JP2005145757A - Method for manufacturing iron oxide powder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method which can control chlorine concentration and a particle diameter in parallel corresponding to their objective values when an iron oxide powder is manufactured from a pickling waste solution at steel plate pickling. <P>SOLUTION: When the iron oxide powder is manufactured by the spray roasting of an iron chloride aqueous solution, residual chlorine concentration is controlled by adjusting the temperature in a furnace. As the particle diameter of the iron oxide powder is decided by the size of a sprayed droplet and the iron concentration in the aqueous solution, the size of the produced iron oxide powder is controlled by fixing the droplet diameter by keeping the ratio of the spray pressure to the spray quantity of the chloride aqueous solution constant and by adjusting the iron concentration in the droplet. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing iron oxide powder having a particle size adjusted from an aqueous iron chloride solution by spray roasting and having a residual chlorine concentration adjusted.

When recovering hydrochloric acid from the pickling waste solution used for pickling of steel sheets, iron oxide is produced by spray roasting the iron chloride aqueous solution in the sense that iron is recovered from the remaining iron chloride aqueous solution at the same time as collecting the acid. doing.
Usually, the roasting furnace 1 to which the spray roasting method is applied is usually an approximately cylindrical roasting furnace body, a combustion burner 5 provided at the lower part of the furnace body, and a furnace body as shown in FIG. It has a spray nozzle 2 provided in the upper part. And after the fuel 4 and air are mixed with the combustion burner 5, it is burned and the combustion gas 12 is blown into the roasting furnace. Since the combustion burner 5 is arranged so as to blow hot air in the tangential direction of the furnace body circumference, the combustion gas 12 blown into the furnace swirls upward from the lower part of the furnace, 9 is produced. On the other hand, iron chloride in the iron chloride aqueous solution 3 sprayed from the upper spray nozzle 2 reacts with water and hydrogen in the swirling flow 9 to obtain particulate iron oxide and gaseous hydrochloric acid. Particulate iron oxide falls to the lower part of the roasting furnace, is stored as iron oxide powder 8, and is taken out using the rotary valve 7 as necessary. The gaseous hydrochloric acid is discharged out of the furnace as the exhaust gas 10 together with the combustion gas 12. Reference numeral 6 denotes a temperature sensor.

By the way, since the obtained iron oxide powder is used as a raw material of a magnetic material or the like, it is required that the residual chlorine concentration is low and uniform, and the particle diameter is uniform.
For this reason, for example, Patent Document 1 discloses the iron concentration and the product in the iron chloride aqueous solution as a raw material in order to control the quality of iron oxide by fuzzy inference of the optimum furnace temperature of the roasting furnace. Detect the compression density, average particle size, and chlorine concentration of iron oxide in a predetermined cycle, and calculate the optimum body temperature and the optimum furnace bottom temperature of the roasting furnace based on the fuzzy theory using these detected values as input variables. A cascade control of the combustion gas flow rate so that the body temperature in the roasting furnace matches the calculation result, and a rotary valve with the body temperature and the furnace bottom temperature detected in a predetermined cycle as input variables It has been proposed to calculate the rotational speed of the rotary valve based on the fuzzy theory and control the rotational speed of the rotary valve so that the furnace bottom temperature matches the result of the computation.

Moreover, in patent document 2, in order to control the particle size of the iron oxide powder obtained relatively large, in order to control the particle size, a plurality of spray nozzles are installed along the supply direction in the flame or high-temperature gas flow from the burner. It has been proposed to adjust the total amount of spray from the spray nozzle and adjust the number of nozzles to be sprayed.
Furthermore, Patent Document 3 discloses a temperature sensor for measuring the temperature inside the roasting furnace in order to stably produce iron oxide powder having a small particle size and a low residual chlorine concentration. It has been proposed to dispose a plurality of sensors in the circumferential direction and to control the spray amount and / or the fuel gas amount of the aqueous iron chloride solution so that the minimum value of the measured value of the temperature sensor becomes the target temperature.

