長岡工業高等専門学校研究紀要

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第45巻

第２号（2009）

文

A MECHANICAL EMULSIFICATION TECHNOLOGY OFPETROLEUM FUELS WITHOUT SURFACE ACTIVE AGENT
Hiroki ISHIDA1 and Kazuya TACHIBANA1
1

Dept. of Electronic Control Engineering, Nagaoka National College of Technology

A mechanical emulsification device using a gear pumping mechanism consisting of somespecified gears has been studied and developed to improve emulsification performance of petroleum
fuel oils. By using the gear pump type emulsifier; stable W/O type emulsions of gas oil and of
A-heavy oil can be produced successfully without surface-active agent. The study revealed someinteresting and important characteristics of the mechanical emulsification process; the limiting
content of water, the limiting revolution of the driving gear, the stability of emulsion, and theemulsification performance and discharge rate of the emulsifier.
Key words: W/O type emulsion, Gear pump mechanism, Micro-explosion, Gas oil, A-Heavy oil

1. INTRODUCTION AND BACKGROUND
In the recent several years, as same as in overabout thirty years ago, the technology of applicationof emulsion fuels to many boilers, furnaces anddiesel engines has attracted much attention from thepoint of view of the energy saving and of theprevention of atmospheric pollution caused by theexhaust from many combustion facilities. It is,mainly, due to the recent high cost of crude oil andto the prevalence of the national consensus of theprotection of environment.
The kind of emulsion fuels, consisting of usual
petroleum fuels and water, is divided into two types;
W/O and O/W emulsions. W/O type emulsion fuelhas dispersed many fine water particles in the basepetroleum fuel. On the other hand, O/W typeemulsion fuel has, inversely, dispersed many finepetroleum fuel particles in the water phase.
The ideas of combustion of emulsified petroleum
fuels by mixing with water in many commercial
furnaces have been reported since many years ago.
Many excellent studies have reported them
1-4,8-17,21-23,25-32,34,37,38,41)
experimentally
and
5-7,11,35).� From the point of view oftheoreticallyfire hazard prevention also, some studies havereported the pool burning characteristics of
10,15,18-20,24,36).
An
emulsified petroleum fuels
excellent review by Kadota and Yamasaki hasreported the recent advances of the study on the.

40)

emulsion combustion . In the recent decade,some studies have reported the new technology for
33,39,41,42).
the emulsification�
2. EMULSION FUEL COMBUSTION
The main advantage of emulsion combustion isdue to the characteristic combustion behaviors of
the sprayed emulsified fuel droplets, caused by the
included many fine water particles in each droplet.
The diameters of the liquid fuel droplets sprayed
into the combustors are, usually, in the range of30~130�m. Under the usual standard atmosphericpressure, the volume of one water droplet isexpanded about 1700 times larger than the original
droplet volume due to the vaporization.
Namely, in the high temperature atmosphere in
the combustion chamber, fine water droplets
included in each emulsion fuel droplet will explodedue to the instantaneous vaporization, and smash
the emulsion fuel droplet. This is called as the
micro-explosion of the fuel droplet, which leads tothe main advantages of the emulsion combustion asshown below;(1) The micro-explosion of the fuel droplets dueto the included water particles promotes theatomization of the fuel particles, namely promotes
the mixing of the fuel with the surrounding air. The
combustion efficiency can be increased thereby inhigh temperature combustion chambers; boilers,― 47 ―

