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Publication numberUS3719811 A
Publication typeGrant
Publication dateMar 6, 1973
Filing dateAug 25, 1971
Priority dateAug 25, 1971
Also published asCA963557A1
Publication numberUS 3719811 A, US 3719811A, US-A-3719811, US3719811 A, US3719811A
InventorsMunson W
Original AssigneeWestinghouse Electric Corp
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Blast furnace computer control utilizing feedback corrective signals
US 3719811 A
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Description  (OCR text may contain errors)

Unite I States Patent Munson March 6, 1973 BLAST FURNACE COMPUTER CONTROL UTILIZING FEEDBACK CORRECTIVE SIGNALS Inventor: William A. Munson, Williamsville,

Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa.

Filed: Aug. 25, 1971 Appl. No.: 174,650

US. Cl ..235/l5l.12, 75/41 Int. Cl. ..C2lb 7/00 Field of Search 75/41; 444/938, 943, 944,

962.2, 444/940, 934, 923; 235/l5l.l, 151.12

References Cited OTHER PUBLICATIONS Some aspects of predicting blast-furnace behavior. by Hodge in Journal of the Iron and Steel Institute Sept. 1961, pp. 6-15 Primary Examiner-Eugene G. Botz Att0rneyF. H. Henson et a1.

[57] ABSTRACT A computer control system for blast furnaces designed to maintain a proper material balance within the blast furnace, taking into account outputs including dust losses, top gas analysis, hot metal analysis and slag analysis. These are converted into feedback signals which correct control signals for the blast furnace process based upon theoretical calculations, thereby providing a complete closed loop control system.

7 Claims, 8 Drawing Figures OPERATOR'S CONSOLE 70 MANUAL INPUT I20 I22 I24 I30 OKE ORE STONE TAL TOP H T LAST A GAS DUST DI IONS ENSA I36 w essential E WNW I CSIBIPEN S ATE FOR ORE b IN LINESTONEE MISC. MATERIALS COKE-PROGRAM I COM E I ToPeAs ANALYSIS P OGRAM-COM PI; ATE F c fiIINJgEEAL" MA E New PRoeRA M H20 ADDITIONS l PROGRAM IMATERIALS BALANCE PROGRAM COKE INDUSTER I48 08 INPUT L661 OUTPUT Lee INPUT [f 351% H Ill 8 LL OPERATING 96-. MECH PATENTEIIIIIII 61973 SHEET 2 OF 5 ,ITO TOTAL COKE INPUT THIS LOAD FIG2 ,Isz ,ISS ,ISS SAMPLE OOMPUTE CALCULATE DUST COKE COKE RATE LOSS LOSS {I64 SISISE COKE [I58 [I60 AVERAGE DETERMINE FROM op GAS y J$ MOISTURE MOISTURE ANALYSIS OGRAM IO LOADS CORRECTION FI l52 ,I54 1 ,I56 I, ,172 I ,IT4 ANALYZE CALCULATE CALCULATE COMPENSATE OOMPENSATE COKE DESIRED E REQUIRED FOR DUST FOR TOP COMPOSITION DRY WEIGHT WET WEIGHT LOSS GAS LOSS I80 |50'J LDESlRED DRY WT.- CARBON ,ITS L ,ITS

ACTUAL DETERMINE PREVIOUS LOAD COMPANSATE WEIGHT DESIRED DISCREPANCY PREVIOUS LOAD THIS LOAD ACTUAL STORAGE DISCRE PANCY L DISCREPANCY 76 l I82 88 F M WE$ H SQ S T EM TO VIB ATING ACTUAL LBS. gifi OF COKE O I- l I70 TOTAL ORE INPUT THIS LOAD ,lsz' ,ISS V ,ISS F SAMPLE COMPUTE CALCULATE SINTER ORE ORE RATE LOSS LOSS ,IS4' ANALYZE DUST FOR ORE LOSS ,ISS ,ISO 0 72 AVERAGE DETERMINE E EI'R EE MOISTURE r MOISTURE I I0 LOADS I CORRECTION l ,I52 ,I54 ,I56 ,IT2 ,ITS' ANglYEZE CAkgslillgE C I I I E OOMPENSATE COMPENSATE FOR DUST PREvIOU L AD COMPOSITION DRY WEIGHT wET WEIGHT LOSS DISCREFAN8Y ISOQ I22 i ACTUAL L, DETERMINE PREVIOUS LOAD wEIGHT DESIRED DISCREPANCY TO IBRATINO THIS LOAD ACTUAL STORAGE 0R FEEDER DISCREPANCY 0 FROM ORE WEIGH SYSTEM HA SE73 SHEET 30F 5 I24 DEsIRED wT. C C0 ,M CO H64 (184 [I86 (I88 ANALYZE E EQIEEE P EVSEIS LSED R T TO VIB ATING STONES WEIGHT DIsCREPANcY I FESJER (I92 I90, F f STONES ACTUAL DETERMINE STORE WEIGHT DEsIRED THIS LOAD ACTUAL DISCREPANCY DISCREPANCY FROM sTONE WEIGH FIGS v l96 ,2I4 ,2Is FUEL sAMPLE SAMPLE FOR SUPPLEMENT TOP GAS BLEEDER INPUT RATE GAS Loss I98 ,2I2 I ,2Ia COKE ANALYZE CORRECT INPUT TOP GAS GAS RATE FOR PRODUCED BLEEDER LOSS ,2OO L' I ,220 HO I AgT COMPARE CggAgElEiATE R 2 CALCULATED KY MOISTURE o8\ I TO ACTUAL BELLS,ETC.

