Note: Descriptions are shown in the official language in which they were submitted.
Wo 95/07761 - PCTNSg~/09768
21 877~5 -
V-JET ATOMIZl;R
This invention is directed to the distribution of an
atomi2ed fluid in an atomizing gas and to mealls for
spraying such. It more particularly refers to a novel
5 dual fluid atomizer apparatus, including a novel spraying
nozzle, and the use thereof.
B~CKGROUND OF THE INVENTION
It is well known that there are mally occasions when
it is necessary or desirable to form a spray of a liquid
10 in a gas. One such time is in the combustion of a liquid
fuel with a gaseous oxidant, for example air, as the means
for heating a boiler. Other uses for this type Or
operation are in humidification as well as in providing
finely divided water droplets for cooling hot gases.
For ease of understanding, since the particular use
to which tllis invention will be put will not substantially
change the nature of this invention, this invention will
be hereinafter described with particular relation to the
use of the atomizer design of t~lis invention in connection
with the heating means in an oil-fired boiler. This is
not to be construed as a limitation on the use to wllich
the atomizing means of this invention may be put.
In the field of combusting liquid fuel, it has been
found that it is important to effectively control tlle
quality of tile sprayed fuel in order to control the
potelltial environmental hazards w~lich the effluent from
tlle combustion may create. Tlle potential for creating
effluent which is detrimental ~o the environment from
combustion processes, particularly larse oil-fired steam
generators, llas been exacerbated in recent years by a
continued reduction in the quality of the liquid fuel
being burne~. This has become particularly troublesome
where residual fuel is being burned.
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WO95/~7761 ? 1 81145 PCTn~S94109768
The problem with t}le residual fuel which is now being
fed to the burners of large steam generation facilities is
that its heavier fractions have a tendency to form larger,
heavier cenosplleric coke particles during combustion. As
5 the Conradson carbon number of the fuel increases, and tlle
llydrogen to carbon ratio of the f uel decreases, as is the
case with the use of residual fuel, the tendency of the
fuel to be less completely combusted increases whereby the
problem of coke particulate emissions is aggravated.
As bad as the situation has become over the recent
past, it is reasonable ta expect that it will get worse
during at least the near term in the future. Thus, it is
important that means be found to assist in the utilization
of residual fuel to fire steam boilers whereby particulate
emissions therefrom are reduced to a manageable level, and
whereby more of the energy contained in the residual fuel
is used.
Oil f ired boilers are usually e~uipped with burners
wllich are specially designed to combust oil with air to
generate tlle heat necessary to create the desired steam.
One of the principal components of the burner is the
atomizer, that is, the member wilich atomizes the oil to
allow it to be readily and efficiently combusted with the
air oxidant. The atomizer produces a spray of droplets
containing the oil which are then contacted with the air.
One of the detrimental ef1uents produced by ti~e
combustion of oil with air is NOX. The quantity of NOX
which is produced is known to be a function of the flame
temperature, the local fuel/air stoichiometry and the
intimacy of fuel/air mixing. The nature o the oil spray
substantially effects the localized fuel/air mixing
tllrough droplet dynamics (droplet inertia) and spatial
spray distribution. Therefore, the intimacy of mixing of
atomizing gas and oil to form the atomized spray, the
intimacy of mixing the combustion air with the atomized
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WO 95/07761 2 1 8 7 7 4 5 PCT~US9.OJ09768
oil droplets, and the nature of the atomization are quite
influential on the NOX emissions of the burner.
The quality of the performance of the burner is often
directly proportional to t11e performance oE the atomizer.
5 Atomizer performance is commonly measured in five (5)
ways: (l) the Sauter Mean Diameter, often abbreviated SMD,
of the size distribution of the atomized oil droplets; (2)
tlle uniformity of oil mass flux around the periphery of
the conically shaped spray of oil; (3) the apex angle of
lO the spray cone; (4) the quantity of atomizing fluid, such
as air, steam, or a mixture thereof, needed to produce a
spray having a given, pre-specified Sauter Mean Diameter;
and (5) the variation of these parameters over a specified
range of oil f low rates in a given burner construction .
