WO1997002366A2

WO1997002366A2 - Method and apparatus for after-burning atmospheric gases in a steel smelting arc furnace

Info

Publication number: WO1997002366A2
Application number: PCT/US1996/011126
Authority: WO
Inventors: Vladimir Alexandrovich Arutyunov; Alexander Yakovlevich Stomakhin; Alexei Varnavievich Yegorov; Vladimir Ilyich Lebedev; Vladimir Andreyevich Romenets; Valery Sergeyevich Valavin; Dmitry Dmitriyevich Kozlov; Gennady Borisovich Beremblum; Valentin Andreysvich Breus; Boris Anatolievich Chumarin; Oleg Petrovich Lopatin
Original assignee: Air Products And Chemicals, Inc.
Priority date: 1995-07-06
Filing date: 1996-06-28
Publication date: 1997-01-23
Also published as: WO1997002366A3; RU95111684A; RU2084542C1

Abstract

Method and apparatus for introducing oxidizing gas, e.g. oxygen into the atmosphere of an electric arc furnace to effect post combustion (after-burning) of gases in the atmosphere and provide a radiant heat source (18, 36) inside the furnace. The apparatus (10, 70) has a generally cylindrical shaped with a first end (34) for introducing oxidizing gas tangentially (54, 56) inside the apparatus (radiant injector) (10, 70) and a second end or exit portion (32) having a flared opening (36) to discharge swirling oxidizing gas into the furnace. The apparatus (10) is refractory or has a refractory coating on the surfaces which are exposed to the furnace atmosphere and which when further heated become a radiant heat source in the furnace.

Description

METHOD AND APPARATUS FOR AFTER-BURNING ATMOSPHERIC GASES IN A

STEEL SMELTING ARC FURNACE

FIELD OF INVENTION

The invention concerns the field of metallurgy, more specifically, equipment for the post combustion of the atmosphere gases in steel smelting arc furnaces.

BACKGROUND OF THE INVENTION

The term "post combustion" is also known in the art as "after-burning". Therefore, these terms will be used interchangeably in this application.

A known method for post combustion of combustible components in the atmosphere in steel smelting vessels includes, feeding a jet of oxygen through an oxygen lance into the working space of the steel smelting unit (vessel) above the level of the metal in the vessel. In this method, the oxygen is fed through an apparatus having several rows of outlets in the form of jets which are aimed in a direction which is inclined with respect to the horizontal plane. The outlets are positioned at different levels in the vessel or furnace.

The apparatus includes an oxygen lance in the form of concentric pipes for the introduction of oxygen into the vessel, and for providing cooling water for the apparatus. At the discharge end of the lance apparatus and extending along its length, blowholes are positioned for the oxygen, in the form of jets, to exit the lance. Such a device is shown by E.D. Merker in his publication "Gas Dynamic Protetiion ofthe Blasting Zone in Steel Smelting Installations," Moscow, Metallurgiya, 1994, at page 20, Figure 5.

A disadvantage of using the known device is the low efficiency seen in both the process of post combustion (after-burning) of the gases evolving in the steel smelting unit and in the creation of a gas dynamic curtain.

Due to the fact that the jets are discrete entities, the necessary intermixing of the furnace atmosphere with the oxygen jets does not take place. Moreover, when the known method and device are used, the heat evolving during the after-burning of the combustible components is not returned to the molten metal. The discrete feeding of oxygen in separate jets does not create a continuous gas dynamic curtain over the metal bath. Under these conditions, the efficiency of after-burning of the combustible components will not exceed 50-60%.

US Patents 5,050,848 and 5,051,127 disclose an apparatus and method for post combustion over a molten bath using a swirling gas flow by means of one or more tuyeres directed at the surface of the metal.

US Patent 5,166,950 discloses a process for post combustion (after¬ burning) in a metallurgical furnace.

European Patent Publication 0 544 044 A1 discloses another post combustion process.

