JPS5839717A - Coolant for protection of tuyere - Google Patents

Abstract

PURPOSE:To provide a coolant for protection which cools tuyeres effectively by mixing a specific amt. of hydrocarbon which produces carbon when thermally decomposed with carbon dioxide as a coolant for protection around the tuyeres which blow refining gases into molten iron. CONSTITUTION:In a gaseous mixture of hydrocarbon and carbon dioxide, hydrocarbon which produces carbon when thermally decomposed is contained at 10-40vol% with the gaseous mixture. The hydrocarbon-base coolant for tuyeres decomposes in the high temp. areas near the preceding end parts of the tuyeres and absorbs heat. For example, if gaseous propane is used as hydrocarbon, the coolant absorbs heat and produces carbon like the equationI. Further, the carbon dioxide reacts with carbon and causes the endothermic reaction as shown by the equation II. Thus the tuyeres are cooled effectively.

Description

[Detailed Description of the Invention] The present invention relates to a coolant for protecting tuyeres, and in particular to a cooling agent for blowing refining gas into a bath of molten iron for oxygen blowing of molten iron, typically in a bottom blowing converter. The purpose of this paper is to propose an improvement in the coolant composition for the tuyeres in order to advantageously protect them from violent reactions in molten iron.

In the above-mentioned type of refining vessel, an oxidizing gas such as pure oxygen is injected as a refining gas into the steel bath through the tuyeres at the bottom of the furnace.
Oxidizes and removes carbon, silicon, phosphorus, etc. contained in molten iron.

Here, the refining gas includes cases where an oxidizing gas is also used as a carrier gas and contains lime or other refined shavings.However, the oxidation reaction mainly consisting of decarburization is an exothermic reaction, As a result, the intense fire point generated in the bath exposes the tuyere, which controls the injection of refining gas, to extremely high temperatures, including the surrounding refractories.

Therefore, a composite tuyere tube consisting of concentric multiple tubes is usually used, and the refining gas is blown into the bath from the central tube and the coolant is blown into the bath from the annular suts in the inner and outer tubes.

Conventionally, hydrocarbon gases and liquids such as propane, natural gas, and petroleum, sometimes in combination with water vapor, are used as coolants for protecting the tuyere, and gaseous or liquid carbon dioxide is also used.

Among these, when using hydrocarbons and steam, there is a disadvantage that the hydrogen generated by decomposition due to Rakuchu injection increases the hydrogen concentration in the molten iron and impairs product quality. On the other hand, carbon dioxide does not have the advantage of increasing the hydrogen concentration in molten iron, but unlike hydrocarbons, it cannot be expected to undergo an endothermic decomposition reaction. Requires approximately 5 times the flow rate, and here in many cases,
Although it is supplied by using exhaust gas from petrochemical factories, the price is not necessarily low, and the use of large quantities as described above increases manufacturing costs.

The purpose of the invention is to solve the above-mentioned problems, that is, to reduce the generation of hydrogen gas by a hydrocarbon-based coolant by using carbon dioxide in combination, and in particular, to reduce the generation of hydrogen gas by a hydrocarbon-based coolant. This aims to effectively utilize endothermic reactions to improve cooling capacity.

That is, this invention consists of a mixed gas of hydrocarbons and carbon dioxide that generate carbon by thermal decomposition around the tuyeres used for injecting molten iron into the refining gas, and the hydrocarbons are mixed with the mixed gas. This is a refrigerant for protecting the siding, characterized in that it has a composition containing % lθ to Koyosha%.

By the way, hydrocarbon-based tuyere coolants decompose and absorb heat in the high-temperature area near the tuyere tip, but propane gas is an example.
A chemical reaction at 100K occurs as shown in the following equation (1).

0, H8-+ 70 + ni, -JO, s koal
/rnot (1) Actually, the temperature at the tip of the tuyere is estimated to be troo K'6! Now, considering the amount of heat required to raise the temperature of propane, hydrogen and carbon produced by its decomposition, the amount of heat required to raise the temperature at too K t is /4C, Jkoal/mot, and then 100 K
The amount of heat required to raise the temperature from to troo K is 4'4-
J kOLl/mol -0sHB.

- By integrating these, the cooling capacity per mole of propane gas at /100 Kt is approximately 90. Irkaal
It can be estimated that the hydrocarbon-based tuyere coolant decomposes and precipitates solid carbon, which plays a major role in increasing the heat of endothermic reaction when used in combination with carbon dioxide, as described below. It is.

