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Патент USA US3049311

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Aug. 14, 1962
‘H. P. LEWIS ETAL
COMBUSTION CONTROL FOR A FURNACE FIRED WITH
FUELS HAVING DIFFERENT OXYGEN-EXCESS
3,049,300
AIR CHARACTERISTICS
Filed April 7, 1960
2 Sheets-Sheet l
4%
%
NATURAL GAS /
I
\OIL
Ay
COPIVBMRXEUYSLDTFNGCM~PR
COAL S COKE /
/
\‘
/
//
KW
EXCESS AIR - PER CENT
FIG. I
INVENTORS
AND
BY
9,4
HENRY P. LEWIS
JOSEPH F. TRIOLO~
Aug. 14, 1962
H. P. LEWIS ETAL
3,049,300
COMBUSTION CONTROL FOR A FURNACE FIRED WITH
A
FUELS HAVING DIFFERENT OXYGEN-EXCESS
-
AIR CHARACTERISTICS
Filed April '7, 1960
2 Sheets-Sheet 2
FLUECAS_
STEAM
GENRATO
‘u
n
O)
—
K
INVENTORS
i
AND HENRY P. LEWIS»
JOSEPH F. TRIOLO
52K 1 xfvzw
ATTORNEY
United States Patent Office
3,049,300
Patented Aug. 14, 1962
1
2
3,049,300
air by maintaining a predetermined ratio between fuel
flow and air flow and readjusting this ratio as required
COMBUS'I‘JIGN CUNTROL FDR A FURNACE FERED
WITH FUELS HAVING DHFFERENT OXYGEN
EXCES§ AIR CHARACTERISTICS
to maintain a predetermined oxygen content in the prod
ucts of combustion, ‘there being a constant relationship
between the percent oxygen and excess air for most com
Henry E’. Lewis, Cleveland, Ohio, and Joseph F. Trioio,
Sharon Hill, Pa, assignors to Bailey Meter Company,
mercially available fuels. The control from oxygen is
introduced as a readjustment of the primary fuel-air ratio
a corporation of Delaware
control for the reason that it is a control having a rela
Filed Apr. 7, 1960, Ser. No. 20,719
12 Claims. (Cl. 236—15)
10
tively long time constant and subject to a transportation
lag whereas the fuel-air ratio control is relatively fast
acting so that a change in fuel flow can be made to
Our invention relates to combustion control and more
particularly to combustion control ‘for a furnace supplied
immediately re?ect a corresponding change in air ?ow or
with blast furnace gas, or other gas containing a large
percentage of inerts, as one ‘fuel and a supplementary
vice versa. Such ratio control cannot be relied upon how
ever to give precise control of excess air as the air re
fuel or fuels such as coke oven gas, natural gas, manu
factured gas, oil, coal or coke.
A primary object of our invention is to maintain the
excess air in such a furnace at a desired or predetermined
15 quired per unit of ‘fuel varies as the composition of the
fuel changes.
That readjustment of the fuel-air ratio to maintain
a predetermined oxygen content in the products of com
bustion will result in a constant excess air will be apparent
from an inspection of FIG. 1 which shows the relation
ship between oxygen and excess air from most commer
value regardless of changes in the ratio between the rate
of ?ow of blast furnace gas and the other fuel or fuels.
In accordance with our invention a predetermined ratio
cially available fuels. Thus, for example, readjusting to
is maintained between the total fuel ?ow and air flow,
‘four percent by volume oxygen will maintain approxi
the predetermined ratio is adjusted to maintain a desired
mately 23% excess air regardless of whether natural gas,
oxygen content in the products of combustion ‘and the
desired oxygen content is determined from the ratio be 25 coke oven gas, oil, coal or coke is fired singly or in com
bination.
tween the rate of ?ow of blast furnace gas and the total
fuel ?ow.
Quite frequently a furnace or other type of combustion
zone is ?red with multiple fuels and particularly in the
Further, in accordance with our invention there is pro
iron and steel industry one of the ‘fuels may be blast
vided a constant ?ow control of the total fuel and a
similar control for the air, the set point of the latter being 30 furnace gas and the other fuel or fuels may be coke
adjusted to maintain the desired heat release and that
oven gas, natural gas, manufactured gas, oil, coal or coke.