CALCULATE K L, TOP GAS ,202 I Q Q Q E24 {222 op CALCULATE TOTAL WATER JAQ- GAS ADDITION USAGE FLOW 204 I 228 DRE 4 CORRECTION. COMPARE INPUT To COKE ACTUAL TO INPUT CALCULATED ,206 FLOW STONE INPUT I PSIDPB I I ST TO BLOCK I74 FLOW RATE FIG.2

-99 HO TO T B SY Eg II FIG.I

PATENTED R 6 973 SHEU 4 0F 5 ACTUAL DEPOSIT WEIGHT 7 QJ T ON LARGE COKE CARS BELL L244 236 I I ACTUAL I LARGE WEIGHT BELL FULL '246 ORE I :,250 23m STOP NO cAN FURNACE ACCEPT LARGE AcTuAL FILLING WEIGHT BELL DUMP? STONES YES I we? ACTUAL BELL 1252 WEIGHT MISC.

I I I FIG.6 CALCULATE ACTUAL VOLUME ADDED I256 ffi DETERMIZ? figs TEMP RATE SEQUENCE r INCREASE 1 OF LOADS I TEMP. I OR TO ADD wATER STORAGE ECREASE MANUAL INPUT I I 258 262 266 274 272 I CALCULATE I Is TEMP. DETERMINE DETERMINE I $33225 BBB? BF IIIIJ R ER TEMP. CHANGE INCREiSING WATER PATTERN & WHEN 254 2621?? 270 I TOP DEcREAsE L GAS gg 7 WATER TEMP DECREASING 'NPUT FROM H6 PATEN'IEUHAR ems SHEET 5 or 5 NORMAL COKE CONTENT FROM STORAGE W T l U U l l NORMAL ORE CONTENT FROM STORAGE COMPARATOR T COMPARATOR 276 DETERMINE COKE CONTENT 27s DETERMINE ORE CONTENT BLAST FURNACE COMPUTER CONTROL UTILIZING FEEDBACK CORRECTIVE SIGNALS BACKGROUND OF THE INVENTION In the past, computer control systems have been devised for blast furnace operations, but these were based entirely upon a mathematical model which included such parameters as heat and material balances as derived from theoretical calculations. Most of these systems did not monitor the actual output conditions of the furnace to correct for deviations from expected performance. As a result, such systems were not altogether accurate and could not optimize furnace performance.

As an example, prior art blast furnace computer control systems do not monitor the amount of coke and iron ore which pass off through the gas gas uptakes as dust. This dust is collected and its weight can be used to estimate the loss in a computer program. However, it has been found that the actual coke dust loss, for example, can vary from one charge to another in the range of about -15 percent by weight. Naturally, this variation is actual loss, which is not taken into account in the theoretical calculations used in prior art computer control systems, can affect the efficiency of the blast furnace operation. Likewise, the quantities of carbon monoxide, carbon dioxide and other gases in the top gas leaving the furnace will affect the efficiency of the process, but were not taken into account in prior art computer control systems, nor were the actual analyses of the pig iron and slag produced.

SUMMARY OF THE INVENTION In the operation of a blast furnace, it is known from experience that in order to produce molten pig iron efficiently of the desired chemical composition, certain specified weights of iron ore, coke and limestone should be charged into the furnace. These specified weights of charged materials should result in specified weights of molten iron, slag, top gas and top dust. Furthermore, the top dust and gas should have certain specified compositions for efficient iron production. If, for example, the carbon monoxide and carbon dioxide in the top gas decrease, it is an indication that possibly not enough coke has been added or that an excessive amount of coke has been lost as dust. Similarly, excessive losses of iron ore as dust will require the addition of additional amounts of this material in order to balance the blast furnace operation.

In accordance with the present invention, the weight and composition of the top gas and top dust are continually monitored to produce electrical signals for computer programs designed to compensate for offnormal variations.

In the coke control program, for example, the carbon content of the coke charged into the furnace is compared with the desired carbon input as determined by an operator to derive a calculated desired dry weight of carbon to be fed into the furnace. This value must then be modified depending upon the percentage of moisture in the coke and also modified to compensate for off-normal dust losses and off-normal quantities of carbon monoxide or carbon dioxide in the top gas. The resulting value is then used to determine the desired weight of coke to be charged into the furnace.

The general control procedure outlined above for additions of coke can also be used for the control of additions of iron ore, limestone and miscellaneous material such as mill scale, scrap, slag and the like. However, in the case of iron ore, no correction need be introduced for variations in top gas composition since the amount of sinter itself has little or no effect upon the carbon content or the BTU content of the top gas. The moisture and dust rate compensations, however, are required for sinter. Limestone (i.e., stone) additions do not require compensation for moisture or for variations in top dust since these are normally constant for limestone. Similarly, the miscellaneous materials charged into the furnace ordinarily do not require compensation for moisture, dust or top gas variations.

