JP2014176808A - Nitrous oxide treatment catalyst and purification method of exhaust gas using the nitrous oxide treatment catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nitrous oxide treatment catalyst in which nitrous oxide in exhaust gas such as biomass fuel and coal fuel in which a sulfur (S) content is large can be performed by decomposition treatment; and a purification method of the exhaust gas using the nitrous oxide treatment catalyst.SOLUTION: A nitrous oxide treatment catalyst is the nitrous oxide treatment catalyst in which the nitrous oxide in exhaust gas in which a sulfur (S) content is large is decomposed, is that iron is supported in a silica and alumina support as an active metal, and is that a ratio of a strong acid that is an acidic property quality of the catalyst is large to the total amount of the strong acid and a weak acid, and decomposition treatment of the nitrous oxide in the gas can be performed without receiving affection of the sulfur (S) content.

Description

The present invention relates to a nitrous oxide treatment catalyst for decomposing nitrous oxide (N ₂ O) in exhaust gas discharged from, for example, a fluidized bed treatment facility, and an exhaust gas purification method using the nitrous oxide treatment catalyst. .

In the second evaluation report (1995) of the Intergovernmental Panel on Climate Change (IPCC), as greenhouse gases (Greenhouse Gas: GHG), carbon dioxide (CO ₂ ), methane (CH ₄ ) Nitrous oxide (N ₂ O), hydrofluorocarbon, perfluorocarbon, and sulfur hexafluoride have been designated, and the reduction of greenhouse gases has become an urgent task due to recent stricter regulations.

In this greenhouse gas (GHG), the global warming coefficient of nitrous oxide (N ₂ O) is 310 times that of carbon dioxide (CO ₂ ), and there is an urgent need to reduce its generation amount.

Therefore, conventionally, it has been proposed to reduce the N ₂ O, which is a greenhouse gas, by maintaining the temperature in the free board section of the circulating fluidized bed boiler at a high temperature of 850 to 950 ° C. (Patent Document 1). ).
In addition, a method for decomposing a high concentration of nitrous oxide (N ₂ O) has been proposed (Patent Documents 2 and 3).

JP 2002-130641 A JP 2006-272239 A JP 2006-272240 A

Meanwhile, in a fluidized bed equipment Patent Document 1, when operating at high temperature (850 ° C. or higher), although the generation of nitrous oxide (N ₂ O) is reduced, the fly ash in the exhaust gas by the hot combustion Melting and ash adhesion problems occur in the convection heat transfer section on the wake side. Therefore, in a circulating fluidized bed boiler, there is a problem that performing high temperature combustion exceeding 900 ° C. has many restrictions in terms of equipment and operation.

Therefore, the appearance of a nitrous oxide treatment catalyst that reduces nitrous oxide (N ₂ O) in exhaust gas while operating at a stable operation temperature of 800 to 900 ° C. in a fluidized bed treatment facility is eagerly desired.

  In addition, the catalysts of Patent Documents 2 and 3 described above use zeolite or the like as a carrier and support a catalyst metal such as rhodium, but the catalyst metal rhodium is contained in the sulfur (S) content in the exhaust gas. Since it is very weak and easily poisoned, there is a problem that it is not suitable as a catalyst for decomposition treatment of nitrous oxide in exhaust gas containing a large amount of sulfur (S) such as biomass fuel and coal fuel.

  In view of the above problems, the present invention provides, for example, a nitrous oxide treatment catalyst and a nitrous oxide treatment catalyst capable of decomposing nitrous oxide in exhaust gas rich in sulfur (S) such as biomass fuel and coal fuel. It is an object to provide a method for purifying exhaust gas used.

  A first invention of the present invention for solving the above-described problem is a nitrous oxide treatment catalyst for decomposing nitrous oxide in exhaust gas having a high sulfur (S) content, and iron is applied to silica and an alumina carrier. The nitrous oxide treatment catalyst is characterized in that it is supported as an active metal and the ratio of strong acid is larger than the total amount of strong acid and weak acid.

  A second invention is the nitrous oxide treatment catalyst according to the first invention, wherein the strong acid is obtained by a pyridine adsorption method, and a ratio of the amount of pyridine desorbed at 450 ° C. or higher is a strong acid amount. .

  A third invention is the nitrous oxide treatment catalyst according to the first or second invention, wherein the iron is in a trivalent state.

  A fourth invention is the nitrous oxide treatment catalyst according to any one of the first to third inventions, wherein ammonia, methanol, and isopropyl alcohol are used as the reducing agent.

