Advanced Blast Furnace Reaction Simulator Combining a Calculation Model and Experimental Furnace

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1 ISIJ Iteratioal, Vol. 55 (015), ISIJ Iteratioal, No. 6 Vol. 55 (015), No. 6, pp Advaced Blast Furace Reactio Simulator Combiig a Calculatio Model ad Experimetal Furace Toshiyuki HIROSAWA, 1) * Akiori MURAO, 1) Nobuyuki OYAMA, 1) Shiro WATAKABE ) ad Michitaka SATO 3) 1) Iromakig Research Dept., JFE Steel Corp., 1 Koka-cho, Fukuyama, Japa. ) Head Office, JFE Steel Corp., --3 Uchisaiwaicho, Chiyoda-ku, Tokyo, Japa. 3) Steel Research Laboratory, JFE Steel Corp., 1-1, Miamiwatarida-cho, Kawasaki-ku, Kawasaki, Japa. (Received o July 17, 014; accepted o November 13, 014) The use of high reactivity coke is a techology that dramatically improves the reactio efficiecy i blast furaces by decreasig the temperature of the thermal reserve zoe. I this study, a blast furace shaft simulator was developed to estimate the temperature of the thermal reserve zoe ad the distributios of the temperature ad gas compositio i the blast furace whe usig cokes with differet reactivity. The shaft simulator combies a experimetal reactio furace ad a calculatio model. Chemical reactio ad mass/heat trasfer pheomea i the blast furace are cosidered i the calculatio model so as to calculate the ore ad coke reactio rate ad the distributio of temperature ad gas compositio. Relatively small amouts of packed coke ad siter specimes are reacted with the temperature ad gas compositio cotrolled based o the calculatio results. The coke gasificatio rate is fed back to the calculatio model, ad it is the possible to estimate the temperature of the thermal reserve zoe ad the distributios of the temperature ad gas compositio i the blast furace. Shaft simulator experimets with high reactivity coke, such as CIC (Carbo Iro Composite), showed that the temperature of the thermal reserve zoe is 140 K lower with high reactivity coke tha with covetioal coke. KEY WORDS: blast furace; blast furace simulator; carbo iro composite; thermal reserve zoe temperature; carbo gasificatio. 1. Itroductio Agaist the backgroud of global warmig, low RAR (reducig aget rate) operatio of blast furaces is idispesable for reducig CO emissios. May steel compaies have tried various approaches, such as ehacemet of iro ore reducibility, improvemet of coke reactivity ad ijectio of pulverized coal (PC) or waste plastics through the tuyeres to achieve low RAR. Whe a mixture of iro coke ad covetioal coke is heated i a reactio gas, the iro coke selectively ad preferetially reacts i a lower temperature rage ad there are o iteractios betwee the iro coke ad the covetioal coke. This selective reactio weakes the iro coke, while the covetioal coke is protected i the mixed layer of iro coke ad covetioal coke. Improvemet of the coke bed permeability is expected to decrease the reactio ratio of the covetioal coke. The use of high reactivity coke is a techology that dramatically improves the reactio efficiecy i blast furaces by decreasig the temperature of the thermal reserve zoe. 1 6) The temperature of the thermal reserve zoe is related to the equilibrium temperature of Eq. (1). If the equilibrium temperature of Eq. (1) decreases, the iro ore reductio proceeds at a lower CO cotet ad a higher * Correspodig author: t-hirosawa@jfe-steel.co.jp DOI: CO cotet. The carbo solutio loss reactio shows Eq. () at a lower temperature, decreases the temperature of equilibrium i blast furace by the CO gas productio ad the heat of edothermic reactio. FeO(s) + CO(g) Fe(s) + CO (g)... (1) CO (g) + C(s) CO(g)... () Ishii et al. developed a blast furace simulator that combied a calculatio with a experimet to predict the temperature ad gas distributios i the blast furace. 7) Assumig that the burde ad gas phase move i a coutercurret flow i the blast furace, the experimetal coditios were calculated i real time by isertig the i-situ measured rates of reductio ad solutio loss i differetial equatios of mass ad heat balace, ad ew experimetal coditios were the set i the ext stage. The multiple regressio equatio of the gasificatio or reductio rate expresses the gasificatio degree or reductio degree ad temperature, as show Eq. (3). t+ t α + βxt + γtt + η vt... (3) Where, t is time, is the rate of coke gasificatio or ore reductio, α, β, γ ad η are multiple regressio coefficiets, X is the coke gasificatio or ore reductio degree, T is the solid temperature ad v is the gas cocetratio. The iitial temperature ad the thermal reserve zoe temperature are ISIJ

