JP2013136968A - Exhaust emission control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make supply quantity of aqueous ammonia to an exhaust pipe simply controllable by reforming urea water to the aqueous ammonia without evaporating it with a urea water reformer, and to efficiently reduce NOx in exhaust gas even when exhaust gas temperature is comparatively low.SOLUTION: A selective reduction catalyst 12 provided in the exhaust pipe 15 of an engine 11 reduces NOx in the exhaust gas to N, and the urea water reformer 14 heats the urea water 13 with a heater 14b to reform it to the aqueous ammonia. A urea water supply means 16 supplies the urea water to the urea water reformer, and an injection nozzle 17 facing the exhaust pipe at an exhaust gas upstream side from the selective reduction catalyst jets the ammonia water or the urea water. A controller 38 controls the heater and the urea water supply means based on detection output by a catalyst temperature sensor 33 detecting the exhaust gas temperature relating to the selective reduction catalyst and detection output by a pressure sensor 34 detecting inlet pressure of the urea water reformer.

Description

  The present invention relates to an apparatus for purifying NOx in exhaust gas by injecting ammonia water reformed from urea water by a urea water reformer into an exhaust pipe of an engine as a reducing agent.

  Conventionally, it has a storage tank of an aqueous solution (for example, urea aqueous solution) containing at least one reducing agent precursor, the storage tank is connected to the evaporation chamber, and the aqueous solution is supplied to the evaporation chamber by a supply means. An apparatus for supplying an air-fuel mixture containing at least one substance of one kind of reducing agent or at least one kind of reducing agent precursor is disclosed (for example, see Patent Document 1). In this air-fuel mixture supply device, the heating means disposed in the evaporation chamber is formed by a heating wire in contact with the evaporation chamber, and the heating means raises the urea aqueous solution in the evaporation chamber to a temperature equal to or higher than the critical temperature at least partially evaporating. Heated. Specifically, the evaporation apparatus has the evaporation chamber having a substantially sealed volume, and the evaporation chamber has a first opening for connecting a transfer pipe for transferring the urea aqueous solution, and an air-fuel mixture. And a second opening for connecting a supply pipe to be discharged. In the first opening, a nozzle is disposed as means for injecting and supplying the urea aqueous solution into the evaporation chamber, and the urea aqueous solution is injected and injected into the evaporation chamber by this nozzle. The evaporation chamber also has a means for preventing liquid droplets from entering the second opening, particularly a means for breaking a gas film located between the liquid droplet and the wall of the evaporation chamber (such as a protrusion on the wall). And one or more structures that generate a large surface for evaporation of the aqueous urea solution. This structure may be a structured surface obtained by placing a coating on the inner surface of the evaporation chamber. Further, the evaporation chamber is connected to the hydrolysis catalytic converter through the second opening, and this hydrolysis catalytic converter is directly connected to the exhaust pipe. This hydrolysis catalytic converter has temperature control means comprising heating lines wound around this hydrolysis catalytic converter.

  In the air-fuel mixture supply apparatus configured as described above, the air-fuel mixture is generated from the urea aqueous solution by the evaporator, and this air-fuel mixture contains at least urea, and in some cases, already contains ammonia generated by thermal decomposition of the urea. . This air-fuel mixture is introduced into the hydrolysis catalytic converter through the second opening. In this hydrolysis catalytic converter, urea is almost completely hydrolyzed to ammonia, and a reducing agent gas mixture containing ammonia is generated.

  On the other hand, a hydrolysis catalyst is connected to at least one supply path for supplying an aqueous solution containing urea, exhaust gas flows through the SCR catalyst, and heats at least one part of the supply path and at least one part of the hydrolysis catalyst. An exhaust gas treatment device for an internal combustion engine in which a rod-shaped heating element is arranged is disclosed (for example, see Patent Document 2). In this exhaust gas treatment apparatus, at least one part of at least a part of the supply path and the hydrolysis catalyst is disposed around the rod-shaped heating element. Further, the rod-shaped heating element is surrounded by a jacket tube, and the jacket tube is formed integrally with the rod-shaped heating element or is material-bonded to the rod-shaped heating element. A passage is provided in the jacket tube. Here, the passage is formed in a substantially spiral shape around the rod-shaped heating element, and has one or more passages having an annular gap cross section bounded by the jacket tube on the inside and bounded by the bush on the outside It is. The urea aqueous solution is evaporated by the rod-shaped heating element at the first portion of the passage, and the air-fuel mixture flows through the second portion of the passage. The second part of the passage is provided with a coating that promotes hydrolysis of urea to ammonia, and the second part of the passage is used as a hydrolysis path and a hydrolysis catalyst. After the urea is hydrolyzed to ammonia, a vapor stream containing ammonia is supplied as a reducing agent from the passage to the exhaust pipe. Further, a bush is placed on the jacket tube. This bushing itself uses, for example, a heating wire, whereby the bushing is also heated, so that the passage is heated from inside and outside.

