A.N.Dmitriev, S.V.Shavrin
Institute of Metallurgy of Ural Division of Russian Academy of Sciences
101 Amundsen st., Ekaterinburg, 620016, Russia
ABSTRACT.
Questions of use of a modern complex of mathematical models of blast furnace smelting process for the analysis of the gas dynamics phenomena, heat exchange and reduction for the decision of practical problems are considered. The problem of targeted shaping of structure and metallurgical properties of the iron-ore raw material is solved, allowing to lower a coke rate in blast furnace process, on an instance of agglomerate from Lisakovsky gravitation-magnetic concentrate. Change of processes of a gasdynamics and heat exchange in volume of a blast furnace is analysed at use of new designs: application of fuel-enriched blast with high rates of flux of natural gas and oxygen, injection of finely pulverized coal, change of a furnace lines. Overlapping of ordinates of time and heights in the diagrams pictorially mapping the phenomena in a blast furnace on balance logic-statistical and on twodimensional models, that, allows to analyse the major elements of process evidently.
Perfection of a two-dimensional mathematical models of a blast-furnace smelting operation by the account of elements of the charging system, a blast pressure and waste gas, has allowed to raise essentially it forecast opportunities.
1. INTRODUCTION
The analysis of most in detail published mathematical models, for example (1), and also the most typical (2), has shown, that the full mathematical description of blast furnace smelting process should include the following models (or submodels): loadings, hearth tuyere, movement of gas and material, filtration of melt, reduction, heat exchange, cohesive zone and balance model.
Estimation of the importance of the developed mathematical models of blast furnace smelting process, in our opinion, it is expedient to make comparison of quantity and importance of practical problems decided on their basis, and complexity of developed mathematical models (i.e. quantity of submodels included in it) should be defined by circle of particularly decided problems.
2. THE DESCRIPTION OF THE COMPLEX OF MATHEMATICAL
MODELS
In Institute of metallurgy UrD the Russian Academy of Science the complex of two-dimensional mathematical models of blast furnace smelting process (3) is developed on the basis of a minimum quantity of the listed models, allowing to analyze influence of various parameters, including metallurgical properties complex iron-ore raw material (reducibilities, durabilities, temperatures of a softening and fusion) on temperature fields material and gas, including a site and the form of cohesive zone in view of the non-uniformity created by the loading device and
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introduction of blasting through tuyere. In this case it is possible to be limited to the following mathematical models: gas dynamics, heat exchange, reduction, cohesive zone and balance model (fig. 1).
Fig. 1.
The block-diagram of a complex of two-dimensional mathematical models.
As against other known models, allowing to solve the limited quantity of practical problems, the complex of mathematical models has allowed to develop a method of analytical research of blast furnace process due to use of the opportunities of change incorporated in him over a wide range of entrance parameters: blasting, systems of loading, material structure and qualities of iron-ore raw material, elements of a design of the furnace. It allows to expect speeds of gas, temperatures of material and gas, a degree of reduction of iron in any point of working space of a blast furnace.
The complex of mathematical models is finished with a commodity product as the program on a personal computer with high consumer properties - presentation of
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representation of results of calculation in the graphic form and an opportunity of processing and the analysis of received images.
The stated below decided problems having both theoretical, and practical value testify to advantages of the developed complex of mathematical models.
2. THE DECISION OF PRACTICAL PROBLEMS OF BLAST FURNACE
SMELTING PROCESS
The problem of purposeful formation of structure and metallurgical properties of iron-ore raw material is solved, allowing to lower the charge of coke in blast furnace process, by the example of agglomerate from Lisakovsky gravitation-magnetic concentrate.
Laboratory researches have shown, that at decrease of a mass fraction monoxide iron in agglomerate from 16 % up to 13 % reducibility of it has increased by 20 %, the temperature interval of a softening was essentially reduced. Calculations of heat exchange have allowed to predict decrease(reduction) of the charge of coke. The subsequent translation of blast furnaces on melting new agglomerate has confirmed this forecast: the charge of coke has decreased on 8-11 kg/tone of pig-iron.
