Rebuild of Great Lakes Steel's No. A Blast Furnace

Transcription

1 16 lronmaking Proceedings, ' Rebuild of Great Lakes Steel's No. A Blast Furnace by John R. Westerholm In many iron-producing companies, blast furnace relines have become a yearly maintenance item. These relines are necessitated by the erosion of furnace brickwork and provide an opportunity for furnace modernization. Modernization is periodically needed to bring into operation the various research developments that have evolved since the last major shutdown. Only with improvements in methods, materials, and equipment can a corporation remain competitive. It is the object of this paper to relate the improvements made on "A" Blast Furnace at Great Lakes Steel, a division of National Steel Corp., and to show the methods employed to blow-out and blow-in the furnace. BLOW-OUT "A" blast furnace was blown out for a complete reline and modernization on the morning of September 10, At this time the furnace had accumulated a total of 2,743,241 tons on the stack lining and 6,877,264 tons on the hearth lining. The difference in tonnage is due to two mantle-up relines, the last completed on Sept. 3, Blast furnace slag (3/4 x 1 % in.) was used for the blow-out material because of its availability and high fusion point. Slag has been utilized in all our blow-outs for the last several years and has proven to be highly satisfactory. Its ability to withstand degradation permits a permeable stack column, thereby reducing the tendency of the furnace to hang and allows rapid quenching of the burden. The physical shape and size of the slag encourages free flow which aids in burden removal. Approximately 16 hr before windoff, all scrap, scale, and nut coke was removed from the burden. For the next 10 hr the burden was reduced, in steps, by 2400 lb of ore and 900 lb of stone. All limestone was removed 6 hr prior to wind-off. In charging the slag, a three skip fill was instituted with the large bell being dumped after every third JOHN R. WESTERHOLM was formerly blast furnace foreman, Great Lakes Steel Div. of National Steel Corp., Ecorse, Detroit, Mich. He is now production systems manager, The Traub Co., Detroit; skip. The slag was fully watered down, both in the bins and in the skip tubs. Exactly 4 hr prior to wind-off, the charging of 1050 tons of slag commenced. The final hours were marked by smooth furnace movement with no unusual occurrences. Wind was held at 107,000 cfm with 21 psig blast pressure. Following the last cast of 365 tons, the furnace was shut down and back drafted. With the realization that a new furnace bottom was needed, a decision was made to bottom tap for removal of the salamander. The time saved was the important factor in this decision. The first major step was the removal of all refractory in the 5 ft high by 2% ft wide salamander tunnel through 8 ft of the furnace concrete foundation. The second step, performed concurrently with the completion of the salamander tunnel, was the erection of pig beds and iron runners. The pig beds were divided into two areas. Area 1 was under the cast house floor and Area 2 in the north slag pit. A tunnel through the slag pit wall was provided for the movement of iron to the second area. The area under the cast house floor was surrounded by a 5 ft high concrete block wall. Both areas were excavated to hold a minimum of 6 ft of slag plus a minimum of 6 in. of sand while retaining the proper slope for the runners. Three-inch vent pipes, 9 ft long, were provided throughout the pig bed system. Each pig mold was 2% ft deep, approximately 7 to 8 ft long, and 4 ft wide. An iron pool was created at the far end of the pig bed system to catch any excess. All the above mentioned construction had to be completed before the blow-out while adhering to cast, flush, and pit digging schedules. Surface and subsurface water also proved to be a problem which necessitated thorough drying of the molds with natural gas and wood fires. The bottom tap drilling started an hour and a half before wind-off. Two and one half hours later, two holes were drilled to a depth of 5 ft with a 500 F and 750 F temperature on the top and bottom holes, respectively. Drilling on the top hole was halted due to a drill bit stuck in the opening. Four and one half hours after wind-off, salamander lancing commenced. The lance pipe was made up of three sections of 21 ft by % in. standard black pipe. Exactly 59 min later; the flow of iron began. The iron flowed steadily for 5% hr, accumulating a total of 645 tons. While one group tapped the bottom, a second group was preparing for the furnace quench. Immediately after wind-off, the top gas was