EP1891265B1 - Method for treating a process material with large surface plasma - Google Patents

Abstract

The invention relates to a method for treating a process material, said process material being contacted with, preferably non-thermal, large area plasma at, preferably, at least atmospheric pressure, the plasma being produced in close proximity to the process material, or a gas discharge - in particular a corona discharge - being produced within the process material or in the immediate vicinity thereof at, preferably, at least atmospheric pressure. In order to improve the treatment of the process material with plasma and to increase the effectiveness thereof, high-voltage pulses (66, 67) with a duration (62) of less than 10 ?s are generated between electrodes (43, 44) for the production of the plasma or the gas discharge.

Description

The invention relates to a process for the treatment of a process material, wherein the process material with, preferably non-thermal, large-area plasma, preferably at least atmospheric pressure brought into contact, the plasma generated in the immediate vicinity of the process material or in the process material or in the immediate vicinity of a gas discharge, in particular, a corona discharge, preferably at least atmospheric pressure, is generated.

• Beseitigung von, "farbigen" Molekülgruppen, dadurch wird eine Aufhellung des Papiers zumindest im Oberflächenbereich erzielt,
• Erhöhung der Absorptionsfähigkeit für eine Druckfarbe,
• Erhöhung der Festigkeit des Papiers.

The treatment of process goods usually depends on a change in a molecular structure of the process material, in particular its surface from. For example, in the paper industry or in the textile industry, process goods, eg entire paper webs or entire textile webs, have to be treated by applying certain substances. Using the example of paper, the following effects are achieved:

• Elimination of "colored" molecular groups, this results in brightening of the paper, at least in the surface area,
• Increasing the absorbency of an ink,
• Increasing the strength of the paper.

In the case of textiles and plastics, the treatment of surfaces is already technically carried out with non-thermal, "cold" plasmas in order to improve the dyeability and / or printability by means of surface functionalization or else to control specific other properties such as, for example, flame retardation, water repellency or water attraction.

Out DE 198 36 669 A1 is a method for surface pretreatment of paper or board with plasma known.

Out WO 2004/101891 A1 and FR-A-2711680 For example, processes for the surface treatment of paper and associated fibers with plasma are known.

Treatment methods, such as those required in the paper industry for controlling the very high process speeds required today, are not yet known.

It is an object of the invention to improve a treatment result, which is achieved by the treatment of a process material with plasma, and / or to increase the effectiveness of the plasma generation.

The object is achieved in that high-voltage pulses having a duration of less than 10 μs are generated between the electrodes for generating the plasma or the gas discharge. The use of such short high voltage single pulses has been found to be particularly advantageous, whereas the use of radio frequency (RF) or microwave pulses or high voltage single pulses of more than 10 μs in duration is far less efficient. In order to obtain a good energy efficiency of the generation of plasma and its positive effects, both in gases and in liquids, it is therefore preferred to work with very short high-voltage pulses. The pulse duration should be significantly shorter than corresponds to a build-up time of the complete breakdown time in the respective medium.

According to the invention, in contrast to the known procedure for textiles and plastics is not worked with a low-pressure plasma reactor, which is very expensive because of the necessary vacuum generation, but it is applied atmospheric pressure.

Preferably, the process material is an unwoven fiber in a suspension, in particular fibers or pulp, a paper to be produced, a cardboard to be produced, a cardboard to be produced, the starting materials for the production, and / or their intermediates during manufacture, in particular a moist or dry and / or unpressed sheet.

The plasma is preferably produced by the process material at a distance of less than 20 cm, preferably less than 10 cm, preferably less than 5 cm. In order to achieve a good treatment result, for example bleaching of a paper web, it is advantageous to produce the plasma in the immediate vicinity of the process material.

It is expedient that the process material is brought into contact with the plasma on both sides or treated by means of the gas discharge. The two-sided treatment of the process material with plasma allows a high treatment efficiency and a preferably high penetration depth of, for example, aggressive carriers in the process material.

A preferred embodiment of the invention is that the plasma or the gas discharge for bleaching the process material, in particular in a digester, in a bleaching container or in a line is used. If the method is used, for example, within a connection element or a supply line which is prepared for the transport of the process material, the method for treating the process material can advantageously already be used during the transport of the process material, and thus a process time is further shortened.

In a further preferred embodiment, the process material is brought into contact with at least one electrode for generating the plasma or the gas discharge.

