JPS6362572B2 - - Google Patents

Description

[Detailed description of the invention] In order to enable the use of fine-grained ores, which are currently mainly traded in the iron ore market, in blast furnaces, such fine-grained iron ores undergo a thermal pre-treatment process. It must then be made into a lump (agglomeration). Sintering is a proven and particularly efficient agglomeration method. In the sintering process, a mixture of fine ore, concentrate, additives and solid fuel (coke powder, pulverized coal) is sintered on a grate using, for example, sucked air.
It is partially melted at temperatures up to °C and after cooling is converted into a bulk product. This bulk product is a very suitable material for use in blast furnaces.

The disadvantages associated with the use of solid fuels, which are still considered favorable from the point of view of energy supply, are that due to the sulfur content of the materials used, oxidized compounds of sulfur, primarily sulfur dioxide gas (SO ₂ ) This means that combustion gas containing
The sulfur concentration in the sintering waste gas is, for example, significantly lower than the sulfur concentration in the combustion gas of a thermal power plant. For example, in the case of a modern sintering facility processing 5 million tons of sintered material per year, the sulfur emissions, hereinafter always expressed as sulfur dioxide emissions, represent the fuel consumption per ton of product sintered material. Approximately 55Kg, approximately 1200 per hour assuming the sulfur content of solid fuel is approximately 1%
on the order of approximately 1.85 Kg of sulfur dioxide gas per Kg or ton of sintered material.

Sintering equipment therefore ranks among the leading sources of sulfur dioxide gas emissions, after coal-fired power plants and chemical plants. Sintering facilities therefore face the problem of the cost burden required to limit the emissions of hazardous substances, especially sulfur dioxide emissions.

Limiting the amount of sulfur dioxide gas emitted per unit time to within certain limits by limiting the daily sintering capacity per ^m2 of suction surface or by systematically purchasing fuels and ores with low sulfur content. can do.

By adjusting the throughput to a lower level, fuel consumption per ton of product can be reduced, thereby reducing the amount of sulfur that enters the process via the fuel. However, the amount of sintered material required by blast furnaces cannot be met without large-scale sintering equipment that requires large equipment costs.

The systematic selection and use of raw materials with low sulfur content is currently becoming more and more constrained, considering the current energy situation and the dwindling availability of raw materials.

Another way to reduce sulfur dioxide emissions is to subsequently desulfurize the combustion gases. In principle, methods for removing sulfur dioxide gas from combustion gas by washing or dry absorption are known. Such a combustion gas desulfurization process is carried out in conjunction with sintering equipment, but it presents various problems for a number of reasons.

During sintering, a large amount of waste gas is generated, which has a low sulfur dioxide content but a very low temperature. For example, a modern 400 m ² facility with the capacity to produce 35 tons of sintered material per m ² in 24-hour operation has a water column of 1600 mm.
Under negative pressure conditions, more than 1 million ^m3 of waste gas containing approximately 0.04% sulfur dioxide gas at a temperature of approximately 130°C is generated per hour. Processing such a large amount of combustion gas requires huge equipment costs, but unlike in the case of thermal power plants, the content of harmful substances is low, so such huge equipment costs are actually reduced. This is very disadvantageous compared to the amount of harmful substances removed. In addition, when adopting a wet method, it is necessary to fully consider the economic efficiency of water, and it is also necessary to reheat the purified gas. This also raises other environmental protection issues. In addition to the low sulfur dioxide concentration in the sintered gas, the low combustion gas temperature makes the adoption of "dry" absorption technology for sintered materials unfavorable; , it is necessary for reasons of reaction kinetics to reheat the combustion gases, or to enlarge the reaction zone to a scale that is no longer economically tenable.

However, even when the technology, which is still in its experimental stages, is successfully used, environmental problems arise. This is because the sulfur removed from the combustion gases is an extremely fine-grained solid substance.
This is because most of the sulfur is passed through a sieve, and this extremely fine sulfur must be removed by precipitation.

It is therefore an object of the present invention to provide a method for effectively reducing the content of harmful substances in sintering waste gases, which does not have the drawbacks associated with conventional methods as mentioned above. . However, the method according to the present invention includes the following five partial problems.

(1) The method of the invention must be able to significantly reduce the emission of sulfur dioxide gas. The amount of sulfur dioxide gas released increases by increasing the sintering capacity, using solid fuel instead of heat treatment gas with low sulfur content, or increasing the amount of sulfur used due to other processing method constraints. We must be able to at least suppress this.

(2) The method of the present invention must be able to be introduced as a supplement to the existing old-style sintering equipment, and in consideration of the lack of space in the existing equipment, it does not take up much space. You must do so. The investment amount must be significantly less than the installation cost required for the flue gas desulfurization equipment.

(3) In the method of the present invention, the operating cost must be lower than the operating cost of the combustion gas desulfurization equipment. Only inexpensive reactants should be used and the additional energy requirements should not be too great.

