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BLAST FURNACE LINES

TUESDAY MORNING, APRIL 30, 1974

The session on Blast Furnace Lines convened at 9:30 am. The chairmen were J. T. Seaman, Jr., Interlake, Inc., Chicago, Ill., and L. G. Maloney,, Inland Steel Co., E. Chicago, Ind.

BLAST FURNACE REFRACTORYLINING WEAR STATUS

USING RADIOACTIVE SOURCES

J. F. Perko, Electromechanical Research Center

E. J. Spirko, Research Center

REPUBLIC STEEL CORPORATION

Cleveland, Ohio

INTRODUCTION

Iron production from a b l a s t furnace began in this country over a century ago. From these natural stone-lined furnaces of long ago we have progressed t o the modern 40 foo t plus diameter b l a s t furnaces operating under high top pressure and producing

. i ron i n excess of 5,000 net tons per day. A b l a s t furnace refractory l i n ing has progressed from the quarry stone l in ings of t he or ig ina l furnaces t o the highly sophis t i - cated, expensive refractory l in ings of today. Refractory l in ings , although complicated today, s t i l l follow a basic procedural sequence. A l i n ing design i s developed, a re- f ractory i s purchased, i n s t a l l ed , and the furnace goes i n t o production. Sometime l a t e r we f ind out how well the refractory performed and how good the or ig ina l design was. This i s perhaps an oversimplification, but i t s purpose i s t o present the basic problem confronting refractory design people. The f ac t t h a t a b l a s t furnace is a

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pressure unit limits the amount of i n t e rna l examination of l i n ing performance. This, coupled with the normal length of service expected from the b l a s t furnace, leads toward estimated designs ra ther than designs based on previous performance. This problem was real ized i n Republic, and research was directed toward developing techniques which would provide useful information on refractory l i n ing wear ear ly i n furnace cam- paigns t o make this information available t o update l in ing designs.

Early work was done with external techniques such as temperature systems, e l e c t r i c a l resistance systems, and even photographic temperature systems. These a l l provided some useful da ta , but none were capable of providing posit ive l i n ing wear conditions. Nothing can be sa id t o be foolproof, but ye t this.-was the system we were searching for . The techniques of 'using radioactive sources t o measure l i n ing wear had been reported i n the l i t e r a tu re . Republic has a research group act ively working with radioactive sources in various s t e e l m i l l applications. Applying t h i s background toward the problem of l i n ing wear measurement, a simple technique was developed using small, low-level radioactive sources t o provide posit ive l i n ing wear measurements, external ly on a b l a s t furnace, ear ly i n the furnace campaign.

THE TECHNIQUE

The most important consideration i n measuring the wear r a t e of a refractory l in ing i s the select ion of radioactive source type and s ize . Cobalt-60 has been used f o r a l l of our i n s t a l l a t i ons t o date. This source has a ha l f - l i fe of 5.3 years; t h a t i s , t he

radioact ivi ty w i l l be one-half of what i t i s today a f t e r 5.3 years , one-fourth as much a f t e r 10.6 years, e tc . Half-life i s independent of temperature o r pressure. Cobalt-60 emits highly penetrating gamma rays, has a high melting point (2723 F) , and i s eas i ly alloyed with molten iron. The source i s sized so tha t it can be detected through the refractory wall and s t e e l . Yet, the quantity must be safe when alloyed with the iron. Based on these considerations, the source s i z e s chosen f o r our s tudies range from 1 .5 t o 5.0 rnillicuries,, depending on t h e i r locat ion i n the refractory l in ing.

From the safety standpoint, the l im i t concentration a s determined by the A.E.C. of Cobalt-60 i n a so l i d i s 5 x 10'4 microcuries per gram o r 454 microcuries per ton. The amount of i r o n per ca s t i s between 200 and 400 tons. The addit ion of other iron- bearing materials , when processing i r o n t o s t e e l , , provides a fu r ther d i lu t ion of the isotope concentration i n the f i a s h e d s t e e l . From a l l of our studj-es t o date , the m a x i - mum calculated concentration was l e s s than one-tenth of the l ega l l imi t concentration determined by the A.E.C.

