JPH09202910A - Method for controlling combustion in melting furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a combustion control method for shortening melting time by effectively utilizing chemical reaction between combustion gas in a melting furnace and raw material to be melted to rise the thermal efficiency. SOLUTION: In the combustion control of the melting furnace by beforehand charging the iron raw material and a component adjusting material and burning with gaseous fuel and gaseous oxygen and heating and melting, the chemical reaction model between the combustion gas and the charged iron raw material and component adjusting material is inclined and the iron raw material temp. during melting is detected, and the detected value is used and inputted to the chemical reaction model to execute the operation and the supplying quantity of at least one side of the gaseous fuel and the gaseous oxygen is decided. Further, the supplying quantity of at least one side of the gaseous fuel or the gaseous oxygen is operated and decided so that carbon monoxide concn. minimizes in the chemical reaction model.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling combustion in a melting furnace, and more particularly, to a raw material to be melted, which is prepared by burning oxygen gas and fuel gas in the furnace and charging the combustion heat into the furnace. The present invention relates to a combustion control method for a rotary melting furnace, which heats and melts.

[0002]

2. Description of the Related Art A rotary furnace is one of melting furnaces. It consists of a horizontally placed cylindrical furnace body, a furnace body drive, and a burner.Heat transfer from the flame generated by the burner as raw material for charging and possessing a rotating refractory wall that is heated and stored by the flame. It is heated and melted by conduction of heat and convection. In recent years, a combination of pure oxygen and a fluid fuel such as propane as a burner fuel has been popularized from the viewpoint of improving energy efficiency, exhaust gas problems, and restriction of raw materials.
As a combustion adjustment method for a burner in the rotary melting furnace, after charging raw materials, the opening of a fuel gas or oxygen gas valve connected to the burner is adjusted so that the melt has a target component range and a tapping temperature. Is being done. In the case of molten iron for cast iron, conventionally, the valve openings of fuel gas and oxygen gas were adjusted so that the flow rates obtained empirically through the operation could be obtained from the blending ratio of the raw materials to be melted, that is, the iron raw materials and auxiliary materials. Was. Here, the auxiliary material is charged together with the iron raw material in order to adjust the composition of the molten metal and the atmosphere in the furnace. The adjustment of each flow rate of the fuel gas and the oxygen gas may be constant throughout the entire melting process or may be changed, but even if it is changed, it is in several steps and is changed stepwise to a predetermined state. It was a thing.

[0003]

FIG. 3 shows the weights of the Fe, C, Si and Mn components contained in the raw material of the charged iron in the rotary melting furnace which is the object of the present invention and all the auxiliary materials, An example of these components remaining in the melt after the completion of dissolution and the weight lost is shown. In Fig. 3, the charging weight of C is 21 kg.
Consists of 8 kg of C component contained in the iron raw material and 13 kg of C component contained in the carburizing material which is one of the auxiliary materials. As a result of melting, C contained in the molten metal was 7 kg, indicating that the remaining 14 kg was lost. As is clear from FIG. 3, in the rotary melting furnace which is the object of the present invention, the loss ratio of C is particularly large, and as described above, a weight equivalent to the total amount of the charged carburizing material is lost. Although the related chemical reactions will be described in detail later, the loss is discharged as carbon monoxide or carbon dioxide,
The endothermic and exothermic amounts of the related reactions have a great influence on the dissolution efficiency. Therefore, it is important to adjust the flow rate of the fuel gas or oxygen gas and the combustion of the burner in consideration of the reaction of the carburizing material.

However, since the reaction form and reaction rate greatly change depending on the temperature and the composition of the atmosphere gas in the furnace, the conventional combustion adjusting method has the following problems. In an atmosphere in which the flow rate of oxygen gas required to completely burn the reference fuel gas to the flow rate of oxygen gas actually supplied (hereinafter referred to as a mixing ratio) is 1.0 or less and oxygen is insufficient, the carburizing material is used. Since it undergoes an endothermic reaction with carbon dioxide and water vapor which are combustion gas components, the thermal efficiency is reduced and the dissolution time becomes longer. On the contrary, if the mixing ratio is simply increased and oxygen is excessively supplied, a part of the oxygen is wastefully heated and discharged without reacting, resulting in a heat loss. Further, the oxidation loss of the melted raw material increases, and the yield of the melted raw material decreases. Therefore, the present invention solves the above-mentioned problems in combustion control due to the characteristics of the rotary melting furnace, lowers the thermal efficiency due to lack of oxygen supplied to the burner, or lowers the thermal efficiency due to excess oxygen and the oxidation loss of the raw material to be melted. An object of the present invention is to provide a combustion control method for a melting furnace that minimizes the amount of combustion.

