DE102018130599A1 - Method and device for plasma-induced water purification - Google Patents

Abstract

The invention relates to a method for the purification of water contaminated with at least one waste water constituent, the waste water constituent having at least one compound with a binding energy that is lower than the binding energy of a simple hydrogen-oxygen bond, comprising the steps: - providing the contaminated water with a predetermined one Level in an unearthed water reservoir within a reaction space; - Acting exactly one, at a predetermined distance above the fill level of the water reservoir, flat-shaped, cooled plasma electrode with a high-frequency alternating voltage at atmospheric pressure such that a plasma is formed in the high-frequency field between the plasma electrode and a surface of the water, the energy input of which is sufficient that Compounds with a binding energy that is less than or equal to that of the simple hydrogen-oxygen bond are dissociated; - Detection of a concentration of the at least one waste water constituent.

Description

The invention relates to a method and a device for plasma-induced water purification.

Water purification, especially wastewater purification, is increasingly presenting wastewater disposal companies with major challenges. Waste water is contaminated by numerous pollutants, with nitrogen compounds being the second most common compounds after carbon compounds. Household wastewater is contaminated with nitrogen in the form of ammonium compounds. With increasing pH and increasing temperature, these react to form highly toxic ammonia (NH3). Nitrites or nitrates from groundwater, for example, also pollute the wastewater. Further burdens arise, for example, from the introduction of hormones or drug residues.

Previous methods for purifying the wastewater are immensely complex and very large amounts of energy are required for this. In addition, sewage treatment plants are only able to purify wastewater to a limited extent. In particular, residual wastewater such as vapor water, press water and centrate water can no longer be easily treated by the mostly biological processes in the prior art. Experimental methods such as the use of conventional plasma processes are not efficient enough for large-scale use as in the paper "Plasma-based water purification: Challenges and prospects for the future" by John E. Foster, in Physics of Plasmas 24, 055501 (2017) described.

This is where the invention comes in, which provides an efficient method for water purification even of highly contaminated wastewater.

According to a first aspect, the invention relates to a method for the purification of water contaminated with at least one waste water constituent, the waste water constituent having at least one compound with a binding energy which is less than the binding energy of a simple hydrogen-oxygen bond.

• - Bereitstellen des belasteten Wassers mit einer vorbestimmten Füllhöhe in einem ungeerdeten Wasserreservoir innerhalb eines Reaktionsraumes;
• - Beaufschlagen genau einer in einem vorbestimmten Abstand über der Füllhöhe des Wasserreservoirs angeordneten flächig ausgebildeten, gekühlten Plasmaelektrode mit einer hochfrequenten Wechselspannung bei Atmosphärendruck, derart, dass sich im Hochfrequenzfeld zwischen der Plasmaelektrode und einer Oberfläche des Wassers ein Plasma ausbildet, dessen Energieeintrag ausreichend ist, dass Verbindungen mit einer Bindungsenergie, die kleiner oder gleich derjenigen der einfachen Wasserstoff-Sauerstoffbindung ist, dissoziiert werden;
• - Erfassen einer Konzentration des mindestens einen Abwasserinhaltsstoffs.

The process includes the steps:

• - Providing the contaminated water with a predetermined level in an unearthed water reservoir within a reaction space;
• - Acting exactly one, at a predetermined distance above the fill level of the water reservoir, flat-shaped, cooled plasma electrode with a high-frequency alternating voltage at atmospheric pressure, such that a plasma is formed in the high-frequency field between the plasma electrode and a surface of the water, the energy input of which is sufficient that Compounds with a binding energy less than or equal to that of the simple hydrogen-oxygen bond are dissociated;
• - Detecting a concentration of the at least one waste water ingredient.

The invention uses what is known as plasma electrolysis, that is to say a non-thermal plasma which initiates electron impact-induced processes. This enables dissociative electron deposits and dissociative excitations of the water and the waste water constituents contained therein. According to the invention, the dissociation reactions do not take place on two electrodes and / or a membrane surface, as in the other methods, but in a plasma-chemical gas and water volume process, which results in much higher efficiencies than in conventional methods for water purification. The discharges in this gas and water volume as well as on the water surface lead to the generation of free electrons in one for the dissociation of compounds with binding energies that are lower than that of the simple hydrogen-oxygen bond, favorable energy range (up to 20 eV). Collisions with the water and gas molecules lead to the formation of numerous excited molecular and atomic species. The dissociation takes place via a two-stroke reaction and an extreme charge shift between the electrode on the one hand and the water and the wastewater constituents it contains.

The invention further includes the finding that a large number of waste water constituents have compounds which have a lower binding energy than that of simple hydrogen-oxygen binding. For example, ammonium or nitrates have a simple N-H bond, and there are often simple carbon compounds in hormones and drug residues. The water can thus be cleaned of the undesired wastewater constituents by dissociating these compounds without the water itself being used up significantly, since the compounds of the wastewater constituents are dissociated faster than the hydrogen-oxygen bond.

The invention is also based on the knowledge that by using high-frequency alternating voltage with only one plasma electrode, plasmas can be ignited at atmospheric pressure and, in particular, flat plasmas can be operated at atmospheric pressure, which is not possible with direct voltage. Operating at atmospheric pressure significantly lowers the cost of equipment and operation. The plasma forms flat between the water surface of the water in the reservoir and the plasma electrode, so that the dissociation of wastewater constituents, which have binding energies that are lower than that of water, takes place flatly and in the entire volume. This also enables large-volume water purification.

