Development of analysis method for physical-chemical phenomena of orien process in electric arc furnaces in energy-metallurgical complex
The base of constructing computer model of the analysis of complex physical-chemical phenomena in the process ORIEN in continuous arc furnace is as the main aggregate of energy-metallurgical complex. A mathematical model of physical-chemical processes.
| Рубрика | Производство и технологии |
| Вид | статья |
| Язык | английский |
| Дата добавления | 02.11.2018 |
| Размер файла | 1,6 M |
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Development of analysis method for physical-chemical phenomena of orien process in electric arc furnaces in energy-metallurgical complex
G.A. Dorofeev, Candidate of technical sciences, Associate Professor,
(Russia, Tula, ООО "NPMP Intermet-servis")
V.A. Erofeev, Candidate of technical sciences, Professor,
A.A. Protopopov, Doctor of technical sciences, Professor, Head of the Department
(Russia, Tula, Tula State University)
L.I. Leontief, Doctor of technical sciences, Professor, RAS Academician,
(Russia, Moscow, Presidium of RAS)
V.Ya. Dashevskii, Doctor of technical sciences, Professor, member of the Academy of Natural Sciences, (Russia, Moscow, Institute of metallurgy and materials science of the name of A. A. Baikov RAS)
P.I. Malemko, Candidate of technical sciences, Associate Professor
Summary
The base of constructing computer model of the analysis of complex physical-chemical phenomena in the process ORIEN in continuous arc furnace (EAF) was developed. The continuous arc furnace is the main aggregate of energy-metallurgical complex. A mathematical model of physical-chemical processes in the EAF during production liquid DRI and coal gasification based on thermodynamic equation of material state was created. This model allows realize complete energy analysis of ORIEN process taking into account the arc heat emission, which based on main chemical reactions, heat-mass transfer melt and the metal vapor.
Keywords: Energy - metallurgical complex, ORIEN process, computer model, physical-mathematical modeling, electric arc furnace, heat-mass transfer, direct reduced iron, coal gasification.
Introduction
ORIEN process relate to a new type of energy-metallurgical technology. It is a combined liquid-phase one-stage process, this process is implements a high efficient technology joint of producing direct reduced iron and gas fuel from coal for subsequent making electrical and thermal energy.
Continuous arc furnace (EAF) is a metallurgical device for the implementation of the ORIEN process. iron ore in the concentrate form of or powdered ore, powdered coal and gas oxygen are initial source of process.
The base of ORIEN technology is combined of the following processes:
1) iron oxides reduction, which fed into the melt iron-carbon bath by dissolved in the iron carbon and in atom-dispersed condition. The oxides transition from the solid to the melt state is caused the liquid-phase nature of the iron reduction in the iron-carbon smelt. Specific rate of recovery is estimated by values ??of more than 5 kg / (m і. C), that is higher than in blast furnaces and shaft furnaces.
2) generation of a gas fuel from the iron with coal which fed into the bath and react with the molten iron oxides from iron ore, and liquid iron oxides which formed during the supply of oxygen gas into the iron-carbon melt.
A distinctive feature of the proposed technology ORIEN is the opportunity non-coking coal and agglomerate iron ore in deficiency products with high added value.
The ORIEN process is able to solve the problem of pyrometallurgical enrichment of natural alloyed ore with contained oxides of chromium, titanium, vanadium and manganese. Which are not using now.
The physical modeling ORIEN process is very complicated, using of the theory of similarity to the multi-scale metallurgical device is unacceptably. The computer simulation method is the only possible research way for design of implementing ORIEN process pilot unit (3 ton EAF is providing cogenerators functioning with total capacity of 6 MW).
1. The physical model
CPD for the hybrid process of simultaneous production direct reduced iron and carbon gasification, on Fig.1 shown housing, where metal and slag baths are induce, three graphite electrodes, three bottom tuyeres for supplying charge (iron ore concentrate) and three bottom tuyeres for supplying powdery coal. Powdery coal fed in greater value than is necessary for the reduction iron reaction from iron ore concentrate. Three tuyeres are oriented for supplying oxygen in the iron-carbon melt.
Producing process of fluid iron direct reduction (in the form of iron-carbon melt) continuous with the cyclic release of molten metal and slag.
