U.S. patent application number 13/133588 was filed with the patent office on 2011-10-20 for flue gas purifying device.
This patent application is currently assigned to MITSUBISHI HEAVY INDUSTRIES, LTD.. Invention is credited to Takashi Fujinaga, Yasushi Mitsuyama, Masazumi Tanoura, Daishi Ueno.
Application Number | 20110252771 13/133588 |
Document ID | / |
Family ID | 42242794 |
Filed Date | 2011-10-20 |
United States Patent
Application |
20110252771 |
Kind Code |
A1 |
Fujinaga; Takashi ; et
al. |
October 20, 2011 |
FLUE GAS PURIFYING DEVICE
Abstract
An object of the present invention is to provide a flue gas
purifying device that can suppress leakage of ammonia and can
efficiently decrease nitrogen oxides in flue gas. The object is
achieved by including: an exhaust pipe that guides flue gas
discharged from an internal combustion engine; a urea-water
injecting unit that injects urea water into the exhaust pipe; a
catalyst unit that includes a urea SCR catalyst that promotes a
reaction between ammonia produced from injected urea water and
nitrogen oxides and a support mechanism arranged inside of the
exhaust pipe on a downstream side to a position where urea water is
injected in a flow direction of the flue gas to support the urea
SCR catalyst; an ammonia-concentration measuring unit that measures
an ammonia concentration in flue gas at a measurement position in a
region where the SCR catalyst is arranged; and an injection control
unit that controls injection of urea water based on a measurement
result acquired by the ammonia-concentration measuring unit.
Inventors: |
Fujinaga; Takashi; (Hyogo,
JP) ; Tanoura; Masazumi; (Kanagawa, JP) ;
Ueno; Daishi; (Tokyo, JP) ; Mitsuyama; Yasushi;
(Tokyo, JP) |
Assignee: |
MITSUBISHI HEAVY INDUSTRIES,
LTD.
Minato-ku, Tokyo
JP
|
Family ID: |
42242794 |
Appl. No.: |
13/133588 |
Filed: |
December 8, 2009 |
PCT Filed: |
December 8, 2009 |
PCT NO: |
PCT/JP2009/070564 |
371 Date: |
July 5, 2011 |
Current U.S.
Class: |
60/295 |
Current CPC
Class: |
B01D 53/90 20130101;
F01N 2560/021 20130101; F01N 13/0093 20140601; B01D 2255/20723
20130101; B01D 53/9477 20130101; B01D 53/9495 20130101; F01N 3/208
20130101; B01D 2251/2067 20130101; B01D 2255/1021 20130101; Y02T
10/12 20130101; Y02T 10/24 20130101; F01N 2610/02 20130101; B01D
2255/50 20130101 |
Class at
Publication: |
60/295 |
International
Class: |
F01N 3/10 20060101
F01N003/10; F01N 11/00 20060101 F01N011/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 8, 2008 |
JP |
2008-312637 |
Claims
1. A flue gas purifying device that reduces nitrogen oxides
contained in flue gas discharged from an internal combustion
engine, the device comprising: an exhaust pipe that guides flue gas
discharged from the internal combustion engine; an ammonia
supplying unit that supplies ammonia into the exhaust pipe; a
catalyst unit that includes an SCR catalyst that promotes a
reaction between supplied ammonia and the nitrogen oxides and a
support mechanism arranged inside of the exhaust pipe to support
the SCR catalyst in the exhaust pipe, and is arranged on a
downstream side to a position where the ammonia is supplied in a
flow direction of the flue gas; an ammonia-concentration measuring
unit that measures an ammonia concentration in flue gas at a
measurement position in a region where the catalyst unit is
arranged; and an injection control unit that controls supply of
ammonia performed by the ammonia supplying unit based on a
measurement result acquired by the ammonia-concentration measuring
unit.
2. A flue gas purifying device that reduces nitrogen oxides
contained in flue gas discharged from an internal combustion
engine, the device comprising: an exhaust pipe that guides flue gas
discharged from the internal combustion engine; a urea-water
injecting unit that injects urea water into the exhaust pipe; a
catalyst unit that includes a urea SCR catalyst that promotes a
reaction between ammonia produced from injected urea water and the
nitrogen oxides and a support mechanism arranged inside of the
exhaust pipe to support the urea SCR catalyst in the exhaust pipe,
and is arranged on a downstream side to a position where the urea
water is injected in a flow direction of the flue gas; an
ammonia-concentration measuring unit that measures an ammonia
concentration in flue gas at a measurement position in a region
where the catalyst unit is arranged; and an injection control unit
that controls injection of urea water performed by the urea-water
injecting unit based on a measurement result acquired by the
ammonia-concentration measuring unit.
3. The flue gas purifying device according to claim 2, wherein the
ammonia-concentration measuring unit detects an ammonia
concentration at a position included in a region of from a position
where a concentration of nitrogen oxides at a time of maximum load
of the internal combustion engine when nitrogen oxides in flue gas
are reduced in a state with ammonia being input excessively into
the urea SCR catalyst becomes either a concentration at an inlet of
the urea SCR catalyst at a time of minimum load of the internal
combustion engine or a concentration half a concentration at the
inlet of the urea SCR catalyst at the time of maximum load of the
internal combustion engine, whichever higher, to a position where
the concentration of nitrogen oxides at the time of maximum load of
the internal combustion engine becomes a theoretical concentration
of nitrogen oxides that can be denitrated with an ammonia
concentration of 10 ppm, of a region of the catalytic unit in which
the urea SCR catalyst is arranged, in a flow direction of flue
gas.
4. The flue gas purifying device according to claim 2, wherein the
urea SCR catalyst in the catalyst unit includes a first catalyst
and a second catalyst that is arranged on a downstream side to the
first catalyst in a flow direction of the flue gas, and the
catalyst unit further includes a connecting pipe for connecting the
first catalyst and the second catalyst, the ammonia-concentration
measuring unit is arranged in the connecting pipe, and the
measurement position is in the connecting pipe.
5. The flue gas purifying device according to claim 2, further
comprising a particulate-matter reducing unit arranged between the
urea-water injecting unit and the internal combustion engine to
reduce particulate matters contained in the flue gas.
6. The flue gas purifying device according to claim 1, further
comprising a nitrogen-oxide-concentration measuring unit that
measures a concentration of nitrogen oxides in flue gas at the
measurement position.
Description
FIELD
[0001] The present invention relates to a flue gas purifying device
that reduces nitrogen oxides discharged from an internal combustion
engine.
BACKGROUND
[0002] Gas discharged from an internal combustion engine such as a
diesel engine, a gasoline engine, and a gas turbine, that is flue
gas, contains nitrogen oxides (NOx) and particulate matters (PM).
Therefore, a device that decreases particulate matters or a device
that decreases nitrogen oxides is provided in an exhaust pipe of an
internal combustion engine. As an example of the device that
decreases nitrogen oxides, there is a device that decreases
nitrogen oxides from flue gas by injecting urea into an exhaust
pipe that guides flue gas, produces ammonia from urea in the
exhaust pipe, causes the produced ammonia to react with nitrogen
oxides in flue gas, and then removes oxygen from nitrogen oxides to
produce nitrogen again.
[0003] For example, Patent Literature 1 describes a flue gas
purifying device in which a DPF device and a selective catalytic
reduction catalytic device are sequentially arranged from an
upstream side in an exhaust path of an internal combustion engine.
Patent Literature 1 also describes a device that calculates NOx
emissions, at the time of a normal operation, based on an NOx
emissions map for the normal operation, or at the time of forced
regeneration of the DPF device, calculates NOx emissions based on
an NOx emissions map for forced regeneration, to calculate a feed
rate of ammonia aqueous solution corresponding to the calculated
NOx emissions, and feeds ammonia aqueous solution into flue gas on
an upstream side of the selective catalytic reduction catalytic
device so as to reach the calculated feed rate.