2 ISIJ Iteratioal, Vol. 55 (015), No. 6 set values. As oted above, use of high reactivity coke dramatically improves the reactio efficiecy i blast furaces by decreasig the temperature of the thermal reserve zoe. I this study, a blast furace shaft simulator was developed to estimate the temperature of the thermal reserve zoe ad the distributios of the temperature ad gas compositio i the blast furace whe usig cokes with differet reactivity. The shaft simulator combies a experimetal reactio furace ad a calculatio model. The chemical reactio ad mass/ heat trasfer pheomea i the blast furace are cosidered i the calculatio model so as to calculate the ore ad coke reactio rate ad the distributios of temperature ad gas compositio.. Blast Furace Shaft Simulator A schematic diagram of the shaft simulator is show i Fig. 1. The shaft simulator comprises a reactio furace, a ifrared gas aalyser ad a temperature cotrol system with a persoal computer. The experimetal procedure of the reactio simulator is show i Fig.. First, the experimetal coditios of the reactio furace are calculated by a oe-dimesioal Fig. 1. Schematic diagram of the shaft simulator of blast furace. mathematical blast furace model. Secod, the rates of coke gasificatio ad ore reductio are measured i the experimetal furace. The rate parameter a of the mathematical model reflects the reactio rate obtaied i the experimetal results. The temperature, gas cocetratio ad reactio fractio distributios i the blast furace height directio are calculated by the mathematical model. It is importat that the rates of coke gasificatio ad ore reductio i the model are measured experimetally. The reactio furace is cotrolled by temperature ad gas distributio depedig o the reactivity of raw materials..1. Experimetal Furace Measuremets were performed with a electric furace coected to a proportioal-itegral- derivative cotroller with a thermocouple. The temperature of the hot zoe was maitaied withi ±10 K. N, H, CO ad CO gases were mixed by mass flow cotrollers. A cotiuous flow of the mixture gas at Nm 3 /s was used to cotrol the atmosphere. The distributios of the gas cotets ad temperature i the blast furace shaft deped o the reactio ad heat trasfer betwee the gas ad the charged burde. I the thermal reserve zoe, coke gasificatio occurs by the gasificatio reactio of coke, which is a edothermic reactio. The thermal reserve zoe temperature is maily determied by the edothermic reactio of coke gasificatio ad the heat trasfer betwee the gas ad solid. I the blast furace shaft simulator, the reactivity of the burde material is measured experimetally, ad the heat ad material balace from the tuyeres to the top of the blast furace is calculated by the mathematical model. The sample temperature is measured by the R thermocouple placed o the top surface of the sample bed. The sample temperature is assiged to the reactio temperature i the model... Measuremet of Rates of Coke Gasificatio ad Ore Reductio The rates of coke gasificatio ad ore reductio are calculated by Eq. (4). First term of Eq. (4) expresses the amout of carbo i the outlet gas, the secod term expresses the amout of carbo i the ilet gas. V exp % {( %) + ( %) ( N ) CO CO O O} ( N% ) I O... (4) { ( CO% ) + ( CO% ) I } I Fig.. Experimetal procedures at blast furace reactio simulator. Where, exp is the rate of coke gasificatio of the experimet, V is the gas flow rate, (CO%) I, (CO %) I ad (N %) I are the ilet gas compoets before reactio, (CO%) O, (CO %) O ad (N %) O are the ilet gas compoets after reactio, ad t is the reactio time (s). The CO ad CO cocetratios i the exhaust gas were aalyzed by a ifrared gas aalyzer (URA-107, SHIMAZU), ad the N cocetratio i the exhaust gas was calculated as the cocetratio of residual gas except CO ad CO. 015 ISIJ 13

