Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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DESCRIPTION
Title of Invention: PETROLEUM RESIDUUM BURNING BOILER AND
COMBUSTION METHOD THEREOF
Technical Field
[0001] The present invention relates to a petroleum residuum burning
boiler which
uses, as fuel, a flame-retardant petroleum residuum, such as asphalt pitch or
petroleum
coke.
Background Art
[0002] Conventionally known are petroleum residuum burning boilers which
use, as
fuel, a flame-retardant petroleum residuum, such as asphalt pitch or petroleum
coke.
PTL 1 discloses this type of boiler.
[0003] The boiler described in PTL 1 includes a high-temperature reduction
combustion chamber and a low-temperature oxidation combustion chamber located
under
the high-temperature reduction combustion chamber and connected to the high-
temperature reduction combustion chamber through a throat. A primary burner
that
supplies petroleum residuum fuel and primary combustion air is provided at the
high-
temperature reduction combustion chamber, and a two-stage combustion air
supply nozzle
is provided at the low-temperature oxidation combustion chamber. In the high-
temperature reduction combustion chamber, the fuel is combusted at a high
temperature of
about 1,450 C to 1,550 C in a fuel ultra-rich and reduction atmosphere. A
combustion
gas generated in the high-temperature reduction combustion chamber flows
through the
throat into the low-temperature oxidation combustion chamber. In the low-
temperature
oxidation combustion chamber, the combustion is completed at a low temperature
of about
1,100 C in an oxidizing atmosphere.
[0004] In the flame-retardant petroleum residuum, such as asphalt pitch or
petroleum
coke, the content of nitrogen and the content of sulfur are large since
nitrogen and sulfur
are concentrated in a petroleum refining process. Therefore, a flue gas of the
flame-
retardant petroleum residuum contains a large amount of NOx. Moreover, in the
flame-
retardant petroleum residuum, the content of vanadium is large since vanadium
is
concentrated in the petroleum refining process. Therefore, combustion ash of
the flame-
retardant petroleum residuum contains vanadium oxide having a low melting
point. If
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the combustion ash adheres to a furnace wall or a heat exchanger tube,
blocking of heat
transfer, blocking of ventilation, and high-temperature corrosion by influence
of the high
sulfur content may be caused. Therefore, when using the flame-retardant
petroleum
residuum as the fuel, reductions in the amount of NOx generated and the amount
of soot
generated are problems to be solved.
[0005] According to the boiler of PTL 1, the amount of NOx generated is
reduced by
combusting the flame-retardant petroleum residuum fuel through two stages that
are high-
temperature reduction combustion and low-temperature oxidation combustion.
Moreover, according to the boiler of PTL 1, the amount of soot generated is
reduced in
such a manner that: steam is added to the primary combustion air; and a water
gas reaction
is caused between carbon and the steam to promote gasification of the carbon.
Citation List
Patent Literature
[0006] PTL 1: Japanese Laid-Open Patent Application Publication No. 2012-
107825
Summary of Invention
Technical Problem
[0007] The water gas reaction that is an endothermic reaction is
advantageous at
higher temperatures from the viewpoint of the equilibrium theory. When steam
that is
significantly lower in temperature than a furnace internal temperature is
supplied as a
gasifying agent to the inside of a furnace, the furnace internal temperature
decreases.
The effects of the water gas reaction are limited by the decrease in the
furnace internal
temperature.
[0008] The present invention was made under these circumstances, and an
object of
the present invention is to propose a petroleum residuum burning boiler and a
combustion
method of the petroleum residuum burning boiler, each of which promotes a
water gas
reaction more effectively than when steam is directly supplied as a gasifying
agent to the
inside of a furnace, and with this, realizes low soot combustion.
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Solution to Problem
[0009] A petroleum residuum burning boiler according to one aspect of the
present
invention includes: a furnace body including a high-temperature reduction
combustion
chamber in which combustion is performed at a temperature of 1,300 C or more
and an air
ratio of less than one and a low-temperature oxidation combustion chamber
which is
connected to the high-temperature reduction combustion chamber and in which
combustion is performed at a temperature of less than 1,300 C and an air ratio
of one or
more; a burner that supplies petroleum residuum fuel and primary combustion
air to the
high-temperature reduction combustion chamber; a two-stage combustion air
supply
nozzle that supplies two-stage combustion air to the low-temperature oxidation
combustion chamber; and an assist gas supply nozzle through which an assist
gas is
supplied to the high-temperature reduction combustion chamber, the assist gas
containing
a component which generates steam by combustion, the steam being used as a
gasifying
agent for unburned carbon of a combustion gas of the petroleum residuum fuel.
