US2874303A - Method and apparatus for controlling refractory lined furnace temperatures - Google Patents

Description

f 2,874,303 Ice l Patented Feb. 17, 1959 METHOD AND APPARATUS FOR CONTROLLING I'EFRACTORY LINED FURNA'CE TEMPERA- The invention described hereinrrlay be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to furnaces and, more particularly, to means for controlling furnace temperatures.

The ability to closely control temperatures in hightemperature smelting or melting furnaces has been a constant challenge and Ymany efforts have been made at providing improved temperature indicating and control means such as pyrometers. As is well known, any furnace installation has a theoretically optimum operating temperature which depends upon its design, the intended furnace practice, and other factors, this optimum, however, being a compromise or balance between the maintenance of a high production rate on the one hand and the economic necessity of prolonging the furnace roof refractory on the other. Obviously, high temperatures produce faster reactions, but, at the same time, the desire for such reactions must be tempered by the fact that excessively intense heats produce a refractory lining sweating during which the refractory spalls or wears atsuch a wasteful rate as to very materially reduce the life or campaign for which the refractory brick is intended. Such wear, of course, necessitates furnace shut-downs for repairs which are so expensive and times-taking'as to 40 render the whole operation uneconomical.

As stated, the importance of heat control has led to the development and adoption of such instruments Ias pyrometers or, when these are not available, it has placedA a premium on the services of experienced furnacemen who are .able to judge temperatures by observing color. Pyrometers, however, have not provided an entirely suitable answer and this has been dueprimarily to their unreliability in the presence of smoke or aine and the diiculty of correcting for emissivity of diierent materials. Further, the critical factor to becontrolled is not so much the temperature as it is the actual quantity or amount of brick wear or spall and, obviously, the' wear of different bricks will vary considerably, particularly when subjected to varying furnace practices. Conse- 5i quently, direct temperature readings, even if exact, do not provide precise data for spall control and, since each heat introduces some varying factors, it becomes very possible for a theoretically optimum temperature to be found inappropriate and uneconomical in practice. Of course, visual temperature determinations also are subject to this criticism and, in addition, control by such a method is, at best, simply an estimate or an opinion which, most certainly, is non-quantitative insofar as refractory wear is concerned.

It is, therefore, an object of thev present invention to provide a manner of controlling a furnace temperature which is based directly upon the amount of wear as opposed to temperature readings.

- A furtherobject is to provide means operative during 7o a furnace heat for selectively and periodically'determinhas been combined.

ing wear at dierent locations of the furnace by obtaining readings from the spall emanating from those particular locations.

Still another object is to provide means for continuously controlling furnace temperatures in accordance with the quantitative amount of spall emanating from a selected location in the furnace. g

According to the invention refractory wear is quantitatively determined by incorporating a radioactive isotope in portions of the refractory lining of the furnace. Such portions then spall or wear at the same rate as the remaining refractory with the result that such spall as is carried into the slag will contain a certain quantity of the radioactive isotope which, when exposed to suitable counting instruments, such as a Berkeley sealer with a Geiger tube, will provide an accurate record of the actual amount of refractory spall occurring during the period in question. Preferably, the isotope is incorporated in selected bricks of the refractory wall so that the reading will be representative of conditions throughout the furnace. Also, if desired, it is possible to incorporate isotopes of differing Vself-identifying counting energies at different critical locations of the furnace and readings then can provide selective data for these separate locations. Y

As to these readings, one phasel of the invention contemplates a periodic ladling of slag samples which then are carried to a counter for testing, while another modification provides a continuous record made froma particular isotope'whose presence can be determined and counted while in the slag bath. Such an isotope can be a gas-evolver in which case the gas can be conducted to a counter, or it can be an isotope with an emission different from that in the ladled testing. In this latter event, the ladled isotopes may be beta emitters while the isotopes for the continuous record may be a gamma emitter. The continuous counter in this arrangement would accept and record only gamma ray energy counts. In the preferred form of the invention, both the continuous reading and the sampling procedures are used.

