U.S. patent application number 17/416597 was filed with the patent office on 2022-03-10 for method and device for the post-combustion of sewage sludge ash produced in a sewage sludge mono-incineration plant.
The applicant listed for this patent is MITSUBISHI POWER EUROPE GMBH. Invention is credited to Martin EHMANN, Gerhard PANNEN, Andreas RUPP, Alexander SIMON, Henning VON KROSIGK, Bernhard ZIMMERMANN.
Application Number | 20220074588 17/416597 |
Document ID | / |
Family ID | 1000006026588 |
Filed Date | 2022-03-10 |
United States Patent
Application |
20220074588 |
Kind Code |
A1 |
ZIMMERMANN; Bernhard ; et
al. |
March 10, 2022 |
Method and device for the post-combustion of sewage sludge ash
produced in a sewage sludge mono-incineration plant
Abstract
In the case of mono sewage sludge incineration, a solution may
be created that enables sewage sludge ash, which may still have a
low proportion of unburned carbon, to be discharged from a mono
sewage sludge incineration plant. This is achieved by a method for
the post-combustion of sewage sludge ash obtained in a mono sewage
sludge incineration in a rotary kiln by means of a hot and a low
oxygen content, such as an oxygen content of 5-10 vol. % oxygen.
The gas stream from the rotary kiln may escape the sewage sludge
ash and is fed to the gas flow. This sufficiently hot gas flow may
cause oxidation or afterburning of unburned carbon contained in the
sewage sludge ash.
Inventors: |
ZIMMERMANN; Bernhard;
(Roesrath, DE) ; EHMANN; Martin; (Rheinberg,
DE) ; PANNEN; Gerhard; (Moers, DE) ; SIMON;
Alexander; (Neuss, DE) ; VON KROSIGK; Henning;
(Meerbusch, DE) ; RUPP; Andreas; (Schwalmtal,
DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MITSUBISHI POWER EUROPE GMBH |
Duisburg |
|
DE |
|
|
Family ID: |
1000006026588 |
Appl. No.: |
17/416597 |
Filed: |
December 16, 2019 |
PCT Filed: |
December 16, 2019 |
PCT NO: |
PCT/EP2019/085369 |
371 Date: |
June 21, 2021 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F23G 5/033 20130101;
F23G 5/006 20130101; F23G 5/20 20130101; F23G 7/001 20130101; F23J
2900/01002 20130101; F23G 5/16 20130101; F23G 2209/30 20130101 |
International
Class: |
F23G 5/00 20060101
F23G005/00; F23G 5/033 20060101 F23G005/033; F23G 5/16 20060101
F23G005/16; F23G 5/20 20060101 F23G005/20; F23G 7/00 20060101
F23G007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 20, 2018 |
DE |
10 2018 133 237.8 |
Mar 26, 2019 |
DE |
10 2019 107 744.3 |
Claims
1. A method for the post-combustion of sewage sludge ash produced
during sewage sludge mono-incineration in a rotary kiln using a hot
gas or flue gas stream having a low oxygen content, wherein the
method comprises: obtaining sewage sludge ash from a fired
incineration chamber of an incineration plant associated with the
rotary kiln or from a power plant associated with the rotary kiln;
feeding the sewage sludge ash exiting the rotary kiln into the gas
or flue gas stream; optionally adjusting the sewage sludge ash to
the low oxygen content required for post-combustion, and oxidizing
or post-combusting unburned carbon contained in the sewage sludge
ash by the hot gas or flue gas stream.
2. The method according to claim 1, further comprising supplying
the mixture of hot gas or flue gas stream and supplied sewage
sludge ash into a reaction space.
3. The method according to claim 1, further comprising adjusting
the temperature of the hot gas or flue gas stream in such a way
that, on the one hand, it is sufficiently high to cause the
oxidation or post-combustion of the unburned carbon contained in
the sewage sludge ash and, on the other hand, it is sufficiently
low so that the temperature increase of the sewage sludge ash and
gas stream mixture or sewage sludge ash and flue gas stream mixture
resulting from the oxidation or post-combustion of the unburned
carbon contained in the sewage sludge ash does not cause slagging
of the reaction chamber or the reaction space or of the gas or flue
gas line carrying the sewage sludge ash and gas stream mixture or
sewage sludge ash and flue gas stream mixture.
4. The method according to claim 2, further comprising supplying
cold flue gas into the reaction space or the reaction chamber;
wherein the cold flue gas comprises a temperature ranging from
100.degree. C. to 250.degree. C.
5. The method according to claim 1, further comprising ginding the
sewage sludge ash in a mill.
