CN102866240A - Online soft measurement method of magnetite oxygenation efficiency distribution in grate pellet material layer - Google Patents

Abstract

The invention provides an online soft measurement method of magnetite oxygenation efficiency distribution in a grate material layer in a production process of an iron ore oxidized pellet. The online soft measurement method comprises the following steps of: dividing the pellet material layer on the grate into virtual elements to be calculated and analyzed; establishing a magnetite oxygenation efficiency distribution model in the pellet material layer according to an unreacted core model theory of a solid product layer and the phenomenon of heat transfer and mass transfer in the grate pellet production process by taking the green-ball magnetite content, the green-ball radius, the material layer temperature and the gas temperature as instrumental variables; and by considering the time sequence of parameters, calculating the material layer oxygenation efficiency in each calculating element on the grate. The method is applied to the production of the grate-rotary kiln iron ore oxidized pellet and capable of realizing the online detection of the oxygenation efficiency distribution in the grate material layer.

Description

Online soft measurement method for magnetite oxidation rate distribution of pellet material layer of chain grate

Technical Field

The invention relates to an online soft measurement method for magnetite oxidation rate distribution of a pellet material layer of a chain grate.

Background

In recent years, the steel industry in China is rapidly developed, the yield of crude steel reaches 6.27 hundred million tons in 2010, the yield of blast furnace iron reaches 5.90 hundred million tons, and the first rank is in the world. The requirements of large-scale and modernization of blast furnaces on furnace materials are higher and higher, and the reasonable furnace material structure of the blast furnace is more and more emphasized.

The iron ore oxidized pellet meets the requirement of reasonable furnace charge of the blast furnace, is suitable for the characteristics of iron ore resources in China, is beneficial to energy conservation and emission reduction compared with a sintering process, has attracted increasing attention, and is gradually developed. As an important production method of the iron ore oxidized pellets, the grate-rotary kiln process is suitable for the development of the iron ore oxidized pellets in China and has a leading position on the yield.

The ferrous oxide content (the pellet production raw materials generally contain magnetite, and the magnetite oxidation, namely the reduction of the ferrous content of the pellets) is an important quality index of the iron ore oxidized pellet and has important influence on blast furnace smelting. Generally, the coke ratio can be reduced by 8-9% when the reduction degree of the raw materials fed into the furnace is improved by 10%; the coke ratio is reduced by 1% when the content of the ferrous oxide is reduced by 1%. According to the regulation of GB 50491-2009, the FeO content of the finished pellet ore is less than or equal to 1.0%.

In the grate-rotary kiln production process, the oxidation process of the pelletized magnetite obviously occurs in the preheating section of the grate. Both theoretical studies and production practices demonstrate the necessity to ensure the oxidation rate of the preheated pellets on the grate. First, the oxidation of magnetite to hematite is an exothermic reactionThe sufficient oxidation reaction can ensure that the preheating ball obtains sufficient heat under the condition of lower fuel consumption, and has sufficient mechanical strength to meet the requirements of the rotary kiln production process; secondly, if the magnetite in the preheating section is not sufficiently oxidized, the magnetite will remain in the center of the pellet, and when the pellet enters a high-temperature roasting zone, the magnetite will be mixed with gangue SiO₂Reacting to generate a low-melting-point compound, wherein a liquid slag phase appears in the pellet, and the compound shrinks when being cooled, so that concentric cracks appear in the pellet, the strength of the pellet is influenced, and the reducibility of the pellet is deteriorated; in addition, the preheated balls with poor mechanical strength and low oxidation rate are easy to wear and break when entering the rotary kiln, and accidents such as ring formation of the rotary kiln and the like can be caused by a liquid phase generated by FeO in the dust. Thus the oxidation rate of the preheated pellet magnetite on the grate has an important influence on pellet production.

At present, regular sampling inspection is generally carried out on the FeO content of finished pellets in pellet production, but online detection of oxidation conditions of the pellets in the preheating process on a chain grate has not been realized due to the difficult sampling of a closed system of the chain grate and a rotary kiln, poor sampling representativeness caused by the uneven distribution of the oxidation rate in a material layer and the like.

Therefore, the technology capable of detecting the magnetite oxidation rate distribution of the grate material layer in the production process of the iron ore oxidized pellets on line is developed, and the technology has very important significance for the production of the grate-rotary kiln iron ore oxidized pellets.

Disclosure of Invention

The invention aims to solve the technical problem of providing an online soft measurement method for magnetite oxidation rate distribution of a grate pellet layer, which can quickly detect the magnetite oxidation rate distribution of the grate pellet layer in the pellet production process.

The technical solution of the invention is as follows:

an online soft measurement method for magnetite oxidation rate distribution of a grate pellet material layer comprises the following steps:

step 1: grid division:

the pelletizing material layer on the chain grate is divided into a size range L₁×L₂×L₃Wherein L is a virtual computing element of₁Is 0.1-1% of the effective length of the chain grate, and the unit is cm; l is₂The width of the pellet material layer is in cm; l is₃The real-time material layer height is 5% -10%, and the unit is cm;

step 2: obtaining the value of the auxiliary variable:

the auxiliary variables comprise the content of the green ball magnetite, the green ball radius, the material layer temperature and the gas temperature;

and step 3: model establishment and solution: and establishing a magnetite oxidation rate calculation model equation of the pellet bed according to an unreacted nuclear model theory with a solid product layer, and solving the magnetite oxidation rate of the pellet bed in each computational infinitesimal.

In the step 2, the acquisition modes of the 4 auxiliary variables are respectively as follows:

1) content of green-ball magnetite

The green magnetite content was calculated from the following equation:

$p=\frac{\mathrm{\Σ}{m}_i{p}_i(1-w_i)}{232(m_{\mathrm{greenpellet}}+m_{\mathrm{return}})}$ equation 1

Wherein, p is the content of the spheromagnetic iron ore, and the unit is mol/g spheronization; m is_iThe unit is the blanking amount of the ith raw material in unit time, and the unit is t/h; p is a radical of_iThe content of FeO in the ith raw material is in percentage by mass; w is a_iThe water content of the ith raw material is; 232 is the molar weight of magnetite and the unit is g/mol; m is_greenpelletThe pelletizing quantity is t/h; m is_returnReturning amount of green pellets, t/h. Collection m_i、p_i、w_i、m_greenpelletAnd m_returnTiming is considered when data is presented.

