Note: Descriptions are shown in the official language in which they were submitted.
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Ammonia Generating Apparatus
BACKGROUND OF THE INVENTION
The present invention relates to an ammonia
generating apparatus for generating, from urea water, ammonia
to be used for NOx removal systems in boilers or the like.
In recent years, there has been a demand for further
reduction in NOx also for boilers. As one of countermeasures
therefor, a method has been taken that a boiler is equipped with
a NOx removal system, where ammonia as a reducing agent is added
to combustion exhaust gas so that the NOx is reduced. Whereas
this ammonia is generated by, for example, heating urea water,
there is a desire for ammonia generating apparatuses having
higher efficiency of heat transfer and a compact body.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to
provide an ammonia generating apparatus having a high efficiency
of heat transfer and being compact.
In order to achieve the above object, in a first aspect
of the present invention, there is provided an ammonia generating
apparatus comprising: a urea water introducing part; a flow
passage for urea water to flow therethrough; and heating means ,
wherein the flow passage is connected to the urea water
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introducing part , and the heating means heats urea water present
within the flow passage.
In a second aspect of the present invention, there is
provided an ammonia generating apparatus as described in the
first aspect, wherein part of the flow passage is formed into
a helical part , and the heating means is placed inside the helical
part.
Now an embodiment of the present invention is
described below. An ammonia generating apparatus according to
the present invention has a urea water introducing part, a flow
passage, and heating means. The urea water introducing part has
an inlet nozzle for introducing urea water. The flow passage
is connected to the urea water introducing part , and urea water
flows through within the flow passage. The heating means, for
heating the urea water within the flow passage to generate
ammonia, is located in proximity to the flow passage. This
heating means is implemented by, for example, an electric heater.
Part of the flow passage is laid out in a helical shape,
and the heating means is placed inside this helical part. By
this arrangement and placement, heat emitted from the heating
means can be received by the whole helical part and, as a result ,
the amount of heat release to outside is suppressed as much as
possible, thus allowing the efficiency of heat transfer to be
improved. Then, by making effective use of a space formed inside
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the helical part , the apparatus can be made more compact in
construction as a whole and thus a space-saving apparatus.
In the flow passage, heat transfer inhibiting means
is provided upstream of the helical part. This heat transfer
inhibiting means functions to inhibit heat from being
transferred from its mounting position to the upstream side,
thereby preventing urea water from being crystallized by
evaporation of moisture content before its arrival at the helical
part, or preventing occurrences of unnecessary intermediates
from the urea water, to a minimum. That is , according to studies
by the inventors of the present application, it has been found
out that it is within a temperature range of about 80 - 180°C
that crystallization of urea water or generation of unnecessary
intermediates is likely to take place. Thus, the heat transfer
inhibiting means is so designed as to have an entrance temperature
of not more than 80°C and an exit temperature of not less than
180° C , while the above temperature range occurs limitedly only
to the site where the heat transfer inhibiting means is provided.
Moreover, the length of the this temperature range site is made
as short as possible, by which the crystallization of urea water
or the generation of unnecessary intermediates is suppressed to
a minimum.
The heat transfer inhibiting means is implemented by
providing a member made of , for example, a material having a large
heat insulating effect ( a . g. ceramics ) at a place halfway on the
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flow passage. The heat transfer inhibiting means may also be
designed so that air is introduced from outside, where heat
transferred from the helical part side is collected by the air,
and the f low of the air that has collected heat is directed toward
the helical part so that the heat is returned to the helical part .
The inlet nozzle is equipped with an elastic sealing
member in such a way that injection holes of the inlet nozzle
are covered with the elastic sealing member. More specifically,
with urea water introduced, when the urea water is pressurized,
the elastic sealing member is pushed by pressure, causing the
injection holes to be opened, so that the urea water flows out r
Then with the urea water released from pressurization, the
elastic sealing member returns to the original position, causing
the injection holes to be closed. Consequently, while the urea
water is not being introduced, the injection holes are sealed
by the elastic sealing member and therefore the urea water
remaining in the inlet nozzle is never crystallized by the
evaporation of moisture content, ensuring the prevention of
blockage of the inlet nozzle. In addition, the elastic sealing
member is made of, for example, synthetic rubber.
An air supply line is connected to the urea water
introducing part. Air supplied along this air supply line
functions to convey urea water in the flow passage, and to blow
out urea water deposited on the inlet nozzle. Accordingly,
supplying air through the air supply line prevents the urea water
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from residing, as it is deposited, within the urea water
introducing part and the flow passage.
