U.S. patent application number 09/794072 was filed with the patent office on 2001-08-23 for process and device for incineration of particulate solids.
Invention is credited to Brunnmair, Erwin, Moosmann, Gerhard.
Application Number | 20010015160 09/794072 |
Document ID | / |
Family ID | 3496118 |
Filed Date | 2001-08-23 |
United States Patent
Application |
20010015160 |
Kind Code |
A1 |
Brunnmair, Erwin ; et
al. |
August 23, 2001 |
Process and device for incineration of particulate solids
Abstract
A process for the incineration of particulate solids, especially
biological waste matter with low caloric value, feeds the solids
into a combustion chamber of a furnace together with a
sub-stoichiometric amount of fresh air to control the rate of
combustion and to inhibit the formation of sintered ash. The
furnace for implementing the process can be a cyclone furnace
having a primary combustion chamber with a first feed inlet for the
solids and air and a second air inlet positioned between the first
inlet and an exhaust gas outlet. A supply tube extends through the
exhaust gas outlet of the primary combustion chamber to supply a
source of fresh air at ambient temperature to maintain the primary
combustion chamber at a desired temperature. The fresh air
maintains the furnace temperature at least at about 850.degree. C.
and generally at about 850.degree. C. to less than about
1100.degree. C. A source of fresh air at ambient temperature can
also be directed into the primary combustion chamber through an
annular air passage surrounding the exhaust gas outlet of the
primary combustion chamber. The less than stoichiometric amount of
air and the secondary air maintains the furnace at a sufficiently
lower temperature to inhibit sintering of the solids.
Inventors: |
Brunnmair, Erwin; (Graz,
AT) ; Moosmann, Gerhard; (Graz, AT) |
Correspondence
Address: |
ROYLANCE, ABRAMS, BERRO & GOODMAN
1300 19TH STREET, N.W.
SUITE 600
WASHINGTON,
DC
20036
US
|
Family ID: |
3496118 |
Appl. No.: |
09/794072 |
Filed: |
February 28, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09794072 |
Feb 28, 2001 |
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09283584 |
Apr 1, 1999 |
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6216610 |
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Current U.S.
Class: |
110/346 ;
110/251 |
Current CPC
Class: |
F23G 2209/12 20130101;
F23G 5/32 20130101; F23G 2205/20 20130101; F23G 5/165 20130101;
F23G 2209/26 20130101 |
Class at
Publication: |
110/346 ;
110/251 |
International
Class: |
F23G 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 17, 1998 |
AT |
A647/98 |
Claims
What is claimed is:
1. A process for incinerating a solid particulate material
comprising the steps of: introducing a feed mixture into a first
combustion zone of a furnace, said furnace having a lower end and
an upper end defining a primary combustion chamber, said feed
comprising said solid particulate material and a first source of
combustion air in an amount less than a stoichiometric amount
needed to completely incinerate said particulate material; and
incinerating said solid particulate material in a first
incinerating stage in said primary combustion zone in an atmosphere
containing less than a stoichiometric amount of air to inhibit the
formation of sintered ash.
2. The process of claim 1, wherein said furnace includes a burner
and said process comprises directing hot combustion gases into said
combustion zone to incinerate said solid particulate material.
3. The process of claim 1, wherein said solid particulate material
is dried biological waste or sludge particles.
4. The process of claim 1, further comprising feeding a second
source of air into a second combustion zone of said primary
combustion chamber to cool said secondary combustion zone, said
second source of air being fed into said secondary combustion zone
at a location above said feed of said first source of combustion
air.
5. The process of claim 4, wherein said second source of air is
moist air having a lower oxygen content than said first source of
air to maintain said second combustion zone at about 850.degree.
C.
6. The process of claim 5, wherein said second source of air is
recycled air from a sludge drying assembly.
7. The process of claim 4, wherein said furnace is a cyclone
furnace and said process comprises feeding a third source of air
into a center portion of said first combustion chamber of said
furnace to cool said first combustion zone, wherein said third
source of air is fresh air at ambient temperature.
8. The process of claim 7, wherein said furnace includes a feed
pipe extending through said primary combustion chamber in an axial
direction with respect to said furnace and having a plurality of
outlet openings, said process comprising feeding said third source
of air through said feed pipe into said primary combustion
chamber.
9. The process of claim 8, wherein said outlet openings of said
feed pipe are spaced along a length of said feed pipe for directing
said third source of air radially outward.
10. The process of claim 7, wherein the amount of said second
source of air fed to said furnace is different from said third
source of air.