Blast furnace gas as the name implies is a by-product of
of the former being adjusted in accordance with the
blast furnace operation. It is a low ‘grade fuel having a
rate of air ?ow and readjusted to maintain a desired
low calori?c value, which must ordinarily be utilized in
oxygen content in the products of combustion as deter
mined from the ratio of blast furnace gas to total fuel. 35 the mill where produced or wasted. It is therefore desir
able to satisfy the requirements of a furance with this
Further, in accordance with our invention, the total
fuel entirely or to the extent that it is available using a
fuel requirement is, if desired, obtained from blast fur
higher grade and more costly fuel or fuels only as re
nace gas and the supplementary fuel or fuels supplied
quired to supplement the blast furnace gas in order to
only as required to make up for a ‘deficiency or lack of
satisfy the heat requirements.
availability of the blast furnace gas.
In the drawings:
As shown in FIG. 1 there is ‘a material difference in
FIG. 1 is a graph illustrating the relationship between
the relationship between oxygen content in the products
excess air and oxygen for various commercial fuels.
FIG. 2 is a schematic illustration of an embodiment
of combustion and excess air for blast furnace gas than
of our invention.
To realize optimum combustion efficiency air and fuel
should be supplied a furnace or other combustion zone
in relative proportions to maintain a desired, or as it may
for all other commercial fuels. This is due principally
45 to the fact that blast furnace gas includes a large per
centage of inerts in the form of free nitrogen. Accord
ingly it is ‘apparent that where blast furnace gas is used
in combination with other fuels readjustment to a pre~
be termed, predetermined excess air. By de?nition “excess
deter-mined oxygen content will not result in a desired
air” is the amount of air supplied in excess of that theo
excess air. Thus as previously stated for all fuels other
retically required for perfect combustion. It is ordinarily
than blast furnace gas readjustment to four percent 0xy~
gen will maintain ‘approximately 23% excess air. With
expressed as the ratio between the air actually supplied
to that theoretically required. Thus 20% excess air
means that 20% more air was ‘supplied than theoretically
required.
Usually the optimum excess air will be the
minimum excess air at which a [furnace or other com
blast furnace gas ‘alone readjustment to 4% oxygen con
tent will maintain approximately 48% excess air, and
with blast furnace gas ?red in combination with another
fuel or fuels a readjustment to 4% oxygen will maintain
an excess air anywhere between these limits depending
bustion zone can be operated with complete combustion
of the fuel. Reducing the excess air below this point re
upon the amount of blast furnace gas ?red relative to the
sults in an unburned fuel loss, while increasing the excess
other fuel or fuels. Our invention is particularly directed
air above this point results in an unnecessary heat loss in 60 to a method and apparatus whereby a desired or pre
the products of combustion which are wasted to the atmos
determined excess air may be maintained notvw'thstanding
phere. These losses are usually spoken of as “avoidable
that blast furnace gas or other gas producing a discrete
losses” as they are eliminated by operating at the opti
oxygen-excess air relationship is ?red with one or more
mum excess air.
supplementary fuels in varying ratio.‘
I
It is well known in the art to maintain a desired excess
In FIG. 2 we show a combustion control system em
3,049,300
n,
J)
bodying our invention applied to a steam generator shown
schematically at 1. The furnace or combustion zone of
may result in actual fuel flow exceeding the available
air, causing a de?ciency of air in the combustion zone
which not only lowers e?iciency but may lead to a haz
the generator is supplied with blast furnace gas, a supple
mentary fuel such as oil and air through conduits 2, 3
ardous condition at the instant when an excess of air is
again available in the combustion zone.
The blast furnace gas and supplementary fuel are pref
erably totalized on an, “air required” basis rather than
on a straight weight or volume basis. Thus, 0.6857 pound
of air are required for perfect combustion of a pound of
and 4 respectively. The steam generated is discharged
through a pipe 5, and the products of combustion, com
monly called “flue gas” are discharged through a duct 6
to a stack (not shown) and wasted to the atmosphere.
In the term “products of combustion” or “line gas” we
include, as is common in the art, not only the carbon
dioxide, sulphur dioxide and water vapor formed in the
usual combustion process but the nitrogen and free oxy
gen as well which does not enter into the combustion
process.
