Hydrodynamics of electric arc furnace bath at stirring with inert gases. S.V. Kazakov, M.P. Gulyaev, V.V. Filippov RUE BMZ, Moscow State Institute of

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1 Hydrodynamics of electric arc furnace bat at stirring wit inert gases. S.V. Kazakov, M.P. Gulyaev, V.V. Filippov RUE BMZ, Moscow State Institute of Steel and Alloys. It is [-3] known, tat metal bottom blowing in steel melting aggregate is an effective element of production growt. However, it is possible to control tis process only on te basis of data of ydrodynamic condition of smelt. Te simplest and te easiest metod of study of ydrodynamics and mass excange is pysical simulation tat allows to study te process varying different factors witin wide ranges, to observe, to fix and to simulate te process under study. Teory of similarity allows in tis case wit certain tolerances to spread te results of simulated researces over similar production units. Evaluation of ydrodynamic condition of electric arc furnace bat wit bottom stirring wit inert gas can answer te following questions: ) Optimal number and te location of blowing units; ) Optimal blowing mode, i.e. te mode providing maximum effectiveness of treatment at minimum gas consumption; 3) Influence of blowing modes on te speed of processes running in steel melting bat. Application of metal bottom blowing in te furnace allows to control series of essential tecnological parameters: suc as speed of carge melting, slag formation, termal and cemical eterogeneity of smelt. Te fact of influence of bottom blowing is evident, owever, it is important to know te level of influence, i.e. ow te processes will run if canges of different blowing parameters take place rate of gas supply, form and size of blowing unit, te location of blowing units. Pysical simulation is te most convenient metod of study of ydrodynamics of steel melting bat because it is difficult or impossible to carry out similar qualitative researc on real aggregate working under conditions of continuous production cycle. Te aim of tis researc was qualitative evaluation of influence of cange of different parameters of bottom blowing wit indifferent gas on ydrodynamics of te bat..pysical simulation. Electric furnace bat model was made of organic glass to scale :5. Te unit simulating bottom blowing includes: compressor, gas-distributing station, furnace model properly, gas supply system and blowing units. Water was used as simulated liquid, inks tat were put into fixed point of smelt served as tracer. Te number and te location of blowing units were canged during te experiment. Gas consumption troug eac blowing unit was constant during te experiments. Te main task of cold simulation was te determination of optimal number and te location of blowing units. Effectiveness of stirring of te bat using different number of blowing units and teir location were evaluated by averaging time of tracer (ink) in te smelt leveling of coloring intensity in different model parts. Te tracer

2 in particular constant quantity was put in fixed point of smelt blown at stationary mode. Te number of blowing units and teir location were canged during experiments. In tis case te number of units was canged from to 4 during tests. measurements were carried out for eac gas supply circuit in order to increase accuracy of results. In total te beavior of smelt was studied by fifteen variants. Te results of experiments (averaging time of tracer depending on te number and te location of lances) are given in table. Cold simulation results Table Variants o Tracer averaging time, s lances Location 3 4 t t t3 t4 t5 t6 T7 t8 t9 t tср х х х х 8, 8,4,,8,6 8,4 9,, 9,8,6 9,7 ххх 8, 6,8, 8,8 9,4 9,8, 7,8,8,4, 3 хх х7,,3, 7,86,9,68, 5,8 4,6 5, 4,5 4 х х х 4,84,, 6,9,43,7,8, 6, 7, 6,3 5 х х х 9,,7,8 9, 7,8,7, 9, 8, 7,6 8,6 6 хх 3,5,8,4 8,6,69, 9,4, 7, 8,4,5 7 х х 8, 8,6 7, 7,8 8,4,8, 8, 8, 7, 8, 8 х х 7,68, 8, 7,8 7, 9,,3 9,9 9, 9,7 9,7 9 х х 7,8 7, 9,,9,8 7,4 7,8 8,8,, 8,8 х х 6,8 7,4 7,8 6, 7, 8,6 7,6,, 6,8 7,8 х х 6, 7,4 7,8 6,4 7,8,8, 6, 7,8 8, 7,6 х,8,, 8,8 3,8,6, 7,, 4,4,5 3 х 3,5,8,,6,6,9,6,4 8,8 3,6 5,7 4 х 9,7,5,4,3,83,,8,6 7,6,8 7, 5 х,84,6, 3,5,3,6, 8, 8,6,,7

