EP1893803B9 - Method for treating a process material during the production of paper, card, or cardboard - Google Patents

Abstract

The invention relates to a method for treating a process material during the production of paper (27), card or cardboard. According to said method, a preferably non-thermal plasma or gas discharge with a large surface area, in particular a corona discharge is applied to the process material under at least atmospheric pressure. The use of chemicals in the production of paper or during the treatment of associated process materials is reduced by means of radicals (59) of a different type or composition, which are used in different process stages or for different types of process materials.

Description

The invention relates to a process for the treatment of a process material in the production of paper, cardboard or cardboard, wherein a, preferably non-thermal, large-area plasma or a gas discharge, in particular a corona discharge, is applied under at least atmospheric pressure and in the plasma generation and / or in the Gas discharge resulting radicals act on the process material.

• Kalandrieren,
• Oberflächenbehandlung mit einer Leim- oder Filmpresse,
• Streichen von Papier und/oder Karton mit verschiedenen Verfahren und Materialien,
• Beschichtung von Papier im Extruderverfahren,
• Kaschierung mit anderen Materialien (z.B. Aluminiumfolie),
• Verklebung von Papier und Karton,
• Tränken von Papier,
• Bleichen.

For example, today's conventional methods of treating and / or refining paper or paper surfaces are

• calendering,
• Surface treatment with a glue or film press,
• Painting paper and / or board with different processes and materials,
• Coating of paper in the extruder process,
• Lamination with other materials (eg aluminum foil),
• Bonding of paper and cardboard,
• Watering paper,
• Bleaching.

• Optische Eigenschaften, wie Glätte, Glanz, Weiße, Gleichmäßigkeit und Kontrast eines später durchgeführten Druckergebnisses,
• Verbesserung der Bedruckbarkeit für moderne Druckverfahren,
• Erhöhung der Papierfestigkeit und der Rupffestigkeit,
• Dimensionsstabilität des Papiers, Unempfindlichkeit gegen Feuchte,
• Erhaltung der Recyclingfähigkeit des Papiers.

Refinement is either integrated into a paper / board machine or on a separate line. Usually, a refinement takes place in several successive process steps. The following quality characteristics are positively influenced by the finishing:

• Optical properties, such as smoothness, gloss, whiteness, uniformity and contrast of a later printed result,
• Improvement of printability for modern printing processes,
• Increase paper strength and pick resistance
• Dimensional stability of the paper, insensitivity to moisture,
• Preservation of the recyclability of the paper.

A majority of these treatment methods are based on treatment with chemical substances. In particular, in the bleaching of paper or its starting materials bleaching chemicals are used to a high degree. Typical bleaching chemicals are chlorine, chlorine dioxide, sulphurous acids, extraction with caustic soda, oxygen, hydrogen peroxide and ozone. Depending on the method used, alkaline or acidic ambient conditions are required. Modern bleaching processes often make use of various bleaching stages in which various bleaching chemicals are used, each bleaching stage typically consisting of a mixing unit and a subsequent reaction tower. In these processes, the sometimes highly toxic (chlorine dioxide) or highly corrosive acids, alkalis or reagents must be transported in large quantities, stored, and after completion of the process also reprocessed or disposed of.

Out " A. Mizuno et al., OH radical generation by atmospheric pressure pulsed discharge plasma and its quantitative analysis by CO oxidation, J. Phys. D: Appl. Phys. 35. (2002), 3192-3198 "is a generation of radicals and ozone in gaseous media known.

So far, however, the application is limited to methods for purifying exhaust gases, see " Winands et al., 16th Intern. Symp. On Plasma Chemistry (ISPC 16), Taormina, Italy, June 22-27, 2003 ", or for the surface treatment of textiles and plastics, see also: Carneiro, N. et al., Industrial Impact of Corona Plasma Treatments in the Wet Processing of Cotton Materials, World Congresses Textiles in the Millennium 1999, pp. 43-44. 207 "or" PAF Herbert, E. Bourdin, New generation atmospheric pressure plasma technology for industrial on-line processing, Index'99. Nonwoven Congress, Manufacturing 1, EDANA, Geneva, CH, Apr 27-30, 1999 ".

Out DE 198 36 669 A1 the use of atmospheric plasmas for the treatment of paper surfaces is known.