During melting iron ore and powder coal is continuous fed through the bottom tuyeres. Iron ore and coal has less dense than the molten iron, they are moved to the surface of the metal bath and create convective flow of the melt. Carbon dissolves in the melt rapidly. Flow mixing melt, that ensure the distribution of iron oxide and carbon by volume metal bath and the possibility of reaction between them. During reducing iron oxides released a considerable amount of carbon monoxide, which together with the impact of the jets of oxygen enhances convective flow and stirring the melt.
Levels of the metal and slag bath rised during supply of iron ore and powdery coal. In the hybrid process, the position of the graphite electrodes is controlled maintaining a constant length (voltage) electrical arcs.
computer model process orien
Fig.1. Structure of arc melting furnace of a energy - metallurgical complex: 1 - a furnace housing, 2 - electrodes 3 - tuyere for supplying iron ore; 4 - tuyere for feeding powdery coal, 5 - drain taphole DRI 6 - slag drain taphole, 7 - oxygen tuyere
2. Statement of the problem
The main goal of physical-mathematical modeling a hybrid process simultaneous production of direct reduced iron and carbon gasification in the EAF is determination of optimal conditions for management this process.
The criteria for assessing the process quality is the thermodynamic state of the material in the CPD, their chemical composition and stability of the mass flow generated carbon monoxide in the EAF.
The thermodynamic state is changing constantly due to the evolution of heat by electric arcs and chemical reactions. The chemical composition is unstable as a result of reactions and fed of reagent in the EAF. The process can be determine as functions of distribution in the furnace and the time variation of the enthalpy and concentration of the main chemical elements involved in the process.
In the DSP energy-metallurgical complex occur phenomena, different in physical nature. These processes are separated in space simulation, which is divided into several areas: carbon electrodes, electric arcs, iron oxide, carbon powder, molten slag, molten metal, the furnace lining.
General process for all areas is a thermodynamic process of change enthalpy, temperature and state of matter under the influence of arc discharges, chemical reactions and heat transfer.
Concentrations material (Chemical composition) in the metal and slag baths change during material and melting during chemical reactions.
Physical-mathematical modeling of ORIEN process is the solving of system of differential equations of energy and mass transfer, the initial and boundary conditions which take into account the design of DSP and external influences on the process. The energy equation should take into account the effects of convective and conductive heat transfer between the arcs, the metal bath and the walls of the furnace. Mass transfer equation should describe the concentration distribution of the chemical elements that enter into the metal and slag bath.
3. Modeling space and the coordinate system
Arc furnace is similar in shape to the body of rotation, which determines the use of a cylindrical coordinate system: radial distance from the axis of symmetry r, - degree of rotation relative to the plane of the electrode axis and the distance from the hearth furnace z. Taking into account the axial symmetry of the third order, it is possible to limit the modeling process only one sixth of the volume of the furnace.
Modeling space is divided into areas, material properties and processes in each of which describes a special system of equations. We can select the following areas: E - area carbon electrodes; D - region of electric arcs; R - region of the molten slag; M - area of the molten metal; F - area of furnace lining; G - area of the gaseous medium.
Modeling space is represented as a quantity points with coordinates r, , z. Affiliation point with coordinates r, , z to the region, such as molten metal M is denoted by r, , z M.
The surface between the regions are defined as the intersection of sets, such as the surface of the metal denotes the slag, and the dividing line between the surfaces as a triple intersection of sets, such as the line of contact between the surface of the molten slag R and M-lined furnace F is designated as . This way of describing the structure of space makes it easy to describe the change in the size and location of specific areas within the furnace as a change of belonging fixed points in space specified sets.
4. The model of the thermodynamic state and heat transfer
In all these areas flows unsteady flows thermodynamic process, which is described by the change of enthalpy H (t) of the set of points in space in time t. Unsteady linear heat equation in cylindrical coordinates r, , z is given in [1]
, (1)
where T - temperature space points; - thermal conductivity of the medium, depending on the location coordinates of a point in space, the type of substance and the temperature at this point; - the velocity of the substance in the direction of the coordinates; - the specific values of the absorption capacity and heat release at a given point. The enthalpy and temperature in this nonlinear equation related by functions T (H), which take into account the heat capacity and heat of phase transformation and aggregate material in each of the selected areas of the space.
