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Iron Ore Materials and Coke Quality Characteristics and Quantitative Indicators of Blast Furnace Smelting
16th IFAC Symposium on Automation in Mining, Mineral and Metal Processing August 25-28, 2013. San Diego, California, USA
Iron Ore Materials and Coke Quality Characteristics and Quantitative Indicators of Blast Furnace Smelting A.N. Dmitriev, G.Yu. Vitkina, Yu.A. Chesnokov, R.V. Petukhov Institute of Metallurgy of Ural Branch of Russian Academy of Sciences, 101, Amundsen st., Ekaterinburg, 620016, Russia (e-mail: [email protected]) Abstract: One of the most effective ways of the technical progress in the blast furnace manufacture is improvement of physical and chemical characteristics the iron ore materials and coke that allows to increase the smelting of pig-iron and to reduce the coke specific consumption without building of new blast furnaces and concentrating plants. The coke consumption in blast furnace smelting make about 40 % of costs for pig-iron production. Therefore essential reduction of the coke consumption at the minimization of the general power costs should be considered as the important problem at the enhancement the blast furnace smelting technology. In the paper following approach to the decision of practical problems of the blast furnace is considered: the laboratory researches at the experimental installations and definition the qualitative characteristics the iron ore raw materials and coke; analytical research by means of the mathematical models; pilot and industrial tests. Keywords: Measured values, Mathematical models, Qualitative analysis, Quantity, Steel industry scales. The material is blown by reducing gas under the gas flow is 30 l/min. The reducing gas must have the following structure – carbon oxide is about 33 %, nitric oxide is about 65 % and the rest is G2, KH2, G2H. During the material blowing the furnace is heating up to temperature of 600 ºC during the 40 minutes, and then it is heating up to 1100 ºC during the 175 minutes. At the material heating and blowing by reducing gas the registration of oxygen mass loss is made. The reducibility is defined as the dependence of oxygen mass loss on the mass of originally connected oxygen, expressed in percentage.
1. INTRODUCTION The most important problem at the blast furnace process developing is the great coke consumption decreasing at the minimization of general energy costs. One of the most effective ways of ironmaking technical progress is the iron ore materials and coke physicochemical characteristics improvement that allows increasing the iron productivity and decreasing specific coke consumption without construction of new blast furnaces and concentrating mills. Some of the quality indicators of the iron ore raw materials and coke and their influence on the main parameters of the blast furnace smelting are considered in the paper.
Also the reducibility can defined as standardized degree of reduction which usually calculates by mass loss or by change of a chemical compound of the reduced sample, as shown in the paper Kobelev et al. (2000).
2. THE IRON ORE MATERIALS QUALITY We choose following parameters of quality – the agglomerate and pellets reducibility and mechanical strength for studying of influence on the blast furnace process efficiency.
The reducibility is defined by mineralogy, structure and porosity of the agglomerate materials. These factors in turn depend on the basicity of agglomerate which also influences on its reducibility, and this influence has complex character. Reducibility essentially improves at the transition from nonfluxed agglomerate to fluxed one up to basicity CaO/SiH2 equal 1.2–1.6. When the basicity is growth the reducibility is decreased, then it is again increased, as shown in the paper Leontiev et al. (2007).
The reducibility of the iron ore materials is the major quality index which is necessary to take into account at the estimation consumer characteristics of the prepared iron ore raw materials, as showN in the papers, e.g. Arzhadeeva et al. (2010), Dmitriev et al. (2006). Reducibility is an ability of iron ore material to give oxygen from ferrous oxide to reducing gas with greater or smaller velocity. Its role increases as the blast furnace improving and the coke consumption decreasing.
The porosity of materials substantially defines the reducibility. The porosity of agglomerates changes depending on the different factors from 25 up to 45 % at a wide range of the pore sizes, as showed in the paper Leontiev et al. (2007).
The reducibility of the iron ore materials is defined in accordance with Russian Federation State Standard ‹ 17212–84. Reduction is made in the vertical reactionary pipe placed in the electric furnace. The iron ore material is charged into the reactionary pipe which is hanged to the
978-3-902823-42-7/2013 © IFAC
On the Russian agglofactoryes the content of ferrous oxide FeO in agglomerate (14–15 %) is set based on the cold strength and low coke consumption correlation that does not allow to receive high reducibility of a finite product. In this 307
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IFAC MMM 2013 August 25-28, 2013. San Diego, USA
4. THE COKE KINETIC CHARACTERISTICS ESTIMATION
connection there is a problem of achievement of extremely low content FeO in agglomerate, thus the maximal reducibility at the preservation of high strength is saved.
The metallurgical coke from the «Ural Steel» metallurgical plant (Novotroitsk, Russia) was investigated. It have been made the experiments for definition of the Coke Reactivity Index and coke kinetic characteristics on the equipment corresponding to requirements the Russian Federation State Standard J 50921–2005 (analogue of the certificated equipment with observance of all parameters). The meaning of the method consists in reaction of the coke with carbon dioxide at the temperature of 1100 °K, and definition of the coke mass after reaction. The CRI is the loss of the coke mass after the reaction with carbon dioxide, expressed in percentage.
