TECHNICAL FIELD
[0001] The present invention relates to a reheat boiler including a reheat furnace and a
reheater provided downstream of an evaporation tube bank and reducing temperature
unevenness of combustion gas near an outlet of the reheat furnace and to a gas temperature
controlling method of such a reheat boiler.
BACKGROUND ART
[0002] Marine boilers including a super heater have been widely used (Patent Document 1).
Furthermore, reheat boilers including a reheat furnace and a reheater provided downstream
of combustion gas in conventional marine boilers have been used.
[0003] An exemplary configuration of the conventional marine reheat boiler is illustrated
in Fig. 6. Fig. 6 is a schematic of a configuration of the conventional reheat boiler.
As illustrated in Fig. 6, this conventional reheat boiler 100 includes: a main boiler
106 including a burner 101, a furnace 102, a front tube bank 103, a super heater (SH)
104, and an evaporation tube bank (rear tube bank) 105; a reheat furnace 108 including
a reheat burner 107 provided downstream of the evaporation tube bank 105; and a reheater
109 provided at a combustion gas outlet side. The combustion gas originating from
combustion in the burner 101 flows from the furnace 102, passes through the front
tube bank 103, the SH 104, and the evaporation tube bank 105, and is mixed with the
combustion gas originating from combustion in the reheat burner 107 in the reheat
furnace 108. With its heat exchanged with the reheater 109, the gas further flows,
and is output from a gas outlet 110. The reheat boiler is thus operated efficiently.
In Fig. 6, the numeral 111 indicates a water drum, the numeral 112 indicates a steam
drum, the numerals 113, 114 indicate headers, and the numeral 115 indicates a wall
tube.
[0004] [Patent Document 1] Japanese Patent Application Laid-open No.
2002-243106.
DISCLOSURE OF INVENTION
PROBLEM TO BE SOLVED BY THE INVENTION
[0005] The conventional marine reheat boiler 100 includes the reheat burner 107 on a front
wall side of the reheat furnace 108, but not on a rear wall side of the reheat furnace
108. Because of this configuration, as illustrated in Fig. 7, large temperature unevenness
of the combustion gas arises between the front wall side (indicated by the letter
X in Fig. 7) and the rear wall side (indicated by the letter Y in Fig. 7) of the reheat
furnace 108 on the outlet side thereof (indicated by the letter B in Fig. 6).
[0006] Temperature unevenness of the combustion gas on the outlet side of the reheat furnace
108 (that is, on the inlet side of the reheater 109) deteriorates heat conductivity
of the reheat furnace 108 and the reheater 109, and may also cause high-temperature
corrosion of reheater tubes and strength drops of support members in the reheater
109. The letter A in Fig. 7 indicates where the reheat burner is provided, and the
letter C indicates the outlet portion of the reheater 109.
[0007] In view of the above problems, an object of the present invention is to provide a
reheat boiler and a gas temperature controlling method of a reheat boiler that change
gas flow patterns of a reheat burner to reduce temperature unevenness of combustion
gas on the outlet side of a reheat furnace.
MEANS FOR SOLVING PROBLEM
[0008] [0008] According to an aspect of the present invention, a reheat boiler that includes
a main boiler in which combustion gas produced by combustion in a burner flows through
a super heater and an evaporation tube bank from a furnace, a reheat furnace with
a reheat burner provided downstream of the evaporation tube bank, and a reheater provided
on an upper side of the reheat furnace, includes a combustion air supply portion that
is provided at a position opposite to the reheat burner in the reheat furnace to supply
a part of combustion air.
[0009] Advantageously, in the reheat boiler, at least two stages of such combustion air
supply portions are provided in a height direction of the reheat furnace.
[0010] Advantageously, in the reheat boiler, a part of the combustion air is supplied to
the combustion air supply portion by a rate of 50% or less.
[0011] Advantageously, in the reheat boiler, at least two stages of such combustion air
supply portions are provided in a height direction of the reheat furnace, and each
stage of the combustion air supply portions supplies a different volume of the combustion
air.
[0012] According to another aspect of the present invention, a gas temperature controlling
method of the above mentioned reheat boiler includes: supplying a part of the combustion
air into the reheat furnace from a position opposite to the reheat burner to reduce
temperature unevenness of the combustion gas on an outlet side of the reheat furnace.
EFFECT OF THE INVENTION
[0013] According to the present invention, by providing the combustion air supply portion
at a position opposite to the reheat burner in the reheat furnace to supply a part
of the combustion air to the reheat furnace, flow patterns of gas discharged from
the reheat burner can be changed. Therefore, temperature unevenness of the combustion
gas on the outlet side of the reheat furnace is reduced.
