Title of Invention
Gas analysis apparatus
Technical Field
10 The present invention relates to a gas analysis apparatus
that measures a substance contained in exhaust gas emitted from
an internal combustion engine or mixed gas in which the exhaust
gas is mixed.
Background Art
15
In the past, a gas analysis apparatus has been used to
measure a composition of exhaust gas emitted from an internal
combustion engine of an automobile, such as NOx, and in recent
years, a composition such as ammonia has also been measured.
20
As specific examples of measuring the gas composition such
as ammonia, which has not been measured in the past, include a
scene of research and development of a urea SCR (Selective
Catalytic Reduction) system that can highly efficiently drive a
25 diesel engine and also suppress a production amount of NOX, and
other scenes. To specifically describe the urea SCR system, the
urea SCR system is configured to, by spraying urea into
high-temperature exhaust gas emitted from a diesel engine, and as
a reducing agent, supplying ammonia produced by pyrolysis of the
3
urea to an SCR catalyst, reduce NOX in the exhaust gas to 5 change
the NOX to harmless N2 and H2O.
In the case where in such a urea SCR system, an excessive
amount of urea is supplied, ammonia is contained in an exhaust gas
10 emitted from a muffler or the like to give rise to a bad odor, or to
failure to meet environmental standards. For this reason, in order
to know whether or not an adequate amount of urea can be supplied
in various driving conditions, ammonia in exhaust gas is measured.
15 For example, Patent Literature 1 discloses a gas analysis
apparatus 100A that measures an amount of urea remaining in
exhaust gas only with ammonia sensors 21A that can measure the
concentration of ammonia. More specifically, as illustrated in Fig.
6, the analysis apparatus 100A is one provided with: a sampling
20 pipe 1A of which one end is opened just before an SCR catalyst 94
and the other ends (of sampling pipe branches) are provided with
the ammonia sensors 21A; and heaters 31A and 32A that are
respectively provided so as to surround the sampling pipe branches
1A on upstream sides of the ammonia sensors 21A. Also, the gas
25 analysis apparatus 100A is configured to measure first
concentration of ammonia while heating the inside of one of the
sampling pipe branches 1A with the heater 31A so as to keep the
urea contained in the exhaust gas at a temperature lower than a
pyrolysis starting temperature of the urea, and second
4
concentration of ammonia while heating the inside of the 5 other
sampling pipe branch 1A with the heater 32A to temperature higher
than the pyrolysis starting temperature of the urea, and from a
difference between the concentrations, calculate an amount of the
remaining urea contained in the exhaust gas.
10
In addition, it is expected that isocyanic acid, which may be
produced in the case of introducing urea into the exhaust gas for
the urea SCR, also becomes increasingly important in measurement
in future because an influence of isocyanic acid on an environment,
15 health, and the like is quantitatively evaluated. Further, Patent
Literature 1 also describes a method for calculating an amount of
isocyanic acid produced from urea by a decomposition reaction.
Meanwhile, even in the gas analysis apparatus as disclosed
20 in Patent Literature 1, it is required to further improve
measurement accuracy and reliability of the remaining urea and
isocyanic acid in the exhaust gas.
Specifically, in order to accurately measure an amount of the
25 remaining urea in the exhaust gas, it is necessary to completely
decompose the remaining urea into the ammonia in the sampling
pipe, and obtain an accurate amount of the ammonia derived from
the remaining urea. However, at present, there is a possibility
that sufficiently heating and completely decomposing urea in a
5
misty state or powdery urea resulting from extracting 5 ting water are not
sufficiently performed
On the other hand, in the case of measuring the amount of
the isocyanic acid produced from the urea by heat of the exhaust
10 gas, if even part of the remaining urea is pyrolyzed in the sampling
pipe, in addition to the isocyanic acid produced by the heat of the
exhaust gas in the first place, isocyanic acid newly produced in the
sampling pipe is included. That is, the evaluation may be made on
the basis of a more excessive amount than the amount of the
15 isocyanic acid emitted from an actual vehicle.
In other words, even in any of the measurement of the urea
and the measurement of the isocyanic acid produced from the urea,
in order to increase accuracy and reliability, it is necessary to
20 appropriately control the decomposition reaction of the remaining
urea contained in mixed gas.
Also, in the case where the powdery urea arrives at each of
the ammonia sensors without being decomposed, there exists
25 another problem that the urea is attached on a surface of a sensor
part, or the like to reduce sensitivity and reduce reliability of a
measured value, and consequently calculated values of the urea
and isocyanic acid amounts may become unreliable.
Citation List
6
Patent 5 Literature
Patent Literature 1: JP-A2010-223650
Summary of Invention
Technical Problem
10
The present invention is made with the intention to solve the
problems as described above at once, and intended to provide a gas
analysis apparatus that is adapted to be able to, in the case of
calculating a remaining urea amount, completely decompose
15 remaining urea contained in exhaust gas emitted from an internal
combustion engine to accurately measure the remaining urea
amount, and in the case of calculating an isocyanic acid amount,
calculate an accurate value with preventing urea from being newly
decomposed at the time of measurement, as well as preventing
20 measurement accuracy and reliability from being damaged due to
the attachment of powdery urea on a sensor or another cause.
Solution to Problem
That is, the gas analysis apparatus of the present invention
25 is provided with: a mixed gas sampling pipe that, from a sampling
port formed on one end side, samples mixed gas that is a mixture of
exhaust gas emitted from an internal combustion engine and a
misty urea aqueous solution; a decomposition reaction controlling
mechanism that controls a decomposition reaction of urea or
7
isocyanic acid in the mixed gas sampling pipe; a produce5 d
substance measuring mechanism that is provided on the other end
side of the mixed gas sampling pipe and measures a value related to
an amount of a substance produced from the urea or the isocyanic
acid in the urea aqueous solution; a calculation part that, on a basis
10 of a measured value measured by the produced substance
measuring mechanism, calculates a urea amount calculated value
that is a value related to an amount of the urea contained in the
mixed gas; and a filter part that is provided between the sampling
port and the produced substance measuring mechanism in the
15 mixed gas sampling pipe to collect the urea in a solid state or in a
state of being dissolved in water in the mixed gas, wherein the
decomposition reaction controlling mechanism is configured to act
on the filter part.
