JP4671136B2 - Combustion control method for rotary melting furnace - Google Patents

Description

  The present invention relates to a melting furnace, and more particularly to a combustion control method suitable for a rotary melting furnace in which oxygen and fuel are combusted in the furnace and the melting raw material charged in the furnace is heated and melted by the combustion heat. is there.

  One type of melting furnace is a rotary melting furnace. This is mainly composed of a cylindrical furnace body that is placed horizontally and rotates around the central axis, a furnace body drive unit, and a burner. The raw material that is loaded rotates with the flame generated by the burner and the heat and heat stored by the flame. It is heated and melted by heat transfer from the refractory wall. In recent years, burner fuels that use pure oxygen in combination with fluid fuels such as propane are becoming widespread in terms of improving energy efficiency, exhaust gas problems, and expanding the range of use of raw materials. Combustion adjustment of the burner in the rotary furnace is performed by adjusting the opening of the fuel or the oxygen valve is connected to the burner. For example, in the case of melting for cast iron, the valve openings of the fuel and oxygen are adjusted so that the flow rate obtained through operation is empirically determined from the blending ratio of the iron raw material and the auxiliary material in the molten raw material to be charged. The flow rate of fuel and oxygen may be constant or may be changed throughout the entire dissolution process, but it can be changed in several steps and is changed stepwise to a predetermined state. . Here, the secondary materials refers to those charged with iron raw material to adjust the components and the inner atmosphere of the molten metal.

Fig. 5 shows the weight of each of the Fe, C, Si, and Mn components contained in the iron raw materials and sub-materials charged in the rotary melting furnace in the case of melting cast iron, and these components remaining in the molten metal after melting is completed. As well as examples of lost weight. In particular, the loss ratio of C is large, and a weight equivalent to the total amount of the carburized material in the sub-material charged is consumed as a result of reaction with fuel and oxygen. Although a related chemical reaction will be described later, the consumed amount is discharged as CO or CO ₂ , and the degree of endothermic reaction and exothermic reaction at this time greatly affects the dissolution efficiency. Therefore, in order to increase the dissolution efficiency, it is important to supply the fuel or oxygen flow rate to the burner so that the reaction of the carburized material promotes an exothermic reaction. However, since the reaction mode and reaction rate vary greatly depending on the temperature and the composition of the atmospheric gas in the furnace, the conventional combustion adjustment method cannot cope. An object of the present invention is to provide a combustion control method for maintaining high combustion efficiency in accordance with the combustion state in the melting furnace and a rotary melting furnace using the same.

The present invention relates to a combustion control method of a rotary melting furnace in which a melting raw material is charged and fuel and oxygen are burned and heated to melt, and the concentration of combustion gas (exhaust gas) that is discharged from the furnace body and can be mixed with the atmosphere A combustion control method for determining a supply flow rate of at least one of fuel and oxygen based on the above, and a stoichiometry of related substances with respect to a chemical reaction occurring between a combustion gas (in-furnace gas) in a furnace body and a dissolved raw material And a ratio (reaction rate) in which the gas in the furnace reacts with the dissolved raw material, and a gas generated by combustion of fuel and oxygen includes a reactive gas that reacts with the molten raw material and an unreacted gas. A chemical reaction model that can calculate the composition of the in-furnace gas after being uniformly mixed as a function of the temperature of the dissolved raw material is created in advance, and the CO, CO _2, and O ₂ in the exhaust gas are created. Concentration is detected and CO Select the oxygen flow rate calculation method based on the temperature, and if the CO concentration is greater than or equal to the set value, obtain the dissolved raw material temperature from the relationship between the predefined ratio of CO concentration and CO2 concentration and the dissolved raw material temperature. Calculating at least the CO concentration in the furnace gas based on the chemical reaction model, and the fuel so that the reaction in the furnace becomes an exothermic reaction based on the supply flow rate of fuel and oxygen and the calculated CO gas concentration An increase flow rate of O ₂ with respect to the supply amount is calculated, and a supply flow rate of at least one of fuel or oxygen is determined. Since CO and H ₂ are generated in a high temperature state and the CO gas concentration is higher than the H ₂ gas concentration, the concentration of CO having a relatively high concentration may be calculated and used. However, it is preferable to calculate the concentrations of both CO and H ₂ gas and to determine the supply flow rate of at least one of the fuel and oxygen so that the reaction in the furnace becomes an exothermic reaction.

In the combustion control method described above, when the CO concentration in the exhaust gas is less than or equal to the set value, it is checked whether or not the O ₂ concentration is greater than or equal to the set value. The amount of unreacted O ₂ is calculated from the oxygen supply flow rate, the O ₂ concentration and the air mixing rate in the exhaust gas, and the decrease flow rate of O ₂ with respect to the fuel supply amount is calculated. It is characterized by deciding. The air mixing rate is preferably defined from the CO2 concentration and O2 concentration of the dry gas in the exhaust gas. In the above description, the determination of the CO concentration is performed first, and the determination process of the O ₂ concentration is performed when the CO concentration is lower than the determination reference value. It varies with the type, O ₂ in such case the concentration detection of the direction is earlier such may be performed first determination of the O ₂ concentration.
Further, according to the present invention, a series of fuel and oxygen supply processes from the start of melting is stored in a storage device, and in the subsequent melting, the stored fuel and oxygen supply processes are regenerated to supply fuel or oxygen. It is preferable to make it.
In the present invention, it is desirable that the melting raw material is an auxiliary material containing an iron raw material and at least a carburized material.