[0004] Further, Patent Literature 2 describes NOx removal equipment
for flue gas discharged from a combustion plant such as a waste
incinerator, although it is not for treatment of flue gas from an
internal combustion engine. Patent Literature 2 describes a
denitration control method in which a NOx concentration in gas
before treatment, an ammonia concentration in treated flue gas, a
NOx concentration in flue gas, and a flow rate of flue gas are
measured, to calculate a flow rate of NOx before treatment, a NOx
concentration after treatment, a record of NOx removal efficiency
by NOx removal equipment, and an ammonia concentration in treated
flue gas based on a measurement result thereof, deviations between
the calculated values and target values thereof are respectively
calculated to thereby calculate correction values based on the
calculated deviations, and a corrected flow rate of NOx is
calculated based on at least one of the calculated correction
values, thereby controlling a flow rate of ammonia to be injected
into flue gas before treatment based on the calculated corrected
flow rate of NOx.
CITATION LIST
Patent Literatures
[0005] Patent Literature 1: Japanese Patent Application Laid-open
No. 2007-154849 [0006] Patent Literature 2: Japanese Patent
Application Laid-open No. 2005-169331
SUMMARY
Technical Problem
[0007] Nitrogen oxides can be decreased and an amount of ammonia
can be adjusted by controlling an injection amount of urea based on
a map created beforehand as described in Patent Literature 1, or by
controlling an injection amount of urea based on the concentration
of nitrogen oxides or the ammonia concentration in treated flue
gas, as described in Patent Literature 2.
[0008] However, even if the injection amount of urea is adjusted
based on a map created beforehand, there is a problem that nitrogen
oxides leak or ammonia leak according to operating conditions.
Further, even when the injection amount of urea is adjusted based
on the concentration of nitrogen oxides or the ammonia
concentration in treated flue gas, if ammonia still remains in
treated flue gas, which is a detection target, there is a problem
of ammonia leakage. Therefore, in flue gas purifying devices of an
internal combustion engine, an oxidation catalyst for oxidizing
ammonia is installed on a downstream side of NOx removal equipment
such as a selective catalytic reduction catalytic device. However,
there is a problem such that nitrogen oxides are produced by
oxidizing ammonia. Further, there is also a problem such that, if
the amount of leakage of ammonia is large, the oxidation catalyst
needs to be increased.
[0009] The present invention has been achieved to solve the above
problems, and an object of the present invention is to provide a
flue gas purifying device that calculates an appropriate amount of
a reducing agent (ammonia) such as urea to be injected into an
exhaust pipe so that ammonia hardly leaks to a downstream side,
thereby efficiently decreasing nitrogen oxides in flue gas.
Solution to Problem
[0010] According to an aspect of the present invention, a flue gas
purifying device that reduces nitrogen oxides contained in flue gas
discharged from an internal combustion engine includes: an exhaust
pipe that guides flue gas discharged from the internal combustion
engine; an ammonia supplying unit that supplies ammonia into the
exhaust pipe; a catalyst unit that includes an SCR catalyst that
promotes a reaction between supplied ammonia and the nitrogen
oxides and a support mechanism arranged inside of the exhaust pipe
to support the SCR catalyst in the exhaust pipe, and is arranged on
a downstream side to a position where the ammonia is supplied in a
flow direction of the flue gas; an ammonia-concentration measuring
unit that measures an ammonia concentration in flue gas at a
measurement position in a region where the catalyst unit is
arranged; and an injection control unit that controls supply of
ammonia performed by the ammonia supplying unit based on a
measurement result acquired by the ammonia-concentration measuring
unit.
[0011] According to another aspect of the present invention, a flue
gas purifying device that reduces nitrogen oxides contained in flue
gas discharged from an internal combustion engine includes: an
exhaust pipe that guides flue gas discharged from the internal
combustion engine; a urea-water injecting unit that injects urea
water into the exhaust pipe; a catalyst unit that includes a urea
SCR catalyst that promotes a reaction between ammonia produced from
injected urea water and the nitrogen oxides and a support mechanism
arranged inside of the exhaust pipe to support the urea SCR
catalyst in the exhaust pipe, and is arranged on a downstream side
to a position where the urea water is injected in a flow direction
of the flue gas; an ammonia-concentration measuring unit that
measures an ammonia concentration in flue gas at a measurement
position in a region where the catalyst unit is arranged; and an
injection control unit that controls injection of urea water
performed by the urea-water injecting unit based on a measurement
result acquired by the ammonia-concentration measuring unit.
[0012] Advantageously, in the flue gas purifying device, the
ammonia-concentration measuring unit detects an ammonia
concentration at a position included in a region of from a position
where a concentration of nitrogen oxides at a time of maximum load
of the internal combustion engine when nitrogen oxides in flue gas
are reduced in a state with ammonia being input excessively into
the urea SCR catalyst becomes either a concentration at an inlet of
the urea SCR catalyst at a time of minimum load of the internal
combustion engine or a concentration half a concentration at the
inlet of the urea SCR catalyst at the time of maximum load of the
internal combustion engine, whichever higher, to a position where
the concentration of nitrogen oxides at the time of maximum load of
the internal combustion engine becomes a theoretical concentration
of nitrogen oxides that can be denitrated with an ammonia
concentration of 10 ppm, of a region of the catalytic unit in which
the urea SCR catalyst is arranged, in a flow direction of flue
gas.
[0013] Advantageously, in the flue gas purifying device, the urea
SCR catalyst in the catalyst unit includes a first catalyst and a
second catalyst that is arranged on a downstream side to the first
catalyst in a flow direction of the flue gas, and the catalyst unit
further includes a connecting pipe for connecting the first
catalyst and the second catalyst, the ammonia-concentration
measuring unit is arranged in the connecting pipe, and the
measurement position is in the connecting pipe.
[0014] Advantageously, the flue gas purifying device further
includes a particulate-matter reducing unit arranged between the
urea-water injecting unit and the internal combustion engine to
reduce particulate matters contained in the flue gas.
[0015] Advantageously, the flue gas purifying device further
includes a nitrogen-oxide-concentration measuring unit that
measures a concentration of nitrogen oxides in flue gas at the
measurement position.
ADVANTAGEOUS EFFECTS OF INVENTION
[0016] The gas purifying device according to the present invention
can accurately ascertain ammonia, which is reacting with nitrogen
oxides by measuring an ammonia concentration in the catalyst unit,
and the flue gas purifying device can suppress leakage of ammonia
from the purifying device and can efficiently decrease nitrogen
oxides in flue gas, by controlling an injection amount of urea,
that is, an input amount of a reducing agent, based on the
measurement result.
BRIEF DESCRIPTION OF DRAWINGS
[0017] FIG. 1 is a block diagram of a schematic configuration of a
vehicle including a diesel engine having a flue gas purifying
device mounted thereon according to an embodiment of the present
invention.
[0018] FIG. 2 is a block diagram of a schematic configuration of a
concentration measuring unit in the flue gas purifying device shown
in FIG. 1.
[0019] FIG. 3 is a graph of a relation between a length from an
inlet of a urea SCR catalyst and the concentration of nitrogen
oxides.
[0020] FIG. 4 is a block diagram of a schematic configuration of a
vehicle including a diesel engine having a flue gas purifying
device mounted thereon according to another embodiment of the
present invention.
[0021] FIG. 5 is a graph of an example of a measurement result.
[0022] FIG. 6 is a graph of an example of a measurement result.
[0023] FIG. 7 is a graph of an example of a measurement result.
