NL1042661B1

NL1042661B1 - Method and device for producing ozone

Info

Publication number: NL1042661B1
Application number: NL1042661A
Authority: NL
Inventors: Jozef Jacques Mayer Mateo; Oudakker Gerrit
Original assignee: Stichting Wetsus European Centre Of Excellence For Sustainable Water Tech
Priority date: 2017-11-27
Filing date: 2017-11-27
Publication date: 2019-06-03

Abstract

The present invention relates to a method and device for producing ozone, characterized by at least a first tubular quartz electrode, filled with a first electrically conducting fluid, and surrounded by a second, preferably stainless steel, tubular electrode whereby a first air gap is present between said first and second electrodes. The first and second electrodes are connected to an electrical high voltage AC power source generating a corona discharge in the first air gap. Ozone is produced by pumping air and / or dried air and / or oxygen through the air gap. The electrically conducting fluid in the first electrode is preferentially circulated over a heat exchanger to minimize the temperature of the first electrode. The second electrode is preferentially cooled by an air or water flow along its shell side. The ozone generator according to the present invention is characterized by lower investment cost, lower energy consumption per kg of produced ozone and lower maintenance cost as compared to alternatives on the market.

Description

Method and device for producing ozone

Introduction

There is a fast growing societal demand for sustainable technologies to disinfect drinking water and to remove micropollutants like pesticides, medicine traces and antibiotic resistance from waste water. Major reason is that there is a growing number of micropollutants ending up in our surface water, thereby affecting our environment and public health. A state of the art technology for large scale industrial water purification is ozonation of the water followed by filtration of the water over an activated carbon filter installation. The economical feasibility of ozonation technology is largely determined by investment cost, energy consumption and maintenance of the ozone generator.

The technology according to the present invention relates to a new type of ozone generator with lower investment cost, lower energy consumption and less maintenance as compared to alternatives on the market.

Technical description of the present invention

The different aspects of the technology according to the present invention are now described. In order to explain the invention, figures 1 and 2 will be used, mentioning numbers 1 to 14, each pointing to specific parts of the present invention.

According to a first aspect, the present invention relates to a first tubular electrode, indicated with 1 in figure 1, consisting of at least an electrical insulator, preferably quartz, and filled with a first electrically conducting fluid 2, preferably consisting of salt containing water. The first tubular electrode is preferably cilindrical. Inside the first electrode, an electrical conductor 5, preferably made from stainless steel, is placed and galvanically connected to the end stage of a high voltage AC power source 7.

According to a second aspect, the present invention relates to a second, electrically conducting, tubular electrode 3, preferably made of stainless steel, in which the first electrode is preferably positioned concentrically. The inner diameter of the second electrode is preferably 0.05 mm to 10 mm larger than the outer diameter of the first electrode, more preferably 0.2 mm to 5 mm larger than the outer diameter of the first electrode and most preferably 0.5 mm to 2 mm larger than the outer diameter of the first electrode. The second tubular electrode is preferably cylindrical and galvanically connected to the end stage of high voltage power source 7.

According to a third aspect of the present invention, a gas flow 4, consisting of air and / or dried air and / or oxygen is pumped through the gap between the outer diameter of the first electrode 1 and the inner diameter of the second electrode 3. Since both first and second electrodes are connected to high voltage power source 7, a corona discharge will occur in the gap between the first and second electrode, resulting in the production of ozone. According to a fourth aspect of the present invention, the power source for the ozone generator consists of a function generator 9 that is operatively connected to a power amplifier 8 and a high voltage output stage 7. Preferably, high voltage power output stage 7 comprises at least a high frequency - high voltage transformer, preferably with galvanically separated coils. The transformer is preferably operated in a frequency range between 1 kHz and 1 MHz. In this patent application high voltage is defined as a voltage higher than 1 kV. Summarizing, the high voltage power source produces an alternating current, preferably in the frequency range between 1 kHz and 1 MHz.

According to a fifth aspect of the present invention, the conducting fluid 11, see figure 2, is continuously refreshed by pumping it through the first electrode. More preferably, the conducting fluid 11 is recycled in a loop 12 over a heat exchanger 13 using a recycle pump 14. In this way, very efficient cooling of the first electrode is realized, resulting in an increase of ozone production.

