U.S. patent number 3,705,784 [Application Number 05/105,212] was granted by the patent office on 1972-12-12 for liquid fuel burner having reduced thermal stress and rapid start-up time.
This patent grant is currently assigned to Burnham Corporation. Invention is credited to Albert Morrison, Jr., Robert Reichhelm.
United States Patent |
3,705,784 |
Reichhelm , et al. |
December 12, 1972 |
LIQUID FUEL BURNER HAVING REDUCED THERMAL STRESS AND RAPID START-UP
TIME
Abstract
A burner for burning gasified liquid fuel such as oil, in which
the fuel is gasified by being mixed with hot burned gases drawn
from the combustion chamber, is provided in which the normal
thermal stresses found in such burners due to the return of the hot
burned gases for gasifying are substantially reduced and, at the
same time, start-up time is reduced. Minimization of the thermal
stresses is accomplished by utilizing the heat of vaporization of
the oil or other fuel to cool the hot returning gases, and so limit
thermal expansion, by having the gasification of the fuel commence
close to the hot gas outlet of the burner, rather than at a more
remote distance, such as a gasification chamber. This permits
elimination of the gasification chamber, which normally has been
required to provide a preheating area for the oil, and so further
reduces stresses. With such elimination, rapid start-up is provided
by preliminarily burning ungasified fuel introduced by the air and
fuel system of the principal unit.
Inventors: |
Reichhelm; Robert (Lancaster,
PA), Morrison, Jr.; Albert (Leola, PA) |
Assignee: |
Burnham Corporation
(Irvington-on-Hudson, NY)
|
Family
ID: |
22304636 |
Appl.
No.: |
05/105,212 |
Filed: |
January 11, 1971 |
Current U.S.
Class: |
431/116 |
Current CPC
Class: |
F23C
99/00 (20130101); F23C 2700/026 (20130101) |
Current International
Class: |
F23C
99/00 (20060101); F23m 009/06 () |
Field of
Search: |
;431/115,116,215 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Favors; Edward G.
Claims
What is claimed is:
1. A liquid fuel burner for burning a gasifiable liquid fuel such
as oil and having reduced thermal stresses, including
a burner made of refractory material and having a fire chamber,
said chamber having a fuel mixture inlet port, a burned gas removal
port, and a hot burned gas feedback port,
a mixing chamber for mixing said fuel and air, said mixing chamber
being connected to said inlet port,
a burned gas and fuel inlet to said mixing chamber,
means directly interconnecting said burned gas removal port to said
burned gas and fuel inlet,
an air inlet to said mixing chamber for directing air under
pressure into said mixing chamber, said air inlet including a
Venturi for drawing burned gas and fuel into said chamber through
said interconnecting means and said burned gas and fuel inlet,
and
a gasifiable liquid fuel inlet connected to said interconnecting
means proximate to said refractory material,
whereby said fuel will be gasified by hot burned gas as it passes
through said interconnecting means and the heat of vaporization of
said fuel will cool said hot burned gases, thereby reducing the
temperatures thereof and reducing thermal stresses therein.
2. A liquid fuel burner as set forth in claim 1 in which there is
insufficient air present in said interconnecting means to support
combustion of said gasified fuel prior to its reaching said fuel
mixture inlet port.
3. A liquid fuel burner as set forth in claim 1 including ignition
means positioned proximate to, but before, said fuel mixture inlet
port, for igniting said mixture of said fuel and air.
4. In a liquid fuel burner for burning a gasifiable liquid fuel
such as oil which includes a burner made of refractory material and
having a fire chamber therein, said fire chamber having a fuel
mixture inlet port, a burned gas removal port and a hot burned gas
feedback port, a source of air under pressure, a mixing chamber for
mixing said fuel and air and being connected to said inlet port,
that improvement for reducing thermal stresses in hot gas feedback
including
means directly interconnecting said hot burned gas feedback port
with said mixing chamber,
means for introducing said gasifiable liquid fuel into said
interconnecting means, so proximate to said refractory material
that said fuel will be gasified by said hot burned gas as it passes
through said interconnecting means and the heat of vaporization of
said fuel will cool said hot burned gases, thereby reducing the
temperatures thereof and reducing thermal stresses.
5. A liquid fuel burner improvement as set forth in claim 4
including a metering valve associated with said gasifiable liquid
fuel inlet to control the rate of flow into said inlet.