3 ISIJ Iteratioal, Vol. 55 (015), No Mathematical Model: Oe-dimesioal Model of Blast Furace The oe-dimesioal mathematical model is a steady model that calculates the mass ad trasport pheomea i the blast furace height directio. The rate equatios of coke gasificatio i the model are expressed as follows: 8) k k cco, c,ho k1 1 + kp + kp + kp + kp co 3 co 5 HO 6 H...(5a) k4 1 + kp + kp + kp + kp... (5b) co 3 co 5 HO 6 H I this study, the rate equatios of coke gasificatio i the model are expressed as follows: k ak...(6a) cco, c, CO kc,ho akc,ho... (6b) Where, k is the rate equatio of coke gasificatio, P is partial gas pressure ad T is temperature. The relatioship betwee the temperature ad blast furace height i the oe-dimesioal mathematical model at differet coke gasificatio rates (a 0.10, 1.0, 10) is show i Fig. 3. The temperature distributio i the blast furace height directio is calculated by the mathematical model of differet coke gasificatio rates. As the result, the temperature icreases with descet i the blast furace. The high reactivity coke has the effect of improvig the reductio degree by shiftig the reductio equilibrium poit to the lower temperature side. The thermal reserve zoe is formed at ay gasificatio rate at h10 0 m, ad the temperature of the thermal reserve zoe decreases as a parameter icreases. The thermal reserve zoe temperature is maily determied by the edothermic reactio of coke gasificatio ad the heat trasfer betwee the gas ad solid. I this study, the thermal reserve zoe temperature was defied as the rate of coke gasificatio icreases ad the temperature chage i the height directio is small. The temperature distributio at h 10 0 m is reversed i a 1.0 ad a 10. This pheomeo is due to a icrease i heat of lower part of blast furace. I this model, RAR (reducig aget rate) is a cost. I the case of high coke reactivity, the direct reductio of iro ore decreases with a icrease of the idirect reductio of iro ore. As the results, the temperature distributio at h10 0 m is reversed i differet coke reactivity. This occurs at aroud 5 s of calculatio time of the oe-dimesio mathematical model..4. Procedure for Evaluatio of Raw Materials by Shaft Simulator First, the experimetal coditios of the reactio furace are calculated by the oe-dimesioal mathematical model. Secod, the rates of coke gasificatio ad ore reductio are calculated by Eq. (4). Diffusio equatio with the reactio of spherical particles is expressed by Eq. (7). Cocetratio distributio of the particles withi the boudary coditios (r0, dc/dr0: rr 0, C A C A0 ) is expressed by Eq. (8). 9) De d r dr r dc kc c 0 dr... (7) C C A A0 ( ) r0 sih r kc / De r sih r k / D 1 / 1 / 0 ( c e)... (8) Where k c is the chemical reactio rate, D e is diffusio coefficiet i particles, r is directio, r 0 is particle surface, C A is cocetratio ad C A0 is surface cocetratio. E f is a fuctio to correct the ifluece of the reactio rate that is defied as the reactio rate o ifluece of the diffusio to the experimetal reactio rate at same particle size E f m m m... (9) tah 1 m r 0 ( k / D ) /... (10) c I this study, the coke gasificatio is cosidered the reactio processes. Gas boudary film diffusio of the reactio gas ad chemical reactio ad diffusio of particles i the reactio gas are expressed are expressed as follows. f πdp k C 0 c CO C CO s φ πdp 1 k 0 P P φ RT c e ( ) ( ) c CO CO s dp w π 3 6 M EkP c f c CO s... (11)... (1) Fig. 3. Calculated gas temperature distributios i blast furace with differet rates of coke gasificatio. Where, calc is rate of coke gasificatio i the mathematical model, a is a parameter, d p is the coke diameter, P CO is the CO partial pressure, R is a gas costat, T is the particle temperature, k f is a mass trasfer coefficiet, w is the carbo weight of a coke particle, ϕ is a shape factor, M c is the atomic weight of carbo. The followig expressio (Eq. (14) is derived o the assumptio that f c, Clearig s the X CO ISIJ

