US3865574A

US3865574A - Process for the production of low-sulfur prereduced iron pellets

Info

Publication number: US3865574A
Application number: US273522A
Authority: US
Inventors: Raymond H Long; William V Bauer
Original assignee: Lummus Co
Current assignee: CB&I Technology Inc
Priority date: 1972-07-20
Filing date: 1972-07-20
Publication date: 1975-02-11
Anticipated expiration: 1992-02-11
Also published as: SE403137B; JPS4944924A; GB1444183A; CA988722A; IT991294B; BR7305466D0; ZA734932B; AU5821073A; FR2193879A1; LU68061A1; JPS5529132B2; DE2336496C2; FR2193879B1; BE802581A; DE2336496A1

Abstract

The present invention discloses a process for producing iron oxide pellets of low residual sulfur. In the pelletizing of finely divided ore with carbonaceous materials as binder, varying amounts of sulfur are introduced. Green pellets are heated under conditions leading to coking of the binder and recovery of the cracked vapors. The coked pellets are then further heated to achieve the desired degree of reduction and to diminish the residual sulfur content. A sulfur scavenger is initially sprayed on the ore. For pellets that will be reduced 85 percent or less, all necessary reductant is incorporated in the pellet, in the form of the coked binder and, optionally, added carbon. Heating to the reduction and calcining temperature is rapid. For highly reduced pellets (+85 percent), the same procedure may be followed, but heating to reduction and calcining temperature must be slow for good desulfurization. A preferred alternative for highly prereduced pellets involves reduction in two stages: initially a 25-50 percent reduction is carried out with rapid heating and with all reductant in the pellet. Then, the pellets are further reduced with a stoichiometric excess of reductant external to the pellet, with fast heating to reduction temperature. Because of the inherently porous nature of pellets produced with liquid carbonaceous binders, reduction is significantly faster and more complete than with conventional pellets.

Description

United States Patent Long et al.

[Ill 3,865,574

PELLETS Feb. '11, 1975 Primary ExaminerA. B. Curtis Attorney, Agent, or Firm-Marn & Jangarathis [57] ABSTRACT [75] Inventors: Raymond H. Long, Morristown, I

w m v Bauer, New York The present Invention discloses a process for produc- NY mg iron oxide pellets of low residual sulfur. in the pelletizing of finely divided ore with carbonaceous mate- [73] Asslgnee: The Lummus Company Bloomfield rials as binder, varying amounts of sulfur are intro duced. Green pellets are heated under conditions 22 Filed; Ju|y 20 972 leading to coking of the binder and recovery of the cracked vapors. The coked pellets are then further [211 Appl' 273522 heated to achieve the desired degree of reduction and to diminish the residual sulfur content. A sulfur scavenger is initially sprayed on the ore. For pellets that will be reduced 85 percent or less, all necessary reduc- U S Cl 75 tant is incorporated in the pellet, in the form of the [51] In. .Cl 1/28 Coked binder and, Optionally added carbon. Heating [58] 75/4 3 to the reduction and calcining temperature is rapid. ie 0 For highly reduced pellets (+85 percent) the Same procedure may be followed, but heating to reduction and calcining temperature must be slow for good de- [56] References Cited sulfurization. A preferred alternative for highly prere- UNITED STATES PATENTS duced pellets involves reduction in two stages: initially 2 805 14] 9/1957 A u 75 a 25-50 percent reduction is carried out with rapid l434 10/1957 X heating and with all reductant in the pellet. Then, the M960 Haworsonm H 75/3 pellets are further reduced with a stoichiometric 3,093,474 6/l963 Collin 75/3 X excess of reductant external to the pellet, with fast 3,2l8,l52 ll/l965 Sasabe 75/3 X heating to reduction temperature. Because of the 3, l1/l965 Heilmflnn Blfllm X inherently porous nature of pellets produced with 7 4/1967 Q W ill-m 75/3 liquid carbonaceous binders reduction is signifigi'i lf f /2 cantly faster and more complete than with 'con' 5:495:97] 2/:970 Ban 75/3 Venmma' pellets 3,642,465 2/1972 Sze et al. 75/4 34 Claims, 3 Drawing Figures Ore Mgcl etc. Residual Oil Preheat F" "1 I Carbonize l 1 l l Pelletl ze Carbonlze l l Coking l l i Hydrocarbon 1 Low Recovery Reduction Carbon i i Lirriestane I High Reduction Screen M t 5.32m.

Cool 8 552M Product PFJENTEU 1 I975 1,865,574

SHEET 10F 3 Cl r e MgCI ,etc. Residual Oil Preheat F"'" "L I Carbonize L I Pelletize Carbonize I t l l Coking i F Hydrocarbon I Low Recovery Reduction l i l CCll'bOn m- I Limestone High Reduction Screen Magnetic Separation 1 Cool 8t Product Recycle Fe Fig. I.

SHEEI 2 BF 3 Pellets containing integral Carbon Conventional Pellets Legend:

n QS BQE Time 0bove|300 F, Hours Fig. 2.

PATENTEU 5 SHEET 3 OF 3 Residual Oil I l 3 Ore L D t Additives Preheat & Carbonize Pelletize r- Recycle L Coking "f'\ I Mill screen Hydrocarbon l Recovery Law Reduction Process By-Product Fuel Gas Liquid Hydrocarbons High Reduction & Recycle Screen Screen Cool Cool Product Separation Pellets l h Iron Recycle Relect a Fines FlG.3

PROCESS FOR THE PRODUCTION OF LOW-SULFUR PREREDUCED IRON PELLETS BACKGROUND OF THE INVENTION In U.S. Pat. No. 3,642,465 issued Feb. 15, 1972 and assigned to the same assignee as the instant application, there is described a process wherein a liquid carbonaceous feedstock at a temperature above 300F. is sprayed on preheated finely divided ore, so that the oil cracks on contact with the ore. Under such conditions, little or no agglomeration takes place, but an evenly dispersed ore-carbon mixture results. After intermediate grinding, if necessary, the mixture is fed to a pelletizer maintained at a lower temperature, where additional residual oil at a high temperature is sprayed thereon, with little or no cracking taking place, and pellets are formed in the A to 2 inch size range. The pellets are passed to a coker maintained at a temperature of 900-l ,400 F. where the volatile content of the pellets is cracked and driven off. Since the amount of volatile material in the pellets is sufficiently low, vapor evolution during coking does not cause significant size degradation, but pellets of a distinct, finely porous structure are produced. Such pellets are described in U.S. Pat. No. 3,420,656, also assigned to the same assignee as the instant application. The coked pellets contain sufficient carbon to achieve the desired degree of reduction of iron oxides in the pellet. The hot coked pellets are then passed to a calciner maintained at a temperature of about 1,800-2,300F. to form highly prereduced pellets. After reduction, the reduced pellets are screened and cooled. Cracked gas is recovered from the carbonizer and the coker and supplied to a combination still, from which by-products are recovered.