Further, in this ammonia generating apparatus, a
cleaning fluid supply line for cleaning the interior of the flow
passage is provided. This cleaning fluid supply line is
connected to the upstream side of the heat transfer inhibiting
' means so that even if part of the urea water is crystallized,
the crystallized urea water can be cleaned. As the cleaning
fluid, water, vapor or the like is used.
As shown above, according to this constitution, the
ammonia generating apparatus allows continuous heating to be
performed while urea water is kept flowing, so that the efficiency
of heat transfer can be greatly improved. That is, since urea
water flows at a specified flow rate in the flow passage, the
resulting efficiency of heat transfer is greatly improved, as
compared with the case in which heating is done with the urea
water residing in the tank. Besides, as compared with the case
of heating with the urea water residing in the tank, the rise
time from when urea water begins to be supplied to when a
steady-state generation of ammonia is reached can be shortened,
and the heating capacity of the heating means can be reduced.
Further, the ammonia generating apparatus can be reduced in size
as a whole, and in particular, with the heating means placed
inside the helical part, the ammonia generating apparatus can
be made more compact in structure.
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In addition, the heating means may be provided either
outside the helical part or both inside and outside thereof . The
heating means may also be provided so as to surround the entire
circumferential periphery of the flow passage along the flow
passage.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a longitudinal sectional explanatory view
of a first embodiment of the invention;
Fig. 2 is an enlarged longitudinal sectional
explanatory view showing details of the urea water nozzle in Fig.
1; -
Fig. 3 is an enlarged longitudinal sectional
explanatory view showing details of the heat transfer inhibiting
means in Fig. 1;
Fig. 4 is a longitudinal sectional explanatory view
of a second embodiment of the invention; and
Fig. 5 is an enlarged longitudinal sectional
explanatory view showing another embodiment of the heat transfer
inhibiting means as a substitute for that of Fig. 3.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Hereinbelow, concrete embodiments of the present
invention are described in detail based on the accompanying
drawings. First, a first embodiment shown in Figs. 1 - 3 is
described.
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The ammonia generating apparatus according to the
present invention is designed to generate ammonia by heating urea
water and, as shown in Fig. 1, has a urea water introducing part
1, where a flow passage 2 for urea water to flow therethrough
is connected to the bottom of this urea water introducing part
1. The urea water introducing part 1 has an inlet nozzle 3
provided so as to be directed downward, and an air supply line
4 is connected to a side face of the urea water introducing part
1. This air supply line 4 is connected so as to be opposed to
the forefront of the inlet nozzle 3, and air supplied along the
air supply line 4 functions to convey urea water in the flow
passage 2 and to blow out urea water deposited at the forefront
of the inlet nozzle 3. In addition, the air supply line 4 may
also be connected to the top face of the urea water introducing
part 1 in parallel to the inlet nozzle 3.
Part of the flow passage 2 is laid out into a helical
shape , forming a helical part 5 , which is f fixed to a cylindrical
member 6 in close contact with the outer circumferential surface
of the cylindrical member 6. Inside the cylindrical member 6,
an electric heater as heating means 7 is provided at a specified
spacing to the inner circumferential surface of the cylindrical
member 6. Also, a temperature sensor 8 is provided in the space
between the cylindrical member 6 and the heating means 7, and
by detecting surface temperature of the heating means 7 with this
temperature sensor 8, electric energy to be supplied to the
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heating means 7 is controlled by a controller 9 so that the surface
temperature of the heating means 7 becomes about 500°C.
Accordingly, the urea water is heated by the heating means 7 while
flowing within the helical part 5, by which gaseous ammonia is
generated continuously. Further, outside the helical part 5,
a heat insulating material 10 is provided so as to cover the entire
helical part 5.
The flow passage 2 is so formed that its upstream side
of the helical part 5 is slightly slanted in order to prevent
the residence of urea water, and heat transfer inhibiting means
11 is provided at a specified position on this upstream side:
This heat transfer inhibiting means 11 functions to inhibit heat
from being transferred from its location to the upstream side,
thereby inhibiting urea water from being crystallized by
evaporation of moisture content before its arrival at the helical
part 5, or inhibiting occurrences of unnecessary intermediates
from the urea water, to a minimum.
The urea water introducing part 1 is so formed as to
be larger in diameter than the flow passage 2, their junction
portion being tapered downwardly so that the urea water does not
accumulate.
Further, the flow passage 2 is connected at its
downstream side end portion to a NOx removal system ( not shown )
provided in the boiler or the like, so that ammonia generated
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in the helical part 5 is supplied continuously to the NOx removal
system.
