Method And Device For A Plasma-Induced Water Purification

Abstract

The invention relates to a method of purifying water contaminated with at least one wastewater substance, wherein the wastewater substance has at least one compound with a binding energy that is lower than the binding energy of a simple hydrogen-oxygen bond. The method comprises the following steps: Providing the contaminated water to a specified fill level in an ungrounded water reservoir within a reaction chamber; applying a high-frequency alternating voltage to precisely one flat cooled plasma electrode arranged at a specified distance above the fill level of the water reservoir at atmospheric pressure, such that a plasma forms in the high-frequency field between the plasma electrode and a surface of the water, the energy input of the plasma being sufficient to dissociate compounds with a binding energy that is lower than or equal to that of a simple hydrogen-oxygen bond; and measuring the concentration of the at least one wastewater substance.

Claims

1. Method of purifying wastewater contaminated with at least one wastewater substance, wherein the wastewater substance has 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 to a predefined fill level of a reaction chamber within an ungrounded water reservoir; applying a high-frequency alternating voltage at atmospheric pressure to flat cooled plasma electrode arranged at a predefined distance above the wastewater at the predetermined fill level so that a plasma forms in the high-frequency field between the plasma electrode and a surface of the wastewater, the energy input of such plasma being sufficient to cause compounds with a binding energy lower than or equal to that of the simple hydrogen-oxygen bond to be dissociated; and measuring the concentration of the at least one wastewater substance.

2. Method according to claim 1, wherein the high-frequency alternating voltage is applied to the plasma electrode creating a contracted plasma.

3. Method according to claim 2, wherein a direct voltage is connected to the water reservoir with its negative pole and the direct voltage is preferably in the range of 100 V to 3000 V and 0.01 mA to 250 mA.

4. Method according to claim 1, further comprising: concentrating the at least one wastewater substance in the contaminated water.

5. Method according to claim 1, wherein the contaminated water is collected in at least one transport container, transported in the transport container, and the contaminated water is then provided in the water reservoir from the transport container.

6. Method according to claim 1, further comprising: comparing the measured concentration with a stored threshold value, at which the following occurs if the measured concentration is below or equal to the threshold value: the application is stopped, or the treated water is drained and replaced with contaminated water.

7. Method according to claim 1, wherein the at least one wastewater substance is a nitrogen, carbon, boron, oxygen, phosphorus, sulfur, or chlorine compounds.

8. Method according to claim 1, wherein a high-frequency generator with a predefined output impedance is used to apply the high-frequency alternating voltage to the plasma electrode; this high-frequency generator connected to the plasma electrode via a matching network for impedance matching of an impedance of the plasma and of the output impedance of the high-frequency generator.

9. Method according to claim 8, wherein the intensity and power of an outgoing and returning wave to the high-frequency generator is measured, and the generator power is stabilized depending on the power of the outgoing wave, and the power of the returning wave is minimized depending on a conductivity of the contaminated water by means of the matching network.

10. Method according to claim 6, wherein the stored threshold value is a statutory limit or below a statutory limit.

11. Method according to claim 1, further comprising: collecting gases generated as a result of the dissociation in a common exhaust pipe in gas communication with the reaction chamber; and separating the generated gases by way of a multi-stage membrane process and/or by using selective adsorption methods.

12. Method according to claim 1, wherein the contaminated water includes at least one nitrogen compound containing at least one nitrogen-hydrogen bond and at least one carbon compound as the wastewater substances, and further comprising: collecting gases generated as a result of the dissociation in a common exhaust pipe; measuring a methane concentration in the common exhaust pipe; maintaining the application until a minimum methane concentration in the exhaust pipe is reached.

13. Method according to claim 12, wherein a catalyst is used for the methanation of carbon monoxide and/or carbon dioxide.

14. Device for purification of water contaminated with at least one wastewater substance, comprising: a reaction chamber disposed within an ungrounded water reservoir; a flat cooled plasma electrode that is arranged at a predefined distance above a predetermined fill level of the reaction chamber; a sensor for measuring the concentration of the wastewater substance; a high-frequency generator with a predefined output impedance that is connected to the plasma electrode via a matching network for impedance matching of an impedance of the plasma forming at the plasma electrode, and of the output impedance of the high-frequency generator disposed outside of the reaction chamber.

15. Device according to claim 14, further comprising a direct current source connected to the water reservoir with its negative pole via an electrode.

