US2878003A

US2878003A - System for determining peak location of temperature

Info

Publication number: US2878003A
Application number: US602859A
Authority: US
Inventors: Dykeman George; Thomas R Schuerger
Original assignee: United States Steel Corp
Current assignee: United States Steel Corp
Priority date: 1956-08-08
Filing date: 1956-08-08
Publication date: 1959-03-17
Anticipated expiration: 1976-03-17

Description

March 17, 1959 a. DYKEMAN' ETAL 2,878,003

SYSTEM FOR DETERMINING PEAK memo: 0F TEMPERATURE Filed Aug. s 1956 s Sheets-Sheet 1 /5 3 P113? 2-. k /2 I P E l0 1 ll c GEORGE DY/(EMA/V and THOMAS R. SCHUERGER,

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gilt 1 ":fiil'g: d353g I March 1959 e. DYKEMAN ETAL 2,878,003

I SYSTEM FOR DETERMINING PEAK LOCATION OF" TEMPERATURE Filed Aug. 8. 1956 2a r 5 j hrs-I 4.

50" p x-o/T 5/ I 5 Shee'fs-Sheet 2 43 55 4 0mm r/c 0 2 //v v/v TO/P r I 6/0 a La g ll RGE DYKEMAIV a THOMAS H. SCHUERGER,'

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March 17, 1959 s. DYKEMAN ET AL 2,878,003-

SYSTEM FOR DETERMINING PEAK LOCATION OF TEMPERATURE Filed Aug. 8, 1956 3 Sheets-Sheet 3 l5 l4 l3 Grate Length Temp, "F

I5 I /4 /3 Grate Lang/h l/VVE/VTORS. GEORGE DY/(EMA/V and THOMAS R. SCHUERGER,

their A flomey mav n k I SYSTEM FOR DETERMINING PEAK LOCATION OF TEMPERATURE 1 George Dykeman, Pittsburgh, and Thomas R. Schuerger, Monroeville, Pa., assignors to United States Steel Corporation, a corporation of New Jersey Application August 8, 1956, Serial No. 602,859 16 Claims. (Cl. 263-28) This invention relates to heating furnaces of a type in which the temperature variation in a lengthwise direction is in the form of a curve which rises to a peak from lower values at opposite ends and, as indicated, to a system for determining the location of such peak temperature. More particularly it relates to an apparatus for determining the location of the burnthroug point in'a sintering apparatus and forutilizing such determination for both indicating purposes and for controlling operation of the sintering apparatus to maintain such burn-through point in a predetermined location. While the invention is especially adapted to sintering apparatus and the following describes its application to a sintering bed as a preferred embodiment, it will be understood that its principles are applicable generally to other types of heating furnaces wherein peak temperatures of a similar nature are encountered as, for example, in the roofs of open hearth furnaces.

In blast furnace operations, considerable quantities of ore and coke in pulverized form are removed by the flue gases as blast furnace flue dust and are recovered in dust catchers and gas washers- Before the recovered dust can be returned to a blast furnace, it must be processed to a larger particle size toprevent its being carried off again by the blast furnace flue gases and, for this purpose, a sintering apparatus is employed. In addition to processing blast'fu rnace flue dust, sintering is required in connection with ores from sources which contain too high a percentage of fines to permit charging directly in a blast furnace. These ore fines are mixed with coke and the resulting mixture is sintered in the manner of blast furnace fine dust. The necessity of using ores of this character has of course increased the sintering apparatus requirements of the steel industry and the importance of obtaining maximum production from presently available sintering facilities.

