JPH10324919A - Method for designing heating furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To execute the optimum design of a heating furnace at a low cost and in a short time by executing the simulation calculation of heat transfer quantity to a heating material by a heat transfer model under consideration of radiation and absorption between the heating material and gas in the furnace, a structure in the furnace, in the heating furnace provided with heat storage type burners. SOLUTION: Firstly, the size of the furnace, the arrangement of zones and burners, etc., are decided by initial stage design. Successively, the temp. field to be targeted, is set and the calculations of a radiation model, gas flow model, combustion model heat exchanging model are sequentially executed, and it is confirmed whether the calculated result becomes self consistent or not. In the case of being no self consistent, the temp. field is corrected little by little and the above sequential heat transfer model calculation is repeated. In the case the calculated result becomes self consistent, the temp. field is decided. It is judged whether the decided temp. field is wholly in the permissible range or the optimum range or not, and in the case of being in the range, the design of the furnace is completed, and in the case of being out of the range, the design of the furnace itself is changed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for designing a furnace using a regenerative burner in a heating furnace, a melting furnace, and the like for a metal or the like utilizing a combustion reaction.

[0002]

2. Description of the Related Art In a furnace for melting and heating a metal using a combustion reaction, the furnace is designed based on past experience. For this reason, when adding new equipment to improve the heating efficiency or thermal efficiency, it is necessary to experimentally study and determine the industrially optimum furnace shape and dimensions, which requires enormous costs. there were. However, in the conventional furnace, experience has been accumulated over a long period to date, and it has been possible to design based on these experiences.

[0003]

However, in the optimization of a furnace that uses a regenerative burner for part or all of the combustion equipment, the heat flow at the time of heat recovery is extremely different from that of a furnace using a conventional combustion method. Therefore, the experience of the conventional furnace cannot be used.

When a regenerative burner is used,
Since the gas flow in the furnace is also significantly different from that of the furnace using the conventional combustion method, the appropriate size and shape of the furnace are different from those of the conventional furnace, and there is a problem that the furnace cannot be easily estimated.

[0005] Therefore, in order to optimize a furnace using a regenerative burner, it has been necessary to perform experiments and the like at a great cost and time.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and an object of the present invention is to provide a method for designing a furnace using a regenerative burner at a low cost and in a short time.

[0007]

SUMMARY OF THE INVENTION The object of the present invention is to provide a heating furnace with a regenerative burner, which uses a heat transfer model in consideration of radiation and absorption between the object to be heated and the furnace gas and furnace structure. The problem is solved by a heating furnace design method (claim 1) in which a simulation calculation of a heat transfer amount to an object to be heated is performed, and a heating furnace is designed based on the result.

[0008] Since the simulation calculation is performed and the furnace is optimally designed based on the result, the heating furnace can be designed without performing an experiment requiring a great deal of cost and time.

In the simulation, it is effective to estimate the amount of heat transfer to the object to be heated by using a heat transfer model that takes into account the flow of the gas in the furnace and the energy transfer accompanying the flow. In a furnace equipped with a regenerative burner, the flow of gas in the furnace and the state of energy transfer therewith are greatly different from those of a conventional furnace. Therefore, by including these items in the simulation calculation,
Accurate design of furnaces with regenerative burners is possible.

In the simulation, it is effective to add a function of estimating the amount of heat transfer to the object to be heated by using a heat transfer model taking into account the combustion reaction between fuel and air. Thereby, the phenomenon in the furnace can be accurately simulated, and the amount of heat transfer to the object to be heated can be accurately estimated.

Further, by having a regenerative burner or an exhaust gas heat exchange model (claim 4), the thermal efficiency of the furnace can be reflected in the design using a simulation model.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a flowchart illustrating an example of the embodiment.

First, in step S1, an initial design of a heating furnace is performed. The initial design includes the dimensions of the furnace (length, width, height, ceiling shape, etc.), the arrangement of zones, the arrangement of burners, the capacity (capacity) of the furnace, the position and size of the exhaust gas outlet, and the like. In addition, the material and thickness of the furnace wall, the position and material of the water-cooled skid, and the like are also included. Next, in step 2, heat transfer calculation is performed. This will be described in more detail.

In step S21, a target furnace temperature field is set. Then, the radiation model (S22),
The calculation of the gas flow model (S23), the combustion model (S24), and the heat exchange model (S25) are sequentially performed, and it is confirmed whether the calculation results are self-consistent in energy (S26). If it is not self-consistent, the temperature field is corrected little by little (S27),
The sequential heat transfer model calculation from S22 to S25 is repeated. Then, when the calculation results are self-consistent in terms of energy, the temperature field is determined (S28).

It is determined whether or not all the temperature fields determined as a result of the heat transfer calculation fall within the allowable range or the optimum range (S30). If so, the furnace design is terminated (S30). S50). If there is a temperature field that does not fall within the allowable range or the optimum range, the design of the furnace itself is changed (S4).
0).

S2 'in FIG. 2 is replaced with the heat transfer model calculation step S2 in FIG. 1, and includes a radiation model (S22), a gas flow model (S23), a combustion model (S24), and a heat exchange model (S25). An example is shown in which the calculations are not performed sequentially but are performed in parallel while relating them to each other to determine the temperature field.

