JPH0524961B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention mainly relates to a method for reducing a raw material containing iron oxide to obtain a molten iron-based alloy. (Prior technology) The current mainstream method for manufacturing iron using iron ore as a raw material is via a blast furnace (more than 95%).
The method of melting this in an electric furnace accounts for the remaining several percent. However, the method using a blast furnace (1) requires a process to agglomerate fine ore, (2) requires a process to coke coal, (3) requires a huge amount of equipment cost, and (4) has limited production flexibility. On the other hand, the method using sea surface iron has the disadvantage of high energy costs for mass production processes. Therefore, over the past 30 years, research has been focused on the smelting reduction method as a method for producing large quantities of molten metal in place of the blast furnace method, which involves a more direct process and uses more compact equipment. It has been. However, none of them have reached the stage where they are put into practical use. The principle of the smelting reduction method is that carbonaceous material (coal or coke), ore, oxidizing gas (oxygen, etc.), and flux (lime, etc.) coexist, and a part of the CO gas generated by the combustion of carbonaceous material or Alternatively, the heat generated by burning most of the ore to CO ₂ can be used to reduce the ore with C, Fe _o O _n + m/2C → nFe + m/2 CO ₂ (n: 1 to 3, m: 1 to 4), and the various raw materials are melted to separate the molten alloy and molten slag. At this time, the greater the amount of heat generated per unit amount of carbonaceous material, the more advantageous it is in terms of the process. When comparing the case where the product when burning C is CO and the case where the product is CO ₂ , the latter generates about four times as much heat. That is, the higher the degree of oxidation of the generated gas, the greater the amount of heat generated per unit amount of coal material. However, the main purpose of melt reduction is to reduce metal oxides, and from the perspective of effective resource utilization, the concentration of metal oxides in the slag discharged outside the system has been reduced to a level comparable to that of the current method. It has to be possible in a way. Furthermore, the generated heat must be effectively used for the reaction. In this way, how to balance the carbon material oxidation reaction to generate heat with the reduction reaction of metal oxides, and even if the oxidation reaction in the atmosphere is promoted by some means, what is the effect of the reaction? Until now, the smelting reduction method has not been put into practical use, as no technological solution has been found to effectively utilize the calorific value to promote the reduction reaction of oxides. This is the reason why this has not been achieved and is a fundamental problem. Therefore, an intermediate method is to burn carbonaceous materials to increase the
A method of obtaining gas with a high CO/CO ₂ ratio and a high H ₂ /H ₂ O ratio and considering this gas as the main product (gasification);
A method has been proposed in which CO/CO ₂ or high H ₂ /H ₂ O gas is used for preliminary reduction of ore in equipment separate from the smelting reduction furnace. These are all methods to avoid the difficulty of coexisting an oxidation reaction and a reduction reaction for exothermic purposes, but the equipment cost and
It must be said that this greatly diminishes the original advantages of the smelting reduction method in terms of operational freedom. (Problems to be Solved by the Invention) This invention achieves the ideal state of the smelting reduction method, that is, the reduction reaction of metal oxides proceeds to reduce their concentration in the slag, and at the same time, the atmosphere is strongly oxidized and generated. The present invention provides a method for increasing the amount of heat and efficiently transmitting the generated heat to the molten material. (Means for Solving the Problems) The above-mentioned object of the present invention is to improve the oxidizing property by suitably combining various operating conditions in smelting under strong stirring using a top-bottom blowing converter. In addition to stably blocking the atmosphere and generated metal, CO→
This is achieved by efficiently transferring the heat generated by the reaction of CO ₂ to the melt, making it available for reduction reactions. A specific method for realizing the present invention will be described below. Unlike conventional shaft-type smelting furnaces, in the present invention, strong stirring of the molten material is an essential condition for the smelting reduction furnace, and the equipment includes equipment that can stably blow gas into the molten material layer and stir it. For example, a converter that can blow oxygen from the top and bottom is used. The purpose of the gas bottom blowing in this case is to stir the melt, and blowing in powder is not an essential condition. Rather, as will be described later, there is an upper limit to the proportion of raw materials (ore, reducing agent) that may be bottom-blown. The main purpose of the blown gas is to stir the melt through bubbles, so
The type of gas is not particularly restricted. From the viewpoint of supplying a portion of the oxygen gas necessary for the progress of the reaction in the furnace, it is naturally possible to use oxygen or a gas containing oxygen. Note that when oxygen or a gas containing oxygen is used, there is an advantage that the C% of the finished molten metal can be lowered below the carbon saturation value depending on the selection of operating conditions. In addition to oxygen, gases such as N ₂ , Ar, CO ₂ , hydrocarbons, or combinations thereof, or gases generated during this process.