20 Also, the gas analysis apparatus of the present invention is
provided with: a mixed gas sampling pipe that, from a sampling
port formed on one end side, samples mixed gas that is a mixture of
exhaust gas emitted from an internal combustion engine and a
misty urea aqueous solution; a decomposition reaction controlling
25 mechanism that controls a decomposition reaction of urea or
isocyanic acid in the mixed gas sampling pipe; a produced
substance measuring mechanism that is provided on the other end
side of the mixed gas sampling pipe and measures a value related to
an amount of a substance produced from the urea or the isocyanic
8
acid in the urea aqueous solution; a calculation part that, on 5 a basis
of a measured value measured by the produced substance
measuring mechanism, calculates an isocyanic acid amount
calculated value that is a value related to an amount of the
isocyanic acid contained in the mixed gas; and a filter part that is
10 provided between the sampling port and the produced substance
measuring mechanism in the mixed gas sampling pipe to collect the
urea in a solid state or in a state of being dissolved in water in the
mixed gas, wherein the decomposition reaction controlling
mechanism is configured to act on a downstream side of the filter
15 part.
If so, between the sampling port and the produced substance
measuring mechanism, the filter part is provided, and therefore the
urea in the solid state such as a powdery state or in the state of
20 being dissolved in water is collected by the filter part. Accordingly,
in the case where the decomposition reaction controlling
mechanism acts so as to start the decomposition reaction of the
urea, the urea can be completely decomposed to then measure an
amount of a urea-derived substance without arriving at the
25 produced substance measuring mechanism as the urea is before the
complete end of the decomposition. Further, the calculation part
can calculate the urea amount calculated value on the basis of an
accurate amount of the urea-derived substance produced by the
decomposition of substantially the whole of the urea contained in
9
the exhaust gas, and therefore accurately calculate an amount 5 of
the remaining urea contained in the exhaust gas. On the other
hand, in the case where the decomposition reaction controlling
mechanism does not start the decomposition reaction of the urea,
the urea in the solid state or in the state of being dissolved in water,
10 which are contained in the exhaust gas, is prevented by the filter
part from arriving at the produced substance measuring
mechanism, and therefore a situation such as a reduction in
reliability of a measured value due to a reduction in sensitivity
caused by, for example, the attachment of the urea on a sensing
15 part or the like of a sensor can be prevented. From another point
of view, the filter part collects the urea in the solid state or in the
state of being dissolved in water, and therefore the decomposition
reaction controlling mechanism can selectively perform a
decomposition reaction of only the isocyanic acid without applying
20 heat to the urea in such a state to cause pyrolysis. Accordingly,
measurement targeting only the isocyanic acid contained in the
mixed gas can be performed to improve measurement accuracy of
the isocyanic acid as well.
25 As described, the gas analysis apparatus is provided with
the filter part, so that accuracy of a measured value of a substance
produced from the urea or isocyanic acid, or accuracy of the
calculated value of the urea or isocyanic acid amount can be
increased to increase reliability of the measured value or calculated
10
value5 .
As a specific aspect for controlling the decomposition
reaction of the urea in the exhaust gas, it is only necessary that the
decomposition reaction controlling mechanism is configured to
10 control temperature of the filter part, and the calculation part is
configured to calculate the urea amount calculated value that is a
value related to an amount of the urea contained in the mixed gas.
Specific aspects of a measuring target and temperature
15 setting for accurately calculating the amount of the urea contained
in the mixed gas by the calculation part include an aspect in which:
the produced substance measuring mechanism is configured to
measure a value related to an amount of ammonia; the
decomposition reaction controlling mechanism is configured to be
20 able to control the temperature of the filter part to a first
temperature that is equal to or more than a temperature at which
water is evaporated and less than a pyrolysis starting temperature
that is a temperature at which production of ammonia and
isocyanic acid is started by a pyrolysis reaction of urea, or a second
25 temperature that is equal to or more than the pyrolysis starting
temperature and less than a hydrolysis starting temperature that
is a temperature at which production of ammonia is started by a
hydrolysis reaction of isocyanic acid; and the calculation part is
configured to calculate the urea amount calculated value on a
11
basis of a first ammonia measured value measured at the 5 e first
temperature by the produced substance measuring mechanism and
a second ammonia measured value measured at the second
temperature by the produced substance measuring mechanism.
10 Other aspects for measuring an amount of a substance other
than ammonia to thereby calculate the amount of the urea
contained in the mixed gas include an aspect in which: the produced
substance measuring mechanism is configured to measure a value
related to an amount of isocyanic acid; the decomposition
15 controlling mechanism is configured to be able to control the
temperature of the filter part to a first temperature that is equal to
or more than a temperature at which water is evaporated and less
than a pyrolysis starting temperature that is a temperature at
which production of ammonia and isocyanic acid is started by a
20 pyrolysis reaction of urea, or a second temperature that is equal to
or more than the pyrolysis starting temperature and less than a
hydrolysis starting temperature that is a temperature at which
production of ammonia is started by a hydrolysis reaction of
isocyanic acid; and the calculation part is configured to calculate
25 the urea amount calculated value on a basis of a first isocyanic acid
measured value measured at the first temperature by the produced
substance measuring mechanism and a second isocyanic acid
measured value measured at the second temperature by the
produced substance measuring mechanism.