[0005]

DISCLOSURE OF THE INVENTION The present invention relates to combustion control of a melting furnace in which an iron raw material and a component adjusting material are charged in advance and burned with a fuel gas and an oxygen gas to be heated and melted. The built-in chemical reaction model of the iron raw material and the component adjusting material entered, the temperature of the raw material to be melted during melting is detected, and the detected amount is used to input to the chemical reaction model for calculation, and the operation of the melting furnace Characterized by determining the amount.

Further, the flow rate is determined by calculating the supply amount of at least one of the fuel gas and the oxygen gas so as to minimize the carbon monoxide concentration in the furnace by using the built-in chemical reaction model. To do.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows a cross section of a melting furnace and a combustion control system of a gas burner according to an embodiment of the present invention, and this melting furnace is used for manufacturing various cast iron melts. The melting furnace shown in FIG. 1 is a furnace body 5 having a cylindrical body 1 and conical portions 2 and 3 connected to both ends thereof, and a fluid fuel is burned with oxygen to be charged into the furnace body 5. A burner 6 for melting raw materials to be melted, and a chimney-shaped exhaust passage 7 for discharging combustion exhaust gas to the outside.
And a charging device (not shown) for charging the melted raw material 8 and the like into the furnace body 5. The burner fuel is propane and oxygen in this example, but methane instead of propane,
Butane or kerosene may be used.

The opening 9 at one end of the furnace body 5 serves as a burner mounting opening, and the opening 10 at the other end of the furnace body 5 serves as an inlet for the raw material 8 to be melted and an exhaust gas outlet. 11 is a conical portion 3 of the furnace body 5.
It is a tap hole provided in the and is closed except when tapping. A temperature detecting terminal 16 is embedded in the wall surface of the furnace body.

Here, the burner 6 has a structure having a fuel injection port in the center and an oxygen supply port on the outer periphery. A fuel and oxygen supply system is connected upstream of the burner 6, and an oxygen valve 30 of the oxygen supply system and a fuel valve 31 of the fuel supply system are connected to each other. An oxygen supply source 32 is connected upstream of the oxygen valve 30, and a fuel supply source 33 is connected upstream of the fuel valve 31.

The combustion control device has a built-in chemical reaction model to calculate a supply amount of oxygen and fuel gas, a flow control valve adjuster 34 for controlling the oxygen amount and fuel gas amount supplied to the furnace, 35, detection terminals 38 and 39 for detecting the amount of oxygen and the amount of fuel gas, and a temperature detection terminal 16 for the raw material to be melted. The computer 20 is connected to the temperature detection terminal 16 and the signal line 18, and calculates the amount of oxygen and the amount of fuel gas supplied to the furnace based on the detected temperature and the built-in chemical reaction model. Flow rate control valve adjusters 34 and 35 are connected to the oxygen valve 30 and the fuel valve 31, respectively, and the flow rate instruction signal line 3 from the computer 20 is connected to each flow rate control valve adjuster.
6, 37 are connected. Flow control valve regulator 3
Reference numerals 4 and 35 feed back the actual flow rate values in the oxygen pipe 40 and the fuel gas pipe 41 in the flow rate detectors 38 and 39 to the flow rate command value from the computer 20, and the oxygen valve 30 and the fuel valve 31. The opening of is controlled. By controlling the opening degree, the oxygen amount and the fuel gas amount supplied to the burner 6 are controlled with high accuracy, and the combustion calorific value and the combustion gas composition of the burner in the furnace are controlled.

Next, the melting process for obtaining the molten metal for cast iron using the melting furnace using the combustion control device of the present invention and the reaction in the furnace will be described. First, a predetermined amount of iron raw materials such as cast iron and steel scraps and auxiliary materials are charged into the furnace body 5. For example, when melting 3 tons, 3 tons of iron raw material having a mixing ratio of 60% cast iron, 30% steel scrap, and 10% pig iron, 160 kg of a carburizing material, 35 kg of a silicifying material, 5 kg of a adding Mn material, and a vulcanizing material 2 as auxiliary materials. 0.4 kg is charged. Then, the burner 6 is set in the opening 9 at one end of the furnace body 5 and ignited to start melting.