  According to a fifth aspect of the present invention, there is provided a nitrous oxide treatment characterized in that the nitrous oxide treatment catalyst according to any one of the first to fourth aspects is used and brought into contact with exhaust gas containing nitrous oxide to decompose the nitrous oxide. An exhaust gas purification method using a catalyst.

  A sixth invention uses the nitrous oxide treatment catalyst according to the fifth invention, wherein the exhaust gas is between or after the heat exchanger after being discharged from the circulating fluidized bed boiler. Exhaust gas purification method.

  A seventh aspect of the invention relates to the purification of exhaust gas using the nitrous oxide treatment catalyst according to the fifth aspect of the invention, wherein the exhaust gas is on the downstream side of the dust removing means after being discharged from the circulating fluidized bed boiler. Is in the way.

  According to an eighth invention, in the fifth invention, the exhaust gas is on the downstream side of the dust removing means after being discharged from the circulating fluidized bed boiler, and the exhaust gas after the dust removal is heated again by a heat exchanger. There exists in the purification method of the waste gas using the nitrous oxide processing catalyst characterized by being.

  According to the present invention, for example, it is suitable for use in the decomposition treatment of nitrous oxide in exhaust gas containing a large amount of sulfur (S) such as biomass fuel and coal fuel.

FIG. 1 is a view showing profiles of a test product according to the present invention and a comparative product by temperature programmed desorption (TPD) of pyridine. FIG. 2 is a diagram showing an XPS (X-ray photoelectron spectroscopy) spectrum of Fe zeolite. FIG. 3 is a graph showing the results of the catalyst temperature and N ₂ O removal rate of the test product and the comparative product. FIG. 4 is a schematic diagram of a fluidized bed processing system according to a first embodiment according to the second embodiment. FIG. 5 is a schematic diagram of a fluidized bed processing system according to a second embodiment of the second embodiment. FIG. 6 is a schematic diagram of a fluidized bed processing system according to a third mode according to the second embodiment. FIG. 7 is a relationship diagram of N ₂ O and NOx removal rates using ammonia and propylene. FIG. 8 is a relationship diagram between the supply amount of the in-furnace supply catalyst and the concentrations of N ₂ O and NOx.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, this invention is not limited by this Example, Moreover, when there exists multiple Example, what comprises combining each Example is also included.

The nitrous oxide treatment catalyst and the exhaust gas purification method using the nitrous oxide treatment catalyst according to the present invention will be described below.
The present nitrous oxide treatment catalyst is a nitrous oxide treatment catalyst for decomposing nitrous oxide in exhaust gas containing a large amount of sulfur (S). The nitrous oxide treatment catalyst carries iron as an active metal on a silica and alumina carrier, The ratio of the strong acid that is the acid property of the catalyst is larger than the total amount of the strong acid and the weak acid.
In particular, the ratio of strong acid is preferably 50% or more, more preferably 80% or more.

  Further, it is particularly preferable that the supported metal catalyst is iron and is in a trivalent state because it is good for the decomposition treatment of nitrous oxide. The reason why iron is used as the metal catalyst is that the influence of poisoning due to sulfur (S) contained in the exhaust gas component is smaller than that of, for example, rhodium.

  In the decomposition treatment of nitrous oxide, examples of the reducing agent include nitrogen-based reducing agents such as ammonia and urea, hydrocarbon-based reducing agents such as methane, ethane, propane, propylene, methanol, and dimethyl ether, hydrogen, CO, and the like. Can do. In particular, it is preferable to use ammonia, methanol, or isopropyl alcohol.

  Here, the ratio of “strong acid” and “weak acid” in the acid nature of the catalyst is determined by a pyridine adsorption method, and the ratio of the amount of pyridine desorbed at 450 ° C. or higher is defined as the amount of strong acid.

  The strong acid and the weak acid obtained by the pyridine adsorption method are obtained from the result of the temperature programmed desorption method (TPD) of pyridine.

The temperature programmed desorption method (TPD) of pyridine will be described below.
First, a predetermined amount of catalyst is filled in a reaction tube, pyridine is first introduced in a pulsed state under a flow of helium (He), and this operation is performed until the amount of pyridine leaking from the outlet side of the reaction tube becomes constant. .
Then, after confirming that the amount of pyridine leaking from the outlet side of the reaction tube has become constant, the temperature rise of the catalyst is started. Then, pyridine desorbed from the catalyst is measured with a flame ion detector (FID) of gas chromatography, and the temperature and desorption amount are plotted to obtain a profile of pyridine by the temperature programmed desorption method (TPD).

