System and method of water purification and hydrogen peroxide generation by plasma

Abstract

A system for generation of radicals in a liquid (e.g., OH and derivatively H.sub.2O.sub.2 in water) by a plasma reactor, including a first electrode having a rod shape or a tubular shape; a dielectric tubular housing coaxial with the first electrode and enclosing the first electrode, and having a gap to the first electrode of 0.3-30 mm; a second electrode on an outside of the dielectric tubular housing and coaxial with first electrode with a gap 0.3-30 mm; a high voltage power supply providing voltage oscillations or pulses of 0.5-30 kV and a frequency 1-50 kHz between the first and second electrodes; and a pump or a Venturi injector on an output of the plasma reactor and a chock valve on an input of reactor for generating a low water pressure in the gap between first and second electrodes so as to generate boiling in the gap.

Claims

1. A system for generation of radicals in a liquid by a plasma reactor, comprising: a first electrode having a rod shape or a tubular shape; a dielectric tubular housing coaxial with the first electrode and enclosing the first electrode, and having a gap to the first electrode of 0.3-30 mm; a second electrode on an outside of the dielectric tubular housing and coaxial with first electrode with a gap 0.3-30 mm; a high voltage power supply providing voltage oscillations or pulses of 0.5-30 kV between the first and second electrodes with a frequency 1-50 kHz; and a pump or a Venturi injector on an output of the plasma reactor and a chock valve on an input of reactor for generating a low water pressure in the gap between first and second electrodes so as to generate boiling in the gap.

2. The system of claim 1, wherein the input and the output of the plasma reactor is directed tangentially.

3. The system of claim 1, wherein the first electrode has sharp ridges on its outer surface to distribute plasma inhomogeneities.

4. The system of claim 1, wherein the first electrode has a thread on its outer surface to distribute plasma inhomogeneities.

5. The system of claim 1, wherein multiple plasma reactors are connected in parallel.

6. The system of claim 1, wherein multiple plasma reactors are connected in series.

7. The system of claim 1, wherein the liquid is water.

8. The system of claim 1, wherein the radicals are OH radicals.

9. The system of claim 1, wherein the plasma reactor also generates hydrogen peroxide (H.sub.2O.sub.2).

10. The system of claim 1, wherein the second electrode is shaped as a wire spiral, a metal grid, a metal foil or a metal tubular shape.

Description

BRIEF DESCRIPTION OF ATTACHED FIGURES

(1) The accompanying drawings, which are incorporated into and form a part of the specification, illustrate the practice of embodiments of the present invention and, together with the description, serve to explain the principles of the invention. The drawings are only for the purpose of illustrating certain embodiments of the invention and are not to be construed as limiting the invention.

(2) In the figures:

(3) FIG. 1 shows a design of OH generation reactor and a flow chart of reactor connections that can provide reactor operation conditions.

(4) FIG. 2 shows another exemplary design of reactor connection including a Venturi tube.

(5) FIG. 3 shows an exemplary design of grounded electrode of rector with sharp thread and tangential water input and output channels of reactor gap.

(6) FIG. 4 shows an exemplary parallel connection of several reactors.

(7) FIG. 5 shows an exemplary power supply based on half-wave fly-back schematic.

(8) FIG. 6 shows an exemplary power supply based on full-wave push-pull circuit with IGBT semi-bridge.

(9) FIG. 7 shows an exemplary power supply based on a full-wave push-pull circuit with IGBT semi-bridge and midpoint transformer primary winding.

(10) FIG. 8 shows an exemplary power supply based on full-wave push-pull schematic with IGBT bridge.

(11) FIG. 9 shows two reactors arranged in series.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(12) Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.

(13) The proposed concept is to organize plasma generation of OH by electric discharge at low pressure close to the water surface and to provide effective generation and transportation of the OH radicals from gas to liquid in a reactor that can be practically used in industry. The proposed reactor (see FIG. 1) includes a dielectric tube with outer high voltage electrode made from metal wire, foil, metal grid or metal tube on outer surface of dielectric tube. Inside the dielectric tube, a grounded electrode is arranged coaxially with the dielectric tube.

(14) The high voltage electrode and the grounded electrode are connected to a high voltage power supply. Between inner surface of dielectric tube and outer surface of grounded electrode there is a several millimeters reactor gap. At the top of tube there is water input that goes to a discharge gap. At the bottom of reactor water goes from the reactor gap to a water output. The output of reactor connects to an input of a water pump, and at the input of reactor a chock valve installed, which can control input water flow, and permits the water pump to create negative pressure in the reactor gap. This negative pressure is controlled by pump capacity and chock valve effective clearing hole. If this pressure will drop up to pressure of water vapor, the water starts to boil, and vapor bubbles appear in the reactor gap.

(15) When high voltage is applied to the high voltage electrode, electric discharge in vapor bubbles can be ignited. This flow setup can provide conditions for effective generation of OH radicals in bubbles, and these radicals can be effectively transported from gas to liquid phase because at low pressure, OH path length is high, diffusion process is fast and number of collision of radicals which can cause reverse reaction is small.