In order to provide a program for top gas analysis, the composition of the top gas is initially calculated from the inputs to the furnace including hot blast enrichment, hot blast rate and the moisture input to the furnace. This calculated top gas analysis is then compared with the actual top gas analysis, continually measured, to produce a correction factor which is, in turn, applied to the coke control program for varying the amount of coke charged into the furnace if the top gas analysis, and particularly the carbon monoxide and carbon dioxide contents, should become off-normal. In addition, the actual top gas flow rate is analyzed and compared with calculated flow rate; and if the two should vary, a correction factor is produced which generates an electrical signal for varying the hot blast rate. The control program further includes a material input program which, from the actual weights of materials fed into a skip car, generates a command signal to cause the skip car to travel to the top of the furnace where its contents are deposited on a large bell. When the large bell is full, the program then checks to determine whether the furnace can accept the large bell dump from a consideration of the material height within the furnace. If the furnace can accept the large bell dump, the large bell is actuated to dump the charged materials into the furnace. If not, a command signal is generated to stop the charging of materials into the top of the furnace.

The control system also includes a computer program for determining, from a consideration of whether the top gas temperature is increasing or decreasing, whether to add water at the top of the furnace for cooling purposes and also determines those skip car loads to which the water should be added. A determination of whether the top gas temperature is increasing is derived by periodically sampling the top gas temperature and storing these temperatures for comparison with subsequent temperature measurements.

Finally, the control system includes a complete materials balance program which compares the calculated analysis and weights of slag and pig iron with the actual weights and analysis. If the actual calculated weights should vary, corrective action is taken to increase or decrease the amounts of materials fed into the furnace.

DESCRIPTION OF PREFERRED EMBODIMENTS The above and other objects and features of the invention will become apparent from the following detailed description taken in connection with the accompanying drawings which form a part of this specification, and in which:

FIG. 1 is a schematic illustration of the overall computer control system of the invention;

FIG. 2 is a flow diagram of the coke control program of the invention;

1 FIG. 3 is a flow diagram of the ore control program of the invention;

FIG. 4 is a flow diagram of the stone control program of the invention;

FIG. 5 is a flow diagram of the top gas control system of the invention;

FIG. 6 is a flow diagram of the material input control system of the invention;

FIG. 7 is a flow diagram for the water addition control system of the invention; and

FIG. 8 schematically illustrates a simplified system for controlling additions of coke and ore as a function of top gas and dust analysis.

GENERAL DESCRIPTION OF BLAST FURNACE AND ITS OPERATION With reference now to the drawings, and particularly to FIG. 1, there is shown a blast furnace 10 having a stack portion 12, a bosh portion 14 and a hearth portion 16. Surrounding the bosh portion 14 is the usual bustle pipe 18 connected to tuyeres 20 which direct a hot blast into the hearth portion 16. The bustle pipe 18, in turn, is connected to a hot blast main 22.

Above the stack portion 12 is a top portion which includes a large bell 24. Above the large bell 24 is a small bell 26 at the bottom of a receiving hopper 28 for ore, coke and limestone to be charged into the furnace. The materials to be charged into the furnace are transported by skip cars 30 which travel on a skip bridge 32 from a lower position where materials are charged into the skip cars to an upper position where the skip car automatically dumps its contents into the receiving hopper 28. After the materials are dumped into the receiving hopper 28, the small bell 26 can be moved downwardly, whereby the materials drop down onto the large bell 24. Thereafter, the small bell 26 is closed and the large bell 24 opened, depending upon other considerations, to dump the charge into the stack portion 12 where the hot blast of air from the tuyeres 20, passing upwardly through the coke, limestone and iron ore reduce the iron oxide to molten iron which drips down into the hearth portion 16 where it can be removed through a tap hole. In the reduction process, slag is also formed which floats on top of the molten iron and can be removed also.

Communicating with the interior of the stack portion 12 above the charge within the furnace are gas uptakes 34 both of which are connected to a downcomer 36 leading to a dust collector or catcher, not shown. At the top of each gas uptake 34 is a bleeder valve 38 which permits a portion of the gases generated in the reduction process to escape into the atmosphere. The major portion of the gases, and the coke and iron ore dust which occur when the charge is dropped by the lower bell 24, pass through the downcomer 36 to the aforesaid dust collector and gas washing equipment. The recovered gas is then used as a fuel to heat the brick checkerwork in blast furnace stoves which, in turn, are used to heat air for the hot blast forced into the bottom of the furnace through the tuyeres 20. The amount of dust inherently generated when the charge is dumped into the furnace from the large bell 24 will depend upon the characteristics of the materials charged into the furnace as well as the moisture content and can vary anywhere from 10-15 percent of the total weight of coke and ore charged into the furnace.

Essentially, the blast furnace process consists of charging iron ore, coke and stones (i.e., limestone and dolomite) into the top of the furnace and blowing heated air into the bottom. The function of the ore, of course, is to supply the element iron which, in turn, represents the major portion of the pig iron produced. The ore is usually in the form of an oxide, either Fe O or Fe O Other iron-bearing materials charged into the furnace as miscellaneous materials include mill scale, sinter, slag from an open-hearth furnace and scrap. The scale is a by-product of hot rolling operations, which drops from the heated strip as it passes through the rolls. Sinter is blast furnace flue dust, which has passed through the uptakes 34 and downcomer 36 and which has been agglomerated to form a coarse granular material. Open-hearth slag is a by-product from a steelmaking process containing about 25 percent iron and an excess of bases over acids, thereby replacing a certain quantity of basic fluxes, but increasing somewhat the total quantity of slag per ton of iron.