Appropriately, the method is applied to different types or states of process goods. In a preferred application, the content of carrier liquid, in particular water, in the process material is in the range between 40% and 99.9%, preferably in the range between 80% and 98%. and in particular between 85% and 98%. With the use of the method according to the invention within a carrier liquid, chemical reactions which produce the result of the treatment can be produced particularly efficiently.

Preferably, radicals are generated in the plasma or by means of the gas discharge, which act on the process material. These radicals cause a chemical reaction, for example with a bleaching effect, which effectively supports the treatment process to achieve the treatment goal.

With particular advantage, radicals of different types or compositions are used for different states of the process material in a paper, board or paperboard production process, in particular at different process stages.

It is particularly preferred and expedient that the process material is exposed within a process stage in a paper or board production process, radicals of different nature or composition, preferably sequentially in time. Advantageously, such an optimal treatment result is achieved step by step.

It is expedient that are generated as radicals ozone, hydrogen peroxide, hydroxyl, HO ₂ and / or HO ₂ ^- .

Advantageously, when bleaching the process material, the plasma or the gas discharge is applied in such a way that as radicals increased ozone and / or hydrogen peroxide are formed.

Starting from the use of different types or compositions of radicals at different process stages, it is advantageous that during sieving and / or on the distributed process material the plasma or the gas discharge in such a way is applied, that as radicals increasingly hydroxyl, HO ₂ and / or HO ₂ ^{- is} formed.

Advantageously, a generation rate of the radicals and / or the composition of the generated radicals is controlled by influencing an amplitude, a pulse duration and / or a pulse repetition rate of the high voltage pulses. Since, in addition to the nature and composition of the radicals, the concentration of the radicals is generated by an electrical process and is thus very easily controllable in real time, such a method is very economical and can be readjusted within a very short time for different treatment results, e.g. in the context of self-learning algorithms.

It is expedient that a concentration of the generated radicals is measured to control and regulate the rate of generation and / or the type of radicals generated. In a control method or control circuit preferably used for plasma generation, the concentration of radicals is used as the actual value.

A further increase in the targeted influence is achieved by measuring a property of the suspension, preferably a quality property, in particular its opacity, gloss, whiteness, fluorescence or color point, for controlling and regulating the production rate or the composition of the radicals produced. On the basis of the results of the measurement of the quality properties, a feedback is obtained, which allows the optimal control of the treatment process.

Appropriately, the concentration or the property "online" is preferably measured. This is particularly advantageous with regard to an automated method, preferably with automation components and sensors, since the reaction to a changing quality property takes place virtually simultaneously.

Appropriately, the amplitude of the high voltage pulses is changed at a constant repetition rate for control.

In a further expedient embodiment, the repetition rate of the high-voltage pulses is varied at a constant amplitude for the purpose of regulation.

A further increase in the treatment result is achieved in that the process material, preferably for bleaching, is enriched with oxygen in the plasma-exposed area.

If the process material is present as suspension or pulp or as pulp, it is particularly advantageous with regard to the treatment result that, preferably for bleaching, a high-voltage pulse duration of less than 100 ns is used. For example, if the electrodes of a bleaching device are arranged completely inside the suspension, it is very advantageous to work with small high-voltage pulse durations due to the high conductivity of the suspension. The higher the conductivity, for example the suspension, the more "resistive losses" can occur if the pulse duration is too long.

Furthermore, it is expedient in the sense of an optimal treatment result that process material distributed in a planar manner, in particular during sieving, be surrounded by a water vapor-enriched atmosphere in the plasma-exposed region.

Preferably, a high voltage pulse duration of 100 ns to 1 μs is used for areal distributed process material, in particular pulp or pulp or forming or formed, still unpressed sheet, in particular during screening.
As already mentioned, suspensions with high conductivity lead to "ohmic"losses; It is therefore advantageous to use pulses with a low pulse duration and a high edge steepness.

Preferably, for suspensions with extremely high conductivity, it is expedient that high-voltage pulses having a duration of less than 3 μs, preferably less than 1 μs, preferably less than 500 ns, are used. The use of short pulses on the one hand has the advantage that the largest part of the pulse energy is not converted into heat as an ohmic component and, on the other hand, a streamer discharge with efficient generation of radicals is generated.

Furthermore, it is particularly advantageous that for flatly distributed process material, in particular for pulp or pulp or forming or formed, still unpressed sheet, in particular during screening, the amplitude corresponding to at least twice, preferably at least three times, a corona threshold voltage the electrodes are applied.

