Bipolar scrubber

Abstract

The invention relates to a bipolar electrostatic scrubber (200) comprising a chamber (210), an aerosol inlet (201) for supplying aerosol comprising particles and gas molecules into the chamber (210) for purifying, a liquid inlet (211), a droplet generation unit (213) producing droplets (208), charging means charging a part of droplets (208) negatively and a part of the droplets (208) positively, a droplet separator (204) removing from the aerosol the droplets (208), and the aerosol particles and the gas molecules, which are attached to the droplets (208) due to electric fields formed between the positively and negatively charged droplets (208) through an aerosol outlet (202) for producing purified aerosol, and a liquid outlet (212) for removing droplets (208) and the aerosol particles and the gas molecules attached to the droplets (208). The invention further relates to an aerosol purification method (400) performed by the bipolar electrostatic scrubber (200).

Description

Technical field

[0001] The present invention relates to a bipolar electrostatic scrubber i.e. a bipolar scrubber device.

[0002] The invention also relates to a method for removing gaseous and particulate impurities from emission aerosol by a bipolar electrostatic scrubber.Background

[0003] Aerosol consists of gaseous compounds and solid or liquid particles suspended in a gas i.e. it is a suspension of fine solid particles or liquid droplets in air or another type of gas. Aerosols can be natural or anthropogenic. Industry, power plants and various combustion processes are examples, which generate harmful gases and particles that must be removed before they can be released into the environment. Gaseous compounds such as SO2 can be purified from the aerosol using, for example, a scrubber technique. In the scrubber technique, water droplets are sprayed into dirty aerosol and gaseous contaminants in the aerosol are adsorbed into the droplets. The droplets can then be removed from the gas by either gravity or a droplet separator.

[0004] The scrubber technology can effectively remove gaseous compounds from aerosol, but solid particles usually need to be removed from the gas by some other technology. An electrostatic precipitator (ESP) is an example of an additional device often used to remove solid particles from aerosol gas. The ESP first produces an electric corona discharge, which produces electrical charges that adhere to the aerosol particles. The charged particles are then collected from the gas by an electric field.Summary

[0005] It is an aim of the invention to provide and present a bipolar electrostatic scrubber device / system configured to remove gaseous and particulate impurities from aerosol. The further aim is to provide a method for removing gaseous and particulate impurities from aerosol by the bipolar electrostatic scrubber. The bipolar electrostatic scrubber, and the method according to the invention are characterized in what will be presented in the independent claims, and the dependent claims relate to advantageous embodiments of the invention.

[0006] According to a first aspect, there is provided a bipolar electrostatic scrubber, which comprises an aerosol inlet for supplying aerosol comprising particles and gas molecules into the chamber for purifying, a droplet generation unit inside the chamber, a liquid inlet for supplying liquid to the droplet generation unit configured to produce droplets from the liquid, adjacent charging electrodes are configured to charge a first part of droplets negatively and the second part of the droplets positively, a droplet separator configured to remove from the aerosol the droplets, and the aerosol particles and gas molecules, which are attached to the droplets due to electric fields formed between the positively and negatively charged droplets through an aerosol outlet for producing purified aerosol, and a liquid outlet in the bottom of the chamber for removing droplets and aerosol particles and the gas molecules attached to the droplets, and wherein every second of the adjacent charging electrode is configured to charge the droplets (208) negatively and every second of the adjacent charging electrode is configured to charge the droplets (208) positively.

[0007] According to an embodiment, the charging means are high voltage electrodes, which the first half of the high voltage electrodes is negative and the second half of the high voltage electrodes is positive. According to an embodiment, the charging means are high voltage electrodes operated with AC, charging positively and negatively charged droplets alternately. According to an embodiment, the direction of the flow of the aerosol is parallel, opposite, perpendicular or at any direction compared to the direction of the droplets. According to an embodiment, the charging means is configured to charge particles of the aerosol, if the supplied aerosol is not naturally charged. According to an embodiment, the droplet separator is a metal mesh filter or an electric filter whose electric field are configured to collect the charged droplets. According to an embodiment, the liquid is water.

