Specification
AMMONIA-ENGINE SYSTEM
Technical Field
The present invention relates to an ammonia-engine
system provided with an ammonia engine using ammonia as fuel
and an ammonia cracking device including an ammonia cracking
catalyst that cracks ammonia and cracking ammonia to produce
hydrogen.
Background Art
There has been an ammonia engine using ammonia as fuel.
Because the ammonia engine has a characteristic that ignition
performance is poor, combustion of ammonia becomes
insufficient during low load operation and high load operation
of the engine. It is therefore necessary for the ammonia engine
to add a combustion improver to promote combustion of ammonia.
Hydrocarbon fuel and hydrogen are available as the combustion
improver. Ammonia is a compound of hydrogen atoms and a
nitrogen atom and it is possible to produce hydrogen by
chemically cracking ammonia. The ammonia engine is therefore
thought to be the most desirable system in that the engine can
be driven by ammonia alone by using hydrogen produced by
cracking ammonia as the combustion improver.
A reaction to produce hydrogen and nitrogen from ammonia
with an ammonia cracking catalyst is an endothermic reaction.
In order to allow this reaction to progress, it is necessary
to bring the ammonia cracking catalyst into contact with
ammonia while conferring a temperature of 2 90°C or above
(preferably 340°C or above) to the ammonia cracking catalyst.
Patent Document 1 discloses an ammonia combustion engine
configured to supply ammonia cracking means with an exhaust
gas after combustion of ammonia in the ammonia combustion
engine.
This ammonia combustion engine promotes a cracking
reaction of ammonia by utilizing the fact that an
ammonia-containing exhaust gas becomes hot due to combustion
in the ammonia combustion engine.
In this device, however, the temperature of the ammonia
cracking catalyst depends on the temperature of the exhaust
gas. Accordingly, combustion efficiency of ammonia in the
ammonia engine is poor during low load operation (engine
start-up) and a hot exhaust gas is not supplied to the ammonia
cracking catalyst. Hence, a reaction to produce hydrogen and
nitrogen from ammonia progresses poorly. Consequently,
hydrogen serving as a combustion improver to promote the
driving of the engine is not supplied to the ammonia combustion
engine in a low load operating condition. It therefore takes
a long time for the ammonia engine to come out of the low load
operating condition.
Disclosure of the Invention
Problems to be solved by the Invention
The invention was devised in view of the foregoing and
has an object to provide an ammonia-engine system capable of
supplying an ammonia cracking catalyst with a temperature
necessary to promote a reaction even during low load operation
in which the temperature of an exhaust gas from an ammonia
engine is lower than an operating temperature of the ammonia
cracking catalyst.
Means for Solving the Problems
As has been described above, in order to stably produce
hydrogen from ammonia using the ammonia cracking catalyst, it
is necessary to maintain the ammonia cracking catalyst at 290°C
or above (preferably at 340°C or above). To this end, the
inventors conducted an assiduous study and discovered that
because ammonia produces heat when it undergoes an oxidation
reaction with oxygen as expressed by Formula (1) below, the
problems described above can be solved by incorporating an
ammonia oxidizing device giving rise to such an exothermal
reaction between the ammonia engine and the ammonia cracking
device.
NH3 + 3/4O2 ? 1/2N2 + 3/2H2O ...(1)
More specifically, an ammonia-engine system of the
invention is provided with an ammonia engine using ammonia as
fuel and an ammonia cracking device including an ammonia
cracking catalyst that cracks ammonia and cracking ammonia to
produce hydrogen, wherein an ammonia oxidizing device is
provided between the ammonia engine and the ammonia cracking
device.
The ammonia oxidizing device can be any device as long
as it is capable of giving rise to the reaction expressed by
Formula (1) above and a platinum-supported catalyst is suitably
used as the ammonia oxidation catalyst. In this case, the
operating temperature of the catalyst is 150°C or above.
Because the temperature of an exhaust gas from the engine is
normally 150°C or above even when the ammonia-engine is
operating at a low load, the temperature of the exhaust gas
is sufficiently high to allow the ammonia oxidation reaction
expressed by Formula (1) above to progress. It is therefore
possible to supply sufficient heat for the ammonia cracking
catalyst in the ammonia cracking device to reach a temperature
of 290°C or above (preferably 340°C or above) from the ammonia
oxidizing device. An amount of ammonia contained in the
exhaust gas from the ammonia engine is controlled by adjusting
a flow rate of gas to be supplied to the ammonia oxidizing device.
It thus becomes possible to control a heat value produced in
the ammonia oxidizing device.