Mechanical strength (Russian Federation State Standard 15137–77) is defined in a rotating steel drum with the subsequent definition of the material screen size change. Strength is defined an output of particles with the fraction content of 0–5 mm (characterizes abrasion resistance) and more 5 mm (characterizes impact strength). Strength of materials at reduction defines in accordance with Russian Federation State Standard 19575–74. 3. THE COKE QUALITY It is possible to conclude that the coke chemical and physical characteristics should correspond to higher requirements basing on the new operating experience of the blast furnaces with the greater specific consumption of coal and black oil.
The coke sample is crushed in to the crusher. The fraction output makes 19.0–22.4 mm. For test the coke portion of 200 g is selected The equipment consists of the reactionary furnace and the thermo controller, the gas equipment, scales, the computer.
Now the Coke Reactivity Index CRI and Coke Strange after Reaction CSR are the main physical and chemical characteristics defined with the conventional method NSC, offered by the corporation Nippon Steel, Japan. On the basis of this method the following standards are developed and applied in the world: the British Standard BS 4262–84, the ASTM Standard D 5341–93 and the project ISO 18894:2006, the Russian Federation State Standard J 50921–2005, as shown in the paper Stepanov (2005).
The gases were applied to work: gaseous nitrogen special cleanliness in accordance with Russian Federation State Standard 9293–74 with a volume fraction of nitrogen isn’t less than 99.9 % and the sum of mass fractions of oxygen and carbon dioxide is no more than 100 mg/kg; gaseous carbonic acid premiums in accordance with Russian Federation State Standard 8050–85 with a volume fraction carbon dioxide isn’t less than 99.8 %.
The CRI is a parameter of intensity of interaction of coke carbon with carbon dioxide in standard conditions of test (the temperature of coke heating is above 1100°K). It is defined by the general coal burden ash level and coal burden grade composition, as shown in the paper Dmitriev et al. (2010). The final (working) value of the CRI is formed inside of the blast furnace at the interaction of coke with fumes and dust of the shaft atmosphere.
The coke was loaded into the ceramic glass, and the glass was suspended on the scales and was located in the electrical pipe furnace. The coke heated up to 1100 °K within 1 hour at the nitrogen blowing of 5 l/min. Then the carbonic gas with the consumption of 5 l/min was supplied, and nitrogen in the furnace wasn’t supplied. The heated coke was blown by carbonic gas during of 120 min. The correction of the rotameter indications was spent. After 120 min a gas stream switched again to nitrogen. The coke decrease is fixed on the scales. Then the furnace was cooled.
It is considered that the CRI should be as it is possible below and to provide the minimal carbon rate on the gasification reaction of the Boudoir (1), as shown in the paper Dmitriev et al. (2011): KH2 + K = 2KH – 166.32 MJ.
The indicator of CRI was defined (2):
(1)
CRI The range of requirements to the quality of coke at the world metallurgical plants is wide enough. However, for the majority chemical-recovery factories the recommended parameter of CRI is within 20–30 %, as shown in the paper Stepanov (2005).
100 ˜
ûG , G
(2)
where 'G – the coke mass loss, g; G – the coke mass, g. For an elementary layer of coke (3) it is possible to write down:
The measurements on the coke various types have shown that the Coke Strange after Reaction greatly raises at the Coke Reactivity Index decreasing. Low value of the CRI defines decrease of a degree of the progress of the iron direct reduction reactions that, in turn, reduces the coke consumption as the heat-carrier and reducer.
dm
˜ K x ˜ CO2' ˜
dG , !
(3)
where m – the quantity of reacted KH2, sm3/s; Do – the constant of reaction speed, s-1; – the degree of use of an internal surface of coke (at t ” 1100 ºC, r0 < 0.2 cm, § 1.0); 3 3 CO2' – the concentration of KH2 on coke surface, m /m ; ! – 3 the apparent density of coke, g/sm .
The parameter of CSR is also defined as the equation of connection between CRI and CSR. It has close correlation.
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IFAC MMM 2013 August 25-28, 2013. San Diego, USA
Using of the joint decision of the equation of chemical reaction with the diffusion equation (4) we receive (5):
˜ (KK 2
dm dm
dG , ! dG dG , ˜ CO2 ˜ D res ˜ KH2 ˜ ! !
CO2' ) ˜ f ˜
1 1 ˜f
1 ˜ Kx
At the small initial contents of KH2 (blast furnace condition) function 3(KH2) can be replaced by function (12)
1 , (12) 1 . where . – the degree of reduction of KH2 equal to the relation of the reacted volume of KH2 to initial one. 2.3lg
(4) (5)
At the speeds of gas observed in the blast furnaces, the external diffusive resistance can be neglected and the equation will take a form (13):
where – the factor of mass transfer, sm/s; KH2 – the concentration of KH2 in a center of gas stream in the considered elementary layer, m3/m3; f – the specific surface of coke, sm-1; Dres – the resulting constant of the reaction velocity, s-1. As f
lg
˜ dk . D
.
1 2 k
d 6Nu ˜ D
CRI 1 CRI 3
(7)
1 ˜ Kx
(8)
D res ˜ G , #0 ˜ !
M(CO2 ) (1 CO20 ) ˜ ln
D res ˜ µ ˜ h . &0
14.75%;
f ûG ˜ G ˜ 273 ˜ P ˜ 2 , f ûG ˜ ! ˜ T ˜ 101.3
(14)
The resulted constant of speed of reaction in our case will become (15):
K ij
Kx
k0 ˜ e
E RT
,
(15)
(9) where k 0 – the pre-exponential factor, s-1;
1 CO2 CO20 ˜ 1 CO20 CO2
energy, kJ/mol;
CO20 CO2 . (10) 1 CO2
? – the activation
R – the gas constant, kJ/mol·degree.