Hiroki ISHIDA，Kazuya TACHIBANA

forging furnaces, etc.
(2) Owing to the increase in the combustion
efficiency in the furnaces and boilers using
emulsion fuels, the needed amount of cold excess
air, which is additionally blown into the furnaces
for the complete combustion of fuels, can be
reduced dynamically. The residence time of the hot
combustion gases in the furnace becomes longaccordingly. Heat loss from the furnaces andboilers can be thereby decreased dynamically,
which leads to the obvious reduction of fuelconsumption.
(3) The amount of soot and particulates in theexhausted gases can be reduced due to theWater-Gas Reaction in the high temperature
combustion chambers.
(4) Concentration of NOx in the exhaust gas canbe decreased owing to the decrease in the
combustion gas temperature.
(5) Owing to the emulsification many kinds ofthe waste oils, from machine and food, can berecycled as the useful fuels in many forging
furnaces and boilers.
For the stable and long running of many emulsion
fuel combustors (including boilers and forging
furnaces) without any trouble, the following
specifications will be needed;(1) Diameters of water particles in the sprayedeach emulsion fuel droplet should be as uniform as
possible and less than about 10�m.
(2) Emulsion should be stable, namely no
separation between the base petroleum fuel and thewater occurs until the emulsion fuel is transported
into the combustors.
(3) The stability of emulsion fuel should not beaffected by the changes of the temperature and of
the flow rate into the combustors.
(4) In the use of emulsion fuel, there is no
corrosion in any parts and devices in combustor.
(5) The amount of the used surface-active agent
for emulsification should be as small as possible.
(6) The system of emulsion production is not so
expensive.
3. DEVELOPMENT OF EMULSIFIED FUELS� To produce and maintain the stable emulsified
fuel there have been some very difficult points;
uniform and stable dispersion of insoluble finewater particles in the petroleum fuels, thetransportation into combustion chambers or
furnaces without any disruption of emulsion state.
It is thereby not easy to attain the stable combustionof sprayed emulsion fuel without any trouble for along running period of many combustors.
Many manufacturers of combustion devices have,.

therefore, tried to develop and improve theemulsification devices and emulsion combustors forrecent over two decades. Almost all the
manufacturers have tried to develop the stableemulsion fuels by using the surface-active agent in
the mixture of petroleum fuel and water, where theratio of water in the mixture is 20~40 vol.% or more.
Although it is the fact in itself that the emulsified
fuels including water can be burned in thelaboratory scale combustors, the application of theexperimental results to the many kinds of realindustrial combustion devices without any trouble is,however, never easy.
Needless to say, the cost of the surface-active
agent in emulsion fuel cannot be negligible during
the long running period of large-scale combustors,
although the needed amount of the surface-active
agent is not so large. In addition, the exhaust gases
from the combustors will contain the species of themolecules of surface-active agent. It should be
noted here that the use of the emulsion fuels that
contains too much water could never be a goodenergy-saving technology owing to the increase infuel consumption due to the large decrease in the
combustion efficiency.
The content of water in the emulsion fuel,therefore, should be determined and controlled
appropriately for the kind of base petroleum fuels,and never be increased so much from the point ofview of the long and safe running of the combustors(furnaces) without any trouble. The appropriate
water content will be less than about 10 vol.% for
the emulsified fuels of gas oil and A-heavy oil, andless than about 20 vol.% even for the emulsion of
C-heavy oil.
� Today, the search of "Emulsion Fuel" through theInternet shows us about 300~600 reports, articles
and research papers even in Japan. From the pointof view of the combustion engineering, however,many random and doubtful reports or articles also
can be found.
Who can believe the article where the emulsion
fuels of which the water content is 60 vol.% can beused in combustors for long period without any
trouble? Who can believe the article that aims
finally at water-combustion by using the emulsion
fuel with ultra high content of water? Needless tosay, we have known already that the use ofemulsion fuel in boilers, forging furnaces and diesel
engines is the excellent combustion technology forenergy saving and for prevention of environmental
pollution. Among many today's reports, articles andpapers concerning the emulsion fuel, we should,
therefore, review them strictly and find the realemulsiontechnologies
thatsatisfythe― 48 ―

A MECHANICAL EMULSIFICATION TECHNOLOGY OF PETROLEUM FUELS WITHOUT SURFACE ACTIVE AGENT

aforementioned Needed Specification of Emulsion
Fuel. The present study aims to develop a newmechanical technology of W/O type emulsificationof petroleum fuels without any surface-active agents,
and to examine the performance of the mechanicalemulsifier.
4. GEAR PUMP TYPE EMULSIFIER
An excellent mechanical emulsification device
using a kind of gear pumping mechanism consistingof some specified gears has been devised by
T.Nakayama since over twenty years ago, which is43)
described in his patent . The mechanicalemulsification device has been improved anddeveloped so that it can produce the stable W/Otype emulsion fuel mechanically without any
surface-active agent.
This mechanical emulsification device gives astrong shear stress to the mixture of water andpetroleum fuel in the squish among the rotating
gears and in the clearance between the gears andsurrounding housing wall. Water particles are
thereby strongly ground and mixed with basepetroleum fuel, and some of them become
extremely fine (less than about 10�m in diameter),which cannot be attained by the usual mechanicalmethods of mixing, atomizing or both. Thismechanical emulsification device enables also therecycling technology of some waste oils (frommachine and food) for the fuels in boilers and many
furnaces.
The present study examined experimentally thefollowing subjects:(1) Stability of the W/O emulsion produced bythis device.
(2) Improvement of the emulsification
performance of this gear pump type mechanicalemulsification device.
Figs.1 and 2 show the top and the side views of
the present gear pump type emulsifier, where thefirst gear is driven directly by motor at 300~1300
rpm. This emulsifier has a series of 3 gears: thediameters of gear tip circle and pitch circle;
27.5~22.5 mm and 25~20 mm respectively, thenumbers of teeth; 20~16, the modules of gears;
1.25~1.23, the teeth length in the axis direction ofgears; 40 mm.
The clearance between the gear tip and the
housing wall; 0.05 mm for the first gear, 0.5 mm at
one side of the second gear, about 0.15 mm at one
side of the third gear and about 0.4 mm at the
opposed side of the third gear. Owing to the verystrong shear stress in the wider clearances aroundthe second and the third gears, the fuel and water
are mixed and emulsified.