JP-T-2009-537723 (Claim 1, paragraphs [0060] to [0065], FIGS. 5 and 6) JP-T-2009-537725 (Claim 1, paragraphs [0027], [0047], [0048], FIGS. 1 and 4)

  However, both of the air-fuel mixture supply apparatus disclosed in the above-mentioned conventional patent document 1 and the exhaust gas treatment apparatus disclosed in the above-mentioned conventional patent document 2 are obtained by hydrolyzing the urea aqueous solution, which is a liquid, after evaporating. Since the reducing agent comprising a mixture or vapor stream containing ammonia is generated, the supply amount of the reducing agent to the exhaust pipe greatly changes due to a change in pressure, and the supply amount of the reducing agent to the exhaust pipe is reduced. There was a problem that was difficult to control. Further, in the air-fuel mixture supply apparatus disclosed in the above-mentioned conventional patent document 1, when the urea aqueous solution flows into the evaporation chamber, the urea aqueous solution evaporates to generate a gas mixture containing urea and ammonia. When it flows into the cracking catalytic converter, urea in the mixture is almost completely hydrolyzed and flows into the exhaust pipe, so that the urea in the aqueous urea solution does not evaporate in the evaporation chamber, but only water evaporates and the urea crystallizes. In this case, crystallized urea may be deposited on the inner surface of the evaporation chamber. Furthermore, in the conventional gas mixture supply apparatus disclosed in Patent Document 1, an evaporation chamber and a hydrolysis catalytic converter are separately provided to generate a reducing agent gas mixture containing ammonia from an aqueous urea solution. For this reason, the number of parts increases, and there is a problem that a large installation space for the evaporation chamber and the hydrolysis catalytic converter must be secured.

  On the other hand, in the above-described conventional exhaust gas treatment apparatus, when the urea aqueous solution flows into the passage of the hydrolysis catalyst, the urea aqueous solution evaporates at the first portion of the passage and then is hydrolyzed at the second portion of the passage. Since it decomposes and flows into the exhaust pipe as a vapor stream containing ammonia, urea in the urea aqueous solution does not evaporate at the first part of the passage, and only water evaporates and urea may crystallize. In some cases, crystallized urea accumulates in the passage and the deposit may clog the passage. Further, in the conventional exhaust gas treatment apparatus disclosed in Patent Document 2, the passage of the hydrolysis catalyst is formed in a substantially spiral shape around the rod-shaped heating element, the inside is bounded by the jacket tube, and the outside is the bush. Because it is one or more passages with an annular gap cross section bounded by, it is necessary to machine the jacket tube and bushing with high precision, and there is also a problem that the man-hours for machining these parts increase. .

  The first object of the present invention is to easily control the supply amount of ammonia water to the exhaust pipe by reforming it to ammonia water without evaporating the urea water with a urea water reformer, and the exhaust gas temperature is reduced. An object of the present invention is to provide an exhaust gas purification device that can efficiently reduce NOx in exhaust gas even when the temperature is relatively low. A second object of the present invention is to provide an exhaust gas purifying apparatus capable of preventing only water from evaporating and crystallization of urea by reforming it into ammonia water without evaporating urea water with a urea water reformer. Is to provide. A third object of the present invention is to reform liquid urea water to liquid ammonia water with a urea water reformer, thereby increasing the urea water reformer without increasing the number of parts of the urea water reformer. It is in providing the exhaust gas purification apparatus which can achieve size reduction. The fourth object of the present invention is to relatively easily reduce the reducing agent circulation pipe with relatively low accuracy without increasing the number of processing steps by winding the reducing agent circulation pipe spirally around the outer peripheral surface of the rod-shaped heater. An object is to provide an exhaust gas purifying apparatus that can be manufactured easily.

As shown in FIGS. 1 and 2, the first aspect of the present invention is an exhaust gas purification device that purifies exhaust gas of the engine 11. NOx in the exhaust gas provided in the exhaust pipe 15 of the engine 11 can be reduced to N _2. A selective catalytic reduction catalyst 12, a urea water reformer 14 for heating urea water 13 by a heater 14 b to reform it into ammonia water, and urea water supply means 16 for supplying urea water 13 to the urea water reformer 14. Either the ammonia water reformed by the urea water reformer 14 facing the exhaust pipe 15 upstream of the selective catalytic reduction catalyst 12 or the urea water passed through without being reformed by the urea water reformer 14. An injection nozzle 17 capable of injecting either or both, a catalyst temperature sensor 33 for detecting an exhaust gas temperature related to the selective catalytic reduction catalyst 12, a pressure sensor 34 for detecting an inlet pressure of the urea water reformer 14, and a catalyst Temperature sensor Characterized by comprising a controller 38 which controls the heater 14b and the urea water supply device 16 based on the detection outputs of the sub 33 and the pressure sensor 34.

  The second aspect of the present invention is an invention based on the first aspect. As shown in FIG. 2, the urea water reformer 14 includes a cylindrical reforming case 14a and the reforming case 14a. And a plurality of inorganic porous bodies 14c filled in the reforming case 14a and transmitting heat of the heater 14b to the inside of the reforming case 14a. And

  The third aspect of the present invention is an invention based on the second aspect, and as shown in FIG. 5, a partition plate 64f is provided in the reforming case 64a with a predetermined interval in the longitudinal direction of the case. Provided, the reforming case 64a is partitioned into a plurality of spaces communicating with each other by the partition plate 64f, the plurality of spaces are filled with a plurality of inorganic porous bodies 64c, and a plurality of urea waters flowing into the reforming case 64a are provided. This is characterized in that it is configured to pass through the space while being reformed into ammonia water.