6. In a liquid fuel burner for burning a gasifiable liquid fuel
such as oil which includes a burner made of refractory material and
having a fire chamber therein, said fire chamber having a fuel
mixture inlet port, a burned gas removal port and a hot burned gas
feedback port, means for connecting said hot burned gas feedback
port to said fuel mixture inlet port, a source of air under
pressure, a mixing chamber for mixing said fuel and air and being
connected to said inlet port, and
means for introducing liquid fuel into said connecting means so
that it may be gasified prior to combustion, that improvement for
start-up of said burner including:
a liquid fuel nozzle disposed in said air source,
ducts interconnecting said nozzle with said liquid fuel introducing
means, and
control valve means for controlling flow of said liquid fuel to
said nozzle or to said connecting means,
whereby said burner may be started by use of said nozzle to inject
liquid fuel into said air for burning in said fire chamber prior to
use of gasified fuel.
7. A liquid fuel burner improvement as set forth in claim 6
including a sequence timing control for said control valve
means.
8. A liquid fuel burner for burning a gasifiable liquid fuel such
as oil and having reduced thermal stresses, including
a burner made of refractory material and having a fire chamber,
said chamber having a fuel mixture inlet port, a burned gas removal
port, and a hot burned gas feedback port,
a mixing chamber for mixing said fuel and air, said mixing chamber
being connected to said inlet port,
a burned gas and fuel inlet to said mixing chamber,
means interconnecting said burned gas removal port to said burned
gas and fuel inlet,
said interconnecting means being a metallic pipe running between
said burned gas feedback port and said burned gas and fuel
inlet,
an air inlet to said mixing chamber for directing air under
pressure into said mixing chamber, said air inlet including a
Venturi for drawing burned gas and fuel into said chamber through
said interconnecting means and said burned gas and fuel inlet,
and
a gasifiable liquid fuel inlet connected to said interconnecting
means proximate to said refractory material,
whereby said fuel will be gasified by hot burned gas as it passes
through said interconnecting means and the heat of vaporization of
said fuel will cool said hot burned gases, thereby reducing the
temperatures thereof and reducing thermal stresses therein.
9. A liquid fuel burner as set forth in claim 8 in which said
gasifiable liquid fuel inlet is sufficiently proximate to said
refractory material relative to the length of said interconnecting
pipe and the temperature of said burned gas so as to gasify said
fuel as it passes through said interconnecting means sufficiently
to substantially avoid appearance of yellow in the flame in said
fire chamber.
10. A liquid fuel burner for burning a gasifiable liquid fuel such
as oil and having reduced thermal stresses, including
a burner made of refractory material and having a fire chamber,
said chamber having a fuel mixture inlet port, a burned gas removal
port, and a hot burned gas feedback port,
a mixing chamber for mixing said fuel and air, said mixing chamber
being connected to said inlet port,
a burned gas and fuel inlet to said mixing chamber,
means interconnecting said burned gas removal port to said burned
gas and fuel inlet,
an air inlet to said mixing chamber for directing air under
pressure into said mixing chamber, said air inlet including a
Venturi for drawing burned gas and fuel into said chamber through
said interconnecting means and said burned gas and fuel inlet,
a gasifiable liquid fuel inlet connected to said interconnecting
means proximate to said refractory material,
and a starter unit for creating a fire in said fire chamber when
starting said burner so as to produce hot burned gas for feedback
and gasification, said starter unit including a nozzle for
inserting said fuel in its liquid form into said air inlet,
whereby said fuel will be gasified by hot burned gas as it passes
through said interconnecting means and the heat of vaporization of
said fuel will cool said hot burned gases, thereby reducing the
temperatures thereof and reducing thermal stresses therein.
11. A liquid fuel burner as set forth in claim 10 including fuel
supply for said fuel inlet and for said nozzle, and control valve
means for controlling flow of said fuel to said nozzle or said fuel
inlet sequentially.