3 3 Averaged results of cold simulation are given in fig.. Te fact attracts te attention tat minimum averaging time, it means te most effective stirring of smelt is reaced wen two blowing units are used. Detailed analysis sowed tat te most effective location of two blowing units is diametrically opposite to eac oter. Время усреднения Количество продувочных устройств Рис.. Average values of averaging time of smelt wit different numbers of blowing units. Hydrodynamic conditions in electric arc furnace differ from simulated due to te existence of factors tat are not taken into account at cold simulation, for example: te existence of ig termal zones witin arc areas, dynamic influence of arcs, convection smelt flows, cold zones at smelt period, constructional peculiarities of te furnace etc. Enumerated factors and te necessity of process intensification in solid periods of eat, tat comprise from 6 to 7% of te total period of furnace work under current, were taken into account at blowing units installation and coice of teir location on real place during production experiment.. Production experiment. Te researces were carried out for tons electric arc furnaces of RUE BMZ equipped wit direct type of bottom blowing. Direct type provides blowing troug cannel refractory lances installed in te furnace bottom.

4 4 Bottom ousing before lining is equipped wit tree metal nozzles wit stop flanges for assembling and disassembling of lances. Blowing mode is supported by gas-distributing unit. Gas-distributing unit for blowing units is completed wit free programmed SIMATIK S5 and automatic bypass in case of unexpected electrical power switc off or pressure decrease of inert gas in te system tat ensures continuous gas flow troug lances at direct blowing or porous bottom lining at idden one. Gas supply unit provides fully automatic adjustment of supplied gas quantity during te eat in total to all lances and/or to eac lance separately regardless of back pressure tat canges constantly during te eat process. Tis unit allows to adjust gradually ( l/min) te quantity of gas supplied to eac blowing unit witin te ranges from to 5 l/min. For direct type of blowing safety is ensured by installation of close-type tube to eac blowing lance for /3 of lance eigt from te bottom. Gas under pressure is continuously supplied to tese tubes. In case of lance wear for /3 of eigt te tube is opened, consumption and pressure of gas cange and te personnel is warned about it. 3. Termotecnical simulation of temperature eterogeneity of steel melting bat Main tolerances and conditions. Te following main tolerances and conditions are accepted at model development:

5 5 ) te bat is divided in two orizontal layers te upper («active») layer wit widt, for eat generation and te lower layer wit widt, wic is equal to te basic volume of liquid melt (Fig. ); Fig.. Conditional dividing of steel bat capacity: «active» layer; basic capacity of steel bat. ) eat generation capability in «active» layer q v (W/m 3 ) is defined; 3) «active» layer participates in eat transfer wit te furnace roof and conducted eat excange (wen te melt is dead) and convection eat excange (wen te melt is stirred) wit te basic capacity of bat; 4) te basic capacity of bat participates in conducted (wen te melt is dead) or convection eat excange (wen te melt is stirred) wit an «active» layer; te portion of eat transfers to environment troug te bottom; 5) cross section F of te bat is permanent along te dept; 6) non - uniformity of temperature distribution along te bat dept is defined by te difference Т = Т Т (), were Т average temperature of an «active» layer; Т average temperature of te basic capacity of bat. 7) in te beginning Т = Т = Т н (), were Т н initial temperature of melt. 3.. Calculation Formula Te density of resultant radiation flow wile radiation eat transfer between te bat surface and furnace roof