According to the present invention, in the case where it is difficult to directly measure the temperature of the gas component and the melting raw material inside the rotary melting furnace, the chemical reaction model of the combustion gas and the melting raw material is created in advance, so that the water vapor content is reduced after sampling. Supply of fuel and oxygen to the burner that achieves maximum thermal efficiency by enabling estimation of gas composition including water vapor inside the furnace from the detected concentration values of CO, CO ₂ and O ₂ in the exhaust gas after dew condensation and dehumidification The flow rate can be determined. In addition, when the dissolution conditions are the same, it is possible to regenerate and dissolve the fuel and oxygen supply flow rate pattern to the burner in the combustion control dissolution by the gas concentration detection performed previously, so the optimal dissolution conditions Can be operated repeatedly, and the molten metal components and raw material yield can be stabilized.

Hereinafter, an embodiment will be described by taking as an example the case of melting cast iron in a rotary melting furnace.
(Embodiment 1)
FIG. 1 shows a cross section of a rotary melting furnace and a combustion control system of a gas burner. A cylindrical body 1 and conical parts 2 and 3 connected to both ends thereof, a furnace body 5 that rotates around the central axis, and a molten raw material charged in the furnace body 5 with fluid fuel with oxygen A burner 6 for burning and melting, a chimney-like exhaust passage 7 for releasing combustion exhaust gas to the outside, and a charging machine (not shown) for charging the melting raw material 8 and the like into the furnace body 5 are provided. In this description, the burner fuel is propane gas and oxygen, but methane gas, butane gas, and kerosene may be used instead of propane gas.

One end opening 9 of the furnace body 5 serves as a burner mounting opening, and the other end opening 10 of the furnace body 5 serves as an inlet for the melting raw material 8 and an exhaust gas outlet. 11 is a tapping hole provided in the conical portion 3 of the furnace body 5 and is closed except during tapping. Further, a detection unit 40 for detecting gas concentrations of CO, H ₂ and O ₂ in the furnace is attached to the other end opening 10 side, and is connected to the converter 42 by a signal line 41. The converter 42 constitutes a gas concentration meter in combination with the detection unit 40, converts the signal detected by the detection unit 40 into a gas concentration value, and outputs it to the outside.

  Here, as the burner 6 has a fuel blowing port in the center, using those oxygen supply port is provided a structure on the outer periphery. A fuel and oxygen supply system is connected to the upstream side of the burner 6, and an oxygen flow control valve 30 of the oxygen supply system and a fuel flow control valve 31 of the fuel supply system are respectively connected. On the upstream side of the oxygen flow control valve 30 the oxygen supply source 32, upstream of the fuel flow control valve 31 is a fuel supply source 33 is connected.

  Flow rate control valve adjusters 34 and 35 are connected to the oxygen flow control valve 30 and the fuel flow control valve 31, respectively. The flow rate control signals from the arithmetic control unit 20 are connected to the flow control valve adjusters 34 and 35, respectively. Lines 36 and 37 are connected. The arithmetic and control unit 20 is connected to a gas concentration meter converter 42 through a signal line 43, and commands for the oxygen flow rate and fuel flow rate supplied to the rotary melting furnace based on the detected gas concentration by a method described later. Calculate and output the value. The flow rate control valve regulators 34 and 35 feed back the actual flow rate values from the flow rate detectors 38 and 39 provided in the oxygen pipe 40 and the fuel gas pipe 41 in response to the flow rate command value from the arithmetic and control unit 20. The openings of the oxygen flow control valve 30 and the fuel flow control valve 31 are controlled. By controlling the opening degree, the flow rate of oxygen and the flow rate of fuel gas supplied to the burner 6 are controlled with high accuracy, and the combustion heat value and combustion gas composition to the burner in the furnace are controlled.

  Described below for the reaction of the combustion gas in the rotary furnace in the melting step for obtaining a cast iron for molten metal using a rotary furnace as described above. First, the dissolution process will be described. Initially charged into the furnace body 5 from the opening 10 of the iron raw materials and auxiliary materials, such as a predetermined amount of cast iron or steel scrap. After the opening 10 fitted with a chimney exhaust passage 7, to set the burner 6 to ignite the opening 9 at one end of the furnace body 5, it starts dissolving. The iron raw material is dissolved by being heated mainly by radiant heat and conduction heat from the refractory material 12 heated by the burner flame, and by radiant heat from the burner flame. The setting of the burner at the start of melting is a reference fuel gas flow rate determined according to the furnace and an oxygen flow rate for complete combustion.

回転溶解炉の場合、溶解原材料の温度が上昇するにつれて、副資材の１つである加炭材と、燃焼ガスすなわちＣＯ₂および水蒸気との間で数２〜３で示す可逆反応の右方向への反応が活発に起こるようになる。

数２、数３の右方向への反応は吸熱反応である。すなわち、周囲から熱を奪うため、熱効率を低下させるように作用する。 Next, the reaction of the combustion gas related to melting in the rotary melting furnace will be described. When the fuel is propane gas and the mixing ratio is 1.0, that is, complete combustion, the reaction between the fuel and oxygen is expressed by Equation 1.

In the case of a rotary melting furnace, as the temperature of the melting raw material rises, the reversible reaction shown in Equations 2 to 3 between the carburized material, which is one of the auxiliary materials, and the combustion gas, that is, CO ₂ and water vapor, proceeds to the right. The reaction becomes active.

The reactions in the right direction in Equations 2 and 3 are endothermic reactions. That is, since heat is taken away from the surroundings, the heat efficiency is lowered.