Conventional sintering apparatus comprises a travelling grate on which a bed of a mixture of ore and coke is continuously deposited at one end. The fuel in the bed is burned and the ore is sintered by applying a down draft of air to the travelling grate through wind boxes arranged along its-length- At the other end of the grate, the sinter is removed in a particle size acceptable for charging in a blast furnace. In sintering apparatus of this character, the fire level burns downwardly through the bed as it is moved toward the sinter discharge end of the apparatus, and the burn-through point is reached when the fire contacts the grate bars. The temperature of the gases of combustion leaving the sintering bed increases from the charging end of the grate to a maximum at the burn-through point and decreases thereafter as the bed moves to the sinter discharge end. of the grate. Maximum efiiciency of operation is bad when the burn-through takes place in a definite location relative to the discharge end of the grate. If the speed of grate movement is too fast, the burn-through point movestoward the discharge end of the grate and sinter containing unburned coke is discharged. If the grate speed is too slow, the burn-through point move s away from the discharge end of the grate and the effective bed length is shortened. In both of these conditions of operation, a production loss is bad. v

Under conventional operating practices, there is no provision for determining the location of the bu rnthrough point and the speed of grate movement is controlled generally according to observations by anoperator of the, condition of the sinter being discharged from the grate. In general, the operator will decrease the speed if the sinter contains unburned coke and will increase the speed if the sinter has too dark a color which indicates that it has been cooling too lon'gfon the bed. These operations are of course entirely manual'and,'be-

ing dependent on visual observation of the condition of 1 the sinter being produced, will vary with different op erators. Careful control by a skilled operator is required to hold the burn-through point within the length of a single wind-box and it is not unusual for the burnthrough point to drift through an interval of two windboxes before corrective steps are taken by the operator. A burn-through point drift of this character of course represents a substantial percentage of bed length and a substantial change in efiiciency of operation. ;Since the efficiency of operation of a sintering apparatus changes in accordance with the location of the burn-through point or, more specifically, with the location of the peak temperature of the exhaust gases along the length of the bed, it will be apparent that this invention is directed to the problem of determining the location of such peak temperature and of usingsuch determination for. indicating and control purposes.

This invention accordingly has as one of its'prin'cipa'l objects the provision of a system for determining: the location of the peak temperature along the lengthof a furnace in which the temperature rises to such peak from lower values at opposite ends thereof. A related and more specific object is to provide a system of this character which is particularly adapted for use in a sintering apparatus and for determining the location of its burn,- through point along the length of the sintering bed on its travelling grate. A further object of the invention is to provide a system for developing a control voltage which varies proportionately with the shift in position'of the peak temperature along the furnace length.- v

Another object of the invention is to provide a system in which the control voltage of the preceding object is derived from thermocouples arranged at spaced intervals along the length of the furnace and which includes a potentiometric circuit for effecting ,the determination of peaktemperature location. A related object is to provide a system of this character in which the number.

Figure 1 is a diagrammaticvview of a conventionally constructed sintering apparatus;

Figure 2 is a temperature curve showing the manner in which the temperature of the exhaust gases varies along the length of the sintering apparatus shown in Figure 1; I

Figure 3 is a diagrammatic sketch of a null-balance potentiometric circuit for determining the location of the peak temperature of the exhaust gases and the burnthrough point of the sintering bed along the lengthof,

the apparatus shown in Figure 1;

Patented Mar. 17, 1959 Figure 4'is a diagrammatic sketch of a circuit which utilizes'thecircuit of Figure 3 for controlling-the operation of the drive motor for the sintering apparatus shown in Figure 1;

Figure. 5' is a graph theory ofth'e invention; and

Figures 6, 7 and'8are sketches showing the change in position of the temperature curve as its peak moves over'an'interval corresponding to the length of a' single wind-box.