  FIG. 1 is a view showing profiles of a test product according to the present invention and a comparative product by temperature programmed desorption (TPD) of pyridine.

An example of measurement conditions is shown below.
Reaction tube: Quartz tube (5 × 3 × 200 mm)
Measuring instrument: Gas chromatography, Hydrogen flame ion detector (FID)
Carrier gas: He (10 cc / min) Column temperature: 150 ° C
Catalyst amount: catalyst (6.3 mg), quartz powder (25.0 mg)
Pyridine: 0.3 μl injection / single pulse Test temperature: Adsorption temperature (150 ° C.)
Desorption temperature (150 to 800 ° C. (heating rate: 26 ° C./min))

The catalyst of the test product had an SiO ₂ / Al ₂ O ₃ ratio of 28.9, a specific surface area of 300 m ² / g or more, and an iron (Fe ₂ O ₃ ) loading of 2.8 wt%.
The comparative catalyst had a SiO ₂ / Al ₂ O ₃ ratio of 23.5, a specific surface area of 500 m ² / g or more, and an iron (Fe ₂ O ₃ ) loading of 3.5 wt%.

The results are shown in FIG.
In FIG. 1 and Table 1, peak α shows a weak acid point at a temperature of 280 ° C., peak β shows a weak acid point at a temperature of 365 ° C., peak γ shows a temperature of 490 ° C., and peak δ shows a strong acid point at a temperature of 650 ° C. The proportions of weak acid and strong acid were determined.

As shown in FIG. 1, the catalyst profile (solid line) of the test product has a high ratio of strong acid (1023/1255 = 0.815).
On the other hand, the catalyst profile (broken line) of the comparative product has a small ratio of strong acid (450/890 = 0.506).

In addition, it was determined from the XPS (X-ray photoelectron spectroscopy) spectrum of Fe zeolite whether the supported iron was in a divalent state or a trivalent state.
The result is shown in FIG.

  FIG. 2 is a diagram showing an XPS (X-ray photoelectron spectroscopy) spectrum of Fe zeolite. As shown in FIG. 2, the test product had a larger peak indicating the trivalent state than the comparative product. Thereby, the catalytic function is exhibited in the state of trivalent iron.

Using this catalyst, the performance of the removal rate of nitrous oxide was compared using a simulated gas containing nitrous oxide. Table 2 shows the test conditions and gas composition. At this time, ammonia was used as the reducing agent.
Table 3 shows the SiO ₂ / Al ₂ O ₃ ratio, Fe ₂ O ₃ content, N ₂ O decomposition performance, weak acid, strong acid, and total amount of weak acid and strong acid for the test product and comparative product, respectively.

FIG. 3 is a graph showing the results of the catalyst temperature and N ₂ O removal rate of the test product and the comparative product. From the results of FIG. 3, assuming that the removal rate at 500 ° C. of the test product is 1, the comparative product is about half, about 0.5, and the decomposition power of nitrous oxide is small.

  From the above, when decomposing nitrous oxide contained in exhaust gas containing a large amount of sulfur (S), iron and iron are supported on silica and alumina carriers, and the ratio of strong acid is between strong acid and weak acid. It has been found that it is better to use a larger amount of catalyst relative to the total amount. Further, it is preferable that the ratio of the strong acid is 50% or more, more preferably 80% or more.

Further, as the metal catalyst, it is preferable to use iron and to be in a trivalent state for the decomposition treatment of nitrous oxide.
Also, the iron loading is 2 to 5% by weight, preferably 2 to 3% by weight.

  Next, a method for purifying exhaust gas containing nitrous oxide using the nitrous oxide treatment catalyst of the present invention will be described.

  In the method for purifying exhaust gas containing nitrous oxide according to the present invention, exhaust gas containing nitrous oxide is brought into contact with a nitrous oxide decomposition catalyst to decompose nitrous oxide contained in the exhaust gas.

  Examples of the exhaust gas containing nitrous oxide include exhaust gas having a high concentration of sulfur (S) in gas from a fluidized bed boiler and a circulating fluidized bed boiler.

  In addition, a catalyst part having a nitrous oxide treatment catalyst is installed between or after the heat exchangers after being discharged from the circulating fluidized bed boiler so as to decompose nitrous oxide in the boiler exhaust gas. ing.