The platinum-supported catalyst can have any shape and
the one having, for example, a monolithic shape is available.
There is a case where the temperature of the exhaust gas
is 150°C or below at the start-up of the engine. In such a case,
because the exhaust gas has not reached the operating
temperature of the catalyst, the platinum-support catalyst is
not able to function to achieve Formula (1) . In this case,
it is advantageous to further provide a heater to, for example,
a pipe between the outlet of the ammonia engine and the ammonia
oxidizing device. When configured in this manner, even when
the exhaust gas from the engine has not reached 150°C at the
start-up of the engine, it becomes possible to provide the
ammonia oxidizing device with a necessary heat value by
actuating the heater until the temperature of the exhaust gas
reaches 150°C. The internal temperature of the ammonia
oxidizing device is therefore maintained in a stable manner
from the start-up of the engine. Consequently, hydrogen can
be produced in a stable manner in the ammonia cracking device
and the engine is enabled to operate in a stable manner.
The ammonia cracking device can have any structure and,
for example, it may have a structure of a plate-type heat
exchanger. In a case where the ammonia cracking device has
the structure of the plate-type heat exchanger, it is
preferable that the ammonia cracking catalyst is filled in the
ammonia cracking device on an ammonia supply side or the
catalyst is coated on the surface of a material on the ammonia
supply side.
The ammonia cracking catalyst in the ammonia cracking
device can be, for example, a catalyst supporting ruthenium,
rhodium, nickel, and/or iron.
In the ammonia-engine system of the invention, an inlet
temperature on an exhaust gas introduction side of the ammonia
cracking device is maintained at 290°C or above (preferably
at 340°C or above) and an inlet temperature of the ammonia
oxidizing device is maintained at 150°C or above.
Also, in the ammonia-engine system of the invention, in
a case where the inlet temperature on the exhaust gas
introduction side of the ammonia cracking device is 300°C or
below, an ammonia gas is further added to the exhaust gas from
the ammonia engine. Further, the ammonia gas may be added also
in a case where an ammonia concentration of the exhaust gas
from the ammonia engine is 3% or less.
Moreover, in the ammonia-engine system of the invention,
only in a case where the inlet temperature of the ammonia
oxidizing device is 150°C or below, ammonia to be supplied to
the ammonia oxidizing device is heated by the heater.
Advantageous effects of the Invention
According to the ammonia-engine system of the invention,
because the ammonia oxidizing device is provided between the

ammonia engine and the ammonia cracking device, in a case where
the temperature of the exhaust gas from the ammonia engine is
lower than the operating temperature of the ammonia cracking
catalyst in the ammonia cracking device, it is possible to raise
the temperature of the exhaust gas with oxidation heat produced
by the oxidation reaction of ammonia. It thus becomes possible
to maintain the temperature of the ammonia cracking catalyst
at or above the operating temperature thereof even during low
load operation in which the temperature of the exhaust gas from
the ammonia engine is low. The ammonia engine is thus enabled
to operate in a stable manner.
Best Mode for Carrying Out the Invention
Hereinafter, an ammonia-engine system of the invention
will be described in detail on the basis of the drawings.
Fig. 1 is a flow sheet showing the ammonia-engine system
of the invention.
An ammonia engine (2) is an engine that uses ammonia
supplied from an NH3 tank (1) as fuel and is driven by combustion
of ammonia.
An exhaust gas from the ammonia engine (2) is supplied
to an ammonia oxidizing device (4) . The exhaust gas from the
ammonia engine (2) may be supplied directly to the ammonia
oxidizing device (4) or may alternatively be passed through
a line heater (3) before it is supplied to the ammonia oxidizing

device (4) . Whether the line heater (3) is driven to heat the
exhaust gas or not depends on the temperature of the exhaust
gas. More specifically, the line heater (3) is an optional
component in the invention. Because a combustion reaction of
ammonia in the ammonia engine (2) is an exothermic reaction,
the exhaust gas from the ammonia engine (2) has a temperature
of 150°C or above when the ammonia engine (2) is driven normally.
However, the exothermic reaction does not progress
sufficiently in the ammonia engine (2) at the start-up of the
ammonia engine (2). Accordingly, there is a case where the
temperature of the exhaust gas does not reach 150°C. When the
temperature of the exhaust gas does not reach 150°C, an
oxidation reaction of ammonia in the ammonia oxidizing device
(4) does not progress sufficiently. In such a case, the line
heater (3) is driven in an auxiliary manner for the exhaust
gas to have a temperature of 150°C or above.
