U.S. patent application number 09/781909 was filed with the patent office on 2001-07-12 for device and method for combustion of fuel..
Invention is credited to Ishinohachi, Toshiyuki, Mukai, Katsuji, Sumitani, Yoshihiko.
Application Number | 20010007233 09/781909 |
Document ID | / |
Family ID | 27318451 |
Filed Date | 2001-07-12 |
United States Patent
Application |
20010007233 |
Kind Code |
A1 |
Mukai, Katsuji ; et
al. |
July 12, 2001 |
DEVICE AND METHOD FOR COMBUSTION OF FUEL.
Abstract
A fuel selected from powder fuels and liquid fuel is ejected
through a fuel ejection means; primary air is ejected through
primary air-ejecting means arranged on outer and inner sides of the
fuel ejection means, to form outer and inner primary air-ejection
straight streams between which the fuel ejection stream is
interposed, and to burn the fuel ejection stream. When a powder
fuel is used, optionally, a liquid fuel is further ejected and
mixed with the above-mentioned primary air streams, and the liquid
and powder fuels are burnt together.
Inventors: |
Mukai, Katsuji; (Tokyo,
JP) ; Sumitani, Yoshihiko; (Tokyo, JP) ;
Ishinohachi, Toshiyuki; (Tokyo, JP) |
Correspondence
Address: |
PAUL & PAUL
2900 Two Thousand Market Street
Philadelphia
PA
19103
US
|
Family ID: |
27318451 |
Appl. No.: |
09/781909 |
Filed: |
February 9, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09781909 |
Feb 9, 2001 |
|
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09125767 |
Aug 21, 1998 |
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6230635 |
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Current U.S.
Class: |
110/347 ;
110/261 |
Current CPC
Class: |
F23G 2201/80 20130101;
F23D 1/00 20130101; F23G 2209/28 20130101; F23G 2209/12 20130101;
F23C 2900/06043 20130101; F23D 17/007 20130101 |
Class at
Publication: |
110/347 ;
110/261 |
International
Class: |
F23D 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 27, 1996 |
JP |
8-351055 |
May 30, 1997 |
JP |
9-142427 |
May 30, 1997 |
JP |
9-142529 |
Dec 25, 1997 |
JP |
PCT/JP97/04858 |
Claims
1. An apparatus for burning a fuel comprising a means for ejecting
at least one fuel selected from powder fuels and liquid fuels; an
outer primary air-ejection pipe (23) arranged on the outer side of
the fuel-ejection means and having a plurality of outer primary
air-ejection openings (24) through which primary air is ejected in
parallel to the fuel-ejection direction of the fuel-ejection means;
and an inner primary air-ejection pipe (27) arranged on the inner
side of the fuel-ejection means and having at least one inner
primary air-ejection opening (28) through which primary air is
ejected in parallel to the fuel-ejection direction of the
fuel-ejection means.
2. The fuel-burning apparatus as claimed in claim 1, wherein the
fuel-ejection means comprises a powder fuel-ejection pipe (25)
having an annular ejection opening (26) through which a powder fuel
is ejected together with air for conveying the powder fuel.
3. The fuel-burning apparatus as claimed in claim 2, wherein the
plurality of air-ejection openings (24) of the outer primary
air-ejection pipe (23) and the plurality of ejection openings (28)
of the inner primary air-ejection pipe (27) are arranged on
concentric circumferences in such a manner that the annular
ejection opening of the powder fuel-ejection pipe is located
between the outer air-ejection openings and the inner air-ejection
openings, and the inner primary air-ejection openings are located
apart from straight lines extending through the center points of
the outer primary air-ejection openings and the center point of the
concentric circumferences.
4. The fuel-burning apparatus as claimed in claim 1, wherein the
fuel-ejection means comprises a plurality of liquid fuel-spraying
pipes (25a) having liquid fuel-spraying openings (26a) for radially
spraying a liquid fuel, arranged on one and the same
circumference.
5. The fuel-burning apparatus as claimed in claim 4, wherein the
inner primary air-ejection pipe (27) has a plurality of inner
primary air-ejection openings (28), and the plurality of inner
primary air ejection openings 28 and the plurality of outer primary
air-ejection openings (24) are respectively arranged on concentric
circumference having a center point identical to the center point
(31) of the circumference on which the plurality of liquid
fuel-spraying openings (26a) are arranged.
6. The fuel-burning apparatus as claimed in claim 4, wherein the
inner primary air-ejection pipe (27) has one inner primary air
ejection opening (28); the center point of the inner primary
air-ejection opening (28) is identical to the center point (31) of
the circumference on which the plurality of liquid fuel-spraying
opening (26a) are arranged; and the plurality of outer primary air
ejection openings (24) are arranged on a concentric circumference
having a center point identical to the center point (31) of the
circumference on which the plurality of the liquid fuel-spraying
opening (26a) are arranged.
7. The fuel-burning apparatus as claimed in claim 5, wherein the
inner primary air ejection openings (28) are positioned apart from
straight lines extending through the center point (31) of the
circumference on which the liquid fuel-spraying openings (26a) are
arranged and the center points of the outer primary air-ejection
openings (24).
8. The fuel-burning apparatus as claimed in claim 5 or 6, wherein
the liquid fuel-spraying openings (26a) are positioned apart from
straight lines extending through the center points of the outer and
inner primary air ejection openings (24, 28) located closest to a
liquid fuel-spraying opening.
9. The fuel-burning apparatus as claimed in claim 1, in which the
fuel ejection means comprises a powder fuel-ejection pipe (25)
having an annular ejection opening (26) for ejecting a powder fuel
together with air for conveying the powder fuel, and which has an
additional fuel-ejection means arranged on the inner side of the
inner primary air ejection pipes (27) and comprising at least one
liquid fuel-spraying pipe (39) having a liquid fuel-spraying
opening (38) through which a liquid fuel is radially sprayed.
10. A fuel-burning apparatus as claimed in claim 9, wherein the
plurality of outer primary air-ejection openings (24) of the outer
primary air-ejection pipe (23) and the plurality of inner primary
air-ejection openings (28) of the inner primary air-ejection pipe
(27) are respectively arranged on outer and inner concentric
circumferences between which the annular ejection opening (26) of
the powder fuel-ejection pipe (25) is located, and the inner
primary air-ejection openings (28) are positioned apart from
straight lines extending through center points of the outer primary
air-ejection openings (24) and the center point of the concentric
circumferences.
11. A method of burning a fuel by using the fuel-burning apparatus
as claimed in claim 1, comprising ejecting at least one member
selected from powder fuels and liquid fuels through the
fuel-ejection means; and ejecting primary air through the outer and
inner primary air-ejection openings in the same direction as the
fuel-ejection direction, to form outer and inner primary
air-ejection streams between which the fuel-ejection stream is
interposed.
12. A method of burning a powder fuel by using the fuel burning
apparatus as claimed in claim 2 or 3, comprising ejecting a powder
fuel together with the powder fuel-conveying air through the
annular fuel ejection opening; and ejecting primary air through the
outer and inner primary air-ejection openings in the same direction
as that of the powder fuel-ejection stream, to form outer and inner
primary air-ejection straight streams between which the powder
fuel-ejection stream is interposed.
13. The fuel-burning method as claimed in claim 12, wherein when
the powder fuel is burnt in a rotary kiln, high temperature
secondary air streams are introduced from a product-cooling system
arranged downstream from the rotary kiln into the rotary kiln; and
the introduced high temperature secondary air is mixed into the
combustion flame of the powder fuel.
14. The fuel-burning method as claimed in claim 12, wherein the
powder fuel is ejected at an ejection velocity of 30 to 50 m/sec
through the annular fuel-ejection opening, and the outer and inner
primary air-ejection straight streams are ejected at an ejection
velocity of 200 to 300 m/sec through the air-ejection openings.
15. The fuel-burning method as claimed in claim 12, wherein the
total amount of the air ejected through the powder fuel-ejection
annular opening and the outer and inner primary air-ejection
openings is controlled to within 8 to 15% based on the theoretical
combustion air amount.
16. A fuel-burning method using the fuel-burning apparatus as
claimed in any of claims 4 to 8, comprising radially spraying a
liquid fuel through the liquid fuel-spraying openings; ejecting
primary air through the outer primary air ejection openings and the
inner primary air-ejection openings in a direction in parallel to
the center axis direction of the liquid fuel-spraying openings,
whereby the sprayed liquid fuel streams are mixed with the outer
and inner primary air-ejection straight streams, and are burnt in
the, mixed streams.
17. The fuel-burning method as claimed in claim 16, wherein the
liquid fuel is selected from liquid state fuels and slurry fuels
containing a combustible powder.
18. The fuel-burning method as claimed in claim 16, wherein, when
the liquid fuel is burnt in a rotary kiln, high temperature
secondary air is introduced from a product-cooling system arranged
downstream from the rotary kiln into the rotary kiln, and the
introduced high temperature secondary air is mixed into the
combustion flame of the liquid fuel.
19. The fuel-burning method as claimed in claim 16, wherein the
outer and inner primary air-ejection straight streams are ejected
at an ejection velocity of 200 to 300 m/sec through the outer and
inner ejection openings, and the size of the liquid fuel droplets
sprayed through the liquid fuel-spraying openings is controlled to
a level of 10 to 300 .mu.m.