12
5
In order to make it possible to accurately measure each of an
amount of a urea-derived substance produced in such a way that
the urea is decomposed by heat of the exhaust gas emitted from the
internal combustion engine and an amount of a urea-derived
10 substance produced in such a way that the urea, which is not
decomposed by the heat of the exhaust gas but remains, is
decomposed by the decomposition reaction controlling mechanism,
it is only necessary that the first temperature is less than 133 ºC,
and the second temperature is equal to or more than 133 ºC and less
15 than 160 ºC. Setting such temperatures makes it possible to, at
the first temperature, without causing the decomposition reaction
of the urea, in the sampling pipe, keep amounts of ammonia and
isocyanic acid originally present in the exhaust gas, and at the
second temperature, produce equal parts of ammonia and isocyanic
20 acid on the basis of the decomposition reaction of the urea
contained in the exhaust gas. Also, at the second temperature, a
hydrolysis reaction of the isocyanic acid can be substantially
prevented from being caused, and therefore a production ratio of
the ammonia with respect to the urea can be kept substantially
25 constant to increase calculation accuracy of the urea amount
calculated value. Preferably, it is cited that the first temperature
is set equal to or more than 40 ºC and equal to or less than 128 ºC,
and the second temperature is set equal to or more than 138 ºC and
equal to or less than 155 ºC. Setting such temperature zones
13
makes it possible to prevent moisture from condensing on a 5 pipe or
the like, and also absorb unevenness and deviation of temperature
control by the decomposition reaction controlling mechanism to
further increase measurement accuracy.
10 In order for the calculation part to be able to use a simple
operation to accurately calculate an amount of the isocyanic acid by
preventing a decomposition reaction from the urea contained in the
mixed gas from being newly caused, it is only necessary that the
decomposition reaction controlling mechanism is configured to
15 control temperature of the inside of the mixed gas sampling pipe on
a downstream side of the filter part, and the calculation part is
configured to calculate the isocyanic acid amount calculated that is
the value related to the amount of the isocyanic acid contained in
the mixed gas.
20
In order for the calculation part to be able to use a simple
operation to calculate the amount of the isocyanic acid by not
directly measuring the isocyanic acid contained in the mixed gas
but performing measurement of a more easily measurable
25 substance, it is only necessary that the produced substance
measuring mechanism is configured to measure a value related to
an amount of ammonia; the decomposition reaction controlling
mechanism is configured to be able to control the temperature of the
filter part to a first temperature that is equal to or more than a
14
temperature at which water is evaporated and less than a py5 rolysis
starting temperature that is a temperature at which production of
ammonia and isocyanic acid is started by a pyrolysis reaction of
urea, or a third temperature that is equal to or more than a
hydrolysis starting temperature that is a temperature at which
10 production of ammonia is started by a hydrolysis reaction of
isocyanic acid; and the calculation part is configured to calculate
the isocyanic acid amount calculated value on a basis of a first
ammonia measured value measured at the first temperature by the
produced substance measuring mechanism and a third ammonia
15 measured value measured at the third temperature by the produced
substance measuring mechanism.
In order for the calculation part to be able to accurately
calculate the amount of the isocyanic acid contained in the mixed
20 gas in such a simple way that the produced substance measuring
mechanism measures only ammonia, it is only necessary that the
first temperature is less than 133 ºC, and the third temperature is
equal to or more than 160 ºC. In order to take into account an
error or the like of temperature control to increase reliability of a
25 measured value, it is preferable to set the third temperature to 165
ºC or more.
Advantageous Effects of Invention
As described, according to the gas analysis apparatus of the
15
present invention, the filter part is provided between the sampli5 ng
port of the sampling pipe and the produced substance measuring
mechanism, and therefore misty or powdery undecomposed urea
from remaining urea contained in the exhaust gas emitted from the
internal combustion engine can be collected before arriving at the
10 produced substance measuring mechanism. Further, the collected
remaining urea can be completely decomposed in the filter part,
and substantially the whole of the remaining urea can be
completely measured in the produced substance measuring
mechanism in a state of being decomposed. Accordingly, the
15 remaining urea that has been unmeasurable in the past because of
passing through the produced substance measuring mechanism as a
state of urea can also be accurately measured to accurately
calculate a remaining urea amount. Also, the remaining urea is
collected in the filter part, and therefore can be separated from the
20 isocyanic acid contained in the mixed gas, and only the isocyanic
acid can be measured without pyrolyzing the urea, so that the
amount of the isocyanic acid contained in the mixed gas can also be
accurately calculated. Further, the misty or powdery urea can be
collected in the filter part and prevented from arriving at the
25 produced substance measuring mechanism, and therefore
measurement accuracy and reliability can be prevented from being
damaged by some cause such as the attachment of the powdery urea
on a sensor.
Brief Description of Drawings
16
5
[Fig. 1]
Fig. 1 is a conceptual diagram of a urea SCR system.
[Fig. 2]
Fig. 2 is a schematic diagram illustrating a gas analysis
10 apparatus according to a first embodiment of the present invention.
[Fig. 3]
Fig. 3 is a schematic diagram illustrating a gas analysis
apparatus according to a second embodiment of the present
invention.
15 [Fig. 4]
Fig. 4 is a schematic diagram illustrating a gas analysis
apparatus according to a third embodiment of the present
invention.
[Fig. 5]
20 Fig. 5 is a schematic diagram illustrating a gas analysis
apparatus according to a fourth embodiment of the present
invention.
[Fig. 6]
Fig. 6 is a schematic diagram illustrating a conventional gas
25 analysis apparatus.
Reference Signs List
100 Gas analysis apparatus
1 Mixed gas sampling pipe
17
111 Sampling 5 ng port
21 Ammonia sensor (produced substance measuring mechanism)
22 Fourier transform infrared spectroscopic analyzed (produced
substance measuring mechanism)
3 Decomposition reaction controlling mechanism
10 4 Filter part
5 Calculation part
Description of Embodiments
A first embodiment of the present invention is described with
15 reference to drawings.