lit, blowpipes dropped, and tuyeres clayed. Six hours after wind-off, quench water was turned on at the rate of 6 gpm through the test rod openings. Two hours later, sprays were inserted into the north and south gas seal doors, which increased the water rate to 22 gpm. The east and west gas seal sprays were inserted 1% hr later. The quench water was then increased 10 gpm every hour until 70 gpm was attained. The entire quenching took 84 hr and was marked by only one small kick, and almost perfect distribution of water. Top temperature remained under 500 F except for one period of 4 hr. This period of high top heat (500 F to 800 F) was caused by a broken hose on the quenching sprays. The next major step was the removal of the slag and burden. This was accomplished by blasting a hole in the side of the furnace thereby creating a portal which extended from No. 7 to No. 8 column, and covered the area occupied by three tuyere assemblies. The preparatory work started during the latter part of the furnace quench when workmen began removing piping, goosenecks and penstocks, cutting bosh bands, and installing kick plates. This preparation consumed a total of 24 hr. Burden removal was. at first, relatively simple. ~owevei, in the later stages, several large scabs fell from the furnace stack, wedging themselves in the portal opening. After considerable effort, it was decided that blasting was the only solution for removal of the scabs. Only after lancing the holes, placing the several charges, and blasting, would the material break up. The entire burden was removed by employing two front end loaders to move the material from the furnace to the slag pit. Exactly 131 hr after wind-off, the furnace stack was cleared and the furnace turned over to the contractor for reline.

2 I rorour L1 L,XE I Fig. 1-Blowout I lines. FURNACE AND AUXILIARY wearing plates and going down, was EQUIPMENT INSPECTION in fairly good condition for the first Immediately after burden removal 27 ft. As Fig. 1 shows, the brick a scaffold was rigged and a visual thickness in this area ranged from inspection made of the furnace 28 to 36 in. The shell around the top brickwork. This inspection revealed row of stack plates was marked by that the dome brick had been corn- little or no brick on the north-west pletely removed except for about 3 side. This condition expanded for ft immediately above the wearing the next 12 ft so that three-quarters plates. The lower six of the 12 rows of the furnace circumference conof wearing plates were severely tained from 0 to 4 in. of brick. It is eroded and had to be replaced. The felt that the absence of any type stack brickwork, starting at the of material in this area was due to C' Blast Furnace Operations-General 1 17 the scabs that fell during the rake out. The remaining portion of the furnace, including the bosh, was in fair condition with a brick thickness of 12 to 21 in. When the new furnace was built in 1955, carbon hearth sidewalls and a ceramic bottom were installed. Ten years and 6.9 million tons later, the carbon was still in good condition except for some erosion around the tap hole. After all hearth material had been removed, it was found that the salamander had penetrated the concrete foundation to a clepth of 2 ft at the center of the furllace. This is shown in Fig. 2. Surrounding this area was another circle of eroded concrete which measured 1 ft in depth. In order to recondition the concrete pad, it was necessary to chip away all damaged concrete so that a good base would be provided. The damaged area was filled with 23 yd8 of Luminite. Inspection of the bustle pipe and hot blast main revealed that these areas were generally in a satisfactory condition. Two sections (one 7% ft and one 13 ft) of the bustle pipe and the straight section of the hot blast main from No. 1 to NO. 3 stove required a new 4% in. top layer of brick. Next on the inspection list were the stoves. The brickwork in all three stoves was in extremely bad condition. The domes were characterized by decomposed surface brick with a large amount of brick missing in No. 3 stove. The upper 14 ft of checkers, in each stove, were plugged with melted refractory from both the checkers and the, dome brick. However, the lower checkers were in excellent condition with no visible damage to the support columns or steelwork. Damage was also experienced in the upper profile walls and 9-in. combustion chamber skin walls. These areas were badly spalled from heat. In regard to the gas cleaning area, Fig. 2-Blast furnace "A" rebuild--concrete cut in furnace Fig. 3--Overall view of large bell as it was removed from "A" bottom. blast furnace in 1965.

