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Патент USA US3049186

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Aug. 14, 1962
R. LlTWlNOFF
3,049,168
METHOD AND MEANS ,FOR CONTROLLING A COMBUSTION
APPARATUS OPERATED BY AT LEAST
TWO DIFFERENT FUELS
Filed Oct. 15, 1958
3 Sheets-Sheet 1
W1
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II
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kg
7
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INVENTOR.
E’l C'HA ED L 1 T'W/NOFI'T
BY
ATTOR/‘VEK
Aug. 14, 1962
3,049,1 68
R. LITWINOFF'
METHOD AND MEANS FOR CONTROLLING A COMBUSTION
APPARATUS OPERATED BY AT LEAST
TWO DIFFERENT FUELS
3 Sheets-Sheet 2
Filed Oct. 15, 1958
GAS
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INVENTOR.
BY
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Aug. 14, 1962METHOD
Filed Oct. 15, 1958
3,049,168
R. LITWINOFF
AND MEANS FOR CONTROLLING A COMBUSTION
APPARATUS OPERATED BY AT LEAST
TWO DIFFERENT FUELS
3 Sheets-Sheet 3
22 I6
2
1P1 chm/P0 LITW/NOFE'
BY
ATTORNEY
is
3&4’9368
Patented Aug. 14, 1962
1
2
3,049,168
tain equal fuel distribution to the burners which are ar
METHOD AND MEANS FOR CONTROLLING A
COMBUSTION APPARATUS OPERATED BY AT
LEAST TWO DIFFERENT FUELS
Richard Litwinoff, Winterthur, Switzerland, assignor to
Snlzer Freres, S.A., Winterthur, Switzerland, a corpo
ration of Switzerland
Filed Oct. 15, 1958, Ser. No. 767,437
Claims priority, application Switzerland Oct. 25, 1957
8 Claims. (Cl. 158-11)
ranged in parallel with respect to the fuel supply. Al
though the resistance of the individual burners to fuel
?ow is substantially the same a much greater portion
of the fuel goes to those burners whose resistance is
somewhat smaller so that relatively more heat is pro
duced by some of the burners than by other burners
Whose resistance to fuel ?ow is somewhat greater. This
entails ununi-form heating, for example, of the interior
walls of a combustion chamber served by the combustion
The present invention relates to a method for con
apparatus.
trolling a combustion apparatus which is ?red by at least
In order to avoid the aforedescribed difficulties the in
two different fuels at a plurality of localities, an individ
vention proposes that in each locality Where burners for
ual burner for each fuel being provided at each locality
different fuels are grouped only some of the burners are
whereby the total output of the apparatus can be pro 15 operated whereby the burners are so designed and so
duced either by one fuel alone or by at least two different
fuels.
The invention also relates to a combustion apparatus
supplied with fuel and combustion air that the heat out
put of the burners multiplied by the number of localities
is equal to the desired output of the combustion apparatus
and that the number of burners operated for each kind
of fuel is adjusted according to the desired ratio between
the different fuels whereby the total output of the plant
capable of being heated by at least two different kinds
of fuel, the apparatus comprising a plurality of combus
tion devices of which each is provided with a plurality
of burners whose number corresponds to the number
is adjusted by simultaneously proportionally changing
of di?erent fuels used for operating the combustion ap
the heat output of all burners which are in operation.
paratus.
The method is simplified, if in each locality only the
in the present speci?cation different fuels are such 25 burner for one kind of fuel is operated.
fuels Whose chemical and physical qualities are so differ
It is of advantage to connect all burners for the same
ent that a different type of burner and, in most cases, a
kind of fuel to a common fuel supply system for this
different fuel conveying system is required for each
kind of fuel whereby the fuel supply in the system is so
fuel.
regulated that the heat production of each operating
In the present speci?cation gases, liquid, and solid fuels 30 burner is proportional to the desired total heat output
are considered different fuels; also a gas having a rela
of the plant and independent of the number of burners
tively high heating value, for example, methane gas is
which ‘are operated with the same kind of fuel.
considered ‘a fuel which is different from a gas having a
The control mentioned in the paragraph next above
can be improved by controlling the supply of fuel to
gas. Similarly, pulverized anthracite coal is a fuel dif 35 the respective fuel supply system according to a value
ferent from pulverized lignite. However, crude oil and
or characteristic which determines the heat output of an
fractions of tar distillation, if they can be burned with a
individual burner.
substantially equal volume of air and if they produce
An operating characteristic of a burner is, for exam
approximately the same amounts of heat, are not con
ple, its fuel consumption or, in the case of liquid or gase
40 ous fuels, the difference between the fuel pressure at the
sidered different fuels in the present speci?cation.