The invention is illustrated in the accompanying drawings of which Fig. 1 is a longitudinal section through an open hearth furnace, and Fig. 2 a vertical section along lines Il-Il of Fig. l. i

vThe furnace illustrated in the drawings represents a conventional open-hearth type provided with a customary hearth 1 formed of layers of silica sand 2, lire clay 3 and burned chrome 4, this hearth forming a bed on whicha bath 6 of molten metal and slag is subjected to open llame coming from burners 7. For purposes of understanding the invention, very little of the actual furnace structure is involved, the only portions of present interest being a furnace roof 8 formed for the most part of refractory bricks, a rear wall 9 and a front wall 11 in which is mounted a charging door 12. These portions generally can be referred to as overhead portions to eonnote the fact that they lie above the furnace bath. Consequently, as might be surmised, the present invention is by no means limited to open hearth practices since, in fact, the

present teachings can be applied to any furnace which operates at sufficiently high temperatures to spall the4 refractories.

As previously indicated, one of the important features of the present invention resides in incorporating a radioactive isotope in the furnace lining so that spalling of this lining will carry the isotope into the slag bath. As shown, the refractory lining includes roof 8 which is formed of a number of conventional refractory bricks 13 among which are interspersed, at selected locations, a

plurality of bricks 14 in which the radioactive isotope Most suitably, bricks 14 arestrategically located about the roof to assure that representative amounts of the isotopes are carried into the spall' fromv all critical` locations withinVY the furnace.- Usually, for instance, thejjtemperature variations are greatest transversely of the furnace so that, as shown in the drawings, it is desirableto mount bricks 14 in transverse rows ofthree spaced'flongitudinally along the roof. With such an arrangement, when the furnace is brought up to melting heat, theV refractory-lining commenced to spall and the spall from bricks V14 drops into slag 6 where it'is ymixed-'thoroughly due to-the roiling motio-n of the bath. However, the mixture will be representative of conditions throughout the furnace and determinations of roof wear 4can'be-made--by taking ,a sample of the slag and subjecting it toaftradiationcounter-of any suitable type As to the -particular- -isotopeused .this-may be any which iss-consistent with'J-thef-furnace praeticel of 'the vparticular installation being equipped; although, preferably,- the isotope .may beV chosen :for its-availability, cheapness-and radiological properties By way-of example, a refractory liningfmay be-formed-by incorporating about 50 millicuries ofSr89 in each brick' 14, although the amount incorporated in the-brick may vary with furnace design and capacity. The present example assumes a 15G-ton open-hearth furnace to which the following conditions are-assigned: (a) a slag `bur'denof 15,000 pounds; (b) a basic bottom and-practice; (c) anormal roof life of 200 heats, and (d) a 90% 'brick usage before roof failure. Sr89 is an isotope which would be consistent with the meltingpractice represented by such a furnace, although otlren isotopes havingzdiiferingichemical properties of oxidation, reduction and volatizat-ion also couldbe substituted providing they are consistent with the melting practice Ato which theywill be subjected. In forming the Sr89 bricks, the 50 millicuries of Sr89 is thoroughly mixed with the raw material and the brick then may be mounted inthe roofof` thek furnace in the manner shown and at any desired time during the heat, a l0 gram sample of slag may be extracted by a ladle and subjected to the counter instrument. Of course, excessive refractory wear orspall willbe indicated by the high count of the instrument and, if such is found to exist, the furnace temperature can be reduced. Low counts will indicate. the desirability of increasing the furnace temperature, and, as would be expected, the counts can be checked against calculated data obtained by, quantitative testing under known conditions.

Another practice which, for certain installations, may have some advantageqoverthat just-described is illustrated iti-Figa 2. v Briey, this practice contemplates the use of radioactive bricks -14a, 1411 and VV14e, each of which is formedwithanpisotope -havinga counting energy that isditferentfromthat ofthe others so that these isotopes each are self-identifying in the slag bath example. The obvious purpose of this modification is to permit determinationsofwear atl selected locations of the furnace liningandfor this reason these isotopes, most suitably,- are included one in each of the three bricks of the transverse rows because, as explained, temperature variations are greatest between the sides and the center. Such differing isotopes are well known and include Y91, Nb95, .Zr95 and many others. Of course, the slag bath always 1s in a constant-state of flux and movement so that the spall from these bricks is vevenly mixed but, nevertheless, such counting -m echa;11i sm as is commerciallyavailable is capable of distinguishing the separate counting energiesV ofthespall fvromcach .ofthesebricks Another featureofthe invention resides in providing a means for` continuously determiningrefractory wear and this'continuously koperating means may supplement the procedurel permitted by bricks 14. Such a continuous reading is made possible by mounting a countinginstrument 16 in a suitable position in a furnacewall, such as rear wall '9, `at approximately the longitudinal position of of a conventional open-hearth furnace. This particular location of thefurnace is Ifrequently thepointat-which the furnace heat becomes most intense so that the incorporation of the counter at this position serves as a means for maintaining the entire furnace temperature below a level that is known to be excessive. Counter 16, as will be noted, is provided with a customary column 17 which is aligned'with a point 18 on the furnace hearth or in the slag bath as the case may-be. Thecounter, in turn, is actuated by energy contained in spall dripping lfrom another brick 19 mounted'in furnace roof 8 and brick 19. as will be noted is mounted in the roof directly above point 18, so that spall from this brick is immediately sighted by column 17 of the counter.

