JP6155015B2 - Ammonia generator and exhaust purification device using the same - Google Patents

Description

  The present invention relates to an ammonia generator capable of generating ammonia from air and water, and an exhaust purification device using the same.

  Conventionally, a diesel engine is equipped with a selective catalytic reduction catalyst having the property of selectively reacting NOx (nitrogen oxide) with a reducing agent even in the presence of oxygen in the middle of an exhaust pipe through which exhaust gas flows. A necessary amount of reducing agent is added upstream of the selective catalytic reduction catalyst so that the reducing agent undergoes a reduction reaction with NOx in the exhaust gas on the selective catalytic reduction catalyst, thereby reducing the NOx emission concentration. There is what I did.

On the other hand, in the field of industrial flue gas denitration treatment in plants and the like, the effectiveness of a method for reducing and purifying NOx using ammonia (NH ₃ ) as a reducing agent is already widely known. Since it is difficult to ensure safety with respect to traveling with ammonia itself, in recent years, the use of non-toxic urea water as a reducing agent has been studied (see, for example, Patent Document 1). .

That is, if urea water is added to the exhaust gas upstream of the selective catalytic reduction catalyst, the urea water is hydrolyzed into ammonia and carbon dioxide gas by the following equation by the heat of the exhaust gas, and the exhaust gas is exhausted on the selective catalytic reduction catalyst. The NOx contained therein is reduced and purified well by ammonia.
[Chemical 1]
(NH ₂ ) ₂ CO + H ₂ O → 2NH ₃ + CO ₂

JP 2002-161732 A

  However, in a system in which urea water is added to the exhaust gas upstream of the selective catalytic reduction catalyst, a large urea water tank for storing urea water must be mounted on the vehicle. There is a problem that it is difficult to secure the mounting space for the urea water tank, and it is necessary to monitor the remaining amount of urea water in the urea water tank and replenish it accordingly. However, there was a problem that the burden on the driver was heavy.

  The present invention has been made in view of the above circumstances, and by providing an ammonia generator capable of generating ammonia from the atmosphere and water, it is unnecessary to mount a large urea water tank and replenish urea water. It is aimed.

The present invention provides a nitrogen-enriched gas generating means for removing oxygen from the atmosphere to generate a nitrogen-enriched gas having a high nitrogen concentration, and superheated steam that is completely in a gaseous state at a temperature above the boiling point by heating water. And a superheated steam generating means for raising the temperature via the nitrogen enriched gas introduced from the nitrogen enriched gas generating means, and the superheated steam and the nitrogen enriched gas introduced from the superheated steam generating means in the discharge plasma. A discharge plasma reactor that generates ammonia by reacting by passing through , wherein the nitrogen-enriched gas generating means includes a hollow tube made of a nitrogen-enriched film that is more permeable to oxygen than nitrogen, and the inside of the hollow tube The oxygen-enriched gas is separated from the pipe by recovering the nitrogen-enriched gas remaining in the pipe by applying atmospheric pressure to the atmosphere, and the superheated steam generating means heats the water. Evaporation to produce water vapor Knit, but according to the ammonia generating device, characterized in that it is constituted by a heating unit for generating a superheated steam superheated to above the boiling point of the water vapor derived from evaporation unit.

Thus, if the ammonia generator is configured in this way, the nitrogen-enriched gas generating means removes oxygen from the atmosphere to generate a nitrogen-enriched gas having a high nitrogen concentration, while the superheated steam generating means The water is heated to generate superheated steam that is completely in a gaseous state at a temperature equal to or higher than the boiling point, and the nitrogen-enriched gas generated by the nitrogen-enriched gas generating means is heated through the superheated steam generating means. Then, the superheated steam from the superheated steam generating means is introduced into the discharge plasma reactor, and the superheated steam and the nitrogen-enriched gas are reacted by passing through the discharge plasma in the discharge plasma reactor. Water vapor is H ⁺ and OH ⁻ , and nitrogen in the nitrogen-enriched gas is dissociated into N, and then H and N are combined to produce NH ₃ (ammonia).