According to a sixth aspect of the present invention, a bundle of parallel first electrodes and surrounding second electrodes are placed in a first housing. The electrical conducting fluid is pumped in parallel flow through the bundle of first electrodes and preferably recycled in a loop over a heat exchanger and a recycle pump. Through the housing and along the second electrodes, air or fluid are optionally pumped as well in order to also cool the outside of the second electrodes. This way a large ozone production unit is obtained. Preferably, more than 5, more preferably more than 10, even more preferably more than 25 and most preferably more than 50 parallel ozone producing first and second electrodes are placed in one first housing. Preferably, each first and second electrode is longer than 50 cm, more preferably longer than 100 cm and most preferably longer than 130 cm.

The different aspects of the technology according to the present invention have now been explained. In the following, the advantages of the technology according to the present invention will be explained, followed by a number of non limiting preferred embodiments of the technology.

Advantages of the technology according to the present invention

The technology according to the present invention will result in the lowest possible energy consumption figures for ozone generation as compared to prior art for the following reasons: e the first conducting fluid in the first electrode ensures perfect wetting of the inner wall of the first electrode thereby realizing ideal electrical contact between the conductor (the fluid) inside the first electrode and the insulating material where the first electrode is made of. Since the conductor in the first electrode is neither a metal nor another corrosion or erosion sensitive material, such as carbon, there will be no preferential electrical currents from the conductor in the first electrode through the insulating layer of the first electrode to the second electrode. Such preferential currents decrease the energy efficiency of the ozone generator and result in enhanced ageing of the electrode due to "hot spots" on the electrode surface. The conducting fluid completely prevents such "hot spots". • the first conducting fluid has a negligible electrical resistance compared to that of the insulating material where the first electrode is made of. Hence there are no electrical losses in the first conducting fluid. • the insulating material where the first electrode is made of can be selected based on low dielectic losses. Selection of quartz as construction material results in an electrical dissipation factor tan delta = 0.0001 which means that energy losses in the first electrode material are minimum. • The already limited amount of heat produced during the ozon generation process is very effectively transferred to the heat conducting fluid on one hand and to the cooling medium in contact with the outside surface of the second electrode on the other hand. This results in a much lower corona temperature as compared to alternative prior art technologies and hence in a lower decomposition rate of produced ozone and thus a higher ozone production rate and higher energy efficiency. • application of software configurable automated high frequency switched power supply technology with corona temperature and ozone concentration sensors and a feed back loop to the switched power supply, continuously optimizes the system for fluctuations in humidity and oxygen content of the air - dried air - oxygen gas mixture fed to the ozone generator, thereby increasing both reliability, availability and energy efficiency of the system.

The technology according to the present invention will result in the lowest possible investment cost figures as compared to prior art for the following reasons: • because of the extremely efficient cooling capacity of the new corona electrodes according to the present invention, it is possible to increase the current per square meter of electrode surface without significantly increase the temperature of the corona. As a result, both the electrode current and the gas flow of air and / or dried air and / or oxygen can be increased without any problems, thereby increasing the ozone production rate per square meter electrode surface area to a much higher value as compared to prior art. This means that an ozone generator according to the present invention has a smaller foot print and less material as compared to prior art. • a non-limiting very efficient and cheap example of a first conducting fluid is saturated brine, which has negligible cost. As very efficient, mass produced and low cost first electrodes, commercially available quartz protection sleeves for UV-C disinfection lamps can be applied. Since this mass product for a completely different application can be used as first electrode according to the present invention, investment cost in the electrode material are very limited.

The technology according to the present invention will result in the lowest possible maintenance cost figures as compared to prior art for the following reasons: • the first conducting fluid and its perfect wetting of the quartz tubes combined with the inert properties of quartz result in completely maintenance free first electrodes. • application of saturated brine as first conducting fluid prevents biofouling in the cooling loop of the first conducting fluid, making the heat exchanger and piping maintenance free. • application of stainless steel second electrodes e.g., 316L steel, results in maintanance free second electrodes. • application of software configurable automated high frequency switched power supply technology, with corona temperature and ozone concentration feed back loops, continuously optimizes the system for fluctuations in humidity and oxygen content of the air - dried air - oxygen gas mixture fed to the ozone generator, thereby decreasing the required attention to the system dramatically as well as the risk of system failure.