さらに、高温状態の炉内では数２〜数４で発生したＣＯ、Ｈ₂と余剰酸素との間で数５、数６の反応の右方向の発熱反応が起こる。

前記数５にてＣＯがＯ₂と反応してＣＯ₂に変化するときに発生する熱量Ｑ５は、数２の反応で同一モル容積のＣＯが生成される際に吸収する熱量Ｑ２よりも大きい。また、数６にてＨ₂が水蒸気に変化するときに発生する熱量Ｑ６は、数３の反応で同一モル容積のＨ₂が生成される際に吸収する熱量Ｑ３よりも大きい。したがって、燃料ガスと酸素ガスの混合比を１．０より大きくした場合、加炭材近傍では数４の発熱反応を促し、さらに加炭材から離れたガス領域では、数２〜数４の反応で生成されるＣＯとＨ₂がＯ₂と反応して、数５、数６の発熱反応が起こるようになる。 Here, when the mixing ratio of the burner fuel is 1.0 or less, a part of the propane gas becomes unreacted, so that the total calorific value generated by the combustion of the fuel is reduced, and the combustion gas And the carburized material cause endothermic reactions of Formulas 2 and 3, further reducing the thermal efficiency and increasing the melting time. On the other hand, when the mixing ratio is 1.0 or more, the surplus oxygen remaining in the combustion reaction with the fuel simultaneously with the reactions of Equations 2 and 3 is mixed into the furnace, and this oxygen reaches the carburized material. Then, an exothermic reaction in the right direction of the reaction shown in Equation 4 occurs.

Further, in the furnace in a high temperature state, the exothermic reaction in the right direction of the reactions of Formulas 5 and 6 occurs between the CO and H ₂ generated in Formulas 2 to 4 and the surplus oxygen.

The amount of heat Q5 that is generated when CO reacts with O ₂ to change to CO ₂ in Equation 5 is greater than the amount of heat Q2 that is absorbed when CO of the same molar volume is generated in the reaction of Equation 2. Further, the amount of heat Q6 generated when H ₂ changes to water vapor in Equation 6 is larger than the amount of heat Q3 absorbed when H ₂ having the same molar volume is generated in the reaction of Equation 3. Therefore, when the mixing ratio of the fuel gas and the oxygen gas is larger than 1.0, the exothermic reaction of Formula 4 is promoted near the carburized material, and the reaction of Formula 2 to Formula 4 is further performed in the gas region away from the carburized material. The CO and H ₂ produced in (5) react with O ₂ to cause exothermic reactions of Formulas 5 and 6.

  Number Direction and speed of reaction of 2 6, the dissolution raw materials temperature as will be described later, affected by the temperature and the gas partial pressure of the gas. On the other hand, supplying excessive oxygen from the burner 6 to the reactions of Formulas 5 and 6 consumes heat for heating wasteful oxygen, and therefore the mixing ratio is excessively increased. However, the thermal efficiency decreases. In addition, since an excessive oxidation reaction of the dissolved raw material occurs, the yield of the dissolved raw material is also reduced.

In order to increase the combustion efficiency, it is necessary to supply an optimal amount of fuel and oxygen that can effectively use the exothermic reactions of Equations 4 to 6 in accordance with the reaction characteristics in the furnace that change with temperature and gas composition. The oxygen flow rate necessary to cause the chemical reactions of Formulas 5 and 6 to the CO and H ₂ gas generated in the furnace is the supply flow rate of propane gas and oxygen at that time, and the CO and H in the furnace. _If the gas concentration of ₂ is known, it can be obtained. As described above, when CO and H ₂ are generated in the furnace gas due to the reaction between the combustion gas and the carburized material, the CO concentration and the H ₂ concentration are detected and necessary for the exothermic reactions of Formulas 5 and 6. If the carburized material disappears or the oxygen supply flow rate becomes excessive and unreacted oxygen remains, the oxygen decrease flow rate is determined and is always optimal for the burner. The right fuel and oxygen. The concept is described below.

バーナーへの酸素ガスの修正増加量Δｗは、炉内ガス中のＣＯガス濃度［ＣＯ］とＨ₂ガス濃度［Ｈ₂］をもとに、数８で求めることができる。

したがって、現在の酸素ガス供給流量に、数８で計算された修正増加量を加えた値に、酸素用流量制御バルブ３０の開度を制御すれば良い。なお、鋳鉄用回転炉において数２および数３の反応にてＣＯとＨ₂が発生する高温状態では、ＣＯのガス濃度はＨ₂のガス濃度よりも大きくなる関係がある。このため、相対的に濃度の大きなＣＯのみの濃度を用いて数８を計算して酸素供給流量を増加しても発熱反応の効果を得ることができる。この時はＨ₂ガス濃度の項は０にすればよい。 In the state where all the oxygen has reacted and there is no unreacted oxygen, assuming that the supply flow rate of propane gas and the supply flow rate of oxygen gas are g and wmol / s, respectively, the total gas flow rate Vmol / s flowing in the furnace is chemical. Quantitatively, it is approximately expressed by Equation 7.

The corrected increase amount Δw of the oxygen gas to the burner can be obtained by Equation 8 based on the CO gas concentration [CO] and the H ₂ gas concentration [H ₂ ] in the furnace gas.

Therefore, the opening degree of the oxygen flow control valve 30 may be controlled to a value obtained by adding the corrected increase calculated in Equation 8 to the current oxygen gas supply flow rate. In a cast iron rotary furnace, CO gas concentration is higher than H ₂ gas concentration in a high temperature state where CO and H ₂ are generated by the reactions of Equations 2 and 3. For this reason, the effect of the exothermic reaction can be obtained even if the oxygen supply flow rate is increased by calculating Equation 8 using the concentration of CO having a relatively high concentration. At this time, the H ₂ gas concentration term may be set to zero.

プロパンガスと燃焼反応しない酸素流量（ｕ＋ｖ）モル/sは、プロパンガスの供給量ｇとバーナー燃料の混合比λを用いると数１２で表わされる。

炉内ガスに占めるＯ₂の割合［Ｏ₂］は、数９〜数１２の関係から数１３となる。

未反応Ｏ₂量ｖモル/sは、既知であるバーナー燃料供給量と排ガス中のＯ₂濃度検出値をもとに数１４で求めることができる。

In addition, the carbonized material disappears as a result of the reaction in the middle of melting, or the mixing ratio of the fuel gas and the oxygen gas becomes too large so that the CO is eliminated and excess O ₂ is discharged. The reduction method is described. Assuming that the supply flow rate of propane gas, the reaction amount of the carburized material, and the unreacted O ₂ flow rate are g, u, and v mol / s, respectively, the reaction in the furnace is stoichiometrically several to several tens when oxygen is in excess. 11 relationships.