  The nitrogen-enriched gas produced by the nitrogen-enriched gas producing means is heated through the superheated steam producing means and then introduced into the discharge plasma reactor because the cooled nitrogen-enriched gas is introduced into the discharge plasma reactor. This is because if it is combined with superheated steam, the temperature of the superheated steam may decrease and condensation may occur.

In the present invention, the nitrogen-enriched gas generating means includes a hollow tube made of a nitrogen-enriched membrane that is more permeable to oxygen than nitrogen, and oxygen is supplied by pumping the atmosphere into the hollow tube to apply a positive pressure. It is configured so as to recover the nitrogen-enriched gas remaining in and tube to separate the enriched gas outside the tube, be recovered nitrogen-rich gas to separate easily the oxygen-enriched gas from the atmosphere It becomes possible.

Further, in the present invention, the superheated steam generating means is composed of an evaporation unit that generates water vapor by heating water, and a superheat unit that generates superheated steam by heating the water vapor led from the evaporation unit to a boiling point or higher. Therefore , it is possible to easily obtain superheated steam by adopting a two-stage heating method in which the steam evaporated by the evaporation unit is heated to the boiling point or more by the superheat unit .

  Further, in the present invention, the discharge plasma reactor includes a cylindrical reactor body made of an insulator, a rod-shaped discharge electrode disposed at the center of the reactor body, and an outer peripheral portion of the reactor body. And a dielectric pellet filled in a discharge space formed between the discharge electrode and the ground electrode, so that a high voltage is applied between the discharge electrode and the discharge electrode. It is preferable.

  In this way, when a high voltage is applied between the discharge electrode and the ground electrode, discharge plasma (non-thermal equilibrium plasma) due to barrier discharge (silent discharge or creeping discharge) is generated in the discharge space. However, since the discharge space is filled with dielectric pellets, an electric field is concentrated at the contact points between the dielectric pellets, and a strong discharge plasma is likely to be generated, and ammonia is efficiently generated by the strong discharge plasma. Will be.

  Furthermore, the present invention includes a selective reduction catalyst having a property of selectively reacting NOx with ammonia even in the presence of oxygen in the middle of an exhaust pipe through which exhaust gas from an engine flows, and upstream of the selective reduction catalyst. Further, the present invention relates to an exhaust emission control device characterized in that the above-described ammonia generator is used as a reducing agent addition device for adding ammonia as a reducing agent in the side exhaust pipe.

  In this way, ammonia can be generated from the atmosphere and water without the need for special infrastructure equipment, and it is not necessary to use urea water as a reducing agent for the selective catalytic reduction catalyst. There is no need to install a water tank or supply of urea water, so that restrictions on the layout of the device are greatly eased and the burden on the driver is also greatly reduced.

  In addition, when starting an engine with a low exhaust temperature or running at a low speed, ammonia generated from the atmosphere and water can be directly introduced into the exhaust pipe as a reducing agent for the selective catalytic reduction catalyst. High NOx reduction performance can be exhibited immediately after reaching the active temperature range of the reduction catalyst.

  That is, in the prior art, by adding ammonia to the selective catalytic reduction catalyst, an NOx reduction effect can be obtained from an exhaust temperature of about 100 ° C. or higher, whereas at least about the time for urea water to hydrolyze into ammonia and carbon dioxide Since an exhaust temperature of 180 to 190 ° C. was required, there was a problem that the NOx reduction performance was not improved easily even when urea water was added at the time of engine start or low speed running where a lower exhaust temperature was assumed. However, this problem will be solved.

  According to the above-described ammonia generator of the present invention and the exhaust gas purification apparatus using the same, various excellent effects as described below can be obtained.

  (I) According to the first aspect of the present invention, since ammonia can be generated from the atmosphere and water, for example, a vehicle as a reducing agent addition device that adds ammonia as a reducing agent of a selective catalytic reduction catalyst. The installation of large urea water tanks and the replenishment of urea water can be made unnecessary, so that restrictions on equipment layout can be greatly eased and the burden on the driver can be greatly reduced. can do.