11. The process of claim 4, wherein said furnace has an exhaust gas
outlet positioned in an upper end of said primary combustion
chamber, a first annular wall surrounding said exhaust gas outlet
and extending axially into said first combustion zone, and a second
annular wall concentric to said first annular wall and forming an
annular air passage between said first and second annular walls,
said process further comprising feeding a third source of fresh air
through said annular air passage downwardly into said first
combustion chamber.
12. The process of claim 1, comprising feeding said first source of
air into said furnace in an amount to incinerate said solid
particulate material at a predetermined rate.
13. The process of claim 4, comprising feeding said second source
of air into said furnace in an amount based on a capacity of said
furnace.
14. The process of claim 1, wherein said furnace is a cyclone
furnace, said process comprising feeding said feed mixture
tangentially into said furnace.
15. The process of claim 1, comprising feeding a further source of
air into said furnace at a location below said feed mixture.
16. The process of claim 1, comprising maintaining said combustion
zone at a temperature of about 850.degree. C.
17. The process of claim 4, wherein said primary combustion chamber
of said furnace includes an exhaust gas outlet, said first
combustion zone being spaced from said exhaust gas outlet, said
process comprising feeding said second source of air into said
second combustion zone, wherein said second combustion zone is
positioned between said first combustion zone and said exhaust gas
outlet, and said second source of combustion air is provided to
supply a stoichiometric excess of oxygen to said second combustion
zone to provide complete combustion of said solid particulates.
18. An apparatus for incinerating a solid particulate material
comprising: a furnace wall defining a primary combustion chamber
and having a lower end and an upper end; a burner coupled to said
furnace wall for introducing hot combustion gases into said primary
combustion chamber; a first feed inlet for feeding a feed mixture
into a first combustion zone in said primary combustion chamber,
said feed mixture including a solid particulate material and a
first source of combustion air in less than a stoichiometric amount
needed for complete combustion of said solid particulate material;
and a second feed inlet for feeding a second source of air into
said primary combustion chamber.
19. The apparatus of claim 18, further comprising a feed pipe
extending axially through said primary combustion chamber for
supplying a tertiary source of air into said primary combustion
chamber in an amount to maintain said primary combustion chamber at
a temperature of about 850.degree. C.
20. The apparatus of claim 19, wherein said feed pipe extends
through a center of said primary combustion chamber, said feed pipe
including a plurality of air outlet openings spaced along a length
of said combustion chamber for feeding said tertiary source of air
radially outward into said primary combustion chamber.
21. The apparatus of claim 18, wherein said second feed inlet is
spaced upward from said first feed inlet with respect to said upper
end of said furnace.
22. The apparatus of claim 18, further comprising an annular air
inlet positioned in said primary combustion chamber for directing
an annular column of fresh air downwardly into said primary
combustion chamber.
23. The apparatus of claim 22, said primary combustion chamber
having a central opening in said upper end communicating with a
secondary combustion chamber, and said annular air inlet
surrounding said central opening.
24. The apparatus of claim 23, wherein said annular inlet comprises
an inner annular wall and an outer annular wall, said inner and
outer annular walls having a length to extend toward said lower end
beyond said first feed inlet.
25. The apparatus of claim 18, wherein said furnace is a cyclone
furnace and said first inlet feeds said feed mixture tangentially
into said furnace.
26. A furnace for incinerating a solid particulate material
comprising: at least one side wall, a bottom wall, a top wall, and
an intermediate wall extending substantially perpendicular to said
side wall in an inward direction toward an axial center of said
furnace, said intermediate wall having a throat opening concentric
with a center axis of said furnace and defining a primary
combustion chamber in a lower portion of said furnace and a
secondary combustion chamber in an upper portion of said furnace; a
feed inlet device in said side wall for feeding a feed mixture
tangentially into said primary combustion chamber, said feed
mixture including a solid particulate material and combustion air
in less than a stoichiometric amount needed for complete combustion
of said particulate material; and at least one feed pipe for
feeding a supply of fresh air into said center of said primary
combustion chamber in an amount to cool said primary combustion
chamber at a temperature of about 850.degree. C.
27. The furnace of claim 26, wherein said feed pipe comprises an
annular pipe having an annular outlet surrounding said opening in
said intermediate wall for feeding fresh combustion air into said
primary combustion chamber a substantially downward direction
toward said bottom wall.
28. The furnace of claim 27, wherein said annular pipe has a length
extending axially into said primary combustion chamber beyond said
feed inlet device and for directing said combustion air in a
downward direction.
29. The furnace of claim 27, wherein said annular pipe comprises an
inner wall forming an axial passage between said primary combustion
chamber and said secondary combustion chamber.
30. The furnace of claim 29, wherein said annular pipe further
comprises an outer wall forming said annular outlet between said
inner and outer walls for directing a substantially annular stream
of air into said primary combustion chamber.