The oxygen flow rate (u + v) mol / s at which combustion reaction does not occur with propane gas is expressed by Equation 12 using the propane gas supply amount g and the mixing ratio λ of the burner fuel.

The proportion of O ₂ occupying the furnace gas [O _2] is a number 13 on the relationship number 9 number 12.

The amount of unreacted O ₂ vmol / s can be obtained from Equation 14 based on the known burner fuel supply amount and the detected O ₂ concentration in the exhaust gas.

Next, a method for performing combustion control by correcting and adjusting the oxygen gas supply flow rate based on the CO, H ₂ , and O ₂ concentrations of the in-furnace gas detected by the gas concentration meter in the actual melting operation will be described. This will be described with reference to the flowchart of FIG. First, at the start, the reference flow rate of the burner fuel gas determined from the amount of the iron raw material and the carburized material charged, and the judgment reference values p1 and p2 of the CO concentration and the O ₂ concentration are given to the arithmetic control device 20. Input and memorize. When the automatic combustion control is started, the arithmetic and control unit 20 uses the reference fuel flow rate value input before the start and the flow rate value of oxygen having a mixing ratio of 1.0 with respect to the fuel as the fuel flow control valve regulator 35. And output to the oxygen flow control valve regulator 34 (step 101). Then, the time corresponding to the control cycle Tc is counted (step 102). Next, the concentration of CO, H ₂ , and O _{2 in} the furnace gas is measured using a gas concentration meter including the detection unit 40 and the converter 42 (step 103). First, CO is present at a determination reference value p1 or more. (Step 104).

When CO is detected to be greater than or equal to the determination reference value p1, the following processing is performed. Using the gas concentrations of CO and H ₂ measured in the previous step and the fuel and oxygen supply flow rates to the burner, the oxygen flow rates required for the reactions of Equations 5 and 6, ie, increased flow rates relative to the current oxygen supply amount Is calculated (step 105), and the output value to the oxygen flow control valve regulator 34 is corrected (step 106).

On the other hand, when the CO concentration equal to or higher than the determination reference value p1 is not detected in step 104, it is determined whether or not unreacted O ₂ exists above the determination reference value p2 (step 107). When the O ₂ concentration is detected to be equal to or higher than the judgment reference value p2, the excess oxygen flow rate is calculated by the formulas 9 to 14 using the O ₂ concentration and the fuel and oxygen supply flow rates to the burner (step 108). Then, the output value to the oxygen flow control valve regulator 34 is corrected (step 106). On the other hand, if the O ₂ concentration is not detected at the determination reference value p2 or more in step 107, the current fuel and oxygen supply flow rates are maintained. And it returns to the time count process which is a control period.

The control cycle Tc is set to, for example, Tc = 1 min in accordance with the target melting furnace, and the oxygen flow rate from the oxygen flow control valve 30 is set to the flow rate value given to the oxygen flow control valve regulator 34 by the arithmetic control device 20. It is time to reach the steady state in which the state of the gas in the furnace reflects the operation result. Further, the determination reference values p1 and p2 of the CO concentration and the O ₂ concentration are set to 1% and 2%, for example, and are set in consideration of values that can be stably detected by the gas concentration meter. Further, although the concentration is lower than that of CO, the determination in step 104 may be performed based on the H ₂ concentration.

  The process described in the flowchart of FIG. 2, possible tapping temperature of the dissolution raw materials dissolved iron temperature, for example repeated until 1520 ° C.. Next, a part of the molten metal is taken out, component analysis is performed, and component adjustment is performed as necessary. And if temperature and a component are satisfied, the burner 6 will be stopped, the hot water outlet 11 will be opened, and hot water will be discharged.

(Embodiment 2)
In the first embodiment, the method of detecting the concentration of gas generated in the furnace and determining the supply flow rate of at least one of fuel and oxygen based on this is described. Detecting the concentration of the exhaust gas instead of the gas in the furnace, calculating the composition of the gas generated in the furnace based on a chemical reaction model created in advance, and based on this, at least one of fuel or oxygen A method for determining the supply flow rate will be described. FIG. 3 shows a rotary melting furnace and a combustion control system in the present embodiment. A gas sampling pipe 16 is attached at a position exiting from the exhaust gas outlet opening 10, and connected to a CO, CO ₂ , and O ₂ gas concentration meter 19 via a pipe 17. The gas concentration meter 19 cools and dehumidifies moisture from the exhaust gas taken in from the gas sampling tube 16, and measures the concentration of each gas in a dry state. The arithmetic and control unit 20 incorporates a chemical reaction model, which will be described later, and is connected to the gas concentration meter 19 and the signal line 18, and oxygen supplied to the rotary melting furnace based on the chemical reaction model and the detected gas concentration. Calculate flow rate and fuel flow rate. Other configurations are the same as those of the first embodiment, and are denoted by the same symbols.

Since the concentration of CO ₂ and CO in the atmosphere is low, the ratio hardly changes even if the exhaust gas entering the gas sampling tube 16 is diluted in the atmosphere or the water vapor content is removed from the entire sampling gas. Therefore, in the second embodiment, in the state where the reaction between the carburized material and the combustion gas has started and CO is detected due to the lack of O ₂ , the CO concentration and the CO ₂ concentration in the exhaust gas are detected and the ratio thereof is detected. Is calculated, and the supply flow rate of the necessary oxygen is calculated and corrected by obtaining the raw material temperature in the furnace and the total composition of the true in-furnace gas from the chemical reaction model described later. Further, when the carburized material disappears or the mixing ratio of the fuel gas and the oxygen gas is excessively increased and CO is eliminated, and excess O ₂ is detected, the detected values of the O ₂ and CO ₂ concentrations in the exhaust gas are detected. From this, the excess oxygen supply flow rate is calculated in consideration of the mixing of air into the sample gas, and is corrected and output. Hereinafter, a chemical reaction model, a method of determining the oxygen flow rate necessary for the exothermic reactions of Equations 5 and 6, using the chemical reaction model, the CO concentration and the CO ₂ concentration in the exhaust gas, and using the ratios, and oxygen excess A method for reducing the oxygen supply flow rate using the CO ₂ and O ₂ concentration detection values will be specifically described.