In the diagrammatic showing of Figure 1, the numeral 1 designates a travelling sintering grate in the form of an'endless conveyor which'is'trainedover spaced sprocket wheels 2 and'3' at the ends of'the apparatus. The grate 1' isdriven by the sprocket wheel Swhich is'rotated in a. counter-clockwise direction by an electric motor 4 through'aspeed-reducing drive 5. A down draft of air for combustion purposes is applied to the grate 1 by a plurality 'of.vertically'extending wind-boxes 6 which are arranged'along the length of the apparatus and which are separated from each other by partitions 7. The lower; ends of'the wind-boxes 6 connect-with a manifold Siwhich has an exhaust at 9 for connection to a flue stack or chimney. The structure and operation of the sintering apparatus thus far described is conventional and it will be sufficient to indicate that a sintering mixture of blast furnace flue dust or a mixture of ore fines and coke is continuously deposited on the grate 1 adjacent the drive sprocket 3, is ignited, and'is burned to sinter the oreparticles as the bed headed by movement of'the grate, to the left as viewed in Figure 1, to the discharge end of the apparatus. The fuel in the sintering mixture on the grate 1 burns downwardly and the speed of grate operation by the sprocket 3 is adjusted so that the fuel burns through to the grate bars, or to" the burnthrough point, just in advance of'movement of the bed to the sinter discharge end over the sprocket wheel 2. At the burn-through point, the gases leaving the grate are at their maximum temperature. Since all of the fuel has burned at this point, the temperature of the exhaust gases decreases as the bed moves to the discharge end of the apparatus.

The diagrammatic showing inFigure 1 is one of a sintering apparatus in which the grate 1 has a length between its ends of about 100 feet and which has fifteen wind-boxes 6 arranged underneath its lower run. In a sintering apparatus of this character, each of the windboxes 6 at its upper end covers an area extending along the lower run of the grate for a length of about six feet. It is to be understood that the dimensions of the sintering apparatus in these respects are given by way of example and that the principles of this invention are applicable to sintering beds of greater and lesser capacities and inwhich the dimensions and number of the wind boxes "vary accordingly.

The curve C in Figure the" temperature ofthe exhaust gases varies length of" the grate 1 and, in this showing, the horizontal axis designates'the bed length and the verticalaxis designates thetemperature of the gases being exhausted through the wind-boxes 6. The points 10 through along the curve C designate the temperatures of the exhaust gases leaving the bed 1 through the wind-boxes 6 which lie directly underneath such points in the showing of. Figure 1. Thermocouples t through t are mounted in thermocouple wells in wind-boxes underneath the points Ill-15 as designated by their respective suflixes, and respectively develop voltages corresponding to the temperatures of the gases being exhausted from such wind-boxes. These temperatures of course represent the average temperature of the gases of combustion being exhausted through each wind-box 6 from a'sintering bed section having a length of about sixfeet. From the showing of Figure Zit will be noted that'the curve Crises to a peak P which falls-between 2 shows the manner in which for use in explanation" of the" along the the

points

14 and 15. Beyond the point P, the temperature decreases and the-slope of the curve C reverses'its direction. The relatively more rapid increase in temperature as the point P is approached is due in part to the fact that the fuel in the sintering bed burns faster as the fire level moves downwardly toward the grate bars in the grate 1. At the point P, the maximum temperature is reached "and; beyond this point, a temperature drop will take place since all of the fuel in the bed will have been burned and the air will be coolingthe bed.

An increase in the speed'of'operation of the grate 1 by the drive motor 4' will shorten the length of time in which any given section of the sintering bed'will 'be supported on the grate 1, and will effectmovement of the burn-through point P to the left or toward the sinter discharge end of the apparatus as viewed in Figure 1. A decrease in the speed of operation of the grate 1 will increasethe length of time the bed is retained. on the grate 1 and the fuel will" be completely burned at an earlier point in its movement toward the sinter discharge end of'the apparatus. A' speed'decrease of this character will'result in a movement of the burn-through point P 'to'the right as viewediin Figure2.

In accordance'with the'principles of this invention, de termination of the" location' of the'burn-through point P is effected electrically by two control'voltages, E and E which are derivedfrom thermocouples in three of the wind-boxes 6. These three wind-boxes are comprised of'the two which contain the pairof points 1015 between which'the'burn-through point'P is to be main tained for maximumxefiiciencyand an adjacent windbox. For example, the following description will be applied toan operation in" whichv the burn-through'point P falls'between the points 13'and 14 and the control voltages are derivedfronr thermocouples? in the windboxes 6 containing the points 13, Hand 15. As shown in Figure 3, the control'voltage E isdeveloped by a pair of thermocouples rm and t1; which as designated by their numeral suffixes are located respectively in the wind-boxes6 containing the