3 18 lronmaking Proceedings, 1966 Fig. 4-Cross-section the main difficulty encountered was the accumulation of a single layer of coke on the top tile bank and the 60% plugging of the top two banks of the gas washer by pellets and ore lumps. This occurrence was caused by numerous holes (Fig. 3) in the large bell which allowed burden material to blow back through the equalizer valve and down into the gas washer. RELINE Our intent in rebuilding " A Blast Furnace was to alter and redesign this furnace to reach the full potential of the unit's hot metal pro- of "A" blast furnace after reline. duction. To accomplish this end, major improvements were needed in the stoves and cast house, with lesser refinements to the gas cleaning system, charging system, and furnace proper. The furnace (Fig. 4) was lined with appropriate grades of Missouri Maximul Brick except for carbon brick in the hearth ring wall. The dome contains a 6-in. lining of castable with 3% ft of High Duty Mortex Brick in the stockline area. The stack, upper bosh, and furnace bottom is made up of Super Duty Maximul brick laid with "Super 3000" cement. The 36-in. thickness of carbon extends up from the furnace bottom to the centerline of the tuyeres. The volume of the furnace was increased due to the reduction in thickness of the stack lining from 36 in. to 22% in. and by lowering the bottom of the hearth 18 in. This action increased the working volume by 4959 ft3 (8.5%) and the hearth volume by 1078 ft3 (12.5%). Table I is a list of the furnace statistics. To provide suitable cooling to complement the thin brick, 11 more rows of stack plates were installed in the lower stack. This addition provided a total of 33 rows of cooling plates (stack and bosh) to cool a vertical height of approximately 40 ft above the mantle. Immediately under the mantle, water cooling boxes were built to provide additional cooling in that area. "A" Blast Furnace is estimated to consume 5000 gprn of cooling water. This figure does not include water to auxiliary equipment or slag pits. The large amount of water is supplied by two sources: a) Service water, providing 3700 gprn furnished via two 16 in. lines, b) Recirculating water providing 1300 gpm, from a 13,000 gal tank. Of the 5000 gprn sent to the furnace, 4800 gprn is returned to the recirculating tank and 200 gprn is lost through evaporation. The bosh remained essentially the same, except that certain cooling plates, which cannot be changed because of their location, will have two compartments or a double nose. When a nose failure occurs, the outer channel can be grouted, and cooling maintained in the inner compartment. In order to remove the predicted 3200 plus tons per day of hot metal, two tap holes were provided spaced 30" apart. The double tap hole is required to reduce the preparation time between casts. They are serviced by two mud guns, located at the outside of the troughs, and a common tap hole drill mounted on the center column. Side-hinged splashers, motivated by remotely mounted electric hoists, were provided. To accommodate the two tap holes, the cast house was divided, as much as reasonably possible, into two separate working areas so that the furnace could be tapped into either of the two systems. This is shown in Fig. 5. The No. 1 iron notch runner assembly has a four bottle setup while the No. 2 side has provisions for a five bottle spot. The last spout in each runner is situated so that the iron can be delivered into the ladle beneath these spouts from either runner. The troughs were constructed so that additional space would be provided to permit better separation of iron and slag. For example, the No. 2 trough is 29 ft from the furnace to the centerline of the skimmer,

4 Blast Furnace Operations-General 1 19 Hearth diameter Bosh diameter Stockline diameter Height. iron notch to top of hopper Height of crucible Height of Bosh Height of straight section Height of inwall section Heiaht of stockline section eight, bottom to iron notch Height, iron notch to cinder notch Height, cinder notch to tuyeres Working vol., tuyeres to stockline Bosh anele ~niall s&pe No. of tuyeres No. of columns Lining thickness, Lining thickness. Lining thickness, Lining thickness, crucible bosh stack throat Largebell diameter NO.