US2625386A - Method and apparatus for controlling blast furnaces - Google Patents

Description

Jan. 13, 1953 O. J. LEONE METHOD AND APPARATUS FOR CONTROLLING BLAST FURNACS 5 sheets-sheet 1 Filed Mayv 20, 1947 )MMM .Nl .Amm

JNVENToR. OTTO J. LEONE awwuf O. J. LEONE Jan. 13, 1953 METHODl AND APPARATUS FOR CONTROLLING BLAST FURNACES 3 Sheets-Sheet 2 Filed May 20, 1947 INI/Elvmfe.l OTTO J, LEONE .EDI L www VI OwFZOU OZ( EPNE 2,625,386 METHOD AND APPARATUS FOR CONTROLLING BLAST FURNACES Filed May 20, 1947 O. J. LEONE Jan. 13, 1953 3 Sheets-Sheet 3 EJ-Om O...

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Patented `an. 13, 1953 UNITED STATES PATENT OFFICE METHOD AND APPARATUS FOR CONTROLLING BLAST FURNACES Otto J. Leone, West Newton, Pa., assignor of onehalf to David P. Leone, Donora, Pa.

Application May 20, 1947, Serial No. 749,238

14 Claimsl l This invention relates generally to blast furnaces and specifically to a method and apparatus for controlling the drop in gas pressure through the charge of stock in the furnace. It is the general object of the invention to obtain a smoother and more regular descent of stock in the furnace minimum the slips which result from hanging stock and the building up of excessive pressure-drops through the stock.

The inadequacy of present methods of control to compensate for furnace irregularities often adversely affects the regularity of stock descent through the furnace shaft. For example, such factors as weight of the stock column, particle size and shape, gas density, gas composition (molecular weight), degree of packing, size of furnace (area and contours), moisture in the charge and blast, viscosity vof gases, wall friction, blast pressure, blowing rate and blast temperature are all factors which vary the effective voids and pressure-drop through the furnace stock. I compensate for variations in these factors by means of a differential pressure controller.

In a stock charge of given effective voids condition, for example, increasing the blowing rate and hot blast temperature, or either of them will increase the pressure-drop through the stock. If this pressure-drop istoo high, hanging and slipping of the furnace charge will result, with consequent loss in furnace efficiency, increased tendl the charge; changes in particle size due to crushing or abrasion, and differences in rate of stock descent at various distances radially from the center of the furnace, or because of changes in cross-sectional area of the furnace shaft. All

' these factors affect the pressure-drop through the furnace.

At the high blowing rates now usually maintained, producing excessive pressure-drop, there is a tendency for small particles to become suspended when a critical velocity is exceeded. This change in lifting velocity causes the lifting of particles whose suspension decreases the pressure-drop through the charge. Because of the unequal velocity distribution across the area traverse of the stock, however, there is a tendency to channel where the lifting velocity is highest. 'I'he lower the gas velocity, the less the tendency to form channels of high gas velocity and high dust-carrying capacity. I employ a differential pressure controller to keep the gas velocities below the critical velocity.

Y In present-day furnace operation, the operator is not aware of a hanging condition until an excessive pressure-drop has built up or the furnace has slipped. Corrective action cannot, therefore, be applied in time. By my invention, using pressure-drop control, corrective action may be applied at the correct time to eliminate vfurnace hangings, slips and consequent delays.

Usually, just before a hanging condition occurs in a blast furnace, the blower attempts to maintain a certain rate of blowing wind. This causes the blast-supply pressure to increase on account of the increased resistance to flow of gases through the voids in the stock column. In order to maintain the mass rate of flow of gases through the stock, the pressure-drop, and therefore, the gas velocity through the stock, increases and may reach the critical lifting velocity mentioned above if the conditions which will finally cause hanging persist. It is the main object of this invention to measure and to control the pressuredrop by one of several methods.