According to the invention described in claim 1, (II) the present invention, only applying a positive pressure by pumping air into the hollow tube of the nitrogen-enriched gas, to separate easily the oxygen-enriched gas from the atmosphere A nitrogen-enriched gas having a high nitrogen concentration can be recovered.

According to the invention described in claim 1, (III) the present invention, to obtain easily superheated steam by employing the two-stage heating method that overheated above the boiling point with superheated unit water vapor evaporated in the evaporation unit can be, discharge plasma reactor with superheated steam Ru can be reliably wiped fear that danger of condensation and temperature decrease by confluence of the nitrogen-enriched gas.

(IV) According to the invention described in claim 2 of the present invention, the electric field is concentrated at the contact points between the dielectric pellets filled in the discharge space, and a strong discharge plasma is easily generated. Ammonia can be efficiently generated by the discharge plasma.

(V) According to the invention described in claim 3 of the present invention, it is possible to eliminate the need for installing a large urea water tank and supplying urea water as already described in (I). In addition to the effect of significantly reducing the driver's constraints and drastically reducing the burden on the driver. Since ammonia can be directly introduced into the exhaust pipe as a reducing agent for the selective catalytic reduction catalyst, high NOx reduction performance can be exhibited immediately after the exhaust temperature reaches the active temperature range of the selective catalytic reduction catalyst.

It is the schematic which shows an example of the form which implements this invention.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 shows an example of an embodiment for carrying out the present invention. In this embodiment, exhaust for vehicles using a selective catalytic reduction catalyst 1 having a property of selectively reacting NOx with ammonia even in the presence of oxygen. The case where an ammonia generating device 3 described later is applied as a reducing agent addition device for adding ammonia 2 as a reducing agent to the upstream side of the selective catalytic reduction catalyst 1 is illustrated in the purification device, and the selective catalytic reduction catalyst 1 is provided in the middle of an exhaust pipe 5 through which exhaust gas 4 from the engine flows, and ammonia 2 generated by the ammonia generator 3 is introduced into the exhaust pipe 5 upstream of the selective catalytic reduction catalyst 1. It has become so.

  Here, the ammonia generator 3 is configured to remove oxygen from the atmosphere 6 to generate nitrogen-enriched gas 7 having a high nitrogen concentration and nitrogen-enriched gas generating means 8 that heats water 9 and has a temperature equal to or higher than the boiling point. The superheated steam generation means 11 that generates the superheated steam 10 in a completely gaseous state and raises the temperature via the nitrogen enriched gas 7 introduced from the nitrogen enriched gas generation means 8, and the superheated steam generation means 11 is provided with a discharge plasma reactor 12 that generates ammonia 2 by reacting the superheated water vapor 10 and the nitrogen-enriched gas 7 led from 11 through the discharge plasma.

  The nitrogen-enriched gas generating means 8 includes a large number of hollow tubes 13 made of a polyimide nitrogen-enriched membrane made of polyimide, which is more permeable to oxygen than nitrogen, in a cylindrical container 15 and is provided with a pump 14 (or a compressor). ), The atmosphere 6 is distributed to the respective hollow tubes 13 and flows, but the orifice 16 disposed on the outlet side of the container 15. Since the flow path is narrowed by the above, the oxygen-enriched gas 17 containing a large amount of oxygen that easily passes through each hollow tube 13 in a state where a positive pressure is applied in each hollow tube 13 is separated outside the tube. The nitrogen-enriched gas 7 containing a large amount of nitrogen that is difficult to permeate the hollow tubes 13 remains in the tubes and is sent out.

Further, the superheated steam generation means 11 generates superheated steam 10 by heating the water 9 to generate the steam 9 ′ and superheating the steam 9 ′ led from the evaporation unit 18 to a boiling point or higher. A superheater unit 19 is used, and a two-stage heating method is employed in which the water vapor 9 ′ evaporated by the evaporator unit 18 is superheated to the boiling point or more by the superheater unit 19 .

