Patent Application
20220074588
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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° C. to 250° C., in particular 120° C. to 200° C., which is extracted, for example, downstream of an electrostatic filter of a/the incineration plant or of a/the associated power plant.
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° C. to 250° C., in particular 120° C. to 200° C., is supplied to the reaction space or the reaction chamber.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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° C. to 250° C., in particular 120° C. to 200° C., opens into the reaction space or the reaction chamber.
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.
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.
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.
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.
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° C. and 250° C., in particular between 120° C. and 200° C. Advantageously, a flue gas (re)circulation is formed.
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.
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.
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.
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.
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° C. to 1100° C., such as 800° C. to 1000° 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.
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.
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.
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.
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:
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.
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2018 133 237.8 | Dec 2018 | DE | national |
| 10 2019 107 744.3 | Mar 2019 | DE | national |
The present application is a national stage entry according to 35 U.S.C. § 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.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2019/085369 | 12/16/2019 | WO | 00 |
