U.S. patent application number 13/162758 was filed with the patent office on 2011-10-06 for exhaust emission purifying apparatus.
This patent application is currently assigned to UD TRUCKS CORPORATION. Invention is credited to Kiminobu HIRATA, Nobuhiko MASAKI, Masakazu YANO.
Application Number | 20110239633 13/162758 |
Document ID | / |
Family ID | 42268633 |
Filed Date | 2011-10-06 |
United States Patent
Application |
20110239633 |
Kind Code |
A1 |
MASAKI; Nobuhiko ; et
al. |
October 6, 2011 |
EXHAUST EMISSION PURIFYING APPARATUS
Abstract
The present invention provides an exhaust emission purifying
apparatus. In the exhaust emission purifying apparatus, while an
ammonia adsorbent is coated on a predetermined length portion on
the exhaust inflow side of a carrier of a catalytic converter which
reduces and purifies NOx in exhaust gas, a NOx reduction catalyst
is coated on the remaining portion on the exhaust outflow side of
the carrier of the catalytic converter. On the other hand, a first
layer containing the ammonia adsorbent and the NOx reduction
catalyst in a mixed state and a second layer containing a
hydrolysis catalyst are coated in that order on a carrier surface
of the catalytic converter. In a transition of an engine operation
state, NOx is reduced and purified with the use of ammonia adsorbed
to the ammonia adsorbent.
Inventors: |
MASAKI; Nobuhiko; (Ageo-shi,
JP) ; HIRATA; Kiminobu; (Ageo-shi, JP) ; YANO;
Masakazu; (Ageo-shi, JP) |
Assignee: |
UD TRUCKS CORPORATION
|
Family ID: |
42268633 |
Appl. No.: |
13/162758 |
Filed: |
June 17, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/JP2009/066134 |
Sep 16, 2009 |
|
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13162758 |
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Current U.S.
Class: |
60/295 |
Current CPC
Class: |
F01N 2250/02 20130101;
F01N 2610/02 20130101; F01N 2250/12 20130101; F01N 2570/18
20130101; F01N 2250/14 20130101; F01N 13/0097 20140603; F01N 3/2066
20130101; F01N 3/035 20130101; Y02T 10/24 20130101; Y02T 10/12
20130101; F01N 3/0222 20130101; F01N 2510/0684 20130101; F01N
3/2073 20130101; F01N 2240/40 20130101; F01N 3/0828 20130101 |
Class at
Publication: |
60/295 |
International
Class: |
F01N 3/035 20060101
F01N003/035 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 19, 2008 |
JP |
2008-323146 |
Claims
1. An exhaust emission purifying apparatus comprising: a catalytic
converter which reduces and purifies nitrogen oxide in exhaust gas
with the use of ammonia generated from a urea aqueous solution by
hydrolysis; a urea aqueous solution tank which stores the urea
aqueous solution therein; an injection nozzle through which the
urea aqueous solution is injection-supplied to the exhaust upstream
side of the catalytic converter; and a urea aqueous solution supply
device which supplies the urea aqueous solution stored in the urea
aqueous solution tank, to the injection nozzle at a flow rate
corresponding to an engine operation state, wherein while an
ammonia adsorbent is coated on a predetermined length portion on
the exhaust inflow side of a carrier of the catalytic converter, a
nitrogen oxide reduction catalyst is coated on the remaining
portion on the exhaust outflow side of the carrier of the catalytic
converter.
2. The exhaust emission purifying apparatus according to claim 1,
wherein the carrier is a diesel particulate filter.
3. An exhaust emission purifying apparatus comprising: a catalytic
converter which reduces and purifies nitrogen oxide in exhaust gas
with the use of ammonia generated from a urea aqueous solution by
hydrolysis; a urea aqueous solution tank which stores the urea
aqueous solution therein; an injection nozzle through which the
urea aqueous solution is injection-supplied to the exhaust upstream
side of the catalytic converter; and a urea aqueous solution supply
device which supplies the urea aqueous solution stored in the urea
aqueous solution tank, to the injection nozzle at a flow rate
corresponding to an engine operation state, wherein a first layer
containing an ammonia adsorbent and a nitrogen oxide reduction
catalyst in a mixed state and a second layer containing a
hydrolysis catalyst are coated in that order on a carrier surface
of the catalytic converter.
4. The exhaust emission purifying apparatus according to claim 3,
wherein the carrier is a diesel particulate filter.
Description
[0001] This application is a continuation of PCT/JP2009/066134,
filed on Sep. 16, 2009.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an exhaust emission
purifying apparatus which reduces and purifies nitrogen oxide (NOx)
in exhaust gas with the use of ammonia generated from a urea
aqueous solution by hydrolysis.
