Patent Application
20160236145
The present invention relates to a flue gas treatment method and to a denitration and
SO3 reduction apparatus, and more specifically relates to a flue gas treatment method and to a denitration and SO3 reduction apparatus for treatment of a combustion flue gas including sulfur trioxide.
BACKGROUND ART
In recent years, a flue gas treatment method and a flue gas treatment apparatus for treating combustion flue gases generated from various combustion furnaces have been strongly desired in order to prevent air pollution. Such flue gases contain nitrogen oxides (NOx) and a large amount of sulfur oxides (SOx). In treating NOx, a method has been applied in which NOx is brought into contact with a denitration catalyst to be decomposed into nitrogen (N2) and water (H2O). Among SOx, sulfur trioxide (SO3) is corrosive, and is a factor that inhibits the continuous long-term operation for treating flue gases due to clogging by ash inside flue gas treatment facilities such as an air preheater and an electric precipitator, dew point corrosion, and the like caused due to SO3.
For a method of treating such SO3, a method has been known in which ammonium (NH3) is charged to a combustion flue gas, then the combustion flue gas is brought into contact with a denitration catalyst constituted by ruthenium (Ru) carried on titania (TiO2), and thereby NOx is reduced and generation of SO3 in combustion flue gases is prevented (e.g., Patent Literature 1). However, even in the exemplary case recited in Patent Literature 1, when ammonia is consumed by a denitration reaction in a treatment of denitrating a combustion flue gas, an oxidation reaction expressed by the following expression (1) predominantly progresses, and therefore the concentration of SO3 may increase. In addition, although a method of reducing SO3 in a combustion flue gas by using a reductant constituted by carbon monoxide (CO) and hydrocarbon has been known, but expensive iridium (Ir) is used in the catalyst (e.g., Patent literature 2).
SO2+1/2O2→SO3 (1)
[Patent Literature 1] JP 3495591
[Patent Literature 2] JP 3495527
Under these circumstances, an object of the present invention is to provide a flue gas treatment method and a denitration and SO3 reduction apparatus that reduce treatment costs, reduce NOx contained in a combustion flue gas, and reduce the concentration of SO3 more efficiently compared with prior art.
In order to achieve the above-described object, according to an aspect of the present invention, a flue gas treatment method is provided, in which a 3C-5C olefinic hydrocarbon (unsaturated hydrocarbon) is added to a combustion flue gas including SO3 as well as NOx as a first additive, and then the combustion flue gas is brought into contact with a catalyst which includes an oxide constituted by one or more of elements selected from the group consisting of Ti, Si, Zr, and Ce and/or a mixed oxide and/or a complex oxide constituted by two or more of elements selected from the group as a carrier but not including a noble metal, and thereby SO3 is treated by reduction to SO2.
In this aspect, it is made possible to denitrate NOx in the flue gas, prevent oxidation of SO2, reduce the concentration of SO3 during the treatment of the combustion flue gas, and reduce the costs for the material of the catalyst without having to use an expensive catalyst containing Ru and the like. In descriptions given herein and in the claims, the term “and/or” is used, as is provided by JIS Z 8301, to collectively express a combination of two terms used in parallel to each other and either one of the two terms, i.e. to collectively express the three possible meanings that can be expressed by the two terms.
It is preferable that the first additive be one or more selected from the group consisting of 2C-5C olefinic hydrocarbon (unsaturated hydrocarbon), 2C-5C paraffinic hydrocarbon (saturated hydrocarbons), alcohols, aldehydes, and aromatic compounds. Further, it is preferable that the 2C-5C olefinic hydrocarbon (unsaturated hydrocarbon) be one or more selected from the group consisting of C2H4, C3H6, C4H8, and C5H10. In addition, the C4H8 and C5H10 may be a geometric isomer or a racemic body of either one thereof.
By using the above-described additive, oxidation of SO2 can be more efficiently suppressed and the concentration of SO3 during the treatment of the combustion flue gas can be more efficiently reduced compared with the case of using NH3 as the first additive.
It is preferable that the carrier include a mixed oxide and/or a complex oxide including one or more selected from the group consisting of TiO2—SiO2, TiO2—ZrO2, and TiO2—CeO2.
With the above-described carrier, the performance of reduction of SO3 into SO2 can be dramatically improved by using a mixed oxide and/or complex oxide with TiO2 and with an amount of solid acid higher than a predetermined value.
In addition, the catalyst may be a catalyst in which a metal oxide including one or more selected from the group consisting of V2O5, WO3, MoO3, Mn2O3, MnO2, NiO, and Co3O4 is carried on the complex oxide as the carrier. In addition, the catalyst may be a catalyst in which one or more selected from the group consisting of Ag, Ag2O, and AgO carried on a carrier constituted by one or more selected from the group consisting of the oxide, the mixed oxide, and the complex oxide.
In addition, a metallosilicate-base complex oxide, in which at least a part of Al and/or Si in a zeolite crystal structure is substituted with one or more selected from the group consisting of Ti, V, Mn, Fe, and Co may be coated onto the catalyst.
With the above-described catalyst, SO3 in the combustion flue gas can be reduced at a high reduction rate by using the first additive, and the SO3 reduction reaction would not be inhibited even if NH3 coexists.
It is preferable that NH3 be added as a second additive simultaneously as the first additive is added and simultaneously perform the reduction of SO3 and the denitration when performing a treatment for reducing SO3 to SO2.
In this aspect, the first additive can be added by partially reforming the ammonia supply line equipment provided to the existing denitration apparatus to contribute to reduction of SO3 in the combustion flue gas.
