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Патент USA US3074654

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Jan. 22, 1963
3,074,644
D. J. GENIESSE
DAMPER CONTROL SYSTEM FOR PROCESS HEATERS
Filed Feb. 24, 1960
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Jan. 22, 1963
D. J. GENIESSE
3,074,644
DAMPER CONTROL SYSTEM FOR PROCESS HEATERS
Filed Feb. 24, 1960
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INVENTOR.
DONALD J. GENIESSE
BY
(2M0. ATTORNEY
WW4!‘
United States Patent 0
3,074,644
rn
1C6
Patented Jan. 22, 1963
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1
walls, or on refractory surfaces, and may be located in
accordance with the general design of the heater. The
signals from the oxygen analyzer, the fuel ?owmeter, and
3,074,644
DAMPER CONTROL SYSTEM FOR
PROCESS HEATERS
the temperature-sensitive devices are transmitted to a con
'
Donald J. Geniesse, West Chester, Pa., assignor to Sun Oil
Company, Philadelphia, Pa., a corporation of New
Jersey
Filed Feb. 24, 1960, Ser. No. 10,677
13 Claims. (Cl. 236-45)
' In brief, the operation is as follows: the controller
This invention relates to a heater control system par
ticularly adapted for use with a process furnace or heater,
to enable the furnace or heater to operate at the highest
practical thermal efficiency. A typical use of the present
system is for the combustion control of a re?nery process
heater.
7
Speaking generally, the present invention constitutes an
improvement over the system disclosed in my prior co
pending application, Serial No. 674,218, ?led July 25,
1957, which ripened on April 18, 1961, into Patent No.
2,980,334.
_
The present trend in process heater design is toward
complete radiant extraction, under conditions in which
the ?ames are in close proximity to the tubes and setting.
Most process heaters are controlled to maintain a sub
stantially constant “product out” temperature. If the tem
perature at the product outlet drops, more fuel is intro
duced, and vice versa. This is the most important con
sideration in the control of the heater, and it is not de
sirable to modify this.
'
The control afforded by the present system is inde
pendent of the product temperature-fuel ?ring rate control
previously referred to. The present system, instead, is
a separate one which operates the heater at a preset low
percentage of excess air under normal operating con
ditions, and which increases this percentage when the
temperature inside the heater has exceeded some preset
value.
troller, the output of which ‘controls a damper to regu
late the amount of air entering the heater (whether there
be either forced or natural draft).
'
Neglecting the effects of poor mixing at very low ?ring
rates, the thermal e?iciency is a function of the percentage
of excess air, the term “excess air” referring to any air
beyond the amount needed for complete combustion.
The lower the percentage of excess air, the higher the
thermal e?‘iciency, and vice versa.
Any heater may conceivably be assigned a ?xed (small)
percentage of excess air, and may be expected to have a
reasonably high thermal e?iciency over a wide range of
?ring rates, at this percentage. A smaller percentage of
air may cause incomplete combustion, while a greater
percentage of air would increase the heat losses through
the stack.
For very high fuel ?ring rates, however, a small per
centage of excess air may result in a larger and hotter
?ame, and although the thermal efficiency then becomes
high, there is danger that the ?ame may becomev large
enough and hot enough to overheat the tubes or the set
ting. In situations of this type, the practice has been to
operate the heater at high excess air rates at all times and
for all ?ring rates, to protect against overheating. This
type of operation demands less attention, but it does pro
‘mote excess fuel consumption and it does reduce thermal
A general object of the present invention is to obviate
the reduced thermal e?iciency resulting from continuously
is preset (this may be a manual adjustment) to operate
the heater with the minimum percentage of excess air
conducive to proper combustion and maximum e?iciency,
at average‘?ring rates. Process heat requirements are
satis?ed with the usual fuel control system or systems;
this system varies the fuel ?ring rate as called for by
changes in product outlet temperature. The signal from
the fuel ?owmeter causes the ‘damper to open and close
with variations in fuel ?ow rate, in such a way as ‘to
maintain an approximately correct fuel-air ratio. This
damper modulation is substantially instantaneous, and
20 prevents any serious air de?ciency which could result
from a lag in the action of the oxygen analyzer.v
Since the fuel-?ow-induced damper position only ap
proximates the preset excess air percentage, and since
variations in fuel heating value and in atmospheric pres
sure will tend to alter this approximation, the signal from
the oxygen analyzer is used to reset the fuel ?ow-air ?ow
portion of the controller, in such a way as to maintain the
preset excess air percentage in‘the heater.
_
‘If a higher ?ring rate is called for by a drop in product
outlet temperature, the ?ame may increase in tempera
ture and size to an extent such that one or more of the
temperatures measured will exceed a preset maximum.
