WO1981002584A1

WO1981002584A1 - Carbonaceous fines in an oxygen-blown blast furnace

Info

Publication number: WO1981002584A1
Application number: PCT/US1981/000326
Authority: WO
Inventors: R Jordan
Original assignee: R Jordan
Priority date: 1980-03-11
Filing date: 1981-03-11
Publication date: 1981-09-17
Also published as: EP0047314A1

Abstract

A process, and apparatus, for the production of carbon monoxide and molten ferrous metals in a blast furnace operated using a relatively cold blast for gaseous oxygen and a suspension of a solid carbonaceous fuel in recycle gas, instead of the conventional hot blast, and wherein the of high temperature heat required is substantially increased by (a) tapping hot gas from the stack, (b) tapping the hot metal and slag at higher temperatures, above 3000 F, 1650 C, ideally much higher, (c) increasing the basicity and amount of slag, ideally producing portland cement, (d) injecting high sulfur carbonaceous fuel, especially high sulfur coal, and (e) removing carbon selectively from the hot metal by oxidation with an oxidizing stream injected through tuyeres below those for injecting oxygen-carbonaceous suspensions.

Description

CARBONACEOUS FINES IN AN OXYGEN-BLOWN BLAST FURNACE Technical Field

This invention relates to a process and apparatus for increasing the high temperature heat consumption in, critical ratios of injected coal to

5. oxygen, cooling hot metal and making steel by, operating a blast furnace with gaseous oxygen and a suspension of a carbonaceous fuel instead of the conventional hot blast. Background Art

This is a continuation-in-part of my^'copendi-ng application, Serial

10 Number 939,431 filed September 5, 1978, now US 4,198,228 issued April 15, 1980, and entitled Carbonaceous Fines In An Oxygen-Blown Blast Furnace. In the conventional operation of a blast furnace to produce blast furnace hot metal, i.e. a molten ferrous metal containing usually from about 3 to about 8 percent carbon, about 4.5 MM Btu's/THM or 1.25 MM kc/t, THM is

15 tons of hot metal, high temperature heat is required to drive the process. Indeed, typically 1,230 pounds, 558 kg, is consumed in the production of a short ton, 0.907 t, of hot metal of which about 3.5 MM Btu's, 0.88 MM kc is provided by the partial combustion of the hot blast and the remain¬ ing heat is that of the sensible heat of the hot blast, about 2 MM Btu's,

20 0.5 MM Kc. But in operating a blast furnace with oxygen and a carbona¬ ceous material suspended in recycle top gas at ambient temperatures all the heat must be provided by the partial oxidation of the carbon. More, according to Oka oto et al , Iron & Steel Institute of Japan, Trans¬ action 1974,14,122-132, it is necessary to maintain an oxygen concentra-

25 tion of about or less than 36% when injecting mixtures of oxygen, nitro¬ gen and recycle gas, even when injecting small quantities of oil. Thus rather enormous quantities of top gas would have to be recycled. Were then even 5 MM Btu's/THM, 1.4 MM kc/t, high temperature heat required, it would be necessary to recycle over 20,000 scf/THM, 625 m³/t, top gas. But

30 one of the reasons for employing oxygen is the value of the recovered top gas as a viable replacement for natural gas, which the steel industry con¬ sumes to the extent of some 600 billion scf, 17 billion ³, annually in the nearby soaking pits, reheating furnaces, annealing furnaces and the like.

35 Further, it would be desirable to inject as much coal as possible to replace much more costly coke, but if such coal must be so diluted by the recycle top gas and the oxygen concentration limited to only about 36%, it would be highly doubtful that only about double that able to be now in¬ jected in the conventional blast furnace process, 150 pounds/THM, ergo about 300 pounds/THM, 150 kg/t, could be gasified in the raceways.

Therefore it is an object of my invention to provide a new and impro ved process for the operation of an oxygen blown, coal fired blast fur¬ nace. It is another object of my invention to provide a new and improved process for the production of carbon monoxide.

It is a further object to provide a new and improved process for the production of port!and cement.

Other objects will become evident later herein. Disclosure of Invention

My invention is a process for the production of molten ferrous metal in a blast furnace comprising charging the top with a ferrous ore,a flux ing agent and coke in an amount at least that for providing the desired carbon in the hot metal, and injecting oxygen of at least 65% purity and a solid carbonaceous fuel suspended in gas withdrawn from the stack, at level below that where reduction begins, through the tuyeres.

I have discovered unexpectedly that the amount of high temperature heat required in the production of a molten ferrous metal in -an oxygen- blown blast furnace- is far less, almost half that required in the conven tional blast furnace process. And as a result the amount of carbon monox¬ ide required in the process is so low as to result in only very little recovered, and that of low concentration because of the high carbon diox¬ ide concentration. Thus to achieve increased high temperature heat requi- rments it is necessary to increase the amount of high temperature heat consumed in the process. For the most part the unexpected reduction in high temperature heat is realized by obviating the "direct reduction" re¬ action, which is actually the carbon dioxide-carbon reaction that takes place in the conventional reduction zone, an be a lesser loss of sensible heat in the top gas. An understanding of how this is effected in an oxygen-blown blast furnace, whereas it is unavoidable in the conventional blast furnace can be had by visualizing the differences in carbon monoxide concentration. In the conventional process a gas of 35% carbon monoxide-65% nitrogen rises from the combustion zone; whereas in an oxygen-blown blast furnace using realtively high purity oxygen, the gas is essentially pure carbon monoxide. Thus in the conventional process the rate of reduction by one- third as concentrated at a given temperature will be less than a third that in concentrated carbon monoxide; clearly then in the oxygen-blown - process the last of the iron oxides will .be reduced, much higher in the

