Patent Application
20230277984
The present invention relates to a method and apparatus that separates atmospheric pollutants contained in exhaust gas to clean the exhaust gas. Note in this patent application, “atmospheric pollutants” implies either or both SOx and NOx.
Exhaust gas, which is discharged from power plants and industrial facilities that use fossil fuels, contains SOx and NOx atmospheric pollutants. In addition to having detrimental effects on the human body that include bronchial inflammation and asthma, SOx atmospheric pollutants also cause of acid rain. NOx atmospheric pollutants detrimentally affect respiratory organs such as the throat and lungs. A method of separating NOx atmospheric pollutants from exhaust gas has been developed (JP2013-32777A, e.g.).
To remove NOx from diesel engine exhaust gas, the exhaust gas purifying apparatus cited in JP2013-32777A disclosure is provided with a reducing agent supply section that supplies reducing agent for reduction of exhaust gas NOx, and an NOx detection system that detects NOx concentration in the exhaust gas. The amount of reducing agent supplied from the reducing agent supply section is regulated based on NOx detection system information to remove NOx from exhaust gas. Aqueous urea solution is used as the reducing agent.
In a large scale cleaning apparatus that supplies aqueous urea solution to exhaust gas to remove NOx, it is difficult to efficiently remove NOx while maintaining low operating cost.
The present invention was developed with the object of eliminating this drawback. Thus one object of the present invention is to provide a method and apparatus for cleaning exhaust gas that reduces operating cost and efficiently removes atmospheric pollutants to clean exhaust gas.
An implementation of the method for cleaning exhaust gas of the present invention is a method that separates atmospheric pollutants to clean the exhaust gas and includes an atomizing step that forms an aqueous alkaline solution mist with an atomizer; a mixing step that mixes the aqueous alkaline solution mist with exhaust gas to absorb atmospheric pollutants contained in the exhaust gas into the mist; and a separating step that separates the mist, which absorbed atmospheric pollutants in the mixing step, from the exhaust gas.
An implementation of the apparatus for cleaning exhaust gas of the present invention is an apparatus that separates atmospheric pollutants to clean the exhaust gas and is provided with an atomizer that atomizes aqueous alkaline solution to form mist; a mixer that mixes the mist generated by the atomizer with exhaust gas to absorb atmospheric pollutants contained in the exhaust gas into the mist; and a separator that separates the mist, which absorbed atmospheric pollutants in the mixer, from the exhaust gas.
By absorbing and separating atmospheric pollutants with fine mist, the method and apparatus for cleaning exhaust gas described above can efficiently separate atmospheric pollutants from exhaust gas with reduced operating cost.
The following describes the present invention in detail based on the figures. Although terms indicating specific direction and/or position (e.g. above, below, and terminology that includes those types of words) are used as required In the following descriptions, use of those terms is for the purpose of making the invention easy to understand with reference to the figures and the technical scope of the present invention is not limited based on the meaning of those terms. Further, components that appear in a plurality of figures with the same reference number (sign) indicate components or materials that are the same or equivalent. The following implementations and embodiments are merely specific examples of the technology associated with the invention, and the present invention is not limited to the implementations and embodiments described below. In the absence of specific annotation, structural component features described in the following such as dimensions, raw material, shape, and relative position are simply for the purpose of explicative example and are not intended to limit the scope of the invention. Descriptive contents relating to one implementation or embodiment may also be applied to describe other implementations or embodiments. Further, properties such as the size and spatial relation of components shown in the figures may be exaggerated for the purpose of clear explanation.
The 1st aspect of the method for cleaning exhaust gas of the present invention is a method that separates atmospheric pollutants to clean the exhaust gas and includes an atomizing step that forms an aqueous alkaline solution mist with an atomizer; a mixing step that mixes the aqueous alkaline solution mist with exhaust gas to absorb atmospheric pollutants contained in the exhaust gas into the mist; and a separating step that separates the mist, which absorbed atmospheric pollutants in the mixing step, from the exhaust gas.
In the 2nd aspect of the method for cleaning exhaust gas of the present invention, the atomizer ultrasonically vibrates the aqueous alkaline solution to form mist in the atomizing step.
In the 3rd aspect of the method for cleaning exhaust gas of the present invention, the atomizer ultrasonically vibrates the aqueous alkaline solution in the atomizing step to form a column of liquid that protrudes from the liquid surface, and blows exhaust gas over the surface of the liquid column to mix the mist and exhaust gas.
