Patent Application
20110123403
The present invention relates to an air pollution control apparatus and an air pollution control system that process flue gas discharged from a combustion device.
Because mercury having high toxicity is included in flue gas discharged from a coal combustion boiler, which is a combustion device, for example, in a thermal power plant, various systems for removing mercury in flue gas have been conventionally studied.
Generally, a wet type desulfurizer for removing sulfur contents in flue gas is provided in the coal combustion boiler. In a flue-gas processing plant where a desulfurizer is attached to the boiler as an air pollution control apparatus, it is well known that if chlorine (Cl) contents in flue gas increase, the percentage of divalent metallic mercury (Hg) soluble in water increases, and thus the desulfurizer can easily collect mercury.
Recently, therefore, various processing methods and processing apparatuses of metallic mercury have been devised by combining NOx removal unit that reduces NOx and a wet type desulfurizer that uses an alkaline absorbent as a sulfur oxide (SOx) absorbent.
As a method of processing metallic mercury in flue gas, a removal method using an adsorbent such as activated carbon or a selenium filter has been known. However, this method requires a special adsorption removal unit, and thus it is not suitable for processing of large-capacity flue gas such as flue gas from a power plant.
Therefore, as a method of processing metallic mercury in large-capacity flue gas, there has been proposed a method such that a chlorinating agent is gas-atomized on an upstream side of NOx removal unit at a high temperature in a flue gas duct, mercury is oxidized (chlorinated) on a denitration catalyst to prepare soluble mercury chloride, and the mercury chloride is absorbed in a wet desulfurizer installed on a downstream side (see, for example, Patent Literatures 1 and 2). Further, an apparatus that atomizes gas to a flue gas duct and a technique therefor have been put to practical use in atomization of NH3 by NOx removal unit and gas atomization of the chlorinating agent.
Further, an injection spot of hydrochloric acid (HCl) is provided in a flue gas duct 19 on an upstream side of the NOx removal unit 13, and hydrochloric acid (liquid) stored in a hydrochloric acid (liquid HCl) supplying unit 20 is gasified in a hydrogen chloride (HCl) atomizing unit 21 and atomized to the flue gas 12 as hydrogen chloride via a hydrogen chloride (HCl) atomizing nozzle 21a.
Further, an injection spot of ammonia (NH3) is provided in the flue gas duct 19 on an upstream side of the NOx removal unit 13, and ammonia (NH3) supplied from an NH3 supplying unit 29 is atomized to the flue gas 12 by an ammonia (NH3) atomizing nozzle 29a, to reduce nitrogen oxides (NOx).
In
The flue gas 12 from the boiler 11 is supplied to the denitration catalyst layer 13 and supplied to the electronic precipitator 30 after having heated air 33 by heat exchange in the air preheater 28, and further supplied to the desulfurizer 16, and then discharged to the air as the purged gas 17.
To suppress the influence of the chlorinating agent on an apparatus such as corrosive breakage and improve the reliability of the apparatus, the mercury concentration in flue gas, which has undergone wet desulfurization, is measured by a mercury monitor, and a feed rate of the chlorinating agent is adjusted based on the mercury concentration after desulfurization (see, for example, Patent Literature 2).
In this manner, conventionally, NOx (nitrogen oxides) in the flue gas 12 is removed and mercury (Hg) in the flue gas 12 is oxidized by supplying hydrogen chloride and ammonia into the flue gas 12.
That is, NH3 is used for reduction and denitration of NOx, and NH3 supplied from the NH3 supplying unit 29 is atomized into the flue gas 12 via the ammonia (NH3) atomizing nozzle 29a. In the denitration catalyst layer 13, NOx is substituted by nitrogen (N2) by a reduction reaction as shown in the following equations, and then denitrated.
