US2582903A

US2582903A - Device for producing chemical reac

Info

Publication number: US2582903A
Authority: US
Publication date: 1952-01-15
Anticipated expiration: 1969-01-15

Description

Jan. 15, 1952 GUANELLA ETAL 2,582,903

' DEVICE FOR PRODUCING CHEMICAL REACTIONS IN A FLOWING GAS BY ELECTRICAL MEANS Filed Aug. 8, 194';

Patented Jan. 15, 1952 DEVICE FORLPRODUCING CHEMICAL REAC- TIONS IN A FLOWING GAS BY ELECTRI- CAL MEANS Gustav Guanella, Zurich, and Otto Albert Lardelli, Baden, Switzerland, assignors to Aktiengesellschaft Brown, Boveri & Cie., Baden, Switzerland Application August 8, 1947, Serial No. 767,540

. In Switzerland August 19, 1941 Section 1, Public Law 690, August 8, 1946 Patent expires August 19, 1961 2 Claims.

The production of chemical reactions with the,

high temperatures due to dissociation. Various ways are known of avoiding the aforementioned heating. By means of magnetic fields, a direct currentand low frequency are is for instance made to wander and is extended, whereby the heating is considerably reduced. By reducing the gas pressure and thus the electrical current it is possible to achieve a low-power form of a glow discharge. It has also been proposed to feed the arc with high frequency. With the high frequency devices known up to the present it is..

however, impossible to increase the yield in a technically satisfactory manner. The known devices of this kind have the disadvantage that the electrodes are arranged unfavourably and have an unsuitable shape, so that the'desired kind of discharge does not occur. Furthermore the very pronounced reactive currents occurring at high frequencies produce an unfavourable load on the generator.

The aforementioned disadvantages are now avoided by the present invention which concerns a device for producing chemical reactions in a flowing gas by means of high frequency electrical discharges. According to the invention this is achieved by forming a reaction chamber in which, by means of a suitable shape and-arrangement of the electrodes, a space is filled by a discharge which is as far as possible uniform, the main part of the gas flowing through this space, and furthermore places of high discharge density being avoided or lying practically outside of the reaction chamber.

The invention is explained in greater detail by means of the constructional examples shown in accompanying drawings, in which:

Figs. 1, 2 and 3 are fragmentary central sections through reaction chambers embodying the invention, each view showing a different arrangement of electrodes for establishing high frequency electrical discharges,

Figs. 4 and 5 are fragmentary central sections through single and multiple reaction chambers in which auxiliary electrodes are employed,"

Fig. 6 is a transverse section through another embodiment of the invention "in which electromagnetic excitation is employed,

electrode R. and the high frequency source.

Fig. 7 is a transverse section through a cylindrical reaction chamber in which there is a central electrodeand acylindrical array of cooperating electrodes,

Fig. 8 is a section, parallel to the path of the gas, of an electrode system comprising two cylindrical electrodes,

Fig. 8a is a fragmentary section at right angles to Fig. 8,

Figs. 9, 10 and 1011 are schematic sections through reaction chambers comprising cavity resonators ofdifferent form, and

Figs. 11 and 12 are transverse sections showing other types of electrode assemblies embodying the invention. V

In several of the views, arrows indicate the direction of flow of the gas through the reaction chambers and the high-frequency electrical discharge spaces or zones therein. The rate of flow or velocity of the gas stream is selected for optimum performance of the particular reaction to be effected, but any elongation or rotation of the electrical discharge by a gas stream of high velocity is purely incidental.

In Fig. 1, the reference character I identifies the cylindrical insulating wall of a reaction chamber in which a centrally located electrode M is spaced axially from a cooperating nozzle electrode D. A source of high frequency voltage HF is connected between the electrodes M and D. As can be seen in Figure 1 the gas is forced to penetrate the high frequency discharge between the centre electrode M and the nozzle D, whereby the discharge is extended upwards in a mushroom-like fashion so that adequate impact ionisation with comparatively small heating occurs. As a result of the skin effect at high frequencies the discharge is uniformly distributed over the entire vcircumference. of the nozzle and has the general form of a surface of revolution.

Whilst the constructional form shown in Figure 2 does not show any important changes when compared with that of Figure 1-thcre is a cen tral electrode M within and projecting above the nozzle electrode and an annular electrode B. through which the main part of the gas flows. As in Fig. 1, the high frequency source HF is connected to the electrodes D and M, and there is no conductive connection between the annular 'As illustrated, the high frequency discharge takes place between the electrodes M and R, and there is no discharge or conductance current between the electrodes R, and D. The discharge is there fore of. the so-called electrodeless type so far as the electrodes R and D are concerned, and this and other constructional forms for developing a discharge which no longer touches at least one of the energizing electrodes are of particular interest. In Figure 3 this is the case with the electrode H which is constructed in the form of a hollow cylinder. A discharge-free intermediate region occurs because the capacitancebetween" by utilising the gas flow, which with the 0011- I structional example shown in Figure 3 is strongest along the centre electrode M, so that under certain conditions the discharge is also separated from this electrode. The spatialextension of the discharge is axially-symmetrical and can for instance take the course indicated in Figure 3.

