U.S. patent application number 10/186366 was filed with the patent office on 2004-03-25 for self-sustaining premixed pilot burner for liquid fuels.
Invention is credited to Mauzey, Joshua, Weschta, Leonhard.
Application Number | 20040058290 10/186366 |
Document ID | / |
Family ID | 31996638 |
Filed Date | 2004-03-25 |
United States Patent
Application |
20040058290 |
Kind Code |
A1 |
Mauzey, Joshua ; et
al. |
March 25, 2004 |
Self-sustaining premixed pilot burner for liquid fuels
Abstract
A burner for liquid fuel comprises a mixture chamber for
producing a liquid fuel air mixture. The mixture chamber has a
heating element, an air inlet for receiving air, the air inlet
being configured so as to facilitate air flow over at least a part
of the heating element, and a liquid fuel inlet. An atomizer is
mounted in a path of flow of the liquid fuel air mixture formed by
the mixture chamber. A combustion chamber for combusting the liquid
fuel air mixture is provided. The combustion chamber has a flame
holder, an ignition source located proximal the flame holder, and a
combustion zone located downstream of the flame holder.
Inventors: |
Mauzey, Joshua; (Huntington
Beach, CA) ; Weschta, Leonhard; (Long Beach,
CA) |
Correspondence
Address: |
JOHN G TOLOMEI, PATENT DEPARTMENT
UOP LLC
25 EAST ALGONQUIN ROAD
P O BOX 5017
DES PLAINES
IL
60017-5017
US
|
Family ID: |
31996638 |
Appl. No.: |
10/186366 |
Filed: |
June 28, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60301546 |
Jun 28, 2001 |
|
|
|
Current U.S.
Class: |
431/243 ;
431/353 |
Current CPC
Class: |
F23D 11/441 20130101;
Y02E 20/348 20130101; F23L 15/00 20130101; F23D 2209/20 20130101;
Y02E 20/34 20130101; F23D 11/102 20130101 |
Class at
Publication: |
431/243 ;
431/353 |
International
Class: |
F23D 011/44; F23D
001/00 |
Claims
1. A burner for liquid fuel, the burner comprising: a mixture
chamber for producing a liquid fuel air mixture, the mixture
chamber having a heating element means, an air receiving means for
receiving air, the air receiving means configured so as to
facilitate air flow over at least a part of the heating element,
and a liquid fuel receiving means; an atomizer mounted in a path of
flow of the liquid fuel air mixture formed by the mixture chamber;
a combustion chamber for combusting the liquid fuel air mixture,
the combustion chamber having a flame holder, an ignition source
located proximal the flame holder, and a combustion zone located
downstream of the flame holder.
2. The burner for liquid fuel as claimed in claim 1 further
comprising a means for preheating the air before its introduction
to the air receiving means.
3. The burner for liquid fuel as claimed in claim 2 wherein the
means for preheating the air comprises an external jacket formed
about at least a portion of the combustion chamber.
4. The burner for liquid fuel as claimed in claim 2 wherein the
means for preheating the air is a preheat coil located within the
combustion chamber.
5. The burner for liquid fuel as claimed in claim 1 wherein the
heating element means comprises a glow plug connected by electrical
leads to a power source.
6. The burner for liquid fuel as claimed in claim 1 further
comprising a catch tray for located between the heating element
means and the for catching liquid fuel droplets.
7. The burner for liquid fuel as claimed in claim 1 wherein the
atomizer has an exit opening configured so as to produce a cone
shaped liquid fuel air mixture stream.
8. A burner for burning a low-volatility liquid fuel, the burner
comprising: an inlet air means through which burner air flows; an
inlet fuel means through which burner fuel flows; a fuel air
mixture preparation chamber downstream of the said inlet air means
and said inlet fuel means and in which a fuel air mixture is mixed;
a combustion housing means for combusting a fuel air mixture that
is in heat exchange relationship with the said burner air flow and
in fluid connection with the said fuel air mixture preparation
chamber.
9. The burner of claim 8 wherein the combustion housing means
further comprises a flame holder and ignition source.
10. The burner of claim 8 wherein the fuel air mixture preparation
chamber means further comprises a heating element to preheat the
said burner air during start-up of the burner.
11. The burner of claim 8 wherein the fuel air mixture preparation
chamber means further comprises a liquid fuel atomizer to enhance
the vaporization of fuel in the fuel air mixture.
12. A method for operating a self-sustaining liquid fueled burner
comprising following the steps: initiating air flow to the burner
through the inlet air means; initiating the electrical energy to
the heating element to preheat the air flow to the burner;
initiating the fuel flow to the burner through the inlet fuel means
to make a fuel air mixture; initiating the electric energy to the
ignition source to ignite the fuel air mixture; monitoring the air
preheat temperature prior to the heating element and once
temperature greater than the lower volatility limit of the fuel is
achieved turn off the energy to the heating element; monitoring the
combustion chamber temperature and turning off the ignition source
when the combustion chamber temperature reaches 1200 F.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application No. 60/301,546 filed Jun. 28, 2001, which is
incorporated herein in its entirety.
FIELD OF THE INVENTION
[0002] The invention relates generally to burners that can be used
with low-volatility liquid fuels. The invention can be used with
pilot burners which are generally used to light off main or primary
burners which use low-volatility liquid fuel. Additionally, the
invention can also be used with the primary burners. Yet
additionally, the invention also relates to low BTU output burners
that can be used to combust soot, which is generated by internal
combustion diesel engines.