In other words, carbon dioxide mainly performs tuyere cooling using its sensible heat, and the sensible heat of the gas is 1.7 kaeLl/mol when the temperature is raised from room temperature to /r00K, but as mentioned above together with carbon dioxide. In the presence of solid carbon, the following endothermic reaction is added and the tuyere cooling capacity is advantageously enhanced.

C02+C→CoCo-IAl,/kaaz/mol
(2) In anticipation of such a reaction, it is conceivable to separately supply carbon powder or the like together with carbon dioxide.

However, 0, j4' kg/ which corresponds to our part in equation (2)
There is a problem in conveying dilute carbon powder of about Nm'' 002 using a simple conveying means.

In this invention, gaseous or liquid hydrocarbons that cause a thermal decomposition reaction to precipitate carbon are used in combination with carbon dioxide.
It can be easily introduced into a composite tuyere, for example, the gap between the inner and outer tubes of a concentric double tube, without the difficulties of conveying it when supplying a carbon source separately. The endothermic reaction heat of equations (1) and (2) can be effectively utilized as a coolant. As a result, the combined feed flow of hydrocarbons and carbon dioxide is much reduced compared to their individual use, thus not only preventing an increase in hydrogen concentration in the molten iron, but also advantageously suppressing the coolant consumption. O The mixed gas according to the present invention can be expressed by the formula (1) and (2).
According to the formula, the endothermic reaction shown in the following formula (8) is exhibited.

J G Og + 03 HB →≦OO+1M, -#
J, ≦kcaj/mo! -03[6(3) Now, assuming that the reaction of equation (8) occurs at too K, Table 1 summarizes the overall cooling capacity of the mixed gas at various mixing ratios up to 1100 K.

As is clear from the formula (3) in Table 1 and Table 1, the mixing molar ratio of 03H8 to 008 is S! l i.e. C02 and C3
0 in a mixed gas of H8. The endothermic reaction occurs most efficiently when the H8 content is 1% by volume of B, which is the ultimate mixing ratio of this invention. For 03H8, the effect of reducing the tuyere cooling gas is large in the range of lO to 4I0 mixed volume%, and even if it is less than tθ Yongsha% and exceeds Shu Yongsha%, the cooling gas reduction effect is recognized, but as will be discussed later. For these reasons, it is excluded from the scope of this invention.

As roughly shown in Table 1, within the scope of the present invention, it has a tuyere protection cooling ability of 37.3 to 4j, 2 kcal/moj, and exhibits the same cooling ability as C3H8. The required positional ratio (required molar ratio) is determined by the mixing ratio of O and H8, and the benefit of cost reduction for tuyere protection cooling can be achieved (see Table 2).

Figure 1 shows the C02-C3H required to obtain equal tuyere cooling capacity.
8 Volume of C5H8 in mixed gas corresponding to mixed gas position It%
The broken line in the figure shows the relationship between C and co of hydrocarbon decomposition,
The above relationship is shown assuming that the reaction with is not considered.

Note that the vertical axis of the graph is an index display where 100 is the amount of gas required to exhibit a constant wall cooling capacity with CO2. From the same figure, it can be seen that the amount of gas required to obtain equal tuyere cooling capacity decreases rapidly up to 0.1 (82%), and after that it shows a gradual decreasing tendency. In the figure, the solid line represents the cooling capacity per mole of CO2-C3H8 mixed gas in the panel cooling arrangement, corresponding to the 03H8 containing position, and the dotted line takes into account that the decomposed C of hydrocarbons reacts with CO2. The above relationship is based on the assumption that 03H8 is not used. Therefore, the difference between the solid line and the dotted line represents the amount of increase in the amount of reaction heat for cooling the tuyere due to the combined use with the coll, depending on the respective 03H8 content position.

As can be seen from Figures 1 and 2, by mixing C3H8 with 002, the tuyere cooling capacity per mole of mixed gas increases rapidly, in other words, the amount of cooling gas required for tuyere cooling is advantageous. It has been shown that it is effective in reducing

Briefly, FIG. 3 shows that the decomposition C of 03HB is 00. The relationship between the 03H8 content position and the reduction of the gas position resulting in equal tuyere cooling capacity is shown. This reduced gas amount corresponds to the dotted line and solid line in FIG.

This reduction in the amount of tuyere cooling gas increases steeply for 03H8 up to B volume I1% with respect to the amount of mixed gas of C02 and 03H8, but after that, the amount of gas for cooling the tuyeres increases according to the 10 ports of 03H8 contained. Although the amount of reduction gradually decreases, there is a noticeable effect in cost reduction due to effective gas reduction compared to the case of using C02 alone. The above is the result obtained by calculation, but next
The scope of the invention will be limited by describing experimental results using a converter.