JP-A-6-56430 JP-A-7-71881 JP 2000-159524 A

However, in the method described in Patent Document 1, since both the particle diameter of the powder and the residual chlorine concentration in the powder are to be controlled by adjusting the furnace temperature, the mutual control is easily affected. . Moreover, since the method described in Patent Document 2 only controls the particle size of the powder as a result, the residual chlorine concentration is small and uniform iron oxide powder cannot be stably obtained. In addition, since the supply amount of the solution, the distribution amount of the solution to each nozzle, and the number of nozzles used for spraying are adjusted in various ways, the control is complicated. Furthermore, the method described in Patent Document 3 also adjusts both the furnace temperature and the spray amount in actual operation. When trying to adjust the spray amount, the spray pressure applied to the nozzle is changed. When spraying with a constant number of nozzles, if the spray pressure becomes too high, the pipes and flanges will be overloaded and there will be a risk of breakage or ejection. On the other hand, if the spray pressure is too low, not only the spray from the nozzle becomes unstable, but also the cooling ability of the nozzle decreases, and there is a concern that the nozzle itself melts. Accordingly, the adjustment range of the spray amount, and thus the adjustment range of the particle size, becomes narrow.
The present invention has been devised to solve such problems. The residual chlorine concentration in the iron oxide powder is controlled by adjusting the furnace temperature, and the particle size of the iron oxide powder is controlled by adjusting the concentration of the spray aqueous solution. By carrying out, it aims at providing the manufacturing method of the iron oxide powder which can be controlled paraly according to the target chlorine concentration and particle size.

  In order to achieve the object of the method for producing iron oxide powder of the present invention, an aqueous iron chloride solution is sprayed into a roasting furnace, the sprayed iron chloride aqueous solution is reacted with a combustion gas in the roasting furnace, and oxidized. When producing iron oxide powder by generating iron, the temperature inside the furnace is adjusted, and the chlorine concentration and particle size of the iron oxide powder produced are controlled by adjusting the iron concentration in the iron chloride aqueous solution to be sprayed. It is characterized by that.

In the method of producing iron oxide powder by spray roasting an aqueous iron chloride solution, the residual chlorine concentration in the iron oxide powder is affected by the furnace temperature. Therefore, in the present invention, the residual chlorine concentration is adjusted by adjusting the furnace temperature.
On the other hand, the particle size of the iron oxide powder to be produced is influenced by the temperature in the furnace, the position of the spray nozzle, etc., but is basically determined by the size of the sprayed droplets and the iron concentration of the aqueous solution. Therefore, even when the spray amount of the chloride aqueous solution is made constant and the diameter of the sprayed droplets is the same, the size of the iron oxide powder produced can be adjusted depending on the iron concentration in the droplets. Since there is no need to greatly change the spray pressure, the burden on the nozzle is reduced, and the spray amount is not greatly changed, so that stable operation is possible.

The basic overall structure of the apparatus used in the present invention will be described with reference to FIG.
The structure of the spray roasting furnace apparatus is basically the same as the apparatus conventionally used. The pickling waste liquid generated in the pickling line L is once collected in the waste acid tank 21. The waste liquid is guided to the hydrochloric acid concentration tower 22 and separated into a hydrochloric acid content H and a concentrated acid content, and the hydrochloric acid content H is recovered as hydrochloric acid. On the other hand, after the concentrated acid content is temporarily stored in the concentrated acid receiving tank 23, it is sequentially sent to the roasting furnace 1 and sprayed into the furnace from the spray nozzle 2 installed at the upper part of the furnace body. And in the apparatus used for this invention, the water supply port 24 and the concentration meter 25 were attached to the supply pipe connected to the spray nozzle 2, and it calculated based on the measurement data of the concentration meter 25 and the data instructed separately. It is piped so that water can be replenished to adjust the chloride aqueous solution concentration. Reference numeral 26 denotes a computer for calculation.