BACKGROUND OF THE INVENTION
[0003] Pilot burners are used to light off the main flame in
industrial burners. They are especially essential in lighting the
main flame in burners, which use heavy liquid fuels such as diesel
or higher-grade oils. Various kinds of pilot burners are used in
such burners.
[0004] One of the essential requirements of a pilot burner is that
the pilot flame should light easily. Often the pilot flame is lit
using a spark from a spark plug. In some cases, the pilot flame is
lit by contacting the pilot fuel with a hot surface such as a glow
element. Therefore an easily ignitable fuel is generally used to
provide the pilot flame in a pilot burner. This is especially true
for burners where the main flame is provided by the combustion of a
heavy liquid fuel such as diesel or higher-grade oils. Thus natural
gas or propane is very often used to provide the pilot flame in
pilot burners, which are used with such burners.
[0005] The use of natural gas or propane to provide the pilot flame
in a burner, which operates primarily on a heavy liquid fuel,
introduces complexity into the burner system. The natural gas has
to be piped to the system using a separate natural gas train. The
natural gas train components add to the cost and complexity of the
system. The additional parts increase the chances for breakdowns
resulting in system shutdowns and additional maintenance.
[0006] Similarly, the use of propane in the pilot burner
necessitates the use of a propane storage and feed system. The
propane system adds to the cost of the system. Additionally the
storage of propane increases the hazards associated with the
system.
[0007] Therefore, it would be advantageous to provide a pilot
burner which is easy to light off and which operates on the same
heavy liquid fuel as the main burner. Such a pilot burner would
greatly reduce the complexity of the burner system. Further, such a
system would greatly reduce the costs associated with the necessity
of providing natural gas or propane to fuel the pilot burner. Yet
further, such as system would greatly reduce the hazards associated
with storing a gaseous fuel such a natural gas or propane on the
user's premises.
[0008] The invention can also be used in a device for burning off
solid particles, in particular soot particles, in the exhaust gas
of internal combustion engines, which use diesel as an operating
fuel.
[0009] Burn-off devices of this kind are used in particular in
motor vehicles having diesel engines, for the direct disposal of
the soot filtered out of the exhaust gas by electrostatic soot
traps. In such a device, the soot is delivered to the combustion
chamber of the burn-off device along with a secondary flow of
exhaust gas that amounts to less than lo of the total exhaust gas.
In the burn-off device, the soot is burned at a flame temperature
between 550.degree. C. and 1000.degree. C. At this high
temperature, essentially complete combustion of the soot and other
combustibles takes place. Therefore, the combustion products are
free of toxic substances and suitable for discharge to atmosphere.
The combustion products are then expelled to the atmosphere via the
engine exhaust system.
[0010] To generate the burn-off flame, a pilot burner is mounted on
the combustion chamber of the burn-off device. Several embodiments
of pilot burners that are suitable for such applications are
described in the prior art. For example, U.S. Pat. No. 4,858,432
(Knauer) describes a pilot burner for an apparatus for burning off
solid particles in the exhaust gas of internal combustion engines.
In this pilot burner, the liquid fuel is injected over a shield,
which covers a glow plug. The liquid fuel is vaporized when it
contacts the hot surface of the shield. The vaporized fuel is then
passed into a combustion chamber wherein it is mixed with preheated
air. The mixture is then passed over a glow element, which ignites
the fuel and helps to maintain the combustion of the fuel. The hot
combustion gases are passed out the combustion chamber. They then
pass into a secondary combustion chamber wherein soot particles
from the engine exhaust are also introduced. The hot gases ignite
the soot particles, which combust to form typical products of
combustion such as carbon dioxide and water. The products of
combustion are then passed out of the combustion chamber to the
atmosphere. Implementation of this type of pilot burner has
durability issues. Under low fuel flow conditions and under
continuous operation, the liquid fuel in direct contact with the
hot surface of the shield may reach a temperature that may promote
decomposition of a portion of the fuel. This typically results in
the formation of carbon or soot that can build up on the shield.
The soot eventually plugs the fuel flow passages or channels and
obstructs the flow of the liquid fuel. This results in unreliable
re-start characteristics and application durability issues.
[0011] U.S. Pat. No. 4,716,728 (Dettling) describes another
embodiment of a pilot burner, which is integrated into the soot
burning apparatus. In this device the liquid fuel is passed over a
glow plug, which evaporates it into a gaseous state. The evaporated
liquid fuel is then passed over a second glow plug, which further
raises its temperature to near it flash point limit. The heated
evaporated fuel is then mixed in a combustion zone with air to
initiate combustion. The fuel and air combine to form products of
combustion, which are passed from the combustion zone into a soot
burning zone. In the soot burning zone, soot is introduced and is
mixed with the hot products of combustion. The soot gets heated to
above its ignition temperature. The heated soot combines with the
oxygen in the hot products of combustion. Further combustion takes
place wherein the soot is burnt to produce relatively harmless
carbon-dioxide.
[0012] It should be noted that in these and other embodiments of
pilot burners, which are described in the prior art, the liquid
fuel is sprayed or otherwise contacted with a hot surface to effect
evaporation. However, when liquid fuel contacts a hot surface, some
of the liquid fuel gets overheated. The overheating causes the
liquid fuel to crack and deposit carbon on the internal surfaces of
the pilot burner. Thus pilot burners, which use liquid fuel are
very susceptible to fouling due to deposited carbon from the liquid
fuel. This is especially true with very low flow burners and
burners that operate under near continuous duty.