. Under present methods of furnace operation, the measurement of such conditions as blast rate Y of flow and pressures below or above the stock are not sufcient indications of the action of gassolid contact within the furnace. Even if these Vconditions were controlled, the occurrence of channelling with resultant change in pressuredrop through the column might not be detected and corrected. The measurement or control of pressure-drop across the stock, in addition to the measurement or control of such conditions as gas fiows or pressures at any particular location, provides an additional tool for obtaining better furnace operation. To this end, I regard the voids in the bed of solids in terms of an equivalent orice. That is, the furnace restriction could be likened to an orifice plate placed in a pipe line. If the pressure above or below the orifice be controlled to a given value, the pressure-drop for a given orifice area and ow (blowing) rate would remain constant. Actually, however such ideal conditions do notexist in the blast furnace.

drop would tend to raise the pressure at the top ,y

of the furnace, to counteract which the pressurecontrol valve would tend to movek toa more open position so as to restore the pressure at the top of the furnace to the set control point. It is obvious then that, while the valve movement would be correct to maintain the set top pressure, it would not compensate for the change in pressuredrop and, therefore, would not counteract the increased dust-carrying capacity due to channelling of gases. It is a further object of this invention,

therefore, to use a differential pressure Controller `in conjunction with straight pressure-control means as one method of operation.

A complete understanding of the invention may be obtained from the following detailed description which refers to the attached drawings showing various embodiments and practices contemplated by my invention. In the drawings,

Figure l is a schematic diagram showing a blast furnace and one form of control system therefor according to my invention embodying a differential pressure controller;

Figure 2 is a similar diagram showing a modified control system utilizing two separate pressure controllers to control the pressure-drop across the furnace; and Y y y Figure 3 is a similar diagram showing a more complete system incorporating additional measurement and control elements so as to eiect closer control. Y K l Figure 1 illustrates one form of control system according to the invention applied to a blast furnace 5 so as to permit the measurement and control of the pressure drop through they furnace stock. A blower 6 forces air through hot-blast stoves 'i and intto the blast furnace by means of tuyeres which lead from the hot blast line 8. After passing through'the stock charge. the'gases 'leave the furnace by means of downcomers 9 and pass to the dust-'catcher equipment. Y For a'given blast rate, and a given state of voids Yin the stock, there will exist a dennite pressure drop through the stock. A change in any of the aforementioned factors which affect the pressure drop will cause it to change, with consequent change in the furnace operation which in some cases may cause derangernent of stock and gas movements. Figure l shows a control system including a differential pressure controller l0 connected to `measure a pressure drop that will be indicative of the stock-charge resistance and control correctively a restrictive valve or valves in theflue gas mains leaving the furnace.

The differential pressure controller 1G which may be of the proportional type, measures the difference between the static pressures at locations indicated by Ii and l2, connection between the points of static pressure measurement 'and the measuring device being made by pipe lines `i3 and ld. Alternately, this measurement can be made by connecting valved branch lines i5 and IB to locations closer to the stock, as for example, between any horizontal planes on the stack proper, as indicated by taps marked Il and I8. These last connections may be single pressure taps or may use piezometer rings with multiple pressure connections between ring and furnace shaft so as to obtain average pressures.

The controller I0 includes automatic control means to regulate the pressure-drop between the ,locations indicated above to a predetermined vxed value as set on the controller; this control- 'ler of which various types are commercially available', "may be non-indicating, indicating,

recording .or indicating-recording. When the `pointer' of the controller i0 deviates from the set control point or control limits, the control mechani'sm causes corrective adjustment of a restrictive' valve I9 in the downcomer 9 by means of a power operator 2li, this action being in suc-h a direction as to restore the pressure-drop value to the set point or limits. Although Ifhave shown the controller and operator asseparate components they may be combined into one 'integrated, self-contained unit. 4

