US3415968A

US3415968A - Gas heating apparatus

Info

Publication number: US3415968A
Application number: US553182A
Authority: US
Inventors: Watson William Stanley
Original assignee: British Titan Products Co Ltd
Current assignee: British Titan Products Co Ltd
Priority date: 1965-06-02
Filing date: 1966-05-26
Publication date: 1968-12-10
Anticipated expiration: 1985-12-10
Also published as: DE1264640B; GB1091498A

Description

Dec. 10, 1968 w. s. WATSON GAS HEATING APPARATUS Filed May 26, 1966 FiG.i

United States Patent ABSTRACT OF THE DISCLOSURE An improvement in an apparatus for the production of gaseous plasmas by induction heating is disclosed. A baffie having peripherally positioned, angularly disposed apertures, is positioned between the gas-feeding means and the induction heating zone to provide streams of gas flowing in a helical path.

The present invention relates to improved apparatus and process for the production of hot gas plasmas by means of induction heating.

The production of hot gaseous plasmas, i.e. gases heated to very high temperatures (usually by electrical energy) and which contain a substantial proportion of active species such as thermally dissociated molecules and/or ions produced by the removal of electron(s) from the molecules, by means of induction heating is known and t has been described, for example, in our co-pending applications 256,386 and 506,109.

In such processes the gas which is to be heated to form the plasma is passed through a refractory (and generally electrically-non-conducting) gas-confining tube around which is a coil of electrically-conducting material.

When the process is in operation the gas which is to be heated is passed through the gas-confining tube and an oscillatory current of suitable power and frequency is passed through the coil surrounding the tube. An electric discharge is induced in the gas (after initiation) by this means and a hot luminous gaseous plasma ball is formed within the gas-confining tube beneath the coil around which the oscillatory current is passed. Where a continuous flow of gas is passed through the confining tube gas heated to a very high temperature is discharged from the outlet from the tube.

Difliculty may be experienced in stabilising the plasma so that its existence is maintained, for example, under varying conditions of gas flow and/ or composition of the gas (e.g. when a mixture of gasses is present in the plasma).

It is an object of the present invention to provide an apparatus and process whereby improved stability is obtained.

Accordingly, the present invention is an apparatus for the production of gaseous plasmas by induction heating comprising a gas-confining tube surrounded by an electrically conducting element, the ends of which are adapted for connection to a source of oscillatory current and containing within the upper end of the gas-confining tube a bafile plate, the peripheral edge of which is provided with a number of apertures which are so formed as to divert the flow of gas over the baffle into streams of gas following a substantially helical path within the gas-confining tube.

The gas-confining tube is normally made from a refractory and substantially electrically non-conducting material, for example silica, at least as far as that portion which encloses the plasma is concerned. It is, however, possible to form the tube from other material, for example an electrically conducting material such as a metal, providing steps are taken to prevent its acting as a susceptor. One

3,415,968 Patented Dec. 10, 1968 method of preventing this is by the insertion of one or more strips of insulating material longitudinally in the wall of the tube, and/or by limiting the thickness of the wall of the tube. Metal gas-confining tubes of this type are described, for example, in our co-pending application 506,109.

The electrically conducting element may conveniently consist of a copper tube formed into a coil around the exterior of the gas-confining tube. Generally, a space is left between the exterior of the tube and the element and each turn of the coil is spaced apart from the adjacent turn (s).

The number of turns in the coil may vary as desired but is preferably at least 3, and particularly at least 5. If desired, the upper and/or lower turn of the coil (in the direction of the gas flow) may be so formed as to conduct electricity in the reversed direction to the adjacent coil in order to provide a magnetic field which assists in confining the plasma to the volume within the coil.

During operation of the apparatus a cooling fluid, for example water, may be passed in heat exchange relationship with the electrically conducting element to prevent its overheating.

The ends of the electrically conducting element are adapted for connection to a suitable source of oscillatory current. A source providing a power of at least 3 kilowatts and preferably at least 8 kilowatts at a frequency from about 10 kilocycles/sec. to about megacycles/ sec. and particularly frequencies in the range 25 kilocycles/sec. to 10 megacycles/ sec. has been found very suitable for use in the process of the present invention.

The baflie plate in the upper part of the gas-confining tube (in the direction of gas flow through the tube) is preferably a substantially circular plate across the tube (i.e. the diameter of which is at right angles to the longitudinal axis of the tube) and generally of slightly smaller diameter than the internal diameter of the tube containing it.

It is preferred to make the baflie from material having good heat conducting properties, for example copper, in order that the heat radiated from the plasma can be dissipated.