[0008] According to a second aspect, there is provided an aerosol purification method. The method comprises: supplying aerosol comprising particles and gas molecules into a chamber of a bipolar electrostatic scrubber for purifying, supplying liquid to a droplet generation unit arranged inside the chamber, producing droplets from the liquid by the droplet generation unit, charging a first part of droplets negatively and the second part of the droplets positively by adjacent charging electrodes, wherein every second of the adjacent charging electrodes is configured to charge the droplets (208) negatively and every second of the adjacent charging electrode is configured to charge the droplets (208) positively, removing from the aerosol the droplets, and the aerosol particles and the gas molecules, which are attached to the droplets due to electric fields formed between the positively and negatively charged droplets through an aerosol outlet for producing purified aerosol, and draining droplets and aerosol particles and the gas molecules attached to the droplets from the chamber.

[0009] According to an embodiment, the method further comprises filtering the drained droplets and aerosol particles and the gas molecules attached to the droplets recycling the working liquid back to the bipolar electrostatic scrubber. According to an embodiment, the charging means are high voltage electrodes, wherein the first half of the high voltage electrodes is negative and the second half of the high voltage electrodes is positive i.e. the first half of the high voltage electrodes is configured to charge droplets negatively and the second half of the high voltage electrodes is configured to charge droplets positively. According to an embodiment, the charging means is one or more high voltage electrodes operated with high voltage AC, forming positively and negatively charged droplets alternately. According to an embodiment, the method further comprises producing turbulent air streams to the chamber, which air streams are configured to mix the droplets and the particles and the gas molecules of the aerosol in the camber. According to an embodiment, the method further charging particles of the aerosol, if the supplied aerosol is not naturally charged. According to an embodiment, the droplet separator is a metal mesh filter, or an electric filter whose electric field are configured to collect the charged droplets. According to an embodiment, the liquid is water.Brief description of the drawings

[0010] In the following, the invention will be described in more detail with reference to the appended drawings, in which Fig. 1shows bipolarly charged droplets in dirty aerosol as a close up in a chamber of a bipolar electrostatic scrubber according to an embodiment of the invention, Fig. 2shows an operation principle of a bipolar electrostatic scrubber according to an embodiment of the invention, Fig. 3shows process steps of a bipolar electrostatic scrubber according to an embodiment of the invention, and Fig. 4shows method steps of a bipolar electrostatic scrubber according to an embodiment of the invention. Detailed description

[0011] There exist solutions, wherein a wet scrubber technology and an electrostatic precipitator (ESP) technology are combined in the same unit i.e. as an ESP Scrubber removing both gaseous and particulate impurities from emission aerosol by a single system. In existing ESP scrubber systems, water droplets are charged by an electric field at the time of forming while dripping from an upper part of an ESP scrubber towards the ground due to the gravity. This kind of charging, however, results in a same polarity net charge i.e. all the water droplets are similarly charged, positively or negatively. The charged water droplets attract oppositely charged particles and gas molecules, allowing them to be collected from the emission aerosol due to the electrostatic force. i.e. charged particles and charged molecules or non-charged i.e. neutral molecules of aerosol are diverted towards charged droplets having different charge than the charged particles. Neutral molecules move by diffusion. Particles and gas molecules build up on the droplets and are removed from the air stream. The direction of gas flow may be opposite to the direction of droplet flow. Particles of the inlet aerosol need to be electrically charged, if they are not naturally charged, with a separate charger for the existing ESP scrubber system to work. The challenge of existing ESP Scrubber systems is insulating of high voltage (HV) electrodes used for charging droplets and leakage current, which allows the voltage droplets to be discharged resulting in that a particle collection does not work. In addition to that, a problem with similarly charged droplets, positive or negative charged droplets, is that they can cancel out the electric fields caused by each other, leaving areas in the gaseous flow where the electric field goes substantially close to zero, which reduces the collection efficiency of the charged particles. In addition, the droplets are only able to collect oppositely charged particles, which means that if the droplets are, for example, positively charged, the positively charged particles are not collected from the aerosol. The same problem relates to negatively charged droplets and particles.

