JP2014066162A - Exhaust emission control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control device capable of suppressing the thermodecomposition of ammonia when heating a heated member provided in an exhaust system for an engine with chemical heat storage using the ammonia.SOLUTION: An exhaust emission control device 1 includes an oxidation catalyst 4 disposed in an exhaust pipe 3 formed of a magnetic substance, and reactors 8 for heating the oxidation catalyst 4 with chemical heat storage using ammonia. The reactors 8 are arranged around the exhaust pipe 3 and divided into a plurality of ones. The outer face of each reactor 8 is formed of a magnetic substance. A coil 15 is wound on the outer face of each reactor 8, and an external power supply 16 is connected to each coil 15 for supplying voltage thereto. Normally, each reactor 8 is being isolated from the outer peripheral face of the exhaust pipe 3. When the external power supply 16 is turned on, current flows in each coil 15 to generate electromagnetic force in each reactor 8. By the electromagnetic force, each reactor 8 is attracted to (put in contact with) the outer peripheral face of the exhaust pipe 3.

Description

  The present invention relates to an exhaust purification device that purifies exhaust gas from an engine.

  The exhaust gas discharged from the diesel engine contains environmental pollutants such as CO, HC, PM, and NOx. In order to purify these environmental pollutants, a catalyst and a filter are provided in an exhaust pipe connected to the engine. There is an optimum temperature for the catalyst to activate the purification capability of environmental pollutants. When the engine is started, the temperature of the engine and exhaust gas is low, and it takes time to reach the temperature at which the catalyst is activated. Therefore, environmental pollutants are released to the atmosphere without being purified. In order to prevent such environmental pollutants from being released into the atmosphere when the engine is started, it is necessary to heat the catalyst to the activation temperature or higher in a short time. In that case, there is a method in which a heater is attached to the catalyst to heat the catalyst, or fuel is injected into the exhaust pipe and ignited by a plug, and the heat is used to heat the catalyst. However, both methods have a problem that fuel consumption is deteriorated because fuel is used for heating the catalyst.

As a method for solving the above problem, in order to reduce fuel consumption loss, for example, as described in Patent Document 1, there is a method of heating a catalyst using reaction heat of a chemical reaction. For example, a reaction material (for example, MgCl ₂ ) is disposed in the vicinity of the catalyst, and the reaction material is reacted with ammonia (NH ₃ ) stored in an adsorber. That is, a reaction of MgCl ₂ + 6NH ₃ → MgCl ₂ -6NH ₃ + heat occurs, and the catalyst is heated by the reaction heat generated at that time. Incidentally, MgCl ₂ -6NH ₃ produced by the above reaction is decomposed into MgCl ₂ and NH ₃ by 200 ° C. or more waste heat is returned to the original.

JP 2011-58678 A

However, the following problems exist in the prior art. That is, it has been confirmed by experiments that NH ₃ which is a heat transport medium for chemical heat storage thermally decomposes at 400 ° C. or higher. Therefore, when the reactor containing the reaction material that reacts with NH ₃ is arranged in contact with the exhaust pipe, when the temperature of the exhaust gas reaches 400 ° C. or higher, NH ₃ present in the reactor is As a result, the heat is decomposed and sufficient reaction heat cannot be obtained.

An object of the present invention is to provide an exhaust emission control device that can suppress thermal decomposition of ammonia when a heated member provided in an engine exhaust system is heated by chemical heat storage using ammonia (NH ₃ ). It is to be.

  The present invention relates to an exhaust gas purification apparatus that purifies exhaust gas from an engine, a heated member provided inside an exhaust pipe connected to the engine, and a periphery of the exhaust pipe, and a chemical reaction with ammonia. A reaction material that heats the member to be heated, an ammonia supply means that supplies ammonia to the reactor, and the reactor is brought into contact with and separated from the outer peripheral surface of the exhaust pipe by magnetic force. And a moving means.

