JPH0717933B2 - Hot metal pretreatment method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a hot metal pretreatment method, and particularly to a hot metal having a lesser variation of the [P] concentration in the hot metal after the pretreatment and the hot metal temperature from the target. The present invention relates to the pretreatment method of.

<Prior Art> Removal of P inevitably contained in the hot metal in the pig iron making process, and its function were left to the conventional converter. However, in recent years, a thermodynamically more advantageous technique for removing P from the hot metal stage has been developed for the purpose of reducing the cost of steelmaking, and the function of the converter has been only to remove C and raise the temperature.

In the de-P treatment at the hot metal stage, iron ore powder, mill scale, and iron oxide-containing substances such as dust collected in the iron and steel industry are used as oxygen sources in order to promote the reaction in a low temperature region that is thermodynamically advantageous. Therefore, the temperature drop during the treatment due to the heat of decomposition reaction of iron oxide is large, especially when performing the treatment to the low P range, the hot metal temperature is significantly lowered, and the thermal margin in the converter, which is the next step, is small. There was a problem that

By the way, with respect to the problem of the decrease in the hot metal temperature, a method of performing thermal compensation by top-blowing and injection of gaseous oxygen has been proposed and put into practical use. However, the estimation of the components and temperature during the treatment is still conducted empirically using the graphs and regression equations shown in FIGS. 7 to 9 rather than the pretreatment conditions and the amounts of the treatment agent and the oxygen gas used. Is the current situation, and due to the shape of the container such as the hot metal truck and the variation in the component and amount of slag brought about by the previous process and pretreatment,
The components and temperature after treatment varied, and it was difficult to bring them into the target range.

In particular, in the heat compensation method in which the generated CO gas is secondarily combusted by blowing up oxygen gas, it is difficult to grasp the amount of heat compensation for each processing unit, and the post-treatment temperature cannot be accurately estimated. It was

The variation in the components and the temperature after the treatment deteriorates the matching with the converter refining which is the next step and causes a problem that the advantages of the hot metal pretreatment cannot be maximized.

That is, when processing is performed to a value lower than the target P,
Decrease in heat margin in the converter due to deterioration of the basic unit of processing agent and increase in temperature drop in pretreatment, and removal of P to the target P
If it is not possible to carry out the above, there arises a problem that an increase in the P-deloading load in the converter or a re-de-Ping process is carried out to hinder the productivity.

<Problems to be Solved by the Invention> An object of the present invention is to solve the above-mentioned problems of the prior art in hot metal pretreatment, improve the target P concentration, and further improve the accuracy of application to the target hot metal temperature. It is an object of the present invention to provide a processing method that makes it possible to more accurately divide the functions of the processing and the converter and to further reduce the P removal cost in the steelmaking field.

<Means for Solving Problems> In the present invention, a blowing lance is immersed in hot metal held in a container such as a piggy car, and a de-Si / P-eliminating agent containing iron oxide as a main component is blown to remove the deionizing agent. In the pretreatment method for hot metal that removes Si and P, the CO gas in the exhaust gas is completely burned and
The CO ₂ concentration and the flow rate of the exhaust gas are sequentially measured, the [P] concentration in the hot metal is estimated from the decarboxylation efficiency calculated from the measured values, and the hot metal is pretreated until a predetermined estimated [P] concentration is reached. Is a pretreatment method of, or in addition to this, by using a non-immersion lance, oxygen gas is blown upward from the hot metal bath,
Some or all of the oxygen in the exhaust gas
A method for pretreatment of hot metal, in which the hot gas temperature is estimated from the secondary combustion efficiency of gaseous oxygen obtained from the lance inner diameter, the lance height, and the oxygen gas flow rate, which are the conditions for the top blowing of the oxygen gas, while completely burning the CO gas is there.

<Operation> First, the background of the present invention will be described.

In order to accurately estimate the components after the hot metal pretreatment, there is a limit to the conventional method of estimating by regression equation from the conditions before and after the treatment, and it is possible to accurately estimate the transition of components during the treatment. The present invention has been reached from the viewpoint that it is necessary to proceed.

However, during the pretreatment, the oxidation reactions of C, Si, and P mainly proceed in competition with each other.
It is also necessary to accurately grasp the transition of Si. Therefore, the present inventors have found that the reaction product C is discharged out of the container to the outside.
Focusing on, we considered to grasp the behavior by measuring the exhaust gas component. The method of estimating the transition of C in the bath from the exhaust gas components is the existing technology that has been put to practical use in converters and vacuum decarburization equipment (RH, VOD, etc.). For the purpose of [], CO and CO ₂ concentrations in exhaust gas are measured online. However, in the hot metal pretreatment, [C] is 3.5 to 4.5% even after the treatment.
Since it is saturated or near saturation, the estimation of [C] is not so important, and the exhaust gas dust collection system is an open type, the estimation of [C] in the hot metal has not been performed.

The inventors of the present invention completely burned CO in exhaust gas to completely remove CO ₂
Then, the decarburization rate (efficiency) was measured online by analyzing only the CO ₂ concentration.

FIG. 1 shows an outline of equipment and system for carrying out a pretreatment by the method of the present invention.

Obtain the solid oxygen supply rate from the de-Si / P-free agent blowing rate and the iron oxide content in the de-Si / P-free agent, and the gaseous oxygen supply rate from the oxygen gas flow rate from the top blowing lance. The total (gaseous oxygen + solid oxygen) oxygen supply rate can be obtained. However, some of the oxygen gas from the top blowing lance is consumed in the secondary combustion of the generated CO gas and does not contribute to the reaction with the components such as C, Si, P in the hot metal bath, so subtract that amount. It is necessary to process it according to the following formula.