[0012] In the present application, the term "bipolar scrubber" corresponds to the terms "bipolar electrostatic scrubber", "bipolar electrostatic scrubber device", and "bipolar electrostatic scrubber system". The terms "aerosol", "aerosol flow", "gas flow" and "air flow" have the same meaning i.e. to refer the aerosol flowing inside a chamber of a bipolar electrostatic scrubber and the term "inlet aerosol" corresponds to the term "dirty aerosol" or "dirty inlet aerosol" that is fed / inputted to a bipolar electrostatic scrubber to be purified.

[0013] In the present invention a wet scrubber technology and a kind of an electrostatic precipitator (ESP) technology are combined in the same unit, as a bipolar electrostatic scrubber removing both gaseous and particulate impurities from dirty aerosol very efficiently and reliably by bipolarly charged droplets instead of collecting plates of an ESP. Thus, bipolarly charged droplets of a bipolar scrubber replace collecting plates of an ESP scrubber. The idea of the bipolar scrubber is thus to produce droplets with two different electrical charges into the dirty aerosol so that a first part of the droplets has a positive net charge and a second part of the droplets has a negative net charge, which creates strong electric fields between the differently charged droplets that collect charged particles regardless of polarity and enhance gas collection. It should be noted that one droplet is not bipolarly charged, but together a plurality of droplets has bipolar charge. Bipolarly charged droplets generate stronger electric field compared to solution comprising unipolar i.e. negatively or positively charged droplets, because in the gaseous flow there would not be areas, where an electric field goes to zero. Bipolarly charged droplets in dirty aerosol in a chamber of a bipolar scrubber according to an embodiment of the invention are shown in figure 1 as a close-up. The droplets of the bipolar scrubber system can be charged, for example, by means of an electric field produced by an HV electrode in the dripping phase, whereby a large net charge is formed in the droplets as a result of induction. The droplets move in the same direction as the aerosol flow, thus increasing the residence time of the individual gas molecules and particles in the electric field generated by the droplets and enhancing the collection. However, the direction of aerosol flow may also be opposite or perpendicular to the direction of droplets in addition to parallel direction. It should also be noted that direction of both the aerosol flow and droplets can be changed compared to the other. Both can move upwards, downwards or laterally or anything between these directions.

[0014] In addition, gas molecules of all gas molecules of aerosol, which are or could or will be attached to charged droplets, may be called as target gas molecules. Target molecules are gaseous impurities, which are certain harmful gases and gas molecules to be removed from inlet aerosol, e.g. SO2. Not all gases or gas molecules can be removed from aerosol by the bipolar electrostatic scrubber of the present invention.

[0015] When charging the droplets, corona discharge can also be generated by the HV electrode, which can be used to charge the dirty aerosol particles. Charging of droplets may also be performed corona discharge generated by one or more corona needles. Corona discharge produces ions, which charge the droplets. If the one or more needles are near the droplet producing, ions may charge droplets as such, but if they are further away, for example, compressed air can be used to blow the ions to the droplets. The operation principle of the bipolar electrostatic scrubber is shown in figure 2.