BRIEF DESCRIPTION OF DRAWINGS
[0014]
[Fig. 1A] Fig. 1A is a schematic of the configuration of a reheat furnace and a reheater
included in a reheat boiler according to a first embodiment of the present invention.
[Fig. 1B] Fig. 1B is a sectional view seen in a direction perpendicular to the vertical
direction of the reheat furnace illustrated in Fig. 1A.
[Fig. 2] Fig. 2 is a schematic of the configuration of the reheat boiler according
to the first embodiment of the present invention.
[Fig. 3] Fig. 3 is an illustrative view of the temperature distribution of combustion
gas at the outlet of the reheat furnace.
[Fig. 4] Fig. 4 is a schematic of the configuration of a reheat boiler according to
a second embodiment of the present invention, extracting its reheat furnace and reheater
alone.
[Fig. 5] Fig. 5 is an illustrative view of the temperature distribution of combustion
gas near the outlet of the reheat furnace.
[Fig. 6] Fig. 6 is a schematic of an exemplary configuration of a conventional reheat
boiler.
[Fig. 7] Fig. 7 is an illustrative view of the temperature distribution near the outlet
of a conventional reheat furnace.
EXPLANATIONS OF LETTERS OR NUMERALS
[0015]
- 10A, 10B
- reheat boiler
- 11, 11b-1 to 11b-3
- combustion air
- 12, 12-1 to 12-3
- combustion air supply portion
- 101
- burner
- 102
- furnace
- 103
- front tube bank
- 104
- super heater (SH)
- 105
- evaporation tube bank (rear tube bank)
- 106
- main boiler
- 107
- reheat burner
- 108
- reheat furnace
- 109
- reheater
- 110
- gas outlet
- 111
- water drum
- 112
- steam drum
- 113, 114
- header
- 115
- wall tube
BEST MODE (S) FOR CARRYING OUT THE INVENTION
[0016] The present invention will be described in detail with reference to the accompanying
drawings. The embodiments below are not intended to limit the scope of the present
invention. Elements described in the embodiments include their variations readily
thought of by those skilled in the art and substantially equivalent elements.
First Embodiment
[0017] A reheat boiler according to an embodiment of the present invention will now be described
with reference to some drawings.
The reheat boiler according to the present embodiment has a similar configuration
to that of a conventional reheat boiler as illustrated in Fig. 6 and has an air supply
portion provided to a reheat furnace; therefore, like elements have like reference
numerals, and repeated descriptions will be omitted.
Fig. 1A is a schematic of the configuration of the reheat furnace and a reheater included
in the reheat boiler according to the first embodiment of the present invention, and
is a sectional view along the line I-I in Fig. 2. Fig. 1B is a sectional view seen
in a direction perpendicular to the vertical direction of the reheat furnace illustrated
in Fig. 1A. Fig. 2 is a schematic of the configuration of the reheat boiler according
to the first embodiment of the present invention.
In Figs. 1A and 1B, the letter X represents a front wall side of the reheat furnace,
and the letter Y represents a rear wall side of the reheat furnace.
[0018] Referring to Figs. 1A, 1B, and 2, this reheat boiler 10A according to the present
embodiment includes, like the configurations of conventional reheat boilers as illustrated
in Fig. 6, the main boiler 106 configured to make combustion gas originating from
combustion in the burner 101 flow from the furnace 102 and pass through the SH 104
and the evaporation tube bank 105, the reheat furnace 108 in which the combustion
gas is reburned with the reheat burner 107, and the reheater 109 through which the
reburned combustion gas passes. Referring to Figs. 1A and 1B, the reheat boiler 10A
also includes a combustion air supply portion 12 provided at a position opposite to
the reheat burner 107 in the reheat furnace 108 to supply a part of combustion air
11a to be supplied to the reheat burner 107 as combustion air 11b.
According to the present invention, the combustion air 11a refers to combustion air
that is a part of the combustion air 11 and is supplied to the reheat burner 107,
while the combustion air 11b refers to combustion air that is another part of the
combustion air 11 remaining after being allocated to the reheat burner 107 and is
supplied to the combustion air supply portion 12.
[0019] By providing the combustion air supply portion 12 at the position opposite to the
reheat burner 107 in the reheat furnace 108, combustion gas 107a discharged from the
reheat burner 107 and the combustion air 11b supplied through the combustion air supply
portion 12 collide head-on with each other, which facilitates mixing of the combustion
gas 107a with the combustion air 11b. Consequently, temperature unevenness of the
combustion gas 107a at the outlet of the reheat furnace 108 can be reduced.