[0024] FIG. 8 is a graph of an example of a measurement result.
DESCRIPTION OF EMBODIMENTS
[0025] Exemplary embodiments a flue gas purifying device according
to the present invention will be explained below in detail with
reference to the accompanying drawings. The present invention is
not limited to the embodiments. In the following embodiments, it is
assumed that an internal combustion engine having the flue gas
purifying device mounted thereon is a diesel engine, and a vehicle
using the diesel engine is explained. However, the internal
combustion engine is not limited thereto, and the present invention
is applicable to various internal combustion engines such as a
gasoline engine and a gas turbine. Further, a device having the
internal combustion engine is not limited to a vehicle, and the
device can be used as an internal combustion engine of various
devices such as a ship and a power generator.
[0026] FIG. 1 is a block diagram of a schematic configuration of a
vehicle including a diesel engine having a flue gas purifying
device mounted thereon according to an embodiment of the present
invention. FIG. 2 is a block diagram of a schematic configuration
of a concentration measuring unit in the flue gas purifying device
for a diesel engine shown in FIG. 1. As shown in FIG. 1, a vehicle
10 includes a diesel engine 12, an exhaust pipe 14 for guiding flue
gas discharged from the diesel engine 12, and a flue gas purifying
device 16 that purifies flue gas flowing in the exhaust pipe 14.
The vehicle 10 also includes various elements required for a
vehicle, such as wheels, a body, operating parts, and a
transmission, other than constituent elements shown in FIG. 1.
[0027] The diesel engine 12 is an internal combustion engine that
uses light oil or heavy oil as a fuel, and burns the fuel to
extract power. The exhaust pipe 14 is connected to the diesel
engine 12 at one end thereof, to guide flue gas discharged from the
diesel engine 12.
[0028] The flue gas purifying device 16 includes an oxidation
catalyst 18, a DPF 20, an injecting unit 22, a urea water tank 24,
a urea SCR catalytic unit 26, a concentration measuring unit 28,
and a control unit 30, and is arranged in an exhaust path of flue
gas, that is, in the exhaust pipe 14 or adjacent to the exhaust
pipe 14.
[0029] The oxidation catalyst 18 is a catalyst such as platinum
provided in the exhaust path of flue gas, specifically, inside of a
downstream portion of an exhaust port of the diesel engine 12 in a
flow direction of flue gas in the exhaust pipe 14. A part of
particulate matters (PM) in flue gas having passed in the exhaust
pipe 14 and through the oxidation catalyst 18 is removed by the
oxidation catalyst 18. The PM here is an air contaminant discharged
from the diesel engine, and is a mixture of solid carbon particles,
unburned hydrocarbon (Soluble Organic Fraction: SOF) formed of
polymeric molecules, and sulfate generated by oxidation of sulfur
contained in the fuel. The oxidation catalyst 18 oxidizes nitrogen
monoxide contained in flue gas flowing in the exhaust pipe 14 to
nitrogen dioxide.
[0030] The DPF (Diesel Particulate Filter) 20 is a filter provided
in the exhaust path of flue gas, specifically, inside of a
downstream portion of the oxidation catalyst 18 in the exhaust pipe
14, to trap particulate matters contained in flue gas having passed
through the oxidation catalyst 18. As the DPF 20, it is desired to
use a continuous-regenerative DPF that can maintain the trapping
performance such that regeneration is performed by removing trapped
PM by burning or the like.
[0031] A urea SCR (Selective Catalytic Reduction) system 21 is an
NOx removal system that reduces nitrogen oxides (NO, NO.sub.2)
contained in flue gas, and includes the injecting unit 22, the urea
water tank 24, and the urea SCR catalytic unit 26. The injecting
unit 22 is an injection device that injects urea water into the
exhaust pipe 14, and an injection port is provided in a portion on
a downstream side to the DPF 20 in the exhaust pipe 14. The
injecting unit 22 injects urea water into the exhaust pipe 14 from
the injection port. The urea water tank 24 stores urea water, and
supplies urea water to the injecting unit 22. A replenishing port
for replenishing urea water from an external device that supplies
urea water is provided in the urea water tank 24, and urea water is
replenished according to need from the replenishing port. The urea
SCR catalytic unit 26 includes a urea SCR catalyst, which is a urea
selective reduction catalyst that promotes a reaction between
ammonia produced from urea with nitrogen oxides, and a support
mechanism provided inside of a downstream portion of the injecting
unit 22 in the exhaust pipe 14 to support the urea SCR catalyst.
Vanadium catalyst or zeolite catalyst can be used as the urea SCR
catalyst. Further, the support mechanism is arranged inside the
exhaust pipe 14, and a hole for aerating flue gas is formed
therein, and the urea SCR catalyst is supported on the surface
thereof.
[0032] The urea SCR system 21 has the configuration described
above, and injects urea water into the exhaust pipe 14 by the
injecting unit 22. The injected urea water becomes ammonia
(NH.sub.3) due to heat in the exhaust pipe 14. Specifically,
ammonia is produced from urea water according to the following
chemical reaction.
(NH.sub.2)2CO+H.sub.2O.fwdarw.2NH.sub.3+CO.sub.2
[0033] Thereafter, produced ammonia flows in the exhaust pipe 14
together with flue gas and reaches the urea SCR catalytic unit 26.
A part of urea water is not used for producing ammonia and reaches
the urea SCR catalytic unit 26 in the state of urea water.
Therefore, even in the urea SCR catalytic unit 26, ammonia is
produced from urea water according to the reaction mentioned above.
Ammonia having reached the urea SCR catalytic unit 26 reacts with
nitrogen oxides contained in flue gas to remove oxygen from
nitrogen oxides and is reduced to nitrogen. Specifically, nitrogen
oxides are reduced according to the following chemical
reaction.
4NH.sub.3+4NO+O.sub.2.fwdarw.4N.sub.2+6H.sub.2O
4NH.sub.3+2NO.sub.2+O.sub.2.fwdarw.3N.sub.2+6H.sub.2O
[0034] The concentration measuring unit 28 is arranged in the urea
SCR catalytic unit 26 in the exhaust path of flue gas, that is, in
such a manner that an upstream face and a downstream face are both
in contact with the urea SCR catalytic unit 26, to measure the
ammonia concentration in flue gas flowing in the urea SCR catalytic
unit 26. As shown in FIG. 2, the concentration measuring unit 28
includes a measuring unit body 40, an optical fiber 42, a measuring
cell 44, and a light receiving unit 46.
[0035] The measuring unit body 40 has a light emitting unit that
emits laser beams in a wavelength region absorbed by ammonia, and a
computing unit that calculates the ammonia concentration from a
signal. The measuring unit body 40 outputs laser beams to the
optical fiber 42 and receives a signal received by the light
receiving unit 46.
[0036] The optical fiber 42 guides laser beams output from the
measuring unit body 40 so as to enter into the measuring cell
44.
[0037] The measuring cell 44 is arranged in the urea SCR catalytic
unit 26, and includes an incident unit that causes light emitted
from the optical fiber 42 to enter into the measuring cell 44, and
an output unit that outputs laser beams having passed through a
predetermined route in the measuring cell 44.
[0038] The light receiving unit 46 receives laser beams having
passed through the inside of the measuring cell 44 and output from
the output unit, and outputs an intensity of received laser beams
to the measuring unit body 40 as a light receiving signal.
[0039] The concentration measuring unit 28 has the configuration
described above, and laser beams output from the measuring unit
body 40 pass through the predetermined route in the measuring cell
44 from the optical fiber 42 and is output from the output unit. At
this time, if ammonia is contained in flue gas in the measuring
cell 44, laser beams passing through the measuring cell 44 are
absorbed. Therefore, an output of laser beams reaching the output
unit changes according to the ammonia concentration in flue gas.