20. The fuel-burning method as claimed in claim 16, wherein the
total amount of the air ejected through the liquid fuel-spraying
openings and the outer and inner primary air-ejection openings is
controlled to within 5 to 10% based on the theoretical combustion
air amount.
21. A method of burning a fuel by using the fuel-burning apparatus
as claimed in claim 9 or 10, wherein a powder fuel is ejected
together with powder fuel-conveying air through the annular
fuel-ejection opening; primary air is ejected through the plurality
of outer and inner primary air-ejection openings in the same
direction as that of the powder fuel-ejection stream, to form outer
and inner primary air ejection straight streams between which
streams the powder fuel ejection streams are interposed; a liquid
fuel is radially sprayed through the liquid fuel-spraying openings
to mix it into the primary air streams; and the powder fuel and the
liquid fuel are mix-burnt.
22. The fuel-burning method as claimed in claim 21, wherein the
liquid fuel is selected from liquid state fuels and slurry fuels
containing a combustible powder.
23. The fuel-burning method as claimed in claim 21, wherein, when
the powder fuel and the liquid fuel are burnt; together in a rotary
kiln, high temperature secondary air is introduced from a
product-cooling system arranged downstream from the rotary kiln
into the rotary kiln, and the introduced high temperature secondary
air is mixed into the combustion flame of the powder fuel and the
liquid fuel.
24. The fuel-burning method as claim 21, wherein the powder fuel is
ejected at an ejection velocity of 30 to 50 m/sec through the
annular fuel-ejection opening; the outer and inner primary air
ejection straight streams are ejected at an ejection velocity of
200 to 300 m/sec through the outer and inner ejection openings; and
the size of the liquid fuel droplets sprayed through the liquid
fuel-spraying openings is controlled to within 10 to 300 .mu.m.
25. The fuel-burning method as claimed in claim 21, wherein the
total amount of air ejected through the annular powder
fuel-ejection opening and the outer and inner primary air ejection
openings is controlled to within 8 to 15% based on the theoretical
combustion air amount.
Description
TECHNICAL FIELD
[0001] The present invention relates to an apparatus and method of
burning at least one fuel selected from powder fuels and liquid
fuels. More particularly, the present invention relates to an
apparatus and method of burning in, for example, a rotary kiln
usable for producing a cement clinker, magnesia clinker or lime, a
powder fuel, for example, a solid powder fuel such as a fine coal
powder or coke powder and a powder fuel containing a combustible
waste such as plastic powder, garbage powder, wood chips and
chaffs; or a liquid fuel, for example, a liquid state fuel such as
a heavy oil or waste oil, and a slurry fuel containing a
combustible powder such as a coal powder or coke powder, or a
powder fuel and a liquid fuel.
BACKGROUND ART
[0002] When a powder fuel such as a fine coal powder is burnt, a
cylinder type burning apparatus for the fine coal powder as
disclosed in Japanese Examined Patent Publication No. 57-35368 can
be used. In the burning apparatus, a plurality of inner primary
air-ejection openings are arranged in the center portion of the
apparatus, a plurality (4 to 8) of fine coal powder-ejection
openings for ejecting a mixture of the fine coal powder and air for
conveying the coal powder are arranged around the inner primary
air-ejection openings and are separated from each other by
partitions, and further an outer circumferential primary
air-ejection slit having an annular cross-sectional profile is
arranged around the fine coal powder-ejection openings. In this
apparatus, the fine coal powder is ejected in the form of 4 to 8
ejection streams through the ejection openings separated from each
other, and a plurality of inner primary air-ejection straight
streams and an annular primary air ejection straight stream are
ejected in such a manner that the fine coal powder ejection streams
are interposed between the inner primary air-ejection streams and
the annular primary air ejection stream. Since the flow speed of
the fine coal powder ejection streams is lower than that of the
inner and outer primary air ejection straight streams, the fine
coal powder-ejection streams are accelerated by the inner and outer
primary air-ejection straight streams and the fine coal powder is
blown away far. During the above-mentioned ejection, high
temperature secondary air is introduced from a product-cooling
apparatus arranged downstream of the burning chamber into the
burning chamber, passes through gaps of the outer primary
air-ejection straight stream, enters inside of the outer primary
air-ejection straight stream, and is sucked and diffused into the
fine coal powder-ejection streams, to burn the fine coal
powder.
[0003] Also, the burner for burning a fine particulate solid fuel
as disclosed in Japanese Examined Patent Publication No. 2-22,289
is provided with a plurality of inner primary air ejection openings
arranged in an annular form in the center portion of the burner and
separated from each other through partitions, a plurality of fine
particulate solid fuel/conveying air-ejection openings arranged in
an annular form around the inner primary air-ejection openings, and
outer primary air-ejection opening formed in an annular form around
the above-mentioned fine particulate solid fuel/conveying
air-ejection openings. In the burner, the flow resistances of the
fine particulate solid fuel at the ejection end surfaces are made
different from each other, and the distribution density of the fine
particulate solid fuel is made uneven, to thereby increase the
combustion speed and form a short flame.
[0004] Where a powder fuel and primary air are ejected, and high
temperature secondary air is mixed into the ejected powder fuel and
primary air streams to burn the powder fuel, generally, the
combustion of the powder fuel is effected by the total primary air
amount and the secondary air in an amount corresponding to the
difference between the theoretical combustion air amount and the
total primary air amount. In this case, the temperature of the
primary air is 60 to 80.degree. C. and the temperature of the
secondary air is 800 to 1,000.degree. C. Therefore, the merits of
the combustion depend on the primary air ratio (which refers to a
ratio of the total primary air amount to the theoretical combustion
air amount), and the lower the primary air ratio, the better the
combustion.
[0005] However, when the primary air ratio is decreased to promote
the combustion, the flow speed of the primary air ejection streams
is decreased accordingly, the mixing of the secondary air into the
combustion mixture becomes insufficient, and thus the
above-mentioned decreases causes a disadvantage in that the burning
velocity of the powder fuel decreases, the fire point temperature
decreases, and incomplete combustion of the fine particulate coal
occurs. For these reasons, in the conventional apparatus and method
for burning the powder fuel, the primary air ratio is generally,
about 20 to 25% and it is difficult to practically use a primary
air ratio lower than the above-mentioned level.
[0006] Also, in the conventional apparatus and method of burning
the powder fuel, it is possible, to a certain extent to adjust the
position of fire point by controlling the ratio in flow speed of
the inner primary air-ejection straight streams to the inner
primary air-ejection turning streams. However, in practice, the
above-mentioned control of one burner is difficult. It is necessary
to change the design of the inner primary air straight
stream-ejection openings and the inner primary air turning
stream-ejection opening, in response to the performance of the
rotary kiln. Also, in this case, when the inner primary straight
air streams are too strong, the resultant burning flame is in the
form of a narrow angle long flame, the fire point temperature is
insufficient. Also, when the inner primary air turning streams are
too strong, the resultant burning flame is in the form of a wide
angle short flame. In this case, while the fire point temperature
is high, the angle of the flame is too wide and thus the furnace
wall is greatly damaged. In a worst case, the furnace wall is
damaged.
[0007] Also, when a liquid fuel is used, in an apparatus and method
for burning a liquid fuel in which the liquid fuel is sprayed into
a combustion furnace, the sprayed liquid fuel is mixed with primary
air, and further with high temperature secondary air, and is burnt.
In this case, the combustion of a combustible substance in the
liquid fuel is effected in response to the total primary air amount
mixed with the liquid fuel and to the secondary air amount
corresponding to the difference between the theoretical combustion
air amount and the total primary air amount. Usually, the
temperature of the primary air is 60 to 80.degree. C. and the
temperature of the secondary air is 800 to 1,000.degree. C.
Therefore, the merits of the combustion vary in response to the
primary air ratio (which refers to a ratio of the total primary air
amount to the theoretical combustion air amount. The smaller the
primary air ratio, the higher the temperature of air used for the
combustion, and as a result, the burning temperature increases and
the fire point temperature rises, and thus good burning occurs.
[0008] However, when the primary air amount is decreased to make
the burning conditions better, disadvantages such as the primary
air-ejection stream velocity decreases, the mixing of secondary air
become insufficient, the fire point temperature decreases and the
liquid fuel is incompletely burnt, occur. For these reasons, when C
heavy oil is used as a fuel in the conventional apparatus and
method of burning the liquid fuel, the primary air ratio is
controlled to about 12 to 15%. When the primary air ratio is
further decreased below the above-mentioned level, good combustion
of the liquid fuel is difficult in practice.
[0009] In the conventional apparatus and method of burning the
liquid fuel, it is difficult to adjust the position of the fire
point by controlling the flow velocity ratio of the liquid fuel
streams sprayed into a combustion furnace to the primary
air-ejection streams concurrently formed with the liquid fuel
streams. Therefore, the combustion flame formed in the combustion
furnace is in a narrow angle long flame form wherein the fire point
temperature may not be sufficiently high, or in a wide angle short
flame form in which the fire point temperature is sufficiently
high, while the flame spreads too widely and thus the furnace wall
is greatly damaged. In a worst case, the furnace wall is
damaged.