Partially reduced pellets of the above-described type are most useful as a blast furnace feed, and can be used as a portion of the ore burden or all of it. The blast furnace is a very efficient reducing device, and does not require, or benefit from, using a very highly reduced burden (see, on this point, Agarwal and Pratt, The Thermodynamic Aspects of Using Partially Reduced Burdens," Transactions, AIME Ironmaking Conference, 1965).

Most of the prior art processes utilize coal or coke as the reductant. The above-noted patents, on the other hand, use a liquid carbonaceous material such as a residual oil, and/or a coal tar pitch. There are several advantages to using residual oils and like materials as a reductant. The main advantage is that the cracked vapors can be recovered and sold as high-grade byproducts. Under theright circumstances, the value of these by-products is at least equal to the cost of the liquid carbonaceous feedstock and the carbon layed down and used as reductant is essentially a no-cost item. Another advantage of using hydrocarbon oils is that they eliminate the need for other binders. Also, the resulting coke structure in the pellets is fine grained, evenly dispersed and porous, making reduction faster and more uniform.

While it is possible to produce highly prereduced pellets by following the teachings of the above patents, commercially available liquid carbonaceous feedstocks contain varying amounts of sulfur, some of which will be found in the prereduced pellet. This will render such pellets less desirable for blast furnace use and, in many instances, unfit for electric furnace melting.

OBJECTS OF THE INVENTION The general object of the present invention is to provide a process for producing prereduced pellets wherein residual sulfur in the prereduced pellets is diminished.

A further object of the invention is to provide prereduced pellets adapted for blast furnace use, and containing less than about 0.25 percent residual sulfur.

Other objects and advantages of the invention will become clear from the following description of embodiments thereof, and the novel features will be particularly pointed out in connection with the appended claims.

THE DRAWINGS Reference will hereinafter be made to the accompanying drawings, wherein:

FIG. I is a simplified flow sheet illustrating a preferred embodiment of the invention adapted to produce highly prereduced pellets employing high-sulfur petroleum residual oils;

FIG. 2 is a chart chowing heating and reduction curves for conventional pellets and pellets made in accordance with the invention; and

FIG. 3 is a simplified flow sheet illustrating an alternative embodiment of the invention.

DESCRIPTION OF EMBODIMENTS In essence, the present invention achieves lowered sulfur levels by a controlled calcining treatment. It has been determined that pellets of less than percent prereduction should be heated quickly to a calcining temperature in the range of l,800-2,500F., generally l,900-2,l00F. to maximize desulfurization. Pellets that will be highly prereduced, on the other hand, contain more carbon and profit from a slow heating to the calcining temperature. However, high prereduction and fast heating can be combined by limiting the carbon in the pellet, and completing the reduction with external carbon. Desulfurization is aided by the addition of known sulfur scavenging compounds. It is to be noted that while 85 percent prereduction is herein considered the change-over point from fast heating to slow heating, the advantages of the respective heating rates are most apparent at reduction levels below 85 percent and above percent, respectively, and desulfurization at reduction levels between these figures is not as dependent on heating rate.

Pellets containing residual sulfur to be treated in accordance with this invention maybe prepared in a variety of ways. The carbonizer may be a rotatingdrum equipped with means for injecting hot residual oil, to

make seed pellets which are then grown to desired size. Recycled coke fines, ore fines etc. may be used as seed particles. Or, coke from resid produced in a delayed coker and then comminuted may be employed.

In the embodiment of the invention wherein highly prereduced pellets of low sulfur content are produced from a high-sulfur residual oil, the carbonizer product is used externally to the ore pellets in the high reduction stage, and no sulfur scavenger is added in the car bonizer.

For pelletizing, it is preferable to deliver the oil at a temperature where it flows readily but below its cracking temperature. With many residual oils, a temperature in the range of 300-750F is satisfactory. For carbonizing, the finely divided ore is heated in a carbonizer to a much higher temperature, 900l ,300F. The resultant average temperature is usually in the 750-l,l00F range. A sulfur scavenging compound may be first sprayed on the hot ore inappropriate amount, when desired. The sulfur-containing oil is then sprayed onto the agitated ore and cracks immediately on contact therewith. Since the carbon is layed down on the ore particles, the particles will grow in size even though little if any agglomeration takes place. it is therefore desireable to grind the carbonized mixture in order to provide a proper feed size for the pelletizing step. Feed to the pelletizer is preferably 50-80 percent minus 325 mesh. It is desireable to limit oil injection into the pelletizer to that level which leads to optimum pelletizer operation and best green pellet properties, usually 7 to 50wt. percent of the solids feed.

Pelletizing is carried out with the ore-carbon mixture and the residual oil at a temperature of 350-800F. (preferably 400-750F.) though variations may occur with particular oils. Desired pellet size is usually in the A to 2 inch range, depending on end use. Any of the well-known types of pelletizers that can operate at elevated temperatures can be employed in this step. The total amount of carbon of any form incorporated into the pellet depends on reduction desired and end use, as will hereafter become apparent.

The green pellets are conveyed while hot directly to the coking kiln. The kiln must be heated by means other than direct firing so as to permit recovery of gases resulting from cracking of the hydrocarbon binder. In the kiln the temperature of the pellets is raised to about 900-l,400, preferably l,00O-l ,300F., and hard, strong pellets are produced having a porous finegrained coke structure. For blast furnace pellets, the total amount of residual oil used in the carbonization and pelletizing steps is controlled so that the carbon content of the pellets is slightly greater than the stoichiometric quantity required for the desired degree of total reduction. It is convenient and economical to use the exhaust gas from the reduction kiln, with supplementary fuel as required, to supply heat to the coking kiln. The hot, coked pellets discharged from the coker are passed directly to the reduction kiln or calciner, which may be directly fired.

