US2891609A - Coke gas and tar firing of open hearths - Google Patents

Description

June 23, 1959 J. H. KELLEY ETAL coma GAS AND TAR FIRING 0F OPEN HEARTHS 2 Sheets-Sheet 1 Filed Feb. 27, 1952 l l -llll u fill/l INVENTORS JOJIJI) E I and Jams 112116;

June 5 J. H. KELLEY ETTAL 2,891,609 v coxa: GAS AND TAR FIRING OF OPEN HEARTHS 2 Sheets-Shet 2 lfiled Feb. 27, 1952 v INVENTORS John E Eberfiar Jqnwa Kalla United States Patent COKE GAS AND TAR FIRING 0F OPEN HEARTHS James H. Kelley, Sparrows Point, Md., and John E. Eberhardt, Bethlehem, Pa., assignors to Bethlehem Steel Company, a corporation of Pennsylvania Application February 27, 1952, Serial No. 273,772

1 Claim. (Cl. 158-1175) This invention relates to improvements in methods of operating open hearth furnaces.

It is an object of this invention to increase the production capacity of an open hearth furnace by shortening the time required for melting and refining a heat of steel therein.

It is a further object of this invention to increase production as aforesaid by operating thecheckerwork of an open hearth furnace at temperatures higher than those heretofore believed feasible.

It is'a still further object of this invention to operate the checkerwork of an open hearth furnace at such higher temperatures without the expected consequent damage to said checkerwork.

, It is a still further object of-this invention to attain such higher temperatures by the use of a combination of gaseous and liquid fuels. a

. :The foregoing and other objects of this invention will be more fully understood from the following description and claim together with the drawings, in which Fig. 1 is a front elevation of the tapping side of an open hearth furnace;

Fig. 2 is a vertical section taken along the line 2-2 of Fig. 1;

Fig. 3 is a view in section of one form of burner adapted for use in the practice of our invention;

Fig. 4 is an end elevation of the nozzle end of the burner shown in Fig. 3;

Fig. 5 is a view in section of another form of burner adapted for use in the practice of our invention; and

Fig. 6 is an end elevation of the nozzle end of the burner shown in Fig. 5.

Among the fuels available for combustion in open hearthfurnaces, in addition to oil, tar, blast furnace gas, producer gas, etc., is coke oven gas. This fuel has never been a major source of heat, however, in spite of the fact that considerations of economy would seem to point to the desirability of its use. Such considerations would seem particularly persuasive in large steel plants where there are sometimes produced surplus quantities of coke oven gas which, in the absence of demand for it as a fuel can only be burned off as waste. Nevertheless, because of operational difiiculties heretofore associated with its use, even when coke oven gas has been used in open hearth furnaces it has comprised only a small proportion of the total fuel.

We have discovered a method of using large quantities of coke oven gas to supply a major portion of the heat to open hearth furnaces, and in so. doing, in addition to the economies effected we have realized important additional benefits not to be anticipated from theoretical considerations. Broadly stated, the invention comprises the combustion of independent streams of coke oven gas and aliquid fuel such as tar. As herein used, by theexpression tarllwemean a liquid fuel in which the ratio of carbon to hydrogen by weight is at least 10, for example, coal tar or derivatives thereof. It will be understood that there may be incorporated in the tar stream a proportion of steam by means of which the tar is atomized.

In the following description of our invention, we refer throughout to coke oven gas, as the gaseous fuel. We wish it understood, however, that the gaseous fuel employed could be any combustible gas, e.g., natural gas, which is substantially free of inerts such as CO and nitrogen, and we intend that the expression coke oven gas as herein used shall include all such combustible gases.

One of the objections to the use of coke oven gas alone as a fuel in open hearth furnaces has been that excessive foaming of the slag occurred during the refining period. In some modifications, a small quantity of the gas was fed in below a liquid fuel stream; it was feared that if gas were fed above the liquid fuel, it would rise and burn adjacent the furnace roof, with consequent damage thereto. In this case the amount of coke oven gas used was small, and no benefit of any consequence was found to result.

