JP2009078951A - Urea modifying apparatus and exhaust gas cleaning system equipped with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a urea modifying apparatus efficiently and continuously producing ammonia even in cold exhaust gas. <P>SOLUTION: The urea modifying apparatus comprises: a pair of electrodes; a pellet-like dielectric put between the pair of electrodes; an emulsion supply means configured such that a urea-containing emulsion can be supplied to the dielectric; a power source means connected to the pair of electrodes and configured such that pulse discharge or AC discharge is caused between the pair of electrodes and the urea reaching the dielectric can be converted to ammonia; and a carrier gas supply means configured such that carrier gas is supplied to the dielectric and ammonia converted from the urea can be extracted. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention is used in the ammonia SCR method, and generates ammonia as a reducing agent for reducing NO _X contained in exhaust gas such as a movable or stationary diesel engine or lean burn engine to nitrogen. The present invention relates to a urea reformer that can be used and an exhaust gas purification device using the same.

In view of the trend of stricter regulations on exhaust gas, technologies for reducing NO _x (for example, NO and NO ₂ ) contained in combustion exhaust gas to nitrogen molecules have been studied. NO _X treatment method according to the known noble metal catalyst, it is impossible to apply to a diesel engine or lean burn engines contains a high concentration of oxygen in the exhaust gas, with ammonia and a catalyst as NO _X processing technique alternative to the method The ammonia SCR method, which reduces NO _X to nitrogen, is widely used for stationary engine denitration. However, since the above-mentioned ammonia SCR method requires the use of toxic ammonia, in a mobile engine, it is stored in the form of urea, the urea is thermally decomposed to produce ammonia, and NO _X is reduced with the ammonia. An exhaust gas purification method (see, for example, Non-Patent Document 1) is employed. In the exhaust gas purification using the ammonia SCR system, the exhaust gas temperature needs to be about 520 to 570K in order to thermally decompose urea to produce ammonia.
Nitrogen oxide prevention technology Hideya Inaba Chemical Industry Co., Ltd. (1973)

  However, when the engine is started, the exhaust gas temperature is low and is 400K or less. In addition, due to improvements in engine thermal efficiency that accompany technological development, the exhaust gas temperature may be 400K or less as described above. When such exhaust gas temperature is relatively low, the above-mentioned conventional urea SCR method does not carry out the reaction of decomposing urea and generating ammonia at a sufficient rate due to lack of heat, and the reducing agent (reducing agent required for the SCR method ( Ammonia) is not supplied. Therefore, there is a demand for a method of reforming urea to generate ammonia corresponding to a low exhaust gas temperature (cold emission).

  An object of the present invention is to provide a urea reformer capable of efficiently and continuously producing ammonia even in low temperature exhaust gas.

Another object of the present invention is to provide an exhaust gas purifying apparatus capable of efficiently reducing NO _x to nitrogen molecules even in low temperature exhaust gas.

  The invention according to claim 1 includes a pair of electrodes, a pellet-shaped dielectric provided between the pair of electrodes, an emulsion supply means configured to supply an emulsion containing urea to the dielectric, and a pair of electrodes A power source means configured to generate a pulse discharge or an alternating current discharge between a pair of electrodes to convert urea reaching the dielectric into ammonia, and to supply ammonia into the dielectric converted from urea by supplying a carrier gas to the dielectric. A urea reformer comprising a carrier gas supply means configured to be extractable.

  Here, the pair of electrodes is preferably a discharge electrode and a ground electrode provided on the outer periphery of the discharge electrode in the form of a coaxial cylinder through a dielectric. A packed-bed type discharge reactor made of a dielectric material and powdered urea can be considered (FIG. 1). A pulse or alternating high voltage is applied to the discharge electrode in the filling type discharge reactor to generate discharge plasma, and the urea in the discharge plasma region is decomposed into ammonia. At this time, in order to continuously supply urea to the reactor, an emulsion in which urea powder or high-concentration urea aqueous solution is dispersed as droplets in oil is used. As another method, the urea aqueous solution is sprayed into the reactor to perform continuous supply. Thereby, it can supply continuously in a reactor by using the pump for liquids.

The exhaust gas purification apparatus includes the urea reforming apparatus described above and a reduction catalyst that reduces nitrogen oxide (NO _x ) using ammonia generated in the exhaust path of the engine and generated by the urea reforming apparatus as a reducing agent. can get.