In combustion apparatuses which must produce a de
burner inlet and the pressure in the combustion chamber.
relatively low heating value, for example, blast-furnace
sired output either with one kind of fuel alone or simul
The fuel supply may be so controlled that this pressure
taneously with several different fuels and having a plu
difference is adjusted, independently of the number of
rality of localities where fuel burners are located, each
burners for the same fuel kind which are in operation,
45
locality is usually provided with a different burner for
according to the total heat output of the combustion ap
each of the fuels to be ?red. In the conventional operat
paratus and is maintained constant when the total heat
ing method all burners are simultaneously supplied with
output of the apparatus is constant.
the respective different-fuels through common distribut
The fuel supply to a burner may be controlled so that
ing conduits or conveyors for each fuel whereby the de
the fuel consumption of the burner is proportional to
sired amounts of fuels are adjusted for the individual 50 the desired total output of the apparatus or plant. This
distributing conduits and/ or conveyors. If, for example,
fuel consumption is maintained constant at constant total
80 parts of a fuel A and 20 parts of a fuel B are supplied,
output of the apparatus, notwithstanding the number of
all burners for the fuel A are adjusted to operate at 80%
burners which are in operation for the same kind of fuel.
of their maximum output and all burners for the fuel B
In plants in which individual burners are provided with
55
are adjusted for 20% of the maximum output. With
return or recirculating conduits for the fuel whereby the
this conventional method di?iculties with respect to com
recirculating conduits of all burners ?ring the same kind
bustion and control accuracy are experienced with the
of fuel terminate in the same recirculating system, the
burners for the fuel B because the load thereon is rela
individual heat production of a burner may be regulated
tively small. These di?iculties are considerably increased,
if the total output of the combustion apparatus is re
duced, for example, to 50% of the maximum output.
In this case an individual burner for the fuel B would
operate only at 10% of its maximum output. In addition
to the above-mentioned di?iculties it is di?icult to ob
by controlling the difference between the pressure in the
60 fuel supply system for the burners ?ring the same kind of
fuel and the pressure in the fuel return or fuel recirculat
ing system of these burners, the regulation being per
formed proportional to the total heat output of the
plant whereby the pressure difference is maintained con
3,049,168
3
stant when the total output of the plant is constant, inde
pendently of the number of burners which are in opera
tion for each kind of fuel.
A combustion apparatus in which the method accord
ing to the invention may be performed when simultane
ously burning, at a plurality of localities, ‘different kinds of
fuel which require substantially the same amount of
combustion air for producing substantially the same
amount of heat is characterized by'the provision, at each
combustion locality, of a burner for one kind of fuel and
at least one different burner for a different kind of fuel
and of an air supply system which is common to the
burners at the same locality.
4
an oil and the other being natural gas, for example,
methane gas. Nine uniformly constructed combustion
devices 2 are provided in a combustion chamber 1, each
device 2 comprising a gas burner 3 and an oil burner 4.
Each device 2 is provided with a common air supply
means 5 for supplying the combustion air required by
the two burners 3' and 4.
The oil burners 4 of all nine combustion devices 2 are
connected to a common fuel supply system which includes
a fuel oil stop valve 6 for each oil burner, three oil pipes
7 whereby each oil pipe is connected for oil ?ow to the
valves 6 of three combustion devices, a manifold 8 to
which the three oil pipes 7 are connected, an oil pump 9
pumping fuel oil from a reservoir 10 into the manifold 8,
A plant according to the invention is particularly suit
able and easy to supervise, if the individual burners at the 15 a recirculating pipe 8’ connecting the manifold 8 with the
reservoir 10, a valve 36 interposed in the pipe 8’ for con
same locality are so designed in relation to their com
trolling the pressure of the fuel oil in the manifold 8, an
mon combustion air supply means that, at constant total
actuating means 11 connected to the pressure control
output of the plant, the burner for one kind of fuel pro
valve 36 for operating the latter and a fuel oil quantity
duces the same heat as the burner for a different kind of
20 measuring means 12 connected with the actuating means
fuel.