It is also expedient that a DC corona discharge is generated to generate the plasma or the corona discharge and the DC voltage corona discharge, the high voltage pulses are superimposed. The superimposition of the high-voltage pulses with a DC voltage has the particular advantage that the high-energy high-voltage pulses can already start from a very high energy level.

It is further preferred that a pulse repetition rate between 10 Hz and 5 kHz, in particular from the range of 10 Hz to 10 kHz, is used.

For the already mentioned automation of the method, it is advantageous that the power coupling of electrical energy into the plasma is controlled predominantly via the regulation of amplitude, pulse duration, and pulse repetition rate of the superimposed high-voltage pulses.

In a preferred application of the method, a homogeneous, large volume plasma with high power density is produced without causing plasma constrictions or breakdowns comes. By generating a "stable" plasma, the generation rate can be kept high and constant, but if plasma constrictions or breakdowns occur, the production rate drops again.

It is also expedient if a DC voltage of such height is used that a stable DC corona discharge is formed in the plasma in conjunction with superposed high-voltage pulses.

It is particularly advantageous that the total amplitude used (DC voltage + pulse amplitude) is above the static breakdown voltage of the electrode assembly.

Furthermore, the total amplitude used preferably corresponds to two to five times the static breakdown voltage of the electrode arrangement.

It is particularly expedient if the amplitude of the high-voltage pulses is between 10% and 1000% of the DC voltage used.

For a uniform distribution of the plasma on the process material, it is expedient that a gas flow is generated perpendicular to the electrode assembly.

Alternatively, it is possible that a gas flow is generated parallel to the electrode assembly.

FIG 1

eine schematische Darstellung einer Papierherstellungsanlage mit einer Siebvorrichtung, einer Pressenvorrichtung und einer Veredelungs- und/oder Trockenanlage,

FIG 2

eine Bleichvorrichtung,

FIG 3

eine Darstellung (Schnitt) einer Anordnung zur Erzeugung von Radikalen in Koronaplasmen in Pulpe oder Luft: Parallelplatten- oder Rohranordnung mit Draht, dem eine gepulste Hochspannung überlagert wird,

FIG 4

eine Prinzipdarstellung von Impulsen zur Erzeugung von Radikalen in Koronaentladungen in Luft oder wässrigen Medien bei Einsatz kurzer (typisch < 1 µs) Hochspannungsimpulse mit hoher Impulswiederholrate,

FIG 5

bis FIG 10 Elektrodenanordnungen und Elektrodensysteme zur Erzeugung von Koronaentladungen: Platte-Platte-, Platte-Draht-Platte-, koaxiale Draht-Rohr-, SpitzePlatte-, Mehrfachspitzen-Platte-, Gitter-Platte (Rohr)-, Gitter-Gitter-Anordnungen,

FIG 11

eine hybride Entladung, wobei sich eine Elektrode vollständig oberhalb des Mediums auf dem Sieb befindet, wogegen die zweite Elektrode durch das Sieb selbst gebildet wird,

FIG 12

eine Platten- oder Gitteranordnung mit gekrümmten Oberflächen zur Anpassung an Gefäßwände bzw. Nutzung derselben als Elektrode, konzentrische Elektroden in Rohrform zur Nutzung der vorhandenen Verrohrung oder Türme für die Pulpe als Reaktorgefäß,

FIG 13

eine gepulste Entladung im oberflächennahen Gasraum über Stoffauflauf auf dem Sieb mit Vielfachdraht Platte-Anordnung, und

FIG 14

ein gepulstes Koronaentladungssystem mit koaxialem Draht-Rohr, mit eingeperlten, feinstverteilten Gasblasen, so dass im Entladungsbereich feinste Gasperlen vorhanden sind und eine Streamerbildung vorwiegend in den Gasblasen abläuft.

