporation and bubbling was little bit longer than diesel oil cases. And also
the viscosity of the heavy oil is higher than diesel so for exploding needs bigger bubble. At
small amount of biofuel in the emulsion, ignition could not be observed. 500 OC is not
enough to ignite the droplets. But at higher percentage of biofuels at 500 OC, ignition
occurred. Ignition occurs started from case with 60 % biofuels in the emulsions. In figure 7
we can see the ignition occurs at 500 OC with 70% biofuels in the emulsions as shown by the
changing of the temperature curves at t = 9 s to t = 11 s.
Fig 6. Suspended droplet results of emulsions of 5% biofuels in heavy oil at 500 OC
-4 0 4 8 12
Time (s)
0
400
800
1200
Tem
per
ature
(OC
)
0
1
2
3
(d/d
0)2
5% Biofuels, 95% HFO
T = 500 OC
d0 = 0.95 mm
Fig 7. Suspended droplet results of emulsions of 70% biofuels in heavy oil at 500 OC
3.4 Burning of Droplets Emulsified
In the burning of droplets emulsified, there were 3 stages or phenomenons can be
observed. All the cases had the same profiles of temperature curves where heat absorption at
the beginning followed by drastic changes of temperature (ignition) and finally the
temperature stabilization. For the (d/d0)2 curves, the phenomenon which can be observed was
the same for the ignition cases. We found microexplosion and random behavior (bubbling
stage), evaporation, expansion, and end with ignition.
In the burning cases, time interval of each phenomenon became the major different.
Figures 8 shows the time interval between each phenomenon. Expansion initiation means the
state where the droplet started to become bigger. In this state, evaporation and bubbling phase
occurred. Ignition means the beginning of burning. And the last is extinction after the burning
was finished and the droplet completely burned.
For biofuels/diesel oil emulsions (see figure 8a), the results shows that more biofuels in
the emulsions, the phenomenon that occurred became longer for not only evaporation and
bubbling but also the expansion and ignition interval. More biofuels means more
carbonaceous particle formed so the expansion became longer and then more biofuels made
the emulsion became more unstable so that the microexplosion and random behavior
(bubbling state) became longer too. And also the burning became longer because more
biofuels means more flammable substance inside and slower burning speed because the
heating value of biofuels is low compared with fuel oils and water content also increased by
increasing the amount of biofuels. For the 70, 80, and pure cases the results was lower than
the previous. That’s because of during microexplosion, small droplets came out from the
-4 0 4 8 12
Time (s)
0
400
800
1200
Tem
per
atu
re (
OC
)
0
1
2
3
(d/d
0)2
70% Biofuels, 30% HFO
T = 500 OC
d0 = 1 mm
main droplet so that the interval between each phenomenon became shorter.
For biofuels/heavy oil emulsions (see figure 8b), ignition did not occur for the cases with
5-50% biofuels inside but when we added more biofuels inside, ignition could occur. It was
difficult to burn heavy oil at 500 OC. Even at 500
OC, the evaporation occurred slower
compared with others fuels. Not enough flammable substance in the emulsion with lower
percentage of biofuels. At higher percentage (more than 50%), ignition was found but the
ignition time is quiet long. Adding more biofuels will decrease the ignition time as shown in
that figure. The key point for biofuels/heavy oil cases at 500 OC is more biofuels, more
flammable substance so that the ignition became faster occurred.
Figure 8. Burning cases of emulsions of biofuels/diesel oil (a), biofuels/heavy oil (b).
4. Conclusions
Suspended droplets experiment was conducted to see the vaporization and burning
phenomenon of the emulsions on the micro point of view. Emulsions was prepared for
biofuels/diesel oil emulsions and biofuels/heavy oil omulsions and also the mixing ratio
became the parameter in this study.
In the experiment using pure biofuels, micro-explosion and random behavior of droplet
occurs. Droplet size changes can not be predicted and also ignition occurs at 500 OC. For the
diesel/biofuel emulsions, random behavior and micro-explosion occurred during the
experiment. The more contents of biofuels in the mixtures, micro-explosion and random
behavior of the droplet occurred more frequently. Some of the particles contained in the
biofuels expanded at the end of the droplet lifetime and the droplet would be in stable state
0 20 40 60 80 100
Mixing ratio (%biofuels)
0
5
10
15
20
25
Tim
e (s
)
Expansion
Ignition
Extinction
biofuels/diesel oil (500 OC)
0 20 40 60 80 100
Mixing ratio (%biofuels)
0
5
10
15
20
25
Tim
e (s
)Expansion
Ignition
Extinction
biofuels/heavy oil (500 OC)
no ignition
a) b)
condition where its size would not change for several seconds before finally burned. In the
case of 500 OC the ignition occurred a moment after the stable state.
For biofuels/heavy oil emulsions, ignition did not occur at low percentage of biofuels in
the heavy oil. Ignition could be observed when the amount of biofuels in the heavy oil was
increased more than 60% but it took longer times for biofuels/heavy oil emulsions to be
burned compared with the biofuels/diesel oil cases.
5. Acknowledgement
The financial support provided by Bureau of Energy (Grant No. 100-D0103) is gratefully
acknowledged.
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