.

Fig.1 The scheme of top view of mechanical emulsifier(3-gears type) in this study.

Fig.2 The side view of mechanical emulsifier (3-gearstype) in this study.

In the present mechanical emulsifier, water istransported by water pump and injected at highspeed (9~13 m/s) from the fine exit hole (0.7 mm india.) nozzle toward the first gear aiming to enhancethe emulsification effect, as shown in Fig.3.
Fig.4 shows the schematic model of
emulsification region in the wider clearance(Emulsification Path shown in Fig.1) between thegear tip and the housing wall, where the mixture offuel and water is transferred (by the pressure due tothe revolution of the first gear) in the opposite
direction to the revolution of gear.
Although the theoretical explanation of thisemulsification mechanism is not easy and can not
be given in the present stage, it should be noted that
there is no other region for the emulsification except
the wider clearance, where the very strong shear
stress exists. We can expect thereby that the increasein the revolution of gear will enhance the stability ofemulsion.
Aiming to improve the emulsification
performance and to increase the discharge fromemulsifier, the emulsifier with two gears also has
been developed, shown in Figs.5 and 6.

― 49 ―

Hiroki ISHIDA，Kazuya TACHIBANA

Fig.3 Scheme of the water injection (Velocity: Vw )from the fine exit of nozzle to the first gear for theemulsification.

Fig.5 The scheme of top view of mechanical emulsifier(2-gears type) in this study.

Fig.4 Schematic model of the emulsification region in
the clearance between the gear teeth and the housing
wall.

This type of emulsifier has a series of the sametwo gears, where the diameters of the gear tip circle
and the pitch circle are 27.5 and 25 mm respectively.
The first gear is driven directly by motor at
300~1300 rpm. The teeth length in the axis
direction of gear is 60 mm, the module is 1.25, andthe number of teeth is 20. The clearance between
the first gear tip and the housing wall is about 0.05
mm. The clearance between the second gear tip andthe housing wall is 0.4 mm at one side
(emulsification path), and about 0.05 mm at theother side.
5. STABILITY OF EMULSIFICATION
A typical W/O emulsified gas oil, where thewater content is about 9 vol.% for gas oil is shownin Fig.7. Fig. 8 shows the typical microscopic
photograph of this emulsion, where we can confirm
many water particles (dispersed small circles) ofwhich the diameters are about 10�m or less.
A typical W/O emulsified A-heavy oil is shownin Fig.9, where the water content is about 6 vol.%for A-heavy oil. As shown in these photographs,
the colors of W/O type emulsified gas oil andA-heavy oil become whitish compared with that of
the original fuels.
.

Fig.6 The side view of mechanical emulsifier (2-gearstype) in this study.

It should be noted, however, that the present gear
pomp type emulsifier should be run in theappropriate condition for the production of stable
W/O emulsion. Too much water content and toostrong mixing with high revolution of driving gearor both will bring about very unstable emulsion, andoften result in the phase inversion from W/O to
O/W type, which is shown in Fig.10. The O/Wtype emulsion due to the phase inversion is
non-uniform and unstable (easy to break), whichleads to complete disruption of the emulsion. Thereexist consequently the limiting water content andthe limiting revolution of the driving gear for the
stable emulsification.
The stability (lifetime) of emulsion was examinedby the measurement of the decay of transmittance oflaser beam (He-Ne) due to the emulsification.
Fig.11 shows the relation of the relativetransmittance of emulsified gas oil; the ratio of thetransmittance of laser beam through the emulsion tothat through the original gas oil, and the elapsed
time from emulsification.