16. Device according to claim 14, wherein the high-frequency generator comprises a measuring device for measuring the intensity and power of an outgoing and returning wave.

17. Device according to claim 14, wherein the plasma electrode is coated with a dielectric and the plasma is designed as a barrier discharge.

18. Device according to claim 14, wherein the plasma electrode comprises several individual electrodes arranged next to each other at a predefined distance above the fill level.

19. Device according to claim 14, wherein the water reservoir has an inlet and at least one outlet, and the sensor is arranged in the area of the at least one outlet.

20. Device according to claim 14, wherein the water reservoir comprises a fill-level control that is designed to keep the fill level of the water nearly constant, or an overflow.

21. The device of claim 13, wherein only a single plasma electrode is provided.

Description

[0129] Examples of embodiments are also indicated in the claims.

[0130] In the following, further exemplary embodiments of the device and method will be described based on the drawings. The drawings show the following:

[0131] FIG. 1 shows a schematic diagram of an exemplary embodiment of a device for plasma-induced water purification according to the second aspect of the invention;

[0132] FIG. 2 shows a schematic diagram of a further exemplary embodiment of a device for plasma-induced water purification according to the second aspect of the invention;

[0133] FIG. 3 shows a schematic diagram of an exemplary embodiment of a device for plasma-induced methane production according to the fourth aspect of the invention;

[0134] FIG. 4 shows a schematic diagram of a further exemplary embodiment of a device for plasma-induced water purification according to the second aspect of the invention.

[0135] FIG. 1 shows an embodiment of a device 100 for plasma-induced purification of water contaminated with at least one wastewater substance, in this case exhaust vapor water, comprising, in a reaction chamber 110, an ungrounded water reservoir 130 as well as at least one flat cooled plasma electrode 120 arranged at a predefined distance, in the depicted exemplary embodiment 1 cm above a fill level 131 of the water reservoir 130. A sensor 135 for measuring the concentration of the at least one wastewater substance, in this case ammonium, is disposed in the water. A common exhaust pipe 160 for hydrogen and oxygen is arranged on the reaction chamber 110. A high-frequency generator 150 is arranged outside of the reaction chamber 110 and connected to the plasma electrode 120 via a matching network 140 for impedance matching of an impedance of the plasma 180 forming at the plasma electrode 120, and of the output impedance of the high-frequency generator. In the embodiment shown, the matching network 140 comprises a motor-controlled capacitor and a variable coil as an electrical oscillating circuit. The matching network is designed to adjust the impedance of the plasma which, in the process, is in particular dependent upon a distance of the plasma electrode 120 to the water surface, a water composition, a temperature in the reaction chamber as well as an atmosphere in the reaction chamber, and the output impedance of the high-frequency generator 150. The output impedance of the high-frequency generator 150 is advantageously 50 ohms. There is atmospheric pressure in the reaction chamber, just like in the surrounding area. The formation of a planar 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 precisely one electrode, namely the plasma electrode 120, is utilized and, as a counterpart, the water itself is used. To produce the plasma 180, a high-frequency alternating voltage, which the high-frequency generator 150 provides, is applied to the plasma electrode 120. In the embodiment shown, this high-frequency alternating voltage has a frequency in the range of 10 to 20 MHz. Power in the range of 1 bis 40 kW is applied to the plasma electrode here. The dissociation reactions of the water and the wastewater substances occur in a plasma-chemical gas and water volume process. Individual bonds of the wastewater substances are separated under the influence of the plasma, which causes the compound partners to be released and to then react to form e.g. gaseous hydrogen, gaseous oxygen, gaseous nitrogen. This way, on the one hand, the water is purified effectively and, on the other hand, desired byproducts, like 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 substances. Impacts with the water and gas molecules lead to the formation of numerous excited molecule and atom species. Dissociation takes place via a dual-impact reaction and an extreme charge displacement between the electrode and the water. With its excess of electrons, the plasma acts as a “reducing agent”.

[0136] The application of plasma continues until the concentration of the wastewater substance falls below a predefined threshold value and the purified water is thus ready to be reused.

[0137] In the exemplary embodiment shown, the plasma electrode 120 has a metallic base, in this case made of aluminum, that is coated with a dielectric, in this case aluminum oxide. The planar plasma 180 is thus formed as a result of a barrier discharge.

[0138] A membrane 170 for separating hydrogen from the residual gas is arranged in the common exhaust pipe 160. These can subsequently be collected separately and stored.