[ raw material moisture and chemical composition test, and storage time in raw material ore tank is t₁Hours; the sum of the time from burdening, mixing, pelletizing to green ball belt transfer is t₂Hours; mixing duration of t₃Hours; the storage time of the mixture ore tank is t₄Hours; a pelletizing time of t₅Hours; the belt transfer time from the metering point of the green ball and returning material belt weigher to the material distribution process is t₆Hours; the grate speed was v m/h. For the infinitesimal at L meters from the inlet end of the chain grate, the raw material blanking amount m is calculated when the content of the pellet green magnetite in the infinitesimal is calculated_iIs ((L/v) + t)₆+t₅+t₄+t₃+t₂) Detection data before hours; FeO content p of the raw material_iAnd raw material water content w_iIs ((L/v) + t)₆+t₅+t₄+t₃+t₂+t₁) Detection data before hours; raw ball amount m_greenpelletAnd raw ball return amount m_returnIs ((L/v) + t)₆) And (5) detecting data before hours. "C (B)

2) Radius of green ball

Carrying out timing sampling detection on the radius of the green ball to obtain the radius r of the green ball₀In cm.

3) Temperature of material bed

The temperature T of the pellet material layer in each calculated infinitesimal is calculated by utilizing the following solid phase heat balance equation_s：

${\mathrm{\ρ}}_s(1-{\mathrm{\ϵ}}_2)C_s\frac{T_s(x_m,t_n)-T_s(x_m,t_{n-1})}{t_n-t_{n-1}}=\mathrm{hA}[T_g(x_m,t_{n-1})-T_s(x_m,t_{n-1})]-q_1(x_m,t_{n-1})+Q_1(x_m,t_{n-1})$

Equation 2

Where ρ is_sIs the density of the ore and has the unit of g/cm³；ε₂The porosity of the pellet material layer is the proportion of the bulk stacking volume of the pellets on the chain grate in unit of% [ the porosity of the pellet material layer ] to the total volume, and the porosity of the pellet material layer is designed to be a certain value according to the flow in a specific production process and can be obtained through a formula

Performing a calculation in which p_tAnd ρ_bThe pellet true density and bulk density are respectively. H ]; c_sThe specific heat of the pellets is J/g.K; x is the height of the material layer and the unit is cm; t is time in units of s; m and n are the height of material layer and the grid position in the length direction of the chain grate, m is measured from the gas feeding layer end to the discharging layer end, and n is measured from the chain grateThe machine material distribution end is counted towards the material discharge end; t is_sCalculating the temperature of a pellet material layer in the infinitesimal, wherein the unit is K, and taking the room temperature as an initial value; t is_gIn order to calculate the temperature of gas in the infinitesimal, the unit is K, and the initial value is the temperature of the gas before entering the pellet material layer; h is the heat transfer coefficient between gas and pellets, and the unit is J/cm²K.s; a is the heat transfer area of the pellet material layer in unit volume and the unit is cm²/cm³A = 1/infinitesimal height; q. q.s₁The heat absorption rate of water evaporation is expressed in J/s.cm³Taking 0 as an initial value; q₁The heat release of the magnetite reaction is expressed in J/cm³S, the initial value is 0;

in the formula 2, the first and second groups of the compound,

(1) specific heat of pellet C_sCalculating according to a fitting formula of laboratory detection data at different temperatures:

$C_s=\left\{\begin{array}{cc}0.1605+1.5000\&times;{10}^{-4}[T_s(x_m,t_{n-1})-273]& T_s<973K\\ 0.2140& T_s\&GreaterEqual;973K\end{array}\right.$ equation 3

(2) The heat transfer coefficient h between the gas and the pellets is calculated according to the following formula:

h=Nu·K_a/(2·r₀) Equation 4

Wherein Nu is Nusselt number and is dimensionless; k_aIs the gas thermal conductivity coefficient, with the unit of J/cm.K.s;

K_aand Nu are respectively:

K_a=16.6670×[1.7187×10^-6+7.3645×10^-9T_g(x_m,t_n-1)]equation 5

Nu=2.0+0.6P_r ^1/3R_e ^1/2Equation 6

Wherein, P_rIs the Prandtl number and is the Prandtl number,

μ is gas viscosity [ calculated μ =16.67 × (5.28 × 10) from laboratory test data fitting equation at different temperatures^-6+1.82×10^-8×T_g)】，g/cm.s；C_gThe specific heat of the gas is expressed in J/g.K, and the calculation formula is as follows:

C_g＝1.0868×10^-7[T_g(x_m-1,t_n)-273]²-0.5097×10^-10[T_g(x_m-1,t_n)-273]³equation 7

-1.7065×10^-5[T_g(x_m-1,t_n)-273]+0.2452

(3) Reaction exotherm Q of magnetite₁Calculated according to the following formula:

Q₁(x_m,t_n)=ΔHr_mag(x_m,t_n-1) N equation 8

Wherein, Delta H is the enthalpy change of the oxidation reaction of the magnetite and is 260 kJ/mol; n is the amount of pellets in unit volume and is 1/cm³，

r_magThe magnetite oxidation reaction rate is expressed in mol/s, and the initial value is 0;

【r_magsee formula 18

(4) Rate of water evaporation heat absorption q₁Calculated according to the following formula:

q₁(x_m,t_n)=hA[T_g(x_m,t_n)-T_s(x_m,t_n)]a(x_m,t_n) Equation 9

Wherein, a is a proportionality coefficient for water evaporation in the heat obtained by the material layer; [ a formula reference English

The research results of national R.W.Young, etc. are the prior art:

$a(x_m,t_n)=\left\{\begin{array}{cc}1-[373-T_s(x_m,t_{n-1})]/100& W_s(x,t)\&GreaterEqual;W_c,T_s(x,t)<373K\\ \{1-[3730-T_s(x_m,t_{n-1})]/100\}{W}_s(x_m,t_n)/W_c& W_s(x,t)<W_c\end{array}\right.$

equation 10

Wherein, W_cTaking 2.0% of pellets with critical value of water content; w_sThe water content of the pellets is the mass percent content, and the initial value is the water content of green pellets, and the unit is;

W_scalculated according to the following formula:

