JPS6361368B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a slag foaming inhibitor that can be suitably used to suppress foaming of hot metal slag in a hot metal treatment process in a steelworks.

[Prior art] Hot metal tapped from a blast furnace is often subjected to desiliconization treatment in a hot metal pot or torpedo car, but the reaction at that time generates a large amount of CO gas, which is deposited in the upper layer. Foam the slag.
When this bubbling becomes large, slag overflows from the hot metal ladle, etc., making it impossible to inject any more hot metal, resulting in a problem of reduced transport efficiency.

The causes of this slag bubbling phenomenon are (1) viscosity, especially at the surface of the slag, (2) surface tension of the slag, (3) presence of suspended solid particles, and (4) oxidation of suspended carbon-saturated iron particles. These factors are explained below.

● Viscosity of slag The relationship between the temperature and viscosity of molten slag is that when the slag temperature is above 1500℃, the viscosity hardly changes, but when it is below 1500℃, it increases rapidly, and in extreme cases, the temperature
When the temperature decreases by 170°C, the viscosity increases approximately 8 times. In particular, since the slag in the foam-like surface layer does not undergo convection, the temperature drop is more significant than in the interior of the slag, which is considered to be a factor in increasing the viscosity and increasing foaming.

●Surface tension of slag A part of the SiO ₂ present in the slag exists as surface active substances such as SiO ₄ ⁴ and is adsorbed to the surface layer, and Fe ₂ O ₃ , P ₂ O ₅ , etc. contained in the slag also exist. is also a surface active substance and is adsorbed on the surface layer along with SiO ₄ ⁴ and the like. Surface tension plays a large role in the stability of slag foam, and the presence of these surface-active substances lowers the surface tension and makes the foam more difficult to break.
In the case of slag, unlike in the case of general aqueous solutions,
It is known that the higher the temperature, the higher the surface tension, and furthermore, the higher the temperature, the shorter the life of the foam.

● Presence of suspended solid particles There are suspended solid particles such as unreacted CaO in the slag, but these exist in the foam layer and prevent the sedimentation and separation of the slag in the foam layer, destroying the foam layer. It's making it difficult.

● Oxidation of suspended fine particles of carbon-saturated iron Slag contains fine particles of carbon-saturated iron, and in the slag layer with a high oxygen potential, carbon content oxidizes to CO gas, but suspended carbon-saturated iron particles It is thought that gas generation occurs rapidly because the particles are small.

The slag bubbling phenomenon referred to here means that the factors (1) to (4) above for slag bubbling are combined, and the bubbling phenomenon occurs rapidly, resulting in a foam layer overflowing to the outside of the system. It refers to the phenomenon that occurs. That is, a significant increase in slag viscosity due to a decrease in temperature, a decrease in surface tension due to the presence of surface viscous substances,
On the other hand, rapid oxidation of carbon in carbon-saturated iron
There is an increase in internal gas pressure due to the generation of CO gas,
It can be considered that at a certain moment, these equilibriums are broken, the gas suddenly protrudes outside, and the slag foam overflows.

To prevent this slag foaming phenomenon, measures such as adjusting operating conditions, destroying the foam layer by blowing gas, thermally destroying it with a burner, and increasing the slag surface temperature by adding valve slag, etc. have been used. However, a satisfactory solution has not yet been reached.

The inventors of the present invention have filed Japanese Patent Application No. 60-274493
No. 136512) proposed that a mixture of metallic aluminum powder and carbonaceous material is effective as this slag foaming inhibitor. this is,
When this inhibitor is added to the slag surface, it will only lower the viscosity of the slag surface by applying heat to the slag surface.

[Object of the Invention] The object of the present invention is to solve the above-mentioned problems, further enhance the effects of the previous application, and provide a slag foaming inhibitor that can extremely effectively prevent foaming of slag when used. Our goal is to provide the following.

[Summary of the invention] The gist of the present invention for achieving the above object is as follows:
A slag foaming inhibitor that is added to slag on hot metal to suppress foaming of slag, and is characterized by containing a light metal powder with a specific gravity of 5 or less, a carbonaceous powder, and an oxidizing agent consisting of sodium nitrate. It is.

