JPS6260829A - Two-stage-ignition sintering method for raw material for iron manufacture - Google Patents

Abstract

PURPOSE:To burn fixed carbon in high efficiency and to obtain an excellent sintered ore by regulating the fixed-carbon concentration in a raw material for iron manufacture for use in sintering to a proper value on the average of whole layer and by blending a fixed carbon-containing material so that said concentration is lower on the upper layer side and is higher on the lower layer side. CONSTITUTION:The raw material for iron manufacture is piled up on the floor of a sintering equipment into two layers in the direction of the height of layer and, at the same time, the respective surfaces of the above two layers are ignited severally, so that the sintering reaction of each layer is allowed to proceed simultaneously in two places in order to increase sharply the sintering reaction velocity and to improve productivity. In the above two-stage- ignition sintering method, the fixed carbon-concentration in the raw material for iron manufacture to be sintered is regulated to <=3.3wt% on the average of whole layer. When coke fines are used as the above fixed carbon-containing material, it is proper to regulate its quantity to 3.6% or below. Simultaneously, the fixed carbon-containing material is blended so that the fixed carbon concentration in the raw material becomes lower on the upper layer side and higher on the lower layer side, respectively. In this way, the fixed carbon contained in the lower layer is efficiently burned, so that deterioration in the strength of sintered ore products can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for sintering raw materials for iron manufacturing, particularly a two-stage ignition method for sintering raw materials for iron manufacturing.

(Prior Art) Powdered iron ore, which is used for iron ore manufacturing, is agglomerated by sintering and then charged into a blast furnace.

Generally, a DL type (Dwight Lloyd type) sintering machine has been used as a method for agglomerating iron manufacturing raw materials (hereinafter simply referred to as "raw materials") such as powdered ore. 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 the sintered strands l, 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 downward by suctioning it with the blower 7 from the wind box 6 placed below the pallet hyperactive area, while the pallet moves toward the ore discharge end. In this method, the sintering of the raw material proceeds 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, with reference numeral 8.
indicates the raw material, the shaded area indicates the sintering reaction zone 9, and the symbol 0 located above the sintering reaction zone indicates the sintered completed zone. 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), and after being ignited in the ignition furnace 5, it is heated from above. 0. Air with a concentration of 21% is aerated to burn fixed carbon, thereby melting and sintering the ore. The combustion exhaust gas is exhausted through the wind box 6, but at this time the exhaust gas contains 0! The concentration is 13
It is about %. Gas at this level of oxygen concentration still has enough oxidizing power to burn fixed carbon, and therefore it is desirable to reuse the exhaust gas.

(Problem to be Solved by the Invention) Therefore, as one of such exhaust gas reuse technologies, there has been a conventional method of using sintered strands of exhaust gas as exemplified in [Tetsu to Hagane J Vol. 69, page 4.72]. Circulation technology is being 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 occurs within the sintered layer are
This is similar to the conventional sintering method shown in FIG. 2, 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 method to specifically realize this, Japanese Patent Application Laid-Open No. 47-263
There is a method shown in No. 04. In this method, a plurality of raw material supply devices and ignition furnaces are provided with their positions shifted in the direction of pallet movement, and the surface of each supplied raw material is ignited to advance the sintering reaction. It is possible to reuse the exhaust gas and significantly increase the sintering reaction rate, 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 symbols are the same as those in FIG. 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 content of 4°C.
For this reason, the coke powder blended in the lower layer tends to be in a state of incomplete combustion, resulting in a decrease in the amount of heat generated by combustion. 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.
This is a drawback of the multistage ignition sintering method.

In this regard, in the case of a single-stage ignition type, by changing the coke content in a gradient or stepwise manner so that it decreases from the upper layer to the lower layer, the heat disparity between the upper and lower layers can be reduced. It has been proposed to make it smaller (Japanese Patent Publication No. 59-31576).

