JPH0723501B2 - Hot metal manufacturing method - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing hot metal by melting iron raw materials such as pig iron and steel scrap, and more specifically, general metallurgical coke for blast furnaces other than cupola. The present invention relates to a method for efficiently producing molten pig iron by melting in a cylindrical furnace having a coke filling layer inside.

Prior art As a method for producing hot metal by melting pig iron and steel scrap,
There are cupola method and blast furnace method. The cupola method uses a large coke, and burns the coke with the air blown from the blast tuyere to produce a high-temperature gas containing a higher concentration of CO ₂ than the composition of the blast furnace Bosch gas. It is a method of flowing the above method through the coke packed bed to melt the pig iron scraps and steel scraps charged from the upper part of the furnace. In this method, the CO ₂ / (CO ₂ + CO) in the furnace is high, and the carburizing and silicifying effects are low. Therefore, in order to produce cast pig iron, it is necessary to blend the raw material of the form pig iron as the C source in the hot metal. At the same time, it was necessary to perform desulfurization outside the furnace depending on the application because the desulfurization effect inside the furnace is low. As measures against this, attempts have been made to promote carburization by a two-stage tuyere, O ₂ enrichment, hot air blowing, dehumidifying air blowing, etc. to reduce the amount of pig iron used and the coke ratio.

The blast furnace method replaces iron ore, burned ore, pellets and other iron oxides commonly used as iron raw materials for blast furnace with iron scrap and steel scrap.
It is a method to use 100%. In the case of the blast furnace method, the air blown from the blast tuyere reacts with coke
CO ₂ / (CO ₂ + CO) and H ₂ O / (H ₂ O + H ₂ ) are almost zero, and since the furnace has a strong reducing atmosphere, it has strong carburizing and silicidizing effects, and it produces steel scrap. Since it can be used 100% and has a strong desulfurization effect, desulfurization outside the furnace is not required. However, the coke ratio is about 220 kg / pt when blown at 1200 ° C, which is higher than that of the cupola method (about 150 kg / pt).

Problems to be Solved by the Invention As described above, the cupola method has a drawback that CO ₂ / (CO ₂ + CO) in the furnace is high and carburizing, silicifying and desulfurizing actions are low, and the blast furnace method has a coke ratio. Has the drawback of being expensive. The present invention proposes an efficient method for producing hot metal which solves these drawbacks.

Means for Solving the Problems This invention is to charge iron raw material and coke, slag forming agent, etc. from the furnace upper part of a cylindrical furnace, burn coke with air blown from tuyere to generate high temperature gas, The iron raw material is melted by the sensible heat of the gas, and the hot metal and slag are extracted from the tap hole at the lower part of the furnace, while the produced gas is recovered from the upper part of the furnace. Coke combustion gas with oxygen to make CO ₂ / (CO ₂ + CO) and H ₂ O / (H ₂ O + H ₂ ) comparable to blast furnace Bosch gas (about zero), resulting in strong reduction in the furnace It proposes a method of maintaining the atmosphere to improve the carburizing, silicifying and desulfurizing actions and suppressing the increase of the coke ratio by introducing the in-layer secondary combustion method.

That is, the gist of the present invention is that CO ₂ / (CO ₂ + CO) and H ₂ O / (H ₂ O + H ₂ ) of the gas generated by the combustion of coke become zero (similar to blast furnace Bosch gas). In the furnace, the blast temperature and oxygen concentration are adjusted so that the generated gas temperature is 2000 ° C or more, and the combustion gas such as air and oxygen is blown from the side wall of the furnace above the tuyere. Combusting CO and H ₂ in gas, sensible heat generated at that time causes iron raw material, coke,
It is characterized by heating a slag forming agent and the like.

Generally, in the reaction between O ₂ and C in coke in the front tuyeres combustion part, first, the reaction of the following formula (1) proceeds to generate CO ₂
Is expressed by the following equation (2), it is considered that it reacts with C in coke to form CO.

C + O ₂ → CO ₂ ΔH = −97000 Kcal / Kmol (1) Formula C + CO ₂ → 2CO ΔH = 38180 Kcal / Kmol (2) Formula On the other hand, the coke surface area S per unit volume of the coke packed bed involved in the reaction is (3) ), It is understood that the particle size and the surface area are inversely proportional.