12. A liquid fuel burner for burning a gasifiable liquid fuel such
as oil and having reduced thermal stresses, including
a burner made of refractory material and having a fire chamber,
said chamber having a fuel mixture inlet port, a burned gas removal
port, and a hot burned gas feedback port,
a mixing chamber for mixing said fuel and air, said mixing chamber
being connected to said inlet port,
a burned gas and fuel inlet to said mixing chamber,
means interconnecting said burned gas removal port to said burned
gas and fuel inlet,
an air inlet to said mixing chamber for directing air under
pressure into said mixing chamber, said air inlet including a
Venturi for drawing burned gas and fuel into said chamber through
said interconnecting means and said burned gas and fuel inlet,
a gasifiable liquid fuel inlet connected to said interconnecting
means proximate to said refractory material,
and means for inserting additional liquid fuel into said mixing
chamber at said air inlet to provide a second stage of liquid fuel
gasification, said second stage utilizing heat energy remaining in
said hot burned gas entering said mixing chamber,
whereby said fuel will be gasified by hot burned gas as it passes
through said interconnecting means and the heat of vaporization of
said fuel will cool said hot burned gases, thereby reducing the
temperatures thereof and reducing thermal stresses therein.
13. In a liquid fuel burner for burning a gasifiable liquid fuel
such as oil which includes a burner made of refractory material and
having a fire chamber therein, said fire chamber having a fuel
mixture inlet port, a burned gas removal port and a hot burned gas
feedback port, a source of air under pressure, a mixing chamber for
mixing said fuel and air and being connected to said inlet
port,
that improvement for reducing thermal stresses in hot gas feedback
including means interconnecting said hot burned gas feedback port
with said mixing chamber,
means for introducing said gasifiable liquid fuel into said
interconnecting means, so proximate to said refractory material
that said fuel will be gasified by said hot burned gas as it passes
through said interconnecting means and the heat of vaporization of
said fuel will cool said hot burned gases, thereby reducing the
temperatures thereof and reducing thermal stresses,
and a starter unit to provide initial hot burned gas for feedback,
said starter unit including means for inserting ungasified fuel
into the air stream in said mixing chamber.
14. In a liquid fuel burner for burning a gasifiable liquid fuel
which includes a fire chamber and a mixing chamber for mixing air
with said liquid fuel after gasification and for feeding same to
said fire chamber, that improvement including
duct means interconnecting said fire chamber and mixing chamber to
carry hot combustion gases from said fire chamber to said mixing
chamber,
said duct means interconnecting said burner and said mixing chamber
by substantially the most direct path,
said duct means having a fuel inlet area for receiving said liquid
fuel prior to gasification,
and said fuel inlet area being positioned sufficiently close to
said firing chamber and sufficiently far from said mixing chamber
as to permit substantial gasification of said fuel in said duct
means before said fuel as carried by said hot combustion gases
reaches said mixing chamber and as to permit the heat of
vaporization of said oil to reduce the temperature of said duct
means.
Description
BACKGROUND OF THE INVENTION
This invention relates to a burner in which a liquid fuel, such as
oil, is first gasified, mixed with air, and then burned.
Gasification occurs by mixing the fuel with hot burned gases coming
from the burner chamber.
Burners using gasified fuel are not new, although the techniques
for gasification, and the success of the techniques, has
varied.
Gasification systems are shown in various of the patents of the
present inventor, Reichhelm, such as U.S. Pat. Nos. 2,197,347, and
3,308,868 where a portion of the oil is burned and used to gasify
the remainder; U.S. Pat. Nos. 2,735,481 and 3,320,743 where the
fuel is gasified by being mixed with heated air; and U.S. Pat. No.
3,361,183, where gasification is obtained by recirculating a
portion of the combustion gases into admixture with the fuel and a
Venturi is used to draw in the gasified fuel and the hot combustion
gases. In addition, multiple burners, such as those adapted to burn
different fuels, or to burn the same fuel in different ways, have
existed. Examples of these are Reichhelm U.S. Pat. No. 3,308,868
and French patent 1,406,040.
In burners being used for gasifying fuel by mixing oil with hot
products of combustion, such as that shown in Reichhelm U.S. Pat.
No. 3,361,183 or in Reichhelm copending application Ser. No.
56,482, filed July 20, 1970, the gasification of the fuel is shown
taking place in a separate chamber. This chamber has hot products
of combustion entering the chamber at one inlet, liquid fuel
entering it at another, and a mixture of the two being drawn out at
an outlet port after gasification. It then goes into a mixing
chamber for mixing with compressed air and into a burning chamber
for burning. This structure, having a gasification chamber, can
preheat for starting for the use of an electric heater around the
gasification chamber. The structure, however, also results in
undesirable thermal stresses due to the fact that the hot
combustion gases must pass from the burning chamber to the
gasification chamber. This method of preheat also takes a
relatively long start-up time.