15 It has been determined in the past that superior atomizer
performance, in terms of these parameters: reduces
carbonaceous particulate emissions, increases the caloric
yield, and therefore expands the range of oils which can
be used in this service.
In the past, a wide variety of atomizer designs have
been used for this service. These have usually fallen
into two general categories: dual fluid atomizers and
mechanical atomizers . Dual f luid atomizers derive the
energy, which they need to convert the liquid fuel into
droplets, by the interaction of the fuel oil with an
atomizing fluid, such as air, steam or a mixture thereof.
Mechanical atomizers usually rely on pressure on the
liquid fuel, which forces such through a restricted
orifice, to disrupt the fuel liquid into droplets.
Dual fluid atomization can usually be accomplished in
one of two ways. ~ccording to the internal mixing method,
the two f luids are bot~l simultaneously impacted against a
suitable plate, such as a back plate of a mixing chamber,
from which impact they then fill that mixing chamber with
t~le intimate mixture of both f luids . The mixture is then
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21 8~745
WO 95/07761 PCrlUS94/09768
.
e~ecte~ through a nozzle, suitably located in the atomizer
6pray plate, into the combustion zone of a f urnace .
I~ccording to another method, the external mixing
method, liquid fuel and gas are each independently fed
5 into a common chamber, or several chambers, one for each
exit aperture, at intersecting angles to intersperse the
two f luids into a mixture. The mixture is then ejected
from a suitable nozzle, which nozzle may be an integral
part of tlle cllamber housing.
Mechanical atomization may be of the type in which
all of the fuel oil, which is to be fed to an atomizing
nozzle, is ejected into the combustion zone of a furnace,
where it meets with combustion supporting air. The amount
of oil fed to the furnace is controlled by controlling the
amount of oil fed to the atomizer. This is referred to as
a ~Dnce througl~, or Simplex, atomization. In the 80 called
return flow type of atomizatioll, the oil flow to the
atomizer is maintained at a constant level, but ollly a
portion of the oil is fed into the furnace with the rest
of it being recycled to tZle fuel oil reservoir. In any oE
these ca6es, in addition to the aerodynamics of the
burner, the creation of droplets containing the fuel oil,
and the physical properties of tZlese droplets are major
determinants witZl respect to the quality of the fuel oil
combustion in the furnace.
BROAD DESCRIPTION OF TliIS INVENTION
It is therefore an object of this invention to
provide an improved atomizer especially designed to
improve the overall efficiency of atomization of a liquid,
30 particularly fuel oil, and therefore to improve tlle
overall Qfficiency of mixing the atomized liquid and a
gas, for example ~:team, in order to improve the overall
efficiency of the combustion of fuel oil in a furnace.
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Wo95/07761 2 1 8 7 7 4 5 PCT/US9~09768
It is another object of this invention to provide a
novel atomizer design, as well a6 a process of atomi~ing
a liquid using this novel designed atomizer.
It is a further object of this inventlon to provide
' 5 an improved process of combusting fuel oil, based on an
improved atomizer design, in which the size and mass
distribution of the less desirable emitted carbonaceous
particles are limited whereby enhancing the burn-out of
these particles.
It is a still further object of this invention to
provide an improved atomizer design which will produce a
spray of atomized particles having characteristics that
promote mixing thereof with combustion air, particularly
in burners wit~1 low primary air flows, or with
recirculation f lows at t~1e axis of t~le burner .
It i5 a still further object of this invention to
produce desirable fuel/air mixture ratios in a zone near
the burner of an oil-fired furnace, and to minimize any
exces6 oxygen requirements of the system, thereby
~0 ~iubstantially reducing the NOX emissions produced by the
~ystem .
It is a still further object of this invention to
provide a novel atomizer design which is capable of
producing a segmented stream oE atomized liquid having
disproportionate stoichiometry ill the various spray
6egments .
Other and additional objects of this invention will
become apparent from a consideration of this entire
specification, including the drawing 1~ereof and the claims
3 0 appended hereto .
