LU82864A1 - IMPROVEMENTS TO CAST REFINING PROCESSES - Google Patents

Description

BL-2985 / EM / 1; * I Claim of the priority of patent applications “T 'filed in Belgium on October 22, 1979 under No. 879.576 y and on October 31, 1979 under No. 879.794 C— j C 1987E / 8010.

t I.

; | ç f METALLURGICAL RESEARCH CENTER - ICENTRUM VOOR RESEARCH IN DE METALLURGIE,

Non-profit association - vereniging zonder winstoogmerk in BRUXELLES, (Belgium).

Improvements to the refining process of cast iron to the converter.

t?

The present invention relates to improvements made to the refining processes of phosphorous or hematite cast iron in the converter. It applies to the case where this refining is "carried out by injection of an oxidizing gas, for example pure oxygen. , in the metal bath, through nozzles housed in the bottom of the converter.

In practice, the bottoms of these types of converters are fitted with a set of nozzles with two concentric tubes, j *, the central tube serving for the introduction of oxidizing gas, most often oxygen. pure, while the peripheral tube is used for the introduction of a protective fluid, for example a gaseous hydrocarbon.

; It has been observed that such a procedure has the following harmful consequences: in the case where the protective fluid is a hydrocarbon, the content of the metal in hydrogen increases and in the case where the protective fluid is nitrogen, the nitrogen content of the metal increases.

ί I This is the reason why the applicant had the idea of replacing the protective fluid by a fluid containing neither N ^, or in this case by CO ^

During the tests, the applicant also found that to very effectively reduce the contents of the metal in m! or in N „, it was not necessary to use CO0 as a protective gas during the whole refining operation, but that it was enough to blow CO ^ only towards the end of the refining or 'more particularly during the short correction phase or in core during the tilting operation of the converter from the cleaning position to the bag emptying position.

It also appeared that to ensure sufficient cooling of the nozzles, the injection of C00 had to be ef- I Δ! carried out in the proportion of approximately 20% of the amount of O ^, I while the injection of hydrocarbons is generally carried out in proportions of 3 to 12% of the quantity of oxygen (C, H:

J O

4r%, natural gas: 10%).

> j Such large variations can cause! problems with the nozzles, with two concentric tubes of which only the es; > space between the central tube and the peripheral tube is used for the passage of the protective gas. Indeed, one should not lose sight of: 1 that the pressure of the protective gas, whatever it is, must be maintained above a minimum value to prevent any re-entry of the metal Ι liquid into the nozzles.

The applicant then had the original idea of using Il nozzles with three well-known concentric conduits for reme- / 3.- oxygen blowing is generally carried out by the central tube and by the space between the central tube and the intermediate tube, while the blowing of the protective fluid is carried out through the space between the intermediate tube and the outer tube.

When we want to reduce the metal content of H2 or N2 by using C02 as a protective gas at the end of refining, we then have the possibility of blowing the O2 only through the central tube and having space between the central tube and the intermediate tube and the space between "the intermediate tube and the peripheral tube to solve the problems of large variations in the quantities of protective gas to be injected.

The present invention specifically relates to a method for carrying out such refining.

The process, object of the present invention, in which use is made of a steelworks converter, the bottom of which is provided with a set of blowing nozzles with three concentric tubes, is essentially characterized in that one blows d on the one hand, of the O 2 through the central tube and on the other hand, a protective gas through the space between the intermediate tube and the peripheral tube, and in that the metal contents in H2 are reduced or in N2 "using C02 as a protective gas at the end of refining, as follows: at the time determined for the blowing of CC> 2 at the end of refining, the blowing of the O2 is continued through the central tube and the CO2 is blown through the space between the intermediate tube and the peripheral tube.

The applicant has in fact found in a completely unexpected manner, that it was possible, under the conditions described above, to blow no gas in the space between the central tube and the intermediate tube without incurring the fl risk of liquid metal entering the said space.

'r-lv' λ— r * »r '4.- j 3 3 | According to an advantageous modality of this process at the moment determined for the blowing of CO 2, CO 2 is also blown through the space between the central nozzle and the intermediate tube.

This method is more advantageous in the case of large variations in the quantities to be injected when a protective gas such as CgHg (4% of the quantity dO2) is replaced by CC> 2 (20% of the quantity of O ^) , because there are two intermediate and peripheral tubular spaces for injecting such a large increase in gas.

i *! The applicant was also able to note that the ï> [amount of C02 to be injected in this way at the end of ripening was! between 18 and 30% of the amount of oxygen / and preferably between 20% and 24%.

According to another advantageous modality of the method of the invention, pure oxygen is blown through the space between the central tube and the intermediate tube, until the moment when one begins to blow C02 through the space between the intermediate tube and the peripheral tube.

EXAMPLE: for a converter producing 150 tonnes of steel, up to 80% of the total volume of oxygen to be blown is blown, an oxygen flow rate of 550 Nm / min. in the central tube and a natural gas flow rate of 60 Nm / min. in the peripheral tube. Beyond these 80% of the total volume of oxygen to be blown, the flow is maintained at 550 Nm ^ / min. into the central tube and blowing through the peripheral tube 55 Nm ^ / min. of CO2. At the same time, 55 Nm ^ / min are also injected. of CO2 by the space between the intermediate tube and the peripheral tube.

i.

Claims (3)

5.- fc 1. Process for refining cast iron with a converter, in which use is made of a steelworks converter, the bottom of which is provided with a set of blowing nozzles with three concentric tubes, characterized in that one blows d 'on the one hand, from ° 2 Through the central tube and on the other hand, from the protective gas through the space between the intermediate tube and the peripheral tube, and in that the contents of the metal are reduced or by using CO2 as a protective gas at the end of refining, as follows: at the time determined for the blowing of CO ^ at the end of refining, we continue to blow ΙΌ2 only through the central tube and we blow the CO2 by the space between the intermediate tube and the peripheral tube. 2. Method according to claim 1, characterized in that at the time determined for the blowing of CO 2 at the end of refining, it is also blown through the space between the central tube and the intermediate tube. 3. Method according to either of Claims 1 and 2, characterized in that pure oxygen is blown through the space between the central tube and the intermediate tube, until the moment when the 'We begin to blow CO through the space between the intermediate tube and the peripheral tube. 1 - Process according to either of claims 1 to 3, characterized in that the quantity of CO 2 to be injected in this way at the end of ripening is between 18 and 30% of the amount of oxygen, and preferably between 20% and 24%.