It is also possible to recycle gas containing CO ₂ or CO as a main component. These gases are blown into the melt through double tube tuyeres or other inlets. Most of the oxygen gas is blown onto the melt using a top blow lance. The purpose of top-blown oxygen gas is to remove CO generated by combustion of carbonaceous materials or reduction reactions.
This is to achieve a high calorific value by burning H ₂ to CO ₂ and H ₂ O. Clumps of raw materials (ore, reducing agent, flux, etc.) are introduced from the top. Powdered materials can be lumped and poured from the top, or they can be poured as they are in powdered form.
It may also be sprayed onto the melt layer through a lance or the like. Note that it is also possible to use scraps as part of the raw material. The method of utilizing the gas discharged from the converter-like smelting and reduction reaction vessel can be implemented in various ways depending on the requirements of the installation location, such as the following. (a) Combination of fluidized bed or rotary kiln,
Gas is used for preheating and preliminary reduction of ore. (b) Combined with a boiler, gas is completely combusted and converted into steam, which is used for power generation, etc. Alternatively, it can be used in combination with a turbine for power generation. (c) Pass the gas through dust removal and CO ₂ removal equipment as necessary and store it in a gas holder. The operating method using these facilities is as follows. Before starting regular operation, a layer of molten iron alloy (for example, Fe-C system) is created in the smelting reduction furnace. The amount depends on the conditions that allow stable bottom blowing (that is, no blow-through occurs), and usually
The height is 30-60cm or more. Such a layer of molten iron alloy can be deposited in a furnace by charging molten metal made in a separate furnace, or by adding solid metal or alloy and carbonaceous material such as coke within this furnace. Oxygen (or hydrocarbon in some cases) is supplied to generate heat and cause dissolution. Once the operation begins, in the second and subsequent cycles, the operation is repeated with some of the produced molten iron alloy remaining. The present invention produces a molten iron alloy by blowing acid while adding iron ore or its pre-reduced product, a solid carbonaceous reducing agent such as coal or coke, and a flux such as lime or silica stone to the molten iron alloy. By keeping the slag produced in the process in an appropriate state, stable coexistence of a high CO ₂ % oxidizing atmosphere and reducing melt can be achieved, and CO→
The aim is to use the heat generated by the combustion of CO ₂ efficiently to advance the reduction reaction, a problem that has not been technically solved in the past. For this purpose, near the molten material to be heated,
A high temperature zone is generated by combustion of CO gas. If the molten iron alloy is exposed to the atmosphere, even if an attempt is made to create a high-temperature zone caused by the combustion of CO gas in the vicinity, a reaction of CO ₂ + Fe → CO + FeO or CO ₂ + C → 2CO will occur. In the former case, since it is a reoxidation reaction, the reduction reaction is inhibited as a whole. Moreover, in the latter case, it is an endothermic reaction, and as a result of the reaction, the CO ₂ /CO+CO ₂ % of the gas decreases. The method to increase the value of CO ₂ /CO + CO ₂ % in conventional steelmaking converters is called "secondary combustion", which is carried out at a location away from the zone where molten iron alloy exists.