The reduced pellets are cooled to a temperature below 250F. in a protected, non-oxidizin g atmosphere.

It is to be noted that p'ellet preparation may be carried out in the manner described in the above mentioned U.S. Patents for some of the processing schemes herein disclosed. it will be appreciated that an intimate ore-carbon mixture may be prepared by mixing any low-volatile carbonaceous material with the ore. Finely ground coal, preferably deashed, or coke may be used in this service. Fluxes and sulfur-acceptors or substances conducive to sulfur elimination should be added to the ore-carbon mixture.

The amount of carbon present and in contact with the pellet in the reduction kiln determines the degree of prereduction that will be achieved. In accordance with the present invention, this can be broken down into five categories or schemes. which are summarized hereinbelow in Table l. The first scheme relates toproducing blast furnace pellets of low prereduction, preferably 35-50 percent. Carbon for reduction is provided solely by the liquid binder material, without added carbon. The binder-to-solids ratio is chosen to provide good pelletizing operation and high pellet strength. Depending on the binder or, more accurately, its Conradson Carbon number, sufficient integral carbon will be laid down in the pellet for the desired reduction. Generally residual oils will provide enough carbon for 25-60 percent reduction.

In the second scheme, some solid carbon is added to the ore prior to pelletizing, thereby increasing the carbon-to-ore ratio while maintaining the binder-to-ore ratio at a level consistent with good pelletizing practice. This is used primarily for prereduction in the 50-80 percent range and, again heating to the calcining temperature should be rapid.

The third scheme differs from the second in that enough solid carbon is added to make high prereduction percent) possible. in this instance, heating to the calcining temperature should be slow, to achieve desired desulfurization.

The fourth scheme can be visualized as combining the first or second schemes (i.e., relatively low reduction with fast heating) and a second reduction treatment including added carbon external to the pellets.

The last scheme utilizes a highly carbonaceous internal binder, such as coal tar pitch, with fast heating for reduction of up to 85 percent, and slow heating where even greater reduction is desired.

FIG. 1 illustrates, in greatly simplified form, the fourth scheme for producing highly reduced pellets (as much as percent).

In forming the pellets, only sufficient residual oil is used so that carbon remaining after coking will be consumed in reducing the pellet about 25-50 percent. The first reduction is carried out with fast heating to reduction temperature in a direct fired furnace, such as a rotary kiln. Essentially all of the carbon in the pellet is consumed in this reduction, and the resulting partially reduced pellets are quite porous. They are immediately charged to the high reduction kiln, along with a substantial stoichiometric excess of carbon and limestone or other sulfur scavenger, the particle size of these additives after reduction is complete being sufficiently smaller than the pellets to permit subsequent separation by screening. For example, if the pellets are in the to A-inch range, the reductant should pass a %-inch screen.

The high reduction kiln is also directly tired, and it is preferred that the load factor be kept low, about 8 to 15 percent, preferably below 12 percent, to maximize heat transfer from the kiln walls to the bed and by direct radiation from the flame. Because of the pellet porosity, reduction proceeds much faster than with solid pellets (i.e., CO can penetrate into the pellet and CO can leave much quicker).

The excess carbon for the high reduction stage may optionally be carbonized residual oil, as shown on the drawing, agglomerated to a proper size, or an external source of carbon may be used, including coal or coke from any source, crushed to the desired size range.

It will be appreciated that in the high reduction stage there is no further contamination of the pellets with sulfur, since nothing is added to the pellets, and sulfur in the reductant is scavenged with limestone or dolomite.

The burden leaving the high reducer kiln is subjected to splitting operations. [f the size of carbon pellets is carefully controlled as previously taught, it is convenient to use screening to achieve the desired splits. The burden is first passed over a screen to retain and discharge finished pellets. The underflow is again subjected to separation according to size. The retained second cut consists primarily of partially used coke which is conveyed back to the feed end of the high reducer for recycle. The undersize material consists of some coke fines, calcium compounds and gangue "and ferruginous fines. Depending upon local and economic factors, this stream may be cooled and discarded or subjected to magnetic separation or other treatment for recovery of iron and carbon values.

Prereduction using external carbon is not in itself novel; the well-known SL-RN process utilizes this approach. In the prior art, the rate of reduction is relatively slow, and it is apparently difficult to achieve high levels of pre-reduction. Residence times of many hours are required and high operating temperatures, sometimes over 2,000F. create attendant fusion and ringing problems. A high load factor (20-40 percent), large kilns and a long residence time are all necessary to achieve reasonable production, because of poor reactivity and the great excess of carbon present.

Pellets produced according to the teachings of the patents noted hereinabove, after coking, contain integral carbon and a uniform porous structure and exhibit markedly superior reducibility as demonstrated in the Examples. The following advantages are to be noted from FIG. 2, which shows heating and reduction curves for pellets of the invention and conventional pellets (purchased):

1. Comparable reduction levels are attainable in a fraction of the residence time required by conventional pellets.

2. Essentially complete reduction is attainable in a practical residence time (2 to 2 A hours), whereas conventional pellets achieved only 54 percent reduction 2 hours and showed little likelihood of achieving much over 60 percent reduction in a practical time interval.

Additionally, the gas make has a significantly lower CO/CO ratio. At comparable levels of prereduction, the ratio would be even more favorable. This implies more efficient utilization of reductant as well as significant reduction in heat duty and equipment size. As a result of these advantages, it is now possible to conduct reduction of pellets in rotary kilns of practical and economical size. Furthermore, the high reactivity of the pellets permits reduced temperatures during the terminal phase of reduction (from about 40 to 60 percent reduction to the desired product pellet reduction level), a range particularly susceptible to tackiness and kiln ranging problems.

petroleum resid binder plus solid TABLE I-Continued Reduction Level.% Heating Broad Preferred Rate Scheme Carbon Range Range 1500F.

to T,-

carbon lV Internal: all from petroleum resid binder. plus External: solid carbon 40-100 50-100 Fast VA internal: all from highly carbonaceous binder such as coal tar pitch 50-85 60-85 Fast VB Internal: all from highly carbonaceous binder such as coal tar pitch -100 -100 Slow After reduction, the product pellets are cooled in a protective atmosphere, to prevent re-oxidation, as is conventional.