Preferred, but by no means limiting embodiments of the invention will now be explained in more detail with reference to the drawing. For clarity, the drawing is not drawn to scale, and certain features are shown only schematically. Corresponding parts are provided in the figures with the same reference numerals. In detail, the shows

FIG. 1

a schematic representation of a papermaking plant with a screening device, a press device and a finishing and / or drying plant,

FIG. 2

a bleaching device,

FIG. 3

a representation (section) of an arrangement for generating radicals in corona plasmas in pulp or air: parallel plate or tube arrangement with wire, which is superimposed on a pulsed high voltage,

FIG. 4

a schematic diagram of pulses for generating radicals in corona discharges in air or aqueous media using short (typically <1 μs) high voltage pulses with high pulse repetition rate,

FIG. 5

to FIG. 10 Electrode assemblies and electrode systems for generating corona discharges: plate-plate, plate-wire-plate, coaxial wire-tube, tip-plate, multi-tip-plate, grid-plate (tube) -, grid-grid arrangements,

FIG. 11

a hybrid discharge, with one electrode located completely above the medium on the screen, whereas the second electrode is formed by the screen itself,

FIG. 12

a plate or grid assembly with curved surfaces for fitting to vessel walls or using same as an electrode, concentric electrodes in tube form to use the existing casing or towers for the pulp as a reactor vessel,

FIG. 13

a pulsed discharge in the near-surface gas space above the headbox on the wire with multiple wire plate arrangement, and

FIG. 14

a pulsed corona discharge system with coaxial wire tube, with bubbled, very finely divided gas bubbles, so that in the discharge region finest gas bubbles are present and a streamer formation takes place mainly in the gas bubbles.

FIG. 1 shows a schematic representation of a complex papermaking plant 1, as in today's paper mills is used. Their construction and the combination of different aggregates are determined by the type of paper, cardboard and paperboard types to be produced as well as the raw materials used. The papermaking plant 1 has a spatial extent of about 10 m in width and about 120 m in length. The papermaking plant produces up to 1400 m of paper per minute 27. It only takes a few seconds from the first impingement of the suspension or the pulp 39 on the screening device 9 to the finished paper 27, which is finally rolled up in a reel 15. Diluted with water at a ratio of 1: 100, the fibers 30 (see FIG. 2 ) applied together with excipients on the sieve 9 with the sieve 10. The fibers are deposited on the screen 10 side by side and on each other. The white water 23 can drain or be sucked off by means of several suction chamber regions 24. In this way, a uniform fiber composite, which is further dehydrated by mechanical pressure in a press device 11 and with the aid of steam heat. The entire papermaking process is essentially subdivided into the areas of stock preparation, paper machine, finishing and equipment.

Waste paper and, as a rule, also pulp reach a paper factory in dry form, while pulp is normally produced in the same factory and pumped into the material center 3 as a fiber / water mixture, ie a suspension of unvarnished fibers. Waste paper and pulp 30 (see FIG. 2 ) are also added with the addition of water in a fiber trough 35 (FIG. FIG. 2 ) dissolved. Non-paper components are discharged via various sorting aggregates (not shown here). In the fabric center 3, depending on the desired type of paper, the mixture of different raw materials. Fillers and auxiliaries are also added here to improve paper quality and increase productivity.

The headbox 7 of the papermaking plant 1. distributes the pulp suspension uniformly over the entire wire width. At the end of the screening device 9, the paper web 27 still contains about 80% water.

Another dewatering process is carried out by mechanical pressure in the press device 11. In this case, the paper web 27 is guided by means of an absorbent endless felt cloth between rolls of steel, granite or hard rubber and thereby dehydrated. The white water 23 taken up by the suction chamber region 24 is fed to a sorter 5 in part and returned to another part to a fabric scavenger 17. The press device 11 is followed by a drying system 13. The remaining residual water is evaporated in the drying plant 13. Slalom-like, the paper web 27 passes through several steam-heated drying cylinders. In the end, the paper 27 has a residual moisture of a few percent. The water vapor formed in the drying plant 13 is sucked off and passed into a heat recovery system, not shown.

For a treatment of the fiber suspension 39 as process material by the method according to the invention, in a first embodiment between the head box 7 and the beginning of the screening device 9, a first electrode 43 below the sieve 9 and a second electrode 44 above the sieve 9. The electrodes 43 and 44 are arranged such that the surface-distributed fiber suspension 39 extends between them. So that a large-area plasma under atmospheric pressure in the immediate vicinity of the fiber suspension 39 can be produced for the treatment of the fiber suspension 39, the electrodes 43 and 44 are connected to a high-voltage pulse generator 46. With the aid of this high-voltage pulse generator 46, a large-volume plasma with a large cross section and with high power density is produced between the electrodes 43 and 44. Here, a plasma density is homogeneously distributed over the treatment area which is covered by the electrodes 43 and 44. According to the invention, this large-volume plasma with high power density is generated by a DC corona discharge intensive, short-lasting high-voltage pulses are superimposed with a high pulse repetition rate of 1 kHz. In this mode of operation, a very homogeneous, large-volume plasma with a high power density is produced without the plasma constrictions that are known in DC corona discharges.