S: Coke surface area per unit volume of coke packed bed (m ² /
m ³⁾ ε: voidage (-) dp: Coke diameter (mm) Therefore, when using a coke having a large particle diameter as a cupola, in addition to coke surface area S is small, cupola coke except for the blast furnace or cupola The reactivity is lower than that of the general metallurgical coke, and it is higher than the blast furnace (air flow rate / hearth area) and low air temperature, so the reaction of the above formula (2) is suppressed and CO ₂ / It is considered that (CO ₂ + CO) becomes high. On the other hand, in order to prevent the generation of CO ₂ to have a Bosch gas composition similar to that of a blast furnace and to create a strongly reducing atmosphere in the furnace, CO ₂ / (CO ₂ + CO) of the combustion product gas, H ₂ O / ( H ₂ O +
H ₂ ) becomes zero and the combustion product gas temperature is 2
The blast temperature and the O ₂ concentration in the blast may be adjusted so as to be 000 ° C or higher. Further, by changing the coke used from the coke for cupola to the coke for general metallurgy including blast furnaces other than cupola, the combustion product gas composition can be easily made equal to the blast furnace Bosch gas composition. . Further, by the above method, the moisture content in the air becomes H ₂ according to the following formula (4) for the same reason, and the inside of the furnace can be maintained in the strongly reducing atmosphere.

C + H ₂ O → CO + H ₂ ΔH = 28391 Kcal / Kmol (4) Formula Equilibrium between C and CO and CO ₂ shown by the formula (2) and C and H ₂ O, H ₂ shown by the formula (4), The equilibrium with CO can be determined thermodynamically, and the equilibrium CO ₂ partial pressure, H at a total pressure of 1 atm
_{The 2} O partial pressure is shown in FIG. As is clear from this figure, CO
_It can be seen that ₂ and H ₂ O decrease with increasing temperature, and become extremely low in equilibrium at high temperatures above 1100 ° C.

On the other hand, when calculating the combustion product gas temperature, the product gas CO
₂ / (CO ₂ + CO) and H ₂ O / (H ₂ O + H ₂ ) are calculated to be zero by the endothermic reaction of the above equations (2) and (4).
₂ , which means that the total amount of H ₂ O is converted to CO and H ₂ , so the combustion product gas temperature obtained based on the above assumption is CO
_It becomes lower than the combustion temperature when ₂ remains. Therefore, if the combustion product gas temperature obtained by calculation based on the above assumption is used, it is possible to set combustion conditions on the safe side with respect to prevention of CO ₂ and H ₂ O production, and the combustion product gas temperature 20
If it is 00 ℃ or more, from Fig. 2, CO ₂ / (CO ₂ + CO), H ₂ O / (H ₂ O + H ₂ )
Can be seen to be close to zero in equilibrium.

However, since the reaction rate is involved in the actual operation, this equilibrium gas composition is not always obtained. Therefore, using a furnace with an inner diameter of 100 mmφ, a coke particle size of 20 to 100 mm, a blast temperature of room temperature to 1200 ° C, and an O ₂ concentration of 21 to 60% during blast were used to conduct a combustion test to investigate the effect on the combustion product gas temperature. as a result, the combustion product gases in CO ₂ / in any of the above conditions _{(CO 2 + CO), H} 2 O / (H 2 O + H 2) substantially zero and becomes conditions, CO combustion product gas ₂ / (CO ₂ + CO), H ₂ O / (H ₂ O +
It was found that the combustion product gas temperature obtained by calculation assuming that H ₂ ) becomes zero is 2000 ° C. or higher.

The formula for calculating the combustion product gas temperature is shown in the following formula (5).

VB = FB ・ (1-1.244 × 10 ^-3・ FM) AA = (0.21 ・ VB + O ₂ ) / VB + O ₂ ) AM = 10 ^-3・ FM ・ FB / (VB + O ₂ ) H1 = 0.34 ・ TB + 0.416AM ・ TB + 2625・ AA A = 0.3 ・ (1.0714 ・ AA + 0.6667 ・ AM) H3 = 1600 ・ AM B = 1 + AA + 2.4889 ・ AM Tf = Combustion product gas temperature (° C) FB = Blower rate (Nm ³ / min) FM = Blower Moisture (g / Nm ³ ) O ₂ = Oxygen enrichment (Nm ³ / min) TB = Blower temperature (° C) By the way, the reactions of the above formulas (2) and (4) are endothermic reactions and C in coke. As such, the coke ratio inevitably increases as it is.