However, it is advantageous to tumble the pellets during cooling, as this tends to close up the pores therein and increase the resistance of the pellets to weathering. Also, the cooling pellets may be tumbled with finely divided ore or limestone, both of which will tend to fill the pores (and both of which will be preheated), with the same effect of increasing resistance to weathering.

As can be seen from Table l, schemes 1, II, N, and VA require fast heating for proper desulfurization. Effective desulfurization is achieved by heating the pellets rapidly, in a period under 1 hour and preferably under 45 minutes, from a temperature of 1,500F. to an upper temperature of l,800-2,500F., preferably 1,9- O0-2,l00F., and maintaining such upper temperature for a period of 15 minutes to 6 hours, and preferably 30 minutes to 2 hours. Desulfurization is defined as:

o SI/SO) where S sulfur content of finished pellets if all the sulfur content of the integral carbon had been retained. S,= actual sulfur content of finished pellet. Using the above method, desulfurization of 50 to 85 percent is achieved with the invention.

For schemes Ill and VB (+85 percent reduction), effective desulfurization is achieved by maintaining a slow heating schedule, a period between 1 and 6 hours,

preferably 1 /2 to 3 hours, from 1,500F. to an upper temperature of 1,800-2,500F., preferably l,900-2,100F., and maintaining such upper temperature for 30 minutes to 6 hours, and preferably 45 minutes to 2 hours. Desulfurization up to 91 percent can be achieved in this manner.

The use of certain additives, in conjunction with the heating schedules disclosed above was found to enhance remarkably the ease and attainable degree of desulfurization. The following combinations have been found effective:

CaCl

CilCO (a0 NaCl MgCl CaSO, FeCl In general, additives may consist of metal chlorides, preferably alkali or alkaline-earth chlorides, or FeCl alone or in combination with calcium sulfate, alkalineearth oxides or carbonates. The additives may be incorporated in the pellets by feeding with the ore to the pelletizer and to the carbonizer, or by suspension in finely divided form in the binder prior to spraying into the pelletizer or the carbonizer. Water soluble additives (viz., the metal chlorides) may be conveniently sprayed into the ore prior to the ore drying and heating operations. The restriction that need be observed is that the additives be uniformly dispersed in the pellet, the particle size of the dispersed additives being at least under 100 mesh and preferably 100 percent under 200 mesh. The dosage of additives may be quite low; good results have been achieved with dosages in the range of 0.01 to percent, but for consistent results in the range of 0.5 to 3 percent is preferred. These dosages are expressed in terms of weight percent relative to ore used.

Use of the above additions in conjunction with the previously specified heat treatments permits desulfurization up to 99 percent for Schemes I, 11, IV, and VA and up to 94 percent for categories III and VB.

pellets and fines generated in the process are ground to about 80 percent minus 325 mesh size. The carbonizer product solids are comminuted to about the same size range.

The mixture at this stage, at a temperature of 700-850F., is passed to the pelletizing drum with preheated ore, where additional quantities of the pre heated oil are sprayed on and pellets are formed. The pellets contain 7.6 percent solid carbon and 13.2 percent residum. The hot pellets, which are mostly in the to inch size range, are conveyed to the coker. As a bed for the pellets during coking, a circulating load of hot sand may be employed. The coker discharge is screened and the sand is recirculated.

Reduction and calcining of various pellets without desulfurizing additives was carried out in accordance with the invention, and the results are set forth in Table 11. Run A demonstrates the advantage of slow heating for high prereduction, and shows that a high final temperature is unnecessary. Run B shows that for lower prereduction fast heating is preferable. Run C, for 85 percent reduction, indicates that fast heating is preferable, but this is a gray area.

TABLE II CONTROL OF SULFUR CONTENT OF PELLETS: EFFECT OF TIME-TEMPERATURE HISTORY HEATING SULFUR CALCULATED ACTUAL OXIDE SULFUR RATE: CONTENT CONTENT IN SULFUR REDUCTION ELAPSED FINISHING SOAKING IN CALCINED PELLET CONTENT IN OBSERVED LEVEL OF IF TIME FROM TEMP.. TIME COKED ALL SULFUR WERE CALCINED DESULFUR- CALCINED I500F T0 T AT PELLETS RETAINED, PELLETS ZATION PELLETS, RUN 'T, HRS. "F T,- HRS. WT. WT. WT. A-l 6.0 (slow) 2000 2.0 0.98/0.99 1.66 0.1 U012 93 99+ A-2 8.0 (slow) 2100 10.0 098/099 1.66 0.10/01 I 94 99+ A-3 0.2 (fast) 2200 0.5 0.98/0.99 1.66 1.43/1.92 0 99+ A-4 0.2 (fast) 2400 0.5 098/099 1.66 109/127 29 99+ A-5 02 (fast) 2500 0.5 0.98/0.99 1.66 0.88/1.62 99+ B-l 8.0 (slow) 2000 8.0 0.54 0.79 0.85 i 0 77/79 13-2 0.2 (fast) 2200 0.5 0.54 0.79 0.38/039 51 77/79 3-3 0.2 (fast) 2000 0.5 0.54 0.79 0.43 45 77/79 B-4 0.2 (fast) 2000 0.5 0.54 0.79 0.59 25 77/79 3-5 0.2 (fast) 2000 0.5 0.54 0.79 0.63 20 77/79 86 0.2 (fast) 1800 0.5 0.54 0.79 0.55 77/79 B-7 0.2 (fast) 2400 0.5 0.54 0.79 0.43 77/79 B-8 0.2 (fast) 2500 0.5 0.54 0.79 0.32 77/79 CI 8.0 (slow) 2200 10.0 0.18 0.27 0.20 26 85 C-2 0.2 (fast) 2000 0.5 0.18 0.27 007/009 C-3 0.2 (fast) 2200 0.5 0.18 0.27 0.08 70 85 EXAMPLES It will be noted that because of pellet weight loss dur- The hot ore, at about 1,200F., is fed to the carbonizing kiln, where a 7.4 API gravity oil is sprayed onto it.

