FIELD OF THE INVENTION

The invention relates to a method defined in the preamble of claim 1 and to a device defined in the preamble of claim 6 for a liquid purifying, and a use of the device defined in the preamble of claim 12. BACKGROUND OF THE INVENTION

There are various methods of water treatment known earlier removing pollutants from water by oxidation using ozone and other powerful oxidants, photo- catalytic oxidation and electric discharge methods. These methods are often lacking either the purifica ^¬ tion performance, rate or cost efficiency. The addi ^¬ tional problem consists in treatment of waters with high electric conductivity.

The electric discharge methods known earlier used basically insulated electrodes. In addition, pre ^¬ viously known devices contain non-insulated electrodes placed horizontally over the water layer.

The patent publication WO2008008958 describes the method and the device designed for purification of liquids with high electric conductivity. The device contains vertical plate electrodes, between which the pulsed corona discharge is applied. The treated liquid is dispersed between electrodes in droplets or as fog. The shape of electrodes is chosen to provide stable liquid flow.

Earlier known solutions based on corona dis ^¬ charge had a difficulty in application for the treat ^¬ ment of water with high electric conductivity since the residual voltage remaining at the electrodes' sur- face is high for a time sufficiently long for the de- velopment of damaging sparks. The long-lasting residu ^¬ al voltage results in the harmful spark development especially when liquids with high electric conductivi ^¬ ty, i.e. waters with high content of salts, are treat- ed and when oxygen-rich gas is used.

Besides, the previously known electric dis ^¬ charge methods applied to water treatment have a prob ^¬ lem of poor contact surface with the pulsed discharge plasma due to their low reliability caused by spark discharge development and breakage of the electrodes.

OBJECTIVE OF THE INVENTION

The objective of the invention is to disclose a new type of method and the device for purifying liq- uid composition. Further, the objective of the invention is to disclose a method and device for the oxida ^¬ tive treatment of liquids with high electric conduc ^¬ tivity based on high reliability. SUMMARY OF THE INVENTION

The method and device according to the inven ^¬ tion are characterized by what has been presented in the claims.

The invention is based on a method for a high conductivity liquid purifying, preferably removing or ^¬ ganic and inorganic substances by oxidation. According to the invention, a liquid mixture is supplied in the form of shower downwards between at least two vertical plate electrodes, where oxygen is present in the form of gas phase containing oxygen between 60 to 99 % by volume, and at least one high voltage electrode is ar ^¬ ranged between the vertical plate electrodes and short pulsed electric discharge is generated between the vertical plate electrodes in order to form an electric discharge zone, e.g. corona discharge zone, and the liquid mixture is arranged to flow between the verti- cal plate electrodes downwards through the electric discharge zone in which oxidants, such as ozone and short-living oxidants, e.g. OH-radicals and atomic ox ^¬ ygen, are formed from the liquid mixture and oxygen, and the oxidants are brought to the immediate contact with organic and inorganic substances of the liquid mixture for their effective oxidation. Preferably, short-living oxidants, including atomic oxygen and OH- radicals, are brought in the device to the direct con- tact with organic and inorganic substances dissolved in the liquid mixture for their oxidation. Preferably, the electric discharge pulse parameters are adjusted so that the residual pulsed voltage in the pulse pro ^¬ file does not persist for long time at a high level, for example by its bipolar shape. Preferably, the liq ^¬ uid mixture is a liquid of high conductivity, up to 140 mS/cm.

In connection with this invention, a liquid mixture may be any liquid mixture, for example aqueous liquid mixture or non-flammable and non-explosive or ^¬ ganic solvent based mixture, e.g. carbon tetrachloride and other halogenated hydrocarbons based mixture from organic synthesis reactions or purification of the sol ^¬ vents, or their combinations.