Another feature of the present invention is to introduce an intra-layer secondary combustion method in order to suppress the increase in the coke ratio.
That is, the combustion-supporting gas blown from the upper side wall of the blast tuyere burns CO and H ₂ in the gas flowing from the blast tuyere to the gas recovery port at the top of the furnace, and the sensible heat generated at that time is generated. It is a method used for heating iron raw materials, coke, slag forming agents, etc. According to this method, the coke ratio used for preheating the raw material in the combustion heat can be reduced without impairing the strongly reducing atmosphere below the combustion-supporting gas blowing port. Particularly, in the present invention, the temperature of the gas produced by burning the combustion-supporting gas blown from the combustion-supporting gas inlet is 1000
It is desirable not to exceed ℃. This is because when the temperature exceeds 1000 ° C, the reactions of the formulas (2) and (4) proceed rapidly and the coke consumption increases. In addition, as the operation mode, CO ₂ / (CO ₂ + CO), H ₂ O
The combustion gas temperature calculated assuming that / (H ₂ O + H ₂ ) becomes zero is set to a higher value, and the amount of gas produced by combustion is reduced to obtain a strong head cold foot heat type in-furnace temperature distribution. It is desirable to increase the effective utilization rate of the sensible heat of gas by increasing the efficiency of preheating the raw material for the secondary combustion heat, reducing the gas flow rate, and using coke of a relatively small mass.

Disclosure Based on Drawings of the Invention FIG. 1 is a schematic view showing the structure of a cylindrical furnace for carrying out the method of the present invention, in which a raw material charging port (1) and a gas recovery port (2) are provided at the furnace top. The side wall (3) is provided with a blower tuyere (4) and an air, oxygen and other combustion-supporting gas inlet (7),
It has a tap hole (5) and a tap hole (6) at the bottom of the furnace.

That is, from the charging port (1) at the top of the furnace, iron raw material (8) such as pig iron and steel scrap, coke (9) and, if necessary, limestone,
A slag forming agent (10) such as silica stone is charged, and air (11) is blown from the blower tuyere (4) to burn coke and generate high-temperature gas, and the sensible heat of the gas produces iron raw material. Melt hot metal (1
2) As a result, after extracting from the taphole (5), the slag (13) produced by melting of the slag forming agent and coke ash is extracted from the taphole (6) and utilizing sensible heat. In the pig iron production method of recovering the generated gas from the gas recovery port (2) in the upper part of the furnace, CO _{2 in} the component of the gas generated by reacting the air blown from the blower tuyere (4) with coke. / (CO ₂ + C
O) and H ₂ O / (H ₂ O + H ₂ ) are both assumed to be zero, and the blast temperature or oxygen concentration is adjusted so that the product gas temperature obtained by calculation is 2000 ° C or higher. Air is blown, and a combustion-supporting gas (14) such as air or oxygen is supplied from an air inlet (7) provided in the furnace side wall between the tuyere (4) above and the gas recovery port (2). Of CO and H ₂ in the gas flowing from the blower tuyere (4) to the gas recovery port (2), and the sensible heat generated is used to heat the iron raw material, coke, slag forming agent, etc. To do.

Example The same model as the furnace shown in FIG. 1, with a furnace diameter of 750 mm and a hearth diameter of 900 m
m, the upper height of the main tuyere was 5000 mm, and the experimental furnace with the combustion-supporting gas blowing port installed 1500 mm above the main tuyere was used, and operation was carried out under the conditions shown in Table 1.

In Table 1, Case 1 uses large coke for cupola, and when operated under conventional cupola operating conditions, Case 2 uses blast furnace coke and contains 100% steel scrap as iron raw material. However, if operation is performed under the conditions that the production rate is the same as in Case 1 without performing in-layer secondary combustion, Case 3
Is an example of the present invention, uses the same raw material as Case 2, operates at the same pre-tuyere combustion temperature as Case 2, and has the same production rate as Case 1, and uses air from the combustion-supporting gas blowing port. This is the case when is blown into the furnace.