In accord with and fulfilling these objects, one
a6pect o~ this invention comprises an novel atomizer
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Wo 95/07761 PCT/US9~/09768
design. ~ccording to this design, the atomizer comprises:
a main body, which defines a generally centrally
located, circumferel~tially defined open space;
a first conduit means, adapted to communicate through
5 said main body with said open space, to carry fuel oil
through said main body and into said open space; and
a second conduit means, adapted to communicate
through said main body with said open space and to carry
atomizing gas through said main body into said open space.
The main body of the atomizer of this invention
comprises -
one or more side walls, which may be straiyht or
curved as desired and required;
a back plate member in closing contact with the side
15 wall(s) defining one end of the main body, and a first
end to the opell space; and
a front member, which defines a second end to the
open space, at the end thereof opposite to the back plate
member .
20 The side wall(s), the back plate member, and the front
member define and confine an internal mixing chamber. The
front member has a generally conical, preferably a right
circular frustroconical, slot therein which may be axially
aligned with the general center of the mixing chamber.
25 Preferably, the mixing chamber is substantially
cylindrical, and there is substantially exact alignment o~
the axes of tilis cylinder and the conical slot.
This conical slot is in the front portion of the
atomizer assembly, suitably either wholly within the front
30 member, or partially within the frol~t member and partially
within or defined by the side wall (s) of the main body.
Preferably the conical slot is at the juncture between the
front member and the side wall (s) of the main body of the
atomizer of tllis invention. This slot serves as an exit
35 means and thereby communicates between the internal mixing
chamber and an area, for example a furnace combustion
chamber, outside the atomizer into whic~ the atomized
SUBSTITUTE SHEET (RULE 26)
W095/07761 21 g7745 PCr/US94/09768
liquid, for example the fuel, iæ intended to be sprayed.
Where required, means may be provided, suitably disposed
through the mixing cl~amber, to operatively support the
front member by at least ti1e back plate member of this
5 apparatus.
In a prQferred aspect of this invention, the conical
spraying nozzle is segmented. ~hat is, the free passage
of atomized material through the cone of the nozzle is
interrupted one or more times, by piers suitably disposed
lO around its periphery. In addition to their functional use
in determining the geometry of the atomized fuel sprayed
from the nozzle, these piers may also form the support
structure for joining the inner surface of the cone to the
outer surface thereof to form the nozzle (channel). In
15 this preferred embodiment of tl~is invention, the conical
spraying nozzle may be formed between the front member and
t~le side wall (s) of the main body, and the front member
may be supportingly joined to the side walls at one or
more places around the periphery oE the conical slot.
20 These joining members, or piers, may extend only part way
along t}le length of the nozzle. That is they may extend
from the front of the conical nozzle in contact with the
furnace combustion chamber part way back along the length
of t~1e conical channel. In the alternative, these joining
25 menlbers can be located toward tilP r~ar et1d of the conical
cllannel starting from the mixing chamber end thereof and
e~tending ollly part way alo1lg the ~e11gt~1 of the conical
channel. If desired, it is within the spirit and scope of
this invention to provide multiple piers along the length
30 of the conical slot. It is preferred, however, to have
t11ese pier members extend along the complete length of the
col1ical slot from the point where the mixing chamber
communicates with tile slot, to the place where the slot
communicates with tlle space into which the atomized f luid
35 will be sprayed. Preferably, there are a multiplicity of
these joining members, or pier assemblies, spaced about
tile periphery of tlle conical slot. The preferred
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Wo 95/077C1 2 ~ 8 7 7 4 5 PC~/US94/0976~
configuration is symmetrical, but the pier distribution
may be asymmetric if desired.
