JP2007138887A - Method and device for purification of exhaust gas containing particulate matter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and a device for purifying exhaust gas containing particulate matters wherein in the case of exhaust-gas purification, NO<SB>2</SB>is generated without oxidizing SO<SB>2</SB>into SO<SB>3</SB>, a small space suffices for evaporation and dispersion of a reducing agent to be blown through in the form of an aqueous solution, and constitutional miniaturization can be achieved. <P>SOLUTION: The exhaust gas purification method aims at removal of nitrogen oxides and unburned-carbon-containing particulate matters in the exhaust gas. In the purification, a mixed solution containing ammonium nitrate and either one of ammonia or urea is blown through, or alternatively individual solutions of the above are blown through the exhaust gas in advance, and then the gas is conducted to a dust collector in which a filter device 4 or inertial impaction is employed. Then, the exhaust gas is passed through a catalytic layer 5 having the function of accelerating the denitration reaction, in which ammonia or urea is employed as the reducing agent. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a purification method and apparatus for particulate matter-containing exhaust gas, and more particularly to a method and apparatus for removing particulate matter (PM) mainly composed of unburned carbon and nitrogen oxides contained in the exhaust gas. Especially in the purification of diesel engine exhaust gas, it prevents the generation of SO ₃ that becomes a problem when SO ₂ is contained in the exhaust gas, and efficiently removes and detoxifies nitrogen oxides by increasing the dispersibility of the reducing agent. The present invention relates to an exhaust gas purification method and apparatus suitable for the above.

Diesel engines are one of those most efficient of the internal combustion engine, a constant output per dioxide (CO ₂₎ emissions low, thereon, because the available fuel low quality, such as heavy oil, is excellent in economical Yes. For this reason, in recent years, vehicles and stationary power generation facilities using diesel engines (DE) with high energy utilization efficiency and low CO ₂ emissions to prevent global warming have been reviewed and tend to be used frequently.

Diesel engines that use heavy oil or light oil as fuels have many particulate materials that integrate unburned hydrocarbons and soot, and are the cause of pollution. For this reason, research and development on removal of particulate matter (PM) has been promoted in various directions, such as diesel engine manufacturers and automobile manufacturers, and filters with excellent removal performance, oxidation catalysts on the front and filters are supported by oxidation catalysts In addition, research and inventions have been made on PM filters (DPF) that can prevent soot clogging for a long period of time by burning soot using nitrogen monoxide (NO) in the exhaust gas as nitrogen dioxide (NO ₂ ). (Patent Document 1). Many of these inventions aim to filter exhaust gas through a thin wall of porous ceramics of several μm, and the shape thereof is a plate or cylindrical metal or ceramic sintered filter, Known is a filter in which the eyes of a honeycomb-shaped ceramic porous molded body are alternately filled, and a filter made of a fine metal wire woven fabric. Furthermore, in order to prevent or alleviate such clogging, it is known that these filters have a function of oxidizing NO to NO ₂ to oxidize and burn soot (Patent Documents 2 and 3).

On the other hand, DE tends to generate NOx, and its concentration is as high as several hundred to several thousand ppm. For this reason, a denitration catalyst used for boiler exhaust gas denitration and the like is installed after the DPF, and a method of removing NH ₃ and urea using a reducing agent is beginning to spread (automotive technology, Vol57 (9), 2003, P17 ~ 99 etc.).
Industrial Environmental Management Association, Environmental Management Vol.37, p441-449 JP-A-1-318715 JP-A-60-235620

  When PM removal and denitration are performed using the above-described conventional technology, as shown in FIGS. 4 and 5, a NO oxidation catalyst and a filter or a filter with a NO catalyst and denitration are sequentially provided in the exhaust pipe of a diesel engine (DE). A catalyst was installed to treat the exhaust gas. Both types have excellent characteristics such as high PM collection efficiency and high NOx removal efficiency, but applications that require compactness such as purification of DE exhaust gas using light oil or heavy oil, automobiles, and small stationary power generation facilities The following points to be improved are left for use in

(1) noble metal-supported NO oxidation catalyst or noble metal-supported DPF installing to promote oxidation of PM generates a SO ₃ by oxidizing the SO ₂ contained in the exhaust gas as well as the oxidation of NO, Ya pollution such as asthma This is the cause of rusting around buildings.

(2) When a noble metal is used as an oxidation active component of NO, SO ₃ produced by oxidation of SO ₂ is adsorbed on the surface of the noble metal to reduce its activity. In particular, the deterioration is remarkable at a low temperature, and it is difficult to generate NO ₂ necessary for oxidizing PM at 300 ° C. or lower. For this reason, when DE is operated for a long time with a low temperature and low load, PM accumulates and causes a problem of blocking the DPF.