In the 4th aspect of the method for cleaning exhaust gas of the present invention, the atomizer ultrasonically vibrates the aqueous alkaline solution in the atomizing step to form a column of liquid that protrudes from the liquid surface, blows a carrier gas over the surface of the liquid column to form a mist of mixed gas, and mixes that mixed gas mist with exhaust gas in the mixing step.
In the 5th aspect of the method for cleaning exhaust gas of the present invention, the atomizer ejects aqueous alkaline solution spray from a nozzle and atomizes that spray via static electricity to form mist in the atomizing step.
In the 6th aspect of the method for cleaning exhaust gas of the present invention, the atomizer blows exhaust gas into the static electricity atomized nozzle spray mist to mix the mist and exhaust gas in the atomizing step.
In the 7th aspect of the method for cleaning exhaust gas of the present invention, the atomizer blows a carrier gas into the static electricity atomized nozzle spray mist to form a mist-and-gas mixture, and mixes that mist-and-gas mixture with exhaust gas in the mixing step.
In the 8th aspect of the method for cleaning exhaust gas of the present invention, the average diameter of the aqueous alkaline solution mist in the atomizing step is less than or equal to 50 µm. Further, in the 9th aspect of the method for cleaning exhaust gas of the present invention, the average diameter of the aqueous alkaline solution mist in the atomizing step is less than or equal to 30 µm.
In the 10th aspect of the method for cleaning exhaust gas of the present invention, the average diameter of the aqueous alkaline solution mist in the atomizing step is greater than or equal to 100 nm.
In the 11th aspect of the method for cleaning exhaust gas of the present invention, the mixing step includes a first mixing step and a second mixing step; exhaust gas SOx is absorbed into the mist in the first mixing step, and subsequently exhaust gas NOx is absorbed into the mist in the second mixing step.
The 12th aspect of the method for cleaning exhaust gas of the present invention includes an oxidizing step that supplies an oxygen containing gas to the exhaust gas, and oxidized NO2 is absorbed into the mist.
In the 13th aspect of the method for cleaning exhaust gas of the present invention, mist that absorbed atmospheric pollutants is separated from exhaust gas by a cyclone separator in the separating step.
In the 14th aspect of the method for cleaning exhaust gas of the present invention, aqueous alkaline solution mist is mixed with exhaust gas using a static mixer in the mixing step.
In the 15th aspect of the method for cleaning exhaust gas of the present invention, aqueous alkaline solution mist is mixed with exhaust gas with a mixer in the mixing step, and temperature in the mixer is maintained at or below the dew point.
In the 16th aspect of the method for cleaning exhaust gas of the present invention, temperature or flow rate of exhaust gas supplied to the mixer is regulated to keep temperature in the mixer at or below the dew point.
In the 17th aspect of the method for cleaning exhaust gas of the present invention, alkaline metal aqueous alkaline solution is used as the aqueous alkaline solution in the atomizing step.
The 18th aspect of the method for cleaning exhaust gas of the present invention includes a particulate matter (PM) separating step that removes fine particles from the exhaust gas, and atmospheric pollutants are separated from exhaust gas, which has particulate matter removed in the PM separating step.
The 19th aspect of the apparatus for cleaning exhaust gas of the present invention is an apparatus that separates atmospheric pollutants to clean the exhaust gas and is provided with an atomizer that atomizes aqueous alkaline solution to form mist; a mixer that mixes mist generated by the atomizer with exhaust gas to absorb atmospheric pollutants contained in the exhaust gas into the mist; and a separator that separates the mist, which absorbed atmospheric pollutants in the mixer, from the exhaust gas.
In the 20th aspect of the apparatus for cleaning exhaust gas of the present invention, the atomizer is an ultrasonic atomizer that ultrasonically vibrates the aqueous alkaline solution to form mist.
The 21st aspect of the apparatus for cleaning exhaust gas of the present invention is provided with a blower mechanism, wherein the ultrasonic atomizer vibrates the aqueous alkaline solution to establish a liquid column that protrudes from the surface of the aqueous alkaline solution, and the blower mechanism blows exhaust gas over the liquid column to mix mist and exhaust gas.
The 22nd aspect of the apparatus for cleaning exhaust gas of the present invention is provided with a blower mechanism, wherein the ultrasonic atomizer vibrates the aqueous alkaline solution to establish a liquid column that protrudes from the surface of the aqueous alkaline solution, the blower mechanism blows a carrier gas over the surface of the liquid column to form a mist-and-gas mixture, and the mixer mixes that mist-gas mixture with exhaust gas.