The novel atomizer described here is adapted to be
operatively associated with peripheral apparatus, such as:
means to supply the atomizing gas,
means to supply the liquid to be atomized, such as
fuel oil,
means to pressurize any or all of: the atomizing gas,
the liquid to be atomiz~d, and atomized liquid,
receptacle means, such as the combustion chamber of
a furnace means, into which the mixture of the atomized
liquid and the atomizing gas, is sprayed, and
where the receptacle means is a furnace combustion
chamber, means to introduce all or additional combustion
supporting gas, such as air, if needed, into the chamber,
or, where the receptacle means is a humidifying chamber,
means to introduce into the chamber the gas in need of
humidification, suitably air.
sRIEF DESCRIPT~ON OF T~E DRAlqING
This invention will be ~etter understood with
reference to the drawing, which is illustrative thereof,
and in which:
Fig. 1 is a side sectional view of an atomizer
deslgned according to one preferred aspect of this
invention, which is provided with mean for adjustment of
the exit channel width;
Fig. 2 is a plan view of one of a preferred nozzle
design which is adapted to use in this invention;
Fig. 3 is a view of the preferre~ nozzle shown in
3 0 Fig . 2 which has been sectioned along the line 3 - 3 .
This Fig. 3 is a perspective view which looks generally in
the direction of the arrows;
SUBSTITUTE SHEET ~RULE 26)
_ _ _ _ . . . . .. .. ..... . .
Wo 95/07761 2 1 ~ 7 7~ 5 PCT/US91~09768
Flg. 4 i5 a sidQ view of the preferred nozzle design
shown in Fig. 2. 6ectioned along the line 4 - 4 looking in
the direction of the arrows;
Figs. 5 - 7 are a typical series of curves depicting
5 various relationships between the design of the atomizer
of this invention and the properties of the spray provided
thereby. These curves are provided as examples of the
operation of this invention. Each specific operation,
with its own unique parameters of operation will produce
its own unique set of similar curves. In each figure, the
specific relationship being depicted is set forth. Fig.
5 shows the relationship between Fuel Flow and supply
Pressure; Fig. 6 shows the relationship between Atomizing
Mass Ratio and Fuel Flow; and Fig. 7 shows the
relationship between Atomizing Spray Quality and Fuel
Flow .
DETAILED DESCRIPTION OF THIS INVENTION
Referring now to the drawing, this invention will be
described with reference to the atomization of fuel oil,
as the liquid to be atomized prior to its combustion, with
steam, as the atomizing gaseous fluid. Referring now to
Fig. 1, an atomizer according to this invention is shown
comprising a generally hollow cylindrically shaped main
body 10; a back plate means 12, substantially diametrally
disposed across and enclosing one end of the generally
hollow main body; and a front plate means 1~,
substantially diametrally disposed across and enclosing
the other end of the generally hollow main body, to
thereby form an enclosed cavity, which serves as a mixing
chamber 16 for use in this invention. There is suitably
provided passage means 18 and 20 communicating sources of
oil to be atomized (not shown) and atomizing steam (not
shown) with the mixing chamber 16, preferably through the
back plate means 12. These passage means are adapted to
allow the introduction into the mixing chamber 16 of the
SU~SIITUTE SHEET (RULE 26)
WO 95/07761 _ 2 1 g 7 7 ~ ~ PCT/US94/09768
.
liquid 22 to be atomized and the atomizing gas 24. It
should be noted that the 6pecif ic arrangement of liquid
oil and atomizing steam supply passages is not critical.
In some applications, the6e passages are reversed from the
5 locations depicted here. The front plate means 14 is
suitably mounted on the other end of the mixing chamber
16, and may be supported by the back plate means 12, such
as by means of a pillar 26 which may pass through the
mixing chamber 16.
At a location which may suitably be anywhere in the
walls ~uLLu.nlding the mixing chamber 16, but is preferably
in, or at least very near to, the front plate means 14 of
this atomizer apparatus, there is provided at least one
suitable opening 28 which is adapted to allow the atomized
15 mixture to be ejected out of the mixing chamber 16. In a
preferred embodiment of this invention, the opening 28 is
a conical passageway of a size and shape sufficient to
produce a conical spray of atomized vaporous material into
the combu6tion chamber. In a preferred aspect of this
20 invention only one such conical shaped passageway is
provided for each mixing chamber, but it is possible for
there to be two or more.