Total oxygen supply rate (Nm ³ / min) that contributes to the reaction with the components in the hot metal bath = α ・ [De-Si / P-removing agent blowing rate (Kg / min)] + (1-
ηpc) ・ [Oxygen gas flow rate (Nm ³ / min)] where α: Solid oxygen content in the blowing agent (Nm ³ / Kg) ηpc: Secondary combustion efficiency of oxygen gas For the secondary combustion efficiency of oxygen gas, , The distance from the bath surface of the tip of the top blowing lance, the oxygen gas flow rate, and the inner diameter of the lance were obtained as shown in Fig. 4. Using this relationship, the total oxygen supply rate at each time point was obtained. Can be accurately determined by the above equation.

As the exhaust gas information, the exhaust gas flow rate is measured with a Pitot tube or the like, the exhaust gas temperature and the CO ₂ concentration are measured together, and the decarburization rate is calculated by a computer, whereby the decarboxylation element efficiency can be obtained.

By measuring the decarboxylation efficiency with various hot metal components, the relationship between the decarboxylation efficiency and the hot metal component can be associated one-to-one. Figures 2 and 3 show the relationship between the decarburization efficiency and the Si and P concentrations in the hot metal at that time.

By using these relationships, it is possible to use the second
The [Si] concentration in the hot metal can be estimated from the relationship in the figure, and after confirming the end of the Si removal period from the transition of the decarbonation efficiency from Fig. 2,
From the relationship shown in FIG. 3, the [P] concentration in the hot metal can be estimated.

Further, since the secondary combustion amount can also be obtained from the relationship of FIG. 4, the amount of heat compensation due to the use of oxygen gas can be accurately grasped, so that the hot metal temperature after the treatment can be accurately estimated.

<Example> The result when the present invention is applied to an actual machine will be described.

Table 1 shows the average components and temperature of the hot metal before treatment.

Using these hot metals, the same P concentration (0.02%), temperature (12
With the target of 60 ° C., treatment was carried out by two kinds of estimation methods, the conventional method and the method of the present invention. The P and temperature distributions after the treatment at that time are shown in FIGS. 5 and 6.

In the conventional method shown here, the processing agent basic unit and the amount of gaseous oxygen for achieving the target P and temperature are shown in FIGS. 7, 8 and 9 only from the pre-treatment [Si], [P] and temperature. The end of treatment is estimated using only the regression equation shown in the figure, and in the method of the invention, the end point is adjusted based on the exhaust gas information during treatment and the oxygen gas top blowing condition in addition to the estimation of the conventional method. . By adjusting the end point according to the exhaust gas information and the oxygen gas top-blowing condition, the accuracy of P and temperature after treatment is obviously improved.

The average conditions for performing the conventional method and the method of the present invention are as follows.

Composition of de-Si and de-P agent: Fe ₂ O ₃ 75% CaO 22% CaF ₂ 3% De-Si and de-P agent blowing rate: 450Kg / min Hot metal amount in the hot metal car: 230ton <Effect of the invention> After hot metal treatment By improving the accuracy of P concentration, the amount of P deoxidizer used can be reduced without lowering P too much. Furthermore, the pretreatment hot metal can be supplied to the converter at the optimum component (P concentration) and temperature required, the total cost of the processes from pretreatment to converter refining can be reduced, and improvement in productivity can be expected.

[Brief description of drawings]

FIG. 1 is a schematic view of the equipment and system of the present invention, FIG. 2 is a graph showing the relationship between the Si concentration in hot metal and decarboxylation efficiency, and FIG. 3 is the relationship between P concentration in hot metal and decarbonation efficiency. 4 is a graph showing the relationship between the lance condition and the secondary combustion efficiency of gaseous oxygen, FIG. 5 is the target P concentration, FIG. 6 is the graph showing the deviation from the target temperature, and FIG. Is hot metal, Si in molten slag
Graph showing the relationship between the average concentration and the oxygen removal efficiency, No. 8
FIG. 9 is a graph showing the relationship between the average P concentration in the hot metal and molten slag and the oxygen removal efficiency from the outside of Si, and FIG. 9 is a graph showing the relationship between the vapor acid ratio and the temperature drop due to the treatment agent.

Claims (2)

[Claims] 1. A hot metal reserve for removing Si and P by immersing a blowing lance in hot metal held in a container such as a piggy car and blowing a de-Si and de-P agent containing iron oxide as a main component. In the treatment method, the CO gas in the exhaust gas is completely burned, the CO ₂ concentration in the exhaust gas and the exhaust gas flow rate are sequentially measured, and the decarboxylation efficiency calculated from the measured values is used to determine [P] in the hot metal. A pretreatment method for hot metal, comprising estimating the concentration and pretreating until a predetermined estimated [P] concentration is reached. 2. The hot metal pretreatment method according to claim 1, wherein oxygen gas is blown from above the hot metal bath using a non-immersion lance, and the CO gas in the exhaust gas is completely removed by part or all of the oxygen. A method for pretreatment of hot metal, which comprises burning and estimating the hot metal temperature from the secondary combustion efficiency of gaseous oxygen obtained from the lance inner diameter, the lance height, and the oxygen gas flow rate, which are the conditions for the upper blowing of the oxygen gas. .