Note: Descriptions are shown in the official language in which they were submitted.
107~04Z
The present invention relates to a boiler containing
a denitrator, and more particularly it relates to a boiler
internally equipped w$th a reactor for reducing and removing
nitrogen oxides contained in combustion gas.
Various combustion devices having boilers or waste
heat boilers have a denitrator attached thereto for removing
nitrogen oxides contained in exhaust gas. Conventionally,
such denitrator is disposed downstream of a dust collector,
i.e., in the flue immediate upstream of a chimney. With
this arrangement, however, since the temperature of the
exhaust gas introduced into the denistrator is too low ~o
cause denitration, it has been necessary to provide said
denitrator with a temperature raising furnace and a rotary heat
exchanger.
More particularly, the present invention relates to
a denitrator which operates on the basis of dry type smoke
denitration which is one of the methods of removing nitrogen
oxides (NO ) from exhaust gas. Of these methods, one which is
based on a reaction with ammonia expressed by the following
formula is most effective.
4NH3 + 6NO ~ 5N2 + 6H2O
Such reaction for denitration as exemplified by the above
formula is caused by the action of a catalyst and the
properties of such catalyst are the most important factor.
Optimum reaction temperatures for such catalysts mostly are
within a range of 350-500C. On the other hand, the
temperature of exhaust gas from a boiler exit is about
200C, which accounts for the necessity of providing
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a denitrator with means for raising waste gas temperature
as described above.
Further, since the catalysts used in conventional
denitrators are in the form of pellets, the construction is
such that the catalyst layer is liable to have soot in
exhaust gas collected thereon. For this reason, it has
been necessary to install the denitrator downstream of the
dust collector, as described above, and hence it cannot be
helped that the temperature of exhaust gas becomes further
decreased.
Further, since the catalyst is in the form of
pellets, no matter how much the catalyst layer is spread to
reduce the thickness, it has been necessary to use a blower
or the like since the pressure loss due to the catalyst
layer ls hi8h. Further, this has been a cause of the
denitrator having to be sepsrately installed.
The present invention has been accomplished by
noting the fact that in the combustion gas channel in a
boiler there is without exception a region where the
temperature conditions are most suited for reduction of
nitrogen oxides. The principal ob~ect of the invention is
to install a denitration catalyst layer and, if necessary,
means for feeding a reductant such as ammonia in said
region having the optimum temperature conditions rearwardly
of one of a plurality of heat exchangers in a combustion
gas channel~ thereby making it possible to remove nitrogen
oxides without providing a temperature raising furnace,
a rotary heat exchanger, a blower and a catalyst-layer~
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filled container, thereby reducing floor space for installa-
tion and saving cost of ~onstruction.
A second object of the invention is to provide a
boiler containing a denitration catalyst layer, wherein
said catalyst layer comprises a number of plate-like
denitration catalyst bodies disposed with their plate
surfaces extending along the direction of flow of combustion
gas, desirably said plate-like denitration catalyst bodies
being assembled in a honey comb fashion. The use of such
plate-like catalyst bodies minimizes pressure loss and soot
collection and facilitates soot blowing, which brings about
the fact that no trouble will be caused even if the catalyst
layer is not disposed rearwardly of the dust collector.
Another feature of an embodiment of the invention is
to provide a denitrator contained in a boiler, wherein said
plate-like catalyst bodies are assembled as a unit block body
in a box whose two opposed surfaces facing in tbe direction
of gas flow are open, such unit block bodies being combined
to form said catalyst layer. Formation of catalyst layer
and maintenance, control and replacement of catalyst are
very easy.
A further feature of an embodiment of the invention
is to provide a wasteheat boiler containing such a denitrator
as described above~ specifically a waste heat boiler into
which waste gas from a gas turbine is introduced, said denitrator
catalyst layer and, if necessary, reductant feeding means
being disposed between a superheater and an evaporator.
According to the invention there is provided
in a waste heat boiler having a superheater, an evaporator
and an economizer disposed ~n a combus~ion gas channel
formed therein, the improvement co~prising, a denitration
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catalyst layer disposed between said superheater and said
evaporator, said catalyst layer being constituted by a
number of plate-like denitration catalyst bodies disposed
with their plate surfaces extending along the direction of
flow of combustion gas, and reductant feeding means for
adding a reductant to the combustion gas provided between
said catalyst layer and said superheater.
Other numerous features and merits of an
embodiment of the invention
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will be read~ly unders~ood from the following description
of a preferred embodiment of the invention given with
reference to the accompanying drawings.
Figure 1 is a schematic view showing the outline of
the construction of a waste heat boiler which is a type of
boiler with which the invention is concerned, and also
showing a preferred manner of use thereof.
Figure 2 is a sectional view taken along the line
II-II of Figure l;
Figure 3 is a perspective view of a catalyst unit
block body;
Figure 4 i8 an enlarged plan view of a part of the
block body; and
Figure 5 is a perspective view of a cstalyst container
into which block bodies will be assembled.