31. The furnace of claim 27, further comprising a cylindrical pipe
concentric with said annular pipe and extending through said first
feed pipe for feeding air into said primary combustion chamber.
32. The furnace of claim 31, wherein said cylindrical pipe includes
a cylindrical side wall having a plurality of outlet openings for
feeding said air in an outward direction with respect to said
cylindrical side wall into said primary combustion chamber.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a process and apparatus for
the incineration of particulate solids and particularly, biological
waste materials with low caloric values. The invention is further
directed to a process and apparatus for incinerating previously
dried solid particulates, such as municipal sludge, with reduced
formation of sintered ash.
BACKGROUND OF THE INVENTION
[0002] Various processes and devices have been developed for
incinerating solid particulate materials for various purposes. In
particular, municipal waste and sewer sludge generally must be
incinerated before disposal in a landfill. The environmental
regulations in many countries limit the amount of organic material
which can be present in the sludge prior to disposal. Accordingly,
various efforts have been proposed to incinerate municipal waste
material and sewer sludge to comply with the regulations.
[0003] One example of a known process for incinerating waste
materials is disclosed in WO 92/14969. This publication discloses a
process for feeding finely ground, previously dried sludge into a
brick lined combustion chamber, together with a supply of primary
combustion air. The furnace is a cyclone combustion chamber having
a lower section where the incineration of the solid material takes
place. A predetermined amount of moist air with a reduced oxygen
content is fed into the combustion chamber to inhibit the sintering
of the ash. The ash discharge area of the combustion chamber is
cooled using the moist air. The amount of air needed as the primary
combustion air and the secondary source of moist air is typically
preset for a specific furnace size. The heat output of the furnace
is regulated by adjusting the amount of the solid material being
incinerated in relation to the fixed amount of the primary
combustion air. This device has several disadvantages and is not
completely efficient in incinerating solid materials. For example,
the process disclosed in this publication is generally difficult to
regulate and the output of the incinerated material can be adjusted
over a very small operating range. Furthermore, fluctuations in the
level of solid material being incinerated and the caloric value of
the solid material produces inconsistent results in the
incineration of the solid material.
[0004] Accordingly, there is a continuing need in the industry for
improved processes and apparatus for incinerating solid
materials.
SUMMARY OF THE INVENTION
[0005] The present invention is directed to a process and apparatus
for the incineration of particulate solid materials. More
particularly, the invention is directed to a process and apparatus
for incinerating biological waste materials with low caloric value
with a reduced output of sintered ash.
[0006] Accordingly, a primary object of the invention is to provide
a process and apparatus for incinerating solid materials containing
organic matter, such as sewage sludge, in a rapid and efficient
manner.
[0007] Another object of the invention is to provide a process and
apparatus for incinerating organic materials at low temperatures
and to incinerate the materials having a lower ash fusion point
without ash sintering.
[0008] A further object of the invention is to provide a process
and apparatus for incinerating organic materials in a furnace and
to remove the ash more effectively from the exhaust gas stream.
[0009] A still further object of the invention is to provide a
process and apparatus for incinerating organic materials in a
furnace and for maintaining a temperature of about 1100.degree. C.
or less, and preferably about 850.degree. C.
[0010] Another object of the invention is to provide a process and
apparatus for incinerating solid particulate materials by blowing a
mixture of the solid materials and a sub-stoichiometric proportion
of fresh air into a combustion chamber of a furnace.
[0011] Another object of the invention is to provide a process and
apparatus for incinerating solid particulate materials where the
solid material is incinerated in a first combustion zone containing
a deficiency of oxygen followed by feeding additional air to a
second combustion zone to provide an excess of oxygen and to
further incinerate the solid particulate materials.
[0012] A further object of the invention is to provide a process
and apparatus for incinerating solid materials containing organic
matter with reduced formation of carbon monoxide.
[0013] Another object of the invention is to provide a process and
apparatus for incinerating solid particulate materials containing
organic matter where a second source of moist air with a reduced
oxygen content compared to the primary combustion air is fed into
the furnace to maintain the operating temperature of the furnace at
about 850.degree. C.
[0014] Another object of the invention is to provide a process and
apparatus for feeding recycled moist air from a drying plant, and
feeding the moist air into the furnace for incinerating solid
particulate materials.
[0015] Another object of the invention is to provide a cyclone
furnace having an annular shaped inlet tube for feeding secondary
air into the combustion zone of the furnace in an axial
direction.
[0016] A further object of the invention is to provide an apparatus
for incinerating solid materials where the furnace includes a
centrally located feed tube extending axially through the furnace
and the feed tube having a plurality of openings therein for
supplying a secondary air source to the combustion zone.