11 and including, for example, an ori?ce plate 13 which
In combustion plants having one burner for each kind of
is interposed in one of the pipes 7 for controlling the fuel
fuel in each locality whereby all burners for the same
oil pressure control valve 36 according to the flow of the
kind of fuel are supplied by the same fuel supply system,
fuel oil through one of the pipes 7.
control means for the fuel supply systems may be pro
The methane gas burners 3 of all fuel burning devices
vided for controlling the heat output of the burners con 25
2 are connected to a common gas supply system which
nected to the same system and in operation proportion
comprises a gas stop valve 14 for each gas burner, three
ally to the total heat output demanded from the plant,
gas pipes 15, a manifold 16 to which the three gas pipes
independently of the number of burners which are in
15 are connected, a gas compressor 17 pumping gas into
operation for the same fuel, the control means for the
the manifold 16, a throttle valve 18 interposed in the gas
supply systems for different kinds of fuel being operatively
?ow between the compressor 17 and the manifold 16, an
interrelated for e?ecting the same heat output of the
actuating means '37 connected with the valve 18 for
burners ?ring different kinds of fuel and simultaneously
actuating the latter, and means 19 connected with the
operated and maintaining this heat output constant at
means 37 for controlling the latter according to the differ
constant total heat output of the plant.
'
Since in the method and apparatus according to the 35 ence between the pressure 20 of the gas entering the gas
burners and the pressure 20’ in the combustion chamber.
invention the number of burners which are in operation
A common air supply system is provided for all com
and ?ring the same kind of fuel de?nes the ratio. of the
bustion devices 2, the system comprising a stop valve 21
amounts of different fuels ?red, only even numbered
for each combustion device, three air supply ‘ducts 22,
ratios can be produced. For example, in a plant having
16 burners for each kind of fuel a maximum of 15 parts 40 each supplying three combustion devices 2, one of the
ducts 22 including a manifold portion 23 to which the
of a fuel A can be ?red simultaneously with 1 part of a
other two ducts 22 are connected, a blower 24 supplying
fuel B. Other possible ratios are: 14:2, 13:3, 12:4, etc.
combustion air to the air supply system, a throttle valve
Should the aforementioned ratios not su?ice, at least
25 placed in the inlet of the ‘blower 24, actuating means
two groups of localities where fuel is ?red may be provid
26 connected to for operating the throttle valve 25, and
ed whereby the size of the ‘burners and the air supply
measuring means 27 measuring the difference between the
means for each kind of fuel are alike in each locality and
pressure 28 in the air supply system and the pressure 28'
the burners and air supply means of the localities of the
in the combustion chamber and being connected with the
same group are so arranged that at each locality of one
actuating means 26 for controlling the latter.
group a greater amount of heat is produced than at
It is assumed that the combustion chamber 1 served by
each locality of another group, at constant output of the *
the combustion apparatus according to the invention is
plant.
part of a steam generator, not shown, having ‘a superheater
The novel features which are considered characteristic
29supplying steam to a stream main 30 and through a
of the invention are set forth with particularity in the
appended claims. The invention itself, however, and ad
ditional objects and advantages thereof will best be
understood from the following description of embodiments
thereof when read in connection with the accompanying
drawing in which:
valve 32 to a turbine 31.
valves forming part ‘of the apparatus shown in FIG. 1
and‘of an operating mechanism therefor.
from the turbine 31, manually or automatically operated
With the control system according to the invention the
heat outputs of the individual burners 3 and 4 are adjusted
proportionally ‘to a value corresponding to the desired
total output of the plant. Such a value, for example, is
the pressure of the live steam which pressure is measured
FIG. 1 is a diagrammatic illustration of a combustion
60 at 33. Other suitable values are the speed of the turbine
apparatus for ?ring two different kinds of fuel.
31, the temperature of a cooker which may receive steam
FIG. 2 is a part sectional diagrammatic illustration of
FIG. 3 is a diagrammatic illustration of a remote control
means for controlling the steam flow from the steam main
36 to consumers, and the like. The value which'is pro
for valves forming part of the apparatus shown in FIG. 1.
portional to the load condition of the turbine 31, in the
FIG. 4 is a diagrammatic illustration of a combustion
illustrated case, the pressure of the live steam measured
by the device 33 is transmitted as a modulated reference
value through a reference value setting device 34 by means
apparatus according to the invention and having recirculat
ingburners.
of pulse transmitting conduits 35, 38, 40 to the servo
FIG. 5 is a diagrammatic illustration of a combustion
apparatus having three groups of combustion devices and. 70 motors or actuating means 11, 37 ‘and 26, respectively,
which operate the control means 36, 18 and 25, respec
in which the heat outputs of the combustion devices of
each group are the same and the heat outputs of the de
vices of different groups are different.
tively.