$\frac{W_s(x_m,t_n)-W_s(x_m,t_{n-1})}{t_n-t_{n-1}}=\frac{q_1(x_m,t_{n-1})}{{\mathrm{\&lambda;\&rho;}}_s(1-{\mathrm{\&epsiv;}}_2)}$ equation 11

Wherein, the lambda is the evaporation latent heat of water and takes 2260J/g. "C (B)

4) Temperature of gas

Calculating the gas temperature in each computational infinitesimal by using the following gas phase heat balance equationT_g：

$M_g{C}_g\frac{T_g(x_m,t_n)-T_g(x_{m-1},t_n)}{x_m-x_{m-1}}=\mathrm{hA}[T_s(x_{m-1},t_n)-T_g(x_{m-1},t_n)]+q_2(x_{m-1},t_n)$

Equation 12

Wherein M is_gIs the mass flow of gas, in g/cm²S; [ Mg is the mass of gas passing through a unit area per unit time, detected by a flowmeter ] q₂The heat release rate of moisture condensation is expressed in J/s.cm³Taking 0 as an initial value;

q₂calculated from the following formula:

q₂(x_m,t_n)=λM_g[W_g(x_m,t_n)-W_gs(x_m,t_n)]equation 13

Wherein, W_gThe water content of the gas is the mass percentage content, and the unit is; w_gsThe content is the mass percentage content of water in saturated air, and the unit is; lambda is latent heat of evaporation of water, and the value is 2260J/g;

W_gand W_gsThe calculation formulas are respectively as follows:

$\frac{W_g(x_m,t_n)-W_g(x_{m-1},t_n)}{x_m-x_{m-1}}=-\frac{q_1(x_{m-1},t_n)}{{\mathrm{\&lambda;M}}_g}$ equation 14

$W_{\mathrm{gs}}(x_m,t_n)=e^{-5.49269+0.0549269[T_g(x_{m-1},t_n)-273]}$ Equation 15

At the present moment (t)_n) Q of (a) to (b)₁（x_m,t_n) Is passed through the last time (t)_n-1) Q of (a) to (b)₁(x_m,t_n-1) Calculate W in turn_s（x_m,t_n）、a（x_m,t_n) And (4) obtaining the product.

Current height (x)_m) Q of (a) to (b)₂（x_m,t_n) Is through a height (x)_m-1) Q of (a) to (b)₁(x_m-1,t_n) Calculate W_g（x_m,t_n) And (4) obtaining the product.

The calculation order is given in the form of x and t subscripts, with the arrangement shown in FIG. 5.

The magnetite oxidation rate calculation model equation of the pellet material layer in the step 3 is as follows:

$\mathrm{\&chi;}(x_m,t_n)=1-{\left[\frac{r_m(x_m,t_n)}{r_0}\right]}^3$ equation 16

Wherein chi is the oxidation rate of magnetite in the pellet, and the unit is percent; r is₀The original radius of magnetite is in cm; r is_mThe radius of unreacted magnetite core is cm, and the initial value is the pellet radius r₀[ instruction: as the oxidation proceeds, the unreacted nuclei shrink, r_mIs a variation value) calculated by the following equation of reaction interface moving velocity:

$\frac{r_m(x_m,t_n)-r_m(x_m,t_{n-1})}{t_n-t_{n-1}}=-\frac{r_{\mathrm{mag}}(x_m,t_n)}{4p{r}_m{(x_m,t_{n-1})}^2{\mathrm{\&rho;}}_s(1-{\mathrm{\&epsiv;}}_1)\mathrm{\&pi;}}$ equation 17

Wherein epsilon₁The porosity is the porosity of the pellets, and the unit is% and is obtained according to the sampling and testing of the pellets; p is the green ball magnetite content in formula 1;

oxidation reaction rate r of magnetite_magThe calculation formula is as follows:

$r_{\mathrm{mag}}(x_m,t_n)=\frac{16\mathrm{\&pi;}{\mathrm{<figure-callout\; id="0"\; label="r"\; filenames="HDA00002149139100021.png"\; state="\{\{state\}\}">r</figure-callout>}}_0^2{\mathrm{<figure-callout\; id="2"\; label="C\; O"\; filenames="HDA00002149139100022.png"\; state="\{\{state\}\}">C</figure-callout>}}_{O_{}}}{\frac{1}{k_{g\left(O_2\right)}}+\frac{1}{k_r}{\left[\frac{r_0}{r_m(x_m,t_{n-1})}\right]}^2+\frac{r_0}{D_{O_2}}[\frac{r_0}{r_m(x_m,t_{n-1})}-1]}$ equation 18

Wherein,

is O in the gas phase₂Concentration in mol/cm³Taking the oxygen concentration of air as Is O in the gas phase₂The mass transfer coefficient passing through the gas boundary layer is in cm/s; k is a radical of_rThe magnetite chemical reaction speed is expressed in cm/s;

is O in the pellet₂Effective diffusion coefficient in cm through the product layer²/s；

k_rAnd

the calculation formulas are respectively as follows:

$k_{g\left(O_2\right)}=\frac{\mathrm{Sh}\&CenterDot;D}{2{\mathrm{<figure-callout\; id="0"\; label="r"\; filenames="HDA00002149139100021.png"\; state="\{\{state\}\}">r</figure-callout>}}_0}$ equation 19

$k_r=3000\&times;e^{-6000/T_s(x_m,t_{n-1})}$ Equation 20

${\mathrm{<figure-callout\; id="2"\; label="D\; O"\; filenames="HDA00002149139100022.png"\; state="\{\{state\}\}">D</figure-callout>}}_{O_{}}=\frac{D{\mathrm{\&epsiv;}}_1}{\mathrm{\&tau;}}$ Equation 21

Wherein Sh is Sherwood number, dimensionless; d is O₂Diffusion coefficient in gas in cm²S; tau is a pitch factor, is dimensionless, and is taken as 5 according to the production condition of the oxidized pellets of the chain grate;

(1) sherwood number Sh is calculated according to the research of Ranz and Marshall, and belongs to the prior art:

Sh=2.0+0.6Re^1/2Sc^1/3equation 22

Wherein Re is the number of Reynolds,

the Sc is the number of Schmidt,

rho is the fluid density in g/cm³(ii) a v is the relative speed between the pellet and the gas, and the unit is cm/s; l is the characteristic linear dimension in units of cm [ the diameter of the ball is 1.3cm ]; other symbols have the same meanings as above, mu is the gas viscosity, and mu is described in the above formula 6;

（2）O₂the diffusion coefficient D in the gas is calculated according to the following formula:

D=9.71×10^-6T_g(x_m-1,t_n)^1.75equation 23

It should be noted that according to the difference of the hot air flow direction, the calculation sequence of the blast drying section infinitesimal elements is from bottom to top, and the air draft drying section, the preheating section I and the preheating section II are all from top to bottom.

