JP2005337112A - Urea water storage method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To retain a concentration of urea water in a tank to a constant value by suppressing evaporation of moisture content of urea water. <P>SOLUTION: In the storage method for urea water 17 to be added as a reducing agent to a selective reduction type catalyst 10 for reducing/cleaning NOx, hardly volatile fats and oils 18 having property that it is separated without being mixed with urea water 17 and smaller specific gravity than urea water 17 are stored with urea water 17 together and a film of fats and oils 18 is laid on urea water 17 by difference of specific gravity to cover a liquid surface of urea water 17. Thereby, evaporation of moisture content of urea water 17 is suppressed to retain a concentration of urea water 17 in the urea water tank 14 to a constant value. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for storing urea water to be added as a reducing agent to a selective reduction catalyst for reducing and purifying NOx.

  Conventionally, diesel engines are equipped with a selective reduction catalyst (selective reduction catalyst) that has the property of selectively reacting NOx with a reducing agent even in the presence of oxygen in the middle of an exhaust pipe through which exhaust gas flows. The required amount of reducing agent is added to the upstream side of the selective catalytic reduction catalyst, and the reducing agent is subjected to a reduction reaction with NOx (nitrogen oxide) in the exhaust gas on the selective catalytic reduction catalyst, whereby NOx emission concentration There is one that can reduce the above.

In addition, in the field of industrial flue gas denitration treatment in plants and the like, the effectiveness of a method of reducing and purifying NOx using ammonia (NH ₃ ) as a reducing agent is already widely known. In recent years, since it is difficult to ensure safety when traveling with a toxic substance such as ammonia, in recent years, the use of non-toxic urea water as a reducing agent has been studied (for example, (See Patent Document 1 and Patent Document 2).
JP 2002-161732 A JP 2002-166130 A

  However, when urea water is used as a reducing agent in this way, urea water is stored in a vehicle-installed urea water tank. However, the tank has an air vent hole so as to maintain atmospheric pressure. Because it is open to the atmosphere, there is a concern that urea water will evaporate vigorously in an environment where the outside air temperature is high, such as in the summer, and the urea water concentration will increase in the tank and adversely affect the control of the amount of urea water added. It was done.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to suppress urea water evaporation and maintain a constant concentration of urea water in a tank.

  The present invention relates to a method for storing urea water to be added as a reducing agent to a selective catalytic reduction catalyst for reducing and purifying NOx, which has a property of separating without mixing with urea water and has a specific gravity higher than that of urea water. Is characterized in that a slightly volatile liquid is stored together with urea water and the liquid film is stretched over the urea water by a specific gravity difference to cover the liquid surface of the urea water. .

  Thus, in this way, the evaporation of the urea water is suppressed by the liquid film stretched over the urea water, and the urea water in the tank is kept even in an environment where the outside air temperature is high in summer. Since the concentration at the time of injection is maintained, the possibility that the urea water is highly concentrated in the tank is avoided in advance.

  Further, when the urea water in the tank is consumed and the urea water needs to be replenished, the urea water may be reinjected from the liquid film as before, and the newly reinjected urea water Is supplied to the bottom of the tank without any trouble through the liquid film due to the difference in specific gravity.

  Furthermore, in carrying out the present invention more specifically, it is possible to employ, for example, a hardly volatile oil having a specific gravity smaller than that of urea water as a liquid to be stored together with urea water.

  According to the urea water storage method of the present invention described above, since the concentration of urea water in the tank can be kept constant by suppressing water evaporation of the urea water, the concentration of urea water is increased in the urea water tank. Thus, it is possible to obtain an excellent effect that the possibility of adversely affecting the control of the addition amount of the urea water can be avoided.

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

  1 and 2 show an example of an embodiment of the present invention. Reference numeral 1 in FIG. 1 denotes an engine that is a diesel engine. In the engine 1 shown here, a turbocharger 2 is provided. The air 4 guided from the air cleaner 3 is sent to the compressor 2a of the turbocharger 2 through the intake pipe 5, and the air 4 pressurized by the compressor 2a is further sent to the intercooler 6 to be cooled. The air 4 is guided from the intercooler 6 to an intake manifold (not shown) and introduced into each cylinder of the engine 1.

  Further, the exhaust gas 7 discharged from each cylinder of the engine 1 is sent to the turbine 2b of the turbocharger 2 through the exhaust manifold 8, and the exhaust gas 7 that has driven the turbine 2b goes out of the vehicle through the exhaust pipe 9. It is supposed to be discharged.

  In the middle of the exhaust pipe 9 through which the exhaust gas 7 circulates, a selective catalytic reduction catalyst 10 is mounted by being held by a casing 11, and this selective catalytic reduction catalyst 10 is a flow-through type honeycomb structure. It is formed and has the property that NOx can be selectively reacted with ammonia even in the presence of oxygen.

