JPH01212717A - Operation of vacuum degassing treatment - Google Patents

Abstract

PURPOSE:To reduce unit requirements of oxygen and a deoxidizing agent and to obtain high purity gaseous CO by stopping blowing into a converter at the time when the amt. of C in molten steel is slightly higher than that in an end product, allowing C to react with oxygen in the molten steel and producing gaseous CO by vacuum degassing treatment. CONSTITUTION:Inert gas or the like is blown into a converter and molten steel is subjected to vacuum degassing treatment. Blowing is stopped at the time when the amt. of C in the molten steel is slightly higher than that in an end product. Gaseous CO is then produced by carrying out vacuum degassing treatment until the desired amt. of C is attained. The produced gaseous CO is recovered.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a vacuum degassing process for generating CO gas in a vacuum degassing facility, separating and recovering the CO gas contained in the exhaust gas, and effectively utilizing the CO gas. Regarding operating methods.

Conventional technology Vacuum degassing equipment is used for a variety of purposes other than degassing molten steel, such as improving the quality of molten steel, improving component accuracy, improving alloy yield, and uniformizing molten steel temperature.

Various processes are in operation as vacuum degassing equipment, such as reflux degassing equipment called RH and equipment called D)I, but since they are almost the same in principle, we will use reflux degassing equipment here. This will be explained below using equipment as an example.

The principle of degassing utilizes the phenomenon that when molten steel flows back in a vacuum chamber, the gas contained in the molten steel is desorbed because the amount of dissolved gas decreases under reduced pressure. The means for refluxing the molten steel is to blow inert gas through one of the immersion pipes (two pipes) and circulate it using the principle of an air lift pump. Ar gas and mineral gas are generally used as inert gases, but
It has also been proposed to use CO gas mixed with At gas for the purpose of manufacturing low nitrogen steel.

In reality, Ar gas and the like used in vacuum degassing treatment were, in most cases, released into the atmosphere as exhaust gas.

However, as a method for recovering generated gas, there is a known method of recovering converter gas generated during converter blowing and utilizing it as fuel gas.
A method for recovering Ar gas from a converter was published in Japanese Patent Application Laid-Open No. 55-5041.
No. 8 proposes an Ar recovery method using a bottom-blown converter. However, no operational method has yet been found for actively generating and recovering CO gas using vacuum degassing equipment.

Problems to be Solved by the Invention As mentioned above, vacuum degassing equipment is used for many purposes other than degassing molten steel. Almost no consideration had been given to the operation method of reusing the waste. The reason why not only special steel but also general steel began to be treated with vacuum degassing equipment was due to the rise in casting temperature due to the availability of continuous casting equipment, and the aim of improving alloy yield.

It is indeed unfortunate that the exhaust gas treatment of vacuum degassing treatment, which has been used not as a special treatment but as one of the normal steelmaking processes, has rarely been seen in the past and has simply been released into the atmosphere. The present invention provides an operating method that actively generates and recovers CO gas.

Means for Solving the Problems The gist of the present invention is that when molten steel is subjected to vacuum degassing treatment, blow-stopping is performed in a converter at a higher C value than the final C value of the molten steel, and then CO gas is removed by vacuum degassing treatment. This is an operating method for vacuum degassing treatment in which CO gas is generated, treated to a final C value, and the generated CO gas is recovered.

Function When separating and recovering effective gas from vacuum degassing equipment,
First, we analyzed the exhaust gas and found that CO
It was found that a large amount of gas was generated.

That is, the equilibrium solubility curve of 9 and 9 in molten steel changes greatly depending on the pressure, as shown in FIG. The blow stop of the converter is set to point A, and the vacuum degree of the vacuum degassing tank is set to 100 Torr.
Then, the reaction changes from point A to point B while causing the reaction C+O→CO, and CO gas is generated. Therefore, it is only necessary to control the blow-stop carbon value of the converter to point A so that the target carbon value is 3 points.This not only reduces the amount of oxygen required, but also reduces the need for expensive deoxidizers such as M. The amount used can also be reduced.

Moreover, if the generated CO is recovered, purified, and effectively used for denitrification treatment, it will be possible to kill two birds with one stone.

Figure 3 shows typical changes in exhaust gas components during vacuum degassing treatment.The CO gas component rises rapidly from around 1 minute after the start of the treatment, and then gradually decreases. It is desirable to selectively recover this initial exhaust gas. On the other hand, since the blown gas is constant, Ar gas is generated stably until the end.

Hereinafter, the configuration of the method of the present invention will be explained in detail. The vacuum degassing equipment is RH (Rhei) as shown in Figure 1.
The explanation will be given as ngtahl-Heraus). Two immersion tubes 2 for suction and discharge are attached to the bottom of the vacuum tank 1. Inert gas such as Ar gas is blown into the immersion tube 2 on the suction side, and the ladle is heated using the principle of an air lift pump. The molten steel in 3 is sequentially circulated through the vacuum chamber and degassed. 1 to 10 in vacuum chamber l
Since it is maintained at 0H10OH, the atmosphere is easily sucked in. Therefore, the sealing structure of the joint must be as strong as possible, otherwise the exhaust gas will be diluted by the mixture of atmosphere, which is not good.

Further, argon, oxygen, and nitrogen gas are blown in from the nozzle 4 for blowing oxygen gas and powder, depending on the purpose. The exhaust gas generated in the vacuum chamber 1 is introduced into a gas cooler 5, a booster 6, and a condenser 7, where it is washed with water. The degree of vacuum is controlled by a vacuum degassing device consisting of a condenser 7, an ejector 8, and a mist separator 9. Conventionally, the exhaust gas exiting the mist separator 9 was discharged from the atmosphere diffusion pipe 10, but in the present invention, the initial exhaust gas with a high CO gas concentration is compressed by the compressor 12 and stored in the gas holder 13. ing.