6. The method according to claim 1, further comprising feeding the
sewage sludge ash, after exiting the rotary kiln, into a first
cooling conveyor configured as a cooling screw.
7. The method according to claim 1, wherein the sewage sludge
ash/gas stream mixture or sewage sludge ash/flue gas stream mixture
is fed downstream of the reaction space or the reaction chamber to
a centrifugal separator, and further comprising separating, in the
centrifugal separator the sewage sludge ash and the gas or flue gas
stream from one another.
8. The method according to claim 7, further comprising feeding the
gas or flue gas stream into the rotary kiln downstream of the
centrifugal separator.
9. The method according to claim 1, wherein the feeding of the
sewage sludge ash into the gas or flue gas stream and the oxidation
or post-combustion of the unburned carbon content contained in the
sewage sludge ash are carried out continuously and without
intermediate storage.
10. The method according to claim 1, wherein the feeding of the gas
or flue gas stream separated from the sewage sludge ash in the
centrifugal separator to the rotary kiln is carried out
continuously and without intermediate storage.
11. A device for carrying out the method according to claim 1,
wherein the device comprises: a sewage sludge mono-incineration
plant comprising a rotary kiln for sewage sludge incineration with
connected sewage sludge feed and a first sewage sludge ash
discharge with connected sewage sludge ash line opening into a gas
or flue gas line in which a gas or flue gas stream branched off
from a fired incineration chamber of an incineration plant
associated with the rotary kiln or a power plant associated with
the rotary kiln is fed.
12. The device according to claim 11, wherein at least one oxygen
supply device or oxygen introduction device is arranged in the gas
or flue gas line upstream of the inlet of the sewage sludge ash
line, by means of which oxygen can be supplied to the flue gas
stream carried in the gas or flue gas line.
13. The device according to claim 11, characterized wherein a
reaction space or a reaction chamber is formed in the gas or flue
gas line downstream of the inlet of the sewage sludge ash line, in
which, during operation of the sewage sludge mono-incineration
plant and the fired incineration chamber, the oxidation or
post-combustion of the unburned carbon contained in the sewage
sludge ash takes place.
14. The device according to claim 11, wherein a first cooling
conveyor is configured as a cooling screw, wherein a rotary valve
and a mill are arranged in the sewage sludge ash line before the
latter opens into the gas or flue gas line in the direction of flow
of the sewage sludge ash, which are integrated into the sewage
sludge ash line and through which the sewage sludge ash can
flow.
15. The device according to claim 11, wherein a centrifugal
separator for separating the sewage sludge ash and gas or flue gas
stream is arranged in the gas or flue gas line in the direction of
flow of the sewage sludge ash/gas stream or flue gas stream mixture
downstream of the confluence of the sewage sludge ash line and the
reaction chamber or reaction space.
16. The device according to claim 15, wherein the centrifugal
separator comprises an exhaust gas line opening into the rotary
kiln and a sewage sludge ash discharge line opening into a further
cooling conveyor configured as a cooling screw.
17. The device according to claim 11, wherein the gas or flue gas
line comprises, in the direction of flow of the gas or flue gas
stream upstream of the confluence with the sewage sludge ash line,
at least one oxygen supply device or oxygen introduction
device.
18. The device according to claim 11, wherein the associated
incineration plant is a waste incineration plant or the associated
power plant is a waste-fired power station.
19. The device according to claim 13, wherein at least one flue gas
introduction device for supplying cold flue gas opens into the
reaction space or the reaction chamber.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a national stage entry according
to 35 U.S.C. .sctn. 371 of PCT Application No. PCT/EP2019/085369
filed on Dec. 16, 2019; which claims priority to German Patent
Application Serial No. 10 2018 133 237.8 filed on Dec. 20, 2018 and
German Patent Application Serial No. 10 2019 107 744.3 filed on
Mar. 26, 2019; all of which are incorporated herein by reference in
their entirety and for all purposes.
TECHNICAL FIELD
[0002] The invention is directed to a method for the
post-combustion of sewage sludge ash produced during sewage sludge
mono-incineration in a rotary kiln, and to a device for carrying
out this method.
BACKGROUND
[0003] With the amendment of the sewage sludge directive, it is
foreseeable that in the future no sewage sludge from medium and
large sewage treatment plants can be used directly as fertilizer.
At the same time, recovery of the phosphorus contained in sewage
sludge will become mandatory in the future. For sewage sludge
incinerated in sewage sludge mono-incineration plants, this means
that the sewage sludge ash produced will be subjected to further
treatment to recover the phosphorus contained therein. However,
unburned carbon components contained in the sewage sludge ash are a
problem for phosphorus recovery.