In order to support the treatment effect which the cold large-area plasma exerts on the fiber suspension, oxygen with argon as carrier gas is optionally introduced into the treatment space between the electrodes 43 and 44 via a gas distributor 81. Hydroxyl radicals are particularly advantageously produced with the aid of the oxygen-argon mixture. Hydroxyl radicals are particularly aggressive and oxidizing, thereby a bleaching effect is achieved at the only a few seconds in the treatment area between the electrodes 43 and 44 lingering process material.

In FIG. 1 is also a second embodiment of the application of the method according to the invention shown:

Analogous to that described above, an electrode system 47, 48 in the press device 11 generates a large-area plasma for the treatment of the paper web 27, which represents the process material here. The first electrode 47 in the press apparatus 11 is designed as a semicircular grid electrode. Due to the semicircular configuration of the electrode 47, it can follow the course of the paper web over a transport roller 12. The second electrode 48 in the press device 11 is configured as a plate electrode and arranged such that the transport roller 12 can be guided between the electrodes 47 and 48. In order to stimulate the formation of radicals in the plasma here as well, the plasma treatment area is optionally also supplied via the gas distributor 81 with the gas line 80 with an oxygen-argon mixture here.

The pressing process compacts the paper structure, a strength increases and a surface quality is decisively influenced. By treating the pressed paper with cold plasma, especially with the generated radicals, the molecular structure of the paper surface is further altered. The strength of the paper 27 is increased and printability improved.

With the above-mentioned electrode arrangements 43 and 44 as well as 47 and 48, it is possible according to the inventive method to guide the paper web 27 between streamer discharges. A streamer is a special form of a linearly moving plasma cloud or a developing discharge channel that forms due to the excited high external field strength. An assembly of such streamer takes place within less than 10 ns and merges very quickly into a thermal breakdown channel. The aforementioned arrangements of the electrode systems, with the paper web 27 between the electrodes used for streamer discharge, is particularly advantageous, as the paper 27 thereby partially acts as a dielectric barrier, thereby suppressing the transition from the streamer puncture.

FIG. 2 shows a bleaching device 38 as a third application example. A raw material 30, in particular pulp, here the process material, is conveyed via a conveyor belt 33 into a fiber trough 35. In the fiber trough 35, the raw material 30 is mixed with water and pumped via a pipeline 36 into a bleaching trough 37. A first electrode 43 'and a second electrode 44' are each designed as a circular-area grid electrode. The first electrode 43 'is arranged in the gas space of the pulp fiber suspension 39 filled in the bleaching trough 37. The second electrode 44 'is arranged inside the bleaching trough 37 and is thus completely covered by the pulp fiber suspension 39. Between the two electrodes 43 'and 44', a large-area cold plasma is generated by means of the high-voltage pulse generator 46.

, HOO ^{- -} by direct treatment of the pulp fiber suspension 39 with the cold plasma, the radical OH in the suspension 39 is preferably, O, O ₃ produced. These radicals trigger a bleaching chemical reaction. The high-voltage pulse generator 46 is operated to generate high-spike pulses having a duration of 1 μs between the electrodes 43 'and 44'. A necessary for the generation of radicals and ozone in the pulp fiber suspension DC voltage is approximately at some 10 kV to 100 kV. The high voltage pulses are superimposed on the DC voltage to form a total amplitude of a few 10 kV to 500 kV. By treating the pulp fiber suspension 39 with a cold electrical discharge, so the plasma, the radicals are generated in situ. Thus, large total amounts of radicals can be introduced into the suspension 39. The radicals are also very finely distributed in the suspension produced, so that the hitherto necessary effort for mixing chemicals with the suspension can be reduced.

For a further increase in the bleaching process, an oxygen-argon mixture, which has been treated in a gas distributor 81, is introduced into the bleaching trough 37 via a gas line 80.

FIG. 3 shows as a fourth application example a sectional view of a bleaching vessel. In the middle of the bleaching vessel, a high voltage electrode 50 is arranged. The outer jacket of the bleaching vessel is prepared as a counterelectrode 51. In the bleaching vessel is a pulp fiber suspension 39. Between the electrodes 50 and 51, a streamer 53 is shown. Radicals are generated in streamers by high-energy electrons colliding with and dissociating or exciting molecules. Upon dissociation, radicals 59 are immediately released, while upon excitation by a subsequent radiant transition, UV light is generated. This generated UV light in turn reacts with water molecules and dissociates them.