[0013] Therefore, it would be advantageous to provide a pilot
burner for a soot burning apparatus used with internal combustion
engines wherein carbonization of the liquid fuel is reduced or
minimized. Such a pilot burner would greatly reduce the down time
of internal combustion engines for the purpose of cleaning the
deposited carbon from the burner system. Further such a pilot
burner will greatly reduce the maintenance required for cleaning
the deposited carbon from the burner system.
SUMMARY OF THE INVENTION
[0014] According to one aspect of the invention, there is provided
a burner for liquid fuel, the burner comprising: a mixture chamber
for producing a liquid fuel air mixture, the mixture chamber having
a heating element means, an air receiving means for receiving air,
the air receiving means configured so as to facilitate air flow
over at least a part of the heating element, and a liquid fuel
receiving means; an atomizer mounted in a path of flow of the
liquid fuel air mixture formed by the mixture chamber; and a
combustion chamber for combusting the liquid fuel air mixture, the
combustion chamber having a flame holder, an ignition source
located proximal the flame holder, and a combustion zone located
downstream of the flame holder.
[0015] According to another aspect of the invention, there is
provided a method for operating a self-sustaining liquid fueled
burner comprising following the steps: initiating air flow to the
burner through the inlet air means; initiating the electrical
energy to the heating element to preheat the air flow to the
burner; initiating the fuel flow to the burner through the inlet
fuel means to make a fuel air mixture, initiating the electric
energy to the ignition source to ignite the fuel air mixture;
monitoring the air preheat temperature prior to the heating element
and once temperature greater than the lower volatility limit of the
fuel is achieved turn off the energy to the heating element;
monitoring the combustion chamber temperature and turning off the
ignition source when the combustion chamber temperature reaches
1200 F.
[0016] This invention relates to a liquid fuel using pilot burner,
which can be used as a pilot for lighting off the main flame in a
liquid fuel fired burner or initiating the reaction in a process
reactor. The invention can be applied to primary combustors and to
a combination of a pilot burner and a primary combustor. More
specifically, the invention relates to a self sustaining burner
that is configured to allow the burner's process air to be
preheated prior to being mixed with the fuel and prior to this fuel
air mixture contacting the surface burner element or flame holder.
Preheating of the process air is achieved by one of two methods,
directly by a heating element during start-up and by flame heat
recuperation during the self-sustaining operation. The preheated
air is used to enhance the atomization of the liquid fuel and to
partially vaporize of the liquid fuel. A heating element or spark
source is used to ignite the partially vaporized liquid fuel air
mixture and the flame is established on the surface burner element
or flame holder.
[0017] The invention is also for integrating a recuperation heat
exchanger surface to the combustion chamber of the burner. This may
be achieved by adding an external shell around the combustion
chamber to create a flow passage through which the burner air is
introduced into the burner. Once the burner is ignited, heat from
the flame may be transferred to the inlet burner air raising its
temperature to above the lower flash point and below the auto
ignition point of the specific fuel being used. This recuperative
heat raises the temperature of the flame, which in turn allows for
additional air to be added to the burner to maintain appropriate
combustion chamber temperatures. The effect of adding the
additional air is to produce a lean flame without reducing the
flame temperature. The increased oxygen content in the combustion
chamber enhances combustion and ensures a soot free flame. The
invention includes other configurations such as coiled tubing or
the use of heat transfer devices such as heat pipes that can be
used to promote the transfer of heat energy from the flame to the
inlet process air, and therefore, the invention is not limited to
the simplest implementation, which is illustrated herein as an
external air-heating jacket.
[0018] A second aspect of this invention is the use of a glow plug
or heating element downstream of the recuperative heat exchanger
section and in heat exchange relationship to the inlet burner air.
This aspect allows for the use of electrical energy to initially
preheat the burner air during burner start-up. This air preheating
is important to promote the initial vaporization of a portion of
the liquid fuel such that a combustible air-fuel mixture is
provided to the ignition device above the flame holder or surface
burner element. By indirectly providing the heat to vaporize the
fuel through the heated airflow, this invention eliminates the
potential of carbon or soot formation within the atomizer and
fuel-air mixing chambers. This aspect directly addresses the
shortcomings of the prior art configurations. This heating element
can controlled based on the air preheat temperature exiting the
recuperative heat exchanger section.
[0019] Once recuperative heat is sufficient to raise the air
temperature to within its desired range, the heating element may be
de-energized. An alternate configuration of the heating element can
be used with this invention. The heating element can be selected
from a group of self-regulating elements that automatically shut
off once the temperature of the element achieves a pre-established
range. This can be achieved by designing the heating element
resistance to increase exponentially above a defined temperature
range or by incorporating a temperature sensitive switch within the
heating element. Both of configuration of the heating element will
eliminate the need for the preheat temperature sensor.
[0020] A third aspect of this invention is the use of an atomizer
with preheated air. The preheated air enhances the atomization
process of the liquid fuel through two mechanisms. First, the hot
air has a lower density, and therefore the actual flow rate per
mass of air increased. Secondly, the hot air causes vaporization of
the liquid fuel as the atomization process is occurring, which
further atomizes the fuel creating smaller droplets which combust
easily.