Additionally, the invention is based on a de ^¬ vice used for a high conductivity liquid purification, in which organic and inorganic substances are removed by oxidation. According to the invention, the device comprises an electric discharge reactor, e.g. a corona dis- charge reactor, which includes at least two vertical plate electrodes and at least one high voltage electrode placed between the vertical plate electrodes in order to generate short pulsed electric discharge between the vertical plate electrodes for forming electric dis- charge zone between the vertical plate electrodes, and in which a liquid mixture to be purified has been ar ^¬ ranged to flow in the form of shower, e.g. in the form of jets, films or droplets, downwards between the ver ^¬ tical plate electrodes through the electric discharge zone, and the device comprises a feeding means for feed ^¬ ing oxygen in the form of gas phase containing oxygen between 60 to 99 % by volume between the vertical plate electrodes wherein oxidants are formed from oxygen and the liquid mixture and wherein the oxidants are brought to the immediate contact with organic and inorganic substances of the liquid mixture between the vertical plate electrodes. In one embodiment the device com ^¬ prises an adjustment means for adjusting the electric discharge pulse parameters during the electric dis ^¬ charge. Preferably, short pulsed electric discharges with pulse repetition frequency from 1 to 1400 pulses per second (pps) are generated. Preferably, short- living oxidants, including atomic oxygen and OH- radicals, are brought in the reactor to the direct contact with organic and inorganic substances dis ^¬ solved in the liquid mixture for their oxidation. Preferably, the electric discharge pulse parameters are adjusted so that the residual pulsed voltage in the pulse profile does not persist for long time at a high level, for example by its bipolar shape providing conditions of reliable electric discharge without de- veloping a spark breaking the electrodes.

Specifically, the invention is based on the method and the device, in which organic and inorganic substances are removed from liquid mixture by oxida ^¬ tion. The liquid mixture flows between electrodes in the form of films, jets and droplets downwards from the top of the reactor. The advantage of the invention is that the electrodes can be cooled with the liquid flow. With the invention, the formation of long lasting residual voltage is prevented, which allows avoid- ing formation of damaging sparks on the electrodes, especially when liquids with high electric conductivi ^¬ ties, preferably up to 140 milli-Siemens per centime- tre (mS/cm), are treated in oxygen-rich atmosphere containing oxygen between 60 to 99 % by volume. The residual pulsed voltage is beneficially released down to the voltage preceding the pulse or even below that, i.e. to the reverse voltage in the end of the pulse. Then the spark is not formed, or the power of potentially formed spark is so small that the spark does not damage the electrodes. When the length of the re ^¬ sidual voltage pulse is limited, the electrodes last indefinitely long undamaged even at the high electric conductivity liquid treatment. The important here is the shape of the pulse, which may be bipolar for the fast release of residual voltage to the electrodes.

Mainly organic and inorganic substances which are dissolved in a liquid mixture are removed from the liquid mixture.

In one embodiment the electric discharge is pulsed corona discharge.

In one embodiment the high voltage electrode is high voltage wire electrode.

In one embodiment the vertical electrode is an earthed plate electrode.

In one embodiment the device includes also a pulse generator for generation of short pulsed elec- trie discharges between electrodes. The pulse genera ^¬ tor is connected to the electric discharge reactor. In one embodiment the pulse generator is arranged to gen ^¬ erate electric discharge pulses, e.g. corona discharge pulses, with the repetition of pulses with frequency from 1 to 1400 pulses per second (pps) . In one embodi ^¬ ment the pulse generator is arranged to generate elec ^¬ tric discharge pulses of the voltage profile for providing reliable avoiding of spark formation at the treatment of high electric conductivity, up to 140 mS/cm, liquids in atmosphere containing oxygen 60 to 99 vol-% with the repetition frequency from 1 to 1400 pulses per second (pps) . In one embodiment at least one high voltage electric discharge electrode is placed between the ver ^¬ tical plate electrodes so that short pulsed electric discharge is generated in order to form a horizontally oriented electric discharge zone between the vertical electrodes, and the liquid mixture is arranged to flow through the electric discharge zone.

In one embodiment at least one high voltage electric discharge electrode is placed between the ver- tical plate electrodes so that multiple streamer dis ^¬ charge channels propagate substantially horizontally, horizontally or at a small angle, e.g. below 30°, in the electric discharge zone between the vertical electrodes, and the liquid mixture is arranged to flow through the electric discharge zone.

In one embodiment pulsed corona discharge chan ^¬ nels are horizontally oriented in the corona discharge zone .

In one embodiment at least one high voltage electrode is placed between vertical electrodes so that multiple horizontally oriented streamer discharge chan ^¬ nels are formed between the vertical plate electrodes to form horizontally oriented short pulsed electric dis ^¬ charge zone and the liquid mixture is arranged to flow, preferably uniformly, through the horizontal electric discharge zone formed between the vertical plate elec ^¬ trodes .