[0004] The invention is therefore based on the problem of providing
a solution which enables the discharge from a sewage sludge
mono-incineration plant of sewage sludge ash which at most still
contains such a small proportion of unburned carbon that the sewage
sludge ash obtained can be used for phosphorus recovery without any
problems.
SUMMARY
[0005] The problem is solved by a method for the post-combustion of
sewage sludge ash produced during sewage sludge mono-incineration
in a rotary kiln using a hot gas or flue-gas stream that has a low
oxygen content, in particular an oxygen content of 6 to 10 vol. %
oxygen, wherein the sewage sludge ash exiting the rotary kiln is
fed to the gas or flue gas stream, which is removed from a fired
incineration chamber of an incineration plant associated with the
rotary kiln or from a power plant associated with the rotary kiln
and, as needed, is adjusted to the low oxygen content required for
post-combustion, and an oxidation or post-combustion of unburned
carbon contained in the sewage sludge ash is caused by this
sufficiently hot gas or flue gas stream.
[0006] Likewise, this problem is solved by a device for carrying
out the method according to any one of claims 1 to 10, which is
characterized by a sewage sludge mono-incineration plant comprising
a rotary kiln for sewage sludge incineration with connected sewage
sludge feed and a first sewage sludge ash discharge with connected
sewage sludge ash line, which opens into a gas or flue gas line in
which a gas or flue gas stream branched off from a fired
incineration chamber of an incineration plant associated with the
rotary kiln or from a power plant associated with the rotary kiln
is fed.
[0007] The method and the device allow that, in the case of sewage
sludge ash initially exiting a rotary kiln in the course of a
sewage sludge mono-incineration, the carbon content of unburned
carbon contained in the sewage sludge ash is oxidized and thus
post-combusted using a sufficiently tempered and oxygen-containing
gas or flue gas stream in a downstream step associated with the
sewage sludge mono-incineration and sewage sludge mono-incineration
plant, respectively. The content of unburned carbon in the sewage
sludge finally discharged from the sewage sludge mono-incineration
plant thereafter can thus be significantly reduced and, in
particular, reduced to such a proportion that the sewage sludge ash
obtained can be readily further processed in subsequent steps, in
particular for phosphorus recovery of the phosphorus contained in
the sewage sludge ash.
[0008] Flue gas streams from incineration chambers of incineration
plants have proven to be advantageous in that they have a
sufficiently high temperature and a sufficiently low oxygen content
on the one hand, but a sufficiently high oxygen content on the
other hand, which is necessary for the post-combustion of the
unburned carbon particles contained in the sewage sludge ash. In
order to be able to ensure post-combustion nevertheless, it can be
advantageous to provide possibilities for still specifically
raising the oxygen content of the flue gas stream.
[0009] In an advantageous manner, the post-combustion takes place
after the sewage sludge ash has been fed into the gas or flue gas
stream, by feeding this sewage sludge ash/gas stream mixture or
sewage sludge ash/flue gas stream mixture into a reaction chamber
or a reaction space; in this respect, it is also possible for the
flow cross-section of the flue gas line carrying this sewage sludge
ash/gas stream mixture or sewage sludge ash/flue gas stream mixture
to be configured as such a reaction chamber or reaction space. In a
further embodiment, the method is therefore characterized in that
the mixture of hot gas or flue gas stream and supplied sewage
sludge ash is supplied to a reaction chamber, in particular a
reaction chamber, in which the oxidation or post-combustion of the
unburned carbon contained in the sewage sludge ash takes place.
[0010] In particular, the conditions for the post-combustion of the
unburned carbon content contained in the sewage sludge ash are set
in such a way that, on the one hand, the temperature is
sufficiently high to ensure post-combustion of the carbon, but, on
the other hand, it is sufficiently low to prevent slagging of the
flue gas line carrying the sewage sludge/gas stream or flue gas
stream mixture. Therefore, in an embodiment of the method, the
temperature of the hot gas stream or flue gas stream is adjusted
such that, on the one hand, it is sufficiently high to cause
oxidation or post-combustion of the unburned carbon contained in
the sewage sludge ash, and, on the other hand, it is sufficiently
low so that the temperature increase of the sewage sludge ash/gas
stream mixture or sewage sludge/flue gas stream mixture resulting
from the oxidation or post-combustion of the unburned carbon
contained in the sewage sludge ash does not cause slagging of the
reaction chamber or the reaction space or of the gas or flue gas
line carrying the sewage sludge ash/gas stream mixture or sewage
sludge ash/flue gas stream mixture.
[0011] The combustion quality is determined, amongst others, by the
mixing of the ash particles with the oxidizing hot flue gas in the
reaction space or reaction chamber. To assist in this, a "cold"
flue gas stream can be used which is connected to the reaction
space or reaction chamber at one or more points.