The function of the coke charged into the blast furnace is twofold. First, it supplies enough heat to attain the necessary temperature for the metallurgical reducing reactions to take place. Secondly, it supplies the reducing agent for the process of reducing or removing the oxygen from the iron oxide in the ore. Sufficient heat is necessary to reduce and melt the iron, the manganese and the silicon and to flux and melt the gang of the ore and the ash of the coke. The incandescent carbon of the coke is inherently a strong reducing agent and accounts for about 20 percent of the reduction taking place in the furnace. The other 80 percent of the reduction results from the combining of oxygen in and hot blast with the carbon of the coke to form carbon monoxide which is also a strong reducing agent. In this process, the carbon monoxide combines with the iron oxide to form iron and carbon dioxide.

The function of the limestone and dolomite is to form a fluid slag of a composition which restrict the other elements entering the pig iron. These other elements, in turn, control the mechanical and chemical properties of the pig iron.

Coke, ore, stones and miscellaneous materials'to be charged into the furnace are stored in bins 40, 42, 44

and 46, respectively. Each of the bins 40-46 is provided with a vibrating feeder 48 controlled by one of four control mechanisms 50-56. The vibrating feeders 48 deposit the materials onto conveyor belts 58; and as the materials pass along the conveyor belts 58, they are weighed by weighing elements 60. The control mechanisms 50-56 operate in conjunction with the vibrating feeders 48 to control the conveyor belts 58 whereby a desired amount of granular material may be deposited on the conveyor belt, weighed, and then conveyed into a transfer car or directly into the skip car 30 which is caused to ascend the skip bridge 32 by means of a skip drive 62, all in accordance with usual practice.

GENERAL DESCRIPTION OF COMPUTER CONTROL OF THE INVENTION AND ITS RELATION TO SENSORS ON BLAST FURNACE The computer control system of the present invention includes a general purpose computer, generally indicated by the reference numeral 64 and having a main signal input panel 66, a signal output panel 68 and an operators console 70 where certain inputs are fed to the computer manually. The input signals to the computer include signals on leads 72 and 73 proportional to the moisture content of the coke and ore in bins 40 and 42. The moisture contents may be derived from moisture detectors 74 of the type manufactured by Kay-Ray, Inc. of Palatine, Illinois and sold as their Model 1000C. Essentially, it is a gamma and beta detector which detects hydrogen and gives an output signal proportional to percent moisture.

Additional inputs to the computer on leads 76 are derived from the weighing devices 60 and are proportional to the actual weights of coke, ore, stones and miscellaneous materials fed into the blast furnace through the skip car system. A signal from flow meter 78 on the hot blast main 22 is applied via lead 80 to the input panel 66 and is proportional to the hot blast flow rate. An additional input is from flow meter 106 on lead 102 comprising a signal proportional to the rate of fuel enrichment added to the hot blast. Finally, a signal from a stock indicator 84, proportional to the level of materials in the blast furnace, is applied through lead 86 to the input panel 66. The stock indicator 84 comprises a rod of steel or the like passing through an opening in the top of the furnace so that one end rests upon the stock. The other end is usually attached to a steel able that leads to the stock house or a cast house below; however these details are not shown herein, it being understood that suitable means will be provided for generating an electrical signal on lead 86 proportional to the height of the materials within the furnace.

The output signals from the computer 64 at panel 68 include signals on leads 88 for controlling the vibrating feeders 48 and the conveyor belts 58 whereby desired weights of coke, ore, stone and miscellaneous materials are fed into the furnace. A signal, or signals, on line 90 control the skip drive 62 to cause the skip cars 30 to ascend the skip bridge 32. Other input signals include a signal on lead 92 for controlling the bell operating mechanism 94 which is connected to the small and large bells 26 and 24, respectively, through a suitable mechanical linkage, schematically indicated at 96. A

signal on lead 98 controls valve 100 for supplying water to the skip cars 30. This water, which is deposited in the skip cars 30 and transported to the top of the furnace, is used to cool the top when an overheating condition occurs as will be explained hereinafter in connection with the computer programs. Finally, a signal on lead 99 controls the hot blast system 101 for applying the hot blast to the furnace.

In addition to the input panel 66 for the computer 64, there is shown, for purposes of emphasis, a separate feedback input panel 109 to which leads 110 are connected. One of the leads 110 is connected to a flow meter 112 connected to the bleeder valve assembly 38 whereby the output of the flow meter will be an indication of the quantity of gas being bled off. As will be understood, the showing hereinv is only schematic and it may be necessary to provide flow meters on more than one bleeder valve. The second one of the leads is connected to a temperature sensor 114 which measures the temperature of the top gas coming out of the furnace 10. Still others of the leads 110 are connected to instruments 116 and 118 which determine the flow rates and analysis of top gas and dust passing out of the furnace and into the downcomer 36. The instrument 116 includes a device for measuring the mass flow rate of the dust passing out of the blast furnace and may be of the type shown and described, for example, in Frazer Pat. No. 2,953,681. The device shown in the aforesaid Frazer patent measures only the mass flow rate of entrained particulate material. Accordingly, a separate flow meter for the carrier gas is required in instrument 116. Alternatively, the instrument 116 may be of the type shown in Gibson et al. U.S. Pat. No. 3,408,866 which measures and produces electrical signals proportional to the flow rates of both the carrier gas and the entrained particles. The instrument 118 may be an automatic spectrograph or absorption analyzing system such as that shown in Smith et al. U.S. Pat. No. 3,156,819 for determining the identity and quantities of gases and particles in the gas stream passing through the downcomer 36. As will be understood, the leads 110 are illustrative only and are not intended to imply that only one conductor connects each of the instruments 116 and 118, for example, to the feedback input panel 109. Also fed back to the computer via leads 108 and 111 are electrical signals representing the composition of the iron and slag produced by the furnace. These are sampled periodically and the signals on leads 108 and 111 charged accordingly.