The iron raw material is melted by being heated by heat transfer and radiant heat from the refractory material 12 heated by the burner 6 and radiant heat from the burner flame. The basic setting of the calorific value of the burner is performed by giving the flow pattern of the fuel gas.

In burner combustion control, as described below, the temperature of the raw material to be melted is detected, and the mixing ratio is controlled based on the built-in chemical reaction model so that the carbon monoxide concentration in the furnace gas is minimized. . If the fuel gas is propane,
In the case of complete combustion with a mixing ratio of 1.0, the reaction between the fuel gas and the oxygen gas is expressed by equation 1.

## EQU1 ## C3H8 + 5O2 = 3CO2 + 4H2O + [+ Q1] Here, [] indicates reaction heat, + indicates exothermic reaction, and − indicates endothermic reaction.

On the other hand, in the case of the rotary melting furnace which is the subject of the present invention, the combustion gas, that is, CO2 and H2O, and the carburizing material which is one of the auxiliary materials shown in FIG. The reaction is active.

[Equation 2] C + CO2 = 2CO + [-Q2]

## EQU3 ## C + H2O = CO + H2 + [-Q3] The reactions of the expressions 2 and 3 are endothermic reactions. That is, since heat is taken from the surroundings, the heat efficiency is reduced.

Here, when the mixing ratio is 1.0 or less and the oxygen is deficient, a part of C3H8 becomes unreacted, so that the total calorific value of the fuel gas combustion becomes small, and at the same time, the combustion gas and the carburizing material are also reduced. Causes an endothermic reaction of the formulas 2 and 3, so that the thermal efficiency is further lowered and the dissolution time is prolonged.

On the other hand, if the mixing ratio is set to 1.0 or more, the excess oxygen remaining in the combustion reaction with the fuel gas will be mixed in the furnace. When this oxygen reaches the carburized material, on the surface of the carburized material, the exothermic reaction shown in the expression 4 simultaneously occurs with the reactions of the expressions 2 and 3.

[Equation 4] 2C + O2 = 2CO + [+ Q4] Further, in the high temperature furnace, the C generated in the equations 2 to 4
Exothermic reactions of several 5 and several 6 occur between O and H2 and excess oxygen.

[Equation 5] 2CO + O2 = 2CO2 + [+ Q5]

[Equation 6] 2H2 + O2 = 2H2O + [+ Q6]

In the above equation 5, CO reacts with O2 to produce CO2.
The amount Q5 of heat generated when the reaction changes to 2 is larger than the amount Q2 of heat absorbed when CO of the same molar volume is generated in the reaction of Equation 2. Further, the heat quantity Q6 generated when H2 changes to H2O in the equation 6 is larger than the heat quantity Q3 absorbed when the same molar volume of H2 is produced in the reaction of the equation 3. Therefore, the mixing ratio of fuel gas and oxygen gas should be 1.0.
When it is made larger, the exothermic reaction of the equation 4 is promoted on the surface of the carburized material, and the CO generated by the reaction of the equations 2, 3, and 4 is further generated.
And H2 react with oxygen to positively cause the exothermic reactions of the equations (5) and (6).

However, if more oxygen than necessary is supplied from the burner 6 to the reactions of the number 5 and the number 6, the heat is consumed for heating the oxygen discharged in vain, so if the mixing ratio is too high. Thermal efficiency decreases. Further, since an excessive oxidation reaction of the melted raw material occurs, the yield of the melted raw material is reduced. That is, there is an optimum mixing ratio of the fuel gas and the oxygen gas that minimizes the melting time depending on the situation in the furnace.

The actual reaction in the furnace is limited by the chemical reaction rate and the mass transfer rate. However, in the rotary melting furnace targeted by the present invention, the fluctuation of the gas components in the furnace is gradual, and the temperature rising and melting processes are phenomena that take much longer than the chemical reaction rate. The chemical reaction rates of 2 to 6 can be approximately modeled by using the chemical thermodynamic equilibrium theory. The original theory of chemical thermodynamic equilibrium gives the direction of reaction and the final equilibrium state of related substances at a certain temperature, but the reaction rate can be set by defining the reaction rate per unit time. .

Next, the chemical reaction model to be incorporated and the principle of determining the oxygen flow rate required for the exothermic reaction of equations (5) and (6) using the reaction model will be described. The following three independent reaction equations are necessary for obtaining the equilibrium state of the gas components related to the in-reactor in the equations 2 to 6.