[Embodiments of the Invention] The inhibitor according to the present invention is a mixture of a light metal powder, a carbonaceous substance, and an oxidizing agent. As the light metal powder, metals having a specific gravity of 5 or less can be used, and for example, aluminum, magnesium, silicon, titanium, etc., and alloys containing these can also be used. FIG. 1 shows the relationship between the specific gravity, free energy of oxide formation, and heat of formation for each metal. In the figure, the ○ mark is the free energy at 1000°C, and the △ mark is the heat of formation at room temperature. Therefore, from this Figure 1, metals that have a higher reactivity with oxygen than iron oxide, that is, metals whose free energy is smaller than that of iron oxide and whose heat of formation is smaller than iron oxide, include manganese, aluminum,
silicon, beryllium, magnesium, calcium,
Light metals such as titanium can be mentioned. However, in consideration of actual economic effects and ease of handling, aluminum, magnesium, silicon, and titanium are preferable as the metals to be added.

When the mixed light metal powder is thrown onto the slag surface, it reacts directly with the iron oxide in the slag, causing a well-known thermite reaction in the case of aluminum, for example, which converts the iron into rings and releases the reaction heat. is applied to the slag surface. Therefore, it is natural that the light metal powder used needs to be selected from light metal elements that have higher reactivity with oxygen than iron oxide, as described above.

Further, as the carbonaceous material, coke, coal, anthracite, etc. are used. In this case, the carbon content is 50%
As mentioned above, it is desirable that the calorific value is 6000 Kcal or more per 1 kg. The content of the carbonaceous material is 20% to 80% by weight relative to 100% of the metal powder.
This is because if the weight ratio is less than 20%, there is a problem that the calorific value is insufficient, and if the weight ratio exceeds 80%, there is a problem that the contribution of the thermite reaction is insufficient, which is not preferable.

For example, in the hot metal treatment process in the previous process, the oxygen partial pressure of the oxidizing agent is relatively low due to the CO gas generated by adding a desiliconizing agent, especially when heat is transferred to the slag surface by burning carbonaceous materials. , can be used when the combustion rate is slow and the sufficient effect cannot be achieved. The oxidizing agent must be able to perform its function at the slag surface temperature, and sodium nitrate is effective in this respect.

When using sodium nitrate as an oxidizing agent,
The mechanism of generating oxygen through thermal decomposition of sodium nitrate is shown as 2NaNO ₃ = Na ₂ O + 2NO + 3/2O ₂ and is an endothermic reaction, and it is necessary to supply 348 Kcal/Kg of heat to decompose sodium nitrate. be. Therefore, the amount of sodium nitrate added must be 1 to 15% or less based on the total amount of light metal powder and carbonaceous material from the viewpoint of thermal equilibrium.

These light metal powders, carbonaceous powders, and sodium nitrate may be used simply as they are mixed, but they can also be made into pellets using a binder. As the binder, inorganic materials such as bentonite and water glass, or organic materials such as starch, which do not generate harmful gases or have no adverse effect on the slag, can be used. Further, the amount of the binder varies depending on the particle size and properties of the light metal powder and carbonaceous material, but a weight ratio of 2 to 10% is suitable. This has the problem that if the weight ratio is less than 2%, the binding effect cannot be fully demonstrated, and if it exceeds 10%, the proportion of light metals and carbonaceous substances decreases, resulting in a problem of insufficient calorific value. Due to undesirable things. Also, the pellet size is, for example, 30mm x 45mm.
mm x 40 mm, and its crushing strength is preferably 2 kg or more so that it will not break during handling.

When the thus configured inhibitor according to the present invention is introduced into, for example, a hot metal desiliconization process, it is possible to suppress the slag bubbling phenomenon. That is, by adding this inhibitor, (1) heat is supplied by the reaction between the light metal powder and the iron oxide in the slag components, and (2)
CO gas generated by high-temperature combustion of carbonaceous materials prevents unnecessary oxidation of light metal powder and supplies heat to the slag surface. (3) The oxidizer decomposes and supplies oxygen, so carbonaceous The combustion rate of the substance can be increased, that is, when this slag anti-foaming agent is added to the slag surface in the hot metal treatment process,
The light metal powder contained reacts with iron oxide in the slag components. For example, using aluminum as a light metal powder, from the reaction of 2Al + 3FeO → Al ₂ O ₃ + 2Fe + 210400Kcal/Kg mole, 210400Kcal/Kg mole of aluminum.
(2・27)=3896Kcal of heat can be supplied to the slag surface.

On the other hand, when carbonaceous materials such as coke are exposed to high temperatures of 1500°C or higher, CO gas is generated by the Boudourd reaction, and this CO gas prevents light metal powder from oxidizing until it reaches the slag surface, and the heat of combustion oxidizes the slag. Heat and contain. It is also a slag component.
It is thought that reduction of iron oxides such as Fe ₂ O ₃ reduces surface active substances and is useful for modifying slag. In this case, for example, in the hot metal treatment process,
When the oxygen concentration is relatively low due to the generated CO gas, the reaction between carbon and oxygen is 2C + O ₂ = 2CO, and the reaction rate, that is, the combustion rate, increases as the oxygen partial pressure increases, and iron oxide The addition of is effective.