[0010] Further, where a powder fuel and a liquid fuel are employed
together, an apparatus and method for burning the powder fuel and
the liquid fuel is known. In the apparatus and method, the powder
fuel and the liquid fuel are ejected together with primary air and
are further mixed with high temperature secondary air. In this
case, generally, the combustion of these fuels is effected in
response to the total primary air amount and the secondary air in
an amount corresponding to the difference between the theoretical
combustion air amount and the total primary air amount. In this
combustion, the temperature of the primary air is 60 to 80.degree.
C., and the temperature of the secondary air is 800 to
1,000.degree. C., and thus the merits of the combustion vary
depending on the primary air ratio (which refers to a ratio of the
total primary air amount to the theoretical combustion air amount),
the lower the primary air ratio, the higher the temperature of air
used for the combustion, and as a result, the burning velocity
increases, the fire point temperature becomes high, and good
combustion occurs.
[0011] However, when the primary air ratio is decreased to make the
combustion conditions better, disadvantages such as the ejection
stream velocity decreases, and thus the mixing of the secondary air
becomes insufficient, the burning velocity of the powder fuel and
the liquid fuel becomes low, the fire point temperature decreases
and the fuels are incompletely burnt, occur. For these reasons, in
the conventional apparatus and method of mix-burning the fuels, the
primary air ratio is usually about 20 to 25%, and it is practically
difficult to carry out the mix-burning in a reduced primary air
ratio at an increased burning velocity and at an increased fire
point temperature. Also, in the conventional mix-burning apparatus
and method, it is possible, to a certain extent, to adjust the
position of the fire point by controlling the flow velocity ratio
of the inner primary air straight streams and the inner primary air
turning streams formed together with the straight streams. In
practice, the above-mentioned control of one burner is difficult,
and thus it is necessary to change the design of the inner primary
air straight stream-ejection openings and the inner primary air
turning stream-ejection opening, in response to the properties of
the rotary kiln. In this case, when the inner primary air straight
streams become too strong, the resultant combustion flame is in a
narrow angle long flame form in which the fire point temperature is
insufficiently low. When the inner primary air turning streams
become too strong, the resultant combustion flame is a wide angle
short flame in which the fire point temperature is sufficiently
high and the flame becomes too wide, and thus the furnace wall is
greatly damaged. In a worst case, the furnace wall is damaged.
[0012] In view of the conventional burning apparatuses and methods
as mentioned above, there is a strong demand for an apparatus and
method capable of forming a combustion flame in a narrow angle
short flame form, of sufficiently rising the fire point temperature
by using a powder fuel or a liquid fuel or using a powder fuel
together with a liquid fuel, and of obtaining good combustion
without damaging a furnace wall.
DISCLOSURE OF THE INVENTION
[0013] An object of the present invention is to provide an
apparatus and method of burning a fuel which is capable of forming
a burning flame in a narrow angle short flame form having a
sufficiently high fire point temperature, by using, for example, a
powder fuel or a liquid fuel or using a powder fuel together with a
liquid fuel, while damage to the combustion furnace wall is
prevented or reduced.
[0014] Another object of the present invention is to provide an
apparatus and method of burning a fuel, which are capable of
rapidly burning a fuel, for example a powder fuel or a liquid fuel
or a powder fuel and a liquid fuel with a high efficiency and which
do not cause the burning furnace wall to be excessively heated.
[0015] The fuel-burning apparatus and method of the present
invention enable a cheap fuel, for example, a coal powder or coke
powder which contains volatile components in a very small content
and thus is considered to be unusable, to be used. Also, the
fuel-burning apparatus and method of the present invention enables
not only a liquid fuel such as heavy oil but also a slurry of cheap
fuel such as a coal powder or cake powder to be used and a
reduction in fuel cost to be possible.
[0016] The fuel-burning apparatus according to the present
invention comprises a means for ejecting at least one fuel selected
from powder fuels and liquid fuels; an outer primary air-ejection
pipe arranged on the outer side of the fuel ejection means and
having a plurality of outer primary air-ejection openings through
which the primary air is ejected in parallel to the fuel-ejection
direction of the fuel-ejection means; and an inner primary
air-ejection pipe arranged on the inner side of the fuel-ejection
means and having at least one inner primary air ejection opening
through which the primary air is ejected in parallel to the
fuel-ejection direction of the fuel-ejection means.
[0017] The fuel-burning method of the present invention is carried
out by using the above-mentioned fuel-burning apparatus of the
present invention and comprises ejecting at least one member
selected from powder fuels and liquid fuels through the
fuel-ejection means; and ejecting primary air through the outer and
inner primary air-ejection openings in the same direction as the
fuel-ejection direction, to form outer and inner primary
air-ejection streams between which the fuel-ejection stream is
interposed.
[0018] The above-mentioned fuel-ejecting means usable for the
apparatus and method of the present invention may consist of a
powder fuel-ejection pipe having an annular ejection opening
through which a powder fuel is ejected together with a powder
fuel-conveying air, may consist of a plurality of liquid
fuel-spraying pipes having liquid fuel-ejection openings which are
arranged in one and the same circumference and through which a
liquid fuel is radially sprayed, or may consist of a powder
fuel-ejection pipe having an annular ejection opening through which
a powder fuel is ejected together with powder fuel-conveying air
and an additional fuel-ejection means consisting of a liquid
fuel-spraying pipes located on the inner side of the inner primary
air-ejection pipes and having liquid fuel-spraying openings through
which the liquid fuel is radially sprayed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is an explanatory view showing an arrangement of the
burning apparatus of the present invention utilized in a rotary
kiln,
[0020] FIG. 2 is an explanatory side view of a heating furnace
containing an embodiment of the burning apparatus of the present
invention, namely, a powder fuel-burning apparatus,
[0021] FIG. 3(A) in FIG. 3 is an explanatory cross-sectional side
view showing the constitution of an embodiment of the powder
fuel-burning apparatus according to the present invention,
[0022] FIG. 3(B) in FIG. 3 is an explanatory front view of the
apparatus shown in FIG. 3(A),
[0023] FIG. 4 is an explanatory side view of a heating furnace
containing another embodiment of the burning apparatus of the
present invention, namely, a liquid fuel-burning apparatus,
[0024] FIG. 5(A) in FIG. 5 is an explanatory cross-sectional side
view showing the constitution of an embodiment of the liquid
fuel-burning apparatus according to the present invention,
[0025] FIG. 5(B) in FIG. 5 is an explanatory front view of the
apparatus shown in FIG. 5(A),
[0026] FIG. 6 is an explanatory side view of a heating furnace
containing still another embodiment of the apparatus of the present
invention, namely a powder fuel and liquid fuel-burning
apparatus,
[0027] FIG. 7(A) in FIG. 7 is an explanatory cross-sectional side
view showing the constitution of an embodiment of the apparatus of
the present invention for mix-burning a powder fuel and a liquid
fuel,
[0028] FIG. 7(B) in FIG. 7 is an explanatory front view of the
apparatus of FIG. 7(A).
BEST MODE OF CARRYING OUT THE INVENTION
[0029] The burning apparatus and the burning method of the present
invention are advantageously employed in rotary kilns for producing
cement clinker, magnesia clinker or lime. On the present invention
the fuel is at least one member selected from powder fuels and
liquid fuels.
[0030] As shown in FIG. 1, an outlet portion of a rotary kiln 1 is
connected to an inlet portion of a product-cooling apparatus 2, a
fuel-burning apparatus 3 is inserted into the outlet portion of the
rotary kiln 1 and is directed to the inlet portion of the rotary
kiln. A product produced in the rotary kiln 1 is introduced into
the product-cooling system 2, cooled by cooling air 4 introduced
into the cooling apparatus 2, and high temperature air 5 generated
by a heat-exchanging in the cooling system 2 is returned, as
secondary air, into the rotary kiln 1 through the inlet portion of
the cooling apparatus 2 and used for burning a fuel.
[0031] In the present invention, when a powder fuel is used as a
fuel, an explanatory side view of an embodiment of a heating
furnace including a powder fuel-burning apparatus of the present
invention is shown in FIG. 2. In FIG. 2, a cylindrical powder
fuel-burning apparatus 11 is inserted into a heating furnace, for
example, a rotary kiln, through a furnace wall 12. The burning
apparatus 11 comprises a powder fuel-ejection pipe having an
annular ejection opening through which a powder fuel is ejected
together with air for conveying the powder fuel; an inner primary
air-ejection pipe having a plurality of inner primary air-ejection
openings and an outer primary air-ejection pipe having a plurality
of outer primary air-ejection openings, the inner and outer
ejection pipes being respectively arranged along the inner and
outer peripheral surface of the powder fuel-ejection pipe.
[0032] In FIG. 2, in an end portion 13 of the powder fuel-burning
apparatus 11 located outside of the heating furnace, a powder
fuel-feeding pipe 14 for feeding a mixed stream of a powder fuel
and fuel-conveying air is arranged. The feeding pipe 14 is
connected to the above-mentioned powder fuel-ejection pipe. Also,
in the end portion 13, a primary air-feeding pipe 15 is arranged.
The feeding pipe 5 is branched into an outer primary air-feeding
pipe 16 and an inner primary air-feeding pipe 17, the outer primary
air-feeding pipe 16 is connected to the outer primary air-ejection
pipe and the inner primary air-feeding pipe 17 is connected to the
inner primary air-ejection pipe. In the burning apparatus of FIG.
2, two heavy oil or gas burners 18 for ignition are arranged in the
center portion of the apparatus.