In the practice of our invention we utilize a water cooled burner structure which includes two tubes. for introducing independent, un-miXed streams of coke oven gas and tar, for example. It is an important feature of our invention that the tar stream be below or surrounded by the coke oven gas stream and that the coke oven gas be fed at a high velocity and be directed slightly downward to cause the flame to travel substantially the entire length of the metal bath without rising to the roof. The tar may be introduced in a single atomized stream or as an atomized multi-jet stream.

Referring now to the drawings, open hearth furnace 1 has a hearth 2 and burners 3, 3. At each end of the hearth are the usual checker chambers 4 and 5 forpreheatingthe air for combustion. The checker chambers connect at their inner ends with the furnace 1 through the vertical lines or upstakes 6 and 7 and slag pockets 8 and 9.

Each checker chamber is divided into two sections by the partition wall 10, as shown in dotted lines in Fig. 1. The checkers themselves are shown as comprising two passes, a first pass 11 and second pass 12. The checker chamber wall is provided with a peephole 13 to enable an observer to take optical readings of the temperature of the checkers in the region 14 at the top of the first pass.

. While this description relates to a two-pass checker, it will be understood that the invention can be practiced equally well with a single pass checker.

Referring to Figs. 3 and 4, the burner shown'comprise the gas pipe 15 surrounded by water-cooling chamber 16. Gas is supplied to theburner through gas inlet 17. Tar pipe 18 is located at the center of gas pipe 15 and terminates at the outer end thereof. Tar and atomizing steam are supplied to tar pipe 18 through inlets 19 and 20. When the burner is operating, it .will be seen that tar and gas enter the furnace in separate streams, without previous mixing.

Referring to Figs. 5 and 6, the burner shown comprises the water-cooled chamber 21 in which are positioned the gas pipe 22, and, below it, the tar pipe 23-. Gas, tar and atomizing steam are supplied to the burner through the respective inlets 24, 25 and 26. In this burner, the tar stream is broken up into a plurality of small streams at the nozzle end of the burner, as shown at 27. This burner also delivers to the furnace separate,: unmixed streams of gas and tar. a

In the operation of a furnace according to our inven: tion, burners 3, 3 will be turned on alternately for specified periods, as is Well known. When the burner of Fig. 3 is used, the inflowing tar stream will enter the furnace surrounded by gas. With the burner of Fig. 5, the gas stream enters the furnace above the tar stream. The efiiuent hot products of combustion traverse the checkers 11 and 12, giving up thereto a substantial portion of their heat. Upon reversal of the furnace, the incoming air for combustion is heated in its passage through the checkers.

We have found that the furnace productivity is improved without excessive damage to the furnace by having the tar stream below or surrounded by the coke oven gas stream as compared to the previous practice of having the tar stream above the coke oven gas stream. Although, we are not prepared to state the exact reasons for this, the explanation probably lies in the relative radiating powers of coke oven gas flames and tar flames. It is well known that coke oven gas burns with a substantially non-luminous flame and that its radiating power, which is substantially lower than that of a luminous flame, stems primarily from the invisible radiation in the infra-red region, of carbon dioxide and water vapor. The non-luminous coke oven gas flame is, nevertheless, relatively opaque to radiation from another source, as for instance a tar flame, in those regions of the spectrum where carbon dioxide and water vapor radiate. The coke oven gas flame surrounding or above the tar flame therefore probably acts, in effect, as a partial shield to prevent the intense radiation from the tar flame from falling directly on the furnace roof thereby preventing damage to said roof. In order to take full advantage of the shielding action of the coke oven gas flame in protecting the furnace roof, it may be desirable when the tar stream is surrounded by the coke oven gas stream to incline the tar stream downward at a slightly steeper angle than the coke oven gas stream.

In the operation of an open hearth furnace with oil, which is currently predominantly employed as open hearth fuel, there are certain inherent limitations on the rate at which the furnace can be fired. Naturally, if this rate could be increased, the result would be an increase in the rate at which steel could be produced. However, in the case of oil, it has been found that if a certain rate of firing be exceeded, serious damage to the checkerwork of the furnace results. For example, expressed in terms of checker temperatures, it has been found inexpedient to run an oil-fired open hearth furnace at a firing rate which results in a temperature higher than approximately 2300 F. as measured at the top of the first pass checker just before the furnace is tapped. Temperatures much in excess of that figure as accompanied by a type of dirt deposit in the checkers which causes severe damage to the brickwork. Tests made with samples of such deposits show that at temperatures above 2300 F. they have a definite fluxing action on the checker brick.