  The evaporation unit 18 and the overheating unit 19 are equipped with heaters 20 and 21 that use heat generated by energizing a heating wire or exhaust heat from the engine block as a heat source, and are illustrated with respect to the water inlet 22 of the evaporation unit 18. The water 9 introduced from the water tank not heated is heated and evaporated by the heater 20, and the water vapor 9 ′ is extracted from the upper side of the evaporation unit 18 and passes through the heat transfer tube 23 wound around the heater 21 in the superheating unit 19. Further, it is heated to the boiling point or higher and discharged as superheated steam 10.

  Here, in the case of urea water that is difficult to obtain unless special infrastructure facilities are in place, a large urea water tank is required to store as much as possible, but it can be easily obtained and replenished anywhere. In the case of the water 9 that can be produced, it is not necessary to store a large amount at a time, and it is only necessary to mount a relatively small water tank. The water tank may be provided with replenishing means for collecting and introducing the condensed water of the vehicle-mounted cooler.

  In addition, the heaters 20 and 21 of the evaporation unit 18 and the superheat unit 19 are provided with another heat transfer tube 24 for flowing and heating the nitrogen-enriched gas 7 introduced from the nitrogen-enriched gas generating means 8. The nitrogen-enriched gas 7 is also heated to a temperature that is almost the same as that of the superheated steam 10.

  The discharge plasma reactor 12 includes a cylindrical reactor body 25 made of an insulator, a rod-shaped discharge electrode 26 disposed at the center of the reactor body 25, and an outer periphery of the reactor body 25. And a dielectric electrode filled in a discharge space 28 formed between the discharge electrode 26 and the ground electrode 27. The ground electrode 27 is disposed between the discharge electrode 26 and a high voltage to be applied to the discharge electrode 26. The superheated steam 10 and the nitrogen-enriched gas 7 sent out from the heat transfer tubes 23 and 24 of the superheat unit 19 are discharged into the discharge space 28 in the reactor main body 25. To be introduced. In the figure, reference numeral 30 denotes a power source for applying a high voltage connected to the discharge electrode 26, and 31 denotes a ground connected to the ground electrode 27.

Thus, the nitrogen-enriched gas generating means 8 removes the oxygen-enriched gas 17 from the atmosphere 6 to generate the nitrogen-enriched gas 7 having a high nitrogen concentration, while the superheated steam generating means 11 generates the evaporation unit 18. The superheated steam 10 is generated by a two-stage heating method in which the steam 9 ′ evaporated in step 1 is heated to a boiling point or higher by the superheat unit 19 and the nitrogen-enriched gas 7 generated by the nitrogen-enriched gas generating means 8 is heated. After raising the temperature of the evaporation unit 18 and the superheat unit 19 of the water vapor generating means 11 via the heat transfer tube 24, the temperature is introduced into the discharge plasma reactor 12 together with the superheated water vapor 10 from the superheated water vapor generating means 11, reaction of superheated steam 10 and nitrogen-rich gas 7 by passing during the discharge plasma in a discharge plasma reactor 12, superheated steam 10 is H ⁺ and OH ^-, nitrogen in the nitrogen-enriched gas 7 Dissociated into, then, NH ₃ (ammonia 2) by bonding H and N will be is produced.

  Here, when a high voltage is applied between the discharge electrode 26 and the ground electrode 27, discharge plasma (non-thermal equilibrium plasma) due to barrier discharge (silent discharge or creeping discharge) is generated in the discharge space 28. However, since the discharge pellets 28 are filled with the dielectric pellets 29, the electric field is concentrated at the contact points between the dielectric pellets 29 and a strong discharge plasma is easily generated. Ammonia 2 is well produced.

  The nitrogen-enriched gas 7 produced by the nitrogen-enriched gas producing means 8 is introduced into the discharge plasma reactor 12 after being heated through the heat transfer tube 24 and the superheated steam producing means 11. This is because if the cooled nitrogen-enriched gas 7 is merged with the superheated steam 10, the temperature of the superheated steam 10 may decrease and condensation may occur.