The Cobalt-60 sources a r e encapsulated i n s t a in l e s s s t e e l cylinders, with t h e i r caps hel iarc welded. Figure 1 shows the small (a inch diameter by 3/4 inch long) s t a in l e s s s t e e l encapsulated Cobalt-60 source. The method used t o i n s t a l l the capsule i n t o a refractory t e s t br ick o r i n t o a refractory castable l i n ing i s simple and s t ra ightfor- ward. For br ick l in ings , the t e s t bricks a r e pre-drilled with a 5/16 inch diameter by 2 inch long hole a t the predetermined depth. Figure 2 shows a typ ica l refractory t e s t brick t h a t has been prepared f o r a t e s t study. These bricks a re i n s t a l l ed i n the normal sequence of i n s t a l l i n g t he refractory l in ing , and jus t p r io r t o being covered, the radioactive source i s in s t a l l ed . Figure 3 shows the radioactive source being inser ted i n t o a t e s t brick. Radiation f i l m badges are issued t o a l l personnel working ins ide the furnace. I n addit ion, routine area radiat ion surveys a re conducted t o insure t ha t the allowable dose of 100 millirems per week i s not exceeded. Actually, analysis of the badges following the completed r e l i ne s has shown no measurable exposure (badge threshold s e n s i t i v i t y i s 10 MR). f igure 4 shows a typ ica l monitoring ( f i b ) badge.

Castable l in ings f o r the b l a s t furnace required a new and d i f fe ren t technique f o r source i n s t a l l a t i on . A castable i s normally gunned i n t o posi t ion i n the furnace, building up the l i n ing thickness i n a gradual manner. Predr i l l ing the l in ing sect ion is , of course impossible, and d r i l l i n g a f t e r the castable i s i n posit ion would or could potent ia l ly damage the castable i n t h a t area , providing a biased r e su l t . The . most p rac t ica l technique i s t o i n s t a l l the radioactive source while the l i n ing thickness i s being b u i l t . I n other words, i n s t a l l i t during the gunning operation. Placing the capsule i n t h e moist cas table immediately a f t e r gunning required a spec ia l too l . A simple ramrod type tube (shown i n fi'gure 5) was developed where the source could be loaded and placed firmly i n t o the gunned castable , and the gunning operation continued t o s e a l the capsule i n place.

One of the problems involved i n a study of a castable l i n ing is determining an accurate depth t o which the capsule i s t o be buried. Area locat ion i s s imilar t o locat ing br ick sources and can be premarked. I n both of the gun castable s tudies made a t Republic t o da te , sources have been located i n the cooler p la te sect ion of the lower s tack of the .

furnace. Here, the depth of the cooler p la tes extending i n t o the furnace served as a depth guide f o r i n s t a l l i n g the sources. Additional sa fe ty precautions a re required ,

when i n s t a l l i n g sources i n castable l in ings due t o the pos s ib i l i t y of "blowing1' the source out of the wall. Precautions a r e taken t o insure t ha t the capsule i s firmly embedded i n t he moist castable, and monitoring the area immediately a f t e r seal ing the source i n place insures posi t ive locat ion of the source.

Details of the monitoring techniques used i n measuring the radiat ion externally on e i t he r the br ick o r castable l in ings a re f a i r l y straightforward. h t e r a l l l eve l s of sources have been in s t a l l ed i n the l in ing , external locat ion of the sources is.marked with a posi t ive i den t i f i ca t i on tag attached t o the she l l . Sensit ive monitoring equip- ment consis ts of a portable rate-meter and associated gamma s c i n t i l l a t i o n detector. The s c i n t i l l a t i o n detector i s housed i n a protective bakel i te cylinder which can be

attached t o extension tubes. In monitoring, the detector is merely placed on the ident i f ica t ion disk and the source i s e i the r noted as being present or having been lo s t . Figure 6 shows the source monitoring i n the b l a s t furnace bosh area. The time sequence between readings i s varied as required by the type of ins ta l la t ion . For example, on the i n i t i a l castable l in ing application, readings are taken a t a f a i r l y short time in te rva l (two-week period) ant ic ipat ing f a i r l y rapid Lining wear. Most readings, however, are taken on a monthly basis and reported as l in ing wear per length of time i n service.

Some question was raised concerning the poss ib i l i ty of diffusion of the encapsulated source i n t o the refractory brick a t elevated temperatures. The resul tant loss of radiation might erroneously indicate a loss of l ining.

A controlled laboratory t e s t was conducted t o study the diffusion question. The refractory brick, with encapsulated source inser ted, was heated and maintained a t a temperature of 2900 F f o r f ive hours. Figure 7 shows tha t the source capsule had completely diffused i n t o the refractory brick, covering a several cubic inch area d i r ec t ly around the or ig ina l location. However, no loss i n radiation was detected. From t h i s experiment we concluded t h a t the diffusion of the encapsulated Cobalt-60 source i n the refractory brick w i l l produce no appreciable loss of radiation a t the outside surface of the b l a s t furnace. I n addition, vaporization of Cobalt-60 occurs a t such a high temperature (in excess of 4000 F) tha t loss of radiation a t the outside of the furnace i s due only t o source loss when the refractory l in ing erodes past the location of the capsule. When there are sources remaining a t the end of the furnace campaign, Research personnel w i l l supervise t h e i r removal from the remaining refractory l ining. To date , we have recovered sources from the l in ings of two furnaces. I n both cases, one with a carbon refractory and one with a ceramic type refractory brick, the remaining sources were recovered without d i f f icu l ty . I n neither case were temperatures suf f ic ien t ly high t o diffuse the capsule i n t o the refractory brick i t s e l f and individual capsules were recovered. However, several capsules had been exposed t o enough temperature t o break the welded s e a l cap and these were disposed of through AX licensed agencies. Addi- t iona l information on the recovery of sources w i l l be presented l a t e r i n the paper. I f a suf f ic ien t number of sources remain, and a new bosh re l ine is not required, the sources can be l e f t i n the furnace f o r a second campaign.