points

13 and 14. The thermocouples and' are connected in' opposition with polarities as'indicated'in Figure-3 so that the voltage E1 is a measure ofthe difference between'the temperatures at the points 13 and 14 (E =t t The voltage E is'applied" across a resistor20which has one terminal connected by a lead 21 to the amplifier and motor drive circuit 22; designated schematically, of a null balance potentiometer indicated as a whole by the numeral 23. The other terminalof the resistor 20 is connected by a lead 24 to a mid-point tap 25 of a voltage dividing resistor 26; A voltage 13 which is developed' by thermocouples at the

points

13,14 and 15 in a manner'to be described, is applied" across the resistor 26 so that one-half of the voltage E is added to the voltage E and the sunrof these voltages, thatJis,

is applied to the amplifier '22 through the lead 21.

The null-balance potentiometer 23 is a conventional apparatus ofa type, for example, obtainable from the Brown InstrumentCompany and usually designated as an Electronik recorder-controlled. Since its construction is specifically shown and described in United States Patent No. 2,423,540 toW; P. Wills, it'has been shown only diagrammatically'in the drawings. It includes a potentiometric resistor 27, connected" in parallel to the resistor 26 and thus subjected to the voltage E and a slide contact 28' which is connected by ad'ead' 29 with the amplifier 22. Theamplifier 22' through a motor 30 drives the slide contact28" to a-position along theresistor 27 at which its potential balances that applied to the contact 28 by the unit 22 as determinedby'the energization of.:the=lead-21i As explained iii-Patent No. 2,616,296,

to W. H. Wannamaker, Jr. the circuit of this diagram is further connected in suchmanner that the slidecontact 28 is driven to a position along the potentiometer resistor 27 which is proportional to the ratio of the voltage applied to the lead 21 (L as explained above) and the voltage applied across the potentiometerresistor 27 (E as explained above). The position of the slide contact 28 along the resistor 27 thus furnishes an indication of the ratio Figures 6 through 8 respectively show-the curve. C and its position relative to the

points

13, 14 and 15 when the point P is mid-way between the

points

13 and 14, when it is adjacent the point 13, and when it is adjacent the point 14. Referring to Figure 6 it willbe-seen that when the pointP is mid-way between the

points

13 and 14,;the temperatures at the

points

13 and 14 are sub-.

stantially equal. Under this condition, the output of the thermocouplest .and 14, that is, E will be zero, and the slide contact 28 will bemoved to a position midway between the ends of the-resistor 27 in which it will provide anull-balance against one-half of the voltage E being applied through the voltage divider 25-26. The mid-point ofthe potentiometer resistor 27 thus indicates that the bum-through point P is mid-way between the

points

13 and 14, or directly above'thetop edge of the partition '7 between the wind-boxes 6 below these points.

When the burn-through point P shifts to a position adjacent the point 13 as shown in Figure 7, I will 'be greater than i and, under this condition, E will be ,a maximum and, since is added to E the slide contact 28 will be moved to a position at the lower end of the resistor 28 to provide a null-balance. Accordingly, it will be seen that when the slide contact 28 is at the lower end of the resistor 27, its position indicates that the burn-through point P is adjacent the point 13.

In a similar manner, it will be seen that movement of the slide contact 28 to the upper end of the resistor 27 will indicate that the burn-through point P is adjacent the point 14. Attention is directed to the fact that the polarity of E changes as it moves through a zero value, and, that it will be subtracted from I 6 as the point "moves toward the point 14. As P approaches'the point'14, thevoltages'E' and j will add up to zero potential which will be balanced by movement of the slide contact 28 tothe upper end of the resistor 27.