  As described above, according to the above-described embodiment, ammonia 2 can be generated from the atmosphere 6 and the water 9, so that the reducing agent addition device that adds ammonia 2 as the reducing agent of the selective catalytic reduction catalyst 1 is applied to the vehicle. When installing, it is not necessary to install a large urea water tank or replenish the urea water, which can greatly ease the restrictions on the layout of the equipment and greatly reduce the burden on the driver. Can do.

  Further, even when the engine is started at a low exhaust temperature or at low speed, ammonia 2 generated from the atmosphere 6 and water 9 can be directly introduced into the exhaust pipe 5 as a reducing agent of the selective catalytic reduction catalyst 1. High NOx reduction performance can be exhibited immediately after the exhaust temperature reaches the activation temperature range of the selective catalytic reduction catalyst 1.

  In other words, conventionally, by adding ammonia 2 to the selective catalytic reduction catalyst 1, an NOx reduction effect can be obtained from an exhaust temperature of about 100 ° C. or higher, whereas urea water is hydrolyzed into ammonia 2 and carbon dioxide gas. Because an exhaust temperature of at least about 180 to 190 ° C. was necessary, NOx reduction performance would not increase easily even if urea water was added at the time of engine start or low speed running, etc., where an exhaust temperature lower than this was assumed. However, this problem will be solved.

  The ammonia generator of the present invention and the exhaust gas purification apparatus using the same are not limited to the above-described embodiments, and various changes can be made without departing from the scope of the present invention. is there.

DESCRIPTION OF SYMBOLS 1 Selective reduction type | mold catalyst 2 Ammonia 3 Ammonia generator 4 Exhaust gas 5 Exhaust pipe 6 Atmosphere 7 Nitrogen rich gas 8 Nitrogen rich gas production | generation means 9 Water 9 'Water vapor 10 Superheated water vapor 11 Superheated water vapor production means 12 Discharge plasma reactor 13 Hollow tube 17 Oxygen-enriched gas 18 Evaporation unit 19 Superheat unit 25 Reactor body 26 Discharge electrode 27 Ground electrode 28 Discharge space 29 Dielectric pellet

Claims (3)

A nitrogen-enriched gas generating means that removes oxygen from the atmosphere to generate a nitrogen-enriched gas having a high nitrogen concentration, and generates superheated steam that is completely in a gaseous state at a temperature above the boiling point by heating water; and A superheated steam generating means for raising the temperature via the nitrogen-enriched gas introduced from the nitrogen-enriched gas generating means, and passing the superheated steam and the nitrogen-enriched gas guided from the superheated steam generating means through the discharge plasma. A discharge plasma reactor that reacts to produce ammonia ;
The nitrogen-enriched gas generating means includes a hollow tube made of a nitrogen-enriched membrane that is more permeable to oxygen than nitrogen, and the oxygen-enriched gas is removed from the tube by pumping the atmosphere into the hollow tube and applying a positive pressure. And is configured to recover the nitrogen-enriched gas remaining in the tube,
The superheated steam generating means is composed of an evaporation unit that generates water vapor by heating water, and a superheat unit that generates superheated steam by heating the water vapor derived from the evaporation unit to a boiling point or higher. An ammonia generator. A discharge plasma reactor includes a tubular reactor body made of an insulator, a rod-shaped discharge electrode disposed in a central portion of the reactor body, and an outer peripheral portion of the reactor body. And a dielectric pellet filled in a discharge space formed between the discharge electrode and the ground electrode. The ammonia generator according to claim 1 . A selective reduction catalyst having the property of selectively reacting NOx with ammonia even in the presence of oxygen is provided in the middle of an exhaust pipe through which exhaust gas from the engine circulates. Ammonia is present in the exhaust pipe upstream of the selective reduction catalyst. An exhaust gas purification apparatus using the ammonia generator according to claim 1 or 2 as a reducing agent addition apparatus for adding as a reducing agent.

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