WO2016074990A1

WO2016074990A1 - Digestion and gasification of sludge occurring in a wastewater-treatment plant

Info

Publication number: WO2016074990A1
Application number: PCT/EP2015/075577
Authority: WO
Inventors: Albert Heindl
Original assignee: Huber Se
Priority date: 2014-11-14
Filing date: 2015-11-03
Publication date: 2016-05-19
Also published as: DE102014116688A1

Abstract

The invention relates to a method for making use of sludge (1) occurring in a wastewater-treatment plant, wherein, with the aid of at least one digestion tank (2) of the wastewater-treatment plant, digester gas (3) is generated from at least some of the sludge (1) occurring, wherein at least some of the digester gas (3) occurring is combusted on site, and wherein at least some of the heat and/or electrical energy resulting from the combustion of the digester gas (3) is utilized in the wastewater-treatment plant. The invention is distinguished in that at least some of the sludge (1) occurring is mixed on site with at least one biogenic fuel (4), preferably wood, in that the fuel mixture (5) made up of sludge (1) and biogenic fuel (4) is fed to a gasifier (9) of the wastewater-treatment plant, in that, with the aid of the gasifier (9), some of the fuel mixture (5) is converted into a combustible gas, and in that the gas is combusted on site, wherein it is likewise the case that at least some of the heat and/or electrical energy resulting from the combustion of the gas is utilized in the wastewater-treatment plant.

Description

DRAINING AND GASIFICATION OF SEWAGE SLUDGE INVOLVED IN A WASTE WATER

The present invention relates to a process for the recovery of sewage sludge arising on a sewage treatment plant, wherein with the aid of at least one digester of the sewage treatment plant from at least a portion of the sewage sludge produced sewer gas, wherein at least a portion of the resulting digester gas is burned on site, and wherein at the combustion of the fermentation gas resulting heat and / or electrical energy is used at least partially on the sewage treatment plant.

On sewage treatment plants regularly falls to a not inconsiderable amount of sewage sludge, which is to be understood in the context of the invention under the term sewage sludge resulting from the wastewater treatment in sewage treatment plants sludge.

It is already known in the prior art to suspend such sewage sludge in digesters (eg so-called digestion towers) from an anaerobic degradation process in which a digester gas is produced which comprises different and at least partially combustible gas species (for example methane). Finally, the digester gas can be incinerated by means of a combustion device, for example a combined heat and power plant (hereafter referred to as a cogeneration unit). The resulting waste heat can be supplied via a heat exchanger to a heat storage or a wärmebenötigenden unit of the sewage treatment plant to make good use of the waste heat can. Likewise, the power generated by the combustion device during combustion by means of a generator for sewage plant-internal processes can be used to also minimize the need for electrical external energy. However, since the energy requirements of a sewage treatment plant can not be fully covered by the measures described, it is also common to burn external energy sources, such as oil or natural gas on site (in the context of the invention this means: on the sewage treatment plant) and the resulting To feed heat or the correspondingly generated electric power in the respective circuits of sewage treatment plants.

Object of the present invention is now to minimize the amount of necessary for the operation of the treatment plant external fuel.

The object is achieved by a method having the features of claim 1.

According to the invention, the method is characterized by the following features:

In general, it is provided to at least partially supply the sewage sludge arising on the sewage treatment plant to a gasifier, in which the sewage sludge is partly converted into a combustible gas, which can then be thermally utilized with the aid of a corresponding combustion device. Since the gasification of sewage sludge due to its relatively low ash softening temperature and the high ash content procedurally complex and problematic, is proposed in the invention beyond at least a portion of the resulting sewage sludge on site and before being fed into the gasifier with at least one biogenic fuel (ie a fuel from renewable resources) to mix.

The biogenic fuel may, for example, be wood in the form of wood chips, wood briquettes, wood chips or, more preferably, wood pellets. Other biogenic solid or liquid fuels (eg straw or vegetable oil) may also be used alone or in combination with wood. come, wherein the biogenic fuel should have a higher ash softening temperature than the thus mixed sewage sludge.