The light receiving unit 46 converts laser beams output from the
output unit to a light receiving signal, and outputs the light
receiving signal to the measuring unit body 40. The measuring unit
body 40 compares the intensity of output laser beams with an
intensity calculated from the light receiving signal, to calculate
the ammonia concentration in flue gas flowing in the measuring cell
44 based on its rate of diminution. Thus, the concentration
measuring unit 28 uses TDLAS (Tunable Diode Laser Absorption
Spectroscopy) to calculate or measure the ammonia concentration in
flue gas passing through a predetermined position in the measuring
cell 44, that is, a measurement position based on the intensity of
output laser beams and the light receiving signal detected by the
light receiving unit 46.
[0040] Only the incident unit and the output unit of the measuring
cell 44 can be made of a light transmitting material, or the
measuring cell 44 on the whole can be made of the light
transmitting material. Further, at least two optical mirrors can be
provided in the measuring cell 44, so that laser beams entering
from the incident unit is multiply-reflected by the optical mirrors
and output from the output unit. By multiply-reflecting laser
beams, laser beams can pass through more regions in the measuring
cell 44. Accordingly, an influence of concentration distribution on
flue gas flowing in the measuring cell 44 can be decreased, thereby
enabling accurate detection of concentrations.
[0041] The control unit 30 controls the amount of urea water to be
injected from the injecting unit 22 and an injection timing based
on a detection result of the concentration measuring unit 28.
Specifically, when the ammonia concentration is lower than a
predetermined value, the amount of urea water to be injected at a
time is increased or an injection interval of urea water is
decreased. When the ammonia concentration is higher than the
predetermined value, the amount of urea water to be injected at a
time is decreased or the injection interval of urea water is
increased.
[0042] The vehicle 10 and the flue gas purifying device 16 have
basically the configuration as described above. In the flue gas
purifying device 16, flue gas discharged from the diesel engine 12
passes through the oxidation catalyst 18 and the DPF 20, and the PM
contained in flue gas is trapped and decreased. Flue gas having
passed through the DPF 20 flows in the exhaust pipe 14, and after
urea water is injected from the injecting unit 22, flue gas passes
through the urea SCR catalytic unit 26 together with urea water and
ammonia produced from urea water. Because flue gas passes through
the urea SCR catalytic unit 26 together with ammonia, nitrogen
oxides contained in flue gas are decreased by the urea SCR system
21. Thereafter, flue gas is discharged to the air from the exhaust
pipe 14. As described above, the flue gas purifying device 16
purifies the amount of urea water injected by the injecting unit 22
and the injection timing based on a measurement result obtained by
measuring the ammonia concentration in flue gas, which passes
through the predetermined position in the urea SCR catalytic unit
26, by the concentration measuring unit 28.
[0043] As described above, the vehicle 10 can decrease the PM in
flue gas discharged from the diesel engine 12, reduce nitrogen
oxides, and discharge flue gas in a state with harmful substance
being decreased, by the flue gas purifying device 16 (for a diesel
engine).
[0044] Further, the flue gas purifying device 16 measures the
ammonia concentration in the urea SCR catalytic unit 26 and
controls the injection amount of urea water according to the result
thereof. In this manner, by controlling the injection amount of
urea water based on the ammonia concentration in the urea SCR
catalytic unit 26, the injection amount of urea water can be
controlled according to the reaction state between ammonia and
nitrogen oxides.
[0045] Specifically, the reaction state between ammonia and
nitrogen oxides and percentage of ammonia adsorbed by the urea SCR
catalytic unit 26 can be ascertained more accurately than by a
measurement on an upstream side to the urea SCR catalytic unit 26.
When a measurement is performed on a downstream side to the urea
SCR catalytic unit 26, it means that ammonia is leaking at a point
in time when ammonia is measured, and thus leakage of ammonia
cannot be prevented. However, by measuring the ammonia
concentration in the urea SCR catalytic unit 26, ammonia can be
reacted with nitrogen oxides also on a downstream side to a
measurement point so that ammonia is adsorbed by a urea SCR
catalyst. Therefore, even if ammonia is detected at the measurement
position, it can be suppressed that ammonia leaks to the downstream
side to the urea SCR catalyst.
[0046] A reaction amount between nitrogen oxides and ammonia and an
adsorption rate of ammonia change according to a plurality of
factors such as a temperature and a concentration. Therefore, even
if the injection amount of urea water is controlled based on a map
created beforehand, the amount of ammonia may increase and leak, or
may decrease and be insufficient for completely reducing nitrogen
oxides, and nitrogen oxides may leak. However, by measuring the
ammonia concentration at the measurement position in the urea SCR
catalyst, the urea SCR catalytic unit 26 can control the injection
amount of urea water more appropriately.
[0047] In the flue gas purifying device 16, an oxidation catalyst
that oxidizes ammonia is normally provided on the downstream side
to the urea SCR catalytic unit 26 so that ammonia does not leak
into the air from the exhaust pipe 14. However, the oxidation
catalyst can be decreased or does not need to be provided.
Accordingly, the device configuration of the flue gas purifying
device can be simplified more, and the weight thereof can be
decreased. Further, by oxidizing ammonia, nitrogen oxides to be
produced can be decreased or removed. As described above, although
the flue gas purifying device 16 can suppress leakage of ammonia;
however, it is desired to provide an oxidation catalyst that
oxidizes ammonia on the downstream side to the urea SCR catalytic
unit 26 in order to further decrease ammonia leaking to the air.
Even if the oxidation catalyst is provided, because the flue gas
purifying device 16 for a diesel engine can decrease the leaked
amount of ammonia, in the flue gas purifying device 16, the
oxidation catalyst can be further downsized and nitrogen oxides to
be produced can be decreased more than those in conventional
devices.
[0048] A target value of an ammonia concentration is preferably set
to a value with buffer, that is, a value that can realize such a
state that ammonia can be absorbed by the urea SCR catalytic unit
26 on the downstream side to the concentration measuring unit 28
even if the ammonia concentration is higher than the target value,
that is, when the ammonia concentration is the target value, a
value that can realize such a state that the urea SCR catalytic
unit 26 has a margin to absorb ammonia. By setting a value with
buffer as the target value, it can be reliably prevented that
ammonia leaks from the urea SCR catalytic unit 26.