[0033] In the burning apparatus of FIG. 2, a powder fuel stream 19
is ejected through an annular ejection opening, a plurality of
inner primary air straight streams 20 are ejected into the inside
of the annular powder fuel stream, and a plurality of outer primary
air straight streams are ejected to the outside of the annular
powder fuel stream, to from a composite stream from the above
mentioned streams, and into the composite stream, high temperature
secondary air streams 5 are mixed to burn the powder fuel.
[0034] The burning apparatus of the present invention for a powder
fuel is characterized by having a powder fuel-ejection pipe having
an annular ejection opening through which a powder fuel is ejected
together with air for conveying the powder fuel, an outer primary
air-ejection pipe arranged along the outer peripheral surface of
the powder fuel-ejection pipe and having a plurality of ejection
openings through which the primary air is ejected in the same
direction as the direction of the powder fuel ejection through the
annular ejection opening, and an inner primary air-ejection pipe
arranged along the inner peripheral surface of the powder
fuel-ejection pipe and having a plurality of ejection openings
through which the primary air is ejected in the same direction as
the direction of the powder fuel ejection through the annular
ejection opening.
[0035] Also, the burning method of the present invention using the
above-mentioned powder fuel-burning apparatus is characterized in
that a powder fuel is ejected together with a powder fuel-conveying
air through the above-mentioned annular ejection opening, and
primary air is ejected through the plurality of outer and inner
primary air-ejection openings in the same direction as the powder
fuel-ejection stream to form outer and inner primary air straight
streams between which the powder fuel-ejection stream is
interposed.
[0036] An explanatory cross-sectional side view and an explanatory
front view of an embodiment of the powder fuel-burning apparatus of
the present invention are shown in FIGS. 3(A) and 3(B). FIG. 3(A)
is an explanatory cross-sectional view of the apparatus shown in
FIG. 3(B) along a bent line X-X'.
[0037] In FIGS. 3(A) and (B), an outer primary air-ejection pipe 23
is arranged inside of an outermost peripheral wall 22 of a
cylindrical burning apparatus 11, and in an ejection end of the
pipe 23, a plurality, for example, 6 to 16, preferably 8 to 14, of
outer primary air-ejection openings 24 are formed. On the inner
side of the outer primary air-ejection pipe 23, a powder
fuel-ejection pipe 25 for ejecting a mixture of a powder fuel with
powder fuel-conveying air is arranged in a concentric circular
relationship to the outer primary air-ejection pipe 23, and in the
end of the pipe 25, an annular powder fuel-ejection opening 26 is
formed. Further, on the inner side of the powder fuel-ejection pipe
25, an inner primary air-ejection pipe 27 is arranged and in an
ejection end of the pipe 27, a plurality, for example, 6 to 16,
preferably 8 to 14, of inner primary air-ejection openings 28 are
formed.
[0038] The above-mentioned annular powder fuel-ejection opening 26,
outer primary air-ejection openings 24 and inner primary
air-ejection openings 28 are formed so that the ejection directions
thereof are the same as each other (or are in parallel to each
other). Accordingly, the powder fuel is ejected through the annular
powder fuel-ejection opening 26 to form a powder fuel stream 19
having an annular cross-sectional profile, the primary air is
ejected through a plurality of outer primary air-ejection openings
24 to form a plurality of outer primary air straight streams. These
streams advance along the outside periphery of the powder fuel
stream 19. Also, the primary air is ejected through a plurality of
inner primary air-ejection openings 28 to form a plurality of inner
primary air straight streams which advance along the inner
periphery of the powder fuel stream having the annular
cross-section. Accordingly, the powder fuel stream is interposed
between the outer and inner primary air straight streams and
thereby is accelerated and diffused. The diffused powder fuel is
mixed with high temperature secondary air passed through gaps
formed between the outer primary air straight streams, and is
burnt. In this procedure, since the outer primary air streams are
ejected into a plurality of divided straight streams at a high
velocity, the high temperature secondary air can easily pass
through the gaps between the plurality of outer primary air
straight streams and can be mixed with the powder fuel stream with
a high efficiency to form a burning flame in a narrow angle short
flame form and to generate a high fire point temperature. Also, in
this burning procedure, the plurality of inner primary air straight
streams effectively serve to promote the diffusion of the powder
fuel and simultaneously to cause an inner circulation flow having a
high temperature to be formed in the burning flame to stabilize the
flame.
[0039] In the burning apparatus of the present invention for the
powder fuel, there is no limitation to the form, dimensions and
arrangement of the inner primary air-ejection openings 28 and the
outer primary air-ejection openings 24. Preferably, the pitch
circle diameter (P.C.D.) of the outer and inner primary
air-ejection openings 24 and 28 is 300 to 800 mm.
[0040] As shown in FIGS. 3(A) and 3(B), preferably, a plurality of
the outer primary air-ejection openings 24 of the outer ejection
pipe 23 and a plurality of inner primary air-ejection openings 28
of the inner ejection pipe 27 are positioned on two concentric
circumferences between which the annular powder fuel-ejection
opening 26 of the ejection pipe 25 is interposed, and the inner
primary air-ejection openings 28 are located apart from straight
lines extending through the centers of the outer primary
air-ejection opening 24 and the center of the concentric circles.
Also, preferably, each of the inner primary air-ejection openings
is positioned between a pair of straight lines 32 and 33 extending
through each of the centers a pair of outer primary air-ejection
openings adjacent to each other and the concentric circle center
31. The above-mentioned arrangement of the primary air-ejection
openings enables air eddies to be positively created on both the
inner and outer peripheral surfaces of the annular powder
fuel-ejection stream. Also, since the inner and outer primary air
streams are constituted from many straight streams, the air eddy
surface area is very large and thus such an advantageous effect
that the powder fuel can be vigorously burnt with a high efficiency
can be obtained. In the above-mentioned burning apparatus of the
present invention, a means for forming conventional inner primary
air turning streams which has been considered necessary to the
conventional burning apparatus is unnecessary. Of course, a means
for forming the inner primary air turning stream as mentioned above
is optionally added to the burning apparatus of the present
invention.
[0041] The burning method of the present invention for the powder
fuel uses the powder fuel-burning apparatus of the present
invention. This method is characterized in that the powder fuel is
ejected together with air for conveying the powder fuel through the
annular ejection opening, and the primary air is ejected through
the outer and inner primary air ejection openings in the same
direction as that of the powder fuel-ejection stream to form outer
and inner primary air straight streams between which the powder
fuel-ejection stream is interposed.
[0042] In the method of the present invention, the powder fuel is
ejected together with the power fuel-conveying air through the
annular ejection opening, and the primary air is ejected through a
plurality of outer and inner primary air-ejection openings in the
same direction as that of the powder fuel-ejection stream to form
the outer and inner primary air straight streams between which the
powder fuel ejection stream is interposed.
[0043] In the method of the present invention, there is no
limitation to the sort of the powder fuel. Generally, solid powder
fuels such as coal powder and coke powder are used. Otherwise,
various wastes, for example, combustible plastic resin powder,
garbage powder, wood waste (wood powder), and chaffs can be
utilized.
[0044] The method of the present invention is very effectively
utilized in the rotary kilns usable for the production of cement
clinkers, magnesia clinkers and lime. In this case, high
temperature secondary air is fed into the rotary kiln through a
product-cooling apparatus arranged downstream from the rotary kiln.
The high temperature secondary air is mixed into a composite
streams comprising the outer primary air straight streams, the
powder fuel stream having an annular cross-section and the inner
primary air straight streams, and the powder fuel can be burnt with
a high efficiency.
[0045] In the method of the present invention using powder fuel,
the powder fuel is ejected through the annular ejection opening at
an ejection velocity of 30 to 50 m/sec, preferably 35 to 45 m/sec,
and simultaneously the outer and inner primary air streams are
ejected through the outer and inner ejection openings at an
ejection velocity of 200 to 300 m/sec, preferably 250 to 300 m/sec,
whereas in the conventional method the primary air-ejection
velocity was about 100 m/sec.
[0046] When the ejection velocities are adjusted as mentioned
above, the primary air ratio which refers to a ratio of the total
amount of the air ejected through the annular powder fuel-ejection
opening and the outer and inner primary air-ejection openings to
the theoretical combustion air amount is reduced from the
conventional value of 20 to 25% to 8 to 15%, preferably 8 to 12%.
Namely, in the burning method of the present invention using the
burning apparatus of the present invention, the ejection stream
momentum can be increased by 25 to 35%, and the accompanying
momentum and the accompanying time of the secondary air can be
maintained at a level similar to those in the conventional method.
The ejection stream momentum and the secondary air-accompanying
momentum can be calculated in accordance with equations (1) and (2)
shown below.
G.sub.o=m.sub.oU.sub.o (1)
G.sub.e=K.multidot.(m.sub.o(X/2R).sup.0.5-1).multidot.V.sub.e
(2)
[0047] In equations (1) and (2),
[0048] G.sub.o: ejection stream momentum
[0049] G.sub.e: secondary air-accompanying momentum
[0050] m.sub.o: ejection stream mass flow rate (kg/sec.)