According to a preferred aspect of this invention,
the conical shaped slot passageway or nozzle 28, which is
25 shown in greater detail in figs. 3 and 4, is made up of a
pair of spaced apart walls 30 and 32 which define the
conical passageway of the nozzle of this invention. These
walls are preferably generally concentric and thereby
define a conical passageway which has a substantially
30 uniform cross-sectional dimension or thickness. In other
words, according to a preferrèd aspect of this invention,
the conical nozzle neither diverges nor converges in
thickness between the mixing chamber 16 and the area into
which the atomized fluid is being sprayed. The width (or
35 thickness) of the conical channel is whatever width is
suited to the throughput of atomized fluid and the
SUBSTITUTE SHEET (RULE 2~)
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~ 77~ PCTIUSg4/09768
11
viscosity thereof. Suitably, the apparatus o~ this
invention is equipped with means for adjusting the
thickness of the conical channel slot. It has been found
that non-limiting channel thicknesses might be about 1/32
5 to 1/2 inch. Thicker or thinner channels are also suited
to use in this invention. The angle of the conical nozzle
passageway is suitably about 50 to 100. However, larger
or smaller angles can be used in special situations.
It iG considered to be within the scope of this
10 invention to provide a conical nozzle means as described
above in which the spaced apart walls, which form the
conical nozzle, do either converge or diverge, as needed,
at the point where the atomized mixture is sprayed out of
the nozzle into the combustion chamber or the like. This
15 divergence or convergence is accomplished by providing the
walls of the nozzle as cones of differing apex angles, but
which preferably have common virtual apices. The angles
of convergence or divergence are not particularly
critical, but are typically small. Thus, convergent or
20 divergent angles of the walls of the conical channel might
be up to about 15, preferably not greater than about 5.
The conical nozzle is preferably made up of two
frustro right circular conical surfaces. However, the
frustro conical sur~aces do not necessarily have to be
25 circular in cross-section. They may alternatively be
elliptical in cross-section, or even irregular in cross-
section, if this gives a desirable spray pattern of the
atomized f luid.
As will be seen in Figs. 2, 3 and 4, the most
30 preferred aspect of this invention provides internal pier
support-spacer means 34, 36 and 38, within the conical
channel passageway 28. In the views shown in Figs. 2, 3
and 4, three such support means are shown. Ilowever, this
specif ic number of support means is not critical to the
35 practice of this invention. It is possible to use two or
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four or even more such support-spacer means as needed for
the particular design of the nozzle being used in the
embodiment of this invention which is being practiced.
According to a preferred practice of this invention, these
5 support-spacer pier means should preferably be spaced
~ymmetrically about the conical nozzle passageway. Thus,
if there are three such support means, they should
preferably be spaced about 120 along the cone axis; if
there are four pier means, they should be spaced apart
l0 about goo each. However, the spacing may be asymmetric if
this will give the spray of atomized f luld that is
des ired .
The support-spacer means used in the conical spray
channel can extend throughout the length of the channel
15 all the way from the mixing chamber end to the combustion
chamber end thereof. 11owever, it is also within the scope
of this invention f or~ the spacer-support means to be
located only partially along the length of the conical
channel. In order to supply specialized support and
20 spacing functions, the spacer-support means may be located
anywhere in the conical channel.
1~owever, it has been discovered, and it is an
extremely important discovery within the context of this
invention, that spacer-support means located at the exit
25 point in the conical nozzle passageway have an important
segmentation effect on the geometry of the spray which
emerges from the nozzle. The number and the spacing of
these exit point spacers has a dramatic effect on the
geometry of the atomized spray, on the characteristics of
30 combustion of that spray, and on the particulate, and NOX
emissions produced.
It has been reported elsewhere, see United States
patent number 4,790,480, that disrupting a conical spray,
from the exit of a nozzle, after it leaves the nozzle and
35 as it is being fed into a combustion chamber, causes
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13
6ubstantial improvement in the combustion characteristics
of the atomized fuel in the combustion chamber. When the
conical stream is broken up after it leaves the nozzle,
there is substantially improved burn-out accomplished, and
5 the combustion of the fuel oil is substantially more
complete thereby reducing the potential adverse efects of
the of f gas generated by the combustion .