In the 23rd aspect of the apparatus for cleaning exhaust gas of the present invention, the atomizer is a static electricity atomizer that electro-statically atomizes aqueous alkaline solution sprayed from nozzles to form mist.
The 24th aspect of the apparatus for cleaning exhaust gas of the present invention is provided with a blower mechanism that blows exhaust gas into the mist electro-statically atomized by the static electricity atomizer to mix exhaust gas with the mist.
The 25th aspect of the apparatus for cleaning exhaust gas of the present invention is provided with a blower mechanism that blows a carrier gas into the mist electro-statically atomized by the static electricity atomizer to form a mist-and-gas mixture, and the mixer mixes that mist-gas mixture with exhaust gas.
In the 26th aspect of the apparatus for cleaning exhaust gas of the present invention, the atomizer produces aqueous alkaline solution mist with an average diameter less than or equal to 50 µm. Further, in the 27th aspect of the apparatus for cleaning exhaust gas of the present invention, the atomizer produces aqueous alkaline solution mist with an average diameter less than or equal to 30 µm.
In the 28th aspect of the apparatus for cleaning exhaust gas of the present invention, the atomizer produces aqueous alkaline solution mist with an average diameter greater than or equal to 100 nm.
In the 29th aspect of the apparatus for cleaning exhaust gas of the present invention, the mixer is provided with a first mixer and a second mixer that are connected together in series. Further, in the 30th aspect of the apparatus for cleaning exhaust gas of the present invention, the second mixer is connected to the outlet side of the first mixer.
The 31st aspect of the apparatus for cleaning exhaust gas of the present invention is provided with an oxidizing unit that supplies an oxygen containing gas to the exhaust gas to oxidize NO1 atmospheric pollutant and form NO2, and the mixer mixes NO2 oxidized in the oxidizing unit with mist.
In the 32nd aspect of the apparatus for cleaning exhaust gas of the present invention, the separator is a cyclone separator.
In the 33rd aspect of the apparatus for cleaning exhaust gas of the present invention, the mixer is a static mixer.
In the 34th aspect of the apparatus for cleaning exhaust gas of the present invention, the mixer mixes exhaust gas and mist while maintaining temperature inside the mixer at or below the dew point.
In the 35th aspect of the apparatus for cleaning exhaust gas of the present invention, temperature or flow rate of exhaust gas supplied to the mixer is regulated to keep temperature inside the mixer at or below the dew point.
In the 36th aspect of the apparatus for cleaning exhaust gas of the present invention, the atomizer forms mist from alkaline metal aqueous alkaline solution.
The 37th aspect of the apparatus for cleaning exhaust gas of the present invention is provided with a PM separator that removes exhaust gas particulate matter, and the mixer mixes mist with exhaust gas, which has particulate matter removed by the PM separator.
The cleaning apparatus 100 shown in the block diagram of
The atomizer 1 converts the aqueous alkaline solution to a mist. The aqueous alkaline solution mist is formed as a fine mist with small particle diameter, and mist particle surface area can be made large with respect to unit particle weight. Fine mist particles with large surface area have a large area of contact with the exhaust gas, and atmospheric pollutants included in the exhaust gas are rapidly absorbed in the mist.
The atomizing chamber 10 is an enclosure that holds aqueous alkaline solution 9 with the liquid surface W maintained at a constant level and internally generates mist. Mist generated in the atomizing chamber 10 is diffused into carrier gas blown into the chamber and a mist-and-gas mixture is discharged from the chamber. The atomizing chamber 10 is not necessarily completely closed and can have openings. The atomizing chamber 10 of the ultrasonic atomizer 1A shown in
The aqueous alkaline solution 9 is supplied to the atomizing chamber 10 by a solution supply system 15. The solution supply system 15 shown in
The ultrasonic transducer 11 shown in the enlarged cross-section of
As shown in
The atomizer 1 of
The atomizer 1 in
The aqueous alkaline solution 9 used to form mist in the atomizer 1 is preferably an aqueous solution of sodium hydroxide or potassium hydroxide. Power plants or factories located close to an ocean preferably use sodium hydroxide aqueous solution that can be derived from sea water to reduce operating cost. However, potassium hydroxide aqueous solution can also be used as aqueous alkaline solution. An apparatus that uses potassium hydroxide as aqueous alkaline solution can advantageously utilize nitrogen components included in exhaust gas to form potassium nitrogen fertilizer with the potassium in potassium hydroxide. Potassium nitrogen fertilizer can be effectively used in agriculture as fertilizer containing both nitrogen and potassium. While separating atmospheric pollutants from exhaust gas, this cleaning apparatus also effectively uses nitrogen components in the exhaust gas as fertilizer, and as a result is extremely economic.