It is preferable that the treatment for reducing SO3 into SO2 be performed in a temperature range of 250° C. to 450° C. . In addition, it is preferable that the treatment for reducing SO3 into SO2 be performed in a temperature range of 300° C. to 400° C.
By employing the temperature ranges, the treatment for reducing SO3 in the combustion flue gas to SO2 by using an existing denitration apparatus and under denitration treatment conditions for a high activity of the catalyst as a denitration catalyst.
According to another aspect of the present invention, the present invention is a denitration and SO3 reduction apparatus. The denitration and SO3 reduction apparatus according to the present invention includes a first injection device configured to obtain add a first additive to a combustion flue gas containing SO3 as well as NOx; and a catalyst layer including a catalyst through which the combustion flue gas is allowed to flow, and in the denitration and SO3 reduction apparatus, the first additive is a 3C-5C olefinic hydrocarbon (unsaturated hydrocarbon), the catalyst does not include a noble metal and includes an oxide including one or more of elements selected from the group consisting of Ti, Si, Zr, and Ce and/or a mixed oxide and/or a complex oxide including two or more of elements selected from the group as a carrier, and the SO3 reduction apparatus is configured to perform a treatment for reducing SO3 into SO2.
According to another aspect of the present invention, the catalyst layer includes a first catalyst layer arranged on a back stream side of the first injection device and configured to reduce the concentration of SO3; and a second catalyst layer arranged on a back stream side of a second injection device arranged close to the first injection device and configured to add NH3 to the combustion flue gas as a second additive, the second catalyst layer being configured to perform denitration, and in this aspect, the first catalyst layer is arranged on a front stream side or a back stream side of the second catalyst layer.
According to the present invention, a flue gas treatment method and a denitration and SO3 reduction apparatus are provided which are configured to denitrate NOx in the combustion flue gas and reduce the concentration of SO3 in the combustion flue gas at the same time at treatment costs lower than those conventionally.
A denitration and SO3 reduction apparatus and a flue gas treatment method according to the present invention will be described below with reference to embodiments shown in the attached drawings. A flue gas generated by combusting an oil-derived fuel or a coal-derived fuel in a boiler and in an oxygen atmosphere will be herein referred to as a “combustion flue gas”. In addition, the stream of gas will be herein referred to as a “front stream” or “back stream” in relation to the direction of flow of a combustion flue gas.
The boiler burns an externally supplied fuel in the furnace 1 and discharges a combustion flue gas generated by the burning into the flue gas chimney 2. The denitration and SO3 reduction apparatus 5, which is arranged on a back stream side of the flue gas chimney 2, simultaneously performs a NOx denitration treatment and an SO3 reduction treatment for the combustion flue gas that flows through the flue gas chimney 2. In the descriptions given herein and in the claims, the treatment for reducing SO3 into SO2 will be referred to as the “SO3 reduction treatment”.
An ECO 3, which is arranged in the combustion flue gas chimney 2 in which the combustion flue gas is circulated, performs heat exchange between boiler feed water and the combustion flue gas that flow through the inside of the ECO 3. More specifically, the ECO 3 increases the temperature of the boiler feed water by using the thermal inertia of the combustion flue gas and thereby improves the efficiency of combustion in the boiler. An ECO bypass 4 is arranged so that one end thereof is in communication with the front stream side of the ECO 3 and the other end thereof is in communication with the back stream side of the ECO 3, and feeds the combustion flue gas before being fed into the ECO 3 to the side of an inlet of the denitration and SO3 reduction apparatus 5, bypassing the ECO 3. In addition, the ECO bypass 4 controls the temperature of the combustion flue gas to be fed into the denitration and SO3 reduction apparatus 5 within a predetermined temperature range appropriate for denitration and reduction reactions.
The denitration and SO3 reduction apparatus 5 is arranged in the combustion flue gas chimney 2, and at least includes a first injection device 6, a second injection device 7, and a catalyst layer 8. The denitration and SO3 reduction apparatus 5 adds a first additive and a second additive to the flue gas and allows the combustion flue gas including the additives to flow through the catalyst layer 8. The denitration and SO3 reduction apparatus 5 performs an SO3 reduction treatment by using the catalyst layer 8, the first injection device 6, and the second injection device 7. It is preferable that the denitration and SO3 reduction apparatus 5 be configured so as to add the first additive and the second additive at the same time.
The first injection device 6 is arranged on a front stream side of the denitration and SO3 reduction apparatus 5 and on a back stream side of the ECO bypass 4, and adds the first additive to the combustion flue gas including SO3 as well as NOx. More specifically, the first injection device 6 collaborates with the catalyst layer 8 to reduce SO3 in the combustion flue gas.
The first additive injected from the first injection device 6 is an SO3 reductant primarily for reduction of SO3 into SO2, and hydrocarbon constituted by carbon element (C) and/or hydrogen element having a capability of reducing SO3 in an oxygen atmosphere can be used. More specifically, the first additive is an additive constituted by one or more selected from the group consisting of: an olefinic hydrocarbon (unsaturated hydrocarbon) expressed by a general formula: CnH2n (n is an integer of 2 to 5), a paraffinic hydrocarbon (saturated hydrocarbon) expressed by a general formula: CmH2m+2 (m is an integer of 2 to 5), alcohols such as methanol (CH3OH) and ethanol (C2H5OH), aldehydes such as acetaldehyde (CH3CHO) and propionaldehyde (C2H5CHO), and aromatic compounds such as toluene (C6H5CH3) and ethyl benzene (C6H5C2H5).