Out WO 2004 101 891 A1 For example, a method of using non-thermal atmospheric plasma for paper treatment is known. A similar procedure is off FR 2711680 known. It is an object of the invention to further reduce the use of chemicals in the paper, board or board production or in the treatment of associated process goods.

The object is achieved by using radicals of different types or compositions for at least two different types of process goods or at at least two different process stages. By the simultaneous generation of a number of differently oxidizing and functionalizing radicals (O, OH, HO ₂ , HO ₂ ^- , O ₂ , O ₃ , ...) and the application of such various radicals to the process material at different points in the process can be beneficial in papermaking, the addition of solid and / or liquid chemicals can be reduced.

• Trockene Fasern,
• unverwobene Faserstoffe,
• voluminöse/r Pulpe oder Faser-Suspension oder Faserbrei,
• aufgelaufene/r und/oder flächig verteilte/r Pulpe oder Faser-Suspension oder Faserbrei,
• sich bildendes oder gebildetes, noch ungepresstes Blatt, mit Restfeuchte.

It is preferred that the process goods are selected from the following starting materials and / or intermediates:

• Dry fibers,
• unwoven fibrous materials,
• voluminous pulp or fiber suspension or pulp,
• accumulated and / or areal pulp or fiber suspension or pulp,
• forming or formed, still unpressed sheet, with residual moisture.

The aforementioned process items occur, e.g. as starting materials and / or intermediates, at different process stages within the papermaking process.

• Kochen,
• Mahlen,
• Bleichen,
• Sieben,
• Pressen.

It is particularly expedient if the process stages are selected from the following stages:

• Cook,
• Grind,
• Bleaching,
• Seven,
• Press.

With further advantage as radicals are produced ozone, hydrogen peroxide, hydroxyl radicals, HO ₂ and / or HO ₂ ^- . Radicals are preferably generated in gas discharges by high energy electrons colliding with and thereby dissociating or exciting molecules. In the dissociation, radicals are released immediately, while in the excitation by subsequent radiant transitions UV light is generated, which in turn reacts with air and / or water molecules and dissociates them.

According to a first preferred embodiment, the bleaching of the process material, the plasma or the gas discharge is applied in such a way that as radicals increasingly ozone and / or hydrogen peroxide are formed.

According to a second preferred embodiment, the plasma or the gas discharge is applied in such a way that the radicals OH, HO ₂ and / or HO ₂ ^{- are} formed during sieving and / or in distributed process material or in forming or formed, still unpressed sheet.

Advantageously, a generation rate of the radicals and / or the composition of the generated radicals is controlled and / or regulated by influencing an amplitude, a pulse duration and / or a pulse repetition rate of high-voltage pulses. Since the generation rate of the radicals generated by an electrical process and thus very well controlled in real time, such a method is very economical and can be readjusted within a very short time for different treatment outcomes, for example by a learning algorithm.

Another preferred embodiment of the invention is that for controlling and / or regulating the rate of production and / or the type of radicals generated a concentration of the generated radicals is measured.

In particular, with regard to a treatment at different process stages, it is advantageous for the control and / or regulation of the generation rate or the composition of the generated radicals for different types of process goods to have in each case a different property of the process material, preferably a quality property, in particular its opacity. Gloss, whiteness, fluorescence or color point, is measured.

It is also appropriate that the concentration or the property "online" is measured. With regard to an automation solution used for the method, it is of particular advantage that a measured value describing the quality characteristics can be evaluated virtually at the same time and reacted to it, for example, by influencing the generation rate.

In order to control the generation rate of the radicals, the amplitude of the high voltage pulses at a constant repetition rate and / or the repetition rate of the high voltage pulses at a constant amplitude can be changed for regulation.

It is particularly advantageous if the plasma and / or the gas discharge are generated between electrodes.

A further increase in the treatment result is achieved by enriching the process material with oxygen in the plasma-exposed area.

According to a particularly advantageous manner, high-voltage pulses having a duration of less than 10 μs are generated between the electrodes to generate 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 of high voltage single pulses of more than 10 μs in duration, is far less efficient.

Preferably, for process products having a 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. High-voltage pulses with a duration of more than 10 μs, as already mentioned, or high-voltage pulses which have a pulse edge which does not rise steeply enough, have the disadvantage here that their energy is nullified in highly conductive materials as an "ohmic component".

Thus, it is also expedient that in the case of a pulp, a fiber suspension or a pulp as process material, preferably when bleaching, a high-voltage pulse duration of less than 100 ns is used.