In that patent, there is described means disposed
outside of the nozzle that breaks up the atomized stream
lO after it leaves the nozzle. This is to be distinguished
from the structure of the instant invention where the
stream comprising fuel passing through conical nozzle
passageway is broken up within the nozzle, that is before
it exits the nozzle and becomes a spray. The spray which
15 is produced according to the practice of this invention is
a segmented, substantially conical spray, with non-uniform
segments of spray about the entire periphery thereoE.
These segments may have different bulk densities and/or
compositions. That is, because of the interposition of
20 the support-spacer pier means in the conical nozzle
passageway, the spray which comes out of the nozzle of
this invention has a non-uniform bulk density, composition
and pattern as a function of the location of the support-
spacers. Thus, alternating fuel-rich and air-ric}1
25 segments can be created around the periphery of the spray
cone. By constricting this spray inside the nozzle means,
the adverse consequences of externally disrupting the
spray, which is shown in the '480 patent, are avoided.
The NOX and particulate emissions have been found to
30 be substantially reduced by the practice of this invention
and particularly by the use of the special nozzle design
which is described herein. During tests of the novel
nozzle design of this invention, using heavy fuel oil as
the atomized feed, it was found that the excess oxygen
35 requirement, that is the amount of excess oxygen which is
required to insure maximum combustion of the fuel oil
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377~}~ S94
1~1
within the operating parameters of the Gystem, was
6ubstantially decreased. This decrease in the excess
oxygen requirement and the alternating fuel-rich and air-
rich spatial distribution of the segmented spray causes
5 the NOX emissions to be substantially decreased.
Increased boiler efficiency was also obtained with the
decrease in the excess oxygen requirement.
The mixing chamber and the nozzle may be made of any
materials which are convenient and which will withstand
10 the rigors of the fluids being contacted therewith and the
temperatures and thQ pressures at which these f luids are
contacted therewith. Thus, if the fluids are corrosive,
the materials of construction should be able to withstand
corrosion by these fluids for at least an acceptable
15 service life. Metals and plastics are the usual materials
of construction, with steel being especially desirable in
most cases. It is considered to be within the scope of
this invention to provide suitable coatings on the
surfaces of the enclosure for the mixing chamber, the
20 spraying nozzle and the other elements of this apparatus.
Suitably, these coatings may render the underlying
construction materials resistant to deterioration by
contact with or passage of the contained f luids . For
typical oil fired furnace-boiler applications, the
25 atomizer assembly (the main body, nozzle assembly,
passageways, and the support shaft if employed) can
preferably be constructed of tool steel, such as 1~-13 Rc
53-56 tool steel, or for more corrosive environments and
application, AISI 440C pre-heat-treated steel.
With the atomizer design according to this invention
specifically adapted for use in atomizing heavy fuel oil
with atomizing steam, it has been found that, for a given
atomized ruel to atomizing fluid pressure differential,
the quality of the spray produced by the practice of this
invention will not vary to any appreciable degree as a
function of the size of the conical nozzle passageway. It
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has been found that when the fuel oil to atomizing 6team
pressure differential was held substantially constant at
about 10 pslg., and the gap in the conical nozzle wa6
varied from about o. 078 inch to 0 .100 inch, the SMD
(Sauter Mean Diameter) varied only about 4 ~m from about
66~1m to about 7011m. However, under these conditions, a6
the gap setting was increased from 0 . 078 inch to 0 .100
inch, the exit velocity of the f luid decreased about 25% .
It was also found that the fluid pressures which were
required to maintain equivalent fuel flow decreased
proportionately to the increase in gap, because the fluids
passing through the gap met less resistance to flow at the
wider atomizer exit.
It was found that the adjustment of the exit gap
width allowed the NOX emissions to be reduced, by
providing lower excess oxygen requirements for a wide
range of fuel to atomizing fluid pressure differentials.