Conventional decomposition of urea by thermal excitation produces ammonium nitrite at 483K or lower. As a result, the production rate of ammonia is slow. In the present invention, a reaction in which urea is decomposed by discharge plasma to generate ammonia is induced. For this reason, even when the exhaust gas temperature is relatively low, for example, 400K or less, a higher concentration of ammonia can be generated when exposed to discharge plasma than when exposed to plasma. In other words, by generating ammonia from urea by discharge plasma, it has become possible to efficiently reduce NO _{x in} low-temperature exhaust gas, which was difficult with the conventional urea SCR method.

  In order to continuously supply urea powder to the discharge device, a method such as blowing the powder into the gas upstream of the gas flowing into the discharge device is required. However, urea is deliquescent and the powder solidifies. There was a problem that the nozzle was blocked by doing so. In the present invention, since a fluid emulsion in which droplets of urea powder or high-concentration urea aqueous solution are dispersed in oil is used, there is no nozzle clogging and continuous supply is possible. Also, continuous supply can be performed by spraying an aqueous urea solution into the discharge device.

  Next, the best mode for carrying out the present invention will be described with reference to the drawings.

  In the exhaust manifold of a diesel engine or lean burn engine, the present invention installs a urea reformer between the rear of the engine and the front of the SCR catalyst, and supplies ammonia generated by the reforming of urea to the SCR catalyst. This is an exhaust gas purification device that removes NOx. As shown in FIG. 1, the structure of the urea reforming apparatus includes a pair of electrodes 1 and 3, a pellet-shaped dielectric 7 provided between the pair of electrodes 1 and 3, and an emulsion containing urea as a dielectric. The emulsion supply means configured to be able to supply the liquid and the urea that reaches the dielectric by generating pulse discharge or AC discharge between the pair of electrodes 1 and 3 and being connected to the pair of electrodes 1 and 3 can be converted to ammonia The power supply unit 9 is configured, and the carrier gas supply unit 5 is configured to be able to extract ammonia converted from urea by supplying a carrier gas to the dielectric 7. In this urea reformer, a packed bed reactor formed by filling a large number of pellet-like dielectrics 7 is used to reform urea into ammonia at a low exhaust gas temperature. That is, the pair of electrodes 1 and 3 includes a discharge electrode 1 and a ground electrode 3 provided on the outer periphery of the discharge electrode 1 in a coaxial cylindrical shape with a dielectric 7 interposed therebetween. And the filling layer which consists of the dielectric material 7 of a pellet form is formed in discharge space.

  In this urea reformer, a carrier gas (for example, air or exhaust gas) containing water vapor is supplied to the filling type discharge reactor through the gas introduction tube 5 while applying a pulse or an alternating high voltage to the discharge electrode. Plasma is generated to decompose urea 8 in the discharge plasma region into ammonia. At this time, a packed layer formed by filling a large number of pellet-like dielectrics 7 is sandwiched between electrodes 1 and 3 and exposed to discharge plasma by applying a pulse or an alternating high voltage. In the discharge plasma region, excitation of electrons and ions accelerates the hydrolysis reaction of urea, generating ammonia. Since the packed bed type reactor is used, only the packed bed portion is exposed to the discharge plasma, so that the energy from the discharge is efficiently given to the urea and ammonia can be effectively generated.

The emulsion supply means comprises a pump and a nozzle, and this emulsion supply means sprays a fluid emulsion in which droplets of urea powder or high-concentration urea aqueous solution are dispersed in oil in a plasma apparatus. Configured to supply. Alternatively, an aqueous urea solution is supplied by spraying. Thus, since a fluid emulsion in which droplets of urea powder or high-concentration urea aqueous solution are dispersed in oil is used, there is no nozzle clogging and continuous supply is possible. Also, continuous supply can be performed by spraying an aqueous urea solution into the discharge device. As a result, ammonia can be continuously produced, and NO _x can be efficiently reduced to nitrogen molecules even in low temperature exhaust gas in the exhaust gas purification device.