Has the advantages that:

the online soft measurement method for the magnetite oxidation rate distribution of the pellet bed of the chain grate has the following characteristics:

(1) fast speed

The content of the preheated pellet ferrous oxide affects the strength of the pellet and the production condition of the rotary kiln, but the chain grate is a relatively closed system, the oxidation rate of magnetite in a pellet bed of the chain grate cannot be detected in the current production, the content of the ferrous oxide is generally tested only by sampling finished pellets, and the oxidation condition of the preheated pellet magnetite is reflected indirectly and lags behind. According to the invention, soft measurement of the magnetite oxidation rate of the pellet bed on the grate is realized through the model, and calculation is carried out through computer software programming, so that the required time is short, the online production operation can be realized, and the real-time performance of the detection result is ensured.

(2) Rich information

The invention divides the pellet material layer of the chain grate into grids, and the infinitesimal height is close to the single-layer pellet height, so the model calculation result not only can reflect the progress of the magnetite oxidation reaction along the running direction of the chain grate, but also can reflect the difference of the proceeding of the pellet oxidation reaction of each layer in the material layer height direction.

(3) Increase the production efficiency

The method is used for detecting and controlling the magnetite oxidation process of the pellet layer of the chain grate, can optimize the production process of the chain grate, ensure the strength and the ferrous content of preheated pellets, reduce the concentric cracks of the pellets, the ring formation in a rotary kiln and the like, fully utilize the oxidation heat release of the magnetite, reduce the power consumption and the energy consumption and improve the production benefit.

Drawings

FIG. 1 is a schematic diagram of meshing;

FIG. 2 is a schematic diagram of a grate-rotary kiln-circular cooler pellet production system;

FIG. 3 is a visual display of the magnetite oxidation rate distribution on the grate bed;

FIG. 4 is a plot of average pellet oxidation rate along the traveling direction of the grate;

FIG. 5 is a schematic diagram of an intermediate variable loop calculation.

Detailed Description

The invention will be described in further detail below with reference to the following figures and specific examples:

an online soft measurement method for magnetite oxidation rate distribution of a grate pellet material layer comprises the following steps:

step 1: grid division:

the pelletizing material layer on the chain grate is divided into a size range L₁×L₂×L₃Wherein L is a virtual computing element of₁Is 0.1-1% of the effective length of the chain grate, and the unit is cm; l is₂The width of the pellet material layer is in cm; l is₃The real-time material layer height is 5% -10%, and the unit is cm;

step 2: obtaining the value of the auxiliary variable:

the auxiliary variables comprise the content of the green ball magnetite, the green ball radius, the material layer temperature and the gas temperature;

and step 3: model establishment and solution: and establishing a magnetite oxidation rate calculation model equation of the pellet bed according to an unreacted nuclear model theory with a solid product layer, and solving the magnetite oxidation rate of the pellet bed in each computational infinitesimal.

In the step 2, the acquisition modes of the 4 auxiliary variables are respectively as follows:

1) content of green-ball magnetite

The green magnetite content was calculated from the following equation:

$p=\frac{\mathrm{\&Sigma;}{m}_i{p}_i(1-w_i)}{232(m_{\mathrm{greenpellet}}+m_{\mathrm{return}})}$ equation 1

Wherein, p is the content of the spheromagnetic iron ore, and the unit is mol/g spheronization; m is_iThe unit is the blanking amount of the ith raw material in unit time, and the unit is t/h; p is a radical of_iThe content of FeO in the ith raw material is in percentage by mass; w is a_iThe water content of the ith raw material is; 232 is the molar weight of magnetite and the unit is g/mol; m is_greenpelletThe pelletizing quantity is t/h; m is_returnReturning amount of green pellets, t/h. Collection m_i、p_i、w_i、m_greenpelletAnd m_returnTiming is considered when data is presented.

[ raw material moisture and chemical composition test, and storage time in raw material ore tank is t₁Hours; the sum of the time from burdening, mixing, pelletizing to green ball belt transfer is t₂Hours; mixing duration of t₃Hours; the storage time of the mixture ore tank is t₄Hours; a pelletizing time of t₅Hours; the belt transfer time from the metering point of the green ball and returning material belt weigher to the material distribution process is t₆Hours; the grate speed was v m/h. For the infinitesimal at L meters from the inlet end of the chain grate, the raw material blanking amount m is calculated when the content of the pellet green magnetite in the infinitesimal is calculated_iIs ((L/v) + t)₆+t₅+t₄+t₃+t₂) Detection data before hours; FeO content p of the raw material_iAnd raw material water content w_iIs ((L/v) + t)₆+t₅+t₄+t₃+t₂+t₁) Detection data before hours; raw ball amount m_greenpelletAnd raw ball return amount m_rentrnIs ((L/v) + t)₆) And (5) detecting data before hours. "C (B)

2) Radius of green ball

Carrying out timing sampling detection on the radius of the green ball to obtain the radius r of the green ball₀In cm.