As mentioned above, according to calculations, the reduction effect of tuyere cooling gas can be expected to reach its maximum when the C3H8 content is B volume % over the entire bald area. However, this calculation is an equilibrium calculation, and in reality, the reaction rate of the gas differs for each composition, and it is expected that the result may differ from the calculated result.

So we conducted an experiment.

The experiment was carried out in a bottom-blowing test furnace, and at the same time oxygen flow rate /J Nm'/min was blown into the inner tube at the side entrance of the double tube, the gap between the ring between the inner and outer tubes was determined by calculation. The mixed gas was flowed to obtain a constant cooling effect. That is, 03H8 and OO2 shown in Table 2 are mixed in each flow device, and 03H8 is
, j , 101 Jj # 170 , jO, 4
717! .

The experiment was conducted to obtain a constant cooling effect at 9 levels of each volume%.0 The tuyere cooling effect was determined by observing the formation state of solidified iron (pine mushroom) at the tip of the tuyere. The product was evaluated as good if a normal-shaped pine mushroom was formed, excellent if the pine mushroom was particularly large and strong, and poor if the pine mushroom was not formed or the tuyere part was severely eroded. . The results are shown in Table 2. As shown in Table 2, the tuyere protection effect was better than good at all mixing ratios, but especially when the storage percentage of O and H8 was 10 ~ Bigger and stronger in terms of performance than other conditions!
Thushroom formation was observed.

This fact was not possible in the above-mentioned (equilibrium) calculations, but it became clear for the first time through experiments. Although the reason for this is not necessarily clear, a mixture ratio close to the stoichiometric range of the reaction results in a reaction closer to the equilibrium value. In other words, it is considered that the reaction efficiency is high.

As mentioned above, from the results of this experiment, the volume percentage of O, H8
It has been found that the tuyere protective effect is particularly excellent in the range of 10 to %.

From these calculation results and experimental results, the scope of this invention is 0.
The capacity of 3H8 is limited to an area of 10% to 10%.

According to the present invention, using a mixed gas containing 10-$117 volumes of O, H8, the total amount of CO□ or 0. Compared to the case of H8, the cost was reduced to about 0.7I times.

The figure below shows 0% in the mixed gas. The mixing volume of C3H8 of the cooling gas 1 shows the relationship between the hydrogen concentration in steel and the H8 content.
It is also possible to control the hydrogen value in steel by selecting the percentage. - The limit for the hydrogen value in steel varies depending on the type of steel manufactured, but since it is higher than the standard, it is possible to dehydrate it using a vacuum degassing device etc. Even in cases where elementary treatment is required, this invention can be used to refine the steel to control the hydrogen level in the steel within specifications, or reduce the burden of vacuum degassing, resulting in significant cost reductions. Realized.

Regarding the soft wire in the bottom blowing converter above, C
Although the case of mixing 3H8 was explained as a typical example, CO2
Hydrocarbons to be mixed with the gas may include propane gas, natural gas, petroleum, and other hydrocarbons that generate carbon through thermal decomposition, and may be used in gas or liquid form.

In addition to bottom-blowing converters, this tuyere-protecting coolant can also be used for molten iron refining in top- and bottom-blowing converters and other refining vessels such as ladle for out-of-furnace processing, as long as they have similar functions. In any case, an advantageous reduction in the increase in hydrogen concentration in the bath pig iron after refining can be realized together with an effective improvement of the cooling capacity, and the use of coolant for tuyere protection can be greatly reduced.

[Brief explanation of the drawing]

Figure 1 shows the CO3-(3,
Volume % of C3H8 in the mixed gas corresponding to H8 mixed gas
Figure 2 is a cooling capacity graph showing the effect of 1% volume of 0.118 in the mixed gas on the tuyere cooling heat amount, Figure 3 is the decomposition of C, H8 reacts with CO2. The amount of gas that can be reduced by this and the amount of gas in the mixed gas can be reduced by 0. A graph showing the relationship between H8 and H8 in the mixed gas, Figure 4I shows the relationship between O and H8 in the mixed gas.
It is a graph showing the relationship between hydrogen concentration in steel and storage attack. Patent applicant Kawasaki Steel Corporation Figure 1 Figure 2 o to 20304050 6070130 q
Of00'51-1g Xfθ0 (volume %) co2+03He Figure 4.

Claims (1)

[Claims] L Consists of a mixed gas of hydrocarbons and carbon dioxide that generate carbon by thermal decomposition around the tuyeres used for injecting molten iron into the refining gas, and the hydrocarbons have a penetration rate of 10 to 10% to the mixed gas. A cooling agent for protecting tuyeres, characterized in that it consists of a composition containing 1%.