Preferred embodiments of the technology according to the present invention Without limiting the extent of the present invention by any means, following preferred embodiments of the technology expressly make part of the invention.

According to a first preferred embodiment the first conducting fluid is water or water with sodium chloride or demineralized water with sodium chloride or a saturated solution of water with sodium chloride or a solution of sodium chloride in water of more than 300 g/liter sodium chloride.

According to a second preferred embodiment the first conducting fluid is water containing an inorganic salt and / or and organic acid and / or an acid and / or an alkaline solution such as sodium hydroxide.

According to a third preferred embodiment, the first conducting fluid is an electrical insulator containing a suspension of conductive particles, such as metal (nano)particles. according to a fourth preferred embodiment, the first conducting fluid is a gel.

According to a fifth preferred embodiment, the first conducting fluid is an ionic liquid. According to a sixth preferred embodiment, the first electrode is made of quartz and / or glass and / or ceramic and / or an ozone resistent polymer such as teflon and / or an ozone resistant composite.

According to a seventh preferred embodiment, the second electrode is made of 316 L steel and / or a polymer coated with carbon and / or a ozone resistance composite containing conductive (nano)particles.

According to an eighth preferred embodiment, a surfactant is added to the first fluid to further improve the interaction of the first conducting fluid with the material the first electrode is made of, thereby increasing the energy efficiency of the system.

Claims

An ozone generator characterized by • at least a first tubular electrode made of an electrical insulator that • contains at least a first electrically conductive fluid • at least a first electric conductor located in the first electrically conductive fluid wherein • the first electric conductor is electrically and operatively connected is with a first high-voltage source characterized in that • the first high-voltage source consists of at least one function generator and an amplifier and produces an alternating voltage • at least a second tubular electrode in which the first tubular electrode is placed and characterized in that • the inner diameter of the second tubular electrode electrode is at least 0.1 mm larger than the outer diameter of the first tubular electrode, whereby a first gap is created between the first tubular electrode and the second tubular electrode • a galvanically effective connection of the second electrode to the first too high voltage source • means for pumping air and / or dried air and / or oxygen through the first gap between the first electrode and the second electrode.

2. Ozone generator as claimed in claim 1, characterized in that the first electrically conductive liquid consists of water with an inorganic salt dissolved therein.

Ozone generator according to one of the preceding claims 1 and 2, characterized in that the first electrically conductive liquid consists of water with a concentration of sodium chloride that is higher than 300 grams per liter.

An ozone generator according to any one of the preceding claims 1 to 3, wherein the first tubular electrode is made of quartz.

The ozone generator according to any of the preceding claims 1 to 4, wherein the second tubular electrode is made of stainless steel.

6. Ozone generator according to one of the preceding claims 1 to 5, wherein the second tubular electrode is made of 316L steel.

The ozone generator according to any of the preceding claims 1 to 6, wherein the first conductive fluid in the first electrically conductive tubular electrode is continuously refreshed by pumping the first electrically conductive fluid through the first electrically conductive tubular electrode.

8. Ozone generator according to one of the preceding claims 1 to 7, wherein the first electrically conductive liquid in the first tubular electrode is continuously refreshed by recycling it through a first pump over a first heat exchanger.

9. Ozone generator as claimed in any of the foregoing claims 1-8, wherein the outer wall of the second tubular electrode is cooled by means of air or a liquid.

Ozone generator according to one of the preceding claims 1 to 9, characterized by • a bundle of parallel placed first tubular electrodes encased in • second tubular electrodes that are housed together in a • first housing in which • the first electrically conductive liquid passes through the parallel switched bundle of first tubular electrodes is pumped and is recirculated over at least a first heat exchanger using at least a first recirculation pump.

U. Ozone generator according to any of the preceding claims 1 to 10 plus a temperature sensor operatively connected to the first tubular electrode and / or the second tubular electrode and software with a feed back loop to the high voltage source for optimizing the ozone generator.

The ozone generator according to any of the preceding claims 1 to 11 plus an ozone sensor and software with a feedback loop to the high voltage source to optimize the ozone generator.

A method for producing ozone characterized by an ozone generator according to any of the preceding claims 1 to 12.