UDC 669.18-932
Studies of NRIM Continuous Steelmaking Process*
By Ry uichi NAKAGAWA:* S hiro YOS HIMATSU:* Taklly a UEDA:* Tatsllro M ITSUI, ** Akira FUKUZA WA:* A kira S ATO:* and TS llyoshi OZAKI**
Synopsis K.)U- 13) The fundamental aspect q! the development of the NRIM multi-stage (2) Tank type continuous steelmaking process at trough type continuous steelmaking process and the results of its recent IRSID (France )14- 16) operations are presented in this jJaper. Though the scale of the plant used (3) Single stage trough type continuous steel was small (7.8 tlhr in hot metal flow rate), a suitable sejJaration of the making process (WORCRA process) at CRA (Austral steelmaking reactions to each stage of the continuous steelmaking furnace ia)17 - 20) and the know-how qf its ojJeration were satiifactorily obtained. As the (4) Single stage trough type continuous steel result of the separation, that is, silicon and phosphorus were mostly removed making process at Bethlehem Steel Co. (U.S.A. )21) in the first stage so that the final carbon level was controlled mainly in the second stage, the product with phosphorus as low as 0.005% (dephosjJhori (5) Single stage multi-chamber type continuous z ation rate 96% ) was obtained with comparable amount of lime to that steelmaking process at MISiS (U.S.S.R.)22) of the conventional batch type steelmaking processes. The industrializ a (6) Multi-stage trough type continuous steelmak tion of this process is confirmed to be feasible. ing process at NRIM (Japan)23- 34) In NRIM the research on the continuous steelmak I. Introduction ing process which takes a part of the integrated con One of the d istinguishing characteristics of the con tinuous iron and steelmaking plant was started in 1964 tinuous steelmaking process is that the measurement to obtain fundamental informations. The NRIM a nd control of steelmaking reactions are more easily three stage trough type continuous steelmaking equip made as compared with other processes. Though con ment was designed and installed in 1967 from the view tinuous operation, in general, accompanies some tech point that the multi-stage reactor would be more ad nical difficulties which are not observed in the case of vantageous for the continuous steelmaking operation. batch operation, it is advantageous in the following As satisfying results have recently been obtained espe points: cially on the dephosphorization, fundamental concepts (I) Feasibility for mass production of the NRIM process and its recent results are reported (2) Reduction of installation and running cost here. (3) Uniformity of the quality of product (4) Facility of process control II. Experimental Equip men t of t h e NRIM Con Any kinds of experimental plant tests which have so tinuous Steelmaking Process far been done for the technical progress and improve ment in the above-mentioned fields, have more or less 1. Fundamental Concepts for the Development of the Ex aimed to draw these advantages, and eventually related perimental Equipment to the continuous operation. The experimental equipment was designed with in In the iron and steelmaking process, various sorts tent to realize a continuous steelmaking furnace in of continuous operation are adopted: continuous cast which complicated steelmaking reactions can be sep ing, hot and cold strip mill, surface treatment of sheet arated into the specified reactions at the specified iron, etc. The blast furnace operation is also con stage, where those reactions can be controlled and tinuous in essence. molten metal can be transported in the simplest way. Due to the complicated reactions at high tempera Through various trials the present unit furnaces and ture, steelmaking process is still in batch operation by their layout have been adopted. electric furnace, open-hearth furnace or converter. At first it was considered that the following condi- Especially the basic oxygen steelmaking process has tions should be fulfilled by every unit furnace: been adopted in many steel plants by virtue of its high (1) Steady state to be easily obtainable productivity. And there is a good chance for the (2) Bath mixing conditions to be changeable continuation of oxygen steelmaking due to the recent (3) Suitable measuring site to be obtainable development in both process control and refractories, (4) Easy slag- metal separation which would result in full continuous operation of the (5) Slag-formation in a short period of time iron and steel industry. Persevere efforts have been (6) Applicability for countercurrent operation made from earlier times to make steel continuously1- 10) between metal and slag and the reports described the technical feasibili ty are A special consideration was paid on the m ixing summarized as follows: 1l- 34 ) condition, since the controllabilities of these reactions (1) Spray steelmaking process at BISRA (U. and the stability of the composition of product were
* Originally published in Tetsu-to-Hagane, 59 (1973), 414, in Japanese. English version received March 29, 1973. ** National Research Institute for M etals, Nakameguro, Meguro-ku, Tokyo 153.