-O~ stoves Stove diameter Stove height Checker openings Heating surface per stove No. of turbo blowers Blower capacity Blower pressure 18 in. deep at the tap hole, and 36 in. deep at the skimmer (trough slopes at a rate of in. per ft). Liberal use of carbon brick was made to protect the trough and its foundation. Four layers of brick in the following order were used: a) 4 in. carbon block (top layer); b) 3 in. carbon brick; c) 4% in. ceramic brick; and d) 3 in. carbon brick. This, topped with Helspot and a layer of gunning material, provides all the protection needed. The two runners are parallel to each other and spaced 301% ft apart. Fig. 5 shows the general arrangement of the casthouse. All portions of the iron runners are lined with 3 in. of carbon brick, upon which a carbonaceous sand is placed. This leaves a runner which is approximately 14 in. deep and 2% ft wide. The dimensions of the runner coupled with a slope of 5/8 in. per foot eliminates some of the scrap build- t Table I. Furnace Statistics. Fig. F A " furnace cast house arrangement. 30ft3 in. 33 ft 3 in. 23ft 0 in. 110 ft 0 in. 13 ft 6 in. 10 ft 6 in. 3 ft 6 in. 59 it 6 in. 10 it 3 in. 3 ft 6in. 4 ft 11 in. 3 ft 9 in. 63,211 ft3 82'24ft20 in. 1,042 in./ft 36 in. 27 in. 22% in 43 in. 16_ f16 in. J 26 in. 140 ft 2 in. and Z5& in. 306,962 it'" I cfm 35 psi up that has been experienced in the past. The- combined length of both runners is only 1714/2 ft compared with 181 ft for the single runner in the old casthouse. The slag runner remained substantially the same in regard to location and arrangement. A 96-ft main slag runner is directed to the westerly direction to feed into either of two slag pits. Feeding this main runner is one runner from each of the two cinder notches and a roughing runner from each trough. All combined, the total length of the cinder runners amounts to approximately 260 ft. The slag from No. 2 trough crosses the No. 1 iron runner at the same elevation so that this area must be prepared according to the tap hole that is to be used. Carbon is employed in the bottom of the roughing runner from the No. 2 iron trough to the crossover. Due to the cast house arrange- I ment, it was necessary to continue the practice of using Baker Dams. These I-ton units retain the molten metal in the trough and permit the separation of iron and slag. At the end of cast, the dam is pulled and the remaining iron and slag is drained into the last ladle. The Baker Dams are placed so that there is a 4-ft space downstream between the centerline of the skimmer and centerline of the dam. The dams are set so that they are surrounded by sand to prevent cutting by the flow of iron. In the No. 1 and No. 3 spouts of the No. 2 runner an innovation, new to Great Lakes Steel, was put into effect. Instead of using the standard spout:; in each of these locations, a tundish was installed. The tundish is simply a basin 16 in. by 16 in. and 48 in, deep which serves to collect and hold the iron while a steady laminar stream is discharged through a hole in the bottom. Three inch intermediate duty fire brick is used to line the tundish which, itself, is covered by a castable lining. Due to the additional runner, it was necessary to provide another railroad track on the south side of the cast house. Prior to its installation, it vras necessary to demolish and partly rebuild the rear section of a storeroom. A smaller building, three stories high, replaced the old two story section. Track work was not limited to the installation of the fourth track. The yard level at "A1' furnace was 580 ft with the adjacent area at 582 ft. This condition caused the tracks to slope uphill from beneath the cast house and also created an area for water collection. To partially remedy this situation, the other three older tracks were raised 12 ft to an elevation of 581 ft. Further elevation was prevented due to a limiting condition at a nearby pig machine. Elevating these tracks also served to minimize the height from the iron spouts to the hot metal ladles. Covering the new track is a leanto type huilding which also covers the new furnace control room. This control room, the old mud gun room, is elevated about 12 ft above the cast house floor and permits the viewing of both iron notches. The front section of the room contains all of the controls for the mud guns, tap hole drill, snort valve, and splasher hoists. These controls are mounted near the windows so that viewing is permitted while operating the various devices. The rear section houses the instrument panelboard which is in a pressurized, glass enclosure. Due to increased hot blast temperature requirements it was necessary to undertake extensive improvements in the stove area. These improvernents included the addition of automatic stove changing and increasing the heating surface of

