US3148973A

US3148973A - Iron ore reduction process

Info

Publication number: US3148973A
Application number: US90370A
Authority: US
Inventors: Michael O Holowaty; Frank W Luerssen
Original assignee: Inland Steel Co
Current assignee: Inland Steel Co
Priority date: 1961-02-20
Filing date: 1961-02-20
Publication date: 1964-09-15
Anticipated expiration: 1981-09-15

Description

P 1964 M. o. HOLOWATY ETAL 3,148,973

IRON DRE REDUCTION PROCESS Filed Feb. 20, 1961 Michael 5%??2315 rssen United States Patent 3,148,973 IRON ORE REDUCTIQN PROCESS Michael 0. Hoiowaty, Gary, and Frank W. Luerssen,

Munster, Ind, assignors to Inland Steel Company, Chicago, 111., a corporation of Delaware Filed Feb. 20, 1961, Ser. No. 90,370 7 Claims. (Cl. 75-41) This invention relates to a novel and improved process and apparatus for effecting reduction of iron ore. More particularly, the invention relates to a novel combined coking and blast furnace operation.

In the conventional blast furnace operation a mixture of iron ore, fuel (coke), and flux (limestone or dolomite) is charged into the top of the furnace and heated air is blown upwardly through the charge from the bottom of the furnace. The function of the coke in the charge is two-fold: first, to supply enough heat to attain the necessary temperature for the metallurgical reactions to take place, and second, to supply the reducing agent for the process. Heretofore, it has been considered that the only satisfactory fuel for use in a conventional blast furnace operation is metallurgical coke which possesses sufficient strength to support the column of solids in the furnace.

Accordingly, the usual blast furnace operation has involved completely separate and independent coking facilities in order to produce the coke to be charged to the blast furnace along with iron ore and flux. For a number of reasons it would be highly advantageous to combine the coking and iron ore reduction steps into a single unitary operation. Obviously, important simplification of equipment and cheaper installation and operating costs could be realized. Furthermore, under present day conditions the supply of good coking coals is rapidly decreasing and the cost of a coke plant is increasing. Thus, it would be extremely advantageous to be able to charge raw coal directly to an iron ore reduction process so as to eliminate the usual separate coking step, particularly if the process could be adapted to use non-coking or non-agglutinating coals.

Accordingly, the primary object of the invention is to provide a novel iron ore reduction process which is adapted to utilize raw coal as a charge material instead of metallurgical coke as in the customary blast furnace process.

A further object of the invention is to provide a novel and highly advantageous combination of coal carbonization, such as occurs in a conventional coke oven, and iron ore reduction, as carried out in a blast furnace.

An additional object of the invention is to provide a novel iron ore reduction process which is capable of utilizing substantially non-coking coal as the charge material in place of metallurgical coke as used in the conventional blast furnace operation.

Another object of the invention is to provide novel apparatus for carrying out a process of the forgoing character.

Other objects and advantages of the invention will become apparent from the subsequent detailed description taken in conjunction with the accompanying drawing which is a generally schematic vertical sectional view of an apparatus comprising one specific embodiment of the invention.

Briefly described, the invention contemplates a unitary shaft type furnace having an upper carbonization or coking section and a lower reducing section. A mixture of subdivided iron oxide ore, raw coal, and limestone or other flux material is introduced into the top of the furnace and passes downwardly by gravity in the usual man- Burners or other suitable sources of external heat are provided for effecting carbonization or coking of the 3,143,973 Patented Sept. 15, 1964 coal during its downward passage through the upper carbonization section of the furnace. As the burden passes downwardly from the carbonization section and thence through the lower reducing section of the furnace, heated air is passed upwardly through the reducing section in generally the same manner as in the conventional blast furnace. Gaseous products are removed from the furnace solely at an intermediate section at the juncture between the carbonization and reducing sections. In other words, the gaseous products of carbonization are withdrawn downwardly through the upper section of the furnace in concurrent relation with the downwardly moving burden and the gaseous products of the reducing step pass upwardly through the reducing section in countercurrent relation with the downwardly moving burden and are combined with the aforementioned carbonization gases for removal as a composite gas stream at the intermediate section of the furnace.

Referring now to the drawing, the invention is illustrated in connection with an upright shaft type furnace identified generally at 10 and having an outermost steel shell 11 and an inner refractory lining 12. The furnace is preferably formed from superimposed upper and lower sections. The upper section, in this instance approximately the upper half of the furnace, is designated as C and comprises a carbonization or coking zone. The lower section, comprising in this instance approximately the lower half of the furnace, is designated at R and comprises an iron ore reduction zone. The upper carbonization section C is preferably supported by means, indicated schematically at 31, so that its lower end is spaced slightly from the upper end of the reduction section R in order to facilitate the removal of gas from the furnace.