For the 2C-5C olefinic hydrocarbon (unsaturated hydrocarbon), it is preferable to use one or more selected from the group consisting of C2H4, C3H6, C4H8, and C5H10, and it is more preferable to use one or more selected from the group consisting of ≧3C olefinic hydrocarbons including C3H6, C4H8, and C5H10. For the C4H8 and C5H10, a geometric isomer or a racemic body of either one of them can be used. Examples of ≧4C unsaturated hydrocarbons include 1-butene (1-C4H8); 2-butenes (2-C4H8) such as cis-2-butene and trans-2-butene; isobutene (iso-C4H8); 1-pentene (1-C5H10); and 2-pentenes (2-C5H10) such as cis-2-pentene and trans-2-pentene. With this configuration, by reactions expressed by the following expressions (2) to (8), the present invention can contribute to the reduction of SO3 in an oxygen atmosphere and reduce the concentration of SO3 in the combustion flue gas.
SO3+CH3OH+3/4O2→SO2+1/2CO+1/2CO2+2H2O (2)
SO3+C2H5OH+5/42O2→SO2 +CO+CO2+2/5H2O (3)
SO3+C2H4+5/2O2→SO2+CO+CO2+2H2O (4)
SO3+3/2C3H6+41/83O2→SO2+9/4CO+9/4CO2+6H2O (5)
SO3+3/2C3H8+63/8O2→SO2+9/4CO+9/4CO2+6H2O (6)
SO3+3/2C4H8+13/2O2→SO2+3CO+3CO2+6H2O (7)
SO3+C5H10+23/4O2→SO2+5/2CO+5/2CO2+5H2O (8)
If C3H6 is used as the first additive, it is useful if the load of the first additive be 0.1 to 2.0 by molar ratio. If the molar ratio of the first additive is less than 0.1, the oxidation of SO2 may become predominant and thus SO3 may increase, and in contrast, if the molar ratio of the first additive is more than 2.0, then a large amount of unreacted excessive C3H6 may be discharged. By controlling the amount of the first additive in the above-described range, the performance of eliminating SO3 in the combustion flue gas can be improved. The effect of removing SO3 can be obtained outside the range specified above.
The second injection device 7 is arranged close to the first injection device 6, and adds NH3 to the combustion flue gas as the second additive. The second injection device 7 is arranged on a front stream side of the denitration and SO3 reduction apparatus 5 and on a back stream side of the ECO bypass 4, and injects the second additive for denitration of NOx to the combustion flue gas. The second injection device 7 collaborates with the catalyst layer 8 to denitrate NOx.
The catalyst layer 8 is constituted by a catalyst which denitrates the combustion flue gas. It is preferable that the shape of the catalyst arranged in the catalyst layer 8 be a honeycomb shape so that the catalyst can efficiently function also as a denitration catalyst and reduce the pressure drop that may occur during treatment of the combustion flue gas. The honeycomb structure is not limited to a structure with a rectangular section, and can include various shapes such as circular, elliptical, triangular, pentagonal, and hexagonal shapes.
The catalyst arranged in the catalyst layer 8 is a catalyst in which the active component is carried on a carrier which is an oxide, a mixed oxide, and/or a composite oxide. More specifically, examples of the carrier include an oxide of one or more of elements selected from the group consisting of titanium (Ti), silicon (Si), zirconium (Zr), and cerium (Ce) and/or a mixed oxide and/or a composite oxide of two or more of elements selected from the above group. In other words, the carrier at least includes the following form.
Among them, the mixed oxide or the complex oxides selected from the group consisting of TiO2—SiO2, TiO2—ZrO2, and TiO2-CeO2 is preferable, and the complex oxides selected from the above group is more preferable.
The complex oxide can be prepared by a process in which an alkoxide compound, a chloride, a sulfate, or an acetate of the above-described elements is mixed, then the resulting mixture is further mixed with water and then stirred in the form of an aqueous solution or sol for hydrolysis. The complex oxide may also be prepared by a known coprecipitation process instead of the above-described sol-gel process.
The active component is a metal oxide constituted by one or more selected from the group consisting of vanadium oxide (V2O5), tungsten oxide (WO3), molybdenum oxide (MoO3), manganese oxide (Mn2O3), manganese dioxide (MnO2), nickel oxide (NiO), and cobalt oxide (Co3O4). The active component may be one or more selected from the group consisting of silver (Ag), silver oxide (Ag2O), and silver monoxide (AgO). With this configuration, an active metal carried by the catalyst acts as an active site, and thus the denitration of NOx such as NO and NO2 can be efficiently performed in an oxygen atmosphere and the reduction of SO3 in an excess oxygen atmosphere can be performed. It is preferable that the active component, among these metal oxides, include tungsten oxide (WO3).
In addition, for the catalyst, a catalyst prepared by coating or impregnating a metallosilicate-base complex oxide in which at least a part of the aluminum element (Al) and/or silicon element (Si) in a zeolite crystal structure is substituted with one or more selected from the group consisting of titanium element (Ti), vanadium element (V), manganese element (Mn), iron element (Fe), and cobalt element (Co). The above-described metallosilicate can be prepared by using a hydrothermal synthesis method in which at least a part of water glass and silicon element that are the silicon source are mixed with a source of metal element to be replaced and a structure directing agent, and the mixture is placed in an autoclave and processed by using the hydrothermal synthesis method under a high temperature and high pressure.
A first embodiment of the flue gas treatment method according to the present invention will be described by describing its mode of operation of the denitration and SO3 reduction apparatus according to the above-described first embodiment. The flue gas treatment method of the present embodiment at least performs an SO3 reduction treatment.