In the prior art, such as the DE 10 2011 081 915 A1 or the paper "Plasma-based water purification: Challenges and prospects for the future" by John E. Foster, in Physics of Plasmas 24, 055501 (2017), known processes of plasma electrolysis that use two electrodes, on the other hand, only form at atmospheric pressure selective discharges between the electrodes. Another advantage of the high-frequency discharges produced in the context of the invention compared to discharge forms operated with direct voltage is that the electrodes need not have any direct contact with the plasma due to the displacement currents occurring in high-frequency plasmas. In this way, the entry of impurities by the electrode material into the plasma is prevented and at the same time a longer service life of the electrode systems themselves is ensured.

The invention further includes the knowledge that the direct contact between the electrode and water, and thus contamination and electrode corrosion, can be avoided by forming a plasma between the plasma electrode and the water reservoir.

It has been shown that, due to the dissociation process in the plasma, hydrogen and oxygen, which are generally released, do not occur locally, but mix as a gas with water vapor and water mist formed in the plasma to form a gas mixture. The plasma process leads to the inertization of the hydrogen / oxygen gas mixture, i.e. the mixture is difficult to ignite. The dissociation does not lead to a recombination of the two gases in the reaction space. This allows hydrogen and oxygen to be routed through a common exhaust pipe and separated by membranes.

With the method according to the invention, larger amounts of contaminated water can therefore be cleaned efficiently at lower costs.

Exactly one flat-shaped plasma electrode is understood in the context of this application in addition to the preferred variant of a one-piece plasma electrode and also a plasma electrode arrangement comprising a plurality of individual electrodes arranged next to one another at a predetermined distance above the water reservoir, which form exactly one plasma electrode.

Advantageous embodiments of the method according to the invention are described below. The additional features of the exemplary embodiments can be combined with one another to form further embodiments, unless they are expressly described in the description as alternatives to one another.

• - Vergleichen der erfassten Konzentration mit einem hinterlegten Grenzwert und bei dem, wenn die erfasste Konzentration kleiner oder gleich dem hinterlegten Grenzwert ist:
• - das Beaufschlagen beendet wird oder
• - das behandelte Wasser abgeführt und durch belastetes Wasser ersetzt wird.

In a preferred embodiment, the method further comprises:

• - Comparison of the recorded concentration with a stored limit value and, if the recorded concentration is less than or equal to the stored limit value:
• - the application is ended or
• - The treated water is removed and replaced by contaminated water.

Alternatively, the application is carried out over a predetermined period of time and only then is the concentration recorded and compared accordingly. The comparisons can be used to ensure that the treated water has been sufficiently cleaned for each connection.

In one embodiment, the concentration is recorded continuously, so that permanent monitoring is possible. Alternatively, the concentration can also be determined at predetermined time intervals.

The stored limit value is preferably a legal limit value or less than a legal limit value. The treated water can therefore also be used for further uses, such as drinking water, for example the limit value for organic carbon in the drinking water is 150 mg / l; for ammonium at 0.5 mg / l. For the discharge of organic carbon into the wastewater, the limit value for heavy polluters is 2000 mg / l.

For example, municipal or industrial wastewater, wood gas condensate water, vapor water, centrate water, press water, ammonia water, liquid manure or liquid digestate can be considered as contaminated water.

The at least one wastewater ingredient is preferably selected from the group of nitrogen compounds, in particular nitrogen-hydrogen compounds, carbon compounds, boron, oxygen, phosphorus, sulfur or chlorine compounds. Hormones or drug residues can also be wastewater constituents in the sense of this application, provided that they have at least one compound with a lower binding energy than that of the simple hydrogen-oxygen bond. The water purification according to the invention thus makes it possible to remove a very wide range of waste water constituents without having to use specific processes for each constituent.

It has been shown that painkillers such as diclofenac, the anti-epileptics carbamazepine and gabapentin, beta-blockers and antibiotics in particular can be easily cleaved with the method according to the invention and thus removed from the waste water.

The following table provides an overview of common compounds that occur in wastewater constituents and have a lower binding energy, also enthalpy of binding, than the simple hydrogen-oxygen bond. Table 1 enthalpy of binding ΔH in kJ per mole of different compounds with hydrogen with carbon with oxygen same element binding ΔH Binding ΔH binding ΔH binding ΔH HH 436 ON 201 HH 436 HC 413 CC 348 OP 335 NN 163 H- 463 CH 413 OF 193 N = N 418 HN 391 CO 358 O-Cl 208 OO 146 HP 322 CN 305 O-Br 234 PP 172 HS 367 CP 264 OI 234 SS 255 H-Cl 431 CS 272 H-Br 366 C-Cl 339 HI 298 C-Br 285 CI 218

As can be seen in Table 1, a large number of hydrogen compounds are equipped with a lower binding energy than that of the hydrogen-oxygen bond, so that hydrogen is advantageously also increasingly released as a by-product of water purification. The waste water constituent advantageously comprises ammonium NH4 + or ammonia NH3. The dissociation of these compounds results in a particularly high hydrogen yield, which is a preferred by-product of the water purification according to the invention. It has been shown in the context of the invention that the dissociation of hydrogen-nitrogen compounds with a simple hydrogen-nitrogen bond, which is favored by the lower binding energy compared to the dissociation of water, means that they can not only be removed from the contaminated water, but also there is also a higher hydrogen yield than with the dissociation of purified water. Thus, hydrogen can also be produced inexpensively as a by-product using the method according to the invention

To apply the high-frequency AC voltage to the plasma electrode, a high-frequency generator with a predetermined output impedance is advantageously used, which is connected to the plasma electrode via a matching network for impedance matching of an impedance of the plasma and the output impedance of the high-frequency generator. A plasma has a complex impedance that is dependent on numerous external parameters (for example on the plasma chemical process taking place) and is variable over time and therefore generally different from the output impedance of the generator. The impedance of the Plasma is particularly dependent on the distance from the plasma electrode to the water surface, water composition, temperature in the reaction space and the atmosphere in the reaction space. A so-called matching network (also matching network or matchbox) is therefore advantageously used as a link between the high-frequency generator and gas discharge, which matches the ohmic and capacitive components of the plasma with the impedance specified by the generator, i.e. the variable load of the plasma on the internal resistance of the generator adapts and thus minimizes reflection of energy from the system.