  Thus, in the exhaust gas purification apparatus of the present invention, when the temperature of the exhaust gas is low, the moving unit brings the reactor into contact with the outer peripheral surface of the exhaust pipe by using magnetic force. In that state, the reaction material and ammonia chemically react in the reactor to generate reaction heat, and the member to be heated is heated by the reaction heat. On the other hand, when the temperature of the exhaust gas becomes high, the reactor is separated from the outer peripheral surface of the exhaust pipe by the moving means. In this state, since an air layer is formed between the exhaust pipe and the reactor, the heat (exhaust heat) of the exhaust gas in a high temperature state passing through the exhaust pipe is hardly transmitted to the reactor. Thereby, thermal decomposition of ammonia in the reactor can be suppressed.

  Preferably, the outer peripheral surface of the exhaust pipe and the outer surface of the reactor are both made of a magnetic material, and the moving means has a coil wound around the outer surface of the reactor and a power source for applying a voltage to the coil. . In this case, when the power is turned on, a current flows through the coil, so that an electromagnetic force is generated in the reactor, and the reactor is adsorbed (contacted) to the outer peripheral surface of the exhaust pipe by the electromagnetic force. In this state, when the power is turned off, no current flows through the coil, so the electromagnetic force generated in the reactor is lost, and the reactor is separated from the outer peripheral surface of the exhaust pipe. Therefore, the moving means can be realized with a simple configuration.

  At this time, preferably, the apparatus further comprises temperature detecting means for detecting the temperature of the exhaust gas, and control means for controlling the moving means based on the temperature of the exhaust gas detected by the temperature detecting means. When the temperature of the exhaust gas is lower than the predetermined temperature, the power is turned on so that the reactor contacts the outer peripheral surface of the exhaust pipe. When the temperature of the exhaust gas is higher than the predetermined temperature, the reactor is connected to the exhaust pipe. The power is turned off so as to be separated from the outer peripheral surface of the power source. In this case, when the temperature of the exhaust gas is higher than a predetermined temperature while the reactor is in contact with the outer peripheral surface of the exhaust pipe, the power is automatically turned off, and the reactor is disconnected from the outer peripheral surface of the exhaust pipe. Leave.

  Preferably, the engine is a diesel engine, and the member to be heated is an oxidation catalyst that oxidizes and purifies harmful substances contained in the exhaust gas, and the exhaust pipe is disposed downstream of the oxidation catalyst in the exhaust gas. A diesel exhaust particulate removal filter that collects and removes harmful substances contained in the exhaust pipe is disposed, and a plurality of reactors are disposed around the exhaust pipe along the circumferential direction of the exhaust pipe. When the diesel exhaust particulate filter (DPF) is regenerated, that is, when PM (soot) deposited on the DPF is burned, the exhaust gas passing through the oxidation catalyst is in a high temperature state of 600 ° C. or higher. Therefore, it is particularly effective to apply the exhaust emission control device of the present invention to the oxidation catalyst provided in the exhaust system of the diesel engine.

  ADVANTAGE OF THE INVENTION According to this invention, when heating the to-be-heated member provided in the exhaust system of the engine by chemical heat storage using ammonia, thermal decomposition of ammonia can be suppressed. This makes it possible to generate sufficient reaction heat from the reactor.

1 is a schematic configuration diagram illustrating an embodiment of an exhaust emission control device according to the present invention. It is a block diagram which shows the principal part of the exhaust gas purification apparatus shown in FIG. It is sectional drawing which shows the principal part of the exhaust gas purification apparatus shown in FIG. It is a flowchart which shows the procedure of the power supply control process by the controller shown in FIG. It is sectional drawing which shows the state which each reactor shown in FIG. 3 contacted the outer peripheral surface of the exhaust pipe.

  Hereinafter, preferred embodiments of an exhaust emission control device according to the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a schematic configuration diagram showing an embodiment of an exhaust emission control device according to the present invention. In the figure, an exhaust emission control device 1 according to the present embodiment is provided in an exhaust system of a diesel engine (sometimes referred to simply as an engine) 2 and contains harmful substances (environmental pollutants) contained in exhaust gas discharged from the engine 2. ).