― 50 ―

A MECHANICAL EMULSIFICATION TECHNOLOGY OF PETROLEUM FUELS WITHOUT SURFACE ACTIVE AGENT

Fig.7 Representative photograph of emulsified gas oil(Water: 9 vol.% for Fuel, 800 rpm).

Fig.10
Representative photograph of O/W typeemulsified gas oil due to the phase inversion from W/O
type.

Relative Transmittance of LASER Beam �

1

Fig.8 Microscopic photograph of water particles in theemulsified gas oil (Water: 9 vol.% for Fuel, 800 rpm).

Fuel: Gas Oil
Water Content: 3 %

0.1

0.01

2-Gears Type, 600 rpm
2-Gears Type, 1200 rpm
3-Gears Type, 600 rpm
3-Gears Type, 1200 rpm

0.001

0.0001

0

12

24

36

48

60

Elapsed Times from Emulsification [hour]

Fig.11 Relative transmittance of laser beam through theemulsified gas oil.

Fig.9 Representative photograph of emulsified A-Heavy
oil (Water: 6 vol.% for Fuel, 800 rpm).

The low transmittance means stable emulsion,and the increase in the transmittance means the
disruption of emulsion; separation of fuel and water.
As shown in this figure, the emulsion of gas oil
begins to break at about 12 hours after theemulsification, and reaches complete disruption
after about 36 hours.
Fig.12 shows the relation between the time forbeginning of the disruption of A-heavy oil emulsion
and the revolution of the driving (the first) gear,
where the disruption was determined as theseparation of a half amount of water.

As shown in this figure, the increase in therevolution of emulsifier enhances the stability ofemulsion, which may be due to the strong mixing in
the emulsification path. The cross of the lines inthis figure may be due to the difference of theclearance in the emulsification path of theemulsifier.
Fig.13 shows the relation of the limit(permissible) of water content in the emulsion (Gasoil and A-heavy oil) and the revolution of drivinggear of emulsifier (2-gears type), where the limitingwater content was determined as the maximum
water content which can sustain the uniform andhigh stable emulsion for at least 30 seconds after thedischarge from emulsifier, and the phase inversion(from W/O to O/W) does not occur. As shown inthis figure, the water contents in the emulsions ofA-heavy oil and Gas oil should be less than 20
vol.% and 4 vol.% respectively if these emulsion
fuels are transported directly (without reserve tank)from this emulsifier to the combustor.

― 51 ―.

Hiroki ISHIDA，Kazuya TACHIBANA

1080

840

4000

Water Content: 3%
Fuel: A-Heavy Oil

Discharged Rate of Emulsion [ml/min]

Time for Water Separation [sec]960

3-Gears

720
600

2- Gears

480
360
240
120
0
500

600

700

800

900

1000

Motor Revolution [rpm]

1100

1200

3500

Emulsifier : 2-Gears Type
Fuel : Gas Oil

3000
2500
2000
1500

Water : 0ml/min
Water : 100ml/min
Water : 200ml/min
Water : 300ml/min

1000
500
0
150

1300

300

450

600

750

900

1050

1200

1350

Fig.14 Discharge rate of emulsified gas oil from
2-gears type emulsifier.
Motor Revolution [rpm]Fig.12 Relation between the time of beginning of
disruption (separation) of A-heavy oil emulsion (water; 3
vol.%) and the revolution of the driving (the first) gear ofemulsifier with 2 and 3 gears

Discharged Rate of Emulsion [ml/min]

4000

24

Limit of Water Content [%]22
20

Emulsifier: 2-Gears

18

A-Heavy Oil

16
14
12
10
8
6

600

700

800

900

1000

1100

1200

2500
2000

Water : 0ml/min
Water : 100ml/min
Water : 200ml/min
Water : 300ml/min

1500
1000
500

300

450

600

750

900

1050

1200

1350

Fig.15 Discharge rate of emulsified A-heavy oil from
2-gears type emulsifier.

1300

Motor Revolution [rpm]Fig.13 Relation of the limiting (permissible) watercontent in the emulsion (Gas oil and A-heavy oil) and therevolution of driving gear of emulsifier with 2-gears.

