# Patent

## Title
Air pollution control system

## Abstract

An air pollution control system includes CO2 absorber that removes CO2, and an absorbent regenerator that releases CO2 from the amine absorbent. The CO2 absorber is equipped with a CO2 absorption unit that absorbs CO2 in the flue gas by the amine absorbent (lean solution), and a water-repellent filter unit that is provided on an upper part (gas flow downstream) side of the CO2 absorption unit and collects the mist amine absorbent accompanied by the CO2-free flue gas. The mist amine accompanied by the CO2-free flue gas is collected.

## Background
FIELD
The present invention relates to an air pollution control system in which discharge of an amine absorbent to the outside of the system is significantly suppressed when absorbing and removing CO2 in a flue gas by the amine absorbent.
BACKGROUND
In recent years, as one of causes of a global warming phenomenon, a greenhouse effect due to CO2 has been pointed out, and countermeasures against the effect have also become an internationally urgent need in protecting the global environment. A source of generation of CO2 ranges in various fields of human activities in which fossil fuel is combusted, and a demand for suppressing the discharge tends to be further strengthened. Accordingly, directed at a power generation apparatus such as a thermal power plant that uses a large amount of fossil fuel, a method of removing and recovering CO2 in a flue gas by bringing the flue gas of an industrial apparatus, such as a boiler and a gas turbine, into contact with an amine-based CO2 absorbent, and an air pollution control system that stores the recovered CO2 without releasing it to the atmosphere have been extensively studied.
A CO2 recovery unit having a process of bringing a flue gas and a CO2 absorbent into contact with each other in a CO2 absorber (hereinafter, also simply referred to as “absorber”), and a process of heating the CO2 absorbent that has absorbed CO2 in a CO2 absorbent regenerator (hereinafter, also simply referred to as a “regenerator”), diffusing CO2, regenerating the CO2 absorbent and circulating the absorbent to the CO2 absorber again to reuse the CO2 absorbent, as a process of removing and recovering CO2 from the flue gas using the above-described amine-based CO2 absorbent, has been suggested (for example, see Patent Literature 1).
In the CO2 absorber, the flue gas is brought into countercurrent contact, for example, with the amine-based CO2 absorbent such as alkanolamine, CO2 in the flue gas is absorbed to the CO2 absorbent by a chemical reaction (exothermic reaction), and the flue gas after removal of CO2 is released out of the system. The CO2 absorbent that has absorbed CO2 is also called a rich solution. The rich solution is increased in pressure by a pump, heated in a heat exchanger by the high-temperature CO2 absorbent (lean solution) obtained by diffusion of CO2 and regeneration in the regenerator, and supplied to the regenerator.
In the CO2 recovery process using the CO2 absorbent, the CO2-free flue gas obtained by removing CO2 from the flue gas is released to the atmosphere. However, since a small part of a small amount of amine absorbent is present in the released gas, it is necessary to reduce an amount of discharge thereof.
In particular, in the future, when the CO2 removal regulation is started, there is a possibility that the CO2 removal device itself increases in size, and thus, it is necessary to further reduce the amount of discharge.
As a technique that prevents the release of the amine absorbent, for example, a method of recovering an amine compound accompanied by a CO2-free flue gas, by providing a plurality of stages of water washing sections on a downstream side of a CO2 absorption section of a CO2 absorber of a CO2 removal device, and by bringing the CO2-free flue gas and washing water into vapor-liquid contact with each other has been suggested (Patent Literature 2).
In addition, as another technique, a method of recovering a basic amine compound in a decarbonator flue gas that sprays a sulfuric acid from a sulfuric acid spray device to a CO2-free flue gas discharged from a CO2 absorber, converts an amine absorbent accompanied by the flue gas into a basic amine compound sulfate, and collects the basic amine compound sulfate has been suggested (Patent Literature 3).
Furthermore, in the air pollution control system, when a mist generation material being a generation source of mist generated in the absorber of the CO2 recovery unit is contained in the flue gas introduced into the CO2 absorber that absorbs CO2 in the CO2 recovery unit, the CO2 absorbent is accompanied by the mist generation material. Therefore, there is a problem that the amount of CO2 absorbent that scatters to the outside of the system increases, and thus, the countermeasures against the problem have been considered (Patent Literature 4).
CITATION LIST
Patent Literature
Patent Literature 1: JP 3-193116 A
Patent Literature 2: JP 2002-126439 A
Patent Literature 3: JP 10-33938 A
Patent Literature 4: WO 2011/152547 A
SUMMARY
Technical Problem
However, in the above-described suggestions, although the gaseous amine absorbent can be reduced in the CO2-free flue gas released from the CO2 absorber, there is a risk of releasing the mist amine absorbent with the flue gas. Accordingly, it is necessary to suppress this problem.
There is concern that the mist amine absorbent released to the outside of the system is converted into, for example, nitrosamines, nitramine, aerosol or the like as a result of reaction with NOx or the like in the atmosphere after diffusion into the atmosphere.
Thus, there has been a desire for establishment of an air pollution control system that can further suppress the release of the amine compound accompanied by the CO2 flue gas from the CO2 absorber.
In view of the above-described problems, an object of the present invention is to provide an air pollution control system that is capable of greatly suppressing entrainment of the amine absorbent when discharging the treated flue gas, from which CO2 is removed, to the outside of the system.
Solution to Problem
According to a first aspect of the present invention in order to solve the above-mentioned problems, there is provided an air pollution control system including a CO2 recovery unit equipped with a CO2 absorber that removes CO2 in a flue gas from a boiler by an amine absorbent, and an absorbent regenerator that regenerates the amine absorbent, wherein the CO2 absorber is equipped with a CO2 absorption unit that absorbs CO2 in the flue gas by the amine absorbent, and a water-repellent filter unit that is disposed on a gas flow downstream side of the CO2 absorption unit and collects mist amine absorbent accompanied by a CO2-free flue gas.
According to a second aspect of the present invention, there is provided the air pollution control system according to the first aspect, wherein the water-repellent filter unit is equipped with a filter cylinder having a gas introduction space into which the CO2-free flue gas rising from the CO2 absorption unit is introduced, and a plurality of water-repellent filters provided on a side surface of the filter cylinder to allow the introduced CO2-free flue gas to pass through the filters in a direction orthogonal to a gas flow direction.
According to a third aspect of the present invention, there is provided the air pollution control system according to the second aspect, wherein a cleaning unit for cleaning a gas in-flow surface of the water-repellent filter is provided in the filter cylinder.
According to a fourth aspect of the present invention, there is provided the air pollution control system according to the second or third aspect, wherein a collecting unit for collecting falling water falling down along the surface of the filter is provided on a lower end side of the water-repellent filter.
According to a fifth aspect of the present invention, there is provided the air pollution control system according to the first aspect, wherein the water-repellent filter unit is integrally provided within the CO2 absorber.
According to a sixth aspect of the present invention, there is provided the air pollution control system according to the first aspect, Wherein the water-repellent filter unit is provided separately from the CO2 absorber.
According to a seventh aspect of the present invention, there is provided the air pollution control system according to the first aspect, wherein a water cleaning unit is provided on one or both of an upstream side and a downstream side of the gas flow of the water-repellent filter unit.
Advantageous Effects of Invention
According to the air pollution control system of the present invention, by collecting the mist amine accompanied by the CO2-free flue gas using a water-repellent filter, it is possible to further reduce the amine concentration of the gas diffused to the atmosphere.



BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a schematic diagram of an air pollution control system provided with a CO2 recovery unit according to a first embodiment.
FIG. 2 is a perspective view of a water-repellent filter unit according to the first embodiment.
FIG. 3 is a longitudinal cross-sectional view of the water-repellent filter unit according to the first embodiment.
FIG. 4 is a cross-sectional view taken along a line X-X of FIG. 3.
FIG. 5 is a perspective view of the water-repellent filter according to the first embodiment.
FIG. 6 is a cross-sectional view of another filter cylinder according to the first embodiment.
FIG. 7 is a cross-sectional view of another filter cylinder according to the first embodiment.
FIG. 8 is a cross-sectional view of another aspect corresponding to FIG. 4.
FIG. 9 is a cross-sectional view of another filter cylinder according to the first embodiment.
FIG. 10 is a schematic diagram illustrating an increase or decrease in a gas passage area of the filter depending on presence or absence of water-repellency.
FIG. 11 is a diagram illustrating an example of the distribution of a mist particle diameter in an outlet gas of a CO2 absorber.
FIG. 12 is a diagram illustrating a relation between a gas passage flow velocity of the water-repellent filter and a filter pressure loss.
FIG. 13 is a diagram illustrating a relation between a SO3 concentration in the gas and a filter pressure loss.
FIG. 14 is a schematic diagram of an air pollution control system provided with a CO2 recovery unit according to a second embodiment.
FIG. 15 is a schematic diagram of the air pollution control system provided with a CO2 recovery unit according to a third embodiment.
FIG. 16 is a schematic diagram of an air pollution control system provided with a CO2 recovery unit according to a fourth embodiment.