In this instance, the lower skirt portion of the section C has a plurality of slots 14 for discharging gas at approximately the mid-point of the furnace.

A circumferential manifold 13 encircles the furnace and encloses the space between the furnace sections, including the slots 14, for collecting and withdrawing gas. The manifold 13 communicates through a pipe 15 with a dust catcher or separator 16 for removing suspended solids. A fan or gas pump 17 is provided in an outlet conduit 18 for effecting withdrawal of the gas stream from the furnace 10.

For the reasons describedbelow, it is preferred to provide a generally conical configuration for the upper carbonization section C so that the latter tapers or enlarges in a downward direction from an upper relatively restricted diameter inlet end portion 19 to a relatively larger diameter bottom end portion at the manifold 13. The lower reducing section R preferably tapers downwardly in the opposite manner from a relatively larger diameter upper end portion at the manifold 13 to a relatively smaller diameter lower end portion 20 at the bottom of the furnace. Thus, the section R corresponds roughly to the bosh portion of a conventional blast furnace.

The usual double bell and hopper arrangement is providedat the top of the furnace, as partially shown at 21, for introducing batches of charge material to the furnace while substantially preventing the escape of gas. A plurality of burners 23 are arranged circumferentially at the upper end of the carbonization section C and are fed by a fuel supply manifold 24 for heating the burden at the top of the furnace. A plurality of oxygen manifolds 25 are provided in vertically spaced relation along the carbonization section C for introducing controlled amounts of an oxygen-containing gas through suitable jets or inlets 26. At the lower reduced diameter end 20 of the reducing section R a plurality of tuyeres 27 are located and are connected to a bustle pipe 28 for supplying heated air to the furnace.

The operation of the furnace is as follows. The charge or burden comprising predetermined quantities of iron oxide ore, raw coal, and flux, such as limestone, is introduced into the upper end 19 of the furnace through the bell and hopper arrangement 21. The top portion of the burden in the furnace is heated by the burners 23 so as to initiate carbonization or coking of the coal in the burden. It will be understood that the furnace is substantially sealed and air-tight at the top so that coking or destructive distillation of the coal takes place in the zone C. It is an important feature of the process that the heat required for the carbonization or coking reactions in the zone C be supplied in such manner that there is an increase in temperature in the direction of movement of the burden through the section C of the furnace. One convenient method of obtaining the desired temperature gradient is by means of the oxygen supply pipes 2545 through which an oxygen-containing gas, such as air or oxygen enriched air, is introduced in controlled quantities so as to effect combustion within the furnace section C of controlled amounts of the gaseous products of the carbonization reactions and possibly also of the carbonaceous solids. By proper regulation of the burners 23-24 and the oxygen supply pipes 25-25, a temperature gradient is readily maintained which may range from about 700 to about 800 F. at the top of the section Cand may be from about 1200 to about 1500 F. at the bottom of the section C.

During the downward movement of the burden through the furnace section C the coal undergoes carbonization or coking so that the coal becomes plastic or fiuid and large quantities of gas, oils, and tars are evolved. Due to the plasticity or fluidity of the coal during carbonization, the coal particles tend to agglomerate with adjoining particles of ore and coal. However, the carbonization gases and tars also move downwardly in concurrent relation with respect to the movement of the burden and this prevents formation of a solid sinter-like layer which would impede proper downward passage of the burden. In addition, the tapered or conical shape of the furnace section C which enlarges downwardly also functions to prevent the carbonized mass from sticking to the walls of the furnace and obstructing downward movement of the burden. As already mentioned, the furnace section C is substantially sealed at the top and the operation of the fan or suction means 17 effects withdrawal of the carbonization gases downwardly through the section C into the gas removal manifold 13. The combined effects of the downward flow of gas in the furnace section C and the increasing temperature gradient from top to bottom in the direction of flow of the burden cooperate to eliminate formation of a stationary tar front thereby insuring trouble-free operation of this section of the furnace. In other words, in the described operation gradual carbonization of the coal in the burden is accomplished without deposition of tars or oils in the critical areas of the furnace. The increasing temperature gradient in a downward direction insures complete volatilization of the tars and oily products of coal carbonization, and the downward flow of gas in the same direction as the burden keeps the tars and oils moving away from the freshly introduced raw coal.