[0020] Fig. 3 is an illustrative view of the temperature distribution of the combustion
gas at the outlet of the reheat furnace illustrated in Fig. 1A. As indicated in Fig.
3, by providing the combustion air supply portion 12 at the position opposite to the
reheat burner 107 in the reheat furnace 108 and supplying the combustion air 11b into
the reheat furnace 108, the temperature distribution of the combustion gas 107a near
the outlet of the reheat furnace 108 (indicated by the letter B in Figs. 1A and 2)
falls within a range from 600 to 800 degrees Celsius, for example. With the average
temperature being kept about 700 degrees Celsius, this range is narrower than the
temperature distribution of the combustion gas 107a near the outlet of the reheat
furnace 108 (indicated by the letter B in Figs. 6 and 7) included in the conventional
reheat boiler 100 as indicated in Fig. 7.
[0021] By thus supplying the combustion air 11 into the reheat furnace 108 from the position
opposite to the reheat burner 107, temperature unevenness near the outlet of the reheat
furnace 108 can be suppressed compared with the temperature of the combustion gas
107a near the outlet of the reheat furnace 108 (indicated by the letter B in Figs.
6 and 7) included in the conventional reheat boiler as indicated in Fig. 7.
[0022] In the reheat boiler 10A according to the present embodiment, the combustion air
11b that remains after subtracting the combustion air 11a to be supplied to the reheat
burner 107 from the combustion air 11 is supplied through the combustion air supply
portion 12 preferably by a rate of 50% or less. This is because allocating a majority
of the combustion air 11 to the combustion air 11b will cause incomplete combustion
of fuel in the reheat burner 107.
[0023] In the reheat boiler 10A according to the present embodiment, the combustion gas
107a is first burned with the combustion air 11a supplied into the reheat burner 107
and then with the combustion air 11b supplied through the combustion air supply portion
12 in a step-by-step manner. Burning the combustion gas 107a in two stages with the
combustion air 11a and the combustion air 11b can suppress the formation of NO
x.
[0024] In the reheat boiler 10A according to the present embodiment, the air volume of the
combustion air 11b supplied through the combustion air supply portion 12 is adjusted
with, for example, a damper or other air volume adjusters.
[0025] In the reheat boiler 10A according to the present embodiment, by supplying the combustion
air 11b into the reheat furnace 108 through the combustion air supply portion 12 provided
at the position opposite to the reheat burner 107 in the reheat furnace 108, the flow
patterns of the combustion gas 107a discharged from the reheat burner 107 can be changed.
Accordingly, temperature unevenness of the combustion gas 107a on the outlet side
of the reheat furnace 108 can be reduced. This configuration prevents heat conductivity
drops of the reheat furnace 108 and the reheater 109 and also prevents high-temperature
corrosion of reheater tubes and strength drops of support members in the reheater
109.
Second Embodiment
[0026] A reheat boiler according to a second embodiment of the present invention will now
be described with reference to Figs. 4 and 5.
Fig. 4 is a schematic of the configuration of the reheat boiler according to the second
embodiment of the present invention, extracting its reheat furnace and reheater alone.
The reheat boiler according to the present embodiment has a similar configuration
to that of the reheat boiler according to the first embodiment; therefore, like elements
have like reference numerals, and repeated descriptions will be omitted.
Referring to Fig. 4, this reheat boiler 10B according to the present embodiment includes
three-staged combustion air supply portions 12-1 to 12-3 disposed at intervals in
the height direction of the reheat furnace 108 and at positions opposite to the reheat
burner 107 in the reheat furnace 108.
[0027] By supplying the combustion air 11b-1 to 11b-3 into the reheat furnace 108 through
the air supply portions 12-1 to 12-3, the mixture degrees of combustion gas with the
combustion air 11b-1 to 11b-3 can be adjusted desirably, whereby the temperature distribution
of the combustion gas near the outlet of the reheat furnace 108 can be controlled.
[0028] In the boiler 10B according to the present embodiment, the flow rates of the combustion
air 11b-1 to 11b-3 supplied through the air supply portions 12-1 to 12-3, respectively,
are adjustable thereby. By adjusting the flow rates of the combustion air 11b-1 to
11b-3 supplied into the reheat furnace 108, the mixture degrees of the combustion
gas 107a with the combustion air 11b-1 to 11b-3 can be adjusted, whereby the temperature
distribution near the outlet of the reheat furnace 108 can be controlled.
For example, by making the air volume of the combustion air 11b-1 relatively large
and the air volumes of the combustion air 11b-2 and the combustion air 11b-3 even,
the temperature distribution near the outlet of the reheat furnace 108 can be smoothed.