As is clear from the above points, the slag antifoaming agent according to the present invention transfers the heat of reaction of the light metal powder contained in the slag with iron oxide and the combustion heat due to combustion of carbonaceous materials to the slag surface, It attempts to destroy the foam layer. In this case,
If the total calorific value is the same, it is necessary to increase the combustion rate in order to increase the achieved temperature, and it is understood that addition of iron oxide is effective for this purpose as well. On the other hand, the temperature reached is also related to the total calorific value of the anti-foaming agent used, and although it is of course desirable that the total calorific value be as large as possible, it is actually desirable that the total calorific value be 5000 Kcal or more. . Furthermore, as will be explained later, as is clear from the heat calculation when using an anti-foaming agent, the heat transfer efficiency to the slag layer is as low as 5%, so if the amount of heat generated is small, the amount used will only increase. However, it is not possible to supply an effective amount of heat to the slag foam layer to destroy the foam in response to the rapidly occurring slag foaming phenomenon. For this reason, it is preferable that the total calorific value of the slag anti-foaming agent be 5000 Kcal or more per 1 kg.

Furthermore, when this slag antifoaming agent is briquette-sized into pellets and added to the hot metal treatment process, it can maintain its effectiveness for a certain period of time. That is, since the combustion rate increases in proportion to the surface area of the slag antifoaming agent, the surface area can be adjusted by briquetting the slag into pellets. However, if the briquette pellets are not dense, not only will they be easily crushed during handling, but the surface area adjustment effect of the briquettes will not occur. Therefore, the crushing strength of the pellets must be 2 kg or more, and the size of the pellets is also preferably determined based on the conditions in which they will be used.

Next, as an aid to understanding, an example of heat settlement when this slag antifoaming agent is used is illustrated. Here, 1 kg of anti-foaming agent with a composition of 15% aluminum, 70% coke, and 15% sodium nitrate was added to the hot metal at 1400°C, and the surface slag temperature was increased to 1500°C.
The heat balance when heated to is as follows.

Heat input Slag anti-foaming agent 5712Kcal Total 5712Kcal Heat output Sensible heat of exhaust gas 2324Kcal Sensible heat of residue 112Kcal Heat radiation loss 2276Kcal Total 5712Kcal The amount of heat that can be used to heat the slag is (Heat input) −
(Sensible heat of exhaust gas) - (heat radiation loss) = 1112Kcal, and the sensible heat of the slag to be heated is 25Kcal/Kg, so the amount of slag that can be heated is 1112/25 = 44Kg.
It is. Therefore, 44 kg of slag can be heated per 1 kg of the present slag anti-foaming agent.

Further, in the desiliconization treatment process of hot metal, the above-mentioned slag antifoaming agent was added, and the slag level was observed using a level meter. The results are shown in FIG. As is clear from FIG. 2, the slag level decreases each time the slag foaming inhibitor is added, and it can be seen that foaming of the slag is reliably suppressed.

[Effects of the Invention] As explained above, the slag antifoaming agent according to the present invention partially increases the slag temperature by being added to the slag in the upper layer of hot metal.
The foam is easily destroyed and the gas inside can easily escape from this part, which not only effectively reduces slag foaming, but also increases the oxygen partial pressure even in situations where the oxygen partial pressure is low. This increases the combustion rate of carbon and makes suppression of slag foaming more effective.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between the free energy of oxide formation and the heat of formation with respect to the specific gravity of each metal, and Figure 2 shows the measured slag level when the slag antifoaming agent of the present invention is added to pig iron. It is a graph diagram.

Claims (1)

[Scope of Claims] 1. A substance that is added to slag on hot metal to suppress bubbling of the slag, and contains a light metal powder with a specific gravity of 5 or less, a carbonaceous powder, and an oxidizing agent consisting of sodium nitrate. Characteristic slag foaming prevention agent. 2. The mixing ratio of the metal powder and the carbonaceous material is 20 to 80% of the carbonaceous material to 100% of the light metal powder, and 1 to 15% of the oxidizing agent to the light metal powder and the carbonaceous material. Slag anti-foaming agent described in . 3. The slag foaming inhibitor according to claim 1, wherein the inhibitor is briquette-shaped.