We will receive for the investigated coke k0 = 3.9·109 s-1, E = 244.7 kJ. The constant of speed, the energy of activation allowing as a first approximation to predict the structure of departing gas on the output from a layer of coke at the various temperatures of process are calculated.
With reference to conditions of the blast furnace the equation it is led to a kind (11)
M (CO2 )
6.025%; CRI 2
where f 'G – the function by means of which the average reduction of CO2 in layer of coke is considered; J – pressure of gas, kPa; 2 – experience time, s; T – the set temperature of heating, K.
We substituted the equation (8) in the equation (5) having divided variables and having integrated in limits from CO20 to KH2 and from zero to G, we will receive (9), (10)
M (CO1 )
D res ˜ KH20 1867 ˜ 1
ûG
The current value of KH2 is connected with initial value of 3 CO20 (on an input in layer) and the gas flow rate #0 (sm /s) considering change of volume (8):
#0 ˜ KH 20 m . #0 m
§ 12.05 · ¸ ˜ 100% ¨ © 200 ¹ 31.45%.
The mathematical apparatus offered in the work of Chentsov et al. (2003) was used for processing of experimental data (14):
where dk – the diameter of coke piece, sm; D – the diffusion factor, sm2/s.
CO 2
(13)
Values of the CRI corresponding to these temperatures are calculated using (1):
(6)
Therefore we received (7) D res
1 .
It has been spent three experiments at the various temperatures of heating L1 = 900 °K, L2 = 1000 °K, L3= 1100 °K. The mass loss was fixed on time.
6 , and the factor of mass transfer is connected with dk
the Nusselt criterion by dependence (6) Nu
˜ Kx ˜ µ ˜ h . 2,3&0
1
(11)
5. INFLUENCE OF THE REDUCICBILITY AND STRENGTH OF IRON ORE MATERIALS ON THE BLAST FURNACE PARAMETERS
where µ – the coke volume fraction; h – the height of considered site of the furnace, sm; &0 – the gas speed led to normal conditions, sm/s.
The calculations for the blast furnace ‹ 4 of the “Ural steel” steel works are made by means of balance logic-statistical 309
IFAC MMM 2013 August 25-28, 2013. San Diego, USA
model, developed with Chentsov et al. (2003). The variant of work of the furnace for 2009 year is taken for the basis: the productivity of the furnace was 3274.4 tons pig-iron/day; the coke consumption is 457.5 kg/tons of pig-iron. Variants of the influence of reducibility change (from 68.71 up to 93.71 %) and strength (from 67.96 up to 92.96 %) on the blast furnace technical and economic parameters are calculated (Fig. 1).
470
4450 460
Coke rate, kg / t of pig iron
1
410
4400
438
4350
432
4300
426
4250
2 4200
1
414
408 80
85
30
34
38
42
7. TECHNIQUE OF QUALITATIVE ANALYSIS THE IRON ORE RAW MATERIALS AND COKE CHARACTERISTICS ON TECHNICAL-ECONOMICS OF THE BLAST FURNACE SMELTING INDEXES On basis of the foresaid the influence analysis technique of the qualitative characteristics the iron ore raw materials and coke on indexes of technical-economics of the blast furnace smelting is developed, allowing define the metallurgical worth of new aspects of raw materials on basis of the representative samples of the mineral raw materials. The values of reductibility and “cold” strength, increase the temperature level and a softening range temperature of the iron ore raw materials is shown, and also lowering of value of coke reactive capacity are economically expedient and allow to improve efficiency of a blast furnace process.
4150
75
26
Fig. 2. Influence of the Coke reactivity index on the coke rate (––), the blast furnace productivity (- - -).
2 70
22
CRI, %
1
65
4050 18
4450
444
60
4200
4500
450
420
430
4100
Furnace productivity, t of pig iron / day
456
4250
4150
4550
2
4300 440
420
1 2
4350
450
Furnace productivity, t of pig iron / day
Coke rate, kg / t of pig iron
4400
Predictably there is a known alternative between these two metallurgical iron ore material characteristics. If the attention to the question on the maximal productivity achievement of the blast furnace is given, it can achieve by increase of iron ore materials strength and, on the contrary, if there is a necessity for the decrease of coke rate as a priority there will be a problem of increase in the material reducibility (with other things being equal). It is recommended to apply the iron ore materials with parameters of reducibility and strength above 80 % for reception of the optimum values of productivity of the furnace and the coke consumption. 462
4500
90
95
4100 100
Reducibility (1); "cold" strength (2), %
Deficiency in Urals Mountains the iron raw materials and coked coals forces to involve in exploitation the new ore minerals deposits. The tentative estimation the index technicaleconomics of the pyrometallurgical processes of such ores by results of trial tests as it is accepted in practice now, is complicated for the technical and economic reasons so the negative result or even an emergency in a blast furnace is possible. We develop a new technique of such estimation. It consists in the following (Vitkina G. Yu, 2012).
Fig. 1. Influence of the reducibility (1) and the strength (2) on the coke rate (––), the blast furnace productivity (- - -). 6. INFLUENCE OF THE COKE REACTIVITY INDEX ON THE BLAST FURNACE PARAMETERS Also the influence of coke characteristics of “Ural Steel” steel works were investigated. The average metallurgical characteristics of coke are: the ash value is 12.1 %; the humidity is 4.6 %; the sulfur content is 0.51 %; the volatile matter is 1.1 %.