SUMMARY OF THE INVENTION

A method and apparatus for introducing oxidizing gas into an electric arc steel making furnace to effect after-burning (post combustion) of combustible gases contained above the metal in the arc furnace. A device (radiant injector) in the form of an open top cylinder having a flared open end is disposed in the roof of the electric arc furnace so that the flared end is directed to or pointing at the metal to be melted or molten metal contained in the hearth portion of the furnace. An oxidizing gas, e.g. pure oxygen, is introduced into the cylindrical portion of the device through tangential openings in the wall of the cylinder so that the oxidizing gas is swirled inside of the cylindrical portion of the device. As more oxidizing gas is introduced into the device, the oxidizing gas expands downwardly and outwardly along the flared surface of the device into the furnace to mix with the furnace atmospheric gases for post-combustion of the combustible gases contained in the furnace atmosphere. Combustion of these gases causes the internal surfaces of the device to become further heated and the device itself becomes a radiant heat source for the interior of the electric arc furnace. The device can be manufactured from a high temperature refractory material or can be fabricated from a metal with the surfaces exposed to the furnace atmosphere coated with a high temperature refractory material. The device can be equipped for water cooling. The device can be incoφorated into the roof or the wall of the furnace when the furnace is first built or relined or rebuilt after use. An opening in the form of an inverted funnel can be formed in the furnace roof or wall to facilitate installation of the device and act as an extension of the device. The roof or wall opening is such that the device according to the invention is deployed in a generally cylindrical portion of the roof opening disposed above the funnel shaped opening.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a fragmentary longitudinal section showing the device of the present invention installed in an electric arc furnace.

Figure 2 is a view taken along lines 2-2 of Figure 1. Figure 3 is a section taken along line 3-3 of Figure 1.

Figure 4 is a fragmentary cross-sectional view of the device of the present invention shown in association with the electrodes in an arc melting furnace.

Figure 5 is a view taken along lines 5-5 of Figure 4.

DETAILED DESCRIPTION OF THE INVENTION

Referring to Figure 1, radiant injector 10 according to the present invention is shown disposed in the roof of electric arc furnace 12 wherein the roof consists of metal shell 14 having disposed therein refractory lining 16 as is well known in the art. Refractory lining 16 is provided with opening 18 in the shape of an inverted funnel wherein the flared portion of the funnel is directed inwardly into the furnace. The flared portion of funnel 18 terminates in a cylindrical portion 20 which extends through refractory 16 and furnace shell 14.

Radiant injector 10 is disposed in opening 20. Radiant injector 10 includes a cylindrical portion 30 in the shape of a shallow cylinder having one closed end. Disposed on the open end of cylindrical portion 30 is exit portion 32 which has cylindrical first section 34 and flared opening 36. Radiant injector 10 is made so that, when it is installed in furnace 12, flared end 36 of radiant injector 10 mates with refractory 16 so that there is one continuous smooth surface from the interior of radiant injector 10, via surface 36 and surface 18, to the interior of furnace 12.

Radiant injector 10 is adapted to be water cooled via water inlet pipe

38 and water outlet pipe 40 through suitable internal passages 42 and 44 as is well known in the art. Pressurized cooling water enters radiant injector 10 through conduit 38 circulates through passage 42 and then through passage 44 and exits from radiant injector 10 via conduit 40. If necessary, stiffening ribs or spacers 41 can be used to define the water jacket for radiant injector 10.

Radiant injector 10 includes first oxidizing gas inlet 46 and second oxidizing gas inlet 48 which communicate with passages 50 and 52 in radiant injector 10. Passages 50 and 52 terminate in elliptical shaped ports or openings 54 and 56 in the wall of cylindrical first section 34 of exit section 32 of radiant injector 10.