[0012] This "cold" flue gas stream has the additional effect of
avoiding temperature peaks and thus further reduces possible
slagging of the reaction space and downstream plant components.
"Cold" flue gas stream is understood to mean a, such as
recirculated, flue gas in the temperature range from 100.degree. C.
to 250.degree. C., in particular 120.degree. C. to 200.degree. C.,
which is extracted, for example, downstream of an electrostatic
filter of a/the incineration plant or of a/the associated power
plant.
[0013] In order to support the combustion quality by intensifying
the mixing of the ash particles with the oxidizing hot flue gas in
the reaction space or in the reaction chamber, a "cold" flue gas
stream is introduced into the reaction space or the reaction
chamber. In this respect, in a further development of the method,
cold flue gas, such as having a temperature in the temperature
range from 100.degree. C. to 250.degree. C., in particular
120.degree. C. to 200.degree. C., is supplied to the reaction space
or the reaction chamber.
[0014] In order to produce a sufficient surface and the smallest
possible particles of unburned carbon in the sewage sludge ash, it
is advantageous to grind the sewage sludge ash before bringing it
into contact with the hot gas or flue gas stream. The method
therefore further provides that the sewage sludge ash is ground in
a mill which is configured as a ball mill, prior to being fed to
the gas or flue gas stream. Ball mills have proven to be
particularly advantageous for grinding the sewage sludge ash.
[0015] In order to prevent evaporation of the sewage sludge ash
obtained after incineration in the rotary kiln and to avoid a
supply of oxygen, as well as to bring the temperature of the sewage
sludge ash to the temperature required for the mill, the sewage
sludge ash, after leaving the rotary kiln, is first fed to a first
cooling conveyor designed as a cooling screw and then, in
particular before entering the mill, to a rotary valve.
[0016] In order to be able to discharge, after oxidation or
post-combustion of the unburned carbon initially still contained in
the sewage sludge ash, the then obtained, post-processed sewage
sludge ash from the sewage sludge mono-incineration plant, but on
the other hand also in order to be able to bring the gas or flue
gas stream to a further use, the method is in an embodiment further
characterized in that the sewage sludge ash/gas stream mixture or
sewage sludge ash/flue gas stream mixture is fed downstream of the
reaction space or the reaction chamber to a centrifugal separator,
in particular a cyclone, and in the centrifugal separator, in
particular a cyclone, the sewage sludge ash and the gas or flue gas
stream are separated from each other.
[0017] A further use of the gas or flue gas stream separated in the
centrifugal separator, which is particularly favorable in terms of
energy, is to feed it to the rotary kiln of the sewage sludge
mono-incineration plant. Therefore, in an embodiment of the method,
the gas or flue gas stream is fed to the rotary kiln downstream of
the centrifugal separator, in particular the cyclone.
[0018] In particular, the method is suitable for continuous sewage
sludge combustion and treatment of obtained sewage sludge ash, so
that the feeding of the sewage sludge ash into the gas or flue gas
stream as well as the oxidation or post-combustion of the unburned
carbon content contained in the sewage sludge ash are carried out
continuously and without intermediate storage. Likewise, it is
provided that the feeding of the gas or flue gas stream separated
from the sewage sludge ash in the centrifugal separator, in
particular the cyclone, to the rotary kiln is carried out
continuously and without intermediate storage.
[0019] According to an embodiment, in order to enable the
adjustment of the oxygen content, the device is characterized in
that at least one oxygen supply device or oxygen introduction
device is arranged in the gas or flue gas line upstream of the
inlet of the sewage sludge ash line, by means of which oxygen can
be supplied to the flue gas stream carried in the gas or flue gas
line.
[0020] It is particularly advantageous with regard to the
configuration of the device if a reaction space or a reaction
chamber is formed in the gas or flue gas line downstream of the
inlet of the sewage sludge ash line, in which, during operation of
the sewage sludge mono-incineration plant and the fired
incineration chamber, the oxidation or post-combustion of the
unburned carbon contained in the sewage sludge ash takes place, the
flow cross-section of the gas or flue gas line being shaped as
forming the reaction space or reaction chamber.
[0021] In order to be able to treat the sewage sludge ash before it
is brought together with the hot gas or flue gas stream for
carrying out the desired reaction, the apparatus is in a further
embodiment characterized in that a first cooling conveyor in the
form of a cooling screw, a rotary valve and a mill, such as
configured as a ball mill, are arranged in the sewage sludge ash
line upstream of the branching of the latter into the gas or flue
gas line in the direction of flow of the sewage sludge ash, which
are integrated into the sewage sludge ash line and through which
the sewage sludge ash can flow.