3) Temperature of material bed

The temperature T of the pellet material layer in each calculated infinitesimal is calculated by utilizing the following solid phase heat balance equation_s：

${\mathrm{\&rho;}}_s(1-{\mathrm{\&epsiv;}}_2)C_s\frac{T_s(x_m,t_n)-T_s(x_m,t_{n-1})}{t_n-t_{n-1}}=\mathrm{hA}[T_g(x_m,t_{n-1})-T_s(x_m,t_{n-1})]-q_1(x_m,t_{n-1})+Q_1(x_m,t_{n-1})$

Equation 2

Where ρ is_sIs the density of the ore and has the unit of g/cm³；ε₂The porosity of the pellet material layer is the proportion of the bulk stacking volume of the pellets on the chain grate in unit of% [ the porosity of the pellet material layer ] to the total volume, and the porosity of the pellet material layer is designed to be a certain value according to the flow in a specific production process and can be obtained through a formulaPerforming a calculation in which p_tAnd ρ_bThe pellet true density and bulk density are respectively. H ]; c_sThe specific heat of the pellets is J/g.K; x is the height of the material layer and the unit is cm; t is time in units of s; m and n are respectively the height of the material layer and the grid position in the length direction of the chain grate, m is measured from the gas feeding layer end to the discharging layer end, and n is measured from the distributing end to the discharging end of the chain grate; t is_sCalculating the temperature of a pellet material layer in the infinitesimal, wherein the unit is K, and taking the room temperature as an initial value; t is_gIn order to calculate the temperature of gas in the infinitesimal, the unit is K, and the initial value is the temperature of the gas before entering the pellet material layer; h is the heat transfer coefficient between gas and pellets, and the unit is J/cm²K.s; a is the heat transfer area of the pellet material layer in unit volume and the unit is cm²/cm³A = 1/infinitesimal height; q. q.s₁The heat absorption rate of water evaporation is expressed in J/s.cm³Taking 0 as an initial value; q₁The heat release of the magnetite reaction is expressed in J/cm³S, the initial value is 0;

in the formula 2, the first and second groups of the compound,

(1) specific heat of pellet C_sCalculating according to a fitting formula of laboratory detection data at different temperatures:

$C_s=\left\{\begin{array}{cc}0.1605+1.5000\&times;{10}^{-4}[T_s(x_m,t_{n-1})-273]& T_s<973K\\ 0.2140& T_s\&GreaterEqual;973K\end{array}\right.$ equation 3

(2) The heat transfer coefficient h between the gas and the pellets is calculated according to the following formula:

h=Nu·K_a/(2·r₀) Equation 4

Wherein Nu is Nusselt number and is dimensionless; k_aIs the gas thermal conductivity coefficient, with the unit of J/cm.K.s;

K_aand Nu are respectively:

K_a=16.6670×[1.7187×10^-6+7.3645×10^-9T_g(x_m,t_n-1)]equation 5

Nu=2.0+0.6P_r ^1/3Re^1/2Equation 6

Wherein, P_rIs the Prandtl number and is the Prandtl number,

μ is gas viscosity [ calculated μ =16.67 × (5.28 × 10) from laboratory test data fitting equation at different temperatures^-6+1.82×10^-8×T_g)】，g/cm.s；C_gThe specific heat of the gas is expressed in J/g.K, and the calculation formula is as follows:

C_g=1.0868×10^-7[T_g(x_m-1,t_n)-273]²-0.5097×10^-10[T_g(x_m-1,t_n)-273]³equation 7

-1.7065×10^-5[T_g(x_m-1,t_n)-273]+0.2452

(3) Reaction exotherm Q of magnetite₁Calculated according to the following formula:

Q₁(x_m,t_n)=ΔHr_mag(x_m,t_n-1) N equation 8

Wherein, Delta H is the enthalpy change of the oxidation reaction of the magnetite and is 260 kJ/mol; n is the amount of pellets in unit volume and is 1/cm³，

r_magThe magnetite oxidation reaction rate is expressed in mol/s, and the initial value is 0;

【r_magsee formula 18

(4) Rate of water evaporation heat absorption q₁Calculated according to the following formula:

q₁(x_m,t_n)=hA[T_g(x_m,t_n)-T_s(x_m,t_n)]a(x_m,t_n) Equation 9

Wherein, a is a proportionality coefficient for water evaporation in the heat obtained by the material layer; [ a formula reference English

The research results of national R.W.Young, etc. are the prior art:

$a(x_m,t_n)=\left\{\begin{array}{cc}1-[373-T_s(x_m,t_{n-1})]/100& W_s(x,t)\&GreaterEqual;W_c,T_s(x,t)<373K\\ \{1-[3730-T_s(x_m,t_{n-1})]/100\}{W}_s(x_m,t_n)/W_c& W_s(x,t)<W_c\end{array}\right.$

equation 10

Wherein, W_cTaking 2.0% of pellets with critical value of water content; w_sIs the mass percent of the water of the pelletsContent, the initial value is the water content of the green ball, and the unit is;

W_scalculated according to the following formula:

$\frac{W_s(x_m,t_n)-W_s(x_m,t_{n-1})}{t_n-t_{n-1}}=\frac{q_1(x_m,t_{n-1})}{{\mathrm{\&lambda;\&rho;}}_s(1-{\mathrm{\&epsiv;}}_2)}$ equation 11

Wherein, the lambda is the evaporation latent heat of water and takes 2260J/g. "C (B)

4) Temperature of gas

Calculating the gas temperature T in each computational infinitesimal by using the following gas phase heat balance equation_g：

$M_g{C}_g\frac{T_g(x_m,t_n)-T_g(x_{m-1},t_n)}{x_m-x_{m-1}}=\mathrm{hA}[T_s(x_{m-1},t_n)-T_g(x_{m-1},t_n)]+q_2(x_{m-1},t_n)$

Equation 12

Wherein M is_gIs the mass flow of gas, in g/cm²S; [ Mg is the mass of gas passing through a unit area per unit time, detected by a flowmeter ] q₂The heat release rate of moisture condensation is expressed in J/s.cm³Taking 0 as an initial value;

q₂calculated from the following formula:

q₂(x_m,t_n)=λM_g[W_g(x_m,t_n)-W_gs(x_m,t_n)]equation 13

Wherein, W_gThe water content of the gas is the mass percentage content, and the unit is; w_gsThe content is the mass percentage content of water in saturated air, and the unit is; lambda is latent heat of evaporation of water, and the value is 2260J/g;

W_gand W_gsThe calculation formulas are respectively as follows:

$\frac{W_g(x_m,t_n)-W_g(x_{m-1},t_n)}{x_m-x_{m-1}}=-\frac{q_1(x_{m-1},t_n)}{{\mathrm{\&lambda;M}}_g}$ equation 14

$W_{\mathrm{gs}}(x_m,t_n)=e^{-5.49269+0.0549269[T_g(x_{m-1},t_n)-273]}$ Equation 15

At the present moment (t)_n) Q of (a) to (b)₁（x_m,t_n) Is passed through the last time (t)_n-1) Q of (a) to (b)₁(x_m,t_n-1) Calculate W in turn_s（x_m,t_n）、a（x_m,t_n) And (4) obtaining the product.

