JPS60215705A - Method for operating melt reducing furnace - Google Patents

Abstract

PURPOSE:To improve the stability of the operation of a reducing furnace by measuring a change in the weight of the furnace, the volume and composition of exhaust gas and setting conditions during the blowing of iron ore, coal and oxygen on the basis of the measured values. CONSTITUTION:The weight of a melt reducing furnace 1 is measured with a load gauge 2, and the flow rate of prereduced ore 10 is adjusted on the basis of a change in the amount of molten iron in the furnace 1. The volume and composition of gas exhausted from the furnace 1 are measured with a flowmeter 3, an N2 analyzer 4 and a CO2 analyzer 5, and the charge rate of coal 11 is controlled on the basis of the measured values. The flow rates of primary oxygen and secondary oxygen are controlled by regulating control valves 8, 9. Optimum conditions during the blowing of iron ore, coal and oxygen are maintained at all times, so very satisfactory operation can be stably carried out.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for obtaining molten iron by reducing iron ore while heating and melting it.

Conventional technology Conventionally, iron has been produced by producing pig iron in a shaft furnace or by melting pre-reduced ore in a shaft furnace or rotary kiln in an electric furnace. few.

The present inventors previously disclosed in Japanese Patent Application No. 58-249O4O that they had a pre-reducing furnace, and that the pre-reduced ore could be converted into coal, coal, etc.
He invented a steelmaking system characterized by bottom blowing with oxygen. However, it was found that this system had some problems in the operation of the smelting reduction furnace. That is, the smelting reduction furnace is designed to transport pre-reduced ore 9 coal etc. in a gaseous manner using a carrier gas and blow it into the iron bath through a tuyere installed at the bottom of the furnace. The technology to accurately grasp the flow rate of powder is incomplete, making it difficult to operate the furnace smoothly. That is, in the bath smelting and reduction furnace, the reaction proceeds at a high temperature of around 1500°C, so the reaction rate is extremely fast, and therefore the flow rate and components of the reactants charged into the furnace deviate from predetermined values. As a result, material balance and heat balance quickly become unmaintainable, and operations become unstable.

In the above invention, a measuring device using Coriolica was used to monitor the flow rate of solid charges (iron ore, coal, etc.) transported by fluid, but the physical properties of the solids (components, specific gravity, etc.) changed. The error was large.The reduction system has a preliminary reduction process, but due to fluctuations in the reduction rate of the product that inevitably exist in the process, the charging speed of iron ore to the smelting reduction furnace was particularly slow. Therefore, the amount of molten iron stored in the furnace could not be predicted by only measuring the molten iron and slag that are intermittently discharged), and the ratio with the amount of coal injected may change, causing the heat balance to collapse. Something happened.

OBJECTS OF THE INVENTION The present invention is intended to avoid the difficulty of grasping the charging rate of iron ore, coal, etc., and to perform stable operation of a smelting reduction furnace.

Structure and operation of the invention The present invention involves blowing iron ore that has been pre-reduced into molten iron containing carbon, coal, a slag-forming agent, and oxygen into the upper part of the molten iron.
In a method for operating an iron ore smelting reduction furnace in which combustible scum generated from an iron bath is combusted by blowing secondary oxygen, changes in the weight of the reduction furnace and the amount and composition of gas discharged from the furnace are measured. This method is characterized in that conditions for blowing iron ore, coal, and oxygen are set based on measured values.

That is, the present invention firstly uses a load meter to grasp the momentary changes in the molten iron lid in the furnace in order to control the iron ore injection rate corresponding to a predetermined production rate, and secondly, the iron ore 9 coal, In order to quickly detect changes in reaction conditions caused by uncertainties in understanding the current current and take countermeasures, process control is performed using gas-side information that allows easy online measurement of flow rate and composition. It is characterized by

The present invention will be explained in detail below. FIG. 1 is a control block diagram of a smelting-reduction furnace for carrying out the method of the present invention, in which 1 is a smelting-reduction furnace, and 2 is a load meter for measuring the weight of the furnace. 3 is a flow meter that measures the flow rate of gas discharged from the melting reduction furnace 1;
4 is the N2 analyzer in the exhaust gas, and 5 is the same <002 analyzer. Further, 6 is a flow rate regulator for maintaining the charging rate of pre-reduced ore 1O obtained based on the change in molten iron weight calculated from the measured value of the load cell 2 at an appropriate value, and 7 is a gas flow meter 3 and N2 Based on the measurement value of analyzer 4! 8 and 9 are N2. This is a control pulp that controls the primary 11bFi and secondary filter ratios based on the N/C ratio calculated from the respective CO2 analysis values.

