阅读说明：本技术 一种氩氧精炼铁合金生产过程中的铁水温度控制方法 (Molten iron temperature control method in argon oxygen refined iron alloy production process ) 是由 尤元 魏丙坤 关常君 于 2020-08-18 设计创作，主要内容包括：本发明公开了一种氩氧精炼铁合金生产过程中的铁水温度控制方法,其方法为：步骤一、建立专家控制规则表；步骤二、将一炉冶炼时间分为五个子区间；步骤三、把估计模型设计为辅助通道的传递函数；步骤四、假定氧气和氩气储罐提供的气源压力恒定；步骤五、完成各时段的氩气恒流量控制,同时,PLC作为推理控制器,计算氧流量调节阀开度,并送给氧流量调节阀,完成针对主输出的推理控制,重复上述过程,直至到冶炼终点。有益效果：能够解决氩氧精炼铁合金生产过程冶炼温度不可测的难题,实现对冶炼温度的实时控制。可有效解决冶炼期内脱碳速率的时变性及不确定性对控制精度的影响,该方法计算量小,算法简单,控制的实时性好,容易实现。(The invention discloses a method for controlling the temperature of molten iron in the production process of argon-oxygen refined ferroalloy, which comprises the following steps: step one, establishing an expert control rule table; step two, dividing the smelting time of a furnace into five subintervals; step three, designing an estimation model as a transfer function of an auxiliary channel; step four, assuming that the pressure of a gas source provided by an oxygen and argon storage tank is constant; and fifthly, controlling the constant flow of argon gas in each time interval, meanwhile, using the PLC as an inference controller to calculate the opening of the oxygen flow regulating valve and send the oxygen flow regulating valve to complete inference control aiming at main output, and repeating the process until the smelting end point. Has the advantages that: the method can solve the problem that the smelting temperature is not measurable in the production process of the argon oxygen refined iron alloy, and realize the real-time control of the smelting temperature. The method can effectively solve the problem of influence of time-varying property and uncertainty of the decarburization rate on the control precision in the smelting period, and is small in calculation amount, simple in algorithm, good in control real-time performance and easy to realize.)

1. A method for controlling the temperature of molten iron in the production process of argon oxygen refined ferroalloy is characterized in that: the method comprises the following steps:

step one, establishing a relation curve of ratios of argon and oxygen in different smelting periods, discretizing the curve, and storing the discretized curve into a PLC in a form called as an equal decarburization rate expert control rule table;

step two, dividing the smelting time of a furnace into five subintervals, namely: Δ tmz- Δ tmin, Δ tmin and Δ t- Δ, Δ t- Δ and Δ t + Δ, Δ t +/Δ and Δ tmax, and Δ tmax and Δ tmm; each interval represents a smelting start period, a smelting initial period, a smelting middle period, a smelting final period and a smelting end period respectively; determining the ratios of oxygen to argon respectively to be Qomax/QNmin, Qmid/QNmid, Qmid/QNmax and Qomin/QNmax in each period, wherein the determination principle of the ratios is that the oxygen supply intensity is gradually reduced along with the reduction of the carbon content of molten iron in the furnace and the nitrogen supply intensity is gradually increased along with the increase of the CO concentration so as to reduce the CO partial pressure, ensure the constant decarburization reaction rate and provide guarantee for the smooth implementation of reasoning control;

designing an estimation model as a transfer function of an auxiliary channel for estimating the influence of disturbance on auxiliary output, designing an estimator as a ratio of a disturbance channel transfer function of the influence of the disturbance on main output to a disturbance channel transfer function of the influence of the disturbance on the auxiliary output for estimating the influence of the disturbance on the main output, designing an inference controller as a reciprocal of a main channel transfer function with a filter for counteracting the influence of the disturbance on the main output and ensuring output tracking input;