If at high ?ring rates the measured ?rebox temperatures
exceed some preset maximum, the temperature-sensitive
devices will transmit a signal to the controller to raise
the excess air set point (thereby causing opening of vthe
damper) to a value which will increase the percentage
of excess air in the heater, thus lowering the temperature
' to the preset maximum. The controller then causes the
heater to operate at or near the new excess air level. :fIf
the high ?ring rate is not maintained, the excess air set
point is lowered, causing the damper .to close._ Ulti
. mately, the system returns to the condition of the preset
minimum percentage of excess air.
_
.
1
As long as the heater is operated inv the manner de
scribed, the control system will maintain the lowest per
centage of excess air possible, while not exceeding the
maximum heater temperature.
7
p
A detailed description of the invention follows, taken
in conjunction with the accompanying drawings, wherein:
FIGURE 1 is a combined structural and wiring‘dia
gram illustrating a preferred embodiment of the invention;
and '
FIGURE 2 is a detailed circuit diagram of a vdiffer
ential ampli?er which may be used in the system 'of
‘FIGURE
1.
l’ .
.
.
‘
‘
Referring now‘ toFIGURE _1, a heater to which the
control system of the invention may be applied is illus
' trated somewhat diagrammatically at 1. ‘ Theproduct
x to -be heated enters at 2 a tube system inclicated'at~ 3,
and leaves the heater at 4. Fuel is ‘introduced at 5
through a control valve ‘6 to a burner indicated at 7.
Between valve 6 and burner 7, an ori?ce-type (?owmeter
8 is connected into the fuel line. Theori?ce for this
?owmeter is indicated at 9, and couplings for the ?ow
meter 8 are made to the fuel line at respective opposite
sides of this ori?ce, as indicated. The operation of ?ow
meter 8 will be described more in detail hereinafter;
providing a high percentage of excess air. 1In accord
ance with the invention, a continuous oxygen analyzer
is used to produce an output signal which is proportional
to the percentage of excess air in the heater. A fuel
?owmeter is used to produce an output signal which is
proportional to the rate of fuel ?ow into the heater. 70 suffice it to say for the present that ?owmeter 8 measures
the ?ow of fuel to burner 7, that is, the fuel ?ring rate.
Temperature-sensitive devices are located in the radiant
portion of the heater, at points where overheating may
?rst be detected; these devices may be located on the tube
" ‘A temperature pickup e.g. a thermocouple 10, senses
the product outlet temperature in pipe 4 and provides a
3,074,644
a
control signal to a conventionalfuel control 11 which op
balancing the bridge and producing an increasing alter~
erates the valve 6 through a motor device 12. The ac
tion of elements lit-12 and 6 is such as to maintain
nating current potential across potentiometer 27. This
potential will cause the ampli?er 28 to energize the
damper motor 16 (by way of lead 30) to open the
a substantially constant “product out” temperature.
If
. .the temperature at thermocouple 10‘ (at the product out—
let) drops, a signal is transmitted to fuel control 11, this
control then operating valve 6 to introduce more fuel to
damper 14, the damper motor 16 then driving the arm
26 of potentiometer 24 upward to rebalance the bridge,
this action continuing until the potential across poten
tiometer 27 becomes a minimum. The reverse action
occurs when the fuel flow to the burner decreases. Thus,
(a decrease of the fuel'?ring rate) occurs. These changes 10 when the fuel ?ring rate varies (as a result of the action
of the fuel control system 11, etc. described herein
of fuel ?ow in the line to burner. 7 are of course sensed
burner 7, i.e., to increase the fuel ?ring rate.
If the
temperature at thermocouple l?irises, a reverse action
by ?owmeter 8.
above), the damper is varied accordingly, in such a way
Air for combustion, under forced or natural draft, en
tersthe furnace at 13, and is controlled by a damper 14
as to maintain an approximately correct fuel-air ratio.
This operation prevents any serious air de?ciency, since
which is mechanically actuated (as indicated by the 15 the fuel-?ow~induced damper modulation is substantially
instantaneous.
dotted line connection 15) by a reversible motor 16
Combustion gases are sampled at ‘32 by an oxygen
(e.g., a two-phase alternating current motor) provided
analyzer 33. This analyzer may be of any conventional
with windings 17 and 18 arranged to be respectively en
type providing an output in accordance with the- oxygen
ergizedi to open and close the damper. The common
junction of windings 17 and 18 is connected to ground, 20 content of the stack gases, being for example of the type
as indicated. Items 1-—7 and 10—18 may be entirely
conventional, but the arrangement thereof may be con~
involving the burning of hydrogen, of the type involving
siderably more elaborate than is shown, involving, possi
utilization of the magnetic susceptibility of oxygen, or of
other type. For the purpose of the present invention, the
bly, av plurality of burners having separate fuel controls,
output (indicator) shaft 34 of the analyzer drives the
multiple air inlets, or the like. The heater itself may 25 movable arm 35 of a potentiometer 36. The arm 35 is
caused to move- in proportion to the percentage of oxy
take many forms commonly used in the art.
gen- in the heater 1, as determined‘ by the analyzer 3'3.