The atomizer 1 is controlled by the controller 5. In addition to controlling the atomizer 1, the controller 5 also regulates exhaust gas and mist-and-gas mixture flow rates. The controller adjusts the environment inside the mixer 6 to suppress mist vaporization based on signals input from temperature sensors 27 and 28. Further, the controller 5 regulates exhaust gas and mist-and-gas mixture flow rates, and controls proportions of exhaust gas SOx and NOx atmospheric pollutants and alkaline components in the aqueous alkaline solution.
The mixer 6 mixes mist-and-gas mixture from the atomizer 1 with exhaust gas, and causes atmospheric pollutants included in the exhaust gas to be absorbed in the aqueous alkaline solution mist. The mixer 6 mixes exhaust gas and aqueous alkaline solution mist to absorb SOx and NOx atmospheric pollutants into the mist. SOx atmospheric pollutants react with mist alkaline components and are absorbed in the mist as sulfates; NOx atmospheric pollutants react with mist alkaline components and are absorbed as nitrates.
The flow rate and temperature of exhaust gas supplied to the mixer 6 affects the amount of mist vaporization inside the mixer 6. If large quantities of high temperature exhaust gas are introduced into the mixer 6, that exhaust gas will heat and vaporize mist. Since atmospheric pollutants are absorbed into liquid mist and separated from the exhaust gas in the mixer 6, atmospheric pollutant separation efficiency is degraded when the mist vaporizes. This adverse effect can be avoided by cooling exhaust gas supplied to the mixer 6 to the dew point (temperature) or below. Exhaust gas temperature is reduced below the dew point and relative humidity is increased when supplied to the mixer 6, and this suppresses mist vaporization. Since vaporization is enhanced when large quantities of low humidity, high temperature exhaust gas is supplied to the mixer 6, exhaust gas is cooled and its relative humidity is increased (relative humidity of mist-and-gas mixture supplied from the atomizer 1 is also controlled) to suppress mist vaporization inside the mixer 6.
A static mixer is preferably used as the mixer 6.
In this static mixer 6A, flow splits in half each time it enters the next element blade 26. For example, a static mixer 6A with 20 stages of right element blades 26A and left element blades 26B divides flow through the mixer a total of 220 (1048576) times. Consequently, exhaust gas and mist-and-gas mixture are efficiently mixed, exhaust gas and mist-and-gas mixture are effectively put in close contact, and atmospheric pollutants can readily dissolve in the aqueous alkaline solution mist. Since the total length of each right element blade 26A and left element blade 26B is short (i.e. 1.5 times the width), the number of element blade stages can be numerous while keeping overall mixer length short. Accordingly, a static mixer of limited length can efficiently mix the two fluids and exhaust gas atmospheric pollutants can be efficiently absorbed in the aqueous alkaline solution mist. However, making element blades longer also results in efficient atmospheric pollutant absorption into aqueous alkaline solution mist.
Mist absorbs exhaust gas atmospheric pollutants with aqueous alkaline solution mist maintained in the mist state. As described above, for efficient absorption of exhaust gas atmospheric pollutants into aqueous alkaline solution mist, it is important to suppress mist vaporization inside the mixer 6. The cleaning apparatus 100 in
The controller 5 controls the temperature and flow rate of mist-and-gas mixture and exhaust gas supplied to the mixer 6 to suppress mist vaporization inside the mixer 6. The controller 5 regulates the flow rate and temperature of carrier gas (air) supplied to the atomizer 1, regulates the temperature of the ultrasonically vibrated aqueous alkaline solution, and controls the temperature and humidity of the mist-and-gas mixture supplied to the mixer 6. If the air flow rate is high and mist-and-gas mixture temperature is high, relative humidity inside the mixer 6 decreases and mist can easily vaporize. Accordingly, the controller 5 detects temperature and humidity inside the mixer 6, regulates the air heater 21 and the solution heater 22, and adjusts air flow rate into the atomizer 1 to keep relative humidity inside the mixer 6 within a set range.