First, the chemical reaction model is described. The chemical reaction model is a mathematical expression of the quantitative relationship of the related substances with respect to the chemical reaction occurring between the combustion gas in the furnace and the dissolved raw material. The target chemical reactions are basically as shown in Equations 2 to 6, but the reaction progress rate of each chemical reaction is limited by the respective chemical reaction rate and mass transfer rate, so individual chemical reaction It is not simply possible to formulate the chemical reaction of the entire furnace based on the above. However, in the rotary melting furnace in this description, the combustion gas generated by the combustion of fuel in the burner is always in a flowing state from the burner side to the outlet, and is continuously stirred even if it reacts with the carburized material in the furnace. Because the soot is mixed and flows out, the fluctuation of the gas components in the furnace is very gradual. For this reason, the atmosphere in the furnace can be regarded as a period of transition to a chemical thermodynamic equilibrium state, and the temperature rising / dissolution process is a much longer phenomenon than the chemical reaction rate. Since the change in the components is related as a function of the temperature of the dissolved material, the chemical reaction of the combustion gas and the carburized material in the furnace is approximated using chemical thermodynamic equilibrium theory. The original chemical thermodynamic equilibrium theory gives the final equilibrium state of the reaction of related substances at a certain temperature, and does not regulate the rate of progress of the reaction. By determining the ratio of the gas that reacts with the dissolved raw material (hereinafter referred to as the reaction rate) to the total amount of combustion gas that is flowing, the quantitative relationship of the related substances at the transient stage where the reaction reaches an equilibrium state is determined. it can. The reaction rate can be identified by measuring the actual reaction state of the melting furnace. That is, the chemical reaction model is that a fuel gas and an oxygen gas are burned by a burner in a rotary melting furnace, and a composition of CO ₂ , H ₂ O, O ₂ corresponding to the flow rate of each gas becomes one end in the furnace. After flowing in from one side, while melting out from the other side, the melting raw material, especially the carburized material, and how much of the whole reacts, and finally the relationship of the gas composition state is dissolved. As a function of the temperature of the raw material, it is expressed so as to suit the blending state of the target rotary melting furnace and the melting raw material used.

Next, a method for determining the gas composition in the furnace using a chemical reaction model will be described. In the chemical reaction model, the inside of the furnace is considered as two layers, a gas layer and a raw material layer. In the case of a rotary melting furnace, the bottom area, which is the reaction rate multiplied by the furnace volume, is regarded as a raw material layer and the rest as a gas layer, and each layer is in a chemical thermodynamic equilibrium state according to the ambient temperature and the partial pressure of the initial gas. I think. Specifically, the following processing is performed.
(1) The temperature tg1 of the gas and raw material in a layer is given.
(2) The amount of gas and moles of O ₂ , H ₂ O, CO ₂ , CO, and H ₂ in the furnace when the fuel and oxygen combustion gas supplied to the burner enter the furnace and are mixed uniformly Find the fraction.
(3) A constant ratio α (reaction rate) is transferred from the combustion gas in the entire furnace to the raw material layer, and the chemical thermodynamic equilibrium state of the chemical reaction between the gas and the carburized material at the temperature tg1 is obtained.
(4) The reaction gas that has reached the above-mentioned chemical thermodynamic equilibrium state is returned to the gas layer, and the intermediate mole number of each gas when uniformly mixed with the unreacted gas is determined.
(5) The chemical thermodynamic equilibrium state of the chemical reaction at the temperature tg1 of the composition gas of (4) is determined.
By the above processing, the composition of the furnace gas corresponding to the furnace temperature tg1, the supply flow rate of fuel and oxygen to the combustion burner, and the reaction rate is obtained.

数１５、数１６、数１７の各反応の平衡定数をＫ１、Ｋ２、Ｋ３、また対象ガスＣＯ₂、Ｈ₂Ｏ、Ｏ₂、ＣＯ、Ｈ₂のガス分圧をＰco₂、Ｐh₂o、Ｐo₂、Ｐco、Ｐh₂で表わすと、ファント・ホッフの等温式と標準自由エネルギー変化から数１８〜数２０の関係式が成り立つ。

すなわち温度が決定されれば、その温度における平衡定数が求まる。 Next, chemical thermodynamic equilibrium, which is the basic idea of the chemical reaction model, will be described. First, the reaction model of the raw material layer (item (3) above) will be described. From the chemical thermodynamic equilibrium theory, the independent reaction equations necessary for obtaining the gas partial pressures of the gas components related to the in-furnace reactions of Equations 2 to 6 are shown in Equations 15 to 17. Can be consolidated. Needless to say, the combination is not limited to the combination of the following three formulas as long as an independent relationship of the related gas components is obtained.

The equilibrium constants of the reactions of Equations 15, 16, and 17 are K1, K2, and K3, and the gas partial pressures of the target gases CO ₂ , H ₂ O, O ₂ , CO, and H ₂ are Pco ₂ , Ph ₂ o, When expressed by Po ₂ , Pco, and Ph ₂ , the relational expressions of Expressions 18 to 20 are established from the Phanto-Hoff isotherm and the standard free energy change.

That is, when the temperature is determined, the equilibrium constant at that temperature is obtained.