The background to this is the fact that sewage sludge has an ash softening temperature which is generally lower than the gasification temperature that prevails during the gasification of the sewage sludge. The ash liquefies therefore during the gasification. When the ash finally cools down, the liquid ash in the form of a cohesive mass solidifies which causes disturbances in the subsequent gasification process.

In order to counteract this disadvantage, it is now provided in a development of the invention that the sewage sludge is supplied before the transfer to the carburetor, a biogenic fuel having a higher ash softening temperature than the sewage sludge to be recycled. In addition, the ash content of the biogenic fuel should be lower than that of sewage sludge, as too high an ash content of the fuel mixture can lead to problems during gasification and in the subsequent gas purification.

The fuel mixture resulting from the mixing of the sewage sludge and the additional biogenic fuel is finally fed to a gasifier of the sewage treatment plant and partly converted into a combustible gas. The resulting gas can in turn be burned on site, for example with a gas engine of the sewage treatment plant, wherein the heat generated during the combustion of the gas and / or electrical energy is also used at least partially on the sewage treatment plant. For example, it would be conceivable that the heat produced during combustion for drying the sewage sludge and / or the waste heat of the condensation line of the drying device for heating the sewage sludge and / or for digester heating. In particular, it would therefore be advantageous to use at least a portion of the heat in order to supply the clarifier to the gasifier. to dry. Also, the electrical current produced during the combustion can be used in a variety of ways on the sewage treatment plant, for example for the operation of corresponding control and regulating devices and / or the drying device.

As a result, the sewage treatment plant can be operated autonomously in the application of the method according to the invention except for the supply of biogenic fuel.

In summary, therefore, the invention provides for mixing the sewage sludge arising on a sewage treatment plant with at least one biogenic fuel and at least partially converting the fuel mixture into a combustible gas (= gas mixture of several gaseous components resulting from the gasification of the fuel mixture), which subsequently can be used thermally directly on site.

There are advantages in this context if the fuel mixture supplied to the gasifier has an ash content A ₃ which satisfies the following equation:

_A _ m _l * A _l * {TR _l ) + m ₂ * A ₂ * {TR ₂ ) ^ _x

3 m _l * 7? _! + m ₂ * TR ₂ where the individual quantities are defined as follows: mi: mass fraction of the sewage sludge of the fuel mixture fed to the carburetor (in mass percent (% -mas)),

Α-ι: ash content of the sewage sludge of the fuel mixture (in% -mas based on the dry matter of the sewage sludge of the fuel mixture), TR-i: dry substance content of the sludge of the fuel mixture (in% -mas), m ₂ : mass fraction of the biogenic fuel of the fuel mixture fed to the carburetor (in mass percentage (% -mas)),

A ₂ : ash content of the biogenic fuel of the fuel mixture (in% - mas based on the dry matter of the biogenic fuel of the fuel mixture),

TR ₂ : dry matter content of the biogenic fuel of the fuel mixture (in% -mas), wherein the mixing of sewage sludge and biogenic fuel is such that X an amount of max. 0.50% -mas, preferably an amount of max. 0.35% -mas, particularly preferably an amount of max. 0.30% mas.

Incidentally, the ash content should be determined in accordance with DIN EN 14775 "Solid biofuels - determination of the ash content" by a thermal treatment at 550 ± 10 ° C. In other words, it is advantageous if the sewage sludge is at least as rich before the carburetor is charged a large amount of biogenic fuel is admixed so that the resulting fuel mixture has an ash content of at most 50% -max, preferably of at most 35% -max, more preferably of at most 30% -max that the maintenance of the carburetor is minimal.