In accordance with the present invention, a mechani
In this connection, it is pointed out that the percentage
cal transducer (indicated by the dotted line connection
of oxygen in the heater is directly proportional to the
19) is coupled to the ?owmeter 8, this mechanical trans
ducer actuating the-movable arm 20 of a potentiometer 30 excess air percentage in the heater.
A “set point”'potentiometer 37 is connected in parallel
21, which latter is a partof the controller. The poten
with potentiometer 36, across an alternating current power
tiometer 2.1 may be thought of as a variable resistance
type of transducer, and the arm 20 thereof moves in
proportion to the fuel ?ow into the heater 1, as sensed
by ?owmeter 8. An alternating current power source
22 is connected across the two ends of potentiometer 21.
source 38, so that the two potentiometers form a second
alternating current bridge. The arm, 39 of potentiometer
37 can be moved either manually (as by a knob 65 cou
Also connected across source 22, in such a way as to
pled to the potentiometer shaft) or by a reversible motor
40 (e.g., a two-phase alternating current motor) provided
form with potentiometer 21 an alternating current bridge,
is the series combination of a potentiometric-type vari
with windings 41 and 42 arranged to be respectively ener
gized to raise and lower, the set point. The motor 40' in
able resistor 23, a potentiometer 24, and another poten
tiometric-type variable resistor 25-. The movable arm
26 of the “damper slidewire” potentiometer 24» is me
chanically driven by damper motor 16, so that the posi
cludes a friction-type overriding clutch mechanism (shown
schematically) which couples this motor to the same po~
tentiometer shaft operated by knob 65. The manual
tlion of arm 26 is proportional to the opening of. damper
preset, which presets the excess air percentage in the
heater.
The arms 39 and 35 of potentiometers 37'and 36, re
spectively, are connected to respective opposite ends of
a potentiometer 43 which provides the input to a differen
4.
The arms 20 and 26 of potentiometers 21’ and 24, re
spectively, are connected to respective opposite ends of
a potentiometer 27 which provides the input to a differ
ential ampli?er 28. One end of potentiometer 27 (e.g.,
. the end connected to arm 26) is grounded, and the input
to ampli?er 28 is taken between the movable arm 29 of
potentiometer. 27 and ground. The ampli?er 28 is re
sponsive to the phase and amplitude of the alternating
. current signal on potentiometer 27 (or, rather, to a por
movement of arm 39‘ enables the oxygen set point to be
tial ampli?er 44. One end of potentiometer 43 (e.g., the
end connected to arm 39) is grounded, and the input to
ampli?er 44 is taken between the movable arm 45 of po
tentiometer ~43 and ground. The ampli?er 44 is respon
sive to the phase and‘ amplitude of the alternating current
potential on potentiometer 43 (or, rather, to a portion of
tion of this signal, as selected by arm 29), to produce
an energizing voltage (with respect to ground) on one
or the other of the ampli?er output leads 30 and 31, the
this potential, as selected by’ arm 45), to produce an ener
1 more in detail later, in connection with FIGURE 2.
URE 2. Lead 46 is connected to one end of one winding
48 of a reversible motor 49‘ (e.g., a two-phase alternating
current motor), while lead 47 is connected to one end of
gizing voltage (with respect to ground) on one or the
other of the ampli?er output leads 46 and 47, the partic
particular output lead effective depending upon the phase
ular. output lead effective depending upon thepha-se of the
of the alternating current signal across potentiometer
alternating current potential. across potentiometer 43.
27. The operation of this ampli?er will be described 60 Ampli?er 44 may also be of the form illustrated in FIG
Lead 30 is connected to the ungrounded end of the
“open” damper motor winding 17, while lead 31 is con
nected to the ungrounded end of the “close” motor wind
ing 18. Therefore, as a result of the above-described
the second winding 50 of motor 49.
The junction of
windings 48 and 50 is connected. to ground. As a result
operation of ampli?er 28, the output of this ampli?er
of the above-described operation of ampli?er 44, the out
causes the damper motor 16 to open, close, or stop the
put of this ampli?er ‘causes the motor 49 to turn in either
direction or stop, depending on the phase and amplitude
movement of, the damper 14, depending on the phase
and amplitude of the alternating current signal across
of the alternating current potential across potentiometer
potentiometer 27.
