JP5447192B2 - Method, apparatus and program for evaluating the amount of NOx produced in the sintering process of the steel industry - Google Patents

Description

The present invention relates to a method, apparatus, and program for evaluating the amount of NO _x produced in a sintering process in the steel industry.

In the iron and steel industry's sintering process, the air above the charged raw material layer is sucked downward, the coke mixed in the raw material is burned, and the heat generated here sinters the raw ore particles. And promote the melting reaction. In the coke combustion process, nitrogen contained in the coke reacts with oxygen and is released into the combustion exhaust gas as fuel NO _x . Environmental regulation values are set for the NO _x value discharged from the sintering machine. From the viewpoint of reducing the load of the exhaust gas treatment device having a denitration function, the NO _x value generated during the coke combustion process in the sintering process There is a great need to suppress this by combustion control.

As a mathematical model describing the combustion reaction of powder coke in the sintering process of the steel industry, for example, Non-Patent Document 1 assumes a combustion reaction of C + O ₂ → CO ₂ .

Further, NO _x for the amount of evaluation, for example, as in Non-Patent Document 2, NO CO concentration was determined by sucking the combustion exhaust gas _x conversion rate near coke particles and O ₂ concentration ratio CO / O ₂ , there is a report example that can be organized.

"Metallurgy Reaction Engineering", Whip, Akira Moriyama, Yokendo (1972) “Examination of CO and NO gas generation factors in coke combustion”, Yukihiro Hida, Satoshi Sasaki, Satoshi Ito, Iron and Steel, No. 13 (1980) No. 66

  However, the combustion reaction described in Non-Patent Document 1 does not occur at a temperature of 700 ° C. or higher at which the powder coke is ignited in the sintering process. In order to solve the mathematical model with assumptions that deviate from the principle of combustion in this way, irrational correction factors, etc. must be introduced into the model, and actual phenomena measured in actual machines and pan tests etc. are rationalized. It was impossible to explain to.

Non-patent document 2 only describes the results of laboratory experiments. In order to predict the amount of NO _x produced when the operating factors are changed, it is necessary to conduct experiments each time, which is fragmentary and quantitative. There are limitations in terms of safety and predictability.

The present invention has been made in view of the above points, clarifying the governing factor of fuel NO _x generation in mathematical formulas, and examining the factors for suppressing NO _x generation from a viewpoint of combustion from a bird's-eye view. The purpose is to be able to.