A gas analysis apparatus 100 of the present embodiment is
one that is intended to measure an amount of urea remaining in gas
emitted from a vehicle mounted with a urea SCR system 200. The
vehicle is one that is mounted with a diesel engine as an internal
20 combustion engine 92, and the urea SCR system 200 is formed in an
exhaust pipe 91 connected to the diesel engine.
The urea SCT system 200 is, as illustrated in Fig. 1,
configured to include, sequentially from an upstream side in the
25 exhaust pipe 91, a first oxidation catalyst 93, a urea injecting
mechanism 96 that injects urea into the exhaust pipe 91, an SCR
catalyst 94, and a second oxidation catalyst 95, and ammonia
produced by the decomposition of the urea injected from the urea
injecting mechanism 96, and the SCR catalyst 94 cooperate to
18
thereby reduce NO and NO2 having passed through the 5 e first
oxidation catalyst 93 to nitrogen and water.
More specifically, in the urea SCR system 200, the urea
injecting mechanism 96 is one that brings a 32.5 % urea aqueous
10 solution, which is prepared by dissolving urea in water, into a mist
state to inject the misty urea aqueous solution into the exhaust
pipe 91, and adapted to facilitate pyrolysis of urea. That is,
between the urea injecting mechanism 96 and the SCR catalyst 94,
the exhaust gas emitted from the internal combustion engine 92
15 and the misty urea aqueous solution are mixed with each other and
brought into a mixed gas state.
Note that if an amount of the urea injected from the urea
injecting mechanism 96 is excessive, and ammonia having an
20 amount more than an amount necessary to reduce NO and NO2 is
produced, ammonia not consumed at the time of reducing NO and
NO2 may be contained in gas emitted from the vehicle to fail to
meet environmental standards. Also, it is necessary to grasp what
ratio of the urea injected from the urea injecting mechanism 96 is
25 decomposed by heat of the exhaust gas to produce the ammonia, and
control the amount of the urea to be injected to an appropriate
value depending on a driving condition or the like.
The gas analysis apparatus 100 of the present embodiment is,
19
in order to solve the problem as described 5 ribed above in the urea SCR
system 200, configured to measure a remaining urea amount
between the urea injecting mechanism 96 and the SCR catalyst 94.
More specifically, the gas analysis apparatus 100 is one that
10 is, as illustrated in Fig. 2, provided with: a mixed gas sampling
pipe 1 that is formed with a sampling port 111 between the urea
injecting mechanism 96 and the SCR catalyst 94 in the exhaust
pipe 91 to sample mixed gas containing the exhaust gas and the
urea aqueous solution; a filter part 4 that is provided in the mixed
15 gas sampling pipe 1 to collect urea in a solid state or in a state of
being dissolved in water in the mixed gas; a decomposition reaction
controlling mechanism 3 that controls a decomposition reaction of
the urea in the mixed gas sampling pipe 1; a produced substance
measuring mechanism that is provided on the other end side of the
20 mixed gas sampling pipe 1 and measures a value related to an
amount of a substance produced from the urea in the urea aqueous
solution; and a calculation part 5 that, on the basis of the measured
value measured by the produced substance measuring mechanism,
calculates a urea amount calculated value that is a value related to
25 an amount of the urea contained in the mixed gas.
In addition, in the gas analysis apparatus 100 of the first
embodiment, the decomposition reaction controlling mechanism 3 is
one that controls temperature inside the sampling pipe 1 to thereby
20
control the decomposition reaction of 5 the urea, and the produced
substance measuring mechanism is an ammonia sensor 21 for
measuring ammonia produced by the decomposition of urea. Also,
the calculation part 5 is configured to, on the basis of ammonia
amounts measured by the ammonia sensor 21, calculate the amount
10 of the urea that remains without being decomposed by the heat of
the exhaust gas in the exhaust pipe 91.
The respective parts are further described in detail.
15 The mixed gas sampling pipe 1 is configured to include: an
introduction part 11 that forms from the sampling port 111 to a
branching point; a branching part 12 that, from the branching point,
branches into two flow paths, which again meet together as one
path at a meeting point; and a terminal part 13 that forms a pipe
20 from the branching point to the produced substance measuring
mechanism. The introduction part 11 is adapted to flow the
exhaust gas introduced from the exhaust pipe 91 in an unchanged
state. The branching part 12 is provided with a first flow path 121
and a second flow path 122, and the filter part 4 is provided for the
25 flow paths. Further, the present embodiment is configured such
that the after-mentioned decomposition reaction controlling
mechanism 3 switches directional control valves B respectively
provided at the branching and meeting points to thereby flow the
mixed gas through any one of the flow paths and also make a urea
21
decomposition condition different. The mixed gas having 5 passed
through the first or second flow path 121 or 122 moves through the
terminal part 13 and arrives at the ammonia sensor 21.
The filter part 4 includes first and second filters 41 and 42
10 respectively provided in the first and second flow paths 121 and 122
in the branching part 12, and each of the filters is a glass fiber
filter for collecting a solid substance or a liquid substance
contained in the mixed gas. In particular, the glass fiber filter in
the present embodiment is formed as a filter having density that
15 makes it possible to collect the misty urea aqueous solution or solid
powdery urea formed by evaporation of water as a solvent of the
urea aqueous solution, which is contained in the mixed gas.
The decomposition reaction controlling mechanism 3 is
20 configured to include: first and second heaters 31 and 32 that are
respectively provided on outer sides of the first and second flow
paths 121 and 122; and a temperature control part 33 that
separately controls temperatures inside the first and second flow
paths 121 and 122 with the first and second heaters 31 and 32.
25 The temperature control part 33 is, together with the calculation
part 5, configured to fulfill its function by a so-called computer
provided with a CPU, memory, A/D and D/A converters, and
input/output interface.