DESCRIPTION OF EMBODIMENTS
Preferred embodiments of the present invention will be described in detail with reference to the attached drawings. Note that the present invention is not intended to be limited by these embodiments. When there is a plurality of embodiments, the present invention also includes an embodiment configured by combining the embodiments.
First Embodiment
FIG. 1 is a schematic diagram of an air pollution control system provided with a CO2 recovery unit according to a first embodiment.
As illustrated in FIG. 1, an air pollution control system 10A provided with a CO2 recovery unit according to the present embodiment is a CO2 recovery apparatus that removes CO2 contained in a coal combustion flue gas (hereinafter, referred to as “flue gas”) 11 discharged from, for example, a coal combustion boiler. The air pollution control system 10A has a cooling tower 20 that cools the flue gas 11, a CO2 recovery unit 30 that removes CO2, and a CO2 compression apparatus 50 that compresses CO2 recovered in the CO2 recovery unit 30 to be CO2 gas of high purity.
In the present embodiment, a first water cleaning unit 62A is provided between a CO2 absorption unit 34 and a water-repellent filter unit 36 in a CO2 absorber 32.
In the first water cleaning unit 62A, the flue gas comes into gas-liquid contact with a cleaning water 63 supplied from the tower top side, and a part of the liquefied amine absorbent and the gaseous amine absorbent accompanied by a CO2-free flue gas 12A is removed prior to introduction into the water-repellent filter unit 36.
In the present embodiment, on a gas flow downstream side of the first water cleaning unit 62A, a demister 37 which is a glass fiber filter is installed.
The cooling tower 20 has a cooling part 20a that injects cooling water 21 from the top side of the cooling tower and brings the cooling water 21 into countercurrent contact with the flue gas 11 introduced from the lower part. Thereby, the gas temperature is reduced to a predetermined temperature, and the cooling water 21 is reused by a circulation line L11, a circulation pump P11, and a cooler 22.
The CO2 recovery unit 30 that removes CO2 in the flue gas 11 after cooling has a CO2 absorber (hereinafter, also referred to as an “absorber”) 32 that removes CO2 by bringing the flue gas 11 introduced from a lateral surface side of the tower lower end into countercurrent contact with the amine absorbent (lean solution) serving as a CO2 absorbent, and an absorbent regenerator (hereinafter, also referred to as a “regenerator”) 33 that releases CO2 from the amine absorbent (rich solution 31a) that has absorbed CO2 and regenerates the amine absorbent, and the CO2 recovery unit 30 supplies a lean solution 31b from which CO2 is removed by the absorbent regenerator 33 to the CO2 absorber 32 side so as to be used as the amine absorbent (lean solution) again.
In FIG. 1, reference numeral L1 represents a rich solution supply line, L2 represents a lean solution supply line, L3 represents a reboiler circulation line, L4 represents a gas discharge line, L5 represents a condensed water line, L6 represents a cleaning fluid circulation line, P5 represents a circulation pump, reference numeral 64 represents a cooler, and reference numeral 65 represents a chimney tray.
The CO2 absorber 32 is provided with the CO2 absorption unit 34 that absorbs CO2 in the flue gas 11 by the amine absorbent (lean solution 31b), and the water-repellent filter unit 36 that is provided on an upper portion (gas flow downstream) side of the CO2 absorption unit 34 and collects the mist amine absorbent accompanied by the CO2-free flue gas 12A.
FIG. 2 is a perspective view of the water-repellent filter unit according to the first embodiment, FIG. 3 is a longitudinal cross-sectional view of the water-repellent filter unit according to the first embodiment. FIG. 4 is a cross-sectional view taken along a line X-X of FIG. 3. FIG. 5 is a perspective view of the water-repellent filter according to the first embodiment. FIGS. 6 and 7 are cross-sectional views of another water-repellent filter unit according to the first embodiment.
As illustrated in these drawings, the water-repellent filter unit 36 is provided with a filter cylinder 42 having a gas introduction space S into which the CO2-free flue gas 12A rising from the CO2 absorption unit 34 is introduced, and a plurality of water-repellent filters 43 that is provided on a side surface 42a of the filter cylinder 42 to allow the introduced CO2-free flue gas 12A to pass in a direction orthogonal to a gas flow direction.
The filter cylinder 42 has the introduction space S into which the CO2-free flue gas 12A is introduced from at least one openings 41a that are provided in a filter base 41 orthogonal to the gas flow direction of the CO2-free flue gas 12A rising from the CO2 absorption unit 34.
The upper side of the gas introduction space S is closed by a ceiling surface 42c provided on a ceiling side of the side surface 42a. 
Furthermore, on the side surface 42a of the filter cylinder 42, the plurality of water-repellent filters 43, through which the introduced CO2-free flue gas 12A passes in a direction orthogonal to the gas rising direction, is provided.
The water-repellent filter 43 is installed on a plurality of openings 42b provided on the side surface 42a of the filter cylinder 42 via a casing and a gasket.