70 43. The two potentiometers 36 and 37, connected in the
That portion of the controller previously described
manner described across an alternating current source,
operate in the fashion of a second self-balancing alternat
operates inthe fashion of a ?rst self-balancing alternat
ing current bridge.
ingcurrent bridge. For example, if the fuel ?ow to the
burner increases, the arm 24) of potentiometer 21 moves
upward (in. response to the urging of ?owmeter 8), un
If the oxygen content of the combustion gases, as sensed
by oxygen analyzer 33, varies (as might happen, for ex
, ‘3,074,644
6
" 5
ample, when the atmospheric pressure changes), the arm
element of the temperature recorder in such a waythat
35 of potentiometer 36 moves (in response to actuation
when the temperature sensed by thermocouple 53 exceeds
by output shaft 34), unbalancing the bridge and produc
a preset value (say, 1400° F.), contacts 59 and 61 are
closed, but when the furnace temperature has decreased to
a value less than the set value, contacts 60 and 61 are
ing a signi?cant alternating current potential across poten
tiometer 43. This potential will cause the ampli?er 44 to
energize the motor 49, either by way of lead 46 or lead
47. The motor 49 will then rotate in one direction or the
other, depending on whether its winding 48 or its winding
50 is energized, which depends in turn on the relative
phase of the alternating current potential produced across
potentiometer 43.
The movable arms 51 and 52 of variable resistors 23
and 25, respectively, are ganged together and are mechan
ically driven by motor 49, as indicated at 62.
For one
closed; this latter position is shown in FIGURE 1. The
switch in unit 58 is adjustable, temperature-wise, so‘ that
the temperature at which the above-described switch ac
tion occurs may be preset, or adjusted.
Contact 59 is connected to one end of the “raise” wind
ing 41 of reversible motor 40, while contact 60 is con
nected through the contacts of a limit switch 63 to one
end of the “lower” winding 42 of this same motor. One
terminal of an alternating current power source 64 is
connected to the common junction of windings 41 and 42,
while the other terminal of this source is connected to
are driven in the directions indicated by the arrows adja
the movable contact 61 of the switch in unit 58. Thus,
cent the arms; in this direction, the effective resistance of
when switch contacts 60 and 61 are closed, the “lower”
resistor 23 decreases, while that of resistor 25 increases.
motor winding 42 is energized from source 64, provided
It should be apparent that for the other direction of rota
tion of motor 49, the effective resistance of resistor 23 20 limit switch 63 is closed; when switch contacts 59 and
61 are closed, the “raise” motor winding 41 is energized
would increase, while that of resistor 25 would decrease.
from source 64.
‘
Thus, when the reversible motor 49 is caused to rotate
In event the temperature at a critical point such as 55
(in the manner described in the preceding paragraph), the
exceeds the preset maximum value, the potential across
variable resistors 23 and 25 are driven in a manner to
the thermocouple 53 causes the switch contacts 59‘ and
cause the total resistance of resistor 23, potentiometer 24,
61 in unit 58 to close. This energizes the “raise” winding
and resistor 25 (which are all connected in series across
41 of motor‘40. This motor, through its mechanical
the alternating current supply 22) to‘ remain constant;
coupling to potentiometer arm 39, then raises this arm
however, the alternating current potential at the arm 26
on potentiometer 37, to raise the oxygen set point. The
of potentiometer 24 is changed. The ?rst-described of the
second-described alternating current bridge then becomes
two alternating current bridges thus becomes unbalanced,
unbalanced, producing an alternating current potential
producing a signi?cant potential across potentiometer 27.
particular direction of rotation of motor 49, these arms
Then, ampli?er 28 energizes the damper motor 16, which
across potentiometer 43 which, through ampli?er 44, re
potentiometer 37. In this connection, it will be recalled
sults in the energiza-tion of motor 49. Motor 49 then
drives the resistors 23 and 25 to unbalance the ?rst
described alternating current bridge in such a direction
content is sensed by oxygen analyzer 33, moving the arm
to the abnormal temperature increase. The action just
moves damper 14 in such a way as to cause the excess air
percentage in the heater to return to the value preset on
as to produce an alternating current potential across po
that the described energization of motor 49 (and the con
tentiometer 27 which, through ampli?er 28, results in the
sequent energization of motor 16) was predicated on the
energization of the “open” damper motor winding 17.