  A fourth aspect of the present invention is an invention based on the second or third aspect, and further, as shown in FIG. 2, a catalyst that promotes hydrolysis of urea water 13 is supported on the inorganic porous body 14c. It is characterized by that.

  A fifth aspect of the present invention is an invention based on the first aspect, and as shown in FIGS. 7 and 10, the urea water reformer 84 includes a rod-shaped heater 84a and an outer peripheral surface of the heater 84a. And a reducing agent circulation pipe 84b through which urea water flows and transfers the heat of the heater 84a to the inner surface, and an adsorbent layer 84c that is coated on the inner peripheral surface of the reducing agent circulation pipe 84b and adsorbs urea water. It is characterized by having.

  A sixth aspect of the present invention is an invention based on the fifth aspect, and further, as shown in FIG. 10, is characterized in that a catalyst for promoting hydrolysis of urea water is supported on the adsorbent layer 84c. To do.

In the exhaust gas purifying apparatus according to the first aspect of the present invention, the urea water reformer reforms ammonia water without evaporating it, and the volume of the ammonia water or urea water hardly changes even when this pressure changes. Since either or both of these are injected into the exhaust pipe from the injection nozzle, the amount of ammonia water or urea water supplied to the exhaust pipe can be easily controlled. Further, the ammonia water injected from the injection nozzle into the exhaust pipe is quickly vaporized into ammonia gas even when the exhaust gas temperature is relatively low, and this ammonia gas converts NOx in the exhaust gas to N on the selective catalytic reduction catalyst. Since it functions as a reducing agent that reduces to ₂ , NOx in the exhaust gas can be efficiently reduced even when the exhaust gas temperature is relatively low. When the exhaust gas temperature is relatively high, the urea water is passed through the urea water reformer without being reformed by the urea water reformer and is ejected from the ejection nozzle to the exhaust pipe. Since the injected urea water is reformed into ammonia gas by the relatively high temperature exhaust gas, the ammonia gas functions as a reducing agent that reduces NOx in the exhaust gas to N ₂ on the selective catalytic reduction catalyst.

  Further, since the urea water reformer reforms the ammonia water without evaporating it, it is possible to prevent only water from evaporating and urea from crystallizing. As a result, it is possible to prevent the crystallized urea from accumulating in the urea water reformer. Furthermore, since the evaporation chamber and hydrolysis catalyst converter are provided separately to generate the reducing agent mixture containing ammonia from the urea aqueous solution, the number of parts increases, and the evaporation chamber and hydrolysis catalyst converter are installed. Compared with a conventional air-fuel mixture supply device that requires a large space, the present invention reforms liquid urea water into liquid ammonia water with a single urea water reformer. The urea water reformer can be reduced in size without increasing the number of parts of the reformer. As a result, the urea water reformer can be installed in a relatively narrow space.

  In the exhaust gas purifying apparatus according to the second aspect of the present invention, the inorganic porous body filled in the reforming case functions as a heat medium for transferring the heat of the heater to the inside of the reforming case, and soaks urea water. Therefore, urea water can be efficiently reformed into ammonia water.

  In the exhaust gas purifying apparatus according to the third aspect of the present invention, the urea water that has flowed into the reforming case passes through a plurality of spaces while meandering, so that the contact rate with the inorganic porous body of urea water increases, and the urea water Can be more efficiently modified to ammonia water.

  In the exhaust gas purifying apparatus of the fourth aspect of the present invention, the hydrolysis of urea water is promoted by the catalyst supported on the inorganic porous body, so that the urea water can be more efficiently reformed to ammonia water.

  In the exhaust gas purifying apparatus according to the fifth aspect of the present invention, the reducing agent circulation pipe transfers the heat of the heater to the inner surface of the reducing agent circulation pipe, and the adsorbent layer adsorbs so as to soak in urea water. By passing through the agent flow pipe, it can be efficiently reformed into ammonia water. In addition, in the present invention, the reducing agent flow pipe is provided on the outer peripheral surface of the rod-shaped heater as compared with the conventional exhaust gas treatment apparatus that requires processing of the outer tube and the bush with high accuracy and increases the number of processing steps of these parts. Since only the spiral winding is required, the reducing agent flow pipe can be manufactured relatively easily with relatively low accuracy without increasing the number of processing steps.

  In the exhaust gas purifying apparatus according to the sixth aspect of the present invention, the hydrolysis of urea water is promoted by the catalyst supported on the adsorbent layer, so that the urea water can be more efficiently reformed to ammonia water.