Various input signals are fed to the computer 64 via the operators console 70. These signals represent the desired operating conditions of the furnace as determined by the operator. Normally, the amounts of ore and stone charged per ton of coke are referred to as the furnace burden, the coke being considered constant in amount.

It is known from experience that in order to produce a certain weight of pig iron, specified weights of stone, coke and iron ore will have to be charged into the furnace. Furthermore, with this information, the amount of slag formed, the amount of top gas leaving the furnace and the amount of top dust produced can also be estimated. In a general way, the solution to the burdening problem can he arrived at in the following manner:

From the physical condition of the various ores and the amount of each on hand, their availability, their relative cost and other considerations, the furnaceman first decides the approximate proportions in which it is desirable to use different types of ores. From these proportions, he is able to determine the average composition of the ore mixture in each charge, the size of which he has also decided upon. From this average, he is able to calculate the amount of mixed ore required to produce one pound of pig iron, and the weight of the impurities therein. Then, since his objective is to make one ton of iron with a specific tonnage of coke, or less, he is able to arrive at the total impurities and the ore and coke required to produce one ton of iron. These impurities he separates into acids and bases, and then combines them according to the slag ratio of acid to base which experience has taught is the best to produce the kind of iron desired. This process gives the excess acids which must be fluxed with limestone. From the analysis of stone, he determines the available base, from which the amount of limestone required to flux the excess acids in accordance with the accepted ratio can be found. The next factor considered is the slag volume, or the amount of slag to be made per ton of iron. The slag volume must be within certain limits to be consistent with good furnace production. If the volume of slag is very low, its ability to remove sulfur from the iron may be interfered with seriously; while if it is very high, the fuel consumption will increase above that desirable, because coke must be consumed to furnish the heat necessary to form and fuse the slag. If the slag volume should fall outside the limits which the furnacemans judgment from experience has set for it, he must begin all over again, starting with a different mixture of ores, or different limestone or coke. With new materials, the solution to the problem involves some cut and try work with different combinations of the materials that may be available.

In accordance with the present invention, the foregoing process is followed with the operator computing the desired amounts of coke, ore and other materials to be fed into the furnace. However, here the similarity with the prior art procedures ends. The furnace operator, while calculating the amount of dust and top gas and their constituents in accordance with prior art practices had no way of knowing the actual analysis and, therefore, had to wait until the iron ore was reduced to determine whether his calculations were correct. In the present invention, on the other hand, the quantity and analysis of the top gas and dust are continually monitored by the instruments 112, 114, 116 and 118 and applied to the computer 64 where the variables selected by the blast furnace operator are varied, depending upon operating conditions.

Reverting again to the operators console, the operator will manually enter into the computer'64 electrical signals proportional to the desired weight of coke and its carbon content (lead 120); the desired weight of ore and its composition (lead 222); and the desired weight of stones and their composition (lead 124). From these, the quantity of top gas expected, its composition and the amount of dust expected and its composition are computed and entered as electrical signals on leads 126 and 128. The expected metal tonnage and its composition, and the expected slag tonnage and its composition, are entered as electrical signals on leads 130 and 132. Finally, any expected hot blast additions are entered on lead 134.

The computer 64 is programmed to perform certain computations, one of which is indicated at 136. This is the program, hereinafter described in detail in connection with FIG. 2, which compensates for coke (or, more importantly, the carbon) lost in the dust and top gas. A second program 138 calculates the ore requirement and compensates for ore lost in the dust. The top gas is not taken into account in the ore program since the amount of sinter (resulting from ore dust) will have little or no effect on the carbon content or the BTU content of the top gas. A third program 140 determines the amount of limestone (stones) and miscellaneous materials which are to be fed into the furnace.

The coke program requires an analysis of the top gas to determine excess carbon lost as carbon dioxide or carbon monoxide and, accordingly, a top gas analysis program 142 is included. A fifth program is the material input program 144 which controls the weighing of the materials derived from hoppers 40-46, control the feeding of these materials into the skip cars 30, controls the movement of the skip cars 30, and also determines when the charge on the lower bell 24 is to be dumped.

A water addition program 146 is included to measure the temperature at the top of the furnace and add water when needed. Finally, a materials balance program 148 is included whereby the expected or desired weight of metal and slag and their compositions as determined by the operator via console are checked against actual weights and analyses and corrective action taken if the two are not the same.

COKE COMPENSATION PROGRAM With reference now to FIG. 2, there is shown a flow diagram of the coke program for computer 64. From the desired tonnage of metal to be produced as entered on the operators console 70, the desired dry weight of carbon is calculated and entered into the program at 150. In addition, from the composition of the coke, and particularly its carbon content, as entered at 120, the coke is analyzed at 152 to determine its carbon content. Let us assume, for example, that the coke comprises percent carbon. From this, and the desired dry weight at 150, the desired dry weight of coke is calculated at 154. Once the calculated dry weight has been established at 154, this value must be corrected dependent upon the amount of moisture in the coke. This is illustrated as a calculation for required dry weight, box 156 in the flow diagram of FIG. 2.