Re se arch Article ( 333 ) (334 J Transactions ISIJ, Vol. 13, 1973 markedly affected by the mixing conditions. There urement and control and also offers the optimum fore, considering the complexity of steelmaking reac application of refractori es depending on the type ofreac tions, a unit furnace which could provide any level of tion and temperature. This mea ns, for example, that mixing characteristics is indispensable. the use of basic refractories for dephosphorization and Proposed continuous steelmaking processes can be the use of cheaper acid refractories for decarburization classified into two types, namely the converter or tank will be acceptable. From the above reasons, a multi type and the trough type. Tank type reactor belongs stage reactor was adopted. to a perfect mixing reactor and seems to be suitable As the consequence of foregoing considerations, for the promotion of bath mixing and formation of steelmaking reactions were supposed to be separated emulsion which play an important role in the steel into three groups, that is, desiliconization and dephos making process. In this type of process, however, it phorization, decarburization, and the final control of is very hard to maintain stable outputs against the steel grade, so that three-stage cascade type continuous variations of inputs, and is not possible to satisfy the steelmaking furnace was adopted. conditions(3) and (4) mentioned above. In addition, Concepts for the development of our experimental an extra vessel is necessary for the slag- metal separa process have been stated here, and the present plant tion. On the contrary, trough type reactor belongs after several alterations is called as the NRIM con to a plug flow reactor which is attractive to control tinuous steelmaking furnace- type 16- 2. the reactions occurring inside of the furnace as a factor of position along the reactor. This is advantageous 2. Constitution of the Experimental Plant for the m easurement and control of steelmaking reac Though the experimental plant must be able to tions. But it has also some problems, such as the con obtain exactly the factors which affect reactions, dis struction of furnace and the heat loss caused by its turbances from some uncertain factors are unavoidable rectangular shape. Since these two types have re because the present plant is so small as compared with spectively the merits and demerits, it is difficult to judge the industrial one. Namely, the scale factor must be which process is more advantageous. taken into account in setting up the equipment. Es An important item considered for the design of a pecially in the case of a small laboratory scale steel unit furnace was the mixing characteristics (modified making plant, it is difficult to select the right configura Peclet number or the ratio between perfect mixing tion of refractories, and the heat capacity is low in a and plug flow), which could easily be selected by the whole. These facts bring about serious problems for combination of the flow rates of oxygen and hot metal experimental operations. Attention should be paid and the lance condition (position, number, height etc.) for the controllable factors as much as possible in order As the result of this consideration, trough type was to raise the accuracy of experiments. adopted in the current work as the most suitable shape 1. Hot Pig Iron Feeding Equipment (Holding Furnace) for a unit furnace. In the case of trough type the The capacity of the holding furnace is 15 t because existence of settling flow zone provides the part of of the restriction of the shop. The size of holding slag- metal separation and the site for measurment, furnace is 1.4 m in inner diameter and 1.6 m in respectively. Simultaneous supplying system of oxy height, and the wall is lined with chamotte and in gen and flux (oxy-flux lance method) was adopted for sulating bricks. By using a LPG burner, 12 t of hot the faster slag-formation. Because of widely variable pig iron at I 400°C can be held in the furnace without lance position, slag- metal countercurrent operation any practical temperature drop. The holding fur is feasible, which would be advantageous for refining nace is equipped with load cells measuring its gross of high phosphorus hot metal. The shape of unit weight and the fe eding rate of hot metal is regulated furnace was then determined. by tilting the furnace oil-hydraulically in accordance In order to make effective continuous steelmaking with the prescribed time- weight diagram. However, operation, the following conditions were proposed as momentary feeding rate by this manual control method the requisites: deviates considerably, and according to the recorded (1) To minimize the decrease of reaction efficien chart the momentary deviations reach to ± 50 kg/min cy which is inherent in continuous operation for the aimed feeding rate, 130 kg/min. From the (2) To perform a specified reaction at a specified consideration of the dynamic response of fluid flow, site a new tundish was designed, which has a suitable size (3) Adaptability for the change in product grade and 14 mm nozzle to keep the deviation always with (4) Reduction