In order` to preclude any possibility of upsetting the controller action by slight disturbances in pressure-drop caused by movement of the large bell 2l Yduring filling operations, an` interlocking device may be incorporateduto, operate in conjunction with the above controllerfth-is interlocking device operating from the opening and closing of the bell, andvso arranged torender the control valve inoperative by locking either the valve position or the differentialhimpressed on the con-troller, or by lockingl both. This last action may be controlled by the useY of an automatic pressure-locking valve on both the pressure lines. Referring to Figure 1, I showan interlocking switch 22 operated by a suitable mechanical connection to the Vbell rod 23, and electrically connected by a circuit 24 to electrical shut-off valves 25 on each of the pressure irnpulse lines. When the bell 2l is in theclosed position, switch 22 maintains valves 25 in the pressure impulse lines open; when the bell rod 23 moves to open the bell, switch 22 cau-ses valves 25 to close so as to lock the pressures into controller lo and prevent movement of the controller 'pointer'or power operator 2i! that would otherwise result if the bell movement causedian vappreciable change'in'the gas pressure at the top of the furnace.

u K in Figurel-I show inaddition to the interlocking valve mechanism2 l, an'interlocking relay 26 connected in circuit 2l by which controlled power is delivered to vthe valve operator 2i); relay 2-5 may also be connected vto'interlock 22 by circuit 2d so that the power circuit will be opened during opening ofthe bell 2| as during charging operations. A hot-blast controller 28, connected' by two connect-ing leads 29 to a thermocouple element 30, and by means of a power circuit 3l to a cold-air mixer valve and power unit 32, provides a pyrmetersystem that will bypass the required amount of cold'air around the heating stoves 'to the tot-blast side thereof, so as to 'maintain 'the temperature of element 3i! substantially constant. v

Although in Figure l I show `the pressure-drop controller l0 'operating a restrictive'valve I9 in the downco'mer leaving the furnace,v the controller may just as well regulatea valve in the blast main 8 leading to the furnace or, a`bleeder and tobe described later.

-to a certain fraction of the total range.

In Figure 1 a temperature element 34 is connected by lead-s 35 to a temperature compensator which is incorporated in the differential controller I0. Temperature compensation may thus be accomplished for both hot-blast and exit-gas densities by regulating the hot-blast temperature to a constant value and by automatically correcting the controller I0 by the variable exit-gas temperature. Elements 30 and 34 should be reasonably close to their respective pressure taps I I and I2. As an alternate correction, element 30 could operate the compensator in controller I il and the temperature at element 34 be maintained constant by using the top-gas constanttemperature controller 53 illustrated in Figure 3; or as also shown in Figure 3, both temperatures can be controlled to substantially constant values.

Figure 2 illustrates another alternate method of control utilizing individual pressure controllers 36 and 31 instead of the diiTerential controller I0 shown in Figure 1, and by causing these pressure controllers .to operate the power operators of valves 38 and 39 located below and above the furnace stock, to maintain the static pressures at points I I and I2 at predetermined values as set on the controllers. In this manner the difference between the static pressures at these points will be maintained substantially constant at a value below the critical value. Although Figure 2 shows the controllers operating valves restricting the air-blast and exit-gas lines, respectively, the method of controlling individual pressures is not to be limited to the control of pressure valves only but may be combined with other control functions as mentioned, for example, where a direct measurement of diiferential pressure is made. For example, pressure controller 36 could maintain constant pressure at points II or Il by operating snorter valve 33, or by regulating the blower output pressure. Likewise controller 31 could be made to operate an atmospheric relief valve. As in the ease of the differential type controller, the individual controllers 36 and 3l could incorporate gas and i air-temperature measuring and compensating mechanisms similar to those described for use with the diiferential pressure controller.

I may also include in the system of Figure 2 a differential-pressure indicator or recorder 40 in addition to the pressure controllers so as to afford a means of measuring directly the pressure drop across the pressure taps. In laddition this instrument may incorporate a control mechanism to operate, for example, a third restrictive valve 4| located either ahead of valve 38 or after valve 39. This last arrangement is an improvement over the method using the two pressure controllers 3B and 31 only in that, by using a suitably designed differential-pressure manometer, it is possible to use a more open scale to cover a more narrow range of pressure-drop than would be possible otherwise. The reason is that there are inherent limitations in industrial types of pressure-measuring elements which limit the smallest increment of pressure change This method, then, oiers the advantage of a Vernier adjustment in addition to the closeness of control available by the method of Figure 2 using pressure controllers 36 and 3l only.