In the SO3 reduction treatment, the first additive for reducing SO3 and NH3 that is the second additive for reducing NOx are injected from the first injection device 6 and the second injection device 7 to the combustion flue gas including SO3 as well as NOx on a front stream thereof. By allowing the combustion flue gas including the charged additives to flow through the catalyst layer 8 constituted by the denitration catalyst on a back stream side thereof, the NOx denitration treatment and the SO3 reduction treatment are carried out at the same time. In the treatment, it is preferable that the first additive and the second additive be added to the combustion flue gas at the same time.
It is preferable that the SO3 reduction treatment be carried out in a temperature range of 250° C. to 450° C., and it is more preferable to carry out the SO3 reduction treatment in a temperature range of 300° C. to 400° C. If the SO3 reduction treatment is carried out at a temperature below 300° C., the denitration treatment may not be sufficiently completed, and in contrast, if the SO3 reduction treatment is carried out at a temperature above 400° C., the reduction of SO3 may not be sufficient.
According to the present embodiment, NOx in the combustion flue gas including SO3 and/or NOx generated when burned in the boiler can be removed by denitration, oxidation of SO2 can be prevented, and thus the concentration of SO3 can be reduced during treatment of the combustion flue gas, and addition, costs for the material of the catalyst can be reduced because no expensive catalyst is used. Further, the above-described effect of the present embodiment can be achieved merely by additionally installing a first injection device configured to inject the first additive for reducing SO3 on a front stream side of an existing denitration apparatus. Accordingly, the SO3 reduction treatment can be carried out at low cost.
A second embodiment of the denitration and SO3 reduction apparatus according to the present invention will be described in detail with reference to
Referring to
The first injection device 16 is arranged in the combustion flue gas chimney 2 on a front stream side of the first catalyst layer 18 and on a back stream side of the second catalyst layer 19. The first catalyst layer 18 is arranged on a back stream side of the second catalyst layer 19. In addition, the first injection device 16 injects the first additive for reducing the concentration of SO3 to the combustion flue gas.
The second injection device 17 is arranged in the combustion flue gas chimney 2 on a front stream side of the second catalyst layer 19. In addition, the second injection device 17 injects the second additive for denitration of NOx to the combustion flue gas. For the second injection device 17 and the second catalyst layer 19, a denitration apparatus installed in an existing plant can be employed, for example.
For the first additive injected from the injection device 16 and the catalyst installed in the catalyst layer 18, an additive and a catalyst similar to those of the first embodiment can be applied. For the second additive injected from the injection device 17 and the catalyst installed in the second catalyst layer 19, not only an additive and a catalyst similar to those of the first embodiment but also a publicly known catalyst (e.g., V2O5—TiO2) can be applied.
A second embodiment of the flue gas treatment method according to the present invention will be described by describing a mode of operation of the above-described second embodiment of the denitration and SO3 reduction apparatus. The flue gas treatment method of the present embodiment at least performs an SO3 reduction treatment.
In the SO3 reduction treatment, as a pretreatment to a combustion flue gas at least including NOx and SO3, NH3 that is the second additive is added from the second injection device 17 to the combustion flue gas, and the combustion flue gas is brought into contact with the denitration catalyst in the second catalyst 19 arranged on a back stream side of the second injection device 17. Then, as a posttreatment, an additive for SO3 is added from the first injection device 16 to the combustion flue gas, and the combustion flue gas is brought into contact with the catalyst for SO3 in the first catalyst layer 18 arranged on a back stream side of the first injection device 16.
For the treatment temperature for the SO3 reduction treatment, temperature ranges similar to those of the first embodiment can be employed.
According to the denitration and SO3 reduction apparatus and the flue gas treatment method of the second embodiment, SO3 can be more efficiently treated on a back stream side of the existing denitration apparatus, and in addition, the catalyst can be easily exchanged according to degradation of the function of the catalyst used for the denitration and the reduction of SO3, respectively.
[Denitration and SO3 reduction Apparatus]
A third embodiment of the denitration and SO3 reduction apparatus according to the present invention will be described in detail with reference to
Referring to
The first injection device 26 is arranged in the combustion flue gas chimney 2 on a front stream side of the first catalyst layer 28 and on a front stream side of the second catalyst layer 29. The first catalyst layer 28 is arranged on a front stream side of the second catalyst layer 29. The first injection device 26 injects the first additive for reducing the concentration of SO3 to the combustion flue gas. The second injection device 27 is arranged in the combustion flue gas chimney 2 on a front stream side of the second catalyst layer 29. In addition, the second injection device 27 injects the second additive for denitration of NOx to the combustion flue gas. Similarly to the second embodiment, for the second injection device 27 and the second catalyst layer 29 also, a denitration apparatus installed in an existing plant can be applied.
For the first additive injected from the injection device 26 and the catalyst installed in the catalyst layer 28, an additive and a catalyst similar to those of the first and the second embodiments can be applied. In addition, for the second additive injected from the injection device 27 and the catalyst installed in the second catalyst layer 29 also, not only an additive and a catalyst similar to those of the first embodiment but also a publicly known denitration catalyst (e.g., V2O5—TiO2) can be applied.
A third embodiment of the flue gas treatment method according to the present invention will be described by describing a mode of operation of the denitration and SO3 reduction apparatus according to the above third embodiment. The flue gas treatment method of the present embodiment at least performs a SO3 reduction treatment.
In the SO3 reduction treatment, as a pretreatment to a combustion flue gas at least including NOx and SO3, an additive for SO3 is added from the first injection device 26, and the combustion flue gas is brought into contact with the catalyst for SO3 in the first catalyst layer 28 arranged on a back stream side of the first injection device 26. Then, as a posttreatment, NH3 is added from the second injection device 27 to the combustion flue gas as the second additive, and the combustion flue gas is brought into contact with the denitration catalyst in the second catalyst 29 arranged on a back stream side of the second injection device 27.