[0051] U.sub.o: ejection stream velocity (m/sec)
[0052] X: ejection stream axis distance (m)
[0053] R: ejection stream diameter (m)
[0054] V.sub.e: ejection stream suction velocity (m/sec)
[0055] K: constant number
[0056] In the method of the present invention, when the ejection
velocity (U.sub.o) of the primary air is increased from about 100
m/sec for the conventional method to 200 to 300 m/sec to increase
the ejection stream momentum (G.sub.o), this increase in the
ejection velocity causes the secondary air-accompanying momentum
(G.sub.e) to increase in proportion to the ejection stream momentum
(G.sub.o). However, when the secondary air-accompanying momentum
(G.sub.e) and the accompanying time are held in the levels similar
to those in the conventional method, since the mixing of flame
ejection stream with air and the combustion in an initial stage are
carried out to the similar extent to the conventional method, the
amount of the primary air can be reduced. In this case, the
reduction in the amount of the primary air can be compensated for
by the high temperature secondary air, and therefore the burning
rate can be enhanced and the burning efficiency can be
improved.
[0057] By utilizing the burning apparatus and method of the present
invention for the powder fuel, a combustion flame in a narrow angle
short flame form can be formed by using the powder fuel, and thus
the swirl number (which is a non-dimensional amount representing
turning intensity as defined by equation (3) shown below) can be
made zero, and a natural ejection stream can be formed. Also, in
the conventional apparatus and method, the content of volatile
substance in the coal usable for the conventional apparatus and
method must be 18% or more. However, by utilizing the apparatus and
method of the present invention, the lower limit of the volatile
substance content of the usable coal can be decreased to about
10%.
SW=G.phi./G.sub.xR (3)
[0058] In equation (3),
[0059] SW: swirl number
[0060] G.cndot.: angular momentum flux in axial direction
[0061] G.sub.x: thrust in axial direction
[0062] R: diameter of burner nozzle
[0063] In the present invention, as a fuel, a liquid fuel can be
used. FIG. 4 shows an explanatory side view of an embodiment of the
heating furnace containing the liquid fuel-burning apparatus of the
present invention.
[0064] In FIG. 4, a cylindrical liquid fuel-burning apparatus 11a
is inserted into a heating furnace, for example, a rotary kiln 1,
through a heating furnace wall 12 of the heating furnace. In this
burning apparatus 11a, a plurality of liquid fuel-spraying pipes
25a having liquid fuel-spraying openings 26a for radially spraying
the liquid fuel are arranged on one and the same circumference, and
an inner primary air-ejection pipe 27 having one or more inner
primary air-ejection opening 28 for ejecting the primary air and an
outer primary air-ejection pipe 23 having a plurality of outer
primary air-ejection openings 24 for ejecting the primary air are
respectively arranged along the inner and outer sides of the
circumference on which the liquid fuel-spraying pipes 25a are
arranged.
[0065] Referring to FIG. 4, a liquid fuel-feeding pipe 14a is
arranged in an end portion 13 of the liquid fuel-burning apparatus
11a located outside of the heating furnace, and connected to the
above-mentioned liquid fuel-spraying pipe. Also, a primary
air-feeding pipe 15 is arranged in the end portion 13. The primary
air-feeding pipe 15 is branched into an outer primary air-feeding
pipe 16 and an inner primary air-feeding pipe 17. The outer primary
air-feeding pipe 16 is connected to the outer primary air-ejection
pipe and the inner primary air-feeding pipe is connected to the
inner primary air-ejection pipe. In the burning apparatus 11a of
FIG. 4, one or more heavy oil burners or gas burners (not shown in
FIG. 4) for ignition may be arranged.
[0066] In the burning apparatus 11a of FIG. 4, liquid fuel streams
19a are radially sprayed through spraying openings, inner primary
air straight streams 20 are ejected inside of the liquid fuel
streams 19a, and outer primary air straight streams 21 are ejected
outside of the liquid fuel streams 19a, to thereby form a composite
stream from these streams, and high temperature secondary air 5 is
mixed into the composite stream to burn the liquid fuel.
[0067] The liquid fuel-burning apparatus of the present invention
is characterized by comprising a plurality of liquid fuel-spraying
pipes arranged on one and the same circumference and having liquid
fuel-spraying openings through which a liquid fuel is radially
sprayed; an outer primary air-ejection pipe having a plurality of
outer primary air-ejection openings which are arranged on the outer
side of the liquid fuel-spraying openings and through which the
primary air is ejected in parallel to the center axis direction of
the liquid fuel-spraying openings; and an inner primary
air-ejection pipe having at least one inner primary air-ejection
opening which is arranged on the inner side of the liquid
fuel-spraying openings and through which the primary air is ejected
in parallel to the center axis direction of the liquid
fuel-spraying openings.
[0068] Also, the liquid fuel-burning method of the present
invention uses the liquid fuel-burning apparatus of the present
invention and is characterized in that a liquid fuel is radially
sprayed through the liquid fuel-spraying openings, and the primary
air is ejected through the outer primary air ejection openings and
the inner primary air ejection openings in parallel to the center
axis direction of the liquid fuel-spraying openings, thereby to mix
the sprayed liquid fuel streams with the outer and inner primary
air straight streams and to burn the sprayed liquid fuel.
[0069] FIGS. 5(A) and 5(B) respectively show an explanatory
cross-sectional side view and an explanatory front view of an
embodiment of the liquid fuel-burning apparatus. FIG. 5(A) shows an
explanatory cross-sectional side view of the apparatus of FIG. 5(B)
along a bent line Y-Y'.
[0070] In FIGS. 5(A) and 5(B), an outer primary air-ejection pipe
23 is arranged inside of the outermost peripheral wall 22 of a
cylindrical liquid fuel-burning apparatus 3, and a plurality, for
example 5 to 20, preferably 8 to 18, of outer primary air-ejection
opening 24 are formed in the ejection end of the ejection pipe 23.
On the inner side of the outer primary air-ejection pipe 23, one or
more, for example, 1 to 6, preferably 1 to 4, liquid fuel-spraying
pipes 25a for spraying a liquid fuel are arranged. In an end of
each of the spraying pipes, a liquid fuel-spraying opening 26a for
radially spraying the liquid fuel is formed. One or more liquid
fuel-spraying openings 26a are arranged on one and the same
circumference around a center 31, and center axes of the liquid
fuel spraying openings 26a are parallel to each other. Further, an
inner primary air-ejection pipe 27 is arranged on the inner side of
the liquid fuel-spraying pipe 25a, and in an end of the spraying
pipe, one or more, for example, 1 to 12, preferably 1 to 8, inner
primary air-ejection opening 28 are formed.
[0071] The above-mentioned outer primary air-ejection openings 24
and inner primary air-ejection openings 28 are formed in a manner
such that the ejection directions of the openings are the same as
(parallel to) the center axis directions of the above-mentioned
liquid fuel-spraying openings 26a. The liquid fuel is sprayed
through each of the liquid fuel-spraying openings 26a to form a
radial stream, and the primary air is ejected through the outer
primary air-ejection openings 24 located outside of the spraying
openings to form outer primary air straight streams which advance
outside of the liquid fuel streams and are mixed with the sprayed
liquid fuel. Also, the primary air is ejected through one or more
inner primary air-ejection openings 28 to form inner primary air
straight streams 20 which advance inside of the liquid fuel streams
and are mixed with the sprayed liquid fuel. Accordingly, the liquid
fuel streams are mixed with the outer and inner primary air
straight streams respectively flowing outside and inside of the
liquid fuel streams, and accelerated and diffused by the primary
air streams, and are further mixed with the high temperature
secondary air passed through the outer primary air straight
streams, and are burnt. In this method, the outer primary air
stream is ejected at a high velocity to form a straight stream,
preferably a plurality of divided straight streams. Therefore, the
high temperature secondary air can easily pass between the
plurality of outer primary air straight streams and can be mixed
with the liquid fuel streams, with high efficiency, to form a
combustion flame in the narrow angle short flame form and having a
high fire point temperature. Also, when a plurality of inner
primary air-ejection openings 24 are formed, the resultant inner
primary air straight streams advantageously serve to promote the
diffusion of the liquid fuel streams and simultaneously to form
high temperature inner circulating streams in the combustion flame
so that the flame is stabilized.
[0072] In the liquid fuel-burning apparatus of the present
invention, there is no limitation on the form and dimensions of the
inner primary air-ejection openings 28 and the outer primary
air-ejection openings 24. Usually, the pitch circle diameters
(P.C.D.) of the outer and inner primary air-ejection openings 24
and 28 are preferably 300 to 800 mm.
[0073] Also, each of the liquid fuel-spraying pipes 25a having the
liquid fuel-spraying openings forms a circular cone-shaped spraying
nozzle expanding outward. For example, when C-heavy oil is used as
a liquid fuel, preferably the C-heavy oil is heated to a
temperature of 85 to 100.degree. C. to reduce the viscosity
resistance thereof to 20 to 30 cst, and is placed under a pressure
of 30 to 40 kg/cm.sup.2 G.
