Note: Descriptions are shown in the official language in which they were submitted.
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This application is directed to an improved combustion
system for heavy fuel oil specifically utili~ing viscosi.ty con-
trol and to that system incorporating an improved A~omi~ing
nozzle for the fuel oil. Parent application Seria~ ~'c~ 2?3,879
filed 6 June 1977 is directed to the improved atomi~ing fue.'
oil no~le and to the nozzle incorporated in a general combustion
system.
This invention pertains to liquid fuel combustion and
in particular combustion of fuel:; having widely varying properties
including so-called ~heavy" oil. The preferred system disclosed
utili~es improved atomization through no~zle design and viscosity
control to achieve successful combu~tion.
DESCRIPTION OF PRIOR ART
Historically, combusion of the so-called "heavy" oils
has been extremely difficult due to a complex hydrocarbon
structure and substantial variations in the properties and con-
stituency of thc fuel. Conventional fuel oil is generally class- ;
ified by the API ~esignation t l to t6 with the 1 to 4 range
provided somewhat variable but generally consistent combustion <~
properties. Oil designated as t5 or t 6 is classified AS re-
sidual and therefore has a broad range of combustion properties.
Impurities of somewhat unknown value are also present in quant-
ities which varv widely, and can include water. Recent efforts
to conserve energy and dispose of by-products of industrial
processes have led to the need for combustion of "waste" oil,
; which can include so-called cutting oil, exhausted automotive
lubricaticn oil and other impurities. These waste oils exhibit
many of the undesirable combustion characteristics of "heavy"
oil and therefore are considered equivalent to "heavy" oil in the
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remainder of the disclosure. The variations which ?rovide the
greatest barrier to efficient combustion include very hign vis-
cosity (greater than 5000 SSU at 20 Centigrade), hish vapori-
zation temperatures, non-uniform distiilation rates, and widely
varying trace elements present as impurities which substantially
influence combustion processes.
Examples of prior attempts to obtain satisfactory com-
bustion of heavy oil are taught in U.5. Patents 3,185,202, and
3,301,305, assigned to the assignee of this application. These
systems essentially utilizc the concept of increased residence
time in the combustion chamber to overcome varying fuel properties
and to insure complete combustion without dep~sition of carbon
on the combustion chamber services. Whiie these approaches have
been moderately successful, they ha~e includ~d various compli-
cated devices in order to produce highly turbulent combustion
gas and vapor flow patterns, and generally speaking do not pro-
vide combustion in the type of relatively compact chamber dis-
closed in this invention.
Other approaches to combustion of heavy oil utili~ing
attempts to improve atomization through noz21e design include
U.S. Patents 1,428,8~6, 3,770,209, and 3,8~0,183.
In general, these approaches have resulted in highly
complicated nozzle geometries involving many internal passages
and intricate air-oil intersections. These structures are sen- j
sitive to variations in the oil characteristics and constituents
indicated above resulting in combustion systems of relatively
low reliability. Frequent cleaning of nozzles is required, and
attemp~s to operate over long periods without substantial main-
tenance have not generally been successful.
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Prior art nozzles discussed above generally utilize
atomizing fluids which generate fuel particles having asym-
metrical velccity and acceleration compo.lents. Tnese particles
tend to imringe on internal passages and agglomerate or re-
combine, requiring additional atomizing air to re-shear or e-
atomize the agglomerated fuel. The re-atomization necessity
proeides non-uniform fuel/air mixtur~ nd results in poor or
inefficient combustion.
In contrast, the invention disclosed in this application
accomplishes proper atomization and good combustion as measured
' by accepted state of the art indicators s~ as absence o~ deposited
j carbon and low bacharach smoke scale in t-~e cGmbustion gases using a
relatively simple nozzle, which is easy to clean and is inherently -
insensitivs to fuel property varlations.