On the other hand, in a furnace operated with our combined coke oven gas and tar, it was found that temperatures as high as 2450 F. measured as stated above, can be reached in the checkers without appreciable damage thereto. We are not prepared to state the exact cause of this phenomenon, but the deposit found in the checkers of a furnace operated with our combined coke oven gas and tar is of a different character from the deposit found in the oil-fired furnace, being much harder and denser and less fluxing in its effect on the brickwork.

Naturally, with the checkerwork so much hotter than is possible in an oil-fired furnace, the incoming air for combustion is correspondingly pre-heated to a greater degree. This increase in air temperature naturally plays a part in shortening the time required for melting and refining a heat of steel. For example, as compared to heats which normally, in an oil fired furnace, require eight hours from charge to tap, we have consistently,

with our gas-tar firing, produced similar heats in seven hours. The increased production of steel to be realized by this method of firing in a large open hearth shop having a number of furnaces running constantly will, it is readily apparent, be very substantial over a long period of operation.

In the practice of our invention, the furnace is given the usual charge of limestone, ore and scrap, with the coke oven gas and tar flames directed on to the charge. As stated above, the coke oven gas should leave the burner at a high velocity, not less than 350 feet per second and preferably of the order of 400 feet per second up to as high as 700 feet per second or more. In order to realize fully the benefits of the invention, the coke oven gas should supply at least half of the heat delivered to the furnace, and preferably in excess of sixty percent of the total heat.

Because of the fact that the checkerwork is not attacked severely by the products of combustion and entrained solid matter resulting from firing in accordance with our invention, it is possible to fire the furnace at a much higher rate during the melt-down period than when firing with oil. This results in hotter checkers, which results in more highly pro-heated air, which in turn results in higher flame temperatures. The higher firing rate and the higher flame temperature during the meltdown period considerably shortens the time required for melt-down, and consequently shortens the total heat time. The obvious result of this shortened heat time is more tons per furnace per hour.

After the melt-down, and as the furnace roof reaches its maximum tolerable temperature, it will be necessary to reduce the rate of firing to prevent damage to the roof.

As hereinabove stated, with a furnace fired in accordance with our invention, the checkerwork can tolerate higher temperatures without excessive damage. To obtain the maximum advantage of this method of firing, the firing should be so regulated as to result in a checker temperature, measured in the region 14, higher than 2350 F. and preferably about 2450 F. just prior to tapping the furnace.

We believe that we are the first to propose and to demonstrate the success of a method of firing an open hearth furnace in which a major portion of the fuel is supplied as coke oven gas throughout the progress of the heat without encountering foaming of the slag on the bath and without damage to the furnace roof. As pointed out above, in addition to the economies resulting from the use of this usually available and often wasted fuel, the increased production resulting from its use is the same as production by additional furnaces, without the necessity of the capital outlay required to build such additional furnaces.

We claim:

A method of firing an open hearth furnace which comprises delivering a stream of coke oven gas and a separate stream of atomized tar through separate conduits to the tips of their respective burners which are mounted adjacent to and substantially parallel with each other at one end of the combustion chamber of the furnace, the tips of the burners being in substantially the same vertical plane, maintaining the gas stream at least partially above the tar stream, injecting said separate streams of coke oven gas and tar into the furnace, maintaining said streams in separate, substantially parallel paths for a substantial distance after leaving the tips of said burners, and burning said stream.

Kernohan et al Sept. 2, 1924 Davies Dec. 1, 1925 (Qther references on following page) UNITED STATES PATENTS Danforth June 25, 1929 Steese Nov. 26, 1929 Parker Sept. 5, 1939 Stephanofi Oct. 6, 1942 Weller Jan. 19, 1943 Kay et a1 Dec. 19, 1950 6 FOREIGN PATENTS Great Britain May 19, 1931 OTHER REFERENCES UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent Noo 2,891,609 June 23, 1959 Ho Kelley et al.9

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should readas corrected below.

(30112111114, line 67, for "stream" read streams e Signed and sealed this 8th day of December 19590 Attest:

KARL AXLINE ROBERT c. WATSON Attesting Ofiicer Commissioner of Patents

Images