From Table 1, it is considered that, in case 1, since the top gas contains 11.7% of CO gas, the combustion gas in the furnace also contains more than the same amount of CO ₂ . Also, since the furnace has a weak reducing atmosphere, the C concentration in the hot metal is 2.8%.
And the S concentration is as high as 0.11%.

On the other hand, CO ₂ in the case 2 top gas is hardly contains, CO ₂ in the gas gas sampled by blowing tuyere level core portion was 0.1% or less. Moreover, since the coke diameter is small, the heat exchange efficiency between the gas and the solid is improved, and the furnace top gas temperature is lowered. Regarding the hot metal components, since the furnace is in a strongly reducing atmosphere, even though the steel scrap mixing ratio was set to 100%, the hot metal [C], [Si]
, And [S] decrease, and improvement of carburization, silicidation and desulfurization action is observed. However, the coke ratio is significantly higher than in Case 1.

In case 3 of the present invention example, as a result of performing in-layer secondary combustion, an increase in the CO ₂ concentration in the furnace top gas is seen, and it can be seen that the CO gas in the furnace is burning. Judging from the furnace top gas analysis value, blast condition, charging coke amount, etc., most of the O _{2 in} the air blown from the air blowing port is consumed for the combustion of CO gas, and the reaction amount with C in the coke is It turned out to be a very small amount.
In addition, since the furnace top gas temperature is only slightly higher than in case 2 without secondary combustion, most of the in-layer secondary combustion heat is absorbed by the raw materials and is effectively utilized. I understand. The coke ratio is much lower than in case 2 due to the effect of this secondary combustion in the formation, and is about the same as in case 1. Further, even if the in-layer secondary combustion is performed, the gas produced by combustion before the main tuyere is CO, N ₂ , and H ₂ as in Case 2,
Below the combustion-supporting gas blowing port, a strong reducing atmosphere is maintained in the same manner as in Case 2, and as a result, the hot metal component also appears in Case 2.
A high quality hot metal similar to that obtained was obtained.

EFFECTS OF THE INVENTION As described above, according to the method of the present invention, the coke is burnt and gasified by the oxygen blown from the blowing tuyere,
By making the generated gases CO ₂ / (CO ₂ + CO) and H ₂ O / (H ₂ O + H ₂ ) similar to blast furnace Bosch gas, a strong reducing atmosphere can be created in the furnace for carburization, silicidation, and desulfurization. Since the action can be improved, 100% of the steel scrap can be used, and no external desulfurization is required. Further, the introduction of the in-layer secondary combustion method can suppress the increase of the coke ratio, and can produce economically good quality hot metal, which is an excellent effect.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of the structure of a cylindrical furnace for carrying out the method of the present invention, and FIG. 2 is the equilibrium CO ₂ in the present invention.
It is a diagram showing the partial pressure and the equilibrium H ₂ O partial pressure. DESCRIPTION OF SYMBOLS 1 ... Raw material charging port, 2 ... Gas recovery port 3 ... Furnace side wall part, 4 ... Blower tuyere 5 ... Iron tap, 6 ... Slag tap 7 ... Combustion-supporting gas blowing port, 8 ... Iron raw material 9 ... Coke, 10 ... Slag making agent 11 ... Air, 12 ... Hot metal 13 ... Slag, 14 ... Combustible gas

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Masahisa Tachibana 1-3, Nishi Nagasumotodori, Amagasaki City, Hyogo Prefecture Sumitomo Metal Industries, Ltd. Research Institute (56) Reference JP 62-56537 (JP, A)

Claims (1)

[Claims] 1. An iron raw material, coke, a slag forming agent, etc. are charged from the upper part of a tubular furnace, and the coke is burned by the air blown from the tuyere to generate a high-temperature gas, which is sensible heat of the gas. CO ₂ / (CO ₂ + of the gas produced by the combustion of coke in the ironmaking process in which the iron raw material is melted and the hot metal and slag are extracted from the tap exit of the furnace bottom, while the product gas is recovered from the furnace top CO), H ₂ O
Adjust the blast temperature and oxygen concentration so that the temperature is 2000 ° C or more assuming that / (H ₂ O + H ₂ ) is zero, and blow air from the furnace side wall above the tuyere. , CO, H ₂ in the gas inside the furnace is blown with combustion-supporting gas such as oxygen, and the iron material, coke, slag forming agent, etc. are heated by the sensible heat generated at that time. Manufacturing method.