  Atmospheric pressure discharge plasma was generated by using the packed bed discharge type plasma apparatus shown in FIG. 1 or the dielectric barrier discharge type plasma reactor in which the filling material was removed in the apparatus of FIG. The packed bed discharge plasma reactor shown in Fig. 1 has a stainless steel rod (reference numeral 3) of 25 mm in length and 11 mm in outer diameter in the center of a borosilicate glass tube (reference numeral 2) having a length of 50 mm and an inner diameter of 19 mm. The outer periphery of the borosilicate glass tube was covered with a stainless steel sheet (reference numeral 1). Filled by filling the borosilicate glass tube and stainless steel rod with dielectric pellets (symbol 7) and powdered urea (symbol 8) with a diameter of 2.5 to 4 mm and sandwiching both ends with ceramics (symbol 4). Layered. The internal stainless steel rod is a high-voltage electrode, a positive pulsed high voltage was applied to it, and the external stainless steel sheet was used as the ground electrode. A discharge plasma was generated by applying a pulse voltage of 15 kVp-p, 5 kHz, and a rise of about 0.25 μs.

  On the other hand, after dissolving 1 g of urea in 1 g of ion exchange water, 10 μL of Triton X was added as a surfactant, and this was added to 3 mL of dodecane and stirred to prepare an emulsion. This emulsion was supplied to the packed bed type plasma reactor at 100 μL per minute. In addition, nitrogen gas was supplied to the plasma reactor at a flow rate of 2 L / min. The temperature of the reactor was 60 ° C., and ammonia was generated.

  Also, change other conditions except that the positive pulse high voltage was changed to (10kVp-p, 5kHz), (15kVp-p, 0.7kHz) and (12.5kVp-p, 3.3kHz). Without generating ammonia again. The relationship between the concentration of ammonia generated under these conditions and time is shown in FIG.

  Also, ammonia is generated under the same conditions and procedures as the previous conditions, except that the material of the packing was changed and a discharge plasma was generated by applying a pulse voltage of 15 kVp-p, 5 kHz, rising 0.25 μs. I let you. FIG. 3 shows the relationship between the ammonia concentration and time at this time.

Further, urea was supplied to the packed bed type plasma reactor by spraying urea water having a concentration of 30% with a mist diameter of 1 to 10 mm into nitrogen gas supplied to the reactor at a flow rate of 5 L / min. The temperature was 120 ° C. Pulse voltage peak value 10kV,
The frequency was 5 kHz. It was confirmed that the urea water mist evaporated in the gas and urea was decomposed in the plasma part to generate ammonia. The relationship between the ammonia concentration and time at this time is shown in FIG.

  According to the present invention, ammonia for reducing NOX can be generated from urea even under low temperature exhaust gas conditions such as when the engine is started. As a result, exhaust gas treatment at a low temperature, which is impossible with conventional technology, is expected. In addition, the reforming of urea by electric energy suggests the possibility of on-demand ammonia supply.

It is the figure which showed the structure of the packed bed discharge plasma reactor. This is the concentration of ammonia produced with and without plasma exposure to the urea emulsion. It is the material of the filler and the ammonia concentration produced. This is the concentration of ammonia produced by spraying urea water.

Explanation of symbols

1 Stainless steel sheet (ground electrode)
2 Borosilicate glass tube 3 Stainless rod (high voltage electrode)
4 Ceramics for supporting high voltage electrodes and pellets 5 Polytetrafluoroethylene tubes 6 Silicon plugs 7 γ-Al2O3 pellets 8 Powdered urea 9 Pulsed power supply

Claims (4)

A pair of electrodes;
A pellet-shaped dielectric provided between the pair of electrodes;
An emulsion supply means configured to supply an emulsion containing urea to the dielectric;
Power supply means connected to the pair of electrodes and configured to convert the urea reaching the dielectric by generating pulse discharge or alternating current discharge between the pair of electrodes into ammonia;
A urea reformer comprising: a carrier gas supply means configured to supply a carrier gas to the dielectric and extract ammonia converted from the urea.   The urea reforming apparatus according to claim 1, wherein the emulsion comprises 10 to 90% by mass of urea, 90 to 0% by mass of water, and the balance comprising oil.   The urea reforming apparatus according to claim 1 or 2, wherein the emulsion supply means comprises a pump and a nozzle. A urea reformer according to any one of claims 1 to 3,
An exhaust gas purification apparatus comprising: a reduction catalyst provided in an exhaust path of an engine for reducing nitrogen oxide (NO _x ) using ammonia generated by the urea reformer as a reducing agent.

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