(16) Instead of direct suction of water by a pump, in some cases a Venturi injector can be used (FIG. 2). In this case requirements for pump resistance to cavitation and chemical reagents are less strict, and the pump can operate in regular operation mode to provide the necessary pressure at the Venturi injector input. Suction input of Venturi injector works in this case for pressure decreasing in reactor like pump suction input. Venturi injector can be made from cavitation and chemical resistive materials and be stable in presence of hydrogen peroxide generated by reactor.

(17) Another option is to use tangential water input (FIG. 3) to rector gap which can provide better uniformity of water treatment in reactor by better intermixing of water and vapor bubbles and making continues water film on dielectric reactor wall.

(18) Another option is using mechanically sharped internal grounded electrodes to prevent electric discharge attaching to some places of internal electrode by spontaneous overheating of certain points caused by flow or plasma instabilities. A sharp electrode makes it more independent of natural inhomogeneities by creation of multiple artificial inhomogeneities with larger sizes and stimulation of multiple breakdowns from the sharp parts. A threaded electrode can fulfil this function.

(19) Another option is using of several reactors installed in parallel (FIG. 4) or in series (FIG. 9) to increase reactor capacity up to any desirable value.

Experimental Example 1—Experimental Oxidation of Easy Oxidative Organic Admixtures

(20) As a model, strong organic colorant Bis-(p-diethylamino) triphenyl anhydrocarbinol oxalate was chosen. Colorant was added to distillated water with small amounts of sulfuric acid or sodium hydroxide for pH control in region from 5 to 9. In the entire pH region, effective oxidation of colorant and complete water decolorization has been demonstrated. Power supply frequency was 30 kHz and voltage on electrodes oscillated from −3 kV to +3 kV. Colorant molecule oxidation energy cost was about 40 eV per molecule, which is close to the energy cost of oxidation by ozone and acceptable for practical applications.

Experimental Example 2—Experimental Oxidation of Hard Oxidative Inorganic Admixtures

(21) As a model, ammonia solution in distillated water was chosen as an example of hard oxidative admixture which cannot be oxidized by traditional technologies (by ozone, for example). Ammonia concentration was varied in region 0.5-5 g/m3. In the entire pH region, effective oxidation of ammonia (ammonia concentration decrease more than in ten times) has been demonstrated. Power supply frequency was 3 kHz and voltage on electrodes oscillated from −3 kV to +3 kV. Ammonia molecule oxidation energy cost was about 30 eV per molecule. Ammonia oxidation is a result that cannot be accomplished by conventional methods and oxidants (such as ozone).

Experimental Example 3—Experimental Synthesis of Hydrogen Peroxide in Water

(22) In experiments distillated water was treated by described reactor according to the flow diagram shown in FIG. 2. Power supply frequency was 30 kHz and voltage on electrodes oscillated from −3 kV to +3 kV. For each 30 seconds of treatment time, concentration of generated hydrogen peroxide was measured. Effective hydrogen peroxide generation with linear dependence on treatment time and power input to plasma was demonstrated. Hydrogen peroxide molecule generation energy cost was about 40 eV per molecule. This energy cost is close to total (including accompanying energy expenditures like air or oxygen preparation and reactor cooling) energy cost of ozone generation and is acceptable for practical applications of generated hydrogen peroxide.

Experimental Example 4—Experimental Cracking of Hexane

(23) In experiments chemical grade hexane was treated by described reactor according to the flow diagram shown in FIG. 2. Power supply frequency was 30 kHz and voltage on electrodes oscillated from −2 kV to +2 kV. Every 5 minutes of treatment time, a sample for chemical analysis was taken. Also, gas samples were taken from gas bubbles generated after the reactor. In gas bubbles methane was measured with small admixtures of propane and hydrogen. In liquid samples of hexane some admixture of benzene was detected with the concentration increasing during treatment time. This way, the hexane cracking process was detected with an energy cost about 10 eV per molecule. This energy cost is compatible with a bound energy in hexane and demonstrates good cracking efficiency.

(24) FIG. 5-FIG. 8 show an exemplary power supplies that can be used in the invention. Power supplies are based on high frequency high voltage transformer with several versions, including an inverter based on a half-wave fly-back schematic (FIG. 5), an inverter based on a full-wave push-pull schematic with IGBT semi bridge (FIG. 6), an inverter based on a full-wave push-pull schematic with IGBT semi-bridge and midpoint transformer primary winding (FIG. 7), and an inverter based on a full-wave push-pull schematic with IGBT bridge (FIG. 8). FIG. 8 shows an exemplary power supply based on full-wave push-pull schematic with an IGBT bridge.

(25) Having thus described a preferred embodiment, it should be apparent to those skilled in the art that certain advantages of the described method and apparatus have been achieved.

(26) It should also be appreciated that various modifications, adaptations and alternative embodiments thereof may be made within the scope and spirit of the present invention. The invention is further defined by the following claims. The entire disclosures of all patents and publications cited above are hereby incorporated by reference.