The oil is preheated to 600F. before spraying, and 60 ing reduction, without any desulfurization, an increase in reported sulfur content would be expected, and decreases in sulfur content are proportionally greater than the numbers indicate.

The desulfurization achieved by the beneficial timetemperature relations as set forth above is further improved by the use of chemical additives, including calcium, sodium, magnesium and iron compounds. Re-

65 sults using various additives are shown in Table III.

TABLE TIL-CONTROL OF SULFURCONIENT F IELLEIS: EFFECT OF ADDITIVES Calculated Actual Sulfur sullur content sullur Oxide content in calcined content in reduction Additives Heating rate.- Soaking in coked pellet il all calcined Observed level of dosage. elapsed time Finishin time at pellets, sulfur were pellets, desuliurcalcined wt. percent from 1.500 F. temp, T wt. retained, wt. ization, pellets. (based on Run to TF hours Tr F. hours percent wt. percent percent percent percent ore weight) D-l 0.2 (last) 2,300 0.5 0.15 0.175 0.15/0 17 0 38/40 D-2 o m 2,300 0.5 0.15 0.175 0. /017 9 38/40 3.0 CaCO; H-1 2.5 (slow) 2,300 1.0 0.78 1.31 0.20 80 08+ 3.0% CaCO 1.0% NaCl H-2 d0 2,300 1. 0 0.78 1. 31 0. 33 75 98+ 3.0% CaO 1.0% NaCl H-3 4.0 (slow) 2,300 16.0 0.78 1.31 0.53 60 08+ 3.0% (7:10

5.05; 8a?! .0 at 11-4 4.0 (slow) 2,300 10.0 0.78 1.31 0.11 92 98+ 2 Nae! J-l 1.0 2,100 16.0 0. 7/0. 78 1.24 0.25 80 08+ 3.0%, MgCl- J-2 2.5 (slow) 2, 300 10.0 0.71078 1. 24 0.10 87 08+ J-3 2.0 (sl0w) 2, 300 2.0 0. 7/0. 78 1. 24 0. 24 81 08+ 4.0% MgCl: J-5 0.5 (last) 2,000 2. 0 0. 47/048 0. 65 01/02 77 64/08 3.0% MgCl To determine the reducibility of pellets produced by the teachings in the patents noted hereinabove, (i.e., produced by balling with resid followed by coking) with commercial pellets produced by conventional methods (i.e., ballingwith bentonite addition followed by calcining), 150 gm samples of each were subjected to similar time-temperature heat cycles.

In each test pellets were packed in a vertical l inch ID tube with a considerable excess of granular coke. The tube was mounted in avertical electric oven, with the 14 inch deep charge completely within the heated zone. The top of the tube was closed and connected to gas sampling and measuring means. In each test the temperature was raised rapidly to l,30()F., then gradually ovcr a period of about I hour to 2,000F. and maintained at this level until gas evolution practically ceased. Gas samples were analyzed periodically for CO and C0 The results of these tests are summarized in Table V and FIG. 2.

TABLE V sumed),'as taught in the preferred embodiment, even lower CO/CO ratios should obtain. This implies corresponding saving in carbon and energy requirements.

The product pellets were uniform, dense, and free of fissures or defects. The conventional pellets yielded product pellets of varying diameters (corresponding generally to variations in degree of reduction), and showed considerable cracks and some fragmentation.

COMPARATIVE REDUCIVILITY IN STATIC BED PACKED WITH COKE ANDPELLETS Pellets Made With Rcsid* Conventional Pellets Initial Pellet Charge I gm Gas Make: CO 25.65 liters CO l0.l5 liters H O (estimated) 2.20 liters Total 38.00 liters CO/CO- Ratio 2.52 Reduction,

Based on Gas Make 97.0% Based on Pellet Analysis 99.5%

I50 gm l8.60 liters 4.40 liters 1.40 liters 24.40 liters "lhcsc pellets contained integral carbon equivalent to V! to prci'educlion This test shows a remarkable improvement in the performance of pellets made according to the teachings of this disclosure and the prior patents as compared to conventional pellets. More rapid reduction is achieved. For example, a 54 percent reduction levelis achieved after 0.8 hour vs. 2 hours for the conventional pellets at a maximum temperature of 1,835F. vs. 2,000F. Within a time interval of 2 hours, compatible with practical and economic rotary kiln design, substantially.

pelletizing said ore and a minor proportion of'a sulfur-scavenging compound by spraying said carbonaceo us material thereon while agitating same, said carbonaceous material being heated to a flowable temperature and maintaining the temperatures in the pelletizing mixture below the cracking temperature and said carbonaceous material;

coking the pellets thus formed, the coked pellets containing sufficient carbon to effect about 25 to percent reduction of said ore;

heating the coked pellets to raise the temperature of the pellets to a final reduction temperature in the range of l,900 to 2,100F, during said heating the temperature of the pellets being raised from l,500F to said final temperature in less than about 1 hour; and

retaining said pellets at said final temperature for from /2 to 2 hours.

2. The process as claimed in claim 1, wherein said fluid carbonaceous material is selected from the group consisting of residual oils and coal tar pitch.

3. A process for producing prereduced iron oxide pellets of low-sulfur content from ore and a sulfurbearing fluid carbonaceous material comprising:

forming a mixture of finely divided ore, a minor proportion of a sulfur-scavenging compound and a predetermined amount of finely divided carbon under non-agglomerating conditions;

pelletizing said mixture by spraying said carbonaceous material thereon while agitating same, said carbonaceous material beig heated to a flowable temperature and maintaining the temperature in the pelletizing mixture below the cracking temperature of said carbonaceous material;

coking the pellets thus formed, the coked pellets containing sufficient carbon to effect about 25 to 85 percent reduction of said ore;

heated the coked pellets to raise the temperature of the pellets to a final reduction temperature in the range of l,900 to 2,100F, during said heating the temperature of the pellets being raised from 1,500F to said final temperature in less than about 1 hour; and

retaining said pellets at said final temperature for from 1 /2 to 2 hours.