The water-repellent filter 43 is disposed in a multistage in a direction of height of the side surface 42a of the filter cylinder 42 according to the flow velocity of the gas to be treated, and is configured to remove the amine mist in the CO2-free flue gas 12A under the condition of a predetermined pressure loss.
In FIG. 2, reference numeral W1 represents a width of the filter base 41, and L1 represents a length of the filter base 41. The width and the length are the same as an inner dimension of the CO2 absorber 32. Reference numeral W2 represents a width of the filter cylinder 42, and L2 represents a length of the filter base 41. The number of installation of the filter cylinder 42 is not limited in the present invention and can be appropriately changed in consideration of the amount of gas to be treated, the pressure loss, or the like.
As illustrated in FIG. 3, in the water-repellent filter unit 36, the filter base 41, which is installed within the tower of the CO2 absorber 32 to block the gas flow of the CO2-free flue gas 12A, is installed. In the filter base 41, the plurality of elongated rectangular openings 41a is provided. Moreover, in the opening 41a, the filter cylinders 42 having a rectangular cross-section are disposed, respectively, and on both side surfaces 42a of the filter cylinder 42, the plurality of water-repellent filters 43 is installed.
The water-repellent filter 43 is disposed such that its gas passage cross-section is orthogonal to the CO2-free flue gas 12A.
Moreover, when the CO2-free flue gas 12A passes through the water-repellent filter 43, the water-repellent filter 43 collects the mist amine absorbent accompanied by the gas, thereby further reducing the amine concentration when a purified CO2-free flue gas 12B is diffused to the atmosphere.
In addition, as illustrated in FIG. 5, the water-repellent filter 43 may be configured to be equipped in a filter frame 49. In such configuration, the water-repellent filter 43 is equipped in the filter frame 49 in the alternately folded pleated shape. By weaving in the pleated shape several times, the filter area through which the CO2-free flue gas 12A passes is improved.
Here, it is preferred that the gas flow velocity (V1) of the CO2-free flue gas 12A be approximately 2.5 m/s (a preferable range is from 2.0 to 3.0 m/s) at the flow velocity of the gas rising from the CO2 absorption unit 34, and a cross-section of standard flow velocity (V2) when passing through the water-repellent filter 43 be approximately 0.3 to 1.2 m/s (a preferable range is from 0.5 to 0.8 m/s).
In addition, it is preferred that the pressure loss of the water-repellent filter 43 be 30 to 120 mmH2O (a preferable range is from 40 to 80 mmH2O).
Thus, in the present invention, from the viewpoint of facilitating the discharge of the collected mist, the water-repellent filter 43 is disposed so that its gas passage cross-section is orthogonal to the CO2-free flue gas 12A (the water-repellent filter 43 itself is vertically disposed).
This is because, when the gas passage cross-section is horizontally disposed with respect to the CO2-free flue gas 12A (the water-repellent filter 43 itself is horizontally disposed), the discharge of the collected mist is poor, the pressure loss increases, and the amount of process gas decreases, which is not preferable.
In addition, as in the present embodiment, in addition to a complete vertical disposition, the water-repellent filter 43 may be obliquely disposed such that the opposite side surfaces thereof have a tapered shape, for example, in a roof shape.
In the present embodiment, as illustrated in FIG. 6, as a collecting unit for collecting the falling water that falls down along the surface of the filter, for example, a trough 44 or the like may be provided on the lower end side of the water-repellent filter 43.
Furthermore, in the present embodiment, as illustrated in FIG. 7, a cleaning unit (for example, a cleaning spray, and a cleaning nozzle) 47 for cleaning the gas in-flow surface of the water-repellent filter 43 by a cleaning water 46 is installed in the filter cylinder 42. The dust adhering to the filter surface may be removed by a spraying water 46a sprayed from the cleaning unit 47. Here, FIG. 8 is a diagram corresponding to FIG. 4, and illustrates a spray region state of the spraying water 46a within the space.
Furthermore, in the present embodiment, as illustrated in FIG. 9, as a shape of the filter cylinder 42 in which the water-repellent filter 43 is provided, a stepped shape may be used.
In the embodiment illustrated in FIG. 9, a width A of the opening 41a of the gas introduction side is wider than a width B of the top of the filter cylinder 42, the side surface 42a has a stepped shape, and the interval between the side surfaces facing each other is narrowed as the CO2-free flue gas 12A rises.
By changing the gas in-flow space on the gas introduction side of the bottom of the filter cylinder 42, it is possible to allow the gas to more uniformly flow in the filters of each stage.
Here, it is essential in the present invention that the filter used in the water-repellent filter unit 36 have water repellency.
FIG. 10 is a schematic diagram illustrating an increase or decrease in a gas passage area depending on presence or absence of water repellency.
