JPS6246606B2 - - Google Patents

Description

Detailed Description of the Invention The present invention relates to a top/bottom blowing converter in which pure oxygen is blown from above and carbon dioxide or inert gas is blown from below. It enables blowing with a high accuracy rate for the amount.
The purpose is to provide a bottom blowing converter, and another purpose is to provide a top/bottom blowing converter that is capable of blowing to bring the P and Mn contents of molten steel at the end point to target values or close to the target values. Another, different purpose is to select in advance a pattern that will serve as an indicator for the amount of oxygen stored in the slag during the blowing period, calculate the amount of oxygen stored in the slag every moment during the blowing period, and calculate the amount of oxygen stored in the slag. The purpose is to provide a top/bottom blowing converter that is capable of blowing with high precision to the target value (temperature, composition) by correcting the difference between the value and the above-mentioned pattern. The object is to provide a top/bottom blowing converter that is capable of so-called automatic blowing, requiring no manual operation or with very little manual operation.Another object is to provide a top/bottom blowing converter that is capable of so-called automatic blowing, and has an excellent stirring effect on molten steel, low fume loss, and high yield. We provide high-quality top and bottom blowing converters.

Now, in recent years, bottom-blown converters have begun to be reconsidered in order to improve the shortcomings of top-blown oxygen converters, namely high oxidation loss and poor dephosphorization reaction. There are problems such as the minimum hot metal content ratio becoming high due to the small amount of hot metal, and the equipment conditions being difficult, making it impossible to change the top-blowing converter to a bottom-blowing converter by simple modification.

Therefore, top/bottom blowing converters have been proposed that carry out top blowing of pure oxygen and bottom blowing of carbon dioxide or inert gas. This does not require cooling gas to protect the tuyere, which is required in the well-known bottom-blowing converter, and the equipment cost is low because it does not require complicated and expensive oxygen piping or control valve mechanisms like O ₂ bottom-blowing. Besides the advantages,
When carbon dioxide gas is injected, there is an advantage that the amount of unburned waste gas recovered increases due to the decomposition reaction of carbon dioxide gas.

However, there are various problems in the operation of the top/bottom blowing converter, and improvements are needed.

That is, in controlling the molten steel temperature and carbon content, generally known top/bottom blowing converters use a sub-lance to control the molten steel temperature and carbon content directly, for example, 1 to 5 minutes before the end of blowing. The amount is measured, and depending on the difference between the target molten steel temperature, target carbon content, and the above-mentioned measured value, changes are made to the lance height, oxygen flow rate, auxiliary material input, carbon dioxide gas injection amount, or inert gas injection amount. It is equipped with a device that can obtain the target values (temperature Tt, carbon content Ct) by appropriately implementing various means such as adjustment.

By the way, the present inventors, who have been engaged in the operation of the above-mentioned well-known top and bottom blowing converters, have found that it is difficult to achieve the target molten steel temperature and target carbon content when operating the well-known top/bottom blowing converter. I learned something. Furthermore, it has been found that the known means cannot effectively adjust the fluctuations in the P and Mn contents in the molten steel components, although these fluctuations are smaller than in the top blowing converter furnace.

In other words, although conventional blowing operations are called dynamic control, they perform static calculations again based on information obtained from actual measurement of molten steel using a sublance, and the decarburization reaction during blowing is controlled. Because it does not recognize changes in the slag-making reaction, there is a problem in the accuracy of target values regardless of operational efforts, and the variation in molten steel [P] and [Mn] due to variations in the slag-making reaction is also large, making it difficult to improve. was necessary.

The present inventors have developed the present invention as a result of their efforts to solve the above-mentioned problems, and have succeeded in significantly increasing the accuracy rate for the target value.

The present invention is equipped with a device that performs comprehensive control by combining static control that performs program settings based on charging conditions and end-of-blowing conditions, and dynamic control that uses process signals during blowing. The static control and dynamic control will be explained in more detail.