Next, construction of the inlet nozzle 3 is described
in detail with reference to Fig. 2. As shown in Fig. 2, a
plurality of injection holes 12, 12, ... are provided on the side
wall of the inlet nozzle 3 on its front end side. Besides, a
tubular elastic sealing member 13 is attached so as to cover these
injection holes 12. More specifically, the elastic sealing
member 13 is made of, for example, synthetic rubber, and when
urea water is pressurized upon its introduction, the elastic
sealing member 13 is pushed by the pressure, causing the injection
holes 12 to be opened, so that the urea water flows out through
between the outer circumferential surface of the inlet nozzle
3 and the inner circumferential surface of the elastic sealing
member 13. When the urea water is released from pressurization,
the elastic sealing member 13 returns to the original position,
causing the injection holes 12 to be closed. In this connection,
Fig. 2 shows a state in which the urea water is flowing out.
Therefore, with the elastic sealing member 13
provided, while the urea water is not being introduced, the
injection holes 12 are sealed and closed by the elastic sealing
member 13, thus preventing the occurrence that urea water
remaining in the inlet nozzle 3 is crystallized by the evaporation
of moisture content , and so ensuring the prevention of blockage
of the inlet nozzle 3.
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Next, construction of the heat transfer inhibiting
means 11 is described in detail with reference to Fig. 3. As
shown in Fig. 3, the heat transfer inhibiting means 11 is so
constituted that the flow passage 2 is intercepted halfway with
the upstream-side end portion of the downstream-side flow
passage 2 larger in diameter than the downstream-side end portion
- of the upstream-side flow passage 2, where the two parts are
concentrically overlapped with each other over a specified
length and a heat insulating material 14 made of ceramics or the
like is provided therebetween. Therefore, heat transferred from
the helical part 5 along the flow passage 2 is inhibited by the
heat insulating material 14 from being further transferred to
the upstream side.
Also, the heat transfer inhibiting means 11 is so
designed that temperature of A point , which is the entrance point ,
will be not more than 80°C while temperature of B point, which
is the exit point , will be not less than 180° C . That is , a
temperature range of about 80 - 180°C, which is more likely to
cause crystallization of urea water or generation of unnecessary
intermediates, is limited to the site where the heat transfer
inhibiting means 11 is provided, while the length of this
temperature range site is made as short as possible. Thus, the
crystallization of urea water or the generation of unnecessary
intermediates is suppressed to a minimum.
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With such a constitution as described above, now its
operation is described. From the inlet nozzle 3, about 20~
concentration urea water is supplied at a flow rate of about 10
milliliters/min. , and this urea water is conveyed within the flow
passage 2 by air (flow rate: about 30 liters/min. ) coming through
the air supply line 4 , thus the urea water air reaching the helical
part 5. Then, the urea water, while flowing through within the
helical part 5, is heated to about 200 - 500°C by the heating
means 7, by which ammonia is generated. The resultant ammonia
is supplied to the NOx removal system (not shown).
Therefore, according to the above constitution, urea
water can be continuously heated while flowing at a flow rate,
so that the efficiency of heat transfer is greatly improved.
Also , because of a small content of urea water within the helical
part 5, the rise time from when the urea water begins to be
supplied until when a steady-state generation of ammonia is
reached is shortened, and besides the heating capacity of the
heating means 7 can be reduced. Also, because of the provision
of the heating means 7 inside the helical part 5 , the amount of
heat release to outside is suppressed as much as possible, and
besides the whole apparatus is compact in structure. Further,
because of the provision of the heat transfer inhibiting means
11 and the elastic sealing member 13 , the crystallization of urea
water and the generation of unnecessary intermediates are
suppressed to a minimum.
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For intermittent generation of ammonia, the supply of
urea water from the inlet nozzle 3 is controlled to an
intermittent one in response to a request signal for ammonia
generation. In this case, the air from the air supply line 4
is supplied at a specified amount continuously even while the
supply of urea water keeps halted, so that the urea water does
not reside within the flow passage 2. Further, with the supply
of urea water halted, the heating means 7 also continues operating
so that the temperature of the helical part 5 is maintained at
a specified temperature. Accordingly, while the ammonia
generation is halted, neither the crystallization of urea water
nor the generation of unnecessary intermediates occurs in the
helical part 5, so that the generation of a specified amount of
ammonia can be started immediately upon resumption of ammonia
generation.
In this connection, for cleaning of the interior of
the flow passage 2, it is also possible to supply water as a
cleaning fluid from the air supply line 4 instead of air, and
to thereby clean the interior of the flow passage 2, while no
ammonia is generated with the supply of urea water halted. That
is, the air supply line 4 is made to serve as a cleaning fluid
supply line. The supplied cleaning fluid cleans away the
remaining urea water or its crystallized matters in the urea water
introducing part 1 and the flow passage 2 , and discharges them
outside via a discharge line (not shown). Also, supply of the
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cleaning fluid may be controlled so as to be effected when a
blockage within the flow passage 2 is detected. Furthermore,
the cleaning fluid supply line may be provided separately from
the air supply line 4 , and connected to the upstream side of the
heat transfer inhibiting means 11 where the crystallization of
urea water is more likely to occur.