4
L
O typical blast furnace gas; 15.9086 pounds are required
for perfect combustion of a pound of typical natural gas
and 14.031 pounds are required for perfect combustion
of a pound of typical oil. Various means are available
for having the output pressure of relay 10 represent total
>
The combustion control we have shown in FIG. 2 for 15 fuel ?ow on an “air required” basis. Thus the maximum
capacity of transmitters 7 and 8 may be selected so that
the steam generator 1 is of the type commonly known as,
a pound change in the loading pressures therefrom repre
“pneumatically operated” for the reason that compressed
sent equal changes in air required; or the proportional
air is used as the operating medium. However, it will
band setting of relay 10 may be adjusted so that changes
be apparent as the description proceeds that our invention
in loading pressure at A and C produce changes in output
may as readily be incorporated in an electric or hydraulic
pressure at D proportional to changes in air required for
control. We have chosen to show a pneumatically oper
the respective fuels.
ated control for the reason that the components making
As previously mentioned all of the heat requirements
up the system are well known in the ‘art and their opera
should be satis?ed from blast furnace gas if available using
tion readily understood.
the supplementary fuel only as a stand-by fuel to take over
Flow transmitters 7, 8 and 9 establish pneumatic load
in the event of a failure in the supply of blast furnace
ing pressures proportional to rate of ?ow of blast furnace
gas or to assist in satisfying the heat requirements if suffi
gas, supplementary fuel and air respectively. We have
cient blast furnace gas is not available. To accomplish
shown the ?ow transmitters schematically as these may
this we show a stacked differential relay 16 into the A
be any one of the several types available. The loading
chamber of which the output pressure of relay 13 is intro
pressure established by transmitter 7, proportional to the
duced and which it will be recalled is the fuel demand
rate of flow of blast furnace gas, is introduced into the
A chamber of a totalizing relay 1t) and the loading
pressure established by transmitter 8 proportional to the
rate of flow of the supplementary fuel is introduced into
the C chamber of this relay. The relay ‘10 serves to
produce an output pressure at D proportional to the sum
signal. Normally this loading pressure, that is, with zero
or some predetermined pressure in chamber B is repro
duced in chamber D and transmitted to the A chamber
of a relay 17 of the proportional plus automatic reset type.
The loading pressure produced by transmitter 7 propor
tional to the ?ow of blast furnace gas is introduced into
of the loading pressures established by transmitters 7
the
B chamber of this relay. The output pressure of relay
and 3. Thus the output pressure at D is proportional to
17 at D is transmitted to and controls operation of control
the total fuel ?ow. The relay 1% may. for example, be of
40 drive 14. Relay 17 thus compares the fuel demand sig
the type illustrated and described in United States Patent
nal with a signal proportional to the ?ow of blast furnace
2,805,678 issued to Michael Panich on Sept. 10, 1957.
gas and effects adjustment of the flow of blast furnace gas
The loading pressure established by ‘transmitter 9, pro
until it is equal to the fuel demand signal or in other
portional to the rate of flow of air to the combustion
zone, is introduced into the A chamber of a relay 11
similar to the relay 10 but having a bellows 12 for auto
words until the entire fuel requirement is satis?ed from
blast furnace gas.
The loading pressure from relay 13, that is the fuel
demand signal, is also introduced into the A chamber
of a stacked differential relay 18 and compared with the
loading pressure introduced into chamber B proportional
to blast furnace gas ?ow. So long as these two loading
hereinafter. The relay 11 serves to produce an output pressures are equal, indicating that the fuel demand is
pressure at D proportional to the loading pressure intro
being met by blast furnace gas, relay 18 is adjusted to pro
duced at A or in other words proportional to the rate of
duce in chamber D a loading pressure maintaining valve
flow of air to the combustion zone. This loading pres
15 closed or at some preselected minimum position. If
sure establishes the fuel demand and the actual total fuel
the loading pressure introduced into chamber B of relay
flow is maintained equal to this demand by comparing the
18, indicative of actual blast furnace gas flow, is less than
output loading pressure of relay 11 with the output load
that introduced into chamber A of this relay indicating
ing pressure of relay 10 in a relay 13, having proportional
that the actual blast furnace gas flow is insufficient to meet
plus automatic reset action, and having the output pres
fuel demand a change in the loading pressure produced in
sure thereof adjust total fuel flow by controlling the
chamber D results which effects an opening of valve 15
operation of ?nal control elements shown as a control 60 to increase the supplementary fuel ?ow until the total
drive 14 for blast furnace gas and a control valve 15
actual fuel flow is equal to fuel demand.