[0016] As mentioned above, bipolarly charged droplets produced by a bipolar electrostatic scrubber according to the invention i.e. bipolar scrubber are shown in dirty aerosol in figure 1 as a close up. The electrically bipolarly charged droplets 101, 102 are produced into dirty aerosol comprising charged aerosol particles 103 and aerosol gas molecules 104 inside a chamber 100 of the bipolar Electrostatic scrubber, substantially a first half of the droplets have a positive net charge i.e. are positively charged droplets 101, and substantially a second half of the droplets have a negative net charge i.e. are negatively charged droplets 102. Different charges of droplets 101, 102 create strong electric fields between the droplets 101, 102 and cause collection of charged aerosol particles 103 regardless of their polarity to the droplets and thus enhance particle collection. The positively charged water droplets 101 attract negatively charged particles and the negatively charged water droplets 102 attract positively charged particles, allowing them to be collected from the emission aerosol. Bipolarly charged droplets 101, 102 generate a stronger electric field compared to unipolarly charged droplets.

[0017] The operation principle of a bipolar electrostatic scrubber 200 according to the invention is shown in figure 2. Dirty inlet aerosol that is a gas flow is led i.e. inputted i.e. supplied into a chamber 210 of the bipolar scrubber 200 through an aerosol inlet 201 arranged in the upper part of the chamber 210. Water is supplied to a droplet generation unit 213 inside the chamber 210 of the bipolar scrubber 200 through a water inlet 211 also arranged in the upper part of the chamber 210. In the droplet generation unit 213 the water is produced, for example, by water spraying noses or by some other suitable means as tiny water droplets 208. It should be noted that it is also possible to use other liquid than water. The selection between water or other liquid may depend on, for example, the gas of dirty aerosol.

[0018] The produced droplets 208 may be simultaneously bipolarly charged by charging means producing an electric field produced in a dripping phase, whereby a large net charge is formed in the droplets 208 as a result of induction i.e. the droplets 208 are charged by an electric field while dripping. In this embodiment the charging means are adjacent high voltage (HV) electrodes 203 that are next to each other and every other adjacent high voltage electrode is connected to a positive potential for forming droplets 208 of + sign i.e. is a high voltage positive electrode and every other adjacent high voltage electrode is connected to a negative potential for forming droplets 208 of - sign i.e. is a high voltage negative electrode. In other words, between two adjacent high voltage positive electrodes there is a high voltage negative electrode and vice versa. In addition to that, high voltage electrodes 203 are arranged in the center area of the bipolar electrostatic scrubber 200 in horizontal direction or at least they are not arranged for the peripheral areas i.e. not next to the sides of the bipolar electrostatic scrubber 200. The dripping phase means, in this context, a phase after water droplets are formed and they start to drip from the upper part of the bipolar electrostatic scrubber 200 towards the ground due to the gravity. The high voltage electrodes 203 are arranged close to the nozzles of the droplet generation unit 213 to cause inductive charging of the droplets 208. They are close to the droplet generation unit 213 so that the droplets 208 are charged as long as possible. It should be noted that there may be other charging means that can be used for bipolarly charging of droplets 208 instead of the high voltage electrodes 203, for example, an AC field produced by high voltage electrodes, charge a first part of droplets negatively and the second part of the droplets positively by forming droplets 208 of + sign and - sign alternately at regular or irregular intervals into the inlet aerosol flow. Corona discharge can also be generated by the AC field produced by HV electrode, which can be used to charge the dirty aerosol particles. In this context, charge of the first and second parts is not restricted, this means that the first part may also comprise positively charged droplets and the second part negatively charged droplets. In addition to that, it is possible that the positive and negative droplets are charged, for example, alternately instead of simultaneous charging by HV electrodes.

