JPH07173547A - Treatment of dust - Google Patents

Abstract

PURPOSE:To remove zinc oxide from the dust with the low consumption of heat by reducing the iron oxide in the dust with COG at a low temp. and utilizing the reaction heat difference due to the reoxidation and the carbon deposited by the decomposition of the COG. CONSTITUTION:The dust contg. zinc oxide is reduced with hydrogen at 500-700 deg.C in a reactor 2 with COG as a reducing gas and then oxidized with air in another reactor 6. The dust is heated to 1000-1150 deg.C by the oxidation heat, the C deposited from the COG is partially burned to produce CO, which reduces the zinc oxide in the dust, and the zinc oxide is removed. Consequently, the heat consumption is reduced by 20-30% as compared with that of the conventional method, and >=90% of zinc is removed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for separating and removing zinc contained in dust generated by metal refining.

[0002]

2. Description of the Related Art Dust is generated as a by-product during metal refining in steel production. Taking steel manufacturing as an example, the components of the dust generated therein include a large amount of iron oxides as shown in Table 1, and are useful as ironmaking resources.

[0003]

[Table 1]

However, this dust contains a zinc compound, which is an obstacle when it is used as a raw material for iron making. When these dusts are recycled and used, they are generally sintered or charged into a blast furnace. For example, in the sintering process, in the process of mixing with ore powder or the like and firing, when evaporated zinc is cooled, it adheres to the great bar or exhaust duct of the sintering device and solidifies to block the ventilation passage. Cause trouble. Also, when charged into the blast furnace, it deposits and deposits on the walls inside the furnace, disturbing the gas flow in the blast furnace and hindering the normal movement of raw materials called hanging, which disturbs the stable operation of the blast furnace. Has become one of the factors.

Therefore, in the case of sintering the dust or recycling it to the blast furnace, it is essential to remove zinc in the dust, and various researches have been conducted so far to invent the treatment method. It was A typical example is a reduction evaporation method of zinc in dust using a rotary kiln. In this rotary kiln method, dust to be dezinced and carbonaceous materials such as coke powder are charged individually or in the form of kneading pellets from one end of the kiln, and the fuel blown by a burner provided at the other end is burned to generate dust. At the same time, while heating, the carbonaceous material is gasified to form CO, and the inside of the furnace is made into a reducing atmosphere to reduce and evaporate zinc. After the zinc is separated from the dust in this manner, the kiln outlet is generally placed in an oxidizing gas atmosphere to re-oxidize the evaporated zinc and remove it as ZnO.

[0006] In the conventional invention, the device for producing the atmosphere in the kiln, the mixture of the dust and the carbonaceous material, etc. have been devised for this purpose. For example, in Japanese Patent Publication No. 57-10170,
In the composition of the reducing material and the atmosphere adjustment, in JP-B-57-44737 or JP-B-61-54094, the composition of the carbon material and the formation of the reducing atmosphere zone and the oxidizing atmosphere zone are devised.

However, in these inventions, all of the required coal or coke as a reducing agent and the required fuel as a heat source are charged from the outside. In this case, C generated by partial combustion of carbonaceous material
O gas forms a reducing atmosphere. At that time, excessive coke or coal is added in order to constantly maintain a reducing atmosphere in the kiln, and wasteful energy is consumed. In particular, in recent years, demands for energy saving, CO ₂ emission reduction, etc., which are of great interest, have fallen behind, and in response to this, attempts have been made to effectively utilize carbonaceous materials as reducing agents. For example, JP-B-55-51014, JP-A-48-42909, or JP-A-60-8.
In the 6219 publication, secondary ash that is blast furnace dust is mixed with other dust, and only carbon contained in the secondary ash is used as a reducing agent to reduce the reducing agent from the outside such as coke. However, the heat source depends on the heat of combustion of the fuel by the burner.

On the other hand, in order to reduce and evaporate and remove the zinc compound in the dust, it is necessary to increase the temperature of the appropriate reducing gas and the dust to the reaction temperature level and maintain the temperature. Conventionally, as described above, CO gas is used as the reducing gas and the combustion heat of the fuel is used as the heat source. The temperature at that time is generally 1100 to
It is in the range of 1300 ° C, and the unit of heat consumption is 2.5 million-
Extremely large at 3 million kcal / t-dust. For example, when the required heat quantity at the reduction reaction temperature of 1100 ° C. is calculated for the steelmaking dust shown in Table 1, it is about 250,000 kcal / t, and only about 10% of the consumed heat quantity is effectively used. Nothing more than. Looking at the breakdown of the trial calculation example, the sensible heat of dust is about 90% and the reaction heat is 10%, and most of it is consumed by the sensible heat of dust. Therefore, in order to reduce the unit consumption of heat energy during dust processing, new devises regarding the temperature raising method of dust are desired.