, (2)
The coefficient of thermal conductivity is different in different areas of the arc and is strongly temperature dependent. Formally, this is described by a nonlinear function.
, (3)
The initial conditions for the solving of the heat equation take into account the state of material at the beginning of melting. It is assumed that all points in space at the initial time are the same temperature
, (4)
Boundary conditions describe heat transfer furnace with environment. It is assumed that the outer surface of the liner is heat , which creates a temperature gradient in the lining
, (5)
where b - coefficient of heat; - coefficient the thermal conductivity of the lining. Process is not modeled in the entire volume of the furnace, there are two fictitious boundary plane and - the plane of symmetry and for which the boundary conditions are as well as the center line , for which .
5. The movement of the melt
In the liquid metal (area M) is a pressure arising from a supply through the bottom tuyeres Fe2O3, C and isolating CO formed during gasification of coal, and the lower density of these substances compared with the melt. Further, the oxygen jet creates pressure on the surface of the metal bath.
The total pressure of the above factors causes the melt movement, Fig.2.
Fig. 2. Scheme of melt movement due to the action of the gravitational pressure of the liquid due to the difference in density of iron by direct reduction of iron oxide - Fe2O, powdered coal - C, carbon monoxide - CO and the molten metal - M
The fluid flow is described by the Navier - Stokes equations, which in the cylindrical coordinate system is given by [1]:
, (6)
where - the components of the velocity of flow in the direction of the coordinates; - melt density; p - the pressure at a given point; - dynamic viscosity. The pressure distribution in the melt is determined by solving the equation of continuity
, (7)
where E - modulus of elasticity; - the gravitational pressure.
Products of the chemical reactions that accumulate in the slag, create gravitational pressure, defined height of the liquid column and the distribution of melt density
, (8)
where - the level of the melt in the furnace.
Melt density , comprising iron oxides, C and CO, calculated on the concentration of these components in the melt
, (9)
where - respectively, the density of the molten iron, iron oxide, C and CO.
The initial conditions for the solution of the Navier-Stokes
. (10)
Boundary conditions. On the surfaces of contact with the molten metal charge-lined and made with no-slip condition
. (11)
On the surface of contact of the melt with the gas environment and the area of the arc adopted the free boundary for the melt, taking into account the component of the pressure jets of oxygen
(12)
Submission of materials in the area are taken into account by specifying the bottom tuyere with diameters of holes lances melt speeds equal to the value
(13)
where G - mass flow rate of the feed material, kg / s; - density material.
Having a continuous stream of material is a continuous growth in the melt and the slag, calculated
. (14)
Determines the current volume level of the melt in the furnace
. (15)
6. Specific capacity heat release and absorption of heat
In different areas of space simulation flow different physical processes responsible for the heat release and absorption of heat. The main source of heat is an electric arc and gasification reaction of coal. Cold feed materials (iron ore and powder coal) is considered as the heat sink.
Of great importance is the heat of endothermic chemical reactions, the main is the reduction reaction of iron oxide with carbon of iron.
The electric arc. The peculiarity of electric arcs in metallurgical furnaces is their relative short length in relation to the diameter of the electrode and the arc torch. Therefore permissible to assume that the entire arc power is allocated evenly in a circle whose radius is slightly greater than the radius of the electrode :
(16)
where - the current and arc voltage; - the potential gradient in the arc column, burning in a metal vapor.
The heat of oxidation of carbon and iron. Is fed into the furnace limited amount of oxygen which oxidises excess carbon and iron in the bulk and subsurface metal bath.
It is assumed that all oxygen supplied through the lance, is distributed over the surface RG completely consumed by oxidation of carbon and iron. The resulting carbon monoxide is removed from the melt and the molten iron oxide flows distributed over its volume and is involved in the reduction reaction of iron with carbon. The specific heat capacity of the downstream oxygen QO2.
(17)
where q = qc + qFe; qc, qFe - heat reaction oxidation, respectively, carbon and iron.
Consumption of heat for heating the incoming materials automatically taken into account in the solving of the heat equation speed terms of heat transfer and boundary conditions of the Navier-Stokes equations that define the velocity of the material through the bottom tuyeres.