[0019] Because the positive and negative droplets 208 move in the same direction as the gas flow of inlet aerosol i.e. both move downwards, towards the ground, the residence time of the individual gas molecules and particles of the inlet aerosol in the electric field generated by the droplets 208 increases and the collection of the gas molecules and particles of the inlet aerosol by the bipolarly charged droplets 208 increase. However, it is also possible that the positive and negative droplets 208 move in opposite directions as the gas flow of the inlet aerosol i.e. droplets 208 move downwards, towards the ground, and the aerosol gas flow moves upwards. In this case, the mixing of the individual gas molecules and particles and the droplets 208 increases and, thus, the collection efficiency of the particles of the inlet aerosol by the bipolarly charged droplets 208 increases. When charging the droplets 208, the corona discharge can also be generated by the HV electrode 203 to charge particles of the inlet aerosol. Particles of the inlet aerosol can also be charged using some other suitable method or device. If inlet aerosol i.e. particles of the inlet aerosol are already naturally charged, it is not necessary to charge particles of the inlet aerosol. This step comprising charging of particles of the inlet aerosol is thus optional. The charged droplets 208 have bipolar charges as the first half of the high voltage electrodes 203 is negative and the second half is positive, therefore substantially one half of droplets 208 is positively charged and substantially the other half of droplets 208 is negatively charged. After producing of bipolarly charged droplets 208, the droplets 208 and inlet aerosol particles and gas molecules are mixed in the camber 210 by turbulent air streams. Strong electric fields between the oppositely charged droplets 208 cause aerosol particles and target gas molecules to move and attach with the droplets 208 so that they are removed from aerosol i.e. gas stream. It should, however, be noted that gas molecules move mainly by diffusion (not by electric field) and thus collide with droplets 208, but the electric field can stimulate their movement, especially if the gas molecule has an electric charge. Neutral gas molecules does not move under the influence of the electric field. Thus, a part of the target gas molecules or even a larger part of the target gas molecules may attach to the charged droplets 208 due to their movement instead of electric fields formed between the charged droplets 208, but particles are attached to the charged droplets 208 due to the electric fields formed between charged droplets 208.

[0020] A droplet separator 204 arranged in the lower part of the chamber 210 of the bipolar electrostatic scrubber removes droplets 208, and aerosol particles and gas molecules attached to the droplets 208 from the aerosol and the purified aerosol flows from the chamber 210 and the bipolar electrostatic scrubber 200 through an aerosol outlet 202. The droplet separator 204 may be, for example, a metal mesh filter. Working liquid part i.e. droplets 208 with aerosol particles and gas molecules attached to the droplets 208 flows to the bottom of the chamber 210 and is removed from the chamber 210 of the bipolar electrostatic scrubber 200 through a water outlet 212 as a wastewater i.e. as waste liquid. The waste can either be pumped away as a waste or recirculated as working liquid back to the bipolar electrostatic scrubber 200. Recirculated wastewater may be filtered and / or cooled, if needed, before reusing in the bipolar electrostatic scrubber 200. The water outlet 212 could as well be called as a liquid outlet.

[0021] Drying of the charged droplets 208 in the chamber 210 may cause a so-called Coulombic fission, where excess charges escape from the droplets 208 into the chamber 210 explosively, which may enhance the electrical charging of the aerosol particles of the inlet aerosol. This can be avoided by controlling temperature and humidity of the input aerosol.

[0022] Insulators of the HV electrodes 203 used for charging the droplets 208 may be protected from the inlet aerosol so that it remains uncontaminated and functional for at least a longer time compared to contaminated HV electrodes.

[0023] The insulators may be made of, for example, Teflon or other suitable insulating material. If AC voltage is used, instead of HV electrodes 203, one protected electrode may be sufficient. In the case of HV electrode charging, usually one or more electrodes are used for charging both negative and positive charged droplets. If DC voltage is used for charging droplets, there are at least two electrodes, with AC voltage one is enough. Further, if both positively and negatively charged droplets are produced at the same time, then there are at least two or some other even number of electrodes. The water used for forming droplets 208 may be cooled before forming of the droplets and dripping them, which may make the thermophoretic collection of aerosol particles and the condensation of gases more efficient compared to a situation wherein dirty inlet aerosol is warmer / hot and not cooled by droplets 208. The chemical composition of the water used for the droplets 208 may be optimized for certain gases to enhance adsorption, or alternatively another liquid may be used instead of water, for example oil for fat-soluble substances.