In the lower or reducing section R of the furnace, the operation is essentially the same as in the lower part of a conventional blast furnace. In other words, the burden containing carbonized coal or coke passes directly from the lower end of the section C to the upper end of the section R and is contacted in countercurrent relation with preheated air introduced at the bottom of the section R through the tuyeres 27. The air introduced at the tuyeres- 27 may contain added amounts of oxygen or steam or both as heretofore practiced in connection with blast furnace operations. Thus, the usual blast furnace reactions are accomplished in the section R with partial combustion of the carbonized coke or coal, reduction of the iron oxide in the ore and melting of the reduced iron, and

formation of slag from the gangue constituents of the ore and the flux in the burden. Molten iron is withdrawn through a tap hole 29 and the slag layer may be removed through an outlet 30.

The gaseous products of the reactions occurring in the reducing section R pass into the manifold 13 at the juncture between the furnace sections C and R, and a combined gas stream comprising both the gaseous products of carbonization and reduction is removed through the conduit 18 by means of the fan 17 which effects Withdrawal of the combined gas stream and movement thereof to suitable gas compressors or the like. The pressure in the mid-region of the furnace at the manifold 13 is substantially atmospheric or slightly below atmospheric,

e.g. a few inches of water, but the pressure at both the top and the bottom of the furnace is greater than atmospheric. For example, the pressure at the upper end of section C may be 5-10 psi. whereas the pressure at the bottom of section R may be 10-15 psi. The volume of air employed at the tuyeres 27 will be comparable to the blast volume used in a conventional coke blast furnace. A very significant advantage of the present invention is the fact that it is possible to employ either coking coals or relatively non-coking or non-agglutinating coals in the process as compared with the limited types of coals suitable for use in making metallurgical coke of the quality required in a conventional blast furnace operation.

Although the furnace sections C and, R have been described as carbonization and reduction sections as indicative of the main reactions carried out in these portions of the furnace,'it will be understood that some reduction of iron ore may be accomplished in the upper furnace section C and some carbonization of coal may occur in the lower section R.

The combined gas stream which is removed from the central portion of the furnace it) at the manifold 13 has a high sensible heat content and excellent heating value. The removal of the combined gas stream from the intermediate section of the furnace at a temperature of from about 1200 F. to about 1500 F. results in a furnace gas having a relatively low flue dust content as compared with the usual blast furnace gas. This is accounted for by the fact that agglomeration of ore fines takes place in the zone C and also by the fact that the furnace gas is being removed at the enlarged diameter portion of the furnace with resultant minimum gas velocity and minimum extent of elutriation of fines. Furthermore, any small amount of dust which is contained in the furnace exhaust gases will very readily coprecipitate with liquid lay-products of coal distillation and will be removed in the dust separator 16 as soon as the gas stream leaves the furnace. haust gases makes them well suited for use in drying or calcining of raw materials to be charged to the furnace and also for the production of steam by means of waste heat boilers or the like.

The gas stream withdrawn at the manifold 13 is a composite gas, as previously described, and the composition of the composite gas may be altered by regulating the type and amount of coal charged and the operating conditions in the carbonization section C of the furnace. Thus, under certain conditions it is possible to produce a low calorific value gas comparable to the usual blast furnace gas, which has 20-30% CO and a calorific value of 100 Btu/cu. ft., or under other conditions it is possible to obtain a richer gas approaching the usual coke oven gas, which has a calorific value of 500 B.t.u./cu. ft. or higher.

narily be the preferred operation, the composite gas stream will have a relatively low calorific value, e.g. from about 15% to about 20% C0 and from about to about Btu/cu. ft. However, under different operating conditions designed to produce a richer gas having an increased hydrogen and hydrocarbon content, the com- The high sensible heat content of the ex- Under the most efficient operating conditions from an iron ore reduction viewpoint, which will ordi-- Percent N 50 H 20 CO CH Higher mol. wt. hydrocarbons 5 CO 5 The components of the gas are listed above in the order of increasing boiling point, and it will be apparent that, by suitable fractionation or separation schemes, the gas can be separated into a low boiling low calorific value fraction containing N H and CO and a higher boiling high calorific value fraction containing hydrocarbons and CO For example, by compressing and cooling the composite gas to a temperature somewhat below 263 F., the higher boiling high calorific value fraction may be separated in liquid form from the residual lower boiling gaseous components. Based on the foregoing typical analysis, the composite furnace gas would be separated into a 25% fraction having a high heating value on the order of 800 B.t.u./cu. ft. and a 75% fraction having a low heating value of about 106 B.t.u./cu. ft. which closely resembles the conventional blast furnace gas. Either before or after the separation of the composite gas stream it will generally be desirable to effect removal of sulfur so that the high calorific value fraction may be used as fuel in an open hearth furnace or the like.

In order to illustrate to a further extent the valuable results which can be obtained by the present invention, the following non-limiting specific example is presented.