for fuel oil. This adjustment is continuous and serves
The availability of blast furnace gas may be determined
to maintain total ‘fuel flow in ‘desired proportion to air
by one or more of several different ways. "It may for
flow. Essentially the system so far described provides
example be established by usage of the gas in more
a constant flow control of total fuel, the set point of
critical areas, rate of production, gas pressure, and for
which is established in accordance with the existing rate
illustrative purposes we have chosen the latter as being
of ‘air flow.
representative. We show a pressure transmitter 19 ar
We prefer to establish fuel demand from actual air
ranged to establish a loading pressure proportional to blast
?ow rather than establishing air demand from actual fuel
furnace gas pressure and which is introduced into the A
flow as a matter of safety and e?iciency as it insures that 70 chamber of a relay 20 of the proportional plus automatic
actual fuel flow will never exceed the available air. A
reset type. So long as the pressure of the blast furnace
control arranged to establish air demand from fuel ?ow
gas is at or above a predetermined value the output pres
will operate satisfactorily under normal conditions, how
sure at D of relay 20 will remain at zero or some ?xed
ever, the available air supply may be limited by fan capac
value.
This output pressure is introduced into the B
75
ity, malfunctioning of the equipment and the like which
matic adjustment of the proportional band, illustrated and
described ‘more particularly in United States Patent
2,743,710 issued to Jack F. Shannon on May 1, 1956,
and the function of which will be discussed more in detail
3,049,300
5
6
chamber of relay 16 and ordinarily produces no effect on
the pressure established in the D chamber of this relay.
However, upon the blast furnace gas pressure decreasing
below the predetermined value the output pressure at D
of relay 20 will increase causing a proportionate decrease
in the pressure in chamber D of relay 16 effecting a cut
son that at low rates of air ?ow a given change in the
,
loading pressure established by relay 25 should cause, for
stable control operation, a proportionately smaller change
in the rate of fuel flow than the same change in ‘loading
pressure established by relay 25 should generate at high
rates of air flow.
‘The “set poin ” of relay 25 is adjusted in accordance
with the ratio between the rate of ?ow of blast furnace
plementary fuel to compensate for the cutback in blast
gas and total fuel ?ow to the combustion chamber. In
furnace gas flow.
10 the embodiment of our invention shown in ‘FIG. 2. we de
In our control, as previously described, the fuel demand
termine the ratio between blast furnace gas flow and total
is established by the rate of air flow. This latter How
fuel ?ow in a relay 26 into the B chamber of which the
we adjust to maintain a desired heat release. r'Ihe particu
loading pressure proportional to blast furnace gas is in
lar index used to determine deviation of actual heat re
troduced. Into the C chamber of this relay the loading
lease from that desired depends upon the type of furnace. 15 pressure proportional to total fuel flow is introduced.
back in the flow of blast furnace gas. Under such a condi
tion the control will function to increase the how of sup
Thus- if the control is applied to a heat treating furnace,
temperature of the furnace or of the work therein may be
used as the index, in another type of furnace it may be the
?ow of product therefrom, with a steam generator such
as we have illustrated in FIG. 1 it is ordinarily the pressure
of the steam generated; and we therefore show a pressure
transmitter 21 arranged to establish a loading pressure
proportional to steam pressure and which is introduced
into the B chamber of a relay 22 having proportional plus
The relay 26 is provided with an integral bellows 27 and
is of the same type as the relay 11. As the loading pres
sure introduced into the bellows 27 is that generated in
the output chamber D thereof the relay 26 operates to
maintain this loading pressure proportional to the ratio
between the loading pressures introduced ‘at B and at C.