[0024] The bipolar electrostatic scrubber 200 can be implemented with several different variations. The direction of the inlet aerosol flow may also be opposite to the droplets 208 i.e. the aerosol inlet 201 may be arranged in the lower part of the chamber 210. The flow on inlet aerosol can also be horizontal i.e. the aerosol inlet 201 may be arranged in the side of the chamber 210. And as already mentioned above, it is possible to remove naturally charged particles of the inlet aerosol so that corona discharge performed by HV electrodes 203 or other means is not required to charge the particles of the inlet aerosol, if particles are naturally charged. It should also be noted that the process performed by the ESP-scrubbed may comprise additional steps or other alternative steps performed by additional or alternative means of the bipolar electrostatic scrubber 200. The bipolar electrostatic scrubber 200 may further comprise mixing means in the chamber configured to mix the droplets and particles and gas molecules of the aerosol by producing turbulent air streams. The mixer may be, for an example, an air mixing unit i.e. an air mixing box or an air mixing plenum.

[0025] The process of a bipolar electrostatic scrubber according to an embodiment of the invention can be described by the following steps which are also shown in figure 3 as a block diagram. A step 301 is an aerosol step, where dirty inlet aerosol is fed to a chamber of the bipolar electrostatic scrubber.

[0026] A 302 step is an optional aerosol particle charging step, wherein inlet aerosol can be charged i.e. particles of inlet aerosol can be charged using, for example, corona discharge, produced, for example, by HV electrodes. If the inlet aerosol is already naturally charged, this step as an optional step, is not necessary, but still possible.

[0027] A 303 step is a liquid step. Liquid that may be called as working fluid, typically water, is fed to a droplet generation unit arranged in the chamber of the bipolar electrostatic scrubber.

[0028] A 304 step is a generation of bipolarly charged droplets step. The nozzles of the droplet generation unit are used to generate tiny droplets. High voltage electrodes (HV) or other charging means arranged close to the nozzles cause inductive charging of the droplets. The droplets have bipolar charges (part +, part -) as the half of the high voltage electrodes are negative and the half are positive.

[0029] A step 305 is a mixing of bipolarly charged droplets and aerosol step. The charged droplets and aerosol particles and gas molecules of dirty inlet aerosol are mixed inside the chamber using turbulent air streams.

[0030] A step 306 is an electrostatic precipitation (agglomeration) of aerosol particles and bipolarly charged droplets and adsorption of gases step. Strong electric fields between the oppositely i.e. positively and negatively charged droplets cause aerosol particles and target gas molecules of all gas molecules of the dirty inlet aerosol to move and attach with / to the droplets so they are removed from gas stream i.e. dirty inlet aerosol.

[0031] A step 307 is a droplet separator step. In this step, droplets and aerosol particles and gas molecules attached to the droplets are removed from gas stream using a droplet separator, which may be, for example, above mentioned metal mesh filter or curved droplet separator or an electric filter whose electric field are configured to collect the charged droplets.

[0032] A step 308 is a purified aerosol out step. In this step, the purified aerosol gas flow is supplied out i.e. the purified aerosol flows out from the bipolar electrostatic scrubber.

[0033] A step 309 is a liquid out step. Working liquid consisting of the droplets wherefrom aerosol particles and target gas molecules are removed by the droplet separator flows from the droplet separator to the bottom of the bipolar electrostatic scrubber and is removed from the system. The working liquid is so-called waste liquid, which can be, for example, drained to a drain, but also be recycled in the process of the bipolar electrostatic scrubber.

[0034] A step 310 is a liquid pumping step. This step is optional, because it is not necessary to recycle the working liquid. If it is however recycled, it may be recirculated by a pump or corresponding back to the bipolar electrostatic scrubber to be used for droplets.

[0035] A step 311 is a liquid filtration step. This step is also optional, it is not needed if the working liquid is not recirculated. In this step recirculated working liquid is filtered before reusing in the bipolar electrostatic scrubber. The working liquid is purified in the recycling process before feeding back to the bipolar electrostatic scrubber, because some chemical compounds may be concentrated in the liquid.