A brief discussion i s in order on the safety procedures followed during a l l of the l in ing wear studies made t o date a t Republic. Following approval of the source study f o r an individual furnace, meetings a re scheduled with Republic and contractor personnel involved i n the re l ine , where the en t i re i n s t a l l a t ion procedure i s reviewed. A l l radioactive source materials are handled by Research personnel. Contractor personnel i n s t a l l the individual t e s t brick or gunned castable l ining. A l l personnel involved i n the furnace l in ing in s t a l l a t ion are required t o wear monitoring badges. Be- cause radiat ion leve ls outside of the furnace s h e l l are a t such low leve ls , personnel involved i n work outside of the furnace a re not required t o wear the monitoring badges. Control badges a re normally in s t a l l ed i n key locations t o monitor the radiat ion leve ls on a &-hour basis. I n a l l source in s t a l l a t ions t o date ( including one involving over 100 sources), radiat ion levels i n work areas have been below the monitoring badge sen- s i t i v i t y .

PLANT STUDIES

Republic has been involved i n 11 separate furnace in s t a l l a t ions of r adoac t ive sources f o r l in ing wear measurement. Ten of these furnaces were Republic furnaces, and most of the in s t a l l a t ions were fo r specific design c r i t e r i a information. We w i l l b r i e f ly cover these individual furnace designs and studies t o outline the r e su l t s obtained and some of the varying techniques tha t were used.

Gadsden No. 2 Blast Furnace

O u r i n i t i a l furnace study was i n October 1968 on the Gadsden No. 2 Blast Furnace

(26 foot hearth diameter) i n our Southern Dis t r ic t . This furnace had a unique bosh cooling design of Shannon Plates ( large i r o n castings) with a t h in refractory l in ing of 13% inches. Figure 8 i s a cross sect ional view of the bosh design showing the lower portion of the Shannon cooling plate. A t o t a l of 30 sources were in s t a l l ed a t three levels i n the bosh. A high concentration of sources was located i n the lower portion of the Shannon plates where a high alumina refractory had been ins ta l led . Sources were located a t depths of 7% inches and 1@ inches from the hot face of the l ining. The in s t a l l a t i on included a small t e s t panel of the fused cas t alumina refractory i n the lower l eve l of the Shannon plates.

Figure 9 i s a graph showing refractory wear versus time i n service on the Gadsden No. 2 Furnace. Note the extremely rapid wear of the high alumina refractory i n the f i r s t l eve l and the somewhat slower but s t i l l rapid wear of the improved superduty refractory i n the upper levels. Seven and one-half inches of refractory were l o s t i n the alumina br ick i n l e s s than t e n weeks. I n an average time of approximately six months, a l l of the sources i n s t a l l ed a t both the 7*&7d lo& inch depths were l o s t .

T h i s type of rapid wear was cer ta inly not expected, but ye t a previous campaign with this type of cooling system had shown l i t t l e o r no refractory l e f t a t the end of the furnace campaign. This study substantiated tha t t h i s refractory loss occurs very ear ly i n the campaign. This furnace reached over three mill ion net tons of production on essen t ia l ly bare cas t i r o n castings and the castings a re s t i l l capable of prolonged service. We w i l l not take time in t h i s paper t o review the t o t a l economics of this type bosh design. It suff ices t o say the thermal l o s s through bare castings, as well a s the rapid lo s s of the expensive refractory l in ing , prompted Republic t o change this design back t o what we c a l l the conventional copper p la te cooler design bosh.