In FIG. 10, the left side is the case of using a water-repellent filter, and the right side is the case of using a water-resistant filter. FIG. 10 illustrates a cross-section of the filter, and in the figure, reference numeral t represents a thickness of the filter, and reference numeral 48 represents a water film. Here, in FIG. 10, the right side of the filter is a space interior side of the filter cylinder 42, and the left side of the filter is an exterior.
As illustrated on the right side of FIG. 10, in the case of the water-resistant filter. Accordingly, a material thereof is glass wool having a low water repellency, the moisture accompanied by the CO2-free flue gas 12A is held on the surface of the filter to become a water film 48 to block the gap of the filter passage gas part and as a result, a pressure loss increases. Thus, the water-resistant filter is not preferable.
In contrast, as in the present invention, in the case of the water-repellent filter illustrated on the left side, since the filter has water repellency, the moisture accompanied by the CO2-free flue gas 12A is not held on the filter surface and falls downward, and the gap of the filter passage gas part remains. Consequently, a decrease in the gas passage area is small, the pressure loss increases but is within a tolerance, and thus, the water-repellent filter is preferable.
Therefore, in order to obtain this effect, it is preferred that the filter be vertically disposed rather than obliquely disposed.
Here, as the water-repellent filter 43, it is desirable to use a polytetrafluoroethylene (hereinafter, referred to as “PTFE”) porous film having a high water repellency.
Furthermore, an average pore diameter of the porous film is about 0.01 to 10.0 μm (preferably, about 0.1 to 0.5 μm).
In addition, as the water-repellent filter 43, it is desirable that a contact angle to water be 60° or more (preferably, 90° or more).
This is because the average particle size of the mist to be collected in the CO2 recovery unit is approximately 1 μm. In particular, when SO2 coexists in the flue gas introduced into the CO2 recovery unit, a phenomenon of an increase in the diffused amine is observed with an increase in the fine mist having the particle size of 1 μm or less (see the above-described Patent Literature 4).
Therefore, in order to increase the collection efficiency of the mist having an average particle diameter or less, the average pore size of the porous film is preferably about 0.1 to 0.5 μm.
In addition, other than a filter made of PTFE, for example, it is preferable to use a water-repellent filter obtained by coating PTFE to polyethylene, polypropylene, and a glass wool, and another water-repellent filter containing a fluorine resin. The filter may have a structure that is reinforced in combination with another low pressure loss porous material (a reinforcement material).
FIG. 11 is a diagram illustrating an example of the distribution of the mist particle diameter in the outlet gas of the CO2 absorber. As illustrated in FIG. 11, it is understood that the mist present in the CO2-free flue gas is present as a mist state having an average particle diameter of 1 μm.
Therefore, by allowing the CO2-free flue gas 12A containing the mist amine having the particle size to pass through the water-repellent filter, it is possible to collect the accompanied mist amine, thereby suppressing the release to the outside.
FIG. 12 is a diagram illustrating a relation between a gas passage flow velocity of the water-repellent filter and the filter pressure loss. The relation between the gas passage flow velocity of the water-repellent filter 43 and the filter pressure loss was obtained using a gas having the SO2 concentration of 3 ppm.
As illustrated in FIG. 12, when the gas passage flow velocity increases, the pressure loss also gradually increases accordingly, but a significant pressure change was not observed.
Therefore, the gas passage flow velocity of the filter unit may be determined in consideration of the amount of gas to be treated, and the pressure loss.
FIG. 13 is a diagram illustrating a relation between the SO3 concentration in the gas and the filter pressure loss.
Since the gas in the CO2 absorber 32 is a moisture-saturated gas, it was observed whether there was any pressure fluctuation in the filter according to the change of the SO3 concentration contained in the gas. Here, the gas flow velocity was 0.35 m/s.
As illustrated in FIG. 13, it was observed that there was no significant fluctuation in the pressure loss by the filter passage even when the SO3 concentration in the gas changed (0.2 to 3 ppm).
It is assumed that there is no significant fluctuation in the pressure loss as a result of the discharge due to the natural drop of the collected mist fraction along the water-repellent filter surface.
Here, in the above-described absorber 32, the flue gas 11 containing CO2 introduced from the tower bottom side comes into countercurrent contact with the amine absorbent based on, for example, alkanolamine, in the CO2 absorption unit 34, and CO2 in the flue gas 11 is absorbed to the amine absorbent side by the chemical reaction (R—NH2+H2O+CO2→R—NH2HCO3).
Then, the CO2-free flue gas 12A after removal of CO2 rises to the water-repellent filter unit 36 side after passing through the demister 37, and the mist amine absorbent is removed by the water-repellent filter unit 36.