  (3) Ammonia or urea water, which is a reducing agent, is sprayed into the exhaust gas at the downstream of the DPF and led to the denitration catalyst. Therefore, between the DPF and the denitration catalyst for vaporization and mixing of ammonia (water) and urea water You must take a large distance. As a result, the apparatus is large-sized, and not only automobiles but also small stationary DEs are limited in installation locations and lack compactness.

The object of the present invention is to eliminate the above-mentioned drawbacks of the prior art, generate NO ₂ without oxidizing SO ₂ to SO ₃ , and reduce the space required for vaporizing and dispersing the reducing agent blown with an aqueous solution, making it compact It is an object of the present invention to provide a method and apparatus for purifying exhaust gas containing particulate matter.

To achieve the above object, the invention claimed in the present application is as follows.
(1) In a method for removing nitrogen oxides and particulate matter containing unburned carbon contained in exhaust gas, a mixed solution containing ammonium nitrate and ammonia or urea is blown into the exhaust gas in advance, or both After the individual solution is blown, it is guided to a filter device or a dust collector using inertial collision, and then passed through a catalyst layer having a function of promoting denitration reaction using ammonia or urea as a reducing agent. Purification method.
(2) A mixed solution containing ammonium nitrate and ammonia or urea, or an individual solution of the two is an ammonium nitrate aqueous solution, a mixed solution of ammonium nitrate and ammonia, a mixed solution of ammonium nitrate and urea, a mixed solution of nitric acid and ammonia, and nitric acid and urea. (1) The exhaust gas purification method according to (1), which is a mixed solution of the above or a combination thereof.
(3) A means for injecting a mixed solution containing ammonium nitrate and ammonia or urea into the exhaust pipe of the combustion apparatus, or an individual solution of the both, and unburned carbon contained in the exhaust gas provided downstream of the injecting means. A filter device that can collect or a dust collector that uses inertial collision, and a catalyst layer that is provided downstream of the dust collector and promotes a denitration reaction using ammonia or urea as a reducing agent. Exhaust gas purification device.
(4) A mixed solution containing the ammonium nitrate and ammonia or urea or a separate solution of the two is an ammonium nitrate aqueous solution, a mixed solution of ammonium nitrate and ammonia, a mixed solution of ammonium nitrate and urea, a mixed solution of nitric acid and ammonia, and nitric acid and urea. The exhaust gas purifying apparatus according to (3), which is a mixed solution of the above or a combination thereof.

The principle and operational effects of the present invention will be described with reference to the block diagram of FIG. 1 in which devices necessary for the present invention are arranged. The apparatus of FIG. 1 includes a blowing means (injection nozzle) 3 such as ammonium nitrate (ammonium nitrate), which is sequentially provided in an exhaust pipe 2 of a diesel engine (DE) 1, a filter device 4, and a denitration catalyst device 5.
(1) First, a mixed aqueous solution containing ammonium nitrate (ammonium nitrate) and a reducing agent such as ammonia is blown into the exhaust gas from the diesel engine 1 using a fuel having a high sulfur content such as A heavy oil. The solution thus blown is immediately evaporated by the heat of the exhaust gas, and ammonium nitrate (ammonium nitrate) and the reducing agent are gasified.
(2) Gasified ammonium nitrate reacts with NO contained in the combustion exhaust gas in the gas phase and on the filter as shown in Formula 1 to generate NO ₂ .
NH ₄ NO ₃ + NO → NO ₂ + N ₂ + 2H ₂ O (1 formula)
(3) The filter 4 collects PM contained in the exhaust gas, and is oxidized and removed by the NO ₂ generated in (2) as shown in equation (2).
Carbon (PM) + 2NO ₂ → CO ₂ + 2NO (2 sets)
(4) NOx in the exhaust gas, unreacted NO ₂ , and the injected reducing agent pass through the filter 4, and NOx reacts with the reducing agent by the action of the denitration catalyst 5 in the rear stream part to produce harmless nitrogen. Reduced / removed.

In the present invention, NO ₂ required for oxidation removal of PM is generated by one set. The reaction in Formula 1 proceeds only with NO and does not oxidize SO ₂ to SO ₃ . As a result, white smoke and pollution are not generated by SO ₃ mist. In addition, there is no concern about catalyst degradation due to SO ₃ , and it is effective for PM removal and denitration at low temperatures.

  In the present invention, the mixed solution of ammonium nitrate and the reducing agent is sprayed before the filter. For this reason, even when the vaporization is not sufficiently performed, the vapor is collected by a filter having a large heat capacity, and the evaporation is accelerated by the latent heat. Therefore, the time for vaporization can be shortened. Moreover, since the exhaust gas and the reducing agent are mixed in the process of passing through the complicated flow path in the filter, a mixer is not necessary. By these effects, the distance between reducing agent injection, DPF, and denitration catalyst can be shortened, and an extremely compact device can be configured.