It is a block diagram which shows the exhaust gas purification apparatus of 1st Embodiment of this invention. It is the sectional view on the AA line of FIG. 3 which shows the urea water reformer of the exhaust gas purification apparatus. FIG. 3 is a sectional view taken along line B-B in FIG. 2. It is a figure which shows the change of the ammonia water generation rate in a urea water reformer with respect to the temperature change of a urea water reformer, and the change of the inlet pressure of a urea water reformer. It is CC sectional view taken on the line of FIG. 6 which shows the urea water reformer of 2nd Embodiment of this invention. It is the DD sectional view taken on the line of FIG. It is the EE sectional view taken on the line of FIG. 8 which shows the urea water reformer of 3rd Embodiment of this invention. It is the FF sectional view taken on the line of FIG. It is a side view of the urea water reformer which shows the state which removed the heat insulation case and heat insulating material of the urea water reformer. It is the GG sectional view taken on the line of FIG.

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

<First Embodiment>
As shown in FIG. 1, the exhaust gas purification apparatus includes a selective reduction catalyst 12 that can reduce NOx in exhaust gas discharged from a diesel engine 11 to N ₂ , and urea water reforming that reforms urea water 13 into ammonia water. And the urea water supply means 16 for supplying urea water 13 to the urea water reformer 14 and the exhaust pipe 15 on the exhaust gas upstream side of the selective catalytic reduction catalyst 12, either ammonia water or urea water or And an injection nozzle 17 capable of injecting both. An intake pipe 19 is connected to the intake port of the diesel engine 11 via an intake manifold 18, and an exhaust pipe 15 is connected to the exhaust port via an exhaust manifold 21. The intake pipe 19 is provided with a compressor housing 23a of the turbocharger 23 and an intercooler 24 for cooling the intake air compressed by the turbocharger 23, and the exhaust pipe 15 is provided with a turbine of the turbocharger 23. A housing 23b is provided. A compressor rotor blade (not shown) is rotatably accommodated in the compressor housing 23a, and a turbine rotor blade (not shown) is rotatably accommodated in the turbine housing 23b. The compressor rotor blades and the turbine rotor blades are connected by a shaft (not shown), and the compressor rotor blades are rotated via the turbine rotor blades and the shaft by the energy of the exhaust gas discharged from the engine 11, and the compressor rotor blades are rotated. Thus, the intake air in the intake pipe is compressed.

The selective catalytic reduction catalyst 12 is provided in the exhaust pipe 15. Specifically, a catalyst case 26 having a larger diameter than the exhaust pipe 15 is provided in the middle of the exhaust pipe 15, and the selective catalytic reduction catalyst 12 is accommodated in the catalyst case 26. The selective catalytic reduction catalyst 12 is a monolith catalyst, and is configured by coating a honeycomb carrier made of cordierite with zeolite or zirconia. Examples of zeolite include copper zeolite, iron zeolite, zinc zeolite, and silver zeolite. The selective catalytic reduction catalyst 12 made of copper zeolite is configured by coating a honeycomb carrier with a slurry containing zeolite powder obtained by ion exchange of copper. The selective reduction catalyst 12 made of iron zeolite, zinc zeolite or silver zeolite is configured by coating a honeycomb carrier with a slurry containing zeolite powder obtained by ion exchange of iron, zinc or silver. Furthermore, the selective reduction catalyst 12 made of zirconia is configured by coating a honeycomb carrier with a slurry containing γ-alumina powder or θ-alumina powder supporting zirconia. When ammonia gas is supplied to the selective catalytic reduction catalyst 12, the ammonia gas functions as a reducing agent that reduces NOx to N ₂ on the selective catalytic reduction catalyst 12.

  On the other hand, as shown in FIGS. 2 and 3, the urea water reformer 14 includes a cylindrical reforming case 14a, a heater 14b spirally wound around the outer peripheral surface of the reforming case 14a, A plurality of inorganic porous bodies 14c filled in the modified case 14a. The reforming case 14a has a cylindrical case main body 14d having one end opened and the other end closed, and a flange that is detachably attached to the open end of the case main body 14d and closes the open end of the case main body 14d to be openable. 14e. A short supply pipe 14f for supplying urea water 13 into the reforming case 14a is connected to the center of the flange 14e. Ammonia water or urea water from the reforming case 14a is connected to the center of the closed end of the case body 14d. A discharge short tube 14g for discharging the gas is connected. The reforming case 14a is formed of a metal having a relatively high thermal conductivity of 15 to 17 W / (m · K) such as SUS316, SUS304, Inconel (registered trademark manufactured by Huntington Alloys Canada Limited). Further, the heater 14b is configured by inserting a heating element such as a nichrome wire into a metal sheath (metal ultra-thin tube) and filling a gap between the metal sheath and the heating element with high-purity inorganic insulating powder. It is preferable to use a so-called sheathed heater.

  Furthermore, it is preferable to use porous zeolite particles having a particle diameter of 0.2 to 10 mm, molecular sieve (trade name of synthetic zeolite developed by Union Carbite), etc., as the inorganic porous body 14c. The inorganic porous body 14c has a function as a heat medium for transmitting the heat of the heater 14b to the inside of the reforming case 14a, and a function as an adsorbent that adsorbs the urea water 13 soaking. The inorganic porous body 14c can carry a catalyst such as titania or zirconia. By supporting the catalyst on the inorganic porous body 14c, the hydrolysis of the urea water 13 can be promoted. The form of the inorganic porous body 14c is spherical in this embodiment, but may be an ellipsoid, a cylinder, a disk, or the like.