A combustion burner 5 is arranged at the lower part of the furnace body so that combustion gas is blown in a tangential direction of the circumference of the furnace body, and a sensor 6 for measuring temperature is also installed. Based on the measured value of this temperature measurement sensor A mechanism for adjusting and controlling the fuel supply amount is also provided. This mechanism itself is basically the same as the conventional one. In order to recover the iron oxide powder in the discharged exhaust gas, the exhaust gas is passed through the cyclone 29, the recovered iron oxide powder is stored in the hopper 30, and the hydrochloric acid-containing gas is passed through the concentration tower 22 to the hydrochloric acid absorption tower. It is forwarded to 31.
Further, a rotary valve 7 is installed at the bottom of the furnace, and a rotary kiln 27 for drying the discharged iron oxide powder and a hopper 28 for storing the manufactured iron oxide powder are attached. This is also no different from conventional roasting equipment.

Next, the roasting method according to the present invention will be described in detail.
A predetermined amount of iron chloride aqueous solution is sprayed into the furnace at a predetermined pressure from a spray nozzle 2 installed at the top. At the same time, fuel and air are supplied to the combustion burner 5 installed in the lower part of the furnace body and burnt, and the combustion gas is blown in the tangential direction of the furnace body circumference.
The amount of combustion gas is determined by the spray amount and the roasting furnace temperature. The amount of combustion gas is controlled so that the roasting furnace temperature becomes a constant value.
In the furnace, the following oxidation-reduction reaction proceeds by the high-temperature combustion gas and the iron chloride aqueous solution sprayed from above.
4FeCl ₂ + 4H ₂ O + O ₂ → 2Fe ₂ O ₃ + 8HCl
The combustion gas is set to air-fuel ratio> 1 in order to supply O ₂ of the above reaction. Also, the reaction becomes faster if the reaction temperature is raised. That is, the higher the furnace temperature, the more the reaction proceeds and the lower the chlorine concentration in the iron oxide. However, in general, the heat resistance temperature of the refractory in the furnace and accessories is taken into consideration, and the target temperature is 600 to 800 ° C.

The sprayed droplets and the rising combustion gas are reacted, and the generated hydrochloric acid gas is discharged out of the furnace as the exhaust gas together with the combustion gas, and the generated iron oxide particles are appropriately taken out from the furnace bottom by the action of the rotary valve.
The component analysis of iron oxide powder taken out from the furnace bottom and dried in a rotary kiln is performed, and the particle size is also measured.
Based on the measured value of residual chlorine concentration in iron oxide powder, referring to the relationship between existing furnace temperature and residual chlorine chlorine, fuel supply amount and air supply amount so that the target residual chlorine concentration is achieved To adjust the furnace temperature. In other words, the residual chlorine concentration increases as the furnace temperature decreases, so if it is higher than the target residual concentration, adjust the fuel combustion amount to increase according to the difference with reference to known data. Feedback control of the furnace temperature.

A droplet sprayed with an aqueous solution of iron chloride at a predetermined pressure and a predetermined amount drifts in the roasting furnace with a certain size, and reacts with the combustion gas to generate iron oxide fine particles. The size of the iron oxide particles generated at this time is determined by the size and concentration of the droplets. When the size of the droplet is constant, the size of the iron oxide particles is determined by the concentration of the droplet, that is, the iron concentration of the aqueous iron chloride solution. Therefore, the particle size of the iron oxide powder discharged from the furnace body and dried in the rotary kiln is measured, the measurement result is fed back, and the water supply for adjusting the concentration of chloride aqueous solution is combined with the measurement data of the densitometer Calculate the amount and supply water from the water supply port.
The particle size and residual chlorine concentration of the extracted iron oxide powder are sampled and measured at regular time intervals, and the concentration of the iron chloride aqueous solution to be sprayed and the furnace temperature are adjusted as described above according to the measured values.

An example in which the method of the present invention is applied to an actual roasting furnace will be described.
This was applied to a roasting furnace having a diameter of 5.6 m and a height of 21 m ³ , and having two combustion burners with LPG gas as a fuel and a maximum capacity of 1,000,000 kcal / Hr and two spray nozzles at the bottom of the furnace.
From the two spray nozzles, the pickling waste liquid was sprayed at a total amount of 1.6 m ³ / Hr. 2
With the basic combustion burner, 75 m ³ / Hr of LPG gas was burned to adjust the temperature at the center of the furnace to 650 ° C.