of refractory consumption in ± 10 % for the aimed value of 130 kg/min. As the (5) Easy maintenance result the feeding rate of hot metal is kept within a To satisfy these conditions, the furnace should be an practical accuracy. ideal plug flow reactor, but it is not so easy to realize 2. Continuous Steelmaking Furnace these requisites by one furnace vessel. As the mean residence time of the continuous steel As it is well known in the field of chemical engineer making furnace, the time required for the completion ing, a successive arrangement of perfect mixing reac of reactions in BOF, which is about 20 min, was tors improves whole reaction efficiency, takes the chosen in the current work. If it is equally dividing characteristics of the plug flow reactor, and conse into three unit furnaces, the mean residence time for quently provides a specified site (furnace) for a speci each unit furnace is 7 min, and the hold-up weight of fied reaction. Therefore it becomes easy in the meas- each unit furnace becomes to be about 900 kg when the
Relearch Article Transactions ISI1, Vol. 13, 1973 ( 335 )
flow rate of hot metal is 130 kg/min. o Hamlll t.' d maJ!Ill'!:>ia o Direcl -ho nd e d Based on the informations obtained from the pre tar' maA'n esia hrick o \\Ia ~ n (>s i a !Iric k liminary experiments,23) the size of a unit furnace I cd '::"9!"!2! (9J ij o C ha rn o!\(' hri c k having the hold up of 900 kg is decided as 3 m long, (5) o In s ulat ing brick o Alum ina cast a bl e 0.30 m wide, and 0.85 m high. Each furnace is lined with tar-dipped magnesia bricks inside and insulating bricks outside as shown in Fig. I. Water-cooled cop per lances for the injection of oxygen or oxygen with flux are installed at the upper part of each furnace. Their position along the furnace, their blowing angle, 4000 - 85 0- - and their height are easily changed by lifting the lance 1. Inlet skimmer 6. Gas sampling hole assembly with an oil cylinder. Lances are placed in 2. Outlet skimmer 7. Burner a series along the flowing way of hot metal near to the 3. Slag-off port 8. Flue inlet part of the unit furnace, so that each furnace may 4. Overflow dam 9. Tap hole have a blowing (reaction) zone and a non-blowing 5. Lance 10 . Coolant feeding chute (settling) zone. Fig. I. Construction of NRIM continuous steelmaking The depth of the molten iron, namely the hold-up furnace (unit furnace), (mm) weight which is about I 000 kg at present is deter mined by the height of dum. A tap-hole is installed in the position below the overflow dum, and hot metal remained is discharged through this hole by tilting the furnace with an oil cylinder when the run is over. A pre-heating burner, a waste gas flue, a chute for solid materials, and a waste gas sampling port are also in Hecri\'ing stalled on the furnace. ladlp The vertical view of the arrange men t of the holding Fig. 2. Multi-stage continuous steelmaking equipment furnace, the tundish, the continuous steelmaking fur 4°°1---;:::======::::;--] nace (each unit furnace has the same size), and receiv min ing ladles is shown in Fig. 2. 3. O x ygen , Flux, and Coolant Supplying EquiplDe nt 1. Oxygen Supplying System 33 ) The system consists of an exclusive line for oxygen and an exclusive line for oxy-flux line. M easurement of flow rate is made at every unit furnace. Total flow rate of oxygen at one unit is measured with an auto matic flow meter and it is regulated to a specified value against the flu ctuation of pressure and tempera ture. The aimed error associated is within ± 1.5 % . Tota l flow is divided into two lines ; the one for oxy flux line regulated with a manual flow indicator and the other for oxygen line supplied the remainder. 10 15 2. Flux Supplying System33 ) Axia l dis tance fr om nozzle outlet or let pol, em A pneumatic conveyer used for the transportation Fig. 3. Variation of jet velocity along axis of a large amount of fin e powder like cement is ap plied for the flux addition by modifying it for the use ness of 50 I'" for the protection against wearing, is used of a small amount and quantitative transportation. in the current work. Oxygen distributed to the system is again divided for Figure 3 shows the relation between the distance the use of floating and transportation of flux. The from nozzle and the axial velocity of oxygen. feeding rate of flux is controlled by tracing the tank The lance height is adjusted so as to maintain the weight- time line drawn on the chart. Flux carried by velocity of oxygen jet on the steel bath surface at 100 oxygen in the transport pipe is ent to lances through to 120 m /sec. a distributing header. The error to the aimed feed 4. Coolant Supplying System ing rate is within 10% as an average over the entire For the improvement of the dephosphorization rate operating time. and the bath temperature control, pre-weighed cool One I m 3 and two 0.5 m 3 tanks are provided for each ants, such as iron ore, steel scrap, and reduced pellets, furnace respectively. are automaticall y added into the bath through the 3. Blowing Lance chutes installed at the blowing zone or the position The lance used for oxygen and flux injection con just before the slag-off skimmer. sists of an inner tube made of stainless steel with a 4. Meas uring Ins trulDents soldered copper nozzle and water-cooled outer tube In the preceding sections, measurements of the feed made of copper. The straight type nozzle of 5 mm in ing rates of hot metal, oxygen, flux, and coolants have diameter, on which chromium is plated in the thick- .already mentioned, and therefore, the temperature