It is also advantageous if the sewage sludge is dried before mixing with the biogenic fuel until its moisture content (ie its water content) is at most 30% -max, preferably at most 20% -max. preferably 10% -mas, is. While methods are also known, with the help of which quite moist goods can be converted into a combustible gas, it is procedurally advantageous to dry the sewage sludge until a defined residual moisture is reached. The drying of sewage sludge can, for example, with the help of a sewage treatment plant's own

Belt driers carried out, wherein the inventive method is not limited to a particular drying process. Also, the biogenic fuel should have a moisture content which is not higher than 30 Bornas, preferably not higher than 20% -max, more preferably not higher than 15% -max. In general, it is also conceivable to post-dry the biogenic fuel on the sewage treatment plant if its moisture content is too high. The sewage sludge (possibly after predrying) and the biogenic fuel mixed with it can also be dried to the desired moisture content after they have been mixed. Alternatively, it is also conceivable to moisten the biogenic fuel or the fuel mixture before it is supplied to the gasifier, if the moisture content of the biogenic fuel or the fuel mixture is below a defined limit.

Likewise, it is advantageous if the sewage sludge is dewatered before mixing with the biogenic fuel with the aid of an HTC process until its moisture content is at most 40% -max, preferably at most 35% -max, particularly preferably 30% -max (HTC The dehydrated sewage sludge is usually heated to 180 ° C to 200 ° C and placed in a boiler at 20 bar to 25 bar under pressure, with the heat energy required for the heating of the Alternatively, however, it is also possible to dewater the sewage sludge before subsequent drying by means of screw presses or centrifuges (or otherwise), until it has a moisture content of about 18% -mas to 35% -mas. It is also extremely advantageous if the sewage sludge mixed with the biogenic fuel at least partly originates from the digester of the sewage treatment plant. The sewage sludge is used in this case particularly comprehensive for energy production, since in addition to the combustible gas produced in the gasifier and the digester gas produced in the digester can be thermally converted and thus used energetically. Preferably, all of the sewage sludge supplied to the gasifier originates from the digester (s) of the treatment plant. In addition, it is advantageous if the sewage sludge originating from the digester is first dried before it is mixed with the biogenic fuel and fed to the gasifier in a further step.

Furthermore, it is advantageous if the dried according to the above description sewage sludge locally using a compacting device to a com pacted bulk material, for example, to pellets, briquettes or granules, processed and then mixed with the biogenic fuel. This has the advantage that the sewage sludge is particularly easy to transport and dose. In this context, it is also advantageous if the biogenic fuel before mixing with the sewage sludge by means of a compacting device to a bulk material, for example, pellets, briquettes or granules processed. The Kompak- tion of biogenic fuel, which is z. B. can be sawdust or sawdust, this can be done outside the sewage treatment plant, so that the treatment plant is already supplied in this case with appropriately compacted biogenic fuel (eg., Wood pellets or wood briquettes). However, it would also be conceivable to supply the sewage treatment plant with non-compacted biogenic fuel and to supply it locally to a compacting device.

Finally, it would also be possible to mix non-compacted, dried sewage sludge with non-compacted biogenic fuel on-site and mix using a wastewater treatment plant's own compacting equipment to process pellets, briquettes or granules and feed the carburetor. The sewage sludge could also be mixed with a biogenic raw material, for example sawdust and / or sawdust, before the drying, and the mixture then dried and compacted.

It is particularly advantageous if the moisture content of the fuel mixture supplied to the carburetor is monitored and, if necessary, increased by the addition of a liquid. Depending on the composition, the fuel mixture should have a defined moisture content or a moisture content within certain limits (ie water content in% -mas) in order to ensure the best possible gasification. If the moisture content of the fuel mixture, which can be monitored with the aid of one or more sensors, is too low, it is advantageous to increase the moisture content by adding a liquid. The liquid may be, for example, water or an aqueous solution. In particular, it is advantageous to use the liquid for wetting the fuel mixture, which is obtained in the purification of the exhaust air of the drying device, with the aid of which the sewage sludge is dried prior to compaction. In this context, a so-called (acidic) scrubber is used, which among other things serves to remove ammonia with the help of sulfuric acid from the exhaust air. The resulting ammonium sulfate solution may eventually be added to the fuel mixture to increase its moisture content.

It would also be conceivable to increase the moisture content of the fuel mixture supplied to the carburetor by adding the condensate which accumulates when the gas produced during the gasification of the fuel mixture is cooled for cleaning purposes. In particular, this is phenol-containing condensate, which usually has to be disposed of separately.