The present invention melts and reduces using the load cell 2! By measuring the major prize of P1! It grasps the momentary changes in the amount of iron bathed in the furnace and controls the flow rate regulator 6 to adjust the flow rate of the pre-reduced ore 10 charged into the furnace. 3. Measure the amount and composition of the gas with a flowmeter. N2 analyzer4. Co2 is measured by the Co2 analyzer 5, and the regulator 7 is adjusted based on the measured value to control the charging rate of 1 liter of coal, and the control pulps 8 and 9 are adjusted to control the primary oxygen and secondary oxygen. Melting reduction furnace 1 by controlling the flow rate
The aim is to operate the system under optimal conditions.

Here, to describe the function of the material charged into the smelting reduction furnace 1, part of the carbon in the coal is used to reduce iron ore and at the same time generates CO gas according to the following equation.

FeO+X-C=Fe+X,-Co・---・(1)
(However, X takes a value between 1.5 and 0 depending on the degree of preliminary reduction, and it is said that carbon does not react directly with iron oxide, but rather dissolves in the iron bath and reacts.) , the remainder of the carbon is simultaneously oxidized by oxygen (denoted as suboxygen) blown into the iron bath, generating heat, the heat for the coal itself to thermally decompose and generate a water system, and the reduction of the iron ore. Provides heat.

C! mHn+-02= m-C0+-=H2--・-・
(, IJ2 (However, m and H are values determined by the components of the coal, and as n increases, the amount of heat required for decomposition increases.) In addition, in order to compensate for the lack of heat, the carbon produced by the above reaction
Oxygen (2
Burn with secondary oxygen and sulfur.

Furthermore, slag-forming agents such as lime are contained in iron ore and coal.
In order to lower the melting point of the gangue components and facilitate separation of impurities such as iron and gangue components and S, the basicity (Oa O/S 102 ) of the generated slag is set to a predetermined value, for example 13 It is cooled so that

On the other hand, the temperature inside the reactor is 1000,000 yen, and the charge charged into the reactor under strong stirring completes the reaction almost all at once. It is necessary to maintain the mass balance and heat balance at all times. In short, coal, oxygen, slag forming agents, etc. must be supplied at a rate that always corresponds to the rate of reduction of iron ore.

The constant measurement of the reactor weight by the load cell 2 of the present invention provides a reliable basis for iron ore supply control in place of measuring the iron ore charging rate, which is difficult to grasp. In other words, iron ore (preliminary reduction f11
), it becomes possible to control the ore properties without being influenced by fluctuations in the preliminary reduction rate. In addition, when the mortar is discharged continuously, the furnace's MW is controlled to be constant.

From the above, the amount of iron charged to reaction r can be controlled, and the amount of coal and oxygen that can maintain a heat and mass balance can be calculated accordingly - similar to the case of iron ore. , it is difficult to grasp the coal charging rate, and for example, if the preliminary reduction rate of ore changes during operation, 1.
Since it is necessary to change the secondary oxygen and the secondary oxygen lid with good responsiveness, detection end information is required to reliably understand the reaction inside the reactor.

The coal injection rate can be determined by measuring the N2 flow rate in the gas discharged from the reactor.

The origin of N2 in exhaust gas is N2 in blown oxygen, carrier gas for transporting powder, and N2 contained in coal, but the former two are gases and their flow rates are easy to determine, so they are not included in exhaust gas. If you subtract these from the N2 inside, you will get the N2 derived from coal.
On the other hand, since the N concentration in coal is constant if the coal brand is a, the coal flow rate can be calculated. In addition,
When the moisture content of the charge charged into the furnace and the gas can be accurately determined, it is possible to use H as an indicator instead of N, and furthermore, it is possible to use H as an indicator instead of N. If present, this component can be used in the operation to replace the function of N.

Next, we will discuss countermeasures when the reduction conditions change for some reason during operation, and the situation inside the furnace changes accordingly.

This mainly occurs when the reduction rate of the pre-reduced ore changes, and when operating in the manner described above, even though it appears that both iron and coal are being charged normally, in reality Since the reduction rate is changing, the reducing agent and amount of heat required for reduction are changing, and if the operation continues for this period of time, the heat and material balance will not be maintained and the operation will become impossible.

