JPH03191016A - Method for refining molten pig iron - Google Patents

Abstract

PURPOSE:To efficiently and inexpensively subject a molten pig iron to dephosphorization and desulfurization refining by treating a molten pig iron with oxygen and a dephosphorizing agent composed essentially of CaO, adding a material composed essentially of MgO or CaO, and carrying out desulfurizing treatment by blowing a desulfurizing agent into the above molten pig iron. CONSTITUTION:A molten pig iron is dephosphorized with oxygen and a dephosphorizing agent composed essentially of CaO, and successively, desulfurizing treatment is carried out by blowing a desulfurizing agent into the above molten pig iron. In the above-mentioned refining method for the molten pig iron, prior to the above desulfurizing treatment, a material composed essentially of MgO or/and CaO is added by a small quantity to slag after the above dephosphorizing treatment. By this method, rephosphorizing and resulfurizing reactions from the slag can be prevented and dephosphorization and desulfurization can be carried out easily and efficiently in a single refining vessel while obviating the necessity of slag removing state and preliminary desiliconizing treatment, by which the molten pig iron reduced in phosphorus and sulfur concentrations can stably be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for obtaining hot metal having a low phosphorus concentration and a low sulfur concentration.

(Prior Art) In recent years, as the environment in which steel materials are used has become stricter, improvements in the properties of steel materials have been desired. On the other hand, in order to improve the properties of steel,
Reduction of impurities such as phosphorus and sulfur is particularly effective.

For this reason, conventionally, in the blast furnace-converter method, a hot metal pretreatment method has been adopted in which CaO-based dephosphorization in the converter and dephosphorization and desulfurization are performed in advance at the hot metal stage. In these techniques, phosphorus is removed into the slag by an oxidation reaction. On the other hand, in order to proceed with desulfurization, which is a reduction reaction, there are two methods: ■ A method in which hot metal is desiliconized in advance and a simultaneous desulfurization reaction occurs during dephosphorization; In addition, as seen in JP-A No. 58-16007, the basicity (Ca
b) / (Sing) ((Cab) and (SiOz) each indicate their weight percentage in the slag) is set to 2 or more, and a desulfurization agent is subsequently blown into the desulfurization treatment, or a Na2CO1-based flux is used during desulfurization. A method has been adopted that uses slag to produce slag with higher dephosphorization and desulfurization ability.

However, in method (2), the silicon concentration of the hot metal is lowered in advance to increase the basicity of the slag, and the silicon concentration generated during desiliconization is further reduced.
It is necessary to remove the slag mainly composed of O□. Therefore, it is necessary to install slag removal equipment and separate desiliconization and dephosphorization treatment equipment, which requires large equipment costs.In addition, because the treatment time is long, productivity is hindered and the temperature of hot metal decreases. There was a problem that the amount of refractory used in the hot metal holding container increased. In addition, in method (2), it is necessary to slag the slag after dephosphorization and perform new desulfurization, so similar to (2), slag removal equipment and separate processing equipment are required, which increases processing time, hinders productivity, and There were problems with a drop in hot metal temperature and an increase in the amount of refractories used. Furthermore, compared to method (2), method (2) does not require a transfer or slag step, so it has the advantages of shorter processing time, lower temperature, and less amount of refractory used. However, in this case CaO or Na2
There was a problem in that a large amount of CO was required, leading to an increase in franking cost. Furthermore, when NazCO:+ is used, it has the disadvantage of causing environmental pollution due to smoke generation.

(Problems to be Solved by the Invention) The present invention has been made in view of the problems of the conventional methods as described above. In other words, without requiring large equipment costs,
Efficient and inexpensive production of hot metal without requiring long processing times, minimizing the amount of refractories used, and increasing the basicity of slag, that is, without requiring large amounts of CaO and NazCO3. It provides a dephosphorization/desulfurization method.

(Means for Solving the Problems) The present invention provides simultaneous desiliconization and dephosphorization treatment in one refining vessel → No slag → In order to perform post-blowing desulfurization treatment and not reduce the desulfurization agent efficiency during desulfurization, the slag after dephosphorization is treated with a substance containing magnesium oxide as a main component, a substance containing calcium oxide as a main component, or both as a main component. By adding a substance that dephosphorizes the hot metal and changing the properties of the slag on top of the hot metal (hereinafter referred to as top slag) so that it does not contribute to the reaction, desulfurization can be carried out efficiently without increasing the amount of dephosphorization/desulfurization agent used. This is a method of dephosphorizing and desulfurizing hot metal.