c- . furnace. Further, as the charged ore iron oxides descend in the furnace they will encounter a gas near the top of only 25% carbon monoxide in the conventional process whereas in the oxygen-blown process the carbon mono¬ xide concentration will be substantially higher, ergo in the oxygen-blown process the reduction of the charged ore will begin at a higher level and at a lower temperature. And in the rapidly increasing carbon monoxide concentration in the reduction zone of the oxygen-blown blast furnace it is clear that the rate will be very rapid. Thus in the conventional pro¬ cess the reduction of the charged ores does not- begin until the tempera- ture has reached 1700°F, 930°C, whist in the oxygen-blown process it will begin at about 1300°F, 700°C, and will be substantially completed probab¬ ly somewhere between 2000°F, 1100°C, and 2500°F, 1400°C.

The carbon dioxide-carbon reaction only begins at a level of about 2000°F, n00°C, slowly, increasing in rate with temperature. But at this level in the oxygen-blown furnace the reversible reaction, C0₂ + C -> 2 CO will be inhibited by the very high concentration of carbon monoxide as by this level the reduction is substantially complete. Thus there will be very little carbon dioxide generated to begin with and further, if much coal is injected the coke concentration will be vary low.

By essentially eliminating this reaction the high temperature heat requirement is lowered by some 1.1 MM Btu's/THM, 0.3 MM kc/t, ergo at a flame temperature of 3600°F, 2000°C, the gas, i.e. essentially carbon r> monoxide, volume needed is lessented by 14,761 scf/THM, 461 m /t, And as the rate of hot metal is increased, see my Serial Number 939,431 of Sep¬ tember 5, 1978, now US 4,198,228 issued April 15, 1980, noted at the int¬ roduction, whist the heat losses to the walls and tuyeres remains cons¬ tant, further heat conservation is effected. Indeed then, an analysis of the amount of high temperature heat required for the process as compared to the conventional blast furnace process results in an unexpectedly low number because additionally the amount of sensible heat loss in the top gas becomes significant. Simplistically then, a comparative analysis as¬ suming a fluxed ore is shown in Table I.

TABLE I High Temperature Heat Consumption, MM Btu's/THM,(MM kc/t) My Process Conventional Process

Tapped hot metal 1.2 (0.3) 1 .2 (0.3)

Tapped slag 0.4 (0.1) 0.4 (0.1 )

Top gas heat 0.4 (0.1) 0.8 (0.2)

Wall and tuyere loss 0.2 (0.1) 0.4 (0.1 )

C0₂-C heat loss 0.0 (0.0) 1 .1 (0.3)

Misc. losses 0.3 (0.1) 0.3 (0- 1 )

Totals 2.5 (0.7) 4.2 (1 .1 )

The amount of carbon monoxide or mixture- thereof with nitrogen needed to hold the heat is temperature dependent, the volume obtained by dividing the high temperature heat by the product of the flame temperature and th mean heat capacity. Thus were my process operated at a flame temperature of 3300°F, 1800°C, ^'about 31,880 scf, 1,080 m³/t, and at 4300°F, 2400°C, about 27,300 scf, 852 nrr/t, gas would be required.

As no significant carbon dioxide-carbon reaction takes place, it ca be seen that the amount of carbon monoxide consumed in providing a ton o hot metal is practically that dictated by the ore, i.e. magnetite, Fe^O_* would consume about 18,000 scf, 560 m³/t, and in turn 18,000 Scf, 560 m³ t, carbon dioxide would be produced, hence at a flame temperature of 4000°F, 2200°C, the maximum of 29,600 scf, 925 m³/t, carbon monoxide fro the combustion zone would result in a top gas of 11,600 scf, 360 m /t, carbon monoxide and 18,000 scf, 560 πr/t, carbon dioxide; clearly as som of this would have to be recycled the recovered carbon monoxide undoubt¬ edly would amount to less than 10,000 scf, 310 m³/t, (3.2 MM Btu's, 0.9

MM kc/t) of hot metal and it's heating value would be about 100 Btu's/sc 3 890 kc/m . Indeed, were the oxygen for this less than 65% purity the top gas carbon monoxide concentration would be less than 20%, only about

3 23,500 scf, 730 m It . contained in the gas from the combustion zone. Thu the oxygen should be substantially pure, a minimum of 65%, preferrably over 85%, ideally over 95% purity. Were then top gas recycled according to my Serial Number 939,431, now US 4,198,228, noted earlier, even at a low flame temperature the car bon dioxide concentration of the top gas would be very high; and were it desired to recycle only carbon monoxide, by removing the carbon dioxide chemically by reactant or solvent, there would hardly be a sufficient quantity. Indeed, at high flame temperatures the amount would be insuffi cient.