The following tab le i s a summary of the refractory wear r a t e data from Gadsden No. 2 Blast Furnace a f t e r 130 weeks of service:

REFRACTORY WEAR RATE DATA

GADSDEN NO. 2 BUST FURNACE

Number of Sources and Average Wear Rate

Refractory Depths from inches-weeks) Level - Location Material Hot Face lo$-"

1 49(l above base high 5 @ 72' 9.2weeks 15.8weeks of Shannon p la te alumina 5 @ lel

1 4$l above base fused cas t 1 @ 7+11 15.0 weeks 15.0 weeks of Shannon p la te 1 @ 1wf

2 above base improved 1 @ 7 9 14.0 weeks 18.0 weeks of Shannon p la te superduty 1 @ lW1

3 50'' above base improved . 4 @ 731 17.3 weeks 25.3 weeks of Shannon p la te superduty 4 @ lo+J1

4 89" above base improved 4 @ 7 9 22.8 weeks 41.0 weeks of Shannon plate superduty 4 @ lopf

Chicago No. 1 Blast Furnace

Our second source i n s t a l l a t i o n was i n our Chicago No. 1 Blast Furnace i n April 1970. This furnace has a hearth diameter of 28 f e e t , 1 8 t u y e r e s , and a bosh of conventional'

design ( s t e e l bands with copper cooling plates) . A t o t a l , of 44 sources were in s t a l l ed a t four leve ls i n the bosh. Figure-10 i s a cross section of this bosh design showing the location of the sources. and the l in ing thickness. de ta i l s . The f i r s t and th i rd levels had 18 sources each, while the second and fourth levels had four sources in- s t a l l ed d i rec t ly i n f ront of the copper cooling plate. Sources in the f i r s t and t h i r d levels were a t t e n inches and 15 inches from the '?lot face", while the sources i n f ront of the copper plates were three inches from the %ot facef1. The refractory i n the Chicagobosh was a superduty, Cone 23, f i rec lay brick.

. .

A s expected, the sources d i rec t ly i n f ront of the copper plates were l o s t i n a week and a half . Ten inches of wear was experienced in both the f i r s t and th i rd leve ls i n a period of approximately a month and a half. Fifteen inches of wear was more rapid higher i n the bosh ( i n the th i rd l eve l ) , with a l l sources i n this leve l l o s t i n an average time of 43 weeks. A more s tab le condition was experienced in the f i r s t l eve l , approximately three f e e t above the centerline of tuyeres, where the "cold face" or 15 inch sources were i n place fo r over two years.

The Chicago furnace studies show tha t any refractory l in ing i n f ront of the copper cooling plates wears away i n a matter of days. Stabi l izat ion of the conventional .bosh design with superduty quali ty brick proceeded rapidly,in a matter of weeks. The l in ing wear was preferent ia l , with the more severe wear occurring i n the bosh, eight f e e t above tuyeres.

The following tab le i s a summary of the refractory wear r a t e data from Chicago No.1 Blast Furnace a f t e r 206 weeks of service:

REFRACTORY WEAR RATE; DATA

CHICAGO NO. 1 BLAST FURNACE


Refractory Depth from (inches-weeks ) Level - Location Material Hot Face 3 " lof1 15"

1 3 7 3 ~ above superduty 9 @ lof1 - 6.4 weeks 8 of 9 tuyere .centerline 9 @ 1 5 " . missing

2 67" above superduty 4 @ 3" 1.5 weeks - - . tuyere center l ine

3 100" above superduty 9 @ lof1 - 4.4 weeks .42.8 tuyere centerline 9 @ 15" weeks

4 130" above superduty 4 @ 3" 1.7 weeks - - tuyere centerline

Cleveland No. 6 Blast Furnace

Our t h i rd furnace source in s t a l l a t ion i n May 1970 was i n one of our large (28 foot diameter) Cleveland furnaces, No. 6 Blast Furnace. This was an expanded study of a conventional copper plate cooled bosh with three leve ls of 58 sources in s t a l l ed i n the bosh and a fourth leve l of four sources in s t a l l ed approximately 4j$ f e e t below the wearing plates i n the upper stack. I n each of the three levels of the, bosh study, 18 sources were in s t a l l ed - nine a t t en inches from the hot face and nine a t 15 inches 1 from the hot face i n a 3lZ inch wall thickness. Four additional sources were in s t a l l ed i n a special fused cas t alumina panel. f igure ' 11 i s a cross sect ional view of this bosh design showing the approximate location of each of the three levels. Again, t h i s bosh study was i n i t i a t e d because of the use of two new types of refractory brick i n

the bosh of a Republic furnace. A high alumina (9% alumina) ' refractory was used i n the lower t h i rd of the bosh, with a low a l k a l i improved superduty brick i n the upper two-thirds of the bosh.

Lining wear i n the Cleveland bosh, compared t o the Chicago bosh, was slower, approximately 3046 of the r a t e experienced in Chicago, but s t i l l f a i r l y rapid. Ten inches of wear was experienced a t the f i r s t two leve ls i n an average time of f i ve months. The upper l eve l of the bosh, approximately 11 f e e t above the centerl ine of the tuyeres, noted a much slower r a t e of wear with t en inches of brick gone i n a matter of e ight months. Within the high alumina refractory section of the bosh, a small t e s t panel of a fused cas t , high alumina refractory had been ins ta l led . The alumina sect ion of the bosh had been b u i l t with an expansion allowance of 1/8 inch/foot incorporated i n t o the l i n ing design. Rate of wear s tab i l ized rapidly a f t e r the i n i t i a l 3% wear was experienced, with 5% wear experienced i n an average time of a year and a half . While t h i s was considerably slower than the wear r a t e experienced in the conventional superduty bosh i n Chicago, the r a t e of wear was s t i l l considered excessive f o r the expensive refractory design.