As compared to the method represented by Figure 1, this method oifers an alternate method of compensating for density chan-ges in the air or gas. In addition to density compensation by the method just described, the auxiliary controller 40 may instead of controlling the power unit and valve 4I control the blower speed, or a valve in the hot-blast line, or snorter valve or. in addition to having controllers 36 and 3l operate their respective pressure-control valves, controller 4U could control the injection of cooling gases or vapors, or combustion-supporting gases such as oxygen into the blast furnace. Thus, although Figure 2 shows another system for the control of pressure drop, it is not limited to the use of the equipment shown in Figure 2. These controllers may operate with other equipment than valves, as illustrated in Figure 3.

With reference to the pressure compensation described in the last paragraph, a more simple, but slightly less accurate means of compensating the control system is obtained by using the pressure-drop controller40 in Figure 2 and only one of the pressure controllers, preferably omitting the blast controller 36, since normal percentage changes of pressure and hence density, are much less at the bottom of the furnace than at the top of the furnace. Where further and closer density compensation is desired, the hot-blast temperature may be automatically controlled by means now commercially available, and the top temperature may be maintained constant by use of a temperature controller controlling a waterinjection spray valve located in the furnace top as shown in Figure 3 and described in detail later. With this arrangement the control index of temperature controller 53 would be set at a point sumciently below the normal top-gas temperatures so that the cooling spray will cool the top gas to a constant predetermined temperature. A principal advantage of this method is Vthat it will give the effect of temperature compensation for gas density either in the case of the differential controller or where a gas-now measurement is made in the gas line leaving the furnace for the purpose of metering the rate of flow of gas. Another advantage from an operating point of view is that it will eliminate one more variable in the furnace operation.

Instead of injecting spray water, in some cases where the top temperature is very low as occurs in some of the latest modern furnaces, I propose to inject a hot or cold gas instead of water. This gas may, for example, be clean blast-furnace gas. In modern furnaces operating under reduced gas velocity and longer gas retention time because of the excess height of the furnace stock, the gases are cooled to too low a temperature for best furnace operation. In this case I propose to inject a heated gas just below the stock line, and thusto raise the top gas temperature to a constant value.

Although I have described the use of a separate pressure controller and differential-pressure controller for density compensation of the pressure drop measurement, a pressure-compensated dierential manometer may be used in which the pressure correction is automatically made inside the manometer in the same manner as is sometimes practiced in the art of orifice flow-metering of compressible fluids which have varying pressures. With this ararngement the pressure compensation may be applied to the blast air or top gas, or to some pressure tap between the tuyeres and top so as to give an average pressure correction or, again as in the case of flow-meter measurement just mentioned, an averagingtype pressure ytube with endconneo'tions to the highand low-pressure taps may be used.

Figure 3 shows an alternate means of furnace control by which other variables are measured and controlled. This system may be operated with all the elements as shown or some of the nner` corrections maybe eliminated, depending upon the degree of control desired.

With the arrangement shown in Figure 3, the diierential-pressure controller lil may be used to directly regulate or by interlocking with other controllers may lregulate combinations of valves or other corrective devices shown as required to maintain the pressure drop across the furnace at desired values. For example, since the pressure `drop is aiected by humidity, density, blower speedV or volume rof air, and temperature of the blast, `the controller may regulate these quantitiesidirectly or indirectly by interlocking or cascade operation.

vTo further describe oneV of these alternate methods for example, the controller iii in AFigure 3, can regulate the flow cfa coolingor heating fluid or gas in such manner as to cause the furnace to cool or get hotter, by (c) injecting moisture into or removing moisture from the blast by directly or indirectly regulating humiditycontrolequipment ,42 or., (o) regulating the cold air mixing valve 32, so as to affect the hot-blast temperatureor, (c) by combining the regulating actionso (a) and (b) into a more exible control. Regulating any or all Yof these variables will affect the pressure drop.