The controller 5 controls the supply fan 29 to regulate the flow rate of gas mixture supplied to the mixer 6 and controls the supply fan 24 to regulate the flow rate of outside air mixed with exhaust gas in the oxidizing unit 8 to keep relative humidity inside the mixer 6 within the set range. The inside of the mixer 6 is preferably in a supersaturated state with relative humidity greater than or equal to 100%. Namely, mixer 6 internal temperature is at or below the dew point to effectively suppress mist vaporization.
Atomizing efficiency of the atomizer 1 can be optimized by adjusting the temperature and flow rate of gas blown at the liquid column P. Atomizing efficiency can also be increased by heating the aqueous alkaline solution 9. The controller 5 adjusts the flow rate and temperature of carrier gas blown at the liquid column P considering atomizing efficiency. If the temperature of gas blown at the liquid column P is too high, aqueous alkaline solution vaporizes and this causes reduced atomizing efficiency. In the mixer as well, mist vaporization also causes reduced atmospheric pollutant separation.
In an atomizer 1 where air is blown as the carrier gas at the surface of the liquid column P, the controller 5 regulates air flow rate and temperature to increase atomizing efficiency. While the atomizing efficiency of this atomizer 1 can be increased by increasing carrier gas (air) flow rate and temperature, the percentage of mist vaporized inside the mixer 6 increases. Therefore, (considering this trade-off) the controller 5 detects temperature and humidity inside the mixer 6 and adjusts the flow rate and temperature of air supplied to the atomizer 1 and blown at the liquid column P. Ideally, the controller 5 keeps atomizing efficiency high with air flow rate and temperature set high while maintaining moisture conditions inside the mixer 6 that attain a supersaturated or nearly supersaturated state to suppress mist vaporization. In an atomizer 1 provided with a solution heater 22, aqueous alkaline solution temperature is increased within a range that allows supersaturated or nearly supersaturated conditions to be maintained inside the mixer 6.
The separator 7 separates mist that has absorbed atmospheric pollutants from the exhaust gas. For example, the separator 7 in the cleaning apparatus 100 is a cyclone separator. A cyclone separator can efficiently separate mist with a simple structure. The cyclone separator 70 shown in
To rapidly circulate exhaust gas that includes mist (i.e. mist-and-gas mixture combined with exhaust gas), the cyclone separator 70 has an inlet duct 73 connected to the cylinder region 71 that introduces the exhaust gas including mist in a tangential direction (with respect to the cylinder region 71). Exhaust gas including mist that flows tangentially into the cylinder region 71 from the inlet duct 73 rapidly circulates inside the cylinder region 71. Mist in the exhaust gas rapidly rotated inside the cylinder region 71 moves towards the outside of the cylinder region 71 due to centrifugal force. Mist forced to the outside of the cylinder region 71 makes contact with the inside surface of the cylinder region wall and flows as a liquid down the cylinder region wall into the tapered region 72. To discharge liquid that flows into the tapered region 72, a liquid outlet 74 is established at the bottom of the tapered region 72. Exhaust gas from which mist has been separated is discharged outside the separator through an exhaust duct 75, which is disposed at the center of the cylinder region 71 and extends vertically in an axial direction. Exhaust gas, which has less specific gravity than the mist is less affected by centrifugal force and can be discharged to the outside from center of the cylinder region 71.
While the separator 7 described above separates mist from exhaust gas with a single cyclone separator 70, a multi-cyclone separator having a plurality of cyclone separators connected in series and parallel can be used to more efficiently separate mist. A multi-cyclone separator has inlet-side cyclone separator(s) connected with outlet-side cyclone separators. Outlet-side cyclone separators are a plurality of cyclone separators, which are smaller than inlet-side cyclone separator(s), connected in parallel. The exhaust duct of an inlet-side cyclone separator branches to connect with inlet ducts of the outlet-side cyclone separators. Exhaust gas including mist, from which (some) mist has been separated by an inlet-side separator, branches into inlet ducts of the outlet-side cyclone separators. The outlet-side cyclone separators further separate mist from the exhaust gas and mist input from the inlet-side separators. A multi-cyclone separator separates mist from exhaust gas that includes mist with both inlet-side separator(s) and outlet-side separators, and this efficiently separates mist.
The cyclone separator 70 can efficiently separate mist with a simple structure. However, the present invention is not specified to have a separator 7 that is a cyclone separator 70, and any separator that can separate mist from exhaust gas (that includes mist) can be used. For example, devices that are already in use such as a static electricity separator or de-mister can also be used. A static electricity separator has discharge electrode(s) that charge mist particles in the flow path of the exhaust gas that includes mist, and collector electrode(s) to which the electro-statically charged mist particles adhere for separation. Since a static electricity separator adheres and collects mist particles electro-statically, smaller mist particles can be separated efficiently.