Research A rticle L 336 J Transactions ISIJ, Vol. 13, 1973 measurem en t and the gas a nalys is are only d escribed El I'J here. El El I . Temperature Measurem ent of Hot M etal ) Q Disposable immersion thermo-couples a re used in J I 8 000 termittently for the measurem ent of bath temperature ODD'r I' as a standard. A two-color pyrometer a nd immersion thermo-couples are used for continuous measurements. The bath temperature is m easured at the p ool be JI tween the slag-off skimmer a nd the outlet d a m. 2. Gas Analysis Three infra red gas a nalyzers are used for the analyses of CO and CO 2 a nd the errors associated are estima ted to be within ± 2% for the indicated values . The fl ow ra te of waste gas is not measured yet. 6000 - 6000 - - 6000 - - 6000 - - After the experimental run, metal and slag samples 6000 are taken out a nd are subjected for the chemical and I . H old ing fu rnace spectrographic analyses. Thermal analysis is used for 2. Tundish the rapid carbon analysis during the experimental 3. Co ntinuous steelmaking furnace ( 1st stage) 4. Continuous steelmaking fu rnace (2 nd stage) run. 5. Continuous steelma ki ng furnace (3rd stage) 5. Another Equipment 6. R eceiving ladle (I ) Cooling water is supplied to la nces, ducts, and 7. Slag bucket parts of furnace bodies with a volute pump by cir 8. Flue cula tion. For preheating, LPG is mainly used a nd it 9. L a nce assembly 10. Oxygen vessel is supplied a t maximum rate of 200 kg/hr from a va II. Flux vessel pori zer. The holding furnace can be heated up to 12. Controll er of oxygen a nd fl ux 1 500°C and each steelmaking furnace up to 1 400°C. 13. O xygen line (2) M elting furnace a nd dust collector: An 14·. Flux line 15. Coola nt feeder H eroult electri c furnace with the maximum power of 16. Platfo rm (oi l hydraulic system, recorder etc.) 1 500 k VA is used for the melting of pig iron of 3 t. 17. T wo-color pyrometer A dust collecter is a bag-filter. 18. Gas a nalyzer 6. Plant Layout Fig. 4. Layout o f N RIM experi mental plant (mm) Present plan t layout is shown in Fig. 4. furnace. III. Experiments The preheating of the holding furnaces is very im pOl"ta nt to a ttain a steady sta te in a short possible 1. Purpose of E xperiments time. As ba th temperatures were occasiona ll y in Purpose of the present experiment is not only to flu enced by the insuffic ient preheating in th e earlier obtain the know-how of the plant operation, but also run, in the recen t runs the holding furnace has been to sepera te the complex steelmaking reactions a nd to kept a t I 350°C for 6 hr before the experiment. carry out the specified reactions in a specifi ed furnace During the opera tion the d ata required for the by making effective use of the multi-stage reactor. a nalyses are collected continuously or intermittently Tha t is, in practice, it aims to remove all of silicon and with various kinds of instruments. When the bath to reduce the content of phosphorus as low as possible temperature exceeds the aimed value, it is regula ted in the first stage, a nd to rem ove the rest of phosphorus by adding the coola nt. After the completion of speci and carbon a nd to control the content of carbon and fi ed reactions in both stages, the hot metal, fl ows into ba th temperature in the second stage. The third stage receiving ladles, a nd the slag produced in each stage is considered as a grading furnace. However, in the fl ows into each slag bucket. present runs, the last two furnaces are res pectively used 2. Experimental Conditions to fill the roles of the first a nd the second stages, and Experimental conditions a re listed in T able 1. In the first furnace is used as a cha nnel for tra nsporting of order to keep the same mean residence time, the hot hot metal. Informations on the steelmaking reactions, m etal is fed in the ra te of 125 or 130 kg/min for every which has not yet been fully understood , may be ex experiment. 34 pected from the res ul ts obta ined . ) For the a nalyses In the first stage, all of the la nces are used for oxy of the results, onl y the data obtained in the steady sta te flux injection, but in the second stage, the lances excep t a re used , but not the da ta a t start-up and hut-down, the second and third ones employed for oxy-flux in which are practicall y importa n t in continuous opera j ection are used for oxygen blowing . The flux is a tion, because of the labora tory scale experiments. mixture of lime a nd fluorspar, a nd silica or iron ore is added partly in p lace of lime for the improvem ent 2. E xperimental Procedure and Conditions of slag properties . 1. Experimental Procedure H ot metal of 12 t is melted in an Heroult electric 3. Results and D iscussion furnace and it is then held in the preheated holding As an example, the varia tions of bath compositions