[0049] It is desired here that the concentration measuring unit 28
measures an ammonia concentration at an arbitrary position in a
region of from a position where the concentration of nitrogen
oxides at the time of maximum load of the diesel engine when
nitrogen oxides in flue gas are reduced in a state with ammonia
being input excessively into the urea SCR catalyst becomes either a
concentration at an inlet of the urea SCR catalyst at the time of
minimum load of the diesel engine or a concentration half the
concentration at the inlet of the urea SCR catalyst at the time of
maximum load of the internal combustion engine, whichever the
higher, to a position where the concentration of nitrogen oxides at
the time of maximum load of the diesel engine becomes a theoretical
concentration of nitrogen oxides that can be denitrated with an
ammonia concentration of 10 ppm, of a region of the urea SCR
catalytic unit 26 in which the urea SCR catalyst is arranged, in a
flow direction of flue gas. The case that nitrogen oxides in flue
gas are reduced in a state with ammonia being input excessively
into the urea SCR catalyst is a case when it is assumed that
ammonia adsorbed by the urea SCR catalyst is saturated, and the
input ammonia is not adsorbed by the urea SCR catalyst at the time
of passing through the urea SCR catalyst and only nitrogen oxides
are reduced. That is, it is a case that nitrogen oxides are reduced
by the urea SCR catalyst at the maximum efficiency. Further, the
theoretical concentration of nitrogen oxides that can be denitrated
(that is, reducible) at the ammonia concentration of 10 ppm is a
concentration of nitrogen oxides that can be denitrated in a state
with ammonia being not adsorbed by the urea SCR catalyst and when
an ammonia concentration in flue gas (air) is 10 ppm. Further, the
position where the concentration of nitrogen oxides at the time of
maximum load of the diesel engine when nitrogen oxides in flue gas
are reduced in a state with ammonia being input excessively into
the urea SCR catalyst becomes either the concentration at the inlet
of the urea SCR catalyst at the time of minimum load of the diesel
engine, or a concentration half the concentration at the inlet of
the urea SCR catalyst at the time of maximum load of the internal
combustion engine, whichever the higher, can be said to be a
position where the concentration of nitrogen oxides at the time of
maximum load of the diesel engine when nitrogen oxides in flue gas
are reduced in a state with ammonia being input excessively into
the urea SCR catalyst becomes the concentration at the inlet of the
urea SCR catalyst at the time of minimum load of the diesel engine,
or a position where the concentration of nitrogen oxides at the
time of maximum load of the diesel engine when nitrogen oxides in
flue gas are reduced in a state with ammonia being input
excessively into the urea SCR catalyst becomes a concentration half
the concentration at the inlet of the urea SCR catalyst, whichever
the closer to the inlet of the urea SCR catalytic unit 26.
[0050] This configuration is explained below in more detail with
reference to FIG. 3. FIG. 3 is a graph of a relation between a
length from the inlet of the urea SCR catalyst and the
concentration of nitrogen oxides. In FIG. 3, the length from the
inlet of the urea SCR catalyst is plotted on a horizontal axis and
the concentration of nitrogen oxides is plotted on a vertical axis.
Further, FIG. 3 represents a result of calculation of the
concentration of nitrogen oxides by simulation at respective
positions of the urea SCR catalyst when nitrogen oxides in flue gas
are reduced in a state where nitrogen oxides are discharged from
the diesel engine with the maximum load, that is, with the highest
concentration, and ammonia is input excessively into the urea SCR
catalyst. FIG. 3 also represents a result of calculation of the
concentration of nitrogen oxides by simulation at respective
positions of the urea SCR catalyst when nitrogen oxides in flue gas
are reduced in a state where nitrogen oxides are discharged from
the diesel engine with the minimum load, that is, with the lowest
concentration, and ammonia is input excessively into the urea SCR
catalyst. L3 denotes a length from the inlet to an outlet of the
urea SCR catalyst, that is, a whole length of the urea SCR
catalyst. CN1 denotes a theoretical concentration of nitrogen
oxides that can be denitrated when the ammonia concentration is
assumed to be 10 ppm. CN2 denotes a concentration of nitrogen
oxides at the inlet of the urea SCR catalyst at the time of minimum
load, and CN3 denotes a concentration of nitrogen oxides at the
inlet of the urea SCR catalyst at the time of maximum load. In FIG.
3, L1 is a position where the concentration of nitrogen oxides at
the time of maximum load of the diesel engine, when nitrogen oxides
in flue gas are reduced in a state with ammonia being input
excessively into the urea SCR catalyst, becomes the concentration
at the inlet of the urea SCR catalyst at the time of minimum load
of the diesel engine. Further, L2 is a position where the
concentration of nitrogen oxides at the time of maximum load of the
diesel engine becomes the theoretical concentration of nitrogen
oxides that can be denitrated with the ammonia concentration of 10
ppm. In FIG. 3, it is desirable that the concentration measuring
unit 28 is arranged between L1 and L2. Specific values of these
vales vary according to the device to be used.
[0051] An adsorption rate of ammonia adsorbed by the urea SCR
catalyst in the urea SCR catalytic unit 26 and the reaction state
between nitrogen oxides and ammonia can be ascertained more
accurately, and appropriate buffer can be provided to the urea SCR
catalytic unit 26, by measuring the ammonia concentration at the
above position between L1 and L2 in FIG. 3, of the region where the
urea SCR catalyst in the urea SCR catalytic unit 26 is arranged.
Further, because the ammonia concentration in flue gas in a state
with unreacted ammonia remaining to some extent can be measured,
the ammonia concentration that can be easily measured can be set as
a target value. Further, in the example shown in FIG. 3, CN2
denotes the concentration of nitrogen oxides at the inlet of the
urea SCR catalyst at the time of minimum load. However, as
described above, CN2 may be a concentration half the concentration
at the inlet of the urea SCR catalyst at the time of maximum load.
In this case, L1 becomes a position where the concentration of
nitrogen oxides at the time of maximum load of the diesel engine,
when nitrogen oxides in flue gas are reduced in a state with
ammonia being input excessively into the urea SCR catalyst, becomes
a concentration half the concentration at the inlet of the urea SCR
catalyst at the time of maximum load. Thus, even if the
concentration half the concentration at the inlet of the urea SCR
catalyst at the time of maximum load is used as a reference, the
same effect as those described above can be obtained. As described
above, it is desired that CN2 is the higher concentration of two
reference concentrations, and L1 is a position closer to the inlet
of the urea SCR catalytic unit 26, of two positions. Even if the
concentration of nitrogen oxides at the inlet of the urea SCR
catalyst at the time of minimum load is extremely low, the ammonia
concentration can be appropriately detected between L1 and L2 by
using either the concentration of nitrogen oxides at the inlet of
the urea SCR catalyst at the time of minimum load or a
concentration half the concentration at the inlet of the urea SCR
catalyst at the time of maximum load, whichever the higher, as a
reference.
[0052] The control unit 30 preferably controls injection of urea
water by the injecting unit 22 so that an ammonia concentration at
an arbitrary position (hereinafter, also "reference position")
becomes within a predetermined range. By setting the ammonia
concentration at the reference position within the predetermined
range, the amount of urea water to be injected into the exhaust
pipe 14 can be made more appropriate, thereby enabling to further
suppress leakage of ammonia from the exhaust pipe 14 and decrease
nitrogen oxides more reliably. In this case, it is desired that the
concentration measuring unit 28 measures the concentration at the
reference position, of the region in which the urea SCR catalyst in
the urea SCR catalytic unit 26 is arranged, and the control unit 30
controls injection of urea water by the injecting unit 22 based on
a measurement result thereof. However, the present invention is not
limited thereto, and the ammonia concentration at a position on an
upstream side to the reference position can be measured, or the
ammonia concentration at a position on a downstream side to the
reference position can be measured. In this manner, when a point of
the measurement of the ammonia concentration is different from the
reference position, the ammonia concentration at the reference
position can be calculated based on a separated distance. Further,
a relation between the ammonia concentration at a position for
measuring the ammonia concentration and the ammonia concentration
at the reference position can be obtained beforehand by
experiments.
[0053] It is also desirable that the control unit 30 adjusts the
injection amount of urea so that the concentration of nitrogen
oxides between L1 and L2, of the region in which the urea SCR
catalyst in the urea SCR catalytic unit 26 is arranged, is equal to
or higher than CN1 and equal to or lower than CN2, based on the
measurement result by the concentration measuring unit 28.