assumption that the oxygen content of the combustion
Damper motor 16 then opens the damper 14, to provide
gases varied. When the excess air percentage in the heater
returns to the preset value, the ensuing change in oxygen 40 more excess air and thus alleviate the condition giving rise
35 back and rebalancing the second-described of the two
alternating current bridges. Thus, as described, the signal
from the oxygen analyzer is used to reset the fuel ?ow-air
described (occurring when the furnace overheats or ex
ceeds a preset maximum temperature) occurs suf?ciently
rapidly to avoid damage to the furnace. It is not neces
?ow portion (potentiometer 21, etc.) of the controller, in 45 sary that the damper be opened instantaneously when an
excessive temperature condition occurs.
such a Way as to maintain'the preset excess air percent
The limit switch 63 is actually physically located adja
age in the heater 1.
cent the potentiometer 37, and when arm 39 of this po
One or more temperature pickup elements, such as ther
tentiometer is manually moved, to adjust the set point.
mocouples 53 and 54, are provided at critical points where
the attainment of excess (dangerous) temperatures may 50 the rotational relationship between the limit switch actu
be expected to appear ?rst, in the event that the ?ame be
comes too large or too hot. For example, thermocouple
53 may be mounted on the refractory body 55 customarily
ation and the slider or arm 39 is changed. Switch 63 is
which is coupled to lead 56, so as to be responsive to the
perature is so exceeded, the thermocouple effects a re
versal of the motor 40 to again raise the set point and
opened by a pin on the gear which is coupled between
motor 40 and the potentiometer shaft, when arm 39 (in
its movement by motor 40) tends to move below the
present at the top of the furnace 1, while thermocouple
54 may be mounted on the product tube 3. The thermo- . 55 manually set (preset) position of this arm. Switch 63
is closed at all other times.
couples 53 and 54 provide their signals through the re
It was previously assumed that the temperature had
spective leads 56 and 57 to a thermostatic type tempera
exceeded the preset maximum value, and it was explained
ture control unit 58. For simplicity of description, de
how the damper 14 was opened, to alleviate this condition.
tailed reference will be made only to the thermocouple
53 and its leads 56, but it will be understood that other 60 When the furnace temperature ‘(as sensed by thermo
couples 53 or 54) has decreased to a value less than the
thermocouples such as 54 may ‘be connected to the same
set maximum value, the contacts in unit '58 reverse, open
temperature control unit 58, or a separate temperature
ing contact 59 and closing contact 61 on contact 60.
control unit (any of which would operate the motor 40,
Since limit switch 63 is closed under these conditions,
in the manner to be described hereinafter) may be used
for each thermocouple. In the event that a single temper 65 the “lower” winding 42 of motor 49' is now energized.
The motor 40, through its clutch mechanism, then lowers
ature control unit is used for two (or more) thermocou
arm 39 to its original position on potentiometer 317 (i.e.,
ples, the several thermocouples would utilize the same con
back to the original or manually adjusted set point),
trol unit on a time-sharing basis.
provided the preset maximum temperature is not exceeded
The temperature control unit 58 may comprise, for ex
ample, a temperature recorder the moving element of 70 in the process. Of course, if the preset maximum tem
potential across the thermocouple 53. This temperature
recorder has embodied therein a single-pole, double-throw
switch including two ?xed contacts 59 and 60, and a mov
able contact 61. This switch is actuated 'by the moving
open the damper, in the manner previously described.
Assuming the preset maximum temperature is not again
exceeded, the arm 39 is lowered back to the original set
7
8
point. This lowering results. in the energization of motor
change, an oxygen analyzer adapted to be receptive of
49, which motor drives the resistors 23 and 25 in such a
direction as to energize the “close” damper motor wind
ing 18. Damper 14 is then closed, or returned to its
products of combustion from a heater and operating to
produce a third output proportional to the oxygen con
tent of said combustion products, means establishing a
set point for oxy en content of said combustion products,
and means responsive to said third output and to said
original position.
Limit switch 63 is opened during the downward return
of arm 39, thus preventing the reversible motor 49 from
establishing means for effecting a control of said ?rst out
put, thereby operating said positioning means to maintain
the oxygen content of said combustion products normally
by opening the winding 42 of this motor as this point is
reached.