In order to separate and purify the CO gas from the exhaust gas, the moisture in the exhaust gas is first removed in the pretreatment tower 14, and then the CO2 gas 1B is separated by the gas separation membrane 15.

Polyimide, cellulose acetate, and the like are typically known as materials for the gas separation membrane 15, and C02 gas can be selectively dissolved and permeated through the organic membrane and separated from other components.

Although separation 115 is not necessarily necessary, since the CO gas to be separated remains on the high-pressure non-permeate side, pressure energy can be used without loss, and it is effective as a pretreatment for the subsequent PSA device.

PSA (Pressure Swing Adsor
The method (ption) is a method in which component gases that are easily adsorbed onto an adsorbent are selectively adsorbed under pressure and recovered under reduced pressure.
The principle is to separate specific components from a mixed gas based on the differences in adsorption power between component gases.

In order to selectively adsorb CO gas, a zeolite-based molecular sieve is preferable, and it is even more effective to use an adsorbent that retains copper (1) compounds and combines chemical and physical adsorption. . The adsorption process is generally controlled so that a cycle of adsorption (pressurization)→desorption (depressurization)→pressure accumulation (pressurization) is repeated using three or more adsorption towers 17.

The CO gas adsorbed on the adsorbent is desorbed by the vacuum pump 18 and passed through the post-treatment tower 20 that performs dehydrogenation to produce high-purity CO.
It is used as gas 21. In addition, 82.
Ar can be separated as off-gas 1B.

This off-gas 1B contains N2. Since it does not contain ATL, it is also possible to separate Ar gas more efficiently.

Separated and purified CO gas can not only be recirculated and used as blowing gas in vacuum degassing equipment, but also used as bottom blowing gas in converters or sold externally as raw material gas for chemical products. It is. In particular, when blowing a mixed gas of CO and Ar in vacuum degassing equipment to promote denitrification of molten steel, the CO gas obtained by the present invention can be used to produce low-nitrogen steel extremely economically. became possible.

EXAMPLE Below, an example in which the present invention is applied to a reflux type degassing facility will be specifically described.

Table 1 shows the molten steel composition, and as shown in Figure 2, the blow-stop C [%] of the converter is 0.07% so that the C [%] after degassing is 0.04%. I stopped high. As shown in Table 2, the operating conditions for the degassing treatment were as follows: 1 batch was 250 tons, the vacuum chamber was maintained at 100 Torr for about 15 minutes, and Ar was blown into one side of the immersion tube at a rate of 15 ON m3/hr to promote reflux of the molten steel. .

9 and 9 in the molten steel react and become CO gas, which is generated concentratedly during the initial 1 to 5 minutes of degassing as shown in Figure 3.
The pressure was increased to am2G and stored in a holder. Since the generation of CO gas occurs only intermittently at about 150 ONm3/hr x 4 to 5 minutes, it is more economical to store it in a holder in consideration of making the post process continuous and compact.

The pre-treatment tower is filled with activated alumina to remove moisture.
It was introduced into a C02 gas separation membrane.

Table 3 shows the operating conditions and component changes of the gas separation membrane. The separation membrane used was a spiral structure membrane made of polyimide and having a high C02 permeation rate. Table 4 shows CO
The operating conditions and results of PSA adsorbing are shown. C.O.
In order to improve the purity and recovery rate of CO at the same time, we used a zeolite-based adsorbent that retains a copper (1) compound that has a high CO adsorption capacity. The H2 remaining in the product gas at the end is
In the post-treatment process, palladium was used as a catalyst to completely remove H and O.

Table 1 Molten ingredients (%) Table 2 Cleaning conditions Table 3 Vacuum production and yarn production As detailed in the invention, according to the method of the present invention, vacuum High purity CO gas can be obtained from the exhaust gas of degassing equipment at a low cost.In addition, the blow-off C value of the converter is set higher than that of the final product, and it is decarburized by reacting with oxygen in the molten steel. - Since deoxidation can be performed at the same time, not only can the oxygen consumption rate in the converter be reduced, but also the consumption consumption of deoxidizers such as aluminum can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of the equipment layout for implementing the present invention. FIG. 2 is a diagram showing the equilibrium values of p and 9 in molten steel. FIG. 3 is a diagram showing a typical exhaust gas composition when the present invention is implemented in a reflux type degassing facility. L...Vacuum tank, 2 chambers...Immersion tube, 3φ...Ladle, 4...
φ・Blowing nozzle, 5・E・Gas cooler, 6・・φ booster, 70 fist condenser, 8・Ejector, 9
・・・Mist separator, lO・・Φ atmosphere diffusion tube, 1
1...LDG, 12-...Compressor, 13
...Gas holder, 14 pre-treatment tower, 15φQ・Gas separation membrane, 18・φ・C02 gas, 17--- PSA
Adsorption tower, 18e*a Ar, N2 gas, 18・Vacuum pump, 20・φ after-treatment tower, 21・φ・CO product gas.

Claims (1)

[Claims] When molten steel is vacuum degassed, the final C of molten steel is
Vacuum degassing is characterized by performing blow-off at a higher C value, then generating CO gas through vacuum degassing treatment, performing treatment to reach the final C value, and recovering the generated CO gas. How to operate gas processing.