  In addition, a catalyst part having a nitrous oxide treatment catalyst is installed on the downstream side of the dust removing means after being discharged from the circulating fluidized bed boiler so as to decompose nitrous oxide in the boiler exhaust gas.

  In addition, a catalyst unit having a nitrous oxide treatment catalyst is installed on the downstream side of the dust removal means after being discharged from the circulating fluidized bed boiler and on the downstream side of the dust-removed exhaust gas heated again by the heat exchanger. In addition, nitrous oxide in boiler exhaust gas is decomposed.

  Next, as a catalyst part using the nitrous oxide treatment catalyst of the present invention, "first and second stationary catalyst parts" installed in a heat transfer part interposed in a boiler flue, dust removal such as a bag filter A fluidized bed processing system including a “third stationary catalyst unit” installed on the downstream side of the means will be described.

FIG. 4 is a schematic diagram of a fluidized bed processing system according to a first embodiment according to the second embodiment. FIG. 7 is a relationship diagram of N ₂ O and NOx removal rates using ammonia and propylene. FIG. 8 is a relationship diagram between the supply amount of the in-furnace supply catalyst and the concentrations of N ₂ O and NOx.
As shown in FIG. 4, the fluidized bed processing system 10A according to the present embodiment is a circulating fluidized bed that performs fluidized bed combustion processing of supplied fuel (biomass fuel F ₁ , coal fuel F ₂ , petroleum coke fuel F ₃ ) F. Boiler 11, heat transfer section 13 that recovers the heat of combustion exhaust gas 12 discharged from circulating fluidized bed boiler 11, and air that is provided on the downstream side of heat transfer section 13 and that is supplied to circulating fluidized bed boiler 11 14, an air preheater 15 that preheats 14, and a bag filter 16 that is provided on the downstream side of the air preheater 15 and removes the dust in the combustion exhaust gas 12. Has at least one superheater (two superheaters 13a ₁ and 13a _{2 in} this embodiment) and at least one economizer (two economizers 13b ₁ and 13b _{2 in} this embodiment). In the heat transfer section 13 Providing at least one or more first electrostatic standing catalyst unit 17, it is to remove the N ₂ O in the combustion exhaust gas 12.
In FIG. 4, reference numeral 18 is a chimney, L _{1 to} L ₄ are combustion exhaust gas lines, L _{11 to} L ₁₃ are fuel supply lines, L ₁₄ is an air supply line for supplying air 14 to the circulating fluidized bed boiler 11, and L ₁₅ Fig. 2 illustrates a startup fuel supply line for supplying startup fuel 22 to the circulating fluidized bed boiler 11.

In the present embodiment, the second superheater 13a ₂ and the primary economizer 13b ₁ of the heat transfer section 13 are respectively located at two locations between the primary economizer 13b ₁ and the secondary economizer 13b ₂ . Although one stationary catalyst unit 17 is provided, the present invention is not limited to this.

The ash 23 from the circulating fluidized bed boiler 11 is cooled by a bed ash cooler 35 and separately collected and processed.
Further, the ash 26 recovered by the bag filter 16 is sent to a metal recovery means 24 for recovering the metal in the ash 26 via the ash recovery line L ₅ , where the recovered metal 25 is separated and then separately recovered and recovered. It is processed.
Metal recovery means recovering metal 25 recovered in 24 by flue catalyst supply unit 27, and supplied to the combustion exhaust gas line L _3, thereby exerting a metal catalysis with flue.

Further, a catalyst (Fe powder, activated carbon, etc.) is sprayed and added to a combustion exhaust gas line L ₃ on the upstream side of the bag filter 16 from a catalyst supply means (not shown) so that N ₂ O in the exhaust gas is further decomposed. Also good.

In the present embodiment, the second stationary catalyst unit 28 is further interposed in the combustion exhaust gas line L ₂ on the downstream side of the heat transfer unit 13, and the combustion exhaust gas 12 is normally disposed in the bypass exhaust gas line L _6. I try to flow.
Then, if necessary, the switching valve 29 is switched to allow the second stationary catalyst unit 28 to pass through to remove N ₂ O in the combustion exhaust gas 12.

Furthermore, in the present embodiment, an in-furnace catalyst supply unit 32 that supplies the in-furnace supply catalyst 31 via the catalyst line L ₇ is provided in the circulating fluidized bed boiler 11 and is discharged from the circulating fluidized bed boiler 11. N ₂ O in the combustion exhaust gas 12 is removed.