  The urea water reformer 14 is covered with a heat insulating case 14i filled with a heat insulating material 14h. Thereby, dissipation of the heat which heater 14b generated can be controlled. Reference numerals 14j and 14j in FIG. 2 are nets that prevent the inorganic porous body 14c from rolling out of the reforming case 14a into the supply short tube 14f or the discharge short tube 14g. When the urea water 13 is supplied to the urea water reformer 14 with the heater 14b turned on, all the urea water 13 is reformed into ammonia water by the urea water reformer 14, and this ammonia water is injected into the injection nozzle 17. Or a part of the urea water 13 is reformed to ammonia water by the urea water reformer 14 and the remaining urea water 13 passes through the urea water reformer 14 as it is without being reformed. The mixture of ammonia water and urea water is configured to be supplied to the injection nozzle 17. On the other hand, when the urea water 13 is supplied to the urea water reformer 14 with the heater 14b turned off, the urea water 13 is not reformed at all by the urea water reformer 14, and the urea water 13 remains as it is. 14 and supplied to the injection nozzle 17.

  Returning to FIG. 1, the urea water supply means 16 includes a urea water tank 16 a in which the urea water 13 is stored, and a first short pipe 14 f for supplying the urea water reformer 14 to the urea water tank 16 a. A supply pipe 16b and a pump 16c provided in the first supply pipe 16b and pumping the urea water 13 in the urea water tank 16a to the urea water reformer 14 are provided. The pump 16c is driven by a pump drive motor (not shown). The pressure of the urea water 13 discharged from the pump 16c can be adjusted by changing the speed of the pump drive motor continuously or stepwise. Further, the discharge short pipe 14g of the urea water reformer 14 is connected to the injection nozzle 17 via the second supply pipe 32, and the second supply pipe 32 is opened and closed by opening and closing the second supply pipe 32. A flow rate adjusting valve 31 that adjusts the flow rate of ammonia water or urea water injected from 17 is provided. The flow rate adjustment valve 31 can adjust the flow rate of ammonia water or urea water injected from the injection nozzle 17 by controlling the number of times of opening / closing per unit time, opening time, and closing time.

  On the other hand, a catalyst temperature sensor 33 for detecting an exhaust gas temperature related to the selective reduction catalyst 12 is provided in the catalyst case 26 on the exhaust gas inlet side of the selective reduction catalyst 12. Further, a pressure sensor 34 for detecting the inlet pressure of the urea water reformer 14 is provided in the supply short pipe 14 f of the urea water reformer 14. A first temperature sensor 41 that detects the temperature of the urea water 13 on the inlet side of the reforming case 14 a is provided on the inlet side of the reforming case 14 a of the urea water reformer 14. On the outlet side of the reforming case 14a, a second temperature sensor 42 that detects the temperature of the ammonia water or urea water on the outlet side of the reforming case 14a is provided. Further, the engine 11 is provided with a rotation sensor 36 that detects the rotation speed of the engine 11 and a load sensor 37 that detects the load of the engine 11. The detection outputs of the catalyst temperature sensor 33, the pressure sensor 34, the first temperature sensor 41, the second temperature sensor 42, the rotation sensor 36, and the load sensor 37 are connected to the control input of the controller 38, and the control output of the controller 38 is the heater 14b. The pump drive motor and the flow rate adjustment valve 31 are connected to each other.

  The controller 38 is provided with a memory 39. The memory 39 stores the speed of the pump drive motor, the number of opening / closing operations per unit time of the flow rate adjustment valve 31, the opening time and the closing time according to the engine speed, the engine load, and the exhaust gas temperature on the inlet side of the selective catalytic reduction catalyst 12. Time is stored in advance. Further, the memory 39 stores a change in the NOx flow rate in the exhaust gas in accordance with changes in the engine speed and engine load as a map. Further, the memory 39 stores an ammonia production rate according to the inlet pressure of the urea water reformer 14, the temperature in the urea water reformer 14, the ammonia water discharged from the urea water reformer 14, or the flow rate of the urea water. For example, is stored as a map as shown in FIG. Although the operation region of the urea water reformer 14 when the urea water 13 is reformed into ammonia water by the urea water reformer 14 varies depending on the shape of the urea water reformer 14 and the flow rate of the ammonia water, It is preferable to control the temperature in the water reformer 14 (the average temperature of the detection outputs of the first and second temperature sensors 41 and 42) within a range of 100 ° C. or more and less than 120 ° C. by the heater 14b. Since the inlet pressure of the urea water reformer 14 at this time is relatively high, the urea water reformer 14 is manufactured to have pressure resistance. Further, the heating efficiency of the urea water 13 by the heater 14b can be detected by the temperature difference between the detection outputs of the first and second temperature sensors 41 and 42.