This can be realized, for example, by measuring an intensity and power of a return wave and a return wave to the high-frequency generator and, depending on the power of the incoming wave, stabilizing the generator power and the power of the return wave depending on a conductivity or the pH of the contaminated water is minimized via the adaptation network. The condenser and coil are changed according to the conductivity or pH of the water, which also changes as the cleaning progresses.

The high-frequency alternating voltage preferably has a frequency in the range from 1 to 40 MHz, in particular in the range from 10 to 20 MHz, and / or the plasma electrode has a power in the range from 100 W to 40 kW, preferably in the range from 1 to 5 kW applied. In these areas, the process delivers a high yield of purified water with optimized energy input.

• - Sammeln von durch die Dissoziation entstehenden Gasen in einer gemeinsamen Abgasleitung,
• - Trennen der entstehenden Gase über einen mehrstufigen Membranprozess und/oder über die Verwendung selektiver Adsorptionsverfahren.

In a further embodiment, the method further comprises the steps

• Collecting gases resulting from the dissociation in a common exhaust pipe,
• - Separation of the resulting gases using a multi-stage membrane process and / or using selective adsorption processes.

Gases such as hydrogen, oxygen or also methane are desired possible by-products of water purification. In this embodiment, a separation of the resulting gases and thus the collection of the desired by-products separately from one another is easily possible.

In a selective adsorption process, the hydrogen-oxygen mixture is passed through a reservoir in which there is at least one adsorber, to which the oxygen is preferably bound via adsorption. The hydrogen is initially released on its own. The adsorbed oxygen can then be released from the adsorber in a further step, for example by pressurization or thermal dissolution.

Ceramic materials with a large surface area and a high adsorption capacity for oxygen, in particular so-called molecular sieves, are preferably used as adsorbers. In addition to zeolites, i.e. crystalline aluminosilicates, these can also be carbon molecular sieves. Silica gel (silica gel) or activated aluminum oxide can preferably be used.

Contaminated water is preferably added to the water reservoir. In addition, the fill level and thus the distance to the plasma electrode can be kept largely constant. This reduces the regulatory effort for plasma generation, for example via an adaptation network.

In an advantageous embodiment, the plasma electrode is coated with a dielectric and the plasma is designed as a barrier discharge. Dielectric barrier discharges, also known as dielectric barrier discharges (DBDS), arise when two electrodes, in the present case the plasma electrode and the water, which itself has a certain impedance but does not have an electrode or a grounding by at least one insulator , for example, separates a dielectric. The barrier discharge usually consists of short-lived filamentary micro-discharges with a low discharge current. It limits the electrical charge transported by the discharge, i.e. it limits the current flow in the system and distributes the discharge over the electrode surface. The yield of purified water can be positively influenced by maximizing the area of micro-discharges at a certain frequency, temperature and impedance. The dielectric on the plasma electrode prevents the charge carriers from recombining with the electrode and increases the dissociation efficiency.

A ceramic material, in particular one which comprises aluminum oxide or titanium dioxide, is preferably used as the dielectric.

In one embodiment, air, Ar, He or Ne is used as the atmosphere in the reaction space as part of a starting process, that is to say when the plasma is ignited.

The water in the water reservoir preferably has a temperature in the range from 3 to 99 ° C., in this temperature range the water is liquid. A range from 10 to 90 ° C. is further preferred, in which the efficiencies are particularly high.

In one embodiment, the plasma electrode is cooled to a temperature in the range from 60 to 70 ° C.

• - Sammeln von durch die Dissoziation entstehenden Gasen in einer gemeinsamen Abgasleitung
• - Messung einer Methankonzentration in der gemeinsamen Abgasleitung
• - Aufrechterhaltung der Beaufschlagung bis eine Mindestkonzentration von Methan in der Abgasleitung erreicht ist.

In a further development, the contaminated water comprises at least one carbon compound as a waste water ingredient. Then it is advantageous if the method additionally comprises the following steps:

• - Collection of gases resulting from the dissociation in a common exhaust pipe
• - Measurement of a methane concentration in the common exhaust pipe
• - Maintenance of the admission until a minimum concentration of methane in the exhaust pipe is reached.

If carbon compounds in the wastewater constituents are dissociated as part of the plasma process, carbon is released which initially reacts to carbon monoxide or carbon dioxide, for example with oxygen from the latent water dissociation or other dissociation reactions. If a sufficient amount of carbon monoxide or carbon dioxide is present, the plasma reacts favorably with the nitrogen to methane, which is also at least from the latent water dissociation. A hydrogen-nitrogen compound is preferably present at the same time as a waste water ingredient, so that larger amounts of hydrogen are released for the methanation. Methane is a desired by-product of water purification and can be used as a fuel alone or together with the hydrogen that is also produced.

An oxygen compound is advantageously present in the water as a further wastewater ingredient.

Various parameters favor methanization while the process still has cleaning performance. Depending on the focus, the exposure can then be adjusted according to the production of the desired amounts of methane or faster cleaning.