Results of the given work have allowed to draw a conclusion on an opportunity of application of machine modeling for an estimation of influence of iron-ore raw material quality on parameters of blast furnace process, character of temperature fields and cohesive zones.
Change of gas dynamics processes and heat exchange in volume of a blast furnace is analyzed at use of new technical decisions: 1 - application of the combined blasting with high charges of natural gas and oxygen, 2 - inflation of a coal dust, 3 - change of a structure of the furnace.
1. Increase of charges of oxygen and natural gas is limited to an essential cold snap in all volume of a blast furnace, is especial in an ore crest. Due to alignment of ore loading on top radius elimination of the critical phenomena in an ore crest and increase of the maintenance of oxygen in blasting up to 45-50 % is possible.
2. Use of coal dust fuel as a substitute of coke except for problems of inflation and burning causes the difficulties connected to change of structure and increase of gas dynamics resistance of a charge layer, increase in difference between temperatures of charge both gas in shaft and increase of top temperature, and in a different degree for periphery, an ore crest and the center. Increase of the charge of a coal dust imposes high requirements to quality of iron-ore raw material and coke.
3. Influence of elements of a design of a blast furnace on processes in its volume is tracked by the example of the working furnace in volume of joint-stock company
"Nizhniy Tagil Iron and Steel Works" (NTMK) of 1719 m
3
, and also an existing profile of a blast furnace № 1 joint-stock companies "Chusovskoi Metallurgical
Works" and a profile of a blast furnace № 3 before her blowout. Fields of speeds of gas, a field of temperatures of gas and material, degrees of reduction of iron and concentration potentials of gas are designed and analyzed. Quantitative influence of change of elements of a structure on development of processes of heat exchange, gas dynamics and reduction in interrelation with technical and economic parameters blast furnace process is established.
Change of character of temperature and high-speed fields is analyzed at deviations from a normal course of blast furnace process: 1 - infringement of heat exchange, 2 - district non-uniformity, 3 - a silent course, 4 - infringement of the schedule of releases.
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1. It is above shown, that the increase in charges of oxygen and natural gas is limited to an essential cold snap in all volume of a blast furnace, is especial in an ore crest. Except for alignment of ore loading, elimination of a cold snap is possible due to submission in shaft of the heated up gas. By calculations it is established, that the level of speeds of gas in shaft above horizon of his submission raises, thus nonuniformity of distribution of speed of gas on radius (more gas moves in an ore crest) that allows to liquidate the crisis phenomenon increases also.
2. It is known, that the supply of blasting to tuyeres through a ring air pipe results in non-uniform distribution of blasting and, hence, gas on a circle on which non-uniform material distribution is imposed by loading devices. It is established, that in the field of an ore crest the attitude of thermal capacities of streams of material and gas can come nearer to unit at decrease of the charge of blasting through tuyere only on 10 % from average and this area becomes critical on heat exchange. It causes of the control of district non-uniformity that it is expedient to do with the help of twodimensional mathematical model and indications of the thermocouples established on peripheries is lower than a charge level. The information received from these thermocouples, can be used in quality for base points at calculations on mathematical model as two-dimensional, and, as a first approximation, neglecting overflows, threedimensional temperature fields by consecutive turn of a settlement plane concerning an axis of the furnace on a corner 3600/quantity of tuyeres (fig. 2). It is known, that alignment of non-uniformity on a circle is possible due to change of charge distribution. Besides it is especial at occurrence of the crisis phenomenon in one of the vertical sections, probably, in our opinion, the following influence - closing air фурмы on the opposite side.
Thus, use of two-dimensional mathematical model and indications of peripheral thermocouples allows to analyze not only radial, but also the district non-uniformity, created фурменным a supply of blasting and the loading device of a blast furnace.
3. Because of time lack on b last-furnace plant of iron-ore raw material or coke there is a necessity of translation of blast furnaces on a silent course. With the help of two-dimensional mathematical model change of character of temperature and highspeed fields in blast furnaces in volume of 218 m
3
and 2700 m
3
working on silent course is investigated. Results of calculations have shown, that while translating a blast furnace on a silent course the tuyere center is shifted to a wall of the furnace, and in rather greater degree for a blast furnace of smaller volume. Temperatures of material and gas on peripheries grow, and in an ore crest are reduced. Hence, influence of hot gases increases for a laying of the furnace, and also the crisis phenomenon in an ore crest amplifies. As have shown calculations, for elimination of similar negative consequences of translation of a blast furnace on a silent course it is necessary to close a part of tuyere.