[0017] The objects and advantages of the invention are basically
attained by providing a process for incinerating solid particulate
materials comprising the steps of: introducing a feed mixture into
a first combustion zone of a furnace, the furnace having a lower
end and an upper end defining a primary combustion chamber, the
feed comprising the solid particulate material and a first source
of combustion air in an amount less than a stoichiometric amount
needed to completely incinerate the particulate material; and
incinerating the solid particulate material in a first incinerating
stage in the primary combustion zone in an atmosphere containing
less than a stoichiometric amount of air to inhibit the formation
of sintered ash.
[0018] The objects and advantages of the invention are further
attained by providing an apparatus for incinerating solid
particulate materials comprising a furnace wall defining a primary
combustion chamber and having a lower end and an upper end; a
burner coupled to the furnace wall for introducing hot combustion
gases into the primary combustion chamber; a first feed inlet for
feeding a feed mixture into a first combustion zone in the primary
combustion chamber, the feed mixture including a solid particulate
material and a first source of combustion air in less than a
stoichiometric amount needed for complete combustion of the solid
particulate material; and a second feed inlet for feeding a second
source of air into the primary combustion chamber.
[0019] The objects and advantages are also attained by providing a
furnace for incinerating a solid particulate material comprising:
at least one side wall, a bottom wall, a top wall, and an
intermediate wall extending substantially perpendicular to the side
wall in an inward direction toward an axial center of the furnace,
the intermediate wall having a throat opening concentric with a
center axis of the furnace and defining a primary combustion
chamber in a lower portion of the furnace and a secondary
combustion chamber in an upper portion of the furnace; a feed inlet
device in the side wall for feeding a feed mixture tangentially
into the primary combustion chamber, the feed mixture including a
solid particulate material and combustion air in less than a
stoichiometric amount needed for complete combustion of the
particulate material; and at least one feed pipe for feeding a
supply of fresh air into the center of the primary combustion
chamber in an amount to cool the primary combustion chamber at a
temperature of about 850.degree. C.
[0020] Other objects, advantages and salient features of the
present invention will become apparent from the following detailed
description which, taken in conjunction with the annexed drawings,
discloses preferred embodiments of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] Referring to the drawings which form a part of this original
disclosure:
[0022] FIG. 1 is a cross-sectional side view of a cyclone furnace
in a first embodiment of the invention;
[0023] FIG. 2 is a cross-sectional side view of a cyclone furnace
in a second embodiment of the invention;
[0024] FIG. 3 is a partial cross-sectional side view of the annular
feed device of the furnace of FIG. 2;
[0025] FIG. 4 is a cross-sectional side view of the cyclone furnace
in a further embodiment showing the opening between a primary
combustion zone and a secondary combustion zone of the furnace;
[0026] FIG. 5 is a cross-sectional top view of the cyclone furnace
in a preferred embodiment of the invention showing the tangential
inlets for the combustion gases; and
[0027] FIG. 6 is a schematic diagram of a sludge drying plant and
an incinerating apparatus in accordance with the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0028] The present invention is directed to a process and apparatus
for incinerating solid particulate materials. In particular, the
invention is directed to a process and apparatus for incinerating
solid materials having an organic component which can be
incinerated to remove the organic component from the solid
particles. The process and apparatus are particularly suitable for
incinerating municipal waste sludges, and particularly sewer
sludge, although other solid materials can be incinerated
efficiently. In embodiments of the invention, the solid material is
previously dried sewage sludge having a moisture content of about
2-10% by weight, corresponding to a dry content of about 90-98% by
weight. The solid materials being incinerated generally contain a
number of different compounds and components such that the solid
particles have a relatively low caloric value.
[0029] In a first embodiment of the invention shown in FIG. 1, the
apparatus is in the form of a cyclone furnace 10 having a side wall
12, a bottom wall 14 and a top wall 16. In the embodiment
illustrated, the bottom wall 14 has a substantially frustoconical
shape converging toward a central discharge opening 18 in the
bottom portion of the furnace 10.
[0030] The furnace 10 includes an intermediate wall 20 extending
substantially perpendicular to the side wall 12 and having a
central opening forming a throat 22. The throat 22 in the
intermediate wall 20 is positioned in the center of the furnace 10
such that the center axis of the furnace extends through the center
of the throat 22. As shown in FIG. 1, the center opening of the
throat 22 in the intermediate wall is aligned with the discharge
opening 18 in the bottom wall 14.