As a catalyst for reducing and removing N ₂ O used in each of the first stationary catalyst unit 17 and the second stationary catalyst unit 28 provided in the heat transfer unit 13 in this embodiment, the catalyst of Example 1 described above is used. A nitrous oxide treatment catalyst is used in which iron is supported as an active metal on a silica and alumina support, and the ratio of strong acid, which is an acid property of the catalyst, is larger than the total amount of strong acid and weak acid.
The stationary catalyst is preferably a honeycomb catalyst.

Even in the heat transfer section 13, the temperature of the combustion exhaust gas 12 is 500 ° C. or less on the downstream side of the secondary superheater 13 a ₂ , and is about 350 ° C. on the downstream side of the primary economizer 13 b ₁ . A copper-based catalyst or the like exhibits a catalytic function.
Further, in order to exhibit the catalytic function of the honeycomb type catalyst, the catalytic activity is enhanced by heating means (indirect heating or direct heating) (not shown) as necessary.

  Moreover, as the catalyst shapes of the first stationary catalyst unit 17 and the second stationary catalyst unit 28, a honeycomb type catalyst is suitable.

In the present embodiment, a ceramic filter 19 for removing the dust in the combustion exhaust gas 12 discharged from the circulating fluidized bed boiler 11 is provided on the upstream side of the heat transfer section 13, and the first stationary catalyst section. The catalyst poisoning used in the 17 and the second stationary catalyst unit 28 is prevented.
Since this ceramic filter 19 is installed at a high temperature environment of about 900 ° C., it can carry a catalyst mainly composed of alumina having high temperature durability.
Thereby, N ₂ O can be efficiently removed.

In the present embodiment, a reducing agent supply unit 21 that supplies the reducing agent 20 into the combustion exhaust gas 12 is provided on the upstream side of the ceramic filter 19.
Here, the reducing agent 20 is supplied to promote the reduction process in the first stationary catalyst unit 17 provided in the heat transfer unit 13.

  Examples of the reducing agent 20 include nitrogen-based reducing agents such as ammonia and urea, hydrocarbon-based reducing agents such as methane, ethane, propane, propylene, methanol, and dimethyl ether, hydrogen, CO, and the like.

In particular, as the reducing agent 20, propylene, as shown in FIG. 7, N ₂ O removal ratio of is higher than ammonia is preferable because achieving N ₂ O removal.
This test uses an iron catalyst as the catalyst, the combustion temperature is 500 ° C., N ₂ O is included in the simulated combustion exhaust gas, and the N ₂ O removal rate due to the difference in the reducing agent (ammonia: 114 ppm, propylene: 140 ppm). Asked.

As shown in the results of FIG. 7, ammonia is effective as a reducing agent for denitration, but the removal rate of N ₂ O was slightly low (70%).
In contrast, propylene was ineffective as a denitration function, but the N ₂ O removal rate was as high as 97%.

When the N ₂ O concentration in the combustion exhaust gas 12 exceeds a predetermined threshold, the supply amount of the reducing agent 20 is gradually increased to efficiently remove N ₂ O.

Even when the reducing agent 20 is not supplied, if the N ₂ O can be removed by the catalytic activity of the stationary catalyst part, the reducing agent 20 may be supplied as appropriate. , Not necessarily supply.

Here, the content of N ₂ O contained in the combustion exhaust gas 12 is obtained by an N ₂ O measuring meter (N ₂ O sensor) 30, for example, combustion exhaust gas on the downstream side of the circulating fluidized bed boiler 11. line L _1, the combustion exhaust gas line L ₂ of the downstream side after the heat transfer section 13, each provided in necessary places, such as the combustion exhaust gas line L ₂ of the downstream side after the second static standing catalyst unit 28, the N ₂ O concentration I am trying to measure.

Examples of the N ₂ O sensor 30 include a detector using a non-dispersive infrared absorption method (NDIR method) and a gas chromatograph / electron capture detector (ECD). It is not limited to.

When the N ₂ O concentration in the combustion exhaust gas 12 is high, the combustion of the circulating fluidized bed boiler 11 is controlled, the fuel type is changed, the type of the reducing agent 20 is changed as appropriate, and the amount of N ₂ O discharged Maintains a predetermined emission standard.

Here, means for reducing the N ₂ O emission amount by controlling the fuel will be described.
As the fuel F, for example, in addition to the biomass fuel F ₁ , which generates less N ₂ O than the coal fuel F ₂ or the like, for example, waste tires, industrial waste solidified materials (for example, Refuse Derived Fuel: RDF, Refuse Paper & Plastic Fuel (RPF)), sludge ash fuel, etc. can be used.