Hereinafter, examples of each model will be described in detail. (1) Radiation model The radiation model is performed assuming heat transfer as shown in FIG. In FIG. 3, each arrow indicates the direction of heat transfer. That is, assuming the temperature of each point of the combustion gas in the zone (initial value of the furnace temperature pattern), taking into account the selective radiation characteristics depending on the wavelength, absorbing the radiation energy emitted from that point in the furnace gas layer, Calculate absorption / reflection at walls and heat input to billets. These calculate the heat transfer between each element in the zone.

In the conventional radiative heat transfer model, absorption in the gas layer in the furnace, absorption / reflection on the furnace wall, and heat input to the steel slab are taken into consideration, but selective radiation depending on the wavelength is not taken into account. Was. In combustion using combustion air preheated by a regenerative burner at high temperature, the combustion becomes slow while entraining the furnace gas.Therefore, the effect of selective radioactivity, which depends on the wavelength of the flame, increases. This has enabled more accurate radiative heat transfer analysis.

(2) Gas Flow Model Normally, the combustion gas flow in the furnace is not a laminar flow with a constant flow velocity over time, but a turbulent flow having a turbulent flow at all times. Therefore, when analyzing the gas flow in the furnace is that the gas flow rate u _i in the average value of flow velocity

(Equation 1) (The bar indicates averaging and the subscript indicates the three-dimensional component. The same shall apply hereinafter.) And the variable u _i ′ (dash indicates the variable component; the same applies hereinafter.) It has been done. In addition, since the combustion phenomenon itself is an unsteady phenomenon, it should be analyzed under unsteady conditions, but it is assumed that the combustion phenomenon in the furnace is stable for many parts,
In the non-stationary analysis, the calculation time is long and the analysis accuracy is not significantly improved.

This means that the heating conditions within the heating time of the billet (usually several hours) are calculated by averaging short-term changes in combustion conditions such as fluctuations in combustion gas flow that may occur at intervals of several seconds in an actual furnace. It is shown that.

The basic equations used in the analysis are shown below.
The present invention shows a method for effectively utilizing the results obtained by the analysis, and thus does not limit the analysis method.

The equations used in the analysis are summarized below in the form of a Favre average (time average).

A continuous equation showing mass conservation (x is the direction,
ρ indicates density)

(Equation 2) Equation of motion showing momentum conservation (μ indicates viscosity coefficient, P indicates pressure)

(Equation 3) With the four variables of velocity and pressure, the gas flow can be analyzed using the above equation. Therefore, it is called Reynolds stress

(Equation 4) Needs to be modeled in some way. A turbulence model is used for this modeling.

Turbulent flow model As a turbulent flow model in the flow field in the furnace, a k-ε model of a high Reynolds number type, which is widely used in industry, was used. (Δ indicates the Kronecker symbol, and the subscript t indicates that the turbulence effect is included. The same applies hereinafter.)

(Equation 5) K representing the turbulence energy, ε representing the dissipation rate, and μ _t are defined by the following equations.

(Equation 6) Turbulence energies and dissipation rates are often analyzed using the following conservative equations:

(Equation 7) Various constants use commonly used numerical values. C ₁ = 1.44, C ₂ = 1.92, C _μ = 0.09, ρ _k = 1.0, σ _ε =
1.3 As described above, by adding two variables of turbulence energy and extinction rate and two equations, the flow is represented by six variables and six equations, and the flow analysis becomes possible.

Since these are conventionally used models, the models themselves have no novelty. However, in the past, it was not possible to obtain such accuracy that it could be used for in-furnace heat transfer calculations. But,
When the regenerative burner is used, most of the gas generated in the unit furnace (80% in the case of by-product gas from steelworks) is recovered in the unit furnace, and the part flowing to the adjacent unit furnace is the remaining part. Only a small part. Therefore, the calculation accuracy is improved,
You will be able to perform calculations that are practical.

(3) Combustion Model A combustion model is required to substitute the amount of heat generated by the combustion reaction into the source term of the energy conservation equation. The analysis method uses a mixing ratio coefficient f indicating a mixing ratio of air and fuel, and a probability density function for considering a turbulent diffusion effect.

The model of the combustion reaction assumes that the reaction rate is sufficiently fast compared to the time required for the fluid to pass through the calculation region, and that in each calculation cell, the composition immediately changes to the composition obtained from the thermal equilibrium calculation and the probability density. Use a model.

Φ representing the average gas composition, gas temperature and gas enthalpy is represented by the following equation as an average value.

(Equation 8) Here, P (f) is called a probability density function. φ _i (f, h ^* ) represents the instantaneous gas composition, gas temperature, and enthalpy of a combustion gas having a certain enthalpy, and an average value can be obtained by multiplying by a probability density function. The integration range 0 to 1 indicates that integration is performed over the entire range of the probability density.

As for the probability density function, the following equation is usually solved to use the β function. Average value of mixture ratio function

(Equation 9) And the root mean square of the turbulence

(Equation 10) Is calculated from the following conservation formula. Cg and Cd are constants.