The ammonia oxidizing device (4) has a
platinum-supported catalyst as an ammonia oxidation catalyst.
The platinum-supported catalyst has, for example, a monolithic
shape. An operating temperature of the platinum-supported
catalyst is 150°C and oxidation of ammonia progresses because
the exhaust gas supplied directly from the ammonia engine (2)
or supplied after it is heated in the line heater (3) has a
temperature of 150°C or above.
An oxidation reaction of ammonia in the ammonia oxidizing
device (4) is an exothermic reaction and a gas in the ammonia
oxidizing device (4) reaches 290°C or above (preferably 340°C
or above) due to this exothermic reaction. The gas having
reached 290°C or above (preferably 340°C or above) in this
manner is supplied to an exhaust gas introduction side of an
ammonia cracking device (5) .
The ammonia cracking device (5) has, for example, the
structure of a plate-type heat exchanger. Also, as a catalyst
to crack ammonia, it has, for example, a ruthenium-supported
catalyst. The ammonia cracking catalyst is filled in the
ammonia cracking device (5) on an ammonia supply side or coated
on a material surface on the ammonia supply side.
To the exhaust gas introduction side of the ammonia
cracking device (5), a gas at 290°C or above (preferably at
340°C or above) is supplied from the ammonia oxidizing device
(4) and ammonia is supplied from the NH3 tank (1) to the ammonia
supply side. Inside the ammonia cracking device (5), the
temperatures of the ammonia gas supplied therein and the
ammonia cracking catalyst increase due to heat exchange between
the exhaust gas and the ammonia gas, and ammonia supplied from
the NH3 tank (1) cracks to hydrogen and nitrogen by a catalytic
action of the ammonia cracking catalyst. A
hydrogen-containing ammonia-cracked gas thus produced is
supplied to the ammonia engine (2) as a combustion improver
for the ammonia engine (2) .
Concrete advantageous eggects of the invention have been
confirmed by examples, which will be described below.
Example 1
In order to schematically demonstrate advantages of the
invention, driving of the ammonia oxidizing device (4) and the
ammonia cracking device (5) was tested using a system
configured as is shown in Fig. 2. The system shown in Fig.
2 imitates the ammonia-engine system of Fig. 1. An air heater
(6) into which heated air is provided instead of the ammonia
engine (2) and ammonia is supplied to the line heater (3) from
the NH3 tank (1) . Thermocouples to measure a heat value are
provided to the ammonia oxidizing device (4) on an inlet side
and an outlet side and to the ammonia cracking device on an
NH3 gas introduction side and an introduction side of gas from
the ammonia oxidizing device (4). The same components are
labeled with the same reference numerals with respect to Fig.
1 and a detailed description of such components is omitted
herein.
In the test of Example 1, heated air was used as a simulant
gas of the exhaust gas from the ammonia engine. Also, a
honeycomb-shaped platinum catalyst (obtained by coating a
cordierite honeycomb substrate with a platinum-supported Al2O3
catalyst, an amount of supported platinum: 2 g/L) was used as
the ammonia oxidation catalyst that the ammonia oxidizing
device (4) has. A ruthenium catalyst in a pellet form (having
a diameter of 1 mmF) (support: activated carbon with the use
of a Ba compound as a promoter, amount of supported Ru: 5 wt%)
was used as the ammonia cracking catalyst that the ammonia
cracking device (5) has. The ammonia cracking catalyst was
filled in the ammonia cracking device (5) on the ammonia supply
side.
A gas flow rate of the heated air was set to 10 NL/min
and the temperature was raised from room temperature to 250°C.
An amount of ammonia directly supplied to the ammonia cracking
device (5) was adjusted to be 0.5 NL/min. The catalyst in each
device was activated while varying an amount of ammonia
supplied to the ammonia oxidizing device (4) and an ammonia
cracking rate in the ammonia cracking device (5) was measured.
The line heater (3) was not driven in Example 1.
Example 2
A test was conducted in the same manner as in Example
1 above except that the line heater (3) was driven.
Comparative Example 1
A test was conducted in the same manner as in Example
1 above except that ammonia was not supplied to the ammonia
oxidizing device.
The test result of Example 1 is set forth in Table 1 below,

the test result of Example 2 in Table 2 below, and the test
result of Comparative Example 1 in Table 3 below.
Table 1
Table 2
Table 3
As are shown in Tables 1 through 3 above, it was found
that in a case where the inlet temperature of the ammonia
oxidizing device (4) is 150°C or above, it is possible to raise
the temperature of the gas with oxidation heat produced by the
ammonia oxidation reaction by supplying ammonia to the ammonia
oxidizing device (4) and that in a case where the temperature
of the ammonia cracking device (5) on the ammonia supply side
is 340°C or above, ammonia cracks at the cracking rate of 100%
to produce hydrogen in the ammonia cracking device (5).