[0022] For the separation of sewage sludge ash and the gas stream
or flue gas stream loaded therewith, the arrangement or
configuration of a centrifugal separator is provided. In an
embodiment, a centrifugal separator, in particular a cyclone, is
arranged in the gas or flue gas line in the direction of flow of
the sewage sludge ash/gas stream or flue gas stream mixture
downstream of the confluence of the sewage sludge ash line and the
reaction chamber or reaction space for separating sewage sludge ash
and gas or flue gas stream.
[0023] In order to be able to bring the components of the sewage
sludge ash/gas stream mixture or sewage sludge ash/flue gas stream
mixture to further uses after passing through the centrifugal
separator, the device is in a further embodiment designed in such a
way that the centrifugal separator, in particular cyclone, has an
exhaust gas line opening into the rotary kiln and a sewage sludge
ash discharge line opening into a further cooling conveyor designed
as a cooling screw. In this way, both the gas or flue gas stream
and the further processed sewage sludge ash can be advantageously
supplied for appropriate further processing.
[0024] In order to be able to selectively enrich the gas stream
with oxygen, in particular if it is a flue gas stream, the gas or
flue gas line has at least one oxygen supply device or oxygen
introduction device in the flow direction of the gas or flue gas
stream upstream of the confluence of the sewage sludge ash line.
This allows the hot flue gas to be adjusted, in particular to be
raised to the oxygen content required for the incineration or
post-combustion of the sewage sludge ash, and the required
oxidizing hot flue gas to be generated if the oxygen content of the
flue gas taken from the incineration plant is otherwise
insufficient for this purpose.
[0025] The sewage sludge mono-incineration by means of a rotary
kiln can be combined in a particularly advantageous manner with a
waste incineration plant or a waste-fired power station, from which
the hot flue gas stream causing the post-combustion of the sewage
sludge ash then originates. The associated incineration plant is a
waste incineration plant or the associated power plant is a
waste-fired power station.
[0026] Finally, the device is in a further configuration also
characterized in that at least one flue gas inlet device for
supplying cold flue gas having a temperature of 100.degree. C. to
250.degree. C., in particular 120.degree. C. to 200.degree. C.,
opens into the reaction space or the reaction chamber.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] The accompanying drawing serves to provide an understanding
of non-limiting embodiments. The drawing illustrates non-limiting
embodiments and, together with the description, serves for
explanation thereof. Further non-limiting embodiments and many of
the intended advantages will become apparent directly from the
following detailed description. The elements and structures shown
in the drawing are not necessarily shown to scale relative to each
other. Like reference numerals refer to like or corresponding
elements and structures.
[0028] FIG. 1 shows a schematic representation of a sewage sludge
mono-incineration plant with an associated waste incineration
plant.
DETAILED DESCRIPTION
[0029] The only FIGURE shows a schematic representation of a sewage
sludge mono-incineration plant 1 with an associated waste
incineration plant 2. The sewage sludge mono-incineration plant 1
comprises a rotary kiln 3 with connected sewage sludge feed 4. By
means of the sewage sludge feed 4, which is configured in the form
of a pipe, sewage sludge originating, for example, from a sewage
treatment plant is fed to the rotary kiln 3 and incinerated in the
rotary kiln 3 to form sewage sludge ash. At its end opposite to the
sewage sludge feed 4, the rotary kiln 3 has a first sewage sludge
ash discharge 5. From the first sewage sludge ash discharge 5, a
connected sewage sludge ash line 6 leads off, which opens into a
gas or flue gas line 7. In the sewage sludge ash line 6, during
operation of the sewage sludge mono-incineration plant 1, sewage
sludge ash discharged from the rotary kiln 3 is fed to a gas or
flue gas stream flowing in the gas or flue gas line 7 and mixed
with it. By means of the sewage sludge ash line 6, the sewage
sludge ash discharged from the rotary kiln 3 is first fed in the
direction of flow of the sewage sludge ash to a first cooling
conveyor 8 configured as a cooling screw, then passed through a
rotary valve 9 and subsequently through a mill 10, which is
configured as a ball mill, before it is then fed to the gas or flue
gas line. Thus, in the sewage sludge ash line 6, the first cooling
conveyor 8 configured as a cooling screw, the rotary valve 9 and
the mill 10 are arranged in the direction of flow of the sewage
sludge ash before it opens into and is integrated into the gas or
flue gas line 7, which are integrated into the sewage sludge ash
line 6 and through which the sewage sludge ash can flow.