SUMMARY OF THE INVENTION
Successful combustion of high viscosity or heavy oils is accomplished
by the system of this invention in a preferred em~odiment through the
use of a unique nozzle design in conjunction with self adjusting
viscosity controi of the fusl. In particular, the nozzle utilizes
a circulating oil flow contained in a cavity adjacent to the atomi-
zing fluid source and exit orifices. Fuel exiting from the cavity is
~sheared" by the atomizing fluid passing through the cavity with re-
combination of the fuel prevented by atomizing air passages which are
coaxial with nozzle exit passages, containing critically sized exit
and expansion orifices,
Preheated fuel is withdrawn from a remote storage tank
after which entrained air and/or vapors o; gases are separated and
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additional -:utomatically controlled heat is supplied, in order to
provide a relatively constant viscosity fuel J;o the burner described
above. Combustion proceeds in a relatively small refractory cnamber
~ which utilizes recirculation zones to stabilize the combustion pro-
cess prior to completed combustion gas exiting through the combustion
chamber choke.
This system allows combustion of heavy or residual fueis
in compact combustion chambers without deposition of carbon on the
chamber inte~ior or significant reduction in combustion chamber life.
The nozzle design employed Also provides for expulsion of impurities
contained in the oil and allows them to be ejected into the -~m~
tion system where they can be utilized and in many cases become a ~-
part of the combustion process.
However, in one broad aspect the invention provides in a
device for atomizing heavy oil; an inner member having a plurality
of passRoes for atomizing gas, each passag having first and second
ends; an outer member having a plurality of passages, ach having
first and second ends; a sharp edged orifice adjacent to the -,econd
end of each of the outer member passages; an exit orifice abutting
the sharp edged orifice; an expansion section adjacent the first end
cf the outer member; means mounting said inner and outer members and
the passages in spaced relationship defining an oil circulation cav-
ity therebetween; the cavity communicating with the second end of the
outer passage and first end of the inner passage; means supplying
pressurized non-atomized oil to the circulating cavity; means supply- -
ing pressurized atomizing fluid to the inner mstnber, ac a pressure
less than that of the oil, wherein oil flowing in the circulating
:a~ity is ~to=ized by flgld flowing in the inne~ passages, at the
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sharp edged orifice, thereby e~pelling fluid entrained atomized oil
from the exit orifice and throu~'a the expansion section.
The invention also provides in another aspect a combustion
system for liquid fuel having in co~bination a combustion air source,
an atornizing fluid source, a combustion chamber, a liquid fuel source
and ; burner assembly with combustion air inlets ignition means and
the atomizing device ger.erally as already described.
In yet another aspect the invencion provides a combustion
system for liquid fuel having; a combustion chamber, a com~ustlon air
source, means supplying pressurized atonizing fluid, a burner having
primary and secondary air sources, ignition means, an atomizing fuel
nozzle; and a liquid fuel viscosity control system comprising; a
first fuel pump; a first fuel heater sùpplying preheated fuel from a
reservoir; air separator meanli for deaerating 'he preheated fuel; and
an orifice, second fuel pumping means and pressure control means
causing flow of deareated, pressurized fuel through the orifice;
n~2ns continuously measuring the pressure arop caused by the fuel
flowing through the orifice, second fuel heating means responsive to
the pressure drop measurement so as to maintain maximum and minimum
values. Preferably in this system the atomizing fuel nozzle is as
already generally described.
DESCRIPTION OF THE DRAWIN~5
Figure 1 - Combustion system includins nozzle, burner assembly com-
bustion chamber, and viscosity control system.
Figure 2 - ~urner assembly including nozzle pilot flame assembly and
air induction means.
Figure 3 - Detail of nozzle design and salient component parts prior
to 2ssembly of the invention.
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Figure 4 - Additional sectional view of salient parts of the novel
burner nozzle prior to assembly.
Figure 5 - Partial section of the nozzle in substantially increased
detail showing salient feature_ of the invention, such as the exit
orifice, the sharp edged orifice, and the oil circulating cavity.
Figure 6 - Schematic of fuel oil viscosity control.
In connection with a preferred embodiment it will be under-
stood that it is not intended to limit the invention to that
embodiment. On the contrary, it is intended to cover all alter-
natives, modifications, and equivalents as may be included within
the spirit and scope of the invention as defined by the pendent
claims.