In the demister 37, it is possible to collect the mist having the large particle diameter generated in the filling unit or the liquid supply unit of the absorber, but for example, the collection characteristics of the fine mist caused by SO2 are low. Meanwhile, since the water-repellent filter unit 36 is able to collect the fine mist, the amine concentration diffused to the atmosphere is further reduced compared to the related art when the purified CO2-free flue gas 12B is discharged to the outside from the tower top of the CO2 absorber 32. In the present embodiment, on the tower top side of the downstream of the water-repellent filter unit 36, a wire mesh demister 38 is provided to further collect the mist components.
This aims to reduce the concentration of the diffused amine by collecting the mist having the large particle diameter generated by re-scattering of a part of the mist collected in the water-repellent filter 43.
The rich solution 31a after absorbing CO2 is increased in pressure by a rich solvent pump P1 interposed in the rich solution supply line L1, is heated by the lean solution 31b regenerated in the absorbent regenerator 33 in a rich-lean solution heat exchanger 39, and is supplied to the tower top side of the absorbent regenerator 33.
The rich solution 31a released to the tower interior from a tower top 33a side of the regenerator 33 releases most CO2 by heating due to water vapor from the tower bottom of the regenerator 33. The introduced amine absorbent (rich solution 31a) becomes the lean solution (amine absorbent) obtained by removing almost all CO2, by the time of flowing down to the tower bottom of the regenerator 33. A part of the lean solution 31b is heated by saturated water vapor 52 in a regenerative heater 51 interposed in the reboiler circulation line L3. The saturated water vapor 52 after heating becomes condensed water 53.
Meanwhile, CO2 gas 54, which is accompanied by the water vapor released within the tower, is discharged to the outside from the tower top 33a of the regenerator 33.
Then, the CO2 gas 54 accompanied by the water vapor is derived by the gas discharge line L4, the water vapor is condensed by a condenser 55 interposed in the gas discharge line L4, and the condensed water is separated in a separation drum 56. The CO2 gas from which the moisture is separated is released to the outside of the system, and is subjected to post-treatment such as compression and recovery, using a plurality of CO2 compressors 57 interposed in the gas discharge line L4. A cooler 58 is interposed between the plurality of CO2 compressors 57 to cool the compressed gas.
A compressed CO2 gas 59 subjected to the compression and recovery is stored, for example, in the ground or used as a high purity CO2.
The condensed water separated in the separation drum 56 is supplied to the top of the absorbent regenerator 33 by a condensed water circulation pump P3 interposed in the condensed water line L5.
The regenerated amine absorbent (lean solution) is sent to the CO2 absorber 32 side by the lean solution pump P2 via the lean solution supply line L2 and is heat-exchanged in the rich-lean heat exchanger 39. Subsequently, the regenerated amine absorbent is cooled to a predetermined temperature in a cooler 61, and is circulated and used as the amine absorbent (lean solution 31b).
Therefore, the amine absorbent forms a closed path that circulates through the CO2 absorber 32 and the absorption solution regenerator 33, and is reused in the CO2 absorption unit 34 of the CO2 absorber 32. Note that an amine absorbent 31 is also supplied by a supply line (not illustrated) if necessary, and the thermostable salt in the amine absorbent is removed by a reclaimer (not illustrated) if necessary.
In the present embodiment, the water-repellent filter unit 36 having the water-repellent filters 43 is installed inside the CO2 absorber 32 forming the CO2 recovery unit 30. By introducing the CO2-free flue gas 12A into the water-repellent filter unit 36 and causing the gas to pass through the water-repellent filters 43, it is possible to collect the mist amine accompanied by the CO2-free flue gas. As a result, even when the purified CO2-free flue gas 12B is released to the outside of the absorber 32, it is possible to further reduce the amine concentration diffused to the atmosphere compared to the demisters such as the conventional glass filter.
In addition, in the present embodiment, since a part of the amine absorbent and the gaseous amine absorbent is removed in the first water cleaning unit 62A prior to introduction into the water-repellent filter unit 36, load to the water-repellent filter unit 36 is reduced and the collection efficiency of the mist amine is also improved.
Second Embodiment
Next, an air pollution control system provided with a CO2 recovery unit according to a second embodiment of the present invention will be described. Note that the components same as those in the first embodiment are denoted by the same reference numerals, and the description thereof will not be provided.
FIG. 14 is a schematic diagram of the air pollution control system provided with the CO2 recovery unit according to the second embodiment of the present invention.
As illustrated in FIG. 14, an air pollution control system 10B equipped with a CO2 recovery unit 30 according to the present embodiment is provided with a second water cleaning unit 62B, on the downstream side of a water-repellent filter unit 36 in the CO2 absorber 32 of the first embodiment.