4. It is known, that the thermal condition of a blast furnace is subject to fluctuations in time, connected with releases of pig-iron. With the help of model, supposing approach, have analysed temperature fields in volume of the furnace at the fixed degrees of filling of a well. By calculations it is established, that changes of temperatures of gas in various vertical sections occur non-uniformly - they more in the center and on periphery and less in an ore crest. For an ore crest after release the attitude of thermal capacities of streams can come nearer to unit that will result in the crisis phenomenon in the given vertical section. The amplitude of fluctuations of temperature fields of material and gas on top radius can serve a degree of radial non-
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Fig. 2.
A three-dimensional temperature field of gas.
uniformity of the attitude of thermal capacities of streams in interrelation with average value one of criteria at definition of quantity of releases.
3. NEW ELEMENTS IN RESEARCH OF THE PHENOMENA OF BLAST
FURNACE SMELTING PROCESS
For last years at vanadic pig-iron smelting the tendency of substantial improvement of parameters of work of furnaces was planned due to optimization of parameters of blasting and material structure. This tendency is looked through as on furnaces in volume 1033 m
3
, and 1513 m
3
.
In this connection is of interest as comparison of the parameters determining levels of technological decisions, and revealing of feature of processes on the furnaces vanadic pig-iron smelting, in comparison with their organization on the furnaces sucelting of usual steel-making iron. The necessary data for the analysis of processes, including a field of speeds, are received with the help of a complex of twodimensional mathematical models and logic-statistic balance model for blast furnace smelting process (3-4).
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In tab. 1 key parameters used at the analysis of process, and results of calculations of the basic parameters of work of furnaces in volume 1513 m
3
(vanadic pig-iron) and 5580 m 3 (steel-making pig-iron) for conditions of practically equal specific parameters under the charge of coke and productivity (433 kg and 1.88 т pigiron / m
3
day) are resulted.
Table 1
The initial data and results of calculations for furnaces in volume of 1513 and 5580 m
3
Volume of the furnace, m
3
Productivity, t/day
1513
2850
5580
10490
Volume of the furnace, m
3
Degree of use:
1513 5580
Use of volume of the furnace, t/м 3 ∙day
1.88 1.88
The charge of components шихты, kg / t of pig-iron: agglomerate
КachGOK
664.3 agglomerate ChMP 715.0 pellets КachGOK pellets КostGOK 873.8 coke 433.3 432.6 limestone 77.6 slag (steel) 22.1 8.0
Content Fe in an ore part of charge, % 58.1 60.2
CO
H
2
Temperature of pigiron, ˚С
0.474
0,458
Structure of pig-iron, %:
[Si]
[Ti]
[S]
[V]
0.20
0,029
0.45
1450
0.477
0,461
0.35
-
0.021
-
[Mn] 0.24
[P] 0.05
1470
Blasting: Output of slag, kg/t of pig-iron quantity, m 3 /minute 2393 8143 (CaO/SiO
2
) temperature, ˚C humidity, g/m
3
1186
10 10
1176
Theoretical temperature burning, ˚С of
Top dust, kg/t of
350
1.06
1940
296
1.1
1990 oxygen, % 22,4 23,5 Losses of metal
(s crap , slag), kg/t of pig-iron
Natural gas, m 3 / t of pig-iron 95 90
Time of movement of material up to a
Top gas: level фурм, hour
Distance between sock level and tuyere, m output, м 3
/t temperature (damp),
˚C
1772,0
260 250 Q
Q arrival expenditure
30
5.9
23
1686,9 Thermal balance, МDj/t pig-iron:
10921
10
6.1
27
10819
10921 10819
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On fig. 3 the data on development of processes of reduction of iron oxides, about change of material temperatures and gas temperature in time on height of blast furnaces (at the left) and fields of speeds on their section (on the right) are resulted: A
– for the furnace in volume 1513 and B – 5580 m 3
. They testify if to compare be integral with the displayed temperature fields, about rather perfect organization of process: ideal S-shaped curves at a high degree of completeness of heat exchange.