Furthermore, it may be advantageous if the fuel mixture and / or the individual fuels (dried sewage sludge, biogenic fuel) before or during the above Kom paktierung liquid is supplied if their moisture content is too low for the Konppaktiervorgang. Also in this context, the above-mentioned (phenol-containing) condensate and / or the liquid can be used, which is obtained in the purification of the exhaust air of the drying device.

Finally, the liquids mentioned above can be used individually or in any combination to humidify the air supplied to the gasifier during the gasification of the fuel mixture.

It is also advantageous if the ashes obtained in the gasifier during the gasification of the fuel mixture are cooled by heat removal and the heat dissipated in this case is also used at least partially on the sewage treatment plant. Also, the combustible gas leaving the gasifier during gasification may be cooled by heat removal before it is burned. As a result, undesirable substances can be condensed and thus removed from the combustible gas, wherein the heat dissipated in this case can be supplied to other processes of the sewage treatment plant or the said heat storage.

It is also extremely advantageous if the vapor produced during the drying of the sewage sludge or of the fuel mixture is condensed by heat removal and the heat removed during the condensation of the vapor is also used at least partially on the sewage treatment plant, if necessary after an intermediate storage in one or more heat accumulators becomes. For example, it would be conceivable to supply said heat via a heat storage and / or one or more heat exchangers to the digester in order to heat the sewage sludge therein and to bring the sewage sludge to the necessary temperature before entering the digester. Finally, it is advantageous if the heat produced during the combustion of the fermentation gas or of the combustible gas from the gasification is supplied to different heat accumulators in order subsequently to be able to use the heat energy again on the sewage treatment plant. In particular, it is advantageous if the heat of the exhaust gases produced during the respective combustion is supplied to a high-temperature heat accumulator (which may comprise, for example, a thermal oil as heat storage medium), while the heat dissipated from the respective cooling circuits of the combustion equipment used is supplied to a low-temperature accumulator (the For example, water used as a heat storage medium). The cached in the individual heat storage heat can eventually serve to heat the sewage sludge in the digester (heat from the low-temperature heat storage) or the drying of sewage sludge (heat from the high-temperature heat storage).

Further advantages of the invention are described in connection with the following embodiment. It shows:

Figure 1 is a schematic diagram of a section of a sewage treatment plant.

The sewage treatment plant operable in accordance with the present method, which is shown fragmentarily and schematically in FIG. 1, comprises inter alia one or more digester 2 for the sewage sludge 1 arising on the sewage treatment plant. The sewage sludge 1 is partially converted within the digester 2 and under exclusion of oxygen (anaerobic) in a biogas 3.

Since the digester gas 3 comprises a multiplicity of combustible gas types (eg methane), it can be thermally converted with the aid of a combustion device, for example a wastewater treatment plant CHP, wherein the feed of the digester gas 3 into the combustion device via a digester gas line. tion 16 takes place. By the combustion of the fermentation gas 3 finally arises (with the aid of a generator) electrical energy which can be fed via a power line 17 units of the wastewater treatment plant, such as a controller, the sewage sludge treatment and / or the drying device, or fed into the public grid.

In addition, during the combustion of the fermentation gas 3 waste heat, which is supplied via corresponding heat carrier lines 18 and heat exchangers, not shown, one or more heat accumulators 14 and stored there for later use on the sewage treatment plant.

In addition, the present invention now also provides the sewage sludge obtained on the sewage treatment plant 1 either directly or after a digestion process in the digester 2 a carburetor 9 to convert the corresponding sewage sludge 1 partially into a combustible gas, which is also used for energy (eg. B. by means of a gas engine 12) can be burned.

However, since the gasification of sewage sludge 1 alone is associated with various problems, the invention proposes that the sewage sludge 1 before its gasification a biogenic fuel 4, preferably wood, admixed and then the resulting fuel mixture 5 is supplied to the carburetor 9. In this case, the biogenic fuel 4 should have a lower ash content and a higher ash softening temperature than the sewage sludge 1 in order to obtain a fuel mixture 5 whose ash content is lower and whose ash softening temperature is higher than the corresponding characteristics of the sewage sludge 1.