In one embodiment the high voltage electrodes are set between the vertical plate electrodes and the pulsed electric discharge is formed between the elec ^¬ trodes so that maximum electric field strength appears in horizontal direction causing the propagation of multiple horizontally positioned electric discharge channels. The flow of the liquid mixture passes the electric discharge zone. Due to the distortion of electric field by the falling water droplets, dis ^¬ charge channels may propagate at some small angle to horizontal plane, e.g. up to 30 °. Besides, the elec ^¬ trodes may be positioned at a small angle to vertical direction, e.g. up to 10 - 20 °, so that no considera ^¬ ble change in water-air flow is observed. Preferably, the streamer discharge channels are evenly distributed along the wire so that the discharge, such as the dis ^¬ charge plasma, covers the whole inter-electrode area. The liquid mixture flows through the pulsed discharge zone. Then the good contact between the purified liq- uid and the pulsed electric discharge, such as the plasma of pulsed electric discharge, is achieved thus providing the high efficiency in water purification. Besides, in the described horizontally positioned dis ^¬ charge gap the probability of short circuit by falling water droplets and jets is much smaller, so spark formation is avoided.

In one embodiment pulse parameters during the electric discharge are adjusted so that the residual voltage remaining after the electric discharge pulse is reduced at least to the voltage level preceding the pulse discharge, for example so that the bipolar pulse profile is achieved. In one embodiment pulse parame ^¬ ters during the electric discharge are adjusted so that the bipolar pulse profile is achieved. Prefera- bly, the pulse parameters of the electric discharge are adjusted so that the bipolar pulse profile is achieved to avoid spark development. The spark devel ^¬ opment in prevented by a non-linear saturation induc ^¬ tor, which is connected parallel to the electric dis- charge reactor. The non-linear saturation inductor is set to reduce and/or totally remove the sparking re ^¬ sidual voltage.

In one embodiment the device comprises a non ^¬ linear saturation inductor, which is connected parallel to the electric discharge reactor. The non-linear satu ^¬ ration inductor is set to reduce and/or totally remove the residual voltage. In a preferred embodiment residual voltage is reduced immediately, for example within 50 to 200 nanoseconds, after ending the pulsed current flow. The residual discharge energy accumulated in the capacitance of the reactor dissipates in the addition- al resistor, such as, for example, water with its resistance, or returns back to the power supply unit.

In one embodiment the device comprises a feed device containing e.g. feed pipe, feed inlet and/or pump, for feeding a liquid mixture into a reactor.

In one embodiment the device comprises a dis ^¬ tributing tool for distributing the liquid mixture evenly between the vertical plate electrodes. Any tool may be used for even distribution of liquid, for example, inlets, pipes, nozzles and/or showering tools, such as perforated plates, pipes, packed columns or tray towers, or similar.

The vertical electrodes and the high voltage electrodes may be formed of any suitable material, which may be the same for both electrodes or differ- ent . In one embodiment, the vertical plate electrodes are made of stainless steel. In one embodiment, the high voltage electrode is made of stainless steel. To reduce the weight of the device the vertical plate electrode may be formed in the form of a conductive wire-mesh. In one embodiment the distance between neighbouring wires within the mesh should not exceed the distance between two neighbouring high voltage wire electrodes and preferably be kept in the range 1 to 10 mm. Preferably, the diameter of the high voltage wire electrodes has to be much smaller than the dis ^¬ tance between the electrodes so that non-uniform elec ^¬ tric field is generated in the inter-electrode gap.

In one embodiment a gas space is formed between two vertical plate electrodes. Preferably, the gas space between vertically positioned electrodes is modified by enriching with oxygen so that the gas space contains ox ^¬ ygen between 60 to 99 % by volume. In one embodiment the device comprises a means for forming oxygen-enriched gas space between the vertical plate electrodes.

The method and the device of the invention may be used in various applications, such as in purifica- tion and disinfection of contaminated potable water, purification or disinfection of the liquid mixture, such as liquid composition e.g. various recycling waters, and in wastewater treatment, such as in purification and disinfection of various wastewaters, espe- cially in oxidation of compounds, which are toxic and/or refractory in biological wastewater treatment, appearing in pharmaceutical industry, hospitals, min ^¬ ing and chemical industries etc.

By means of the method and the device accord- ing to the invention the noticeable benefits are achieved when compared with the techniques known ear ^¬ lier .

By means of the method and the device accord ^¬ ing to the invention various types of liquid mixtures, including high electric conductivity, up to 140 mS/cm, liquid mixtures, may be treated and purified. In the device of the invention electric spark discharges can ^¬ not damage the device and disturb the method, making the device and the method reliably working for indefi- nitely long time.