In FIG. 4 the voltage waveform of the high voltage pulses used according to the invention is shown. A first pulse 66 and a second pulse 67, each having a pulse width 62 of less than 10 μs, have a spacing of one pulse repetition time 63. The abscissa shows the time in ms and the ordinate the voltage in kV. The units are chosen arbitrarily. A level of about 100 kV DC voltage coincides with the abscissa shown. The illustrated pulse voltage is thus superimposed on the DC voltage. The pulses 66 and 67 have a high rising edge with a rise time of 64 and a less steeply falling edge. The pulse repetition time 63 is typically between 10 μs and 100 ms.

In this case, the individual pulses 66, 67 have such a total amplitude that a predefined energy density is achieved beyond the predetermined direct voltage. As mentioned, the pulse rise time 64 is short compared to the pulse fall time. By such a kind of pulses is achieved that electrical breakdowns that would lead to spatial and temporal disturbances in the homogeneous plasma density distribution can be avoided.

FIG. 5 to FIG. 10 show further examples of electrode systems for generating corona discharges in preferably aqueous media, which can be used in the inventive method. In FIG. 5 For example, a plate-and-plate arrangement of a first plate 70a as an electrode and a second plate 70b as an electrode is illustrated. The first plate 70a and the second plate 70b are arranged parallel to each other. The first plate 70a forms the high voltage electrode and is connected to the high voltage pulse generator 46 via a high voltage cable. The second plate 70b forms the counter electrode and is connected as a grounded electrode to the high voltage pulse generator 46 in connection.

A corresponding arrangement with specially flat plate electrodes is in FIG. 6 shown. There are two again solid plate electrodes 70a and 70c at a fixed distance, wherein a high voltage electrode 71 extends centrally. In this plate-wire plate assembly, the high voltage electrode 71 is made of a solid wire and connected to the high voltage output of the high voltage pulse generator 46. The grounded plates 70a, 70c are also in communication with the high voltage pulse generator.

FIG. 7 shows a wire-tube arrangement as an electrode system. A high-voltage electrode 71 projects centrally into a cylindrical electrode 72. As in FIG. 6 the high voltage electrode 71 is made as a solid wire and connected to the high voltage pulse generator 46. The cylindrical electrode 72, which is preferably configured as a wire mesh, is grounded and communicates with the high voltage pulse generator 46.

FIG. 8 shows a tip-plate assembly as an electrode system. Three tips 73 are connected to the high voltage pulse generator 46 via a high voltage line. The tips 73 are arranged at right angles to a grounded plate electrode 74. The distance of the tip electrodes 73 to the plate electrode 74 is adjustable and thus can be adapted for different process conditions.

FIG. 9 shows an electrode system assembly comprising 3 plates 70a, 70d and 70e. The first plate 70a, which is connected as a high-voltage electrode to the high-voltage pulse generator 46, is arranged centrally between two solid plates 70d and 70e. The plates 70a and 70b are connected via a plate connector 70f. Since the plate 70d as a grounded counter electrode is in communication with the high voltage pulse generator 46, the plate 70e above the plate connector 70f also functions as a grounded counter electrode.

FIG. 10 shows an electrode system as a grid-grid arrangement. Analogous to FIG. 5 here are a first grid 75a and a second grid 75b parallel to one another. The first grid 75a forms the high voltage electrode and is connected to the high voltage pulse generator 46. The second grid 75b forms the grounded counter electrode and communicates with the high voltage pulse generator 46.

A hybrid discharge in which an electrode 75a is entirely outside a pulp 39 to be bleached and a second electrode 76b is wholly or partially immersed in the pulp 39 is shown in FIG FIG. 11 generated. In this further example of application, the electrode 76a is designed as a grid electrode and is connected to the high-voltage pulse generator 46. The grounded counter-electrode 76b is also designed as a grid electrode.