[0036] A step 312 is a liquid cooler step. Also this step is an optional step, wherein the recirculated working liquid is cooled, if needed or desired, before feeding the recirculated working liquid to the bipolar electrostatic scrubber.

[0037] Figure 4 shows a block diagram of an aerosol purification method 400. In step 410, aerosol comprising particles and gas molecules is supplied i.e. introduced into a chamber of a bipolar electrostatic scrubber for purifying. In step 420, liquid is supplied i.e. introduced to a droplet generation unit arranged inside the chamber. In step 430, droplets are produced from the liquid by the droplet generation unit. In step 440, a first part of droplets is charged negatively and the second part of the droplets is charged positively by charging means. In step 450, the droplets, and the aerosol particles and the gas molecules, which are attached to the droplets due to electric fields formed between the positively and negatively charged droplets are removed from the aerosol for producing purified aerosol. In step 460, droplets and aerosol particles and gas molecules attached to the droplets are drained i.e. lead out from the chamber.

[0038] It is also possible that a bipolar scrubber further acts as a heat exchanger in addition to purifying aerosol from particles. This is because droplets gain energy from hot flue gases in the bipolar scrubber, outgoing liquid, for example, water, is warmer than liquid supplied to the bipolar scrubber.

[0039] A bipolar scrubber can operate, for example, at a temperature that is between the melting temperature and the boiling temperature of the liquid used.

[0040] In a bipolar electrostatic scrubber positively and negatively charged droplets are generated in the same chamber, for example, at the angle between 45 - 180 towards to the air flow and thus the droplet and thus aerosol particles are mixed efficiently. The mixing chamber that is designed to mix efficiently the inlet air flow, droplets and aerosol particles so that they form homogenized mixture and thus the electric fields between the oppositely charged droplets are more efficient to remove the particles. A mesh droplet separator may be at the angle between 45-90 towards to the air flow, and thus the droplets are separated efficiently. In addition, the applied high voltage in electrodes is usually more than 10 kV,

[0041] The high voltage electrodes are insulated by dielectric materials and protected using, for example, sheath air flow to keep the insulates clean and dry to avoid electric breakdown and discharge of the high voltage. Generated droplets are in size range of 1- 25 µm. Droplets in the size range of 1-25 µm are easier to remove by droplet separator than smaller droplets and they are easier to charge than larger droplets.

[0042] The bipolar electrostatic scrubber is designed to remove naturally charged aerosol particles, and thus an external charger is not needed to charge incoming particles. natural charged particles are formed, for example, in the combustion process. That is why the system could be less complicated. Considerable advantages are achieved by the present invention when compared to existing ESP scrubber methods and ESP scrubbers. Advantages are achieved by combining of the certain features of ESP and scrubber as a bipolar electrostatic scrubber that uses bipolarly charged droplets and removes gases (target gas molecules) and particles from dirty inlet aerosol efficiently. Longer residence time of target gas molecules and particles in the electric fields formed by bipolarly charged droplets enhances the collection of target gas molecules and particles from the inlet aerosol. Bipolarly charged droplets are further able to collect bipolarly charged particles. Particle collection also works over a wide range of particle sizes. Further, a bipolar scrubber has a simple structure because it does not need typical collection plates that are required by typical ESPs. A bipolar scrubber is also affordable to implement because it combines both particle and gas cleaning in one system. The further great benefit of a bipolar scrubber is that it is easy to scale to a variety of sizes and applications.

[0043] It is obvious that the present invention is not limited solely to the above-presented embodiments, but it can be modified within the scope of the appended claims.