Research Article Transactions ISIJ, Vol. 13, 1973 [ 337 J
Table I. Conditions for operations
Number of operation 48 49 50 51 52 53 56 57
Stage of furnace 2 1_ I 2 2 2 1 2 2 2 2
1 Total (t) 12 1 12 12 12 I. 12 12 12 12
Pig iron Flow rate 1 125 125 125 130 130 130 130 130 (kg/min) 1
~~~;!~g ratCN%' /min) 2.2 3. 1 2.2 I 3. 1 1.76 4.4 1 2.2 1 4.4 ~ I 4~ ~ I ~ 2.2 1 3 . 2 2.2 1 3.6
T Feed~g rate 4 2 5 5 4 6 4 --8 -1 4 8.45 4.51 9 4 --;- 1 4 9 4 I (kg/min) . 1 Flux CaO:CaF2 : 5' 1'0 17-:3-: ' 5: 1 ~ 1 * 5:~1-* - 1 5:1:0 1--* - ~ 1 5: 1 :0 5:1:0 5: 1:0 5: 1: 0 4: 1 : 1 1 5: 1:0 1 ~ 1 Si02 _. _' _1_5__ Ore (kg/min) - I I -=- ---=-10.; ---=- - 1.-0 1 - - 1.0 -= 1.0 = ~ I---=- Scrap ~ k g / min) I - 1 1 ~ ---=-1 - 2.0** -=-1 2.0 1 1.0 1 - 1 - .-= -I - ~~a~b er of _ _5 _1 __7 I 5 1--7 - -; - 7- 4 7 I 4 1 5 4 5 4 1 5 4 5
Number of 3 6 3 5 3 3 3 3 Lances oxygen only 5 -=--1_5 Angle CO) 5 5 5 5 5 5 5 5 5 5 5 2.5 5 5 2.5 -;--1-- I H eight (mm) I 100 100 1:0 1 100 WOr l30 150 1 130 ISO 160 150 130 150 130 150 140
* Slag from BOF. * * R educed pell et...... Raw iron - I st stage .-2nd stage
U 1700 ~~-.~~ '--:- 1600 _ ...... a nd temperature at the outlet of each furnace with the 111500 ~ I( lapse of time is shown in Fig. 5. From this fi gure the ~ 1400 ~ smooth transitional changes of th e compositions and ~ 4 • • • *- 3 ... . . • • • • • • temperatures at start-up a nd the stabilities of them at ~ 2 U 1 ~.-...... the steady state can be recognized as the character '? 0.8 istics of the multi-stage trough type reactor. ~ 0.6 • . - 0.4 · · R esu lts obtained at the steady state are given in (/) 0.2 \ Table 2. Following discussions a re made on the 0.5 • • basis of these data. *~ 0.4 · ~ 0.3 One of the purposes of this study is to know the 0.2 ~:'I.--:--:- Z, • d ephosphorization behaviour in the first stage. For 0 20 ~c'-. 0.15 . • • example, in the 57th run, a hot metal ofO .O I9% P and ;:( 0:1 0 0.0 5 ~ the dephosphorization rate of 77.7% were obtained ...... -~.-...... -~. at the basicity 3.3 in spite of high carbon content ~ 0.0 8 *- 0.0 6 . • • 3.07% C. This result clearly indicates that the NRIM -en 0.0 4 0.02 ~: ...... --...-- ...... process is very effective for the dephosphorization even o 20 40 60 80 100 for the high carbon melt. Furthermore the hot m etal Time (min ) obta ined in the second stage is O.005% P and O.38% C. Fig. 5. R esults of operation (No. 51) From these, it can be concluded that this process IS very advantageous for the dephosphoriza tion. Photograph I shows the plant in opera tion. 1. D esiliconization In order to reduce the content of phosphorus in the first stage, it is required to remove all of silicon, a nd a lso, to keep the bath temperature as low as possible (details a re described in the section III. 3. 4), because the residual sili con in the metal bath suppresses the ox idation of phosphorus and the increase of bath temper ature decreases the dephosphorization ra te. There fore it is necessary to know the amount of oxygen required for the oxidation of all silicon in hot m etal. Moreover, the es timation of the temperature increase would become possible by knowing the a mount of
Research A rticle ::0 ..(I) w (I) w 00 ..... ~ () Table 2. Results of experiments :>" ....., ;to Number of operation 48 49 50 51 52 53 56 57 ::!. I:l'" o· Stage of furnace 2 2 2 2 2 2 2 "' iD I 2 '"~ ---I(0C) o· Pig iron 1360 1410 1380 1 430 -I 1420 1420 1400 1410 tl Temp. Steel (0C) 1620 1680 1700 1 710 I 590 I 1 640 1 560 1 600 1 520 1 1 590 '" I 1600 1 1660 1520 I I I 550 I 650 1 15~ 1 § · C (% ) 3.92 3.88 3.80 3.85 3.89 3.84 3.87 4.02 ::-< --- - . Si (% ) 0.55 0.70 0 .70 0.61 0.77 0 .92 0.52 0 .51 < ComposI- ~
tion of Mn (%) I 0.74 0.79 0.47 0.50 0.61 0 .43 0.63 0.63 ~ ,w pig iron p (%) 0.15 1- 0.14 0.16 0.17 0. 15 0.14 0.16 0.12 ~ (() 1 0.059 ,- 0.065 1 S (% ) 1 0.067 0.072 - 0-.080- 0.070 0.060 0.059 '-l W C (%) 3.18 1.12 1.16 1- 3.49- 0.29 I' 3.05 0.06 3.24 0.14 2.96 0.64 3.03 1.02 0.38 - 1. ~ 8 - -- _ 3'~ 1 Composi- I· Si (%) 0.02 < 0.01 0.037 < 0.01 _ 0_.25_ < ~ < 0.01 < 0.01 0 .09 < 0.01 < 0.01 < 0 .01 1< 0.01_1 < 0.01 < 0 .01 < 0.01 tion of ------hot Mn (%) 0.46 O .~~_J 0.47 0.37 0.35 0.35 0.33 0.24 0.38 0.30 0.25 0.26 0.35 I 0.20 - Q.321 0.17 - _ I I metal at p discharge (%) 0.090 0.060 0.079 0.057 0. 13 , 0. 18 0.080 0.031 0.084 0.054 0.059' 0.056 0.034 0.012 0.019 1 0.005 S (% ) 0.043 0.034 0.033 0.033 0.039 0.040 0.022 0.030 0.023 0 .027 0.021 0.025 0.040 0.035 0.025 0.025 - - -1- - CaO (%) 42.3 39.8 56.5 47.7 58.5 47.7 62 .5 47.0 50.7 43.9 50.3 40.0 51.5 50. 1 57.7 1_ 48.5 - -- SiO, (% ) 24.0 22 .8 22.5 22.5 18.8 _ 29~J ~O 23 .7 18.4 22.0 18.5 20.5 17.7 20.4 17.3 19.1 --1--- 1-- P,O s (%) 3.5 1.8 2.5 4.0 2.5 1.5 3.7 4.7 2.6 3.2 2.4 2.2 3.8 1.9 2.7 _ 0.8 -- - FeO (% ) 7.7 4.3 5.2 6.3 8.3 3.2 2.6 12 .6 6.1 11 .3 4.0 7.6 2.6 7.8 4.3 1 5.7 Composi- tion of Fe,O. (%) 3.5 1.5 5.0 8.8 3.0 1.0 1.2 5.7 5.5 2.6 1.7 2.7 0.8 2.4 1.2 1- 2.6 - 1- slag at T. Fe (% ) 8 .3 4.3 6.3 12 .6 2.3 12.3 8 .6 10.7 4 . 1 7.8 2.6 7.8 4 .2 6.3 discharge -- ~ I ~' O MnO (% ) 6.5 4.0 8.2 2.1 4.3 2.5 9. 