Under the scheme just described, should the pressure drop increase because the furnace runs too hot, for example, controller le would move the cold-air mixing valve 32 to a more open position, or alternately, particularly if the cold-air mixing valve is too small, as is the case in many old furnaces, the controller i3 would, in addition, inject moisture in theform oi steam or Water spray by the humidity control equipment 42. This cooling of the blast and furnace stock will permit the passage of greater mass rate of air through the saine voids in the stock. Alternately, the steam valve in humidity controller 42 may be used in combination with the cold-air mixing valve 32 in such manner that moisture will be injected only when cooling is required. The cold-air valve 32 may be operated only to cut oli cold air so as to raise the hot-blast temperature or it may be operated in conjunction with moisture injection for cooling and without moisture injection when hotter blast air is required. This means of operating two valves 'is well known in the art of automatic control and presents no difficulty from an operational standpoint. As an alternate to the method of moisture injection or humidity control, the controller 42 can be moved closer to the furnace stack and controller it can regulate the conditioning of the air by injecting relatively inert quenching gases to alter the chemical composition of the blast gases and cause the furnace to become more or less heated or cooled. Nitrogenor gases high in carbon monoxide, for example, would have a cooling eiect at the bottom oi the furnace, while a gas composition containing carbon dioxide would dissociate because oi the high hearth temperatures, and would tend to cool the furnace by the endothermic reaction, and would affect the pressure drop.

In recent years there has been much discussion of using oxygen to enrich the air blast The effect of injecting oxygen to enrich the blast, I

believe, would be to increase the hearth temperature but less blast would be required, Vif it were enriched with oxygen, to maintain a given reducing rate Vthan if no enriching oxygen were used. 'The volume of reactant gases corresponding to the reducing rate would be less with enriched blast thanwith ordinary blast with normal oxygen, so that the pressure-drop through-the furnace 'may be considerably decreased. The net effect on .pressures-drop due to the hotter hearth and the :smaller volume of reactant gases will depend upon the ratio of oxygen to blast air. It can vbe seen then, that the controller l0 can be used to regulate the flow of oxygen andother "gases to maintain the pressureedrop below the Vaid the reducing action in the furnace `in the `'case of gases'rich in carbon `monoxide or hydrogen.

' Should proportional .type of control not be desired, this Acontroller may be equipped for on-oi type of control 'so as to give corrective action only when the pressure diierential reaches predetermined limits above or below the predetermined point. It can be seen that this type of control would not necessarily be continuous and might be advantageous where a steam saving is desired at the sacrifice of some control accuracy.

In case temperature compensation for density changes is desired, as when it is desired to obtain more accurate blast-air or exit-gas ilows, this may be accomplished by maintaining the temperature constant as by controlling the hot-blast temperature by use of the hot-blast controller and a cold-.air mixing valve, or by cooling the top-gas temperature to a constant lower value than would otherwise normally exist. Alternately,.as in the case of pressure-compensation, a temperature-sensing device can transmit a loading .force or impulse to a temperature-compensated diierential-pressure manometer similar to that which .was described for pressure cornpensation but having the compensation linkages inverted. -Such measuring instruments are commercially available and are fairly standard.

In the 'same manner a sample of hot blast or discharge gases can be piped to a density or specific-gravity meter which in turn may apply a compensating loading force or pressure impulse to the compensated diierential-pressure controller.

Referring to Figure 3, the pressure-dinerential controller I0 is connected by pipe lines I5 and I6 to measure the pressure-drop across the furnace, as between taps il and I8. This controller can operate valve power units 3i! or 20 or 4l, being interlocked by suitable transfer switches and interlocks 43 through 46, so that it may operate any of the valves. If it is desired, controller I0 may operate either the blast-air conditioning controller 42 or the blower-volume controller 41 by suitable setting of the transfer switch 43 and similar switches 48 and 49.

The electrical interlock switch 22 serves during opening of the bells to prevent the controller l0 from operating valves during this period. Circuit 24 connects switch 22 with power-operated valves 25 and interlocks 50, 5I and 52.

A top-gas temperature controller 53 is connected to a sensitive detector 34. Controller 53 is interlocked with controller l0 through interlock 43 so that it may operate valve 54 supplying spray nozzles 55 or, if desired, correct the controller I for temperature Variations.