[0004] 2. Description of Related Art
[0005] As a catalytic purification system that removes NOx
contained in exhaust gas of an engine, there has been proposed an
exhaust emission purifying apparatus described in Japanese
Laid-open (Kokai) Patent Application Publication No. 2000-27627. In
the exhaust emission purifying apparatus, a urea aqueous solution
corresponding to an engine operation state is injection-supplied to
the exhaust upstream side of a NOx reduction catalytic converter
arranged in an exhaust pipe, and ammonia that is a reducing agent
is generated from the urea aqueous solution by hydrolysis using
exhaust heat and water vapor in exhaust gas. In the NOx reduction
catalytic converter, ammonia and NOx are selectively subjected to
reduction reaction, and NOx is purified to harmless water
(H.sub.2O) and nitrogen (N.sub.2).
[0006] In a transition of an engine operation state, since the
generation of ammonia may not follow a rapid SV (spatial velocity)
change, there has been an attempt to add a hydrolysis function or
an ammonia adsorption function to a NOx reduction catalytic
converter to enhance a NOx purification efficiency. However, even
if the hydrolysis function or the ammonia adsorption function is
added to the NOx reduction catalytic converter, it may not be
concluded that hydrolysis for generating ammonia from a urea
aqueous solution is satisfactorily carried out in a wide range of
the engine operation state, and it has been a fact that the NOx
purification efficiency that would be expected may not be
obtained.
SUMMARY OF THE INVENTION
[0007] Thus, in view of the above related art problems, an object
of the present technique is to provide an exhaust emission
purifying apparatus which devises a coating structure of an ammonia
adsorbent, a hydrolysis catalyst, and a NOx reduction catalyst
coated on a carrier of the NOx reduction catalytic converter to
thereby enhance the NOx purification efficiency.
[0008] According to a first aspect of the present technique, an
exhaust emission purifying apparatus includes: a catalytic
converter which reduces and purifies NOx in exhaust gas with the
use of ammonia generated from a urea aqueous solution by
hydrolysis; a urea aqueous solution tank which stores the urea
aqueous solution therein; an injection nozzle through which the
urea aqueous solution is injection-supplied to the exhaust upstream
side of the catalytic converter; and a urea aqueous solution supply
device which supplies the urea aqueous solution, stored in the urea
aqueous solution tank, to the injection nozzle at a flow rate
corresponding to an engine operation state. In the exhaust emission
purifying apparatus, while an ammonia adsorbent is coated on a
predetermined length portion on the exhaust inflow side of a
carrier of the catalyst converter, a NOx reduction catalyst is
coated on the remaining portion on the exhaust outflow side of the
carrier of the catalytic converter. In a second aspect of the
present technique, instead of the constitution of the first aspect,
a first layer containing the ammonia adsorbent and the NOx
reduction catalyst in a mixed state and a second layer containing a
hydrolysis catalyst are coated in that order on a carrier surface
of the catalytic converter.
[0009] According to the first aspect of the present technique, when
an engine performs a steady operation, ammonia generated from the
urea aqueous solution by hydrolysis is adsorbed to the ammonia
adsorbent coated on the exhaust inflow side of the carrier of the
catalytic converter. In a transition of the engine operation, when
the generation of ammonia may not follow a rapid SV change, ammonia
adsorbed to the ammonia adsorbent is released to be supplied to the
NOx reduction catalyst coated on the exhaust outflow side of the
carrier. Thus, even if hydrolysis for generating ammonia from the
urea aqueous solution is not satisfactorily carried out, the
reduction reaction between NOx and ammonia occurs in the NOx
reduction catalyst, and especially a NOx purification efficiency in
the transition of the engine operation state can be enhanced.
[0010] According to the second aspect of the present technique,
among the urea aqueous solution injection-supplied from the
injection nozzle, the urea aqueous solution that is not converted
to ammonia by hydrolysis is in contact with the hydrolysis catalyst
to be converted to ammonia in the second layer coated on a carrier
surface of the catalytic converter. When the engine performs the
steady operation, ammonia is adsorbed to the ammonia adsorbent
contained in the first layer. In the transition of the engine
operation state, when the generation of ammonia may not follow a
rapid SV change, ammonia adsorbed to the ammonia adsorbent is
released to be supplied to the NOx reduction catalyst contained in
the same first layer. Thus, the NOx purification efficiency can be
enhanced in the transition of the engine operation state.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a schematic configuration view of an exhaust
emission purifying apparatus to which the present technique is to
be applied;
[0012] FIG. 2 is an explanatory view of a method of coating an
ammonia adsorbent and a NOx reduction catalyst;
[0013] FIG. 3 is an explanatory view of the operation and effect of
a NOx catalytic converter according to a first embodiment;
[0014] FIG. 4 is an explanatory view of the operation and effect of
a NOx catalytic converter according to a second embodiment; and
[0015] FIG. 5 is an explanatory view of experimental data showing
enhancement of a NOx purification efficiency.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0016] Hereinafter, the present technique will be described in
detail referring to the attached drawings.