  The exhaust purification device 1 includes an oxidation catalyst (DOC) 4, a diesel exhaust particulate removal filter (DPF) 5, and a selective reduction catalyst (SCR) arranged in order from the upstream side to the downstream side of the exhaust pipe 3 connected to the engine 2. ) 6. A fuel addition valve 7 for adding fuel into the exhaust pipe 3 is provided between the engine 2 and the oxidation catalyst 4. The oxidation catalyst 4 is a catalyst that oxidizes and purifies HC, CO, etc. contained in the exhaust gas. The DPF 5 is a filter that collects and removes PM (soot) contained in the exhaust gas. The SCR 6 is a catalyst that supplies urea water or the like to reduce and purify NOx contained in the exhaust gas.

Further, the exhaust purification apparatus 1 further includes a reactor 8 that heats the oxidation catalyst 4 using chemical heat storage. A reservoir 9 for storing ammonia (NH ₃ ) is connected to the reactor 8 via an NH ₃ supply pipe 10. The NH ₃ supply pipe 10 is provided with an on-off valve 11.

  FIG. 2 is a configuration diagram showing a main part of the exhaust purification apparatus 1, and FIG. 3 is a cross-sectional view showing a main part of the exhaust purification apparatus 1. In each figure, the oxidation catalyst 4 is disposed in a cylindrical exhaust pipe 3 formed of a magnetic material (for example, SUS). The oxidation catalyst 4 is formed of a honeycomb substrate 12 that supports a catalyst material. The honeycomb substrate 12 is made of ceramics such as cordierite or metal such as stainless steel. As the catalyst material supported on the honeycomb substrate 12, a noble metal such as platinum or palladium is used.

The reactor 8 is divided into a plurality (four in this case). Each reactor 8 has a curved cross section, and is disposed at a position corresponding to the oxidation catalyst 4 around the exhaust pipe 3 with a predetermined interval. The reactor 8 has a housing 13 made of a magnetic material (for example, SUS). That is, the outer surface of the reactor 8 is made of a magnetic material. A solid or powdery reaction material (not shown) that generates heat by chemically reacting with NH ₃ is accommodated in the housing 13. Examples of the reaction material include metal chloride, metal bromide, and metal iodide compounds such as MgCl ₂ , CaCl ₂ , NiCl ₂ , ZnCl ₂ , and SrCl ₂ .

  Between the exhaust pipe 3 and each reactor 8, an elastic body 14 such as a spring that urges each reactor 8 in a direction away from the outer peripheral surface of the exhaust pipe 3 is provided. Each reactor 8 is supported by a support member (not shown) so as to be movable in the radial direction of the exhaust pipe 3.

  Coils 15 are wound around the outer surface of the casing 13 of each reactor 8. Each coil 15 is connected to an external power supply 16 for applying a voltage to the coil 15. Each coil 15 and each external power source 16 constitute moving means for bringing the reactor 8 into contact with and away from the outer peripheral surface of the exhaust pipe 3 in the radial direction of the exhaust pipe 3. Normally, each reactor 8 is separated from the outer peripheral surface of the exhaust pipe 3 by the urging force of the elastic body 14 (see FIG. 3).

  Further, the exhaust emission control device 1 includes an ignition switch (IG switch) 17 for instructing start and stop of the engine 2, a temperature sensor 18 for detecting the temperature of exhaust gas passing through the oxidation catalyst 4, A controller 19 that controls ON / OFF of each external power supply 16 based on the operation signal and the detection signal of the temperature sensor 18 is provided.

  FIG. 4 is a flowchart showing a procedure of power supply control processing by the controller 19. This flowchart shows a processing procedure until the temperature of the exhaust gas is changed from a low state to a sufficiently high state by starting the engine 2.

  In FIG. 4, first, based on the operation signal of the IG switch 17, it is determined whether or not the IG switch 17 is turned on (step S101). When the IG switch 17 is turned on, a voltage is applied to each coil 15 by each external power supply 16 by controlling each external power supply 16 to be turned on (step S102). Then, since an electric current flows through each coil 15, an electromagnetic force is generated in each reactor 8. Therefore, as shown in FIG. 5, each reactor 8 is adsorbed (contacted) to the outer peripheral surface of the magnetic exhaust pipe 3 against the urging force of the elastic body 14. In the state where each reactor 8 is adsorbed on the outer peripheral surface of the exhaust pipe 3, the elastic body 14 is accommodated in a recess (not shown in FIGS. 2 and 3) formed in each reactor 8.