In Figure 4 the aforementioned principle of the high frequency discharge which does not touch the electrodes is developed a step further by inserting, between opposed electrodes E1, E2, a suitably formed insulator J with a bore of approximately Venturi shape including a contracting inlet portion, a cylindrical portion and an expanding outlet portion which cause the discharge to extend towardsboth electrodes E1 and E2. This device is set into operation by applying a high frequency voltage to the electrodes E1, E2 whose opposed surfaces are arranged transversely of the bore through the insulator J, spaced axially from the bore and of larger cross-section than the bore. The minimum diameter of the bore is substantially less than its axial length and small in comparison with the axial spacing of the electrodes E1 and E2. As indicated in Figure 4 leads Z1, Z2 can be arranged in the insulators J, the ends of these leads being of a metal which does not easily melt and projecting into the discharge space to con stitute auxiliary electrodes. If the voltage is also applied to both these auxiliary electrodes only a small ignition voltage is' necessary to establish the discharge on account of the shorter distance between the ends of leads Z1, Z2 as compared with that between E1 and E2.

An important advantage of these constructional forms is that several of these devices can be connected in series, as indicated in Figure 5, by providing the tubular insulating wall I of the reaction chamber with a plurality of inwardly projecting flanges J1, J2, J3 in each of which sets of auxiliary leads or electrodes Z1, Z2 are located. This particularly suitable arrangement comprises, in effect, a multiplication of a throttling insulator and auxiliary electrodes of the kind shown in Figure 4. This enables a high voltage to be applied to the electrodes, this being desired for such high frequency discharges. For setting the device into operation the ignition voltage can be applied to the sets of auxiliary electrodes l1, 12 so that the voltage across the electrodes E1 and E2 has only to be of sufiicient magnitude to maintain the discharge.

A device without electrodes for producing a high frequency discharge. with as little heating as possible, is shown in Figure 6. The high frequency excitation current is passed through a Winding S composed of one or more turns, which together with the condenser K forms an oscillation circuit. Inside of S strong high frequency alternating fields occur which cause a discharge Q in the gas flowing axially through the insulat- 4 ing tube P forming the reaction chamber. In order to avoid undesirable discharges outside of the reaction chamber the gas pressure in the inside space can be kept below atmospheric, thereby facilitating ionization within the chamber.

It is important that the discharge should be as uniform as possible. This can be achieved by using a cylindrical array of several electrodes which are capacitively coupled with one of the high frequency leads, the other lead from the high frequency source being connected to a central electrode M. With the arrangement shown in Figure 7 the electrodes A are arranged insulated inside the conductive casing Z. They can, however. be held in position by means of metallic elements which are bent downwards, since these latter form a large inductive resistance at the high frequencies which occur. The capacitance which occurs between A and Z forms a series reactance for the discharge currents of each of these electrodes. As soon as such a partial discharge decreases, the voltage drop between A and Z increases again and the discharge current immediately attains a certain average value again. On the otherhand excessive discharge currents of individual electrodes are avoided by these series reactances.

With the device shown in Figure 8 two rodshaped electrodes T1 and T2 are provided, which are enclosed in a metallised insulating cover N1 and N2 respectively. As indicated in the figure the metallisation is subdivided in the longitudinal direction. As in the case of the arrangement according to Figure 7, the capacitances occurring here between the individual metallised portions and rods form series reactances which stabilise the discharge.

The compensation of the reactive currents which occur due to the internal capacitances or the conductor inductance is of particular importance. The coil inductance of S in Figure 6 is compensated by the capacitance K which is adjusted to be in resonance. The inductances oi the leads must also be compensated by suitably dimensioned condensers. When the capacitance between the electrodes is large, series or parallel inductances which are correspondingly tuned should be used.

The discharge vessel can also be constructed in the form of hollow cavity resonators, as shown in Figures 9, l0 and 1011, the gases flowing through the cavities of these resonators in the direction indicated by the arrows. The cavity resonator of Fig. 9 comprises two hemispherical shells C, with projecting radial flanges c, which provide the capacitance of the cavity resonator. The shells C are connected by a diametrically located conducto'r or struts which constitutes the inductance. The strut is tubular on at least one end to provide a passage for introducing a gas into the interior of the cavity resonator. In this and other cavity resonator embodiments of the invention, thehigh frequency discharge is established in the space between the shells or walls of the cavity.