10 approximately at said set point.
returning below the manually adjusted “set point” value,
The resistance of resistors 23 and 25 (which are con
trolled by motor 49) is a small percentage (e.g., 15-20
percent) of the total resistance of the damper slide-wire
potentiometer 24. These resistors 23 and 25 are thus only
2. Apparatus for control of a fuel-burning heater com
prising damper means adapted to be located in the com
bustion air supply for a heater, means for adjustably posi
tioning said damper means to control the heater combus
large enough to compensate for changes in fuel heating
tion air supply, means controlled by said positioning
value and in atmospheric pressure, and in addition to
effectuate opening of the damper when the furnace tern»
perature tends to become excessive. Since this relation
means for producing a ?rst output proportional to the
opening provided by said damper means, means con
trolled by the flow of fuel into a heater for producing a
second output proportional to the fuel flow rate, means
of resistances holds, even if a failure occurred in the
second-described bridge (i.e., in the oxygen analyzer and
oxygen set point part of the system), there would be an
error of only about 15 to 20‘ percent in the proper posi
tion of the damper 14'. The damper 14 would, under
these circumstances, be controlled only by the fuel ?ring
responsive to changes in said second output for operating
said damper positioning means to return the fuel-air ratio
in a heater approximately to that existing before such a
change, an oxygen analyzer adapted to be receptive of
products of combustion from a heater and operating to
25 produce a third output proportional to the oxygen content
rate, the rate of the fuel feed into the burner 7.
of said combustion products, means establishing a set
Reference will now be made to FIG. 2, which is a
point for oxygen content of said combustion products,
circuit schematic of a differential ampli?er which may
11'. ans responsive to said third output and to said estab
be usedv in the FIGURE'l system. It will be described as
lishing means for effecting a control of said ?rst output,
ampli?er 28, although it will be realized that identical cir
cuitry can be used for ampli?er 44. Speaking generally, 30 thereby operating said positioning means to maintain the
oxygen content of said combustion products normally
this ditferential ampli?er 28 responds to the phase and
approximately at said set point, temperature-responsive
amplitude of an alternating current potential across the
input’ potentiometer 27, to energize either a relay 66 or a
means adapted to be placed in a heater, and means con
relay 67, thereby to energize either the “open” winding
trolled by said temperature-resp-onsive means for causing
17 or the “close” winding 13 of the damper motor 16.
operation of said positioning means to increase the open
Starting off in ampli?er 28, two stages of alternating cur
rent ampli?cation are provided in the twin triode tube 68.
ing provided by said damper means when the temperature
exceeds a predetermined value.
3. Apparatus for control of a fuel~burning heater com
prising damper means adapted to be located in the com
The signal is then fed in parallel to the grids of two tri
ode structures contained in a tube 69, the anodes of these
triodes being fed antiphaseally with raw alternating cur 4-0 bustion air supply for a heater, means for adjustably posi
tioning said damper means to control the heater combus
rent from a source 76), by way of a transformer 71. Since
tion air supply, means controlled by said positioning
the signal fed‘to the grids of these triodes is an alternating
means for producing a ?rst output proportional to the
current signal of the same frequency as the alternating
‘opening provided by said damper means, means con
current on thevanodes, only one of the two triode struc
tures will conduct at any one time, the one conducting 45 trolled by the ?ow of fuel into a heater for producing a
second output proportional to the fuel flow rate, means
being that one whose anode is positive when the alter
responsive to changes in said second output for operating
nating current grid signal is of the proper polarity to
bias the triodes to conduction. The winding of relay 56
is connected into the anode circuit of the left-hand triode
structure, so this relay is energized (to close its contacts)
when the left-hand triode structure conducts. The wind
ing of relay 67 is connected into the anode circuit of the
said damper positioning means to return the fuel-air ratio
in a heater approximately to that ‘existing before such a
change, an oxygen analyzer adapted to be receptive of
products of combustion from a heater and operating to
produce a third output proportional to the oxygen con
right-hand triode structure, so this latter relay is ener
tent of said combustion products, means establishing a
set point for oxygen content of said combustion products,
gized (to close its contacts) when the right-hand triode
‘structure conducts. The normally-open contacts of relay 55 means responsive to said third output and to said estab
66 are in series between the alternating current power
source 70 and “open” winding 17 of motor 16, so motor
winding 17 is energized when relay 66 is energized. The
lishing means for effecting a control of said ?rst output,
thereby operating said positioning means to maintain the
oxygen content of said combustion products normally
approximately at said set point, temperature-responsive
normally-open contacts of relay 67 are in series between
the power source 70 and “close” winding 18 of motor 16, 60 means adapted to be placed in a heater, and means con
trolled by said temperature-responsive means for causing
so motor winding 18 is energized when relay 67 is ener
operation of said positioning means to increase the open
gized.
ing provided by said damper means when the temperature
The invention claimed is:
exceeds a predetermined value, and to decrease the open
1. Apparatus for control of a fuel-burning heater com
prising damper means adapted to be located in the com 65 ing provided by said damper means following such in
crease when said‘ temperature drops below said predeter
bustion air supply for a heater, means for adjustably posi
mined value.