(Function) Generally, the dephosphorization reaction of hot metal is carried out using an oxidation reaction, while the desulfurization reaction is carried out using a reduction reaction. However, in the reaction in hot metal, it has been revealed that by keeping the basicity and oxygen potential of the slag within a certain range, dephosphorization and desulfurization reactions can occur simultaneously. However, for example, in order to cause simultaneous dephosphorization and desulfurization reactions using CaO-based Franks, the final slag basicity (Cab)/(SiOz) ((Cab
) and (SiOz), each representing their weight percentage in the slag, must be maintained at approximately 3.5 or higher, so in order to reduce CaON, desiliconization treatment was required in advance. In such a process, the C required for dephosphorization is
If you increase the amount of oxygen to reduce the amount of aO, the desulfurization efficiency will decrease, and conversely, if you decrease the amount of oxygen and increase the amount of CaOil, the desulfurization efficiency will decrease.
The a0O dephosphorization efficiency decreases. Therefore, low-linked cutlet,
In order to obtain hot metal with low sulfur, both oxygen and CaO must be increased, and there is a limit to the reduction of refining fusics. On the other hand, a process in which desiliconization, dephosphorization, and desulfurization are separated, and the slag is removed in between, may reduce the amount of refining agent used, but the total processing time will be longer, resulting in the release of natural heat and sensible heat from the slag. There were problems in that energy loss increased and the processing equipment became enormous.

In order to efficiently dephosphorize and desulfurize hot metal without increasing the amount of franks used in a short period of time while ensuring productivity, the present inventors devised As a method for performing dephosphorization and desulfurization treatment, in the process of simultaneous desiliconization and dephosphorization treatment without prior desiliconization → no slag → post-blowing desulfurization treatment, a substance mainly composed of magnesium oxide, Alternatively, by adding a small amount of a substance whose main component is calcium oxide or both, the efficiency of the desulfurization agent during desulfurization treatment by fine powder injection can be increased, reducing the total amount of refining agent used and reducing heat loss. We have invented a method for dephosphorizing and desulfurizing hot metal that requires less waste and a shorter processing time.

During fine powder blowing desulfurization, there is a reaction between the injected fine powder while it floats (hereinafter referred to as transitory reaction) and a reaction with the top slag that is generated by the fine powder after floating or is already present on the hot metal (hereinafter referred to as permanent reaction). ) occurs. In simultaneous desiliconization and dephosphorization treatment without pre-desiliconization → no slag → post-blowing desulfurization treatment, the basicity of the top slag produced after dephosphorization (CaO) / (SiO□
) is small and the oxidizing power is large, so even if a new desulfurization agent is added to the top slag, the desulfurization reaction does not occur easily, resulting in a disadvantage that the efficiency of the desulfurization agent is low. Also,
During the desulfurization process, the reduction of slag by carbon in the hot metal progresses,
There was a problem in that the oxidizing power decreased and rephosphorization occurred.

Therefore, in order to prevent the properties of the slag after dephosphorization from contributing to the reaction during the subsequent desulfurization treatment, the present inventors
After dephosphorization, a substance mainly composed of magnesium oxide, a substance mainly composed of calcium oxide, or a substance mainly composed of both is added to the slag after dephosphorization, and the slag after dephosphorization is converted into 2CaO, a compound with a high melting point. 5iOz (melting point:
2130°C) or MgO (melting point 2800°C) is crystallized and solidified to stabilize phosphorus, and by not allowing these products to contribute to the reaction during desulfurization treatment, the reaction can be carried out mainly through transition reactions. It has been found that dephosphorization and desulfurization of hot metal can be efficiently carried out by allowing the dephosphorization to proceed or by preventing the resulfurization from the top slag and the resulfurization reaction occurring in a permanent reaction in parallel during the desulfurization.

(Example) Table 1 shows examples according to the present invention together with comparative examples.

In Example 1, quicklime, iron ore, Mn ore,
A dephosphorizing agent made of fluorite is added upward, and after desilicification and dephosphorization are performed while blowing oxygen gas upward from lance 2, the top blowing oxygen gas is stopped, and 2. This is the case where, after adding 3 kg/l, fine powder of soda ash and quicklime at a weight mixing ratio of 1:2 was subsequently blown into the tuyere 1. In this example, the initial silicon, phosphorus, and sulfur concentrations are
O931% by weight, 0.102% by weight, 0.030% by weight
Add all quicklime to hot metal! 11.2kg/l, soda ash addition amount 1.1kg/l, phosphorus and sulfur concentration each 0.0
Low phosphorus and low sulfur hot metal of 15% by weight and 0.006% by weight was obtained.

