JPH0567686B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for sintering raw materials for iron manufacturing, and particularly to a method for sintering raw materials for iron manufacturing using a two-stage ignition method. (Prior Art) Powdered iron ore, which is used for iron ore manufacturing, is agglomerated by sintering and then charged into a blast furnace. Generally, as a method for agglomerating ironmaking raw materials (hereinafter simply referred to as "raw materials") such as powdered ore,
A DL type (Dwight Lloyd type) sintering machine has been used. As shown in FIG. 1, bedding ore and sintering raw materials are sequentially supplied from hoppers 3 and 4 onto a large number of pallets 2 which are rotated around a sintered strand 1, and an ignition furnace 5 is started. During the process of passing, the surface of the sintered raw material is ignited, and air is circulated from above the raw material to below by suctioning it with a blower 7 from a wind box 6 placed below the pallet movement area, and as the pallet moves toward the discharge end. In this method, the raw material is sintered from the top to the bottom, and the sintering is completed just before the ore discharge end to obtain agglomerated sintered ore. The progress of sintering during this period is as shown in Figure 2, where numeral 8 indicates the raw material, the shaded area indicates the sintering reaction zone 9, and the numeral 10 located above the sintering reaction zone indicates the sintering completion zone. are shown respectively. The raw material is pre-blended with fixed carbon-containing materials such as coke powder and blast furnace gas ash as fuel (coke powder is mainly used, so it will be referred to as coke powder below).
After ignition in the ignition furnace 5, air with an O ₂ concentration of 21% is vented from above to burn the fixed carbon, thereby melting and sintering the ore. The combustion exhaust gas is exhausted through the wind box 6, but the
The _O2 concentration is around 13%. Gas at this oxygen concentration level still has enough oxidizing power to burn fixed carbon, and therefore it is desirable to reuse the exhaust gas. (Problems to be Solved by the Invention) Therefore, as one of the exhaust gas reuse technologies, the exhaust gas reuse technology as exemplified in "Tetsu to Hagane" Vol. 69, No. 4, p. 72 has been proposed. Circulation technology to sintered strands is implemented. This extracts the exhaust gas from the latter half of the strand and sprays it onto the surface of the raw material again to reuse it as firing gas, which is effective in reducing the amount of gas released into the atmosphere, reducing nitrogen oxides, and increasing the amount of waste heat recovered. . However, the combustion of fixed carbon and the sintering reaction itself that occur within the sintered layer are secondary to
This is similar to the conventional sintering method shown in the figure, and therefore the productivity improvement effect by increasing the sintering progress rate cannot be achieved. In order to use the exhaust gas again to promote the sintering reaction and to speed up the sintering progress, it is necessary to allow the sintering reaction to proceed simultaneously in the raw material layer. As a concrete method for realizing this, JP-A-47-
There is a method shown in No. 26304. In this method, a plurality of raw material supply devices and ignition furnaces are provided at different positions in the pallet advancing direction, and the surfaces of each supplied raw material are ignited in sequence to advance the sintering reaction. Reuse and sintering reaction rates can be significantly increased, resulting in improved productivity. The progress of sintering in the case of the two-stage method is schematically shown in FIG. In the figure, the symbol is the second
It is the same as that in the figure. The exhaust gas that has passed through the upper layer is used again for combustion in the lower layer. However, in this two-stage ignition sintering method, the gas flowing from the upper layer to the lower layer during the sintering process has a low oxygen concentration, so the coke breeze blended in the lower layer tends to be incompletely combusted, causing combustion heat generation. The amount will decrease. As a result, the temperature within the layer decreases, making it impossible to achieve sufficient melting and sintering, leading to deterioration in the strength of the finished sintered ore, which is a drawback of the multi-stage ignition sintering method. In this regard, in the case of a single-stage ignition type,