Furthermore, it is expedient that in the case of distributed process material or in forming or formed, still unpressed sheet, in particular when screening, a high-voltage pulse duration of 100 ns to 1 microseconds is used.

In order to achieve a further increase in the treatment result in an advantageous manner, the region exposed to plasma is surrounded by an atmosphere enriched with water vapor in process material which is distributed over a wide area or in which the sheet is still undpressed, in particular during sieving.

In addition, it is preferred that in the case of flatly distributed process material or in forming or formed, still unpressed sheet, in particular during screening, an amplitude corresponding to at least twice, preferably with at least three times the value of a corona threshold voltage applied to the electrodes ,

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.

Depending on the lifetime or type or composition of the generated radicals, it is expedient that a pulse repetition rate between 10 Hz and 5 kHz, in particular from the range of 10 Hz to 10 kHz, is used.

Furthermore, the power coupling of electrical energy into the plasma is preferably controlled predominantly via the regulation of amplitude, pulse duration and pulse repetition rate of the superposed high-voltage pulses.

It is also expedient that a homogeneous, large-volume plasma with high power density is produced, without resulting in plasma constrictions or punctures. By generating a "stable" plasma, the production rate can be kept high and constant, but if plasma constrictions or breakdowns occur, the production rate decreases again.

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

Advantageously, the DC voltage used is below the voltage for stable operation without high voltage pulse superposition.

Furthermore, it is expedient that the total amplitude used (DC voltage + pulse amplitude) is above the static breakdown voltage of the electrode arrangement.

It is expedient if the total amplitude used corresponds to two to five times the static breakdown voltage of the electrode arrangement.

Preferably, the voltage is selected so that the amplitude of the high voltage pulses is between 10% and 1000% of the DC voltage used.

In a preferred embodiment, the plasma is generated at a distance of less than 20 cm, preferably less than 10 cm, preferably less than 5 cm from the process material.

FIG 1

eine schematische Darstellung einer Papierherstel- lungsanlage mit einer Siebvorrichtung, einer Pressen Vorrichtung und einer Veredelungs- und/oder Trocken- anlage,

FIG 2

eine Bleichvorrichtung,

FIG 3

eine Darstellung (Schnitt) einer Anordnung zur Erzeu- gung 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) Hochspan- nungsimpulse mit hoher Impulswiederholrate,

FIG 5 bis FIG 10

Elektrodenanordnungen und Elektrodensysteme zur Erzeugung von Koronaentladungen: Platte-Platte-, Platte-Draht-Platte-, koaxiale Draht-Rohr-, Spitze- Platte-, Mehrfachspitzen-Platte-, Gitter-Platte (Rohr)-, Gitter-Gitter-Anordnungen,

FIG 11

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

FIG 12

eine Platten- oder Gitteranordnungen 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 Gasbla- sen, 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 pressing device and a finishing and / or drying plant,

FIG. 2

a bleaching device,

FIG. 3

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

FIG. 4

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

FIG. 5 to FIG. 10

Electrode arrays 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 completely above the medium on the screen, while the second electrode is formed by the screen itself,

FIG. 12

a plate or grid arrangement with curved surfaces for adaptation to vessel walls or use thereof as an electrode, concentric electrodes in tube form to use the existing piping or towers for the pulp as a reactor vessel,

FIG. 13

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

FIG. 14

a pulsed corona discharge system with coaxial wire tube, with beaded, very finely divided gas bubbles, so that in the discharge area 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 used in today's paper mills. 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 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 by mechanical pressure in a press device 11 and with the aid of steam heat on is drained. 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 mill 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 pulp. 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 the first type of process material, a first electrode 43 below the sieve device 9 and a second electrode 44 above the sieve device 9 are arranged according to the inventive method between the headbox 7 and the beginning region of the sieve device 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 produced by superimposing intensive, short-lasting high-voltage pulses having a high pulse repetition rate of typically 1 kHz on a DC corona discharge. 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 the carrier gas can be introduced into the treatment space between the electrodes 43 and 44 by means of 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 on the only a few seconds in the treatment area between the electrodes 43 and 44 lingering fiber suspension.

Analogous to that described above, an electrode system 47, 48 in the press device 11 generates a large-area plasma for treating the paper web 27 as a second type of process material. 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 can also be flowed 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 the streamer discharge, are particularly advantageous, as the paper 27 thereby partially acts as a dielectric barrier, which can delay or suppress the transition from streamer breakdown.