SUMMARY OF THE INVENTION
The inherent heat of vaporization of a gasifiable fuel, such as oil
is used to reduce thermal stresses within a gasification type
burner by reducing the temperature of the components most subject
to stress. This is accomplished by injecting the liquid fuel into
the hot combustion gas stream at an earlier point in the system's
operation so that its heat of vaporization will be taken up sooner
and so serve to reduce the temperature of the returned gases before
thermal expansion occurs. This permits elimination of the
gasification chamber, further reducing thermal stresses and also
adding to compaction.
The fuel and air supply system used for the above is also
integrally used to provide a start-up system for a cold burner
using the fuel without gasification.
DESCRIPTION OF THE DRAWINGS
The invention is best understood through reference to the drawings,
as follows:
FIG. 1 is a schematic drawing showing flow and operation of the
unit.
FIG. 2 is a perspective view of the burner.
FIG. 3 is a side elevation of the burner partially cut away in a
section to show portions of the burning chamber and return gas
duct.
DETAILED DESCRIPTION OF THE INVENTION
Structure
The figures show the burner 1 which includes a burner block 5 made
of a refractory material, such as ceramic, mixing area 6, and a
fuel supply system 7.
Burner block 5 contains a generally conical burning chamber 10
leading from mixed fuel inlet 11 to discharge gas outlet 12 at the
opposite end. At one side of chamber 10, proximate to the outlet
12, is a return port 14. Port 14 leads from chamber 10 rearwardly
of the unit in the general direction of burner chamber inlet or
throat 11, through the refractory material to an interconnecting
point 15 where it leads to interconnecting means or duct 17,
normally a metal pipe. The purpose of outlet 14 is to carry hot,
burned gases, i.e., the products of combustion, from the end of
burner chamber 10 back towards the mixing chamber 6, the gases
being used to gasify or vaporize liquid fuel.
Mixing chamber 6 mixes the gasified fuel with combustion air and
feeds it into the burning chamber 10. The air, under pressure,
enters mixing chamber 6 through air inlet duct 20 and air inlet 7.
Duct 20, as it approaches mixing chamber 6 is constructed to form a
Venturi 22 within chamber 6 to create a suction in line 17. This
suction serves to draw the hot burned gases from burning chamber 10
through outlet 14 into chamber 6.
The liquid fuel to be burned comes from a fuel source inlet 25.
Source 25 branches to form fuel supply system 7. Branch 26 passes
through metering valve 27 to an inlet 28 in interconnecting duct
17. Fuel for use in the start-up system, to be described below,
follows duct 30 through valve 31 and duct 32 to a nozzle 33 located
just within the Venturi construction 22 in air inlet 20.
It should be noted that the oil inlet 28 into the interconnecting
duct 17 is positioned proximate to the exit from the refractory
material 5 near point 15. Preferably, it should be located as close
to the refractory material as is practical. The oil may be fed by
either mechanical or gravity pressure, as is desired. The oil is
mixed with the hot burned gas in interconnecting duct 17 at oil
inlet 28. Duct 17 then carries the mixture of oil and hot
combustion gases to mixing chamber 6; the mixture enters chamber 6
at burned gas and fuel inlet 8.
An electrically operated igniter plug 35 is located at the burning
chamber inlet 11 or slightly toward the mixing chamber from that
point. It has been found that by having the igniter 35 positioned
slightly outside of, but before, the burning chamber, the plug has
less tendency to become fouled by products of combustion.
It will be noted that the above structure permits elimination of
the gasification chamber, (compare chamber 14 in Reichhelm U.S.
Pat. No. 3,361,183). It will also be noted that the oil has been
mixed with hot gas at a point much closer to the point of exit of
hot gases from the refractory material (point 15; compare the
liquid fuel inlet 21, FIG. 1, of the Reichhelm patent). If the
gasification chamber is eliminated, however, the electric preheater
is also eliminated (compare heater 18 of Reichhelm U.S. Pat. No.
3,361,183); in its stead a completely distinct but integrally
operating start-up unit identified by circuit 30 has been provided.
This start-up unit is operatively associated with fuel supply
system 7.
This start-up system is integral with the overall system using and
the same fuel source. It is adapted for sequential operation, i.e.,
operation of the start-up followed by operation of the principal
gasifying system. The start-up unit has liquid fuel passing from
source 25 through duct 30, valve 31, and duct 32 to nozzle 33
within, or proximate to, Venturi 22.