Referring to Figure 1, the numeral 1 designates a
waste heat boiler shown as an example of one of various
boilers. The lower end of said boiler is formed with a
combustion gas inlet 2 and the upper end with an outlet 3
to a flue 18. Disposed inside said boiler, from bottom
upward, are a superheater 4, an evaporator S and an
economizer 6, in the order mentioned. Connected to the
combustion gas inlet 2 is a waste gas channel 8 from a -
gas turbine, for example, in an electric power station,
and in this case, the heat exchangers are usually so
designed that combustion gas may have a temperature of
about 650C when entering the superheater 4, about 300C
when entering the evaporator 5 and about 200C when entering
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the economizer 6. Therefore, it follows that the optimum
reaction temperature region for the catalyst exists between
the superheater 4 and the evaporator 5. The numeral 9
designates a compressor for the gas turbine 7; 10, a naphtha
supplying device; 11, a turbine; and 12 designates an elec-
tric generator connected to the output shaft of the turbine
11. The heat exchangers 4, 5 and 6 in said waste heat
boiler 1 are used for additional electric power generation
by recovered heat. More particularly, there are provided
an accumulator 13, a steam turbine 14 having its output
shaft connected to a electric generator 15, and a steam
condenser 16, and these units and said superheater 4,
evaporator 5 and economizer 6 are connected together in the
manner shown in Flgure 1 to constltute a heat cycle engine.
Designated at 17 is a water replenishing pipe.
In the waste heat boiler 1 constructed in the manner
described above, a denitration catalyst layer 20 is
provided between the superheater 4 and the evaporator 5, and
ammonia feedin8 means 21 for adding ammonia, which is a
reductant, to combustion gas is provided upstream of said
denitration catalyst layer 20, i.e., on the superheater 4
side. The ammonia feedin8 means 21~ as shown in Figure 2,
comprises a plurality of in~ection pipes 22 extending into
the gas channel of the waste heat boiler 1, and an ammonia
supply unit 23 disposed outside the gas channel. The
in~ection pipes 22 are each formed with a number of
in~ection ports 22a, whereby ammonia can be unifonmly added
to w ~te g-L. Furthtr~ the unlt 23 co=prises an =moDIa
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gas b~mb, replacing means and a pressure adjusting deYice
therefor, and a gas leakage preventing device.
The denitration catalyst layer 20 ls constituted by
a number of plate-like denitration catalyst bodies disposed
with their plate surfaces extending along the d~rection of
flow of combustion gas. In a desired fonm, as shown in
Figures 3 and 4, there is used a honey-comb-shaped catalyst
25 which is a combination of plate-like catalyst bodies
25a and corrugated catalyst bodies 25b. Further, in this
embodiment, said catalyst 25 is formed into a unit block
body 27 by being built in a box 26 whose two opposed surfaces
facing in the direction of flow of gas are open, as shown.
A predetermined number of such unit block bodies 27 sre
assembled into a framework 20 having support grids 29 at
the lower end, and such frameworks 28 are arranged
longitudinally, transversely and vertically on a support
frame in the waste heat boiler 1, thereby constituting
the catalyst layer 20.
As for said catalyst 25, those described in the
applicant~s Canadian Patent Application No.255,472 and
modifications thereof are desirable, but the present
invention is not concerned with the composition of such
catalyst itself ant hence catalysts known per se and
catalysts of new compositions may be used.
According to the arrangement described above, since
the denitratlon catalyst layer 20 and ammonia feeding
means 21 are disposed between the superheater 4 and the
evaporator 5, i.e. in an optimum catalytic reaction tempera-
ture region there is no need to use a temperature raising
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furnace, rotary heat exchanger and catalyst-layer-fllled
container, and further, by forming the catalyst layer 20
using plate-like catalyst bodies, pressure loss in the
catalyst layer is minimized and hence it is not necessary
to use a separate blower for the denitrator. Further, even
if the catalyst layer 20 is formed inside the boiler 1,
there is no trouble. Moreover, this construction decreases
the tendency of soot to collect thereon and facilitates
soot blowing. Further, by forming a catalyst into a unit
block body 27 and combining such unit block bodies to form
a catalyst layer, formation, exchange, maintenancs and
control of the catalyst layer are greatly facilitated.
In the description of the embodiment, the boiler has
been descrlbed as a waste heat boiler~ specifically a waste
heat boiler using waste gas from a gas turbine. The
essence of the invention, however, lies in the formation of
a catalyst layer~ specifically a catalyst layer consisting
of plate-like catalyst bodies in an optimum catalytic
reaction temperature region in a combustion gas channel,
and, therefore, the invention is not limited to a waste
heat boiler but i9 applicable to other boilers. Further, -~
the tenitration has been described as a reaction with
am~onla~ which ls most effective~ but the invention i8
applicable to other reactions for denitration employing
other reductants such as carbon monoxide, hydrogen gas,
methane gas and other hydrocarbons and corresponding
catalysts. For example, catalysts described in the
applicant's Canadian Patent Application 186,879 and
modifications thereof may be used. Further~ the reductant
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107104Z
used is CO, H2 or a hydrocarbon or combination thereof
which is to be fed by the reductant feeding means. Further,
in the case of such reductants, instead of feeding such
reductants by said feeding means, it is possible to have
them inially included in the combustion gas in the boiler
as by means for causing incomplete combustion, in which
case the reductant feeding means can be omitted.
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