step four, assuming that the pressure of gas sources provided by the oxygen and argon storage tanks is constant, installing two regulating valves and two flowmeters on a pipeline between the two gas sources and the furnace respectively, detecting the flow of oxygen and argon on line according to a sampling period under the control of a PLC (programmable logic controller), wherein the regulation of the flow of oxygen and argon is completed by the regulating valves installed on an oxygen supply pipeline and an argon supply pipeline, the PLC and an electromagnetic flowmeter on the oxygen supply pipeline and the regulating valves form a PID (proportion integration differentiation) constant oxygen flow control loop, the similar PLC and the electromagnetic flowmeter on the argon supply pipeline and the regulating valves form a PID constant argon flow control loop, and the given values of the two loops are from an industrial personal computer respectively and depend on a smelting process control rule;

and fifthly, firstly, calculating the total oxygen supply amount by an industrial personal computer, then respectively calculating the oxygen supply amount and the argon supply amount in each time interval according to an equal decarburization rate expert control rule table, sending the oxygen supply amount and the argon supply amount to a PLC (programmable logic controller) as a set value in each time interval, using the PLC as a PID (proportion integration differentiation) controller, performing PID (proportion integration differentiation) operation according to the argon flow measured by an argon flow sensor and the set value in the time interval, further controlling the opening of an argon flow regulator, completing the argon constant flow control in each time interval, meanwhile, using the PLC as an inference controller, calculating the opening of an oxygen flow regulating valve, sending the oxygen flow regulating valve to an oxygen flow regulating valve, completing inference control.

2. The method of claim 1, wherein the method comprises the following steps: the smelting process control rule table refers to the ratio of oxygen to argon determined to ensure that the decarburization rate is substantially constant throughout the smelting period, and the ratio of oxygen to argon is 6:1 when the carbon content is 8% -6%, 3:1 when the carbon content is 6% -4%, 1:1 when the carbon content is 4% -2%, 1:3 when the carbon content is 2% -1%, and 1:6 when the carbon content is 1% -0.25%.

3. The method of claim 1, wherein the method comprises the following steps: the argon constant flow control is the argon constant flow control which is finished by a closed-loop control loop formed by a flow sensor and a regulating valve which are arranged on an argon supply pipeline through a PLC according to the given flow sent by an industrial personal computer through a PID algorithm.

4. The method of claim 1, wherein the method comprises the following steps: the smelting beginning period, the smelting initial period, the smelting middle period, the smelting final period and the smelting end period are five smelting processes which divide the whole smelting time from beginning to end at equal intervals, and the carbon content stages specifically correspond to 8% -6%, 6% -4%, 4% -2%, 2% -1% and 1% -0.25%.

Technical Field

The invention relates to a molten iron temperature control method, in particular to a molten iron temperature control method in an argon oxygen refined iron alloy production process.

Background

The metallurgical principle of the AOD refining technology is to inject a mixed gas of oxygen and inert gas (Ar, N2) into a furnace, dilute the partial pressure of CO gas generated by decarburization reaction with Ar (or N2), thereby promoting the progress of the decarburization reaction and suppressing the oxidation of chromium in molten steel. The AOD furnace has the disadvantages of high refining temperature, long smelting period, violent gas stirring, serious steel slag scouring, large change range of the pH value of the smelting period in the furnace and the like, and the working conditions in the furnace are very bad, so that the online real-time measurement of the smelting temperature is always a difficult problem, which brings more difficulty to the real-time control of the smelting temperature.