Further, in recycling top gas as obtained, the quantity recycled in the simplest-sys-tem-wherein coke-breeze, -containing-no-hydrogen, would b injected determined by first ascertaining the quantity of carbon dioxide to be used. _ _,

T.G. C0/C0₂ x scfC0₂ + 3.5 scfC0₂ = C.Z. CO difference where the combustion zone carbon monoxide difference is that required to hold the heat THM,t less that provided by the carbon necessary. For exam¬ ple, 621 pounds, 311 kg/t, of carbon for 2.5 MM Btu's/THM, 0.7 MM kc/t, would result in 19,633 scf, 614 m /t, carbon monoxide ergo at 4000°F, 2200°C, the difference would be 29,600 scf, 924 m³/t, minus 19,633 scf,

614 m³/t, or 9,967 scf, 311 m³/t carbon monoxide. As the top gas ratio is

3 0.644 the amount of recycle carbon dioxide is 2,394 scf, 75 m /t, and

1,542 scf/THM, 48 m³/t, carbon monoxide or a total of 3,936 scf/THM,

123 m³/t, which would weigh 393 pounds, 197 kg/t. At the very most the quantity of coke breeze that could be susepnded in this gas would be just under 800 pounds, 400 kg/t, and transfer of the suspension would be diffi- cult; preferrably the solids to gas ratio should be about or less than 1.5:1 and ideally about or less than 1:1 weight of solids to weight of gas. Clearly, under the ideal conditions only 393 pounds, 197 kg/t, coke breeze would be suspended. ' '

As the ratio of carbon monoxide to carbon dioxide in the top gas would increase as, for example by increasing the amount of heat required in the process, the amount of recycle gas in volume and weight would increase.

Thus it is my invention to. remove hot gas from the stack at a point or level below that where reduction begins. Preferrably about that where sub¬ stantial reduction occurs or below, and ideally at a level where the reduc- tion is practically complete or lower whence the gas would be essentially pure carbon monoxide, It would be diluted, if at all, only be hydrogen from coal and moisture and nitrogen contained in the oxygen. Again a rea¬ son for employing oxygen of the highest practical purity. For example, if gas were removed from the stack at the 3000°F, 1650°C, level to the extent of 20,000 scf/THM, 625 M³/t, it would remove about 1.2 MM Btu's/THM, 0.33 m³/t which would have to be added to the heat available from the combus¬ tion zone representing 14,285 scf, 446 m³/t, carbon monoxide at a flame temperature of 4000°F, 2200°C. Again this difference of 5,715 scf, 178 m³/ t, would be reflected in a much lesser amount of carbon monoxide in the top gas. Clearly, v/ere the 20,000 scf, 625 m³/t, replaced in the combustion zone it would hold at 4000°F, 2205°C,^*hold 1.68 MM Btu's, 0.47 MM kc/t, a difference of 0.48 MM Btu's, 0.13 MM kc/t, which would result in changing the 3,000°F, 1650°C, level and in a higher top gas temperature. Normally the top gas must be maintained-below 700°F, 370°C, because- structural dam- age to the top can result.

Note that the total carbon monoxide is increased whist the carbon di- oxide remains constant, at 18,000 scf, 560 m°/t, (for magnetite). -Of cour se, by selecting some level in the reduction zone it is possible to take off and composition lying between essentially pure carbon monoxide and that of the top gas, ergo the exact composition of the desired recycle ga can be had in terms of carbon dioxide concentration.

However, many chemical processes require a stream of carbon monoxide free of carbon dioxide, for example in the production of methyl formate from carbon monoxide and methanol using sodium methylate as a catalyst. Having such a stream therefore simplifies the process because were any fo mate ester so made from the top gas,the carbon dioxide would require ano¬ ther step employing expensive facilities. Removal of small quantities of whatever acid gases in the stack stream can be effected by in-line methods for example using molecular sieves very cheaply. Further, even in making acetic acid from carbon monoxide and methanol using rhodium or other metal compounds as catalysts, the rate of the process is adversely affected by substantial concentrations of carbon dioxide, ergo it is advantageous to have a relatively pure stream. More, in removing a stream of essentially pure carbon .monoxide from the stack, it can be mixed with the top gas in what proportions needed to arrive at a desired recycle gas composition. Thus the stack gas removed can be used alone for the recycle gas, mixed with the top gas to obtain the desired recycle composition or employed for making carbon monoxide based chemicals. Clearly were stack gas removed and mixed with recovered top gas while top gas alone were recycled, the effect would be to increase the high temperature heat consumption of the process of my Serial Number 939,431, now US 4,198,228 noted earlier. This would represent a signifi¬ cant improvement as the top gas-stack gas recovered mixture would contain more carbon monoxide and its heating value increase.

While most any amount can be withdrawn from the stack it should be realized that a given furnace is limited in gas flow rate and lifting eff¬ ect at high rates of hot metal production; for example a typical 29 foot, 9 m, hearth diameter blast furnace proper is limited to about 190,000 scf, 5,380 πrVminute. And while removing gas lower in the stack may somewhat increase this, it cannot do so substantially without significantly decrea¬ sing productivity.

As noted the recycle gas can range in carbon dioxide concentration; indeed,-from essentially carbon monoxide alone to carbσn- dioxide alone and all the mixtures in between. Assuming essentially pure oxygen is injected to minimize nitrogen, in using coal its hydrogen and contained moisture which results in hydrogen will affect the carbon monoxide concentration in the stack, top gas and recycle stream. In lignite, bituminous coal and an-

5 thracite the hydrogen content can vary widely, for example in bitiminous coal from about 2% to about 6%. Thus were 1,000 pounds/THM, 551 kg/t, of a typical 4.5% bituminous coal injected it would result in the direct intro- duction of 8,460 scf, 264 m"/t, hydrogen and as perhaps a fifth would be recycled, 1,700 scf, 53 m³/t, some 10,160. scf/THM, 317 m³/t, would be pre-