4. The process as claimed in claim 3, wherein said fluid carbonaceous material is a residual oil.

5. A process for producing highly prereduced iron oxide pellets of low-sulfur content from ore and a sulfur-bearing fluid carbonaceous material comprising:

forming a mixture of finely ore, a minor proportion of a sulfur-scavenging compound and a predetermined amount of finely divided carbon under nonagglomerating conditions;

pelletizing said ore mixture by spraying said carbonaceous material thereon while agitating same, said carbonaceous material being heated to a flowable temperature and maintaining the temperature in the pelletizing mixture below the cracking temperature of said carbonaceous material;

coking the pellets thus formed, the coked pellets containing sufficient carbon to effect about 85 to 100 percent reduction of said ore;

heating the coked pellets to raise the temperature of the pellets to a final reduction temperture in the range of l,900 to 2,lOF, during said heating the temperature of the pellets being raised from l,500F to said final temperature in from aboutl /z to 3 hours; and

retaining said pellets at said final temperature for from to 2 hours.

6. The process as claimed in claim 5, wherein said fluid carbonaceous material is a residual oil.

7. A process for producing highly procedured iron oxide pellets of low-sulfur content from ore and a sulfur-bearing fluid carbonaceous material comprising:

pelletizing said ore and a minor proportion of a sulfur-scavenging compound by spraying said carbonaceous material thereon while agitating same, said carbonaceous material being heated to a flowable temperature and mantaining the temperature in the pelletizin g mixture below the cracking temperature of said carbonaceous material;

heating the coked pellets to raise the temperature of the pellets to a final reduction temperature in the range of l,900 to 2,100F, during said heating the temperature of the pellets being raised from 1,500F to said final temperature in less than about 1 hour;

retaining said pellets at said final temperature for from to 2 hours; and

mixing said partially reduced pellets with a stoichiometric excess of carbon containing a minor proportion of a sulfur-scavenging compound and maintaining the pellet-carbon mixture at said final reduction temperature for a period sufficient to effect in excess of 90 percent reduction of said ore. 8. The process as claimed in claim 7, wherein said fluid carbonaceous material is a residual oil.

9. A process for producing prereduced iron oxide pellets of low-sulfur content from iron oxide pellets containing integral carbon comprising:

pelletizing iron oxide with a sulfur-bearing carbonaceous fluid as binder to produce iron oxide pellets;

subjecting the iron oxide pellets to coking conditions to coke said binder and produce integral carbon, said binder providing at least a portion of the integral carbon in said pellets, the coked pellets containing sufficient integral carbon to effect from about 25 to about percent prereduction of the iron oxide pellets; heating the iron oxide pellets containing integral carbon to raise the temperature of the iron oxide pellets to a final prereduction temperature of from about l,800 F, during said heating the temperature of the pellets being raised from a temperature of about 1,500F to the final reduction temperature in a time of less than about 1 hour; and

maintaining the iron oxide pellets at the final reduction temperature to produce prereduced iron oxide pellets.

10. The process of claim 9 wherein the iron oxide pellets heated to the final reduction temperature integrally include a minor proportion of a sulfur scavenging compound.

11. The process of claim 10 wherein the sulfur scavenging compound is at least one member selected from the group consisting of calcium chloride, magnesium chloride, ferric chloride, a mixture of sodium chloride and calcium carbonate and a mixture of sodium chloride and calcium oxide.

12. The process of claim 9 wherein the final reduction temperature is from l,900 to 2,100F, and the temperature of the pellets is raised from a temperature of about l,500F to the final reduction period in a time less than /1 hour.

13. The process of claim 12 wherein the coked binder provides a portion of the integral carbon, the remainder of the integral carbon being provided by the addition of finely divided carbon to said iron oxide prior to the pelletizing.

14. The process of claim 13 wherein the finely divided carbon is added to the iron oxide by spraying fluid carbonaceous material onto a preheated, agitated bed of finely divided iron oxide, said iron oxide being at a temperature sufficient to crack the fluid carbonaceous material to produce a finely divided carbon.

15. The process of claim 9 wherein said iron oxide pellets are reduced at the final reduction temperature in the presence of external carbon in a stoichiometric excess of the amount required to achieve the prereduction and a minor portion of a sulfur scavenging material.

16. The process of claim 15 wherein the external carbon is selected from the group consisting of coal, coke and mixtures thereof.

17. The process of claim 16 wherein the sulfur scavenging compound is selected from the group consisting of limestone and dolomite.

18. The process of claim 17 wherein the final reduction temperature is from about l,900 to about 2,lF, the temperature of the pellets being raised from a temperature of 1,500F to the final reduction temperature in a time of less than /1 hour.

19. The process of claim wherein the iron oxide pellets heated to the final reduction temperature integrally include a minor proportion of a sulfur scavenging compound.

20. The process of claim 15 wherein the coked binder provides a portion of the integral carbon, the remainder of the integral carbon being provided by the addition of finely divided carbon to said iron oxide prior to the pelletizing.

21. The process of claim 20 wherein the finely divided carbon is added to the iron oxide by spraying fluid carbonaceous material onto a preheated, agitated bed of finely divided iron oxide, said iron oxide being at a temperature sufficient to crack the fluid carbonaceous material to produce a finely divided carbon.

22. The process of claim 9 wherein the sulfur bearing carbonaceous fluid employed as binder is selected from the group consisting of residual oils and coal tar pitch.

23. The process of claim 9 wherein the final reduction temperature is from l,900 to 2, l 00F, the temperature of the pellets being raised from a temperature of 1,500F to the final reduction temperature in a time less than hour.

24. The process of claim 23 wherein the iron oxide pellets are held atthe final reduction temperature for from A to 6 hours.

25. A process for producing prereduced iron oxide pellets of low-sulfur content from iron oxide pellets containing integral carbon, comprising:

subjecting the iron oxide pellets to coking conditions to coke said binder and produce integral carbon, said binder providing at least a portion of the integral carbon in said pellets, the coked pellets containing sufficient carbon to effect a greater than 85 percent prereduction; heating the iron oxide pellets containing integral car bon to raise the temperature of the iron oxide pellets to a final reduction temperature of from about l,800 to about 2,500F, during said heating the temperature of the pellets being raised from a temperature of l,500F to the final reduction temperature in a time of from 1 to 6 hours; and

26. The process of claim 25 wherein the iron oxide pellets heated to the final reduction temperature integrally include a minor proportion ofa sulfur scavenging compound.