1 3.5 2.3 5.2 5.2 4.2 3.5 I 3.8 9 .2_1 1= 3.8 MgO (%) 11.2 17.8 2.5 7.8 8.7 5.5 7.2 7.9 3.0 3.2 6 .8 --- 7~J ~5 I~ I ~O CaF, (%) 7.1 7.4 7.5 2.6 5.8 1.8 5.8 2.2 6 .9 2.1 6.2 2.8 9. 1 10.0 ~5.7 I 6.2 - -1-- CaO/SiO, 1.7 2.0 2.6 2. I 3TI 1. 6 2.7 1.9 2.7 2.0 2.7 1.9 2.9 2.4 3.3 2.5 - C (%) 18 .9 52.5 15.5 54.6 8.2 84.2 20.4 72.6 11 .7 79.7 22.8 60.5 21 .7 52.0 23.4 65.7 - I - Si (%) 96.5 1.8 94.8 3.9 64.3 34.2 98 .4 88.3 10 .4 99.0 98.0 92.6 Rate of -I Mn (%) 37.8 5.4 40.5 12.7 25.5 32.7 18.4 37.7 13.1 41.2 44 .4 23.8 45.6 22.1 removal - --I - 1 P (%) 42.0 19.3 43.6 15.7 21.2 52.8 28 .9 45.8 19 .4 59.3 2.8 78.8 13.7 77 .7 10.8 __ I-S - (%) 36.8 19.11 5 2.8 51.3 69.0-1 61.6 64.5 38 .5 7.7 59.6 ------Oxygen efficiency* (% ) 65.5 86.0 59.8 81.7 34. I 90.6 66.0 87.9 62.5 90.6 67 .3 91.2 70.4 81.5 78.0 94.7 ------* ---.2x~~or CO __ X 100 Oxygen for CO and CO, Transactions ISIJ, Vol. 13, 1973 ( 339 )
I. 5 r--,--r-----y-----,~----y-__, 80 4.0 ,j C 1 s t o 70 " Manganese !? ;;r. ~ 60 3.0 Si "re 1. 0 0 ' " 0 o ~ &6 0 50 X to' O" - I 0 • o o " I " , ",:: " ;:;;:" 40 "- ~ ~ 2.0 ~ 8 Mn u / ( .~,: iii:.:: " 30 '.- ~'" ;:;;: U 7 0.5 " i.i)0 ~_ u'" • ;:;;: 20 ~ " " 1. 0 -, '" • Firs t s tage (S i2: 0.01 %) ~~~ U~ ~s t ,,~e l '. 0. 10 o F irs t s tage (S i< O.OI %) a Second st agt> i' o Total " Second s tage " ~:S 0.0 / 0 - ---' 1 2~.0~~14~.0~1~6.70~1 8~.0~7.20~.0~2~2~. 0~24.0 0 1300 1400 1500 1600 1700 0 Amount of oxygen blown ( Nm 3/ T ll;l ) 10 20 30 40 50 60 T emperature (O C ) HI O\\11 !l:\y).!en \m : '1' 11\1
Fig. 6. R ela tion between the amount of Fig. 7. R elation between the removal of Fig. 8. R elation between the removal of oxygen blown and the removals of manganese and the temperature carbon and the amount of oxygen silicon, carbon, and manganese in hot of molten metals blown in each stage furnace and metal above 0.01 % Si in the aggregate carbon a nd ma nganese oxidized along with the oxida remove a ll of silicon and to keep the bath temperature tion of silicon. Figure 6 shows the rela tions between approximately at I 550°C in the first stage by blowing the amount of oxygen blown per one ton of hot meta l oxygen 10 % more than the a mount required for the a nd the amounts of the oxidized sili con, carbon, a nd si li con removal. By this way, excellent dephosphoriza manga nese under the existence of si li con in the first tion is a ttained . The amount of oxygen used for the stage. In F ig. 6 the amount of oxygen required is not silicon removal in the first stage will be regarded simi corrected for the oxidation of iron, phosphorus, sulfur, lar to that of BOF, as the oxidation ofO.5 % Si in BOF and the secondary oxidation of carbon. Although the needs about 15 Nm3 of oxygen per one ton of hot experimental condition is limited in a na rrow range metal.35) shown in Table 1 and the data are not sufficient enough 2. Removal of Manganese in number, these relations can be expressed by the As apparently seen in Table 2, th is process gives following experimental equa tions: fairly low removal rate of manga nese, which seems to be influenced by low FeO content in slag. Cx; = 0.059Qo, - 0.40 ...... (1) Effect of the bath temperature on the removal rate Cc = 0.12Qo, - 1.4 ...... (2) of manganese is shown in Fig. 7. In the first stage,
CMIl = 0.054Qo, - 0.65 ...... (3) good correlation is not obtained between them , but in 3 the second stage, the bath temperature has an effect where, Q o, : amount of oxygen blown (Nm /T IlM ) on the removal of manganese with some correla ti on CSt, Ce, CMIl : amounts of sili con, carbon and manganese removed by oxidation, as written in Eq. (6). respectively (% ). D )ln(2) = 530-0.30 t...... (6) The proportional constants of these equations may r = - 0.78 indicate that the amounts of oxygen distributed for where, D~l n (2) : demanganization ratio in the second the oxidations of silicon, carbon, and manganese are stage (% ) approximately in the ratio of I : 2: I. Constant terms t: temperature (OC). may show mainly the amounts of oxygen required for 3. Decarburization the oxidation of iron. The first stage in the current experiment corre The a mounts of carbon and manganese oxidized sponds to silicon blow and the second stage to carbon together with sili con are obtained by eliminating Qo, blow. Figure 8 provides the rela tions between the from Eqs. (I), (2), and (3). amount of oxygen supplied and the amount of carbon Cc = 2.0Cs;-0.59 ...... (4) removed in the whole and respective stages. In the first stage, the correlation between the de CMn = 0.9 I Cs;-0.28 ...... (5) carburization ratio is not apparent because the rate The negative signs in the constant terms of Eqs. (4) of oxygen blowing is not varied widely and also the and (5) are indicating the selective oxidation of silicon oxygen efficiency is lowered by the presence of the to carbon and manganese, and from these equations it simultaneous oxidation of silicon, manganese, and is obvious that the oxidation of carbon and manganese phosphQrus. However, in the second stage and also starts after about 0.3% of silicon is oxidized. the entire stage, fairly good correlations are obtained In the recent experiments, it becam e possible to as shown in the following equa tions.