22
The temperature control part 33 is configured to, in a 5 state
where the directional control valves B are switched such that the
mixed gas flows only through the first flow path 121, use the first
heater 31 to control temperature inside the first flow path 121, in
particular, temperature near the first filter 41 to a first
10 temperature that is equal to or more than a temperature at which
water is evaporated, and less than a pyrolysis starting temperature
that is a temperature at which the production of ammonia and
isocyanic acid is started by the pyrolysis reaction of urea. More
specifically, the first temperature is set less than 133 ºC.
15 Considering an effect of preventing condensation on the pipe, and
unevenness and deviation of temperature control, the first
temperature is preferably set to 40 ºC or more and 128 ºC or less.
That is, in the case where the mixed gas flows through the first flow
path 121, the present embodiment is adapted to, in the exhaust
20 pipe 91, keep an amount of the ammonia produced by the
decomposition of the urea, and regulates temperature to keep the
temperature at 113 ºC so as to prevent the remaining urea from
being pyrolyzed.
25 Further, the temperature control part 33 is adapted to, in a
state where the directional control valves B are switched such that
the mixed gas flows only through the second flow path 122, use the
second heater 32 to control temperature near the second filter 42 to
a second temperature that is equal to or more than the pyrolysis
23
starting temperature and less than a hydrolysis star5 ting
temperature that is a temperature at which the production of
ammonia is started by a hydrolysis reaction of isocyanic acid.
More specifically, the second temperature is set to be equal to or
more than 133 ºC and less than 160 ºC. In order to consider
10 unevenness and deviation of temperature control to provide a more
reliable measured value, the second temperature is also preferably
set equal to or more than 138 ºC and equal to or less than 155 ºC.
In the present embodiment, the temperature control part 33
performs the temperature control to keep the inside of the second
15 flow path 122 equal to or more than 135 ºC and less than 160 ºC so
as to surely start the pyrolysis of the urea. By setting the
temperature to such a second temperature, in the second flow path
122, in particular, near the second filter 42, the following pyrolysis
reaction is caused because the temperature is higher than 133 ºC.
20
(NH2)2CO → NH3 + NH=C=O (chemical formula 1)
Here, (NH2)2CO is urea, and NH=C=O is isocyanic acid.
25 In addition, in the presence of water at 160 ºC or more, the
hydrolysis reaction as expressed by a chemical formula 2 is caused
in the isocyanic acid.
NH=C=O + H2O → NH3 + CO2 (chemical formula 2)
24
5
Accordingly, rewriting the above chemical formulae as a
urea-based chemical formula leads to the following chemical
formula.
10 (NH2)2CO + H2O → 2NH3 + CO2 (chemical formula 3)
That is, depending on how to set the second temperature, it
is determined that with respect to urea, ammonia is produced on a
one-to-one basis as expressed by the chemical formula 1, or in a
15 one-to-two basis as expressed by the chemical formula 3. As will
be described later, the present embodiment is adapted to produce
ammonia constantly on the one-to-one basis with respect to urea by
setting the second temperature to the hydrolysis reaction
temperature or less so as to decrease a calculation error at the time
20 of calculating the remaining urea amount from measured amounts
of ammonia.
Further, apart from the chemical formulae described above,
by heating urea, biuret or cyanuric acid may be produced to change
25 a yield of ammonia. To describe this more specifically, in the case
of heating urea at a temperature higher than 133 ºC, crystalized
biuret and gaseous ammonia are produced as expressed by the
following chemical formula 4.
25
2(NH2)2CO → H2N-CO-NH-CO-NH2 + NH3 (chemical formul5 a
4)
Here, H2N-CO-NH-CO-NH2 is biuret.
10 Further, in the case of heating biuret at a temperature
higher than 188 ºC, solid cyanuric acid and ammonia are produced
from the biuret as expressed by the following chemical formula 5.
3H2N-CO-NH-CO-NH2 → 2C3H3N3O3 + 3NH3 (chemical
15 formula 5)
Here, C3H3N3O3 is cyanuric acid.
In the present embodiment, the second temperature is set to
20 a temperature lower than 188 ºC at which cyanuric acid is produced,
and therefore a relationship in production amount between the
remaining urea and the newly produced ammonia can be kept at
approximately one to one. Accordingly, the calculation part 5 can
calculate an accurate value at the time of calculating the remaining
25 urea amount.
The ammonia sensor 21 as the produced substance
measuring mechanism is a sensor of which a sensing part formed of
zirconia, which has responsiveness only to ammonia, and for
26
example, even in the case where isocyanic acid arrives at 5 the
ammonia sensor 21, an output is not provided as a measured value.
Also, the ammonia sensor 21 is configured to output the
concentration of ammonia contained in the mixed gas.
10 The calculation part 5 is configured to, on the basis of a first
ammonia measured value that is ammonia concentration measured
in a state where the mixed gas is flowed through the first flow path
121 and kept at the first temperature in the first flow path 121, and
a second ammonia measured value that is ammonia concentration
15 measured in a state where the mixed gas is flowed through the
second flow path 122 and kept at the second temperature in the
second flow path 122, calculate a urea amount calculated value that
is the amount of the remaining urea not decomposed in the exhaust
pipe 91. More specifically, the calculation part 5 calculates the
20 urea amount calculated value on the basis that from the
above-described chemical formula 1, a difference between the
second ammonia measured value and the first ammonia measured
value corresponds to an amount of ammonia produced by pyrolysis
of the remaining urea. For example, the calculation part 5 is
25 adapted to calculate a molar number of the ammonia on the basis of
the difference between the second ammonia measured value and the
first ammonia measured value, and on the assumption that urea
having an equivalent molar number remains on the basis of the
chemical formula 1, output the urea amount calculated value.