数２４〜数２８を数１８〜数２０に代入することにより数２９〜数３１の関係が求まる。

温度が決まればＫ１、Ｋ２、Ｋ３は数１８〜数２０から一義的に定まる。したがって、変数がｘ、ｙ、ｚの３つに対し関係式が３つであることから解が求まり、平衡状態でのＣＯ₂、Ｈ₂Ｏ、Ｏ₂、ＣＯ、Ｈ₂のモル数と分圧の関係が求まる。 Pco ₂ , Ph ₂ o, Po ₂ , Pco, and Ph ₂ are determined by the following method from the fact that the total pressure in the furnace is 1 atm and the initial condition of the fuel gas supply flow rate. When the number of moles of CO ₂ , H ₂ O, O ₂ , CO, and H ₂ in the furnace is represented by A, B, C, D, and E, respectively, the chemical reaction model moves to the raw material layer of the furnace gas. The rate (reaction rate) to be considered is α. The number of moles of CO ₂ , H ₂ O, O ₂ , CO, and H ₂ before the reaction is set to a (= α · A), b (= α · B), c (= α · C), d (, respectively). = Α · D), e (= α · E), and the reaction direction and reaction amount (number of moles) of Equations 15, 16, and 17 are defined as Equations 21, 22, and 23, the reaction The relationship between the partial pressure of each subsequent gas and the number of moles is expressed by several 24 to 28.

By substituting Equations 24 to 28 into Equations 18 to 20, the relationship of Equations 29 to 31 is obtained.

If the temperature is determined, K1, K2, and K3 are uniquely determined from Equations 18 to 20. Therefore, since there are three relational expressions for three variables x, y, and z, a solution is obtained, and the number of moles and minutes of CO ₂ , H ₂ O, O ₂ , CO, and H _{2 in} the equilibrium state are obtained. The relationship of pressure is obtained.

Ｐco₂、Ｐh₂o、Ｐo₂、Ｐco、Ｐh₂は炉内全圧が１atmであることと、燃料ガスの供給流量の初期条件から以下の方法で決定する。ＣＯ₂、Ｈ₂Ｏ、Ｏ₂、ＣＯ、Ｈ₂の反応前のモル数は各々ａ1(＝(１−α)・Ａ＋(ａ−ｘ−ｙ))、ｂ1(＝(１−α)・Ｂ＋(ｂ−ｚ))、ｃ1(＝(１−α)・Ｃ＋(ｃ＋ｙ＋１/2・ｚ))、ｄ1(＝(１−α)・Ｄ＋(ｄ＋２・ｘ))、ｅ1(＝(１−α)・Ｅ＋(ｅ＋ｚ))とし、数５、数６の反応の方向と反応量(モル数)を数３４、数３５のように定めると、反応後の各ガスの分圧とモル数の関係は数３６〜数４０となる。

ただし、数３６から数４０においてＡは炉内ガスの反応後の総モル数であり、数４１である。

数３６〜数４０を数３２、数３３に代入することにより数４２、数４３の関係が求まる。

温度が決まればＫ４、Ｋ５は数３２、数３３から一義的に定まる。以上により変数がｘ1、ｙ1の２つに対し関係式が２つあることから解が求まり、炉内の最終的なＣＯ₂、Ｈ₂Ｏ、Ｏ₂、ＣＯ、Ｈ₂のモル数と分圧が求まる。炉内圧は全圧が１atmであるから、分圧はガス濃度に等しい。 Next, the reaction model in the gas layer (item (4) above) will be described. There are two target reaction equations, Equation 5 and Equation 6. When the equilibrium constants of the reactions of Equations 5 and 6 are expressed by K4 and K5, the following relational expression is established in the same manner as the raw material layer.

Pco ₂ , Ph ₂ o, Po ₂ , Pco, and Ph ₂ are determined by the following method from the fact that the total pressure in the furnace is 1 atm and the initial condition of the fuel gas supply flow rate. The number of moles of CO ₂ , H ₂ O, O ₂ , CO, and H ₂ before the reaction is a1 (= (1−α) · A + (a−xy)) and b1 (= (1−α) · B + (b−z)), c1 (= (1−α) · C + (c + y + 1/2 · z)), d1 (= (1−α) · D + (d + 2 · x)), e1 (= (1− α) · E + (e + z)), and the reaction direction and reaction amount (number of moles) of Equations 5 and 6 are determined as in Equations 34 and 35, the partial pressure and the number of moles of each gas after the reaction The relationship is expressed by Equation 36 to Equation 40.

However, in Equations 36 to 40, A is the total number of moles after the reaction of the in-furnace gas, and is Equation 41.

By substituting Equations 36 to 40 into Equations 32 and 33, the relationship between Equations 42 and 43 is obtained.

If the temperature is determined, K4 and K5 are uniquely determined from Equations 32 and 33. From the above, there are two relational expressions for the two variables x1 and y1, and the solution is obtained. The final number of moles and partial pressure of CO ₂ , H ₂ O, O ₂ , CO, and H _{2 in} the furnace Is obtained. Since the internal pressure of the furnace is 1 atm, the partial pressure is equal to the gas concentration.

The reaction rate α of the chemical reaction model that determines the amount of gas in the raw material layer relative to the gas in the entire furnace can be identified by measuring the CO and CO ₂ gas concentrations and the temperature change of the raw material in the model operation of the actual furnace. . Using the reaction rate of the chemical reaction model as a variable parameter for the fuel gas supply conditions of the actual furnace model operation, the relationship between the raw material temperature and the gas concentration of CO and CO ₂ with the water vapor content removed is calculated, and the actual measured value The reaction rate closest to the change is set as the reaction rate under the fuel gas supply conditions. As a result of model melting with respect to the mixing ratio of different fuels for the raw material of the actual rotary melting furnace, the relationship between the temperature of the raw material, the amount of charging of the carburized material, and the reaction rate is as shown in FIG. It was found that the reaction in the installed rotary melting furnace can be modeled. Once the chemical reaction model can be created, the gas composition in the furnace corresponding to the temperature of the molten raw material can be obtained by calculation even if the supply process of fuel and oxygen changes.