The reason 'for'using two thermocouples r a single thermocouple t and a single thermocouple r in the development of the voltage E will be best understood by referring to the graph of Figure 5 in which the axes of abscissas and ordinates are respectively designated'by the letters x and y. In this showing, the horizontal axis represents length of bed, the vertical axis represents temperature, and the curve C has been drawn with its peak P at the point 14. -A curve C of this-type'may be defined in terms of a quadratic equation'as follows:

y ax +bic+c- Taking the first derivative of this equation and setting it equal to zero which is the slope of the curve at the point P, it can be shown that Using numerical differences between adjacent points 'on the curve C and assigning x a value of unity between such points; the slope of the curve C between the

points

13 and 14 may be expressed as follows:

v ZYrr-lra I v the slope of the curve C between the

points

14 and 15 may be expressed as follows:

y15 y14 and the second derivative of the curve C or the slope of the slope between the

points

13, 14 and 15 may be expressed as the algebraic diiference of the aboveslopes as follows; i I 1 s v y15 y14+y13 1 Using standard numerical techniques to solve for aand b, where x is limited to values between O-and 1; 3 1 3' and y are the discrete ordinates;.and x'==0 at-y and x=1 at y as indicated by Figure 5, it can be shown that ills- 914+ 1 /13 In the above formulait will be seen that the numerator of the fraction corresponds to E and is developed by the In this solution, thermocouples develop voltages corresponding' to ordinates of the

points

13, 14 and 15, and

the thermocouples r and 1 are substituted for the points y g, y and in the above formula, and the numerical value of x ,will vary between 0 and l as the point P shifts from 13 to 14.

A scale calibrated between 0v and 1 is provided along the resistor 27 as shown in Fig. 3 for indicating the position of the burn-through point P.- When. the slide contact 28 is at the lower end of the scale at a point opposite the 0 scale calibration, the bum-through point P will be located adjacent the pointl3, and when the contact 28 is at the upperend of the scale, the bumthrough point P will be located adjacent the point 14 according to the showing of Figure 5. In this respect the calibration of the scalebetweent) and 1 corresponds to the values of x between 0 and 1 as explained in connection with the graph of Figure 5.

The position ofthe' pointer- 28 of course provides an indication of'the location of theburn-through point P between the points Band 14. If the bum-through point of ithermocouples for'developing the voltages E and E willbeprovided at these points inthe manner explained above.

In. addition to. indicatingthe. location of the burnthrough-pointP, the determination of its location by movement ofthe; slidecontact 28 is'utilized .in accordance withsthe principlesaof this invention'to. maintain such point in aselectedposition alongthelengthofthe grate 1. A circuit toreffecting sucha. control operation is shown diagrammatically in Figure 4. In this showing,

the sintering bed drive'motor 4 is" illustrated as being adirect. current motor: comprised; of. anarmature 40 havingga. speed". control fieldrwinding 41and an adjustable rheostat 42 for controlling theienergizationor. field strength of the winding 41. The rheostat 42 is operated in opposite directions by a. reversing motor 43 having split reversing

control fields

44 and 45 respectively operable upon energization thereof to rotatethe armature ofthemotor 43in opposite directions. A switch 46 is selectively movable toautomatic' or manual positions, as indicated, to set up controlcircuits for energization of the

fields

44 and 45. In the down or manual position of the switch 46, energiZation of the motor 43 is placed under'the'control of manually operable switches 47 and 48. Depression of the switch 47 opens the circuit for the winding and closes the circuit for the winding 45 so that motor 43. adjusts the rheostat 42 in one directionto .increase .the speed of the armature 40' and the operation of the sintering bed 1. In a similar manner, depression ofthe switch 48 completes the energizing circuit through the field .winding 44 to reverse the motor 43 and the direction'ofadjustment of the rheostat 42 to.slow the speed of operation of the sinteringbed 1.