10 sent in the combustion zone. Thus even at 4 MM Btu's/THM, 1.1 MM Kc/t, of high temperature heat wherein 31,415 scf, 981 m /t, carbon monoxide would be made from the carbon necessary to provide the heat, a total of 29,874 scf, 933 m³/t, gas of the some 47,620 scf, 1,487 m /t, required would leave only 7,746 scf, 242 m³/t, as the difference. Under any circumstances

15 this would be too low, weighing but about 470 pounds, 235 kg/t, to suspend 1,000 pounds, 500 kg/t, of the coal. While it would appear necessary to inject less coal, the problem can be overcome by increasing the amount of high temperature heat required while holding the amount of coal injected constant, for example to 5.0 MM Btu's/THM, 1.4 MM Kc/t, or by reducing the

20 flame temperature, for example to 3300°F, 1800°C, and increasing the heat to a lesser extent. Thus at 5.0 MM Btu's/THM, 1.4 MM kc/t, the difference would become 12,272 scf, 383 m³/t, which would be tolerable. The point is that the amount of high hydrogen coal that can be injected is limited un¬ less one operates at a very low temperature, which would result in low

25 productivity, or increases the amount of high temperature heat required. And if the amount of heat is increased some method must be found to remove it from the process, else the top gas temperature would go too high.

Another method for increasing the high temperature heat required lies in tapping at a much higher temperature or increasing the amount of slag

30 coproduced. Slag is relatively valueless, composed of mono-calcium sili¬ cate and mono-calcium aluminate. It is thus my invention to increase the lime or lime containing compounds such as limestone, super-fluxed iron ore etc.; thus the basicity of the slag is greatly increased, but so too is its melting temperature. In conventional practice the basicity is expres-

35 sed as the ratio of alkaline earth oxides to those of silica and aluminum or other such acids. By increasing the basicity from the 1.03 now usually employed in domestic blast furnaces to about or greater than 2, the amount of slag needed could even be reduced since its effectiveness in sulfur

- from the hot metal would be substantially increased..- But-as the melting

" _^ :-< -A (j temperature of the higher basicity slag can be adjusted by adjusting the amount of calcium alu inates present to some degree and as portland cement is composed of tricalciu silicate or mixtures of it with dicalciu sili¬ cate and calcium aluminates, especially tricalcium aluminate, it is ideal

5 to produce a slag of portland- cement compositions. This is especially true of domestic ores which are very high in silica. Thus by my new process the amount of lime or its compounds added, ideally to the burden, is increased greatly to practically double the amount of slag whist the alumina added in its various forms such as gravel, bauxite, etc., in effect control the

10 melting temperature as well as result in the desired portland cement com¬ position.

In making a molten portland cement slag the Si02~Al 03 of ore, coke and injected carbonaceous material realized in the hearth, for instance 300 pounds, 150 kg/t, is combined with 600 -900 pounds, 300 - 450 kg/t,

15 of lime to make tricalcium silicate; alumina ores being added as necessi¬ tated by the portland cement composition desired. Thus some 900 to 1,200 pounds, 450 to 600 kg/t, molten portland cement would be realized. As it is a further^"invention of my process to increase the tapping" temperature from the maximum of about 2800°F, 1500°C, by the conventional blast fur-

20 nace to at Teast 3000°F, 1650°C, preferrably above about 3300°F, 1800°C, and ideally about or above 3500°F, 1900°C, not only is the additional heat required by the material increase realized, but additionally that result¬ ing from tapping at a much higher temperature of both the slag and the hot metal. Again, in effecting these increases, the amount and concentration 5 of carbon monoxide recovered is substantially increased.

This cannot be effected in the conventional blast furnace process be¬ cause of the relative collness of the hot blast which results in tapping the slag and hot metal at temperatures far below the flame temperature, i.e. these must pass near the raceways and thus are cooled. But by my pro- 0 cess the raceways temperature can be adjusted practically at will as will be discussed later herein.

Many ores are low in silica and high in alumina or titania, ergo by employeing coke, coal and other materials in the furnace of low silica by the same technique of increasing the basicity, for example with lime, i.e. 5 here calcium oxide, the slag can be.of calcium aluminates or titanates, or even mixtures if desired. Indeed, calcium titanate or even monocalcium titanate slags are not produced in the conventional blast furnace process because of the viscosity and melting temperature consideration; but by my

- process such can- be produced. -As tricalicum aluminate- is-said to-be solub- le in water, such a process for its production affords an interesting route to alumina by adding an acid whose calcium salt is soluble in water, ergo precipitating hydrous alumina.

When considering the basicity of alkaline earth metal aluminates by my

5 process,the alumina should be considered AlO_j 5, and by my process the basicity should be about or over 2:1 or 2.

The ability to tap at higher temperatures enables the coproduction of phosphorus or its oxides as components of the top gas, readily removed by water or solvent washing, using phosphate- rock as the source of lime,

10 whist the silica required can be had from the ore, coke, etc. and addi¬ tional coke can be compacted with phosphate rock and silica if desired.

By employing a very high ratio of injected carbonaceous fuel as com¬ pared to injected oxygen, a raceways gas of reducing character can be rea¬ lized, as will be discussed later herein. By adding large quantities of

15 lime or limestone, ideally to the burden, with excess coke, ideally as lime-coke compacts, a slag of calcium carbide, ideally as such or as its eutectic with lime can be tapped. Here again the ore, coke and injected carbonaceous material could be low in interefering minerals.' Fortuitously, as calcium carbide is CaC₂ where the atomic weight is 40 for calcium and

2012 for carbon, ergo a ratio of about 2, (40:24) the same, but looser in- terpetation of basicity can be employed. Indeed, it is applicable because the carbide, C₂ radical, is hardly acidic.