Next, a method for determining the oxygen flow rate necessary for the exothermic reactions of Equations 5 and 6 using the concentration ratio of CO and CO ₂ based on the chemical reaction model will be described. FIG. 7 shows the CO gas concentration [CO] obtained based on the chemical reaction model using the reaction rate identified from the actual dissolution experiment results when the mixing ratio of propane gas to oxygen is 1.0. The relationship between the ratio of the CO ₂ gas concentration [CO ₂ ] and the raw material temperature is shown. The [CO] / [CO ₂ ] ratio increases from 0 with increasing raw material temperature. That is, when the mixing ratio is 1.0, there is no CO at first, the temperature of the raw material rises, and the reaction between the combustion gas and the carburized material starts to occur and increases with the temperature rise. . Even when the mixing ratio of oxygen is excessive with respect to propane gas, the value is different but there is no difference in upward change, and there is a 1: 1 correspondence between the raw material temperature and the [CO] / [CO ₂ ] ratio. Therefore, if the [CO] / [CO ₂ ] ratio is obtained from the detected gas concentration, the temperature of the raw material in the furnace can be estimated, and the molar volume of the CO gas and H ₂ gas in the furnace can be estimated from the chemical reaction model. Pressure and gas concentration can be determined. That is, the amount of oxygen necessary for the reactions of Equations 5 and 6 is obtained.

Next, the amount of oxygen supply in the state where the carburized material disappears as a result of the reaction in the middle of melting, or the mixing ratio of the fuel gas and the oxygen gas becomes too large to eliminate CO and exhaust excess O ₂ . The reduction method is described. Assuming that the supply flow rate of propane gas, the reaction amount of the carburized material, and the unreacted O ₂ flow rate are g, u, and v mol / s, respectively, the reaction in the furnace stoichiometrically occurs when the O ₂ is excessive. ˜Expression 11

これより、空気の混入を考慮した未反応Ｏ₂量ｖモルは、空気の混入率βとＯ₂濃度［Ｏ₂］から数４５で求められる。

したがって、数４５で計算された酸素量をバーナー燃料から減ずれば、過剰酸素を無くすことができる。 Assuming that the mixing rate of air into the gas sampling tube is β, the mixing rate β can be obtained from the CO ₂ concentration [CO ₂ ] and the O ₂ concentration [O ₂ ] of the dry gas by Equation 44.

From this, the unreacted O ₂ amount v mol considering the air mixing can be obtained from the air mixing ratio β and the O ₂ concentration [O ₂ ] by the formula 45.

Therefore, excess oxygen can be eliminated by reducing the amount of oxygen calculated in Equation 45 from the burner fuel.

Next, in the actual melting operation, the oxygen gas supply amount is corrected and adjusted using the built-in chemical reaction model based on the CO, CO ₂ and O ₂ concentrations of the exhaust gas detected by the gas concentration meter 19. A method for controlling combustion will be described with reference to the flowchart of FIG. First, at the start, the reference flow rate of the burner fuel gas determined from the amount of the iron raw material and the carburized material charged, and the amount of the raw material, and the determination criteria for the CO concentration and the O ₂ concentration are given to the arithmetic and control unit 20. The values p1 and p2 are input and stored. When the automatic combustion control is started, the arithmetic and control unit 20 uses the reference fuel flow rate value input before the start and the flow rate value of oxygen having a mixing ratio of 1.0 with respect to the fuel as the fuel flow control valve regulator 35. And output to the oxygen flow control valve regulator 34 (step 201). Then, the time corresponding to the control cycle Tc is counted (step 202). Next, the concentration of CO, CO ₂ , and O _{2 in} the exhaust gas is measured using the gas concentration meter 19 (step 203), and it is first determined whether or not CO is present above the determination reference value p1 (step 204).

When CO is detected to be greater than or equal to the determination reference value p1, the following processing is performed. First, the CO / CO ₂ concentration ratio [CO] / [CO ₂ ] = r is calculated (step 205). Then, after determining the reaction rate α to be applied from the mixing ratio of the current fuel and oxygen supply flow rate based on the built-in chemical reaction model, the raw material temperature tr at which the CO / CO ₂ concentration ratio is r is obtained, The gas concentration of CO and H _{2 including} H ₂ O in the furnace is calculated (step 206). Then, using the gas concentrations of CO and H ₂ calculated in the previous step and the fuel and oxygen supply flow rates to the burner, the oxygen flow rates necessary for the reactions of Equations 5 and 6, that is, the current oxygen supply amount The increased flow rate is calculated (step 207), and the output value to the oxygen flow rate control valve regulator 34 is corrected (step 208).

On the other hand, when the CO concentration equal to or higher than the determination reference value p1 is not detected in step 204, it is determined whether or not unreacted O ₂ exists above the determination reference value p2 (step 209). When O ₂ is detected to be equal to or greater than the determination reference value p2, the excess oxygen flow rate is calculated using Equations 44 to 45 using the O ₂ concentration and the fuel and oxygen supply flow rate values to the burner (Step 210). The output value to the oxygen flow control valve regulator 34 is corrected (step 208). On the other hand, if the O ₂ concentration is not detected at the determination reference value p2 or more in step 209, the current supply amount of fuel and oxygen is maintained. And it returns to the time count process which is a control period.