6 р q w = ε пр σ 4 4 ( T T ) с (3), 6 were ε пр emissivity degree; σ = 5,67-8 Вт/(м К 4 ) Boltzmann constant; T с roof temperature. Te density of conducted eat flow discarged from te active layer to te basic bat capacity in case of liquid melt is T конд q = λ (4) x were λ termal conductivity of melt; x axis direction from top, zero point is equal to surface separating te active layer from te bat basic capacity. Convective eat flow transferred from te «active» layer to te bat basic capacity during te melt stirring is Q ( T ) конв = сmn T (5), were с specific eat of melt; M melt weigt; Intensity of bat stirring. N = M dm dt (6), q Heat waste density to te environment troug te furnace bottom is ( T T ) = kт (7), were k т eat transfer factor (for single layer bottom k т = λ'/δ, λ' termal conductivity, δ widt); T ambient temperature Calculation of Non-Uniform Temperature Distribution Along te Bat Dept at Dead Melt History of «active» layer temperature variation T (t) is described by te following equation cm dt = T + λ ε σ 4 4 ( T T ) F, T () = н qvv пр с T dt x, (8)

7 or 7 dt cρ dt = + T λ ε σ 4 4 ( T T ), T () = ; qv T пр с н x (9), were M weigt of an «active» layer; ρ melt density. Te temperature field of base melt is determined by te termal conduction equation (a = λ/(cρ) diffusivity) T t T = а, < x < x wit initial condition, () ( x, ) T =, () Tн wit boundary condition on te surface wic separates te basic volume of melt from te «active» layer T λ x = q v dt cρ dt ε пр σ 4 4 ( T T ) с () and wit boundary condition on te bottom surface T λ = kт x ( T T ). (3) After te determination of temperature field T(x,t) te average temperature of basic volume is calculated as follows: T () t T ( x,t) dx. = (4) For computational solution of above mentioned equations te iterative implicit difference sceme is used [4] Non-Uniform Temperature Distribution Calculation Along te Bat Dept at Stirred Melt

8 8 Temporal variation of «active» layer temperature T (t) and te basic volume of melt T (t) are described by te following equations of termal balance for active layer and melt basic volume 4 4 dt ( ) q εпрσ T T v с = N( T T ), T () = Tн, (5) dt cρ d cρ dt dt ( T T ) kт = N( T T ), T () = н ; (6) d cρ T were M weigt of melt basic volume; d = / и d = / parts of «active» layer and basic melt on te wole. For computational solution of simple differential equations (5), (6) te iterative implicit difference sceme is used [4]. As an example te diagrams of average temperature variation of «active» layer and basic volume of melt obtained under te following initial data: с = 7 J/(kgК); ρ = 7 kg/m 3 ; λ = 3 W/(mК); =,8 m; T н = 5 о С; q v =,5 MW/m 3 ; =, m; T с = 6 о С; ε пр =,5; k т = 5 W/(m К); N =,5 min ; time interval t = 5 sec; coordinate interval for termal conduction equation x =,8 m, are sown on Figure Температура, град Время, мин Температура 'активного' слоя без перемешивания Температура основного объема без перемешивания Температура 'активного' слоя с перемешиванием Температура основного объема с перемешиванием Fig. 3 Te basic volume and active layer temperature variation 3.5. Fluid Dynamics Parameter Computation Under conditions of RUE «BMZ» te melt eigt is

9 = + =,8m (7) 9 In Electric Arc Furnace wile an «active» layer formation te pacing factor is te influence of electric arcs (dividing dial diameter electrode breakdown d р, grapite electrode diameter d э, electric arc lengt l д ) Capacity of melt bat is М V = (8) ρ at ρ = 7 t/m 3 for М=t V=4,3 m 3 or for М=t V=7, m 3 Volume of an «active» layer V wit determined assumption πd V = х Н =,88 m 3 (9) 4 were D=dp+dэ=,4+,6=m Н = l д =,8m Te portion of «active» layer of melt is determined as volume proportion V d = () V and amounts d =,65 for cast М=t, and portion of te basic melt is consequently d =-d =,9385 On te basis of data d = ; d = ; =,8м te widt of «active» layer and base melt are: =,5m and =,75m respectively. Te content of steel bat even witout bottom blowing is not absolutely dead, i.e. tere is an excange inside of melt.

