US3190746A

US3190746A - Process for use of raw petroleum coke in blast furnaces

Info

Publication number: US3190746A
Application number: US227080A
Authority: US
Inventors: Alfred A Triska
Original assignee: SGL Carbon Corp
Current assignee: SGL Carbon Corp
Priority date: 1962-09-28
Filing date: 1962-09-28
Publication date: 1965-06-22
Anticipated expiration: 1982-06-22
Also published as: JPS5010802B1; GB999352A; BR6353005D0

Description

United States Patent 3,190,746 PROCESS FOR USE OF RAW PETROLEUM COKE IN BLAST FURNACES Alfred A. Trisha, Chicago, Ill., assignor to Great Lakes Carbon Corporation, New York, N.Y., a corporation of Delaware No Drawing. Filed Sept. 28, 1962, Ser. No. 227,080 8 Claims. (Cl. 75-42) This invention relates to a modification of, or departure from, conventional ore reduction practices. The invention is particularly suitable with respect to ore reduction practices in blast furnaces.

It is standard practice in the operation of such furnaces to build up a charge within the furnace consisting of a metallurgical coke, such as produced in a by-product coke oven, a flux or fiuxing agent such as limestone, and the iron ore to be reduced. The blast furnace is so designed that the ore, coke, and flux, in proper proportions, can be charged through a specially constructed opening in the top of the furnace; the top gas and flue dust are withdrawn for recovery, and use. At the same time, heated air from stoves, which obtain their heat from the combustion of a part of this top gas, is blown in near the bottom through openings called tuyeres, burning the coke thus releasing heat and forming carbon monoxide. This carbon monoxide passes up through the voids in the charge and re duces the iron ore. In this reduction the carbon monoxide is oxidized to carbon dioxide which in turn is reduced to carbon monoxide by the coke. This process continues up the stack until the gas escapes as top gas. The extent to which the top gas contains carbon dioxide is the extent to which the coke carbon has been completely utilized. The lower the reactivity of coke the less carbon dioxide is converted to carbon monoxide in the upper cooler portion of the blast furnace Where, principally, the time of contact with solid ore is short and rate of ore reduction is slower, due to low temperatures; and therefore more gasified carbon remains as carbon dioxide in the top gas and thus coke usage is reduced. The process is a continuous one except for the periodic removal of the impurities, in

the form of slag, and of the metal, through separate openings in the crucible of the furnace.

The charging cycle, viz. the sequence in which the principal raw materials-iron ore, limestone, coke-are charged into the furnace, varies from plant to plant. It

depends upon the physical character and chemical analyknown to the art. Only petroleum cokes having a volatile sis of the available ores and other raw materials, and also from time to time within an individual furnace, upon the kind of iron being produced and the irregularities in the furnace. Under normal conditions, furnaces are burdened with alternate layers of ferrous materials and coke, the latter sufiicient in amount to make a layer about inches in depth.

Although the operators of blast furnaces are not entirely uniform in their practices, they are in fairly general accord as to the properties which determine the value of coke as a metallurgical fuel. These properties are:

(a) Size-Ordinarily from 1 to 4 inches, with minimum fines;

, (b) HardnessTo produce minimum fines as the coke descends in furnace; V

(c) Strength-Adequate to support the ore and limestone;

(d) Porosity-To secure adequate rate of gasification;

(e) Absence of volatile or smoke-producing properties (not over 2 percent volatile matter);

(f) Presence of a minimum of fusing and coking prop erties;

(g) High percentage of fixed carbon (ash should not exceed 10 percent);

(h) Low content of sulfur and phosphorus;

(i) Cleanliness.