Evaluation of the NO _x generation amount in the sintering step of the steel industry of the present invention, 2C + O ₂ → 2CO as the surface reaction of coke _{particles, C + CO 2 → 2CO,} CaCO 3 → CO 2 + CaO, and, the sintered layer Targeting a combustion reaction including 2CO + O ₂ → 2CO ₂ as a gas reaction, at least the mass balance of oxygen (O ₂ ) in the sintered layer, the mass balance of carbon dioxide (CO ₂ ) in the sintered layer, Material balance of carbon monoxide (CO) in the sintered layer, material balance of carbon (C) in the sintered layer, material balance of limestone (CaCO ₃ ) in the sintered layer, heat balance of combustion gas and sintering A first calculation step for calculating a sintering layer temperature, a CO concentration and an O ₂ concentration in the combustion exhaust gas based on a combustion model in the sintering layer configured to include the heat balance of the layer; Sintered layer temperature calculated in the calculation step, C in the combustion exhaust gas And the input value the concentration and the O ₂ concentration, and a second calculation step on the basis of a combustion model in the gas boundary layer of coke breeze particle, to calculate the gas boundary film CO concentration and the O ₂ concentration of the coke particles, said second computed at the computation step, evaluating step of evaluating the NO _x generation amount calculated ratio CO / O ₂ value of the CO concentration and the O ₂ concentration in the gas boundary layer of coke breeze particles in the combustion process It is characterized by having.
The apparatus for evaluating the amount of NO _x produced in the sintering process of the steel industry of the present invention is 2C + O ₂ → 2CO, C + CO ₂ → 2CO, CaCO ₃ → CO ₂ + CaO, and the surface reaction of the powder coke particles. Targeting a combustion reaction including 2CO + O ₂ → 2CO ₂ as a gas reaction, at least the mass balance of oxygen (O ₂ ) in the sintered layer, the mass balance of carbon dioxide (CO ₂ ) in the sintered layer, Material balance of carbon monoxide (CO) in the sintered layer, material balance of carbon (C) in the sintered layer, material balance of limestone (CaCO ₃ ) in the sintered layer, heat balance of combustion gas and sintering First calculation means for calculating the sintering layer temperature, the CO concentration and the O ₂ concentration in the combustion exhaust gas based on a combustion model in the sintering layer configured to include the heat balance of the layer; The sintered layer temperature calculated by the calculation means, the CO concentration in the combustion exhaust gas, and And the O ₂ concentration in the input value, based on the combustion model in the gas boundary layer of coke particles, and second calculating means for calculating the gas boundary film CO concentration and the O ₂ concentration of the coke particles, the first And an evaluation means for obtaining a ratio CO / O ₂ value of the CO concentration and the O ₂ concentration in the gas film of the powder coke particles in the combustion process calculated by the calculation means of No. ₂ .
The program of the present invention is a program for evaluating the amount of NO _x produced in the sintering process of the steel industry, and the surface reaction of the powder coke particles is 2C + O ₂ → 2CO, C + CO ₂ → 2CO, CaCO ₃ → CO ₂ + CaO. And at least a mass balance of oxygen (O ₂ ) in the sintered layer, carbon dioxide in the sintered layer, for a combustion reaction including 2CO + O ₂ → 2CO ₂ as a gas reaction in the sintered layer (CO ₂ ) material balance, carbon monoxide (CO) material balance in the sintered layer, carbon (C) material balance in the sintered layer, limestone (CaCO ₃ ) material balance in the sintered layer, A first calculation for calculating the sintering layer temperature, the CO concentration and the O ₂ concentration in the combustion exhaust gas based on a combustion model in the sintering layer configured to include the heat balance of the combustion gas and the heat balance of the sintering layer. Calculated by the calculation means and the first calculation means Binding layer temperature, then the input value of the CO concentration and the O ₂ concentration in the combustion exhaust gas, on the basis of the combustion model in the gas boundary layer of coke particles, the gas boundary film CO concentration and the O ₂ concentration of the coke particles Second calculating means for calculating, and evaluation for calculating the ratio CO / O ₂ value of the CO concentration and the O ₂ concentration in the gas boundary film of the powder coke particles in the combustion process, calculated by the second calculating means Make a computer function as a means.

According to the present invention, the combustion reaction of coke breeze in the sintering process is based on the principle of combustion and rationally described by a mathematical model, and the laboratory experiment results of Non-Patent Document 2 are reinterpreted by a mathematical model. By doing so, the governing factor of the fuel NO _x generation can be clarified on the mathematical formula, and the factor for suppressing the NO _x generation amount can be examined from a viewpoint from the viewpoint of combustion. Thereby, the load reduction effect of the exhaust gas treatment apparatus having a denitration function can be expected.

It is a diagram for explaining the outline of the evaluation method of the NO _x generation amount according to the present invention. Is a flowchart showing the evaluation method of the NO _x generation amount in this embodiment. It is a figure for demonstrating the outline | summary of a pan test. It is a characteristic view which shows the actual value of the temperature in a pan test. It is a characteristic view which shows the calculated value of the temperature in a pan test. It is a characteristic view which shows the measured value and calculated value of the sintered layer maximum temperature in a pan test. It is a characteristic diagram showing the calculation examples and CO / O ₂ value of the gas concentration in the vicinity of coke particles. CO / O ₂ value calculated values and measured values of the NO _x in the pot test (NO _x conversion) and is a characteristic diagram showing the. The particle size of the coke breeze particles are a diagram for explaining the evaluation of effects on NO _x generation amount.

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.
FIG. 1 is a diagram for explaining the outline of the NO _x generation amount evaluation method to which the present invention is applied. If the reaction of the sintering process is captured by a one-dimensional model, the lower layer has a raw material layer 102 made of a raw material containing powdered coke, and the upper layer has a sintered layer 101 that has completed the sintering reaction. The combustion zone 103 below the layer 101 descends with time. The temperature distribution at this time is such that the temperature increases toward the lower part of the sintered layer 101 and becomes the highest temperature (sintered layer maximum temperature) at the lower part of the combustion zone 103.