For the treatment temperature for the SO3 reduction treatment, temperature ranges similar to those of the first and the second embodiments can be employed.
According to the denitration and SO3 reduction apparatus and the flue gas treatment method of the third embodiment, SO3 can be more efficiently treated on a back stream side of the existing denitration apparatus, and in addition, the catalyst can be easily exchanged according to degradation of the function of the catalyst used for the denitration and the reduction of SO3, respectively.
The effects of the present invention will be clarified by more specifically describing the present invention with reference to examples. The flue gas treatment method and the denitration and SO3 reduction apparatus according to the present invention are not limited by the following examples by any means.
By using a different catalyst, the effect of the first additive (SO3 reductant) for reducing SO3 into SO2 were examined.
A catalyst A including ruthenium (Ru), which functions as a catalyst for reducing SO3 into SO2, was prepared. An aqueous solution of ruthenium chloride (RuCl3) was impregnated with an anatase type titania powder including 10 wt. % tungsten oxide (WO3) per 100 wt. % titania (TiO2), thereby 1 wt. % Ru was carried on the powder per 10.0 wt. % of anatase type titania powder, and the resultant was evaporated and dried. Then the residue was fired at 500° C. for 5 hours, and the obtained powder was used as the catalyst A.
(Preparation of Catalyst B)
A catalyst B was prepared as a typical catalyst having a denitration function by ammonia. Ti(O-iC3H7)4, a Ti alkoxide, and Si(OCH3)3, a Si alkoxide, were mixed at a ratio of 95:5 (wt. %) (as TiO2, SiO2, respectively), the mixture was added to 80° C. water for hydrolysis, then the reaction mixture was stirred and matured, the produced sol was filtered, and the obtained gelled product was washed, dried, and heated and fired at 500° C. for 5 hours to obtain a powder of TiO2—SiO2 complex oxide (TiO2—SiO2 powder). Ammonium metavanadate (NH3VO3) and ammonium paratungstate ((NH4)10H10W12O46.6H2O) were impregnated into the complex oxide by using a 10 wt. % aqueous solution of methylamine, 0.6 wt. % V2O5 and 8 wt. % WO3 were carried per 100 wt. % complex oxide, the resultant was evaporated and dried, and then heated and fired at 500° C. for 5 hours. The obtained powder was used as the catalyst B.
A catalyst C, a typical catalyst having a function of denitration by ammonia, was prepared. Ti(O-iC3H7)4, a Ti alkoxide, and Zr(Oi-C4h9)4, a Zr alkoxide, were mixed at a ratio of 95:5 (wt. %) (as TiO2, ZrO2, respectively), the mixture was added to 80° C. water for hydrolysis, then the reaction mixture was stirred and matured, the produced sol was filtered, and the obtained gelled product was washed, dried, and heated and fired at 500° C. for 5 hours to obtain a powder of TiO2—ZrO2 complex oxide (TiO2-ZrO2 powder). Ammonium paratungstate ((NH4)10H10W12O4.6H2O) was impregnated into the complex oxide by using a 10 wt. % aqueous solution of methylamine, 8 wt. % WO3 was carried per 100 wt. % complex oxide, the resultant was evaporated and dried, and then heated and fired at 500° C. for 5 hours. The obtained powder was used as the catalyst C.
A catalyst D containing titania (TiO2) only was prepared. A powder of anatase type titania of the same amount as the catalyst A was fired at 500° C. for 5 hours to prepare a powder of catalyst D.
80 wt. % of water was added respectively to 20 wt. % of catalysts A to D, and the mixture was pulverized by wet ball mill to obtain wash coat slurry. Then a monolith base material (pitch: 7.4 mm, wall thickness: 0.6 mm) produced by Cordierite was coated with the slurry by dipping, and the obtained product was dried at 120° C. and then fired at 500° C. The amount of the coating was 100 g per surface area of 1 m2 of the base material. A case of using the catalyst A and ammonia (NH3) was used as the SO3 reductant was used as Test Example 1. On the other hand, a case of using the catalyst A and propylene (C3H6) was used as the SO3 reductant was used as Test Example 2. A case of using the catalyst B and C3H6 was used as the SO3 reductant was used as Test Example 3. A case of using the catalyst C and C3H6 as the SO3 reductant was used as Test Example 4. In addition, a case of using the catalyst D and C3H6 as the SO3 reductant was used as Test Example 5.
By bench-scale testing in which an actual machine is assumed, the SO3 reductant was added to the combustion flue gas, and the combustion flue gas containing the SO3 reductant was allowed to flow through the catalyst of the respective Test Examples installed in the denitration and SO3 reduction apparatus, and thereby variation of the concentration of SO3 (ppm) in the combustion flue gas in terms of 0.03 to 0.8 (1/AV (m2·h/Nm3) after the combustion flue gas had flowed through the catalyst layer was examined. The test results and the test conditions are shown in
It was observed that in Test Example 1 in which the catalyst A containing Ru was used and NH3 was used as the SO3 reductant, the concentration of SO3 at the inlet of the catalyst layer did not substantially vary. It was observed that in Test Example 2 in which the catalyst A containing Ru was used and C3H6 was used as the SO3 reductant, the concentration of SO3 in the combustion flue gas decreased. In addition, it was observed that in Test Example 3 using the catalyst B not including expensive Ru, by using C3H6 as the SO3 reductant, the concentration of SO3 in the combustion flue gas remarkably decreased. In addition, it was observed that in Test Example 4 using the catalyst C, by using C3H6 as the SO3 reductant, the concentration of SO3 in the combustion flue gas remarkably decreased. Furthermore, it was observed that also in Test Example 5 using the catalyst D, by using C3H6 as the SO3 reductant, the concentration of SO3 in the combustion flue gas remarkably decreased. From these results, it was found that by using C3H6 as the SO3 reductant, concentration of SO3 in the combustion flue gas could be reduced.