The burner assembly preferred c~bodiment as shown in
Figures 1 and 2 consists of a burner assembly 65 combustion chamber
86, and combustion air box and blower, 90. With reference to
Figure 2 the burner assembly contains an atomizing nozzle 35 in-
ternally mounted and coaxial with burner skirt 45, contained near
the apex of the stabilizing cone 40, aIso mounted coaxial to the
burner nozzle axis. Combustion air for the burner enters through
primary air inlet 36 and passage 37 in the burner skirt. Second-
ary air enters the peripheral passage 80 between the skirt 45
and combustion chamber refractory 85.
The burner nozzle consists of the nozzle holder 67
(Ref. Fig. 5) containing the atomizing ::luid inlet and nozzle inner-
member 69 having a plurality of atomizing fluid orifices 30. A -~
nozzle outermember or shell 25 is mounted so as to encircle the
nozzle holder and ~ontains a plurality of exit orifices 38, ex-
pansion orifice 41 and sharp edged orifice 7 held in alignment
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with the atomizing air inlet orifice 30 bv the nozzle retainer
125. The nozzle outer member 25 is supported at a shoulder 126
~ on the nozzle holder 67 so as to maintain a circulating cavity
6 between the nozzle inner member and shell.
In operation, reference Figs 2 and 5, liquid fuel under
pressure enters the oil inlet passing through orifice 8 of the
nozzle inner member 69. Fuel is supplied through the inlet
conduit Y66 (Fig 2) which terminates in the nozzle holder 67.
The fluid enters through the inlet 15 under pressure somewhat
less than that of the fuel entering through fuel liquid passage 8.
The cavity 20 formed by nozzle inner member 69 and shell 25 pro-
vldes passage for circulating oil flow within the cavity. The
cavity design provides a radial "minimum gap" 40 which is cir- ,
cumferential and adjacent to both the atomizing air orifice 30
exit, and the sharp edged orifice 7 of the nozzle exit orifice 38.
This gap aligns certain solids which pass through the fuel filters
and permits their expulsion by the atomizing air flowing through
The alignment of these particles is crucial since the minimum
orifice 40 and the flow passaae or cavity 6 cooperate to allow
':hese particles to move .into the exit orifice with an attitude
which allows their expulsion and subsequent combustion.
Returning now to tha oil under pressure circulating
in the cavity 6, cavity geometry and the pressure differentials
between 6 and the atomizing air inlet15 is such that oil flows in
a path which is radial to the sharp edged orifice 7, where it is
sheared by the atomizing fluid flow from the atomizing fluid ori-
fice 30 forming particles of oil which move through the exit o i-
fice 38. This action, produced by the radial oil flow at the
sharp edged orifice 7 and the atomizing fluid flow through the
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orifice 30 results in generating a stream of fluid entra;ned fuel
particles which pass rapidly through the exit orifice 38 without
agglomeration, and into the expansion orifice 41 where they under-
go additional expansion and are then further entrained by the
primary air flowing past the nozzle. Radial flow is essential
in the formation of fuel particles which are repelled by fuel
flowing from the counterparts location on the opposite side of
the critical gap. This essentially neutralizes radial velocity
components, resulting in fuel particles which flow essentially
in a direction parallel to the exit orifice axis, thereby mini-
mizing wall attachment. The length of the exit orifice 38 has
also been found co be significant relative to the amount of
agglomeration of the particles sheared by sharp edged orifice 7
and in the amount of recombination of the sheared oil particles
which might occur in the time of their passage between the sharp
edged orifice the exit orifice 35 and resulting flame shape.
The minimum amcunt of agglomeration accompanying the structure
disclosed and claimed here has resulted in a functional and re-
liable burner usable in small combustion chambers.
Combustion of the atomized fuel now entrained by the
primary air adjacent to the nozzle shell 25 proceeds as a spinning - ~
action is imparted by the secondary air passing through the per- ~¦
ipheral passage 80 and containing spinning vanes. Ignition and
combustion occurs in the region just outside the stabilizing cone !
40 and is accomplished by the ignitor and pilot assembly 50.
Although a gaseous pilot which is electrically ignited is disclosed
it will be realized by tnose skilled in the art that any other
means of ignition such as direct electric arc or other pilot systems
can be utilized.
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The now ignited mixture of primary, secondary, and
atomized fuel droplets proceed into the com~ustion chamber 86
where the circulation zones 152 and 153, 154 and 151 are esta-
blished to stabilize the complex combustion phenomen 3 . Combustion
gases formed by the process then proceed through th~ circular
combustion chamber choke or exit 155 where they pro~eed to scrub
the heat exchange surfaces of ar.y particular or des red config-
uration (not shown).