First, as the fuel F, for example, biomass fuel F ₁ is used, and combustion is started in the circulating fluidized bed boiler 11. The combustion start temperature is assumed to be from 850 ° C. which is an upper limit temperature of 800 ° C. to 850 ° C. which is a preferable combustion temperature in the circulating fluidized bed boiler 11.

In general, the combustion of biomass fuel F ₁ is considered to generate little N ₂ O, but due to differences in the composition and type of biomass fuel F ₁ , if combustion is continued for a predetermined time at 850 ° C., the concentration of N ₂ O May reach a predetermined reference value (for example, 10 ppm).
When this predetermined standard is reached, the combustion temperature is set slightly higher (for example, 860 ° C.), and the amount of N ₂ O generated is reduced by high-temperature combustion.

Thus, by using the biomass fuel F _1, it is possible to maintain the combustion of the low N ₂ O.
When the removal of N ₂ O in the heat transfer section 13 is appropriate, the catalyst in the second stationary catalyst section 28 and the flue catalyst supply section 27 on the downstream side is not necessary.

Therefore, in this case, the combustion exhaust gas 12 is allowed to pass through the bypass exhaust gas line L ₆ that bypasses the second stationary catalyst unit 28, and the supply of the recovered metal 25 is stopped.
In contrast, in N ₂ O sensor 30 installed in the combustion exhaust gas line L ₂ of the downstream side of the downstream side of the combustion exhaust gas line L ₂ and the second electrostatic standing catalyst portion 28 of the heat transfer section 13, N ₂ O When the concentration exceeds a predetermined value (10 ppm), a switching valve 29 interposed between the reheating unit 34 and the second stationary catalyst unit 28 so as to pass through the second stationary catalyst unit 28. Or the supply of the recovered metal 25 is started to remove N ₂ O.

In addition, even if it is below a normal predetermined value (N ₂ O: 10 ppm), N ₂ O is removed by passing and supplying these catalysts. Therefore, N ₂ O discharged from the chimney 18 to the outside is removed. It can contribute to lowering the emission concentration.

Then, when measures are taken to reduce N ₂ O by increasing the combustion temperature, for example, when the temperature reaches 900 ° C., the fuel F is switched from, for example, biomass fuel F ₁ to coal fuel F ₂ and petroleum coke fuel F ₃ to flow Continue layer combustion.

When combustion is performed using coal fuel F ₂ or petroleum coke fuel F ₃ having a large amount of fixed carbon, in addition to removal of N ₂ O by a stationary catalyst, an in-furnace supply catalyst 31 is further supplied from the in-furnace catalyst supply unit 32. Is gradually introduced into the circulating fluidized bed boiler 11 to decompose and remove N ₂ O in the circulating fluidized state, and the N ₂ O concentration of the combustion exhaust gas 12 discharged from the circulating fluidized bed boiler 11 is discharged from the biomass fuel F ₁ . The N ₂ O sensor 30 is used to monitor and reduce the amount to the same level as the amount.

Thus, in the catalyst of the static standing, treatment with biomass fuels N of the combustion exhaust gas 12 in using F _{1 2} O concentration similar to the first static-standing catalyst unit 17, the second electrostatic standing catalyst unit 28 Therefore, N ₂ O can be reduced.

Here, as the furnace supply catalyst 31, for example, aluminum oxide (alumina: Al ₂ O ₃ ), calcium oxide (CaO), or the like can be used.

  Here, the supply amount of the in-furnace supply catalyst 31 supplied to the circulating fluidized bed boiler 11 may be 100% that completely replaces the fluidized material. In this case, since the supply amount of the in-furnace supply catalyst 31 is increased, the running cost is increased.

As described above with reference to FIG. 7, ammonia is effective as a reducing agent for denitration, but the removal rate of N ₂ O is slightly low (70%).
On the other hand, propylene is ineffective as a denitration function, but the N ₂ O removal rate is as high as 97%.
Therefore, in the case where the in-furnace supply catalyst 31 is supplied and the reducing agent 20 is used, propylene is first used as the reducing agent, and then when the supply of alumina as the in-furnace supply catalyst 31 exceeds 30 wt%, By switching to ammonia as the reducing agent, efficient removal of N ₂ O can be performed.