The advantage of the invention is that power ^¬ ful oxidative removal capability of organic and inor ^¬ ganic substances can be achieved. The purification ef ^¬ ficiency is also improved due to sufficient contact surface between the treated liquid and electric dis ^¬ charge. The invention allows the device working with moderate contact surface in shape of liquid droplets, jets and films without formation and using mists and aerosols; the surface is sufficient for oxidation at high energy efficiency. The energy required for the contact surface formation is low. In addition, the time of the purification of the liquid mixture is shorter at high pulse repetition frequency.

The achievement of the invention is the com ^¬ pact construction of the purification device. The de- vice according to the invention provides efficient us ^¬ age of the area occupied by the device due to its ver ^¬ tical reactor configuration.

The invention provides easy, simple and effi ^¬ cient industrial way for purification of various liq- uid mixtures. The device according to the invention is simple, reliable and economically beneficial. In addi ^¬ tion, the invention provides high energy efficiency at high equipment reliability. LIST OF FIGURES

Fig. 1 presents a device according to the in ^¬ vention,

Fig. 2 presents a part of the device accord ^¬ ing to the invention,

Fig. 3 presents a shape of the electric pulse, and

Fig. 4 presents a part of the device accord ^¬ ing to the invention. DETAILED DESCRIPTION OF THE INVENTION

In the following, the invention will be described by detailed examples of its embodiments with reference to the accompanying Fig. 1 to 4. Example 1

The device according to the invention is pre ^¬ sented in Figs. 1, 2 and 4.

The device comprises a corona discharge reactor (6), which is a wire-to-plate liquid treatment reactor. The reactor includes at least two vertical plate elec ^¬ trodes (la, lb) which are earthed, and high voltage electrodes (2) which are high voltage wire electrodes. The high voltage electrodes (2) are placed between the vertical plate electrodes in order to generate pulsed corona discharge between the vertical plate electrodes. A corona discharge zone (4) is generated between the vertical plate electrodes. Preferably, the high voltage electrodes (2) are placed between the vertical plate electrodes so that short pulsed corona discharge is gen ^¬ erated and multiple corona streamer discharge channels (9) propagate horizontally between the vertical elec ^¬ trodes (la, lb) in order to form horizontally oriented corona discharge zone (4) between the vertical elec ^¬ trodes (la, lb) . High voltage electrodes are positioned with insulators (7) . The power is fed to the high volt- age electrodes using high voltage bus (8) .

A liquid mixture (3) which may be water based mixture in this embodiment is supplied, e.g. by pump, via a liquid inlet (10) into the reactor (6) and is arranged to flow in the form of shower downwards be- tween the vertical plate electrodes (la, lb) through the corona discharge zone (4) . The device includes dis ^¬ tributing tools, such as the liquid inlet (10) and a perforated plate (11) , for distributing the liquid mix ^¬ ture (3) evenly between the vertical plate electrodes (la, lb) . Treated water is delivered to the inter- electrode space as a shower distributed through, for example, perforated plate.

The device comprises a feeding means (not shown in Figs.) for feeding oxygen in the form of gas phase between the vertical plate electrodes (la, lb) wherein oxidants are formed from oxygen and the liquid mixture. The oxidants are brought to the immediate contact with organic and inorganic substances of the water mixture between the vertical plate electrodes. The liquid may contain organic compounds to be oxidized, and mineral salts imparting electric conductivity to the liquid. Organic compounds are oxidized in the liquid, whereas mineral salts remain intact. The device may comprise a means (not shown in Figs.) for forming oxygen-enriched gas space, containing 60 to 99 vol-% oxygen, between the vertical plate electrodes (la, lb) .

The device comprises a voltage pulse genera ^¬ tor (5) . The pulse generator produces the high voltage pulses of 100 to 400 nanosecond length delivered to the high voltage wire electrodes with the frequency from 1 to 1400 pps . The pulses are formed and deliv- ered to the wire electrodes so that the corona dis ^¬ charge between the high voltage wire electrodes and the earthed plate electrodes takes place in the inter- electrode space.

The device is able to treat liquids in wide diapasons of organic compounds and mineral salts con ^¬ tents. The electric conductivity of the liquids treat ^¬ ed in the device with pulsed corona discharge may vary from 0 to 140 milli-Siemens per centimetre (mS/cm), which exceeds, for example, the conductivity of satu- rated at 20 °C sodium sulphate solution. The experi ^¬ ments were carried out with the pulse voltage ampli ^¬ tude 18 to 20 kV and the current amplitude 380 to 400 A, making the pulse energy from 0.3 to 0.35 J/pulse.

The device comprises an adjustment means (not shown in Figs.) for adjusting the corona discharge pulse parameters during the corona discharge so that the bipolar pulse profile is achieved. Preferably, the electric pulse is in the form of bipolar pulse profile in the method of the invention, such as presented in Fig. 3.