In .the up or: automatic position ofthe switch 46, speed controlis. placed under a pair oflimit switches 50 and 51 which have a movablesupport 52 for adjusting their position in opposite directions relative to and along a line parallel to the length of the resistor 27. The

switches

50 and 51 are arranged on opposite sides of the contact 2.8v so that, when the position of the burn-through point Pshiftsthe slide contact 28 will move to the right or leftlas viewed inFigure 4 and close one of the switches 50' andf51l Closure of such switches sets up energizing circuits for relays 53 and 54 which operate respectively, uponenergization thereof, to close relay contacts 55 .and56. The relay contacts 55 and56 serve the same fiinctionas the manual switches. 47 and 48 under the manual operating. condition. of above. The energizing circuits. for the relays. 53 and 54"include

contacts

57 and 58 which are cam-operated intermittently to closed positions by

clock motors

59 and 60." Intermittent operation'of the

contacts

57 and 58 in this manner provides regulation of the adjustment of the rheostat 42 in a timed and step-by-step manner so that the change in speed of operation of the sintering bed will not cause the burn-through point P to overshoot the position which the position of'the support 52 calls for. The position of the burn-through point P may be regulated by adjusting the position of the support 52 for the

contacts

50 and 51 relative to the slide contact 28- andin a-direction parallel to and along-the length of the resistor27i' From the foregoing, it will be'app arent that the control system shown in Figure-*4 will operate to maintain the burn-through point P in a' predetermined position according-'to the'locationof the contacts-50 and 51 relthe switch 46 described.

to develop the voltage E ative tothe;slide-contact-28; andthat' such position is selectiyelyadjustable overra length of a single wind-box by; adjusting gtl e position ofi thesupport 52 along the length of the resistor 27. Any change in-operating conditions which causes a shift in the location of the point P from that called for by the position of the support 52 will result in closure'of one of the

contacts

50 or 51 by the slide contact 28 and a change in speed of the operationof the, grate 1 in a manner which will return i theburn-through-pointto its predetermined position as It will be further apparent that the.

explained above. position of the contact 28 along the length of the resistor 27, for the circuit shown in Figure 3, furnishes an indication of the relative position of the point P between the

points

13 and 14.

While only a single burn-through point determining circuit has been shown in Figure 3, and such circuit is.

for the specific purpose of determining the relative location of the point P between the

points

13 and 14, it

' will be understood that the invention includes additional circuits of a similar nature which may be switched selectively intooperating relation with respect to the potentiometer- 23 if'operating conditions call for the location of'the burn-through' point P between other of the points '10- through 15'. As has been indicated above, a pair of thermocouples t and t15 will be used to develop the voltage E if thepoint P is to be located between the

points

14 and 15. Iffthe point P is to be located between the points 11 and 13, then a similar arrangement of four thermocouples comprising two of t and one each of t and will be used to develop the voltage E and a pair of thermocouples, either t or t or t and according to a location of the point P between the

points

12 and 13 or between 11 and 12, will be used The manner in which such circuits are arranged and the switching mechanism required for selectively connecting themto thepotentiometer 23 will be apparent to one skilled in the electrical art.

Although the above furnishes a preferred example of the invention-as appliedto an ore sintering apparatus, it will-be understood that the principles of the invention have general applicability to other types of furnaces, for example, an open hearth furnace as has been indicated above. In open hearth furnaces, a peak roof temperature is had between its uptakes and downtakes at a point which is usually located closer to the downtake than to the uptake. To determine the location of the peak open hearth roof temperature, an arrangement of temperature responsive generators and a potentiometric circuit as shown in Figure 3 may be employed. In such case, the potentiometer 23 may-be used to indicate the position of the peak roof temperature or to control the fuel supply means for the furnace to maintain it in a predetermined location. Further adaptations of the invention to other types of furnaces in which peak temperatures of this type are encountered will of course be apparent. Such other adaptations and modifications are contemplated and may be made without departing from the scope of the following claims.

We claim:

1. In. a furnace in which the temperature along its length rises to a peak. from lower values at opposite ends thereof, and there is provided a heat supply means operable to control the location of said peak temperature, the combination with said heat supply means of temperature responsive means for developing a voltage which changes as said peak temperature moves relative to said furnace ends, and means operated by said voltage for controlling the operation of said heat supply means to maintain said peak temperatures in a predetermined location.