When using such a continuous reading in conjunction with the'ntermittentsampling outlined from-the spall of bricks 14, it is necessary to form brick 19 of an isotopewhich can be distinguished from the isotopes used for these other bricks. For this purpose, the isotope of brick-19 may-beCsz" which, as is known, is a gamma ray emitter as opposed to vSr89 which is a beta ray emitter. Brick 19 may be'foi'med in the same manner as the other bricks vand it has been notedthat the incorporation of isotopes in these bricks in no'way affectsl the-normal spalling rate/of thebricks or theirstrength or'refractory capacity.v If desired, it is possible to dispense'with the necessity'of mounting a counter inthe wall of the furnace and this may be accomplished `by incorporating an'isotope in brick 10 which, when subjected-'to the heat of'ajbath evolves 1a gas that then `maybe taken out of the'furnace through vany discharge opening and conducted yto a counter which maybe located at' any'desired Vconvenient 'and protected position.l

With a refractory lining-formed as described above; it has been furtherpossibleto determine-with'an unusualv degreezof `precision the exact amount-of-lining wearand, based upon such'y determination, it is-#possibleto vary thefurnace-temperatures so vas torprolo'ng-the rooflife to a maximum extent consistent with a-desired production rate. If desired, suitable.-mechanism can-'be combined with counten, 16 so .that the continuous count can be utilizedto aetuate' anaudible.or.visual signal when the temperatureexceeds ga. desired degree. As another possibility which should vrequire no morethan ordinary skill,- counter 16 can be kused toactuate control mechanismy for automatically increasing or; decreasing temperatures.

The principal advantage vof the present invention liesin thefact that the. Wear determinationsvare ymade directly from the quantitative amount oth-wear orspall and,lconse quently, the necessity--of;rel atingwear to :observations made Ybypyrlorneters or by the-human v eye-is eliminated; Further, the useof the radioactive:isotopesfcompletely avoids. errors produ-cedby, the ;presence of smoke-tete. which sometimes vhas veryseriously` affected g operations controlled by pyrornetric; means.;

Obviously 4many modifications and ,variationsgof the. present invention-are possible-in the light of theabov teachings. It istherefore to Abe understood' that within the scope ofthe appendedclaims the invention may be practiced otherwise than as specifically described.

I claim:

l. A methodof controlling refractory lining wearof a furnace, comprising aligning, a radioactive energy counter vwitha selected position in the furnace slag rbath, incorporatingaradioactive isotopecf a;.cer,tai n ray emanationgin said refractory lining above -said' selected position, incorporating different rayemanating radioactive isotopes of mutually differingselffdentifying counting energies in other selected locations of said refractory lining, controlling, temperature conditions inaccordance withjreadings of said aligned-counter, and determining wear in said other Aselected locations by readings obtained from slag bath samples.

2. A method of controlling `temperature.conditions of a refractory-lined furnace, comprising` rendering ,an over-..

head portion of said refractory lining radioactive, applying OTHER REFERENCES furnace heat in Sumcient amounts for producing spa. Radioactive isotopes as Tracers, Kramer Power Plant drop, counting the radioactive energv present 1n sald Enoineeng November 1947) p11 105 w8' Span dlop 39d regulating said heat applicano in accord' ladioactive Cutting Tools for Rapid T ooi-Life Testing, ance Wlth Sald count' 5 Merchant et al., Transactions of the ASME, May 1953,

References Cited in the le of this patent pages 549-559 UNITED STATES PATENTS 2,315,845 Ferris Apr. 6, 1943 lo 2,365,553 Hill Dec. 19, 1944

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