5 20 lronmaking Proceedings, 1966 each stove. The additional heating surface was provided by increasing the stove height to 140 ft. This 25- ft increase provided 27% more surface area per stove. Using checker openings of 2 in. and 2% in., the heating surface per stove now amounts to 307,180 ft'. Repairs to the checkers involved replacing the top 14 ft. This amount, coupled with the next 20 ft of new checkers, is of the semi-silica type. The above checker work was topped with 5 ft of high alumina type Ufala checker. Ufala brick was also used in the lower 20 ft of the combustion chamber skin wall. The remaining portions of the skin wall, dome, and profile wall, were made up of semisilica brick. New burners were installed on each of the three stoves. The' burners are rated at 50,000 cfm of gas with 40% excess air to limit the dome temperature to 2200 F. The new fans are capable of handling a volume of 45,000 cfm of air at 33 lb static pressure, and are driven by 300 hp motors. Connecting the burners to the stoves are gate type 56-in. Bailey valves. The gas downleg contains a 48-in. gate valve, a gas regulating valve, and a gas shutoff valve (Pratt Valve). All stove operating valves are equipped with Limitorque operators which are controlled by the new combustion equipment. The control station for the new equipment is located immediately. adjacent to the "C" furnace stove control room. This station serves two functions: a) it acts as a motor control center, and b) it houses the graphic panel and recorders. The motor control center contains all the electrical components, motor starters, and relays to regulate the operation of valves, fan motors, and dampers. The graphic panel presents a flow diagram of the three stoves with lights to show the position of the valves and the condition of each stove as to whether it is On Blast, On Gas, or Bottled Up. Also mounted on this panel are the transfer switches, signal lights, pressure indicators, ind recorders. The equipment is designed to control the stove changing operations by any of the following methods: a) Automatic operation, b) Semi-automatic operation, c) Remote manual operation, d) Local manual operation, and e) Manual operation. This system is substantially the same as on "C" Furnace, with the exception that the automatic operation was added. The automatic system coordinates, sequences, and interlocks the operations of the stove valves, so that the stoves will be put On Blast, On Gas, or in the Bottled Up position without the assistance of the Stove Tender. The stove changing mechanism unit. The time cycle is that of the On Blast period. The semi-automatic sequence is designed so that the Stove Tender may initiate a stove change operation without the use of the timer. In this case, the operator need only push one of three buttons to place the stove in the condition desired: On Blast, On Gas, or Bottled Up. The remote-manual and localmanual operation consists of individual pushbuttons for each valve. In the remote-manual operation the buttons are located on the graphic panel. The buttons for the localmanual operation are placed by each individual valve. This system, unlike "C" Furnace, requires that backdrafting be carried out under the local-manual condition. The manual operation consists of simply engaging a clutch and turning a wheel. This 'condition is mechanical rather than electrical. In order to upgrade the low Btu blast furnace gas, a natural gas injection system was installed. The natural gas is regulated so that the furnace gas is enriched to a constant value of 90 Btu. In the gas cleaning area, the system was altered considerably. A 12-ft unlined downcomer was installed to replace the old 10-ft gunned downcomer. The additional surface area was required to reduce the gas velocity to a level which would minimize damage to the downcomer. The unlined type used on our "C" furnace (Blown-in September 1964) has proven satisfactory to date. The dust catcher received a complete new dome lining due to excessive loss of brick during the preceding campaign. However, instead of using brick, a 6-in. lining of gunite was used. This procedure saved considerable time and money. In the downleg, from the discharge of the dust catcher to the water seal, a variable orifice of Kop- is initiated by adjustable timers Fig. &Side view of slide type variable oriwhich send a signal to the control fice. pers design (Fig. 6) was installed. The orifice is hydraulically controlled by a askania unit to maintain a constant pressure drop of 60-in. water column. The orifice opening is a rectangular shape with the length varying for control. To