Thus, variations in fluid Yelocities, small changes in
effective spray angle, and the relative penetration of the
fuel spray into and about the internal recirculation zone
(IRZ) in the combustion chamber, which are associated with
variations in the gap size, appear to have a significant
impact on the excess oxygen requirement, and the fuel/air
mixing rate that is required to support substantially
complete fuel combustion with a minimum of NOX emissions.
The internal recirculation zone (IRZ) is a zone formed
downstream of the atomizer exit at suf f iciently high
levels of combustion air swirl in which combustion
products are caused to be circulated back towards the fuel
spray exiting the atomizer nozzle.
It has been pointed out above that the front plate
means can suitably be supported by means of a center body
26 extending from the back plate means to the front plate.
It has also been pointed out that this is not an essential
configuration of the apparatus of this invention, but that
the front plate means and nozzle means could be assembled
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16
in a different manner. In initial prototype evaluation,
it has been found that it is preferred to utilize a center
body support means which is threaded at the nozzle-front
plate means end. In this manner, the gap in the conical
nozzle passageway can be readily adjusted by bimply
turning one surf ace thereof relative to the other about
this threading.
Designs of nozzle means according to this invention
can be assembled so that the spray is of only one or more
portions of a cone. Thus, a full conical 6pray may be
used, a partial conical spray may be used, or multiple
spray segments, which are each portions of a cone, may be
used. As an example of such multiple partial conical
areas, a segmented V-jet with two (2) conical exit slots
has also demonstrated reductions in NOX emissions of up to
about 40% by being able to minimize the excess oxygen
requirements of the system, by being able to adjust the
stoichiometry of air and fuel about the conical spray, and
by producing desirable fuel/air ratios in the zone near
the burner. Further, such segmented nozzle sprays have
encouraged more thorough combustion and have therefore
produced off gases of substantially lower opacity, which
are therefore more environmentally acceptable.
In practicing this invention, it has been f ound that
the angle at which the atomizing gas and the f luid being
atomized, respectively, enter the mixing chamber of the
apparatus of this invention is an important consideration
in the design of this apparatus from the perspective of
efficiency of operation. It has been found to be most
prcferred for each of the atomizing gas and the fluid
being atomized to impinge upon the back plate means of the
mixing chamber and to impact thereon at about a right
angle. Of course, this is not an absolute limitation.
The angle may vary from goo to some extent, for example
from about 75~ to 105, without substantially jeopardizing
the advantageous results which are achieved by the
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practice of this invention. This provides for dynamic
mixing of the atomizing gas and the fluid to be atomized,
improves atomization, and reduces the consumption of
atomizing gas in the operation.
The transport conduits which bring the atomizing gas
and the atomized f luid into the mixing chamber may be
located in a radial or a tangential manner with respect to
the chamber. Where tangential introduction is employed,
the two fluids can be introduced in co- or counter-current
rotational direction with respect to the external air flow
established by the burner flame stabilizer and registers.
By introducing angular momentum to the f luids being
introduced into the mixing chamber, it is possible to
influence some of the combustion characteristics of the
atomized fuel. For example, co-rotating the fluids will
decrease the f luid volume f lux in the near portion of the
burner zone, and t~lereby reduce fuel rich areas therein.
5uch a design will increase the spray quality uniformity,
and it will also positively effect fluid velocities and
penetration of the atomized mixture into the near burner
zone .
In designing the mixing chamber and conical nozzle
assembly of this invention, and in establishing t}le
operating conditions for a process usil1g t~lis apparatus,
it is possible to introduce variations in size and shape
which will affect the residence time in the mixing
cllamber. Thus it is possible to optimize this residence
time. It i5 preferred that the mixing chamber be directly
upstream of the conical nozzle, and that the combustion
ci~amber be immediately downstream of the conical nozzle.
sy assembling these elements in very close proximity, it
is possible to minimize t~le time lag between atomization
in the mixing chamber and combustion in t~1e combustion
chamber. The closer these elements are to each other, the
less is tlle likelihood that the atomized condition of the
fuel will break down prior to combustion thereof.