In the second water cleaning unit 62B of the present embodiment, a flue gas comes into gas-liquid contact with cleaning water 63 supplied from the tower top side, the liquefied amine absorbent and the gaseous amine absorbent accompanied by CO2-free flue gas 12A are removed after being removed in the water-repellent filter unit 36. Reference numeral P6 represents a circulation pump, reference numeral 66 represents a cooler, and L7 represents a cleaning fluid circulation line.
Installation of the second water cleaning unit 62B on the downstream side of the water-repellent filter unit 36 allows further reduction of the diffused amine concentration, compared to the first embodiment, by collecting the re-scattered mist from a water-repellent filter 43 and the re-scattered amine components evaporated from the mist collected in the water-repellent filter 43.
Third Embodiment
Next, an air pollution control system provided with a CO2 recovery unit according to a third embodiment of the present invention will be described. Note that the components same as those in the first and second embodiments are denoted by the same reference numerals, and the description thereof will not be provided.
FIG. 15 is a schematic diagram of the air pollution control system provided with the CO2 recovery unit according to the third embodiment of the present invention.
As illustrated in FIG. 15, an air pollution control system 10C equipped with a CO2 recovery unit 30 according to the present embodiment is provided with a second water cleaning unit 62B, on the downstream side of the gas flow of the water-repellent filter unit 36 in the CO2 absorber 32 of the first embodiment.
In the present embodiment, it is possible to further reduce the diffused amine concentration compared to the first embodiment, by collecting the re-scattered mist from a water-repellent filter 43 and the amine components generated by evaporation from the mist collected by the water-repellent filter 43 in the second water cleaning unit 62B.
Fourth Embodiment
Next, an air pollution control system provided with a CO2 recovery unit according to a fourth embodiment of the present invention will be described. Note that the components same as those in the first to third embodiments are denoted by the same reference numerals, and the description thereof will not be provided.
FIG. 16 is a schematic diagram of the air pollution control system equipped with the CO2 recovery unit according to the fourth embodiment of the present invention.
As illustrated in FIG. 16, in an air pollution control system 10D equipped with a CO2 recovery unit 30 according to the present embodiment, a water-repellent filter unit 36 and a second water cleaning unit 62B installed in the CO2 absorber 32 of the second embodiment 2 are provided in a gas cleaning tower 70, which is separately placed.
This configuration avoids an increase in the vertical placement of the CO2 absorber 32.
Furthermore, by using the conventional CO2 absorber 32, and by separately additionally providing the gas cleaning tower 70 on which the water-repellent filter unit 36 and the second water cleaning unit 62B of the present embodiment are disposed, it is possible to further reduce the diffused amine concentration without a large modification.
Note that, even in the first, second, and third embodiments, the water-repellent filter unit 36 may be provided in a gas cleaning tower 70 installed outside the CO2 absorber 32.
EXAMPLE
Hereinafter, Examples illustrating the effects of the present invention will be described. However, the present invention is not limited thereto.
As Example 1, as a mist removal unit, a glass fiber filter (GS) was installed in a first stage, the water-repellent filter unit 36 of the water-repellent filter was installed in a second stage of the downstream side of the gas flow, and a wire mesh demister (MD) was installed in a third stage of the downstream side of the gas flow.
As Example 2, as a mist removal unit, a glass fiber demister (GD) was installed in the first stage, the water-repellent filter unit 36 of the water-repellent filter was installed in the second stage of the downstream side of the gas flow, and a glass fiber demister (GD) was installed in the third stage of the downstream side of the gas flow.
As Comparative Example 1, as a mist removal unit, the glass fiber demister (GD) was installed in the first stage, and the wire mesh demister (MD) was installed in the second stage of the downstream side of the gas flow.
As Comparative Example 2, as the mist removal unit, the glass fiber demister (GD) was installed in the first stage, the wire mesh demister (MD) was installed in the second stage of the downstream side of the gas flow, and the glass fiber demister (GD) was installed in the third stage of the downstream side of the gas flow.
As Comparative Example 3, as the mist removal unit, the glass fiber demister (GD) was installed in the first stage, a water-resistant filter was installed in the second stage of the downstream side of the gas flow, and the wire mesh demister (MD) was installed in the third stage of the downstream side of the gas flow.
The diffused amine concentration was measured under the conditions where the SO3 mist concentration in the gas was set to 1 ppm and 3 ppm. The results are illustrated in Table 1.