Specifically, it is desired that the control unit 30 sets a
reference value or a reference range of an ammonia concentration at
a measurement position, so that the concentration of nitrogen
oxides at the measurement position is equal to or higher than the
theoretical concentration of nitrogen oxides that can be denitrated
with an ammonia concentration of 10 ppm, and is equal to or lower
than a concentration of nitrogen oxides at the inlet of the urea
SCR catalyst at the time of minimum load or a concentration half
the concentration at the inlet of the urea SCR catalyst at the time
of maximum load, whichever is higher. Further, it is desired to set
the reference value or the reference range of the ammonia
concentration at the measurement position so that the concentration
of nitrogen oxides at respective positions is respectively within a
hatched region in FIG. 3. Specifically, it is desired to set the
reference value or the reference range of the ammonia concentration
at the measurement position so that the concentration of nitrogen
oxides between L1 and L2 at the measurement position is equal to or
higher than CN1 and equal to or lower than CN2, and the
concentration of nitrogen oxides at respective positions is,
respectively, equal to or higher than a simulation result of the
concentration of nitrogen oxides at the respective positions of the
urea SCR catalyst when nitrogen oxides in flue gas are reduced at
the time of minimum load and in a state with ammonia being input
excessively into the urea SCR catalyst, and is equal to or lower
than a simulation result of the concentration of nitrogen oxides at
the respective positions of the urea SCR catalyst when nitrogen
oxides in flue gas are reduced at the time of maximum load and in
the state with ammonia being input excessively into the urea SCR
catalyst. By setting the reference of the ammonia concentration at
the measurement position so that the concentration of nitrogen
oxides is within the predetermined rage, nitrogen oxides can be
reduced more efficiently, while further decreasing leakage of
ammonia. In FIG. 3, when the concentration at L1 and CN2 is the
concentration of nitrogen oxides at the inlet of the urea
[0054] SCR catalyst at the time of minimum load or a concentration
half the concentration at the inlet of the urea SCR catalyst at the
time of maximum load, whichever the higher, the positions of L1 and
CN2 become different positions. Also in this case, in FIG. 3, only
the positions of L1 and CN2 become different positions, and
definition of other ranges is the same.
[0055] Further, the control unit 30 can change the target value of
the ammonia concentration at the measurement position according to
operating conditions such as accelerator opening, velocity, and
engine speed, or can set it constant regardless of the operating
conditions. When changing the target value according to the
operating conditions, the control unit 30 can control the injection
amount of urea water corresponding to an increase or decrease of
the amount of nitrogen oxides contained in flue gas, thereby
enabling to decrease nitrogen oxides more appropriately, and
maintain the ammonia concentration at the measurement position at a
value close to the target value. The same effects can be obtained
when the target value is maintained constant to control the
injection amount and injection timing of urea water based on a
relation between the target value and the operating conditions.
When the target value of the ammonia concentration is set constant
regardless of the operating conditions, the operating conditions do
not need to be detected, thereby enabling to decrease the number of
measuring units, and simplify the device configuration of the flue
gas purifying device. Further, because the target value does not
need to be calculated according to conditions, control is
simplified.
[0056] In the flue gas purifying device 16, the PM is trapped by
the oxidation catalyst 18 and the DPF 20, to decrease the PM in
flue gas; however, the present invention is not limited thereto.
Various types of particulate-matter reducing apparatuses that
reduce the PM can be used for the flue gas purifying device for a
diesel engine, and, for example, only a filter for trapping the PM
can be arranged without providing the oxidation catalyst.
[0057] In the flue gas purifying device 16, the concentration
measuring unit 28 uses the TDLAS that outputs laser beams in a
wavelength region absorbed by ammonia and detects an absorption
rate of laser beams, to measure the ammonia concentration. However,
the present invention is not limited thereto, and various measuring
units that can measure the ammonia concentration in flue gas can be
used. For example, a branch pipe can be provided at the measurement
position, and a part of flue gas is made to flow into the branch
pipe to measure the ammonia concentration in flue gas flowing in
the branch pipe.
[0058] Further, in the flue gas purifying device 16, one urea SCR
catalytic unit 26 is provided and the concentration measuring unit
28 is provided in the urea SCR catalytic unit 26, that is, in
between the urea SCR catalytic unit 26; however, the present
invention is not limited thereto. A flue gas purifying device for a
diesel engine according to another embodiment of the present
invention is explained below with reference to FIG. 4.
[0059] FIG. 4 is a block diagram of a schematic configuration of a
vehicle including the flue gas purifying device according to
another embodiment of the present invention. A vehicle 50 shown in
FIG. 4 is the same as the vehicle 10, except for the configuration
of a urea SCR system 54 in a flue gas purifying device 52, and
therefore explanations of constituent elements identical to those
of the vehicle 10 will be omitted, and features specific to the
vehicle 50 are mainly explained below. The vehicle 50 shown in FIG.
4 includes the diesel engine 12, the exhaust pipe 14, and the flue
gas purifying device 52. The flue gas purifying device 52 (for a
diesel engine) includes the oxidation catalyst 18, the DPF 20, the
injecting unit 22, the urea water tank 24, a urea SCR catalytic
unit 56, a concentration measuring unit 64, and the control unit
30. The oxidation catalyst 18, the DPF 20, the injecting unit 22,
the urea water tank 24, and the control unit 30 respectively have
the same configuration as that in the flue gas purifying device 16
described above, and thus detailed explanations thereof will be
omitted.
[0060] The urea SCR catalytic unit 56 includes a first catalyst 58,
a connecting pipe 60, and a second catalyst 62. The first catalyst
58 and the second catalyst 62 respectively include a urea SCR
catalyst, which is a urea selective reduction catalyst that
promotes a reaction between ammonia produced from urea with
nitrogen oxides, and a support mechanism that supports the urea SCR
catalyst. The same catalyst can be used or a different catalyst can
be used for the urea SCR catalyst of the first catalyst 58 and the
second catalyst 62. The connecting pipe 60 is arranged between the
first catalyst 58 and the second catalyst 62, to guide flue gas
having passed through the first catalyst 58 to the second catalyst
62.
[0061] The concentration measuring unit 64 is installed in the
connecting pipe 60, to measure the ammonia concentration in flue
gas flowing in the connecting pipe 60. The configuration of the
concentration measuring unit 64 is the same as that of the
concentration measuring unit 28 except for the arrangement thereof,
and thus detailed explanations thereof will be omitted.
[0062] The flue gas purifying device 52 has the configuration
described above, in which flue gas discharged from the diesel
engine 12 flows in the exhaust pipe 14, and passes through the
oxidation catalyst 18 and the DPF 20, to decrease the PM.
Thereafter, flue gas further flows in the exhaust pipe 14, and
after urea water is injected by the injecting unit 22, flue gas
passes in the first catalyst 58 and through the connecting pipe 60,
and then in the second catalyst 62. When flue gas passes through
the first catalyst 58 and the second catalyst 62, nitrogen oxides
contained in flue gas react with ammonia produced from urea water,
to reduce nitrogen oxides. Flue gas having passed through the
second catalyst 62 is discharged from the exhaust pipe 14 to the
air.
[0063] As described above, even when the catalyst constituting the
urea SCR catalyst in the urea SCR catalytic unit 56 is divided into
a plurality of numbers, and the catalysts are connected by a pipe,
the injection amount of urea water can be controlled according to
the reaction state between ammonia and nitrogen oxides by measuring
the ammonia concentration at a position where the catalysts are
arranged both on an upstream side and on a downstream side thereof
in a flow direction of flue gas by the concentration measuring unit
and controlling injection of urea water by the injecting unit. As
shown in FIG. 4, when the urea SCR catalyst is divided into the
first catalyst and the second catalyst, it is desired that a ratio
between the length of the first catalyst and the length of the
second catalyst in the flow direction of flue gas satisfies the
relation described above, so that the measurement position is at a
distance from the inlet of the urea SCR catalyst, equal to or
longer than L1 and equal to or shorter than L2. That is, when it is
assumed that the length of the first catalyst in the flow direction
of flue gas is La, and the length of the second catalyst is Lb, it
is desired that a total length of La and Lb becomes L3, that is,
La+Lb=L3, and the length of La is a length between L1 and L2. As
explained above, by setting a position having passed through the
first catalyst to a position having passed through a region of the
urea SCR catalyst of from the length L1 to the length L2 inclusive
in the flow direction of flue gas, the concentration measuring unit
arranged in a connecting pipe can measure the ammonia concentration
in flue gas at a preferable position. Accordingly, the reaction
state between nitrogen oxides and ammonia can be ascertained more
accurately, and appropriate buffer can be provided to the urea SCR
catalytic unit.