[0010] A combustion method of a petroleum residuum burning boiler
according to
another aspect of the present invention is a combustion method of a petroleum
residuum
burning boiler, the petroleum residuum burning boiler including: a high-
temperature
reduction combustion chamber to which petroleum residuum fuel and primary
combustion
air are supplied and in which combustion is performed at a temperature of
1,300 C or
more and an air ratio of less than one; and a low-temperature oxidation
combustion
chamber which is connected to the high-temperature reduction combustion
chamber and in
which combustion is performed at a temperature of less than 1,300 C and an air
ratio of
one or more, the combustion method including: supplying an assist gas to the
high-
temperature reduction combustion chamber; and gasifying unburned carbon of a
combustion gas of the petroleum residuum fuel by a water gas reaction by using
steam,
generated by combustion of the assist gas, as a gasifying agent.
[0011] According to the petroleum residuum burning boiler and the
combustion
method of the petroleum residuum burning boiler, the steam (H20 gas) is
generated by the
combustion of the assist gas supplied to the high-temperature reduction
combustion
chamber, and the unburned carbon of the combustion gas of the petroleum
residuum fuel
can be gasified by the water gas reaction by using the steam as the gasifying
agent. In
addition, since the decrease in the furnace internal temperature can be
suppressed more
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than when the steam is directly supplied as the gasifying agent to the inside
of the furnace,
the inside of the furnace is maintained at a high temperature that is
advantageous for the
progress of the water gas reaction. As above, since the gasification of the
unburned
carbon is promoted, the amount of soot generated by the combustion can be
reduced.
Advantageous Effects of Invention
[0012] The present invention can propose the petroleum residuum burning
boiler and
the combustion method of the petroleum residuum burning boiler, each of which
promotes
the water gas reaction more effectively than when steam is directly supplied
as the
gasifying agent to the inside of the furnace, and with this, realizes low soot
combustion.
Brief Description of Drawings
[0013] FIG. 1 is a schematic functional diagram for explaining a petroleum
residuum
burning boiler according to one embodiment of the present invention.
FIG. 2 is a schematic sectional view for explaining the structure of a burner.
FIG. 3 is a graph showing a relation among the supply of an assist gas, the
amount of soot, and combustion efficiency.
Description of Embodiments
[0014] Hereinafter, the present invention will be described based on an
embodiment
with reference to the drawings. FIG. 1 is a schematic functional diagram for
explaining a
combustion chamber of a petroleum residuum burning boiler 1 according to one
embodiment of the present invention.
[0015] The petroleum residuum burning boiler 1 shown in FIG. 1 is
constituted as an
inverted vertical furnace. A furnace body 20 of the petroleum residuum burning
boiler 1
includes combustion chambers including a high-temperature reduction combustion
chamber 2 and a low-temperature oxidation combustion chamber 3 located under
the high-
temperature reduction combustion chamber 2. The high-temperature reduction
combustion chamber 2 and the low-temperature oxidation combustion chamber 3
are
connected to each other through a throat 4. The throat 4 is a passage which
reduces a
horizontal sectional area of the combustion chamber by 20% to 50%.
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[0016] Walls of the high-temperature reduction combustion chamber 2 are
covered
with a fire-resistant material 6 that withstands a high temperature of 1,550 C
or more.
Burners 5 are provided on each of a pair of opposing furnace walls of the high-
temperature
reduction combustion chamber 2. The burners 5 are lined up in a horizontal
direction to
form burner rows, and the burner rows are provided in an upper-lower
direction. The
burners 5 are opposed to each other and arranged in a zigzag manner such that
axes of
flames from the opposing burners 5 do not intersect with each other.
[0017] FIG. 2 is a schematic sectional view of the burner S. The burner 5
is a
coaxial mixed combustion burner which uses petroleum residuum fuel and an
assist gas.
An assist gas supply nozzle 52 is provided at a center axis of the burner 5. A
main fuel
supply nozzle 51 is provided around the assist gas supply nozzle 52. A
secondary
combustion air nozzle 56 is provided around the main fuel supply nozzle 51.