In operation, when the radiant injector 10 of Figure 1 is installed in the roof or crown of the electric arc furnace, cooling water is introduced into the device as is well known in the art. Oxidizing gas, e.g. pure oxygen, is introduced into radiant injector 10 through conduits 46 and 48 passages 50 and 52 and outlets or apertures

54 and 56. Oxidizing gas exiting apertures 54 and 56 does so tangentially to the wall of cylindrical part 30 of radiant injector 10. A swirling motion is imparted to the oxidizing gas and, as additional gas enters the radiant injector 10, the swirling gases expand downwardly and outwardly from radiant injector 10 through the opening in the roof of the furnace. The swirling expanding gases cause intimate mixing of the oxidizing gas with the furnace atmosphere to effect combustion of combustible gases in the furnace atmosphere. Combustion of these gases further heats surface 18 of the furnace roof as well as surface 36 of radiant injector 10. These heated surfaces become radiant heat sources for directing heat into the furnace toward the metal. Of course, one or more radiant injectors 10 can be built into the roof or wall of the furnace.

The presence of cylinder portion 30 with its closed end at the top of radiant injector 10 in the crown or roof of the furnace prevents the entrainment of gases from the space above the cylinder. Referring to Figures 4 and 5, identical reference numerals are used to identify similar functioning parts. The difference between the embodiment of Figures 1-3 and the embodiment of Figures 4 and 5 is the fact that radiant injector 70 is made so that it does not have a closed end. Radiant injector 70 has open top 72 so that radiant injector 70 can be disposed around furnace electrodes 74, 76 and 78. In the device of Figures 4 and 5, cylindrical baffle or annular screen 80 is disposed between the interior portion of radiant injector 70 and electrodes 74, 76 and 78. The oxidizing gas, introduced through conduits 38, 40, exits ports 54, 56 in the same manner to cause the oxidizing gas to swirl around the sleeve or screen 80 and exit radiant injector 70 in the same manner as the swirling oxidizing gas exits radiant injector 10 in Figure 1.

An increase in the efficiency of the process of post combustion (after¬ burning) of the combustible components of the atmosphere in the steel smelting arc furnaces will take place as a result of the creation of a continuous gas dynamic curtain from oxygen in the form of a fan-like jet over the metal in the furnace bath. In this case, intensive catalytic combustion of the carbon monoxide and hydrogen occurs on the surface of the radiant injector and the depression in the refractory. Moreover, intensive radiation onto the metal from the surface of radiant injector 10, 70 and depression 18 occur. Under these conditions the discrete spectrum of the gas radiation from carbon dioxide and water molecules is transformed into a continuous spectrum of radiation from the surface of the radiant injector and depression. The swirling tangentially guided jets of oxygen create the necessary vacuum in the axial region of the radiant injector and the depression, thus assuring significant inflow of the combustible components of the furnace gases toward the stream of oxygen on the inner surface of the diffuser. The method and apparatus for a steel smelting arc fumace could be operated as follows.

Radiant injector 10 would be installed in the roof or crown of the fumace for the purpose of post combustion (after-burning) of the combustible components of the atmosphere forming in the working space of the fumace above the metal. Pressurized oxygen would be fed to inner cylindrical surface 20 of radiant injector 10 along the tangent to the horizontal plane.

A number of radiant injectors, typically, between 2-8, could be placed in the crown of the fumace. These could be uniformly distributed in the crown (roof of the fumace) or around the electrodes.

The inner surface of radiant injector 10 can be covered with refractory material which was formed by plasma spray coating or any other known coating technique.

Radiant injector 10 can be made from refractory material such as corundum, mullite-corundum or periclase chromite. The angle made by opening 18 in refractory lining 16 inside roof 12 and flared opening 32 in radiant injector can be between 140-179°. For example, the inner diameter of the cylinder portion of radiant injector 10 can be 200 mm, its height 200 mm, and the cross-section of passage 50 leading to openings 54 and 56 can be 5-80 mm.

When oxygen is fed tangentially through openings 54 and 56 to the inner cavity of radiant injector 10, a swirling jet of oxygen is formed which, on exiting from cylindrical portion 20 of radiant injector 10, as a result of gas dynamic laws (centrifugal force and the Coanda effect) spreads out in a continuous layer over surface 32 of radiant injector 10 and surface 18 of refractory 16 of roof 12 creating a continuous gas curtain above the metal in the fumace. At this time, in radiant injector 10 and opening 18 in roof refractory 16, the created vacuum leads to the entrainment of the atmosphere containing combustible components into the oxygen gas. The velocity of oxygen exiting passages 46 and 48 is 150-250 meters per second (m/s). As the mixture of oxygen and combustible components from the fumace atmosphere moves along surface 36 of radiant injector 10 and roof opening 18 combustion takes place. Under these conditions, the body of radiant injector 10 and the surface of roof opening 18 radiate and reflect radiant energy in the direction of the metal and the slag in the fumace, thereby increasing their temperature. The gases flowing from roof opening 18 strike the peripheral part of the fumace bath. The gas layer of the burning mixture also reflects spatters of Iiquid metal and slag in the direction of the bath containing the metal.