Similarly, by using oxygen of less than 98% purity, but over 65% pur- 25 ity, the calcium carbide can be converted in situ to calcium cyanamide. Both are tapped at over 3000°F, 1650°Cby my process.

When coal injection is attempted in the conventional blast furnace process, only smallish quantities can be viably injected, typically only about 150 pounds/THM, 75 kg/t, but using heroic methods such as oxygen en- 30 richment and higher hot blast temperatures it is said that as much as 300 pounds/THM, 150 kg/t, can be injected; but economic levels of injection have not been achieved. To inject coal by the conventional process it is necessary to suspend the powdered coal in a relatively cold stream of air and inject the suspension at the tuyeres. Because of the velocity of the 35 hot blast, 700 to 900 fps, 230 to 300 m/sec, laminar flow problems inhibit mixing in the suspension, the low, 21% oxygen concentration, tends to re¬ sult in isolating the particles in the 79% inert nitrogen, and, as the raceways are but 4 feet, 1.2 , deep into the burden the residence time for mixing and gasification is but 0.005 seconds. By my process the gases near ambient temperature, ergo their volumes actually near to their stand ard. However, as by my process the rate of production is greatly increase so too is the rate of gas flow compared to what would be at the same rate of hot metal production. According to Oka oto et al , noted earlier, the oxygen concentration entering the raceways should be less than about 36%. But I have discover ed that this problem can be overcome by injecting massive quantities of carbonaceous fuel such that the ratio If injected carbon to injected oxy¬ gen limits the gasification to mostly carbon monoxide. In this way the oxygen and carbon dioxide content of the resulting gas is low and there¬ fore has little influence on the carbon content while limiting the temper ature of the raceways. Heretofore this has been- overlooked, but it is a critical factor in practical stable operation. The problem is illustrated by assuming the gasification of increasing quantities suspended in 11,400 scf, 320 m , recycle gas comprised of 7,600 scf, 215 m³, carbon monoxide and 3,800 scf, 108 m³, carbon dioxide by 15,200 scf, 430 m³, gaseous oxy¬ gen per ton of hot metal. In Table II the temperatures shown are uncorrec ted for carbon dioxide dissociation, but the difficulty is cle^*ar.

TABLE II Raceway Temperatures From Carbon Injection

C injected, lbs (kg) 0 (0) 120(55.5) 240(110) 360(164) 480(218) CO, Mscf(m³) 0 (0) 0( 0) 0( 0) 0( 0) 8(215) C0₂, Mscf(m³) 11(320) 15(430) 19(540) 23(650) 19(538) 02, Mscf(m³) 11(320) 8(215) 4(108) 0( 0) 0( 0) MM Btu's(MM kc) 2.4(0.6) 4.1(1.0) 5.8(1.5) 7.5(1.9) 6.8(1.7)

T, °F(°C) 3750(2070)5680(3100)7200(3980)8250(4580)7150(395

Clearly, such temperatures as are approximated far exceed the boiling tem perature of iron, ergo gasification thereof, and uneven distribution of heat to the surroundings would result from injecting even 480 pounds, 218 kg, carbon. And indeed, at the higher temperatures, above the boiling tem perature of iron, the carbon dioxide would be practically equivalent to oxygen as an oxidant; it would remove carbon from any contacted hot metal Fortuitously, as the injected carbon is increased the raceway tempera tures decrease, as suggested by carbon above but shov/n clearly in Table III. π.

TABLE III Raceway Temperatures From Carbon Injection (continued)

C injected , l bs ( kg) 600(273) 720(327) 840(382) 960(436)

CO, Mscf(m³) 15 (430 ) 23 (645 ) 30(861 ) 38(1 076 )

C0₂, Mscf(m³ ) 1 5 (430) 11 (320) ■ 8(215 ) 4(1 08)

°2 0 0 0 0

MM Btu ' s (MM kc ) 6.1 (1 .5) 5.3(1 .3) 4.6(1 .1 ) 3.9 (1 .0)

T, °F(°C) 6350(3500) 5450(3010) 4750(2620) 4150(2290) Indeed, the raceways temperature could be further lowered by injecting another 120 lbs, 55.5 kg, to consume the remaining 3,800 scf, 108 , carbon dioxide endothermically.

Clearly the temperature must be held at below the boiling temperature of iron because that volatilized would in part swept from the furnace by the rushing gas. A_.rough approximation in correcting for carbon dioxide dissociation discloses that the ratio of injected carbon to injected oxy¬ gen must be over 1.3:1 mole ratio to realize a raceway temperature below the boiling temperature of iron. Thus in injecting 40 lb moles/THM, 26 kg moles/t, it would be necessary to inject over 624 lbs, 313 kg^", of carbon. As coal is typically 80% carbon, some 780 pounds coal/THM, 391 kg/t, would have to be injected. While the ratio changes a little as the carbon dioxide is increased or. decreased, it is a fair approximation. Indeed, preferrably the ratio should be over 1.5:1, ideally about 1.7:1. Another way of expressing it lies in temperatures, again the raceway temperature should be below the boiling temperature of iron, preferrably about or be- low 5000°F, 2760°C, and ideally about or below 4600°F, 2540°C. Of course the raceway temperature can be made much lower by injecting a coal-inert gas or liquid, but that is undesirable as noted earlier.