[0018] A first air supply device 53 that supplies combustion air (primary
combustion
air) by pressure is connected to the main fuel supply nozzle 51. A second air
supply
device 57 that supplies combustion air (secondary combustion air) is connected
to the
secondary combustion air nozzle 56. The second air supply device 57 can adjust
the
amount of combustion air supplied. Moreover, a petroleum residuum fuel supply
device
54 that supplies petroleum residuum fuel to the primary combustion air
supplied by
pressure is connected to the main fuel supply nozzle 51. The petroleum
residuum fuel
supply device 54 can quantitatively supply the petroleum residuum fuel. The
petroleum
residuum fuel is flame-retardant solid fuel prepared by, for example, finely
crushing
asphalt pitch or petroleum coke.
[0019] An assist gas supply device 55 that supplies an assist gas by
pressure is
connected to the assist gas supply nozzle 52. The assist gas supply device 55
can adjust
the amount of assist gas supplied. The assist gas is a gas containing
components which
generate steam (H20 gas) by combustion. The assist gas is, for example, a by-
product
gas in a petroleum refining step. The by-product gas in the petroleum refining
step
contains components, such as hydrogen (H2), methane (CH4), ethane (C2H6), and
propane
(C3H8), which generate steam by combustion. Table 1 below shows compositions
of the
by-product gases in the petroleum refining step which gases may be used as the
assist gas.
The assist gas used in the present invention is not limited to the by-product
gases having
the compositions shown in Table 1.
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[0020] Table 1
By-product gas 1 By-product gas 2 By-product gas 3 By-product gas 4
H2 33.3 39.7 23.6 83.3
H2S 0 0.01 0.0005 0
CO 0.5 0.1 0.05 0.1
CO2 0.3 0.09 0 0
N2 6.0 0 0 0
CH4 19.0 36.8 45.4 16.1
C2H6 11.5 11.5 19.1 0.04
C2H4 11.0 0.1 1.1 0.4
C3118 8.8 4.8 5.6 0
C3H6 0.9 0.2 1.2 0
C4-total 6.0 5.9 3.6 0
CS-total 2.6 0.6 0.3 0
C6 or more 0 0.2 0.1 0
[The unit is mol.%]
[0021] The petroleum residuum fuel supplied to the combustion air supplied
by
pressure to the main fuel supply nozzle 51 is conveyed by the flow of the
combustion air.
The primary combustion air and the petroleum residuum fuel flowing together
with the
primary combustion air are ejected from the main fuel supply nozzle 51 to the
high-
temperature reduction combustion chamber 2. Moreover, the assist gas is
ejected from
the assist gas supply nozzle 52. To be specific, the assist gas and the
mixture of the
primary combustion air and the petroleum residuum fuel are coaxially ejected
from the
burner S. A calorie ratio R (R = B/A) [%] that is a ratio of a calorie B
[Kcal/h1 of the
assist gas to a calorie A [Kcal/h1 of the petroleum residuum fuel is not
limited but is
preferably 10 or more and 30 or less. The amount of combustion air supplied by
the
second air supply device 57, the amount of fuel supplied by the petroleum
residuum fuel
supply device 54, and the amount of assist gas supplied by the assist gas
supply device 55
are adjusted such that the calorie ratio R is maintained.
[0022] A known swirling flow generator (not shown) including a swirler is
provided
at the burner S. The secondary combustion air swirls by the action of the
swirling flow
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generator, and therefore, the combustion gas forms swirling flow. By the
swirling flow
generated by each burner 5, the fuel and the combustion gas in the high-
temperature
reduction combustion chamber 2 are collected at a middle portion of a ceiling,
and this
brings about an extension effect of a residence time of the fuel and the
combustion gas in
the high-temperature reduction combustion chamber 2.
[0023] Referring back to FIG. 1, a cooler 9, a two-stage combustor 10, and
an ash
discharger 8 are formed in the low-temperature oxidation combustion chamber 3.
Two-
stage combustion air supply nozzles 7 through which two-stage combustion air
is supplied
are provided in the low-temperature oxidation combustion chamber 3 so as to be
located
on a furnace wall downwardly away from the throat 4.
[0024] In the low-temperature oxidation combustion chamber 3, the cooler 9
is
located between the throat 4 and the two-stage combustion air supply nozzles 7
in the
upper-lower direction. The cooler 9 cools the high-temperature combustion gas
flowing
downward from the high-temperature reduction combustion chamber 2 through the
throat
4. Heat exchanger tubes (not shown) for steam generation extend at a
furnace wall of the
cooler 9.
[0025] In the low-temperature oxidation combustion chamber 3, the two-
stage
combustor 10 is located under the two-stage combustion air supply nozzles 7.