[0029] Fig. 5 is an illustrative view of the temperature distribution of the combustion
gas near the outlet of the reheat furnace illustrated in Fig. 4. By adjusting the
flow rates of the combustion air 11b-1 to 11b-3 supplied through the combustion air
supply portions 12-1 to 12-3 as illustrated in Fig. 4, temperature unevenness of the
combustion gas 107a on the outlet side of the reheat furnace 108 can be reduced as
indicated in Fig. 5.
[0030] By thus supplying the combustion air 11b into the reheat furnace 108 in multiple
stages, the temperature distribution of the combustion gas 107a near the outlet of
the reheat furnace 108 (indicated by the letter B in Fig. 4) falls within a range
from 620 to 780 degrees Celsius, for example. With the average temperature being kept
about 700 degrees Celsius, this range is narrower than the temperature distribution
of the combustion gas 107a near the outlet of the reheat furnace 108 (indicated by
the letter B in Fig. 6) included in the conventional reheat boiler 100 as indicated
in Fig. 7.
[0031] This configuration can achieve a smoother temperature distribution than the temperature
distribution of the combustion gas 107a near the outlet of the reheat furnace 108
(indicated by the letter B in Fig. 2) included in the reheat boiler 10A according
to the first embodiment as indicated in Fig. 3.
[0032] By thus supplying the combustion air 11b-1 to 11b-3 into the reheat furnace 108 from
the positions opposite to the reheat burner 107 and finely adjusting the air volumes
of the combustion air 11b-2 and the combustion air 11b-3, temperature unevenness near
the outlet of the reheat furnace 108 can be suppressed.
[0033] Fine adjustment of the flow rates of the combustion air 11b-1 to 11b-3 can in turn
adjust temperature, retention time, and other conditions of an area where reduction
takes place, thereby suppressing the formation of NO
x. For example, making the flow rate of the combustion air 11b-1 small and the flow
rate of the combustion air 11b-3 large to cause a shortage of air in the reheat furnace
108 can suppress the formation of NO
x.
[0034] Accordingly, in the reheat boiler 10B according to the present embodiment, by delivering
the combustion air 11b-1 to 11b-3 through the combustion air supply portions 12-1
to 12-3 disposed at intervals in the height direction and at the positions opposite
to the reheat burner 107 in the reheat furnace 108 and finely adjusting the flow rates
of the combustion air 11b-1 to 11b-3 supplied into the reheat furnace 108, the gas
flow patterns from the reheat burner 107 can be changed. Consequently, temperature
unevenness of the combustion gas 107a on the outlet side of the reheat furnace 108
can be further reduced. This configuration prevents heat conductivity drops of the
reheat furnace 108 and the reheater 109 and also prevents high-temperature corrosion
of the reheater tubes and strength drops of the support members in the reheater 109.
[0035] The mixture degrees of the combustion gas 107a with the combustion air 11b-1 to 11b-3
can be finely adjusted, whereby the temperature distribution at the outlet of the
reheat furnace 108 can be controlled. Furthermore, fine adjustment of the air volumes
of the combustion air 11b-1 to 11b-3 can in turn adjust conditions of an area where
reduction takes place in the reheat furnace 108, thereby suppressing the formation
of NO
x.
[0036] While three stages of the combustion air supply portions 12-1 to 12-3 are disposed
at intervals in the height direction of the reheat furnace 108 in the reheat boiler
10B according to the present embodiment, the present invention is not limited thereto.
Three or more stages of such air supply portions 12 may be provided.
[0037] With the reheat boilers 10A and 10B according to the present invention, by supplying
a part 11b of the combustion air into the reheat furnace 108 from the position(s)
opposite to the reheat burner 107 in the reheat furnace 108, the flow patterns of
the combustion gas are changed, whereby temperature unevenness of the combustion gas
on the outlet side of the reheat furnace 108 can be reduced. Therefore, they are applicable
for marine boilers; however, the present invention is not limited thereto.
INDUSTRIAL APPLICABILITY
[0038] As described above, the reheat boilers and methods for adjusting the temperature
of gas output from a reheat boiler according to the present invention can change the
flow patterns of combustion gas by supplying a part of combustion air into a reheat
furnace through at least one combustion air supply portion disposed at intervals in
the height direction of the reheat furnace and at position(s) opposite to a reheat
burner in the reheat furnace. Therefore, they are applicable for marine reheat boilers
intended to reduce temperature unevenness of the combustion gas on the outlet side
of the reheat furnace.