The oxidizing unit 8 oxidizes exhaust gas NO1 to form NO2. Exhaust gas contains NOx in the form of NO1 and NO2, but NO1 is not very soluble in water (i.e. aqueous solution). To oxidize exhaust gas NO1 and form more soluble NO2, the cleaning apparatus 100 in
Exhaust gas with NO1 oxidized to NO2 by the oxidizing unit 8 is supplied to the mixer 6. The cleaning apparatus 100 in
The cleaning apparatus 100 in
The PM separator 3 can employ, for example, an electrostatic dust collector to effectively remove extremely small particles. As shown in
The discharge electrodes 31 have a positive electrode 31A and negative electrodes 31B disposed in opposition within the air (gas) circulation path 35. The negative electrodes 31B are two thin metal wires disposed in a parallel configuration via insulating material (not illustrated). A positive electrode 31A in the form of a plate is disposed between the two negative electrodes 31B. The positive electrode 31A is fixed in an orientation parallel to the air flow direction to allow air to flow smoothly around the positive electrode plate. The positive electrode 31A is directly connected, and the negative electrodes 31B are connected through a switch 34 to the power supply 33. The power supply 33 applies a voltage that can induce corona discharge (e.g. 3000 V to 10000 V) between the positive electrode 31A and negative electrodes 31B. When the switch 34 is on, high negative potential is applied to the negative electrodes 31B. The positive electrode 31A is connected to the power supply ground. In normal operation, metal wire negative electrodes 31B are connected to the negative side of the power supply 33, and the positive electrode 31A plate is connected to positive side of the power supply 33 to induce negative corona discharge. This is because negative corona discharge causes higher current flow than positive corona discharge and enables particulate matter in the air to be effectively electro-statically charged. However, the metal wire electrodes could also be connected to the positive side of the power supply to act as positive electrodes, and the plate electrode could be connected to the negative side of the power supply to act as a negative electrode.
The collector electrodes 32 are disposed within the air (gas) circulation path 35 closer to the air outlet than the discharge electrodes 31. The collector electrodes 32 cause particulate matter charged by the discharge electrodes 31 to adhere to the collector electrodes 32 via electro-static attraction. Accordingly, the collector electrodes 32 are plate electrodes disposed in parallel orientation via insulating material. The collector electrode plates are connected to the power supply 33 and a potential (e.g. 2000 V to 15000 V) capable of attracting and adhering particulate matter is imposed on the electrodes by the power supply 33.
The electrostatic dust collector 30 described above electro-statically charges particulate matter included in exhaust gas with the discharge electrodes 31, and recovers the charged particulate matter on the surface of the collector electrodes 32 by electro-static adhesion. The electrostatic dust collector 30 can efficiently collect extremely small particles included in the exhaust gas. However, the PM separator does not necessarily employ an electrostatic dust collector, and any equipment that can separate particulate matter from exhaust gas (e.g. a bag filter or cyclone separator) can also be used.
The cleaning apparatus 100 in
This processing step separates particulate matter from exhaust gas supplied to the mixer 6. The cleaning apparatus 100 in
The atomizing step forms mist from an aqueous alkaline solution with the atomizer 1. The atomizer 1 makes mist from aqueous alkaline solution and mixes that mist with a carrier gas to form a mist-and-gas mixture. The atomizer 1 makes mist from caustic soda (sodium hydroxide) used as the aqueous alkaline solution. However, the aqueous alkaline solution used by the atomizer 1 to form mist is not specifically limited to caustic soda (sodium hydroxide). For example, aqueous solutions of other alkaline metals such as potassium hydroxide can also be used. As shown in
The mixing step mixes exhaust gas with mist-and-gas mixture in the mixer 6, induces exhaust gas atmospheric pollutant absorption into the mist. For example, the mixing step mixes exhaust gas and mist-and-gas mixture with a static mixer 6A to absorb exhaust gas atmospheric pollutants in the mist. The static mixer 6A mixes mist-and-gas mixture supplied from the atomizer 1 with exhaust gas to absorb exhaust gas atmospheric pollutants in aqueous alkaline solution mist. SOx atmospheric pollutants react with mist alkaline components and are absorbed in the mist as sulfates; NOx atmospheric pollutants react with mist alkaline components and are absorbed as nitrates.
