EP0612130A1 - Apparatus for non thermal excitation and ionisation of vapors and gases - Google Patents

Abstract

The excitation cell has a multiplicity of rod-shaped electrode elements (1). Each electrode element is surrounded by a chemically and thermally stable protective jacket which can also withstand electric fields. The electrode elements are held in vertically running bridges (2, 2', 3, 3'). This provides a construction in a plurality of modules, each of which modules consists of electrode elements arranged one on top of another and two bridges. The electrode elements of each module are electrically connected to a conducting rail (11) and are at the same potential. The modules are alternately applied to phase and earth. The excitation cell described is largely insensitive to condensates, so that even humid or polymerising gases can be excited. In addition, the modular construction allows individual electrode elements to be replaced with ease. <IMAGE>

Description

The invention relates to a device for exciting vapors and gases by means of electrical fields, which has a plurality of electrodes.

The non-thermal excitation of gases and vapors is becoming increasingly widespread in the field of fission and degradation, as well as in the synthesis of simple to high molecular weight compounds of organic and inorganic nature.

Because of the simplicity of the equipment, electric fields and discharges are used for excitation. Discharges are flows of electrical current through a gas. They are divided into different forms according to their current-voltage characteristics, e.g. Townsend (independent and dependent dark discharges), corona or barrier discharges, normal and abnormal glow, sparks and arc discharges.

In technology, corona and glow discharges are used for weak excitations up to multi-stage ionization (cold plasma). Spark and arc discharges are not required for non-thermal processes.

Previously known excitation devices can be divided into two basic types: devices with plate-shaped, flat electrodes and devices with concentric, tubular electrodes.

As a result of the excitation, the partial or the complete ionization of the gases, clusters very often form in the excitation chambers, which form collisions as a result of collisions, form aerosols and finally larger droplets. Experience shows that too with moist gases, condensation occurs on the discharge surfaces (lowering of the dew point). Such condensates, which are deposited on the electrodes or their coatings, can strongly influence the passage of current through local changes in the electrical resistance. For example, locally increased conductivity, for example due to water droplets, can locally lead to spark discharges, breakdowns and even arcing. This leads to damage to the barriers rsp. Coatings of the electrodes, excessive current consumption and undesired heating.

Depending on the gas composition, polymerizations can also occur, which can result in a mist of polymers, which is deposited on the electrodes or the dielectric and thus changes the discharge conditions. Such phenomena are known e.g. in the treatment of gases containing styrene or ethylene oxide. When such gases are excited, the polymerization of the monomers is initiated and the barrier material and / or the electrodes are coated with a polymer layer after a short time. As a result, an additional insulation layer is created and the discharges lose their intensity.

Therefore, the task arises to design a device that does not have these disadvantages. In particular, the device should enable the problem-free treatment of moist gases and polymerizing vapors.

This object is achieved by the device described in the first claim.

A preferred embodiment of the excitation cell is derived from the principle of parallel plate electrodes. At least one electrode is divided into a larger number of small, rod-shaped electrode elements. Each electrode element is surrounded by a protective jacket. The protective jacket preferably consists of a chemically and thermally stable material, that is also resistant to the fields and discharges.

An advantage of the excitation cell according to the invention is that the gas flow takes place in a non-laminar manner even at low flow rates. This largely prevents deposits on the protective sheaths of the electrodes, since the condensate cannot deposit at all or is immediately blown away again.

In a preferred embodiment of the cell, the arrangement of the electrodes is selected such that any condensate drops deposited are brought by gravity and / or the gas flow into an area of the protective jacket where the electric field is small and therefore they cannot have a strong influence on the discharge process.

Thanks to the division of the electrodes into a large number of small electrode elements with their own protective barriers, the costs for any repairs are also reduced. If, for example, a protective jacket of an electrode element is damaged by uncontrolled arc discharge, it is sufficient to replace this individual electrode element or its protective jacket. The replacement of such a small element is relatively inexpensive. In conventional apparatuses, an entire electrode or its barrier must be replaced for such repairs. Since these are much larger elements, the costs are correspondingly higher.

By suitably arranging the electrode elements and selecting the holders, the cell can also be constructed in such a way that the electrode spacing and thus the field strength can be varied by simple mechanical manipulation. This allows a simple adjustment of the field strength to the respective operating requirements and the achievement of very high fields.

• Figur 1 eine schematische Gesamtansicht einer bevorzugten Ausführung;
• Figur 2 einen Schnitt durch ein Modul von Elektrodenelementen mit dem versetzt dahinterliegenden nächsten Modul;
• Figur 3 einen horizontalen Schnitt durch zwei nebeneindanderliegende Elektrodenelemente;
• Figur 4 einen vertikalen Schnitt durch die Stege;
• Figur 5 eine alternative Ausführungsform der Stege;
• Figur 6 eine alternative Ausführung des Abschlusses der Schutzmäntel, und
• Figur 7 einen vertikalen Schnitt durch die Stege mit Schutzmänteln nach Figur 6.