27. The process of claim 26 wherein the sulfur scavenging compound is at least one member selected from 5 the group consisting of calcium chloride, magnesium chloride, ferric chloride, a mixture of sodium chloride and calcium carbonate and a mixture of sodium chloride and calcium oxide.

28. The process of claim 27 wherein the sulfur bearing carbonaceous fluid employed as binder is selected from the group consisting of residual oils and coal tar pitch.

29. The process of claim 27 wherein the final reduction temperature is from l,900 to 2,lO0F and the temperature of the pellets is raised from a temperature of l,500to the final reduction temperature in a time from one and /2 to 3 hours.

30. The process of claim 25 wherein said iron oxide pellets are reduced at the final reduction temperature in the presence of external carbon in a stoichiometric excess of the amount required to achieve the prereduction and a minor portion of a sulfur scavenging material.

31. The process of claim 25 wherein the coked binder provides a portion of the integral carbon, the remainder of the integral carbon being provided by the addition of finely divided carbon to said iron oxide prior to the pelletizing.

32. The process of claim 31 wherein the finely divided carbon is added to the iron oxide by spraying fluid carbonaceous material onto a preheated, agitated bed of finely divided iron oxide, said iron oxide being at a temperature sufficient to crack the fluid carbonaceous material to produce a finely divided carbon.

33. A process for producing 70-85 percent prereduced iron oxide pellets of low-sulfur content from ore and a coal tar pitch, comprising:

pelletizing said ore and a minor proportion of a sulfur-scavenging compound by spraying said pitch thereon while agitating same, said pitch being heated to a flowable temperature and maintaining the temperature of the pelletizing mixture below the cracking temperature of said pitch;

coking the pellets thus formed, the coke pellets containing sufficient integral carbon to effect 70-85 percent reduction;

heating the iron oxide pellets containing integral carbon to raise the temperature of the pellets to a final reduction temperature of from l,900 to 2,l0O"F, during said heating the temperature of the pellets being raised from a temperature of l,500F to the final reduction temperature in a time of less than 5 1 hour; and

15 16 coking the pellets thus formed, the coked pellets conbeing raised from a temperature of 1,500F to the taining sufficient integral carbon to effect a greater .final reduction temperature in a time of from 1 to than 85 percent prereduction; -6 hours; and heating the iron oxide pellets containing integral carholding the iron oxide pellets at the'final reduction bon to raise the temperature of the pellets to a final temperature to produce prereduced iron oxide pelreduction temperature of from 1,900 to 2,l0OF, lets.

during said heating the temperature of the pellets UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 5,865, 571+ D t d February 11 1975 Invent Ravmond H. Long et a1 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Columns 9 and 10, Table III, along Run D-l, "0.15/0-17" should be 0.-l5/o,l7

Column 10, line so, "and" should be of Column 11, line 15, "beig should be being line 22, "heated" should be heating line 35, insert divided after "finely";

line 58, delete "procedured" and insert prereduced Column 12, line 35, insert to about 2500F after "l800F". Column 14, line s, "l500 should be l500F Signal and Sealed this Seventh Day of December 1976 [SEAL] RUTH C. MASON C. MARSHALL DANN A! ff Commissioner oflqrents and Trademarks

Claims

1. A PROCESS FOR PRODUCING PRE-REDUCED IRON OXIDE PELLETS OF LOW-SULFUR CONTENT FROM ORE AND A SULFUR-BEARING FLUID CARBONACEOUS MATERIAL COMPRISING: PELLETIZING SAID ORE AND A MINOR PROPORTION OF A SULFURSCAVENGING COMPOUND BY SPRAYING SAID CARBONACEOUS MATERIAL THEREON WHILE AGITATING SAME, SAID CARBONACEOUS MATERIAL BEING HEATED TO A FLOWABLE TEMPERATURE AND MAINTAINING THE TEMPERATURE IN THE PELLETIZING MIXTURE BELOW THE CRACKING TEMPERATURE AND SAID CARBONACEOUS MATERIAL; COKING THE PELLETS THUS FORMED, THE COKED PELLETS CONTAINING SUFFICIENT CARBON TO EFFECT ABOUT 25 TO 70 PERCENT REDUCTION OF SAID ORE; HEATING THE COKED PELLETS TO RAISE THE TEMPERATURE OF THE PELLETS TO A FINAL REDUCTION TEMPERATURE IN THE RANGE OF 1,9000* TO 2,100*F, DURING SAID HEATING THE TEMPERATURE OF THE PELLETS BEING RAISED FROM 1,500*F TO SAID FINAL TEMPERATURE IN LESS THAN ABOUT 1 HOUR; AND RETAINING SAID PELLETS AT SAID FINAL TEMPERATURE FOR FROM / TO 2 HOURS.

3. A process for producing prereduced iron oxide pellets of low-sulfur content from ore and a sulfur-bearing fluid carbonaceous material comprising: forming a mixture of finely divided ore, a minor proportion of a sulfur-scavenging compound and a predetermined amount of finely divided carbon under non-agglomerating conditions; pelletizing said mixture by spraying said carbonaceous material thereon while agitating same, said carbonaceous material beig heated to a flowable temperature and maintaining the temperature in the pelletizing mixture below the cracking temperature of said carbonaceous material; coking the pellets thus formed, the coked pellets containing sufficient carbon to effect about 25 to 85 percent reduction of said ore; heated the coked pellets to raise the temperature of the pellets to a final reduction temperature in the range of 1,900* to 2, 100*F, during said heating the temperature of the pellets being raised from 1,500*F to said final temperature in less than about 1 hour; and retaining said pellets at said final temperature for from 1 1/2 to 2 hours.

5. A process for producing highly prereduced iron oxide pellets of low-sulfur content from ore and a sulfur-bearing fluid carbonaceous material comprising: forming a mixture of finely ore, a minor proportion of a sulfur-scavenging compound and a predetermined amount of finely divided carbon under non-agglomerating conditions; pelletizing said ore mixture by spraying said carbonaceous material thereon while agitating same, said carbonaceous material being heated to a flowable temperature and maintaining the temperature in the pelletizing mixture below the cracking temperature of said carbonaceous material; coking the pellets thus formed, the coked pellets containing sufficient carbon to effect about 85 to 100 percent reduction of said ore; heating the coked pellets to raise the temperature of the pellets to a final reduction temperture in the range of 1,900* to 2,100*F, during said heating the temperature of the pellets being raised from 1,500*F to said final temperature in from about 1 1/2 to 3 hours; and retaining said pellets at said final temperature for from 3/4 to 2 hours.