It caused a reaction of CO+1/2O ₂ →CO ₂ and generated heat. However, when the molten iron alloy is exposed to the atmosphere, there is an upper limit to the value of CO ₂ /CO + CO ₂ that can be obtained (for example, about 40% or less), and the further the distance between the object to be heated and the high-temperature heating zone, the higher the However, there was a problem that heat transfer was disadvantageous and thermal efficiency was reduced. In contrast, in the present invention, the molten iron alloy layer and its splash produced by bottom blowing are brought into direct contact with the high temperature atmosphere by keeping the amount of slag above a predetermined value. The required amount of slag for this purpose is the required amount of slag (Kg/t-metal) 250 (1) on the premise that foaming of the slag is suppressed below a specified value by the method described below. It is expressed as Especially 300~480Kg/t-metal
A range of is optimal. Under such conditions
The ratio of CO ₂ /CO + CO ₂ depends on the dynamic balance between the amount of oxygen (the amount of blown acid and the oxides that are reduced) and the amount of carbon (the amount of carbonaceous solids present on the slag and the amount of CO gas generated). In particular, by controlling the combination of the amount of blown acid and the amount of carbonaceous solids present,
Arbitrarily high values can be obtained. In this case, instead of the secondary combustion described above, a main combustion zone (i.e., a high-temperature zone due to combustion) is formed in a portion where oxygen and carbon associate. In this case, the molten material adjacent to the high temperature zone due to combustion is not a molten iron alloy but a molten slag layer. Therefore, in order to make the molten slag layer the main endothermic reaction site, that is, the place where Fe _n O _o + nC → mFe + nCO occurs, the proportion of raw materials (ore or its reduced product, carbonaceous solid) above a certain lower limit value is , it is desirable to add it directly to the slag layer rather than the molten iron alloy layer. FIG. 1 shows the relationship between the ratio of the added ore + carbonaceous reducing agent (hereinafter referred to as carbonaceous material) to the total weight of the slag layer and the heat utilization efficiency. It has been observed that the higher the proportion of raw materials (ore + carbon material) added directly to the slag layer rather than the metal layer, the higher the heat utilization efficiency.
Preferably, 60% or more is added directly to the slag layer. In addition to the above reasons, the following may be cited as causes for this. (1) A portion of added materials such as ore and carbonaceous material floats on the slag, and its surface acts as an efficient site for absorbing heat from the atmosphere. (2) Compared to the case where slag is added through the metal layer, the reduction reaction sites move to the upper part on average, so even if the amount of gas generated is the same, the degree of slag forming can be reduced. In order to directly add ore (or its pre-reduced product) and carbonaceous material to the slag layer, if it is originally lumpy (5mmφ or more), it can be added from the top, or if it is powder, it can be added through the upper lance. It is sprayed onto the slag surface and penetrated into the molten slag by inertia, but a part of the powder or a mixture of two or more of the powders is made into briquettes (concave or roller compacted) or pellets and is charged from above.
In addition, in the part where the powder is directly added to the metal layer, the powder is blown from, for example, the bottom blowing tuyere. Bottom blowing an appropriate amount of powder (especially coal powder) can be used for purposes other than heating, such as suppressing erosion of the tuyeres and increasing the C% of molten metal by carburization.
It may be effective in terms of adjustments, etc. The volume ratio of the total amount of blown acid to the total amount of bottom blown gas is the second
As shown in the figure, this has a large effect on heat utilization efficiency. The total amount of gas blown out (oxygen, hydrocarbons, etc.) is too low, and the stirring of the melt is too weak.
Since sufficient heat generated by combustion cannot be received, heat utilization efficiency decreases. On the other hand, if the total amount of bottom blown gas is too large, the blown gas
Alternatively, the amount of generated gas passing through the slag layer increases, and the slag swells accordingly, resulting in a decrease in heat utilization efficiency. Also, as the proportion of bottom-blown oxygen gas increases, the amount of exhaust gas increases.