[0074] As shown in FIGS. 5(A) and 5(B), where the inner primary
air-ejection pipe 27 has a plurality of inner primary air-ejection
openings 28, it is preferable that the plurality of inner primary
air-ejection openings 28 and the plurality of outer primary
air-ejection openings 24 be located on concentric circumferences
around the center point 31 of the circumference on which the
plurality of liquid fuel-spraying-openings 26a are arranged. Also,
where the inner primary air-ejection pipe 27 has only one inner
primary air-ejection opening 28, it is preferable that the center
point of the one inner primary air-ejection opening be identical to
the center point 31 of the circumference on which the plurality of
liquid fuel-spraying openings 26a are arranged, and that the
plurality of outer primary air-ejection openings 24 be located on a
circumference concentric with the circumference around the center
point 31 on which circumference the plurality of liquid
fuel-spraying openings 26a are arranged. The above-mentioned
arrangement of the primary air-ejection openings 24 and 28 allows
eddies to be positively created on both the outer and inner sides
of the liquid fuel streams, and the primary air to be uniformly
mixed with the liquid fuel. Preferably, both the outer and inner
primary air streams are respectively formed into numerous straight
streams. In this case, it is possible that the eddy surface area
becomes large and thus the liquid fuel can be vigorously burnt with
a high efficiency. In the liquid fuel-burning apparatus of the
present invention, the conventional means for forming inner primary
air-turning streams which means is necessary to the conventional
apparatus is unnecessary. However, the conventional means for
forming the inner primary air-turning stream can be optionally
added to the burning apparatus of the present invention.
[0075] The liquid fuel-burning method of the present invention uses
the above-mentioned liquid fuel-burning apparatus of the present
invention. In this method, the liquid fuel is radially sprayed
through the liquid fuel-spraying openings, and the primary air is
ejected through the outer and inner primary air-ejection openings
in parallel to the center axis direction of the liquid
fuel-spraying pipes, to thereby mix the sprayed liquid fuel streams
with the outer and inner primary air streams and to burn the liquid
fuel.
[0076] In the method of the present invention, there is no
limitation to the sort of the liquid fuel. Usually, the liquid fuel
can be selected from liquid state fuels, for example, heavy oils,
waste oils and regenerated oils and slurry fuels containing a
combustible powder such as coal powder, coke powder and combustible
plastic powder, or a waste powder such as garbage, waste wood piece
(wood powder), and chaff. The medium for the slurry may be a liquid
state fuel (for example, heavy oil, waste oil or regenerated oil)
or water.
[0077] The method of the present invention can be very
advantageously utilized in a rotary kiln usable for the production
of cement clinker, magnesia clinker and lime. In this utilization,
high temperature secondary air is fed through a product-cooling
apparatus arranged downstream to the rotary kiln into the rotary
kiln. The high temperature secondary air is mixed into a composite
stream formed from the outer primary air straight streams, the
liquid fuel-spraying streams and the inner primary air straight
streams, to burn the liquid fuel with high efficiency.
[0078] In the process of the present invention, the spraying
procedure of the liquid fuel through the liquid fuel-spraying
openings 26a is controlled to such an extent that the sprayed
liquid fuel droplets have a size of preferably 10 to 300 .mu.m,
more preferably 10 to 150 .mu.m. The droplet size is established in
response to the sort and viscosity of the liquid fuel and the form
and dimensions of the spraying opening. The desired droplet size
can be obtained by controlling the pressure applied to the liquid
fuel and the form and dimensions of the spraying opening.
[0079] The outer and inner primary air is ejected at an ejection
velocity of preferably 200 to 300 m/sec, more preferably 250 to 300
m/sec at each ejection opening, whereas the conventional ejection
velocity was about 100 m/sec. Under the above-mentioned conditions,
the primary air ratio (which refers to a ratio of the total amount
of air ejected through the liquid fuel-spraying openings and the
outer and inner primary air-ejection openings to the theoretical
combustion air amount) can be reduced from the conventional value
of 12 to 15% to 5 to 10%, preferably 6 to 9%. Namely, in the
burning method using the burning apparatus of the present
invention, the spraying stream momentum of the liquid fuel can be
enhanced by 25 to 35% based on the conventional momentum, while the
secondary air-accompanying momentum and accompanying time are held
at levels similar to those of the conventional method.
[0080] The spraying stream momentum of the liquid fuel and the
accompanying momentum of the secondary air can be calculated in
accordance with equations (1) and (2) as mentioned above, in the
same manner as for the powder fuel.
[0081] In the method of the present invention, when the ejection
velocity (U.sub.o) of the primary air is increased from the
conventional method value of about 100 m/sec to 200 to 300 m/sec,
to increase the spraying stream momentum (G.sub.o), this increase
causes the second air-accompanying momentum (G.sub.e) to be
increased in proportion to the spraying stream momentum (G.sub.o)
In this case, when the secondary air-accompanying momentum
(G.sub.e) and the accompanying time are held at levels similar to
those in the conventional method, the mixing of the flame stream
with air and the initial stage combustion are carried out to an
extent similar to those in the conventional method, and thus the
amount of the primary air can be reduced. In this case, since the
reduction in the amount of the primary air can be compensated for
by the high temperature secondary air, the combustion velocity is
enhanced and the combustion efficiency is improved.
[0082] By utilizing the liquid fuel-burning apparatus and method of
the present invention, the combustion flame in the narrow angle
short flame form can be generated in similar manner to that using
the powder fuel. Therefore, the swirl number (which is a
non-dimensional amount showing a turning intensity defined by
equation (3) mentioned above) can be made zero and a natural
ejection stream can be formed. Also, in the conventional apparatus
and method, there is a limitation on the sort of liquid fuels
usable. However, by utilizing the apparatus and method of the
present invention, the scope of the usable liquid fuels can be
expanded.
[0083] In the present invention, a powder fuel can be used together
with the liquid fuel. FIG. 6 shows an explanatory side view of an
embodiment of the heating furnace containing a mix-burning
apparatus of the present invention as mentioned above.
[0084] Referring to FIG. 6, a cylindrical mix-burning apparatus 11b
for a powder fuel and a liquid fuel is inserted into a heating
furnace, for example, a rotary kiln, through a wall 12 of the
heating furnace. This mix-burning apparatus, which will be
explained by referring to FIG. 7 hereinafter, comprises a powder
fuel-ejection pipe 25 having an annular ejection opening 26 for
ejecting the powder fuel together with air for conveying the powder
fuel; an inner primary air-ejection pipe 27 having a plurality of
inner primary air-ejection openings 28 for ejecting primary air and
arranged along the inner periphery of the powder fuel-ejection pipe
25; an outer primary air-ejection pipe 23 having a plurality of
outer primary air-ejection openings 24 for ejecting primary air and
arranged along the outer periphery of the powder fuel-ejection pipe
25; and a liquid fuel-spraying pipe 39 having liquid fuel-spraying
openings 38 for radially spraying a liquid fuel and arranged in the
inside of the inner primary air-ejection pipe 24.
[0085] In FIG. 6, in an end portion 13 of the mix-burning apparatus
11b located outside of the heating furnace, a powder fuel-feeding
pipe 14 for feeding a mixed flow of a powder fuel with powder
fuel-conveying air is arranged, and the powder fuel-feeding pipe 14
is connected to the above-mentioned powder fuel-ejection pipe.
Also, in the end portion 13, a primary air-feeding pipe 15 is
arranged, and this feeding pipe is branched into an outer primary
air-feeding pipe 16 and an inner primary air-feeding pipe 17, the
outer primary air-feeding pipe 16 is connected to the outer primary
air-ejection pipe and the inner primary air-feeding pipe 17 is
connected to the inner primary air-ejection pipe.
[0086] In the mix-burning apparatus 11b of FIG. 6, one or more
liquid fuel-feeding pipes 18a are located in the central portion of
the apparatus. Also, in the central portion, one or more heavy oil
burners or gas burners for ignition may be arranged.
[0087] In the mix-burning apparatus of FIG. 6, the powder fuel
stream 19 is ejected through the annular ejection opening, inner
primary air straight streams 20 are ejected into the inside of the
annular powder fuel stream, outer primary air straight streams 21
are ejected to the outside of the annular powder fuel stream, and
radial liquid fuel spraying streams 37 are sprayed into the inside
of the inner primary air straight streams, to thereby form a
composite stream from the above-mentioned streams, and high
temperature secondary air 5 is mixed into the composite stream to
burn the powder fuel and the liquid fuel.
[0088] The mix-burning apparatus of the present invention for the
powder fuel and the liquid fuel comprises a powder fuel-ejection
pipe having an annular ejection opening for ejecting a powder fuel
together with powder fuel-conveying air; an outer primary
air-ejection pipe having a plurality of outer primary air-ejection
openings arranged along the outside periphery of the powder
fuel-ejection pipe and capable of ejecting the primary air in the
same direction as the direction of the powder fuel-ejection through
the annular opening; an inner primary air-ejection pipe having a
plurality of inner primary air-ejection openings arranged along the
inside periphery of the powder fuel-ejection pipe and capable of
ejecting the primary air in the same direction as the direction of
the powder fuel-ejection through the annular ejection opening; and
a liquid fuel-spraying pipe having liquid fuel-spraying openings
arranged inside of the inner primary air-ejection pipe and capable
of radially spraying a liquid fuel.
[0089] Also, the mix-burning method of the present invention for
the powder fuel and the liquid fuel uses the above-mentioned
mix-burning apparatus of the present invention for the powder fuel
and the liquid fuel and comprises ejecting a powder fuel together
with air for conveying the powder fuel through the annular ejection
opening; ejecting primary air through the plurality of outer and
inner primary air-ejecting openings in the same direction as the
direction of the powder fuel ejection stream, to form outer and
inner primary air straight streams between which the powder
fuel-ejection stream is interposed; and radially spraying a liquid
fuel through the liquid fuel-spraying openings, thereby to mix the
powder fuel and the liquid fuel with the primary air streams and to
burn the powder fuel and the liquid fuel.