The cheapest of coals are high sulfur bituminous coals that now sell for a fraction of the cost of low sulfur coal. By my process wherein high raceway temperatures are employed and highly basic slags such as portland cement, calcium carbide, calcium aluminate or other alkaline earth simi¬ lar slags are made, either or both of high sulfur coke and coal may be used. In the steel .industry high sulfur coal would be that containing over 1.5% sulfur. In injecting high sulfur carbonaceous fuels into the very hot raceways a considerable portion of the sulfur will be gasified, some of which will be caught by the burden iron, iron oxides and bases, but a goodly portion will escape in the top gas as carbonyl sulfide. Ergo, even without a very highly basic slag it allows the use of high sulfur coals, but somewhat limited, perhaps to about 4.0% sulfur; but the most available high sulfur coals contain well over that, up to about 6% sulfu and to use such high sulfur coals necessitates using a very highly basic slag of about or over 2:1 basicity. Clearly too, in both cases high sul¬ fur coke can be employed, in the first because so little is used and in the second because of the very basic slag. It is true that the sulfur re moved by the slag will end up as the alkaline earth sulfide thereof, but it can be removed if desired; for example by blowing very hot steam through portland cement while molten, ergo liberating hydrogen sulfide, whist any free lime formed will immediately combine with dicalcium sili- cate to form tricalcium silicate. While sulfur has been the very anathem .of the conventional blast furnace process, it can be easily managed by m process- The accepted specifications for sulfur in blast furnace hot metals are easily met; these are listed with a maximum of about 0.06% in The Making, Shaping and Treating of Steel, Eighth Edition, U.S. Steel Corp., Pittsburgh, PA 1964, page 386, Table 14-11.

While the injection of suspension of carbonaceous materials and oxy¬ gen can be effected by well known methods, as a practical matter it is necessary to operate blast furnaces with a minimum of tuyere changes and down time. I have therefore invented an arrangement whereby the tuyeres can be protected. In this method the oxygen is supplied by a pipe or mul tiplicity of pipes extending into the tuyere, wherein the diameter of th pipe or resulting effective diameter of the pipes is smaller by at least one-forth, ideally about half and the depth adjustable such that under the conditions of velocities and pressures for each of the streams mixin and initial partial combustion is begun within the tuyere but the flame front only minimally impinges on the inner tuyere surface if at alt. By obviating or minimizing contact the tuyere life can be greatly prolonged Of course the oxygen pipe(s) may be tipped with nozzles or other devices to improve mixing with the suspension .and inhibit backfiring. As noted, the temperature of the slag and metal by my process may be quite high as a result of high raceway temperatures. By inserting a sec¬ ond set of tuyeres below those for injecting the oxygen and carbonaceous susepnsion, recycle stack gas containing practically no carbon dioxide can be injected at any desired temperature and quantities to adjust the slag and hot metal temperatures as desired. Again it should be realized that whatever gas is injected or results therefrom must be considered in the heat balance. By having an upper set of tuyeres in which to inject the oxygen and carbonaceous suspension and a lower set of tuyeres for injecting other gas, it is another invention to inject an oxidizing gas or suspension to control the carbon in the hot metal to whatever level desired below that descending from above. Thus by injecting carbon dioxide or oxygen, idally as mixtures with carbon monoxide, a hot(molten)metal of carbon content of from about 0.0% to about 4% can easily be realized. For example a hot mixture of carbon monoxide-dioxide, the latter to the extent needed to adjust the carbon level, can be injected, or a mixture of relatively cold carbon monox de-oxygen, the latter as needed to effect the desired carbon removal, that would control the temperature of the hot metal by the exo¬ thermic reaction.

Indeed, suspension of oxidizing materials may be added to effect car¬ bon adjustment and provide other benefits such as alloying. Thus a carbon monoxide suspension of the oxides of nickel, manganese, chromium, vana-.^'... dium and others may be injected to adjust the carbon content while produ¬ cing the desired alloy. Indeed, other compounds of may alloying metals may be employed including the carbonates, sulfides, silicates, aluminates and others. The process can be operated over a wide range of temperatures and pressures, a flame temperature of from about 3300°F, 1800°C, to about 4400°F, 2450°C, whist the pressure may range from about atmospheric to 50 atmospheres, although ideally from about 2 to 6 atmospheres absolute. It is ideal to tap the slag and hot metal as high a temperature as can be managed; especially beneficial results are realized since by transferring the hot metal to the basic oxygen steelmaking process or electric furnace process, a much larger than normal amount of scrap can be dissolved ther¬ ein and the the latter less electrical energy is needed in the subsequent processing. Typically the amount of scrap added to the BOP furnace is_. about that which ςan be accomodated by the added heat available, about or over 20%, preferrably about or over 25%, and ideally over 30%.

My process necessitates careful control of the recycle carbonaceous fuel suspension; were the concentration to drop markedly excessive race¬ way temperatures would result. Normally, one can add the carbonaceous fuel to the recycle gas via a hopper or other known device. But to achie¬ ve the ideal control I have discovered that placing the pulverizing mill in the' recycle gas stream so that at least a portion of the gas passes through it, more uniform suspensions can be realized and further classi- fication of the particles can be had; the larger particles recycled withi the mill. More, even a relatively warm stream of recycle gas can be im¬ pinged on the walls or rings of the pulverizing mill to prevent agglomera tion as might occur if wet coal is employed. While the unexpected method can necessitate an in-place standby mill or hopper arrangement to acco o- date failure or maintence, its benefits far outweigh the disadvantages.