The output loading pressure of relay 26 is modi?ed in a
calibrating relay 28 by setting of the proportional band
therein so that the output pressure in chamber D thereof
reset action. So long as the pressure of the steam remains 25 varies in desired proportion to changes in the output pres
at the desired value the output pressure established in
sure at chamber D of relay 26. The output pressure in
chamber D of relay 22 will remain at the then existing
chamber D of relay 28 is transmitted to the A chamber
of relay 25 and serves to adjust the “set point” of this
relay as the proportion between blast furnace gas flow and
crease in the loading, pressure at D and thereafter a con 30 total fuel flow varies. By proper setting of the propor
tional band adjustment of calibrating relay 28 the “set
tinuing increase until the pressure of the steam is restored
point” of relay 25 is automatically varied as required to
to the desired value. An increase in steam pressure above
value. A decrease in steam pressure below the predeter—
mined value will immediately cause a proportionate in
the desired value causes a similar action except that the
maintain an oxygen content in the products of combus
changes in the loading pressure established at D of relay
tion resulting in the maintenance of the desired excess air.
22 are in opposite sense. The loading pressure established 35 'Ilhus referring to FIG. 1 if 20% is the desired excess air
at D of relay 22 is transmitted to a control drive 23 and
the “set point” of relay 25 will be automatically adjusted
serves to adjust the rate of air ?ow through conduit 4.
to maintain approximately 2% oxygen in the products of
Such adjustments cause corresponding changes in the
combustion when burning 100% blast furnace gas and
approximately 3.8% oxygen in the products of combus
rate of total fuel supply as heretofore described. It is
apparent therefore that the rate of ?ow of fuel and air 40 tion when burning a supplementary fuel entirely. In be
tween these extremes the “set point” will be adjusted as
to the combustion zone of steam generator 1 will be ad
required to maintain an excess air of 20% regardless of
justed as required to maintain the heat release therein
the ratio between blast furnace gas and total fuel.
equal to the desired or predetermined release.
What we claim as new and desire to secure by Letters
We have explained that a fuel-air ratio control will not
maintain a desired excess air in the combustion zone for 45 Patent of the United States is:
the reason that the pounds of air required per pound of
1. The method of controlling combustion in a com
bustion zone supplied with multiple fuels and air, the
fuel change with changes in the composition of the fuel.
Thus while we have given the pounds of air required for
combustion of one of said fuels with varying amounts of
air producing a substantially different oxygen-excess air
perfect combustion of a pound of typical blast furnace
gas, natural gas and oil these fuels in the forms com 50 relationship than produced by any of the other fuels,
mercially available vary from time to time in composition.
which includes, adjusting the relationship between total
Hence a fuel-air ratio control may at times produce an
excess air greater than that desired and at other times
fuel ?ow and air ?ow to maintain a desired oxygen con
an excess air less than that desired or even a de?ciency
sired oxygen content from the ratio between the rate of
flow of said one fuel and the total rate of fuel ?ow to
the furnace in a direction tending to maintain a desired
of air. We therefore readjust the primary fuel-air ratio
tent in the products of combustion and adjusting the de
control from a measure of the oxygen content in the prod
ucts of combustion or ?ue gas and to eifect this show
diagrammatically in FIG. 2 an oxygen analyzer 24 ar
ranged to establish a loading pressure which is introduced
into the B chamber of a proportional plus reset relay 25.
The loading pressure introduced into the A chamber of
_ 2. The method of controlling combustion in a combus
tron zone supplied with blast furnace gas fuel and a sup
this relay establishes the “set point” that is, the oxygen
plementary fuel, the combustion of said blast furnace gas
excess air in the products of combustion regardless of the
éelalttive rates of supply of said one fuel and the other
ue s.
content in the products of combustion which the control
with varying amounts of air producing a different oxygen
will maintain. The output pressure generated in cham
excess ‘air relationship than said supplementary fuel, which
ber D of relay 25 is transmitted to the ‘bellows 12 of relay ca Ci includes, adjusting the relationship between total fuel flow
11 and serves to adjust the proportionality constant be
and air ?ow to maintain a desired oxygen content in the
tween the input pressure to this relay and the output pres
products of combustion and adjusting the desired oxygen
sure therefrom. Thus, the “fuel demand” established
content from the ratio between the rate of ?ow of blast
‘by a given rate of air ?ow is adjusted depending upon
furnace ‘gas and the supplementary fuel in a direction
tending to maintain a desired excess air in the products
the oxygen content, or in other words upon the excess
‘air in the products of combustion. It will be noted that
of combustion regardless of the relative rates of supply
the loading pressure established by relay 25 adjusts the
of blast furnace gas and supplementary fuel.