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The V-jet atomizer of this invention provides
substantially constant spray quality into the combustion
20ne. The droplet size and atomizing mass ratios (6team
to oil) are substantially constant over a wide range of
fluid input pressures for a given atomizing gas to fluid
pressure di$ferential in the range of between about 10 and
30 psig. In a V-jet operation according to this invention
at a pressure differential of about 10 psig, a typical
operating system can operate at mass ratios of only about
10%. ~3ecause operating in the manner of this invention
with the apparatus of this invention still provides
excellent atomization even at very low input pressures and
flows, this condition allows the operator to be able to
turn down the furnace/boiler, that is to reduce boiler
load, without having to shut off burners and thereby
remove burners f rom service .
The following example is illustrative of the practice
of this invention. It is not to be considered as being in
any way limiting on the scope of the invention or of the
claims appended hereto. In this example, parts and
percentages are by weight unless specif ied to be on some
other basis.
~a_ple
An internal mix V-jet atomizer design was tested
using a heavy oil to feed the burners of a 150 klbs/hr
utility package boiler . The conventionally boiler f ired
low sulfur (<0. 3%) No. 6 fuel oil and used steam as the
atomizing fluid. The prototype atomizer tested had an
adjustable gap setting feature and an effective spray
angle of between 70 and 75. Reference is made to ~ig. 1
of the attached drawings for design details.
The conical spray nozzle-atomizer was tested at three
exit gap settings, 0.078", 0.089" and 0.100". As the gap
setting was increased from 0.078" to 0.100", the fluid
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Wo 9Sl07761 2 1 8 7 7 4 5 pcr/uss4/o9768
19
exit velocities were significantly decreased, by about
25%. The fluid pressures required to maintain a
particular ~uel f low were also reduced as the exit gap
width increased. At each of the gap settings, a range of
5 operating parameters was evaluated, including: 1) fuel oil
to atomizing steam pressure differential, 2) fuel flow, 3)
excess 2 requirement levels, 4) burner register swirl, 5)
various flame 6tabilizer designs, and 6) oil gun and
stabilizer axial position.
For each of the curved vane swirlers and V-Jet Qxit
gap settings (and combinations thereof) ~minP-I, it was
noted that the NOX emissions were signif icantly decreased
as the fuel oil to steam pressure differential (~P) was
increased from 0 to 20 psi. In most cases, as the ~P was
15 increased, and the spray quality thereby improved (reduced
droplet sizes), less excess 2 was required to maintain
low opacity levela. This reduction in the reguired excess
2 level resulted in a signif icant reduction in NOX
emissions. This effect was particularly apparent under
20 moderate register swirl conditions.
For a given fuel oil to atomi2ing steam pressure
differential, the spray quality (as calculated) did not
vary signif icantly as a function of gap settings .
However, the mid-range gap setting of 0 . 089", provided
25 lower NOX emissions and lower excess 2 requirements for
fuel oil to atomizing steam pressure differentials of 0
and 10 psi. Thus, variations in the fluid exit velocities
(and perhaps slight variations in the ef fective spray
angle), and variations in the relative penetration of the
30 fuel spray into and about the IRZ, associated with the
variation of the gap size, had signif icant impacts on the
level of excess 2 required, the local fuel/air ratios,
the fuel/air mixing rates, and the resulting NOX
emissions .
A segmented V-jet design was also evaluated during
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Wo 95107761 2 1 8 7 7 4 5 PCTIUS94/09768
the above test program. This design, which segmented the
fuel spray into two portions of a complete cone (highly
fuel rich areas), was shown to produce the lowest NOX
emissions of all atomizers tested during the f ield
5 demonstration. That is, lower than all standard, Low-~OX,
and other novel atomizer designs. A NOX reduction of
approximately 43% (as compared to the original boiler
hardware) was documented, with no observed increase in
particulate matter emissions.
An additional segmented V-jet with two (2) exit
slots, was tested on a face-fired boiler with eight (8)
Peabody APR 21 burners. Again, the use of this atomizer
design resulted in NOX emission reductions of about 40%
from the baseline conditions, despite significant
15 differences in burner configuration from the previous
example .
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