Specifically, when the preliminary reduction rate shifts to a low level, the carbon and heat in the molten iron are consumed, the temperature of the molten iron decreases, and the carbon supply from the coal cannot keep up, causing the C concentration to decline. Eventually, the reduction reaction shown in equation 1 stops proceeding.

On the other hand, if the preliminary reduction rate deviates to a high level, carburization and heat supply will result in surplus and generation of molten metal.

In this way, understanding the reduction rate of ore charged into the reactor is
Although it is essential for stable operation, there are many difficulties in online analysis. In order to solve this problem, the present invention utilizes the NZC ratio in the exhaust gas.

After completely oxidizing the gas sampled from the exhaust gas,
N2 and 00 by N2 analyzer 4 and C02 analyzer 5
2 can be precisely analyzed to calculate the total N/total C in the waste. In the above-mentioned situation, C in the gas changes because C in the iron bath, which is constant in steady operation, increases or decreases. Since the amount of coal supplied remains unchanged, the amount of N in the exhaust gas remains constant. Therefore, the change in N/C4 in the gas proves that there is a change in the O mass balance in T. It would be better to implement controls to correct this.

Example Next, examples of the present invention will be shown.

When manufacturing molten iron using iron ore with a preliminary reduction rate of 70%, coal (calorific value e 980 Fdz4'-e
L, a, f, ash 8.5 mph; 84 B, 11 (g,
', lime; 11BΔV.

- Secondary oxygen: 409N, secondary oxygen: 172N- was used for operation. At this time, the amount of gas generated as indicated by the flow meter 3 is 1709 N per ton of molten iron produced as indicated by the load cell 1, and the N2 flow rate calculated from the N2 analyzer 4 is 1 B, 9 N.
i, NZC calculated from the measurement results of the co2 analyzer 5
The ratio was 0.0150. However, after changing the iron ore cutting hopper, the NZC ratio decreased to 0.014 despite the change in the load meter and the N2 flow rate. This indicates that the decarburization reaction from the iron bath due to iron oxide is progressing selectively, even though the amounts of iron and coal charged are appropriate. -, and when the secondary oxygen was increased to 212 N- by Control Pulp 9, taking thermal compensation of the decarburization reaction into consideration, the N10 ratio returned to 0.0150 after a while.

In reality, this was due to the fact that the preliminary reduction rate of iron ore had not reached 70% and there was only 6 oz. if,
If the operation continues without changing the conditions, carbon equivalent to p33Q per ton of finished iron will be lost from the molten iron,
This process, which relies on reduction by carbon in molten iron, will no longer be able to maintain operation.

In addition, the criteria for changing conditions when the NZC ratio changes is based on the iron ore analysis value 9 before preliminary reduction, coal analysis value, oxygen purity, etc., and operation that takes into account the characteristics of various equipment such as the smelting reduction furnace and preliminary reduction furnace. Place it in advance by simulation. Also, is it actually 1M? In 1.1, only oxygen was used, but other methods such as increasing the preliminary reduction rate of iron ore and charging calorific value coal may also be considered.

As described in detail, the present invention avoids the difficult sound of measuring the solids flow rate by changing charging conditions to the reactor, which requires slow response due to a fast reaction, and reduces the weight of the reaction vessel. It is characterized by the fact that it is based on simple measurement information such as the change in gas flow rate and the gas flow rate, and as a result, extremely good operational stability can be achieved.

[Brief explanation of the drawing]

FIG. 1 is a control block diagram of a smelting reduction furnace that implements the method of the present invention. l... Melting reduction furnace 2... Load cell 3... Flow meter 4... N2 analyzer 5... C02 analyzer 6.・・・・Flow rate regulator 7・・・・・・Adjuster 8.9・・Hot control pulp 10・・Preliminary reduced ore 11・・・・Coal applicant Japan Corps steel federation

Claims (1)

[Claims] Iron ore is pre-reduced to molten iron containing carbon, and coal, slag-forming agent, and oxygen are blown into the furnace. Secondary nitrogen is blown into the upper part of the furnace to burn the hot gas generated from the iron bath. In the operating method of the smelting reduction furnace, the weight change of the reduction furnace, the amount of gas discharged from the furnace, and the composition sound are measured, and the conditions for blowing iron ore 1 coal and oxygen are set based on the measured values. Characteristic method of operating a melting reduction furnace.