(4) In the method of the present invention, the sintering process and the quality of sintering must not be impaired.

(5) In removing the recovered sulfur, which is an important harmful substance in the method of the present invention,
The sulfur must be removed in such a way that less fresh leaching products are deposited than would be the case with the precipitation of reaction products from lime-based flue gas desulfurization equipment.

According to the invention, the above object has been achieved by the method as defined in the features of claim 1.

It is surprising that by applying the method according to the invention it was possible to carry out a desulphurization step on a sintered belt. To carry out the method of the invention, a sintered belt with a thickness of 2 to 3 cm is usually placed on the grate bars to protect the grate bars from thermal overload. Instead of, or in addition to, a normal grate lining, which also serves to prevent fine mixture components from flowing down,
Pellet-shaped charge material prepared in a blast furnace (pellets,
Ore chips, LD - slag, finished sintered product - also called treatment layer) are deposited in very large layer thicknesses on the sintering grate. The thickness of such an external grate lining layer can be chosen freely within the limits set by the maximum grate bed height and the customary deposition thickness for the sintering mixture. When operating a sintering plant with a grate height of 50 cm and a layer height of 40 cm (including the normal grate lining), the grate lining must have a layer thickness of e.g. up to 13 cm. can be applied. Before forming such an external grate lining on the sintering grate, it can be impregnated with water or sprayed with water or, for greater effectiveness, treated with an alkaline solution or basic suspension. Wet with milk of lime as a liquid. Even in the case of wetting with only water, no desulfurization agent is used and the reaction area is slightly shorter than that of a desulfurization device, as shown in the following example, by using the above configuration, It has become clear that it has a very significant desulfurization effect.

Example 1 54.7% fine ore passed through the sieve and concentrate
19.3%, steel mill recycle material 9.3%, and base carrier 16.7% with the addition of 60Kg of coke powder per ton of finished sintered material.
In a test sintering facility, an ore-rich mixture consisting of It was sintered. Basicity of finished sintered material when total iron content is 57%
CaO/SiO ₂ was 1.6. per ton of sintered material
The amount of SO ₂ released was measured at 1440 g of SO ₂ .
The amount of SO ₂ released was found to be reproducible. When the sintering capacity per ^m2 is 35t/day and the suction area is ^400m2 ,
The SO ₂ release amount was equivalent to a release of 840 Kg SO ₂ per hour (baseline test).

If a 7.5 cm layer of sintered material moistened with water only is used instead of the normal grate lining,
Although the amount of SO ₂ observed decreased to 1270 g per ton of freshly produced sintered material, this amount of SO ₂ was found to be reproducible. The amount of SO ₂ released was equivalent to a desulfurization effect of 11.8%.

By increasing the thickness of the moistened grate lining layer to 15 cm (although the layer thickness of the sintered material mixture was always 40 cm), the thickness of the moistened grate lining layer was increased to 15 cm, which differed from the standard test to 1130 g/
The amount of SO ₂ was confirmed to be 21.5% (desulfurization degree 21.5%). In the latter case, 180 for the above example of an installation of 400 m ²
This is a calculation that reduces the amount of SO ₂ emissions in kg/h.

Example 2 In the second series of tests, a layer thickness of 2.5 cm was used instead of the sintered material moistened with water supplied for desulphurization.
Menera ore (iron content 50.5%) moistened with tap water was filled to a thickness of 5 cm on top of a conventional grate lining before filling with the sintering mixture. Since the measured amount of SO ₂ in the waste gas was 1220 g per ton of sintered material, the degree of desulfurization was calculated to be 15.3%.

Instead of Menera ore with a layer thickness of 5 cm, the layer thickness is 5 cm.
By using wet LD slag with particle size larger than 6.3 mm in cm, the observed amount of SO ₂ was reduced to 1100 g per ton of sintered material, but this amount of SO ₂ was reduced by 23.6%.
The degree of desulfurization corresponded to that of

Example 3 In the third series of tests, instead of the usual grate lining with a layer thickness of 2.5 cm, a layer thicker than said layer of sintered material or iron ore pellets, which had been previously sprayed with milk of lime and dried, was used. was used. For a sintered layer with a layer thickness of 7.5 cm with lime milk deposited by treatment with 3.8% milk of lime, Ca(OH) ₂ of 730 g per ton of freshly produced sintered material.
SO ₂ was confirmed, but the degree of desulfurization was calculated to be 49.3
It was %. Speaking of sintered belt of ^400m2 ,
The above desulfurization degree means that, in the case of a processing capacity of 580 tons per hour, 116 tons of desulfurization treatment layer and 4.4 tons of slaked lime were used per hour.

With a 15 cm thick pellet layer deposited with 4.1% Ca(OH) ₂ , 390 g of SO ₂ per ton of sintered material was still measured during waste gas sintering;
This corresponded to a degree of desulfurization of 72.9%.