It has been proposed to reduce the heat disparity between the upper and lower layers by changing the coke content gradually or stepwise so that it decreases from the upper layer to the lower layer (Japanese Patent Publication No. 59-31576). issue). Thus, an object of the present invention is to provide a sintering method that efficiently burns the fixed carbon contained in the lower layer in a two-stage sintering method. (Means for solving the problem) The strength of the sintered ore product is determined by the sintering reaction temperature, and the main factors determining this are the amount of fuel fixed carbon and the bed height position. In other words, increasing the amount of coke breeze increases the combustion calorific value and raises the reaction temperature, and the lower the bed height is, the higher the temperature of the gas flowing into the sintering reaction zone, which also increases the reaction temperature. This is a well-known phenomenon. Therefore, in the conventional one-stage ignition sintering method, as disclosed in the above-mentioned Japanese Patent Publication No. 59-31576, the temperature of the gas flowing into the upper reaction zone is lowered by heat exchange, which prevents the strength from decreasing in the upper layer. For this purpose, more coke powder is mixed in the upper layer and less in the lower layer to make the reaction temperature more uniform. However, this method only works when igniting the charged raw material at only one location, and the two-stage ignition sintering method, in which the raw material layer is ignited at two locations to allow the sintering reaction to proceed simultaneously, is extremely difficult to achieve. This results in a decrease in the strength of the lower layer, making the product unsuitable for use as a blast furnace charge. The reason for this is thought to be as follows. That is, in general, the combustion of coke breeze in the sintered layer occurs due to the oxidation reaction of the fixed carbon contained therein due to oxygen in the passing gas. Complete combustion occurs, and the calorific value is 93.989kcal/mole of oxygen. On the other hand, when oxygen is insufficient, incomplete combustion occurs as shown in equation (2), and the calorific value at this time is 52.796kcal/
Based on 1 mole of oxygen, the amount of heat generated during incomplete combustion is 44% lower than that during complete combustion. C + O ₂ = CO ₂ ... Equation (1) (Calorific value = 93.989 kcal / oxygen mole) 2C + O ₂ = 2CO ₂ ... (2) Equation (calorific value = 52.796 kcal / oxygen mole) During the two-stage sintering described above The lower layer strength decreases because the combustion reaction of the lower layer coke powder proceeds with the low O ₂ concentration gas after burning the upper layer coke powder, which tends to cause incomplete combustion in the lower layer, making it difficult to secure the amount of heat required for melting and sintering. It is. Similar to the above-mentioned one-stage ignition sintering method, if the blend of coke breeze in the upper layer is increased, this operation further induces incomplete combustion of the coke breeze in the lower layer, leading to an extreme decrease in the strength of the lower layer. Therefore, in the two-stage sintering method, it is important to improve the combustibility of the coke breeze blended in the lower layer, but as a result of our studies, the present inventors first decided to limit the coke breeze concentration throughout the entire layer from the viewpoint of oxygen consumption. Furthermore, contrary to conventional knowledge, it was discovered that a gradient blending operation in which the upper layer contains less coke breeze and the lower layer contains more coke breeze is an appropriate method. Based on this knowledge, we operated the two-stage sintering method by limiting the amount of coke blended in all layers as described above and by changing the amount of coke blended in the upper and lower layers. It was confirmed that motsuta sintered ore could be obtained, and the present invention was completed. Therefore, the gist of the present invention is to load steelmaking raw materials in two layers in the layer height direction on the floor of a sintering device, simultaneously ignite the surface of each steelmaking raw material layer, and simultaneously and multiple times cause a sintering reaction in each layer. In the two-stage ignition type sintering method, the fixed carbon concentration in the steelmaking raw material to be sintered, for example, the amount of fuel coke mixed, is limited to a certain concentration or less in all layers, and this concentration is This is a method for sintering raw materials for iron making, which is characterized by blending fuel source materials so that they are less in the upper layer and more in the lower layer. Here, "steelmaking raw materials" include powdered ore generated during the pre-processing stage of iron ore, powdered ore existing in that state from the beginning, various ironmaking dust, scale, etc., and slag such as powdered limestone. This is the result of adding minerals and return minerals. It is well known as a so-called sintering raw material in the steel industry, and its specific content is not particularly limited. When sintering raw materials for steelmaking, fixed carbon-containing materials such as coke breeze and blast furnace gas ash are blended into the raw materials as fuel, but in the method of the present invention,
In order to ensure a balance between the required amount of oxygen and the supplied amount, a quantitative limit is placed on the amount of fixed carbon-containing material incorporated. In other words, as shown in Figure 5, the average concentration of coke powder in the raw material is 3.6wt.