27
5
As described, according to the gas analysis apparatus 100 of
the first embodiment, the powdery or misty urea remaining in the
mixed gas can be collected by the first and second filters 41 and 42
respectively provided in the first and second flow paths 121 and 122.
10 Accordingly, a measurement error caused on the basis that the
remaining urea arrives at the ammonia sensor 21 without being
decomposed and the urea cannot be fully decomposed can be
substantially eliminated. Also, a reduction in sensitivity due to
the attachment of a solid substance such as the powdery urea on
15 the ammonia sensor 21 can be prevented.
Further, the decomposition reaction controlling mechanism 3
performs the temperature control so as to cause only the pyrolysis
of the urea expressed by the chemical formula 1, and therefore an
20 error can be prevented from occurring in the estimation of the
remaining urea amount due to, for example, the creation of another
reaction system for cyanuric acid, biuret, or the like associated
with the hydrolysis reaction, or the like.
25 From these, it can be verified with an exact value whether or
not the amount of the urea injected into the exhaust pipe 91 from
the urea injecting mechanism 96 in the urea SCR system 200 has an
adequate value, and therefore the gas analysis apparatus 100
having high reliability can be configured.
28
5
Next, a second embodiment of the present invention is
described. In the following description, members corresponding to
those described in the first embodiment are denoted by the same
reference signs.
10
A gas analysis apparatus 100 of the second embodiment is
configured not to measure ammonia but, as illustrated in Fig. 3, to
measure isocyanic acid to thereby measure an amount of urea
remaining in mixed gas.
15
More specifically, a produced substance measuring
mechanism is not the ammonia sensor 21, and the ammonia sensor
21 is replaced by a Fourier transform infrared spectroscopic
analyzer 22. Further, a calculation part 5 is also configured to
20 calculate a urea amount calculated value on the basis of a first
isocyanic acid measured value measured at the first temperature by
the produced substance measuring mechanism and a second
isocyanic acid measured value measured at the second temperature
by the produced substance measuring mechanism.
25
In other words, the calculation part 5 is one that, on the
basis that in the case where urea is pyrolyzed, isocyanic acid is
produced on a one-to-one basis on the basis of the above-described
chemical formula 1, calculates a remaining urea amount, and
29
calculates a molar number or the like of the remaining urea from 5 om a
difference between the second isocyanic acid measured value and
the first isocyanic acid measured value.
Even with such a configuration, the amount of the urea
10 remaining in the exhaust gas can be measured.
Further, a third embodiment of the present invention is
described. In the following description, members corresponding to
those described in the first embodiment are denoted by the same
15 signs.
The decomposition reaction controlling mechanism 3 in the
first embodiment is configured to establish the state where the
pyrolysis of urea is prevented and the state where only the
20 pyrolysis of urea is caused by regulating the temperatures of the
first and second flow paths 121 and 122 with the first and second
heaters 31 and 32; however, the third embodiment is adapted to
calculate an amount of urea by electrolyzing urea into ammonia.
25 More specifically, as illustrated in Fig. 4, a second filter 42 is
an electrically conductive one, and a decomposition reaction
controlling mechanism 3 is configured to include: a power supply
part 34 that applies AC voltage to the second filter 42; and a
voltage control part 35 that controls the voltage applied by the
30
power supply part 34. Also, inside a sampling pipe 1, temper5 ature
is kept less than the first temperature so as to prevent a
decomposition reaction from being caused in remaining urea.
The gas analysis apparatus 100 of the third embodiment is
10 adapted such that the power supply part 34 generates a discharge
in the filter 42 to produce the ammonia from the urea. Also, the
voltage control part 35 is configured to apply the voltage
appropriate to produce the ammonia from the urea by the discharge
generated by the power supply part 34.
15
Even with such a configuration, a calculation part 5 can
calculate an amount of the urea remaining in exhaust gas from a
difference between a second ammonia measured value measured in
a state where an ammonia amount is increased by the discharge
20 and a first ammonia measured value measured in a state where a
decomposition reaction is not caused.
Still further, a fourth embodiment of the present invention is
described. In the following description, members corresponding to
25 those described in the first embodiment are denoted by the same
signs.
A gas analysis apparatus of the fourth embodiment is
configured to calculate an amount of isocyanic acid contained in
31
mixed gas by measuring ammonia. More specifically, 5 , as
illustrated in Fig. 5, a mixed gas sampling pipe 1 branches halfway
into two pipes to form a first flow path 121 and a second flow path
122, and the respective flow paths 121 and 122 are, sequentially
from upstream sides, provided with: first and second filters 41 and
10 42 constituting a filter part 4; first and second heaters 31 and 32
constituting a decomposition reaction controlling mechanism 3; and
ammonia sensors 21 provided at terminals thereof. That is,
differently from the above-described first or second embodiment,
the first and second heaters 31 and 32 are provided on a
15 downstream side of the filter part 4 so as not to heat the filter part
4 itself, but to heat only mixed gas having passed through the filter
part 4. Further, a calculation part 5 is, differently from those in
the above-described first to third embodiments, configured to
calculate not a urea amount but an isocyanic acid amount
20 calculated value that is a value related to an amount of the
isocyanic acid contained in the mixed gas.
In the following, described are a configuration and operation
of a temperature control part 33 that controls the respective
25 heaters 31 and 32, and those of the calculation part 5 in the fourth
embodiment.
The temperature control part 33 is configured to use the first
heater 31 to control temperature of the mixed gas having passed
32
through the first filter 41 to a first temperature that 5 is equal to or
more than a temperature at which water is evaporated, and less
than a pyrolysis starting temperature that is a temperature at
which the production of ammonia and isocyanic acid is started by a
pyrolysis reaction of urea. More specifically, the first temperature
10 is set less than 133 ºC. Preferably, the first temperature is set
equal to or more than 40 ºC and less than 128 ºC. That is, in the
case where the mixed gas flows through the first flow path 121, the
present embodiment is adapted to, while preventing condensation,
keep amounts of ammonia and isocyanic acid produced by the
15 decomposition of urea from changing in an exhaust pipe 91, and
also regulate the temperature so as to keep the temperature at 113
ºC to prevent the isocyanic acid contained in the mixed gas from
being decomposed.