1. Making in the laboratory conditions (Fig. 3) the sinter or pellets, taking their metallurgical properties (the strength, reductibility, softening and smeltings temperature). Reductibility of raw materials is making according to Russian Federation State Standard ‹ 17212-84, strength - Russian Federation State Standard ‹ 15137-84, temperatures of beginning of softening and fusion of the material - Russian Federation State Standard ‹ 26517-85.
The variant of work of the furnace “Ural Steel” steel works for 2009 year is taken for the basis. The value of the coke reactivity index varied from 21.2 to 41.2 % (Fig. 2) for calculation of the productivity and the coke consumption dependences in the blast furnace. The productivity of the blast furnace has decreased on 212.1 tons pig-iron/day (6.3 %) at the coke reactivity increase by 20 %, the coke consumption has increased for 33.75 kg/tons of pig-iron (7.6 %), i.e. on 1 % of the coke reactivity index increase productivity decreases on 0.315 %, the coke consumption increases for 0.38 %.
2. Z. The calculating forecasting of the coke properties (strength, reactive capacity) on the basis of the properties of components of the mix material for the carbonization. b. The coke reactive capacity (CRI, %) and hot strength (CSR, %) are defined according to Russian Federation State Standard ‹ J 50921-2005
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IFAC MMM 2013 August 25-28, 2013. San Diego, USA
furnace efficiency. Also the improvement of technology of reception of coke with low parameter of CRI is expedient. 9. ACKNOWLEDGMENTS This work was executed with financial support from: – Council under Grants for Leading Scientific Schools of Russia (School ‹ 864.2012.3); – Project of Ural Branch of Russian Academy of Sciences ‹ 12-M-23457-2041. REFERENCES Arzhadeeva G.Yu., Dmitriev A.N., Chesnokov Yu.A. (2010). Investigation of influence of qualitative iron ore materials characteristics on parameters of a blast furnace process. Proceedings of the Ninth international scientifically-practical conference “Research, development and application of high technologies in the industry”. St.-Petersburg, Russia. P. 175–176. Dmitriev A.N. (2006). The role of reducibility in achievement of the minimal coke consumption in the blast furnace smelting. Defect and Diffusion Forum. Vols. 258–260. P. 91–100. Dmitriev A.N., Chesnokov Yu.A., Arzhadeeva G.Yu. (2010). Mathematical Model of Forecasting of Coke Quality Indicators. Defect and Diffusion Forum. Vols. 297–301. P.1290–1294. Dmitriev A.N., Chesnokov Yu.A., Arzhadeeva G.Yu., Lazebnaya Yu.P. (2011). Mathematical Model of Forecasting the Iron Ore Materials and Coke Quality Indicators. Defect and Diffusion Forum, Vols. 312–315. P.1198–1203. Kobelev V.A., Puzanov V.P. (2000). To a problem of sinter reducibility. Steel. Vol. 12. P. 6–8. Leontev L.I., Yusfin Y.S., Malysheva T.Y. (2007). Iron ore and fuel base of ferrous metallurgy. Moscow: Academic Book. P. 304. Stepanov Yu.V. (2000). About methods of definition and an estimation of quality of coke. Ferrous metallurgy. Vol. 1. P. 24–32. Chentsov A.V., Chesnokov Yu.A., Shavrin S.V. (2003) Logic-statistic balance model of blast furnace smelting process. Ekaterinburg: Ural Branch of Russian Academy of Sciences. P. 164. Vitkina G.Yu. (2012) Investigation and perfection of estimation technique of metallurgical properties influence the iron ore raw materials and coke on efficiency of the blast-furnace smelting. Ekaterinburg: Institute of Metallurgy of Ural Branch of Russian Academy of Sciences. P. 24. Dmitriev A.N. (2011). Mathematical modeling of blast furnace process. Ekaterinburg: Ural Branch of Russian Academy of Sciences. P. 168.