The conventional blast furnace complex has evolved historically, wher as the complex ideal for my process should encompass a blast furnace pro¬ per having the usual top gas handling facilities.and additionally at leas one stack gas take-off pipe at a level at or below where reduction is sub stantially completed with means for withdrawing the stack gas without a ■substantial pressure drop within the furnace and means for cooling the withdrawn gas by heat^* transfer to the desired temperature. A recycle com¬ pressor is required that can handle either or both top gas and stack gas with ductwork to convey the gas recycled to the pulverizer which can be o roller ring, attrition, ball or other types mills. And the mill can be fe by known means with a solid carbonaceous fuel larger in particle size than will be produced by the mill, ideally the mill will provide uel of minus 325 mesh, 44 microns, preferrably minus 100 mesh, 149 microns, but it can be larger, whist the feed to the mill is ideally about one-eighth inch, 3 mm, coal. The recycle gas in part passes through the mill assisting in classifying the particles and leaves carrying suspended carbonaceous fines which^'are ducted to the tuyeres by known means, even via the in-place bustle pipe. Optionally another recycle gas stream or separate gas stream is handled by ductwork to the lower tuyeres, wherein such ductwork is in¬ corporated a hopper for adding powders, for example of metal oxides- such as nickel, iron, manganese and others. The carbonaceous suspension is fed to the upper tuyeres as noted, whereas pipes carry the oxygen into the tuyeres as detailed earlier. The in-place top gas boilers are optionally converted to firing by pulverized coal, which steam of course drives the blowers which are incorporated into the oxygen facility to obviate in part purchased compressor capacity. The cryogenic oxygen facility provides gas¬ eous oxygen at the desired pressure to the pipes into the tuyeres, which pipes are adjustable in terms of depth within the tuyere and optionally also adjustable in nozzle size.

The blast furnace proper has heretofore always been lined with silica, aluminosilica and alumina refractories; more recently there has been a trend to carbon linings for the hearth and bosh. Indeed, it is desirable

^"BUK O.V. to employ carbon brick linings for the process of the instant i vention. However, such refractories are very expensive. But to employ alumina re¬ fractories in my process at very high temperatures and highly basic slags will result in relatively short lining life. It is therefore another in- vention to employ linings of dead-burned dolomite, ideally tar bonded dead-burned dolomite or magnesia. Such linings may be employed alone or in conjunction with carbon brick for the hearth and bosh linings.

According to the provision of the patent statutes, I have explained the principle of my invention and have illustrated and described what I now consider to represent its best embodiment. However, I desire to have it understood that within the scope of the appended claims the invention may be practiced otherwise.

Claims

I cl aim:

1. A process for the production of molten ferrous metals in a blast fur¬ nace comprising charging the top with a ferrous ore, fluxing agent and coke in an amount at least that desired in the molten ferrous metal, and, injecting oxygen of at least 65% purity and a solid carbonaceous fuel suspended in gas withdrawn from the stack, at a level below that where reduction begins, through the tuyeres.

2. A process for the production of molten ferrous metals and carbon mono¬ xide in a blast furnace comprising charging the top with a ferrous ore, fluxing agent and coke in an amount at least that desired in the molte ferrous metal whist withdrawing,from the stack at a level about or be¬ low that where substantial reduction takes place,carbon monoxide, and injecting oxygen of at least 65% purity and a suspension of a solid carbonaceous fuel in recycle gas through the tuyeres.

3. A process for the production of molten ferrous metals and a slag of at least 2:1 basicity in a blast furnace comprising charging the top with a ferrous ore, a fluxing agent in an amount required to result in a slag of at least 2:1 basicity and coke at least to the extent desired in the ferrous metal, injecting through the tuyeres oxygen of at least 65% purity and a suspension of a solid carbonaceous fuel in recycle gas and withdrawing the molten ferrous metal and slag at a temperature of about or higher than 3000°F, 1650°C.

4. A process for the production of molten ferrous metals of about or less than 0.05% sulfur in a blast furnace comprising charging the top with a ferrous ore_» a fluxing agent and coke at least to the extent of carbon in the molten metal and injecting oxygen of at least 65% purity -and a suspension of a solid carbonaceous fuel of over 1.5% sulfur in recycle gas through the tuyeres.

5. A process for the production of molten ferrous metals of about or less that 0.05% sulfur and a slag of about or greater than 2:1 basicity in a blast furnace comprising charging the top with a ferrous ore, a fluxing agent in an amount required to result in a slag of at least 2ιl basic¬ ity and coke at least to the extent of carbon desired in the molten metal, and injecting oxygen of at^"least 65% purity and a suspension of a solid carbonaceous fuel of over 1-5% sulfur in recycle gas through the tuyeres.

6. A process for the production of a molten ferrous metal and portland cement in a blast furnace comprising charging the ^"top with a ferrous ore, a fluxing agent comprising-calcium-oxide-and-alumina to the extent necessary to result in the portland cement composition and coke at least to the extent desired in the molten metal and injecting oxygen of at least 65% purity and a suspension of a solid carbonaceous fuel of up to about 6% sulfur in recycle gas through the tuyeres and withdrawing the molten metal and portland cement at a temperature of about or over 3000°F, 1650°C.