[0064] In the above embodiments, the injecting unit injects urea
water to produce ammonia, because control is easy and urea water is
easily available. However, the present invention is not limited
thereto. Only ammonia needs to be supplied to the urea SCR catalyst
(SCR catalyst), and gaseous ammonia can be directly injected, or
ammonia water can be supplied, for example.
[0065] The flue gas purifying device is explained in detail with
reference to experiment examples. FIGS. 5 to 8 are graphs
respectively representing an example of a measurement result. In
experiments described below, gaseous ammonia was supplied instead
of urea water, and a 30-kW engine for power generation
(manufactured by Mitsubishi Heavy Industries, Ltd) was used as the
internal combustion engine. An ammonia-concentration measuring unit
measured an ammonia concentration at a position shifted by 1/4,
that is, 25% from an upstream side of the SCR catalyst toward a
downstream side. In the experiments, the internal combustion engine
was driven under certain conditions, and when a driven state was
stabilized, the flow rate of flue gas discharged from the engine
was decreased, and a certain amount of air (air other than flue
gas) was mixed therein separately. By mixing air, not only the
concentration of nitrogen oxides but also the temperature of flue
gas changes, to change treatment conditions with the SCR catalyst.
In such a manner, an input amount of ammonia was adjusted based on
a measurement result by the ammonia-concentration measuring unit
arranged at the position shifted by 1/4 from the upstream side of
the SCR catalyst, when the treatment conditions changed. The
control target value was made variable according to the conditions,
and control was performed to reach a preset target value based on
the conditions.
[0066] In this manner, conditions of flue gas passing through the
flue gas purifying device were changed, and an input amount of
ammonia, an ammonia concentration at the measurement position (a
measurement result acquired by the measuring unit), a temperature
at the inlet of the SCR catalyst, and a concentration of nitrogen
oxides and ammonia in flue gas discharged from the outlet of the
SCR catalyst (the flue gas purifying device) were measured. The
measurement result is shown in FIG. 5. In FIG. 5, an elapsed time
[a time, h] immediately after start of treatment was plotted on a
horizontal axis, and the concentration of nitrogen oxides (NOx
concentration) [ppm], the ammonia concentration (NH.sub.3
concentration) [ppm], the temperature at the inlet of the SCR
catalyst [.degree. C.], and the input amount of ammonia (NH.sub.3)
[.times.100 NL/min] were plotted on a vertical axis.
[0067] In the measurement example shown in FIG. 5, a measurement
was performed by supplying only flue gas from the engine to the
flue gas purifying device for 30 minutes immediately after start of
treatment (from an elapsed time 0 h to an elapsed time 0:30 h).
Thereafter, for 1 hour (from the elapsed time 0:30 h to an elapsed
time 1:30 h), flue gas from the engine was mixed with added air
(not flue gas but air mixed in flue gas) and supplied to the flue
gas purifying device, and for another 1 hour (from the elapsed time
1:30 h to an elapsed time 2:30 h), only flue gas from the engine
was supplied to the flue gas purifying device to perform a
measurement. As a result of measurements of flow rate of gas (air)
supplied at the time of the measurements, the flow rate of flue gas
from the engine was 41 Nm.sup.3/h for 30 minutes immediately after
start of treatment (from the elapsed time 0 h to the elapsed time
0:30 h), and for subsequent 1 hour (from the elapsed time 0:30 h to
the elapsed time 1:30 h), the flow rate of flue gas from the engine
was 24 Nm.sup.3/h, the flow rate of added air was 45 Nm.sup.3/h,
and the flow rate of air flowing in the flue gas purifying device
was 69 Nm.sup.3/h. Thereafter, for another 1 hour (from the elapsed
time 1:30 h to the elapsed time 2:30 h), the flow rate of flue gas
from the engine was 43 Nm.sup.3/h.
[0068] For comparison, a measurement was then performed for a case
that the input amount of ammonia was controlled based on mapping
data calculated beforehand. In this measurement example, because
the engine was stably operated (the number of rotations, operating
conditions and the like), control was performed by using an input
amount of ammonia calculated from experiments under respective
conditions and an input amount of ammonia calculated from
experiments when a certain amount of air was mixed in ammonia. In
the mapping data, an input amount of ammonia at which the
concentration of nitrogen oxides discharged from the flue gas
purifying device in steady state is 5 to 10 ppm is associated with
the operating conditions. The measurement result is shown in FIG.
6. Vertical and horizontal axes in the graph shown in FIG. 6 are
the same as those in the graph shown in FIG. 5.
[0069] Also in the measurement example shown in FIG. 6, only flue
gas from the engine was supplied to the flue gas purifying device
for 30 minutes immediately after start of treatment (from the
elapsed time 0 h to the elapsed time 0:30 h). Thereafter, for 1
hour (from the elapsed time 0:30 h to the elapsed time 1:30 h),
flue gas from the engine was mixed with added air (not flue gas but
air mixed in flue gas) and supplied to the flue gas purifying
device, and for another 1 hour (from the elapsed time 1:30 h to the
elapsed time 2:30 h), only flue gas from the engine was supplied to
the flue gas purifying device to perform the measurement. As a
result of measurements of flow rate of gas (air) supplied at the
time of the measurements, the flow rate of flue gas from the engine
was 43 Nm.sup.3/h for 30 minutes immediately after start of
treatment (from the elapsed time 0 h to the elapsed time 0:30 h),
and for subsequent 1 hour (from the elapsed time 0:30 h to the
elapsed time 1:30 h), the flow rate of flue gas from the engine was
26 Nm.sup.3/h, the flow rate of added air (not flue gas but air
mixed in flue gas) was 45 Nm.sup.3/h, and the flow rate of air
flowing in the flue gas purifying device was 71 Nm.sup.3/h.
Thereafter, for another 1 hour (from the elapsed time 1:30 h to the
elapsed time 2:30 h), the flow rate of flue gas from the engine was
44 Nm.sup.3/h.
[0070] As shown in FIGS. 5 and 6, by adjusting the input amount of
ammonia based on the measurement result of the ammonia
concentration in the SCR catalyst, leakage of nitrogen oxides as
well as leakage of ammonia can be further decreased by adjusting
the input amount of ammonia only based on the mapping data of the
relation between operating conditions and the input amount.
Particularly, such characteristics of the catalyst can be
compensated that when the temperature of flue gas suddenly drops,
the catalyst temperature also drops, and ammonia is not used for
the reduction reaction of NOx and easily adsorbed by the catalyst,
or when the temperature of flue gas suddenly rises, the catalyst
temperature also rises, and ammonia adsorbed by the catalyst is
released. As shown in FIG. 5, an ammonia concentration can be
measured in a certain concentration or higher, at a point where the
ammonia concentration is measured. That is, ammonia in a
concentration higher than that of near the outlet is a measurement
target, and thus changes in value can be easily detected, thereby
simplifying the measurement.
[0071] Experiments were performed also for a case that the
operating conditions were repeatedly changed in a shorter time than
the cases shown in FIGS. 5 and 6. The measurement result when
control is performed based on the result acquired by the
ammonia-concentration measuring unit is shown in FIG. 7, and the
measurement result when control is performed based on the mapping
data is shown in FIG. 8 for comparison. Vertical and horizontal
axes in the graph shown in FIGS. 7 and 8 are the same as those in
the graph shown in FIG. 5.