Fig. 3. Installation on studying of behavior of iron ore materials at reduction: computer 1, scales 2, electric furnace 3, reactionary glass 4, thermo controller 6 (with thermocouple 5), rotameter 7, gas analyzer 8, reducers 10, cranes 11, exhaust ventilation 15, gas cylinders 12, 13, 14, gas generator of carbon oxide 9. 3. The calculation by means of mathematical model the indexes of technical-economics of the blast furnace smelting. The mathematical models of the blast furnace smelting include a balance logic-statistical model (Chentsov et al., 2003) and the complex of two-dimensional models: gas kinetics, heat interchange, reduction, cohesion zone (an viscous-plastic state) (Dmitriev, 2011). These mathematical models among the few allow use as input data the metallurgical characteristics of the iron ore raw materials and coke, including the two-dimensional alternative. A mathematical analysis allows size up really possibility of usage the iron raw materials and coke as mix burden of the blast furnace smelting. 4. The trial tests with the secured reception of the positive result. 8. CONCLUSIONS Thus influences of the reducibility and the strength of iron ore materials, the coke reactivity index on the blast furnace efficiency is shown by means of balance logic-statistical model of blast furnace process. At the arrangement of priorities of improvement of this or that blast furnace technical and economic parameter it is necessary to consider that the optimal results of productivity and the coke consumption it is possible to reach by the iron ore material application with the parameters of the reducibility and the strength are above 80 %. It is obvious that the decrease of the coke reactivity index is economically expedient and will allow improving the blast 311
Iron Ore Materials and Coke Quality Characteristics and Quantitative Indicators of Blast Furnace Smelting A.N. Dmitriev, G.Yu. Vitkina, Yu.A. Chesnokov, R.V. Petukhov Institute of Metallurgy of Ural Branch of Russian Academy of Sciences, 101, Amundsen st., Ekaterinburg, 620016, Russia (e-mail: [email protected]) Abstract: One of the most effective ways of the technical progress in the blast furnace manufacture is improvement of physical and chemical characteristics the iron ore materials and coke that allows to increase the smelting of pig-iron and to reduce the coke specific consumption without building of new blast furnaces and concentrating plants. The coke consumption in blast furnace smelting make about 40 % of costs for pig-iron production. Therefore essential reduction of the coke consumption at the minimization of the general power costs should be considered as the important problem at the enhancement the blast furnace smelting technology. In the paper following approach to the decision of practical problems of the blast furnace is considered: the laboratory researches at the experimental installations and definition the qualitative characteristics the iron ore raw materials and coke; analytical research by means of the mathematical models; pilot and industrial tests. Keywords: Measured values, Mathematical models, Qualitative analysis, Quantity, Steel industry scales. The material is blown by reducing gas under the gas flow is 30 l/min. The reducing gas must have the following structure – carbon oxide is about 33 %, nitric oxide is about 65 % and the rest is G2, KH2, G2H. During the material blowing the furnace is heating up to temperature of 600 ºC during the 40 minutes, and then it is heating up to 1100 ºC during the 175 minutes. At the material heating and blowing by reducing gas the registration of oxygen mass loss is made. The reducibility is defined as the dependence of oxygen mass loss on the mass of originally connected oxygen, expressed in percentage.
1. INTRODUCTION The most important problem at the blast furnace process developing is the great coke consumption decreasing at the minimization of general energy costs. One of the most effective ways of ironmaking technical progress is the iron ore materials and coke physicochemical characteristics improvement that allows increasing the iron productivity and decreasing specific coke consumption without construction of new blast furnaces and concentrating mills. Some of the quality indicators of the iron ore raw materials and coke and their influence on the main parameters of the blast furnace smelting are considered in the paper.
Also the reducibility can defined as standardized degree of reduction which usually calculates by mass loss or by change of a chemical compound of the reduced sample, as shown in the paper Kobelev et al. (2000).
2. THE IRON ORE MATERIALS QUALITY We choose following parameters of quality – the agglomerate and pellets reducibility and mechanical strength for studying of influence on the blast furnace process efficiency.
The reducibility is defined by mineralogy, structure and porosity of the agglomerate materials. These factors in turn depend on the basicity of agglomerate which also influences on its reducibility, and this influence has complex character. Reducibility essentially improves at the transition from nonfluxed agglomerate to fluxed one up to basicity CaO/SiH2 equal 1.2–1.6. When the basicity is growth the reducibility is decreased, then it is again increased, as shown in the paper Leontiev et al. (2007).
The reducibility of the iron ore materials is the major quality index which is necessary to take into account at the estimation consumer characteristics of the prepared iron ore raw materials, as showN in the papers, e.g. Arzhadeeva et al. (2010), Dmitriev et al. (2006). Reducibility is an ability of iron ore material to give oxygen from ferrous oxide to reducing gas with greater or smaller velocity. Its role increases as the blast furnace improving and the coke consumption decreasing.
The porosity of materials substantially defines the reducibility. The porosity of agglomerates changes depending on the different factors from 25 up to 45 % at a wide range of the pore sizes, as showed in the paper Leontiev et al. (2007).
The reducibility of the iron ore materials is defined in accordance with Russian Federation State Standard ‹ 17212–84. Reduction is made in the vertical reactionary pipe placed in the electric furnace. The iron ore material is charged into the reactionary pipe which is hanged to the
978-3-902823-42-7/2013 © IFAC
On the Russian agglofactoryes the content of ferrous oxide FeO in agglomerate (14–15 %) is set based on the cold strength and low coke consumption correlation that does not allow to receive high reducibility of a finite product. In this 307
10.3182/20130825-4-US-2038.00025
IFAC MMM 2013 August 25-28, 2013. San Diego, USA
4. THE COKE KINETIC CHARACTERISTICS ESTIMATION
connection there is a problem of achievement of extremely low content FeO in agglomerate, thus the maximal reducibility at the preservation of high strength is saved.
The metallurgical coke from the «Ural Steel» metallurgical plant (Novotroitsk, Russia) was investigated. It have been made the experiments for definition of the Coke Reactivity Index and coke kinetic characteristics on the equipment corresponding to requirements the Russian Federation State Standard J 50921–2005 (analogue of the certificated equipment with observance of all parameters). The meaning of the method consists in reaction of the coke with carbon dioxide at the temperature of 1100 °K, and definition of the coke mass after reaction. The CRI is the loss of the coke mass after the reaction with carbon dioxide, expressed in percentage.