The actuating means 11 for the fuel oil pressure con
trolling means 36 is ‘a conventional device which is adapted
The apparatus diagrammatically illustrated in FIG. 1
is operated by two different kinds of fuel, one fuel being 75 to produce a signal which corresponds to the difference
5
53,049,168
between the signal received from the device 34 and a sig
nal corresponding to 1a characteristic of the oil supply to
6
be made in the respective combustion device 2. The
valves 6, 14, and 21 and the actuating mechanism shown
the oil burners 4 which characteristic is, in the example
shown in FIG. 1, the oil consumption of the burner 4'
in FIG. 2, of course, are outside of the combustion
chamber 1 in contradistinction to the diagrammatic illus
measured at 13 and transformed at 12 into a signal which
tration, FIG. 1.
can be subtracted in 11 from the signal produced in 34.
Instead of the hand operation of the shaft 41 shown
The burner 4' is the last one connected to an oil distribut
in FIG. 2, the shafts may be provided With worm gears
ing pipe 7. Also suitable for use as the ‘actuating means
42' whose worms are actuated by electric motors 42"
11 is ‘a conventional device adapted to produce a signal
which are remotely controlled from a switch box 48.
corresponding to the quotient of the signals produced in 10 Two shafts are shown only for actuating the stop valves
the devices 34 and 12. Since a difference producing as
of two devices 2. The upper shaft is in the position B
Well as ‘a quotient producing device is suitable, the device
in which the fuel oil valve of the respective device 2 is
11 has been termed comparing device for describing the
open and the gas valve is closed. The lower shaft is
invention. The fuel 'oil pressure control valve 36 is actu
shown in the position A in which the fuel gas valve is
ated by the device 11 according to the difference signal or
open and the oil valve is closed. Instead of the electric
the quotient signal produced therein depending on what
remote control shown in FIG. 3 a conventional mechani
cal or hydraulic remote control may be provided.
kind of device is used. The valve 36 is opened for de
creasing the fuel supply to the pipes 7 when the difference
FIG. 4 is a diagrammatic illustration of a combustion
apparatus according to the invention in which the oil
between or the quotient of the output signal of the device
burners are of the oil recirculating type. The oil burners
34 which corresponds to the steam pressure ‘and the output
4" are arranged in three groups of four burners which are
signal of the device 12 which corresponds to the fuel con
individually connected by means of valves 6 to oil supply
sumption, increases beyond a predetermined value, i.e.,
pipes 7 of which there is one for each group. The pipes
when the pressure at 33 rises because of decreased steam
7 are connected to a manifold 8 receiving fuel oil from a
consumption. If the difference or the quotient, i.e. the
reservoir 10 through a pump 9. Each burner includes an
ratio, between the output signals of the devices 34 and 12
oil recirculating pipe 43 in which a valve 6’ is interposed.
decreases below a predetermined value because of in
All recirculating pipes 43 terminate in a common oil re
creased steam consumption, the valve 36 is closed to in
turn system comprising oil return pipes 44 which indi~
crease the fuel supply.
vidually serve the oil burners of four combustion devices
The pressure controlling means 37, 18 of the fuel sup
ply system for the methane gas burners is actuated simi 30 and which terminate in an oil return manifold 45 which
returns fuel oil through a throttle valve 36' to the oil
larly to the aforedescribed control of the fuel oil system.
reservoir 10.
The device 37 is connected with the reference value setting
The throttle valve 36' forms part of an oil pressure
device 34 by means of a pulse transmitting conduit 38 and
controlling means including an actuating means 11' which
compares the reference value with the ‘amount of fuel gas
is connected with the reference value settin'g device 34
which is supplied to the burners and de?ned by the differ
through a pulse transmitting conduit 35'. The actuating
ence of the pressure 20 of the gas supplied to a burner
means 11’ are not only responsive to the pulses received
and of the pressure 20' in the combustion chamber. This
from the device 34 but also to pulses received from a
difference is measured by the device 19 and a correspond
device 46 which is responsive to the pressure in the fuel
ing pulse is transmitted through conduit 39 to the actuat
oil return system. The pressure in the fuel oil supply
ing means 37. The latter adjusts the position of the gas
system is measured by a device 47 which transmits con
pressure control valve 18 until the measurement of the
trol pulses to actuating means 11" for a throttle valve
device 19 corresponds to the reference value pulse trans
36” which is arranged in series relation with the fuel oil
mitted from the device 34 to the device 37.