[Equation 7] C + CO2 = 2CO

[Equation 8] C + O2 = CO2

[Equation 9] H2 + 1/2 · O2 = H2O Equilibrium constants of the reactions of Eqs. 7, 8, and 9 are K1, K2, K
3, the target gas CO2, H2O, O2, CO, H2 gas partial pressure PCO2, PH2O, PO2, PCO, PH
Expressed by 2, the following relational expression holds from the van der Hoff's isotherm and standard free energy change.

[Expression 10] K1 = PCO2 / PCO2 = log-1 {-(170710-174.5T) /2.303RT}

[Expression 11] K2 = PCO2 / PO2 = log-1 {-(-394577-1.13T) /2.303RT}

## EQU12 ## K3 = PH2O2 / (PH22.PO2) = log-1 {-(-492698 + 109.84T) /2.303RT} where R is a gas constant and T is an absolute temperature. That is, once the temperature is determined, the equilibrium constant at that temperature is determined.

PCO2, PH2O, PO2, PCO, P
H2 is determined by the following method from the fact that the total pressure in the furnace is 1 atm and the initial condition of the supply flow rate of the fuel gas. CO2,
The in-furnace mole numbers of H2O, O2, CO, and H2 gases are represented by A, B, C, D, and E, respectively, and the proportion of in-reactor gas that reacts during the calculation cycle handled by the reaction model is α. And C
The molar numbers of O2, H2O, O2, CO, and H2 before the reaction are a (= α · A), b (= α · B), c (= α · C), d (=
If α · D) and e (= α · E) are set and the reaction direction and the reaction amount (mol number) of Equations 7, 8 and 9 are determined as in Equations 13, 14 and 15, after the reaction The relationship between the partial pressure of each gas and the number of moles is from several 16 to several 20.

[Equation 13] C + CO 2 → 2CO x mol

[Equation 14] C + O2 ← CO2 y mol

[Equation 15] H2 + 1/2 · O2 ← H2O z mol

PCO2 = (a−x−y) / (a + b + c + d)
+ E + 1 / 2.z + x)

## EQU17 ## PH2O = (b−z) / (a + b + c + d + e
+ 1 / 2.z + x)

[Equation 18] PO2 = (c + y + 1/2 · z) / (a + b + c +
d + e + 1/2 ・ z + x)

PCO = (d + 2x) / (a + b + c + d + e)
+ 1 / 2.z + x)

[Formula 20] PH2 = (e + z) / (a + b + c + d + e + 1)
/ 2 · z + x) By substituting the equations 16 to 20 into the equations 10 to 12, the relationships of the equations 21 to 23 can be obtained.

[Expression 21] K1 = (d + 2x) 2 / {(a + b + c + d + e
+ 1 / 2.z + x) (a-xy)}

[Equation 22] K2 = (a−x−y) / (c + y + 1/2 · z)

[Equation 23] K3 = (b−z) 2 (a + b + c + 1/2 · z + x)
/ {(E + z) 2 (c + y + 1/2 · z)} As described above, the solution is obtained from the three relational expressions for the three variables x, y, and z, and CO2 and H2 in the equilibrium state are obtained.
The number of moles of O, O2, CO and H2 and the partial pressure can be obtained. Finally, the chemical reaction in the entire furnace is modeled by obtaining the number of moles and partial pressure of each gas in the entire furnace when the reaction gas that has reached the equilibrium state and the unreacted gas in the furnace are uniformly mixed. it can. That is, the number of moles of CO and H2 generated in the furnace can be obtained from the amount of fuel supplied to the burner and the temperature of the raw material to be melted, and the flow rate of O2 required for the exothermic reaction of Formulas 5 and 6 can be derived.

The ratio α of the in-furnace gas that reacts during the calculation cycle handled by the reaction model is determined by measuring the exhaust gas composition in the actual model operation. 3 described in the embodiment
When the above idea is applied to the ton melting, the calculation cycle is 10m.
In the case of sec, if α is 0.02, it is possible to obtain a result in which the relationship between the temperature of the raw material to be melted and the composition of the exhaust gas is relatively consistent, and it is possible to model the chemical reaction related to the carburizing material in the entire furnace by the above idea. Do you get it.