tioning said damper means to control the heater combus
4. Apparatus for control of a fuel-burning heater com
tion air supply, means controlled by said positioning
prising damper means adapted to be located in the com
means for producing a ?rst output proportional to the
opening provided by said damper means, means con 70 bustion air supply for a heater, means for adjustably posi
tioning said damper means to control the heater combus
trolled by the ?ow of fuel into a heater for producing a
tion air supply, means controlled by said positioning
second output proportional to the fuel ?ow rate, means
means for producing a ?rst output proportional to the
responsive to changes in said second output for operating
opening provided by said damper means, means con
said damper positioning means to return the fuel-air ratio
in a heater approximately to that existing before such a 75 trolled by the ?ow of fuel into a heater for producing a
Pm,
7 3,074,644
10
responsive to changes in said second output for operating
combustion products normally approximately at said set
point, temperature-responsive means adapted to be placed
said damper positioning means to return the fuel-air ratio
in a heater approximately to that existing before such a
responsive means to operate said establishing means to
second output proportional to the fuel ?ow rate, means
in a heater, and means controlled by said temperature
change, an oxygen analyzer adapted to be receptive of
products of combustion from a heater and operating to
produce a third output proportional to the oxygen con
raise the set point, thereby to control said ?rst output
and operate said positioning means to ‘increase the open
tent of said combustion products, means establishing a
ture exceeds a predetermined value.
7. Apparatus for control of a fuel-burning heater
ing provided by said damper means when the tempera
set point for oxygen content of said combustion products,
means responsive to said output and to said establishing 10 comprising damper means adapted to be located in the
combustion air supply for a heater, means for adjustably
means for elfecting a control of said ?rst output, thereby
positioning said damper means to control the heater
operating said positioning means to maintain the oxygen
content of said combustion products normally approxi
combustion air supply, means controlled by said posi
tioning means for producing a ?rst output proportional
mately at said set point, temperature-responsive means
adapted to be placed in a heater, means controlled by 15 to the opening provided by said damper means, means
controlled by the ?ow of fuel into a heater for producing
said temperature-responsive means for causing operation
a second output proportional to the fuel ?ow rate, means
of said positioning means to increase the opening pro
responsive to changes in said second output for operat
vided by said damper means when the temperature ex
ing said damper positioning means to return the fuel-air
ceeds a predetermined value and to decrease the opening
provided by said damper means following such increase 20 ratio in a heater approximately to that existing before
when said temperature drops below said predetermined
such a change, an oxygen analyzer adapted to be re
value; and means limiting the last-mentioned decrease of
ceptive of products of combustion from a heater and
operating to produce a third output proportional to the
the damper opening.
oxygen content of said combustion products, means es
5. Apparatus for control of a fuel-burning heater
comprising damper means adapted to be located in the 25 tablishing a set point for oxygen content of said com
bustion products, said last-mentioned means being oper
combustion air supply for a heater, means for adjustably
able to vary said set point, means responsive to said
positioning said damper means to control the heater
third output and to said establishing means for effecting
combustion air supply, means controlled by said posi
a control of said ?rst output, thereby operating said posi
tioning means for producing a ?rst output proportional
to the opening provided by said damper means, means 30 tioning means to maintain the oxygen content of said
combustion products normally approximately at said set
controlled by the ?ow of fuel into a heater for pro
point, temperature, responsive means adapted to be placed
ducing a second output proportional to the fuel ?ow
in a heater, and means controlled by said temperature
rate, means responsive to changes in said second output
responsive means to operate said establishing means to
for operating said damper positioning means to return
raise the set point, thereby to control said ?rst output
the fuel-air ratio in a heater approximately to that exist
and operate said positioning means to increase the open
ing before such a change, an oxygen analyzer adapted to
ing provided by said damper means when the tempera
be receptive of products of combustion from a heater
ture exceeds a predetermined value, and to lower the set
and operating to produce .a third output proportional
point following such raising when said temperature drops
to the oxygen content of said combustion products,
below said predetermined value.
means establishing a set point for oxygen content of
8. Apparatus for control of a fuel-burning heater
said combustion products, said last-mentioned means
comprising damper means adapted to be located in the
being operable to vary said set point, means responsive
combustion air supply for a heater, means for adjustably
to said third output and to said establishing means for
positioning said damper means to control the heater
e?ecting a control of said ?rst output, thereby operating
combustion air supply, means controlled by said posi
said positioning means to maintain the oxygen content
tioning means for producing a ?rst output proportional
of said combustion products normally approximately at
to the opening provided by said damper means, means
said set point, temperature-responsive means adapted
controlled by the flow of fuel into a heater for producing
to be placed in a heater, and means controlled by said
a second output proportional to the fuel ?ow rate, means
temperature-responsive means to operate said establish
responsive to changes in said second output for operat
ing means to vary the set point, thereby to control said
ing said damper positioning means to return the fuel
?rst output and operate said positioning means to in
air ratio in a heater approximately to that existing before
crease the opening provided by said damper means when
such a change, an oxygen analyzer adapted to be recep
the temperature exceeds a predetermined value.