[0030] The sewage sludge mono-incineration plant 1, in particular
the rotary kiln 3, is assigned as associated incineration plant 2a
the waste incineration plant 2, which has a fired incineration
chamber 11. The gas or flue gas line 7 branches off from the boiler
12 of the incineration plant 2a and thus from the boiler 12
associated with the incineration chamber 11, so that flue gas
originating from the incineration chamber 11 can be fed through
this gas or flue gas line to the junction point where the sewage
sludge ash line 6 opens in the gas or flue gas line 7. On the way
there, along the gas or flue gas line 7, an oxygen supply device or
oxygen introduction device 13 is arranged, by means of which the
gas or flue gas stream carried in the gas or flue gas line 7 can be
supplied in metered doses with the oxygen that may be necessary to
set the desired oxygen content which is as low as possible. Air
serves as the oxygen carrier. In the embodiment example, the gas or
flue gas line 7 is assigned a plurality of so-called "blowing guns"
or compressed air introduction devices 13a, by means of which
compressed air can be blown into the gas or flue gas line 7. The
blowing guns 13a are arranged at structurally suitable locations
and keep the gas or flue gas line 7 or this flow channel free of
deposits by blowing in compressed air under increased pressure.
[0031] During operation of the sewage sludge mono-incineration
plant 1 and the incineration plant 2a or of the waste incineration
plant 2, the hot gas or flue gas stream 7 conducted in the gas or
flue gas line 7 and the sewage sludge ash supplied by means of the
sewage sludge ash line 6 to the confluence with the gas or flue gas
line 7 mix to form a sewage sludge gas stream or flue gas stream
mixture which is supplied to a reaction space 20 not shown in
greater detail or to a reaction chamber 20 not shown in greater
detail, which can also be configured as a corresponding
configuration of the flow cross-section of the gas or flue gas line
7. This reaction space 20 or this reaction chamber 20 is thus
formed in the direction of flow of the sewage sludge/gas stream or
flue gas stream mixture downstream of the confluence of the sewage
sludge ash line 6 with the gas or flue gas line 7 and is indicated
in the FIGURE by means of dashed lines. In this reaction chamber 20
or in this reaction space 20, during operation of the sewage sludge
mono-incineration plant 1 and the fired incineration chamber 11,
the oxidation or post-combustion of the unburned carbon contained
in the sewage sludge ash takes place by means of the hot gas or
flue gas stream having a suitable oxygen content as low as possible
and supplied through the gas or flue gas line 7.
[0032] Lines for supplying "cold" flue gas 19 are connected to the
reaction space 20 or the reaction chamber 20 at one or more points.
The supply of "cold" flue gas 19 causes good mixing of the sewage
sludge/gas stream mixture or sewage sludge/flue gas stream mixture
present in the reaction space 20 or the reaction chamber 20,
increases the degree of conversion of the residual carbon to be
burned in the sewage sludge/gas stream mixture or sewage
sludge/flue gas stream mixture, and prevents the occurrence of
temperature peaks in the reaction space or reaction chamber. "Cold"
flue gas or "cold" flue gas stream means, for example, flue gas
branched off from the exhaust line 15 of the centrifugal separator,
in particular cyclone 14, or recirculated from the incineration
plant 2a or the waste incineration plant 2, which, if necessary
after appropriate cooling or in particular after an electrostatic
filter, is taken from the incineration plant 2a or the waste
incineration plant 2 and has a temperature between 100.degree. C.
and 250.degree. C., in particular between 120.degree. C. and
200.degree. C. Advantageously, a flue gas (re)circulation is
formed.
[0033] In the direction of flow of the sewage sludge ash/gas stream
or flue gas stream mixture, a centrifugal separator, in particular
cyclone 14, for separating the sewage sludge ash/gas stream or flue
gas stream mixture into a sewage sludge ash portion and a gas
stream or flue gas stream portion is arranged downstream of the
confluence of the sewage sludge ash line 6 with the gas or flue gas
line 7 and downstream of the reaction chamber 20 or the reaction
space 20.
[0034] An exhaust gas line 15 branches off from the centrifugal
separator, in particular cyclone 14, which opens into the rotary
kiln 3 in the area of the first sewage sludge ash discharge 5.
Through this exhaust gas line 15, the gas stream or flue gas stream
separated from the sewage sludge ash/gas stream mixture or sewage
sludge ash/flue gas stream mixture in the centrifugal separator, in
particular cyclone 14, during operation of the sewage sludge
mono-incineration plant 1 and the incineration plant 2a or the
waste incineration plant 2, respectively, is introduced into the
rotary kiln 3 and serves there to support the combustion of the
remaining volatile components of the sewage sludge.