The cleaning apparatus 100 in
The separating step separates mist, which absorbed atmospheric pollutants, from exhaust gas using a separator 7 connected to the outlet side of the mixer 6. For example, the separating step separates mist, which absorbed atmospheric pollutants, from exhaust gas using a cyclone separator 70 as the separator 7.
The cleaning apparatus 100 in
The cleaning apparatus 200 in
In the cleaning apparatus 200, since exhaust gas is supplied to the atomizer 1 as carrier gas and mist-and-exhaust gas mixture is formed, exhaust gas and mist are mixed in the atomizer 1 and exhaust gas atmospheric pollutants can be absorbed into the mist. The atomizer 1 in the cleaning apparatus 200 can serve the dual purpose as atomizer and mixer in a single unit, and the outlet side of the atomizer 1 does not necessarily have to connect to a mixer. A cleaning apparatus with an atomizer that also serves as a mixer can connect directly to the separator without an intervening mixer, and mist can be separated from the exhaust gas to separate atmospheric pollutants. However, the cleaning apparatus 200 in
The cleaning apparatus 300 in
The first separating unit 2A primarily absorbs exhaust gas SOx into mist in the first mixer 6X to separate atmospheric pollutant SOx from the exhaust gas, and the second separating unit 2B primarily absorbs exhaust gas NOx into mist in the second mixer 6Y to separate atmospheric pollutant NOx from the exhaust gas. Since SOx is more reactive with aqueous alkaline solution than NOx and is efficiently absorbed by contact with alkaline mist, SOx is separated first. The second separating unit 2B separates NOx from exhaust gas that has been treated by the first separating unit 2A to remove SOx. A cleaning apparatus 300 with a series connected first separating unit 2A and second separating unit 2B can efficiently separate SOx and NOx atmospheric pollutants. This is because the mixer 6 established in the second separating unit 2B puts NOx atmospheric pollutants in contact with aqueous alkaline solution mist that has not absorbed atmospheric pollutants (mist supplied directly from the atomizer 1) for efficient NOx absorption.
Since the cleaning apparatus 300 in
Further, since the cleaning apparatus 300 in
The cleaning apparatus 300 in
This processing step separates particulate matter from exhaust gas supplied to the mixer 6. The cleaning apparatus 300 in
In this processing step, the atomizer 1 forms mist by ultrasonic vibration of sodium hydroxide aqueous alkaline solution, and mixes that mist with a carrier gas to form a mist-and-gas mixture. Since the cleaning apparatus 300 in
Since the cleaning apparatus 300 in
In the mixing process, mist-and-gas mixture from the atomizer 1 is mixed with exhaust gas in each mixer 6, and this induces absorption of exhaust gas atmospheric pollutants into the mist. This mixing process includes a first mixing process that absorbs atmospheric pollutants into mist in the first mixer of the first separating unit 2A, and a second mixing process that absorbs atmospheric pollutants into mist in the second mixer of the second separating unit 2B. In the first mixing process, exhaust gas supplied to the first mixer 6X is mixed with mist-and-gas mixture and primarily exhaust gas SOx is absorbed into the mist. SOx reacts with alkaline components in the mist and is absorbed into the mist as sulfates primarily in the first separating unit 2A. Further, in the second mixing process, exhaust gas with SOx removed by passage through the first mixer 6X is mixed with mist-and-gas mixture in the second mixer 6Y and NOx is absorbed into the mist. Exhaust gas NOx reacts with alkaline components in the mist and is absorbed into the mist as nitrates in the second separating unit 2B.
In the separating process, the separator 7, which is a cyclone separator 70, separates mist that has absorbed atmospheric pollutants from exhaust gas. Specifically, the cyclone separator 70 in the first separating unit 2A separates SOx primarily absorbed in mist as sulfates from the exhaust gas, and the cyclone separator 70 in the second separating unit 2B separates NOx primarily absorbed in mist as nitrates from the exhaust gas.