Operation
Operation of the liquid fuel burner will be first described in the
operating stage, and then the start-up aspects considered.
In operation, oil or other liquid fuel capable of being gasified
enters the system from source 25 passes through duct 26 and valve
27 and is fed into the hot combustion gases at the intersection
point of duct 28 and interconnecting duct 17. Meanwhile hot gases,
a portion of the total volume of combustion gases, have been taken
from combustion chamber 10 through hot gas discharge port 14
passing through refractory block 5 to point 15 and then into
interconnecting duct 17 and into mixing chamber 6. Air under
pressure enters through air inlet 20 and passes through Venturi 22
into mixing chamber 6. The passage of the air through Venturi 22
creates a suction which draws the hot burned combustion gases
through inlet 14 and duct 17 into mixing chamber 6. These hot
combustion gases (mixed with and carrying gasified oil) are mixed
with the air in chamber 6 and pass through burning chamber inlet 11
to be burned in chamber 10. Electrical plug 35 provides ignition.
Most of the combustion gases are then discharged through discharge
opening 12 with only a small portion returning through outlet
14.
As noted above, the oil is injected into interconnecting duct 17 as
close to the source of hot gas as is practical. Since the oil, as
with any vaporizable liquid, requires heat of vaporization, the
heat energy necessary for the gasification of the liquid fuel comes
from the hot burned gases from duct 14. Thus the gasification of
the oil serves to cool the hot gases. By placing inlet 28 close to
the source of hot gas, the cooling takes place early in
interconnecting pipe 17. Thus pipe 17, a gas delivery pipe, does
not reach the usual red-hot temperature normally found in prior art
structures. Reduction of the temperature of the duct 17 reduces its
thermal expansion (the expansion primarily being in a longitudinal
direction), and so reduces thermal stresses in the area between
mixing chamber 6 and refractory material 5. This is particularly
important at points of junction.
Interconnecting duct 17 must have sufficient length after injection
of the oil to allow adequate time for gasification of the fuel, if
a gasification chamber is not used. Determination of adequate
length relative to quantities of returned gas used can readily be
made by observing the color of the flame in burner chamber 10. If
blue, adequate gasification has taken place; if yellow is present,
it is likely that some of the fuel has remained liquid.
If duct 17 has sufficient length after inlet 28, relative to the
volume and temperature of hot return gases in duct 17,
substantially complete gasification will take place in duct 17
prior to the oil reaching mixing chamber 6. Under these
circumstances and if there remains sufficient heat energy in the
mixture entering inlet 13, additional liquid fuel may also be
injected at nozzle 33 for enhanced heat capacity of the overall
burner. This, then, would result in two-stage operation if all oil
is gasified, but will have yellow in it if there is too much oil
from nozzle 33 (acceptable under some circumstances).
Though gasification using hot, burned gases only appears to be
preferable, the presence of air with the hot gas in duct 17 is not
objectionable provided it does not cool the gas to the point of
incomplete gasification of fuel (i.e., yellow flame) and provided
that premature ignition does not occur.
When the burner unit is cold and needs to be started, feedback of
combustion gases will not, of course, serve to gasify the oil being
fed into the system. Consequently, some other method of preheating
is necessary. In the present invention the start-up system is an
integral part of the total system since it uses the same air
supply, Venturi, and fuel supply. The oil passes through ducts 30
and 32 through the nozzle 33 and is picked up by the air entering
through the air inlet duct 20. It will be ignited by plug 35 and
will burn in burning chamber 10. This start-up operation is
essentially full operation of the burner, not just a pilot light,
but uses ungasified fuel and so is less efficient.
Valves 27 and 31 are used to determine which oil supply system is
used. At start-up, valve 31 is open and valve 27 closed, allowing
the oil to flow to nozzle 33. Once the warm-up period is over,
valve 27 is opened to permit oil to flow into interconnecting duct
17, and valve 31 is closed. If desired, valves 27 and 31 may be
combined at inlet source 25 and may also be operated automatically
by a sequence timing control. If, after start-up, two-stage
gasification is to be used, both valves be left open by an amount
that will give desired combustion balance.
It has been found that a unit can be started in under half a minute
to the point where the hot burned gases can vaporize the oil. One
unit built has had a preheating time of approximately 16
seconds.
* * * * *