It was found that instead of using the catalyst A including Ru, by using a hydrocarbon including hydrogen element (H) and carbon element (C) such as C3H6, concentration of SO3 in the combustion flue gas at the inlet of the catalyst layer could be reduced more even if a normal denitration catalyst was used, compared with the case of using NH3 as the SO3 reductant. Next, based on the elementary reaction model on the surface of the catalyst described in the following items 1 to 4, it was estimated that to obtain these results, sulfonation occurring due to the reaction on the catalyst between the matter obtained by decomposition of hydrocarbon and SO3 was important.
1. Hydrocarbon adsorption reaction
Hydrocarbon (CxHy)+surface→CxHy−surface
2. Hydrocarbon decomposition reaction (hydrogen abstraction reaction)
CxHy−surface→CxHy−1(surface-coordination)+H−surface
3. Reaction with SO3(g)(conversion into sulfonic acid)
CxHy−1(surface-coordination)+SO3(g)→SO2+CxHy−1—SO3−H− surface)
4. Decomposition of SO3
CxHy−1—SO3−H− surface→SO2+CO2+CO
By using a hydrocarbon with a different composition as the first additive (SO3 reductant), the effect of reducing SO3 into SO2 depending on the composition of the 20 hydrocarbon compound was examined.
Similarly to Example 1, the catalyst B was coated on a monolith base material produced by Cordierite. The amount of the coating was 100 g per surface area of 1 m2 of the base material. The case in which C3H6 was used as the SO3 reductant was used as Test Example 6, the case in which propane (C3H8) was used as the SO3 reductant was used as Test Example 7, the case in which methanol (CH3OH) was used as the SO3 reductant was used as Test Example 8, and the case in which ethanol (C2H5OH) was used as the SO3 reductant was used as Test Example 9. In addition, for comparison with the other Test Examples, the case in which ammonia (NH3) was used as the SO3 reductant was used as Test Example 10.
(SO3 removal Test II)
Similarly to Example 1, the SO3 reductant was added to the combustion flue gas, and the combustion flue gas containing the SO3 reductant was allowed to flow through the catalyst layer using the SO3 catalyst installed in the denitration and SO3 reduction apparatus, and thereby variation of the concentration of SO3 in the combustion flue gas at 0.04 to 0.08 m2·h/Nm3 after the combustion flue gas had flowed through the catalyst layer. The variation of the concentration of SO3 before and after the combustion flue gas had flowed through the catalyst layer was examined. The test conditions were the same as those of Example 1. The test results and the test conditions are shown in
Then, further, by using a hydrocarbon having a different composition as the first additive (SO3 reductant), the effect of reducing SO3 into SO2 and the denitration effect depending on the composition of the hydrocarbon compound were examined.
A catalyst E was prepared in a similar manner as the case of preparing the catalyst B except that the ratio of TiO2 and SiO2 was changed to 88:12 (wt. %), that the amount of V2O5 was 0.3 wt. %, and that the amount of WO3 was 9 wt. %.
Similarly to Example 1, the catalyst E was coated onto the monolith base material produced by Cordierite. The case in which methanol (CH3OH) was used as the SO3 reductant was used as Test Example 11, the case in which ethanol (C2H5OH) was used as the SO3 reductant was used as Test Example 12, and the case in which propane (C3H8) was used as the SO3 reductant was used as Test Example 13. In addition, the case in which ethylene (C2H4) was used as the SO3 reductant was used as Test Example 14, the case in which propylene (C3H6) was used as the SO3 reductant was used as Test Example 15, the case in which 1-butene (1-C4H8) was used as the SO3 reductant was used as Test Example 16, the case in which 2-butene (2-C4H8) was used as the SO3 reductant was used as Test Example 17, the case in which isobutene (iso-C4H8) was used as the SO3 reductant was used as Test Example 18.
By using Test Examples 11 to 18, similarly to Example 1, the SO3 reductant was added to the combustion flue gas, and the combustion flue gas containing the SO3 reductant was allowed to flow through the catalyst layer using the SO3 catalyst installed in the denitration and SO3 reduction apparatus, and thereby the variation of the concentration of SO3 and the denitration rate before and after the combustion flue gas had flowed through the catalyst layer was examined. The SO3 reduction rate and the denitration rate were determined in the following manner. The test results and the test conditions are shown in
SO3 reduction rate (%)=(1−concentration of SO3 at catalyst layer outlet/concentration of SO3 at catalyst layer inlet)×100
Denitration rate (%)=(1−concentration of NOx at catalyst layer outlet/concentration of NOx at catalyst layer inlet)×100
In Test Examples 11 and 12 using alcohols, the denitration rate of Test Example 11 was 92.6%, and the denitration rate of Test Example 12 was 93.2%. In Test Examples 13 and 14 using a saturated hydrocarbon and an unsaturated hydrocarbon, the denitration rate of Test Example 13 was 94.1%, and the denitration rate of Test Example 14 was 94.0%, which were high values. In Test Examples 15 to 18 using ≧3C unsaturated hydrocarbons, the denitration rate of Test Example 15 was 95.1%, the denitration rate of Test Example 16 was 92.1%, the denitration rate of Test Example 17 was 92.3%, and the denitration rate of Test Example 18 was 91.8%, which were sufficiently high values.