In the case when a diffuser is positioned on the axis of the fumace crown (Figure 4 and 5), annular screen or baffle 80 is made from metal, e.g., stainless steel which serves to protect electrodes 74, 76 and 78 against the jets of oxygen emerging from openings 54 and 56. The size of the gap between cylindrical portion 20 and annular screen 80 can typically be between 5 and 200 mm.

When there are insufficient quantities of combustible gases in the fumace atmosphere an outside fuel, e.g. natural gas can be mixed with the oxidizing gas in the radiant injector so that the radiant injector is maintained as radiant heat source. The fuel can be introduced in any known manner, such as by a pipe disposed inside passage 54 or 56 or both, or via a separate pipe terminating inside cylindrical portion 30.

The use of the apparatus permits an increase in the efficiency of the after-burning of the combustible components of the atmosphere in steel smelting installations by thirty to forty percent (30-40%). The industrial benefit resulting from the application of the invention is increased efficiency of the process of after-buming of the combustible components of the atmosphere in the steel smelting installation and also higher efficiency of the transfer of the evolving heat to the metal.

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Claims

1. A device for effecting post combustion of combustible gases present in an electric arc fumace comprising:

a generally cylindrical housing having a first or oxidizing gas entry end and a second or discharge end, said open end terminating in flared discharge opening said flared opening having a generally smooth surface; and

means to introduce an oxidizing gas proximate to said first end of said housing tangentially to an interior wall of said housing; whereby a swiriing motion is imparted to the oxidizing gas so that said swirling oxidizing gas expands and exits said device to effect mixing and combustion of oxidizing gases with said fumace atmosphere gases and heating of exposed surfaces of said device to provide radiant heat to said fumace.

2. A device according to Claim 1 wherein said flared opening has an opening angle between 140° and 179°.

3. A device according to Claim 1 wherein said flared opening is disposed in a conical opening in the roof of an electric arc fumace.

4. A device according to Claim 1 fabricated from metal wherein surfaces of said device exposed to said fumace atmosphere are coated with a high temperature refractory material.

5. A device according to Claim 1 including means for water cooling the device during use.

6. A device according to Claim 1 wherein said first or gas entry end of said device is adapted for placing in the roof opening around one or more electric arc fumace electrodes.

7. A device according to Claim 6 wherein a baffle is disposed between said electrode or electrodes and an inner surface of said entry end of said device.

8. A device according to Claim 1 adapted to introduce fuel along with oxidizing gas into said device.

9. A process for post combustion of gases in an electric arc fumace used to melt metals comprising the steps of:

installing at least one radiant injector in said fumace said radiant injector having the general shape of cylinder with one closed end and one flared open end, with said flared open end directed into said fumace toward a hearth portion of said fumace;

introducing an oxygen containing gas tangentially into said radiant injector proximate to said closed end;

continuing flow of said oxygen containing gas in order to create a swirling flow of oxygen containing gas exiting outwardly from said flared end of said radiant injector, whereby said oxygen containing gas reacts with atmospheric gases in said fumace and said radiant injector becomes heated and radiates heat into said fumace.

10. A process according to Claim 9 wherein said radiant injector flared opening is manufactured with an opening angle between 140 and 179°.

11. A process according to Claim 9 including the step of installing a plurality of radiant injectors in said fumace.

12. A process according to Claim 9 including the step of introducing fuel into said radiant injector to maintain the temperature of said inner surface of said radiant injector during periods when the quantity of the combustible gases is diminished.