Aiming at the influence of high furnace temperature on refractory materials in the furnace. The literature (Wangbuiping et al, measures for improving the service life of the Tai-gang AOD furnace, Steel & 2 (2004), Vol.39, No.2) studies show that the erosion rate of the refractory material of the furnace lining is improved by 1 time when the temperature of the molten pool is improved by 50 ℃ every time when the temperature of the molten pool is higher than 1700 ℃. When AOD is used for smelting iron alloy, the temperature of a melting pool in the decarburization period is as high as 1800 ℃, and the working time of the refractory material in the furnace at high temperature is longer. Therefore, the bath temperature and refining time during the decarburization period of the AOD have a great influence on the life of the refractory in the furnace. The service life of the conventional thermocouple sheath is short, usually within dozens of hours, and the requirement of industrial continuous production in a smelting process is not met. The method is a remedy method for shortening the smelting time, avoiding the long-time corrosion of the refractory material at high temperature and indirectly improving the service life of the refractory material, and the method researches the judgment of the end point by utilizing furnace gas analysis in documents (Shizhiji, and the like, application of furnace gas analysis end point control technology in a horse steel converter, iron and steel, 2007,42(4). -24-26;) so as to avoid the after-blowing and achieve the purpose of shortening the smelting time.

Aiming at the influence of large furnace temperature change on the service life of the refractory material. Firstly, AOD production is intermittent, during the period of equal molten iron, the temperature of a furnace lining can be reduced to about 1300 ℃, the temperature of the furnace lining of a molten pool in a decarburization period can be up to more than 1750 ℃, and the temperature of the furnace lining of the molten pool in a reduction period can be reduced to about 1650 ℃; secondly, the gas supply elements are all air-cooled, and the temperature of a refractory material of a furnace lining around the air gun is suddenly reduced to below 850 ℃ during the molten steel waiting period; thirdly, the temperature of the furnace lining in the air hole area with uneven furnace lining temperature is higher in the smelting process, and the temperature of the furnace lining in other areas is lower; fourthly, since a large amount of slag-making materials, alloys, metals, etc. need to be added into the molten bath during the stainless steel refining, the temperature of the lining of the slag line portion is rapidly reduced in a short time. These cause a large change in the furnace temperature of the AOD, and cause the refractory to peel off, which affects the life of the AOD, and also makes it difficult to select the thermocouple mounting position. The document (Tangxingzhi et al, construction and baking of walking beam furnace linings, Industrial heating, 2004,33(5) — 53-55) establishes a reasonable AOD lining baking schedule, so that the furnace lining bricks can be slowly raised to high temperature and the lining bricks are guaranteed to be baked through, and in the case of long-time waiting for molten steel, the furnace lining is also baked to avoid the peeling caused by the sudden heating of the refractory materials of the furnace lining when contacting the molten steel or the excessive temperature drop when the molten steel is in long-time waiting.

Aiming at the influence of the serious scouring of gas and steel flow on the service life of the refractory material. During the whole operation of the AOD, a large amount of gas (1-2.5 m) is blown into the molten bath³Min-1. t-1). With the continuous development of the technology, the oxygen supply intensity and the stirring intensity of the molten pool are continuously improved. This causes a strong erosion of the bath refractory, especially the rear wall of the AOD is subjected to large gas and steel flows, which reduces the refractory life. The slag splashing furnace protection technology is researched in the literature (Zhang Fei, etc., development and application of the converter slag splashing furnace protection technology, iron and steel technology 2007(4) -9-10,30), and the slag splashing furnace protection technology has a good effect on maintenance of a furnace lining and a furnace type through a smelting process, slag adjustment and process parameter adjustment, so that the furnace life is greatly improved. However, the widespread use of this technique makes it more difficult to ensure the accuracy of a thermocouple, a contact measurement method.