In FIG. 12 is shown as a further application example, a bleaching tub with a vessel wall 77 in a plan view. For the bleaching tub, a plate or grid arrangement with curved surfaces for adaptation to the vessel walls or use of the vessel walls is used as the electrode. A multiple wire electrode 79 is arranged as a concentric electrode following the course of the vessel wall 77 and communicates with the high voltage pulse generator 46. It faces two counterelectrodes: on the one hand the vessel wall 77 and on the other hand a plate electrode 78. The high voltage electrode 79 is arranged without contact between the vessel wall 77 and the plate electrode 78. The vessel wall 77 and the plate electrode 78 are electrically conductively connected to each other and thus form the grounded counterelectrodes which are in communication with the high voltage pulse generator 46.

In order to generate pulsed discharges in the near-surface gas space above the pulp 39 is in FIG. 13 represented as a further application example, a special electrode arrangement. A high-voltage electrode 50 comprises a plurality of electrically connected rod electrodes and is arranged in the near-surface gas space of the pulp 39 such that their rods parallel to the surface. A grounded counter electrode 51 is designed as a solid plate and arranged in distributed over the entire surface equidistant distances to the high voltage electrode 50.

FIG. 14 shows in a last embodiment, a pulsed corona discharge system in an aqueous solution or pulp 39. The electrode system is analogous to FIG. 3 formed as a coaxial wire tube electrode system. The high voltage electrode 50 is arranged coaxially with the counter electrode 51 forming the vessel wall. In order to support the bleaching effect, the finest gas bubbles are introduced into the discharge area via a gas line 80 by means of a gas distributor 81. In the gas bubbles 82 and 83 are preferably formed to FIG. 3 mentioned streamer. Owing to the streamer discharges, oxidants 57 are formed. Thus, certain radicals are generated in the suspension.

Claims (36)

1. Method for treating a process material, in which

   - the process material is brought into contact with, preferably non-thermal, large-area plasma, preferably at atmospheric pressure at least,

   - the plasma is produced in direct proximity to the process material or a gas discharge, in particular a corona discharge, is produced within the process material or in the immediate vicinity thereof, preferably at atmospheric pressure at least,