As mentioned above, devices that have a device for performing static control, a device for performing dynamic control, or a device that includes both devices and performs blowing while coordinating them are already well known. It is. Static control is a control in which refining conditions such as lance height, amount of blown oxygen, and amount of various auxiliary materials used are set before the start of refining, and refining is completed according to this program.Dynamic control is a control that completes refining according to this program. This control completes refining while changing refining conditions such as lance height, amount of blown oxygen, and amount of various auxiliary materials used by measuring dynamic information of the process.

The dynamic information referred to here includes, for example, the well-known "Converter Control Method" (see Japanese Patent Publication No. 42-23695) or the "Monitoring and Control Method for Oxygen Top Blowing Method" (Japanese Patent Publication No. 43-4088). A method of analyzing refining exhaust gas such as the method described in U.S. Pat. Quantity Estimation Method” (Unexamined Japanese Patent Publication No. 1983-
A number of methods have been devised, including those that utilize the exhaust gas information and sublance found in 101617). In particular, the control method that uses exhaust gas information and sublance greatly improves the accuracy of the end point carbon content and molten steel temperature. Others include ``Production method and equipment for alloy steel'' (Japanese Patent Application Laid-Open No. 51-8109), ``Operation Method of Converter Furnace'' (Japanese Patent Application Laid-open No. 52-8109),
-146711), which focuses on operation as a top/bottom blowing converter, has also been proposed. However, these methods have the following problems.

In other words, when we expect changes in the decarburization reaction and slag-forming reaction due to changes in oxygen distribution caused by lance operation as a temperature raising means, oxygen flow rate control, carbon dioxide gas flow rate, or inert gas flow rate control, there is no measured amount of the change. Since the effect cannot be estimated, correction of changes in molten steel temperature and carbon content near the end point must be limited to cooling means only.

In this way, the method of mixing auxiliary raw materials in advance so that the end point temperature of molten steel is slightly higher than the target end point, and adjusting the amount of additional auxiliary raw materials near the end point based on the latest information, does not improve blowing. For most of the time, the temperature of molten steel is always high, which has an unavoidable negative effect on the converter bricks, and even in dephosphorization, which is one of the purposes of converter blowing, the temperature of molten steel is always high. As the transition progresses, the metallurgical atmosphere becomes unfavorable for the dephosphorization reaction, making it necessary to increase the basicity of the charging or to increase the degree of oxidation of the slag, which poses problems in terms of quality and cost. Become. Also, the above-mentioned "Method for estimating molten steel temperature and carbon content"
(Japanese Patent Application Laid-open No. 101617/1983) and “Method for controlling molten steel temperature and carbon content in an oxygen converter”
101618), where the distribution of oxygen in the furnace to the decarburization reaction and the oxidation reaction of iron near the end of blowing is continuously measured to improve control accuracy, the temperature and carbon content of molten steel can be improved. In order to correct the direction of the change in quantity, additional input of auxiliary raw materials is used as a cooling means, lance operation is used as a heating means, and desorption is performed by changing the oxygen distribution by changing the carbon dioxide gas flow rate or inert gas operation in addition to the oxygen flow rate. Changes in the carbon reaction and slag-making reaction can also be detected, so there is no need to limit the correction direction to only one direction and mix auxiliary materials so that the end point temperature of molten steel is slightly higher than the target end point. If the direction of change in the molten steel temperature and molten steel carbon content that have passed through up to that point is significantly different from the direction that satisfies each target at the end point, in addition to the oxygen flow rate, the carbon dioxide gas flow rate or inert It becomes necessary to greatly manipulate the gas flow rate, auxiliary raw materials, or lance height, and the oxygen distribution in the furnace changes greatly, making the slag-making reaction unstable and reducing the molten steel phosphorus, manganese content, and oxygen content at the end point. This increases the variation in quantity and becomes a bigger problem than cost and quality.