An absolute humidity controller 56 operates from measuring mechanism 51 through two connections 58 and by means of connections 59 sends correcting impulses to humidity controllerv 42.

An air-blast flow-meter controller 60 shown also in Figure 1 measures air flow through a primary metering element by means of pipe lines 6l and operates the regulator 4l on the blowing engine by means of correcting impulse line 62. Controller I0 and controller 60 can be interlocked for cascade operation, as indicated by line 63.

A gas-volume controller E4 measures gas flow by means of a primary flow-metering element in downcomer 9 and impulse lines 65. If desired, it can operate valve operator 4I by means of impulse-correcting line 66 or, alternately, by means of interlock connection 61, and setting transfer switches 43 and 46 as required, it can be operated in cascade with controller I0.

A top-pressure controller 68 is provided in case a non-compensated differential-pressure controller is used, to measure the gas pressure in downcomer 9 and operate Valve I3 as required to keep the gas pressure constant at the top of the furnace.

A hot-blast temperature controller 69 operates from thermocouple 30 and circuit 29. Correcting impulses may be sent to either cold-air mixer valve 32 over circuit 3l, or over a circuit 104for cascade connection to controller lo by proper setting of-transfer switches 43 and 45. Temperatureand pressure-compensation mechanisms are usually incorporated in the differential-pressure controllers and controller I3 may be either an uncompensated or a pressure-compensated instrument. No extra outside pressure-impulse lines are needed since one or the other of the two pressure lines l5, I6 would also operate the pressure compensator.

As an alternate method of gas-density control a specific-gravity controller may be used to correct the differential controller for density change by applying a loading impulse, such as an air pressure to a compensating element in the differential controller I0. The specic-gravity controller would be used as an alternate to a pressure-compensated controller where ner corrections are desired than is possible with temperature or pressure correction only.

It will be appreciated that the various permutations and combinations described above affect the actual gaseous flow, without referral to standard conditions, in one or more parts of the new system by means of which the pressuredrop is controlled and maintained at a constant value or otherwise below the critical differential pressure value. Thus, a change in the gaseous flow at any particular part may impart a corrective change in the actual volume or in the rate of flow or in a combination of the two in such one or more parts of the new system.

Although I have confined my description to the iron blast furnace it is to be understood that pressure-drop control can be applied equally well to non-ferrous smelting furnaces which are similar to the iron blast furnace, and to certain types of gas generators which resemble blast furnaces in construction, using the same method of charging solid fuel and using counter-current flow of blast air, but which do not charge any ilux or ore solids. Ihe physical principles governing the orderly descent ofthe solid charge,

however, is the same as in the iron blast furnace.

Advantages of this controller may be summed up as follows:

1. Better furnace efliciency through more regular control of stock and gas flows, better Working furnace, less hangings, slips, and channelling.

2. Decreased dust losses as result of less channelling and slip-s.

3. Improved fuel economy because of better gas distribution; permits use of highest possible blast temperatures and drier air on dry blast furnaces.

4. Less trouble due to poor coke and fine ores. Finer ores can be used than are now being used and with less attention to sizing.

5. Automatic control anticipates slips and applies corrective action in time, as contrasted to corrective measures being applied after slip occurs as under manual control methods.

6. Automatic pressure-drop control, by giving better and slower gas-velocity control through the center of the furnace, will put the operation of large-diameter furnaces on the same basisl as smal-diameter furnaces, particularly in regard to the relative output of iron per square foot of hearth area. Past experience indicates that most large-diameter furnaces will not take as much blast per square foot of hearth area as smaller furnaces, because of the poorer distribution of gas velocities. Pressure-drop control will reduce this difference.

7. Increased output will be more easily obtained with differential-pressure control.

Although I have illustrated and described but a preferred practice and various embodimentsof the invention, it will be recognized thatchanges in the construction and procedure may be made without departing from the spirit of the invention or the scope of the appended' claims.