[0031] The intermediate wall 20 divides the furnace 10 into a
primary combustion chamber 24 located in the lower portion of the
furnace and a secondary combustion chamber 26 located in the upper
portion of the furnace 10. A burner 28 is positioned in an opening
30 in the side wall 12 in the primary combustion chamber 24 which
feeds a fuel and air mixture and hot combustion gases into the
furnace to ignite the fuel material being incinerated and assist in
the combustion of material being fed into the furnace. In the
embodiment illustrated, the burner 28 is positioned to direct the
hot combustion gases radially into the primary combustion chamber
24 toward the axial center and is positioned at approximately the
midpoint between the intermediate wall 20 and the discharge opening
18.
[0032] An injection nozzle 32 is mounted tangentially in the side
wall 12 in the primary combustion chamber 24. The nozzle 32 is
provided to supply a feed mixture of the solid particulate material
and primary combustion air. The solid material is generally a
biological waste material which functions as a fuel for feeding
into the primary combustion chamber 24 for incineration. In
preferred embodiments of the invention, the feed mixture supplied
through nozzle 32 contains fresh air in an amount less than a
stoichiometric amount needed to support complete combustion of the
solid material. Generally, the amount of the primary combustion air
supplied with the solid material is in an amount to transport the
solid particles through the feed nozzle 32 and into the furnace.
The nozzle 32 is adjustable to control the feed rate of the feed
mixture and to direct the feed mixture in a circular fashion around
the side wall 12 of the furnace 10.
[0033] The solid particulate material of the feed mixture is
incinerated in the primary combustion chamber 24 with the
assistance of the burner 28. The feed mixture follows a spiral path
in a generally downward direction and then flows upwardly in a
generally axial direction toward the throat 22. Ash is formed in
the primary combustion chamber and removed from the cyclone furnace
through the discharge opening 18. The amount of the fresh air
stream fed through the nozzle 32 can be selected to provide the
desired extent of combustion and can be adjusted according to the
combustion capacity of the furnace and the amount of the solid
material in the feed mixture as well as the caloric value of the
solid material in the feed mixture.
[0034] The larger incinerated particles fall downwardly through the
primary combustion chamber 26 and are discharged through the outlet
18. The fine particles are generally carried upwardly along the
side wall 12 in a secondary stream indicated by arrows 34. As shown
in FIG. 1, the nozzle 32 for supplying the feed mixture is spaced
axially from the throat opening 22 in the intermediate wall 20. The
nozzle 32 is positioned at the upper end of the primary combustion
chamber 26 and above the burner 28.
[0035] A nozzle 36 is provided in the side wall 12 in the primary
combustion chamber 24 and is positioned between the throat opening
22 in the intermediate wall 20 and the injection nozzle 32. The
nozzle 36 feeds a source of secondary air tangentially into the
primary combustion chamber 24 to direct a secondary air stream 34
in a circular fashion around the interior of the side wall 12.
Preferably, the nozzle 32 supplies a secondary source of air to
provide an excess amount of oxygen for supporting substantially
complete combustion of the solid material in the feed mixture. The
secondary air is fed at a temperature less than the internal
temperature of the furnace to provide a cooling effect and prevent
overheating of the furnace and the solid material being
incinerated. The secondary air supplied through the nozzle 32
reduces the amount of the fine particle size solid material from
being discharged through the opening 22 and being carried to the
secondary combustion chamber 26. The secondary air preferably has
an oxygen content less than the normal oxygen content of
atmospheric air. Typically, the secondary air has an oxygen content
of about 8.0-10.0% compared to about 21% of air. In embodiments,
the secondary air is recycled drying air from a drying plant
containing moisture and exhaust gases and has an oxygen content of
about 8.0 to 10% and a temperature of about 45.degree. C. to about
60.degree. C.
[0036] In the embodiment illustrated in FIG. 1, the feed mixture of
solid material and primary combustion air are fed into the primary
combustion chamber 24 through the nozzle 32 such that the solid
material is at least partially incinerated in a first combustion
zone 38 in the vicinity of the nozzle 32. The feed mixture contains
less than a stoichiometric amount of oxygen for the solid
particulate fuel material such that the solid material is only
partially incinerated in the first combustion zone 38. By feeding
less than a stoichiometric amount of oxygen with the solid
material, the temperature in the first combustion zone can be
maintained at a temperature of about 850.degree. C. and prevents or
inhibits the formation of sintered ash.
[0037] The supply of secondary air through the nozzle 36 which is
positioned above the nozzle 32 forms a second combustion zone 40 in
the upper portion of the primary combustion chamber 24. The
secondary air is supplied in an amount to effect complete
combustion and incineration of the solid material. This provides a
two stage combustion process which prevents overheating of the
solid material and prevents sintering of the ash. The secondary air
typically has a reduced oxygen content which reduces the rate of
combustion to maintain the temperature in the first and second
combustion zones below the sintering temperature of the ash. The
incinerated particles fall downwardly through the furnace and are
discharged through the opening 18 and the exhaust gases are
discharged through the opening 22 where they are conveyed through
the secondary combustion chamber 26 for complete combustion of fuel
and unburned materials.