10 Te fluid dynamics parameter is calculated for inert (indifferent) gas blowing using te experiment data of temperature fall measurements ( Т=5 С) d =, min, wic describes te excange rate between two layers. Using te prior results, te parameter d for blowing of different intensity at pressure 5bar and melt eigt,8 m was calculated. Calculated data are sown in Table. Table Fluid Dynamics Parameter Calculation Results Parameters Dime Name Ident ificat ion nsion Parameters value Blowing intensity for one blowing unit У l/min Weigt rate of m Kg/s 7,7 9 3, 3,8 38,5 46, melt in one gasliquid flame Fluid dynamics d,,3,4,5,6,83 parameter min Te calculation results of dependence of non uniformity temperature in bat upon melt stirring by te inert (indifferent) gas intensity are sown on Figure 4. Температурная неоднородность, град 8 6 4,,4,6,8,, Интенсивность перемешивания, /мин

11 Figure 4. Dependence of non uniformity temperature in bat upon te stirring intensity 3.6. Termotecnical Simulation Results On te diagram sown on Figure. 7, you can see tat witout bottom blowing wit inert (indifferent) gas for values d=, min te temperature non-uniformity (experimental value) of melt is 5 С. Te minimal temperature difference is acieved at blowing intensity about J=6 l/min. However, assurance of te best blowing performance, i.e.te performance wic optimizes te non-uniformity of melt temperature is acieved at blowing intensity about J= l/min. wat meets to value m=9 kg/sec. for one gas-liquid flame. Tus, te termotecnical simulation elped to ground te best performance of melt blowing wit inert (indifferent) gas. For commercial operation te bottom blowing wit inert (indifferent) gas sown at Table is recommended. Inert Gas Blowing Cast Interval tap to- start time from start to 9 kw/ from 9 kw/ to 8 kw/ during additional carge (carge of te second basket) after te additional carge up to 3 kw/ from 3 kw/ to 48 kw/ from 48 kw/ to steel tap at dead time Table 3 Inert gas consumption for one blower, nl/min

12 Te developed optimized blowing is implemented on tree electric arc furnaces at RUE «BMZ». Te implementation of tis tecnology improves greatly performance caracteristics as well as qualitative caracteristics of furnaces operation. In particular, te time of current operation was decreased by 3 minutes and electric power specific consumption was decreased by 5- kw/t. Togeter wit te improvement of cost-performance ratio te content of detrimental impurities and gases was reduced as follows: posporus by 45-5%, sulfur 5-%, nitrogen 5-% (rel), oxidation by 44% (rel). References. Imbovitsa B.A., Yakovenko V.V. Bottom Blowing in Open-Heart Furnace // Metallurg p... Kutakov A.B., Derevyancenko I.V., Kazantsev B.V., Galcenko A.V., Lozin G.A. Steelmelting Development at Moldavian Steel Works // Stal pp Gulyaev M.P., Filippov V.V., Enders V.V., Sumacer Ev., Sumacer Ed., Frantski R., Brener H. Te First Systems of Bottom Blowing Wit Inert Gas in Electric Arc Furnace in CIS Countries // Proceedings of te 6-t Congress of Steelmakers (Cerepovets, October,7-9,.) / М.: Cermetinformatsiya.. - p Artyunov V.A., Bukmirov V.V., Krupennikov S.A.Matematical Simulation of Industrial Furnaces Termal Operation. - М.: Metallurgiya p 5