% or less, fixed carbon (FC) concentration is 3.3wt%
The following shall apply. In addition to this quantitative restriction on the average concentration of all layers, in the present invention, the blending amount of the FC-containing material is varied for each layer so that the FC concentration in the raw material is lower in the upper layer and higher in the lower layer. . Therefore, according to the present invention, in the suction gas,
Almost all of the O ₂ is used for fixed carbon combustion, and the heat generated can also be efficiently used for combustion reactions, making it possible to produce products with uniform properties in which the strength of the sintered ore in the lower layer hardly decreases compared to that in the upper layer. It is possible to achieve a significant improvement in overall strength. (Operation) Next, the present invention will be further explained with reference to the accompanying drawings. First, the sintering pot device will be described. FIG. 4 shows a partially sectional view of the sintering pot for carrying out the present invention. In the figure, numeral 11 indicates the main body, which has a cylindrical shape with a height of 600 mm and an inner diameter of 300 mm.
Grate 12 consisting of a grid at intervals on the bottom
A wind box 13 is provided at the bottom of the air box 13, and suction is performed by an exhaust fan (not shown).
Ignition is performed by a coke oven gas combustion burner 14 installed in the shape of the pot body. Using this test pot, bedding ore 15 is laid out in the shape of a grate 12, and predetermined raw materials 16 are charged thereon in two stages, and the surface of the filled raw materials is ignited and fired after each stage is charged. Ta. Next, to explain the operation during the firing test, first, raw materials equivalent to a bed height of 300 mm are charged and ignited, and immediately after the ignition is completed, raw materials are charged again for a bed height of 300 mm.
After igniting it again, it was fired by atmospheric suction. The coke powder and blast furnace gas ash to be mixed into the raw materials were adjusted to preset amounts before use. Example In this example, two-stage sintering was carried out using the apparatus shown in FIG. The raw material composition and sintering conditions are summarized in Tables 1 and 2, respectively. In Table 1, the blended amount of coke powder is % by weight when the total of raw materials other than coke powder is 100%.

【table】

[Table] FIG. 5 shows the effects of implementing the method of the present invention in a graph together with those of comparative examples. In the figure, the ● mark indicates the strength (TI value disclosed in JIS M8712) when the blending ratio of coke breeze in the upper and lower layers is the same (comparative example), and the △ and ▲ marks indicate the blending ratio of coke breeze in the lower layer. On the other hand, the circles indicate the strength results when the coke powder blending ratio in the upper layer was higher than that in the lower layer (comparative example). In addition, the broken line in the figure shows the result of implementing the method of the present invention, and the solid line shows the result of implementing the comparative example. In this case, under the condition that the coke content ratio in all layers is 3.6wt% or less (fixed carbon concentration is 3.3wt% or less),
Strength is improved by increasing the coke powder blending ratio.