Mechanical strength (Russian Federation State Standard 15137–77) is defined in a rotating steel drum with the subsequent definition of the material screen size change. Strength is defined an output of particles with the fraction content of 0–5 mm (characterizes abrasion resistance) and more 5 mm (characterizes impact strength). Strength of materials at reduction defines in accordance with Russian Federation State Standard 19575–74. 3. THE COKE QUALITY It is possible to conclude that the coke chemical and physical characteristics should correspond to higher requirements basing on the new operating experience of the blast furnaces with the greater specific consumption of coal and black oil.
The coke sample is crushed in to the crusher. The fraction output makes 19.0–22.4 mm. For test the coke portion of 200 g is selected The equipment consists of the reactionary furnace and the thermo controller, the gas equipment, scales, the computer.
Now the Coke Reactivity Index CRI and Coke Strange after Reaction CSR are the main physical and chemical characteristics defined with the conventional method NSC, offered by the corporation Nippon Steel, Japan. On the basis of this method the following standards are developed and applied in the world: the British Standard BS 4262–84, the ASTM Standard D 5341–93 and the project ISO 18894:2006, the Russian Federation State Standard J 50921–2005, as shown in the paper Stepanov (2005).
The gases were applied to work: gaseous nitrogen special cleanliness in accordance with Russian Federation State Standard 9293–74 with a volume fraction of nitrogen isn’t less than 99.9 % and the sum of mass fractions of oxygen and carbon dioxide is no more than 100 mg/kg; gaseous carbonic acid premiums in accordance with Russian Federation State Standard 8050–85 with a volume fraction carbon dioxide isn’t less than 99.8 %.
The CRI is a parameter of intensity of interaction of coke carbon with carbon dioxide in standard conditions of test (the temperature of coke heating is above 1100°K). It is defined by the general coal burden ash level and coal burden grade composition, as shown in the paper Dmitriev et al. (2010). The final (working) value of the CRI is formed inside of the blast furnace at the interaction of coke with fumes and dust of the shaft atmosphere.
The coke was loaded into the ceramic glass, and the glass was suspended on the scales and was located in the electrical pipe furnace. The coke heated up to 1100 °K within 1 hour at the nitrogen blowing of 5 l/min. Then the carbonic gas with the consumption of 5 l/min was supplied, and nitrogen in the furnace wasn’t supplied. The heated coke was blown by carbonic gas during of 120 min. The correction of the rotameter indications was spent. After 120 min a gas stream switched again to nitrogen. The coke decrease is fixed on the scales. Then the furnace was cooled.
It is considered that the CRI should be as it is possible below and to provide the minimal carbon rate on the gasification reaction of the Boudoir (1), as shown in the paper Dmitriev et al. (2011): KH2 + K = 2KH – 166.32 MJ.
The indicator of CRI was defined (2):
(1)
CRI The range of requirements to the quality of coke at the world metallurgical plants is wide enough. However, for the majority chemical-recovery factories the recommended parameter of CRI is within 20–30 %, as shown in the paper Stepanov (2005).
100 ˜
ûG , G
(2)
where 'G – the coke mass loss, g; G – the coke mass, g. For an elementary layer of coke (3) it is possible to write down:
The measurements on the coke various types have shown that the Coke Strange after Reaction greatly raises at the Coke Reactivity Index decreasing. Low value of the CRI defines decrease of a degree of the progress of the iron direct reduction reactions that, in turn, reduces the coke consumption as the heat-carrier and reducer.
dm
˜ K x ˜ CO2' ˜
dG , !
(3)
where m – the quantity of reacted KH2, sm3/s; Do – the constant of reaction speed, s-1; – the degree of use of an internal surface of coke (at t ” 1100 ºC, r0 < 0.2 cm, § 1.0); 3 3 CO2' – the concentration of KH2 on coke surface, m /m ; ! – 3 the apparent density of coke, g/sm .
The parameter of CSR is also defined as the equation of connection between CRI and CSR. It has close correlation.
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Using of the joint decision of the equation of chemical reaction with the diffusion equation (4) we receive (5):
˜ (KK 2
dm dm
dG , ! dG dG , ˜ CO2 ˜ D res ˜ KH2 ˜ ! !
CO2' ) ˜ f ˜
1 1 ˜f
1 ˜ Kx
At the small initial contents of KH2 (blast furnace condition) function 3(KH2) can be replaced by function (12)
1 , (12) 1 . where . – the degree of reduction of KH2 equal to the relation of the reacted volume of KH2 to initial one. 2.3lg
(4) (5)
At the speeds of gas observed in the blast furnaces, the external diffusive resistance can be neglected and the equation will take a form (13):
where – the factor of mass transfer, sm/s; KH2 – the concentration of KH2 in a center of gas stream in the considered elementary layer, m3/m3; f – the specific surface of coke, sm-1; Dres – the resulting constant of the reaction velocity, s-1. As f
lg
˜ dk . D
.
1 2 k
d 6Nu ˜ D
CRI 1 CRI 3
(7)
1 ˜ Kx
(8)
D res ˜ G , #0 ˜ !
M(CO2 ) (1 CO20 ) ˜ ln
D res ˜ µ ˜ h . &0
14.75%;
f ûG ˜ G ˜ 273 ˜ P ˜ 2 , f ûG ˜ ! ˜ T ˜ 101.3
(14)
The resulted constant of speed of reaction in our case will become (15):
K ij
Kx
k0 ˜ e
E RT
,
(15)
(9) where k 0 – the pre-exponential factor, s-1;
1 CO2 CO20 ˜ 1 CO20 CO2
energy, kJ/mol;
CO20 CO2 . (10) 1 CO2
? – the activation
R – the gas constant, kJ/mol·degree.