[0021] The use of a surface burner element as the flame holder
provides a mixture of fine pore structures and coarse pore
structures. The coarse pores allow easy passage of the vapor state
fuel air mixture at low-pressure drops. The fine pore structures
provide a high surface tension region that attracts and holds the
liquid portion of the fuel air mixture. The surface element
promotes both combustion within the mesh and radiant heat and
promotes the formation of flame-lets that are held close to the
surface. The heat from the flame is partially transferred to the
mesh, which supports the continued vaporization of the liquid fuel
and its subsequent combustion.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is a cross-section of a longitudinal view of an
embodiment of a pilot burner according to the present
invention;
[0023] FIG. 2 is a cross-section of a longitudinal view of another
embodiment of a pilot burner according to the present
invention;
[0024] FIG. 3 is a cross-section of a longitudinal view of the
embodiment of the pilot burner shown in FIG. 2 further modified for
the combustion of soot particles from the exhaust of an internal
combustion diesel engine; and
[0025] FIG. 4 is a representation of a liquid-fuel fired burner
which uses the pilot burner assembly FIG. 2 for igniting and
maintaining the main flame of the burner.
DETAILED DESCRIPTION OF THE INVENTION
[0026] Referring now to FIG. 1 of the drawings, the pilot burner
comprises a mixture preparation chamber 10 and a combustion chamber
102. The mixture preparation chamber (MPC) 10 is configured as a
hollow, horizontal cylindrical housing 11, which is open at its
first end 12 and closed at its second end 14. The first end 12 has
an adaptation 16 wherein a glow plug adapter 24 is attached to the
first end 12. The adaptation could be internal threads, which
engage mating threads on glow plug adapter 24. However, other means
of attaching end 12 to glow plug adapter 24 could also be used.
[0027] A glow plug 20 is attached to glow plug adapter 24 such that
glow plug 20 extends at least partially into the housing 11 of the
mixture preparation chamber 10. Electrical leads 22 are provided in
the glow plug 20 for attachment to a source of electricity to
enable glow plug 20 to reach its normal operating temperature
within the range of 800.degree. F. to 1600.degree. F. It should be
noted that the glow plug 20 is mounted along the longitudinal axis
of housing 11. The relative dimensions of the diameter of housing
11 and the diameter of glow plug 20 are such that an annular flow
space 26 is formed between the glow plug 20 and the inner surface
28 of the housing 11. Further, the glow plug 20 and glow plug
adapter 24 closes the housing 11 at the first end 12 to prevent
leakage.
[0028] The glow plug 20 can be any of a variety of heating elements
with or without shields, and the term glow plug is intended to
refer to any and all of these components throughout this
disclosure. The glow plug 20 is a standard component which is
readily available from suppliers such as Wellman Thermal Systems,
Inc., USA.
[0029] Air inlet ports 17 are provided circumferentially near the
end 12 of the housing 11. The air inlet ports 17 are located to
allow for fluid communication with annular flow space 26 between
the glow plug 20 and the inner surface 28 of the housing 11. The
air inlet ports 17 are used to introduce preheated air in to the
combustion chamber 102 as will be described later.
[0030] At the second end 14 of the housing 11, an opening 18 is
provided for the gas-tight entry of a fuel tube 30. As shown in
FIG. 1, the fuel tube 30 has an opening 32 at one end for the entry
of the fuel and a threaded end 34 for connection of the fuel tube
30 to an atomizer 50 at the other end. The threaded end 34 on fuel
tube 30 is configured to engage the threads on the fuel flow
passage of the atomizer 50.
[0031] Between the heated end 23 of glow plug 20 and the end wall
14 of the mixture preparation chamber 10, there is positioned an
adapter 56 which provides a seating for the atomizer 50. The
adapter 24 is an annular piece of metal whose outer diameter
generally matches the inner diameter of housing 11 of the mixture
preparation chamber 10. The adapter 24 slides into the housing 11
and is received snugly inside the housing 11. The inner diameter of
the adapter 56 is threaded and engages a matched threaded tube 57
through which the hot air is introduced into atomizer 50. The
threaded tube 57 engages threads on the air-flow passage of the
atomizer 50.
[0032] The atomizer 50 is a standard component that is readily
available from suppliers such as Lechler Inc, USA. As shown in FIG.
1, the atomizer 50 has an inverted "T" shape. On one side, the
atomizer 50 has a threaded air inlet flow passage 54 for the
introduction of air into the atomizer 50. On its other side, the
atomizer 50 has a threaded fuel-inlet flow passage 58 for the
introduction of fuel into atomizer 50. The fuel and air mix within
the atomizer 50, and a fine spray of atomized fuel, is carried on a
stream of air through a vertical ejection port 52. The air-inlet
passage 54 of the atomizer 50 is connected to the air flowing from
the mixture preparation chamber 10 by the threaded tube 57. The
fuel-inlet passage 58 of the atomizer 50 is connected to the fuel
flowing into chamber 10 by t tube 30. An opening 19 accommodates
the atomizing orifice 52 of atomizer 50.
[0033] A housing 100 is connected to the opening 19 of combustion
chamber 102. In FIG. 1, the housing 100 is a substantially vertical
tube open at both ends. The lower end of housing 100 is connected
in a gas tight manner around the opening 19 of the mixture
preparation chamber 11. The lower end of housing 100 is bounded by
atomizer 50.