20 Further, regarding the second flow path 122, the
temperature control part 33 uses the second heater 32 to control
temperature of the mixed gas having passed through the second
filter 42 to a third temperature that is equal to or more than a
hydrolysis starting temperature that is a temperature at which the
25 production of ammonia is started by a hydrolysis reaction of
isocyanic acid. More specifically, the third temperature is set to
be equal to or more than 160 ºC. In the case of considering
unevenness and deviation of temperature control, the third
temperature is preferably set equal to or more than 165 ºC. In the
33
fourth embodiment, the remaining urea is collected by 5 the second
filter 42, so that no urea is presented around the second heater 32
on the downstream side of the second filter 42, and therefore even
in the case of heating at 160 ºC or more, only the hydrolysis of the
isocyanic aid is caused.
10
The calculation part 5 is configured to, on the basis of a first
ammonia measured value that is ammonia concentration measured
in a state where the mixed gas flowing through the first flow path
121 is kept at the first temperature, and a third ammonia measured
15 value that is ammonia concentration measured in a state where the
mixed gas flowing through the second flow path 122 is kept at the
third temperature, calculate an isocyanic acid calculated value
corresponding to an amount of the isocyanic acid produced by the
decomposition of the urea in the exhaust pipe 91. More
20 specifically, on the basis that, from the above-described chemical
formula 2 that is a formula related to the hydrolysis of isocyanic
acid, a difference between the third ammonia measured value and
the first ammonia measured value corresponds to the amount of the
isocyanic acid originally contained in the mixed gas, the calculation
25 part 5 calculates the isocyanic acid amount calculated value. For
example, the calculation part 5 is adapted to calculate a molar
number of ammonia on the basis of the difference between the third
ammonia measured value and the first ammonia measured value,
and on the assumption that isocyanic acid having an equivalent
34
molar number is contained in the mixed gas on 5 the basis of the
chemical formula 2, output the isocyanic acid amount calculated
value.
As described, the gas analysis apparatus 100 of the fourth
10 embodiment is adapted to, before starting to heat the mixed gas
with the first and second heaters 31 and 32, collect the remaining
urea with the first and second filters 41 and 42, and therefore at
the time of the measurement, the amounts of ammonia and
isocyanic acid can be prevented from being varied by new urea
15 decomposition. Accordingly, only the ammonia originally
contained in the mixed gas, and ammonia produced from the
isocyanic acid by the hydrolysis can be measured, and therefore
from the ammonia measured values, the calculation part 5 can
accurately calculate the amount of the isocyanic acid contained in
20 the mixed gas.
A variation of the fourth embodiment is described.
In the fourth embodiment, the calculation part 5 is
25 configured to calculate the accurate amount of the isocyanic acid on
the basis of the first ammonia measured value and the third
ammonia measured value; however, for example, the calculation
part 5 may be adapted to calculate whether or not isocyanic acid is
contained in the mixed gas. Examples include one configured such
35
that in the case where the difference between 5 tween the third ammonia
measured value and the first ammonia measured value is equal to
or more than a predetermined value, the calculation part 5
determines that isocyanic acid is contained in the mixed gas,
whereas in the case where the difference is substantially zero, the
10 calculation part 5 determines that isocyanic acid is not contained in
the mixed gas to the extent of being detected. Even with such a
configuration, the presence or absence of isocyanic acid contained
in the mixed gas, or whether or not the predetermined amount of
isocyanic acid or more is contained can be accurately determined.
15 Further, the presence or absence of solid urea contained in the
mixed gas can also be determined in the same manner.
Other embodiments are described.
20 Each of the above-described embodiments is one that is
provided with: the first flow path for making the ammonia or
isocyanic acid originally contained in the exhaust gas arrive at the
produced substance measuring mechanism without change; and the
second flow path for making the mixed gas in which the remaining
25 urea is decomposed arrive at the urea-derived substance measuring
instrument; however, the present invention may be adapted to be
able to measure two ammonia measured values or isocyanic acid
measured values necessary to calculate the remaining urea amount
by performing temperature control or the like to switch a reaction
36
state in a common 5 flow path.
Also, the calculation part calculates an amount of the urea
remaining in the mixed gas on the assumption of an ideal state
where ammonia or isocyanic acid is produced on the one-to-one
10 basis with respect to urea; however, for example, the present
invention may be adapted to make a correction in consideration of a
reduction in yield due to the production of biuret or cyanuric acid.
Specifically, it is only necessary that the present invention is
adapted to, on the basis of a temperature condition set for the
15 inside of the mixed gas sampling pipe, preliminarily measure a
yield of ammonia or isocyanic acid, and on the basis of the yield,
correct the urea amount. In the case of making the correction, the
correction may be made on the basis of production ratios of
ammonia in the chemical formulae 4 and 5. Also, the second
20 temperature range may be set equal to or more than 133 ºC and less
than 188 ºC in order to prevent the production of cyanuric acid to
decrease a measurement error.
It is only necessary that a measured or calculated value of
25 ammonia, isocyanic acid, or urea is a value related to quantity such
as concentration, molar number, or flow rate.
As the produced substance measuring mechanism, a
mechanism using a measuring instrument or measuring device
37
other than the ammonia sensor using zirconium or FTIR is al5 so
possible. For example, ammonia and isocyanic acid may be
measured with a laser. In short, any measuring mechanism is
possible as long as a measured value is not significantly changed by
the influence of a non-target substance.
10
Besides, it should be appreciated that unless contrary to the
scope of the present invention, various modifications and
combinations of the embodiments may be made.