To promote methanization, the plasma electrode is preferably cooled to a temperature in the range from 80 to 90 ° C. It is also advantageous if a catalyst is used for the methanation of carbon monoxide and / or carbon dioxide.

Various catalysts and catalyst systems are suitable for the methanation of CO ₂ and CO, in particular combinations of active components, substrates and promoters. Transition metals are preferably used as the active component, nickel, ruthenium in particular, but also cobalt or iron forming good catalysts. Ni / Al ₂ O ₃ and other Ni systems for CO methanation and Ni, Ru, Co on various substrates, for example Al ₂ O ₃ , SiO ₂ , TiO ₂ , ZrO ₂ or CeO ₂ or the ashes of are particularly preferred Rice husks, for CO ₂ methanation.

The methanation is carried out, for example, supported by a catalyst, which can be implemented as a coating on the plasma electrode or as a bed or foam in a catalyst chamber in the plasma electrode or in the exhaust line. In one embodiment, the coating is a pure catalyst layer, for example Ni, on the plasma electrode or, as an additive, the catalyst is part of a dielectric coating of the plasma electrode, for example an Al2O3Ni layer. Alternatively, the catalyst is present as a catalyst powder / granulate or open-cell foam in a chamber of the plasma electrode. This chamber can then be flowed through and the plasma electrode has corresponding openings. Finally, the catalyst can also be arranged in a chamber in or on the exhaust pipe as a powder, granulate or open-cell foam.

To promote methanization, CO ₂ and / or CO can be used as the atmosphere in the reaction space as part of a starting process, so that CO ₂ and / or CO is available for methanization from the start, thus shortening the starting phase of the methanization.

It is furthermore advantageous if methane is subsequently separated off via at least one further membrane or a selective adsorption process, so that pure methane is available for further use or this is specifically mixed with hydrogen in a predetermined ratio in accordance with the requirements for a methane-hydrogen fuel can be. ZSM-5, Zeolite Socony Mobil-5, a synthetic high-silica aluminosilicate zeolite, is used here as the adsorber.

According to a further development, by setting a temperature in the range of less than 70 degrees and using a plasma electrode made of aluminum or steel and / or with an Al2O3 coating from the dissociation of carbon compounds in the contaminated water, carbon dioxide and hydrogen in the reaction space largely become the formation of methane suppressed, so that removed carbon dioxide and hydrogen can be converted into carbon monoxide in an inverse CO-shift compression by supplying electricity and heat. The resulting carbon monoxide is then fed with further hydrogen from the purification to a Fischer-Tropsch synthesis and then in turn, together with further hydrogen from the purification via hydrocracking, isomerization or distillation, converted to gasoline, kerosene or diesel. Alternatively, carbon monoxide generated directly from the cleaning process can also be used.

• in einem Reaktionsraum
  • - ein ungeerdetes Wasserreservoir;
  • - genau eine flächig ausgebildete, gekühlte Plasmaelektrode, die in einem vorbestimmten Abstand über einer Füllhöhe des Wasserreservoirs angeordnet ist,
  • - einen Sensor zum Erfassen einer Konzentration des Abwasserinhaltsstoffs
  und außerhalb des Reaktionsraumes
  • - einen Hochfrequenzgenerator mit vorbestimmter Ausgangsimpedanz, der mit der Plasmaelektrode über ein Anpassungsnetzwerk zur Impedanzanpassung einer Impedanz eines an der Plasmaelektrode entstehenden Plasmas und der Ausgangsimpedanz des Hochfrequenzgenerators verbunden ist.

According to a second aspect, the invention relates to a device for cleaning water contaminated with at least one waste water constituent, comprising:

• in a reaction room
  • - an unearthed water reservoir;
  • exactly one flat, cooled plasma electrode which is arranged at a predetermined distance above a fill level of the water reservoir,
  • - A sensor for detecting a concentration of the waste water content
  and outside the reaction space
  • - A high-frequency generator with a predetermined output impedance, which is connected to the plasma electrode via a matching network for impedance matching of an impedance of a plasma arising at the plasma electrode and the output impedance of the high-frequency generator.

A so-called matching network (also matching network or matchbox) is advantageously used as a link between the high-frequency generator and the plasma, which matches the ohmic and capacitive components of the plasma with an output impedance specified by the generator. The impedance of the plasma is particularly dependent on the distance of the plasma electrode from the water surface, water composition, the nature of a housing around the reaction space, temperature in the reaction space and the atmosphere in the reaction space.

The device also shares the advantages and embodiments of the method according to the first aspect of the invention.

In one embodiment, the high-frequency generator comprises a measuring device for measuring an intensity and a power of a returning and a returning wave. It is particularly preferred if the measuring device comprises a directional coupler and two detectors in the high-frequency generator.

The output impedance of the high-frequency generator is preferably 50 ohms and / or an output power of the high-frequency generator is between 100 W and 40 kW. It has been shown that, particularly with this output impedance, a plasma is formed particularly reliably with good cleaning performance at the same time.

The adaptation network advantageously comprises at least one motor-controlled capacitor and at least one variable coil. Together they form an electrical resonant circuit, via which the impedance matching can react continuously to fluctuating loads caused by the plasma. In a further embodiment, the capacitors and coils are tuned automatically using a reflection and standing world control loop method.

A common exhaust gas line for emerging gases is preferably arranged on the reaction chamber. It is particularly advantageous for the extraction of different gases if in the common Exhaust line or a plurality of membranes and / or adsorbers for separating gases formed are arranged at one end of the common exhaust line.

In one embodiment, the exhaust gas line is arranged in the plasma electrode, i. H. the plasma electrode has at least one opening to the reaction space and at least part of the exhaust pipe.