  Reference numeral 43 in FIG. 1 denotes an EGR pipe that connects the exhaust manifold 21 and the intake pipe 15 to bypass the engine 11. The EGR pipe 43 branches from the branch pipe portion of the exhaust manifold 21 and joins to the intake pipe 19 on the intake downstream side of the intercooler 24. 1 is an EGR valve that is provided in the EGR pipe 43 and adjusts the flow rate of exhaust gas (EGR gas) recirculated from the EGR pipe 43 to the intake pipe 19. Further, reference numeral 46 in FIG. 1 is an EGR cooler that cools the exhaust gas (EGR gas) passing through the EGR pipe 43.

  The operation of the exhaust gas purification apparatus configured as described above will be described. The exhaust gas temperature is as low as 100 to 180 ° C. immediately after the engine 11 is started or during a light load operation of the engine 11. When the exhaust gas temperature in this temperature range is detected by the catalyst temperature sensor 33 and the rotation sensor 36 and the load sensor 37 detect no-load operation or light load operation of the engine, the controller 38 detects the catalyst temperature sensor 33, the rotation sensor 36 and the load sensor. On the basis of the detection outputs 37, the heater 14b is turned on and the speed of the pump drive motor is gradually increased. When the pressure sensor 34 detects that the inlet pressure of the urea water reformer 14 has reached a predetermined pressure, the pump drive motor is operated at this speed. In this state, when the first and second temperature sensors 41 and 42 detect that the temperature of the urea water 13 in the urea water reformer 14 has reached a predetermined temperature (for example, average temperature 110 ° C.), the controller 38 The flow regulating valve 31 is opened and closed at a predetermined number of opening / closing times per unit time, a predetermined opening time and a predetermined closing time.

  As a result, the urea water 13 supplied to the urea water reformer 14 is completely evaporated to ammonia water without evaporating and then injected from the injection nozzle 17 into the exhaust pipe 15. The urea water reformer 14 at this time reacts as shown in the following equations (1) and (2) to reform the urea water 13 into ammonia water.

NH ₂ —CO—NH ₂ + H ₂ O → NH ₃ + HNCO + H ₂ O (1)
HNCO + H ₂ O → NH ₃ + CO ₂ (2)
The above formula (1) is a thermal decomposition formula of urea water 13, and water does not contribute to this reaction. Formula (2) is a hydrolysis formula from isocyanic acid (HNCO) to ammonia (NH ₃ ). Ammonia (NH ₃ ) produced by this hydrolysis is easily soluble in water, so it becomes ammonia water (saturated water vapor pressure or higher), carbon dioxide (CO ₂ ) is difficult to dissolve in water, and part of it is heated into ammonia water by heating. It melts and becomes mostly dispersed in aqueous ammonia.

As described above, the urea water reformer 14 reforms the ammonia water 13 without evaporating it, so that it is possible to prevent only water from evaporating and urea from crystallizing. As a result, it is possible to prevent the crystallized urea from accumulating in the urea water reformer 14. Although the ammonia water reformed by the urea water reformer 14 contains gaseous carbon dioxide, most of the ammonia water is liquid and the volume does not change much even if the pressure changes. The supply amount of ammonia water can be easily controlled to an optimum flow rate. The ammonia water injected from the injection nozzle 17 into the exhaust pipe 15 is quickly vaporized into ammonia gas even when the exhaust gas temperature is relatively low, and this ammonia gas flows into the selective catalytic reduction catalyst 12 together with the exhaust gas. . Ammonia gas flowing into the selective catalytic reduction catalyst 12 together with the exhaust gas functions as a reducing agent for reducing NOx (NO, NO ₂ ) in the exhaust gas. That is, the selective reduction catalyst 12 quickly reduces NOx in the exhaust gas to N ₂ as shown by the following formula (3).

NO + NO ₂ + 2NH ₃ → 2N ₂ + 3H ₂ O (2)
The above formula (3) represents a chemical reaction formula in which NO and NO ₂ in the exhaust gas react with ammonia gas in the selective reduction catalyst 12 and NO and NO ₂ are reduced to N ₂ . As a result, even when the exhaust gas temperature is relatively low, NOx in the exhaust gas can be efficiently reduced.

On the other hand, when the exhaust gas temperature exceeds 180 ° C., the controller 38 turns off the heater 14 b based on the detection output of the catalyst temperature sensor 33. However, the controller 38 operates the pump drive motor at a predetermined speed, and opens and closes the flow rate adjustment valve 31 with a predetermined number of times of opening / closing (per unit time), a predetermined opening time, and a predetermined closing time. As a result, the urea water 13 is not reformed into ammonia water by the urea water reformer 14 but passes through the urea water reformer 14 as it is and is injected from the injection nozzle 17 into the exhaust pipe 15. Since the injected urea water is reformed into ammonia gas by a relatively high temperature exhaust gas, the ammonia gas functions as a reducing agent for reducing NOx in the exhaust gas to N ₂ on the selective catalytic reduction catalyst 12, and the exhaust gas NOx inside is efficiently reduced.