[0090] FIGS. 7(A) and 7(B) respectively show an explanatory
cross-sectional side view and an explanatory front view of an
embodiment of the mix-burning apparatus of the present invention
for the powder fuel and the liquid fuel. FIG. 7(A) is an
explanatory cross-sectional side view of the apparatus shown in
FIG. 7(B) along a bent line Z-Z'.
[0091] Referring to FIGS. 7(A) and 7(B), an outer primary
air-ejection pipe 23 is located inside an outermost peripheral wall
22 of a cylindrical mix-burning apparatus, and in an ejection end
of the ejection pipe 23, a plurality, for example 5 to 20,
preferably 8 to 18, of outer primary air-ejection openings 24 are
located. Inside the outer primary air-ejection pipe 23, a powder
fuel-ejection pipe 25 for ejecting a powder fuel together with air
for conveying the powder fuel is arranged in a concentric circular
relationship to the outer primary air-ejection pipe 23, and in an
end of the powder fuel-ejection pipe, an annular ejection opening
is formed. Further, an inner primary air-ejection pipe 27 is
arranged on the inner side of the powder fuel-ejection pipe 25, and
a plurality, for example, 6 to 16, preferably 8 to 14, of inner
primary air-ejection openings 28 are formed in an end of the inner
primary air-ejection pipe 27.
[0092] Inside the inner primary air-ejection pipe 27, one or more
(2 in FIGS. 7(A) and 7(B)) liquid fuel-spraying pipes 39 are
arranged, and a liquid fuel-spraying opening 38 for radially
spraying a liquid fuel is formed in an end of each of spraying pipe
39. In the liquid fuel spraying opening 38, as shown, for example,
in FIG. 7(A), a circular cone-shaped spraying nozzle space
expanding outward is formed, and the liquid fuel is sprayed
radially through the liquid fuel-spraying opening 38 and mixed with
the primary air.
[0093] The above-mentioned annular ejection opening 26, the outer
primary air-ejection openings 24 and the inner primary air-ejection
opening 28 are formed in such a manner that the ejection directions
through the openings are the same as (parallel to) each other.
Therefore, the powder fuel is ejected through the annular ejection
opening 26, to form a powder fuel stream 19 having an annular
cross-section and the liquid fuel fed through the liquid
fuel-ejection pipes 39 is radially sprayed through the liquid
fuel-spraying openings. Further, the primary air is ejected through
a plurality of outer primary air-ejection openings 24 to form a
plurality of outer primary air straight streams which advance along
the outer side of the powder fuel stream 19. Also, the primary air
is ejected through a plurality of inner primary air-ejection
openings 28 to form a plurality of inner primary air straight
streams which advance along the inner side of the powder fuel
stream 19 having an annular cross-sectional profile. Accordingly,
the powder fuel stream 19 is interposed between the outer and inner
primary air straight streams and thereby accelerated and diffused,
and mixed with high temperature secondary air passed between the
outer primary air straight streams, and burnt. In this case, since
the outer primary air streams are ejected at a high velocity in the
form of straight streams, preferably a plurality of divided
straight streams, the high temperature secondary air can easily
pass between the plurality of center primary air straight streams
and be mixed with the powder fuel stream 19 and liquid fuel spray
streams with a high efficiency, and thus a combustion flame in the
narrow angle short flame form can be formed and a high fire point
temperature can be generated. Also, in this case, the inner primary
air straight streams contribute to promoting the diffusion of the
powder fuel stream 19 and the liquid fuel spray streams 37, and to
simultaneously forming high temperature inner circulating streams
in the combustion flame to stabilize the flame.
[0094] In the mix-burning apparatus of the present invention, there
is no limitation to the form and dimensions of the inner primary
air-ejection openings 28 and the outer primary air-ejection
openings 24. Usually, the pitch circle diameters (P.C.D.) of the
outer and inner primary air-ejection openings 24 and 28 are
preferably 300 to 800 mm. Also, the liquid fuel-spraying openings
38 of the liquid fuel-spraying pipe 39 form a circular cone-shaped
spray nozzle expanding outward. For example, if C heavy oil is used
as a liquid fuel, preferably the C heavy oil is heated to a
temperature of 80 to 100.degree. C. to reduce the viscosity
resistance of the fuel to 20 to 30 cst and is put under a pressure
of 30 to 40 kg/cm.sup.2G.
[0095] As shown in FIGS. 7(A) and 7(B), preferably the plurality of
outer primary air-ejection openings 24 of the outer primary
air-ejection pipe 23, and the plurality of inner primary
air-ejection openings 28 of the inner primary air-ejection pipe 27
are respectively arranged on outer and inner concentric
circumferences between which the annular opening 26 of the powder
fuel-ejection pipe 25 are interposed. Also, preferably, the inner
primary air-ejection openings 28 are positioned apart from straight
lines extending through the center points of the outer primary air
ejection openings 24 and the center point of the above-mentioned
concentric circumferences. Further, more preferably, each of the
inner primary air-ejection openings 28 is arranged between a pair
of straight lines 32 and 33 extending through each of the center
points of a pair of outer primary air-ejection openings 24 adjacent
to each other and the center point 31 of the above-mentioned
concentric circumferences.
[0096] The above-mentioned arrangement of the primary air-ejection
openings contributes to positively creating eddy streams on both
the outer and inner sides of the annular powder fuel stream.
Preferably both the inner and outer primary air streams consist of
numerous straight streams. In this case, the surface area of the
eddy streams becomes very large and, as an advantageous result, the
powder fuel and the liquid fuel can be vigorously burnt with a high
efficiency. In the above-mentioned mix-burning apparatus of the
present invention, the conventional means for forming inner primary
air-turning streams which are necessary to the conventional
apparatus, is unnecessary. However, the means for forming the inner
primary air-turning streams may be optionally added to the
mix-burning apparatus of the present invention. Also, one or more
ignition burner (heavy oil burner or gas burner) may be arranged in
the center portion of the mix-burning apparatus of the present
invention, if necessary.
[0097] The mix-burning method of the present invention for the
powder fuel and the liquid fuel uses the powder fuel and liquid
fuel-mix-burning apparatus of the present invention. In this
method, the powder fuel is ejected together with air for conveying
the powder fuel through an annular ejection opening, the primary
air is ejected through the plurality of outer and inner primary
air-ejection openings in the same direction as that of the powder
fuel-ejection stream, to form outer and inner primary air straight
streams between which the powder fuel-ejection stream is
interposed, and further the liquid fuel is radially sprayed through
the liquid fuel-spraying openings, and is mixed with the primary
air, to thereby mix-burn the powder fuel and the liquid fuel.
[0098] In the mix-burning method of the present invention, there is
no limitation to the powder fuel. Usually, the powder fuel
comprises a solid powder fuel, for example, a coal powder or a coke
powder. Otherwise, as a powder fuel, a waste material, for example,
combustible plastic powder, waste garbage, waste wood pieces (wood
powder) and chaff can be employed.
[0099] There is no limitation to the sort of the liquid fuel usable
for the mix-burning method of the present invention. Usual liquid
state fuels, for example, heavy oils, wasted oils and regenerated
oils and combustible powder-containing slurry fuels, for example,
slurries containing coal powder, coke powder, combustible plastic
powder, and combustible rubber powder, are preferably employed.
Also, as a medium for the slurry, water and liquid state fuels
(heavy oils, waste oils and regenerated oils may be utilized.
[0100] The mix-burning method of the present invention can be very
advantageously utilized in the rotary kiln for the production of
cement clinker, magnesia clinker and lime. In this case, high
temperature secondary air is fed from a product-cooling apparatus
arranged downstream from the rotary kiln into the rotary kiln. The
high temperature secondary air is introduced into and mixed with a
composite stream formed from the outer primary air straight
streams, the powder fuel stream having an annular cross-section,
the inner primary air straight stream and radially expanding liquid
fuel spray streams, and the powder fuel and the liquid fuel can be
burnt with a high efficiency.
[0101] In the mix-burning method of the present invention, the
powder fuel is preferably ejected through the annular ejection
opening 26 at an ejection velocity of 30 to 50 m/sec, more
preferably 35 to 45 m/sec, and simultaneously the outer primary air
and the inner primary air are preferably ejected respectively
through the outer and inner ejection openings at an ejection
velocity of 200 to 300 m/sec, more preferably 250 to 300 m/sec,
whereas the conventional primary air ejection velocity is about 100
m/sec. Also, in the mix-burning method of the present invention,
the size of droplets of the liquid fuel sprayed through the
spraying openings is preferably controlled to 10 to 300 .mu.m, more
preferably 10 to 150 .mu.m. By carrying out the powder fuel
ejection, the primary air ejection and the liquid fuel spray in the
above-mentioned manner, the primary air ratio which refers to a
ratio of the total amount of the primary air ejected through the
annular powder fuel-ejection opening and the outer and inner
primary air-ejection openings to the theoretical combustion air
amount can be reduced from the conventional value of 20 to 25% to 8
to 15%, preferably 8 to 12%, and the reduction in the primary air
amount is compensated by an increase in the high temperature
secondary air amount, and thus the burning can be effected to an
extent such that the combustion velocity increases, the combustion
flame is formed in the narrow angle short flame form, and the fire
point temperature can be satisfactorily increased, while no damage
is given to the furnace wall. Namely, in the burning method using
the mix-burning apparatus of the present invention, the ejection
stream momentum can be increased by 25 to 35% based on that in the
conventional method, while the secondary air-accompanying momentum
and the accompanying time are held in the similar levels to those
in the conventional method.