For the heating of urea water by the heating means 7 ,
it has been arranged that the helical part 5 is previously heated
by the heating means 7 before supplying the urea water, so that
the interior of the helical part 5 is heated up to a specified
temperature in advance. However, there is a time delay until
the flow passage 2 between the heat transfer inhibiting means
11 and the helical part 5 is heated up to a specified temperature.
Therefore, during the time interval, the crystallization of urea
water or the generation of unnecessary intermediates is more
likely to occur in the flow passage 2 between the heat transfer
inhibiting means 11 and the helical part 5. Thus, it is also
possible to pre-heat the flow passage 2 between the heat transfer
inhibiting means 11 and the helical part 5 by supplying humidified
air (temperature: about 350°C) to part of the flow passage 2
immediately downstream of the heat transfer inhibiting means 11 .
Next, a second embodiment as shown in Fig. 4 is
described, where the same constituent members as those of the
foregoing first embodiment are designated by the same reference
numerals and their detailed description is omitted. In this
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second embodiment , inside the cylindrical member 6 , a threaded
member 15 is inserted and the helical part 5 is formed. More
specifically, the threaded member 15 is formed into a trapezoidal
thread, where a screw thread with a trapezoidal cross section
is formed at the outer circumferential surface of the threaded
member 15, the top of this screw thread is in contact with the
inner circumferential surface of the cylindrical member 6, and
the thread groove forms the flow passage 2. Also, an insertion
hole 16 for inserting the heating means 7 is provided inside the
threaded member 15.
According to this second embodiment , since the helical
part 5 is formed only by inserting the threaded member 15 into
the cylindrical member 6 , assembly work becomes simpler and the
number of assembly man-hours is reduced. Also, even upon
occurrence of blockage within the helical part 5 due to the
crystallization of urea water, the threaded member 15 can be
pulled out and removed, and the outer circumferential surface
of the threaded member 15 and the inner circumferential surface
of the cylindrical member 6 can be cleaned with great ease.
Further, another embodiment of the heat transfer
inhibiting means 11 is described with reference to Fig. 5. The
heat transfer inhibiting means 11 shown in Fig. 5 has a so-called
ejector structure, where air is introduced from outside, and heat
that has been transferred from the helical part 5 side is
collected by the air, and a flow of the air that has collected
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the heat is directed toward the helical part 5, by which heat
is returned to the helical part 5. That is, part of the flow
passage 2 is formed into a double-cylindrical structure
comprising an outer cylindrical part 17 and an inner cylindrical
part 18. A specified number of air inlet holes 19, 19, ... are
formed in the outer cylindrical part 17 along its periphery, a
front-end opening 20 of the inner cylindrical part 18 is placed
inside a tapered portion 21 in the downstream-side end portion
of the outer cylindrical part 17, and an annular flow port 22
is formed therebetween. In addition, the upstream-side end
portion of the outer cylindrical part 17 is closed.
Accordingly, when the air accompanied by urea water
passes through the front-end opening 20 , outside air is sucked
up through the flow port 22 via the air inlet holes 19. Then,
heat that has been transferred from the helical part 5 to the
outer cylindrical part 17 is collected by inflow outside air so
as to return to the helical part 5 , thus inhibiting the heat from
being transferred to the inner cylindrical part 18. Also, the
heat transfer inhibiting means 11 is so designed, as that shown
in Fig. 3 , that the temperature of A point , which is the entrance ,
will be not more than 80° C , and that the temperature of B point ,
which is the exit , will be not less than 180° C . That is , a
temperature range of about 80 - 180°C, which is more likely to
cause crystallization of urea water or generation of unnecessary
intermediates, is limited to the site where the heat transfer
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inhibiting means 11 is provided, while the length of this
temperature range site is made as short as possible . Thus , the
crystallization of urea water or the generation of unnecessary
intermediates is suppressed to a minimum.
In addition, the heat transfer inhibiting means 11
shown in Fig. 5 can be used either in the first embodiment or
in the second embodiment.
According to the present invention , urea water can be
continuously heated while flowing, so that the efficiency of heat
transfer can be greatly improved. Besides, the size of the
ammonia generating apparatus can be downsized as a whole and,
in particular, with the heating means provided inside the helical
part in the flow passage, the ammonia generating apparatus can
be formed more compact in structure.