Fuel heat entrained exhaust gases is determined by their quantity and enthalpy at the melt surface.
Heat loss through the lining taken into account in the decision of the heat equation, the boundary conditions which take into account the heat transfer from the outer surface of the particle board.
Intensity endothermic chemical reactions. The main heat sink is a reduction reaction of iron oxide with the release of carbon monoxide. The reaction proceeds in the amount of metal M bath. The reaction is determined by the concentrations of iron oxide and carbon at the point of the metal bath.
In implementing the process ORIEN acceptable to assume that the intensity of the absorption of heat by the concentration of elements in the melt. Specific Absorption heat of chemical reaction is defined as
, (17)
where m - the distribution of the reactant concentration, kg/m3; Q - the energy of a chemical reaction, J / kg.
7. Concentration distribution of elements in the slag and metal baths
The concentration of elements in the melt changes during melting component and charge transfer elements in the melt of metal charge, chemical interaction of the elements in the melt and move the reaction products flow. The change in concentration Ci i-th element of the melt is described by the transport equation
, (18)
where Di - diffusion coefficient of the i-th element in the liquid iron; - the speed of the melt determined from the solutions of the Navier - Stokes equations.
The boundary conditions of the transport equation:
On the surfaces of contact with the walls of the melt particle board and medium gas is used the condition of impermeability of these surfaces for the liquid components of the
; (19)
The gaseous components of the melt at the contact surface of the melt and the gas medium used condition complete removal of gas from the melt
; (20)
on output of bottom tuyeres set flows Fe2O3 and C
. (21)
The initial conditions at the start of the cycle (after draining of the metal and slag) decided that no particle board unreacted Fe2O3 and C
(22)
8. Algorithm for the numerical simulation
The system of equations of heat transfer, melt movement and concentration distribution is a self-consistent physical-mathematical model of the process of producing liquid DRI into the EAF. The input data are:
Dimensions of EAF and the elements of its design;
Thermodynamic and physico-chemical properties of materials;
The parameters of hybrid process.
During the simulation are determined by the current distribution in the volume of melt intensity of heat release, enthalpy and temperature, melt flow rate and concentration of substances. The intensity distribution of heat release is determined by the location and distribution of electric arcs concentration of substances chemically react. The concentration distribution depends on the position of the tuyeres for supplying substances and on the velocity distribution of the melt. Distribution of velocities of the melt determined by the distribution of the gravitational pressure which depends on the density distribution of the melt. The density distribution is determined by the distributions of the temperature and chemical reaction products, primarily carbon monoxide with a density much lower than the density of the melt. Distribution enthalpy and temperature depends on the intensity distribution of heat and velocity distribution of the melt [2-5].
The algorithm for the numerical simulation is shown in Fig.3.
9. Preliminary results of a computer simulation
The simulation results are presented in terms of the current distribution of the melt: the intensity of the volume of heat, enthalpy and temperature of the melt density, gravitational pressure, speeds the flow in the direction of each of the coordinates, the concentration of each substance.
Figures 4 to 7 show some preliminary results of the calculation of the parameters of the process ORIEN.
|
Input initial data: the size of the furnace and the elements; parameters of the process of smelting. |
||
|
Status of the furnace at the start of heat cycles: Distribution enthalpy H (r, , z) and the temperature T (r, , z). With the concentration of substances C (r, , z). |
||
|
Melting time t= t + dt |
||
|
Calculation of intensity chemical reactions and determination of the concentration of substancesС (r, , z). |
||
|
Determination of the melt density (r, , z) and gravitation pressure р (r, , z) |
||
|
Solving of the Navier-Stokes equations and the determination of the velocity distribution of the melt нr (r, , z), н (r, , z), нz (r, , z),. |
||
|
Calculation of the intensity distribution heat emission in the melt q (r, , z). |
||
|
Solving of the heat distribution equation and determining the enthalpy Н (r, , z) and temperature Т (r, , z). |
||
|
Determining the current value Z (t) of the melt in the furnace. |
||
|
Calculation of the current value integral characteristics of the of smelting process |
||
|
Output current simulation resultsС (r, , z), нr (r, , z), н (r, , z), нz (r, , z), Т (r, , z). |
||
|
Till melting level doesn't reaches a predetermined level Z (t) <Z0. |
||
|
Calculation of integral rate melting cycles. |
||
|
Integral indicators melting. |
Fig.3. Algorithm for numerical simulation of the hybrid process of obtaining liquid iron by direct reduction and carbon gasification in the EAF
Figure 4. The pressure distribution in the melt surface (a) and bottom (b) layers of melt
The pressure distribution on the surface of the melt 4a, determined by the arrangement of tuyeres for supplying oxygen. In the bottom zone 4b, the primary pressure source is a stream of carbon powder and iron oxide.