FIG. 2 is a flowchart showing the NO _x generation amount evaluation method of the present embodiment. In FIG. 1, the reference numerals of the steps described below are also given.

Surface reaction of powder coke particles 2C + O ₂ → 2CO, C + CO ₂ → 2CO, C + H ₂ O → CO + H ₂ , CaCO ₃ → CO ₂ + CaO, and gas reaction 2CO + O ₂ → 2CO ₂ , 2H ₂ + O ₂ in the sintered layer 101 → For the combustion reaction composed of 2H ₂ O, the mass balance of oxygen (O ₂ ) in the sintered layer 101, the mass balance of carbon dioxide (CO ₂ ) in the sintered layer 101, and the water in the sintered layer 101 (H ₂ O) material balance, carbon monoxide (CO) material balance in sintered layer 101, hydrogen (H ₂ ) material balance in sintered layer 101, carbon (C) in sintered layer 101 On the basis of the combustion model in the sintered layer 101, including the material balance of limestone (CaCO ₃ ) in the sintered layer 101, the heat balance of the combustion gas, and the heat balance of the sintered layer 101, sintered layer maximum temperature, the CO concentration and the O ₂ concentration in the combustion exhaust gas Calculated (step S1).

Next, using the sintering layer maximum temperature calculated in step S1, the CO concentration and the O ₂ concentration in the combustion exhaust gas as input values, and based on the combustion model of the powder coke particles in the gas boundary film, the powder coke particles The CO concentration and O ₂ concentration in the gas boundary film are calculated (step S2).

Then, the ratio CO / O ₂ value between the CO concentration and the O ₂ concentration in the gas boundary film of the powder coke particles in the combustion process calculated in step S2 is obtained to evaluate the NO _x generation amount (step S3). . As described in Non-Patent Document 2, fuel NO _x is generated by two reactions in the very vicinity of the coke surface, the reaction on the coke surface and the reaction in the gas boundary film, but the CO concentration is high and the O ₂ concentration is high. The lower the value, the more suppressed.

Hereinafter, the NO _x generation amount evaluation method of the present embodiment will be described in detail.
First, details of step S1 will be described.
(Combustion model in the sintered layer 101)
The surface reaction of the powder coke particles is represented by the following (R1), (R2), (R3), and (R6).

The gas reaction in the sintered layer 101 is expressed by the following formulas (R4) and (R5).

Reaction rates (reaction rates when one particle burns) w _{1 to} w ₆ of the reactions R1 to R6 are expressed by the following formulas (1.1) to (1.6). r _C is the radius of the powdered coke particles, r _lime is the radius of limestone, B _{1 to} B ₆ are rate constants (subscripts correspond to reactions R1 to R6), and E _{1 to} E ₆ are activation energies (attached) The letters correspond to reactions R1 to R6), R is a gas constant, t is a solid temperature (temperature of the sintered layer 101), T is a gas temperature, C _O2 , C _CO2 , C _H2O , C _CO , and C _H2 are respectively Molar concentration, C _CO2 ^* is the equilibrium molar concentration of CO ₂ .

Next, considering the continuous equation representing the overall mass balance, the following equations (2.1) and (2.2) are used. [rho _g is the gas mean density, u _g is the wind speed, z is the height direction position, M _C is the number of particles per unit volume of the molar mass, M _CO2 molar mass of CO _2, n _C is coke breeze particle carbon , N _lime is the number of particles per unit volume of limestone, U is the superficial velocity, and ε is the porosity. n _C and n _lime are obtained by the following formulas (2.12) and (2.13). In the following formulas (2.12) and (2.13), r _{C — 0} is the initial (before combustion) radius of the powder coke particles, and r _{lime — 0} is the initial radius of limestone.

The mass balance of O ₂ , CO ₂ , H ₂ O, CO, H ₂ , carbon, and limestone in the sintered layer 101 is expressed by the following expressions (2.3) to (2.9). θ is time, ρ _lime is the density of limestone, and M _lime is the molar mass of limestone.

Further, the heat balance of the combustion gas is represented by the following formula (2.10), and the heat balance of the sintered layer 101 is represented by the following formula (2.11). h _p a is the overall heat transfer coefficient, ΔH is the production enthalpy (subscripts correspond to reactions R1 to R6), c _g is the specific heat of the combustion exhaust gas, and c _s is the specific heat of the solid (specific heat of the sintered layer 101).