[0009]

DISCLOSURE OF THE INVENTION The present invention introduces a new concept for raising the temperature of dust to dezincify dust with less heat energy consumption.

[0010]

A method for treating dust according to the present invention is a method for treating dust generated during metal refining such as in steel production, in which a reducing gas containing hydrocarbon and hydrogen as main components is used. 50 iron oxides in the dust
After reducing by 50% or more at a temperature of 0 to 700 ° C., the dust is reoxidized by using an oxygen-containing gas such as air or oxygen-enriched air, and at least 900 ° C. or more by heat generated at that time. , Preferably 1000-115
The temperature was raised to 0 ° C., and at the same time, the dust atmosphere was made into a CO gas reducing atmosphere by the CO gas obtained by partially burning the carbon generated by the decomposition of hydrocarbons in the reduction reaction, under the above temperature conditions and under the atmosphere. It is characterized in that the zinc compound contained in the dust is reduced and evaporated to be removed.

[0011]

The present invention utilizes the difference in iron oxidation-reduction energy due to the difference in gas species. That is, as shown in Table 1, the dust contains a large amount of iron oxide.
This iron oxide is reduced at low temperature using hydrogen gas as a reducing gas, and then reoxidized with oxygen. The reduction of iron oxide with hydrogen is an endothermic reaction, and the reaction heats are 6,500 kcal / kmol and 22,8, respectively, as shown in the following formulas (1) and (2).
It is 00 kcal / kmol. On the other hand, the oxidation reaction by oxygen is an exothermic reaction, and the heat of reaction is 64,300 kcal / kmol as shown in the following formula (3). The present invention utilizes this difference in heat of reaction to raise the dust to the high temperature required for the reaction. Further, carbon is made to exist in the process of reoxidation, and this is partially burned to form CO. This acts as a reducing agent, reduces and evaporates the zinc compound in the dust, and discharges it together with the gas.

[0012] _{FeO + H 2 = Fe + H} 2 O-6,500kcal / kmol ··· (1) Fe 2 O 3 + 3H 2 = 2Fe + 3H 2 O-22,800kcal / kmol ··· (2) Fe + O 2/2 = FeO + 64, 300 kcal / kmol (3)

The present invention will be described in more detail below.
FIG. 1 shows a process flow for carrying out the present invention.
Put the raw material dust from the hopper 1 into the reduction reaction container 2,
A reduction reaction gas containing hydrogen and hydrocarbons as main components is supplied thereto through the gas supply pipe 4, and iron oxide in the dust is reduced at a reaction temperature of 500 to 700 ° C. The gas supplied for this reduction may be only hydrogen gas. However, since hydrocarbons generate hydrogen gas during decomposition, they can be used as a hydrogen source, and at the same time, carbon that is decomposed and produced at low temperature is mixed well with dust here, and as a reducing agent during zinc reduction in the next step. It is added because it can be used very effectively. This reducing gas may be produced by appropriately mixing hydrogen and hydrocarbon, but in view of cost, it is preferable to use the coke oven gas (hereinafter simply referred to as COG) at the time of producing coke as it is. . Since the gas discharged from the reducing reaction container 2 still contains excess hydrogen, it is returned to the reducing gas main pipe 3 via the dust removing device 5 and is recycled.

Thus, the reduced dust is transferred to the reaction vessel 6 in the next step, where it is oxidized by an oxygen-containing gas such as air and the reduced iron returns to iron oxide again. The reaction vessel 6 contains reduced iron as a material to be oxidized and carbon produced by decomposition of hydrocarbon during the reduction reaction. Generally, the oxidation reaction of reduced iron occurs at a lower temperature than the oxidation reaction of carbon, but in the present invention, the dust heats up mainly due to the heat of oxidation reaction of reduced iron generated at this time. However, in order to prevent dust from fusing and agglomerating due to excessive temperature rise, the dust temperature is set to 10
The temperature detection end 7 installed on the dust outlet side of the reaction vessel 6 detects the dust temperature so that the temperature becomes 00 to 1150 ° C., and the oxidation is performed by the control valve 9 provided in the air pipe 18 through the signal processing adjustment device 8. The amount of air used is regulated to control the oxidation reaction. As the temperature of the dust rises as the reaction proceeds, the reactions of the following formulas (4) to (7) continue to occur in the presence of carbon, and the Zn compound in the dust is reduced.