When the concentrated acid specific gravity after passing through the concentration tower was 1.47 and the Fe concentration was 143.3 g / L, the nozzle spray pressure was 0.4 MPa. The spray droplet diameter assumed from the spray pressure and the nozzle characteristics is 150 to 160 μm. At this time, the average particle diameter of the iron oxide was 0.82 μm and the chlorine concentration was 0.083%.
In order to reduce the average particle size, water was added to the concentrated acid to reduce the concentrated acid specific gravity to 1.45 and the Fe concentration to 132.7 g / L. As a result, the iron oxide particle size was reduced to 0.78 μm. . At this time, there was no change in chlorine concentration, roasting furnace temperature, and nozzle spray pressure.
Then, by changing the amount of water replenished, the concentrated acid specific gravity of the pickling waste liquid, that is, the concentration of the aqueous iron chloride solution was varied and spray-roasted, and the particle size of the obtained iron oxide powder was measured. FIG. 3 shows the measurement results arranged according to the relationship between the concentrated acid specific gravity of the pickling waste liquid and the particle size of the iron oxide powder.

Although there is variation, it can be seen that the concentrated acid specific gravity and the particle size of the obtained iron oxide powder have a linear relationship. That is, it can be seen that the particle size of the iron oxide powder can be controlled by adjusting the concentrated acid concentration.
Note that the variation seen in FIG. 3 is due to the variation in the size of the sprayed concentrated acid droplets. When a predetermined amount of liquid is sprayed with the spray nozzle, the spray pressure gradually increases due to the clogging of foreign matter inside the nozzle. As can be seen in Table 1, the relationship between the spray pressure and the spray droplet diameter is smaller as the spray pressure is higher. For this reason, even if the initial conditions are not changed, the spraying pressure gradually increases due to clogging of foreign matters in the nozzle, and the particle size of the iron oxide powder produced as a whole varies.

To control the chlorine concentration of the iron oxide powder, the furnace temperature, which is often used in other patents, is controlled.
It processed with the pickling waste liquid 1.6m < ³ > / Hr on the same equipment and the same conditions as the above-mentioned. As described above, the furnace temperature was adjusted to 650 ° C., and the obtained iron oxide powder had an average particle size of 0.82 μm and a chlorine concentration of 0.083%.
From this state, in order to further reduce the chlorine concentration, the combustion amount was increased and the furnace temperature was adjusted to 680 ° C. As a result, the chlorine concentration decreased to 0.077%, but the average particle size increased to 0.85 μm. Therefore, the concentrated acid specific gravity was further adjusted to 1.46, and the Fe concentration was adjusted to 133 g / L. Other conditions remain the same.
As a result, the chlorine concentration remained at 0.077% and the average particle size was reduced to 0.82 μm.

  As can be seen from the above description, the residual chlorine concentration in the iron oxide powder can be controlled by the furnace temperature, and the particle size can be controlled by the concentration of the concentrated acid. That is, by separating and controlling both, the chlorine concentration and the particle size can be controlled separately to the target values.

A longitudinal sectional view explaining the structure of a spray roasting furnace The figure explaining the aspect which collects hydrochloric acid and iron oxide powder from pickling waste liquid The figure which shows the relationship between the concentrated acid specific gravity of the pickling waste liquid and the iron oxide powder particle size

Claims (1)

  When the iron chloride aqueous solution is sprayed into the roasting furnace, the sprayed iron chloride aqueous solution is reacted with the combustion gas in the roasting furnace, and iron oxide is produced to produce the iron oxide powder. A method for producing an iron oxide powder, characterized by controlling the chlorine concentration and particle size of the iron oxide powder produced by adjusting and adjusting the iron concentration of the iron chloride aqueous solution to be sprayed.

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