[Equation 11] That is, two variables of the average value and the fluctuation value of the mixing ratio function and 2
The analysis can be performed by adding the equations.

(4) Heat Exchange Model The heat exchange in the heat storage medium is performed by sensible heat of the combustion exhaust gas and preheating of the combustion air via the heat storage medium. Since the actual value of the heat exchange is known depending on the type of the heat storage type burner, the heat exchange efficiency can be accurately calculated by using this, and the preheated air temperature and the heat efficiency can be accurately calculated.

When these equations are discretized and analyzed using a computer, the temperature distribution in the furnace can be accurately known. As an example, FIG. 4 shows the result of a simulation of the furnace temperature distribution under the following conditions.

Calculation area: Furnace width 4.0m, Furnace height 4.0m, Furnace length 8.0m ・ Air outlets: 4 places ・ Fuel outlets: 2 places per air outlet ・ Exhaust gas outlet: Facing air outlet One place (the same size as the air discharge port) ・ Escape: Installed separately from the above exhaust gas port The following conditions are used for various boundary conditions.

-Burning amount: 1.175 MW per burner (1 million kcal / h)-Air ratio: 1.05-Air flow rate: 96 m / s, 1300 ° C-Fuel flow rate: 99 m / s, 27 ° C-Exhaust condition: Exhaust gas 80% is the exhaust gas outlet facing, 20%
Is an escape ・ Wall conditions: Non-slip (use of wall function) ・ Wall boundary: Overall heat transfer coefficient 2J / m ² s, atmospheric temperature 300K Slabs take into account conduction heat transfer, lower slabs adiabatic conditions ・ Slab speed: 1.2mm / s In FIG. 4, 1 is a heating furnace, 2 is a burner, 3 is an exhaust gas outlet, 4 is an escape, and 5 is a partition wall. The numbers in the figure indicate the temperature (° C.).

As a result of an operation test in an experimental furnace, under various synergistic conditions, the error of the actual measurement value with respect to the calculated extraction temperature of the billet is within ± 10 ° C., and the model in this embodiment is This proved to be sufficient to design the furnace.

[0035]

EXAMPLE As an example of the present invention, FIG. 5 shows an example in which the optimum value of the installation position of the burner in the furnace length direction is obtained. In this simulation, for the continuous heating furnace for steel, a zone method heat transfer model and a model that calculates energy transfer by gas flow in the furnace by gas temperature and flow rate were used, and the combustion model was uniform near the burner. Heat generation was omitted, and the heat exchange status of the regenerative burner was approximated by temperature exchange.

FIG. 5 shows the ratio between the distance from the insertion port to the first burner and the fuel injection amount standardized by the minimum fuel injection amount. As is clear from the drawing, the furnace can be optimized by setting the installation start position of the burner at a predetermined distance from the insertion port.

[0037]

As described above, according to the present invention, a heat transfer model in which radiation and absorption between a heated object of a heating furnace having a regenerative burner, furnace gas, and furnace internal structures are considered. The simulation calculation of the amount of heat transfer to the object to be heated in the furnace is performed, and the heating furnace is designed based on the results, so that the heating furnace can be designed without conducting experiments that require a great deal of cost and time. It is.

[Brief description of the drawings]

FIG. 1 is a flowchart illustrating an example of an embodiment of the present invention.

FIG. 2 is a flowchart showing an example of another embodiment of the present invention.

FIG. 3 is a diagram showing a heat transfer state assumed when calculating a radiation model.

FIG. 4 is a diagram showing a furnace temperature distribution obtained by a simulation.

FIG. 5 is a diagram showing a relationship between a burner position and a total fuel ratio.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Heating furnace 2 Burner 3 Exhaust gas exhaust port 4 Escape 5 Partition wall

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[Procedure amendment]

[Submission date] July 18, 1997

[Procedure amendment 1]

[Document name to be amended] Drawing

[Correction target item name] All figures

[Correction method] Change

[Correction contents]

FIG. 2

FIG. 3

FIG. 5

FIG.

FIG. 4

──────────────────────────────────────────────────続 き Continued on front page (51) Int.Cl. ⁶ Identification symbol FI // F27B 3/20 F27B 3/20 F27D 17/00 101 F27D 17/00 101A G05B 17/02 G05B 17/02

Claims (4)

[Claims] 1. A heat transfer model that considers radiation and absorption between an object to be heated of a heating furnace having a regenerative burner, a gas in the furnace, and a structure inside the furnace, to determine a heat transfer amount to the object to be heated in the furnace. A heating furnace design method comprising performing a simulation calculation and designing a heating furnace based on the result. 2. The heating furnace design method according to claim 1, wherein the heat transfer amount to the object to be heated is estimated by a heat transfer model in which the flow of the gas in the furnace and the energy transfer accompanying the flow of the gas in the furnace are considered. 3. The heating furnace design method according to claim 2, further comprising a function of estimating the amount of heat transfer to the object to be heated by a heat transfer model taking into account the combustion reaction between fuel and air. 4. The method for designing a heating furnace according to claim 1, further comprising a regenerative burner or a heat exchange model of exhaust gas.