I claim:

1. In a method of operating a blast furnace or the like having a shaft repeatedly charged with a heterogeneous stock of material, the steps comprising, blowing a heated atmosphere upward through said stock, removing reaction gases from the top of said furnace, measuring the static pressure of said heated atmosphere adjacent the bottom of said stock, measuring the static pressure of said reaction gases adjacent the top of said stock, controlling the difference between said static pressures to a value below that predetermined value at which said furnace has a tendency to generate slipping conditions therein, and effecting said controlling by selective variation of at least one of the temperature, pressure and rate of flow relationship-s of said heated atmosphere and said reaction gases.

2. In a method of operating 'a blast furnace system having a hearth, a b'osh and a stack', means for supplying a heterogeneous charge of solid fuel, flux and ore adjacent the top of the stack, means for supplying blast air under pressure adjacent the hearth, and means for taking off gaseous products adjacent the top of the stack, the steps of feeding said charge to the furnace, maintaining it substantially filled, substantially continuously supplying blast air, and taking off gaseous products, the air and evolved gaseous products traveling upwardly through the interstices of the stock, periodically determining the pressure drop over at least the major portion of the stack, and regulating the gaseous flow in the system in accordance with such determination so as to maintain the pressure drop below a differential conducive to disorderly downward movement ofthe stock.

said determination so as to maintain said pressure. drop below a pressure differential conducive to the interruption of the orderly downward movement of the stock.

11,. In combination with a blast furnace systern' having a hearth, a bosh and a stack, means for supplying a heterogeneous charge of stock adjacent the top of the stack, means for supplyingA blast air under pressure adjacent the hearth, means for taking o gaseous products adjacent the top of the st-ack, the apparatus comprising, pressure responsive means connected axially across at least a substantial portion of the stack and adapted to determine the pressure drop generally across the stock, and means for Varying the gaseous products from the furnace in accordance "with said determination so as to maintain said pressure drop below a pressure differential conducive to the interruption of the orderly downward movement of the stock.

12. In combination with a blast furnacev system having a hearth, a bosh and a stack, means for supplying a heterogeneous charge of stock adjacent the top of the stack, means for supplying blast air under pressure -adjacent the hearth, means for taking off gaseous products adjacent the top of the stack, the apparatus comprising,

pressure responsive means connected axially across at least a substantial portion of the stack 1 and adapted to determine the pressure drop generally across the stack, and means for varying the pressure of the blast air relative to the pressure of the gaseous products in accordance with said determination so as to maintain said pressure drop below a pressure diierential conducive to reaction gases from the top of said furnace,y

measuring the static pressure of said blast air,

measuring the static pressure of said reaction.

gases, controlling the diierence between said static pressures to a substantially constant value below that predetermined value at which said furnace has a tendency to generate hanging and slipping conditions therein, and e'iecting said controlling by selective variation of at least one of the furnace humidity, gas density, blast air volume and blast air temperature relationships.

14. In a method of operating a blast furnace system having a hearth, a bosh and a stack, means for supplying a heterogeneous charge of stock adjacent the top of the stack, means for supplying blast air under pressure adjacent the hearth, and means for taking off gaseous prodv, ucts adjacent the top of the stack, the steps of feeding said charge to the furnace, maintaining it substantially lled, substantially continuously supplying blast air, and taking off gaseous products, the air and evolved gaseous products traveling upwardly through the voids of the stock, substantially continuousiy determining the pressure drop over at least the major portion of the stack, substantially continuously regulating the gaseous iiow in the system in accordance with such determination so as to maintain the pressure drop below a differential value conducive to disorderly downward movement of the stock, and locking the valve regulating the take-01T of said evolved gaseous products during said feeding of said charge.

OTTO J. LEONE.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,338,899 Brown et al. May 4, 1920 1,523,414 Gibson Jan. 20, 1925 1,677,664 Stevens July 17, 1928 1,683,714 Emmel et a1 Sept. 11, 1928 1,695,472 Roucka Dec. 18, 1928 1,716,572 Wright June 11, 1929 1,858,972 Snyder May 17, 1932 1,952,004 Weigel Mar. 20, 1934 2,131,031 Avery Sept. 27, 1938 2,395,385 Green et al. Feb. 19, 1946 2,418,673 Sinclair et al. Apr. 8, 1947 2,447,306 Bailey Apr. 7, 1948

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