Aiming at the influence of large slag alkalinity fluctuation on the service life of refractory materials. The AOD furnace lining is not only eroded and washed by slag, but also has a large fluctuation range of slag alkalinity in a refining period, and the value fluctuates within 1.0-3.0. Particularly, during the reduction period, the content of Si oxygen in the slag suddenly increases, and the Si oxygen in the slag reacts with MgO and CaO in the lining of the basic refractory material under stirring of argon gas, so that low-melting-point Calmalloyte (CaO. MgO. Si oxygen) and magnesiopyroxene (3 CaO. MgO. 2Si oxygen) are generated, and the bonding between the periclase is broken. These low melting products soften and fall off during AOD refining, thereby reducing refractory life. It is worth mentioning that the amount of lean ores is greatly increased along with the reduction of the amount of concentrate, particularly, the content of sulfur, phosphorus and silicon in the lean ores is larger, so that the change range of the pH value in the furnace is larger, which givesThe research on the refractory material used for the thermocouple sheath brings about greater difficulty. Literature (Wangbei, Tai Steel AOD campaign improvement measures, Steel, 2 months 2004, Vol.39, No.2) tests found that CaF in slag₂The service life of the furnace lining is greatly reduced with the increase of the content of MgO in the slag, and the service life of the furnace lining is correspondingly improved with the increase of the content of MgO in the slag. Therefore, the alkalinity and the components of the reducing slag are adjusted, the slag alkalinity CaO/Si oxygen is controlled to be 1.8-2.0, the (CaO + MgO)/Si oxygen is controlled to be 2.0-2.4, and the CaF is strictly controlled₂Amount of addition and CaF₂The ratio of/CaO.

In a word, thermocouple sheath materials which can resist high temperature, have large temperature difference, have large mechanical scouring resistance and have large acid and alkali resistance change range are not mature, so that the AOD furnace (converter) smelting temperature online real-time contact measurement technology is not successful, and a sublance or projectile type intermittent measurement method has to be adopted at present. And the operator determines the next operation or judges whether the smelting end point is reached according to the measured temperature. This method obviously does not allow to obtain real-time smelting temperatures, which causes great difficulties in real-time temperature control. The invention provides a real-time control method for solving the problem of smelting temperature under the condition that the smelting temperature of an AOD furnace cannot be measured in real time, so that the quality of smelting iron alloy is ensured.

Disclosure of Invention

The invention aims to solve the problem that the quality of iron alloy smelting cannot be ensured under the condition that the smelting temperature of the existing AOD furnace cannot be measured in real time, and provides a method for controlling the temperature of molten iron in the production process of refining the iron alloy by argon oxygen.

The invention provides a method for controlling the temperature of molten iron in the production process of argon oxygen refined ferroalloy, which comprises the following steps:

step one, establishing a relation curve of ratios of argon and oxygen in different smelting periods, discretizing the curve, and storing the discretized curve into a PLC in a form called as an equal decarburization rate expert control rule table;

step two, dividing the smelting time of a furnace into five subintervals, namely: Δ tmz- Δ tmin, Δ tmin and Δ t- Δ, Δ t- Δ and Δ t + Δ, Δ t +/Δ and Δ tmax, and Δ tmax and Δ tmm; each interval represents a smelting start period, a smelting initial period, a smelting middle period, a smelting final period and a smelting end period respectively; determining the ratios of oxygen to argon respectively to be Qomax/QNmin, Qmid/QNmid, Qmid/QNmax and Qomin/QNmax in each period, wherein the determination principle of the ratios is that the oxygen supply intensity is gradually reduced along with the reduction of the carbon content of molten iron in the furnace and the nitrogen supply intensity is gradually increased along with the increase of the CO concentration so as to reduce the CO partial pressure, ensure the constant decarburization reaction rate and provide guarantee for the smooth implementation of reasoning control;

designing an estimation model as a transfer function of an auxiliary channel for estimating the influence of disturbance on auxiliary output, designing an estimator as a ratio of a disturbance channel transfer function of the influence of the disturbance on main output to a disturbance channel transfer function of the influence of the disturbance on the auxiliary output for estimating the influence of the disturbance on the main output, designing an inference controller as a reciprocal of a main channel transfer function with a filter for counteracting the influence of the disturbance on the main output and ensuring output tracking input;

step four, assuming that the pressure of gas sources provided by the oxygen and argon storage tanks is constant, installing two regulating valves and two flowmeters on a pipeline between the two gas sources and the furnace respectively, detecting the flow of oxygen and argon on line according to a sampling period under the control of a PLC (programmable logic controller), wherein the regulation of the flow of oxygen and argon is completed by the regulating valves installed on an oxygen supply pipeline and an argon supply pipeline, the PLC and an electromagnetic flowmeter on the oxygen supply pipeline and the regulating valves form a PID (proportion integration differentiation) constant oxygen flow control loop, the similar PLC and the electromagnetic flowmeter on the argon supply pipeline and the regulating valves form a PID constant argon flow control loop, and the given values of the two loops are from an industrial personal computer respectively and depend on a smelting process control rule;