[0017] FIG. 1 shows a schematic configuration of an exhaust
emission purifying apparatus to which the present technique is to
be applied.
[0018] In an exhaust pipe 14 connected to an exhaust manifold 12 of
an engine 10, a nitrogen oxidation catalytic converter 16 which
oxidizes nitric oxide (NO) to nitrogen dioxide (NO.sub.2), a NOx
reduction catalytic converter 18 which reduces and purifies NOx in
exhaust gas with the use of ammonia, and an ammonia oxidation
catalytic converter 20 which oxidizes ammonia passed through the
NOx reduction catalytic converter 18 are arranged in this order
along an exhaust gas flow direction.
[0019] An injection nozzle 22 which injection-supplies a urea
aqueous solution to the exhaust upstream side of the NOx reduction
catalytic converter 18 is attached to the exhaust pipe 14 located
between the nitrogen oxidation catalytic converter 16 and the NOx
reduction catalytic converter 18. The urea aqueous solution stored
in a urea aqueous solution tank 26 is supplied to the injection
nozzle 22 through a urea aqueous solution supply device 24 having
an electric pump and a flow rate control valve which are
incorporated therein.
[0020] The urea aqueous solution supply device 24 is electronically
controlled by a reducing agent dosing control unit (hereinafter
referred to as "DCU (Dosing Control Unit)") 28 with a built-in
computer in order to supply the urea aqueous solution stored in the
urea aqueous solution tank 26 to the injection nozzle 22 at the
flow rate corresponding to an engine operation state. The DCU 28
receives an input of an exhaust temperature signal from a
temperature sensor 30 attached to the exhaust pipe 14 located
between the nitrogen oxidation catalytic converter 16 and the
injection nozzle 22 and, at the same time, receives an input of an
engine rotation speed signal and a fuel injection flow rate signal
from an engine control unit (ECU) 32 electronically controlling the
engine 10. The DCU 28 calculates a urea aqueous solution dosing
flow rate corresponding to an exhaust temperature, an engine
rotation speed, and a fuel injection flow rate in accordance with a
control program stored in a ROM (Read Only Memory) and the like,
and controls the electric pump and the flow rate control valve of
the urea aqueous solution supply device 24 based on the calculation
result.
[0021] In the exhaust emission purifying apparatus, the urea
aqueous solution injection-supplied from the injection nozzle 22 in
response to the engine operation state is hydrolyzed by utilizing
exhaust heat and water vapor in exhaust gas, so that ammonia is
generated. In the NOx reduction catalytic converter 18, ammonia and
NOx in exhaust gas are selectively subjected to reduction reaction,
and NOx is purified to harmless H.sub.2O and N.sub.2. At that time,
in order to enhance the NOx purification efficiency in the NOx
reduction catalytic converter 18, NO is oxidized to NO.sub.2 in the
nitrogen oxidation catalytic converter 16, and the ratio between NO
and NO.sub.2 in exhaust gas is improved to the ratio appropriate
for the reduction reaction. On the other hand, since ammonia having
passed through the NOx reduction catalytic converter 18 is oxidized
by the ammonia oxidation catalytic converter 20 arranged at the
exhaust downstream side of the NOx catalytic converter 18, the
ammonia is prevented from being emitted as it is into the
atmosphere.
[0022] In order to further enhance the NOx purification efficiency
in the NOx reduction catalytic converter 18, as shown in FIG. 2,
while an ammonia adsorbent A is coated on a predetermined length
portion on the exhaust inflow side of a carrier 18A having a
honeycomb structure, a NOx reduction catalyst B is coated on the
remaining portion on the exhaust outflow side of the carrier 18A.
Although applicable examples of the ammonia adsorbent A include an
arbitrary compound having a strong solid acid, it is preferable to
use ZSM-5, mordenite, .beta., and so on, which are a kind of
zeolite having a relatively high ammonia adsorption ability. As the
NOx reduction catalyst B, a NOx reduction catalyst mainly composed
of titanium oxide and vanadium oxide or tungsten oxide can be used
as described in Japanese Laid-open (Kokai) Patent Application
Publication Nos. H07-275656 and H10-235206, for example.
[0023] Each component used as the ammonia adsorbent A and the NOx
reduction catalyst B is regulated to have an appropriate particle
diameter by a well-known mill such as a dry grinding mill or a wet
grinding mill and thereafter coated on the carrier 18A. At that
time, each component is mixed with a solvent such as water to be
made into the form of slurry and then coated on the carrier 18A.