The actual moisture percent of the coke is question is determined through the use of the moisture gauge 74, described above in connection with FIG. 1. This moisture content in percent, on lead 72, is averaged for 10 skip loads at 158 and used in block 160 to determine a moisture percent correction value which is used in block 156 as explained above to calculate the required wet weight of coke. As was explained above, when the coke is dumped into the furnace through the large bell 24, relatively large amounts of dust will be created, at least some of which will pass through the uptakes 34 to the downcomer 36. Accordingly, it is necessary to modify the calculated wet weight of coke as determined in block 156 to compensate for the dust loss.

In determining the dust loss, the dust rate is determined by instrument 116 and sampled at block 162 to determine the pounds per hour (or other unit of time) of dust passing through the downcomer 36. This dust will include not only the coke but also sinter and possibly other materials. Accordingly, the dust is analyzed at block 164 (i.e., instrument 118 in FIG. 1) to determine the percentage of the dust comprising coke. This, then is used in block 166 to compute the actual coke dust loss in pounds per hour or other unit of time. This is converted to a percentage as shown by block 168 in the flow diagram of FIG. 2, taking into account the total coke input for a predetermined length of time, such as for a large bell dump as shown by block 170. This calculated percentage of coke lost in the dust is then used in block 172 to determine how much additional coke must be added to compensate for this loss when coke is to be added.

Once it has been determined how much coke is required, taking into account the loss in the dust passing out of the furnace together with the amount of moisture compensation required, it is necessary to check to see whether compensation must be made for any correction due to a top gas analysis as shown at block 174 in the flow diagram of FIG. 2. The method of determining whether compensation must be made from a consideration of the top gas analysis is shown in connection with FIG. and will hereinafter be described in detail. Assuming, however, that compensation has been made for top gas losses, a check is made to see what was the previous load discrepancy as shown by block 176. Compensation for the previous load discrepancy is derived from a location in storage, represented by block 178. The output of block 176, therefore, is a compensated desired total weight of coke taking into account the discrepancies from prior loads, dust losses, top gas analysis and moisture content. A load, incidentally, is not a single skip car load, but a a total calculated desired load based on the amount of iron to be produced over a given time period.

The output of the block 176, in the actual computer circuitry, is converted into an electrical signal which is applied via one of the leads 88 to the vibrating feeder control 50 (FIG. 1) to feed the desired weight of coke into the skip cars 30 and, hence, into the top of the furnace. At the same time, the actual weight of the coke as measured by the weighing devices 60 is applied via a lead 76 back to the program where the actual weight of the total load fed into the furnace is determined at 180. This actual weight is then compared with the desired weight as calculated by the program in block 182 and the discrepancy stored in storage 178 for the next load.

ORE COMPENSATION PROGRAM The ore compensation program shown in FIG. 3 is very similar to that of FIG. 2 and accordingly, elements in FIG. 3 which correspond to those of FIG. 2 are identified by like, primed reference numerals. In this case, however, compensation for top gas loss (block 174 in FIG. 2) is not necessary since the amount of sinter will have little or no effect upon the carbon content or the BTU content of the top gas. However, the moisture compensation and dust rate deviations are still required for sinter and operate similar to that described for coke. In this case, the calculated desired dry weight in block 154 is derived from the analyzed ore composition as fed into the computer along with the desired weight of ore on lead 122 from FIG. 1. Similarly, the output of block 176 comprising the total weight of ore desired for this load is fed to the vibrating feeder control 52 for the ore bin 42; and the actual weight in block 180 is derived from the weighing device 60 for the ore bin.

LIMESTONE AND MISCELLANEOUS MATERIALS PROGRAM The control program shown in FIG. 4 for the addition of stones is much simpler than that for the addition of coke and ore since neither moisture, dust nor top gas corrections are required. The stone is analyzed for its chief constituents which enter into the formation of slag, namely CaCO; and MgCO This occurs a at block 184. This is used in block 186 with the desired weight of CaCO and MgCO from lead 124 connected to the operators console (FIG. 1) to calculate the desired weight of the stones to be fed into the furnace. This calculated desired weight is then compared with the previous load discrepancy at 188 to derive total pounds of stones per load which is fed to the vibrating feeder control 54 for the stone bin 44 shown in FIG. 1. At the same time, the calculated desired weight is compared at 190 with the actual weight of stones for this load from 192 to derive the discrepancy. This discrepancy is stored in storage 194 for comparison with the next load.

The control program, not shown, for miscellaneous materials is similar to that of FIG. 4 except that the miscellaneous materials are ordinarily not analyzed for their composition; and the weight of these materials as dictated by the operator is simply compared with the previous load discrepancy to make any correction.

TOP GAS ANALYSIS PROGRAM With reference now to FIG. 5, the top gas analysis program is shown. The inputs to the program are the hydrocarbon content of enrichment fuels introduced into the hot blast, as derived from flow meter 106 of FIG. 1, and the BTU content of the enrichment gas being used. This latter value can be assumed to be constant, at least for purposes of the present description. This is represented by the block 196 in FIG. 5. Other inputs are the coke input 198, the hot blast rate and moisture content at 200, the amount of water fed into the furnace top 202, the ore input 204 and the stone input 206. The coke input is derived from the program of FIG. 2 while the ore and stone inputs are derived from the programs of FIGS. 3 and 4, respectively. The hot blast rate is derived from flow meter 78 on hot blast main 22; while the moisture content of the hot blast rate is a manual input, which is an approximation based on experience. The amount of water fed into the furnace top at 202 is derived from the program of FIG. 7, hereinafter described.