and fifthly, firstly, calculating the total oxygen supply amount by an industrial personal computer, then respectively calculating the oxygen supply amount and the argon supply amount in each time interval according to an equal decarburization rate expert control rule table, sending the oxygen supply amount and the argon supply amount to a PLC (programmable logic controller) as a set value in each time interval, using the PLC as a PID (proportion integration differentiation) controller, performing PID (proportion integration differentiation) operation according to the argon flow measured by an argon flow sensor and the set value in the time interval, further controlling the opening of an argon flow regulator, completing the argon constant flow control in each time interval, meanwhile, using the PLC as an inference controller, calculating the opening of an oxygen flow regulating valve, sending the oxygen flow regulating valve to an oxygen flow regulating valve, completing inference control.

The AOD furnace is a production device for refining stainless steel or ferroalloy by blowing oxygen and argon mixed gas from the top and the bottom.

The gas source is liquid oxygen and liquid argon with specific temperature and pressure stored in a gas storage tank, and in some cases, nitrogen can be used for replacing argon in the initial stage and the middle stage of smelting in order to reduce cost.

The smelting process control rule table refers to the ratio of oxygen to argon determined to ensure that the decarburization rate is substantially constant throughout the smelting period, the ratio of oxygen to argon is 6:1 when the carbon content is between 8% and 6%, the ratio of oxygen to argon is 3:1 when the carbon content is between 6% and 4%, the ratio of oxygen to argon is 1:1 when the carbon content is between 4% and 2%, the ratio of oxygen to argon is 1:3 when the carbon content is between 2% and 1%, and the ratio of oxygen to argon is 1:6 when the carbon content is between 1% and 0.25%.

The mixed gas is a mixed gas of argon and oxygen with a fixed ratio of argon to oxygen determined according to a smelting process control rule table.

The argon constant flow control is the argon constant flow control which is finished by a closed loop control circuit formed by a flow sensor and a regulating valve which are arranged on an argon supply pipeline through a PLC according to the given flow sent by an industrial personal computer through a PID algorithm.

The smelting beginning period, the smelting initial period, the smelting middle period, the smelting end period and the smelting end period are five smelting processes which divide the whole smelting time from beginning to end at equal intervals, and the specific corresponding carbon content stages are 8% -6%, 6% -4%, 4% -2%, 2% -1% and 1% -0.25%.

Dividing the smelting time of the AOD furnace into [ △ t_mz，△t_min]、(△t_min，△t-△]、(△t-△，△t+△)、[△t+△，△t_max) And [ △ t_max，△t_mm]And 5 sub-intervals, wherein the finer the quantization interval is divided, the more constant the decarburization rate is, the higher the accuracy of the established mathematical model is, and the higher the control accuracy of the corresponding smelting temperature is.

The control program is an application program of the smelting process which is compiled by Vc language and ladder diagram language, automatically operated by an industrial personal computer and PLC, controlled by argon constant flow, suppressed in decarburization rate time-varying expert control and controlled by smelting temperature inference.

The invention has the beneficial effects that:

the method for controlling the molten iron temperature in the production process of the argon oxygen refined iron alloy provided by the invention takes the smelting temperature as main output, takes the oxygen flow as auxiliary output, takes the oxygen amount which does not react with carbon as disturbance, and designs an estimation model, an estimator and an inference controller by establishing mathematical models of a main channel, an auxiliary channel and a disturbance channel, thereby solving the problem that the smelting temperature in the production process of the argon oxygen refined iron alloy is not measurable and realizing the real-time control of the smelting temperature. The expert control method does not need to establish a complicated mathematical model, only needs to determine the argon oxygen ratio of each smelting interval according to expert experience and offline experiments, and ensures that the decarburization rate is basically constant by reducing the partial pressure of CO, so that the method can effectively solve the influence of time-varying property and uncertainty of the decarburization rate in the smelting period on the control precision.