The control cycle Tc, the determination reference values p1 and p2 of the CO concentration and the O ₂ concentration are the same as in the first embodiment, the response of the flow control valve system of the fuel and oxygen, the stable detection of the gas concentration meter, or the gas sampling tube Set the value to take into account the effects of air contamination. The process described in the flowchart of FIG. 4 is repeated until the temperature of the melting raw material reaches a temperature at which iron can be melted and can be discharged, and the components are adjusted as necessary. Stop and open the tap 11 to pour out hot water. By applying the chemical reaction model as described above and detecting the concentration of CO and CO ₂ in the exhaust gas and controlling the oxygen supply flow rate of the combustion burner, the maximum thermal efficiency is achieved according to the chemical reaction state in the furnace. Combustion control of the resulting burner can be realized. Although the thermodynamic equilibrium theory is applied to the chemical reaction model in the above explanation, as reported for char or coke, a model consisting of the overall reaction rate of the chemical reaction resistance and the diffusion resistance in the fluid film is used. May be.

In Embodiments 1 and 2, the oxygen to be controlled has been described as being supplied to the burner, but an auxiliary oxygen supply path may be provided separately. In addition, when the maximum supply amount of oxygen to the burner is limited and the CO remains even when the oxygen supply amount is set to the maximum value, the flow rate of the fuel may be reduced. Furthermore, the fuel may be increased or decreased with the oxygen flow rate kept constant. Any of them can be easily implemented by the method described in the present invention, if the relationship between the fuel and oxygen of Formula 1 is used. In the first and second embodiments, the determination of the CO concentration is performed first, and the determination process of the O ₂ concentration is performed when the CO concentration is lower than the determination reference value. If the response characteristics differ depending on the type of gas and the O ₂ concentration detection is faster, the O ₂ concentration may be determined first.

  Furthermore, when dissolution with the same composition of the raw material to be charged is repeated, the dissolution is initially performed by the combustion control method using the gas concentration detection described in the first or second embodiment, and at that time The fuel and oxygen supply process to the combustion burner is stored in the memory of the arithmetic and control unit 20, and the subsequent melting is performed by using the stored fuel and oxygen supply process data having the same composition of the melting raw material as the dissolution time. It is also possible to use a method of sequentially reading and controlling the flow rate of fuel and oxygen as the time elapses. According to this method, it is not necessary to constantly measure the gas concentration, so that heat resistance is required, which reduces the cost of heat loss of the gas sampling pipe, and maintenance and inspection of the gas concentration meter dust filter and reference gas. The work can be reduced.

A schematic diagram of a melting furnace for cast iron and a combustion control system for explaining the first embodiment of the present invention Flowchart for explaining the combustion control method of Embodiment 1 of the present invention Schematic diagram of a melting furnace for cast iron and a system diagram of a combustion control device for explaining Embodiment 2 of the present invention The flowchart for demonstrating the combustion control method of Embodiment 2 of this invention. Weight examples of charging components, molten metal components, and loss components in the rotary melting furnace subject to the present invention Relationship between fuel mixing ratio and reaction rate in the rotary melting furnace of the present invention Example of relationship between raw material temperature and (CO gas concentration) / (CO ₂ gas concentration) in the rotary melting furnace of the present invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 5 ... Melting furnace main body 6 ... Burner 19 ... Gas concentration meter 20 ... Arithmetic control device 30 ... Flow control valve for oxygen 31 ... Flow control valve for fuel 34 ... Oxygen flow control valve regulator 35 ... Fuel flow control valve regulator 38 ... Oxygen flow detector 39 ... Fuel flow detector 40 ... Gas concentration meter detector 42 ... Gas concentration meter converter

Claims (5)

In a combustion control method for a rotary melting furnace in which melting raw materials are charged and fuel and oxygen are burned to heat and melt, based on the concentration of the combustion gas (exhaust gas) that is discharged from the furnace body and can be mixed with the atmosphere A combustion control method for determining a supply flow rate of at least one of fuel and oxygen,
A mathematical expression showing the stoichiometric relationship of the substances concerned with the chemical reaction that occurs between the combustion gas (in-furnace gas) and the melting raw material in the furnace and the rate (reaction rate) at which the in-furnace gas reacts with the melting raw material. The gas generated by the combustion of fuel and oxygen is divided into a reaction gas that reacts with the dissolved raw material and an unreacted gas, and the composition of the gas in the furnace after it has been uniformly mixed is determined. Create a chemical reaction model that can calculate temperature as a function in advance,
The concentration of CO, CO ₂ and O _{2 in} the exhaust gas is detected, and the oxygen flow rate calculation method is selected based on the CO concentration. The temperature of the dissolved raw material is obtained from the relationship between the ratio of the CO2 concentration and the dissolved raw material temperature, and at least the CO concentration in the furnace gas is calculated based on the chemical reaction model, and the supply flow rate of the fuel and oxygen is calculated. A rotary melting furnace characterized in that an increase flow rate of O ₂ with respect to a fuel supply amount is calculated so that a reaction in the furnace becomes an exothermic reaction based on a gas concentration, and a supply flow rate of at least one of fuel or oxygen is determined. Combustion control method. In the combustion control method of the rotary melting furnace according to claim 1, when the CO concentration in the exhaust gas is equal to or lower than a set value, it is checked whether or not the O ₂ concentration is equal to or higher than the set value. The amount of unreacted O ₂ is calculated from the supply flow rate of fuel and oxygen, the O ₂ concentration and the air mixing rate in the exhaust gas, and the decrease flow rate of O ₂ with respect to the fuel supply amount is calculated. A combustion control method for a rotary melting furnace characterized by determining a flow rate. The aeration rate, combustion method of the rotary furnace according to claim 2, wherein the defined from CO2 concentrations and O2 concentrations in the dry gas in the exhaust gas. A series of fuel and oxygen supply processes from the start of dissolution are stored in a storage device, and the subsequent fuel and oxygen supply processes are regenerated to supply fuel or oxygen in the subsequent melting. The combustion control method for a rotary melting furnace according to any one of claims 1 to 3. The combustion method for a rotary melting furnace according to any one of claims 1 to 4, wherein the melting raw material is an auxiliary material containing an iron raw material and at least a carburizing material.

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