Theoretical temperature of burning at melt of vanadic pig-iron below approximately on 50 degrees, and temperatures of gas on top differ (250 and 260 о С) a little.
Fig. 3.
Fields of speeds of gas and it is warm and mass change processes in blast furnaces in volume 1513 (А) and 5580 m 3
(В): t m
and t g
- temperatures of material and gas; 1 – 6 – a degree of reduction
ω
: 1 - hematite, 2 – magnetite, 3 – wustite, 4 – total,
5 and 6 – the same, for the account CO and Н
2
accordingly.
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The charge of heat on ton at melt of vanadic pig-iron on 102 МDj is more, than at melt usual steel-making pig-iron.
Processes of reduction of iron oxides in a “dry” zone of the furnace proceed at melting of steel-making mix material (А), in structure of which up to 50 % легковосстановимых Kostomukshsky pellets more intensively. Their reducibility is higher 6-10 %, than at Kachkanarsky pellets, at the best parameters of quality and on hot durability (the relation of fractions of-5 mm is 1.2). The total degree of reduction of iron oxides, loaded with charge, on the furnace of 5580 m
3
makes 0.64 against 0.7 for the furnace of 1513 m
3
. At the analysis of a field of speeds in the top zone of furnaces more precise display in registration of peripheral and central zones in a blast furnace in volume of 5580 m
3
though in a peripheral zone of speed of gas, as well as in the furnace in volume of 1513 m
3
, approximately on 0.5 m/s it is more, than in central is revealed. The general tendency increase of speeds of gas in the furnace in volume of 5580 m
3
is marked.
It is necessary to note especially, that the used method of the analysis of process by overlapping time ordinates with height of the furnace for the first time has allowed to observe visually development of determining elements of blast furnace process on height of the furnace in time. The analysis shows, that time for which the material goes from a stock level of mix material on top up to tuyere horizon, for researched operating conditions of blast furnaces, variously. For the furnace in volume of 5580 m
3
it is equal 6.1, and for the furnace of 1513 m
3
– 5.9 hours.
It allows, as the distance from a stock level up to a tuyere level is known, to estimate speeds of movement of a material. For the furnace in volume of 5580 m 3 it will make 27/6.1=4.4 m/h, and for the furnace in volume of 1513 m
3
– 23/5.9 = 3.9 km/h. Thus, loading on a fire-resistant laying for the big furnace is higher in 4.4/3.9 =
1.3 times.
Thus, overlapping of ordinates of time and heights in the diagrams graphically displaying processes in a blast furnace on balance logic-statistical and on twodimensional models, allows to show and compare evidently the major elements of process at a high level of its organization for the furnaces smelting vanadic and steelmaking pig-irons, to reveal distinctions in the organization of a gas stream and speeds of movement of material and gas on furnaces in volume of 1513 and 5580 m
3
at identical specific parameters of their work, to estimate increase in speed of movement of material and growing loading on a fire-resistant laying with increase in volume of furnaces.
Efficiency of use of thermal and regenerative potentials of gas in a blast furnace in many respects is defined by structure of a column of mix materials. She, in turn, is formed by system of loading to which it was always given and the big attention pays.
The account and evident display of influence of parameters of loading at modeling expand opportunities of the analysis of domain process and a circle of decided problems on forecasting parameters of work of furnaces.
In works of Institute of metallurgy of Ural Division of the Russian Academy of
Science and the Ural State Technical university (5) problems connected to system of loading, are solved on the basis of modeling representations about a constancy of height of a charge layer (from an axis фурмы up to a stock level of mix material) for each variant of calculation at the certain structure of a blast furnace (3). Meanwhile the stock level which is one of the major parameters of formation of structure of a column of materials, can change in real conditions quickly enough and over a wide range (for example, at blowout of furnaces). Therefore in last version of twodimensional mathematical model of blast furnace process in the program of
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calculation the changes are brought, allowing to take into account it as size a variable.