In this case, when alumina is supplied as the in-furnace supply catalyst 31, since NOx is not generated at the beginning of supply, N ₂ O is removed using propylene. Then, when the supply of alumina is increased and the amount of NOx generated due to the action as an oxidation catalyst increases, when the alumina supply exceeds 30 wt%, the reducing agent 20 is switched from propylene to ammonia so that denitration is efficiently performed. Yes.
Be switched reducing agent 20 to ammonia, as shown in FIG. 8, the concentration of N ₂ O is reduced, even those slightly lower N ₂ O removal efficiency compared to propylene, N ₂ O removal is surely performed.

In this manner, the biomass fuel F ₁ is sequentially switched from the coal fuel F _{2 to} the petroleum coke fuel F ₃ and burned in the circulating fluidized bed boiler 11. As a result, the N ₂ O sensor 30 exceeds the predetermined reference value. In this case, if the operation is continued any longer, N ₂ O exceeding the reference value is released to the outside together with the combustion exhaust gas 12, so that the N ₂ O emission from the current fuel state (for example, petroleum coke fuel F ₃ ). The biomass fuel F ₁ is reduced and the combustion is restarted at 850 ° C.
Thus, by using the biomass fuel F ₁ low emissions of N ₂ O, it is possible to continue the operation.

As described above with reference to the embodiments, according to the present invention, N ₂ O in combustion exhaust gas can be efficiently removed when combustion is performed in a fluidized bed boiler using different types of fuel. As a result, the fluidized bed boiler combustion can be performed with a low warming coefficient of 310 times that of carbon dioxide (CO ₂ ) and low N ₂ O emission.

Note that, in the decomposition treatment of N ₂ O by the in-furnace mixed catalyst method in the circulating fluidized bed boiler 11 using the in-furnace supplied catalyst, the consumption amount of the input catalyst becomes the running cost as it is, so that it is steady. It can be difficult to operate.
However, when the fuel type is various and it is necessary to follow load fluctuations such as factory operation, the combined use with the decomposition treatment of N ₂ O by the stationary catalyst parts 17 and 28 with low running cost is possible. , Fluidized bed boiler combustion with less N ₂ O emission can be performed.

  Further, in this embodiment, the circulating type circulating fluidized bed boiler is used as the fluidized bed boiler. However, the present invention is not limited to this, and may be applied to, for example, a bubble type fluidized bed boiler. it can.

FIG. 5 is a schematic diagram of a fluidized bed processing system according to a second embodiment of the second embodiment. The same members as those of the fluidized bed processing system 10A according to the first embodiment of the second embodiment are denoted by the same reference numerals, and the description thereof is omitted.
As shown in FIG. 5, the fluidized bed processing system 10B according to the present embodiment branches and circulates the exhaust gas from the combustion exhaust gas line L ₄ on the downstream side of the bag filter 16 and then returns to the circulating fluidized bed boiler 11 side. A line L ₈ is provided, and a heat exchanger 36 and a third stationary catalyst unit 37 are interposed in the branch / circulation line L ₈ .

Some fuel F in the circulating fluidized bed boiler 11 has a large amount of dust in the fuel exhaust gas 12. When processing such flue gas 12, dust is removed by the bag filter 16, the exhaust gas is reheated by the heat exchanger 36, and then N ₂ O is decomposed through the third stationary catalyst unit 37. -It can be removed.

As a catalyst for reducing and removing N ₂ O used in the third stationary catalyst part 37, iron is supported as an active metal on the silica and alumina carrier of Example 1 described above, and the acid property of the catalyst. A nitrous oxide treatment catalyst is used in which the ratio of strong acid is greater than the total amount of strong acid and weak acid. The stationary catalyst is preferably a honeycomb catalyst.

The reheating of the combustion exhaust gas 12 may be either indirect heating or direct heating. For example, in the case of indirect heating, as shown in FIG. 5, in a heat exchanger 36 of a fluidized bed inner tube of the circulating fluidized bed boiler 11. Heat exchange is performed, for example, the temperature is raised to about 300 to 400 ° C., and then the heated exhaust gas is passed through the third stationary catalyst unit 37 to decompose and remove N ₂ O in the exhaust gas.

In the case where bypass lines L ₂₀ , L ₂₁ , and L ₂₂ that bypass the ceramic filter 19 and the first stationary catalyst parts 17 and 17 in the heat transfer part 13 are provided, and the dust concentration in the combustion exhaust gas 12 is high. The switching valve 29 is switched to pass through the first stationary catalyst unit 17 and the second stationary catalyst unit 28 and dust is removed by the bag filter 16, and then the switching valve 33 is switched to change the combustion exhaust gas 12. After being introduced into the branch / circulation line L ₈ and heated by the heat exchanger 36, the exhaust gas is heated by passing through the third stationary catalyst unit 37 to decompose and remove N ₂ O in the exhaust gas. ing.