[0035] The exhaust gas from the rotary kiln 3 is fed into the
boiler 12 of the waste incineration plant 12 via a further flue gas
line 21 at its end having the sewage sludge feed 4. Thus, it is
possible to return a portion of the boiler flue gas to the boiler
12 through the gas or flue gas line 7, the cyclone 14, the exhaust
gas line 15, the rotary kiln 3 and the further flue gas line 21,
thereby recirculating flue gas.
[0036] Furthermore, the centrifugal separator, in particular
cyclone 14, is connected to a sewage sludge ash discharge line 16,
through which the sewage sludge separated from the sewage sludge
ash/gas stream or flue gas mixture in the centrifugal separator, in
particular cyclone 14, post-combusted and oxidized, is discharged
from the centrifugal separator, in particular cyclone 14, and fed
to a further cooling conveyor 17 configured as a cooling screw,
into which the sewage sludge ash discharge line 16 opens. At the
opposite end of the further cooling conveyor 17 there is then a
discharge line 18 which forms the final, second sewage sludge ash
discharge 18a of the sewage sludge mono-incineration plant 1.
[0037] By means of the combination of a sewage sludge
mono-incineration plant 1 with an incineration plant 2a shown in
the FIGURE, by way of example a sewage sludge mono-incineration
plant 1 comprising a rotary kiln 3 and an incineration plant 2a
configured as a waste incineration plant 2, the sewage sludge ash
produced by incineration of sewage sludge fed to the rotary kiln 3
is subjected to oxidation or post-combustion of unburned carbon
contained in the sewage sludge ash by means of a hot gas stream or
flue gas stream having an oxygen content as low as possible and
suitable for the post-combustion of sewage sludge incinerated in
the rotary kiln 3 or sewage sludge ash formed therein, in
particular having an oxygen content of 6 to 10 vol. % oxygen. The
sewage sludge ash exiting the rotary kiln 3 is fed to a gas stream
or flue gas stream guided in the gas or flue gas line 7, and this
sufficiently hot, in particular 750.degree. C. to 1100.degree. C.,
such as 800.degree. C. to 1000.degree. C., gas stream or flue gas
stream then causes the oxidation and post-combustion of the
unburned carbon contained in the sewage sludge ash. The gas or flue
gas stream taken from the fired incineration chamber 11 of the
associated incineration plant 2a is adjusted, if desired, to the
low oxygen content required for the post-combustion of the sewage
sludge by means of at least one oxygen supply device or oxygen
introduction device 13 arranged on the gas or flue gas line 7. The
portions of unburned carbon present in the mixture of hot gas or
flue gas stream and supplied sewage sludge ash are oxidized and
post-combusted in the reaction space 20 or the reaction chamber 20.
For this purpose, the hot gas or flue gas stream flowing in the gas
or flue gas line 7 has such a set temperature which, on the one
hand, is sufficiently high to cause the oxidation or
post-combustion of the unburned carbon contained in the sewage
sludge ash and, on the other hand, is sufficiently low so that the
temperature increase of the sewage sludge ash/gas stream mixture or
sewage sludge ash/flue gas stream mixture resulting from the
oxidation or post-combustion of the unburned carbon contained in
the sewage sludge ash does not cause slagging of the reaction
chamber 20 or of the reaction space 20 or of the gas or flue gas
line 7 carrying the sewage sludge ash/gas stream mixture or sewage
sludge ash/flue gas stream mixture. In order to flush or keep the
gas or flue gas line 7 free of deposits, blowing guns 13a with a
flow outlet directed and acting into the flow cross-section of the
gas or flue gas line 7 are also arranged on the latter.
[0038] The feeding of the sewage sludge ash into the gas or flue
gas stream as well as the oxidation or post-combustion of the
unburned carbon content contained in the sewage sludge ash are
carried out continuously and without intermediate storage.
Likewise, the feeding of the gas or flue gas stream separated from
the sewage sludge ash in the centrifugal separator, in particular
cyclone 14, to the rotary kiln 3 is carried out continuously and
without intermediate storage.
[0039] The process measures and process steps set out above each
arise during ongoing operation of the sewage sludge
mono-incineration plant 1 and the incineration plant 2a. In this
connection, the sewage sludge mono-incineration plant 1 comprises,
in particular, the complex comprising the sewage sludge feed 4, the
rotary kiln 3, the first cooling conveyor 8, the rotary valve 9,
the mill 10, the cyclone 14, the further cooling conveyor 17, and
the lines 6, 15, 16 respectively connecting these and the gas or
flue gas line 7 with associated oxygen introduction device 13 and
associated blowing guns 13a and the discharge line 18, as well as
the reaction space 20 or the reaction chamber 20 with associated
feed lines/flue gas introduction devices 19 for supplying "cold"
flue gas.