Increasing CO ₂ % is increasingly constrained. Therefore, the optimum ratio of the amount of bottom blown gas (relative to the total amount of blown acid) is in the range of 3% to 40%, preferably 3 to 30%. The present invention aims to suppress slag foaming, burn _CO2 close to the slag surface, and efficiently transfer the generated heat to the slag for use in the reduction reaction. There is. Slag containing a large amount of gas makes the combustion site unstable and acts as a barrier against heat. Slag foaming is affected by the ease with which gas escapes based on the slag composition, in addition to the amount of gas generated below the slag surface and the location where the gas is generated, as described above. The influence of the slag composition on the heat utilization efficiency is related to the CaO/SiO ₂ ratio and (MgO+Al ₂ O ₃ )%, as shown in FIGS. 3 and 4. CaO/SiO ₂ ranges from 0.8-1.9, MgO+
It is desirable to keep Al ₂ O ₃ at 23% or less. In order to satisfy both the conditions of the slag amount (defined by formula (1)) and the above-mentioned slag composition, a flux such as lime or silica stone is added. Alternatively, some of the slag from the previous heat may remain,
Alternatively, the slag once discharged outside the furnace may be recycled. When the above-mentioned bottom blowing gas amount condition is satisfied and the melt is stirred to the extent necessary for carrying out the present invention,
The temperature of the melt layer of both metal and slag is almost uniform, and the difference is so small that it can be ignored. In order to perform bottom blowing stably, the temperature of the molten material must be at least 20°C higher than the liquidus temperature of the molten metal, but there are no other operational restrictions. but,
When the temperature is low, the slag tends to form due to its viscosity, which tends to reduce heat utilization efficiency. Moreover, if the temperature becomes too high, the exhaust gas temperature increases, which is a loss. Therefore, 1450° to 1550°C is the optimum operating temperature. Note that the definition of heat utilization efficiency used in this specification is as follows. Heat utilization efficiency = (Amount of heat used to heat the metal and reduce oxides) / Total calorific value from combustion * * + (Amount of heat required to heat the exhaust gas to the same temperature as the molten material) / As above After the operation is carried out to satisfy various conditions and the added ore (or its semi-reduced product) is melted and reduced, if necessary, the amount of iron oxide in the slag is further reduced, and at the same time, the amount of iron oxide in the slag is reduced. When attempting to advance the desulfurization reaction, after stopping the supply of ore (or its half-reduced product), continuing blowing acid for a specified period of time will reduce the iron oxide content of the slag to an arbitrary value depending on the time. be able to. In addition, compared to the case where a molten alloy with a chromium or manganese content of 20% or more is obtained by the smelting reduction method, when the iron ratio is higher than that, oxides are also affected by the C in the molten alloy. Since it is reducible, the reduction reaction tends to proceed on the surface of the molten alloy layer, and therefore the slag as a whole tends to form easily. In order to suppress this, (i) operations should be carried out in a state where the carbon content of 20% or more of the slag weight remains in the slag and the slag-charcoal material interface area is maintained large; The residual carbon content in the slag is the difference between the carbon content in the carbon material added to the system and (the amount carburized into the molten metal) + (the dust containing CO, CO ₂ and C in the exhaust gas). (2) Adjust the slag composition, (iii) Add carbonaceous material containing lime to the top of the slag, and increase the foaming effect of the generated gas. It is desirable to suppress forming (for this purpose, approximately 60% or more of the total carbonaceous material should be added from above the slag). Using the method described above, _reduce CO to a predetermined value.