As mentioned above, in order to solve the above problems, it is necessary to develop a highly accurate static control means and a dynamic control means that matches it. Various attempts have been made regarding static control in the past, but as far as the present inventors are aware, no highly accurate static control has yet been found.

The present invention was devised to solve the above-mentioned problems, and one of the features of the present invention is that in the static control, the flow rate of oxygen supply, the flow rate of carbon dioxide gas or the flow rate of inert gas, the brand of input auxiliary raw materials, and the input speed,
The purpose is to use the amount of oxygen accumulated in the slag, which is calculated from the amount of exhaust gas and the composition of the exhaust gas, as one of the calculation parameters.

When the amount of oxygen accumulated in the slag is used as a calculation parameter for static control, its handling is naturally determined by the mathematical formula of the static control method. As is widely known in the static control method, among the factors that affect material balance and heat balance, in order to simplify the model, factors that have a weak correlation or whose fluctuations are small in practice are explained in detail. , factors that can be manipulated to control only the difference from the reference heat (mostly the amount of blown oxygen,
The most common method is to correct it to the amount of carbon dioxide gas, inert gas amount, or iron ore amount, but various expressions are used in mathematical formulas. Therefore, as a simple example, we will explain how the amount of oxygen accumulated in slag is introduced into a static control model. Of course, it can be applied to other static control models as well. When using other static control models, the amount of oxygen accumulated in the slag may be similarly incorporated into the appropriate material balance equation and heat balance equation.

〔example〕

The conventionally known static control model represented by the following ~ and formulas is changed to the static control model represented by ~ and formulas.

End point temperature T _E = T _E

Claims (1)

[Scope of Claims] 1. A top/bottom blowing converter having the following devices (a) to (g), characterized in that it is equipped with the devices (h) to (k). . (a) A first device that blows pure oxygen from above and carbon dioxide or inert gas from below. (b) A second device for recovering exhaust gas in an unburned state. (c) A third device that inputs auxiliary materials at any time during blowing. (d) A fourth device that actually measures the temperature and carbon content of molten steel in the furnace at any time during blowing. (e) A fifth device for detecting the composition of exhaust gas. (f) A sixth device for measuring the flow rate of exhaust gas. (g) A seventh device that detects a carbon dioxide gas flow rate or an inert gas flow rate in addition to the oxygen flow rate. (h) Determine the lance height, blown oxygen amount, auxiliary material input amount, and carbon dioxide gas flow rate or inert gas flow rate from the charging conditions and blow-off conditions, and
and an eighth device that gives an operating command to the third device. (i) Using statistical calculations or theoretical calculations from the charging conditions, end-of-blowing conditions, and past similar blowing patterns, calculate the continuous change in the target amount of oxygen accumulated in the slag, which is the reference target for the blowing, and A ninth device that provides the amount of change to the eighth device as a reference value when determining the lance height, the amount of blown oxygen, and the amount of auxiliary material input in the eighth device. (j) Calculate the amount of oxygen accumulated in the slag over time from the exhaust gas composition, exhaust gas flow rate, oxygen supply flow rate, amount of auxiliary raw materials input, as well as the carbon dioxide gas flow rate or inert gas flow rate, and input the calculated value into the eighth device. In the eighth device, the lance height, the oxygen flow rate,
A tenth device for determining a corrective operation amount for the reference value of the input amount of auxiliary raw materials. (k) The end point molten steel temperature is determined from the actual measured values of molten steel temperature and carbon content obtained by operating the fourth device just before the end of blowing, and information on the amount of oxygen accumulated in the slag from the 9th and 10th devices. A command signal for estimating the end point carbon content and reducing the difference between the target molten steel temperature and the target carbon content is given to the eighth device, and the eighth device receives the lance height, oxygen flow rate, amount of auxiliary material input, and carbon dioxide gas. an eleventh device for determining a corrective actuation amount of the flow rate or inert gas flow rate;