Further advantages of the invention will become apparent from the following description of an embodiment using the figures. Show:

• Figure 1 is a schematic overall view of a preferred embodiment;
• FIG. 2 shows a section through a module of electrode elements with the next module located behind them;
• FIG. 3 shows a horizontal section through two adjacent electrode elements;
• Figure 4 shows a vertical section through the webs;
• Figure 5 shows an alternative embodiment of the webs;
• Figure 6 shows an alternative embodiment of the closure of the protective sheaths, and
• 7 shows a vertical section through the webs with protective sleeves according to FIG. 6.

The basic structure of an exemplary embodiment of the device according to the invention is shown in FIG. 1.

The excitation cell shown here consists of a plurality of rod-shaped, horizontally lying electrode elements 1, which are held at both ends by vertically extending webs 2, 2 'and 3, 3'. The cell is thus subdivided into a plurality of modules arranged upright, each module consisting of two opposing webs and the electrode elements held equidistantly therein.

All electrode elements of a module are electrically connected to rails 11 via leads 4. The modules are alternately grounded or connected to a phase P.

In the present example, the gas flow G through the cell is preferably from top to bottom. As discussed below, this reduces the influence of deposited condensate drops on the field distribution.

The structure of the electrode elements can be seen in FIG. 2, which shows a vertical section through a module with the next module located behind it.

Each electrode element 1 is surrounded by a protective jacket 5. A tube of suitable diameter is preferably used as the protective sheath, which consists of a chemically and thermally stable material which is also resistant to the electrical fields and discharges. Pipes made of quartz, homogeneous ceramics or special glasses such as borosilicate melts are particularly suitable for this.

The protective jacket 5 protects the electrode element 1, which consists of a conductive material. As electrode material e.g. non-insulated copper strands are used. Thanks to the irregular surfaces of these strands, the discharges can start from many individual surface points and not only build up in a few places (peak discharge). This also results in greater tolerances for the positioning and alignment of the electrodes without impairing the homogeneity of the discharge or the field.

The protective sleeves 5 are closed at one end 6, while at the other end 7 they have an opening for the introduction of the electrode element 1. This opening is sealed gas-tight against the electrode material. Thanks to this structure, gas or plasma remains enclosed in the interior of the protective jacket. This highly reactive mixture cannot therefore escape to the outside where it could cause damage to the webs 2, 2 ', 3, 3', for example. Air, but also a suitable protective gas can be used as the gas in the interior of the protective jacket.

The end regions of the protective sheaths are shown in detail in FIG. 3. This figure shows a horizontal section through two electrode elements of adjacent modules in the area of the webs.

Damage to the webs can occur if they are exposed to fields that are too high. High electrical fields, for example in the case of webs based on silicone, can lead to decomposition of the material. To prevent this, the protective jackets in the area of the webs are preferably provided with protective electrodes 9, 10. It can e.g. are at least weakly electrically conductive foils, hoses or coatings, as are known to the person skilled in the art. These protective earths are arranged between the protective jackets and the bars.

In the present exemplary embodiment according to FIG. 3, the end 6 of the one protective jacket, the electrode element of which is in phase, is provided with a protective electrode 9 which is grounded. The protective electrode 10 of the end 7 of the second protective jacket, the electrode element of which is on earth, is also connected to the earth. The field in the area of the webs 2, 2 'between the electrode elements is thus small.

At the opposite ends of the electrode elements, in the area of the webs 3, 3 '(not shown), similar protective electrodes are provided, which are preferably connected to the earth or at most to another, defined potential.

It is also conceivable that not all electrode elements or protective jackets are provided with protective electrodes.

As already apparent from FIGS. 1 and 2, adjacent modules can be arranged offset from one another, so that, for example, each electrode element of a module comes to lie at the height between the electrode elements of the adjacent modules. This results in an optimally homogeneous field.

The arrangement of the electrode elements can also be seen in FIG. 4, which shows a vertical section through the webs.

The cell is preferably constructed in such a way that adjacent modules can be displaced in the vertical direction relative to one another, as is indicated by the arrows S. This makes it possible to regulate the electrode spacing and thus the electrical field and the discharge.

Figure 4 shows a possible structure of the webs 2, 2 '. The webs here consist of strips of an elastic material, e.g. based on silicone. In these webs are formed on one side edge at regular intervals for receiving the electrode elements, respectively. protective coats attached. Thanks to the elastic design of the webs, the protective sleeves can be snapped into these recesses. This construction has the advantage that damaged electrode elements can be easily replaced, since they can easily be removed from the web and reinserted therein. To simplify the replacement of the electrode elements or the protective sheaths, the connections of the electrode elements to the rails 11 (see FIG. 2) are preferably designed to be pluggable.