Polymer membranes are preferably used, for example for the separation of hydrogen and oxygen. Alternatively, a reservoir is arranged in the common exhaust line or at one end of the common exhaust line, in which there is at least one adsorber, for example in the form of a bed or an open-cell foam. The adsorber for separating hydrogen and oxygen is advantageously designed in such a way that oxygen is preferably bound to it via adsorption. Combinations of membranes and adsorbers can also be used for the different gases produced. Polymer membranes separate CO2 and CH4 and N2 well, but also, for example, zeolites such as ZSM-5, a synthetic high-silica “aluminosilicate zeolite can be used here.

In a further development, a device for dissolving the adsorbed oxygen is present on the reservoir. This can be designed, for example, in the form of a heater for the thermal dissolution of the oxygen or in the form of a vacuum pump for the application of negative pressure. The reservoir can also have a closable opening through which the loaded absorber can be exchanged for an unloaded one after adsorption.

Ceramic materials with a large surface area and a high adsorption capacity for oxygen, in particular so-called molecular sieves, are preferably used as adsorbers. In addition to zeolites, i.e. crystalline aluminosilicates, these can also be carbon molecular sieves. Silica gel (silica gel) or activated aluminum oxide can preferably be used. In one embodiment, the plasma electrode has a metal, in particular aluminum, which is preferred because of the good conductivity at relatively low cost.

The plasma electrode is advantageously coated with a dielectric, in particular comprising aluminum oxide and / or nickel and / or titanium dioxide. This allows the plasma to be formed via a barrier discharge. The dielectric preferably has a layer thickness of 200 to 1000 μm.

The device preferably has at least one supply for at least one gas into the reaction space, in particular for air, Ar, He, Ne, CO and / or CO ₂ .

In one embodiment, a plasma electrode arrangement from a plurality of individual electrodes arranged next to one another forms the exactly one plasma electrode at a predetermined distance above the water reservoir. With this embodiment, the energy input can be optimized and at the same time the manufacturing and cooling effort can be improved compared to a one-piece plasma electrode of the same area.

In this embodiment, each individual electrode is connected to the high-frequency generator. Alternatively, however, it is also possible to use a plurality of high-frequency generators with a predetermined output impedance, each of which is connected to a single electrode or a group of individual electrodes via a respective matching network for impedance matching of an impedance of a plasma produced at the respective single electrode or group of individual electrodes and the output impedance of the high-frequency generator .

The water reservoir preferably has an inlet and at least one outlet. It is further preferred if the sensor is arranged in the area of the at least one outlet. The water reservoir thus enables a continuous process in which continuously contaminated water is added and purified water is removed via the drain. The removal can be made dependent on the measurement result of the sensor, i.e. on the actual degree of cleaning. For this purpose, for example, a valve can be arranged on the outlet that is opened in the area of the sensor only when the limit falls below the limit.

In a further embodiment, the water reservoir comprises a fill level control, which is designed to keep the fill level of the water almost constant, or an overflow. The filling height is preferably in the range from 1.5 to 10 cm.

For the most complete possible cleaning of the water volume in the water reservoir, the plasma electrode is at a distance of 1 to 2 cm from each wall of the reaction space. An area dimension of the plasma electrode between 15 cm ² and 450 cm ² is advantageous for treating large amounts of water.

It is further preferred if the predetermined distance between the plasma electrode and fill level of the water reservoir is in a range from 0.2 to 2 cm, more preferably in the range from 0.2 to 1 cm.

If the production of methane is absolutely in the foreground, the step of recording the concentration of the at least one wastewater ingredient can also be omitted. According to a third aspect, the invention therefore relates to a method for extracting methane from water contaminated with at least one waste water constituent, the waste water constituent having at least one carbon compound with a binding energy which is lower than the binding energy of a simple hydrogen-oxygen bond.

• - Bereitstellen des belasteten Wassers mit einer vorbestimmten Füllhöhe in einem ungeerdeten Wasserreservoir innerhalb eines Reaktionsraumes;
• - Beaufschlagen genau einer in einem vorbestimmten Abstand über der Füllhöhe des Wasserreservoirs angeordneten flächig ausgebildeten, gekühlten Plasmaelektrode mit einer hochfrequenten Wechselspannung bei Atmosphärendruck, derart, dass sich im Hochfrequenzfeld zwischen der Plasmaelektrode und einer Oberfläche des Wassers ein Plasma ausbildet, dessen Energieeintrag ausreichend ist, dass Verbindungen mit einer Bindungsenergie, die kleiner oder gleich derjenigen der einfachen Wasserstoff-Sauerstoffbindung ist, dissoziiert werden;
• - Sammeln von durch die Dissoziation entstehenden Gasen in einer gemeinsamen Abgasleitung
• - Messung einer Methankonzentration in der gemeinsamen Abgasleitung
• - Aufrechterhaltung der Beaufschlagung bis eine Mindestkonzentration von Methan in der Abgasleitung erreicht ist.

The method according to the third aspect then comprises the steps:

• - Providing the contaminated water with a predetermined level in an unearthed water reservoir within a reaction space;
• - Acting exactly one, at a predetermined distance above the fill level of the water reservoir, flat-shaped, cooled plasma electrode with a high-frequency alternating voltage at atmospheric pressure, such that a plasma is formed in the high-frequency field between the plasma electrode and a surface of the water, the energy input of which is sufficient that Compounds with a binding energy less than or equal to that of the simple hydrogen-oxygen bond are dissociated;
• - Collection of gases resulting from the dissociation in a common exhaust pipe
• - Measurement of a methane concentration in the common exhaust pipe
• - Maintenance of the admission until a minimum concentration of methane in the exhaust pipe is reached.