proportionality constant of relay 11 rather than merely
3. The method of controlling combustion in a combus
adding or subtracting from the loading pressure propor
- tion zone supplied with at least two fuels and air, the com
' tional to the rate of air flow. This we prefer for the ma, _75 bustion of one of said fuels with varying amounts of air
3,049,300
7
the rate of flow of blast furnace gas relative to the rate
of ?ow of oneof the other fuels in a direction tending
to maintain a desired excess air in the products of com
bustion.
8. The method of controlling combustion in a com
bustion zone supplied with blast furnace gas, at least one
from the rate of ?ow ‘of one fuel relative to the rate of
?ow of another fuel to the combustion zone in a direction
other fuel and air, the combustion of said blast furnace
gas with varying amounts of air producing a different
to maintain a desired excess air in the products of com
bustion regardless of the relative rates ‘of supply of said
8
tion and adjusting the desired oxygen content in part from
producing a different oxygen-excess air relationship than
‘the other of said fuel or fuels, which includes, maintain
ing a predetermined ratio between total fuel flow and air
?ow to the combustion zone, adjusting the predetermined
ratio to maintain a desired oxygen content in the products U!
of combustion; and adjusting the desired oxygen content
10
one fuel and said other fuel or fuels.
4. The method of controlling combustion in a com
oxygen-excess air relationship than the other of said fuel
or fuels, which includes, maintaining a predetermined
ratio between the rate of air flow and the total of the rate
of ?ow of blast furnace gas and the other fuels, adjusting
the predetermined ratio to maintain a desired oxygen
bustion zone supplied with at least two fuels and air, the
combustion of one of said fuels with varying amounts
of air producing a different oxygen-excess air relation
ship than the other fuel or fuels which includes, maintain
ing a predetermined ratio between total fuel flow and
air flow to the combustion zone, adjusting the predeter
content in the products of combustion; and adjusting
the desired oxygen content in part from the rate of flow
of blast furnace gas relative to the rate of total fuel
flow to the combustion zone in a direction tending to
maintain a desired excess air in the products of com
mined ratio to maintain a desired oxygen content in the
rates of supply of said one fuel and the other fuel or
bustion.
9. The method of controlling combustion in a com
bustion zone supplied with blast furnace gas, a supple
mentary fuel and air, the combustion of said blast fur
nace gas with varying amounts of air producing a sub
stantially different oxygen-excess air relationship than
tween the flow of blast furnace gas and the sum of the
the air regulating means to maintain a desired heat re
products of combustion; and adjusting the desired oxygen
content in part from the rate of flow of one fuel relative
to the total rate of fuel flow to the combustion zone in
a direction tending to maintain a desired excess air in
the products of combustion regardless of the relative
the supplementary fuel, which includes, adjusting the rate
fuels.
of flow of air to the combustion zone of maintain a de
5. The method of controlling combustion in a com
sired heat release, adjusting the flow of blast furnace gas
bustion zone supplied with blast furnace gas, a supple—
and supplementary fuel to the combustion zone to main
mentary fuel and air, the combustion of said blast fur
nace gas with varying amounts of air producing a differ 30 tain a predetermined ratio between the total of the fuel
?ows and air ?ow, adjusting said predetermined ratio
ent oxygen-excess air relationship than said supplementary
to maintain a desired oxygen content in the products of
fuel, which includes, producing a ?rst control effect pro
combustion and adjusting the desired oxygen content
portional to the rate of air flow to the combustion
from'the rate of flow of blast furnace gas relative to the
zone, producing a second control effect varying in pre
total rate of fuel ?ow to the combustion zone in a direc
determined ratio with variations in said ?rst effect, pro
tion tending to maintain a desired excess air in the prod
ducing a third control effect proportional to the total of
nets of combustion.