Research Article ( 340 J Transactions lSI], Vol. 13, 1973
Cc(2) = 0.11Qo,-0.50 ...... (7) ,.-::-;::;-: 1_ r = 0.96 3 0 Firs t stagel 6
Cc( Z) = 0.096Q0 2- 1.0 ...... (8) -~ec on~ag.:J 6 - p'" c: o r = 0.87 6 ] ;/ 66 I where, C(,( 2), Cc(Z ): removals of carbon in the sec '" 2 . a 6 • ond and entire stages (%) B ~ -;;; ~ 3 Qo,: amount of oxygen blown (Nm j U
perature, compositions and weight of slag, lance con <=> 6 <=> 60 j ditions (number, arrangement, and height of lances, '<
and type, size, and number of nozzles, etc .), mean res ~ 50 idence time, mixing conditions of bath metal, etc . 40 1° Among the factors men tioned a bove, only the slag c.: • First stage Si ' 0.01 ",) weight and the number and height of lances have so o First stage (Si< O.O I',) cL 6. Second 5 (age
far been examined as the variable factors. However, 6 no effect has been observed in the current work. Since there is a close relation between the rate of oxy 10 gen blowing and the amount of carbon removed in the second stage as it is obvious from Fig. 8, it will be O~-L __~ __~~ __~ __~ ~ o 7 possible to control the carbon content accurately in Basicity of s lag (CaO ' S i02) the second stage if the outlet level of carbon in the Fig. 10. Relation between the dephosphorization rate and first stage is known. The amount of oxygen necessary the basicity of slag in each stage furnace for refining the pig iron of4.2%C to the steel of 0.1 % C is about 53 Nm3 jt of hot metal as a total, and this vantages that it is in high level of carbon and low value is nearly equal to that of BOF.35) basicity caused by SiOz formation, and requires a long Continuous waste gas analysis has been examined slag-forming time because of low bath temperature. as one of the carbon control method. However, the For the production of high carbon steel by this process, quantitative determination of carbon from waste gas it is necessary to dephosphorize in a high carbon range is not so easy because the flowing rate of waste gas is of the first stage. This seems to be desirable from the not m easured . As for the check of the gas analysis, view point of the separation of steelmaking reactions. the amount of carbon removed which was calculated Thus the improvement of the dephosphorization rate from the result of metal analysis was compared with in the first stage became one of the major purposes of the value obtained from the total amount of oxygen this study. blown which was required for the oxidation of silicon, Relations between the dephosphorization rate and manganese, phosphorus, and iron, and from the com the basicity of slag are shown in Fig. 10. The de phosphorization rate in each stage is expressed as fol position ratio of CO and CO2 and is shown in Fig. 9. Choke of sampling probes, breathing-in of air, and lows. fluctuation in the flow rate of waste gas caused by the In the first stage, there is a good correlation be dumper of the dust collector are supposed to be the tween the dephosphorization rate and the basici ty of causes of the error of the gas analysis. slag and it is expressed as follows : 4. D ephosphorization D p(l) = 21(CaO/SiOz)+8.0 ...... (9) In the first stage, dephosphorization proceeds ef r = 0.83 fe ctively because of low bath temperature, high where, Dp(l ): dephosphorization rate in the fluidity and foaming ability of slag due to high SiOz first stage (%) content caused by the selective oxidation of silicon, CaO jSi0 : basici ty of slag. and no reversion of phosphorus in the next stage due 2 to the discharge of slag through a slag-off hole in the This figure clearly shows that the dephosphoriza first stage. On the other hand, this stage has disad- tion rate in the first stage exceeds 80% when the
Research Article Transactions ISIJ, Vol. 13, 1973 ( 341 )