6. DISCHARGE PERFORMANCE
Figs.14 and 15 show the discharge rate ofemulsions of gas oil and of A-heavy oil at eachrevolution of the driving gear of emulsifier.
As shown in the result, we can see no obvious
difference due to the water content and to the fuel,although the difference in the viscosity of emulsion
due to the change of water content may affect thedischarge rate of gear pump type emulsifier.
7. EFFECT OF INLET PORT ORDER ON THE
EMULSIFICATION
Since the high-speed water injection toward thedriving gear will enhance the emulsification effectin the present emulsifier, we can infer that the orderof inlet ports of fuel and water also has somenoticeable effect on the stability of emulsion.

.

Emulsifier : 2-Gears Type
Fuel : A-Heavy Oil

Motor Revolution [rpm]

2
0
500

3000

0
150

Gas Oil

4

3500

Fig.16 shows the effect of the order of inlet ports
of fuel and water of the 3-gears type emulsifier(shown in Fig.1) on the time of disruption (theseparation of a half amount of water, as shown in
Fig.12). In the result, we can see a noticeable
increase in the stability of emulsion when the water
injection is the first and the fuel suction is thesecond. Although the clear explanation for thisresult can not be given in the presents stage, theemulsification effect due to high-speed water jet
near the driving gear before the inlet of fuel may
bring about it.
It should be noted also that the distribution rangeof water jet toward the driving gear will have a
noticeable effect on the emulsification in particular
for the emulsifier with large gears. Fig.17 showsthe effect of divergence of the water inlet; jet fromthe single fine hole (� 0.7) of nozzle and thatwithout nozzle, toward the driving gear on the timeof disruption (the separation of a half amount ofwater, as shown in Fig.12) for 2-gears typeemulsifier (the teeth length in the axis direction ofgear is 60 mm).

― 52 ―

A MECHANICAL EMULSIFICATION TECHNOLOGY OF PETROLEUM FUELS WITHOUT SURFACE ACTIVE AGENTIn the result, we can see a noticeable increase in
the stability of emulsion owing to the wide
divergence of water without nozzle. Consequently,
multi directional and wide range water injection
toward the driving gear will be needed for theemulsifier with large gears.

1200

Time for Water Separation [sec]1080

Emulsifier: 3-Gears Type
Water Content: 3%
Fuel: A-Heavy Oil

960
840
720

1-Water, 2-Fuel

600
480

1-Fuel, 2-Water

360
240
120
0
500

600

700

800

900

1000

1100

1200

1300

Motor Revolution [rpm]Fig.16 Effect of the order of inlet ports of fuel andwater on the time for water separation.

Time for Water Separation [sec]720

Emulsifier: 2-Gears Type (Order: 1-Fuel, 2-Water)
Water Content: 3%
Fuel: A-Heavy Oil

600

Without Nozzle

480

With Nozzle

360
240
120
0
500

600

700

800

900

1000

1100

1200

1300

Motor Revolution [rpm]Fig.17 Effect of the distribution of water injection to
the driving gear on the stability of emulsion.

8. CONCLUDING REMARKSThe present gear pump type mechanicalemulsifier is able to produce the stable W/O typeemulsions of gas oil and of A-heavy oil without
surface-active agent. The present study revealed
some interesting and important characteristics in theemulsification process of the gear pump typemechanical emulsifier as follows;(1) The narrow clearance and the long path length
between the second gear tip and the housing wall
will increase the stability of emulsion although they
decrease the discharge rate from emulsifier.
(2) There are some limiting conditions in thewater content and in the revolution of the driving.

ACKNOWLEDGEMENTS
The authors would like to express their sincere
thanks to Mr. T. Nakayama, N-Techno Co., Ltd. forhis great help in constructing the experimental setup
and providing the gear pump type mechanicalemulsifier. Messrs. A.Hoshino, H.Inotume andA.Kamiyama are appreciated also for their great
help in conducting the experiment. The authors
are indebted for the financial support by Nissan
Science Foundation and Yamaguchi ScholarshipFoundation through this study.
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960
840

gear for the prevention of phase inversion from
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(3) The water content in the emulsions ofA-heavy oil and of gas oil should be less than 20
vol.% and 4 vol.% respectively if they aretransported directly (without reserve tank) from thisemulsifier to the combustor.
(4) The order of inlet ports of water and of fuel,and the initial diverging water jet toward the firstgear will have a noticeable effect on the stability ofemulsion.

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― 54 ―(Received August 24, 2009)