4NO+4NH3+O2→4N2+6H2O (1)
NO+NO2+2NH3→2N2+3H2O (2)
Hydrogen chloride is used for mercury oxidation, and the hydrogen chloride used as the chlorinating agent is supplied from the liquid HCl supplying unit 20 to the HCl atomizing unit 21, where hydrochloric acid is gasified, and atomized into the flue gas 12 as hydrogen chloride (HCl) by the HCl atomizing nozzle 21a. Accordingly, in the denitration catalyst layer 13, Hg having low solubility is oxidized (chlorinated) on the denitration catalyst as shown in the following equation, and converted to highly soluble mercury chloride (HgCl2), thereby removing Hg contained in the flue gas 12 by the desulfurizer 16 provided on a downstream side.
Hg+2CHl+½O2→HgCl2+H2O (3)
Further, when coal or heavy oil is used as a fuel, because Cl is contained in the fuel, combustion gas contains Cl components. However, the content of the Cl components in the fuel varies depending on the type of fuel, and thus it is difficult to control the Cl concentration in flue gas. Therefore, it is desired that HCl and the like in an amount more than required is added to the flue gas on an upstream side of the denitration catalyst layer 13 to remove mercury reliably.
Further, as the denitration catalyst layer 13, as shown in
An air current of the flue gas 12 supplied to the conventional denitration catalyst layer 13 is rectified by a rectifying unit (not shown) just before the denitration catalyst layer 13 to be in a laminar flow state, and flows into the honeycomb passage 14 in the denitration catalyst layer 13 in this state. Therefore, a contact area between the denitration catalyst and flue gas is limited, and as a result, it is difficult to further improve the oxidation reaction efficiency of mercury.
The present invention has been achieved to solve the above problems, and an object of the present invention is to provide an air pollution control apparatus and an air pollution control system that can increase a contact area between flue gas supplied into NOx removal unit and a denitration catalyst to further improve the oxidation reaction efficiency of mercury in the flue gas.
According to an aspect of the present invention, an air pollution control apparatus includes at least one denitration catalyst layer that removes nitrogen oxides in flue gas from a boiler and atomizes hydrogen chloride into flue gas to oxidize mercury. The denitration catalyst layer is a honeycomb catalyst, and the air pollution control apparatus includes a swirling-flow generating member that changes the flue gas from a laminar flow to a turbulent flow in a passage of the honeycomb catalyst.
Advantageously, in the air pollution control apparatus, the swirling-flow generating member includes a vertical axis provided in the passage, and a plurality of swirling-flow generating vanes provided radially and orthogonally to the vertical axis with a predetermined gap therebetween to generate a turbulent flow in the flue gas.
Advantageously, in the air pollution control apparatus, the swirling-flow generating member includes a vertical axis provided in the passage, and a plurality of ring members provided orthogonally to the vertical axis with a predetermined gap therebetween.
Advantageously, in the air pollution control apparatus, the swirling-flow generating member includes a vertical axis provided in the passage, and a spiral board spirally wound on the vertical axis.
Advantageously, in the air pollution control apparatus, the swirling-flow generating member is a plate member having a fine pore corresponding to each passage of a honeycomb catalyst, and when the denitration catalyst layers are provided at a plurality of stages in a flow direction of the flue gas, the swirling-flow generating member is provided in each passage between the denitration catalyst layers at respective stages.
According to another aspect of the present invention, an air pollution control system includes: the boiler; a chlorinating-agent supplying unit that injects a chlorinating agent into flue gas discharged to a flue gas duct on a downstream side of the boiler; the air pollution control apparatus according to any one of the air pollution control apparatus described above; a NOx removal unit that removes sulfur oxides in flue gas after denitration; and a stack that discharges denitrated gas to outside.
Advantageously, in the air pollution control system, an ammonia supplying unit that injects ammonia into flue gas discharged to a flue gas duct on a downstream side of the boiler is provided.
According to the present invention, the swirling-flow generating member that changes the flue gas from a laminar flow to a turbulent flow is provided in the passage in a denitration catalyst layer that removes nitrogen oxides in the flue gas from the boiler. Therefore, a swirling flow can be generated in the flue gas in the passage in the denitration catalyst layer to change an airflow of the flue gas from a laminar flow to a turbulent flow, and the flue gas in the turbulent state can flow in the passage in the denitration catalyst layer, thereby enabling to increase a contact time between the flue gas and the denitration catalyst.