The partial differential equation group which is the above macro-scale sintering model is _combined to calculate the maximum temperature of the sintered layer, the CO molar concentration C _CO and the O ₂ molar concentration C _O2 in the combustion exhaust gas.

Next, details of step S2 will be described.
(Combustion model of gas coke particles in gas film)
The reaction rates W _CO , W _O2 , W _H2O , W _CO2 , and W _H2 of CO, O ₂ , H ₂ O, CO ₂ , and H ₂ are expressed by the following formulas (3.1) to (3.5). Moreover, r _s is the distance from the center in the radial direction of the powder coke particles to the gas boundary film, and in the following formulas (3.6) to (3.8), the reaction rates w _{1 to} w ₃ are those of the powder coke particles. It is assumed that it is represented by the molar concentration at the gas boundary film and the distance r _s . The maximum temperature of the sintered layer calculated by the macro-scale sintering model in step S1 is used as the solid temperature t of the following equations (3.6) to (3.8).

Consider the group of ordinary differential equations of the following formulas (4.1) to (4.5) representing the mass balance of one powder coke particle. I represents O ₂ , CO ₂ , H ₂ O, H ₂ , CO. u is a gas velocity, m is a gas generation amount (weight velocity), and D _g is a gas diffusion coefficient. The CO molar concentration C _CO and O ₂ molar concentration C _O2 in the combustion exhaust gas calculated by the macro-scale sintering model in step S1 are used for C _I → C _I ∞ of the following formula (4.5).

The solution of the equation (4.1) is expressed by the following equation (5.1) using the constants a _I and b _I under the condition of the equation (4.3), and is lower than the equation (4.5). Equation (5.2) is obtained. Further, the following equation (5.3) is obtained from the equation (4.2).

In the case of I = O _2, the following formula (6.1) is obtained from the formula (3.2), the formula (3.6), the formula (5.1), and the formula (5.3). .2), the constants a _O2 and b _O2 are obtained as the following equations (6.2) and (6.3).

When I = CO _2, the following formula (7.1) is obtained from formula (3.4), formula (3.7), formula (5.1), and formula (5.3). When solving with (5.2), the constants a _CO2 and b _CO2 are obtained as the following equations (7.2) and (7.3).

When I = H ₂ O, the same formula as formula (7.1) is obtained from formula (3.3), formula (3.8), formula (5.1), and formula (5.3). Therefore, when solving with equations (5.2), the constants a _H2O and b _H2O are obtained as the following equations (8.1) and (8.2).

In addition, when I = H ₂ , 4παa _H2 = w ₃ is obtained from the equations (3.5) and (5.3), so that it can be combined with the equations (3.3) and (5.2). When solved, the constants a _H2 and b _H2 are obtained as the following equations (9.1) and (9.2).

In the case of I = CO, 4παa _CO = W _CO = w ₁ + 2w ₂ + w ₃ is obtained from the expressions (3.1) and (5.3), so that the expressions (3.2) and (3. 3) If the equations (3.4) and (5.2) are simultaneously solved, the constants a _CO and b _CO are obtained as the following equations (10.1) and (10.2).

Here, Equation (3.2), Equation (3.3), Equation (3.4), Equation (5.3), and Equation (4.4) yields the following equation (11.1), and α = m / than 4πρ _g, the formula (11.2). Therefore, the following expressions (11.3) and (11.4) are obtained, and α including m which is an unknown number can be determined.

The CO concentration C _CO and O ₂ concentration C _O2 in the gas film of the powder coke particles are calculated by the above combustion model of the powder coke particle in the gas film.

Next, an example of the evaluation of the NO _x generation amount in step S3 will be described.
With reference to FIGS. 3-6, the result of having verified the accuracy of the combustion model of this embodiment is shown. As shown in FIG. 3, the sintering process was reproduced using a pan having a height of 60 cm, and the temperature at the position (T1), 30 cm (T2), and 49 cm (T3) at 15 cm from above was measured by a thermocouple. It was measured. The result is shown in FIG. The horizontal axis in FIG. 4 is time, and the vertical axis is temperature. Further, the temperatures at the position (T1) 15 cm, the position 30 T (T2), and the position 49 T (T3) from the top were calculated by the combustion model of this embodiment. The result is shown in FIG. The horizontal axis in FIG. 5 is temperature, and the vertical axis is temperature. As shown in FIGS. 4 and 5, the measured value and the calculated value of the temperature show the same behavior, and it can be seen that the temperature reproducibility by the combustion model of the present embodiment is high.