[0034] The upper end of housing 100 terminates in an opening 104
through which the products of combustion are exhausted from the
combustion chamber 102. Depending on the application of the pilot
burner, the opening 104 could communicate to the atmosphere, or to
the main burner chamber, or to a soot burning combustion
chamber.
[0035] A flame holder 60 is located above the atomizer 50. The
flame holder could be any suitable matrix such as a fiber mesh, a
metal screen, or steel-wool, whose function is to evenly distribute
the fuel air mixture ensuring even combustion, to support a stable
flame formation, and to temporarily adsorb liquid components of the
fuel air mixture. The flame holder 60 can also support radiant
surface combustion of the air fuel mixture.
[0036] A spark-plug 70 is located above flame holder 60 to ignite
the fuel air mixture. The spark plug 70 is inserted into the
combustion chamber 102 through an opening 106 in the wall of the
housing 100.
[0037] The hot products of combustion are removed from the
combustion chamber 102 through the exhaust opening 104, which could
be connected to the atmosphere or to a main chamber of the main
burner or the soot-burning chamber.
[0038] As shown in FIG. 1, a preheater 80 is provided for
preheating the air. The air enters at air inlet ports 17 of the
housing 11 of the mixture preparation chamber 10. The preheater 80
comprises a jacket 82 which is formed around the housing 100 of the
combustion chamber 102 and the housing 11 of the mixture
preparation chamber 10. The jacket 82 is cylindrical in
cross-section and is sized so that an annular space 81 is created
for the flow of air between the wall forming the housing 100 of the
combustion chamber 102 and the internal cylindrical surface of the
jacket 82. The upper end of the jacket 82 is sealingly connected in
to an upper closure piece 83. The lower horizontal end of the
jacket 82 is sealingly connected to a lower closure piece 84.
[0039] The upper closure piece 83 has an outer diameter 87
substantially equal to the diameter of jacket 82, and is attached,
for example by welding, brazing, etc., to the upper end of the
jacket 82. The upper closure piece 83 has an inner diameter 86
which is substantially equal to the outer diameter of the housing
100 of the combustion chamber 102. The inner diameter 86 of upper
closure 83 is connected to the outside of the housing 100 of the
combustion chamber 102.
[0040] The lower closure piece 84 has an outer diameter 89
substantially equal to the diameter of jacket 82. This outer
diameter 89 is attached to the end of jacket 82, as shown in FIG.
1. The lower closure 84 has an inner diameter 88 substantially
equal to the outer diameter of the housing 11 of the chamber
10.
[0041] The housing 100 of the combustion chamber 102 functions as a
heat transfer surface to transfer heat from the hot products of
combustion within combustion chamber 102 to the relatively colder
air flowing in the annular space 81. The extent of heat transfer
area is selected to provide an air preheat temperature of 160 to
600.degree. F. The actual preheat temperature would depend on the
flash point and auto-ignition points of the liquid fuel used in the
burner. For example, diesel fuel has a flashpoint of 160OF and an
auto-ignition point of about 600.degree. F. Thus, if diesel is used
as a fuel in the burner, the preheat temperature of the air would
be maintained above 160.degree. F. to cause the fuel in the chamber
10 to vaporize when it contacts the preheated air. However, the
preheat temperature of the air would also be maintained at less
than 600.degree. F. so as not to cause ignition of the fuel when it
is mixed with the preheated air 44 in the chamber 10. The
combination of preheated air 44 and atomized fuel from the fuel
orifice 36 contacting the surface element 60 facilitates a soot
free, lean combustion, self-sustaining pilot burner. The actual
dimensions of the jacket 82 would be selected based upon factors
such as the preheat required for the particular fuel used in the
burner as well as the rate of heat transfer through the housing 100
between the hot products of combustion in combustion chamber 102
and the air in the annular space 81.
[0042] As shown in FIG. 1, an opening 98 is provided in the jacket
82 of the preheater 80 to accommodate an air inlet nozzle 90. The
air inlet nozzle 90 has an open inlet end 92 through which air
introduced into jacket 82. An opening 94 is also provided in the
jacket 82 for receiving a spark-plug adapter 72. A spark plug 70 is
located in the adapter 72 and extends through the annular space 81
and into an opening 106 formed in the combustion chamber housing
100. An opening 96 is also provided in jacket 82 for the
introduction of the fuel tube 30 which passes through the annular
space 81 and is received in the opening 18 formed in the chamber
11.
[0043] The operation of the pilot burner will now be described.
[0044] To start the operation of the pilot burner 5, the leads 22
of the glow plug 20 are connected to a source of electricity. This
activates the electrical heating element (not shown) within glow
plug 20. After a period of time (usually a few minutes or less),
the glow plug 20 will have reached its normal operating
condition.
[0045] Ambient air 40 is now introduced through the inlet nozzle 90
and the opening 92, where it enters the jacket 82 of the preheater
80 and flows downwardly (see arrow 42) through annular space 81.
Since the pilot burner 5 is still cold, there is no combustion
taking place in combustion chamber 102. Thus, there is no heat to
transfer to the air, which is still at ambient temperature when it
reaches the air inlet ports 17. The location of air inlet ports 17
is chosen so that the air is distributed over at least a portion of
the hot surface of glow plug 20. The air 40 absorbs heat from the
glow plug 20 and is heated to a temperature between the flash-point
temperature and the auto-ignition temperature of the fuel that is
used in the pilot burner 5. The preheated air is shown in FIG. 1 as
44.