[0038] The exhaust gases in the secondary combustion chamber 26 are
discharged through an outlet opening 42 in the side wall of the
secondary combustion chamber 26. The exhaust gases are then fed
through a heat exchanger for recovering the heat for various
process steps, such as the drying of sewer sludge in a drying
plant. Alternatively, the exhaust gases can be recycled to a
preceding drier loop or treated appropriately for discharging to
the atmosphere.
[0039] As shown in FIG. 1, a plurality of nozzles 44 are provided
in the lower section of the primary combustion chamber 24 to feed a
source of air tangentially into the bottom portion of the furnace.
Preferably, the air fed through the nozzles 44 is moist air with a
reduced oxygen content fed from a drier loop in a drying plant. The
amount of moist air fed through the nozzles 44 can be adjusted to
maintain the temperature in the primary combustion chamber 24
sufficiently low to prevent the sintering of ash in the combustion
chamber as it falls downwardly toward the discharge opening 18. In
this manner, the temperature in the lower portion of the primary
combustion chamber can be controlled to prevent overheating of the
incinerated particles. The moist air typically has an oxygen
content of about 8.0% to 10% which is lower than the oxygen content
of the feed mixture supplied through nozzle 32. The moist air is
able to maintain the temperature substantially uniform throughout
the height of the primary combustion chamber 24. In addition, the
moist air allows the combustion of solid organic materials or fuels
with a low ash fusion point without the risk of sintering the
ash.
[0040] In the embodiment of FIG. 1, a distribution pipe 46 is
centrally located within the care of the furnace and extends along
the center axis of the primary and secondary combustion chambers 24
and 26, respectively. As shown, the distribution pipe extends
through the opening 22 in the intermediate wall 20 and extends
downwardly through the primary combustion chamber 24 to the
discharge outlet 18. A plurality of outlet openings 48 are spaced
apart along the length and around the periphery of the distribution
pipe 46 within the primary combustion chamber 26. A supply of fresh
tertiary air is fed through the distribution pipe and discharged
through the openings 48 into the primary combustion chamber 24. In
the embodiment illustrated, the fresh air at ambient temperature is
supplied upwardly through the pipe 46. The air is discharged
radially outward from the distribution pipe 46 and supplies the air
along the axial length of the primary combustion chamber 24 to cool
the primary combustion chamber and maintain a substantially uniform
temperature throughout the primary combustion chamber 24. In
addition, the air fed through the distribution pipe provides a
cooling effect to prevent overheating in the primary combustion
chamber, and thus, inhibits the fusion and sintering of the ash.
The amount of fresh air supplied to the furnace through the pipe 46
is sufficient to maintain the temperature of the furnace below
1100.degree. C. and preferably at about 850.degree. C. The
additional air fed through the distribution pipe 46 also reduces
the nitrogen oxide content in the flue gases discharged through the
outlet 42 of the furnace. In the embodiment illustrated, the
openings 48 are uniformly spaced along the length of the pipe 46 to
uniformly cool the combustion chamber. In further embodiments, the
openings 48 are selectively positioned to direct cooling air to hot
spots in the combustion chamber.
[0041] In the process of the invention, the feed mixture of the
solid material being incinerated and the primary combustion air are
fed through the nozzle 32 into the furnace where the solid
particles are partially incinerated in first combustion zone 38.
The feed mixture contains a less than stoichiometric amount of
oxygen to prevent complete combustion of the solid particles in the
first combustion zone 38. The particles are then carried to the
second combustion zone 40 where the particles are mixed with the
secondary air supplied through the nozzle 36. The combustion of the
solid particles is substantially complete in the second combustion
zone 40 at a temperature which prevents the formation of sintered
ash. Moist air can be supplied through the nozzles 44 and fresh air
is supplied through the distribution pipe 46 having a temperature
below the operating temperature of the furnace to provide a cooling
effect and prevent overheating of the particles and the formation
of sintered ash. The amount of cooling air supplied through the
nozzles 36 and/or the distribution pipe can be varied to vary and
control the temperature of the furnace. The amount of cooling air
is controlled as a function of the burner capacity to optimize
incineration at low temperatures.