  FIG. 6 shows measured values and calculated values of the maximum sintered layer temperature in the pan test. A pot test was performed by changing the weight% (Table 1) and particle size (Table 2) conditions of the powdered coke particles, and the actual measurement value and the calculated value were plotted. As shown in FIG. 6, even when the weight percent and the particle size conditions of the powder coke particles are changed, the measured value and the calculated value of the sintered layer maximum temperature are substantially the same, and the combustion model of the present embodiment It can be seen that the temperature behavior of the pan test can be explained with high accuracy.

FIG. 7 shows the calculation example of the gas concentration (CO concentration C _CO and O ₂ concentration C _O2 in the gas boundary film) and the CO / O ₂ value in the vicinity of the powder coke particles by the combustion model of the present embodiment in the pan test. FIG. The CO / O ₂ value indicates an average value (average within 0.05 cm) of CO / O ₂ values on the surface of the powder coke particles.

FIG. 8 shows the CO / O ₂ value when the weight percent (Table 1) and particle size (Table 2) conditions of the powder coke particles are changed, and the actual measured value (NO _x conversion rate) of NO _{x in} the pan test. FIG. As shown in FIG. 8, when regression analysis was performed, the behavior of NO _{x based} on the CO / O ₂ value calculated by the combustion model of the present embodiment even when the weight percent and the particle size conditions of the powder coke particles were changed. Can be explained.

FIG. 9C is a characteristic diagram showing the particle size of the powder coke particles and the maximum temperature of the sintered layer calculated by the combustion model of the present embodiment. As shown in FIG. 9C, it was found that the maximum temperature of the sintered layer tends to increase as the particle size increases. FIG. 9B is a characteristic diagram showing the particle size of the powder coke particles and the CO / O ₂ value calculated by the combustion model of the present embodiment. As shown in FIG. 9B, it was found that the CO / O ₂ value tends to increase as the particle size increases.

FIG. 9A is a characteristic diagram showing the particle size of the powder coke particles and the NO _x amount obtained based on the CO / O ₂ value calculated by the combustion model of the present embodiment. The vertical axis, a regression equation between the measured value of CO / O ₂ value and the NO _x as described in FIG. 8, a amount of NO _x to be expected at the regression equation. As shown in FIG. 9A, it was found that the NO _x amount tends to decrease as the particle size increases. More specifically, in a fine particle region having a small particle size, there is a possibility that the amount of NO _x rapidly increases even when the particle size changes slightly. On the other hand, in the coarse particle region having a large particle size, the effect of reducing the NO _x amount due to the change in particle size is saturated. From this point of view, it was found that there was an appropriate particle size range in the pan test.

As described above, the combustion reaction of powder coke in the sintering process is based on the principle of combustion and is rationally described with a mathematical model, and the laboratory experiment results of Non-Patent Document 2 are reinterpreted with the mathematical model. By doing so, the governing factor of the fuel NO _x generation can be clarified on the mathematical formula, and the factor for suppressing the NO _x generation amount can be examined from a viewpoint from the viewpoint of combustion. Thereby, the load reduction effect of the exhaust gas treatment apparatus having a denitration function can be expected.

The NO _x generation amount evaluation apparatus to which the present invention is applied can be specifically configured by a computer system including a CPU, a ROM, a RAM, and the like, and is realized by the CPU executing a program. Further, the NO _x generation amount evaluation apparatus to which the present invention is applied may be composed of one apparatus or a plurality of devices.

The object of the present invention can also be achieved by supplying a storage medium storing a program code of software for realizing a function of calculating a CO / O ₂ value by a combustion model as described above to a system or apparatus. . In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments, and the program code itself and the storage medium storing the program code constitute the present invention. As a storage medium for supplying the program code, for example, a flexible disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, a CD-R, a magnetic tape, a nonvolatile memory card, a ROM, or the like can be used.