The preparation of cokes having such properties as listed, viz. desired size, hardness, strength, volatile matter content, etc., is a time consuming and expensive process for the coke manufacturer, and typically involves selecting and/or blending suitable starting materials such as certain bituminous coals, coking these in a coking oven at a suitable temperature for about 24 hours, and then screening out the fines from the total coke produced so that coke which has the proper minimumsize is furnished to the blast furnace. The proper minimum coke size varies in practice from /2" to 1" with the top size generally 3-4". The end product has been found to give very satisfactory results in a blast furnace if the blast furnace operator observes normal care in his methods of transferring the coke into the blast furnace. b Because of these satisfactory results there is, or has een, furnace operators to experiment with or try cokes in their furnaces which cokes have properties considerably different from those which they have found to give them satisfactory and predictable results.

It is a finding of this invention that raw petroleum coke, which has properties considerably different from many of those of standard metallurgical cokes, may be advantageously employed in the ore reduction process in blast furnaces.

It is preferable that the use of raw petroleum coke as a reducing agent in a blast furnace be as a partial replacement for conventional metallurgical cokes, rather than as a complete replacement therefor.

The raw petroleum cokes, 'whichmay be suitably employed as a reducing agent in a blast furnace, result from the thermal cracking and polymerization of heavy petroleurn residues such as reduced or top crudes, thermally or 'catalytically cracked residuums, etc. The coking is normally conducted in a vertical cylindrical drum such as those manufactured by Kellogg, Lummus and Foster 7 Wheeler Companiesf The heavy hydrocarbons are ad mitted into the drum at a temperature between 875 and 950 F., and are permitted to soak and carbonize until the drum is nearly filled with a solid coke. The material is removed from the drum'by various decoking methods matter content averaging from about 8% to about 20% by weight and which are made in such delayed cokers? are employed in the present invention.

The volatile matter being discussed here is determined by ASTM method D 271-48 modified for sparking fuels and is exclusive of the moisture and free oil which would be removed by heating to temperatures of 400-500 F. Volatile matter is determined in a plantium crucible in an electrically heated furnace maintained at temperatures of 1742" F.i36 F. A one gram sample of dry-60 an understandable reluctance on the part of blast amount of fines. A suggested or typical analysis of a satisfactory sized raw petroleum coke is as follows:

Cumulative per- Screen size: cent retained (Sizing would probably be at least 70% A"; could be as high as 90%+1".)

The material will also typically have an apparent specific gravity of about 0.94 weigh about 40 pounds per cubic foot, have an ash content of about 0.2%, and a volatile matter content of about 23-14%.

The following examples, in tabular form, illustrate the present invention. In Example I normal blast furnace operation is compared to results obtained when replacing l2 /2% of the metallurgical coke with raw petroleum coke having the previously described characteristics. In Example II at the same blast furnace the results are shown when replacing 14.2 and 16.7% of the metallurgical coke with raw petroleum coke.

The foregoing physical and chemical tests with respect to both cokes were conducted in accordance with A.S.T.M. Standard Procedures on Coal and Coke prepared by A.S.T.M. Committee D-5.

It will be noted from the foregoing that the raw petroleum coke differed from the metallurgical coke in several respects. The volatile matter content of the raw petroleum coke was 8.7-10.0% as compared to 0.7l.l% for the metallurgical coke. The petroleum coke had an ash content of about 0.20.3% as compared to 9.41l.7%. it also differed markedly in size (approximately 17% plus 2 inch compared to 78%), bulk density (approximately pounds per cubic foot compared to 25), and porosity, etc. The combustion characteristics of the raw petroleum coke are also considerably diiferent with respect to ignition temperature, reactivity, temperature of combustion, burning rate, etc.

Bespite these considerable difierences from conventional and tried and true metallurgical cokes, the employment of petroleum coke as a fuel and reducing agent in a blast furnace was found not only to be possible or permissive but very advantageous, as is apparent from the table.