Thereafter, the coating is subjected to drying and heat processing
at a predetermined temperature to be baked. In this case, each
component may contain a specific amount of a mixture of alumina and
silica sol as a "binder material" enhancing adhesion with the
carrier 18A.
[0024] When the engine 10 performs a steady operation, as shown in
FIG. 3, ammonia generated from the urea aqueous solution by
hydrolysis is adsorbed to the ammonia adsorbent A coated on the
exhaust inflow side of the carrier 18A. In a transition of the
engine operation state, when the generation of ammonia may not
follow a rapid SV change, ammonia adsorbed to the ammonia adsorbent
A is released to be supplied to the NOx reduction catalyst B coated
on the exhaust outflow side of the carrier 18A. Thus, even if
hydrolysis for generating ammonia from the urea aqueous solution is
not satisfactorily carried out, the reduction reaction between NOx
and ammonia occurs in the NOx reduction catalyst B, and in
particular, the NOx purification efficiency in the transition of
the engine operation state can be enhanced. Accordingly, in a wide
range of the engine operation state, the NOx purification
efficiency can be enhanced.
[0025] In order to further enhance the NOx purification efficiency
in the NOx reduction catalytic converter 18, instead of the
configuration of FIG. 2, as shown in FIG. 4, a first layer
containing the ammonia adsorbent A and the NOx reduction catalyst B
in a mixed state and a second layer containing a hydrolysis
catalyst C may be coated in this order on a surface of the carrier
18A. As described in Japanese Laid-open (Kokai) Patent Application
Publication No. 2002-514495, as the hydrolysis catalyst C, titanium
dioxide containing vanadium pentoxide, aluminum oxide, and/or
silicon oxide can be used, for example. However, it is preferable
to particularly use titanium dioxide containing vanadium pentoxide
in an amount of 0.02 to 1.3 wt %. Since the method of coating the
first layer and the second layer on the surface of the carrier 18A
is similar to that shown in FIG. 2, the description will not be
repeated here.
[0026] Among the urea aqueous solution injection-supplied from the
injection nozzle 22, the urea aqueous solution that is not
converted to ammonia by hydrolysis is in contact with the
hydrolysis catalyst C to be converted to ammonia in the second
layer coated on the surface of the carrier 18A. When the engine 10
performs the steady operation, ammonia is adsorbed to the ammonia
adsorbent A contained in the first layer. In the transition of the
engine operation state, when the generation of ammonia may not
follow the rapid SV change, ammonia adsorbed to the ammonia
adsorbent A is released to be supplied to the NOx reduction
catalyst B contained in the same first layer. Thus, even if
hydrolysis for generating ammonia from the urea aqueous solution is
not satisfactorily carried out, the reduction reaction between NOx
and ammonia occurs in the NOx reduction catalyst B, and in
particular, the NOx purification efficiency in the transition of
the engine operation state can be enhanced. Accordingly, in a wide
range of the engine operation state, the NOx purification
efficiency can be enhanced.
[0027] In the above described embodiments, although the ammonia
adsorbent A, the NOx reduction catalyst B, and the hydrolysis
catalyst C are coated on the carrier 18A having a honeycomb
structure, they may be coated on a diesel particulate filter (DPF)
which collects and removes a particulate matter (PM) in exhaust
gas. In this case, the particle diameter and coating amount of each
component of the ammonia adsorbent A, the NOx reduction catalyst B,
and the hydrolysis catalyst C are preferably previously optimized
in actual use of the DPF taking into the fact that a pressure loss
occurs due to the collection of the PM.
[0028] In an exhaust emission purifying apparatus in which the
nitrogen oxidation catalytic converter, the DPF, and the ammonia
oxidation catalytic converter are arranged in series, each NOx
purification efficiency is detected in JE05 mode in a case in which
the NOx reduction catalyst B is coated to the DPF (comparative
technique), a case in which the coating is applied as shown in FIG.
2 (first embodiment), and a case in which the coating is applied as
shown in FIG. 4 (second embodiment). As shown in FIG. 5, it can be
confirmed that the NOx purification efficiency is enhanced in a
wide range of an engine operation region relative to the
comparative technique. As seen in the same drawing, the NOx
purification efficiency is significantly enhanced, in particular,
in the region where a DPF entrance temperature is low.
[0029] It should be appreciated that the entire contents of
Japanese Patent Application No. 2008-323146, filed on Dec. 19,
2008, on which the convention priority is claimed is incorporated
herein by reference.
[0030] It should also be understood that many modifications and
variations of the described embodiments of the invention will occur
to a person having an ordinary skill in the art without departing
from the spirit and scope of the present invention as claimed in
the appended claims.
* * * * *