101: Sintered layer 102: Raw material layer 103: Combustion zone

Claims (3)

Surface reaction as 2C + O ₂ → 2CO of coke _{particles, C + CO 2 → 2CO,} CaCO 3 → CO 2 + CaO, and the target combustion reactions to include 2CO + O ₂ → 2CO ₂ as gas reaction sintered layer, At least the material balance of oxygen (O ₂ ) in the sintered layer, the material balance of carbon dioxide (CO ₂ ) in the sintered layer, the material balance of carbon monoxide (CO) in the sintered layer, in the sintered layer Based on a combustion model in a sintered layer comprising the carbon (C) material balance, the limestone (CaCO ₃ ) material balance in the sintered layer, the heat balance of the combustion gas, and the heat balance of the sintered layer A first calculation step for calculating the sintered layer temperature, the CO concentration and the O ₂ concentration in the combustion exhaust gas,
Based on the combustion model in the gas film of the powder coke particles, the sintering layer temperature calculated in the first calculation step, the CO concentration in the combustion exhaust gas, and the O ₂ concentration are input values. A second calculation step for calculating the CO concentration and the O ₂ concentration in the gas boundary film;
Said second computed at the computation step, evaluating step of evaluating the NO _x generation amount calculated ratio CO / O ₂ value of the CO concentration and the O ₂ concentration in the gas boundary layer of coke breeze particles in the combustion process And a method for evaluating the amount of NO _x produced in the sintering process of the steel industry. Surface reaction as 2C + O ₂ → 2CO of coke _{particles, C + CO 2 → 2CO,} CaCO 3 → CO 2 + CaO, and the target combustion reactions to include 2CO + O ₂ → 2CO ₂ as gas reaction sintered layer, At least the material balance of oxygen (O ₂ ) in the sintered layer, the material balance of carbon dioxide (CO ₂ ) in the sintered layer, the material balance of carbon monoxide (CO) in the sintered layer, in the sintered layer Based on a combustion model in a sintered layer comprising the carbon (C) material balance, the limestone (CaCO ₃ ) material balance in the sintered layer, the heat balance of the combustion gas, and the heat balance of the sintered layer First calculating means for calculating the sintered layer temperature, the CO concentration and the O ₂ concentration in the combustion exhaust gas,
Based on the combustion model in the gas boundary film of the powder coke particles, the sintering layer temperature calculated by the first calculation means, the CO concentration in the combustion exhaust gas, and the O ₂ concentration are input values. A second calculating means for calculating the CO concentration and the O ₂ concentration in the gas boundary film;
Evaluation means for obtaining a ratio CO / O ₂ value of the CO concentration and the O ₂ concentration in the gas film of the powder coke particles in the combustion process calculated by the second calculation means, NO _x generation amount of the evaluation device in the sintering process of the steel industry to be. A program for evaluating the amount of NO _x produced in the sintering process of the steel industry,
Surface reaction as 2C + O ₂ → 2CO of coke _{particles, C + CO 2 → 2CO,} CaCO 3 → CO 2 + CaO, and the target combustion reactions to include 2CO + O ₂ → 2CO ₂ as gas reaction sintered layer, At least the material balance of oxygen (O ₂ ) in the sintered layer, the material balance of carbon dioxide (CO ₂ ) in the sintered layer, the material balance of carbon monoxide (CO) in the sintered layer, in the sintered layer Based on a combustion model in a sintered layer comprising the carbon (C) material balance, the limestone (CaCO ₃ ) material balance in the sintered layer, the heat balance of the combustion gas, and the heat balance of the sintered layer First calculating means for calculating the sintered layer temperature, the CO concentration and the O ₂ concentration in the combustion exhaust gas,
Based on the combustion model in the gas boundary film of the powder coke particles, the sintering layer temperature calculated by the first calculation means, the CO concentration in the combustion exhaust gas, and the O ₂ concentration are input values. A second calculating means for calculating the CO concentration and the O ₂ concentration in the gas boundary film;
A program for causing a computer to function as evaluation means for obtaining a ratio CO / O ₂ value of the CO concentration and the O ₂ concentration in the gas boundary film of the powder coke particles in the combustion process, calculated by the second calculation means .

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