In the cavity resonator of Fig. 10, the spherical shell C has a pair of alined hollow radial conductors or studs s terminating in flanges c which contribute to the capacitance of the resonator. The gas flows into the cavity resonator through the studs 3' and between the condenser flanges c, and flows from the cavity resonator through openings 0 in the outer spherical Wall C.

As shown in Fig. 10a, the gas may flow through a tube t of insulating material which extends diametrically through the cavity resonator C, and auxiliary electrodes e1, ez may be located within, and at opposite ends of, the tube t to confine or stabilize the discharge within the tube t.

The several cavity resonators may be energized, in known manner, by a coaxial cable connected to the high frequency source and terminating in a loop within the resonator cavity.

In many cases, especially when the electrodes are not uniformly constructed, the discharge has a different character in each direction. Symmetrical loading can then be achieved by feeding two similar discharge gaps in push-pull connection.

Instead of single-phase high frequency currents it is also possible to provide multi-phase discharges. With the arrangement shown in Figure 11 three external electrodes E1-E3 are for instance provided which are connected to the poles of a three-phase high frequency generator. The nozzle electrode D can be connected with the middle conductor or neutral point of this generator system. The gas emerging from the nozzle flows in axially between the three electrodes and is subjected to the three-phase discharge. This three-phase discharge enables a uniform current density to be obtained across the interelectrode space, because the discharge currents to Ei-Es are all equal due to the symmetrical arrangement.

Another arrangement for multi-phase discharge is shown in Figure 12. The voltages at the rod-shaped electrodes F1-F shown in crosssection are mutually displaced by 90", so that two discharges bordering on each other occur. Those parts lying in the vicinity of the axis of symmetry of the device are subjected to both discharges, so that ionisation is strongest there. By this means the concentration of the discharge at a definite centre point where there is no electrode is possible.

The quality and insulation of the elements surrounding the gas discharge is of great importance as regards the invention. In view of the relatively small heating which occurs in many cases, ceramic elements can be used, these elements having excellent insulating properties. The electrodes can consist of ceramic elements which have been metallised as required. The electrode H in Figure 3 can for instance be produced by metallising the inside of a ceramic tube. With the arrangement shown in Figure 6 a ceramic tube P can also be used to separate the low-pressure gas from the external atmosphere. The winding through which the high frequency current flows can be produced by a solenoid-like metallisation of the internal and external surfaces of this tube. With the arrangement illustrated in Figure 7 ceramic material can be used as a dielectric between the electrodes E and the layer Z. A and Z are then also formed by metallising the surface of the ceramic element.

The discharge currents and gas pressure are also of great importance as regards the invention. In order to avoid undue heating the density or unit magnitude of the discharge currents should be kept as low as possible. It is advisable to employ small gas pressures so that a glow discharge occurs. In this case the reaction space must, however, be closed off from the atmosphere.

With certain chemical reactions better results can be achieved if the gas flows through several of the electrode devices described above, each device being of a different construction. so that the gas is subject to different reaction conditions occurring in a certain sequence.

We claim:

1. Apparatus for producing chemical reactions in a flowing gas by high frequency electrical discharges; said apparatus comprising insulator means having a bore of approximately Venturi form therethrough providing a reaction chamber, gas inlet and outlet means at opposite ends of said bore for establishing a stream of gas through said reaction chamber, and electrode means operative when energized by a source of high frequency energy to establish a luminous discharge within said bore and spaced from said electrode means; said electrode means comprising electrodes spaced axially form the ends of said insulator bore with opposed surfaces extending transversely of the axis of said bore and of across-sectional area in excess of the crosssection of said bore, and auxiliary electrodes mounted in said insulator means and located transversely of the minimum cross-section of said bore.

2. Apparatus for producing chemical reactions in a flowing gas by high frequency electrical discharges; said apparatus comprising insulator means including a plurality of radial flanges extending inwardly from an outer cylindrical wall to provide an axial bore having a plurality of axially spaced sections of minimum cross-section constituting a reaction chamber, gas inlet and outlet means at opposite ends of said bore for establishing a stream of gas through said reaction chamber, and electrode means operative when energized by a source of high frequency energy to establish a luminous discharge within said bore and spaced from said electrode means; said electrode means comprising electrodes spaced axially from the ends of said insulator bore with opposed surfaces extending transversely of the axis of said bore and of a cross-sectional area in excess of the cross-section of said bore, and auxiliary electrodes mounted in said insulator means transversely of each of said sections of minimum cross-section.

- GUSTAV GUANELLA.

OTTO ALBERT LARDELLI.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES Babot, Journal of Institute of Electrical Engineering, London, vol. 94, part III, Jan. 1947, pp. 27-37.

The Electrochemistry of Gases and Other Dielectrics by G. Glockler and S. C. Lind. 1939. pages 61. 62.