The various inputs 196-206 are applied to block 208 where the top gas analysis and its rate are calculated from known equations. The carbon content of the top gas is calculated by:

The oxygen content of the top gas (excluding oxygen entering through top water addition) is calculated by hydrogen entering through the top water addition)is calculated by some of this hydrogen exits the furnace in steam. The

steam content of the top gas (excluding steam formed by hydrogen reducing ore) is calculated by hzaJu h2o,tw hlmcoke hzmb MuJ Thus the total hydrogen content in the top gas is calculated by hzJu hzmla NH. and the total oxygen content in the top gas is calculated by o.10 o.10 h2u.tu

EXPLANATION OF SYMBOLS C mole percent N lb-moles/lb-mole iron subscripts w wind hm hot metal fd flue dust f flux fu fuel b burden r removable oxygen tw top water The calculated analysis is compared with the actual analysis in block 210 which, in turn, receives the actual analysis from block 212 via instrument 118 of FIG. 1. If the actual and calculated analyses are not the same, the block 210 generates a correction factor, the function of which will hereinafter be described.

The top gas rate (i.e., of the carrier gas) is also sampled by instrument 116 at 214. This gas rate is modified in block 218 by a signal derived from block 216 (i.e., flow meter 112) to compensate for bleeder gas losses. This corrected gas rate, taking into account any bleeder losses, is then compensated for such other losses as might be experienced due to leaky bell seats, valves and the like as shown by block 220. The correction factor utilized in block 220 is an assumption based upon experience.

Once compensation has been made for all losses, a total gas flow rate results as illustrated by block 222, which is utilized together with the actual top gas analysis from block 212 to calculate in block 224 the total carbon usage. This total actual carbon usage is then modified by the output of block 210 in block 226 to determine if any correction to coke input is needed. Ifa correction to coke input is needed, a signal is applied from block 226 to block 174 in the program of FIG. 2.

In addition, the total gas flow from block 222 is compared against the calculated flow of gas from block 208 as shown in block 228; and this output is treated as a correction, if necessary, to the hot blast flow rate as shown by block 230. This output, in turn, acts as a setpoint correction or set-point value for the hot blast system.

MATERIAL INPUT PROGRAM With reference now to FIG. 6, the material input program is shown. The actual weight of coke for a given load is entered at 232. This is the same value of material obtained in the coke program of FIG. 2, block 176. This material weight, once known, is then sent to the sequence system for controlling transportation of the material to the furnace top at 234. In this portion of the program, determination is made of when to actuate the skip car drive means 62 of FIG. 1 to cause a load of coke or other material to be transported to the furnace top and when to dump it through the furnace top.

Similarly, the actual weight of ore at 236, the actual weight of stones at 238 and the actual weight of miscellaneous materials at 240 are entered into the transport system 234 along with the volumes of these various materials as determined at 242. The volumes are obtained by dividing the actual weights by the specific gravities of the various materials. As will be understood, the volumes are important since a skip car can transport only a specified volume, regardless of its weight. Once a skip car is at the top of the furnace, its contents are dumped onto the large bell 24 of FIG. 1, through the normal procedures of being first dumped onto the small bell 26 and rotated, if necessary, in accordance with a predetermined distributor program and then finally dumped onto the large bell 24.

The next point of information which must be ascertained, prior to the dumping of material into the furnace, is whether the large bell 24 is full. This determination is made at 246 in FIG. 6 and is derived from the total volume of material deposited on the large bell from a consideration of the actual volumes of materials determined at 242. Assuming that the large bell is full, which means that enough loads have been deposited to go ahead and dump in accordance with a predetermined sequence, then the question arises as to whether the furnace itself can actually accept the large bell dump load as shown by block 248. This determination is made via the element 84 in FIG. 1 and its corresponding signal on lead 86 which informs the computer as to whether or not the level of materials in the furnace is such that it can accept a further load. If the answer derived from logic block 248 is No, block 250 signals the skip drive system to stop filling the large bell. If the answer from logic block 240 is Yes, then block 252 actuates the system to dump the large bell into the furnace and acts to continue the filling operation via the skip cars.

WATER ADDITION PROGRAM The program for water additions to the furnace top is shown in FIG. 7. The top gas temperature is sensed as by sensing element 116 in FIG. 1 as represented by the block 254 in FIG. 7. The actual top gas temperature is then compared with the previous top gas temperature, block 256 and block 258, to calculate the rate of top gas temperature change. This, then, is fed to storage, indicated by the block 260. The previous stored value from storage 260 is then compared with the rate of rise, if it is rising, in block 262. It is also compared with the rate of temperature change in block 264 to determine if the temperature rate of rise is decreasing. If it is increasing as indicated by a Yes output from block 262, the program progresses to block 266 where a determination is made as to which loads are to receive water, as determined by a manual input 268 indicating the sequence of loads with which to add water. Similarly, if the output of block 264 is Yes" indicating that the rate of temperature rise is decreasing, a determination is made in block 270 with the information from block 268 to determine how much the water addition should be reduced. Once this is determined, the next step in the program is to determine at block 272 the amount of water to be added and when. If the temperature rate of rise is increasing, the output of logic block 266 is applied to block 274 which asks whether the quantity and pattern of water addition should be changed. This, then, progresses to block 272 where the quantity of water and when it should be added or reduced is determined and is used to control the valve 100 of FIG. 1 which adds water to the skip cars traveling to the top of the blast furnace.