The difference in pressure creates a flow of melt, Fig.5.
Figure 5. Distribution components melt flow rate (a - Vx; б - Vy; в - Vz) in orthogonal coordinates in the average cross-sectional
Amount of components in the direction orthogonal coordinates in the plane of the cross section is the rotational motion of the melt caused by the oxygen jets fed tangentially to the surface of the melt, fig.5a. Feed of carbon powder and iron oxide causes the melt in the form of three vertical vortices .
The movement of the melt causes the carbon and iron oxide in the melt distribution and determines their concentration Cc CFeO, Fig.6.
Figure 6. The distribution of carbon concentration Cc, oksid iron CFeO and emission rates of carbon monoxide in the middle section of the EAF.
The concentration of carbon and iron oxide rapidly decreases with distance from the bottom of feed lances. The interaction of these substances causes the release of carbon monoxide, which is most intense in areas equidistant from the bottom tuyeres.
Absorption heat reduction reaction of iron with carbon offset and carbon oxidation heat generated by electric arcs. These sources and heat sinks are in different zones of the melt, which leads to uneven temperature distribution Fig.7.
Figure 7. The temperature distribution in the cross sections at the surface of the molten EAF (a) and bottom (b).
Electric arcs and carbon oxidation heat the surface region,temperature of the surface layers above, Fig.7а. In the bottom layers of the incoming cold carbon and iron oxide, the reaction of between which absorbs heat, which reduces the temperature of the melt, ris.7b.
Heat transfer is occurring only on melt stream temperature which equalize line by volume.
Results
1. For analyze efficiency of the hybrid process simultaneous production of liquid iron direct reduction and carbon gasification in DSP energy-metallurgical complex, a mathematical continuous physical-chemical model, which is designed as a system of heat equations, Navier - Stokes and mass transfer, respectively, the solution of which determines the thermodynamic state of the DSP, speed melt flow and the concentration distribution of charge material in the melt.
2. The model allows to determine the geometry of the elements of the CPD and the parameters of a hybrid process to ensure specified performance DSP energy-metallurgical complex for the direct reduction iron and carbon monoxide, intended for the subsequent generation of electric energy.
Conclusion
Preliminary results of a computer simulation of the ORIEN process showed that the developed physical-mathematical hybrid process model of obtaining a of liquid iron by direct reduction and carbon gasification in EAF energy-metallurgical complex solves the problem of optimizing the design elements of the EAF and technology of the process.
Obviously, the rate of chemical interaction with the powdered coal and coal with dissolved and oxygen gas depends on the constructive characteristics of the feeding systems of these materials in an oven mode of operation, as well as of the melt, the amount of oxygen supplied to the DSP power and electric arcs.
Optimal technology of the ORIEN process can be ensure by choosing a program to provide feed material in particle board, chipboard and construction of power change electrical arcs in the course of the process.
References
1. Tikhonov A.N., Samarskii A.A. The equations of mathematical physics. - Moscow: Nauka, 1972. - 735 c.
2. Tikhonov A.N. Mathematical modeling of technological processes and the method of inverse problems in engineering / A.N. Tikhonov, V.D. Calco, V.B. Glasko. - M.: Mechanical Engineering, 1990. - 264 p.
3. Belashchenko D. K.computer simulation of liquid and amorphous materials / D. K. Belashchenko. - Moscow: MISIS, 2005. - 408 p.
4. Ryabov A.V. Current methods of steelmaking in electric arc furnaces / A.V. Ryabov, I.V. Chumanov, M.V. Shishimirov - M: Teplotekhnik, 2007. - 192 p.
5. Modelling, Optimization and Control of an Electric Arc Furnace / Richard MacRosty. - Hamilton: McMaster University, 2005. - 160 p.
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