FIG. 5 shows an alternative web structure, in which the webs 2, 2 'each consist of a spacer strip 13 and a strip 12, the electrode elements 1 and the protective sleeves 5 being arranged in the strip 12. The strip 12 may e.g. are a layer of a curable, electrically insulating and durable sealing material, in which the protective sheaths 5 are integrated.

FIG. 6 shows a possible constructive embodiment of the termination of a protective jacket 5 in the end region of the electrode element 1. Here, in order to close the tubular protective jacket 5, the tube in the region 14 was heated and squeezed together. So that results a tight seal of the protective jacket. Depending on the shape of the tool used, the cross section of the protective jacket can be selected in the region 14. In the present example, a square cross section was chosen. Figure 7 shows a section through webs that hold such closed protective sheaths. Thanks to the narrowing of the protective sleeves in the area of the webs caused by the crushing, the protective sleeves are held very well in the webs.

However, it is conceivable to close the protective jacket in another way (see also FIG. 3), e.g. by fusing or by grafting a suitable sealing material.

In operation, as mentioned at the beginning, a gas stream is passed through the cell from above. Thanks to the many individual electrode rods, the gas flow does not flow through the cell in a laminar manner, even with small gas flows. This results in better gas mixing and a longer gas path, which increases the efficiency of the excitation. In addition, the turbulence has the effect that any condensate deposited on the protective sleeves of the electrode rods is carried away and that the deposition of condensate is made more difficult.

If condensate drops should nevertheless deposit on the protective sheaths of the electrode rods, they will collect in the lower area of the rods, since they are pushed down by gravity and the gas flow. The electrical fields are smallest in this area, however, since electrode elements lying one above the other have the same potential. This means that these condensate drops do not disturb the discharge.

The basic structure according to FIG. 1 shows only one of the possibilities for building an excitation cell according to the invention. For example, part of the electrode elements can be replaced by electrode plates. The electrodes can also be used in other directions and do not necessarily all have to be arranged in parallel.

The individual electrode elements or the protective shells do not necessarily have to be round. For example oval and flattened cross sections are also conceivable.

In the present structure, each electrode element is held by two webs. However, it is also possible to use more than two webs per module. Modules can also be produced with only one web, the electrode elements in this case benefiting from the additional hold provided by the busbar 11.

In any case, the described invention makes it possible to construct a modular, efficient and less pollution-prone excitation device which can be used in many areas of application.

Claims (14)

Device for exciting vapors and gases by means of electrical fields, which has a plurality of electrodes, characterized in that at least some or all of the electrodes are designed as spaced, essentially rod-shaped electrode elements (1), each electrode element being protected by a protective jacket (5, 6, 7) is surrounded. Device according to claim 1, characterized in that the electrode elements are aligned essentially parallel to one another. Device according to one of the preceding claims, characterized in that the electrode elements (1) are aligned substantially horizontally. Device according to one of the preceding claims, characterized in that the electrode elements (1) are combined in modules, each module comprising a plurality of parallel electrode elements arranged in one plane, the electrode elements of a module via at least one web (2, 2 ', 3 , 3 ') are mechanically connected to each other. Device according to claim 4, characterized in that the electrode elements (1) of a module are electrically connected to one another. Device according to one of claims 4 or 5, characterized in that it has a plurality of modules arranged side by side. Device according to claims 5 and 6, characterized in that the modules alternately at a first and a second electrical potential lie, so that modules lying next to each other each have different potentials. Apparatus according to claim 7, characterized in that the electrode elements (1) are arranged equidistantly in each module and that the modules are displaceable relative to one another. Device according to one of the preceding claims and claim 4, characterized in that the at least one web (2,2 ', 3,3') with the protective sheaths (5,6,7) of the electrodes is connected (1), at least one Part of the protective sheath in the area of the web is surrounded by an at least partially conductive layer (9, 10) which is at a given potential, so that the electric field is reduced in the area of the web. Device according to one of the preceding claims, characterized in that each protective jacket (5, 6, 7) is essentially designed as a tube, the first end (6) of the tube being closed and the electrode element being inserted through the second end (7), and wherein the tube is sealed at the second end against the electrode element (1). Device according to one of the preceding claims, characterized in that the surfaces of the electrode elements (1) are designed to be uneven to improve the field homogeneity. Device according to one of the preceding claims, characterized in that strands are used as electrode elements (1). Device according to one of the preceding claims, characterized in that the protective sheaths (5,6,7) at least partially consist of ceramic or glass, in particular quartz glass or borosilicate glass. Module for a device according to one of the preceding claims and claim 4.

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