Current height (x)_m) Q of (a) to (b)₂（x_m,t_n) Is through a height (x)_m-1) Q of (a) to (b)₁(x_m-1,t_n) Calculate W_g（x_m,t_n) And (4) obtaining the product.

The calculation order is given in the form of x and t subscripts, with the arrangement shown in FIG. 5.

The magnetite oxidation rate calculation model equation of the pellet material layer in the step 3 is as follows:

$\mathrm{\&chi;}(x_m,t_n)=1-{\left[\frac{r_m(x_m,t_n)}{r_0}\right]}^3$ equation 16

Wherein chi is the oxidation rate of magnetite in the pellet, and the unit is percent; r is₀The original radius of magnetite is in cm; r is_mThe radius of unreacted magnetite core is cm, and the initial value is the pellet radius r₀[ instruction: as the oxidation proceeds, the unreacted nuclei shrink, r_mIs a variation value) calculated by the following equation of reaction interface moving velocity:

$\frac{r_m(x_m,t_n)-r_m(x_m,t_{n-1})}{t_n-t_{n-1}}=-\frac{r_{\mathrm{mag}}(x_m,t_n)}{4p{r}_m{(x_m,t_{n-1})}^2{\mathrm{\&rho;}}_s(1-{\mathrm{\&epsiv;}}_1)\mathrm{\&pi;}}$ equation 17

Wherein epsilon₁The porosity is the porosity of the pellets, and the unit is% and is obtained according to the sampling and testing of the pellets; p is the green ball magnetite content in formula 1;

oxidation reaction rate r of magnetite_magThe calculation formula is as follows:

$r_{\mathrm{mag}}(x_m,t_n)=\frac{16\mathrm{\&pi;}{\mathrm{<figure-callout\; id="0"\; label="r"\; filenames="HDA00002149139100021.png"\; state="\{\{state\}\}">r</figure-callout>}}_0^2{\mathrm{<figure-callout\; id="2"\; label="C\; O"\; filenames="HDA00002149139100022.png"\; state="\{\{state\}\}">C</figure-callout>}}_{O_{}}}{\frac{1}{k_{g\left(O_2\right)}}+\frac{1}{k_r}{\left[\frac{r_0}{r_m(x_m,t_{n-1})}\right]}^2+\frac{r_0}{D_{O_2}}[\frac{r_0}{r_m(x_m,t_{n-1})}-1]}$ equation 18

Wherein,

is O in the gas phase₂Concentration in mol/cm³Taking the oxygen concentration of air as

Is O in the gas phase₂The mass transfer coefficient passing through the gas boundary layer is in cm/s; k is a radical of_rThe magnetite chemical reaction speed is expressed in cm/s;is O in the pellet₂Effective diffusion coefficient in cm through the product layer²/s；

k_rAnd

the calculation formulas are respectively as follows:

$k_{g\left(O_2\right)}=\frac{\mathrm{Sh}\&CenterDot;D}{2{\mathrm{<figure-callout\; id="0"\; label="r"\; filenames="HDA00002149139100021.png"\; state="\{\{state\}\}">r</figure-callout>}}_0}$ equation 19

$k_r=3000\&times;e^{-6000/T_s(x_m,t_{n-1})}$ Equation 20

${\mathrm{<figure-callout\; id="2"\; label="D\; O"\; filenames="HDA00002149139100022.png"\; state="\{\{state\}\}">D</figure-callout>}}_{O_{}}=\frac{D{\mathrm{\&epsiv;}}_1}{\mathrm{\&tau;}}$ Equation 21

Wherein Sh is Sherwood number and is dimensionless; d is O₂Diffusion coefficient in gas in cm²S; tau is a pitch factor, is dimensionless, and is taken as 5 according to the production condition of the oxidized pellets of the chain grate;

(1) sherwood number Sh is calculated according to the research of Ranz and Marshall, and belongs to the prior art:

Sh=2.0+0.6Re^1/2Sc^1/3equation 22

Wherein Re is the number of Reynolds,

the Sc is the number of Schmidt,

rho is the fluid density in g/cm³(ii) a v is the relative speed between the pellet and the gas, and the unit is cm/s; l is the characteristic linear dimension in units of cm [ the diameter of the ball is 1.3cm ]; other symbols have the same meanings as above, mu is the gas viscosity, and mu is described in the above formula 6;

（2）O₂the diffusion coefficient D in the gas is calculated according to the following formula:

D＝9.71×10^-6T_g(x_m-1,t_n)^1.75equation 23

It should be noted that according to the difference of the hot air flow direction, the calculation sequence of the blast drying section infinitesimal elements is from bottom to top, and the air draft drying section, the preheating section I and the preheating section II are all from top to bottom.

Example 1:

the specific embodiment of the present invention will be further explained by taking the online detection of magnetite oxidation rate distribution in the grate production process in the typical grate-rotary kiln iron ore oxidized pellet production process flow as an example, as shown in fig. 2, and combining with the attached drawings. This example is further illustrative of the invention and does not limit the scope of the invention.

The effective length of the chain grate studied in the example is 50m, the width is 4.5m, the height of the designed cloth is 0.2m, and the chain grate is divided into an air blowing drying section, an air draft drying section, a preheating I section and a preheating II section. The raw materials include hematite, magnetite, bentonite and fly ash.

The detection data of the material level instrument on the real-time material distribution height on the chain grate is 188mm, so that the material layer of the pellets on the chain grate is divided into virtual calculation infinitesimals with the size of 0.2m multiplied by 4.5m multiplied by 1.88cm, and the total number is 2500.