Control of the fuel viscosity as supplied to the fuel
nozzle 35 is accomplished through the system depicted in Figs 1
and 6. In particular reference to Fig 6, the system disclosed
provides for proper oil flow through the r.ozzle for a wide range
of oil characteristics usually encountered. In operation, oil
stored in a remote tank is preheated and pumped to the separator
100 by fuel supply pump 101. The separator maintains a reservoir
of deaerated oil and its reservoir lOS, and also provides for re-
turning excess oil and entrained gases and/or vapors to the fuel
storage tank.
Preheated deaerated oil is now supplied to che fuel
pump 104 whose output is monitored by a by-pass type fuel pressura
relief valve 102, whereby excessive fuel which causes the pressure
' to exceed a preset value is returned to the reservoir 105.
Preheated and deaerated oil now operating at a pressure
controlled by the combir.ation of fuel pressure relief valve 102
is now pumped into the optionll fuel steam heater 106. The func-
tion of the heater 106 and 108 are identical and both are only
I disclosed for completeness. The following description will in-
i volve a system where the elcctric fuel heater has baen selected
and provides ~he major source of viscosity control. The fuel oil
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is r,umped through the electric heater 108 and continues on through
fixed orifice 112. A differential pressure switch llO is con-
nected to monitor the fuel pressure drop across the orifice 112
and aiso controls the application of heat to the fuel heater 108,
in a manner which continues to apply heat until the pressure drop
is less ~han a certain preset value. The pressure of the heated
fuel oil is further monitored by pre~sure regulating valve 114,
prior to passing through the filter 116. The l:OW correct vis-
cosity and filtered fuel is pumped through the fuel metering valve
120 whose throughput (volume flow) is controlled by the demand
for heat on the overall combustion system and therefore forms a
capacity control for the burner. The pressure of fuel exiting
the metering valve 120 is monitored by differential pressure valve
122 which also monitors the pressure of t..e incoming atomizina
fluid. The funotion of differential regulator 122 is to maintain
a proper pressure differential between the atomizing fluid ar.d the
fuel inlet to the nozzle 35. As discussed above, it is desirable
to maint3in a fuel preqsure slightly in excess of that of the
atomizing fluid in order to irsure the radial flow of fuel through -
the sharp edged orifice 7 and exit orifice 30 of the nozzle. Gther ~ ;
pressure t~mperature and flow control components, namely, the low
fuel temperat~re switch 121, dial thermometer ll9, bypass sole-
r.oid valve ll~l and the burner safety valve assembly 123 and check
valve 126 do not form part of this invention and are only included
as part of the disclos~re of a complete combustion system.
The system described above comprising the burner a~sembly,
combustion chamber and fuel viscosity control provide reliable com-
bustion of heavy fuel in small combustion over a wide variety of
fuel characteristics. In practice it has been found that the
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combustion obtained with this combustion require minimal main-
tenance and operates with good efficiency over a ratio of burner
demand in excess of 6 to 1. Deposits of carbon or tho refractor~
of the combustion chamber have been essentially eliminated and oper-
a~ion OL the nozzle has been made substantially more reliable than
ailable units through the ability of the burner no~zle to pass
relatively large amounts of unfilterable solids normally found
in fuels of this type. This has been accomplished without restor-
ing to combustion assists such as ultra-sonic atomi~ation or water
injection and provides a simple and economic way to efficiently
utili~e the large potential of fuel energy available in the so-
called heavy or residu;l oils, and waste oil. Combustion of
- , lighter distillates is of course easily accomplished since many
of the above mentioned difficulties do not exist.
Thus, it is apparent that there has been pro~ided in
accordance with the invention a novel combustion system that fully
satisfies the objects, aims and ac~ antages set forth above. While
the invention has been described in conjunction with specific
' embodiments it is evident that many alternatives, modifications
! 20 and variations will he apparent to those skilled in tr.e art in
light of the foregoing description. Accordingly, it i3 intended
to embrace all such alternatives, modifications, and variations
~ as included in the s~irit and broad scope of the following claims.
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