[0102] In the present invention, the adjustment of the droplet size
of the sprayed liquid fuel to 10 to 300 .mu.m can be effected by
appropriately controlling the spraying pressure applied to the
liquid fuel, and the form and dimensions of the spraying openings
in response to the type and viscosity of the liquid fuel, the
spraying rate and the spraying temperature. The droplet size of the
sprayed liquid fuel can be calculated in accordance with the
equation shown below. 1 d _ = 47 ( D V e ) ( g e g ) 0.25 [ 1 +
3.31 e ( e e D ) 0.5 ] dmax=(2-2.5){overscore (d)}
[0103]
[0104] d: Average droplet size [m]
[0105] V.sub.e: Fuel-spraying velocity [m/s]
[0106] .delta..sub.g: Ambient gas density [kg/m.sup.3]
[0107] .delta..sub.e: Fuel density [kg/m.sup.3]
[0108] .sigma..sub.e: Surface tension of fuel [N/m]
[0109] D: Diameter of spraying opening [m]
[0110] dmax: Largest droplet size [m]
[0111] .mu..sub.e: Viscosity of fuel [Pa.cndot.S]
[0112] The ejection stream momentum and the accompanying momentum
of the secondary air can be calculated in accordance with the
afore-mentioned equations (1) and (2).
[0113] In the mix-burning method of the present invention, the
ejection velocity (U.sub.o) of the primary air is increased from
the conventional value of about 100 m/sec to a level of 200 to 300
m/sec, to increase the ejection stream momentum (G.sub.o), the
accompanying momentum (G.sub.e) of the secondary air increases in
proportion to the ejection stream momentum (G.sub.o) However, when
the accompanying momentum (G.sub.e) and the accompanying time of
the secondary air are held at the similar levels to those in the
conventional method, the mixing of the flame ejection stream with
air and the combustion in an initial stage are effected in the
similar conditions to those in the conventional method, and
therefore, the amount of the primary air can be reduced. In this
case, the reduction in the primary air amount is compensated by the
high temperature secondary air, and thus the combustion velocity is
enhanced and the combustion efficiency is improved.
[0114] By utilizing the mix-burning apparatus and method of the
present invention, the narrow angle short flame type combustion
flame can be generated, and thus the swirl number (which is a
non-dimensional amount representing a turning intensity defined by
the afore-mentioned equation (3)) can be made zero and the flame
stream can be formed into a natural ejection stream.
EXAMPLES
Example 1 and Comparative Example 1
[0115] In Example 1, a powder fuel-burning apparatus of the present
invention as shown in FIGS. 2, 3(A) and 3(B) is used for a
cement-calcining rotary kiln, and a cement was produced by the
rotary kiln under the conditions shown in Table 1. The results are
shown in Table 1.
[0116] In Comparative Example 1, a cement was produced by using a
conventional coal powder-burning apparatus under the conditions
shown in Table 1. The results are shown in Table 1.
1 TABLE 1 Comparative Example 1 Example 1 Production conditions
Calorific value of coal 6800 6800 (kcal/kg) Fineness of fine coal
powder 10 to 20 10 to 20 (Residue % on 90 .mu.m mesh) Outer primary
air straight 250 to 300 100 to 120 stream velocity (m/sec) Inner
primary air straight 250 to 300 80 to 0 stream velocity (m/sec)
Coal powder stream 30 to 50 30 to 50 velocity (m/sec) Inner primary
air turning None 0 to 80 stream velocity (m/sec) Primary air ratio
11 20 Results Ejection stream momentum 125 to 135 100
ratio.sup.(*).sup..sub.1 Secondary air-accompanying 100 to 110 100
momentum ratio 1.sup.(*).sup..sub.1 Secondary air-accompanying time
90 to 100 100 ratio.sup.(*).sup..sub.1 Swirl number (SW) 0 0.03 to
0.10 Production rate (T/day) 2800 2795 Combustion ratio (kcal/kg)
719 744 Furnace end temperature (.degree. C.) 1040 1090 CO amount
at furnace end (%) Undetected 1 to 2 .sup.(*).sup..sub.1Each value
of Example 1 is a relative value to the value 100 of Comparative
Example 1
[0117] As Table 1 clearly shows, in Example 1, even when the
secondary air-accompanying momentum and accompanying time were held
in the similar levels to those of Comparative Example 1, the
ejection stream momentum could be increased at 25 to 35%, the swirl
number could be decreased, the production rate could be increased,
the combustion ratio could be reduced and the furnace end
temperature could be decreased.
Example 2 and Comparative Example 2
[0118] In Example 2, a liquid fuel-burning apparatus of the present
invention as shown in FIGS. 4, 5(A) and 5(B) is used for a
cement-calcining rotary kiln, and a cement was produced by the
rotary kiln under the conditions shown in Table 2. The results are
shown in Table 2.
[0119] In Comparative Example 2, a cement was produced by using a
conventional heavy oil-burning apparatus under the conditions shown
in Table 2. The results are shown in Table 2.
2 TABLE 2 Comparative Example 1 Example 1 Production conditions
Calorific value of liquid fuel 10,200 10,200 (C heavy oil)
(kcal/kg) Outer primary air straight 250 to 300 100 to 120 stream
velocity (m/sec) Inner primary air straight 250 to 300 80 to 0
stream velocity (m/sec) Droplet size of liquid 150 150 fuel (.mu.m)
Inner primary air turning None 0 to 80 stream velocity (m/sec)
Primary air ratio 7 15 Results Ejection stream momentum 125 to 135
100 ratio.sup.(*).sup..sub.- 1 Secondary air-accompanying 100 to
110 100 momentum ratio.sup.(*).sup..sub.1 Secondary
air-accompanying time 90 to 100 100 ratio.sup.(*).sup..sub.1 Swirl
number (SW) 0 0.03 to 0.10 Production rate (T/day) 2880 2795
Generated calory (kcal/kg) 719 744 CO amount at furnace end (%)
Undetected 1 to 2 .sup.(*).sup..sub.1Based on the value 100 in
Comparative Example 2
[0120] As Table 2 clearly shows, in Example 2, even when the
secondary air-accompanying momentum and accompanying time were held
in the similar levels to those of Comparative Example 2, the
ejection stream momentum could be increased at 25 to 35%, the swirl
number could be decreased, the production rate could be increased,
the combustion ratio could be reduced and the furnace end
temperature could be decreased.
Example 3 and Comparative Example 3
[0121] In Example 3, a mix-burning apparatus of the present
invention as shown in FIGS. 6, 7(A) and 7(B) is used for a
cement-calcining rotary kiln, and a cement was produced by the
rotary kiln under the conditions shown in Table 3. The results are
shown in Table 3.
[0122] In Comparative Example 3, a cement was produced by using a
conventional coal powder and liquid fuel-mix-burning apparatus
under the conditions shown in Table 3. The results are shown in
Table 3.
3 TABLE 3 Comparative Example 1 Example 1 Production conditions
Calorific value of coal 6800 6800 (kcal/kg) Fineness of fine coal
powder 10 to 20 10 to 20 (Residue % on 90 .mu.m mesh) Outer primary
air straight 250 to 300 100 to 120 stream velocity (m/sec) Inner
primary air straight 250 to 300 80 to 0 stream velocity (m/sec)
Coal powder stream 30 to 50 30 to 50 velocity (m/sec) Inner primary
air turning None 0 to 80 stream velocity (m/sec) Liquid fuel
C-heavy C-heavy oil oil Calorific value (kcal/kg) 10,200 10,200
Droplet size (.mu.m) 150 150 Primary air ratio 11 20 Results
Ejection stream momentum 125 to 135 100 ratio.sup.(*).sup..sub.1
Secondary air-accompanying 100 to 110 100 momentum
ratio.sup.(*).sup..sub.1 Secondary air-accompanying time 90 to 100
100 ratio.sup.(*).sup..sub.1 Swirl number (SW) 0 0.03 to 0.10
Production rate (T/day) 2880 2795 Generated calory (kcal/kg) 719
744 Furnace end temperature (.degree. C.) 1040 1090 CO amount at
furnace end (%) Undetected 1 to 2
[0123] As Table 3 clearly shows, in Example 3, even when the
secondary air-accompanying momentum and accompanying time were held
in the similar levels to those of Comparative Example 3, the
ejection stream momentum could be increased by 25 to 35%, the swirl
number could be decreased, the production rate could be increased,
the combustion ratio could be reduced and the furnace end
temperature could be decreased.
[0124] Industrial Applicability
[0125] By using the burning apparatus and method of the present
invention, a powder fuel or a liquid fuel or a powder fuel and a
liquid fuel can be burnt to form a narrow angle short flame-type
flame and the fire point temperature can be sufficiently increased,
without damaging the furnace wall. Therefore, the practical effect
of the apparatus and method of the present invention is very
good.
* * * * *