[0015] _{C + O 2/2 = CO} + 29,400kcal / kmol ··· (4) C + O 2 = CO 2 + 67,000kcal / kmol ··· (5) ZnO + CO = Zn + CO 2 -15,560kcal / kmol ··· (6 ) CO ₂ + C = 2CO-8, 600 kcal / kmol (7)

Metallic zinc has a melting point of about 420 ° C. and a boiling point of 90.
Since the temperature is 7 ° C., the vaporization and evaporation proceed at 900 ° C. or higher to be separated from the dust and discharged from the reaction container 6 together with the exhaust gas. The gas discharged from the reaction vessel 6 in this way is
In the gas treatment device 10, the air blown through the air pipe 17 is mixed with the metal zinc gas contained therein to be oxidized into zinc oxide. Thereafter, the gas containing zinc oxide is cooled by the cooling device 11, separated and collected by the dust collecting device 12, and the remaining gas is diffused to the atmosphere through the chimney 13.

On the other hand, the dezincified dust in the reaction vessel 6 is in a high temperature state, and after leaving the reaction vessel 6, the air sent from the air blower 15 through the air pipe 16 in the cooling and heat exchanger 14 is removed. It is cooled by heat exchange and reused as the processed dust 20 as a raw material for iron making. Further, the heat exchange air obtained here can be used as the hot air 19 and, if necessary, as the air for oxidizing the reduced dust in the reaction vessel 6.

[0018]

【Example】

(Example 1) FIG. 1 shows blast furnace dust having the composition shown in Table 1.
Is supplied at a rate of 15 kg / hr to the reduction reaction container 2 of the process shown in FIG.
The treatment was carried out at 50 ° C. for 1 hour, then air was blown into the oxidation reaction vessel 6 while controlling the temperature at 1000 ° C., and the treatment was carried out for 1 hour to obtain the results shown in Table 2. Total heat consumption intensity 1.9 million k
A dezincification rate of 93% was obtained in the dust with a cal / t which is extremely smaller than that of the conventional method.

[0019]

[Table 2]

Example 2 Electric furnace dust having the composition shown in Table 1 was placed in a reducing reaction vessel 2 of the process shown in FIG.
It is supplied at a rate of 0 kg / hr, treated with COG as a reducing gas at a reduction reaction temperature of 700 ° C. for 0.5 hour, and then blown with air while controlling the temperature in the oxidation reaction vessel 6 to 1100 ° C. for 1 hour. The results shown in Table 3 were obtained. The basic unit of total heat consumption was 198,000 kcal / t, which was reduced by 50 to 100 kcal / t as compared with the conventional method, and the dezincification rate in dust was as high as 95%.

[0021]

[Table 3]

[0022]

By carrying out the method of the present invention in the dezincing treatment, it is possible to achieve a dezincification rate of 90% or more by reducing the unit consumption of heat by 20 to 30% as compared with the conventional method. The energy saving effect is great.

[Brief description of drawings]

FIG. 1 shows a process flow for implementing the present invention.

[Explanation of symbols]

 1 Dust hopper 2 Reaction container for reduction 3 Reduction gas main pipe 4 Gas feed pipe 5 Dust removal device 6 Reaction container 7 Temperature detection end 8 Signal processing adjustment device 9 Control valve 10 Gas processing device 11 Cooling device 12 Dust collector 13 Chimney 14 Cooling Combined heat exchanger 15 Air blower 16 Air piping 17 Air piping 18 Air piping 19 Hot air 20 Treated dust

Claims (1)

[Claims] 1. A method for treating dust generated during metal refining, wherein an iron oxide in the dust is reduced using a reducing gas containing hydrocarbon and hydrogen as main components, and then an oxygen-containing gas is added. CO obtained by re-oxidizing the dust by using it and raising the temperature to at least 900 ° C. or higher by the heat generated at that time, and at the same time, partially burning the carbon produced by the decomposition of hydrocarbon during the reduction reaction. A dust treatment method characterized in that a dust atmosphere is made into a CO gas reducing atmosphere by a gas, and a zinc compound contained in the dust is reduced and evaporated under the above temperature conditions and the atmosphere.