pump 9 in the oil supply system. The actuating means
The pressure, i.e., the supply of the combustion air is
controlled similarly. The combustion air control means 45 11" is connected through a pulse transmitting conduit
35 with the reference value setting device 34 and ac
26, 25 is connected through a ‘conduit 49 to the reference
tuates the valve 36" until the ‘oil pressure in the fuel oil
value setting device 34. The control means 26 is also
supply system corresponds to the pressure of the live
connected with a device 27 which measures the difference
steam measured at 33.
between the pressure of the air ?owing to the combustion
FIG. 5 shows an arrangement in which three groups of
devices and measured at 28 and the pressure 28' in the
fuel burning devices 2 are provided, each device being
combustion chamber. The device 26 compares the refer
adapted to burn different fuels at the same time whereby
ence value pulse received from the device 34 with the
the same amount of heat is produced by the individual
pulse received from the pressure difference measuring de
devices of the same group and the devices of different
vice 27 which corresponds to the actual air consumption
groups produce different amounts of heat. The handles
of the combustion devices. The controlling device 26
or cranks 42 for manipulating the cam shafts 41 for open
actuates the throttle 25 until the combustion air supply
corresponds to the reference value measured by the de
vice 34.
As shown in FIG. 2, the fuel oil stop valve 6, the
methane gas stop valve 14 and the combustion air stop
valve 21 of each combustion device 2 are actuated by
a common mechanism including a shaft 41 which can be
revolved by manipulating a crank 42 and a cam on said
shaft for each of the valves 6, 14 and 21. The cams are
so shaped that when the shaft 41 is in the angular posi
tion A gas can flow from the pipe 15 through the valve
14 to the ‘burner 3. The oil valve 6 is closed and the
air valve 21 is open. When the shaft 41 is in the angular
position B the fuel oil valve 6 is open, the gas valve 14
is closed and the air valve 21 is open. In the diagram on
top of FIG. 2 the closed position of a valve is inidcated
by an X and the open position is indicated by an arrow.
It is advisable that the cams are so shaped that if the
shaft 41 is in the angular position C, all three valves
ing and closing the burners for different fuels of the in
dividual devices are diagrammatically indicated and the
air supply means are omitted in FIG. 5. If the heat out
put of a device 2 of group I is taken as fundamental
unit and if group I has n devices 2, the heat output In
of each device ‘of group II preferably is n+1. If group
II has I devices the heat output s of each fuel burning
device of group III preferably is t.m+n+l. The desired
different capacities of the burners of different groups
can be obtained, for example, by making the nozzles of
the burners of one group larger than the nozzles of the
burners of another group.
If group III has r fuel burning devices, the accuracy of
the distribution of the total desired heat production on the
different fuels is
1
n+t-m+r-s
If there are four fuel ‘burning devices in each of three
are closed. In this position repairs or replacements can 75 groups I, II and III and the heat output of each device
3,049,168
7
of group I is 1 unit, the heat output of each device of
group II is 5 units and the, heat output of each device
of group III is 25 units. Based on these ?gures the fol
lowing table shows four examples of possible distribu
tions ‘of the total desired heat output on two different
fuels. In this table the devices operated with fuel oil
are designated by + and the devices operated with gas
are designated by 0.
Group ____ __
I
II
1234
III
Oil
| Gas
Device ____ _-
1234
+
0
Example A__
+ 0 0 0
0 0 o 0
1/124
123/124
ExampleB__
0 o 0 0
+ + o 0
+ 0 0 0
35/124
89/124
Example 0..
Example D-
+ + 00
++ 00
+ + + 0
+ + 0 0
+ + + 0
+ + + +
92/124
112/124
0 0 0 0 '
1234
‘
52/124
12/124 15
8
ing the heat output of all burners’ which are in operation
upon a decrease of the total heat demand.
2. The method de?ned in claim 1 wherein the di?erent
kinds of fuel are supplied to a plurality of groups of
bumers, each group including a burner for one kind of
fuel and a burner for the other kind of fuel, only the
burner for one kind of fuel being operated‘ at a time in
each group.
3. The method de?ned in claim 1 wherein the fuel
supply to all burners supplied by one kind of fuel and
in operation is increased as the difference between the
total heat demand and a value corresponding to the heat
output of one of the burners supplied by said one kind
of fuel and in operation increases and the fuel supply to
all burners supplied by one kind of fuel and in operation
is decreased as the difference between the total heat de
Example D corresponds to the setting of the individual
mand and a value corresponding to the heat output of
one of the burners supplied by said one kind of fuel and
burners shown in FIG. 5. With the system according to
in operation decreases.
the invention for burning different fuels a great ?exibility
4. The method according to claim 3 wherein said one
20
of the division of the load on the individual fuels is
kind
of fuel is of the ?uid type and wherein said value is
possible although the division is produced by operating
the difference between the pressure of said one kind of
the burners at full on and full off condition only so that
fuel entering said one of said burners and the pressure
ine?‘icient operation of burners operating at low load is
in the combustion space of the apparatus.
avoided.