<Second Embodiment>
5 and 6 show a second embodiment of the present invention. 5 and 6, the same reference numerals as those in FIGS. 2 and 3 denote the same components. In this embodiment, the urea water reformer 64 includes a cylindrical reforming case 64a, a heater 64b spirally wound around the outer peripheral surface of the reforming case 64a, and the reforming case 64a filled. A plurality of inorganic porous bodies 64c. The reforming case 64a has a square cylindrical case main body 64d with both ends open, and a pair of square plates that are detachably attached to both end faces of the case main body 64d and close both open ends of the case main body 64d. Flanges 64e, 64e, and a plurality of partition plates 64f provided in the case body 64d at predetermined intervals in the longitudinal direction of the case body 64d. The inside of the case main body 64d is partitioned into a plurality of spaces communicating with each other by these partition plates 64f, and these spaces are filled with a plurality of inorganic porous bodies 64c. The modified case 64a is formed of the same material as the modified case of the first embodiment, and the inorganic porous body 64c has the same shape as the inorganic porous body of the first embodiment. It is formed.

  On the other hand, a supply short pipe 64g for supplying urea water into the reforming case 64a is connected to the lower part of the flange 64e that closes the inlet side end face of the case main body 64d, and closes the outlet side end face of the case main body 64d. A discharge short pipe 64h for discharging ammonia water or urea water from the reforming case 64a is connected to the upper part of the flange 64e. The urea water reformer 64 is covered with a heat insulating case 64j filled with a heat insulating material 64i. Thereby, dissipation of the heat which heater 64b generated can be controlled. Further, reference numerals 64k and 64k in FIG. 5 denote nets that prevent the inorganic porous body 64c from rolling out of the reforming case 64a into the supply short pipe 64g or the discharge short pipe 64h. The configuration other than the above is the same as that of the first embodiment.

  In the exhaust gas purification apparatus configured as described above, the urea water that has flowed into the reforming case 64a passes through a plurality of spaces while meandering, so that the contact rate with the inorganic porous body 64c of the urea water increases, and the urea water Can be more efficiently modified to ammonia water. Since the operation other than the above is substantially the same as the operation of the first embodiment, repeated description will be omitted.

<Third Embodiment>
7 to 10 show a third embodiment of the present invention. 7-9, the same code | symbol as FIG.2 and FIG.3 shows the same component. In this embodiment, the urea water reformer 84 includes a rod-shaped heater 84a, a reducing agent circulation pipe 84b that is spirally wound around the outer peripheral surface of the heater 84a and through which urea water flows, and a reducing agent circulation pipe 84b. It has an adsorbent layer 84c (FIG. 10) coated on the inner peripheral surface and adsorbing urea water. As the heater 84a, a heating element 84d such as a nichrome wire is loosely inserted in a metal sheath (metal microtubule), and a high-purity inorganic insulating powder is filled in the gap between the metal sheath and the heating element 84d. It is preferable to use a so-called sheathed heater. The reducing agent distribution pipe 84b is made of a metal having a relatively high thermal conductivity of 15 to 17 W / (m · K) such as SUS316, SUS304, Inconel (registered trademark manufactured by Huntington Alloys Canada Limited). Thereby, the heat of the heater 84a is efficiently transmitted to the inner surface of the reducing agent circulation pipe 84b.

  On the other hand, the adsorbent layer 84c may be formed to a thickness of 0.01 to 0.1 mm by using porous zeolite, molecular sieve (trade name of synthetic zeolite developed by Union Carbide), or the like. Preferred (FIG. 10). The adsorbent layer 84c functions as a heat medium that transfers the heat of the heater 84a transmitted to the reducing agent circulation pipe 84b to the inside of the reducing agent circulation pipe 84b, and as an adsorbent that adsorbs so as to soak urea water. With functions. The adsorbent layer 84c can carry a catalyst such as titania or zirconia. By supporting the catalyst on the adsorbent layer 84c, hydrolysis of urea water can be promoted. The urea water reformer 84 is covered with a heat insulating case 84f filled with a heat insulating material 84e (FIGS. 7 and 8). Thereby, dissipation of the heat which heater 84a generated can be controlled.

  On the other hand, the pressure sensor 86 for detecting the inlet pressure of the urea water reformer 84 is provided in the reducing agent circulation pipe 84b just before being wound around the heater 84a, and the pressure of the urea water in the reducing agent circulation pipe 84b is set. It detects (FIGS. 7 and 9). Further, the surface temperature of the heater 84a in the vicinity of the winding start portion of the reducing agent circulation pipe 84b to the heater 84a is detected by the first temperature sensor 91, and the surface temperature of the heater 84a in the vicinity of the winding end portion of the reducing agent circulation pipe 84b to the heater 84a is detected. It is detected by the second temperature sensor 92. That is, with the heater 84a turned on, the temperature of the urea water in the reducing agent circulation pipe 84b that has started to be heated by the heater 84a is indirectly detected by the first temperature sensor 91, and the temperature of the urea water is detected by the second temperature sensor 92 by the heater 84a. The temperature of the ammonia water in the reducing agent circulation pipe 84b that has been heated is indirectly detected. Further, one end of the reducing agent circulation pipe 84b (the end on the supply side of urea water to the urea water reformer 84) is connected to the first supply pipe 16b, and the other end of the reducing agent circulation pipe 84b (the urea water reformer 84). A discharge side end portion of ammonia water or urea water) is connected to the second supply pipe 32. The configuration other than the above is the same as that of the first embodiment.