The periphery of the bafl'le is provided with a number of apertures, preferably spaced equidistantly. The number of such apertures will depend upon the circumference of the baflle plate since they are preferably spaced at intervals of about /2" and there are generally at least 4 and preferably at least 8 such apertures.

The apertures are so shaped that they divert a stream of gas flowing over the baffle (and over the edges thereof) into streams which follow a substantially helical path within the gas-confining tube. One method of achieving this is to make the apertures in the form of slots and to bend the corresponding edge of each of the slots at an angle to the plane of the baffle. Generally, where this method is used, the edge of the slot may be bent downwardly (i.e. in the direction of gas flow) at an angle between about and 60, particularly between 40 and to the plane of the bafile. A baffle of this type is described, for example, in the accompanying drawings.

In addition to the apertures around the periphery of the bafile it may also be desirable to provide an aperture in the centre of the baflle, through which can be introduced fluids and/ or finely-divided solids, as desired, into the plasma.

One convenient method of suspending the baffle in the gas-confining tube is to fix it to a rod or tube which is, in turn, fixed to a cap or similar structure at the top of the gas-confining tube. Where the baffle is supported on a tube (as opposed to a rod) this may pass through the baffle and its upper end may pass through the cap on the gas-confining tube, thus providing a conduit leading to the aperture through the baffle for the introduction of fluids and/or finely-divided solids into the plasma.

It has been found during operation of the present invention that a back pressure is created upon the battle by the expansion of the gas when this is rapidly heated on contact with the plasma. The effect of this may be reduced, when necessary, by providing one or more additional apertures through the bafile, for example consisting of holes drilled through the baffie between the centre and periphery. These holes are preferably placed equidistantly on a line concentric with the centre of the baflle.

The gas, for example an inert gas, oxygen or a metal halide, which flows over the baflle and through the apertures around the periphery may be introduced into the gas-confining tube by any convenient method. One method which has been found to be very suitable particularly when the gas-confining tube is provided with a cap at its upper end, is to introduce the gas through a pipe or pipes set in the cap. Two or more pipes are preferred which are so positioned as to direct the flow of gas on either side of an imaginary plane passing through the longitudinal axis of the gas-confining tube, for example as shown in the accompanying drawings.

It is believed that by the use of a bafile plate according to the present invention the flow of gas is so directed i.e. as a number of streams following a substantially helical path within the gas-confining tube that greater stabilisation of the plasma is obtained than has been possible hitherto and that greater variations can be tolerated in the flow rates and/or variation in gas composition without extinguishing the plasma.

In the drawings accompanying this specification FIG- URE 1 is a diagrammatic longitudinal section of an apparatus according to the present invention and FIGURE 2 is a plan view of the bafile plate.

Referring to FIGURE 1 the gas which is to be heated is introduced into the gas-confining tube 1 through inlets 2 and 3. The upper part of the gas-confining tube is enclosed by a copper cap 4, the lower end 5 of Which is internally threaded to engage with the externally threaded centre portion 6 of the brass cap 7. Between these threaded portions of copper cap and brass cap are placed a brass insert 8 and a silicone O-ring 9 to form a fluid tight seal with the gas-confining tube.

The outer rim of the brass cap is threaded to engage with internal threads at the upper end of a Perspex cylinder 10. The brass cap is provided with an outlet 11 for coolant and an inlet for the coolant 12 is also provided in the wall of the Perspex cylinder.

Around the exterior of the gas-confining tube is wound copper tubing 13 which is coated with polyvinyl chloride. The ends of the copper tubing pass through the walls of the Perspex cylinder and are provided with means for (a) Connection to a source of oscillatory current of the appropriate frequency, and,

(b) Passing a fluid coolant such as water through the tube.

The lower end of the Perspex cylinder is similarly provided with a brass cap 14 through which the gas-confining tube projects. A fluid tight seal is provided between the brass cap and the lower end of the gas-confining tube.

In the upper end of the gas-confining tube is fixed bafile support tube 15 to which bafile 16 is attached.

The periphery of baffle 16 is provided with apertures 17 spaced equidistantly and formed by cutting radial slots in the battle and thereafter bending downwardly the corresponding sides of the slots to an angle of 45 to the plane of the baflle.

Referring to FIGURE 2, this shows the bafile 16 and apertures 17. There are also shown holes 18 equidistantly spaced on a line concentric with the centre of the baflle and approximately halfway between the centre and the periphery of the baflle. These holes serve to reduce back pressure upon the baflle when the apparatus is in use.

