Specialized metallurgical processes – compositions for use therei – Processes – Producing or treating free metal
Reexamination Certificate
2001-07-26
2003-02-04
Andrews, Melvyn (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Processes
Producing or treating free metal
C075S530000, C075S553000
Reexamination Certificate
active
06514310
ABSTRACT:
PROCESS FOR INJECTION OF A GAS WITH THE AID OF A NOZZLE
1. Field of the Invention
The present invention relates to the injection of a gas into a liquid, and in particular a liquid metal. More particularly, it relates to the field of metallurgical reactors, such as melting furnaces, converters of pig iron, of alloyed or non-alloyed steels or of non-ferrous materials, as well as the electric arc furnaces used in particular for the production of steel from scrap iron or scrap iron substitutes, and generally to any injection of a gas into a liquid.
2. Description of the Related Art
In the technology of production of steel in an electric arc furnace, scrap iron or its substitutes are melted by establishing an electric arc between the electrodes of the furnace and the metal such as to supply the energy to melt the metal during the melting phase and to keep it in the molten state during the phase of refining the said metal.
During this refining phase, oxygen is used to decarburize the metal and to form a so-called foaming slag by reaction of the oxygen with the carbon produced from the metal or injected at the surface of the metal bath specifically for this purpose.
This injection of oxygen can be carried out with the aid of door lances which are expendable or cooled with water. In this case, the lance is mounted on a mobile component, which involves an employee assigned to its use, and high maintenance. Furthermore, the oxygen is not injected uniformly into the bath, which adversely affects the high performance of the furnace, the metal bath being homogeneous neither in temperature nor in chemical composition.
This injection can also be carried out with the aid of injectors arranged in the wall of the furnace. This arrangement allows the oxygen to be distributed more uniformly in the metal bath and the slag and the thermal yield of the furnace to be increased, which enables the steel production time to be reduced and the air intakes to be reduced due to a better tightness of the furnace (the door of the furnace can be closed due to the omission of the door lance). However, such an injector must be capable of withstanding the high thermal loads without being destroyed prematurely, and capable of injecting the oxygen under conditions such as may be reached in the bath of liquid metal and of penetrating into this. The obvious solution to the person skilled in the art comprises placing the injector of oxygen close to the metal bath to ensure that the oxygen reaches the said bath. However, the closeness of the metal bath causes premature wear of the injector.
To reduce the wear, the person skilled in the art tends to move the end of the lance away from the surface, to the detriment of the penetration of the jet into the liquid metal.
It is known from GB-A 623 881 to use a supersonic injection lance to inject the oxygen at supersonic velocity for the decarburization of steel in a liquid bath. The problem which results from this type of installation is that the jet of oxygen opens out at the exit of the injector nozzle, which reduces the force of penetration of the jet into the bath and increases the risks of splashes.
In order to improve the force of penetration of the jet of oxygen into the metal bath, it is known from Re 33 464, in particular col. 7, lines 32 to 41, to use a supersonic jet of oxygen and to surround this jet with a flame, the envelope of this flame extending substantially up to the surface of the molten metal. Due to the flame surrounding this jet (and its high temperature), such systems are said to be capable of preserving all the coherence of this jet, avoiding disintegration thereof. Such systems are thus said to improve the penetration of the oxygen into the bath.
While in theory it appears obvious to the person skilled in the art that the increase in the temperature around the jet will cause a reduction in the density of the ambient medium and therefore cause an effect of lower resistance of this medium with respect to a cooler medium, which in theory enables the supersonic jet to remain more “coherent”, it has been found, however, that in practice the interactions between the flame and the jet, such as, for example, buoyancy effects, in fact have adverse effects on the jet and reduce the force of penetration. These buoyancy effects are caused by the hot current of a flame in a medium which is colder than this flame. The flame which surrounds the supersonic jet and which passes through a medium at a temperature of about 1500° C., while the temperature of the flame is close to 2300° C. or higher, thus bends upwards, and interacts with the jet during this ascent, in particular in the vicinity of the bath, precisely where it could have been hoped to preserve the “coherence” of the supersonic jet. This coherence is now in fact destroyed.
It is furthermore known that the use of a flame created by a burner in an electrical metallurgy furnace is an effective complement for supplying energy to the charge, and thus increases the rate of melting. The exchange of energy between the flame and the charge is effective as long as the exchange surface is significant, that is to say as long as the scrap iron has not melted, and the temperature difference between the flame and the charge is high.
The process according to the invention enables these disadvantages to be avoided.
SUMMARY OF THE INVENTION
According to the invention, a process is provided for injection of a gas, such as oxygen, with the aid of a nozzle into a liquid metal bath contained in a metallurgical vessel, the said nozzle being installed in the side wall of the said vessel above the metal bath and orientated at an angle &agr; with respect to the perpendicular, the downstream end of the nozzle through which the gas escapes in the direction of the liquid metal bath being situated at a distance L from the surface of the liquid metal, the said nozzle being fed by the gas which penetrates into the nozzle through its upstream end at a pressure P
1
, and being ejected from the nozzle through its downstream end at a pressure P
2
, which process is characterized in that the downstream pressure P
2
of ejection of the gas into the metallurgical vessel and the pressure P
3
in the metallurgical vessel are connected to one another by the relationship:
0.9
P
3
≦P
2≦1.1
P
3
in that the distance L between the downstream end of the nozzle and the surface of the liquid metal is equal to:
L
(meters)=
C*{square root over (qe)}±
0.15
m
Where
C
=
4
π
*
P
2
*
M
[
γ
RTo
(
1
+
γ
-
1
2
M
2
)
]
-
1
/
4
*
[
4.2
+
1.1
*
(
M
2
+
1
-
T
j
T
a
]
ρ
j
ρ
a
Notation:
P
2
: pressure of the jet at the exit (Pa), which must be equal to the pressure in the metallurgical vessel. In the case of an arc furnace, P
2
=10
5
Pa.
M: Mach number calculated according to the following formula:
M
2
=
2
(
γ
-
1
)
*
[
(
P
1
P
2
)
(
γ
-
1
γ
)
-
1
]
(this can be taken between 1.5, corresponding to an upstream pressure P
1
of 3.7×10
5
Pa, and 3.15 for a pressure P
1
of 45×10
5
Pa).
T
o
: temperature of the gas (K) (in general 294K)
R: ideal gas constant (8.314/molar mass of the gas),
qe: mass flow rate (kg/s)=volume flow rate (Sm
3
/h)*molar mass of the gas/3600/0.0224 (l/mol)
T
j
: temperature at the exit of the nozzle (K)
&rgr;
j
: density of the jet at the exit of the nozzle (kg/m
3
), calculated from:
P
2
R
*
T
j
T
a
: temperature of the ambient medium (K)
&rgr;
a
: density of the ambient medium (kg/m
3
), calculated from:
P
3
R
*
T
a
and in that the injection of gas is carried out when the temperature of the gases in the metallurgical vessel is greater than 800° C., preferably 1000° C.
The gas injected will preferably be chosen from oxygen, nitrogen, argon, hydrogen, carbon monoxide, carbon dioxide, hydrocarbons and, in particular, alkanes, alkenes and alkynes, natural gas and sulphur hexafluoride, these gases being injected by themselves or as mixtures.
According to a preferred embodiment, the velocity of the gas during its ejection by
Allemand Bruno
Champinot Christel
Flichy Sabastien
Laurent Jacky
Melen Stéphane
Andrews Melvyn
L'Air Liquide Societe Anonyme a Directoire et Conseil de Su
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