  Here, as the selective catalytic reduction catalyst 10, a conventionally known catalyst such as a noble metal catalyst such as platinum or palladium or a base metal catalyst such as an oxide of vanadium, copper or iron can be employed.

  In addition, an oxidation catalyst 12 formed as a flow-through type honeycomb structure is provided at the subsequent stage of the selective reduction catalyst 10 in the casing 11, similarly to the selective reduction catalyst 10. A small amount of leaked ammonia or CO that has passed through unreacted is oxidized.

  An injection nozzle 13 is installed on the upstream side of the casing 11, and the urea water supply line 15 connects between the injection nozzle 13 and the bottom of the urea water tank 14 provided at a required location. The urea water 17 (reducing agent) in the urea water tank 14 can be added to the upstream side of the selective catalytic reduction catalyst 10 through the injection nozzle 13 by driving the supply pump 16 provided in the middle of the line 15.

  Here, in the urea water tank 14, together with the urea water 17, a hardly volatile fat and oil 18 having a specific gravity smaller than that of the urea water 17 is stored. They are separated without being mixed with each other, and the liquid surface of the urea aqueous solution 17 is coated by the oil and fat 18 forming a film on the urea aqueous solution 17 due to the difference in specific gravity.

  Note that the hardly volatile oil 18 described above refers to an oil 18 having a property of hardly evaporating at room temperature, in other words, an assumed storage temperature in the urea water tank 14. It refers to the fats and oils 18 that hardly evaporate in the region (about 60 ° C. or less).

  The fats and oils 18 stored together with the urea water 17 in the urea water tank 14 may be injected in advance before the urea water 17 is injected into the urea water tank 14. You may make it inject | pour immediately after inject | pouring the urea water 17 initially.

  In the figure, reference numeral 19 denotes an air vent hole provided at the upper end of the urea water tank 14 so that the inside of the urea water tank 14 is opened to the atmosphere via the air vent hole 19 so that the tank internal pressure is maintained at atmospheric pressure. It has become.

  Thus, if the urea water 17 is stored together with the fats and oils 18 in this way, moisture evaporation of the urea water 17 is suppressed by the film of the fats and oils 18 stretched over the urea water 17, and the outside air temperature in summer and the like is increased. Even in a high environment, the urea water 17 in the urea water tank 14 is kept at the concentration at the time of injection, so that the possibility that the urea water 17 is highly concentrated in the urea water tank 14 is avoided. Will be.

  Further, when the urea water 17 in the urea water tank 14 is consumed and the urea water 17 needs to be replenished, the urea water 17 may be reinjected from above the film of the oil 18 without changing from the conventional one. Due to the difference in specific gravity, the urea water 17 that has been reinjected into the water passes through the film of the oil 18 and is supplied to the bottom of the urea water tank 14 without any trouble.

  At this time, air is entrained by the re-injected urea water 17 and a bubble layer is formed at the boundary between the urea water 17 and the oil 18, but the urea water 17 is formed by setting the film thickness of the oil 18 to about 5 mm or more. Can be kept in a coated state. Incidentally, the mixed bubbles gradually dissipate to the upper part of the tank through the film of the oil 18 as time passes.

  Therefore, according to the above embodiment, the concentration of the urea water 17 in the urea water tank 14 can be kept constant by suppressing the water evaporation of the urea water 17, so that the urea water 17 is contained in the urea water tank 14. The possibility of adversely affecting the control of the addition amount of the urea water 17 by increasing the concentration can be avoided in advance.

  Note that the urea water storage method of the present invention is not limited to the above-described embodiment, and is a hardly volatile liquid having a property of separating without being mixed with urea water and having a specific gravity smaller than that of urea water. Of course, other than fats and oils may be adopted, and various modifications may be made without departing from the scope of the present invention.

It is the schematic which shows an example of the form which implements this invention. It is sectional drawing which expands and shows the detail of the urea water tank of FIG.

Explanation of symbols

7 Exhaust gas 9 Exhaust pipe 10 Selective reduction catalyst 14 Urea water tank 17 Urea water 18 Oils and fats (liquid)

Claims (2)

  A method for storing urea water to be added as a reducing agent to a selective catalytic reduction catalyst for reducing and purifying NOx, which has the property of separating without being mixed with urea water, and is less volatile than urea water A method for storing urea water, characterized in that a liquid is stored together with urea water, and a film of the liquid is stretched over the urea water by a specific gravity difference to cover the surface of the urea water.   2. The urea water storage method according to claim 1, wherein the liquid stored together with the urea water is a hardly volatile oil having a specific gravity smaller than that of the urea water.

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