[0042] The amount of moist air supplied through the nozzles 44 can
be adjusted to control the temperature within the primary
combustion chamber 24. Preferably, the temperature of the primary
combustion zone is maintained at a temperature to substantially
inhibit the sintering of the ash particles. The operating
temperature of the primary combustion zone is determined by the
caloric content of the solid material, the volume of solid material
being fed to the combustion chamber and the ratio of the solid
material and primary air supplied to the first combustion zone. The
supply of secondary air for cooling the interior of the combustion
zone can be regulated as a function of the burner capacity and to
provide optimum incineration of the particles without the formation
of sintered ash.
[0043] FIG. 5 is a cross-sectional end view of the furnace showing
the supply inlets into the furnace 10 of FIG. 1. As shown, the
burner 28 is coupled to a housing 62 and includes a suitable
control linkage 64 for controlling the amount of hot air supplied
to the furnace. The housing 62 is connected to the opening 66 in
the side wall 12 of the furnace 10 to direct the hot gases radially
inward toward the axial center of the furnace. The side wall 12 of
the furnace includes a refractory lining material 68 forming a
substantially cylindrical shaped combustion chamber 24. The nozzles
32, 36 and 44 extend through the side wall 12 to supply the
secondary air tangentially into the combustion chamber 24 in a
manner typical in cyclone furnaces. A suitable control valve 70 is
coupled to each of the nozzles to control the volume of flow
through the nozzles.
[0044] Referring to FIG. 2, a further embodiment of the cyclone
furnace is illustrated which is similar to the embodiment of FIG.
1, except for the addition of a submerged feed tube 50. Thus,
identical components of the furnace are identified by the same
reference number with the addition of a prime. As shown in FIG. 2,
a submerged feed tube 50 extends axially downward into the primary
combustion chamber 24 from the intermediate wall 20. The submerged
tube 50 defines the center throat opening 22 in the intermediate
wall 20 and is coaxial with the center axis of the furnace.
Preferably, the submerged tube 50 extends axially downward through
the second combustion zone 40 and into the first combustion zone 38
below or in the vicinity of the nozzle 32 for supplying the primary
feed mixture of the solid material and primary combustion air.
[0045] Referring to FIG. 3, the submerged tube 50 includes an inner
annular wall 52 which forms an axial passage 54 at the throat
between the primary combustion chamber 24 and the secondary
combustion chamber 26. An outer wall 56 is spaced outwardly from
the inner wall 52 to form an annular air supply passage 58. Feed
pipes 60 extend through the intermediate wall 20 to the annular
passage 58 to supply tertiary combustion air to the primary
combustion chamber 24. The annular passage 58 directs an annular
air stream downwardly into the primary combustion chamber 24.
[0046] In the process of the invention, the feed mixture of the
solid material and the primary combustion air is fed through the
nozzle 32 into the first combustion zone 38 where the solid
particles are at least partially incinerated. A secondary air
supply is fed through the nozzles 36 in the second combustion zone
40 and through the nozzles 44 as in the previous embodiment. The
secondary air preferably has an oxygen content less than the oxygen
content of the primary air supplied through nozzle 32. The
secondary air can be recycled drying air having a high moisture
content and an oxygen content of about 8% to 10% by volume.
[0047] The tertiary air is fed through the supply pipes 60 and
through the annular passage 58 to direct an annular flow of fresh
air at ambient temperature downwardly through the primary
combustion chamber 24. The fresh air is supplied through the
annular passage 58 to provide a cooling effect in the primary
combustion chamber and directs the air to the lower portion of the
primary combustion chamber to the core of the cyclone furnace. The
secondary air mixes with the combustion gases in the primary
combustion chamber where they are directed upwardly through the
axial passage 54 and into the secondary combustion chamber 26. As
shown in FIG. 2, the secondary air fed through the annular passage
58 is supplied to the primary combustion chamber below the nozzle
32 where the feed mixture is introduced to the furnace. The fresh
air is supplied through the annular passage 58 at a rate to
maintain the temperature of the furnace below 1100.degree. C., and
preferably about 850.degree. C.
[0048] An alternative embodiment of the invention is illustrated in
FIG. 4, which is similar to the furnace in the embodiments of FIGS.
1 and 2. As shown in FIG. 4, a distribution pipe 46 extends axially
through the axial passage 54 of the submerged tube 50 into the
primary combustion chamber 24. A supply of fresh air is fed through
the distribution pipe 46 and is discharged through the openings 48
into the primary combustion chamber 24. Simultaneously, fresh air
is fed through the annular passage 58 into the primary combustion
chamber 24. In this manner, fresh air can be supplied to the
furnace to control the temperature and extent of combustion of the
solid material being incinerated. As in the previous embodiments,
the fresh air is at ambient temperature and supplied at a rate to
maintain the furnace temperature below 1100.degree., and preferably
about 850.degree.. Preferably, a furnace temperature of at least
about 850.degree. C. is maintained to prevent odors from being
discharged in the exhaust gas. The fresh air mixes with the
combustion gases in the furnace. The combustion gases are carried
upward through the axial passage 54 into the secondary combustion
chamber where they are eventually discharged through the outlet
42.