[0072] In the measurement example shown in FIG. 7, only flue gas
from the engine was supplied to the flue gas purifying device for
20 minutes immediately after start of treatment (from the elapsed
time 0 h to an elapsed time 0:20 h). Thereafter, a state of
supplying air in which flue gas from the engine was mixed with
added air and a state of supplying only flue gas from the engine
were repeated every 5 minutes four times to perform measurements.
As a result of measurements of flow rate of gas (air) supplied at
the time of the measurements, the flow rate of flue gas from the
engine was 43 Nm.sup.3/h for 20 minutes immediately after start of
treatment (from the elapsed time 0 h to the elapsed time 0:20 h).
Thereafter, for 5 minutes (from the elapsed time 0:20 h to an
elapsed time 0:25 h), the flow rate of flue gas from the engine was
26 Nm.sup.3/h, the flow rate of added air was 45 Nm.sup.3/h, and
the flow rate of air flowing in the flue gas purifying device was
71 Nm.sup.3/h. For subsequent 5 minutes (from the elapsed time 0:25
h to the elapsed time 0:30 h), the flow rate of flue gas from the
engine was 45 Nm.sup.3/h. For subsequent 5 minutes (from the
elapsed time 0:30 h to an elapsed time 0:35 h), the flow rate of
flue gas from the engine was 26 Nm.sup.3/h, the flow rate of added
air was 45 Nm.sup.3/h, and the flow rate of air flowing in the flue
gas purifying device was 71 Nm.sup.3/h. For subsequent 5 minutes
(from the elapsed time 0:35 h to an elapsed time 0:40 h), the flow
rate of flue gas from the engine was 44 Nm.sup.3/h. Further, for
another 5 minutes (from the elapsed time 0:40 h to an elapsed time
0:45 h), the flow rate of flue gas from the engine was 26
Nm.sup.3/h, the flow rate of added air was 45 Nm.sup.3/h, and the
flow rate of air flowing in the flue gas purifying device was 71
Nm.sup.3/h, and for another 5 minutes (from the elapsed time 0:45 h
to an elapsed time 0:50 h), the flow rate of flue gas from the
engine was 44 Nm.sup.3/h. Thereafter, for another 5 minutes (from
the elapsed time 0:50 h to an elapsed time 0:55 h), the flow rate
of flue gas from the engine was 27 Nm.sup.3/h, the flow rate of
added air was 45 Nm.sup.3/h, and the flow rate of air flowing in
the flue gas purifying device was 72 Nm.sup.3/h, and for another 20
minutes (from the elapsed time 0:55 h to an elapsed time 1:15 h),
the flow rate of flue gas from the engine was 44 Nm.sup.3/h.
[0073] Also in the measurement example shown in FIG. 8, only flue
gas from the engine was supplied to the flue gas purifying device
for 20 minutes immediately after start of treatment (from the
elapsed time 0 h to the elapsed time 0:20 h). Thereafter, a state
of supplying air in which flue gas from the engine was mixed with
added air and a state of supplying only flue gas from the engine
were repeated every 5 minutes four times to perform measurements.
As a result of measurements of flow rate of gas (air) supplied at
the time of the measurements, the flow rate of flue gas from the
engine was 44 Nm.sup.3/h for 20 minutes immediately after start of
treatment (from the elapsed time 0 h to the elapsed time 0:20 h).
Thereafter, for 5 minutes (from the elapsed time 0:20 h to the
elapsed time 0:25 h), the flow rate of flue gas from the engine was
27 Nm.sup.3/h, the flow rate of added air was 45 Nm.sup.3/h, and
the flow rate of air flowing in the flue gas purifying device was
72 Nm.sup.3/h. For subsequent 5 minutes (from the elapsed time 0:25
h to the elapsed time 0:30 h), the flow rate of flue gas from the
engine was 45 Nm.sup.3/h. For subsequent 5 minutes (from the
elapsed time 0:30 h to the elapsed time 0:35 h), the flow rate of
flue gas from the engine was 29 Nm.sup.3/h, the flow rate of added
air was 45 Nm.sup.3/h, and the flow rate of air flowing in the flue
gas purifying device was 74 Nm.sup.3/h. For subsequent 5 minutes
(from the elapsed time 0:35 h to the elapsed time 0:40 h), the flow
rate of flue gas from the engine was 45 Nm.sup.3/h. Further, for
another 5 minutes (from the elapsed time 0:40 h to the elapsed time
0:45 h), the flow rate of flue gas from the engine was 28
Nm.sup.3/h, the flow rate of added air was 45 Nm.sup.3/h, and the
flow rate of air flowing in the flue gas purifying device was 73
Nm.sup.3/h, and for another 5 minutes (from the elapsed time 0:45 h
to the elapsed time 0:50 h), the flow rate of flue gas from the
engine was 45 Nm.sup.3/h. Thereafter, for another 5 minutes (from
the elapsed time 0:50 h to the elapsed time 0:55 h), the flow rate
of flue gas from the engine was 28 Nm.sup.3/h, the flow rate of
added air was 45 Nm.sup.3/h, and the flow rate of air flowing in
the flue gas purifying device was 73 Nm.sup.3/h, and for another 20
minutes (from the elapsed time 0:55 h to the elapsed time 1:15 h),
the flow rate of flue gas from the engine was 44 Nm.sup.3/h.
[0074] As shown in FIGS. 7 and 8, by adjusting the input amount of
ammonia based on the measurement result of the ammonia
concentration in the SCR catalyst, leakage of nitrogen oxides as
well as leakage of ammonia can be further decreased by adjusting
the input amount of ammonia only based on the mapping data of the
relation between operating conditions and the input amount.
Specifically, in the measurement example shown in FIG. 8, ammonia
leaks from the outlet at the time of changing the condition;
however, in the measurement example shown in FIG. 7, leakage of
ammonia is suppressed. Accordingly, the leaked amount of ammonia is
decreased without increasing the amount of nitrogen oxides leaking
from the outlet. Particularly, it is possible to compensate such
characteristics of the catalyst that, when the temperature of flue
gas suddenly drops, the catalyst temperature also drops, and
ammonia is not used for the reduction reaction of NOx and easily
adsorbed by the catalyst, or when the temperature of flue gas
suddenly rises, the catalyst temperature also rises, and ammonia
adsorbed by the catalyst is released. Further, as shown in FIG. 7,
the ammonia concentration can be measured in a certain
concentration or higher, at a point where the ammonia concentration
is measured. That is, ammonia in a concentration higher than that
of near the outlet becomes a measurement target, and thus changes
in value can be easily detected, thereby simplifying the
measurement.
INDUSTRIAL APPLICABILITY
[0075] As described above, the flue gas purifying device according
to the present invention is useful for purifying flue gas
discharged from an internal combustion engine, and the flue gas
purifying device is particularly suitable for purifying flue gas
discharged from a diesel engine mounted on a vehicle.
REFERENCE SIGNS LIST
[0076] 10, 50 vehicle [0077] 12 diesel engine [0078] 14 exhaust
pipe [0079] 16, 52 flue gas purifying device [0080] 18 oxidation
catalyst [0081] 20 DPF [0082] 21, 54 urea SCR system [0083] 22
injecting unit [0084] 24 urea water tank [0085] 26, 56 urea SCR
catalytic unit [0086] 28, 64 concentration measuring unit [0087] 30
control unit [0088] 40 measuring unit body [0089] 42 optical fiber
[0090] 44 measuring cell [0091] 46 light receiving unit [0092] 58
first catalyst [0093] 60 connecting pipe [0094] 62 second
catalyst
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