[0139] In addition, an inlet 111 for introducing at least one gas into the reaction chamber, in this case air, Ar, He, CO, CO.sub.2 and/or Ne, is arranged on the reaction chamber 110. These gases are used especially as an atmosphere in the reaction chamber during the startup process, i.e. when igniting the plasma 180.

[0140] The contaminated water in the water reservoir preferably has a temperature in the range of 5 to 25° C. This temperature range promotes the formation of a contracted plasma not shown here). Contracted plasma results in an improved purification capacity. However, it is also possible to use the filamented mode shown here.

[0141] FIG. 2 shows a further exemplary 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 device 100 from FIG. 1, which is why only the differences are described below; apart from that, reference is made to the description of FIG. 1. In contrast to the flat single electrode shown in FIG. 1, an electrode arrangement with three flat single electrodes 120a, 120b, 120c, which together make up the plasma electrode, is set up in FIG. 2. All single electrodes are interconnected, and connected to the high-frequency generator 150 via the matching network 140. In the depicted exemplary embodiment, wastewater with carbon compounds is used as the wastewater substance. For this reason, a membrane 171 is arranged in the common exhaust pipe 160; this membrane separates methane from the gas mixture. In addition, an adsorber 172 is arranged for adsorbing oxygen. This means that only hydrogen and possibly other residual gases remain in the exhaust gas mixture. These can be separated by additional membranes or adsorbers.

[0142] FIG. 3 shows an exemplary embodiment of a device 300 for producing methane from water polluted with at least one wastewater substance according to the fourth aspect of the invention. The device 300 largely corresponds to the device 100 from FIG. 1, which is why only the differences are described below; apart from that, reference is made to the description of FIG. 1. In contrast to the device in FIG. 1, in the embodiment shown here, a sensor for measuring the concentration of a wastewater substance is not provided, but instead a sensor 165 for measuring a concentration of methane in the exhaust pipe 160. In addition, the plasma electrode 320 is designed in such a way in this case that the exhaust pipe 160 runs through it. The plasma electrode has openings 121 through which the gases that form enter the exhaust pipe, in addition, in the plasma electrode 320, a catalyst chamber 161 with a catalyst 162 in the form of granulate is arranged in the exhaust pipe 160 for methanation of carbon. At the end of the exhaust pipe, methane is separated from the residual gas by a membrane 371. In this arrangement, the focus is on the extraction of methane from water contaminated with carbon compounds; the basic structure corresponds to that of a device for water purification. If carbon compounds in the wastewater substances are dissociated as part of the plasma process, carbon is released that initially reacts to form carbon monoxide or carbon dioxide, for example with oxygen from the latent water dissociation or other dissociation reactions. Once a sufficient quantity of carbon monoxide and/or carbon dioxide is available, a reaction, supported by the plasma, takes place with the hydrogen also available in least from the latent water dissociation to form methane. This reaction is intensified by the catalyst used. For the production of methane, it is preferable to purify water that also contains ammonium so that larger quantities of hydrogen are released than through water dissociation.

[0143] FIG. 4 shows a further exemplary embodiment of a device 400 for plasma-induced water purification according to the second aspect of the invention. The device 400 largely corresponds to the device 100 from FIG. 1, which is why only the differences are described below; apart from that, reference is made to the description of FIG. 1. In the device 400, an electrode 190 is arranged in the water reservoir 130 and connected to the negative pole of a direct-voltage source 191. The direct voltage connected to the water reservoir in this manner works similarly to an offset voltage and results in a contracted plasma 280, here symbolized by a broad flash, and thus improved purification capacity. A low direct current is generated in the contaminated water in the process, which only flows across the plasma of the electrode.

List of Reference Numbers

[0144] 100, 200, 300, 400 device

[0145] 110 reaction chamber

[0146] 111 inlet for at least one gas

[0147] 120, 320 plasma electrode

[0148] 120a, 120b, 120c, single electrode

[0149] 121 opening

[0150] 130 water reservoir

[0151] 131 fill level

[0152] 135 sensor for concentration of wastewater substance

[0153] 140 matching network

[0154] 150 high-frequency generator

[0155] 160 exhaust pipe

[0156] 161 catalyst chamber

[0157] 162 catalyst

[0158] 165 sensor

[0159] 170, 371 membrane

[0160] 171 additional membrane

[0161] 172 adsorber

[0162] 180 plasma

[0163] 190 electrode

[0164] 191 direct voltage source

[0165] 280 contracted plasma