As a result, in the case of the combustion exhaust gas 12 with a large amount of dust, the ceramic filter 19, the first stationary catalyst parts 17, 17 and the second stationary catalyst part 28 are bypassed to poison these catalysts. After the dust is removed by the bag filter 16, the switching valve 33 is switched, the combustion exhaust gas 12 is introduced into the branch / circulation line L ₈ , heated by the heat exchanger 36, and then the third stationary catalyst unit 37. The N ₂ O in the combustion exhaust gas 12 can be decomposed and removed.

FIG. 6 is a schematic diagram of a fluidized bed processing system according to a third mode according to the second embodiment. The same members as those in the fluidized bed processing systems of Examples 1 and 2 are denoted by the same reference numerals, and the description thereof is omitted.
As shown in FIG. 6, the fluidized bed processing system 10 </ b> C according to the present embodiment is provided with a branch / circulation line L ₈ that branches from the combustion exhaust gas line L ₄ on the downstream side of the bag filter 16. ₈ includes a heat exchanger 36 and a third stationary catalyst unit 37.
In this embodiment, a heat exchanger 36 is installed in a bed ash cooler 35 that cools the ash 23 discharged from the circulating fluidized bed boiler 11, and the exhaust gas is heat-exchanged and raised to, for example, about 300 to 400 ° C. The gas is passed through the third stationary catalyst unit 37 to decompose and remove N ₂ O in the exhaust gas.

Here, in this embodiment, a third stationary catalyst unit 37 is added to the fluidized bed processing system in which the ceramic filter 19, the first stationary catalyst units 17 and 17, and the second stationary catalyst unit 28 are installed. However, the present invention is not limited to this, and the processing in which the ceramic filter 19, the first stationary catalyst parts 17 and 17, and the second stationary catalyst part 28 are not installed is provided. In the system, a heat exchanger 36 and a third stationary catalyst unit 37 are provided in the branch / circulation line L ₈ , dust is removed by the bag filter 16, and then the exhaust gas is reheated by the heat exchanger 36, and then 3, N ₂ O in the flue gas 12 having a high dust concentration may be decomposed and removed through the stationary type catalyst unit 37.

10A to 10C Fluidized bed treatment system 11 Circulating fluidized bed boiler 12 Combustion exhaust gas 13 Heat transfer unit 14 Air 15 Air preheater 16 Bag filter 17 First stationary catalyst unit 20 Reducing agent 21 Reducing agent supply unit 28 Second stationary type Catalyst part 31 Furnace supplied catalyst 36 Heat exchanger 37 Third stationary catalyst part F ₁ biomass fuel F ₂ coal fuel F ₃ petroleum coke fuel

Claims (8)

A nitrous oxide treatment catalyst for decomposing nitrous oxide in exhaust gas rich in sulfur (S),
In addition to supporting iron as an active metal on a silica and alumina support,
A nitrous oxide treatment catalyst characterized in that the ratio of strong acid is large relative to the total amount of strong acid and weak acid. In claim 1,
The strong acid is obtained by a pyridine adsorption method, and the ratio of the amount of pyridine desorbed at 450 ° C. or higher is defined as the strong acid amount. In claim 1 or 2,
A nitrous oxide treatment catalyst, wherein the iron is in a trivalent state. In any one of Claims 1 thru | or 3,
A nitrous oxide treatment catalyst using ammonia, methanol, or isopropyl alcohol as a reducing agent.   An exhaust gas using a nitrous oxide treatment catalyst, wherein the nitrous oxide treatment catalyst according to any one of claims 1 to 4 is contacted with an exhaust gas containing nitrous oxide to decompose nitrous oxide. Purification method. In claim 5,
A method for purifying exhaust gas using a nitrous oxide treatment catalyst, characterized in that the exhaust gas is between or after the heat exchanger after being discharged from a circulating fluidized bed boiler. In claim 5,
An exhaust gas purification method using a nitrous oxide treatment catalyst, characterized in that the exhaust gas is on the downstream side of the dust removing means after being discharged from the circulating fluidized bed boiler. In claim 5,
The exhaust gas is on the downstream side of the dust removing means after being discharged from the circulating fluidized bed boiler,
A method for purifying exhaust gas using a nitrous oxide treatment catalyst, wherein the dust-exhausted exhaust gas is heated again by a heat exchanger.

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