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 that determine 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, the above-mentioned
--As disclosed in No. 31576, a large amount of coke breeze is added to the upper layer in order to prevent a decrease in the strength of the upper layer where the temperature of the gas flowing into the upper reaction zone becomes low due to heat exchange.
(!A small amount is added to QIJ 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 an oxidation reaction of the fixed carbon contained therein by oxygen in the passing gas, and if there is sufficient oxygen, ti
The state of complete combustion shown in the + formula is reached, and the heating lid is 93.98.
It becomes 9 kcal/oxygen mole. On the other hand, if there is a lack of oxygen, incomplete combustion will occur as shown in equation (2), and the calorific value at this time will be 52.796 kcal/mole of oxygen. The calorific value during combustion is reduced by 44% compared to that during complete combustion.

c+o, = co, ... Equation (1) (heat generation ff
1=93.989 kcal/oxygen mole)2C+ oz
= 2CO□ ... Equation (2) (calorific value = 52.
796 kcal/oxygen mol) The lower layer strength mentioned above during two-stage sintering is due to the low Ot after burning the upper layer powder coke?
This is because the combustion reaction of the lower layer coke powder progresses with the 71i degree gas, so incomplete combustion tends to occur in the lower layer, making it difficult to secure the amount of heat required for melting and sintering. Similar to the one-stage ignition sintering method described above, if the upper layer coke breeze mixture is increased, this operation will further cause incomplete combustion of the lower layer coke breeze,
This results in 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 mixed in the lower layer, but as a result of our studies, the present inventors found that it is necessary to limit the concentration of coke breeze 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 powder and the lower layer contains more coke powder is an appropriate method.

Based on this knowledge, when we operated the two-stage sintering method by limiting the amount of coke blended in all layers and changing the amount of coke blended in the upper and lower layers as described above, we were able to obtain sufficient bond strength. It was confirmed that sintered ore could be obtained, and the present invention was completed.

Therefore, the gist of the present invention is to load steelmaking raw materials on the floor of a sintering device in two layers in the layer height direction, simultaneously ignite the surface of each steelmaking raw material layer, and proceed with the sintering reaction of each layer simultaneously and multiple times. In the two-stage ignition type sintering method, the fixed carbon concentration in the steel raw material to be sintered, for example, the amount of fuel powder coke blended, is limited to a certain level of 4 degrees or less in all layers, and this concentration is The fuel source material is blended so that it is less in the upper layer and more in the lower layer,
This is a method for sintering raw materials for steelmaking.

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 includes wood and return ore. 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 mixed into the raw materials as fuel, but the method of the present invention ensures a balance between the required amount of oxygen and the amount of oxygen supplied. Therefore, quantitative restrictions are placed on the amount of fixed carbon-containing material added. That is, as shown in FIG. 5, the coke breeze concentration in the raw material is 3.64% or less, and the fixed carbon (F, C 18 degrees) is 3.64% or less in terms of the average concentration in all layers.
3 wt% or less.

In addition to this quantitative restriction on the average concentration of all layers, in the present invention, the amount of F, C, and materials contained in the raw material is set so that the amount of F, C, and ft1 degree in the raw material is lower in the upper layer and higher in the lower layer. is changed for each layer.

Therefore, according to the present invention, almost all of the 0□ in the suction gas is used for fixed carbon combustion, and the heat generated thereby can also be efficiently used for the combustion reaction, so the strength of the sintered ore in the lower layer is lower than that of the upper layer. Compared to that, it is possible to obtain a product with uniform properties with almost no deterioration, and it is also possible to achieve a comprehensive improvement in strength.

(effect) The invention will now 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, reference numeral 11 indicates the main body, which has a cylindrical shape with a height of 600 mm and an inner diameter of 300 mm, and a grate 12 consisting of a grid at intervals is provided at the bottom, and a wind box 13 is located below the grate 12. It is designed to be sucked in by an exhaust fan (not shown). Ignition is performed by a coke oven gas combustion burner 14 installed on the pot body. Using this test pot,
A bedding ore 15 was spread on a grate 12, and predetermined raw materials 16 were charged thereon in two stages, and firing was performed on the surface of the charged raw materials at each stage of charging.