The cleaning apparatus 300 in
While the cleaning apparatus 100, 200, 300 described above generate fine mist by ultrasonic vibration of aqueous alkaline solution, cleaning apparatus for the fourth, fifth, and sixth embodiments generate aqueous alkaline solution mist with a static electricity atomizer. (The fourth, fifth, and sixth embodiments are the same as the first, second, and third embodiments respectively except that the atomizer is a static electricity atomizer.). As shown in
The static electricity atomizer 1B shown in
The nozzle block 54 has a flange region 54a inside the outside perimeter and holds a plurality of capillary tubes 53 at its center region. The nozzle block 54 in
The plurality of through-holes 54x established in the plate 54B of the nozzle block 54 in
The nozzle unit 50 described above is provided with numerous thin-tube capillary tubes 53 and aqueous alkaline solution mist is sprayed from each capillary tube 53. However, the nozzle unit can also have a perforated plate (with multiple fine-spray hole openings) in place of the capillary tubes. The perforated plate is fabricated from (electrically) conducting material such as metal. The perforated plate can be sheet metal with fine-spray holes opened via laser pulse. The perforated plate can also sintered metal with fine-spray hole openings. An (electrically) conducting perforated plate can be connected to a high voltage power supply to apply high voltage between the perforated plate and the atomizing electrodes. However, the perforated plate does not necessarily need to be (electrically) conducting material. This is because the aqueous alkaline solution is (electrically) conducting and high voltage can be applied between the atomizing electrodes and aqueous alkaline solution sprayed from the spray holes to electro-statically atomize the sprayed mist. Accordingly, materials such as open-cell plastic foam with fine-spray holes can also be used as the perforated plate.
The spray case 47 is provided with atomizing electrodes 42 that are insulated with respect to the spray assembly 41. High potential is applied to the atomizing electrodes 42 with respect to the spray assembly 41. Accordingly, the atomizing electrodes 42 and spray assembly 41 are attached to the spray case 47 in a mutually insulated configuration. A static electricity atomizer 1B with the spray assembly fixed to the metal spray case without insulation has atomizing electrodes insulated from the spray case. Similarly, a static electricity atomizer 1B with the spray assembly insulated from the spray case has atomizing electrodes fixed to the spray case. However, both the spray assembly and the atomizing electrodes can be fixed to the spray case in an insulated manner.
Electric discharge takes place between atomizing electrodes 42 and static discharge protrusions 51 in the spray assembly 41, and this atomizes mist sprayed from the spray assembly 41 into fine particles. The atomizing electrodes 42 are positioned separated from, and in line with the spray direction of mist from the fine-spray holes 52. The atomizing electrodes 42 in
In addition, metal mesh can also be used as atomizing electrodes. Metal mesh atomizing electrodes are disposed separated from, and in line with the spray direction of mist from the static discharge protrusions 51. Metal mesh atomizing electrodes can make electric discharge from each static discharge protrusion 51 uniform to atomize mist sprayed from each fine-spray hole 52 into fine particles.
Atomizing electrodes 42 are disposed in front of each nozzle unit 50. Since the spray assembly 41 in the static electricity atomizer 1B of
The high voltage power supply 43 applies high voltage between the atomizing electrodes 42 and the nozzle units 50. The high voltage power supply 43 is a direct current (DC) power supply with the positive-side connected to the atomizing electrodes 42 and the negative-side connected to the nozzle units 50. However, the positive-side can also be connected to the nozzle units and the negative-side connected to the atomizing electrodes.
In the static electricity atomizer 1B in
The air chamber 62 is an enclosed structure connected with a blower mechanism 67 that supplies air, and carrier gas (air) blown in from the blower mechanism 67 flows through flow inlets 64 opened through the partition wall 63 into the spray chamber 61. The flow inlets 64 are through-holes in the form of slits opened between the nozzle units 50 in a manner that blows carrier gas around each nozzle unit 50. However, the flow inlets are not necessarily slits. A plurality of circular or polygonal shaped through-holes can also be established between nozzle units as flow inlets that blow carrier gas between the nozzle units. Carrier gas blown into the spray chamber 61 from the flow inlets 64 transports the atomized mist. The spray case 47 in
As shown in
The method and apparatus for cleaning exhaust gas of the present invention can be applied advantageously as a method and apparatus that separates atmospheric pollutants from exhaust gas emitted from an industrial facility and/or equipment such as a power plant or blast furnace.
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| Number | Date | Country | Kind |
|---|---|---|---|
| 2020-120178 | Jul 2020 | JP | national |
The present application is a national phase application of PCT Application No. PCT/JP2022/014553, filed on Jul. 13, 2021, and claims priority under 35 U. S. C. §119 to Japanese Patent Application No. 2020-120178, filed on Jul. 13, 2020, the contents of which are incorporated herein by references in their entirety.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2021/026217 | 7/13/2021 | WO |