Considering time lag, the water contents of magnetite, hematite, bentonite and fly ash corresponding to the green ball at the inlet of the current chain grate are respectively 11%, 5.2%, 3.5% and 0.2%, the FeO contents are respectively 27.88%, 7.38%, 0.21% and 0.34%, and part of magnetite is dried before being mixed, and the water content after being dried is 6.1%. The real-time blanking amount of each raw material in the burdening process is detected on line by adopting an electronic belt scale, and the data of the same raw material are added and calculated to obtain the instant blanking amounts of the undried magnetite, the dried magnetite, the hematite, the bentonite and the dedusting ash corresponding to the green ball at the inlet of the current chain grate, which are respectively 161.13t/h, 132.06t/h, 127.03t/h, 6.55t/h and 11.52 t/h. The total amount of the green pellets and the green pellet return materials is 443 t/h. The content of the green ball magnetite is 0.002618mol/g-pellet through the formula calculation. The radius of the green ball is about 6.5mm, the inlet temperature of the green ball is 25 ℃, the porosity of the material layer is 0.4, the moisture of the green ball is 10.1 percent, the machine speed of the chain grate is 3.43m/min through online detection, the height of the material is 188mm, and the material layer feeding per unit area of the blowing drying section, the air draft drying section, the preheating I section and the preheating II section are carried outThe air volume of the hot air is 0.1144g/cm respectively².s、0.1430g/cm².s、0.0918g/cm²S and 0.1290g/cm²S, the hot air temperature of 17# and 16# wind boxes of the blast drying section is respectively 235 ℃ and 233 ℃, and the temperature of the fume hood of the exhaust drying section, the preheating I section and the preheating II section is respectively 294 ℃, 867 ℃ and 1067 ℃.

And substituting the data into a soft measurement model equation to calculate to obtain the oxidation rate of the magnetite in all the infinitesimal elements of the material layer of the chain grate. And performing corresponding conversion of the oxidation rate and bitmap RGB values through data-graph mapping, and visually displaying the oxidation rate distribution of each material layer of the chain grate as shown in figure 3. As can be seen from fig. 3, the magnetite in the pellets on the grate is significantly oxidized beginning at the preheating section, and since the hot air in the preheating section passes through the material layer from top to bottom, the pellets on the upper layer have a higher oxidation rate than those on the lower layer. And when the magnetite reaches the pellet outlet of the chain grate, the magnetite oxidation rate in the upper layer of pellets is 98.65 percent, the magnetite oxidation rate in the lower layer of pellets is 66.24 percent, and the magnetite oxidation rate is distributed along the height direction of the material layer to have certain difference. The average oxidation rate curve of the pellets along the running direction of the chain grate is drawn by taking the length of the chain grate as a horizontal coordinate and the average oxidation rate of the pellets of 10 layers in the material layer height direction on the same horizontal coordinate on the chain grate as a vertical coordinate, so as to reflect the oxidation condition of the pellet magnetite on the chain grate, as shown in figure 4. As can be seen from FIG. 4, the average oxidation rate of the preheated pellets at the exit of the grate pellets reached 85.27%.

Claims (3)

1. An online soft measurement method for magnetite oxidation rate distribution of a grate pellet material layer is characterized by comprising the following steps:

step 1: grid division:

the pelletizing material layer on the chain grate is divided into a size range L₁×L₂×L₃Wherein L is a virtual computing element of₁Is 0.1-1% of the effective length of the chain grate, and the unit is cm; l is₂The width of the pellet material layer is in cm; l is₃The real-time material layer height is 5% -10%, and the unit is cm;

step 2: obtaining the value of the auxiliary variable:

the auxiliary variables comprise the content of the green ball magnetite, the green ball radius, the material layer temperature and the gas temperature;

and step 3: model establishment and solution: and establishing a magnetite oxidation rate calculation model equation of the pellet bed according to an unreacted nuclear model theory with a solid product layer, and solving the magnetite oxidation rate of the pellet bed in each computational infinitesimal.

2. The on-line soft measurement method for magnetite oxidation rate distribution of a grate pelletizing material layer according to claim 1, characterized in that the acquisition modes of 4 auxiliary variables in step 2 are respectively:

1) content of green-ball magnetite

The green magnetite content was calculated from the following equation:

$p=\frac{\mathrm{\&Sigma;}{m}_i{p}_i(1-w_i)}{232(m_{\mathrm{greenpellet}}+m_{\mathrm{return}})}$ equation 1

Wherein, p is the content of the spheromagnetic iron ore, and the unit is mol/g spheronization; m is_iThe unit is the blanking amount of the ith raw material in unit time, and the unit is t/h; p is a radical of_iThe content of FeO in the ith raw material is in percentage by mass; w is a_iThe water content of the ith raw material is; 232 is the molar weight of magnetite inIs g/mol; m is_greenpelletThe pelletizing quantity is t/h; m is_returnReturning amount of green pellets, t/h. Collection m_i、p_i、w_i、m_greenpelletAnd m_returnTiming is considered when data is presented.

2) Radius of green ball

Carrying out timing sampling detection on the radius of the green ball to obtain the radius r of the green ball₀In cm.

3) Temperature of material bed

The temperature T of the pellet material layer in each calculated infinitesimal is calculated by utilizing the following solid phase heat balance equation_s：

${\mathrm{\&rho;}}_s(1-{\mathrm{\&epsiv;}}_2)C_s\frac{T_s(x_m,t_n)-T_s(x_m,t_{n-1})}{t_n-t_{n-1}}=\mathrm{hA}[T_g(x_m,t_{n-1})-T_s(x_m,t_{n-1})]-q_1(x_m,t_{n-1})+Q_1(x_m,t_{n-1})$

Equation 2

Where ρ is_sIs the density of the ore and has the unit of g/cm³；ε₂The porosity of the pellet layer is expressed in unit; c_sThe specific heat of the pellets is J/g.K; x is the height of the material layer and the unit is cm; t is time in units of s; m and n are respectively the height of the material layer and the grid position in the length direction of the chain grate, m is measured from the gas feeding layer end to the discharging layer end, and n is measured from the distributing end to the discharging end of the chain grate; t is_sFor calculating the temperature of the pellet material layer in the infinitesimal with the unit of K, an initial value is taken out of a chamberWarming; t is_gIn order to calculate the temperature of gas in the infinitesimal, the unit is K, and the initial value is the temperature of the gas before entering the pellet material layer; h is the heat transfer coefficient between gas and pellets, and the unit is J/cm²K.s; a is the heat transfer area of the pellet material layer in unit volume and the unit is cm²/cm³A = 1/infinitesimal height; q. q.s₁The heat absorption rate of water evaporation is expressed in J/s.cm³Taking 0 as an initial value; q₁The heat release of the magnetite reaction is expressed in J/cm³S, the initial value is 0;

in the formula 2, the first and second groups of the compound,

(1) specific heat of pellet C_sCalculating according to a fitting formula of laboratory detection data at different temperatures:

$C_s=\left\{\begin{array}{cc}0.1605+1.5000\&times;{10}^{-4}[T_s(x_m,t_{n-1})-273]& T_s<973K\\ 0.2140& T_s\&GreaterEqual;973K\end{array}\right.$ equation 3

(2) The heat transfer coefficient h between the gas and the pellets is calculated according to the following formula:

h=Nu·K_a/(2·r₀) Equation 4

Wherein Nu is Nusselt number and is dimensionless; k_aIs the gas thermal conductivity coefficient, with the unit of J/cm.K.s;

K_aand Nu are respectively:

K_a=16.6670×[1.7187×10^-6+7.3645×10^-9T_g(x_m,t_n-1)]equation 5

Nu=2.0+0.6P_r ^1/3Re^1/2Equation 6

Wherein, P_rIs the Prandtl number and is the Prandtl number,

μ is gas viscosity, g/cm. s; c_gThe specific heat of the gas is expressed in J/g.K, and the calculation formula is as follows:

C_g=1.0868×10^-7[T_g(x_m-1,t_n)-273]²-0.5097×10^-10[T_g(x_m-1,t_n)-273]³

equation 7

-1.7065×10^-5[T_g(x_m-1，t_n)-273]+0.2452

(3) Reaction exotherm Q of magnetite₁Calculated according to the following formula:

Q₁(x_m,t_n)＝ΔHr_mag(x_m,t_n-1)N equation 8

Wherein, Delta H is the enthalpy change of the oxidation reaction of the magnetite and is 260 kJ/mol; n is the amount of pellets in unit volume and is 1/cm³，

r_magThe magnetite oxidation reaction rate is expressed in mol/s, and the initial value is 0;

(4) rate of water evaporation heat absorption q₁Calculated according to the following formula:

q₁(x_m,t_n)=hA[T_g(x_m,t_n)-T_s(x_m,t_n)]a(x_m,t_n) Equation 9

Wherein, a is a proportionality coefficient for water evaporation in the heat obtained by the material layer;

4) temperature of gas

Calculating the gas temperature T in each computational infinitesimal by using the following gas phase heat balance equation_g：

$M_g{C}_g\frac{T_g(x_m,t_n)-T_g(x_{m-1},t_n)}{x_m-x_{m-1}}=\mathrm{hA}[T_s(x_{m-1},t_n)-T_g(x_{m-1},t_n)]+q_2(x_{m-1},t_n)$

Equation 10

Wherein M is_gIs the mass flow of gas, in g/cm².s；

q₂The heat release rate of moisture condensation is expressed in J/s.cm³Taking 0 as an initial value;

q₂calculated from the following formula:

q₂(x_m,t_n)=λM_g[W_g(x_m,t_n)-W_gs(x_m,t_n)]equation 11

Wherein, W_gThe water content of the gas is the mass percentage content, and the unit is; w_gsIs saturated water quality in airAmount percent content in units of%; lambda is latent heat of evaporation of water, and the value is 2260J/g;

W_gand W_gsThe calculation formulas are respectively as follows:

$\frac{W_g(x_m,t_n)-W_g(x_{m-1},t_n)}{x_m-x_{m-1}}=-\frac{q_1(x_{m-1},t_n)}{{\mathrm{\&lambda;M}}_g}$ equation 12

$W_{\mathrm{gs}}(x_m,t_n)=e^{-5.49269+0.0549269[T_g(x_{m-1},t_n)-273]}$ Equation 13

3. The on-line soft measurement method for magnetite oxidation rate distribution of the pellet bed of the drying grate as claimed in any one of claims 1-2, wherein the magnetite oxidation rate calculation model equation of the pellet bed in step 3 is:

$\mathrm{\&chi;}(x_m,t_n)=1-{\left[\frac{r_m(x_m,t_n)}{r_0}\right]}^3$ equation 14

Wherein chi is the oxidation rate of magnetite in the pellet, and the unit is percent; r is₀The original radius of magnetite is in cm; r is_mThe radius of unreacted magnetite core is cm, and the initial value is the pellet radius r₀[ instruction: as the oxidation proceeds, the unreacted nuclei shrink, r_mIs a variation value) calculated by the following equation of reaction interface moving velocity:

$\frac{r_m(x_m,t_n)-r_m(x_m,t_{n-1})}{t_n-t_{n-1}}=-\frac{r_{\mathrm{mag}}(x_m,t_n)}{4p{r}_m{(x_m,t_{n-1})}^2{\mathrm{\&rho;}}_s(1-{\mathrm{\&epsiv;}}_1)\mathrm{\&pi;}}$ equation 15

Wherein epsilon₁The porosity is the porosity of the pellets, and the unit is% and is obtained according to the sampling and testing of the pellets; p is the green ball magnetite content in formula 1;

oxidation reaction rate r of magnetite_magThe calculation formula is as follows:

$r_{\mathrm{mag}}(x_m,t_n)=\frac{16\mathrm{\&pi;}{r}_0^2{C}_{O_2}}{\frac{1}{k_{g\left(O_2\right)}}+\frac{1}{k_r}{\left[\frac{r_0}{r_m(x_m,t_{n-1})}\right]}^2+\frac{r_0}{D_{O_2}}[\frac{r_0}{r_m(x_m,t_{n-1})}-1]}$ equation 16

Wherein,

is O in the gas phase₂Concentration in mol/cm³Taking the oxygen concentration of air as

Is O in the gas phase₂The mass transfer coefficient passing through the gas boundary layer is in cm/s; k is a radical of_rThe magnetite chemical reaction speed is expressed in cm/s;

is O in the pellet₂Effective diffusion coefficient in cm through the product layer²/s；

k_rAnd

the calculation formulas are respectively as follows:

$k_{g\left(O_2\right)}=\frac{\mathrm{Sh}\&CenterDot;D}{2r_0}$ equation 17

$k_r=3000\&times;e^{-6000/T_s(x_m,t_{n-1})}$ Equation 18

$D_{O_2}=\frac{D{\mathrm{\&epsiv;}}_1}{\mathrm{\&tau;}}$ Equation 19

Wherein Sh is Sherwood number and is dimensionless; d is O₂Diffusion coefficient in gas in cm²S; tau is a pitch factor, has no dimension and is produced according to the oxidation pellets of a chain grateThe production condition is 5.

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