Drawings

Fig. 1 is a schematic view of the gas supply system according to the present invention.

Fig. 2 is a schematic block diagram of the inference control of the present invention. In the figure, Y(s), Y_s(s) primary and secondary outputs of the process, respectively; g_p(s),G_ps(s) transfer functions for the primary control channel and the secondary control channel, respectively; r(s) is a set value; d(s) is an undetectable disturbance of the process; a(s), B(s) are transfer functions of disturbance channels.

FIG. 3 is a graph showing the relationship between the ratio of argon to oxygen in the whole smelting period. The ordinate represents the flow rate, the abscissa represents the smelting time, the solid line in the figure represents the oxygen flow rate, and the broken line represents the argon flow rate.

Detailed Description

Please refer to fig. 1 to 3:

firstly, determining the caliber of an air supply pipeline according to the smelting tonnage of the AOD furnace, and then selectively installing an adjusting valve and a flowmeter according to the caliber of the pipeline, wherein the adjusting valve and the flowmeter must meet the requirements of gas flow adjustment and measurement, and a transmitter of the adjusting valve and the flowmeter adopts a 485 communication protocol so as to simplify the design of a hardware circuit of a controller.

And secondly, establishing a main channel mathematical model and a disturbance channel mathematical model of the influence of disturbance on main output according to an oxidation reaction heat release principle, then establishing an auxiliary channel mathematical model according to the working characteristics of the regulating valve, and finally establishing a disturbance channel mathematical model of the influence of disturbance on auxiliary output by adopting a BP neural network method.

And step three, designing an estimation model as a transfer function of an auxiliary channel, designing an estimator as a ratio of a disturbance channel transfer function influenced by disturbance to main output to a disturbance channel transfer function influenced by disturbance to auxiliary output, designing an inference controller as a reciprocal of the main channel transfer function with a filter, wherein the control method can only adjust a time constant of the filter, and when the mathematical model has high precision and requires fast dynamic response, a filter time constant of a smaller point can be selected, otherwise, a larger point is selected to ensure the robustness of the control system, and the value can also be determined by field experiments.

And step four, establishing an equal decarburization rate expert control rule table according to expert experience and off-line experiments, dividing the whole smelting period into 5 intervals of a smelting start period, a smelting initial period, a smelting middle period, a smelting end period and a smelting end period, and adopting equal interval intervals. The oxygen and the weight proportion of each interval are respectively designed to be 6:1, 3:1 and 1: 1. 1:3 and 1:6, and storing the rule into an industrial personal computer in a table form according to the relation curve of the ratio of argon to oxygen in the argon smelting period.

Step five, firstly, according to the traditional smelting process, calculating the total oxygen supply amount by an industrial personal computer according to the parameters of the weight of hot-blended molten iron, the initial carbon content, the type of iron-smelting alloy, the initial molten iron temperature, the target molten iron temperature and the like, then respectively calculating the oxygen supply amount and the argon supply amount in each time interval according to an equal decarburization rate expert control rule table, and is sent to the PLC as the set value of each time period through a 485 bus, the PLC is used as a PID controller, PID operation is carried out according to the argon flow measured by the argon flow sensor and the set value of the time period, further controlling the opening of the argon flow regulator to complete the constant flow control of argon in each time interval, and simultaneously, using the PLC as an inference controller, according to the reasoning control transfer function block diagram shown in figure 2, the oxygen flow measured by the oxygen flow sensor and the given value at the time, the opening degree of the oxygen flow regulating valve is calculated, and the output is sent to the oxygen flow regulating valve through a 485 bus to finish the reasoning control aiming at the main output. Repeating the process according to the sampling period of 1s until the smelting end point.