Also, it was found that in a case where the temperature
of the heated air is 150°C or below, by further raising the
temperature of the heated air by actuating the line heater (3)
and thereby raising the inlet temperature of the ammonia
oxidizing device (4) to 150°C or above, the oxidation reaction
in the ammonia oxidizing device (4) is promoted and the
temperature of the gas in the ammonia oxidizing device (4)
consequently rises, which makes it possible to produce hydrogen
by activating the ammonia cracking catalyst in the ammonia
cracking device (5) . Hence, it is found that even in a case
where the temperature of the exhaust gas is low, it is possible
to produce hydrogen in the ammonia cracking device (5) by
actuating the line heater (3) .
Further, it is found that production of heat in the
ammonia, oxidizing device (4) can be increased to over 340°C
by adjusting an amount of ammonia to be supplied to the ammonia
oxidizing device (4), which makes it possible to promote
cracking of ammonia in the ammonia cracking device.
Brief Description of the Drawings
Fig. 1 is a flow sheet showing an ammonia-engine system
of the invention; and
Fig. 2 is a flow sheet showing the configuration of an
ammonia oxidizing device (4) and an ammonia cracking device
(5) used in examples to schematically demonstrate advantageous
effects of the invention.
Explanation of Reference Numerals and Signs in the Drawings
1: NH3 tank
2: ammonia engine
3: line heater
4: ammonia oxidizing device
5: ammonia cracking device
Claims
1. An ammonia-engine system comprising an ammonia engine
using ammonia as fuel and an ammonia cracking device including
an ammonia cracking catalyst that cracks ammonia and cracking
ammonia to produce hydrogen, characterized in that:
an ammonia oxidizing device is provided between the
ammonia engine and the ammonia cracking device.
2. The ammonia-engine system according to claim 1, wherein:
the ammonia oxidizing device has a platinum-supported
catalyst.
3 . The ammonia-engine system according to claim 2, wherein:
the platinum-supported catalyst has a monolithic shape.
4. The ammonia-engine system according to any one of claims
1 through 3, further comprising:
a heater provided between an outlet of the ammonia engine
and the ammonia oxidizing device.
5. The ammonia-engine system, according to any one of claims
1 through 4, wherein:
the ammonia cracking device has a structure of a
plate-type heat exchanger.

6. The ammonia-engine system according to claim 5, wherein:
the ammonia cracking catalyst is filled in the ammonia
cracking device on an ammonia supply side or the catalyst is
coated on a surface of a material on the ammonia supply side
of the ammonia cracking device.
7 . The ammonia-engine system according to claim 6, wherein:
the ammonia cracking catalyst is a catalyst supporting
ruthenium, rhodium, nickel and/or iron.
8. The ammonia-engine system according to any one of claims
1 through 7, wherein:
an inlet temperature on an exhaust gas introduction side
of the ammonia cracking device is maintained at 290°C or above.
9. The ammonia-engine system according to any one of claims
1 through 8, wherein:
an inlet temperature of the ammonia oxidizing device is
maintained at 150°C or above.
10. The ammonia-engine system according to any one of claims
1 through 9, wherein:
an ammonia gas is further added to the exhaust gas from
the ammonia engine in a case where an inlet temperature on an
exhaust gas introduction side of the ammonia cracking device

is 300°C or below.
11. The ammonia-engine system according to claim 10,
wherein:
the ammonia gas is added also in a case where an ammonia
concentration of the exhaust gas from the ammonia engine is
3% or less.
12. The ammonia-engine system according to any one of claims
4 through 11, wherein:
ammonia to be supplied to the ammonia oxidizing device
is heated by a heater only in a case where the inlet temperature
of the ammonia oxidizing device is 150°C or below.

An ammonia-engine system is capable of supplying an
ammonia cracking catalyst with a temperature necessary to
promote a reaction even during low load operation in which a
temperature of an exhaust gas from an ammonia engine is lower
than an operating temperature of the ammonia cracking catalyst.
In an ammonia-engine system provided with an ammonia engine
(2) using ammonia as fuel and an ammonia cracking device (5)
including an ammonia cracking catalyst that cracks ammonia and
cracking ammonia to produce hydrogen, an ammonia oxidizing
device (4) is provided between the ammonia engine (2) and the
ammonia cracking device (5).