The table shows the employment of a combination of metallurgical coke and raw petroleum coke as the fuel and reducing agent in a blast furnace to be very advantageous. It increased the hot metal output of the furnace, and reduced both the amount of limestone and the Comparison of results of partial replacement of metallurgical coke with raw petroleum coke in blast furnaces Example I--Operatio11 Example II-O peration Test conditions Normal Petroleum Normal Petroleum coke coke Coke analysis:

Metallurgical coke:

Percent ash Percent volatile Percent sulfur Petroleum coke:

Percent volatile Percent sulfur Percent h Furnace charge:

Metallurgical coke, pounds per ton iron..- Petroleum coke, pounds per ton iron. Total coke, pounds per ton iron. Lime stone, pounds per ton iron Theoretical iron yield, percent- Production:

Tons iron per day Iron, percent silicon. Iron, percent sulfur Operating conditions:

Blast temperature, F Blast moisture, grains per cu. ft. On. it. air per pound total coke Pounds metallurgical coke replaced per pound of raw petroleum cnl'e Percent petroleum coke of total coke The metallurgical coke employed in the foregoing examples had the following properties which are typical:

8 Typically at least 70%.

amount of total coke required to produce each ton of iron. The metallurgical coke required to produce each ton of iron was reduced on the average 336 pounds, at an average raw petroleum coke usage of 204 pounds. In

other words, each pound of raw petroleum coke replaced about 1.58-1.76pounds of metallurgical coke. This replacement resulted in an average reduction of 132 pounds from the total pounds of coke required to produce each ton of hot metal with normal metallurgical coke. Be-

cause the cost of raw petroleum coke is much less than rates are not excessive.

metallurgical coke (because it does not first have to be processed and coked in a coking oven as does the metallurgical coke), the cost savings to the blast furnace operator are increased for this reason also, provided freight In other words, he uses less total coke and normally pays less per ton for a portion of the coke that he does use.

Without being bound by theoretical considerations, it is believed that what occurs in the blast furnace is this:

Because the raw petroleum coke possesses a relatively high amount of volatile matter, it devolatilizes to a considerable degree in the upper section of the blast furnace. This removes heat and thus lowers the temperature in this portion of the furnace, which results in depressing the reactions of forming CO and hydrogen with coke, (viz. CO +C 2CO; and H O+C I-I +CO) which in the lowered temperature range are not fully utilized to reduce oxides and therefore are lost as off gases (a waste of carbon and hydrogen). Therefore, the initial result is an increase in carbon dioxide and reduction of hydrogen in the off gas. This means better utilization of carbon. The devolatilized petroleum coke then gasifies at lower levels in the shaft than normal metallurgical coke because it possesses low reactivity; and that portion arriving at the combustion zone burns at higher temperatures because of its combustion characteristics (caused by less internal coke surface).- This results in increased carbon dioxide concentration reaching further into the furnace from the .tuyeres. This higher temperature is also of importance i-f metal desulfurization or increased silicon or manganese content are sought or desired. In other words, the amount of coke employed to produce each ton of hot metal can be substantially reduced, as discussed above, in order to produce metal having equivalent properties. Metals having altered properties, viz. reduced sulfur, increased silicon, increased manganese etc., may also be conveniently produced. However, in these cases even greater coke savings are expected since the higher hearth temperatures due the petroleum coke combustion characteristics are ideal for the production of these special irons. The petroleum coke employed may then, for example, approach the complete replacement of the metallurgical coke normally employed to produce these special irons.

It is believed that the employment of raw petroleum coke as a reducing agent in a blast furnace, in any amount, is new with the present invention and meritorious pected advantages arising therefrom. However, for optimum results when employing the raw petroleum coke as a normal part of the charge to the blast furnace, it is preferred that it be employed in minor percentages along with a major percentage of standard metallurgical coke. In other words, it is preferable that it not be the sole reducing agent employed but that it be used in amounts such as from about 5 to about 40 percent of the total amount of reducing agent employed; the balance of 95 to 60 percent being standard metallurgical coke. Even more preferred proportions of these two materials are to 25 percent ra-w petroleum coke and 90 to 75 percent of the standard metallurgical coke.