Next, the gas composition in the furnace is calculated from the temperature of the raw material to be melted detected using the built-in chemical reaction model,
A method of controlling the oxygen flow rate so as to minimize the CO concentration will be described with reference to the flowchart of FIG. First, upon starting, the computer 20 inputs and stores the amounts of the iron raw material and the carburized material and the reference flow rates of the fuel gas and the oxygen gas of the burner determined from the amounts of the raw materials. When the automatic combustion control is started, the computer 20 takes in the temperature value of the raw material to be melted from the temperature detection terminal 16 (step 101). The flow rates of the fuel gas and oxygen gas at that time and the raw material temperature are applied to the chemical reaction model to determine the number of moles of CO and H2 in the furnace (step 10
2) The increased oxygen gas flow rate required for these oxidation reactions is calculated and output as a new oxygen flow rate value to the oxygen flow rate control valve regulator 34 (step 103). Then, in preparation for the next temperature detection, time counting is performed for Ts required for stabilizing the operation result (step 104), and the process returns to the first process.

The time count value Ts is set to, for example, Ts = 1 min according to the target melting furnace, and the oxygen valve 3 is used.
The time when the oxygen flow rate from 0 reaches the flow rate value given to the oxygen flow rate control valve regulator 34 by the computer 20, and the state of the gas in the furnace reaches the steady state in which the operation result is reflected.

The above-described processing is repeated until the temperature of the raw material to be melted detected by the temperature detecting terminal 16 reaches a temperature at which iron can be melted and tapped out, for example, 1520 ° C. next,
Take out a part of the molten metal, analyze the components, and adjust the components as necessary. When the temperature and the components are satisfied, the burner 6 is stopped, the hot water outlet 11 is opened, and hot water is discharged. By detecting the temperature of the raw material to be melted and controlling the flow rate of the oxygen gas in the combustion burner as described above, it is possible to perform combustion control of the burner that achieves maximum thermal efficiency in accordance with the chemical reaction state in the furnace.

Although the equilibrium theory was applied to the chemical reaction model in the examples, a model consisting of the overall reaction rate of the chemical reaction resistance and the diffusion resistance in the fluid film as described for char or coke was used. You may use. Further, although the oxygen gas to be controlled is supplied to the burner in this embodiment, a control oxygen supply path may be separately provided. It is also possible to control the fuel gas flow rate or both the oxygen gas and the fuel gas. Further, the temperature detector may not be embedded in the wall surface of the furnace body but may be something like a radiation thermometer. Further, the reaction amount tracing of the carburizing material may be added to the chemical reaction model to determine that all the carburizing material has reacted, and the reaction model to be applied may be switched to the one without the carburizing material. The combustion control method for increasing the thermal efficiency of the melting furnace for obtaining the cast iron melt has been described above.

[0027]

In the melting furnace using the present invention, even if the carburizing material as an auxiliary material undergoes an endothermic reaction with carbon dioxide and water vapor generated as a result of combustion of fuel gas, carbon monoxide and hydrogen generated as a result Since the exothermic reaction of oxygen is performed at the maximum efficiency, the overall thermal efficiency can be increased. As a result, the dissolution time is shortened, excessive oxidation of the raw material is prevented, and the yield is improved. Further, it is possible to cope with operating conditions in which the temperature rising rate of the melted raw material changes every time due to the influence of the temperature condition of the furnace body at the start of melting and the charged iron raw material and auxiliary materials.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a melting furnace for cast iron and a system diagram of a combustion control device schematically showing an embodiment of the present invention.

FIG. 2 is a flowchart illustrating a combustion control method according to the present invention.

FIG. 3 shows examples of weights of charged components, molten metal components, and loss components in a rotary melting furnace according to the present invention.

[Explanation of symbols]

 5 ... Melting furnace main body 6 ... Burner 16 ... Temperature detection terminal 20 ... Computer 30 ... Oxygen valve 31 ... Fuel valve

Claims (2)

[Claims] 1. A method for controlling combustion in a melting furnace in which an iron raw material and a component adjusting material are charged in advance and burned with a fuel gas and an oxygen gas to be heated and melted, and a supply amount of the fuel gas and the oxygen gas and a raw material to be melted. With the temperature of the input as a input, a chemical reaction model for obtaining the number of moles and partial pressure of the reaction gas that has reached the equilibrium state in the furnace is created, and the reaction of the entire furnace is made based on the output of the chemical reaction model at each sampling time. A combustion control method for a melting furnace, which comprises determining the number of moles of gas and the partial pressure, and determining the supply amount of at least one of fuel gas and oxygen gas so that an exothermic reaction occurs. 2. Based on the number of moles of carbon monoxide and hydrogen and the exothermic reaction equation obtained from the output of the chemical reaction model,
Obtain the oxygen flow rate ratio to minimize the carbon monoxide concentration,
The combustion control method for a melting furnace according to claim 1, wherein the supply amount of at least one of the fuel gas and the oxygen gas is determined.