100 80 300 / • First stage 0 70 U ( 5i2: 0.01 %) 250 t- o . / " ~~ 0 o F irst stage " ( 5i < 0.01 %) o e " 60 • I 200 - " U j I> 5 econd stage ~ " " 60 0 " " x * 0 B- e Cl.. 50 • )50 -B-r- " ~ 0 ;:.:: x I> I> 40 '\ - u 1 " t;- Cl.. " (f) 40 f )00 .... . -. --+- " ---- • I V i- :... 6 " • /"'" 6 6 20 " JJ 30 I :- 50 -+ .- J AI> i (f) 4 I> / " ~ 20 °0 20 40 60 80 )00 V I> st age (5 i"> 0.0 )"01 ESl im Research Article [ 342 J Transactions ISIJ, Vol. 13, 1973 hot metal flowing still, there is no serious problem on (U.K .), 39 ( 1966), 166. eros ion. 10) N. K. Leonidob, A. N. Pogbisnob, M. A. Glinkob, and B. A. Since continuous steelmaking operation is char Kudrih : Proizbodstbo Chuguna i Stali , ( 1969), !togi acterized by having no variation of temperature and Nauki i T ehniki. II ) D. R . G. Davies, M.J. Rhydderch, and L. J . Shaw: PSI, basicity to the refractory used at every site along the 205 ( 1967), 8 10. furnace, this merit can be realized when the optimal 12) M.J. Rhydderch: J ISJ, 205 ( 1967), 8 14. refractories configuration is adopted in each stage ac 13 ) Iron Steel (U.K.), 40 ( 1967), 374. cording to its specified reactions, and could bring the 14) A. Berthet,J. R ouanet, P. Vayssiere, and B. Trentini: JISI, reduction of refractory consumption. 207 ( 1969), 790. 15) A. Berther, J. C. Krud, J. R ouanet, and P. Vayssiere: IV. Conclusion Proceedings ICSTlS, ( 197 1),272, Suppl. T rans. ISlJ. Basic concepts for the development of the NRIM 16 ) A. Berthet, J. Blum, M . Girard, and D. M artin : Proceed continuous steelmaking process and the recent experi ings of the meeting "Alternative R outes to Steel " ( 197 1), mental results were reported here. In spite of a 107, I ron Steel lnst., London. small-scale experimental p lant and a short running 17 ) H . K. Worner : J. Aus. In st. M etals, 6 ( 196 1), 167. 18) H . K . Worner, F. H . Baker, 1. H . Lassam, and R . Siddons: time of about 100 min, satisfactory results were ob J. Metals, 21 ( 1969),50. tained in the separation of reactions in to each stage 19 ) H. K . Wo rner and F. H . Ba ker : Proceedings l CSTIS, and the operational technics. We are convinced that ( 197 1),277, Suppl. Trans. l S I]. this process would sati sfactorily have practical applica 20) F. H . Baker and H. K . Worner : Proceedings of the meeting tion. "Alternative R o utes to Steel ", ( 197 1), 99, I ron Steel Inst. , The characteristics of this multi-stage continuous London. steelmaking process have been confirmed, that is, as 2 1) E . M. Rudzki , H . L. Gills, B. K . Pease, and G. E. Wie la nd : for the dephosphorization, steel of 0.005%P is pro J. Metals, 21 ( 1969),57. duced (dephosphorization rate 96%), and as for the 22) M . A. Glinkov: Proceedings of the meeting "Alternative decarburization, carbon level could be controlled R outes to Steel ", ( 197 1), 88, iro n Steel Inst., Londo n . 23) R . Nakagawa, T . Ueda, S. Yoshimatsu, T. Mitsui, 1. mainly in the second stage. Uehara, A. Fukuzawa, and Y. 1 akamura: ReI). Nat. Res. Comparing with other continuous steelmaking pro blSt. Metals, 10 ( 1967), 557. cesses, the NRIM multi-stage continuous steelmaking 24) R . Nakagawa, T . Ueda, S. Yoshimatsu, T. Mitsui, 1. Ue process has the characteristics of separating the com hara, A. Fukuzawa, and Y. Nakamura: Tetsu-to-Hagane, plex steelmaking reactions into several simple ones, a nd 54 ( 1968), S481. it will result in easy control of reaction and mixing, 25) R . Nakagawa, S. Yos himatsu, T. Mitsui, 1. Uehara, A. proper selection of refractories, and reduction of capi tal Fukuzawa, a nd Y. Nakamura: Tetsu-to-Hagan!, 56 ( 1970), and maintenance cost. S65. At present the fo llowing works are being carried 26) R. Nakagawa, T. Ueda, S. Watanabe, and H. Saito: T etsu out steadily, i.e., (1 ) preliminary continuous desulfuri to-Hagane, 56 ( 1970), S65. zation, (2) finer control of carbon content, (3) tem 27) R . Nakagawa, T . Ueda, S. Yoshimatsu, T. Mitsui, A. Sato, perature control, and (4) study in the field of chemical A. Fukuzawa, 1. Uehara, and T. Ozaki: Tetsu-to-Hagan!, engineering including scale-up and optimization. 57 ( 197 1), S400. 28) R. Nakagawa, T . Ueda, S. Yoshimatsu, T. Mitsui, A. Sato, A cknowledgements 1. Uehara, and A. Fukuzawa: Trans. Nat. Res . Inst. The authors wish to express their grati tude for the Metals, 13 ( 197 1), 54. valuable d iscussions given by the Continuous Steel 29) R. Nakagawa, T. Ueda, S. Yoshimatsu, T. Mitsui, A. Sato, making Research Committee of the Iron a nd Steel 1. Uehara, and A . Fukuzawa: P roceedings ICSTIS,( 197 1), Institute of Japan. 290, Suppl. Trans. ISIJ. The contributions of assistants of the Melting and 30) R. Nakagawa: Japan Patent 6269 13, 653978; French Roll ing Section, the First and the Second Laboratory Patent 1576970; British Patent 1207003; U.S. Patent 3617042. in Development Division to the experiments are also 3 1) T. Uehara, T . Mitsui, Y. Nakamura, R . 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