4 ISIJ Iteratioal, Vol. 55 (015), No. 6 calc φ RT 1 Mc 1 / + π dp PCO kf wk EP c f CO... (13) The rate parameter a of the mathematical model reflectig the reactio rate of the experimetal results is show by Eq. (14). Fially, the coke gasificatio rate is fed back to the calculatio model, ad it is the possible to estimate the temperature of the thermal reserve zoe ad the distributios of the temperature ad gas compositio i the blast furace. calc φ RT 1 Mc 1 / + π dp PCO kf wak ( ) E P c f CO... (14) Assumig that the rate-cotrollig step of 0.1 mm coke is the chemical reactio, the fuctio E f to correct the ifluece of particle size is expressed by Eqs. (15) 10) ad (16). 11) E E f f 05. dp d ( 75. < p < 0 mm, m 75. )... (15) dp d ( 0 < p < 60 mm, m 0. 0)... (16) 0.5. CIC Reactio Behavior The reactio rate of CIC reacted i CO 80 vol.%+co 0 vol.% is show i Fig. 4. This experimet was coducted i a test method similar to the previous work. 1) The reactio rate of CIC is 30 times larger tha that of covetioal coke. I additio, the ifluece of the CIC reactio rate o temperature shows the same value as covetioal coke. I this study, it is assumed that the ifluece of the CIC reactio rate o temperature is expressed by the above Eq. (14)..6. Experimetal Coditios The amouts of ore ad coke i the siter were 85 g ad 190 g, respectively, with raw ore comprisig the balace of the material. I the case of CIC, the amouts of ore ad CIC i the siter were respectively 707 g ad 69 g. The properties of the ore ad mixed coke are show i Tables 1 ad. The advaced reactio simulator was used to test sitered ore ad coke or CIC. Samples were filled i the alumia pot (ϕ 75 mm 30 mm) of the reactio furace. The size of the sitered ore ad coke was mm, ad the bed structure was a mixture of the two. CIC is a carboizatio product i the form of molded briquettes (30 mm 10 mm) cosistig of 70 wt.% ore ad 30 wt.% coal coke with carboizatio. I CIC chargig, sitered ore is replaced with CIC with correspodig iro ad carbo cotets. I this experimet, CO CO N mixed gas was itroduced ito the furace tube while cotrollig the gas compositio with a automatic cotroller. The flow rate was Nm 3 /s. Outlet gas collected from the furace top was aalysed every 10 s by a ifrared gas aalyser. After raisig the temperature with a N atmosphere to 773 K, the CO CO N mixed gas was itroduced ito the furace. The reactio furace is cotrolled to the temperature ad gas distributio calculated by the oe-dimesioal blast furace model every 5 mi. I additio, the maximum heatig rate is up to K/s ad is carried it out from the maximum temperature to K. The sample compositio is show i Table 3, ad the assumed operatio coditio of the blast furace is show i Table Results 3.1. Coke Gasificatio Rate ad the Blast Furace Shaft Simulator Test The relatioship betwee the temperature ad coke gasificatio rate i the shaft simulator with sitered ore ad coke Table 1. Chemical compositio of sitered ore (mass.%). T.Fe FeO SiO Al O 3 CaO MgO Table. Aalyses of coke. Proximate Aalysis Ultimateaalysis Ash VM C H N S Fig. 4. Gasificatio rate of coke ad CIC with temperature. Table 3. Aalyses of CIC. Proximate Aalysis Ultimate aalysis Ash VM M Fe H C H N S Table 4. Operatig coditios. RAR CR PCR BT Moisture TGP Coke d p Productivity kg/t-pig kg/t-pig kg/t-pig K g/nm 3 kpa mm t/day/m ISIJ 134

5 ISIJ Iteratioal, Vol. 55 (015), No. 6 Fig. 5. Gasificatio rate of coke ad CIC with temperature at blast furace coditio. Fig. 7. Temperature distributio i blast furace with coke ad CIC. I the case of the icrease of parameter a, the experimetal coditios were chaged to a costat temperature ad low CO cocetratio. The gasificatio rate was decreased i those experimetal coditios. This chage is caused by the trasitio to chage from old experimetal coditios to ew experimetal coditios. Uder the ew coditios of temperature ad gas cotets, the gas temperature icreases with burde descet ad the gasificatio rate icreases with icreasig temperature. Fig. 6. Temperature, gasificatio rate of coke ad CO cocetratio i blast furace by the shaft simulator. (case 1) or CIC (case ) is show i Fig. 5. The gasificatio parameter is costat i the oe-dimesioal model. I both cases, the coke gasificatio rate icreased with icreasig temperature. The gasificatio start temperature over a rate of /s is K i case ad 1 73 K i case 1. As a result of a catalytic effect, the temperature of the CIC is 140 K lower tha i case 1. It has bee reported that Fe is a promisig catalyst for improvig coke reactivity uder blast furace coditios. The relatioship betwee the blast furace height ad coke gasificatio rate, gas temperature ad CO cotets i the shaft simulator with sitered ore ad CIC (case ) is show i Fig. 6. The gas temperature icreases as the burde desceds from the furace top. Aroud a height over 15 m, the gasificatio rate icreases with icreasig temperature (A), the decreases with icreasig temperature (B), ad agai icreases (C). Because a coke gasificatio rate over /s was detected i the simulator, the experimetal coditios of temperature ad gas cotets are chaged to appropriate values for CIC chargig. I this case, the correctio factor is fed back from a5 to a Blast Furace with Coke ad CIC The temperature distributios i the blast furace with coke ad CIC are show i Fig. 7. The temperature icreases with decreasig height with the cokes of both reactivities. I the case of the covetioal coke, the gasificatio start temperature is 1 83 K ad a is updated. O the other had, i the case of CIC, the gasificatio start temperature is K ad a is updated. Shaft simulator experimets with high reactivity coke, such as CIC, showed that the temperature of the thermal reserve zoe is 140 K lower with high reactivity coke tha with covetioal coke. Regardig this poit, i the case CIC, the rate of coke gasificatio is higher tha that of covetioal coke (a0.1, Fig. 3). Because a coke gasificatio rate over /s was detected i the blast furace simulator, the experimetal coditios of the temperature ad gas cotets are chaged to appropriate values as CIC chargig coditios. The coke gasificatio rate is fed back to the calculatio model, ad it is the possible to estimate the temperature of the thermal reserve zoe ad the distributios of the temperature ad gas compositio i blast furace. Shaft simulator experimets with high reactivity coke, such as CIC, showed that the temperature of the thermal reserve zoe is 140 K lower with high reactivity coke tha with covetioal coke ISIJ

6 ISIJ Iteratioal, Vol. 55 (015), No Coclusio A advaced blast furace shaft simulator was developed by combiig a experimetal reactio furace ad a calculatio model. The followig coclusios were obtaied. (1) The blast furace shaft simulator was developed to estimate the temperature of the thermal reserve zoe ad the distributios of the temperature ad gas compositio i the blast furace whe usig cokes with differet reactivity. () The coke gasificatio rate is fed back to the calculatio model, eablig estimatio of the temperature of the thermal reserve zoe ad the distributios of the temperature ad gas compositio i the blast furace. (3) Shaft simulator experimets with high reactivity coke, such as Carbo Iro Composite (CIC), showed that the temperature of the thermal reserve zoe is 140 K lower with high reactivity coke with tha with covetioal coke. Captios a ( ): parameter D e (m /s): diffusio coefficiet i particles d p (m): particle diameter E f ( ): a fuctio to correct the ifluece of particle size k c (m/s): chemical reactio rate k f (m/s): mass trasfer coefficiet k i (1/s): chemical reactio coefficiet M c (kg/kmol): the atomic weight of carbo calc (mol/s): the rate of coke gasificatio i the mathematical model exp (mol/s): the rate of coke gasificatio of the experimet P i (Pa): partal pressure(i compoet) R (J/mol/K): gas costat t (s): time T (K): temperature v ( ): gas compoet V (Nm 3 /s): gas flow rate w (kg): particle weight X ( ): the rate of coke gasificatio or ore reductio α (mol/s): multiple regressio coefficiet β ( ): multiple regressio coefficiet γ (1/K): multiple regressio coefficiet η ( ): multiple regressio coefficiet ϕ ( ): shape factor REFERENCES 1) M. Shimizu: CAMP-ISIJ, 1 (008),, CD-ROM. ) S. Nomura, H. Ayukawa, H. Kitaguchi, T. Tahara, S. Matsuzaka, M. Naito, S. Koizumi, Y. Ogawa, T. Nakayama ad T. Abe: Tetsu-to- Hagaé, 9 (006), 3. 3) T. Yamamoto, T. Sato, H. Fujimoto, T. Ayashiki, K. Fukada, M. Sato, K. Takeda ad T. Ariyama: Tetsu-to-Hagaé, 97 (011), 50. 4) M. Naito, A. Okamoto, K. Yamaguchi, T. Yamaguchi ad Y. Ioue: Tetsu-to-Hagaé, 87 (001), ) A. Okamoto, M. Naito, K. Oo ad Y. Hayashi: Tetsu-to-Hagaé, 73 (1987), 7. 6) S. Nomura, K. Higuchi, K. Kuimori ad M. Naito: CAMP-ISIJ, (009), 746, CD-ROM. 7) K. Ishii, Y. Kashiwaya, H. Yamaguchi ad S. Kodo: Tetsu-to- Hagaé, 7 (1986), 0. 8) N. Miyasaka ad S. Kodo: Tetsu-to-Hagaé, 54 (1968), ) K. Hashimoto: Haoukougaku, Baihuuka, Tokyo, (001), 7. 10) S. Taguchi ad K. Okabe: Kawasaki Steel Giho, (1970), ) M. Hatao, T. Miyazaki ad Y. Iwaaga: Tetsu-to-Hagagé, 65 (1979), ) T. Yamamoto, T. Sato, H. Fujimoto, T. Ayashiki, K. Fukada, M. Sato, K. Takeda ad T. Ariyama: Tetsu-to-Hagaé, 97 (011), ISIJ 136