We will receive for the investigated coke k0 = 3.9·109 s-1, E = 244.7 kJ. The constant of speed, the energy of activation allowing as a first approximation to predict the structure of departing gas on the output from a layer of coke at the various temperatures of process are calculated.
With reference to conditions of the blast furnace the equation it is led to a kind (11)
M (CO2 )
6.025%; CRI 2
where f 'G – the function by means of which the average reduction of CO2 in layer of coke is considered; J – pressure of gas, kPa; 2 – experience time, s; T – the set temperature of heating, K.
We substituted the equation (8) in the equation (5) having divided variables and having integrated in limits from CO20 to KH2 and from zero to G, we will receive (9), (10)
M (CO1 )
D res ˜ KH20 1867 ˜ 1
ûG
The current value of KH2 is connected with initial value of 3 CO20 (on an input in layer) and the gas flow rate #0 (sm /s) considering change of volume (8):
#0 ˜ KH 20 m . #0 m
§ 12.05 · ¸ ˜ 100% ¨ © 200 ¹ 31.45%.
The mathematical apparatus offered in the work of Chentsov et al. (2003) was used for processing of experimental data (14):
where dk – the diameter of coke piece, sm; D – the diffusion factor, sm2/s.
CO 2
(13)
Values of the CRI corresponding to these temperatures are calculated using (1):
(6)
Therefore we received (7) D res
1 .
It has been spent three experiments at the various temperatures of heating L1 = 900 °K, L2 = 1000 °K, L3= 1100 °K. The mass loss was fixed on time.
6 , and the factor of mass transfer is connected with dk
the Nusselt criterion by dependence (6) Nu
˜ Kx ˜ µ ˜ h . 2,3&0
1
(11)
5. INFLUENCE OF THE REDUCICBILITY AND STRENGTH OF IRON ORE MATERIALS ON THE BLAST FURNACE PARAMETERS
where µ – the coke volume fraction; h – the height of considered site of the furnace, sm; &0 – the gas speed led to normal conditions, sm/s.
The calculations for the blast furnace ‹ 4 of the “Ural steel” steel works are made by means of balance logic-statistical 309
IFAC MMM 2013 August 25-28, 2013. San Diego, USA
model, developed with Chentsov et al. (2003). The variant of work of the furnace for 2009 year is taken for the basis: the productivity of the furnace was 3274.4 tons pig-iron/day; the coke consumption is 457.5 kg/tons of pig-iron. Variants of the influence of reducibility change (from 68.71 up to 93.71 %) and strength (from 67.96 up to 92.96 %) on the blast furnace technical and economic parameters are calculated (Fig. 1).
470
4450 460
Coke rate, kg / t of pig iron
1
410
4400
438
4350
432
4300
426
4250
2 4200
1
414
408 80
85
30
34
38
42
7. TECHNIQUE OF QUALITATIVE ANALYSIS THE IRON ORE RAW MATERIALS AND COKE CHARACTERISTICS ON TECHNICAL-ECONOMICS OF THE BLAST FURNACE SMELTING INDEXES On basis of the foresaid the influence analysis technique of the qualitative characteristics the iron ore raw materials and coke on indexes of technical-economics of the blast furnace smelting is developed, allowing define the metallurgical worth of new aspects of raw materials on basis of the representative samples of the mineral raw materials. The values of reductibility and “cold” strength, increase the temperature level and a softening range temperature of the iron ore raw materials is shown, and also lowering of value of coke reactive capacity are economically expedient and allow to improve efficiency of a blast furnace process.
4150
75
26
Fig. 2. Influence of the Coke reactivity index on the coke rate (––), the blast furnace productivity (- - -).
2 70
22
CRI, %
1
65
4050 18
4450
444
60
4200
4500
450
420
430
4100
Furnace productivity, t of pig iron / day
456
4250
4150
4550
2
4300 440
420
1 2
4350
450
Furnace productivity, t of pig iron / day
Coke rate, kg / t of pig iron
4400
Predictably there is a known alternative between these two metallurgical iron ore material characteristics. If the attention to the question on the maximal productivity achievement of the blast furnace is given, it can achieve by increase of iron ore materials strength and, on the contrary, if there is a necessity for the decrease of coke rate as a priority there will be a problem of increase in the material reducibility (with other things being equal). It is recommended to apply the iron ore materials with parameters of reducibility and strength above 80 % for reception of the optimum values of productivity of the furnace and the coke consumption. 462
4500
90
95
4100 100
Reducibility (1); "cold" strength (2), %
Deficiency in Urals Mountains the iron raw materials and coked coals forces to involve in exploitation the new ore minerals deposits. The tentative estimation the index technicaleconomics of the pyrometallurgical processes of such ores by results of trial tests as it is accepted in practice now, is complicated for the technical and economic reasons so the negative result or even an emergency in a blast furnace is possible. We develop a new technique of such estimation. It consists in the following (Vitkina G. Yu, 2012).
Fig. 1. Influence of the reducibility (1) and the strength (2) on the coke rate (––), the blast furnace productivity (- - -). 6. INFLUENCE OF THE COKE REACTIVITY INDEX ON THE BLAST FURNACE PARAMETERS Also the influence of coke characteristics of “Ural Steel” steel works were investigated. The average metallurgical characteristics of coke are: the ash value is 12.1 %; the humidity is 4.6 %; the sulfur content is 0.51 %; the volatile matter is 1.1 %.