A wet grate lining layer consisting of ore chips, iron ore pellets, blast furnace slag, LD slag or sintered material's own return material or a grate lining layer supplementarily treated with a basic carrier will exceed expectations. It has been confirmed in a number of tests that a strong desulfurization effect can be obtained using various base carriers, but this desulfurization effect has not been completely elucidated. . Since the conditions related to temperature and gas composition for good desulfurization of the emitted combustion gases are very favorable directly below the sintering mixture, a height of 5.
Despite the extremely short reaction area, which is only 15 cm from There was no need to add any reactants.

Furthermore, the method measures mentioned above can not only reduce the SO ₂ contained in the combustion gas;
It has also been found that the small amounts of gaseous chlorine and fluorine contained in the sintering waste gas can be significantly reduced.

The presence of the pollutant-absorbing grate lining layer directly beneath the freshly mixed sintering mixture does not significantly affect the sintering process. Since the particles in the treated layer are coarse, the pressure loss caused by the presence of the treated layer is negligible, and even when the grate lining is 15 cm thick and the negative pressure is kept constant, the treatment capacity is only 2.5%. The loss was only measured. In large-scale facilities, the above effects can be automatically corrected while maintaining the supply amount.

Therefore, the method according to the present invention can economically desulfurize the sintering gas to a large extent without making any major modifications while keeping the height of the sintering grate stand at the generally adopted level. I can do it. Additionally, sulfur-rich feedstocks can be used without lowering the emission factor, or fuel consumption can be increased to increase throughput. Moreover, it does not have a negative effect on the sintering process.

Regarding the fifth point in the objective setting section above,
Attempts were made to combine the sulfur to be separated from the combustion gases with blast furnace slag. The sulfur compounds are not stored on the surface of the blast furnace slag, but are embedded within the matrix of silicate layers and are therefore difficult to leach out. 50% ore-rich sintered material comes from specialized equipment at the latest blast furnace factory.
When loading, the above-mentioned amount of 1.85Kg per ton of sintered material
Carrying in 25% of the SO ₂ emissions will increase the amount of sulfur input into the blast furnace by a maximum of 3 to 4%. This increases the sulfur content of crude pig iron to a maximum
Since it only increases the sulfur content of the slag by about 0.001% and slightly more than 0.1%, it does not have any disadvantageous effect on the iron-making process of the blast furnace. Furthermore, many evaluation results have demonstrated that the sulfur content does not affect the leaching characteristics of blast furnace slag as long as it remains within this range.

In addition, other features of the present invention are as follows.

(1) Even if SO ₂ emission increases due to increased sintering capacity, SO ₂ separation can be enhanced. If the suction area is constant, the sintering capacity can generally be increased by lowering the height of the mixture layer, so that the height of the grate bed of the desulfurization layer can be further increased.

(2) A portion of the heat that is normally carried away with the combustion gases is transferred to the desulfurization layer. This increases the durability of the grate bars. Since the temperature of the waste gas is relatively low, the power consumed by the blower can be saved. Since more heat is supplied to the cooler via the waste gas,
By returning the waste heat of the cooler to the sintering process, it is possible to improve the energy utilization in the method.

(3) When working with a wet desulfurization layer, the humidity contained in the waste gas increases. This makes it possible to improve the degree of dust separation in the electric filter.

(4) When working with a desulfurization layer impregnated with basic substances, the basicity of the sintered mixture can be influenced within certain limits through the base carrier mixed in the desulfurization layer. Quality features that depend on the basicity of the binder can be corrected.

Claims (1)

[Claims] 1. Reducing the release of gaseous harmful substances in the combustion gas discharged from the sintering equipment by providing a granular treatment layer between the sintering grate and the raw material mixture to be sintered. In the method, the treated layer includes ore pieces,
consisting of iron ore pellets, sintering material, blast furnace slag, LD slag or mixtures of these materials, and before feeding these materials onto the sintering grate,
When moistened with water and/or an alkaline solution or milk of lime as a basic suspension, the particle size of the material is generally determined during the sieving operation carried out in the sintering plant or before the blast furnace. During sintering, the material of the treatment layer is selected to have a particle size that can remain in the form of a residue, and after sintering the raw material mixture to be sintered, the material of the treatment layer is loaded into a blast furnace together with the finished sintered product. Methods of reducing the release of hazardous substances. 2. Claim 1, characterized in that the substance of the treatment layer is wetted with an aqueous solution of potassium carbonate.
Method for reducing the release of harmful substances during sintering as described in Section 1. 3. The substance of the treated layer is treated with a basic suspension, and the basic substance is added in such an amount that the weight of the treated layer increases by at least 0.5 to 5% due to the basic additive. 2. A method for reducing the release of harmful substances during sintering as claimed in claim 1, wherein the concentration of the basic suspension is adjusted to adhere to particles of material in the treatment layer.