[0046] The preheated air 44 flows through the tube 57 into the air
inlet flow passage 54 of the atomizer 50, and then out of atomizing
orifice 52 under the flame holder 60. The preheated air 44 then
flows through the flame holder 60 into the combustion chamber 102
and exits through the outlet or opening 104. After the heated air
44 has flowed through the various components of the pilot burner 5
for a period of time and an operating temperature is reached, fuel
46 is introduced into the system through the opening 32 of fuel
tube 30. The fuel 46 flows through fuel tube 30 to the fuel inlet
flow passage.
[0047] The heated air 44 and the fuel 46 mix within the atomizer 50
to provide a finely atomized fuel-air stream 48 formed by the low
vapor pressure portion of the liquid fuel 46 evaporating within the
hot air 44. The stream 48 exits from the atomizing orifice 52 and
passes through the flame holder 60. The liquid components of the
fuel-air stream 48 adsorb on the surfaces of the flame holder 60,
while the vapor components travel through the flame holder 60.
[0048] The angle of the stream 48 exiting the orifice 52, and the
distance between the orifice 52 and lower surface of flame holder
60, are selected such that the stream 48 covers a most of the flame
holder 60. Typically, a full cone shaped stream 48 is desired, but
other shapes such as hollow cones and oval shaped cones can be
used. Other configurations of atomizers 50 which minimize or
eliminates the need for pressurized air can also be used instead of
the atomizer 50 shown in FIG. 1. In fact, any atomizer 50 can be
used as long as the output from the atomizer 50 is an atomized
air-fuel stream 48 which flows to contact the lower surface of
flame holder 60.
[0049] The vapor portion of the stream 48 passes through flame
holder 60 and enters the lower portion 105 of the combustion
chamber 102, between the flame holder 60 and the firing tip 107 of
the spark plug 70. An electric current is passed through spark plug
70 to create a spark at the firing tip 107 which ignites the stream
48 to create flame. The flame is held by the flame holder 60 and
heats the flame holder 60 so that it is able to transfer heat to
the incoming stream 48 and initiate its ignition without the
assistance of a spark from spark plug 70. The products of
combustion 110 flow upward through the combustion chamber 102 and
exit through the opening 104.
[0050] The combustion process raises the operating temperature
within combustion chamber 102 to around 1,600 to 2,000F. As the hot
products of combustion 110 flow through combustion chamber 102,
they contact the housing 100 and lose some of their heat to the air
42 which is flowing through the annular space 81 outside housing
100. The heat transfer raises the temperature of the air 42 and
decreases the temperature of the products of combustion 110 exiting
the burner through the opening 104.
[0051] As cold air 40 continues to pass over the housing 100, it
gradually increases in temperature until it reaches its target
temperature before entering the chamber 10 through the air inlet
ports 17. A temperature sensor 140, located in the flow path of
preheated air 42 before it enters the inlet ports 17, senses the
temperature of the preheated air 42. When the air preheat target
temperature is reached, the temperature sensor 140 activates
control circuitry (not shown) to switch off the flow of electricity
to the leads 22 of the glow plug 20. Thus, excessive preheating of
the air is avoided to reduce the chances of auto-ignition or
premature combustion of the fuel-air mixture.
[0052] The flow of air 40 and fuel 46 into the pilot burner are
continued for the duration of the operation of the pilot burner.
Thus a self-sustaining flame is provided on flame-holder 60 by the
preheating of air 40 to a temperature greater than the flash-point
temperature of fuel 46, mixing the preheated air 44 and fuel 46
using atomizer 50 and passing the fuel-air stream mixture 48 over
the hot flame-holder 60. As the temperature of the air 44
increases, the flame temperature above flame holder 60 increases,
which allows for the amount of air 40 to be increased to lean out
the combustion increasing the oxygen content in the combustion
chamber. This increased amount of air enhances combustion and
ensures the elimination of the soot formation in the product of
combustion 110.
[0053] The temperature of the products of combustion 110, which are
exhausted through the exhaust opening 104 of the combustion chamber
102, is high enough such that it can provide the thermal energy for
initiating the ignition of a fuel-air mixture within the main
chamber of a liquid fuel burner or can initiate reaction within a
downstream reactor. Thus the hot products of combustion 110 can act
as a pilot flame to initiate and maintain the main flame in a
liquid-fuel burner.
[0054] Alternately, the hot products of combustion 110 are hot
enough such that they can initiate the combustion of soot
particles, which may come into contact with it. Such an application
can be found in diesel engines, wherein the soot from the exhaust
of the engine is trapped and burnt in a combustion chamber using a
small pilot flame-producing device. This application of the
invention is described further in FIG. 3 below.
[0055] The use of preheated air to vaporize the liquid fuel has
several advantages over the prior art implementations of the
invention wherein the liquid fuel is vaporized by injection over
the hot surface of a glow-plug. Pilot burners of the prior art are
therefore susceptible to coking due to the cracking of the fuel by
contact with excessive hot surfaces. This causes un-necessary
equipment shut-downs and maintenance requirements as well as loss
of production in steam-generating equipment which use liquid-fuel
fired burners as the source of energy.