Therefore, the oxidation reaction efficiency between mercury in the flue gas and the denitration catalyst can be improved by supplying HCl beforehand into the flue gas. With this configuration, mercury in the flue gas can be removed highly efficiently by the NOx removal unit provided on a downstream side of the air pollution control apparatus.
Further, because reduction performance of NOx and oxidation performance of mercury in flue gas can be improved, an amount of denitration catalyst used in the denitration catalyst layer can be reduced, and a feed rate of the chlorinating agent supplied to the flue gas can be also reduced.
Exemplary embodiments of the present invention will be explained below in detail with reference to the accompanying drawings. The present invention is not limited to the embodiments. In addition, constituent elements in the following embodiments include those that can be easily assumed by persons skilled in the art or that are substantially equivalent.
An air pollution control system that applies the air pollution control apparatus according to an embodiment of the present invention is explained with reference to the drawings. The configuration of the air pollution control system applying the air pollution control apparatus according to the present embodiment is identical to the configuration of the air pollution control system shown in
The configuration shown in
As shown in
As shown in
Further, in the present embodiment, the four swirling-flow generating vanes 23 are arranged in a cruciform on the vertical axis 22 as viewed from a direction of the vertical axis 22, and a shape of the swirling-flow generating vane 23 as viewed from a direction of the vertical axis 22 is elliptical.
Further, a set of the swirling-flow generating vanes 23 provided on a downstream side of the flue gas 12 as viewed from a direction of the vertical axis 22 is provided to overlap on a set of the swirling-flow generating vanes 23 provided on an upstream side of the flue gas 12.
In this manner, by providing the swirling-flow generating member 15A in each of the honeycomb passages 14 in the denitration catalyst layer 13, a swirling flow can be generated in the flue gas 12 in the passage 14 in the denitration catalyst layer 13, and the flue gas 12 can pass through the passage 14 in the denitration catalyst layer 13, in a state with an airflow of the flue gas 12 being changed from a laminar flow to a turbulent flow. Therefore, the contact time between the flue gas 12 and the denitration catalyst can be increased. Accordingly, the oxidation reaction efficiency between mercury in the flue gas 12 and the denitration catalyst can be improved by supplying HCl beforehand into the flue gas 12.
With this configuration, Hg in the flue gas 12 can be removed highly efficiently by the desulfurizer (not shown) provided on a downstream side of the air pollution control apparatus 10.
Because reduction performance of NOx and oxidation performance of mercury in the flue gas 12 can be improved, an amount of denitration catalyst used in the denitration catalyst layer 13 can be reduced, and an HCl amount supplied to the flue gas 12 can be also reduced.
The number of the swirling-flow generating vanes 23 fixed to the vertical axis 22 is not limited to four, and two or three, or five or more vanes can be provided, so long as the flue gas 12 can be swirled to generate a turbulent flow. The vertical axis 22 is fixed on both sides above and below the denitration catalyst layer 13. A fixing method thereof is not particularly limited, and a fixing member (not shown) for fixing the vertical axis 22 on the both sides above and below the denitration catalyst layer 13 can be provided.
A reaction container for housing the denitration catalyst layer 13 outside of the denitration catalyst layer 13 or a fixing member (not shown) for fixing the vertical axis 22 to the flue gas duct 19 can be provided to fix upper and lower sides of the vertical axis 22 protruding from the denitration catalyst layer 13.
As shown in
Further, in the air pollution control apparatus 10 according to the present embodiment, the set of the swirling-flow generating vanes 23 is provided in a plurality of numbers so that the set of the swirling-flow generating vanes 23 provided on a downstream side of the flue gas 12 as viewed from the direction of the vertical axis 22 overlaps on the set of the swirling-flow generating vanes 23 provided on an upstream side of the flue gas flue gas 12. However, the present invention is not limited thereto. For example, a part or all of the set of the swirling-flow generating vanes 23 provided on a downstream side of the flue gas 12 as viewed from the direction of the vertical axis 22 can be provided, with the position thereof being shifted with respect to the vertical axis 22, so that the swirling-flow generating vanes 23 do not overlap on the set of the swirling-flow generating vanes 23 provided on an upstream side of the flue gas 12. Accordingly, a swirling flow can be generated in the flue gas 12 more efficiently.