5 . In a combustion apparatus for simultaneously burn
Aside from ‘the described and illustrated examples 25
ing different kinds of fuel which fuels require substantial
many other variations of the number of groups of fuel
ly the same amount of combustion air for producing sub
burning devices and of the number and size of the devices
stantially the same heat of combustion: a plurality of
in each group are possible.
fuel burning devices individually including at least one
The control method and the combustion apparatus ac
cording to the invention are not limited to the described 30 fuel burner for each kind of fuel, separate fuel supply
means for the different kinds of fuel, said supply means
and illustrated embodiments in which only two different
being individually connected to all burners burning the
kinds of fuel are used. The method and apparatus are
same kind of fuel, means for supplying combustion air
also applicable to plants in which more than two different
to all of said burners, means individually connected to
kinds of fuel are ?red. In this case each combustion de
vice includes as many burners as there are kinds of fuel 35 said burners for stopping the supply of fuel and combus
to be ?red and there are, of course, a corresponding num
ber of fuel and air supply systems.
The individual com
bustion devices may ‘be so arranged that burners for two
different fuels may be operated simultaneously in one
locality and the burner or burners for the other fuel or
fuels are not operated. If the air consumption of two
tion air to the individual burners, whereby the number
of burners in operation for one kind of fuel relative to
the number of burners in operation for a different kind of
fuel can be adjusted corresponding to the desired ratio
between the different kinds of fuel to be ?red, and means
responsive to a value corresponding to the total heat out
put ‘demanded from the apparatus and connected to said
different kinds of fuel is substantially different for pro
fuel and combustion air supply means for individually
ducing the same amount of heat by each kind of fuel,
controlling the amounts of different fuels and of air sup
the combustion device according to the invention may in
plied to the burners which are in operation.
clude separate air supply means for each burner. These
6. In a combustion apparatus as de?nedin claim 5 and
combustion air supply means may be connected to the
wherein
said fuel burning devices are alike and adapted
same air supply system whereby stop valves are provided
to
produce
the same amounts of heat.
for stopping air supply to burners which are not in opera
7. In a combustion apparatus as de?ned in claim 5
tion.
50 and wherein at least two groups of fuel burning devices
In the example shown in FIG. 1 and described sepa
are provided, the fuel burning devices of each group being
rate air supply means for the different burners of the
alike and adapted to produce the same amounts‘ of heat,
individual fuel burning devices are unnecessary because
‘and the fuel burning devices of different ‘groups being
the methane gas produces 8770 kg.-cal. with 11.2 normal
cubic meter combustion air and fuel oil produces with 55 different for producing different amounts of heat by the
fuel burning devices of different groups.
the same amount of air 8815 kg.-cal. In this case the
8. In a combustion apparatus as de?ned in claim 5 and
two burners can be provided with a common air supply
wherein said means for stopping the supply of fuel to the
means.
individual burners include means operatively connected
What is claimed is:
to the individual fuel burning devices and including means
1. The method of ?ring at least two different kinds of 60
for stopping the fuel supply to the burner for one kind of
fuel at variable ratios in a combustion apparatus and
fuel in the individual devices and simultaneously starting
altering the heat output of the entire combustion apparatus
the fuel supply to the burner for another kind of fuel in
to satisfy varying heat demands, including the steps of
the respective fuel burning device and vice versa.
separately distributing each kind of fuel to a plurality of
References Cited in the ?le of this patent
burners, of operating a number of the burners receiving 65
one kind of fuel and a number of burners receiving the
UNITED STATES PATENTS
other kind of fuel at a ratio between said numbers corre
sponding to the desired ratio between the quantities of
the different kinds of fuel fired, and of uniformly increas
ing the heat output of all burners which ‘are in operation
upon an increase of the total heat demand and decreas
1,512,132
2,390,806
2,470,996
Pfahl ________________ __ Oct. 21, 1924
Nagel ________________ .._ Dec. 11, 1945
McGrath _____________ __ May 24, 1949
2,657,347
Bristol ______ -,____, ____ .._ Oct, 27, 1953
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