[0056] Another embodiment of the pilot burner shown in FIG. 1 is
shown in FIG. 2 wherein the pilot burner assembly 5 is constructed
in a straight-line configuration rather than the L-shaped
configuration of FIG. 1. In the embodiment shown in FIG. 2, a
housing 11 of the chamber 10 is integrated into a housing 100 of
the combustion chamber 102. Thus, the housing 100 is extended under
the atomizer 50 to form the chamber 10 while eliminating the
housing 11 shown in FIG. 1. The pilot burner 5 of FIG. 2 also is
simpler to construct than the pilot burner 5 of FIG. 1.
[0057] Another difference in the construction is the location of an
adapter 56, which directly engages the atomizer 50 around the
atomizing orifice 52. Thus the short tube 57 shown in FIG. 1 for
holding the atomizer 50 in the chamber 10 is eliminated.
[0058] The major components of the pilot burner 5 of FIG. 2
function similarly to the major components of the pilot burner 5 in
FIG. 1 and are therefore given the same reference numbers. An
additional component that is incorporated into the pilot burner 5
of FIG. 2 is a perforated catch tray 120 that is located in between
the atomizer 50 and the glow plug 20. The function of catch tray
120 is to catch any fuel drops that may inadvertently fall from a
threaded fuel nipple 34, especially during startup. A plurality of
through perforations 122 are provided in catch tray 120 to allow
the preheated air 44 to pass through the catch tray 120. The
preheated air 44 evaporates any liquid fuel that may have been
trapped by the catch tray 120. Thus the liquid fuel is prevented
from contacting the hot surface of the glow-plug 20 and being
carbonized. Therefore, nuisance shutdowns and unnecessary
maintenance is reduced through the use of the catch tray 120.
[0059] The catch tray 120 is also used to evenly flow the heated
air 44 out of chamber 10 and to direct it into the air-inlet
passage 54 of the atomizer 50.
[0060] The operation of the pilot burner 5 of FIG. 2 is
substantially identical to the operation of the pilot burner 5 of
FIG. 1. The only additional step is that the preheated air 44 flows
through the perforations 122 of catch tray 120 before reaching the
air-inlet passage 54 of the atomizer 50. [061] An embodiment of the
pilot burner 5 shown in FIG. 2 that is adapted for the burning of
soot particles is shown in FIG. 3 of the drawings. The pilot burner
5 of FIG. 3 is substantially identical in construction and
operation to the pilot burner of FIG. 2 except for the provision of
means to inject a fluidized air stream containing soot particles
into the combustion chamber 102.
[0061] In FIG. 3, this means to inject the soot-particles
containing a fluidized air stream is a straight injection tube 140,
which is inserted vertically into the combustion chamber 102. The
injection tube 140 has a fluidized air inlet opening 142 at its
upper end and a fluidized air outlet opening 144 at its lower end.
The soot, which is trapped from the exhaust of an internal
combustion engine, is fluidized using a small portion of the engine
exhaust gas. A fluidized soot stream 132 is introduced into inlet
opening 142 of the tube 140. The soot stream 132 flows downwardly
in the tube 140 and absorbs heat from the hot products of
combustion 110 flowing over the outer surface of the tube 140. The
soot stream 132 therefore is heated to a temperature which is
selected to be below the auto-ignition temperature of carbon to
prevent premature combustion of the carbon in the tube 140. Thus
the danger of flashback due to premature combustion of the carbon
in tube 140 is reduced.
[0062] The heated soot stream 132 is shown in FIG. 3 by reference
number 134. The heated soot stream 144 exits through the outlet
opening 144 into the combustion chamber 102. Upon contact with the
hot products of combustion in the combustion chamber 102, the soot
particles in the heated soot stream 144 are heated to a temperature
greater than the auto-ignition temperature of carbon. The soot
particles therefore combust and are converted to carbon-dioxide
which is carried away in the hot products of combustion 110 as it
passes through the exhaust opening 104 of the combustion chamber
102.
[0063] The tube 140 is arranged for counter-flow between the soot
stream 132 and the hot products of combustion 110 so that
heat-transfer between the two gas streams can take place using a
minimum heat-transfer area for the given heat-duty. Other
arrangements can be used instead of the tube 140. For example, the
tube 140 could be configured as a helical coil that is inserted
into the combustion chamber 110 to further provide a more compact
arrangement while maximizing the heat transfer.
[0064] All other aspects of the operation of the pilot burner 5 of
FIG. 3 with respect to the combustion of liquid fuel 46 follows the
description given for the pilot burner 5 of FIG. 2.
[0065] The overall heat transfer efficiency of the pilot burner 5
could be further enhanced by providing other means to recover heat
from the hot products of combustion. For example, the hot products
of combustion could be passed through other heat-transfer devices
such as water-heaters, space-heaters, etc. to further recover the
residual heat in the hot products of combustion.
[0066] An embodiment of a main burner, which utilizes the pilot
burner shown in FIG. 2 for igniting and maintaining the main flame,
is shown in FIG. 4. The main burner comprises a combustion chamber
200 and an atomization chamber 202 which form the upper zone and
the lower zones respectively of a cylindrical tube 228. The two
zones are separated by a flame holder 224. The lower end of tube
228 is closed in a gas tight manner by an oversized end-wall 240.
Thus the atomization chamber 202 is bounded by the end-wall 240,
the flame-holder 224, and a portion of the tube 228.
[0067] A cylindrical jacket 226 is provided around the tube 228.