The heat generated by the combustion can be efficiently used to advance the reduction reaction. If fuel gas is required unsteadily due to location conditions, the exhaust gas can be controlled by controlling the amount of blown acid and the ratio of carbon remaining in the slag while detecting the composition of the exhaust gas. The CO ₂ /CO ratio can be changed arbitrarily. By removing dust and CO ₂ from this exhaust gas if necessary, and then guiding it to the gas holder, the required amount of the required composition gas can be obtained. (Example) Top-bottom blowing converter with rated molten metal capacity of 120 tons [4 bottom-blowing tuyeres,
Triple pipe; inner pipe (inner diameter 16mm, wall thickness 1mm): CO/CO ₂
For coal powder injection by mixed gas (1800Nm ³ /hr) carrier, second pipe (inner diameter 20mm, wall thickness 1mm): O ₂
For gas blowing; outermost tube (inner diameter 24 mm): cooling gas propane, 60 Nm ³ ) for blowing], Fe-C (4.2%)-Si
Charge 40 tons of (0.3%) molten metal. Iron ore (T.Fe: 67%, _SiO2 : 4.6%, _TiO2 :
0.2%, P ₂ O ₅ : 0.2%) are sieved, and those larger than 5 mm (55% of the total charge) are fed into the furnace from the hopper above the furnace, and those smaller than 5 mm are mixed with 30% by weight of coal powder. After mixing, the roll-compressed green compact is introduced into the furnace from another hopper. Coal (TC: 73%, VM (volatile matter): 15
%: Ash: 12%, P: 0.08%, S: 0.6) are sieved and those larger than 10 mm are fed directly into the furnace from the hopper above the furnace. The bottom of the sieve is crushed to 1 mm or less, a part is used for roll compression with the above-mentioned ore, 10% of the total charge is blown into the furnace through the bottom blowing tuyere, and the rest is Top blowing lance (7 holes in total, one in the center is for blowing coal powder with CO/CO ₂ mixed gas, the other six holes are for blowing oxygen)
30000Nm ³ /hr). Note that lump coke (excluding numbers) in an amount of about 5% by weight of the amount of coal used is introduced from above the furnace. This is effective in controlling CO ₂ /CO + CO ₂ . Flux uses lime and silica. Blowing acid (top blowing 20000Nm ³ /hr, bottom blowing 1800Nm ³ /hr)
While performing this, the temperature of the molten material in the furnace was measured and the temperature reached 1450
Add iron ore so that the temperature is in the range of ~1520℃,
Accordingly, the amount of slag is 300±40Kg/t-metal,
Slag composition is CaO/SiO ₂ = 1.2±0.3MgO+Al ₂ O ₃
= 8±6%. In addition, the amount and composition of exhaust gas are detected, and the amount of coal coke input is adjusted using a C balance formula so that the amount of carbon remaining in the slag in the furnace is 25±5% of the amount of slag. There are two types of operation depending on the time of day:

[Table] The components of the tapped metal (70% of the amount produced) and slag (approximately 90% of the amount produced) are as follows for cases A and B above, respectively.

【table】

[Table] After tapping, repeat the above operation using the remaining hot water. (Effects of the Invention) As described above, the present invention utilizes equipment similar to the existing top-bottom blowing converter for steelmaking, and adopts operating conditions that are completely different from those of the normal steelmaking method. This method is characterized by the ability to obtain molten iron-based alloys with high iron efficiency and the ability to flexibly change the generated gas depending on the location conditions.It is an economical method that solves the drawbacks of the conventional blast furnace method. big.

[Brief explanation of the drawing]

Figure 1 shows the ratio of what is added to the slag layer to the total weight of added ore + carbonaceous material, and
A diagram showing the relationship between heat use efficiency. Figure 2 is a diagram showing the influence of the ratio of the total amount of bottom-blown gas to the total amount of blown acid on heat use efficiency. Figures 3 and 4 are diagrams showing the relationship between heat use efficiency. It is a figure showing the influence of slag composition on.

Claims (1)

[Scope of Claims] 1. In producing a molten iron-based alloy by supplying a raw material containing iron oxide, a carbonaceous reducing agent, flux, and gaseous oxygen in a converter-like reaction vessel capable of blowing gas from top to bottom, ( 1) Keep the slag amount above 250Kg/t-metal (2) Ore and carbonaceous material added to the slag layer (weight) / Total added ore + carbonaceous material (weight) x 100≧30% (3) Bottom Total amount of gas blown (Nm ³ )/Total amount of blown acid (Nm ³
) × 100 = 3 to 40% (4) By operating under conditions that simultaneously satisfy the conditions of MgO + Al ₂ O ₃ ≦23% of slag, the furnace suppresses foaming of slag and generates CO gas. A method for producing molten iron-based alloy, which is characterized by increasing heat utilization efficiency while arbitrarily controlling the degree of burnup to CO ₂ within the molten metal.