   characterised in that to produce the plasma or gas discharge, high-voltage pulses (66, 67) with a duration (62) of less than 10 µs are generated between electrodes (43, 44).
2. Method according to claim 1,
   characterised in that the process material comprises a nonwoven fibrous material in a suspension, in particular fibres or pulp (39), a paper to be manufactured (27), a cardboard to be manufactured, a paperboard to be manufactured, their raw materials (30) for manufacture and/or their intermediate products during manufacture, in particular a wet or dry and/or unpressed sheet.
3. Method according to claim 1 or 2,
   characterised in that the plasma is produced at a distance of less than 20 cm, preferably less than 10 cm, preferably less than 5 cm from the process material.
4. Method according to one of claims 1 to 3,
   characterised in that the process material is brought into contact with the plasma or treated by means of the gas discharge on both sides.
5. Method according to one of claims 1 to 4,
   characterised in that the plasma or gas discharge is used to bleach the process material, in particular in a digester, in a bleach container (37) or in a feed line.
6. Method according to one of claims 1 to 5,
   characterised in that the process material is brought into contact with at least one electrode (44) for producing the plasma or gas discharge.
7. Method according to one of claims 1 to 6,
   characterised in that the content of carrier liquid, in particular water, in the process material is in the range between 40% and 99.9%, preferably in the range between 80% and 98% and in particular in the range between 85% and 98%.
8. Method according to one of claims 1 to 7,
   characterised in that radicals (59) are produced in the plasma or by means of the gas discharge and these act on the process material.
9. Method according to claim 8,
   characterised in that radicals (59) of a different type or composition are used for different states of the process material in a paper, cardboard or paperboard manufacturing process, in particular at different process stages.
10. Method according to claim 8 or 9,
    characterised in that the process material is exposed within a process stage in a paper or cardboard manufacturing process to radicals (59) of a different type or composition, preferably in temporal succession.
11. Method according to one of claims 8 to 10,
    characterised in that the radicals (59) produced are ozone (O₃) , hydrogen peroxide (H₂O₂) , hydroxyl (OH), HO₂ and/or HO₂ ^- .
12. Method according to one of claims 8 to 11,
    characterised in that during bleaching of the process material the plasma or gas discharge is applied in such a manner that the radicals (59) predominantly formed are ozone (O₃) and/or hydrogen peroxide (H₂O₂) .
13. Method according to one of claims 8 to 12,
    characterised in that during sieving and/or in the two-dimensionally distributed process material the plasma or gas discharge is applied in such a manner that the radicals (59) predominantly formed are hydroxyl (OH), HO₂ and/or HO₂ ^-.
14. Method according to one of claims 8 to 13,
    characterised in that the rate of production of the radicals (59) and/or the composition of the radicals (59) produced is/are controlled by influencing an amplitude (U), a pulse duration (62) and/or a pulse repetition rate (63) of the high-voltage pulses (66, 67).
15. Method according to one of claims 8 to 14,
    characterised in that a concentration of the radicals (59) produced is measured to control and regulate the production rate and/or type of radicals (59) produced.
16. Method according to one of claims 8 to 15,
    characterised in that a property of the suspension, preferably a quality property, in particular its opacity, gloss, whiteness, fluorescence or colour locus, is measured to control and regulate the production rate or composition of the radicals (59) produced.
17. Method according to one of claims 15 to 16,
    characterised in that the concentration or property is measured online.
18. Method according to one of claims 14 to 17,
    characterised in that the amplitude (U) of the high-voltage pulses (66, 67) is changed at a constant repetition rate (63) for regulation purposes.
19. Method according to one of claims 14 to 18,
    characterised in that the repetition rate (63) of the high-voltage pulses (66, 67) is changed at a constant amplitude (U) for regulation purposes.
20. Method according to one of claims 1 to 19,
    characterised in that the process material is enriched with oxygen in the region to which plasma is applied, preferably for bleaching purposes.
21. Method according to one of claims 1 to 20,
    characterised in that a high-voltage pulse duration (62) of less than 100 ns is used, preferably for bleaching purposes.
22. Method according to one of claims 1 to 21,
    characterised in that two-dimensionally distributed process material, in particular during sieving, is surrounded by an atmosphere enriched with water vapour in the region to which plasma is applied.
23. Method according to one of claims 1 to 22,
    characterised in that a high-voltage pulse duration (62) of 100 ns to 1 µs is used for two-dimensionally distributed process material, in particular pulp (39) or fibrous stock or forming or formed, as yet unpressed sheet, in particular during sieving.
24. Method according to one of claims 1 to 23,
    characterised in that high-voltage pulses (66, 67) with a duration (62) of less than 3 µs, preferably of less than 1 µs, preferably of less than 500 ns, are applied.
25. Method according to one of claims 14 to 24,
    characterised in that the amplitude (U) corresponding to at least twice the value, preferably at least three times the value, of a corona threshold voltage is applied to the electrodes for two-dimensionally distributed process material, in particular pulp (39) or fibrous stock or forming or formed, as yet unpressed sheet, in particular during sieving.
26. Method according to one of claims 1 to 25,
    characterised in that to produce the plasma or the corona discharge a DC voltage corona discharge is produced and the high-voltage pulses (66, 67) are superimposed on the DC voltage corona discharge.
27. Method according to one of claims 14 to 26,
    characterised in that a pulse repetition rate (63) between 10 Hz and 5 kHz, in particular from the range from 10 Hz to 10 kHz, is used.
28. Method according to one of claims 14 to 27,
    characterised in that the power injection of electrical energy into the plasma is predominantly controlled by way of the regulation of amplitude (U), pulse duration (62) and pulse repetition rate (63) of the superimposed high-voltage pulses.
29. Method according to one of claims 1 to 28,
    characterised in that a homogeneous, large-volume plasma with a high power density is produced without plasma constrictions or breakdowns occurring.
30. Method according to one of claims 1 to 29,
    characterised in that use is made of a DC voltage of such a height that in the plasma a stable DC corona discharge is formed in conjunction with superimposed high-voltage pulses.
31. Method according to claim 29,
    characterised in that the DC voltage used lies below that for stable operation without high-voltage pulse superimposition.
32. Method according to claim 30 or 31,
    characterised in that the total amplitude (DC voltage + pulse amplitude) used lies above the static breakdown voltage of the electrode arrangement.
33. Method according to one of claims 30 to 32,
    characterised in that the total amplitude used corresponds to two to five times the static breakdown voltage of the electrode arrangement.
34. Method according to one of claims 30 to 33,
    characterised in that the amplitude (U) of the high-voltage pulses is between 10% and 1000% of the DC voltage used.
35. Method according to one of claims 1 to 34,
    characterised in that a gas flow is produced perpendicular to the electrode arrangement (43, 44).
36. Method according to one of claims 1 to 35,
    characterised in that a gas flow is produced parallel to the electrode arrangement (43, 44).

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