Again, through the use of the radioactive sources, we were able t o evaluate a new furnace l in ing design i n a r e l a t i ve ly short period of time. The use of the higher cost refractory product was not jus t i f ied i n t h i s bosh design.

The following tab le i s a summary of the refractory wear data from Cleveland No. 6 Blast Furnace a f t e r 190 weeks of service:

REFRACTOFX WEAR RATE DATA

CLEVaAND NO. 6 BLAST FURNACE


Refractory Depths.from (inches-weeks ) Level Location Material Hot Face 10" 15"

1 37$? above high 9 @ lof1 16.6 wkeks 8 of 9 tuyere centerl ine alumina 9 @ 15" missing

1 37gf above fused cast 1 @ 10,' 18.0 weeks 186.0 weeks tuyere center l ine 1 @ 15"

2 7 e 1 above high 9 @ lof1 2l. 9 weeks 93.7 weeks tuyere center l ine alumina 9 @ 15" '

2 - . 7 e 1 above fused cas t 1 @ 10" 18.0 weeks 103.0 weeks tuyere centerl ine 1 @ 15"

3 1213~ above improved 9 @ loll 32.0 weeks 6 of 9 tuyere center l ine superduty 9 @ 15" missing

4 66" below wear improved 2 @ 10" 47.0weeks 135.0weeks plates supe rduty 2 @ 15"

Carbon Refractory Bosh

Our f i r s t opportunity t o evaluate a carbon'lined bosh i n a b l a s t furnace was i n July 1970 f o r another s t e e l company i n the Cleveland, Ohio area. This was a carbon l ined externally cooled (shower cooled) bosh of a 30 foot diameter furnace. This was a limited study using a t o t a l of nine sources and in s t a l l ed i n two levels above tuyere centerl ine. A t 27 inches above tuyere center l ine , two sources a t 15 inches, and three

sources a t 21 inches from the "hot facew were ins ta l led . A t 50 inches above tuyere centerline, four sources were in s t a l l ed a t 18 inches from the "hot facew. After a service campaign of approximately two years, the furnace was removed from service and a t o t a l replacement of the bosh was done. A l l nine of the or ig ina l sources in s t a l l ed were s t i l l i n place a t the end of the campaign showing tha t l in ing wear was l e s s than 1 5 inches.

This was the first attempt a t recovery of sources a f t e r a furnace campaign. A l l nine sources were recovered with no problem. To i l l u s t r a t e the accuracy of the radioactive source technique, Figure 12 i s a photograph showing one of the t e s t b r i c k from this furnace where l i n ing wear had approached the approximate posit ion of the source. The pre-drilled hole was exposed i n the refractory block, but wear had not reached the source i t s e l f . Although the capsule had carburized and opened, the radiation was s t i l l detectable from outside the furnace, and l in ing wear had barely approached the 18 inch depth i n the second level. Wear i n this par t icular furnace was greater i n the second leve l (50 inches above tuyere center l ine) than i n the leve l c loser t o the tuyere centerline (27 inches above).

A second limited isotope study of the bosh l in ing of t h i s furnace was conducted .during the 1972 re l ine and i s currently i n service.


The most extensive refractory wear study in Republic was in s t a l l ed i n February 1972 on the Cleveland No, 5 Blast Furnace. A t o t a l of 106 radioactive sources were in- s t a l l e d i n seven levels through the bosh, mantle area, lower stack, and upper stack regions of the furnace. 'This was a major complete re l ine of the furnace system, en- larging the hearth from a 28 foot diameter t o a 29 foot , six inch diameter furnace with external e a r t h cooling (channel cooling). Several unique refractory designs were incorporated i n the furnace design which accounts f o r the extent of the study. To b r i e f ly review some of the design features involved i n this r e l ine , the bosh sect ion was of conventional copper plate design, although of high density cooling throughout, and incorporated external channel cooling i n the tuyere breast area. The mantle area, which had been a vulnerable spot on t h i s furnace, had a special new copper plate cooler i n s t a l l ed with an 18 inch thick refractory l in ing i n f ront of the cooler. The stack, although not unique i n Republic, was what we consider a t h i n l ining, 27 inches thick, cooled with conventional copper plates. I n the stack region, the l i n ing wear study was primarily t o substantiate l in ing wear patterns. Refractory quali ty i n the stack was the same as the Cleveland No. 6 Furnace, but from a d i f fe ren t supplier. This a l so was a reason fo r performing the s tack l i n ing wear study. Figure 13 i s a cross section of the bosh area showing the high density of cooling and the special de- s ign cooling p la te incorporated i n t o the mantle area.