In the present embodiment, the shape of the swirling-flow generating vane 23 as viewed from the direction of the vertical axis 22 is elliptical. However, the present invention is not limited thereto, and it is only necessary to generate a swirling flow in the flue gas 12. Therefore, the shape of the swirling-flow generating vane 23 can be, for example, triangle or square.
In the air pollution control apparatus 10 according to the present embodiment, only one denitration catalyst layer 13 is arranged. However, the present invention is not limited thereto, and a plurality of denitration catalyst layers 13 can be arranged.
In the present embodiment, because only one denitration catalyst layer 13 is arranged in the flue gas duct 19, only one swirling-flow generating member 15A is provided. However, when a plurality of denitration catalyst layers 13 are provided in the flue gas duct 19, the swirling-flow generating member 15A can be provided between respective denitration catalyst layers 13.
In the air pollution control apparatus 10 according to the present embodiment, as the denitration catalyst used in the denitration catalyst layer 13 for reduction and denitration, metal oxides such as V, W, Mo, Ni, Co, Fe, Cr, Mn, and Cu, or sulfate, or noble metals such as Pt, Ru, Rh, Pd, and Ir, or one in which a mixture thereof is supported on a carrier such as titania, silica, zirconia, complex oxides thereof, or zeolite can be used.
In the present embodiment, although there is no particular limitation on the concentration of HCl to be used, for example, from concentrated hydrochloric acid to dilute hydrochloric acid of about 5% can be used. In the present embodiment, hydrogen chloride (HCl) is explained as the chlorinating agent to be used. However, the present invention is not limited thereto, and the chlorinating agent can be an agent in which Hg in flue gas reacts in the presence of a denitration catalyst to generate mercury chloride of HgCl and/or HgCl2. As such a chlorinating agent, ammonium chloride, chlorine, hypochlorous acid, ammonium hypochlorite, chlorite, ammonium chlorite, chlonic acid, ammonium chlorate, perchloric acid, ammonium perchlorate, amine salts of above acids, and other salts can be exemplified.
The amount of chlorinating agent to be added in the flue gas 12 can be a stoichiometric amount or more with respect to poorly water-soluble mercury. As the concentration of the chlorinating agent in the flue gas 12 in the flue gas duct 19, the chlorinating agent can be atomized in an amount of 1000 ppm or less with respect to the flue gas 12, taking into consideration efficient removal of Hg in the flue gas 12 and the concentration of chlorine in discharged water discharged on a downstream side.
A mixing position of HCl with the flue gas 12 in the flue gas duct 19 is set to be on an upstream side of a mixing position of NH3; however, it can be on a downstream side of the mixing position of NH3.
In the present embodiment, both the HCl and NH3 are added to the flue gas 12 discharged from the boiler 11. However, NH3 may not be added to the flue gas 12 in the flue gas duct 19. It is because the denitration catalyst layer 13 in the air pollution control apparatus 10 is for removing NOx in the flue gas 12 and oxidizing Hg in the flue gas 12 to remove Hg by the desulfurizer (not shown) provided on a downstream side, and there is the same effect of removing Hg by the desulfurizer (not shown) by converting Hg to chlorides by HCl in the presence of the denitration catalyst in the denitration catalyst layer 13, even if NH3 is not added to the flue gas 12 in the flue gas duct 19.