This aspect of the invention is based on the knowledge that carbon and hydrogen released from waste water constituents are converted to methane in the plasma process. If carbon compounds in the wastewater constituents are dissociated as part of the plasma process, carbon is released which initially reacts to carbon monoxide or carbon dioxide, for example with oxygen from the latent water dissociation or other dissociation reactions. If there is a sufficient amount of carbon monoxide and / or carbon dioxide, for example at least 10% carbon dioxide, the plasma reacts favorably with the hydrogen to methane which is also at least from the latent water dissociation. Hydrogen should be present in a concentration of at least 30%. So methane is not only a desired by-product of water purification, but in this aspect of the invention the focus is on the inexpensive production of methane, which is subsequently used alone or, for example, together with the hydrogen that is also produced as a fuel. This aspect of the invention thus represents a comparatively inexpensive, energy-efficient and inexpensive method for producing methane.

At the same time, a hydrogen-nitrogen compound is preferably present as the wastewater ingredient, so that larger amounts of hydrogen are released for the methanation and thus the energy efficiency is further improved.

To promote methanization, the plasma electrode is preferably cooled to a temperature in the range from 80 to 90 ° C. It is also advantageous if a catalyst is used for the methanation of carbon monoxide and / or carbon dioxide.

Various catalysts and catalyst systems are suitable for the methanation of CO ₂ and CO, in particular combinations of active components, substrates and promoters. Transition metals are preferably used as the active component, nickel, ruthenium in particular, but also cobalt or iron forming good catalysts. Ni / Al ₂ O ₃ and other Ni systems for CO methanation and Ni, Ru, Co on various substrates, for example Al ₂ O ₃ , SiO ₂ , TiO ₂ , ZrO ₂ or CeO ₂ or the ashes of are particularly preferred Rice husks, for CO ₂ methanation.

The methanation is carried out, for example, supported by a catalyst which acts as a coating on the plasma electrode or as a bed or foam in a catalyst chamber in the plasma electrode or can be implemented in the exhaust pipe. In one embodiment, the coating is a pure catalyst layer, for example Ni, on the plasma electrode or, as an additive, the catalyst is part of a dielectric coating of the plasma electrode, for example an Al2O3Ni layer. Alternatively, the catalyst is present as a catalyst powder / granulate or open-cell foam in a chamber of the plasma electrode. This chamber can then be flowed through and the plasma electrode has corresponding openings. Finally, the catalyst can also be arranged in a chamber in or on the exhaust pipe as a powder, granulate or open-cell foam.

To promote methanization, CO ₂ and / or CO can be used as the atmosphere in the reaction space as part of a starting process, so that CO ₂ and / or CO is available for methanization from the start, thus shortening the starting phase of the methanization.

It is furthermore advantageous if methane is subsequently separated off via at least one further membrane or a selective adsorption process, so that pure methane is available for further use or this is specifically mixed with hydrogen in a predetermined ratio in accordance with the requirements for a methane-hydrogen fuel can be. ZSM-5, Zeolite Socony Mobil-5, a synthetic high-silica aluminosilicate zeolite, is used here as the adsorber.

The method according to the third aspect of the invention also shares the advantages and embodiments of the method according to the first aspect of the invention.

• in einem Reaktionsraum
  • - ein ungeerdetes Wasserreservoir;
  • - genau eine flächig ausgebildete, gekühlte Plasmaelektrode, die in einem vorbestimmten Abstand über einer Füllhöhe des Wasserreservoirs angeordnet ist,
  und außerhalb des Reaktionsraumes
  • - einen Hochfrequenzgenerator mit vorbestimmter Ausgangsimpedanz, der mit der Plasmaelektrode über ein Anpassungsnetzwerk zur Impedanzanpassung einer Impedanz eines an der Plasmaelektrode entstehenden Plasmas und der Ausgangsimpedanz des Hochfrequenzgenerators verbunden ist; sowie
  • - eine gemeinsame Abgasleitung am Reaktionsraum und einen darin oder an einem Ende der Abgasleitung angeordneten Sensor zum Erfassen einer Konzentration von Methan.

According to a fourth aspect, the invention relates to a device for extracting methane from water contaminated with at least one waste water constituent, comprising:

• in a reaction room
  • - an unearthed water reservoir;
  • exactly one flat, cooled plasma electrode which is arranged at a predetermined distance above a fill level of the water reservoir,
  and outside the reaction space
  • a high-frequency generator with a predetermined output impedance, which is connected to the plasma electrode via a matching network for impedance matching of an impedance of a plasma generated at the plasma electrode and the output impedance of the high-frequency generator; such as
  • - A common exhaust pipe on the reaction chamber and a sensor arranged therein or at one end of the exhaust pipe for detecting a concentration of methane.

In one embodiment, the exhaust gas line is arranged in the plasma electrode, i. H. the plasma electrode has at least one opening to the reaction space and at least part of the exhaust pipe.

A catalyst is preferably used, which can be implemented as a coating on the plasma electrode or as a bed or foam in a catalyst chamber in the plasma electrode or in the exhaust gas line. In one embodiment, the coating is a pure catalyst layer, for example Ni, on the plasma electrode or, as an additive, the catalyst is part of a dielectric coating of the plasma electrode, for example an Al2O3Ni layer. Alternatively, the catalyst is present as a catalyst powder / granulate or open-cell foam in a chamber of the plasma electrode. This chamber can then be flowed through and the plasma electrode has corresponding openings. Finally, the catalyst can also be arranged in a chamber in or on the exhaust pipe as a powder, granulate or open-cell foam.