Thus the initial equations of gas dynamics, heat exchange and restoration (3) have remained constant. Changes of character of a temperature field in this case are caused by changes of a course of processes on height of the furnace (for example, local speed of gas and the total factor of heat exchange connected to it) at a variation of height of a layer from an tuyere axis up to a stock level of mix material for each line of a current. On fig. 4 results of calculations of a temperature field in a blast furnace in volume of 1719 m
3
are resulted at decrease of a stock level on one and a half meter because of the termination of loading {2} and at long work of the furnace with such stock level {3}. In the first case the temperature field is deformed on all height of the furnace, and temperature of material and gas on topе furnaces grow, accordingly, up to 450 and 550 о С. In the second case of deformation of a field of temperatures it is not observed. Only insignificantly the temperature grows by 30-50 degrees against base top gas.
Fig. 4.
Temperature fields in a blast furnace in volume of 1719 m
3
under various conditions: 1-base stock level, 2 – decrease of a stock level on 1,5 m because of the termination of loading, 3 - long work with the level lowered on 1,5 m stock level.
Thus, perfection of two-dimensional mathematical model of blast furnace process by introduction of the important elements of system of loading has essentially raised her opportunities of the forecast .
Till now influence of the general pressure difference on two-dimensional fields of speeds of gas and a field of temperatures of material and gas in a blast furnace with the help of mathematical models practically was not investigated. The changes which have allowed in an obvious kind to investigate influence of pressure of blasting, pressure are brought in two-dimensional mathematical model (3) on top, the general pressure difference on character of two-dimensional fields of speeds of gas both temperature fields of material and gas. On fig. 5 results of calculations of a temperature field in a blast furnace in volume of 1719 m 3 are resulted at change of pressure of gas on колошнике from 1.7 gauge atmosphere (variant 1) up to 1.5 gauge atmosphere (variant 2). Pressure of blasting in both variants – 2.8 gauge atmosphere.
It is visible, that fields of speeds of gas and a field of temperatures of gas have undergone significant changes, and not only on height, but also on radius of the furnace.
Thus, introduction of an opportunity of the account of influence of pressure of blasting and pressure of gas on top of blast furnace on character of fields of speeds and temperatures has allowed to expand opportunities of model under the analysis of the phenomena of blast furnace process.
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Fig. 5. T wo-dimensional fields of speeds of gas (А) and temperatures of gas (В) in a blast furnace in volume of 1719 m
3
at various pressure on колошнике: 1 – 1.7 gauge atmosphere; 2 – 1.5 gauge atmosphere.
4. THE CONCLUSION
Thus, the decision of the equations of heat exchange, mass exchange and reduction in conditions of a two-dimensional field of speeds allows to expand areas of analytical research and the decision of practical problems of blast furnace process.
AKNOWLEDGEMENTS
Work is executed at support of Council under grants for conducting scientific schools of Russia (№ 1997.2003.3).
THE LITERATURE
1. Blast Furnace Phenomena and Modeling. - The Iron and Steel Institute of Japan,
Elsevier Applied. London and New York, 1987, 631 p.
2. Sugiyama T., Sugata M. Development of Two-Dimensional Mathematical Model for the Blast Furnace "BRIGHT." - Nippon Steel Technical Report, 1987, № 35, p.32-
42.
3. Dmitriev A.N., Shavrin S.V. Two-Dimensional Mathematical Model for Blast
Furnace Smelting Process. - Steel, 1996, № 12, p.7 - 13.
4. Chentsov A.V., Chesnokov Y.A., Shavrin S.V. The Logic-Statistic Balance Model for Blast Furnace Smelting Process. – Ekaterinburg.: UD RAS, 2003, 164 p .
5. Modeling loading and heat- masschange processes in a blast furnace / Shavrin V.S.,
Kudinov D.Z., Shvidky В.S, Dmitriev A.N., Shavrin S.V. // Thermophysics and computer science in metallurgy: achievements and problems. Materials of the
International conference devoted to the 300-anniversary of metallurgy of Ural. -
Ekaterinburg: UGTU, 2000, p.166-171.
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