Data collected i n the 18 month service time since the furnace was put back i n February 1972 has again shown us cer ta in l in ing wear patterns useful i n improving our furnace l in ing designs. For example, we experienced extremely rapid wear i n the f i r s t l eve l of sources i n the bosh. A t l e a s t nine inches of wear had occurred in t h i s f i r s t l eve l i n an average time of a l i t t l e over three weeks. The upper two leve ls of the bosh, as w e l l as the a rea ' in f ront of the mantle band, had not l o s t a source. There i s a c l ea r indication tha t cooling design i n this lower par t of the bosh, which depends on the ex- t e rna l channel cooling i n the upper tuyere breast area, i s not suf f ic ien t t o protect ceramic brick i n t h a t area. The area we f e l t t o be vulnerable, d i r ec t ly in f ront of the mantle band, has shown minimum wear t o date, and apparently shows the effectiveness of the new cooler plate design protecting the mantle. Lining wear i n the lower stack region has shown nine inches of wear over approximately 5% of the furnace, but has not been an accelerated wear.


REFRACTORY WEAR RATE. DATA

CIEVFLAND NO. 5 BLAST mTRNACE


Refractory Depths from (inches-weeks ) Level Location Material Hot Face 9 " 1 3 9

1 41eq above improved 9 @ 9" 3.2 weeks 11.6 weeks tuyere centerline superduty 9 @ 1%"

2 9 4 9 above . improved 9 @ 9 " 3 of 9 - tuyere centerline superduty 9 @ 133" missing

3 Il+73l above improved 9 @ 9" - - tuyere centerline superduty 9 @ 13+?

' 4 72' below top improved 4 @ 611 - - of mantle l ine superduty 8 @ 12"

5 1 4 e 1 above top improved 8 @ 9" 6 of 8 - of mantle l i n e superduty 8 @ l3$" missing

6 262" above top of improved . 8 @ 9 1 1 - - mantle l ine superduty 8 @ l & l

7 72" below wear improved 4 @ lof1 - - plates superduty 4 @ 1511

Warren No. 1 Blast Furnace Repair

A unique type of repair was required on our Warren Blast Furnace in October 1971 which we wi l l br ief ly describe. The upper stack region, beneath the wearing plate or throat area of the furnace, had l o s t i ts ent i re refractory l ining andsubsequent s h e l l dis- tor t ion was occurring. The decision was made t o r e p a i r t h i s section of l ining from outside the furnace she l l . Access holes were cut in to the s t e e l she l l around the perimeter of the furnace and a 7$ foot high, 2% inch thick l ining instal led up t o , and under-pinning the wearplates. This repair work was done with the f u l l burden i n the furnace direct ly below this area. This was the second such fa i lure 'of the upper stack l in ing in this furnace.

A 2% inch thick lining of an improved superduty brick was ins ta l led and a t o t a l of 12 radioactive sources were s t ra tegica l ly placed t o monitor wear rate. These sources were a t depths of ~g inches, 11 inches, and 16$ inches, placed on the quadrants around the furnace. After 20 months service, only two of the inch sources had been l o s t , leaving t en of the original 12 sources i n place when the furnace came down f o r reline. When this section of l in ing was visually examined, it showed that the wear pattern ob- served had been accurately measured by the external source study (wear was minimal).

Removal of the t en remaining sources i n a refractory brick compared t o a carbon brick proved t o be somewhat more d i f f i cu l t . The d i f f icu l ty was i n removing the whole brick from the furnace lining. Extraction of the source capsule from the t e s t brick was

eas ie r than anticipated.' Due t o the low temperature tha t a l l t en remaining sources were exposed t o , none of the sources had deteriorated, and were actual ly salvaged and reused i n the Warren furnace during the 1973 rel ine.


There are two furnaces in Republic t ha t have a carbon refractory bosh. I n September 1972, we had an opportunity t o i n s t a l l sources i n the carbon bosh of the Cleveland No. 1 Blast Furnace. W s i s an externally (channel cooled) bosh (minimum spacing required f o r welding between channels) and the l in ing thickness varies from 18 inches d i rec t ly above the tuyere' breast t o a 13% inch l in ing just below the mantle. A t o t a l of 48, sources were ins ta l led i n three leve ls of 16 sources each. These sources were located a t l i n ing depths of t o 2/3 t o t a l depth. For example, i n the 18 inch thick section of l ining, the 'Pnot facer1 sources were ins ta l led a t nine inches, and the "cold faceu source a t 12 inches. Eight sources a t each depth were spaced a t every other tuyere on the 16 tuyere furnace. Figure 14 i s a cross sect ional view of this ins t a l l a - t i o n giving the source locations.