ALTERNATIVE EMBODIMENT OF THE INVENTION With reference now to FIG. 8, a simplified version of the invention is shown wherein a mass flow meter 116 and spectrograph 118 or other gas analysis instrument are again connected to the downcomer 36 for the purpose of determining the rates at which coke and iron ore passing out of the top of the furnace as dust. The signals from the flow meter 116 and spectrograph 118 are applied to a circuit 276 for determining the quantity of coke passing off as dust, and to circuit 278 for determining the quantity of ore passing off as dust. The outputs of the circuits 276 and 278, comprising signals proportional to the actual amounts of coke and ore passing off as dust, are then compared in comparators 280 and 282, respectively, to determine whether the amounts are above or below predetermined normal rates. If the output of circuit 276 is above the predetermined rate for coke, for example, the comparator 280 will generate a signal which is fed back to the vibrating feeder control system 50 for the coke bin 40 to increase the amount of coke fed into the furnace, thereby compensating for the increased coke loss. If the output of the comparator 280 indicates that the dust loss is below normal, then the comparator 280 generates a signal for reducing the amount of coke fed into the system.

Similarly, if the actual rate of ore dust is above normal, the vibrating feeder control system 52 for the ore bin 42 decreases the amount of coke supplied to the blast furnace. Likewise, if the actual amount of dust is below normal, the comparator 282 actuates the vibrating feeder control system 52 to decrease the amount of ore fed to the oven. The general idea, of course, is the same as that described above in connection with the computer control system. That is, feedback signals proportional to actual rates of coke and ore dust loss are fed back to the material supply system for the blast furnace to compensate for variations in dust lost above or below normal.

Although the invention has been shown in connection with certain specific embodiments, it will be readily apparent to those skilled in the art that various changes in form, arrangement of parts and method steps can be made to suit requirements without departing from the spirit and scope of the invention.

I claim as my invention:

1. In the method for controlling a blast furnace, the steps of measuring the rate at which coke dust passes off from the top of the furnace, and controlling the amount of coke fed into the furnace as a function of the dust rate thus measured.

2. In the method for controlling a blast furnace, the steps of measuring the rate at which ore dust passes off from the top of the furnace, and controlling the amount of ore fed into the furnace as a function of the ore dust rate thus measured.

3. In the method for controlling a blast furnace, the steps of measuring the rate at which coke dust passes off from the top of the furnace, measuring the rate at which ore dust passes off from the top of the furnace,

controllin the amount of coke fed into the furnace as a function 0 the coke dust rate thus measured, and controlling the amount of ore fed into the furnace as a function of the ore dust rate thus measured.

4. The method of claim 1 including the step of varying the amount of coke fed into the furnace as a function of the gases present in the top gas passing off from said furnace.

5. The method of claim 3 including the step of varying the amount of coke and ore fed into said blast furnace as a function of the moisture contents thereof.

6. The method of claim 4 including the step of calculating the flow rate and analysis of gases present in the top gas from a consideration of the coke, top water, ore and stone inputs to the furnace, together with the hot blast rate and its moisture content and the enrichment fuels added to the furnace hot blast.

7. The method of claim 6 including the steps of determining the actual flow rate and analysis of the top gas, and comparing the actual values with the calculated values to derive a correction factor for varying the amount of coke fed into the furnace.

Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3853539 *Mar 2, 1973Dec 10, 1974Sumitomo Metal IndMethod for controlling the blast furnace condition
US4158562 *Apr 26, 1978Jun 19, 1979Betz Laboratories, Inc.Evaluating carbon content of off-gases
US4227921 *Feb 12, 1979Oct 14, 1980Sumitomo Kinzoku Kogyo Kabushiki KaishaMethod of controlling a blast furnace operation
US4273312 *Mar 22, 1979Jun 16, 1981Dravo CorporationMethod of process off-gas control
US4421553 *Mar 24, 1981Dec 20, 1983Centre De Recherches MetallurgiquesProcess for operating a blast furnace
US4432790 *Jun 23, 1982Feb 21, 1984Bethlehem Steel CorporationBlast furnace control method
US5690717 *Mar 29, 1995Nov 25, 1997Iron Carbide Holdings, Ltd.Iron carbide process
US5804156 *Jul 19, 1996Sep 8, 1998Iron Carbide Holdings, Ltd.Large scale production in a fluid bed reactor; controlling temperature, pressure so that hydrogen concentration is above equilibrium concentration.
US6165249 *Aug 20, 1997Dec 26, 2000Iron Carbide Holdings, Ltd.Iron carbide process
US6171364Mar 21, 1997Jan 9, 2001Steel Technology CorporationMethod for stable operation of a smelter reactor
US6328946Feb 8, 1999Dec 11, 2001Iron Carbide Holdings, Ltd.Two step process for the conversion of iron oxide into iron carbide using gas recycle
US6428763Mar 22, 2000Aug 6, 2002Iron Carbide Holdings, Ltd.Multistage reduction of magnetite or hematite using hydrogen to form iron, then carbiding
Classifications
U.S. Classification700/274, 266/80, 75/385, 75/387, 75/468
International ClassificationC21B7/24
Cooperative ClassificationC21B7/24
European ClassificationC21B7/24