the rate of ?ow of blast furnace gas and supplementary
10. In a combustion control system, a furnace, sepa
fuel to the combustion zone, adjusting the rate of ?ow
rate means for supplying blast furnace gas, a supple
of blast furnace gas and the supplementary fuel to main
mentary fuel and air to the furnace, the combustion of
tain a predetermined relation between the second and
said blast furnace gas with varying amounts of air pro
third control effects, producing a fourth control effect in
ducing a substantially different oxygen-excess air rela
accordance with the oxygen content in the products of
tionship than the supplementary fuel, separate means for
combustion, adjusting said predetermined ratio to main
regulating the flow of blast furnace gas, the supple
tain the fourth control effect at a desired value, produc
mentary fuel and air to the furnace, means for adjusting
ing a ?fth control effect proportional to the ratio be
lease in the furnace, means for maintaining the total of
the flows of blast furnace gas and supplementary fuel
constant at a predetermined value, means for adjusting
said predetermined value in accordance with the rate of
air ?ow to the furnace, means for readjusting said pre
rate of flow of blast furnace gas and supplementary fuel;
and adjusting the fourth control effect in accordance
with the ?fth control effect in a direction tending to main
tain a desired excess air in the products of combustion
regardless of the relative rates of supply of blast fur
determined value to maintain a desired oxygen content in
nacc gas and supplementary fuel.
6. The method of controlling combustion in a furnace
one of said fuels with varying amounts of air producing
a different oxygen-excess air relationship than the other
the products of combustion, and means for establishing
the desired oxygen content responsive to the ratio between
the rate of ?ow of blast furnace gas and the total of the
rate of flow of blast furnace gas and supplemental fuel
fuels, which includes, maintaining a predetermined ratio
between total fuel flow and air flow, adjusting the pre
in the products of combustion regardless of the relative
supplied with multiple fuels and air, the combustion of
in a direction tending to maintain a desired excess air
rfatels of supply of blast furnace gas and supplementary
determined ratio to maintain a desired oxygen content
in the products of combustion; and adjusting the desired 60
oxygen content from the rate of flow of one fuel relative
to the total fuel flow in a direction tending to maintain a
substantially constant excess air in the products of com
bustion regardless of the relative rates of supply of said
one fuel relative to the other fuels.
7. The method of controlling combustion in a com
bustion zone supplied with blast furnace gas, at least
one other fuel and air, the combustion of said blast
ue
11. In a combustion control system, a furnace, sepa
rate means for supplying blast furnace gas fuel, a sup
plementary fuel and air to the furnace, the combustion
of said blast furnace gas fuel with varying amounts of air
producing a substantially different oxygen-excess air re
lationship than the supplementary fuel, constant flow
a control of the total fuel flow to the furnace having an ad
justable set point, means for adjusting said set point in
accordance with the rate of air flow to the furnace, means
furnace gas with varying amounts of air producing a
different oxygen-excess air relationship than the other 70 for readjusting said set point to maintain a desired oxy
gen content in the products of combustion, means for
of said fuel or fuels, which includes, maintaining a
determining the ratio between the rate of flow of blast
predetermined ratio between the rate of air flow and the
furnace gas and the total fuel ?ow to the furnace, and
total of the rate of ?ow of blast furnace gas and the
other fuels, adjusting the predetermined ratio to main
tain a desired oxygen content in the products of combus
means responsive to said last named means for establish
75 ing the desired oxygen content in the ?ue gas to maintain
3,049,300
a desired excess air in the products of combustion re
gardless of the relative rates of supply of blast furnace
gas fuel and supplementary fuel.
12. In a combustion control system for a furnace sup
plied With multiple fuels and air, the combustion of one 5
of said fuels with varying amounts of air producing a
ditferent oxygen-excess air relationship than the other
of said fuels in combination, means for controlling the
relative rates of fuel and air flow to maintain a desired
oxygen content in the products of combustion, and means 10
for adjusting the desired oxygen content responsive to
10
the ratio between the rate of flow of one fuel and the
total fuel ?ow to the furnace to maintain a desired excess
air in the products of combustion regardless of the rela
tive rates of supply of said one fuel and the other fuels.
References Cited in the ?le of this patent
UNITED STATES PATENTS
2,052,375
Wunsch ____________ __ Aug. 25, 1936
2,134,745
Ziebolz ______________ __ Nov. 1, 1938
2,143,820
Payn _______________ __ Jan. 10, 1939
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