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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.
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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 pro- gressed 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 to- ward estimated designs ra ther than designs based on previous performance. This prob- lem 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 prob- lem 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
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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 nor- mal 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 thick- ness 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
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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 ex- ample, 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 re- fractory brick, with encapsulated source inser ted, was heated and maintained a t a tem- perature of 2900 F f o r f ive hours. Figure 7 shows tha t the source capsule had com- pletely 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 per- sonnel 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 per- sonnel i n s t a l l the individual t e s t brick or gunned castable l ining. A l l personnel in- volved 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
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(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'
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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
Number of Sources and Average Wear Rate
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
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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, approxi- mately 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 experi- enced, 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 fur- nace 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
Number of Sources and Average Wear Rate
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
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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 tu- yere 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.
Cleveland No. 5 Blast Furnace
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.
The following tab le i s a summary of the refractory wear data from Cleveland No. 5 Blast Furnace a f t e r 97 weeks of service:
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REFRACTORY WEAR RATE. DATA
CIEVFLAND NO. 5 BLAST mTRNACE
Number of Sources and Average Wear Rate
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
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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.
Cleveland No. 1 Blast Furnace
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 tu- yere 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 approxi- mately 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 tu- yeres, have shown a much reduced r a t e of wear.
The following tab le i s a summary of the refractory wear data from Cleveland No. 1 Blast Furnace a f t e r 66 weeks of service:
REFRACTORY WEAR RATE DATA
CLE;VELAND NO. 1 BLAST FURNACE
Number of Sources and Average Wear Rate
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
Cleveland No. 4 Blast Furnace
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 lo- cated i n the mid-cooling plate section of the lower stack.
I
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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 in- cludes 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 pro- duction furnaces i n Republic, and it w i l l also be used i n smaller furnaces where partic- ular 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 re- maining 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 measure- ments 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, de- pending 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
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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:
REFRACTORY WEAR RATE DATA
YOUNGSTOW'N NO. 1 BLAST FURNACE . .
Number of Sources and Average Wear Rate
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 approxi- mately 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 thick- ness ceramic linings and therefore, i f used, should have minimum ceramic protec- t ion f o r best economics.
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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
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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