The desulfurization efficiency defined by equation (1) had a value of 0.52.

4s Here, (S)t: Sulfur concentration after desulfurization treatment (wt%) [s
)r: Sulfur concentration after desulfurization treatment (wt%) -s: Desulfurization agent consumption (kg/l) After performing desiliconization and dephosphorization treatment while blowing in phosphorus agent from lance 11 and blowing oxygen gas upward from top blowing lance 12, the oxygen gas is stopped and 1.6 per unit weight of hot metal is removed.
This is a case where after adding kg/l of quicklime from above, fine powder of soda ash and quicklime with a weight mixing ratio of 1:2 was blown in from the lance 11.

In this example, the initial silicon, phosphorus, and sulfur concentrations are each 0.25.
Weight%, 0.09% by weight, 0.029% by weight of hot metal,
Total quicklime addition 3112.3kg/l, soda ash addition 1
．． At 2 kg/l, low phosphorus and low sulfur hot metal with phosphorus and sulfur concentrations of 0.016% by weight and 0.010% by weight, respectively, was obtained. The desulfurization efficiency value was 0.30.

In Comparative Example 1, the same refining vessel as in Example 1 was used, other operating conditions were almost the same as in Example 1, and no upward addition of MgO was performed after dephosphorization. The sulfur concentration is 0.28% by weight, 0.080% by weight, and 0.080% by weight, respectively.
026% by weight of hot metal has a quicklime consumption of 14.5 kg/
t, soda ash consumption rate was 1.9 kg/t, and the phosphorus concentration was only reduced to 0.023% by weight and the sulfur concentration was reduced to 0.015% by weight.

Comparative Example 2 used the refining vessel shown in FIG. 2, and while blowing in a dephosphorizing agent consisting of finely divided quicklime, mill scale, and fluorite powder from the blowing lance 11, and blowing oxygen gas upward from the top blowing lance 12, This is an example of simultaneous desiliconization, dephosphorization, and simultaneous desulfurization treatment. Initial silicon and phosphorus sulfur concentrations are each 0.
．． As a result of processing hot metal of 25% by weight, 0.090% by weight, and 0.031% by weight, the phosphorus and sulfur concentrations were each 0.02%.
, the consumption of quicklime decreased to 0.014%, but the basic unit of quicklime was 21kg.
/l, soda ash basic unit was 3kg/l, and a large amount of refining agent was required. Furthermore, the processing time was long and the temperature drop was also large.

FIG. 3 shows the changes in phosphorus, sulfur concentration, and hot metal temperature during the experiments of the above examples and comparative examples. In Comparative Example 1, a rephosphorus reaction occurs during desulfurization, resulting in the target phosphorus concentration (0.02
% by weight or less). In Comparative Example 2, the treatment was carried out for a long time, and the temperature of the hot metal decreased significantly.

(Effect of the invention) According to the present invention, compared to the conventional hot metal membrane phosphorus/desulfurization method,
Only one refining vessel is required, no slag removal process or preliminary desiliconization treatment is required, only the addition of equipment for adding a small amount of refining agent from above, and compared to conventional methods, there is less heat loss and excessive personnel. It is now possible to stably obtain hot metal with low phosphorus and low sulfur concentrations without the need for chlorine.

[Brief explanation of drawings]

Figure 1 is a side sectional view showing the refining equipment used in Example 1 of the present invention and Comparative Example 1, and Figure 2 is Example 2 of the present invention.
FIG. 3 is a side cross-sectional view showing the refining equipment used in Comparative Example 2, and FIG. 3 is a diagram showing changes in phosphorus, sulfur concentration, and hot metal temperature during experiments of Examples of the present invention and Comparative Examples. Fig. 1 1...Bottom blowing slit, 2...Oxygen top blowing lance, 3...
...Furnace humper 4...Refining container, 5...Blow tank, 6...Blowing gas, 7...Oxygen gas, 8
...Top slag, 9...Hot metal. Fig. 2 11... Blowing lance, 12... Oxygen top blowing lance, 13... Refining vessel, 14... Hopper, 15...
... Blowing gas, 16... Refining agent, 17... Oxygen gas. Figure 3 Time (minutes)

Claims (1)

[Claims] When performing dephosphorization and desulfurization treatment of hot metal, it is necessary to dephosphorize the hot metal with a dephosphorization agent containing oxygen and calcium oxide as the main components, and to subsequently blow in the desulfurization agent and use magnesium oxide as the main component before performing the desulfurization treatment. A method for refining hot metal characterized by adding a substance having calcium oxide as a main component, a substance having calcium oxide as a main component, or a substance having both as main components.