Electric heating – Metal heating – By arc
Patent
1994-08-12
1996-01-02
Paschall, Mark H.
Electric heating
Metal heating
By arc
21912147, 21912149, 21912151, 31511121, B23K 1000
Patent
active
054810809
DESCRIPTION:
BRIEF SUMMARY
Cross reference to related applications; this application is related to co-pending applications Ser. Nos. 08/244,297 filed May 26, 1994, pending; 08/244,298 filed Sep. 22, 1994, pending; 08/307,835 filed Nov. 7, 1994; 08/244,296 filed Dec. 21, 1994, pending; 08/313,301 filed Dec. 22, 1994; 08/307,836 filed Dec. 22, 1994, pending; 08/307,834 filed Dec. 22,1994; 08/244,295 filed Dec. 29, 1994; 08/244,300 filed Jan. 10,1995 and 08/454,116 filed Jun. 2, 1995.
FIELD OF THE INVENTION
The present invention concerns a lead-in tube for the supply of a reactant to a plasma torch. The plasma torch is used for the chemical treatment of a reactant, and it can be supplied with both plasma-forming gas and reactant.
BACKGROUND OF THE INVENTION
From Norwegian patent no. 164 846 there is known an electrically insulated supply tube for admixtures, which is provided centrally in an internal electrode in a plasma torch designed for submersion in a metallurgical smelt.
In U.S. Pat. No. 4 122 293 there is described an external liquid-cooled supply tube for the supply of gas, admixture and electric current to a hollow electrode which is used in an electric arc smelting furnace.
Furthermore, EP 0 178 288 describes a nozzle for a plasma torch specially designed for heating a metallurgical melting pot. The nozzle has an electrode tip attached to a liquid-cooled electrode holder which simultaneously acts as a supply tube for plasma-forming gas and electric current. The electrode tip has a central boring for the plasma-forming gas and the outlet of the boring is designed first as a Laval nozzle and thereafter as a diffuser to permit the gas to be sprayed when it leaves the electrode.
GB 995 152 describes an electric arc torch for a cutting apparatus which emits a jet of gas heated to a very high temperature by means of an electric arc which is struck between a torch body and a workpiece. The torch body consists of one elctrode within an arcing chamber and the exit end of the cutting gas supply pipe can be provided with a venturi nozzle. However, the nozzle is not replaceable.
From U.S. Pat. No. 4 275 287 is known a water-cooled lead-in tube for supply of a reactant to a plasma torch. The lower pare of the lead-in tube is removable in order to facilitate replacement when it is worn after use. However, the lead-in tube is not movable.
During chemical treatment of a reactant, for example during pyrolysis, it is essential that the gas has the correct temperature when it reaches the plasma flame. If the temperature of the gas exceeds a certain value it will react too early. This is undesirable as decomposition products can be formed before the gas reaches the plasma flame, and this can lead to precipitation of such products in the lead-in device and on the electrodes.
It has been found that the known designs of supply devices for gas produce unsatisfactory results when used in a plasma torch which is utilized for chemical treatment of reactant.
SUMMARY OF THE INVENTION
Thus it is an object of the present invention to provide a lead-in device wherein the required temperature and correct rate of reactant supplied to such a plasma torch are achieved.
This object is achieved by a lead-in tube which is characterized by the features in the claims presented.
The plasma torch is composed of tubular electrodes located coaxially inside one another. In its simplest form the torch consists of two electrodes, an external electrode and an internal electrode. The plasma torch can also be provided with more electrodes.
The electrodes can be hollow, provided with cooling channels for the transport of a coolant. All types of solid materials with good thermal and electrical conductivity can be used for liquid-cooled electrodes.
It is preferable to use solid electrodes. Solid electrodes are usually constructed of a material with a high melting point and with good conductivity, such as graphite.
The reactant is fed in through a separate lead-in tube located coaxially in the internal electrode.
The term reactant refers to pure gas or gas mixed with liq
REFERENCES:
patent: 4275287 (1981-06-01), Hiuratake
patent: 4924061 (1990-05-01), Labat et al.
patent: 5103072 (1992-04-01), Eikeland et al.
patent: 5285046 (1994-02-01), Hansz
Haugsten Kjell
Hox Ketil
Hugdahl Jan
Lynum Steinar
Kvaerner Engineering A.S.
Paschall Mark H.
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