From the results of Examples 1 and 2, it was found that by using a hydrocarbon including the elements H and C as the SO3 reductant, the concentration of SO3 in the combustion flue gas at the inlet of the catalyst layer decreased. It was also found that by using C3H8, C2H4, C3H6, or C4H8, i.e., a saturated hydrocarbon or an unsaturated hydrocarbon, as the SO3 reductant, the concentration of SO3 in the combustion flue gas decreased more compared with the case of using alcohols such as CH3OH and C2H5OH. Further, it was found that among them, by using C2H4, C3H6, or C4H8, i.e., an unsaturated hydrocarbon, as the SO3 reductant, the concentration of SO3 in the combustion flue gas could be efficiently decreased. It was found that by using ≧3C unsaturated hydrocarbons as the SO3 reductant, in particular, the concentration of SO3 in the combustion flue gas remarkably decreased. It was estimated that this was because the decomposition activity of ≧3C unsaturated hydrocarbons is high and the intermediate body thereof has high reactivity with SO3.
A catalyst having another composition was prepared and the effect of reducing SO3 into SO2 and the denitration rate depending on the catalyst composition was examined.
Ti(O-iC3H7)4, a Ti alkoxide, and Ce(OCH3)4, a Ce alkoxide, were mixed at a ratio of 88:12 (wt. %) (as TiO2, CeO2, respectively), the mixture was added to 80° C. water for hydrolysis, then the reaction mixture was stirred and matured, the produced sol was filtered, and the obtained gelled product was washed, dried, and heated and fired at 500° C. for 5 hours to obtain a powder of TiO2—Ce2O3 complex oxide (TiO2—Ce2O3 powder). The obtained powder was used as the catalyst F.
A catalyst including zirconia (ZrO2) only was prepared. A powder of zirconium oxychloride (ZrOCl2) was fired at 500° C. for 5 hours, and the obtained powder was used as the catalyst G.
A catalyst including cerium oxide (Ce2O3) only was prepared. A powder of cerium nitrate (Ce(NO3)2) was fired at 500° C. for 5 hours, and the obtained powder was used as the catalyst H.
80 wt. % water was added respectively to the TiO2—SiO2 powder of the catalysts D and B, the TiO2—ZrO2 powder of the catalyst C, and the catalysts F, G, and H, of which the amount was 20 wt. %, respectively, and the mixture was pulverized by wet ball mill to obtain wash coat slurry, and then the slurry was coated onto a ceramics base material including kaolinite as its main component, and the obtained pieces were used as Test Examples 19 to 24. Table 1 shows the composition of the respective Test Examples. In Table 1, for the coating amount average value, an average value was used which was obtained by measurement of 2 samples by using values calculated by dividing a carriage amount, which had been obtained based on the difference in the weight before and after the coating by the surface area of the base material.
The capability of reducing SO3 when propylene (C3H6) was used as the SO3 reductant was examined for the respective Test Examples. Similarly to Example 2, the SO3 reductant was added to the combustion flue gas, and the combustion flue gas including the SO3 reductant was allowed to flow through the catalyst layer using the SO3 catalyst installed in the denitration and SO3 reduction apparatus, and thereby variation of the concentration of SO3 before and after the combustion flue gas had flowed through the catalyst layer was examined. The test results and the test conditions are shown in
In addition, in Test Examples 19, 23, and 24 in which an oxide including a single component was used, the denitration rate of Test Example 19 was 32.8%, the denitration rate of Test Example 23 was 6.7%, and the denitration rate of Test Example 24 was 19.1%. On the other hand, in Test Examples 20 to 22 in which a complex oxide containing TiO2 was used, the denitration rate of Test Example 20 was 60.4%, the denitration rate of Test Example 21 was 39.3%, and the denitration rate of Test Example 22 was 42.3%.
From these results, in all of Test Examples 19 to 24, the concentration of SO3 in the combustion flue gas at the inlet of the catalyst layer decreased. In Test Examples 20 to 22 in which the TiO2—SiO2 powder, TiO2—ZrO2 powder, or the TiO2—Ce2O3 powder was used, the SO3 reduction rate was higher than that in Test Examples 19, 23, and 24 in which the TiO2 powder, ZrO2 powder, or the Ce2O3 powder was used. In addition, in Test Examples 19, 23, and 24 in which an oxide including a single component was used, the reduction rate of Test Example 19 in which the TiO2 powder was used was high, and the reduction rate of Test Example 23 in which the ZrO2 powder was used was the highest. In addition, among Test Examples 20 to 22 in which the complex oxide was used, the SO3 reduction rate of Test Example 19 using the TiO2—SiO2 powder was the most remarkable. From these results, it was found that by using a complex oxide containing TiO2, in particular, the SO3 reduction rate could be high. It was estimated that the above results were obtained due to increase of the solid acid amount, which occurred due to the use of the complex oxide.
Then the relationship between the solid acid amount and the SO3 reduction rate was examined. The solid acid amount in Test Examples 19 to 24 was measured by a pyridine thermal adsorption desorption method. More specifically, the same amount of 25 mg of a powder of quartz was added to the respective Test Example and the mixture was fixed in a quartz glass tube with Kaowool. The quartz glass tube was installed in an electric furnace installed in FID gas chromatography, then the reaction mixture was treated under the condition of the temperature of 450° C. for 30 minutes in a helium (He) gas stream. Then the electric furnace was maintained at 150° C., pyridine was injected by 0.5 μl for 4 to 6 times until saturation in terms of pulse was obtained, and the pyridine was adsorbed to the respective Test Examples. Then the temperature of the electric furnace was raised at the rate of 30° C./min, the desorbed pyridine was measured by FID gas chromatography, and the solid acid amount of the respective Test Examples was determined based on the obtained peak value in TPD spectrum.