Heat
exchanger tubes (not shown) for steam generation extend at a furnace wall of
the two-
stage combustor 10. The two-stage combustor 10 is maintained at a low
temperature by
a cooling medium flowing through the heat exchanger tubes.
[0026] The two-stage combustion air supply nozzles 7 are provided at each
of a pair
of opposing furnace walls of the low-temperature oxidation combustion chamber
3. The
two-stage combustion air supply nozzles 7 are lined up in a horizontal
direction to form
nozzle rows, and the nozzle rows are provided in the upper-lower direction. By
the air
supplied from the two-stage combustion air supply nozzles 7, an unburned gas
in the
combustion gas cooled by the cooler 9 is subjected to two-stage combustion in
a low-
temperature oxidizing atmosphere in the two-stage combustor 10.
[0027] The ash discharger 8 is formed at a bottom portion of the low-
temperature
oxidation combustion chamber 3. An ash discharging mechanism (not shown) is
provided under the ash discharger 8. Combustion ash accumulated at a bottom of
the
furnace is discharged from the ash discharger 8 to an outside of the furnace.
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[0028] A gas outflow port 11 communicating with a gas duct 12 is provided
at a
lower side surface of the two-stage combustor 10. A flue gas generated in the
two-stage
combustor 10 flows in a U shape to flow into the gas duct 12. Steam
superheater tubes
13 and an economizer 14 are provided at the gas duct 12. An ash outlet port 15
through
which the combustion ash flowing together with the combustion gas is
discharged after
being precipitated is provided at a bottom portion of the gas duct 12 where
the steam
superheater tubes 13 and the economizer 14 are provided.
[0029] A combustion method of the petroleum residuum burning boiler 1
configured
as above will be described. The fuel and the primary combustion air are
supplied from
the burners 5 to the high-temperature reduction combustion chamber 2, and the
combustion of the fuel is started. Introduction of air to the high-temperature
reduction
combustion chamber 2 is suppressed, and the high-temperature reduction
combustion
chamber 2 is maintained in a reduction atmosphere in which an air ratio is
less than one
(for example, about 0.6 to 0.8). The high-temperature reduction combustion
chamber 2
is maintained at a high temperature of 1,300 C or more, desirably 1,450 C or
more and
1,550 C or less by the combustion of the fuel and, according to need, the
combustion of
auxiliary fuel.
[0030] When the fuel combusts in the high-temperature reduction atmosphere
in the
high-temperature reduction combustion chamber 2, a high-temperature combustion
gas is
generated. The combustion gas is pushed out from the high-temperature
reduction
combustion chamber 2 by the combustion gas generated continuously, to flow
downward
through the throat 4 to the low-temperature oxidation combustion chamber 3.
The
combustion gas is cooled to less than 1,300 C, desirably 1,200 C or more and
less than
1,300 C while flowing through the cooler 9. Then, the combustion gas flows
downward
to the two-stage combustor 10.
[0031] The two-stage combustion air having a relatively low temperature is
supplied
from the two-stage combustion air supply nozzles 7 to the two-stage combustor
10. With
this, the two-stage combustor 10 is maintained in an oxidizing atmosphere in
which the air
ratio is one or more (for example, about 1.1). An unburned portion of the
combustion
gas is completely combusted in the oxidizing atmosphere of the two-stage
combustor 10.
The flue gas is cooled to about 1,000 C to 1,100 C by the two-stage combustor
10 and
then flows out to the gas duct 12.
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[0032] The flue gas flowing through the gas duct 12 is subjected to heat
exchange
with boiler feedwater at the steam superheater tubes 13 and the economizer 14
and then
flows out to a post-process step connected to the gas duct 12.
[0033] Typically, the amount of NOx generated in the combustion of the
petroleum
residuum fuel strongly depends on a combustion temperature and the air ratio.
To be
specific, in the reduction atmosphere, the amount of NOx generated decreases
as the
temperature of the combustion increases. Moreover, in the oxidizing
atmosphere, the
amount of NOx generated decreases as the temperature of the combustion
decreases. In
the petroleum residuum burning boiler 1 according to the present embodiment,
the
generation of fuel NOx is suppressed by combusting the fuel in the high-
temperature
reduction atmosphere in the high-temperature reduction combustion chamber 2,
and the
generation of thermal NOx is suppressed by completely combusting the unburned
portion
of the combustion gas in the low-temperature oxidizing atmosphere in the low-
temperature
oxidation combustion chamber 3. In the petroleum residuum burning boiler 1
according
to the present embodiment, the amount of NOx generated can be effectively
reduced by
adopting the above two-stage combustion system.