2. In a furnace in which the temperature along its length rises to a peak from lower values at opposite ends thereof, and there is provided a heat supply means operable to control the location of said peak temperature,

the combination 'withsaid heat supply'means of at least a pair of temperature responsive generators for developing voltages which respectively vary with the temperature of said furnace at spaced points along its length, circuit means responsive to said voltages for developing a control voltage which changes as said peak moves toward one of said furnace ends, and means operated by said control voltage for controlling the operation of said heat supply means to maintain said peak temperature in a predetermined location.

3.'In a furnace in which the temperature along its length rises to a peak from lower values at opposite ends thereof, and there is provided a heat supply means operable to control the location of said peak temperature, the combination with said heat supply means of a temperature responsive circuit means for developing a control voltage which changes as said peak temperature moves toward one of said furnace ends, a second circuit means for developing a second control voltage, means for obtaining the ratio of said control voltages comprising a potentiometer havinga slide contact and means for moving said contact in accordance with changes in said ratio, and means operated according to the movement of said contact for controlling the operation of said heat supply means to maintain said peak temperature-in apredetermined location.

4. In a furnace in which the temperature along its length rises to a peak from lower values at opposite ends thereof, and there is provided a heat supply means operable to control the location of said peak temperature, the combination with said heat supply means of a first circuit means including four thermocouples arranged at three stations at spaced intervals along said furnace and with two of said thermocouples at the intermediate one of said stations, and a circuit connecting said thermocouples in series to produce a control voltage which varies as the difference between the sum of the voltages produced by the two of said thermocouples at said one station and the sum of the voltages produced by the other two of said thermocouples; a second circuit means including two thermocouples respectively arranged at two of said stations including said intermediate one station, and a circuit connecting said last-named thermocouples in series opposition to produce a second control voltage which varies as the difference of the respective voltages produced thereby, a potentiometer means including a slide contact and means for adjusting its position in accordance with the ratio of said first and second control voltages, and means actuated according to the movement of said slide contact for operating said heat supply means to maintain said peak temperature in a predetermined location.

5. In a furnace in which the temperature along its length rises to a peak from lower values at opposite ends thereof, the combination comprising: a first circuit means including four thermocouples arranged at three stations at spaced intervals along said furnace and with two of said thermocouples at the intermediate one of said stations, and a circuit connecting said thermocouples in series to produce a control voltage which varies as the difierence between the sum of the voltages produced by the two of said thermocouples at said one station and the sum of the voltages produced by the other two of said thermocouples; a second circuit means including two thermocouples respectively arranged at two of said stations including said intermediate one station, and a circuit connecting said last-named thermocouples in series opposition to produce a second control voltage which varies as the difference of the respective voltages produced thereby; and means for determining the ratio of said first and second control voltages to thereby determine the location of said peak temperature along the length of said furnace.

6. An apparatus as defined in claim characterized by said ratio and peak temperature determining means comprising a potentiometer including a slide contact'and means for changing the'position of said slide contact in accordance with changes in said voltage ratio.

7. An apparatus as defined in claim 6 characterized by the provision of a scale cooperating with said slide contact and being calibrated to provide an indication of the position of said peak temperature along the length of said furnace.

8. An apparatus as defined in claim 6 characterized by said furnace having a heat supply means operable to control the position of said peak temperature, and' means cooperating with said slide contact for operating said heat supply means to maintain said peak temperature in a predetermined position.

9. An apparatus as defined in vclaim 5 characterized by said furnace comprising a sintering apparatus including a travelling grate and wind-boxes for applying a downdraft to said grate at spaced intervals along its length, and in which three consecutive ones of said wind-boxes constitute said three furnace stations.

10. In a sintering apparatus, the combination with a travelling grate for supporting a sintering bed of a mixture of ore and fuel, a plurality of wind-boxes for applying draft to said grate at spaced intervals along its length, of circuit means for developing a control voltage which changes with the location of the burn-through point of said sintering bed relative to the ends of said grate, means responsive to said voltage for determining the location of said burn-through point along said grate, a variable speed drive for said grate, and means operated by said burnthrough point location determining means for adjusting the speed of said drive to maintain said burn-through point in a predetermined position.