Industrial Applicability
15
As described, according to the gas analysis apparatus of the
present invention, remaining urea that has been unmeasurable in
the past because of passing through a produced substance
measuring mechanism as a state of urea can also be accurately
20 measured to accurately calculate a remaining urea amount.
Accordingly, by applying the present invention, an exhaust gas
analysis apparatus suitable to be used for research or the like of
urea SCR or the like can be provided.
38

We Claim:5 -
1. A gas analysis apparatus comprising:
a mixed gas sampling pipe that, from a sampling port formed
on one end side, samples mixed gas that is a mixture of exhaust gas
emitted from an internal combustion engine and a misty urea
10 aqueous solution;
a decomposition reaction controlling mechanism that
controls a decomposition reaction of urea or isocyanic acid in the
mixed gas sampling pipe;
a produced substance measuring mechanism that is provided
15 on the other end side of the mixed gas sampling pipe and measures
a value related to an amount of a substance produced from the urea
or the isocyanic acid in the urea aqueous solution;
a calculation part that, on a basis of a measured value
measured by the produced substance measuring mechanism,
20 calculates a urea amount calculated value that is a value related to
an amount of the urea contained in the mixed gas; and
a filter part that is provided between the sampling port and
the produced substance measuring mechanism in the mixed gas
sampling pipe to collect the urea in a solid state or in a state of
25 being dissolved in water in the mixed gas, wherein
the decomposition reaction controlling mechanism is
configured to act on the filter part.
2. The gas analysis apparatus according to claim 1, wherein
39
the decomposition reaction controlling mechanism is configured 5 to
control temperature of the filter part.
3. The gas analysis apparatus according to claim 2, wherein:
the produced substance measuring mechanism is configured
10 to measure a value related to an amount of ammonia;
the decomposition reaction controlling mechanism is
configured to be able to control the temperature of the filter part to
a first temperature that is less than a pyrolysis starting
temperature that is a temperature at which production of ammonia
15 and isocyanic acid is started by a pyrolysis reaction of urea, or a
second temperature that is equal to or more than the pyrolysis
starting temperature and less than a hydrolysis starting
temperature that is a temperature at which production of ammonia
is started by a hydrolysis reaction of isocyanic acid; and
20 the calculation part is configured to calculate the urea amount
calculated value on a basis of a first ammonia measured value
measured at the first temperature by the produced substance
measuring mechanism and a second ammonia measured value
measured at the second temperature by the produced substance
25 measuring mechanism.
4. The gas analysis apparatus according to claim 2, wherein:
the produced substance measuring mechanism is configured
to measure a value related to an amount of isocyanic acid;
40
the decomposition controlling mechanism is configured to b5 e
able to control the temperature of the filter part to a first
temperature that is less than a pyrolysis starting temperature that
is a temperature at which production of ammonia and isocyanic
acid is started by a pyrolysis reaction of urea, or a second
10 temperature that is equal to or more than the pyrolysis starting
temperature and less than a hydrolysis starting temperature that
is a temperature at which production of ammonia is started by a
hydrolysis reaction of isocyanic acid; and
the calculation part is configured to calculate the urea
15 amount calculated value on a basis of a first isocyanic acid
measured value measured at the first temperature by the produced
substance measuring mechanism and a second isocyanic acid
measured value measured at the second temperature by the
produced substance measuring mechanism.
20
5. The gas analysis apparatus according to claim 3, wherein
the first temperature is less than 133 ºC, and the second
temperature is equal to or more than 133 ºC and less than 160 ºC.
25 6. A gas analysis apparatus comprising:
a mixed gas sampling pipe that, from a sampling port formed
on one end side, samples mixed gas that is a mixture of exhaust gas
emitted from an internal combustion engine and a misty urea
aqueous solution;
41
a decomposition reaction controlling mechanism that 5 controls a
decomposition reaction of urea or isocyanic acid in the mixed gas
sampling pipe;
a produced substance measuring mechanism that is provided
on the other end side of the mixed gas sampling pipe and measures
10 a value related to an amount of a substance produced from the urea
or the isocyanic acid in the urea aqueous solution;
a calculation part that, on a basis of a measured value
measured by the produced substance measuring mechanism,
calculates an isocyanic acid amount calculated value that is a value
15 related to an amount of the isocyanic acid contained in the mixed
gas; and
a filter part that is provided between the sampling port and
the produced substance measuring mechanism in the mixed gas
sampling pipe to collect the urea in a solid state or in a state of
20 being dissolved in water in the mixed gas, wherein
the decomposition reaction controlling mechanism is
configured to act on a downstream side of the filter part.
7. The gas analysis apparatus according to claim 6, wherein
25 the decomposition reaction controlling mechanism is
configured to control temperature of an inside of the mixed gas
sampling pipe on the downstream side of the filter part.
8. The gas analysis apparatus according to claim 7, wherein:
42
the produced substance measuring mechanism is configure5 d
to measure a value related to an amount of ammonia;
the decomposition reaction controlling mechanism is
configured to be able to control the temperature of the inside of the
mixed gas sampling pipe on the downstream side of the filter part
10 to a first temperature that is less than a pyrolysis starting
temperature that is a temperature at which production of ammonia
and isocyanic acid is started by a pyrolysis reaction of urea, or a
third temperature that is equal to or more than a hydrolysis
starting temperature that is a temperature at which production of
15 ammonia is started by a hydrolysis reaction of isocyanic acid; and
the calculation part is configured to calculate the isocyanic
acid amount calculated value on a basis of a first ammonia
measured value measured at the first temperature by the produced
substance measuring mechanism and a third ammonia measured
20 value measured at the third temperature by the produced
substance measuring mechanism.
9. The gas analysis apparatus according to claim 8, wherein
the first temperature is less than 133 ºC, and the third temperature
25 is equal to or more than 160 ºC.
Dated this 7th day of April, 2014