TABLE 1










Diffused amine



Mist removal unit
concentration













First
Second
Third
SO3: 1
SO3: 3



stage
stage
stage
ppm
ppm
















Example 1
GS
Water-
MD
0.7
1




repellent




filter


Example 2
GD
Water-
GD
0.15
0.3




repellent




filter


Comparative
GD
MD
—
20
37


Example 1


Comparative
GD
MD
GD
2
7


Example 2


Comparative
GD
Water-
MD
—
—


Example 3

repellent




filter





GD: glass fiber demister


MD: wire mesh demister


Water-repellent filter


Water-resistant filter






As illustrated in Table 1, in Comparative Example 1 of the related art, when the SO3 mist concentration was 1 ppm, the amine concentration of absorber outlet was 20 ppm.
In Comparative Example 1 of the related art, when the SO3 mist concentration was 3 ppm, the amine concentration of absorber outlet was 37 ppm.
As in Comparative Example 2, when the SO3 mist concentration was 1 ppm, even in a case where the glass fiber demister (GD) was installed in the third stage, the amine concentration of the absorber outlet was lowered only to 2 ppm.
Furthermore, as in Comparative Example 2, when the SO3 mist concentration was 3 ppm, even in a case where the glass fiber demister (GD) was installed in the third stage, the amine concentration of the absorber outlet was lowered only to 7 ppm.
In contrast, as in Example 1, in a case where the water-repellent filter was installed in the second stage and the wire mesh demister (MD) was installed in the third stage, when the SO3 mist concentration was 1 ppm, the amine concentration of the absorber outlet was significantly lowered to 0.7 ppm. Furthermore, when the SO3 mist concentration was 3 ppm, the amine concentration of the absorber outlet was significantly lowered to 1.0 ppm.
As in Example 2, in a case where the water-repellent filter was installed in the second stage and the glass fiber demister (GD) was installed in the third stage, when the SO3 mist concentration was 1 ppm, the amine concentration of the absorber outlet was further lowered to 0.15 ppm. Furthermore, when the SO3 mist concentration was 3 ppm, the amine concentration of the absorber outlet was significantly lowered to 0.3 ppm.
As in Comparative Example 3, in a case where the water-resistant filter was installed, the filter pressure loss increased, and the measurement was not possible.
Thus, when using the water-repellent filter as in the present invention, it was observed that it is possible to collect the mist amine accompanied by the CO2 flue gas and to further reduce the concentration of amine diffused to the atmosphere.
REFERENCE SIGNS LIST


    
    
        10A to 10D AIR POLLUTION CONTROL SYSTEM
        11 COAL COMBUSTION FLUE GAS (FLUE GAS)
        12A CO2-FREE FLUE GAS
        12B PURIFIED CO2 FLUE GAS
        20 COOLING TOWER
        30 CO2 RECOVERY UNIT
        32 CO2 ABSORBER
        33 ABSORBENT REGENERATOR
        34 CO2 ABSORPTION UNIT
        36 WATER-REPELLENT FILTER UNIT
        41 FILTER BASE
        42 FILTER CYLINDER
        43 WATER-REPELLENT FILTER
        44 TROUGH
        46 CLEANING WATER
        47 CLEANING unit
        50 CO2 COMPRESSION APPARATUS
        62A FIRST WATER CLEANING UNIT
        62B SECOND WATER CLEANING UNIT

## Claims

1. An air pollution control system comprising a CO2 recovery unit equipped with a CO2 absorber that removes CO2 in a flue gas from a boiler by an amine absorbent, and an absorbent regenerator that regenerates the amine absorbent,
wherein the CO2 absorber is equipped with a CO2 absorption unit that absorbs CO2 in the flue gas by the amine absorbent,
a water-repellent filter unit that collects mist amine absorbent accompanied by a CO2-free flue gas is disposed on a gas flow downstream side of the CO2 absorption unit, wherein the water-repellent filter unit is equipped with a filter cylinder having a gas introduction space into which the CO2-free flue gas rising from the CO2 absorption unit is introduced, and a plurality of water-repellent filters provided on a side surface of the filter cylinder to allow the introduced CO2-free flue gas to pass through the filters in a direction orthogonal to a gas flow direction,
a first water cleaning unit, provided between the CO2 absorption unit and the water-repellent filter unit, in which the flue gas comes into gas-liquid contact with a cleaning water and a gaseous amine absorbent accompanied by the CO2-free flue gas is removed prior to introduction into the water-repellent filter unit,
a demister that collects mist having a large particle diameter is provided in a gas flow downstream side of the water cleaning unit, and
a wire mesh demister that collects mist generated by re-scattering is provided on a tower top side of a downstream side of the water-repellent filter unit.

2. The air pollution control system according to claim 1,
wherein a cleaning unit for cleaning a gas in-flow surface of the water-repellent filter is provided in the filter cylinder.

3. The air pollution control system according to claim 1,
wherein a collecting unit for collecting falling water falling down along the surface of the filter is provided on a lower end side of the water-repellent filter.

4. The air pollution control system according to claim 1,
wherein the water-repellent filter unit is integrally provided within the CO2 absorber.

5. The air pollution control system according to claim 1,
wherein the water-repellent filter unit is provided separately from the CO2 absorber.

6. The air pollution control system according to claim 1,
further comprising a second water cleaning unit provided on a downstream side of the gas flow of the water-repellent filter unit.