1. Making in the laboratory conditions (Fig. 3) the sinter or pellets, taking their metallurgical properties (the strength, reductibility, softening and smeltings temperature). Reductibility of raw materials is making according to Russian Federation State Standard ‹ 17212-84, strength - Russian Federation State Standard ‹ 15137-84, temperatures of beginning of softening and fusion of the material - Russian Federation State Standard ‹ 26517-85.
The variant of work of the furnace “Ural Steel” steel works for 2009 year is taken for the basis. The value of the coke reactivity index varied from 21.2 to 41.2 % (Fig. 2) for calculation of the productivity and the coke consumption dependences in the blast furnace. The productivity of the blast furnace has decreased on 212.1 tons pig-iron/day (6.3 %) at the coke reactivity increase by 20 %, the coke consumption has increased for 33.75 kg/tons of pig-iron (7.6 %), i.e. on 1 % of the coke reactivity index increase productivity decreases on 0.315 %, the coke consumption increases for 0.38 %.
2. Z. The calculating forecasting of the coke properties (strength, reactive capacity) on the basis of the properties of components of the mix material for the carbonization. b. The coke reactive capacity (CRI, %) and hot strength (CSR, %) are defined according to Russian Federation State Standard ‹ J 50921-2005
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furnace efficiency. Also the improvement of technology of reception of coke with low parameter of CRI is expedient. 9. ACKNOWLEDGMENTS This work was executed with financial support from: – Council under Grants for Leading Scientific Schools of Russia (School ‹ 864.2012.3); – Project of Ural Branch of Russian Academy of Sciences ‹ 12-M-23457-2041. REFERENCES Arzhadeeva G.Yu., Dmitriev A.N., Chesnokov Yu.A. (2010). Investigation of influence of qualitative iron ore materials characteristics on parameters of a blast furnace process. Proceedings of the Ninth international scientifically-practical conference “Research, development and application of high technologies in the industry”. St.-Petersburg, Russia. P. 175–176. Dmitriev A.N. (2006). The role of reducibility in achievement of the minimal coke consumption in the blast furnace smelting. Defect and Diffusion Forum. Vols. 258–260. P. 91–100. Dmitriev A.N., Chesnokov Yu.A., Arzhadeeva G.Yu. (2010). Mathematical Model of Forecasting of Coke Quality Indicators. Defect and Diffusion Forum. Vols. 297–301. P.1290–1294. Dmitriev A.N., Chesnokov Yu.A., Arzhadeeva G.Yu., Lazebnaya Yu.P. (2011). Mathematical Model of Forecasting the Iron Ore Materials and Coke Quality Indicators. Defect and Diffusion Forum, Vols. 312–315. P.1198–1203. Kobelev V.A., Puzanov V.P. (2000). To a problem of sinter reducibility. Steel. Vol. 12. P. 6–8. Leontev L.I., Yusfin Y.S., Malysheva T.Y. (2007). Iron ore and fuel base of ferrous metallurgy. Moscow: Academic Book. P. 304. Stepanov Yu.V. (2000). About methods of definition and an estimation of quality of coke. Ferrous metallurgy. Vol. 1. P. 24–32. Chentsov A.V., Chesnokov Yu.A., Shavrin S.V. (2003) Logic-statistic balance model of blast furnace smelting process. Ekaterinburg: Ural Branch of Russian Academy of Sciences. P. 164. Vitkina G.Yu. (2012) Investigation and perfection of estimation technique of metallurgical properties influence the iron ore raw materials and coke on efficiency of the blast-furnace smelting. Ekaterinburg: Institute of Metallurgy of Ural Branch of Russian Academy of Sciences. P. 24. Dmitriev A.N. (2011). Mathematical modeling of blast furnace process. Ekaterinburg: Ural Branch of Russian Academy of Sciences. P. 168.
Fig. 3. Installation on studying of behavior of iron ore materials at reduction: computer 1, scales 2, electric furnace 3, reactionary glass 4, thermo controller 6 (with thermocouple 5), rotameter 7, gas analyzer 8, reducers 10, cranes 11, exhaust ventilation 15, gas cylinders 12, 13, 14, gas generator of carbon oxide 9. 3. The calculation by means of mathematical model the indexes of technical-economics of the blast furnace smelting. The mathematical models of the blast furnace smelting include a balance logic-statistical model (Chentsov et al., 2003) and the complex of two-dimensional models: gas kinetics, heat interchange, reduction, cohesion zone (an viscous-plastic state) (Dmitriev, 2011). These mathematical models among the few allow use as input data the metallurgical characteristics of the iron ore raw materials and coke, including the two-dimensional alternative. A mathematical analysis allows size up really possibility of usage the iron raw materials and coke as mix burden of the blast furnace smelting. 4. The trial tests with the secured reception of the positive result. 8. CONCLUSIONS Thus influences of the reducibility and the strength of iron ore materials, the coke reactivity index on the blast furnace efficiency is shown by means of balance logic-statistical model of blast furnace process. At the arrangement of priorities of improvement of this or that blast furnace technical and economic parameter it is necessary to consider that the optimal results of productivity and the coke consumption it is possible to reach by the iron ore material application with the parameters of the reducibility and the strength are above 80 %. It is obvious that the decrease of the coke reactivity index is economically expedient and will allow improving the blast 311