  In the present invention, the ammonium nitrate and reducing agent may be blown in a mixed state or in separate lines. However, preparing a mixed solution in advance and blowing it with a two-fluid nozzle or one-fluid nozzle requires less equipment. However, if you want to have a separate PM removal rate or NOx removal rate, use a separate line. Since they may be blown in, they can be appropriately selected and used. The concentration is not particularly limited, but considering transportation, freezing in winter, etc., about 30 to 40% are likely to give good results.

Moreover, the filter of this invention uses the well-known thing used for PM collection of DE. For example, a porous cordierite honeycomb flow path is alternately filled with plugs to form a filter structure, a ceramic foam, a metal woven fabric or a metal mesh laminate, or Japanese Patent Application Laid-Open No. 2005-177733. Any filter structure that uses a corrugated ceramic non-woven fabric disclosed so far and has a function of accumulating PM (soot) may be used. Further, when there is a large amount of ash such as A to C heavy oil, accumulation of ash gradually occurs even if the soot can be removed by NO ₂ , so that it is possible to provide an ash removal function by ash extraction or water washing. Furthermore, titanium oxide, aluminum oxide and the like effective for promoting the reaction of one set can be supported and used.

As the denitration catalyst, a catalyst using known titanium oxide, Cu-zeolite, Fe-zeolite or the like disclosed in JP-A-50-128681 can be used, but the concentration of SO _{2 in} the exhaust gas can be used. When the thickness is high, the Ti—W—V system or the Ti—Mo—V system is desirable because of its high durability. Since the shape of the catalyst is also removed by DPF, any shape such as granular, plate or honeycomb can be used, but a plate or honeycomb having a small pitch is preferable because of its low pressure loss. .

FIG. 2 is a flowchart showing an embodiment of the present invention using a mixed solution of ammonium nitrate and NH ₃ . In FIG. 2, exhaust gas from the diesel engine 1 is guided to the exhaust pipe 2, and a mixed solution of ammonium nitrate and NH ₃ water is sprayed from the two-fluid nozzle 3 through the storage tank 6 through the pump 8. Thereafter, the exhaust gas is purified by sequentially passing through the DPF 4 and the honeycomb-shaped denitration catalyst 5 which function as a filter by alternately plugging the channels of the cordierite porous honeycomb disposed in the flow section. . An aqueous solution of ammonium nitrate and NH ₃ is prepared by dissolving ammonium nitrate in 10-28 wt% NH ₃ water, and the molar ratio of NH ₃ / ammonium nitrate is the number of ammonium moles required for PM oxidation of formula 2 / denitration. It is selected to be greater than the required NH ₃ mole ratio and is usually operated around 0.2 mole / mole. Filter 4 is filled with 300 cells / in 2 of cordierite DPF with SV = 10,000 to 40,000 h-1, and denitration catalyst 5 contains Ti / W / V catalyst components at 280 cells / in 2 of silica. A catalyst supported at 200 g / liter on an alumina-based inorganic fiber nonwoven fabric corrugated carrier is filled. In the figure, 7 is an air injection line.

FIG. 3 is different from the embodiment of FIG. 2 in that an ammonium nitrate storage tank 10 and a reducing agent storage tank 11 are provided, and an aqueous ammonium nitrate solution and NH ₃ used as a reducing agent via a pipe 10, a pump 8, and a pipe 9, respectively. It is a flowchart which shows the Example at the time of inject | pouring aqueous solution with another line, and laminating | stacking the metal lath made from SUS on a filter, and using it as a filter.

Hereinafter, the present invention will be described in detail using specific examples.
[Example 1]
Cut from a commercial DPF made of porous cordierite ceramic (manufactured by Hitachi Metals, 300 cps cells, each cell 5.66 inches φ × 6 inches long) to a cross section of 30 mm × 30 mm-length 50 mm, and the flow paths alternate with ceramic adhesive A small DPF was created.

Separately, a slurry in which a powder of Ti-WV catalyst (TI / W / V atomic ratio = 88/10/3) is suspended in water on a silica-alumina based inorganic fiber corrugated honeycomb carrier (manufactured by NICHIAS, model number 3722). After impregnating and coating with 200 g / liter of the catalyst component, it was calcined at 500 ° C. for 2 hours. The obtained catalyst body was cut into a size of a cross section of 30 mm × 30 mm and a length of 50 mm to obtain a small denitration catalyst.
The above small DPF and small denitration catalyst are installed in series in the reaction tube, and 20% by weight of ammonium nitrate water is atomized with an ultrasonic atomizer upstream of the DPF to inject into the reaction tube with a small amount of air. A nozzle was provided, and a test apparatus having the same configuration as in FIG. 1 was produced.