Next, a detection signal of the temperature sensor 18 is acquired (procedure S103), and it is determined whether or not the temperature of the exhaust gas detected by the temperature sensor 18 is higher than a threshold value (procedure S104). Here, the threshold value is set to a temperature slightly lower than the temperature at which NH ₃ is thermally decomposed (for example, about 400 ° C.).

  When the temperature of the exhaust gas is higher than the threshold, application of voltage to each coil 15 by each external power supply 16 is stopped by controlling each external power supply 16 to be turned off (step S105). Then, since no current flows through each coil 15, the electromagnetic force generated in each reactor 8 is released, and each reactor 8 comes away from the outer peripheral surface of the exhaust pipe 3 by the biasing force of the elastic body 14 (FIG. 2 and FIG. 3). That is, each reactor 8 returns to the original normal position.

  In such an exhaust purification device 1, when the engine 2 is started by the IG switch 17, each external power source 16 is turned on, and a current flows through each coil 15, so that each reactor 8 is exhausted as described above. It contacts the outer peripheral surface of the tube 3 (see FIG. 5). Immediately after the engine 2 is started, the temperature of the exhaust gas is low, so that the oxidation catalyst 4 is heated by each reactor 8.

Specifically, the on-off valve 11 is opened, and NH ₃ stored in the reservoir 9 is introduced into each reactor 8 via the NH ₃ supply pipe 10. Then, the reaction material (MgCl ₂ ) and NH ₃ filled in each reactor 8 reacts chemically (coordination) to occlude NH _3, and heat (reaction heat) is generated from each reactor 8. . That is, a reaction from the left side to the right side (exothermic reaction) occurs in the following reaction formula. At this time, since each reactor 8 and the exhaust pipe 3 are in contact with each other, the thermal conductivity is good. For this reason, the reaction heat generated from the reactor 8 is sufficiently transmitted to the oxidation catalyst 4, and the oxidation catalyst 4 is effectively heated to the activation temperature suitable for the purification of pollutants by the reaction heat.
MgCl ₂ + 6NH ₃ ＭｇMgCl ₂ -6NH ₃ + heat (ΔH)
(ΔH = 67 kJ / mol (NH ₃ ))

Thereafter, when the temperature of the exhaust gas is increased to, for example, about 200 ° C., the heat (exhaust heat) of the exhaust gas is applied to each reactor 8 to separate MgCl ₂ and NH ₃ . That is, a reaction (regeneration reaction) from the right side to the left side in the above reaction formula occurs. Then, with the on-off valve 11 being opened, the separated NH ₃ returns from each reactor 8 to the reservoir 9 via the NH ₃ supply pipe 10.

When the temperature of the exhaust gas further increases and reaches the above threshold value (for example, a temperature slightly lower than about 400 ° C.), each external power supply 16 is turned off, and no current flows through each coil 15. Then, each reactor 8 moves away from the outer peripheral surface of the exhaust pipe 3 (see FIGS. 2 and 3). For this reason, an air layer is formed between each reactor 8 and the exhaust pipe 3, and heat insulation is ensured. Therefore, in order to burn the soot (PM) accumulated in the DPF 5, even if the oxidation catalyst 4 is brought to a high temperature state of 600 ° C. or higher by the fuel added from the fuel addition valve 7, the high temperature heat is still generated in each reactor 8. Therefore, the thermal decomposition of NH ₃ present in each reactor 8 is suppressed.

As described above, according to the present embodiment, a plurality of reactors 8 are arranged around a portion corresponding to the oxidation catalyst 4 in the exhaust pipe 3, and each reactor 8 is connected to the outer periphery of the exhaust pipe 3 using electromagnetic force. Since it is configured to be able to contact and separate from the surface, it is possible to suppress the thermal decomposition of NH ₃ in the reactor 8 while effectively heating the oxidation catalyst 4. Thereby, since the total amount of NH ₃ is secured, the above exothermic reaction can be promoted to generate sufficient reaction heat. As a result, the heating performance of the oxidation catalyst 4 can be improved.