The jacket 226 is closed at its lower end by the end wall 240 and
at its upper end by an end-wall 242. The end-wall 242 is attached
in a gas tight manner to an outer surface of the tube 228 at its
inside diameter and at its outside diameter to the jacket 226. Thus
an annular flow volume 225 is defined by the outer surface of the
tube 228, the inner surface of the jacket 226, the end wall 240,
and the end-wall 242.
[0068] A main fuel atomizer 206 is located in the atomization
chamber 202, and is held in place by an adapter 244 in a manner
similar to that described previously for the pilot burner 5 in FIG.
2. A main fuel supply tube 208 is inserted in a gas tight manner
through the jacket 226 and the tube 228 and is attached to the
fuel-inlet passage of the atomizer. The atomizer 206 is a scaled up
version of the atomizer that is used in pilot assembly 5 in order
to accommodate the higher flow-rate of the main fuel stream in the
main burner.
[0069] Primary air inlet ports 229 are located in the atomization
chamber 202 under the atomizer adapter 244 for introduction of the
primary air for atomization of the liquid fuel. As will be
described, a small portion of the total air that is required for
complete combustion of the liquid fuel is introduced into the
atomization chamber 202 through primary air inlet ports 229. The
air enters the atomizer 206 and atomizes the fuel to produce an
air-spray containing droplets of fuel. The fuel containing
air-stream is blown against the lower side of the flame-holder
224.
[0070] Also located in atomization chamber 202 above atomizer
adapter 244 are secondary air inlet ports 226. The secondary air
inlet ports 226 introduce a larger quantity of air than the primary
air inlet ports 229. This air can be cold or preheated as shown in
FIG. 4. The purpose of the secondary air is to vaporize the
low-boiling fraction of the liquid fuel and to provide additional
oxygen for the combustion process to take place.
[0071] The pilot burner assembly 5 is located above the flame
holder 224 in the combustion chamber 200. The exhaust gas outlet
104 of the pilot burner assembly 5 is inserted above the flame
holder 224 through suitable gas tight openings 222 and 223 in the
jacket 226 and the tube 228 respectively. The hot exhaust gases 110
from the pilot burner 5 are directed so that they ignite the
fuel-air mixture flowing through the flame-holder 224. All of the
primary and secondary air is introduced into the annular flow space
225 through the main air inlet 246 connected to the jacket 226.
Since a large excess of combustion air is used, the combustion of
the liquid fuel takes place at a relatively lower temperature than
in conventional liquid fuel fired burners. Thus relatively lower
quantities of thermal NOx are generated in the burner of the
present invention compared to conventional liquid fuel-fired
burners.
[0072] During operation, the pilot burner 5 is first lit as
described previously with respect to FIG. 2. The hot exhaust gas
110 produced by the pilot burner 5 is directed into the combustion
chamber 200. Heat from the hot exhaust gas 110 is transferred to
the flame-holder 224 and the tube 228. When the flame-holder 224
and the tube 228 are sufficiently heated, the main air 212 is
introduced into annular volume 225 through the main air inlet 246
in the jacket 226. The main air 212 flows through the annular
volume 225 and is preheated. As it passes through the annular
volume 225, a portion 218 of the main air is diverted into the
atomization chamber 202 above the atomizer adapter 244 through
secondary air inlet ports 226. The final portion of the main air
212, shown in FIG. 4 as primary air 220, passes into atomization
zone 202 through primary air inlet ports 229.
[0073] It is not necessary that secondary air 218 be supplied by
main air 212. It may be advantageous to use separate sources of air
for the primary and secondary air requirements of the burner,
especially where a high pressure is required for the primary air in
order to provide the motive force for atomization of the liquid
fuel in the atomizer. In such cases, a lower pressure source could
be used for the secondary air resulting in savings of energy
required for compression of the air to a high pressure for carrying
out the atomization.
[0074] It is also not necessary that the secondary air be heated.
Air at ambient temperatures could be used for the secondary air and
only the primary air could be heated as shown in FIG. 4. This may
be required to maintain flame temperature within certain limits to
produce lower quantities of pollutants such as thermally produced
NOx.
[0075] While not shown in FIG. 4, it is well known to provide means
to individually control the proportions and amounts of air that are
used as primary and secondary air for burner-tuning and flame
optimization purposes. Such means could include manually or
automatically controlled flow-control dampers or other such
devices.
[0076] After the air 212 has been sufficiently heated, fuel 210 is
introduced to the atomizer 206 through the fuel supply tube 208.
The air 220 causes the fuel 210 to atomize to produce an air spray
232 containing droplets of fuel. The angle 204 of the air spray 232
is selected to cover the complete lower surface of flame-holder
224. Heat is transferred from the hot air to the fuel within air
spray 232 to vaporize the low boiling fraction of the fuel to
produce an easily combustible mixture, which ignites on contact
with the hot flow-passage surfaces within flame-holder 224. The
heat of combustion further maintains the flame-holder 224 at a high
temperature and vaporizes the high boiling fraction of the fuel.
The partially combusted fuel-air mixture contains a mixture of
liquid fuel and products of combustion and is shown in FIG. 4 as
234.
[0077] As the partially combusted fuel-air mixture 234 passes
across the pilot burner 5, further combustion takes place to
produce a relatively clean combustion product gas 238, which flows
out of combustion chamber 200 through exhaust gas outlet 230.
* * * * *