Using this equipment, in order to confirm that NO ₂ is generated without oxidizing SO _2, which is a feature when using ammonium nitrate, it is processed with the simulated gas and processing conditions shown in Table 1, and the NO generation concentration and SO _{2 The} oxidation rate was examined. The obtained results are shown in Table 2. When PM is present, NO ₂ consumption occurs. On the other hand, when a reducing agent is added, NO and NO ₂ are consumed by the denitration reaction. Therefore, the simulation gas was used under conditions that do not contain PM and a reducing agent.

[Comparative example]
The small DPF prepared in Example 1 was impregnated with titania sol (manufactured by Ishihara Sangyo Co., Ltd., TIO ₂ content 30% by weight), drained with a centrifuge, supported with 60 g / L of TiO ₂ , dried at 150 ° C. and dinitro A diammine platinum acid solution was impregnated so that the amount of Pt supported on DPF was 0.3 g / L, dried, and calcined at 600 ° C. for 2 hours to prepare a small DPF with catalyst.

The DPF of the apparatus of Example 1 was replaced with the above DPF, and the NO ₂ generation concentration and the SO ₂ oxidation rate were measured without injection of ammonium nitrate. The obtained results are shown in Table 2.
As is apparent from Table 2 comparing the results with Example 1 and the comparative example, according to the present invention, it becomes possible to generate NO ₂ without oxidizing SO ₂ to SO _{3. 3} Pollution caused by mist and generation of white smoke can be prevented. In addition, since the present invention does not use a noble metal catalyst, SO ₃ is adsorbed on the noble metal at a low temperature to reduce the activity, and there is no problem that sufficient NO ₂ cannot be generated. As a result, NO ₂ can be efficiently generated in a wide temperature range, and PM can be efficiently removed even in a low temperature range where the engine load is low.

  Since the ammonium nitrate of the present invention can be arbitrarily mixed with ammonia or urea, a conventional denitration reducing agent injection line can be used as it is. Furthermore, it is possible to blow the reducing agent in the upstream of the DPF and use the DPF for promoting evaporation and mixing, and it is possible to realize an extremely compact exhaust gas purification apparatus because no mixing equipment or dead space is required.

The block diagram which arranged the apparatus required for this invention. Flow diagram illustrating an embodiment of the present invention using a mixed solution of ammonium nitrate and NH _3. The flowchart which shows the Example of this invention. The flowchart which shows a prior art. The flowchart which shows a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Diesel engine, 2 ... Exhaust pipe, 3 ... Injection nozzle, 4 ... Filter, 5 ... Denitration catalyst, 6 ... Ammonium nitrate-reducing agent mixed solution storage tank, 7 ... Air injection line, 8 ... Pump, 9, 10 ... Piping 11 ... Ammonium nitrate storage tank, 12 ... Reducing agent storage tank.

Claims (4)

In a method for removing nitrogen oxides and particulate matter containing unburned carbon contained in exhaust gas, a mixed solution containing ammonium nitrate and ammonia or urea is previously blown into the exhaust gas, or separate solutions of the two are used. A method for purifying exhaust gas, characterized in that after blowing, the exhaust gas is guided to a filter device or a dust collector using inertial collision, and then passed through a catalyst layer having a function of promoting denitration using ammonia or urea as a reducing agent. The mixed solution containing ammonium nitrate and ammonia or urea, or the individual solutions of the two are ammonium nitrate aqueous solution, ammonium nitrate and ammonia mixed solution, ammonium nitrate and urea mixed solution, nitric acid and ammonia mixed solution, and nitric acid and urea mixed solution. The exhaust gas purifying method according to claim 1, wherein the exhaust gas purifying method is a combination thereof. A means for injecting a mixed solution containing ammonium nitrate and ammonia or urea into the exhaust pipe of the combustion apparatus, or a separate solution of the both, and unburned carbon contained in the exhaust gas provided downstream of the injecting means can be collected. An exhaust gas purification system comprising: a filter device or a dust collector using inertial collision; and a catalyst layer that is provided downstream of the dust collector and promotes a denitration reaction using ammonia or urea as a reducing agent. apparatus. The mixed solution containing the ammonium nitrate and ammonia or urea, or the individual solutions of the both are an ammonium nitrate aqueous solution, a mixed solution of ammonium nitrate and ammonia, a mixed solution of ammonium nitrate and urea, a mixed solution of nitric acid and ammonia, and a mixed solution of nitric acid and urea. The exhaust gas purifying device according to claim 3, wherein the exhaust gas purifying device is a combination thereof.

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