[0040] The essential aspect of the device and the method is
directed to the post-treatment of the sewage sludge ash discharged
from the rotary kiln 3 by corresponding oxidation and
post-combustion of the unburned carbon fractions contained in the
sewage sludge ash, so that a reduction of the content of unburned
carbon in the sewage sludge ash is achieved and a corresponding use
of the post-treated sewage sludge ash discharged from the further
cooling conveyor 17 is possible, in particular for phosphorus
recovery.
[0041] The reduction of the unburned carbon content is achieved by
oxidation and post-combustion. The process or procedure runs in
particular continuously and without intermediate storage of
resulting sewage sludge ash and consists of the following,
substantial steps: [0042] the sewage sludge ash exiting the rotary
kiln 3 is conveyed by means of a cooling screw or the first cooling
conveyor 8 and passed through the rotary valve 9 under exclusion of
air; [0043] subsequently, the sewage sludge ash is ground to
increase the particle fines content therein in the mill 10; [0044]
the ground sewage sludge ash exiting the mill 10 is fed to the hot
flue gas stream drawn off from the furnace or incineration chamber
11 or the boiler 12 downstream thereof and guided in the gas or
flue gas line 7. The temperature of the hot flue gas is both
sufficiently high for the initiation of the oxidation or
post-combustion and sufficiently low so that the temperature
increase resulting from the oxidation or post-combustion does not
cause slagging of the downstream flue gas section in the gas or
flue gas line 7 following the reaction space 20 or the reaction
chamber 20. The flue gas stream led from the incineration plant 2
to the inlet of the sewage sludge ash line 6 in the gas or flue gas
line 7 has a reduced or decreased, i.e. a low proportion of oxygen
compared to air. By admixing air or oxygen by means of the oxygen
introduction device 13, the oxygen content of this gas or flue gas
stream can be controlled to a value suitable for the
post-combustion of the unburned carbon present in the sewage sludge
ash; [0045] after the sewage sludge ash has been fed into the gas
or flue gas stream conducted in the gas or flue gas line 7, the
desired oxidation or post-combustion of the unburned residual
carbon content contained in the sewage sludge ash takes place in
the reaction chamber 20 or the reaction space 20 in order to lower
the unburned residual carbon content in the sewage sludge ash;
[0046] the sewage sludge ash/gas stream mixture or sewage sludge
ash/flue gas stream mixture exiting the reaction chamber 20 or the
reaction space 20 is passed into the cyclone 14, where separation
of the sewage sludge ash and gas or flue gas stream occurs. The
sewage sludge ash discharged from cyclone 14 is brought to a
subsequent treatment by means of suitable conveying means, for
example the further cooling conveyor 17; [0047] the gas or flue gas
stream exiting the cyclone is fed to the rotary kiln 3.
[0048] Sewage sludge mono-incineration is understood to mean the
incineration of at least substantially exclusively sewage sludge,
i.e. only sewage sludge is incinerated without any intended
admixture of other fuels or fuel components. However, unintentional
or insignificant additions of other fuels or fuel components, in
particular in the sense of components contained in the sewage
sludge, are possible. However, processes and devices in which an
intended and deliberate co-combustion of sewage sludge with other
fuels, e.g. coal, takes place are to be excluded.
[0049] The feed of sewage sludge ash and a gas or flue gas stream,
in particular a flue gas stream recirculating from and to the
boiler 12 of the incineration plant 2a, may be directly into a/the
reaction space 20 or a/the reaction chamber 20. That is, the sewage
sludge ash line 6 and the gas or flue gas line 7 and, if
applicable, the flue gas introduction device 19 for supplying
"cold" flue gas may all open directly into the reaction space 20 or
the reaction chamber 20.
LIST OF REFERENCE SIGNS
[0050] 1 sewage sludge mono-incineration plant [0051] 2 waste
incineration plant [0052] 2a incineration plant [0053] 3 rotary
kiln [0054] 4 sewage sludge feed [0055] 5 first sewage sludge ash
discharge [0056] 6 sewage sludge ash line [0057] 7 gas or flue gas
line [0058] 8 first cooling conveyor [0059] 9 rotary valve [0060]
10 mill [0061] 11 fired incineration chamber [0062] 12 boiler
[0063] 13 oxygen introduction device [0064] 13a blowing gun [0065]
14 cyclone [0066] 15 exhaust gas line [0067] 16 sewage sludge ash
discharge line [0068] 17 cooling conveyor [0069] 18 discharge line
[0070] 18a second sewage sludge ash discharge [0071] 19 feed line
of "cold" flue gas; flue gas introduction device for supplying
"cold" flue gas [0072] 20 reaction space/reaction chamber [0073] 21
further flue gas line
* * * * *