Data collected thus f a r have shown preferent ia l wear i n the f i r s t l eve l of sources (40 inches above centerline of tuyeres) where half of the l in ing had worn i n approximately 26 weeks, and two-thirds of the l in ing had worn in about a year t s time. The second and t h i r d leve ls , which were approximately seven f ee t and 11 f e e t above tuyeres, have shown a much reduced r a t e of wear.



CLE;VELAND NO. 1 BLAST FURNACE


Refractory Depths from (inches-weeks ) Level Location Material Hot Face 9 " 12"

1 4%'' above carbon 8 @ 9 " 7 of 8 5 of 8 tuyere centerline 8 @ 12" missing missing

2 above carbon 8 @ 8 p 2 of 8 2 of 8 tuyere centerline 8 @ 11" missing missing

3 12%" above carbon tuyere centerline


A second source in s t a l l a t ion i n a carbon bosh was done l a t e in 1973 i n the Cleveland No. 4 Blast Furnace. This i n s t a l l a t ion was designed f o r f u r t h e r study of the lower area of t he channel cooled carbon bosh, as well as i nves t iga t e a,new brand of improved superduty;-brick ins ta l led i n the stack of the furnace. This study includes a t o t a l of 40 sources. Two leve ls (16 sources and eight sources) a re i n s t a l l e d f o u r f e e t and eight f ee t above tuyere centerline. Another two leve ls of e ight sources each. are located i n the mid-cooling plate section of the lower stack.

I

Warren No. 1 Blast Furnace

A limited source ins ta l la t ion was made on the Warren Blast Furnace during the 1973 re- l ine. The current technique i s t o i n s t a l l two levels of eight sources each i n the bosh, approximately four fee t and e igh t ' f ee t above tuyeres. A study of the stack includes two levels of eight sources each i n the mid-cooling plate section of the lower stack, and a f i n a l level of eight sources ins ta l led beneath the wearing plates. The f ive levels w i l l give us a representation of the lin5ng wear i n the c r i t i c a l parts of the furnace lining. We have established this as a standard practice o n a l l large production furnaces i n Republic, and it w i l l also be used i n smaller furnaces where particular l ining studies need t o be made.

Gunned Castable Studies

We have saved discussion of our most unique ins ta l la t ions t o date fo r l a s t . These studies involved two major gun castable l ining ins ta l la t ions on the Youngstown No. 1 and Youngstown No. 2 Blast Furnaces. Both of these furnaces required a pa r t i a l re- l ine in l a t e 1972 and early 1973, respectively. In the Youngstown No. 1 Furnace, approximately 450 net tons of a Class "Eft refractory castable was gunned in the bosh and stack of the furnace. The existing brick l ining had been scaled down and cleaned, and was generally i n f a i r condition. Several t o t a l void areas, back t o the s t e e l she l l , were present i n the mid-stack area. A portion of the bosh had been removed t o f a c i l i t a t e burden removal from the furnace and this was completely rebricked. The re- mainder of the bosh had several areas of brick repair but, i n general, had from four $0.

12 inches of castable applied.' The stack gunned castable l ining also ranged from a few inches thick t o 25 inches thick, or the f u l l thickness of the copper cooling plates.

Five levels of eight sourcks each were instal led i n the No. 1 furnace with the upper- most level ins ta l led i n a brick repair area beneath the wearing plates. The four remaining source levels were ins ta l led i n the castable refractory. A s mentioned e a r l i e r i n the paper, the technique developed f o r ins ta l l ing the sources u t i l ized a ramrod principle. To br ief ly review, the source was carried i n the t i p of the rod and placed firmly against the gunned castable on the wall. The source was then forced in to the castable and a small amount of material used t o replug the area. All of this was done from the suspended scaffold while other sections of that particular area were being gunned. The most d i f f i cu l t portion of the source ins ta l la t ion i n a gunned castable l ining i s the determination of depth i n the lining. Horizontal and ver t ica l alignment were easi ly determined and marked prior t o the gunning of the area. I n a l l of the source locations, copper cooling plates were available t o use as guides f o r determining depth of source instal la t ion. A l l gunning was done f lush t o cooler t i p s and measurements were based on depth from "hot facew of these copper cooling plates.

In the f i r s t level ( in the bosh) sources were buried from four t o nine inches deep, depending on location. F'igure 15 i s a cross sectional view of the bosh showing these source locations. Three levels of sources were ins ta l led i n the stack a t eight f ee t , 16 f e e t , and 23 f ee t above the mantle. Depth of sources in the stack ranged from f ive inches t o 2l inches from the "hot facew. Figure 16 i s a cross sectional view of the stack ins ta l la t ion of sources.