FIG. 2 shows how in a bleaching device 38 of the same system 1, a raw material 30, in particular pulp, is conveyed as a third type of process material via a conveyor belt 33 in 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 voltage pulses having a duration of typically 1 μs between the electrodes 43 'and 44'. A voltage necessary for the generation of radicals and ozone in the pulp fiber suspension is about 100 kV. The high voltage pulses are superimposed on the DC voltage to form a total amplitude of a few 10 kV to over 100 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 of the bleaching process, an oxygen-argon mixture, in the bleaching trough 37 via a gas line 80, which has been processed in a gas distributor 81, to be initiated.

FIG. 3 shows a sectional view of - to FIG. 2 alternative - 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 curve of the applied high voltage pulses is shown. A first pulse 66 and a second pulse 67, each having a pulse width 62, 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 some 10 kV of the 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 pulse width 62 of less than 1 microseconds, wherein the individual pulses 66, 67 have a high rising edge with a rise time 64 and a Wen.iger 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 the impulses is achieved that electrical breakdowns, to spatial and temporal Disturbances in the homogeneous plasma density distribution would be avoided.

FIG. 5 to FIG. 10 show examples of other electrode systems for generating corona discharges in preferably aqueous media. 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. Again there are two solid plate electrodes 70a and 70c at a fixed distance with a high voltage electrode 71 in the middle. 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. In the example shown, three tips 73 are connected to the high voltage pulse generator 46 via a high voltage line. The tips 73 are perpendicular to a grounded one Plate electrode 74 is arranged. 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 70d and 70e 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, a first grid 75a and a second grid 75b are parallel to each other. 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.

With regard to an increase in a treatment result or a bleaching process, it is advantageous for all listed electrode arrangements that a gas flow is generated perpendicular to the electrode arrangement. Likewise, it is expedient that a gas flow is generated parallel to the electrode arrangement

A hybrid discharge, wherein an electrode 76a is located entirely outside a pulp 39 to be bleached and a second electrode 76b is wholly or partially immersed in the pulp 39, is provided with the arrangement in FIG FIG. 11 generated. The electrode 76a is implemented as a grid electrode and forms the high voltage electrode which is in communication with the high voltage pulse generator 46. Also the grounded Counter electrode 76b is implemented as a grid electrode and communicates with the high voltage pulse generator 46.

In FIG. 12 a bleaching tub is shown 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 connected to each other and thus form the grounded counter electrodes, 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 another electrode arrangement shown. 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 are 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 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 (30)

1. Method for treating a process material during the production of paper (27), board or cardboard, a preferably non-thermal large-area plasma or a gas discharge, in particular a corona discharge, being applied under at least atmospheric pressure and radicals (59) produced during the plasma production and/or during the gas discharge acting on the process material,
   characterized in that, for at least two different types of process materials or in at least two different process stages, radicals (59) of different type or composition are used.
2. Method according to Claim 1,
   characterized in that the process materials are chosen from the following starting materials and/or intermediate products:

   - dry fibres,

   - unwoven fibrous materials,

   - voluminous pulp or fibrous suspension or fibrous stock (39),

   - discharged and/or two-dimensionally distributed pulp or fibrous suspension or fibrous stock (39),

   - a forming or formed, as yet unpressed sheet having residual moisture.
3. Method according to Claim 1 or 2,
   characterized in that the process stages are chosen from the following stages:

   - digestion,

   - refining,

   - bleaching,

   - screening,

   - pressing.
4. Method according to one of Claims 1 to 3,
   characterized in that the radicals (59) produced are ozone (O₃), hydrogen peroxide (H₂O₂), hydroxyl radicals (OH), HO₂ and/or HO₂ ^-.
5. Method according to one of Claims 1 to 4,
   characterized in that, during the bleaching of the process material, the plasma or the gas discharge is applied in such a way that the radicals (59) formed are increasingly ozone (O₃) and/or hydrogen peroxide (H₂O₂).
6. Method according to one of Claims 1 to 4,
   characterized in that, during the screening and/or in the case of two-dimensionally distributed process material or in the forming or formed, as yet unpressed sheet, the plasma or the gas discharge is applied in such a way that the radicals (59) formed are increasingly OH, HO₂ and/or HO₂ ^-.
7. Method according to one of Claims 1 to 6,
   characterized in that a production rate of the radicals (59) and/or the composition of the radicals (59) produced is controlled and/or regulated by influencing an amplitude (U), a pulse duration (62) and/or a pulse repetition rate (63) of high voltage pulses (66, 67).
8. Method according to Claim 7,
   characterized in that, in order to control and/or regulate the production rate and/or the type of radicals (59) produced, a concentration of the radicals (59) produced is measured.
9. Method according to Claim 7 or 8,
   characterized in that, in order to control and/or regulate the production rate or the composition of the radicals (59) produced for various types of process materials, in each case another property of the process material, preferably a quality property, in particular the opacity, gloss, whiteness, fluorescence or colour locus thereof, is measured.
10. Method according to either of Claims 8 and 9, characterized in that the concentration or the property is measured "online".
11. Method according to one of Claims 7 to 10,
    characterized in that, for the purpose of regulation, the amplitude (U) of the high voltage pulses (66, 67) is varied at constant repetition rate (63).
12. Method according to one of Claims 7 to 11,
    characterized in that, for the purpose of regulation, the repetition rate (63) of the high voltage pulses (66, 67) is varied at constant amplitude (U).
13. Method according to one of Claims 1 to 12,
    characterized in that the plasma or the gas discharge is produced between electrodes (43, 44).
14. Method according to one of Claims 1 to 13,
    characterized in that the process material is enriched with oxygen in the region to which plasma is applied.
15. Method according to one of Claims 7 to 14,
    characterized in that high voltage pulses (66, 67) with a duration (62) of less than 10 µs are produced between the electrodes (43, 44).
16. Method according to Claim 15,
    characterized in that high voltage pulses (66, 67) with a pulse duration (62) of less than 3 µs, preferably of less than 1 µs, preferably of less than 500 ns, are applied.
17. Method according to Claim 15 or 16,
    characterized in that, in the case of a pulp (39), a fibrous suspension or a fibrous stock as process material, preferably during bleaching, a high voltage pulse duration (62) of less than 100 ns is used.
18. Method according to one of Claims 13 to 15,
    characterized in that, in the case of two-dimensionally distributed process material or in the forming or formed, as yet unpressed sheet, in particular during screening, a high voltage pulse duration (62) of 100 ns to 1 µs is used.
19. Method according to one of Claims 1 to 18,
    characterized in that, in the case of two-dimensionally distributed process material or in the forming or formed, as yet unpressed sheet, in particular during screening, the region to which plasma is applied is surrounded by an atmosphere enriched with water vapour.
20. Method according to one of Claims 7 to 19,
    characterized in that, in the case of two-dimensionally distributed process material or in the forming or formed, as yet unpressed sheet, in particular during screening, an amplitude (U) corresponding to at least twice the value, preferably at least three times the value, of a corona strike voltage is applied to the electrodes.
21. Method according to one of Claims 7 to 20,
    characterized in that, in order to produce the plasma or the corona discharge, a DC corona discharge is produced and the high voltage pulses (66, 67) are superimposed on the DC corona discharge.
22. Method according to one of Claims 7 to 21,
    characterized 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.
23. Method according to one of Claims 7 to 22,
    characterized in that the power injection of electrical energy into the plasma is predominantly controlled via the regulation of amplitude (U), pulse duration (62) and pulse repetition rate (63) of the superimposed high voltage pulses.
24. Method according to one of Claims 1 to 23,
    characterized in that a homogeneous, large-volume plasma with a high power density is produced without plasma pinching or breakdowns occurring.
25. Method according to one of Claims 1 to 24, characterized in that use is made of a DC voltage of such a level that, in the plasma in conjunction with superimposed high voltage pulses, a stable DC corona discharge is formed.
26. Method according to one of Claims 7 to 25,
    characterized in that the DC voltage used lies below that for stable operation without high voltage pulse superimposition.
27. Method according to one of Claims 13 to 26,
    characterized in that the total amplitude used (DC voltage + pulse amplitude) lies above the static breakdown voltage of the electrode arrangement.
28. Method according to Claim 27,
    characterized in that the total amplitude used corresponds to two to five times the static breakdown voltage of the electrode arrangement.
29. Method according to one of Claims 26 to 28,
    characterized in that the amplitude (U) of the high voltage pulses is between 10% and 1000% of the DC voltage used.
30. Method according to one of Claims 1 to 29,
    characterized in that the plasma is produced at a distance from the process material of less than 20 cm, preferably less than 10 cm, preferably less than 5 cm.

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