  In the exhaust gas purification apparatus configured as described above, when the urea water is circulating in the reducing agent circulation pipe 84b spirally wound around the heater 84a, the reducing agent circulation pipe 84b reduces the heat of the heater 84a. Since it is transmitted to the inner surface of the agent flow pipe 84b and adsorbed so that the adsorbent layer 84c soaks in the urea water, the urea water can be efficiently reformed into the ammonia water in the spiral reducing agent flow pipe 84b. Further, since the reducing agent circulation pipe 84b only needs to be spirally wound around the outer peripheral surface of the rod-shaped heater 84a, the reducing agent circulation pipe 84b can be produced relatively easily with relatively low accuracy and without increasing the number of processing steps. . Since the operation other than the above is substantially the same as the operation of the first embodiment, repeated description will be omitted.

  In the first to third embodiments, the exhaust gas purifying apparatus of the present invention is applied to a diesel engine. However, the exhaust gas purifying apparatus of the present invention may be applied to a gasoline engine. In the first to third embodiments, the exhaust gas purifying apparatus of the present invention is applied to a turbocharged diesel engine. However, the exhaust gas purifying apparatus of the present invention is a naturally aspirated diesel engine or a naturally aspirated gasoline. It may be applied to the engine. In the first to third embodiments, the catalyst temperature sensor is provided on the exhaust gas inlet side of the selective reduction catalyst in the catalyst case. However, if the temperature related to the selective reduction catalyst can be detected, the catalyst temperature sensor May be provided on the exhaust gas outlet side of the selective reduction catalyst in the catalyst case, or a catalyst temperature sensor may be provided on both the exhaust gas inlet side and the exhaust gas outlet side of the selective reduction catalyst in the catalyst case.

11 Diesel engine (engine)
DESCRIPTION OF SYMBOLS 12 Selective reduction type | mold catalyst 13 Urea water 14, 64, 84 Urea water reformer 14a, 64a Reforming case 14b, 64b, 84a Heater 14c, 64c Inorganic porous body 16 Urea water supply means 17 Injection nozzle 15 Exhaust pipe 33 Catalyst Temperature sensor 34, 86 Pressure sensor 38 Controller 64f Partition plate 84b Reducing agent flow pipe 84c Adsorbent layer

Claims (6)

In the exhaust gas purification device that purifies the exhaust gas of the engine (11),
A selective reduction catalyst (12) provided in the exhaust pipe (15) of the engine (11) and capable of reducing NOx in the exhaust gas to N ₂ ;
A urea water reformer (14, 64, 84) for heating the urea water (13) with a heater (14b, 64b, 84a) to reform it into ammonia water;
Urea water supply means (16) for supplying the urea water (13) to the urea water reformer (14, 64, 84);
Ammonia water reformed by the urea water reformer (14, 64, 84) facing the exhaust pipe (15) upstream of the exhaust gas from the selective reduction catalyst (12) or the urea water reformer (14, 64, 84) and an injection nozzle (17) capable of injecting one or both of the urea water that has passed through without being reformed,
A catalyst temperature sensor (33) for detecting the exhaust gas temperature related to the selective catalytic reduction catalyst (12);
A pressure sensor (34) for detecting the inlet pressure of the urea water reformer (14);
A controller (38) for controlling the heater (14b, 64b, 84a) and the urea water supply means (16) based on the detection outputs of the catalyst temperature sensor (33) and the pressure sensor (34). An exhaust gas purification apparatus characterized by that.   The urea water reformer (14, 64) includes a cylindrical reforming case (14a, 64a) and a heater (14b, 64a) wound spirally around the outer peripheral surface of the reforming case (14a, 64a). 64b) and a plurality of inorganic porous bodies (14c, 64c) filled in the reforming case (14a, 64a) and transferring heat of the heater (14b, 64b) to the inside of the reforming case (14a, 64a). The exhaust gas purification apparatus according to claim 1, further comprising:   A partition plate (64f) is provided in the reforming case (64a) at a predetermined interval in the longitudinal direction of the case, and the reforming case (64a) communicates with each other by the partition plate (64f). The plurality of spaces are filled with the plurality of inorganic porous bodies (64c), and the urea water flowing into the reforming case (64a) passes through the plurality of spaces while meandering. The exhaust gas purification device according to claim 2, wherein the exhaust gas purification device is configured to be reformed into the ammonia water.   The exhaust gas purifying apparatus according to claim 2 or 3, wherein a catalyst for promoting hydrolysis of the urea water (13) is supported on the inorganic porous body (14c, 64c).   The urea water reformer (84) is a rod-shaped heater (84a) and is wound spirally around the outer peripheral surface of the heater (84a) so that the urea water flows and the heat of the heater (84a) is transferred to the inner surface. The exhaust gas purifying apparatus according to claim 1, further comprising: a reducing agent circulation pipe (84b) that transmits to the gas, and an adsorbent layer (84c) that is coated on an inner peripheral surface of the reducing agent circulation pipe (84b) and adsorbs the urea water. .   The exhaust gas purifying apparatus according to claim 5, wherein a catalyst for promoting hydrolysis of the urea water is supported on the adsorbent layer (84c).

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