The device according to the fourth aspect of the invention also shares the advantages and embodiments of the device according to the third aspect of the invention.

Exemplary embodiments can also be found in the claims.

• 1 Eine schematische Darstellung eines Ausführungsbeispiels einer Vorrichtung zur plasmainduzierten Wasserreinigung gemäß dem zweiten Aspekt der Erfindung;
• 2 Eine schematische Darstellung eines weiteren Ausführungsbeispiels einer Vorrichtung zur plasmainduzierten Wasserreinigung gemäß dem zweiten Aspekt der Erfindung;
• 3 Eine schematische Darstellung eines Ausführungsbeispiels einer Vorrichtung zur plasmainduzierten Methangewinnung gemäß dem vierten Aspekt der Erfindung;

Further exemplary embodiments of the device and of the method are described below with reference to the drawings. Show it:

• 1 A schematic representation of an embodiment of a device for plasma-induced water purification according to the second aspect of the invention;
• 2nd A schematic representation of a further embodiment of a device for plasma-induced water purification according to the second aspect of the invention;
• 3rd A schematic representation of an embodiment of a device for plasma-induced methane production according to the fourth aspect of the invention;

1 shows an embodiment of a device 100 for the plasma-induced cleaning of water contaminated with at least one wastewater constituent, here of vapor water, comprising in a reaction space 110 an unearthed water reservoir 130 and exactly one flat, cooled plasma electrode 120 which are at a predetermined distance, in the exemplary embodiment shown 1 cm, above a fill level 131 of the water reservoir 130 is arranged. There is a sensor in the water 135 for detecting the concentration of the at least one waste water constituent, here arranged from ammonium at the reaction space 110 is a common exhaust pipe 160 arranged for hydrogen and oxygen. Outside the reaction space 110 is a high frequency generator 150 arranged with the plasma electrode 120 via an adaptation network 140 for impedance matching of an impedance at the plasma electrode 120 emerging plasma 180 and an output impedance of the high frequency generator is connected. The adaptation network 140 in the embodiment shown comprises a motor-controlled capacitor and a variable coil as an electrical resonant circuit. The matching network is formed, the impedance of the plasma, which in the process depends on its dependence on, in particular, a distance from the plasma electrode 120 to the water surface, a water composition, a temperature in the reaction space and an atmosphere in the reaction space, and the output impedance of the high-frequency generator 150 adapt. The output impedance of the high frequency generator 150 is advantageously 50 ohms. As in the environment, there is atmospheric pressure in the reaction space. The formation of a flat plasma between the plasma electrode 120 and the surface of the water in the water reservoir 130 under atmospheric pressure is possible here because only one electrode, namely the plasma electrode 120 is used and the water itself is used as a counterpart. To generate the plasma 180 becomes the plasma electrode 120 supplied with a high-frequency AC voltage, which the high-frequency generator 150 provides. In the embodiment shown, this high-frequency AC voltage has a frequency in the range from 10 to 20 MHz. A power of 1 to 40 kW is applied to the plasma electrode. The dissociation reactions of the water and the wastewater constituents take place in a plasma chemical gas and water volume process. Individual compounds of the wastewater constituents are separated under the action of the plasma and the connection partners are released via them, which then react, for example, to gaseous hydrogen, gaseous oxygen, gaseous nitrogen. On the one hand, the water is effectively cleaned and, on the other hand, desired by-products such as hydrogen are released. The discharges in the gas and water volume as well as on the water surface lead to the generation of free electrons in an energy range that is favorable for the dissociation of water and the wastewater constituents. Collisions with the water and gas molecules lead to the formation of numerous excited molecular and atomic species. The dissociation takes place via a two-stroke reaction and an extreme charge shift between the electrode and the water. The plasma with its excess of electrons acts as a "reducing agent".

The exposure to plasma continues until the concentration of the wastewater constituent is below a predetermined limit value and the purified water can thus continue to be used.

The plasma electrode 120 in the exemplary embodiment shown has a metallic base body, here made of aluminum, which is coated with a dielectric, here aluminum oxide. The flat plasma 180 is therefore formed via a barrier discharge.

In the common exhaust pipe 160 is a membrane 170 arranged to separate hydrogen from the residual gas. These can then be collected and stored separately from each other.

In addition is at the reaction space 110 a feeder 111 arranged for at least one gas in the reaction space, for this air, Ar, He, CO, CO ₂ and / or Ne. These gases are used in particular as an atmosphere in the reaction space during a starting process, i.e. when the plasma is ignited 180 used.

2nd shows a further embodiment of a device 200 for plasma-induced water purification according to the second aspect of the invention. The device 200 largely corresponds to the contraption 100 out 1 , which is why only the differences are described below 1 referred. In contrast to in 1 shown flat single electrode is in 2nd an electrode arrangement with three flat individual electrodes 120a , 120b , 120c arranged, which together form the plasma electrode. All individual electrodes are among themselves and over the matching network 140 with the high frequency generator 150 connected. In the exemplary embodiment shown, waste water with carbon compounds is used in particular as waste water ingredient. Therefore is in the common exhaust pipe 160 , a membrane 171 arranged, via which methane is separated from the gas mixture. It is also an adsorber 172 arranged to adsorb oxygen. This leaves only hydrogen and any other residual gases in the exhaust mixture. These can be separated using other membranes or adsorbers.