7. A process for the production of a molten ferrous metal and a slag of tricalcium aluminate in a blast furnace comprising charging the top with a ferrous ore, a fluxing agent comprising calcium oxide and alumina to the extent necessary to result in tricalcium aluminate and coke at least to the extent of carbon desired in the molten metal, and injec¬ ting oxygen of at least 65% purity and a suspension of a solid carbon¬ aceous fuel of up to about 6% sulfur in recycle gas through the tuyeres.

8. A process for the production of molten ferrous metals, calcium carbide and calcium cyanamide in a blast furnace comprising charging the top with a ferrous ore, a fluxing agent comprising calcium oxide and coke at least to the extent that required for calcium carbide and desired in the molten metal and injecting oxygen of at least 65% purity and a sus¬ pension of a solid carbonaceous fuel of up to 6% sulfur in the recycle gas through the tuyeres.

9. A process for the production of mol en ferrous metals, phosphorus and phosphorus oxides and a slag of basicity of about or over 2:1 basicity in a blast furnace comprising charging the top with a ferrous ore, a phosphate material, a fluxing agent comprising calcium oxide to the ex¬ tent necessary to result in a slag of or over 2:1 basicty and coke at least to the extent desired in the molten metal, and injecting oxygen of at least 65% purity and a suspension of a solid carbonaceous fuel of up to about 6% sulfur in recycle gas through the tuyeres.

10. A process for the production of ferrous metals in a blast furnace com¬ prising charging the top with a ferrous ore, fluxing agent and coke at least to the extent of carbon desired in the molten metal and injecting oxygen of at least 65% purity and a suspension of coal of at least 2% hydrogen in recycle gas, the mole ratio of injected coal carbon to in¬ jected oxygen being about or over 1.3:1.

11. An improved process for the production of molten ferrous metals in a blast furnace wherein the hot blast is replaced by a blast of oxygen of at least 65« purity and a suspension of a solid carbonaceous fuel sus¬ pended in recycle gas, the improvement which comprises a mole ratio of -injected carbon to injected oxygen of about or over- 1.3:1 and a wei ratio of suspended carbonaceous fuel to recycle gas of about or less than 1.5:1.

12. An improved process for producing molten steel, from blast furnace hot metal of about or over 3% carbon and scrap ferrous metal using a blast furnace and basic oxygen furnace wherein the improvement comprises re¬ placing the hot blast by injecting oxygen of at least 65% purity and a suspension of a solid carbonaceous fuel in recycle gas such that the mole ratio of injected carbon to injected oxygen is about or greater than 1.3:1, withdrawing hot metal froπrthe blast furnace at a tempera- ture of about or above 3000°F, 1650°C, transporting the hot metal to th basic oxygen furnace along with at least 25% scrap ferrous metal, injec ting oxygen and withdrawing molten steel from the basic oxygen furnace.

13. A complex for the production of molten ferrous metals comprising a blas furnace proper, charged at the top with a ferrous ore, coke and fluxing agent, means for removing top gas to a recycle gas compressor, which re compresses a portion of the top gas, means for conducting the recycle top gas to a pulverizing mill, through which at least a portion of the gas flows whist being fed with larger particles of a solid carbonaceous fuel to provide a suspension of smaller particles in the gas, means for conducting the suspension -to the tuyeres wherein each at least oneoxyge pipe extended to provide gaseous oxygen so that the injected carbona-r ceous fuel is largely gasified by the oxygen in the raceways.

14. An apparatus for injecting gaseous oxygen and a suspension of a solid carbonaceous fuel into a blast furnace comprising a tuyere into which a pipe for oxygen extends, said pipe of an inner diameter smaller than th inner diameter of any part of the tuyere, and whereby the depth -of the oxygen pipe into the tuyere is adjustable to enable mixing and gasifi¬ cation of the carbonaceous suspension to begin within the tuyere whist minimizing or preventing contact of the flame therefrom with the inner tuyere walls.

15. A modified blast furnace for the production of molten ferrous metals comprising a set of upper tuyeres through which oxygen and a suspension of a solic carbonaceous fuel in recycle gas is injected and a lower set of tuyeres through whicfii carbon monoxide and mixtures thereof with oxy gen and carbon dioxide is injected.

16. A process for the production of 'steel in a blast furnace equipped with an upper set of tuyeres for injecting oxygen and a suspension of a soli carbonaceous fuel, in recyc e gas and a lower set of tuyeres for injec-

^" ting gases comprising charging a ferrous ore, fluxing agent and cokg-a£ __c^y. the top, injecting oxygen of at least 65% purity and a suspension of a solid carbonaceous fuel in recycle gas through the upper set of tuyeres and injecting an oxidizing gas through the lower set of tuyeres in suf¬ ficient quantities as to remove carbon to the extent desired from the carbon containing iron above to produce molten steel.

17. The process of claim 16 where the oxidizing gas comprises carbon dioxid^

18. The process of claim 16 where the oxidizing gas comprises oxygen.

19. The process of claim 16 where alloying agents are suspended in the gas to make it oxidizing.

20. The process of claim 19 wherein the alloying agent is comprised of manganese oxides.

21. The. process of claim 19 wherein the alloying agent is comprised of nickle oxides.

22. The process of claim 19 wherein the alloying agent is comprised of chromium oxides.

23. The process of operating an oxygen-blown blast furnace for the produc¬ tion of molten ferrous metals comprising use of a slag of.basicity of about or greater than 2:1 in a blast furnace proper lined wholly or in part with a magnesia refractory.

24. The process of claim 23 where the refractory is. a dead-burned dolomite.