[0034] Typically, when petroleum residuum fuel is combusted in a high-
temperature
reduction combustion atmosphere, part of carbon is not gasified and remains as
unburned
carbon. This increases the amount of soot. However, in the petroleum residuum
burning boiler 1 according to the present embodiment, the assist gas is
supplied to the
high-temperature reduction combustion chamber 2, and the high-temperature
reduction
combustion chamber 2 is maintained at a high temperature of 1,300 C or more
(desirably,
1,450 C or more). With this, a water gas reaction is caused in the high-
temperature
reduction combustion chamber 2, and this promotes the gasification of carbide.
The
amount of soot generated by the combustion of the petroleum residuum fuel can
be
reduced by the gasification of the carbide.
[0035] The petroleum residuum fuel, the assist gas, and the combustion air
are
ejected from the burners 5 in the high-temperature reduction combustion
chamber 2.
Since the petroleum residuum fuel is flame-retardant, the assist gas starts
combusting prior
to the petroleum residuum fuel. When the assist gas combusts by the combustion
air,
steam is generated.
2H2 +02 ¨> 2H20, CH4 +02 ¨> CO2 + 2H20,
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The generated H20 gas serves as a gasifying agent, and the unburned carbon
of the combustion gas is subjected to the water gas reaction to be converted
into a CO gas
and an H2 gas.
C + H20 ¨> CO + H2
When the temperature of the combustion gas is less than 1,300 C, and the
percentage of the assist gas in mixed combustion of the petroleum residuum
fuel and the
assist gas increases, the amount of oxygen becomes inadequate, and therefore,
the water
gas reaction is not caused. As a result, the amount of soot may increase.
[0036] When the assist gas is supplied to the high-temperature reduction
combustion
chamber 2, and the steam is generated by the combustion of the assist gas, a
decrease in
the furnace internal temperature can be suppressed more than when the steam
lower in
temperature than the furnace internal temperature is directly supplied as the
gasifying
agent to the inside of the furnace. To be specific, the inside of the furnace
is maintained
at a high temperature that is advantageous for the progress of the water gas
reaction.
[0037] FIG. 3 is a graph showing a relation among the supply of the assist
gas, the
amount of soot, and the combustion efficiency. In FIG. 3, a horizontal axis
indicates a
calorie ratio [%] that is a ratio of the amount of assist gas supplied to the
amount of
petroleum residuum fuel supplied in terms of calorie, and a vertical axis
indicates (1) a
ratio of the amount [Kg] of soot to the amount [t] of petroleum residuum fuel
supplied and
(2) combustion efficiency [%]. The amount of soot contains bottom ash
discharged from
the ash discharger 8 and the ash outlet port 15 and fly ash collected by a
dust collector in
the post-processing step connected to the gas duct 12.
[0038] As shown in the graph of FIG. 3, as the amount of assist gas
supplied
increases, the amount of soot decreases. Therefore, it is apparent that the
amount of soot
can be reduced by the supply of the assist gas. Moreover, as the amount of
soot
decreases, the combustion efficiency increases. Therefore, it is apparent that
the
combustion efficiency increases by the decrease in the amount of soot.
[0039] As described above, the petroleum residuum burning boiler 1
according to the
present embodiment includes: the furnace body 20 including the high-
temperature
reduction combustion chamber 2 in which combustion is performed at 1,300 C or
more
and the air ratio of less than one and the low-temperature oxidation
combustion chamber 3
which is connected to the high-temperature reduction combustion chamber 2 and
in which
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combustion is performed at a temperature of less than 1,300 C and the air
ratio of one or
more; the burner 5 that supplies the petroleum residuum fuel and the primary
combustion
air to the high-temperature reduction combustion chamber 2; the two-stage
combustion air
supply nozzle 7 that supplies the two-stage combustion air to the low-
temperature
oxidation combustion chamber 3; and the assist gas supply nozzle 52 that
supplies the
assist gas to the high-temperature reduction combustion chamber 2. The assist
gas
contains a component which generates steam by combustion, and the steam serves
as the
gasifying agent for the unburned carbon of the combustion gas of the petroleum
residuum
fuel.