On the other hand, when the coke content in all layers is 3.6wt% or more (fixed carbon concentration is 3.3wt% or more), the strength is significantly reduced. As mentioned earlier, the amount of O ₂ required for combustion of fixed carbon is smaller than the amount of supplied O ₂ when the coke blending ratio is 3.6% or less, and although there are problems with combustibility, oxygen deficiency will not occur. Not required, but necessary if coke content is 3.6% or higher
This is because the amount of O ₂ becomes larger than the amount of O ₂ supplied, causing oxygen deficiency, which not only causes a significant decrease in strength, but also, in the worst case, makes it impossible to burn and sintering becomes impossible. Therefore, in order to carry out the two-stage ignition sintering method, strength decreases when the coke content is 3.6% or more on average for all layers, regardless of the coke content in the upper and lower layers. Now, when the coke blending ratio in all layers is 3.6wt% or less, that is, when the amount of O ₂ necessary for combustion is secured, the upper layer is fired in an atmosphere with 21% O ₂ , so the coke powder blending ratio is lower than 3.6wt%. The strength improves with an increase in coke breeze, but as a matter of course, an increase in the coke breeze blending ratio in the upper layer leads to a decrease in the O ₂ gas concentration supplied to the lower layer, which worsens the combustibility of the coke breeze in the lower layer. In other words, although the strength of the upper layer is improved, the strength of the lower layer is reduced, and the improvement effect is canceled out. On the other hand, an increase in the blending ratio of coke breeze in the lower layer results in increased heat generation due to the increase in fuel, even though the combustibility is _poor , resulting in an increase in strength. As a result, the strength is improved. Therefore, during two-stage ignition sintering, which is completely different from one-stage ignition sintering, there is a limit to the coke powder blending ratio of 3.6% or less (fixed carbon concentration of 3.3% or less) throughout the entire layer, and the coke blending ratio in the lower layer is In order to improve the strength, it is preferable to make the coke ratio higher than that of the upper layer.Conversely, it is preferable to make the coke powder mixture ratio of the upper layer and the lower layer the same, or to add coke powder to the upper layer as disclosed in Japanese Patent Publication No. 59-31576. It can be said that it is not preferable to increase the blending ratio and lower the lower layer. Furthermore, as another application example of the present invention, a case will be described in which the coke powder blending ratio in the upper layer and the lower layer is the same and blast furnace gas ash containing fixed carbon is added only to the lower layer. The raw material blending ratio is shown in Table 3. The firing method was the same as in the previous example. As a result, the product strength TI was 59%, which can be evaluated as being good compared to the results shown in FIG. In Table 3, the blended amount of coke powder is the total amount of raw materials other than coke powder.
% by weight. In this way, in the present invention, it is only necessary to operate so that the concentration of fixed carbon used as fuel is 3.3wt% or less on average in all layers and is higher in the lower layer than in the upper layer, and the brand is not limited to coke breeze. In addition to blast furnace gas ash, lime may also be used.

【table】 [Brief explanation of the drawing]

Figure 1 is a schematic illustration of a conventional DL type sintering machine;
Figure 2 is a graph showing the sintering progress in the one-stage sintering method; Figure 3 is a graph similar to Figure 2 in the multi-stage sintering method; Figure 4 is the graph of the sintering machine used in the present invention. A cross-sectional view of the bucket; and FIG.
FIG. 2 is a graph showing the difference in the coke powder blending ratio between the upper and lower layers and the relationship between the coke powder blending ratio and TI in the average of all layers. 1: Sintered strand, 2: Pallet, 3, 4:
Hopper, 5: Ignition furnace, 6: Wind box, 7: Blower, 8: Raw material zone, 9: Reaction zone, 10: Sintering completion zone, 11: Sintering pot, 12: Grate, 13: Wind box, 14: Burner, 15: Bed ore, 16: Raw material.

Claims (1)

[Scope of Claims] 1. Iron-making raw materials are loaded in two layers in the layer height direction on the floor of a sintering device, and at the same time, the surface of each iron-making raw material layer is ignited, so that the sintering reaction of each layer proceeds simultaneously and multiple times. 2.
In the staged ignition sintering method, the fixed carbon concentration in the steel raw material to be sintered is set to 3.3wt% or less on average for all layers, and the fixed carbon concentration in the raw material is lower in the upper layer and higher in the lower layer. A method for sintering raw materials for iron making, characterized by blending a fixed carbon-containing material into a material containing fixed carbon. 2 Using coke powder as a fixed carbon-containing material,
The sintering method according to claim 1, wherein the average amount of coke powder mixed in all layers is 3.6 wt% or less.