11. In a sintering apparatus, the combination with a travelling grate for supporting a sintering bed of a mixture of ore and fuel, a plurality of wind-boxes for applying draft to said grate at spaced intervals along its length, of a first circuit means including four thermocouples arranged at three stations at spaced intervals along said grate and with two of said thermocouples at the intermediate one of said stations, and a circuit connecting said thermocouples in series to produce a control voltage which varies as the difference between the sum of the voltages produced by the two of said thermocouples at said one station and the sum of the voltages produced by the other two of said thermocouples; a second circuit means including two thermocouples respectively arranged at two of said stations including said intermediate one station, and a circuit connecting said last-named thermocouples in series opposition to produce a second control voltage which varies as the difference of the respective voltages produced thereby; a variable speed drive for said grate, and means responsive to said first and second control voltages for adjusting the speed of said drive to maintain the burn-through point of said bed in a predetermined position relative to the ends of said grate.

12. In a sintering apparatus, the combination with a travelling grate for supporting a sintering bed of a mixture of ore and fuel, a plurality of wind-boxes for app1ying draft to said grate at spaced intervals along its length, of circuit means for developing a control voltage which changes with the location of the burn-through point of said sintering bed relative to the ends of said grate, a variable speed drive for said grate, and means responsive to said control voltage for adjusting the speed of said drive to maintain the burn-through point of said bed in a predetermined position relative to the ends of said grate.

13. In a sintering apparatus, the combination with a travelling grate for supporting a sintering bed of a mixture of ore and fuel, a plurality of wind-boxes for applying draft to said grate at spaced intervals along its length, of at least a pair of temperature responsive generators for developing voltages which respectively vary with temperatures at spaced points along the length of said grate, circuit means responsive to said voltages for developing a control voltage which changes with the location of the burn-through point of said sintering bed relative to the ends of said grate, a variable speed drive for said grate, and means responsive to said control voltage for adjustingthe speed of said drive to maintain the burnthrough point of said bed. in a predetermined position relative to the ends of said grate.

14. In a furnace in which the temperature along its length rises to a peak from lower values at opposite ends thereof, a pair of temperature responsive generators for developing voltages which respectively vary with the temperature of said furnace at spaced points along its length, means for obtaining the ratio of the said voltages developed by said generators including means for develop- 1 ing a control voltage corresponding to such ratio, and means responsive to said control voltage for determining the location'of said peak temperature along the length of said furnace.

15. In a sintering apparatus, the combination with a travelling grate for supporting a sintering bed of a mixture of ore and fuel, a plurality of wind-boxes for applying draft to said grate at spaced intervals along its length, of a first circuit means including four thermocouples arranged at three stations at spaced intervals along said grate and with two of said thermocouples at the intermediate one of said stations, and a circuit connecting said thermocouples in series to produce a control voltage which varies as the difference between the sum of the voltages produced by the two of said thermocouples at said one station and the sum of the voltages produced by the other two of said thermocouples; a second circuit means including two thermocouples respectively arranged at two of said stations includingsaid intermediate one station, and a circuit connecting said last-named thermocouples in series opposition to produce a second control voltage which varies as the difference of the respective voltages produced thereby; and means responsive to said first and second control voltages for determining the location of the burn-through point of said sintering bed along the length of said grate.

16. In a sintering apparatus, the combination with a travelling grate for supporting a sintering bed of a mixture of ore and fuel, a plurality ofwind-boxes for applying draft to said grate at spaced intervals along its length, of at least a pair of temperature responsive generators for developing voltages which respectively vary with temperatures at spaced points along the length of said grate, means for obtaining the ratio of the said voltages developed by said generators including means for developing a control voltage corresponding to such ratio, and means responsive to said control voltage for determining the location'of the burn-through point of said sintering bed along the length of said grate.

References Cited in the file of this patent UNITED STATES PATENTS