[0040] Moreover, the combustion method of the petroleum residuum burning
boiler 1
according to the present embodiment includes, in the petroleum residuum
burning boiler 1
including the high-temperature reduction combustion chamber 2 to which the
petroleum
residuum fuel and the primary combustion air are supplied and in which
combustion is
performed at a temperature of 1,300 C or more and the air ratio of less than
one and the
low-temperature oxidation combustion chamber 3 which is connected to the high-
temperature reduction combustion chamber 2 and in which combustion is
performed at a
temperature of less than 1,300 C and the air ratio of one or more, supplying
the assist gas
to the high-temperature reduction combustion chamber 2 and gasifying the
unburned
carbon of the combustion gas of the petroleum residuum fuel by the water gas
reaction by
using the steam, generated by the combustion of the assist gas, as the
gasifying agent.
[0041] According to the petroleum residuum burning boiler 1 and the
combustion
method of the petroleum residuum burning boiler 1, the steam (H20 gas) is
generated by
the combustion of the assist gas supplied to the high-temperature reduction
combustion
chamber 2, and the unburned carbon of the combustion gas of the petroleum
residuum fuel
can be gasified by the water gas reaction by using the steam as the gasifying
agent. In
addition, since the decrease in the furnace internal temperature can be
suppressed more
than when the steam is directly supplied as the gasifying agent to the inside
of the furnace,
the inside of the furnace is maintained at a high temperature that is
advantageous for the
progress of the water gas reaction. As above, since the gasification of the
unburned
carbon is promoted, the amount of soot generated by the combustion can be
reduced. To
be specific, the water gas reaction is promoted more effectively than when the
steam is
directly supplied as the gasifying agent to the inside of the furnace, and
with this, the
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petroleum residuum burning boiler 1 and the combustion method of the petroleum
residuum burning boiler 1, both of which can realize the low soot combustion,
can be
provided.
[0042] In the petroleum residuum burning boiler 1 according to the present
embodiment, the burner 5 is a coaxial mixed combustion burner including the
assist gas
supply nozzle 52 and the main fuel supply nozzle 51 through which the
petroleum
residuum fuel and the primary combustion air are supplied.
[0043] Similarly, in the combustion method of the petroleum residuum
burning boiler
1 according to the present embodiment, the assist gas and the mixture of the
petroleum
residuum fuel and the primary combustion air are coaxially supplied to the
high-
temperature reduction combustion chamber 2.
[0044] As above, since the assist gas and the mixture of the petroleum
residuum fuel
and the primary combustion air are coaxially supplied (ejected) to the high-
temperature
reduction combustion chamber 2, the primary combustion air and the assist gas
can be
made to react with each other prior to the flame-retardant petroleum residuum
fuel.
Then, the steam generated by the combustion reaction between the primary
combustion air
and the assist gas can be made to react with the unburned carbon contained in
the
combustion gas generated by the combustion of the petroleum residuum fuel.
[0045] In the petroleum residuum burning boiler 1 and the combustion
method of the
petroleum residuum burning boiler 1 according to the present embodiment, the
assist gas
may be the by-product gas generated in the petroleum refining step.
[0046] Since the petroleum residuum burning boiler 1 uses, as the fuel,
the petroleum
residuum generated in the petroleum refining step, the petroleum residuum
burning boiler
1 may be provided at or adjacent to a petroleum refinery. In such a case, when
the assist
gas is the by-product gas generated in the petroleum refining step, both the
petroleum
residuum fuel and the by-product gas which are generated in the petroleum
refining step
can be effectively utilized, which is preferable.
[0047] The foregoing has described a preferred embodiment of the present
invention.
Modifications of specific structures and/or functional details of the above
embodiment
may be included in the present invention as long as they are within the scope
of the present
invention. The above configuration may be changed as below, for example.
[0048] For example, in the above embodiment, the burner 5 is a coaxial
mixed
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combustion burner which uses the petroleum residuum fuel and the assist gas.
However,
the burner 5 may be a single-fuel burner which uses petroleum residuum fuel.
In this
case, the assist gas supply nozzle 52 that ejects the assist gas such that the
assist gas is
mixed with the petroleum residuum fuel and the primary combustion air ejected
from the
single-fuel burner which uses the petroleum residuum fuel may be provided
independently
from the burner 5.
Reference Signs List
[0049] 1 petroleum residuum burning boiler
2 high-temperature reduction combustion chamber
3 low-temperature oxidation combustion chamber
4 throat
burner
6 fire-resistant material
7 two-stage combustion air supply nozzle
8 ash discharger
9 cooler
two-stage combustor
11 gas outflow port
12 gas duct
13 steam superheater tube
14 economizer
ash outlet port
furnace body
51 main fuel supply nozzle
52 assist gas supply nozzle
53 air supply device
54 petroleum residuum fuel supply device
55 assist gas supply device
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