Next, to explain the operation during the firing test, first, the layer height is 300.
A raw material equivalent to mm was charged and ignited, and immediately after the ignition was completed, another raw material was charged in an amount equivalent to a bed height of 30011II11, ignited again, and then 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 blending amount of coke powder is expressed as % by weight when the total amount of raw materials other than coke powder is 100%.

Table 2] Figure 5 of Table 1 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 powder in the upper and lower layers is the same (comparative example), and the mark △ indicates the blending ratio of coke powder 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 results of the present invention, and the solid line shows the results of the comparative example.

In this case, under the condition that the coke blending ratio in all layers is 3.5 wt% or less (fixed carbon concentration is 3.3 wL% or less),
Strength is improved by increasing the coke powder blending ratio.

On the other hand, under conditions where the coke content in all layers is 3.6 ht% or more (fixed carbon concentration is 3.3 wt% or more), the strength is significantly reduced. As mentioned earlier, this means that the coke content is 3.6% or less, which is necessary for the combustion of fixed carbon.
□ is smaller than the supplied otM, and although there are problems with combustibility, it does not cause oxygen deficiency. However, at coke blending ratios of 3.6% or more, the required O2 amount is larger than the supplied O2 amount, and oxygen This is because not only does this cause a deficiency and a significant decrease in strength, but in the worst case, it becomes 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 content ratio in all layers is 3.6 wt% or less, that is, when the amount of coke necessary for combustion is secured, the upper layer is fired in an atmosphere of 0□21%, so the coke powder is The strength improves as the blending ratio increases, but as a matter of course, an increase in the coke breeze blending ratio in the upper layer leads to a decrease in the 0□ gas concentration supplied to the lower layer, which worsens the combustibility of the coke breeze in the lower layer. As a result, 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 causes an increase in heat generation due to the increase in fuel and improves strength even though the combustibility is poor, but in this case, even if the concentration of exhaust gas emitted from the lower layer is low, it does not affect other As a result, the strength is improved.

Therefore, during two-stage ignition sintering, which is completely different from that during first-stage ignition sintering, there is a limit to the coke breeze blending ratio of 3.6% or less (fixed carbon concentration 3.3% or less) throughout the entire layer, and In order to improve strength, it is preferable that the coke blending ratio be higher than that of the upper layer.Conversely, it is preferable to make the coke powder blending ratio of the upper layer and the lower layer the same, or
It can be said that the operation disclosed in No. 31576, in which the blending ratio of coke powder is high and the lower layer is low in the shoe part, is not preferable.

Furthermore, as another example of application of the present invention, a case will be described in which the coke ratio in the upper and lower layers is the same, and light 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 good compared to the results shown in FIG. In Table 3, the blended amount of coke powder is expressed as % by weight when the total amount of raw materials other than coke coke is 100%.

In this way, in the present invention, it is sufficient to operate so that the fixed carbon concentration serving as the fuel is 3.3 wt% or less on average in all layers and is higher in the lower layer than in the upper layer, and the brand does not need to be particular about coke breeze. Instead, it may be blast furnace gas ash or coal.

[Brief explanation of the drawing]

Figure 1 is a schematic explanatory diagram of a conventional DL type sintering machine; Figure 2 is a rough illustration of the sintering progress in the one-stage sintering method; Figure 4 is a bucket of the sintering machine used in the present invention. and FIG. 5 are graphs showing the difference in the blending ratio of coke powder between the upper and lower layers and the relationship between the blending ratio of coke powder and TI in the average of all layers. l: Sintered strand 2: Valent 3.4: Honopah 5: Ignition furnace 6: Wind box
7: Blower 8: Raw material zone 9: Reaction zone lO; Sintering completion zone 11: Sintering pot 12 Nigerate 13; Wind box 14: Burner
15: Bed ore 16: Raw materials

Claims (2)

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