The purified water is supplied out via an outlet (13) from the reactor into a storage tank (14) . Alternatively the water may be recirculated back into the reactor. Example 2

In the experiments of this example the aque ^¬ ous liquids with high conductivity were treated with the device according to Figs. 1, 2 and 4 at the pulse voltage amplitude 18 to 20 kV and the current ampli ^¬ tude 380 to 400 A, making the pulse energy from 0.3 to 0.35 J/pulse.

The black liquor, the cellulose pulp produc- tion liquid waste with the electric conductivity 110 mS/cm, was treated for oxidation of reduced sulphur compounds in 90 vol-% oxygen gas. The sufficient re ^¬ sult was achieved with the energy dose of 15 kWh/m ³ . The device according to the invention showed no trace of damage or corrosion.

The recycling water of paper machine, such as "white water", was treated in 90% oxygen for the se ^¬ lective removal of resin and fatty acids, lignin and colour. The electric conductivity was 56 mS/cm. The desired result in colour, lignin and acids control achieved at the energy dose of 12 kWh/m ³ . The device according to the invention showed no trace of damage or corrosion.

Cellulose hydrolyzate before reverse osmosis membrane filtration was treated in 90% oxygen. The electric conductivity was 65 mS/cm. The permeability of the membrane increased four times with indefinitely prolonged lifetime of the membrane. The device accord ^¬ ing to the invention showed no trace of damage or cor- rosion.

The mixed liquid waste from the hazardous waste treatment plant, containing cyanides, oils, phthalates and methanol was treated in 90% oxygen for the removal of cyanides. The electric conductivity was 100 mS/cm. The desired reduction in cyanides was achieved at 5 to 10 kWh/m ³ of energy dose. The oxida- tion of methanol was observed. The device according to the invention showed no trace of damage or corrosion.

The wastewater containing immunity depressant Azathioprine in 30% acetic acid was treated. The oxi- dation was carried out in 90% oxygen. The electric conductivity was 140 mS/cm. The sufficient result was observed in alkaline media at 25 kWh/m ³ . The device according to the invention showed no trace of damage or corrosion.

Example 3

In this example the aqueous solutions were treated by the method with the device according to Figs. 1, 2 and 4 at the pulse voltage amplitude 18 to 20 kV and the current amplitude 380 to 400 A, making the pulse energy from 0.3 to 0.35 J/pulse in air.

The aqueous solutions include: phenol solu ^¬ tions in acidic, neutral and alkaline media; coloured waters containing humic substances; lignin solutions; lake and ground water for disinfection; wastewaters containing pharmaceuticals and estrogens; and wastewaters containing urobilin.

Phenol solutions in acidic, neutral and alka- line media were treated. The energy efficiency of oxi ^¬ dation with the method and the device according to the invention surpassed the efficiency of conventional ozonation by the factor of minimum three in air and by the factor six when 90% oxygen was used.

Coloured waters containing humic substances were treated. Humic substances oxidation by the method with the device according to the invention surpassed conventional ozonation treatment in energy efficiency by the factor of minimum 2.2 in air.

Lignin solutions were treated. The lignin ox ^¬ idation by the method in the device according to the invention is characterized with the energy efficiency minimum three times higher than by conventional ozona ^¬ tion.

Lake and ground waters for disinfection were treated. The reliable bacterial control was achieved by the dose of energy of 20 to 50 Wh/m ³ delivered to the reactor surpassing the conventional ozonation for two to three times in energy efficiency. The device according to the invention was working for one year with no trace of damage or corrosion.

Wastewaters containing pharmaceuticals (para ^¬ cetamol, ibuprofen, indometacin) and estrogens (17- ethynil-estradiol ) were treated. The treatment of pa ^¬ racetamol aqueous solutions by the energy efficiency was comparative with or surpassing the one of conven- tional ozone application.

Wastewaters containing urobilin (urochrome, the substance responsible for the yellow colour of urine) with the electric conductivity of 5 mS/cm were successfully treated for discolouration with the de- livered energy dose of 2 kW/m ³ by means of the method and the device according to the invention.

It was observed that different liquid compo ^¬ sitions and mixtures can be purified easily by means of the method and device according to the invention. The product liquids had good level of purification.

The method and the device according to the invention are applicable as different embodiments for use in the treatment and purification of different liquid mixtures.

The invention is not limited merely to the examples referred to above; instead, many variations are possible within the scope of the inventive idea defined by the claims.