[0049] FIG. 6 is a schematic diagram of a sludge drying plant
including the incinerating apparatus of the invention. Referring to
FIG. 6, the sludge drying plant includes a drying section 72 and an
incinerating section 74. Previously dewatered sludge is fed through
a supply pipe 76 to a storage silo 78. The previously dewatered
sludge is then conveyed through a screw conveyor 80 to a mixing
device 82. A portion of previously dried sludge material is
supplied from a storage silo 84 by a screw conveyor and mixed with
the dewatered sludge in the mixer 82 to adjust the solid-liquid
ratio of the feed mixture. The resulting mixture is conveyed
through a line 86 to a drier 88. In the embodiment illustrated, the
drier 88 is a triple pass, hot air drier as known in the art. Hot
air is supplied to the drier 88 through line 90. Alternatively, the
drier can be a fluidized bed, moving fluidized bed drier or other
directly or indirectly heated drier.
[0050] Moist air and the dried sludge particles are carried through
line 92 to a separator 94 to remove the large particles from the
exhaust gas stream. The large particles are carried through a
cooling screw conveyor and discharged to a screen separator 96. The
larger dried sludge particles are separated and carried to a silo
98 and then fed to a crusher 100. The crushed and ground dried
sludge particles are discharged to a feed pipe 102 which is
supplied with air from a blower 104 to carry the sludge particles
through a feed pipe 106 to the incinerating portion of the
plant.
[0051] The exhaust gas from the separator 94 is directed through a
pipe 108 by blower 110 to a spray condenser 112. Water or other
purifying liquid is sprayed into the condenser 112 to remove
soluble contaminants and fine dust particles. The moist air from
the spray condenser is carried through a pipe 114 where a portion
of the hot exhaust gas is carried to a heat exchanger 116 through a
pipe 118. The exhaust gas is heated in the heat exchanger 116 by
the exhaust gases from the incinerator portion of the plant to
reheat the air which is then supplied to the inlet of the drier
88.
[0052] A second portion of the exhaust gas from the separator 94 is
carried through a pipe 120 to a second separator 122 where the
smaller particulates are recovered from the exhaust gas stream and
carried to the silo 84 containing the recycled dried material. A
portion of the dried sludge particles separated in the separator 96
are carried through a pipe 126 to the storage silo 84.
[0053] The incinerating section 74 includes a cyclone furnace 128
substantially as shown in the previous embodiments of FIGS. 1-5. A
burner 130 is provided to supply hot combustion gases to the
furnace in a primary combustion chamber 132 in the lower portion of
the furnace 128. The ground, previously dried sludge particles are
directed into the furnace 128 through the feed pipe 106 which is
positioned above the burner 130 in the primary combustion chamber
132. Fresh combustion air can be supplied through a pipe 134 to the
burner 130. Moist recycled air from the spray condenser 112 is
supplied through the feed pipe 114 to the primary combustion
chamber 132. A source of fresh air is supplied to the distribution
pipe or the annular feed pipe 135 as in the embodiments of FIGS.
1-5. The incinerated sludge particles are removed from the furnace
through an outlet 136 where they are conveyed through a cooling
conveyor 138. The cooled incinerated sludge particles are conveyed
through conveyors 140 and 142 to a suitable discharge site.
[0054] The combustion gases in the cyclone furnace 128 are carried
from the primary combustion chamber 132 through the secondary
combustion chamber 144 and discharged through an outlet pipe 146.
The hot exhaust gases are carried through the pipe 146 to the heat
exchanger 116 for heating the feed air to the drum drier of the
drying section. The exhaust gases exit the heat exchanger 116
through a pipe 148 to a separator 150 for separating particles in
the exhaust gas stream. The exhaust gas stream is then carried
through a pipe 152 to a spray condenser 154 for treating the
exhaust gas before discharging through a discharge pipe 156.
[0055] In the process of FIG. 6, previously dried sludge particles
are supplied to a cyclone furnace above the burner to incinerate
the sludge particles and remove the organic components of the
sludge particles prior to discharge. Moist air from the spray
condenser in the drying section is fed to the furnace to control
the temperature in the furnace and prevent overheating of the
sludge particles thereby preventing the formation of sintered
ash.
[0056] While several embodiments have been shown to illustrate the
invention, it will be understood by those skilled in the art that
various changes and modifications can be made therein without
departing from the scope of the invention as defined in the
appended claims.
* * * * *