As described above, according to the air pollution control apparatus 10 of the present embodiment, the denitration catalyst layer 13 that removes NOx in the flue gas 12 from the boiler 11, and atomizes HCl into the flue gas 12 to oxidize Hg is provided. The denitration catalyst layer 13 is a honeycomb catalyst, and the swirling-flow generating member 15A including the vertical axis 22 and the four swirling-flow generating vanes 23 provided radially with respect to the vertical axis 22 is provided in each of the passages in the denitration catalyst layer 13, with the four swirling-flow generating vanes 23 being arranged in a plurality of numbers with a gap therebetween in the direction of the vertical axis 22. Accordingly, a swirling flow can be generated in the flue gas 12 in the passages 14 in the denitration catalyst layer 13, and the flue gas 12 can pass through the passages 14 in the denitration catalyst layer 13 in a state with the airflow of the flue gas 12 being changed from a laminar flow to a turbulent flow, and thus the contact time between the flue gas 12 and the denitration catalyst can be increased. Because HCl has been supplied beforehand into the flue gas 12, the oxidation reaction efficiency between Hg in the flue gas 12 and the denitration catalyst can be improved. As a result, in the air pollution control system applying the air pollution control apparatus 10 according to the present embodiment, Hg can be removed highly efficiently by the desulfurizer (not shown) provided on a downstream side of the air pollution control apparatus 10.
Further, because reduction performance of NOx and oxidation performance of Hg in the flue gas 12 can be improved, the amount of denitration catalyst to be used in the denitration catalyst layer 13 can be decreased, and the amount of HCl to be supplied to the flue gas 12 can be also decreased.
The present embodiment has been explained above by using flue gas discharged from a boiler of a thermal power plant that burns fossil fuel including sulfur, mercury and the like, such as coal and heavy oil. However, the present invention is not limited thereto, and can be applied to flue gas having a low concentration of NOx and containing carbon dioxide, oxygen, SOx, dust, or moisture, boiler flue gas discharged from a factory or the like that burns fuel containing sulfur, mercury and the like, and heating furnace flue gas discharged from a metal factory, a petroleum refining plant, a petrochemical plant and the like.
An air pollution control system that applies an air pollution control apparatus according to a second embodiment of the present invention is explained with reference to the drawings. The configuration of the air pollution control system applying the air pollution control apparatus according to the present embodiment is identical to the configuration of the air pollution control system shown in
The configuration of the air pollution control apparatus according to the present embodiment is identical to that of the air pollution control apparatus according to the first embodiment, and thus illustrations of the configuration of the air pollution control apparatus according to the present embodiment are omitted and explanations are made only by referring to the drawings of a configuration of a swirling-flow generating member.
Like reference numerals are denoted to like members in the air pollution control apparatus shown in
As shown in
By providing the swirling-flow generating member 15B including the vertical axis 22 provided in the passage 14, and the ring members 24 provided orthogonal to the vertical axis 22 with a predetermined gap therebetween, in the passage 14 in the denitration catalyst layer 13, as in the above embodiment, a swirling flow can be generated in the flue gas 12 in the passages 14 in the denitration catalyst layer 13, and the flue gas 12 can pass through the passages 14 in the denitration catalyst layer 13, in a state with the airflow of the flue gas 12 being changed from a laminar flow to a turbulent flow, and thus the contact time between the flue gas 12 and the denitration catalyst can be increased. Because HCl has been supplied beforehand into the flue gas 12, the oxidation reaction efficiency between Hg in the flue gas 12 and the denitration catalyst can be improved.
Accordingly, in the air pollution control system applying the air pollution control apparatus according to the present embodiment, Hg in the flue gas 12 can be removed highly efficiently by a desulfurizer (not shown) provided on a downstream side of the air pollution control apparatus according to the present embodiment.
An air pollution control system that applies an air pollution control apparatus according to a third embodiment of the present invention is explained with reference to the drawings. The configuration of the air pollution control system applying the air pollution control apparatus according to the present embodiment is identical to the configuration of the air pollution control system shown in
Further, the configuration of the air pollution control apparatus according to the present embodiment is identical to that of the air pollution control apparatus according to the first embodiment, and thus illustrations of the configuration of the air pollution control apparatus according to the present embodiment are omitted and explanations are made only by referring to the drawings of a configuration of a swirling-flow generating member.
Like reference numerals are denoted to like members in the air pollution control apparatus shown in
As shown in
By providing the swirling-flow generating member 15C including the vertical axis 22 and the spiral board 25 spirally wound on the vertical axis 22, in the passage 14 in the denitration catalyst layer 13, as in the above embodiments, a swirling flow can be generated in the flue gas 12 in the passages 14 in the denitration catalyst layer 13, and the flue gas 12 can pass through the passages 14, in a state with the airflow of the flue gas 12 being changed from a laminar flow to a turbulent flow, and thus the contact time between the flue gas 12 and the denitration catalyst can be increased. Because HCl has been supplied beforehand into the flue gas 12, the oxidation reaction efficiency between Hg in the flue gas 12 and the denitration catalyst can be improved.