  The present invention is not limited to the above embodiment. For example, in the said embodiment, it has the coil 15 wound around the outer surface of the reactor 8, and the external power supply 16 which applies a voltage to this coil 15, and generate | occur | produces electromagnetic force in the reactor 8, and the reactor 8 However, the present invention is not limited to the above configuration as long as the reactor 8 is brought into contact with and separated from the outer peripheral surface of the exhaust pipe 3 by using magnetic force. For example, a magnet may be attached to the reactor 8 and means for moving the reactor 8 with the magnet in the radial direction of the exhaust pipe 3 may be provided.

  In the above embodiment, the exhaust pipe 3 itself is made of a magnetic material. However, the present invention is not limited to this, and a magnetic material layer may be formed on the outer peripheral surface of the exhaust pipe 3 made of a non-magnetic material.

  In the above-described embodiment, the oxidation catalyst 4 provided on the upstream side of the DPF 5 is heated by the plurality of reactors 8, but the member to be heated heated by the plurality of reactors 8 is particularly an oxidation catalyst. For example, the SCR 6 provided on the downstream side of the DPF 5 or an ammonia slip catalyst (ASC) (not shown) provided on the downstream side of the SCR 6 may be used. The member to be heated may be any member other than such a catalyst provided in the exhaust pipe 3 and requiring heating.

  Furthermore, the present invention is not limited to the exhaust system of the diesel engine 2 but can also be applied to those provided in the exhaust system of a gasoline engine.

DESCRIPTION OF SYMBOLS 1 ... Exhaust purification device, 2 ... Diesel engine, 3 ... Exhaust pipe (exhaust system), 4 ... Oxidation catalyst (heated member), 5 ... Diesel exhaust particulate filter (DPF), 8 ... Reactor, 9 ... Reservoir (Ammonia supply means), 10 ... NH ₃ supply pipe (ammonia supply means), 15 ... coil (moving means), 16 ... external power supply (moving means), 18 ... temperature sensor (temperature detecting means), 19 ... controller (control) means).

Claims (4)

In an exhaust purification device that purifies exhaust gas from an engine,
A heated member provided in an exhaust pipe connected to the engine;
A reactor that is disposed around the exhaust pipe and includes a reaction material that chemically reacts with ammonia to generate heat, and heats the heated member;
Ammonia supply means for supplying the ammonia to the reactor;
An exhaust purification apparatus comprising: moving means for bringing the reactor into contact with and away from the outer peripheral surface of the exhaust pipe by magnetic force. Both the outer peripheral surface of the exhaust pipe and the outer surface of the reactor are made of a magnetic material,
The exhaust gas purification apparatus according to claim 1, wherein the moving means includes a coil wound around an outer surface of the reactor and a power source for applying a voltage to the coil. Temperature detecting means for detecting the temperature of the exhaust gas;
Control means for controlling the moving means based on the temperature of the exhaust gas detected by the temperature detecting means,
When the temperature of the exhaust gas is lower than a predetermined temperature, the control means performs ON control of the power source so that the reactor contacts the outer peripheral surface of the exhaust pipe, and the temperature of the exhaust gas is 3. The exhaust gas purification apparatus according to claim 2, wherein when the temperature is higher than a predetermined temperature, the power source is turned off so that the reactor is separated from the outer peripheral surface of the exhaust pipe. The engine is a diesel engine;
The member to be heated is an oxidation catalyst that oxidizes and purifies harmful substances contained in the exhaust gas,
A diesel exhaust particulate removal filter that collects and removes harmful substances contained in the exhaust gas is disposed downstream of the oxidation catalyst in the exhaust pipe,
The exhaust gas purification apparatus according to any one of claims 1 to 3, wherein a plurality of the reactors are arranged around the exhaust pipe along a circumferential direction of the exhaust pipe.

Images