6. Apparatus for control of a fuel-burning heater com
tive of products of combustion from a heater and oper
rating to produce a third output proportional to the
prising damper means adapted to be located in the com
oxygen content of said combustion products, means
bustion .air supply for a heater, means for adjustably
establishing a set point for oxygen content of said com
positioning said damper means to control the heater
bustion products, said last-mentioned means being oper
combustion air supply, means controlled by said posi
able to vary said set point, means responsive to said third
tioning means for producing a ?rst output proportional
to the opening provided by said damper means, means 60 output and to said establishing means for effecting a
control of said ?rst output, thereby operating said posi
controlled by the flow of fuel into a heater for producing
a second output proportional to the fuel ?ow rate, means
tioning means to maintain the oxygen content of said
combustion products normally approximately at said set
responsive to changes in said second output for operat
point, temperature-responsive means adapted to be
ing said damper positioning means to return the fuel-air
ratio in a heater approximately to that existing before 65 placed in a heater, means controlled by said tempera
ture-responsive means to operate said establishing means
such a change, an oxygen analyzer adapted to be re
to raise the set point, thereby to control said ?rst output
ceptive of products of combustion from a heater and
and operate said positioning means to increase the open
operating to produce a third output proportional to the
ing provided by said damper means when the tempera
oxygen content of said combustion products, means
establishing a set point for oxygen content of said com 70 ture exceeds a predetermined value, and to lower the set
bustion products, said last-mentioned means being oper
point following such raising when said temperature drops
below said predetermined value; and means limiting the
last-mentioned lowering of the set point.
third output and to said establishing means for effecting
9. Apparatus for control of a fuel-burning heater com
a control of said ?rst output, thereby operating said
positioning means to maintain the oxygen content of said 75 prising means for controlling the supply of combustion
able to vary said set point, means responsive to said
serge-ts
11
air to‘ a heater, a balanceable bridge circuit having an
perature-responsi-ve means operates said establishing
output coupled to operate said controlling means; means
controlled by iiow of fuel to a heater for producing an
output proportional to the fuel flow rate, means respon
sive to changes in said last-mentioned output for un—
balancing said bridge, thereby to cause operation of said
means to. raise the, set point.
12. Apparatus as set forth in claim 9, wherein the
means establishing a set point is operable to vary such
point, and wherein the means controlled by said tem
perature-responsive means operates said establishing
means to raise the set point, and to lower the set point
following such raising when said temperature drops be
heater approximately to that existing before such a
low said predetermined value.
change, an oxygen analyzer adapted to be receptive of
13. Apparatus as set forth in claim 9, wherein the
products of combustion from a heater and operating 1O
means establishing a set point is operable to vary such
to produce an, output proportional to the oxygen con
Fulfil, and wherein the means controlled by said tem
tent of said combustion products, means establishing
peraturerresponsive means operates said establishing
a set point for oxygen content of said combustion prod
means to raise the set point, and to lower the set point
ucts, means responsive to said last-mentioned output and
following such raising when said temperature drops
to said establishing means for unbalancing said bridge,
below said predetermined value; said apparatus including
thereby to cause operation of said controlling means so
also means limiting the last-mentioned lowering of the
as to maintain the oxygen content of said combustion
a controlling means to return the fuel-air ratio in said
set point.
products normally approximately at said set point, tem
perat e-responsive means adapted to be placed in a
heater, and means controlled by said temperature-respon
sive means, when the temperature
References tilted in the ?le of this patent
UNITED STATES PATENTS
xceeds a predeter
mined value, for unbalancing said bridge, thereby to
cause operation of said controlling means to increase the
air ?ow in a heater.
10. Apparatus as set forth in claim 9, wherein the =. U!
means establishing a set point is operable to vary such
2
a
point, and wherein the means controlled by said tem
perature-responsive means operates said establishing
1,949,355
2,052,375
2,370,897
2,426,415
2,980,334
Knapp ______________ __ Dec. 19,
Wunsch et al. ________ __ Aug. 25,
Whitcomb ____________ __ Mar. 6,
Bristol ______________ __ May 13,
Geniesse _____________ __ Apr. 18,
1933
1936
1945
1947
1961
OTHER REFERENCES
Greene:
pages
121-128 of the Iron and Steel Engineer
11. Apparatus as set forth in claim 9, wherein the 30
for March 1956.
means establishing a set point is operable to vary such
point, and wherein the means controlled by said tem~
means to vary the set point.
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