Accordingly, in the air pollution control system applying the air pollution control apparatus according to the present embodiment, Hg in the flue gas 12 can be removed highly efficiently by a desulfurizer (not shown) provided on a downstream side of the air pollution control apparatus according to the present embodiment.
An air pollution control system that applies an air pollution control apparatus according to a fourth embodiment of the present invention is explained with reference to the drawings. The configuration of the air pollution control system applying the air pollution control apparatus according to the present embodiment is identical to the configuration of the air pollution control system shown in
Further, because the configuration of the air pollution control apparatus according to the present embodiment is identical to that of the air pollution control apparatus according to the first embodiment, and thus illustrations of the configuration of the air pollution control apparatus according to the present embodiment are omitted and explanations are made only by referring to the drawings of a configuration of a swirling-flow generating member.
Like reference numerals are denoted to like members in the air pollution control apparatus shown in
As shown in
That is, the fine pore 26 corresponding to the honeycomb passage becomes an opening for the flue gas 12 to come out in a jet flow, and functions as an orifice. Because the fine pore 26 functions as a diaphragm of a flue gas passage, the fine pore 26 has a function of controlling a flow rate of the flue gas 12. When the flue gas 12 passes through the fine pores 26, the flue gas 12 comes out in a jet flow from the fine pore 26, and thus the flue gas 12 can swirl in the passage 14 and pass through the passage 14.
In the present embodiment, because the denitration catalyst layer 13 includes four stages in the flow direction of the flue gas 12, in total three swirling-flow generating members 15D are provided in the passages 14 between the four denitration catalyst layers 13. However, the swirling-flow generating member 15D can be provided between the respective denitration catalyst layers 13 according to the number of the denitration catalyst layers 13.
In the present embodiment, the swirling-flow generating members 15D are provided between the respective denitration catalyst layers 13. However, the present invention is not limited thereto, and the swirling-flow generating member 15D can be provided in the passage 14 in the denitration catalyst layer 13.
Accordingly, by providing the swirling-flow generating members 15D formed of the plate member 27 having the fine pore 26 corresponding to each of the passages 14 of the honeycomb catalyst at a plurality of stages in the flow direction of the flue gas 12, as in the above embodiments, a swirling flow can be generated in the flue gas 12 in the passages 14 in the denitration catalyst layer 13, and the flue gas 12 can pass through the passages 14, in a state with the airflow of the flue gas 12 being changed from a laminar flow to a turbulent flow, and thus the contact time between the flue gas 12 and the denitration catalyst can be increased. Because HCl has been supplied beforehand into the flue gas 12, the oxidation reaction efficiency between Hg in the flue gas 12 and the denitration catalyst can be improved.
With this configuration, in the air pollution control system applying the air pollution control apparatus according to the present embodiment, Hg in the flue gas 12 can be removed highly efficiently by a desulfurizer (not shown) provided on a downstream side of the air pollution control apparatus according to the present embodiment.
In this manner, according to the air pollution control apparatus of the present embodiment, by providing the swirling-flow generating member 15A including the vertical axis 22 and the four swirling-flow generating vanes 23, for example, as shown in
As described above, the air pollution control apparatus according to the present invention is suitable to be used in processing of flue gas discharged from an apparatus that burns fossil fuel such as coal and heavy oil containing mercury, in a thermal power plant or the like, because a swirling flow can be generated in flue gas and the flue gas passes through a passage in a denitration catalyst layer, in a state with an airflow of flue gas being changed from a laminar flow to a turbulent flow, thereby increasing the contact time between the flue gas and the denitration catalyst to improve the oxidation reaction efficiency between mercury and the denitration catalyst.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2008-204707 | Aug 2008 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2009/063194 | 7/23/2009 | WO | 00 | 1/28/2011 |