complete the scrubbing action, 1350 gpm of water is added above the orifice. The water seal, due to the variable orifice, was converted to the wet type. Two 2-in. discharge lines were added: one to act as the normal discharge, and the other to act as the emergency discharge. The height of the water in the seal is governed by a liquid level controller which operates a butterfly valve in each discharge leg. Discharged water is routed to a flume for transfer to the Dorr thickeners. The gas washer was converted to a low pressure gas cooler by relocating the septum valve. The valve was moved from a location downstream of the gas cooler to a point between the water seal and the gas cooler. Fig. 7 shows the general arrangement of the gas cleaning system.. To provide for additional filling capacity, the volume of the two skip tubs was increased by 50 ft3 each for an individual total of 375 ft3. The change was accompanied by the installation of new coke weigh hoppers with vertical lift sliding doors. The top charging mechanism was reconditioned by installing new receiving and revolving hopper wear plates. These plates, along with the small bell wear rings and the small bell itself, are of HC-250 construction. The small bell with its "ski jump" design provides an extra inch of thickness in the wearing surface immediately above the seat. Other improvements include Manganese steel rails at the top and bottom of the skip incline, a labyrinth seal on the revolving distributor, and a Bailey-type large Bell rotating mechanism. BLOW-IN The first major step in preparation for a blow-in is the drying of the various refractories and the heating of the stoves to provide adequate blast temperature. The heating process was started 17% days prior to wind-on when wood fires were started at the base of the chimney and in No. 2 stove. As the brickwork was completed in each of the other two stoves, wood fires were subsequently started. Twelve days before wind-on, the firing of the stoves with blast furnace gas was started using natural draft. No. 2 stove, being the warmest, received the most attention. The stoves were changed every 4 hr on a sequence. Dome temperature was, at first, limited to 1000 F. As the electrical checkout of the fans was

6 1 I1 Blast Furnace Operations-General 1 21 Fig. 7-Gas completed, the utilization of natural draft was replaced by fans. Eight days prior to blow-in, dry blast was put on the furnace at an average rate of 40,000 cfm. Blast temperature was limited to 45O0F at the beginning and never exceeded 650 F for dry out. One day after the dry out began, the bleeders were capped off, water seal filled, and the dry blast blown out the dust catcher valves. All together, approximately 120 hr (5 days) of dry blast was put on the furnace prior to blow-in. The tap holes were prepared by first centering a 4 in. by 10 ft pipe in each of the two tap holes and surrounding them with clay. Inside the furnace, two "dog houses" were built to prevent damage and plugging by the coke during the initial charging. These rectangular shapes enclosed the pipe and were constructed of angle iron, wire mesh, and tap hole clay. No. 2 tap hole was then plugged while No. 1 hole was left open for blowing through. The cinder notches were prepared by installing a carbon plug in the No. 2 notch and a monkey and intermediate in No. 1 notch. The No. 2 notch was not expected to be used but was a safeguard in the event the tap hole was lost. Each of the cinder notch runners were lined with Helspot for a distance of 6 ft out from the furnace. Prior to the charging of the blowin burden, the tuyeres were installed and blowpipes set. The tuyeres on either side of the tap hole were 5 in. x 15 in. straight gas injection, while the remaining 20 were 6 in. x 15 in. x 5" angle flow, gas injection. Originally, plans were made to put ceramic inserts in the tuyeres to reduce the area and therefore increase the tuyere velocity. However, due to cleaning system. an oversight, the blowpipes were put up without the installation of the inserts. With little time left in the schedule it was decided to plug five tuyeres instead of dropping the blowpipes. This resulted in a lower tuyere velocity than desired. The goal was to reach 180 cfm/iri.ht approximately 70,000 cfrn wind, then maintain that velocity up to full wind by removing inserts as the blow-in progressed. Actually, the 180 cfm/in.' was not reached until 91,000 cfrn was attained. The first step in burden charging was the filling of the hearth with coke. This was accomplished by regular charging methods