A catalyst having yet another composition was prepared and the effect of an active metal for reducing SO3 into SO2 and the denitration rate were examined.
Ti(O-iC3H7)4, a Ti alkoxide, and Si(OCH3)3, a Si alkoxide, were mixed at a ratio of 95:5 (wt. %) (as TiO2, SiO2, respectively), the mixture was added to 80° C. water for hydrolysis, then the reaction mixture was stirred and matured, the produced sol was filtered, and the obtained gelled product was washed, dried, and heated and fired at 500° C. for 5 hours to obtain a powder of TiO2—SiO2 complex oxide (TiO2—SiO2 powder). The obtained powder was used as the catalyst H.
80 wt. % water was added to 20 wt. % catalyst H, and the mixture was pulverized by wet ball mill to obtain wash coat slurry, and then the slurry was coated onto a ceramic base material including kaolinite as its main component, and the obtained piece was used as Test Example 25. In addition, a predetermined amount of the respective solution of sulfate or nitrate used as the raw material of V2O5, MoO3, Ag, WO3, Mn2O3, NiO, and Co3O4, respectively, was added to the catalyst H, the solution was impregnated and the component was carried, then the obtained product was coated onto the ceramic base material similarly to Test Example 25, and the resultant product was used as Test Examples 26 to 32. The coating amount for each Test Example was measured similarly to Example 3, i.e., about 100 g/m2. Table 2 shows the composition of the respective Test Examples.
The capability of reducing SO3 when propylene (C3H6) was used as the SO3 reductant was examined for the respective Test Examples. Similarly to Example 2, the SO3 reductant was added to the combustion flue gas, and the combustion flue gas including the SO3 reductant was allowed to flow through the catalyst layer using the SO3 catalyst installed in the denitration and SO3 reduction apparatus, and thereby variation of the concentration of SO3 before and after the combustion flue gas had flowed through the catalyst layer was examined. The test results and the test conditions are shown in
The denitration rate of Test Example 25 was 60.4%. On the other hand, the denitration rate of Test Example 26 was 94.4%, the denitration rate of Test Example 27 was 82.4%, the denitration rate of Test Example 28 was 55.5%, the denitration rate of Test Example 29 was 73.4%, the denitration rate of Test Example 30 was 50.9%, the denitration rate of Test Example 31 was 46.2%, and the denitration rate of Test Example 32 was 44.3%.
From these results, it was verified that the SO3 reduction effect and the denitration effect could be obtained by using C3H6 as the SO3 reductant for all Test Examples in which V2O5, MoO3, Ag, WO3, Mn2O3, MnO2, NiO, or Co3O4 was carried. In Test Examples 27 to 32 in which MoO3, Ag, WO3, Mn2O3, MnO2, NiO, or Co3O4 was carried, a high SO3 reduction effect was observed. The SO3 reduction effect and the denitration effect were observed particularly in Test Example 29 among them, in which WO3 was carried. From this result, it was found that a catalyst impregnated with WO3 was effective.
A catalyst having yet another composition was prepared and both the SO3 reduction capability and the denitration capability were evaluated.
A catalyst I, in which V2O5—WO3 was carried on TiO2, was prepared in a similar manner as the case of preparing the catalyst B except that 0.3 wt. % V2O5 was carried by using ammonium metavanadate and 9 wt. % WO3 was simultaneously carried by using ammonium paratungstate, per 100 wt. % of complex oxide, and the catalyst I was used as Test Example 33.
A catalyst J, in which V2O5—WO3 was carried on a TiO2—SiO2 complex oxide, was prepared in a similar manner as the case of preparing the catalyst B except that 0.3 wt. % V2O5 was carried and 9 wt. % WO3 was simultaneously carried, per 100 wt. % of complex oxide, and the catalyst J was used as Test Example 33. The catalyst J was coated with metallosilicate at 25 g/m2 to obtain a catalyst K, and the obtained catalyst K was used as Test Example 35. The catalyst B was used as Test Example 36. A catalyst L, in which V2O5—WO3 was carried on TiO2, was prepared in a similar manner as the case of preparing the catalyst B except that 0.7 wt. % V2O5 was carried and 9 wt. % WO3 was simultaneously carried, per 100 wt. % of complex oxide, and the catalyst L was used as Test Example 37.
The capability of reducing SO3 when propylene (C3H6) was used as the SO3 reductant was examined for the respective Test Examples. Similarly to Example 2, the SO3 reductant was added to the combustion flue gas, and the combustion flue gas including the SO3 reductant was allowed to flow through the catalyst layer using the SO3 catalyst installed in the denitration and SO3 reduction apparatus, and thereby variation of the concentration of SO3 before and after the combustion flue gas had flowed through the catalyst layer and the denitration rate were examined. The test results and the test conditions are shown in
From these results, it was found that in all these Test Examples, both the high SO3 reduction capability and the high denitration capability could be obtained. In addition, in Test Examples 34 to 37, a high performance of reducing SO3 to SO2 higher than that of Test Example 33 was observed as expected.
According to the flue gas treatment method and the denitration and SO3 reduction apparatus of the present invention, it is made possible to denitrate NOx in the combustion flue gas and reduce the concentration of SO3 in the combustion flue gas at the same time at treatment costs lower than those conventionally.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2014-227577 | Nov 2014 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2015/067449 | 6/17/2015 | WO | 00 |