Example The burden charged to the upper section C comprises 3760 lbs. of Leslie iron ore, 970 lbs. of limestone, and 3500 lbs. of Illinois coal (3% moisture). The analyses of the raw materials are as follows.

A total of 160,000 cu. ft. of air is introduced to the furnace, 55,000 cu. ft. being injected at the upper inlets 26 and 105,000 cu. ft. being introduced at the tuyeres 27.

From the bottom section R are withdrawn 1167 lbs. of

slag and 2000 lbs. of molten iron having the following analysis (wt. percent):

Fe 93.36 c 4.0

From the central manifold of the furnace 230,000 cu. ft. of composite gas are withdrawn having a calorific value of 91.5 B.t.u./cu. ft. and the following composition (vol. percent):

co -1 10 H 7 H2O 10 N 52 Although the invention has been described with reference to certain specific embodiments, it is to be understood that various modifications and equivalents may be resorted to without departing from the scope of the invention as defined in the appended claims.

We claim:

1. An iron ore reduction process which comprises passing a burden comprising iron oxide ore, coal, and flux downwardly through a pair of superimposed upper and lower reaction zones, supplying heat to the upper zone and effecting carbonization of said coal during passage of the burden through said upper zone, regulating the temperature in said upper zone so as to maintain an increasing temperature gradient in the direction of movement of the burden through said upper zone whereby to prevent deposition of tars and oils in said upper zone, passing heated air upwardly through the lower zone in countercurrent contact with the downwardly passing burden and effecting reduction of the iron oxide in said lower zone, withdrawing molten iron from said lower zone, withdrawing carbonization gases downwardly through said upper zone, withdrawing reduction gases upwardly through said lower zone, and removing a combined gas stream at substantially the juncture between said zones.

2. The process of claim 1, further characterized in that said combined gas stream is thereafter separated into a lower boiling low calorific value fraction and a higher boiling high calorific value fraction.

3. The process of claim 1 further characterized in that heat is supplied to the top of the burden in said upper zone by means of fuel burners and said temperature gradient is obtained by introducing con-trolled amounts of an oxygen-containing gas at vertically spaced points along said upper zone.

4. A combined carbonization and iron ore reduction process which comprises passing a burden containingiron oxide ore, coal, and'flux downwardly through successive superimposed upper carbonization and lower reduction zones, heating the burden in said upper carbonization zone to effect carbonization of the coal therein and maintaining an increasing temperature gradient from the top to the bottom of said upper zone, withdrawing carbonization gas from the bottom of said upper zone in concurrent relation to the downwardly moving burden, introducing heated air at the bottom of said lower reduction zone and passing the same upwardly through the burden and effecting reduction of the iron oxide therein, removing molten iron from the bottom of said lower zone, withdrawing reduction gases from the top of said lower zone-in countercurrent relation to the downwardly moving burden, and removing a combined gas stream at the juncture between said upper and lower zones.

5. The process of claim 4 further characterized in that said temperature gradient in said upper zone ranges from about 700 F. to about 800 F. at the top of said upper 7 zone and from about 1200 F. to about 1500 F. at the bottom of said upper zone.

6. The process of claim 4 further characterized in that heat is supplied to the top of the burden in said upper zone by means of burner flames and said temperature gradient is obtained by introducing an oxygen-containing gas at predetermined points in said upper zone to efiect combustion of a part of the carbonization products therein.

7. An iron ore reduction process which comprises feeding a burden comprising iron oxide ore, coal, and flux into the upper end of an elongated upright reaction chamber, supplying heat to the top of the burden to effect carbonization of the coal in a carbonization zone at the upper portion of said chamber, introducing an oxygencontaining gas into said carbonization zone at vertically spaced points and effecting combustion of a portion of the gas evolved during said carbonization so as to maintain an increasing temperature gradient of from about 700-800 F. at the top of said carbonization zone to about 12001500 F. at the bottom of said carbonization zone, introducing heated air at the lower end of said chamber and passing the same upwardly in countercurrent contact with the downwardly moving burden and effecting reduction of iron oxide in a reduction zone at the lower portion of said chamber, withdrawing molten iron from the bottom of said reduction zone, passing gaseous products of earbonization downwardly through said carbonization zone to the bottom thereof in concurrent relation with the downwardly moving burden, combining said gaseous products of carbonization with gaseous products of reduction withdrawn from the top of said reduction zone after passage upwardly therethrough in countercurrent relation with the downwardly moving burden, and removing the combined gas stream from an intermediate point of said chamber at the juncture between the bottom of said carbonization zone and the top of said reduction zone.

References Cited in the file of this patent UNITED STATES PATENTS