with the large bell being dumped every second skip. The tuyeres were not removed during this initial charging and no protection was provided for the tuyere nose ends. After the calculated amount of coke was charged, an inspection was made to insure that the coke was up to the centerline of the tuyeres. When the proper amount was present, the furnace crew entered the furnace (through a tuyere cooler opening) and leveled off the coke burden. Great care was taken to insure that no foreign material such as paper, wood, etc. entered the furnace to initiate premature lighting. Following the hearth fill, coke was again'charged so as to reach a little over the mantle level. The next 25 in. was filled with coke and a little limestone (50% calcite and 50% dolomite). The remainder of the furnace contained a burden consisting of ore, stone, and coke. When the furnace was filled, it contained 90.1% coke, 5.5% limestone, and 4.4% ore (by volume). The layered effect and composition of the filled furnace can be seen by referring to Fig. 8. After lighting, when filling had resumed, the schedule provided for eight additional burdens to reach a ratio (ore/coke) in increments of approximately At the completion of the last calculated burden, the ratio was increased as the furnace permitted. On Thanksgiving Day, Nov. 25, 1965, "A" blast furnace was blownin. This completed 76 days of work by the rebuild contractor and the personnel of Great Lakes Steel Corp. Wind was put, on the furnace at the rate of 40,000 cfrn (32% of normal wind) with a blast temperature of 1025 F and a pressure of 2% psig. The blast pressure was increased one-half psig every hour until the snort valve was closed (2 hr later). At this time the wind was increased at the rate of 1000 cfrn every 2 hr until 50,000 cfrn was reached. The next 20,000 cfrn was attained in half hour increments of 1000 cfrn each. At 70,000 cfm, the rate was increased to 1000 cfrn per hr. With this schedule, the wind was held to between 32 and 43% of full wind for the first 24 hr and attained 70% in 48 hr. For tho first 20 hr, the furnace gas was blown out through the bleeders. Thereafter, the gas was brought down into the regular gas cleaning system. This was accomplished by dumping the water seal, closing the dirty gas and explosion bleeder, and allowing ventilation through the clean gas bleeder. The septum valve and the precipitator valves were then opened (clean gas bleeder closed) to complete the process. The tap hole remained in excellent condition in the early hours of blowin. A positive connection to the tuyeres was always present with no plugging by coke or slag. Twenty hours and 10 min after wind on, the tap hole was plugged with clay due to excessive coke being blown through the hole. The first cast of the campaign finished 37% hr after wind on. Cast results showed 179 tons of metal with 4.56% Si and 0.011% hi. The casting schedule for the first two days was every 2% hr. Thereafter the schedule was lengthened to casting every 3 hr. CAST HOUSE PRACTICE As is well known, a single tap hole-high production furnace (over 3000 tpd) furnace presents serious iron handling problems in the cast house. These rates require frequent and/or excessj.vely large casts. Either of these approaches has its problems. As the number of casts per day increases, little time remains for cast house work. On the other hand, high tonnage casts increase the hazard of a breakout, and the accumulation of liquid metal in the hearth reduces the normal rate of stock descent. In this reline we have redesigned the furnace to minimize the iron handling problem by providing two

7 22 Ironmaking Proceedings, 1966 / / / / r I CMRPE BV1DIN Fig. 8-Layered tap holes. Periodic alternation from one iron notch to the other allows sufficient runner and trough make up time so that increasing the num- 6' BELOW LARGE BELL 71,955 F T ~ -~~%'ABov MANTLf 61,299 ~r~ 3-58,32 4 FT. ~ S ~ B O VMANTLE E 50,600 f13 3 _~B'ABOVE MANTLE 43,144 FT 10% ABOVf MANTLE 31,316 F Z ~ MANTLE 21,800 F T ~ JOP OF BOSH 18,616 F X ~ CLTUYERE 8,175 FT:' effect of blow-in burden. RTH 9,702 FT,~ ber of casts per day becomes much less of a problem. Previous to this reline, the furnace operated on a six cast per day cched- ule with flushing between casts. This was accomplished by employing a blower, a stovetender, a keeper, three keeper helpers, 'and three cindersnappers per shift. When "A" furnace was blown-in, our first experience with two tap hole operation began. The first schedule called for an alternation of tap holes every 24 hr, with eight casts per