Claims

1. A bipolar electrostatic scrubber comprising a chamber (210), an aerosol inlet (201) configured to supply aerosol comprising naturally charged_particles and gas molecules into the chamber (210) for purifying, a droplet generation unit (213) inside the chamber (210), a liquid inlet (211) for supplying liquid to the droplet generation unit (213) configured to produce droplets (208) from the liquid, adjacent charging electrodes configured to charge a first part of droplets (208) negatively and the second part of the droplets (208) positively, a droplet separator (204) configured to remove from the aerosol the droplets (208), and the aerosol particles and the gas molecules, which are attached to the droplets (208) due to electric fields formed between the positively and negatively charged droplets (208) through an aerosol outlet (202) for producing purified aerosol, and a liquid outlet (212) in the bottom of the chamber (210) for removing the droplets (208) and the aerosol particles and the gas molecules attached to the droplets (208), and wherein every second of the adjacent charging electrodes is configured to charge the droplets (208) negatively and every second of the adjacent charging electrode is configured to charge the droplets (208) positively.

2. A bipolar electrostatic scrubber according to claim 1, wherein charging means are high voltage electrodes (203), wherein the first half of the high voltage electrodes (203) is negative and the second half of the high voltage electrodes (203) is positive.

3. A bipolar electrostatic scrubber according to claim 1, wherein the charging means are high voltage electrodes (203) operated with AC, charging positively and negatively charged droplets (208) alternately.

4. A bipolar electrostatic scrubber according to any of the previous claims, wherein the direction of the flow of the aerosol is parallel, opposite, perpendicular or at any direction compared to the direction of the droplets (208).

5. A bipolar electrostatic scrubber according to any of the previous claims, wherein the charging means is configured to charge particles of the aerosol, which particles are not naturally charged.

6. A bipolar electrostatic scrubber according to any of the previous claims, wherein the droplet separator (204) is a metal mesh filter or an electric filter whose electric field are configured to collect the charged droplets (208).

7. A bipolar electrostatic scrubber according to any of the previous claims, wherein liquid is water.

8. An aerosol purification method comprising: supplying aerosol comprising naturally charged particles and gas molecules into a chamber (210) of a bipolar electrostatic scrubber (200) for purifying, supplying liquid to a droplet generation unit (213) arranged inside the chamber (210), producing droplets (208) from the liquid by the droplet generation unit (213), charging a first part of droplets (208) negatively and the second part of the droplets (208) positively by adjacent charging electrodes, wherein every second of the adjacent charging electrodes is configured to charge the droplets (208) negatively and every second of the adjacent charging electrode is configured to charge the droplets (208) positively, removing from the aerosol the droplets (208), and the aerosol particles and the gas molecules, which are attached to the droplets (208) due to electric fields formed between the positively and negatively charged droplets (208) through an aerosol outlet (202) for producing purified aerosol, and draining the droplets (208) and the aerosol particles and gas molecules attached to the droplets (208) from the chamber (210).

9. An aerosol purification method according to claim 8, wherein the method further comprises: filtering the drained droplets (208) and the aerosol particles and the gas molecules attached to the droplets (208) recycling the working liquid back to the bipolar electrostatic scrubber (200).

10. An aerosol purification method according to claim 8 or 9, wherein the charging means are high voltage electrodes (203), wherein the first half of the high voltage electrodes (203) is negative and the second half of the high voltage electrodes (203) is positive11. An aerosol purification method according to claim 8 or 9, wherein the charging means is one or more high voltage electrodes (203) operated with high voltage AC, forming positively and negatively charged droplets (208) alternately.

12. An aerosol purification method according to any of the claims 8 to 11, wherein the method further comprises: producing turbulent air streams to the chamber (210), which air streams are configured to mix the droplets (208) and particles and gas molecules of the aerosol in the chamber (210).

13. An aerosol purification method according to any of the claims 8 to 12, wherein the method further comprises: charging particles of the supplied aerosol, which particles are not naturally charged.

14. An aerosol purification method according to any of the claims 8 to 13, wherein the droplet separator (204) is a metal mesh filter, or an electric filter, whose electric field are configured to collect the charged droplets (208).

15. An aerosol purification method according to any of the claims 8 to 14, wherein liquid is water.

Images