The foregoing percentages are to be interpreted as averages only of the reducing agent charged to the furnace. In other words, the two materials may be separately charged to the furnace, such as 7 charges of 100% metallurgical coke followed by a single charge of 100% raw petroleum coke, etc; or the two materials may be pre blended with each other, in the desired proportions, before they are added as a mixture to the blast furnace; or a given amount of petroleum coke can be added to each coke charge.

' While raw petroleum coke from which fines have been screened out will typically be employed in the invention, this is not to be interpreted as precluding the use of fines or run of pile raw petroleum coke. In other words, it may sometimes be advantageous to employ fines or run of pile petroleum coke. The sized petroleum coke typically employed will be screened to plus 4" or /2" etc. with a top size of about 4". The raw petroleum coke fines may also be agglomeratedwith a binder such as starch etc. to make pellets or briquets prior to its addition to the blast furnace. Or the raw petroleum coke may first be ground or milled and then pelletized, etc. In any of these cases the material is still considered to be raw because it still possesses, essentially, the same volatile matter content as raw petroleum coke, and essentially also has the same combustion and reactivity characteristics.

Having thus described the nature of my invention, but

being limited only by the appended claims with respect to its scope, I claim: 1. In the process of producing ferrous metals and ferro-alloys in a blast furnace wherein a charge comprising coke, ore and flux is heated to reduce said ore by oxidation of said coke, the improvement which comprises employing rawpetroleum coke produced in a delayed coker as at least a part of the coke charged to said furnace, said raw petroleum coke having a volatile matter content between about 8 and about 20 percent.

2. In the process of producing iron in a blast furnace wherein a charge comprising coke, ore and flux is heated to reduce said ore by oxidation of said coke, the improvewherein a charge comprising coke, iron ore and flux is heated to reduce said ore by oxidation of said coke, the improvement which comprises employing, as the coke charged to said furnace, from about 95 to about percent of a metallurgical coke, which possesses a volatile matter content no higher than about 2%, and from about 5 to about 40 percent of raw petroleum coke produced in a delayed coker and having a volatile matter content between about 8 andabout 20 percent.

4. The process of claim 3 wherein the raw petroleum coke comprises from about 10 to about 25 percent of the reducing coke.

5. The process of claim 3 wherein the raw petroleum coke is added to the blast furnace separate from the metallurgical coke.

6. The process of claim 3 wherein the raw petroleum coke is added to the blast furnace in admixture with the metallurgical coke.

7. The process of claim 3 wherein at least about percent of the raw petroleum coke is retained on a onequarter inch screen.

8. In the process of producing ferrous metals and ferro-alloys in a blast furnace wherein a charge comprising coke, ore and flux is heated to reduce said ore by oxidation of said coke, the improvement which comprises employing, as the coke charged to said furnace, from about 95 to about 60 percent of a metallurgical coke, which possesses a volatile matter content no higher than about 2%, and from about 5 to about 40 percent of raw petroleum coke produced in a delayed coker and having a volatile matter content between about 8 and about 20 percent.

References Cited by the Examiner UNITED STATES PATENTS DAVID L. RECK, Primary Examiner.

WINSTON A. DOUGLAS, Examiner.

12/39 Ruzicka 42

Claims

1. IN THE PROCESS OF PRODUCING FERROUS METALS AND FERRO-ALLOYS IN A BLAST FURNACE WHEREIN A CHARGE COMPRISING COKE, ORE AND FLUX IS HEATED TO REDUCE SAID ORE BY OXIDATION OF SAID COKE, THE IMPROVEMENT WHICH COMPRISES EMPLOYING RAW PETROLEUM COKE PRODUCED IN A DELAYED COKER AS AT LEAST A PART OF THE COKE CHARGED TO SAID FURNACE, SAID RAW PETROLEUM COKE HAVING A VOLATILE MATTER CONTENT BETWEEN ABOUT 8 AND ABOUT 20 PERCENT.