day and the elimination of flushes except when necessitated by a late cast. This was soon revised so that changing would be twice a week--on Tuesdays and Fridaysmainly because of the life of the trough and runner materials. The manpower requirement for these schedules was reduced by one cindersnapper per shift from the "before reline" operation. Two extra helpers were scheduled to work the 16 hr immediately prior to changeover time. Recently, a new plan was put into operation. The changeover is now performed on an "as needed" basis with the virtual elimination of extra helpers. Changeovers are now made at least once every three weeks to keep the tap hole alive. This increase in time has been primarily the result of the use of carbonaceous sand in the runners and slight modifications of our roughing runners, spouts, and gates. To date, tap hoie lengths have been extremely good. Short holes, due to our method of operation, have been non-existent. The only difficulty experienced is the hard drilling of the holes after change over. Our automatic drill has been a substantial help in this respect. SUMMARY In this paper, we have seen the improvements made on the "A" blast furnace of Great Lakes Steel and the1 techniques employed to blowout' and blow-in a furnace. The techniques have been standardized and have been the result of studying the past 18 relines at Great Lakes, along with the experiences of other companies. It is hoped that the information contained herein will in some way aid in the library of knowledge concerning blast furnace operations.

8 Blast Furnace Operations-General 1 23 Discussion J. L. Coulis I am sure the blow-out and blowin procedures will be most interesting to the operators but the design modifications, especially the tap-hole conversion, are of concern to me. I. L. COULlS is senior project engineer, Republic Steel Corp., Cleveland, Ohio. You state the length of the single runner before rebuild was 181 ft and the combined length of both new runners is 171% ft. Does this mean the old main runner extended roughly 80 ft further? Since we are contemplating such a conversion, could you elaborate on how much work was involved? I was amazed at the number of cooling plates in this furnace. Apparently you now have 20 rows of coolers at 27 per row. Following our design standard, this would require 108 feeds and 4320 gpm in the stack alone. I then must question whether 5000 gpm is adequate for the entire furnace and if settlement and build-up in the coolers have been a problem. Prior to the installation of the dual runner system, the single runner ran straight away from the furnace with Nos. 3, 4, and 5 spouts at the end of the straight section. Nos. 1 and 2 spouts were at the end of a side runner which branched off the main runner, at approximately the half way point, and flowed back toward the furnace (at a lower level). This accounts for the 181-ft length. In order to rebuild the casthouse, complete removal of all casthouse flooring was necessary. All that remained were the steel beams. From there the dual runner system was built, using the same overall casthouse length but slightly increasing the width. The 33 rows of cooling plates are distributed as follows: 1) Bosh Cooling a) Rows 1, 2, and 3 are con- Author's Reply nected in 11 groups of 3 plates each and 13 groups of 4 plates. b) Rows 4, 5, 6, 7, and 8 are connected in 24 groups of 5 plates alternately with 12 groups of 4 plates in rows 5, 6, 7, and 8. C) ROWS 9 to 13 inclusive are connected in 36 groups of 5 plates. 2) Stack Cooling a) Rows 14 to 25 inclusive have 5 horizontal groups in each row. The five groups are arranged in series of 6, 5, 5, 5, and 6 plates in each row. b) Rows 26 to 33 inclusive are composed of 4 horizontal groups. The groups are in a series of 6, 7, 7, and 7 plates in each row. Cooling water is supplied by two sources: service and recirculating. Service water (approx gpm) cools the furnace up to row 23 while recirculating water (1300 gpm) cools the remaining 11 rows and the shell sprays. Our design standard for the cooling of stack plates is 3 gpm per stack plate, which we consider adequate. Settlement and build-up in the coolers have not been a problem on A, B, or C Furnaces. However, we have experienced some difficulties on our D-4 Furnace. On A, B, and C Furnaces the settlement occurs in the long mains, whereas on D-4 Furnace, the short distance between the intake and the furnace causes the buildup in the cooling members. We are presently employing a commercial cleaner to reduce the settlement problem on D-4 Furnace.