7. A process for producing highly procedured iron oxide pellets of low-sulfur content from ore and a sulfur-bearing fluid carbonaceous material comprising: pelletizing said ore and a minor proportion of a sulfur-scavenging compound by spraying said carbonaceous material thereon while agitating same, said carbonaceous material being heated to a flowable temperature and mantaining the temperature in the pelletizing mixture below the cracking temperature of said carbonaceous material; coking the pellets thus formed, the coked pellets containing sufficient carbon to effect about 25 to 70 percent reduction of said ore; heating the coked pellets to raise the temperature of the pellets to a final reduction temperature in the range of 1, 900* to 2,100*F, during said heating the temperature of the pellets being raised from 1,500*F to said final temperature in less than about 1 hour; retaining said pellets at said final temperature for from 1/2 to 2 hours; and mixing said partially reduced pellets with a stoichiometric excess of carbon containing a minor proportion of a sulfur-scavenging compound and maintaining the pellet-carbon mixture at said final reduction temperature for a period sufficient to effect in excess of 90 percent reduction of said ore.

8. The process as claimed in claim 7, wherein said fluid carbonaceous material is a residual oil.

9. A process for producing prereduced iron oxide pellets of low-sulfur content from iron oxide pellets containing integral carbon comprising: pelletizing iron oxide with a sulfur-bearing carbonaceous fluid as binder to produce iron oxide pellets; subjecting the iron oxide pellets to coking conditions to coke said binder and produce integral carbon, said binder providing at least a portion of the integral carbon in said pellets, the coked pellets containing sufficient integral carbon to effect from about 25 to about 85 percent prereduction of the iron oxide pellets; heating the iron oxide pellets containing integral carbon to raise the temperature of the iron oxide pellets to a final prereduction temperature of from about 1,800* F, during said heating the temperature of the pellets being raised from a temperature of about 1,500*F to the final reduction temperature in a time of less than about 1 hour; and maintaining the iron oxide pellets at the final reduction temperature to produce prereduced iron oxide pellets.

12. The process of claim 9 wherein the final reduction temperature is from 1,900* to 2,100*F, and the temperature of the pellets is raised from a temperature of about 1,500*F to the final reduction period in a time less than 3/4 hour.

18. The process of claim 17 wherein the final reduction temperature is from about 1,900* to about 2,100*F, the temperature of the pellets being raised from a temperature of 1, 500*F to the final reduction temperature in a time of less than 3/4 hour.

19. The process of claim 15 wherein the iron oxide pellets heated to the final reduction temperature integrally include a minor proportion of a sulfur scavenging compound.

23. The process of claim 9 wherein the final reduction temperature is from 1,900* to 2,100*F, the temperature of the pellets being raised from a temperature of 1,500*F to the final reduction temperature in a time less than 3/4 hour.

24. The process of claim 23 wherein the iron oxide pellets are held at the final reduction temperature for from 1/4 to 6 hours.

25. A process for producing prereduced iron oxide pellets of low-sulfur content from iron oxide pellets containing integral carbon, comprising: pelletizing iron oxide with a sulfur-bearing carbonaceous fluid as binder to produce iron oxide pellets; subjecting the iron oxide pellets to coking conditions to coke said binder and produce integral carbon, said binder providing at least a portion of the integral carbon in said pellets, the coked pellets containing sufficient carbon to effect a greater than 85 percent prereduction; heating the iron oxide pellets containing integral carbon to raise the temperature of the iron oxide pellets to a final reduction temperature of from about 1,800* to about 2,500*F, during said heating the temperature of the pellets being raised from a temperature of 1,500*F to the final reduction temperature in a time of from 1 to 6 hours; and maintaining the iron oxide pellets at the final reduction temperature to produce prereduced iron oxide pellets.

26. The process of claim 25 wherein the iron oxide pellets heated to the final reduction temperature integrally include a minor proportion of a sulfur scavenging compound.

27. The process of claim 26 wherein the sulfur scavenging compound is at least one member selected from the group consisting of calcium chloride, magnesium chloride, ferric chloride, a mixture of sodium chloride and calcium carbonate and a mixture of sodium chloride and calcium oxide.

29. The process of claim 27 wherein the final reduction temperature is from 1,900* to 2,100*F and the temperature of the pellets is raised from a temperature of 1,500*to the final reduction temperature in a time from one and 1/2 to 3 hours.

33. A process for producing 70-85 percent prereduced iron oxide pellets of low-sulfur content from ore and a coal tar pitch, comprising: pelletizing said ore and a mInor proportion of a sulfur-scavenging compound by spraying said pitch thereon while agitating same, said pitch being heated to a flowable temperature and maintaining the temperature of the pelletizing mixture below the cracking temperature of said pitch; coking the pellets thus formed, the coke pellets containing sufficient integral carbon to effect 70-85 percent reduction; heating the iron oxide pellets containing integral carbon to raise the temperature of the pellets to a final reduction temperature of from 1,900* to 2,100*F, during said heating the temperature of the pellets being raised from a temperature of 1,500*F to the final reduction temperature in a time of less than 1 hour; and holding the iron oxide pellets at the final reduction temperature to produce prereduced iron oxide pellets.

34. A process for producing prereduced iron oxide pellets of greater than 85 percent prereduction and low-sulfur content from ore and a coal tar pitch, comprising: pelletizizng said ore and a minor proportion of a sulfur-scavenging compound by spraying said pitch thereon or agitating same, said pitch being heated to a flowable temperature and maintaining the temperature of the pelletizing mixture below the cracking temperature of said pitch; coking the pellets thus formed, the coked pellets containing sufficient integral carbon to effect a greater than 85 percent prereduction; heating the iron oxide pellets containing integral carbon to raise the temperature of the pellets to a final reduction temperature of from 1,900* to 2,100*F, during said heating the temperature of the pellets being raised from a temperature of 1,500*F to the final reduction temperature in a time of from 1 to 6 hours; and holding the iron oxide pellets at the final reduction temperature to produce prereduced iron oxide pellets.