3rd shows an embodiment of a device 300 for the production of methane from water contaminated with at least one waste water constituent according to the fourth aspect of the invention. The device 300 largely corresponds to the device 100 out 1 , which is why only the differences are described below 1 referred. In contrast to the device in 1 In the embodiment shown here, no sensor is provided for detecting the concentration of a wastewater constituent, but rather a sensor 165 for detecting a concentration of methane in the exhaust pipe 160 . Furthermore, the plasma electrode 320 here designed such that the exhaust pipe 160 runs through them. The plasma electrode has openings 121 through the resulting gases into the exhaust pipe. It is also in the plasma electrode 320 in the exhaust pipe 160 a catalyst chamber 161 with a catalyst designed as granules 162 arranged for the methanization of carbon. At the end of the exhaust pipe, methane passes through a membrane 371 separated from the residual gas. In this arrangement, the focus is on the extraction of methane from water contaminated with carbon compounds, the basic structure is the same as that of a device for water purification. The carbon compounds in the wastewater constituents are dissociated as part of the plasma process, thereby releasing carbon which initially reacts to carbon monoxide or carbon dioxide, for example with oxygen from the latent water dissociation or other dissociation reactions. If a sufficient amount of carbon monoxide and / or carbon dioxide is then available, the plasma encourages a reaction with the hydrogen to methane, which is also present at least from the latent water dissociation. This reaction is intensified by the catalyst used. For methane production, water is preferably cleaned which additionally has ammonium, so that larger amounts of hydrogen are released than through water dissociation.

Reference symbol list

100, 200, 300

contraption

110

Reaction space

111

Supply for at least one gas

120, 320

Plasma electrode

120a, 120b, 120c,

Single electrode

121

opening

130

Water reservoir

131

Level

135

Waste water content concentration sensor

140

Adjustment network

150

High frequency gerator

160

Exhaust pipe

161

Catalyst chamber

162

catalyst

170, 371

membrane

171

additional membrane

172

Adsorber

180

plasma

QUOTES INCLUDE IN THE DESCRIPTION

This list of documents listed by the applicant has been generated automatically and is only included for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• DE 102011081915 A1 [0010]

Claims (15)

A process for the purification of water contaminated with at least one waste water constituent, wherein the waste water constituent has at least one compound with a binding energy which is lower than the binding energy of a simple hydrogen-oxygen bond, comprising the steps: - Providing the contaminated water with a predetermined level in an unearthed water reservoir within a reaction space; - Acting exactly one, at a predetermined distance above the fill level of the water reservoir, flat-shaped, cooled plasma electrode with a high-frequency alternating voltage at atmospheric pressure such that a plasma is formed in the high-frequency field between the plasma electrode and a surface of the water, the energy input of which is sufficient that Compounds with a binding energy less than or equal to that of the simple hydrogen-oxygen bond are dissociated; - Detecting a concentration of the at least one waste water ingredient. Procedure according to Claim 1 , further comprising: - comparing the recorded concentration with a stored limit value and in which, if the recorded concentration is less than or equal to the stored limit value, - the application is ended or - the treated water is removed and replaced by contaminated water. Method according to one of the preceding claims, in which the at least one waste water ingredient is selected from the group of nitrogen compounds, in particular nitrogen-hydrogen compounds, carbon compounds, boron, oxygen, phosphorus, sulfur or chlorine compounds. Method according to one of the preceding claims, in which a high-frequency generator with a predetermined output impedance is used to apply the high-frequency AC voltage to the plasma electrode, which is connected to the plasma electrode via a matching network for impedance matching of an impedance of the plasma and the output impedance of the high-frequency generator. Procedure according to Claim 4 , wherein an intensity and power of a return wave and a return wave to the high-frequency generator is measured and, depending on the output of the incoming wave, the generator power is stabilized and the output of the return wave is minimized depending on a conductivity of the contaminated water via the adaptation network. Method according to one of the preceding claims, in which the stored limit value is a legal limit value or less than a legal limit value. The method of any preceding claim, further comprising Collecting gases resulting from the dissociation in a common exhaust pipe, - Separation of the resulting gases using a multi-stage membrane process and / or using selective adsorption processes. The method of any preceding claim, wherein the contaminated water has at least one nitrogen-hydrogen compound and at least one carbon compound as wastewater ingredients, further comprising: - Collection of gases resulting from the dissociation in a common exhaust pipe - Measurement of a methane concentration in the common exhaust pipe - Maintenance of the admission until a minimum concentration of methane in the exhaust pipe is reached. Procedure according to Claim 8 , in which a catalyst for the methanation of carbon monoxide and / or carbon dioxide is used. Apparatus for cleaning water contaminated with at least one waste water constituent, comprising: in a reaction space - an unearthed water reservoir; exactly one flat, cooled plasma electrode which is arranged at a predetermined distance above a fill level of the water reservoir, a sensor for detecting a concentration of the waste water constituent and outside the reaction space - a high-frequency generator with a predetermined output impedance, which is connected to the plasma electrode via a matching network for impedance matching of an impedance of a plasma arising at the plasma electrode and the output impedance of the high-frequency generator. Device after Claim 10 , wherein the high-frequency generator comprises a measuring device for measuring an intensity and a power of a return and a returning wave. Device according to one of the Claims 10 or 11 , in which the plasma electrode is coated with a dielectric and the plasma is formed as a barrier discharge. Device according to one of the Claims 10 to 12 , in which a plasma electrode arrangement comprising a plurality of individual electrodes arranged next to one another forms the exactly one plasma electrode at a predetermined distance above the water reservoir. Device according to one of the Claims 10 to 13 , in which the water reservoir has an inlet and at least one outlet and the sensor is arranged in the region of the at least one outlet. Device according to one of the Claims 10 to 14 , in which the water reservoir has a fill level control, which is designed to keep the fill level of the water almost constant, or an overflow.

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