In principle, the biogenic fuel 4 can be mixed with the sewage sludge 1 in different ways. While it is conceivable that the clarification Schlmm 1 undried to mix with the biogenic fuel 4 and only to subject the fuel mixture 5 to a drying, it is advantageous to first dry the sewage sludge 1 until its moisture content is at most 20% -max and only then with the dried biogenic fuel to mix.

A procedural possibility is shown in FIG. In this exemplary embodiment, it is provided that the sewage sludge 1 originating from the digester is first fed via a sewage sludge line 21 to a drying device (for example one, one or more conveyor belts 7 for the sewage sludge 1, belt drier 23) and dried there.

Following the drying step, the dried sewage sludge 1 is fed to a compacting device 6, in which it z. B. to pellets, briquettes or specially shaped granules is processed, wherein the drying device and the compacting device 6, a buffer, such as a silo 24, may be interposed.

After compaction, the sewage sludge 1 is finally mixed with the aid of a fuel mixer 25 with the biogenic fuel 4, wherein the biogenic fuel 4 preferably before (on the sewage treatment plant or outside) was konnpaktiert and z. B. in the form of wood pellets and / or can be cached in a silo 24.

The fuel mixture 5 passes through a fuel line 20 in a carburetor 9, wherein previously a moistening of the fuel mixture 5 can be made if the moisture content is too low. The moistening can be carried out, for example, by adding an ammonium sulfate solution which is obtained during the cleaning of the drying device leaving the drying device via an exhaust air line 8 in a so-called scrubber 22, the ammonium sulfate solution being fed via a corresponding moistening line 15. can be performed. Optionally, the humidification can also be carried out with phenol-containing condensate from the gas purification of the carburetor 9.

In the carburetor 9, a partial conversion of the present in the fuel mixture 5 organic constituents in a combustible gas, wherein the biomass gasification is known per se and therefore will not be explained in detail here. The gas leaving the carburetor 9 via a gas line 19 can finally in a suitable combustion device, for. B. a (Zündstrahl-) gas engine 12, to be burned to generate electricity and / or generate waste heat, which can be used either directly or under caching in one or more heat accumulators 14 on the sewage treatment plant to z. B. sewage sludge 1 or to dry. Since carburettor plants should always be operated at rated load for operational reasons, peak loads in the electricity or heat consumption can be covered by (not shown) natural gas-fired combined heat and power plants (with reciprocating engines or gas turbines).

Prior to the combustion of the combustible gas is preferably still a filtering and / or a single or multi-stage cooling thereof to eliminate tars or other undesirable in the combustion of substances from the combustible gas. Schematically, this is illustrated in FIG. 1 by a gas conditioning arrangement 1 1 which is placed between the gasifier 9 and the gas engine 12 serving as an example of a combustion device. The heat removed from the combustible gas during gas conditioning 11 can finally be reused on site, it also being possible in this case for the heat initially to be supplied to a heat store 14 via corresponding heat carrier lines 18 and heat exchangers, not shown. Incidentally, the same applies to the heat that is extracted from the ashes obtained during gasification in a possibly existing ash cooler. In this context, it should be noted that Figure 1 shows only a heat storage 14. Of course, several heat storage 14 may be present with different heat storage media, reference being made in this regard to the above description.

The present invention is not limited to the illustrated and described embodiments. Variations within the scope of the claims are also possible as any combination of the features described, even if they are shown and described in different parts of the description or the claims.

LIST OF REFERENCES

1 . sewage sludge

2. Digester

3. Digester gas

4. biogenic fuel

5. Fuel mixture

6. compacting device

7. Conveyor belt

8. exhaust duct

9. Carburetor

10. Ash cooler

1 1. Gaskonditionieranordnung

12. Gas engine

13. CHP

14. heat storage

15. Humidification line

16. Digester gas line

17. Power line

18. heat carrier line

19. Gas line

20. Fuel line

21. sewage sludge line

22. Scrubber

23. Belt dryer

24. silo

25. Fuel mixer

Claims

Patent claims

1 . Process for the recovery of wastewater from a sewage treatment plant

Sewage sludge (1),

- wherein with the aid of at least one digester (2) of the sewage treatment plant from at least a portion of the resulting sewage sludge (1) digester gas (3) is generated,