Example I A device similar to that described above was set up in which the gas-confining tube consisted of a silica tube 1 ID. and 1 OD. and 15" in length. The bafile plate was made of copper and was 1 in diameter. Eight apertures were formed around the edges by cutting radial slots 4;" deep and by bending downwardly the corresponding edges to an angle of The bafile plate was also provided with 3 holes /33" diameter.

The baffle plate was fixed from the lower end of the bafile plate supporting tube which was 7 OD. and this was introduced into the gas-confining tube in such a manner that the baffle plate was held horizontally in the gas-confining tube A from its upper end.

The copper tubing forming the coils was ID. and 6 coils were provided, each coil being about 7 apart.

Cooling water was passed through the interior of the Perspex cylinder through the copper tube. Argon was introduced through the inlet (which were at an angle of to the top of the device) at a rate of 40 l.p.m. and through the interior of the baffle support tube at a rate of 10 l.p.m.

An oscillatory current having a frequency of 5.3 megacycles/sec. and a power of 8 kilowatts was supplied to the ends of the copper tube and a plasma discharge was initiated in the gas-confining tube beneath the coils. The flow of argon was then gradually replaced by oxygen l.p.m. through the inlets and 24 l.p.m. through the bafile support tube) and the power was introduced to 36 kilowatts.

The device operated smoothly during the change-over and for a prolonged period thereafter with markedly greater stability than had been experienced under similar conditions in the absence of a battle plate.

Example 2 The process as described in Example 1 was repeated using an oscillatory current having a frequency of 5.3 megacycles/sec. and a power input of 36 kilowatts.

The stability of the device in operation was shown by varying the rate of gas flow through the angled inlets between 20 and 200 litres/min. and that through the baffle support tube between 5 and 40 litres/min. while maintaining the plasma in the gas confining tube.

What is claimed is:

1. In an apparatus for the production of gaseous plasmas comprising a gas-confining tube, an electrically conducting element in surrounding relation to said gasconfining tube adapted for the induction heating of gases within said gas-confining tube when said electrically conducting element is connected to a source of oscillatory current, and means associated with said gas-confining tube for feeding gases into said gas-confining tube and into the induction heating zone formed within said gas-confining tube by said electrically conducting element, the improvement which comprises bafile means positioned within said gas-confining tube between said gas-feeding means and said induction heating zone, said baffie means provided with peripherally positioned, angularly disposed apertures adapted to divert the flow of gas from said gas-feeding means into streams of gas of substantially helical flow path into said induction heating zone within said gas-confining tube.

2. An apparatus as claimed in claim 1 wherein the baffle means is a circular plate positioned with the diameter substantially at right angles to the longitudinal axis of the gas-confining tube.

3. An apparatus as claimed in claim 1 wherein said bafile means comprises a baflie plate having at least 8 apertures in the peripheral edge thereof.

4. An apparatus as claimed in claim 1 wherein the baflle apertures are formed from peripheral slots by bending the corresponding edges of the slots to form an angle of between 30 and 60 with the plane of the baffle.

5. An apparatus as claimed in claim 4 wherein the angle between the edge of the slot and the plane of the baffle is between 40 and 50.

6. An apparatus as claimed in claim 1 wherein said bafiie means is additionally provided with apertures between the center and the periphery thereof.

7. An apparatus as claimed in claim 1 wherein said baflie means is additionally provided with a central aperture.

8. An apparatus for the production of plasma heating comprising in combination, a gas-confining tube; an electrically conducting element comprising copper tube coiled in surrounding relation to said gas-confining tube with at least three coils surrounding a portion of said gas-confining tube, the ends of said copper tube connected to a current source; feeding means associated with one end of said gas-confining tube adapted for feeding gas into said gas-confining tube and into the portion of said gasconfining tube surrounded by said coils; and bafiie means positioned between said gas-feeding means and the portion of said gas-confining tube within said coils, said bafile means provided with at least 8 apertures formed from peripherally positioned slots by bending corresponding edges of the slots to form an angle between 30 and 60 with the plane of the bafile.

9. An apparatus as claimed in claim 8 wherein said UNITED STATES PATENTS 2,686,621 8/1954 Horn et al. 21910.65X 3,108,169 10/1963 Keller 21910.79 X 3,114,626 12/1963 Dombrowski et al. 219-1065 X 3,277,265 10/1966 Reboux 219-10.65 X

RICHARD M. WOOD, Primary Examiner.

L. H. BENDER, Assistant Examiner.

US. Cl. X.R. 21910.43