Results from this castable source study showed an extremely rapid wear i n the bosh castable. The f i r s t four inches of castable were l o s t i n a period of less than one week. The remaining bosh sources continued t o be l o s t i n a short period of time, showing tha t gunning i n the bosh t o any depth other than protection gunning does not seem practical. Wear i n the stack castable l ining was experienced a t eight f ee t above the mantle i n an average time of 2$ months. The "cold facev sources a t t h i s elevation showed service l ives of up t o a year. Most of the "cold face" sources 16-23 fee t above the mantle are s t i l l i n place a f t e r over 14 months of operation.

Based on this study, our i n i t i a l anticipation of rapid castable loss i n the stack was not realized. The 'hot faceft portion of the castable was l o s t i n a relat ively short

time (four months) but the castable l ining i n the void areas of the stack has remained fo r over a year.

The following table is a summary of the refractory wear ra te data from Youngstown No. 1 Blast Furnace a f t e r 59 weeks of service:


YOUNGSTOW'N NO. 1 BLAST FURNACE . .


Refractory Depths from (inches-weeks ) Level Location Material Hot Face 4'l 6-9 fl -

1 5 ; above tuyere cast able 4 @ 4tf . 2.5 weeks 20.8 weeks centerline 4 @ 6-9" .

7 .- 8'-1" above top castable 4 @ 5" 10.8 weeks 3 of 4 of mantle l ine 1, @ 10-15" missing

3 161-111 above top cas table 4 @ 5" 16.8 weeks - of mantle l ine 4 @ 15-21"

4 22'-1!' above top castable 4 @511 3 of 4 1 of 4 of mantle. l i ne 4. @ 7-20" missing missing

5 52" below wear improved 4 @ 11-p - - plates - superduty 4 @ 15"

The Youngstown No. 2 Furnace also had a gunned castable l in ing in the stack portion of the furnace. Here, two levels of eight sources each were ins ta l led a t approximately nine f ee t and 16 fee t above the mantle. A t o t a l of 16 sources were ins ta l led a t depths ranging from five inches t o 16 inches from the "hot facef1. This furnace has had only brief production periods since the pa r t i a l rel ine and none of the sources have been los t . LLning wear i s l e s s than f ive inches.

CONCLUSIONS

The use of radioactive sources t o measure refractory wear r a t e has proven t o be an accurate, pract ical and economic tool i n the overall study of b las t furnace operations. The basic concept can be applied i n almost a l l sections of a b las t furnace, as well as other types of furnaces.

Some of the specific conclusions we have been able t o obtain using our source studies include : ' '

1. External cooling systems do not provide adequate cooling f o r conventional thickness ceramic linings and therefore, i f used, should have minimum ceramic protec- t ion f o r best economics.

REFRACTORY WEAR RATE

1 3 5 ~ GADSDEN * 2 BLAST- FURNACE

. . . . . . . . . . . . . . . . . . . . . * ............- . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ,*

10 - / ...; ..:.....

i ; 8 - . . : ................ *... . . . * . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

* FUSED-CAST - I " LEVEL - HIGH-ALUMINA - 1" LEVEL

.--, IMPROVED SUPERDUTY - 2"d LEVEL

- - IMPROVED SUPERDUTY - 3 'd LEVEL

. IMPROVED SUPERDUTY - 4Ih LEVEL

0 ib zb 3'0 . 4 0 50 60 7 0 8 0

TIME IN SERVICE

(WEEKS I

Figure 9 ' - Refractory Wear Rate - Gadsden No. 2 Blast Furnace

CHICAGO

Figure 10 - Cross Section of Bosh - Chicago Blast Furnace

RADIOACT lVE SOURCES, .. .

M A N T L E LEV€

3 RD. LEVEL

2 N D . LEVEL

CLEVELAND N0.5

D U T Y

Figure 13 - Cross Section of Bosh - Cleveland No: 5 Blast F ' a c e

IST. L E V E L

GUNNED CAS TABLE

E X I S T I N G BRICKWORK

YOUNGSTOWN .NO. O

Figure 15 - Cross Section of Bosh - Youngstown No. 1 Blast Furnace

I O A C T I V E SOURCES

CARBON BRICK

CLEVELAND NO. I

Figure l.4 - Cross Section of Bosh - Cleveland No. 1 Blast Furnace

4 T H . LEVEL

ADlOACTlVE SOURCES

3 RD. LEVEL

GUNNED CASTABLE L IN ING

2 ND. LEVEL

EXISTING BRICKWORK

YOUNGSTOWN NO. I

Figure 16 - Cross Section of Stack - Youngstown No. 1 Blast Furnace

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