- Wherein at least a portion of the resulting digester gas (3) is burned on site, and

wherein the heat and / or electrical energy produced during the combustion of the fermentation gas (3) is used at least partly on the sewage treatment plant,

characterized,

- That at least a portion of the resulting sewage sludge (1) is mixed on site with at least one biogenic fuel (4), preferably wood,

that the fuel mixture (5) from sewage sludge (1) and biogenic fuel (4) is supplied to a gasifier (9) of the sewage treatment plant,

- That with the aid of the carburetor (9) a part of the fuel mixture (5) is converted into a combustible gas, and

- that the gas is burned on site,

- Wherein the generated during the combustion of the gas heat and / or electrical energy is also used at least partially on the sewage treatment plant.

2. Method according to the preceding claim, characterized in that

in that the sewage sludge (1) of the fuel mixture (5) supplied to the carburetor (9) has a mass fraction nrii, an ash content Α-1 and a dry matter content related to the fuel mixture (5). stamped content TRi,

- That the biogenic fuel (4) of the carburetor (9) supplied fuel mixture (5) has a relation to the fuel mixture (5) mass fraction m ₂ , an ash content A ₂ and a dry matter content TR ₂ , and

in that the mixing of sewage sludge (1) and biogenic fuel (4) takes place in such a way that the fuel mixture (5) fed to the gasifier (9) has an ash content A ₃ which satisfies the following equation: m _l * A _L * { TR _X ) + m ₂ * A ₂ * (TR ₂ )

<X

m _l * TR _L + m ₂ * TR ₂ where X is an amount of max. 0.50% -mas, preferably an amount of max. 0.35% -mas, particularly preferably an amount of max. 0.30% sm.

A method according to claim 1 or 2, characterized in that the sewage sludge (1) is dried before mixing with the biogenic fuel (4) until its moisture content is at most 30% -max, preferably at most 20% -max, particularly preferably 10% - mas, is.

Method according to one of the preceding claims, characterized in that the sewage sludge (1) is dehydrated before mixing with the biogenic fuel (4) by means of an HTC process until its moisture content is at most 40% -max, preferably at most 35% -mas , more preferably 30% -mas.

5. The method according to any one of the preceding claims, characterized in that the mixed with the biogenic fuel (4) te sewage sludge (1) at least partially from the digester (2) of the sewage treatment plant comes.

6. The method according to any one of claims 2 to 5, characterized in that the dried according to claim 2 sewage sludge (1) on site by means of a compacting device (6) to a bulk material, for example, to pellets, briquettes or granules, processed and then with the biogenic fuel (4) is mixed, preferably also the biogenic fuel (4) prior to mixing with the sewage sludge (1), in particular on site, by means of a compacting device (6) to a compacted bulk material, for example to pellets, briquettes or granules , is processed.

7. The method according to any one of claims 1 to 5, characterized in that, preferably dried according to claim 2, sewage sludge (1) and the biogenic fuel (4) mixed and the fuel mixture (5), possibly after an intermediate drying step, on site is processed by means of a compacting device (6) into a compacted bulk material, for example into pellets, briquettes or granules.

8. The method according to any one of the preceding claims, characterized in that the moisture content of the carburetor (9) supplied fuel mixture (5) is monitored and increased if necessary by adding a liquid.

9. The method according to any one of the preceding claims, characterized in that in the gasifier (9) during the gasification of the fuel mixture (5) resulting ash is cooled by heat dissipation and / or that the carburetor (9) during the gasification leaving combustible gas Heat removal is cooled before it is burned to eliminate unwanted substances. the, and that the heat dissipated during cooling of the ash and / or the heat dissipated during cooling of the combustible gas is also at least partially used on the sewage treatment plant.

10. The method according to any one of the preceding claims, characterized in that the drying of the sewage sludge (1) or the fuel mixture (5) resulting vapor condenses by heat dissipation and the heat dissipated in condensing the vapor heat is also used at least partially on the sewage treatment plant.

1 1. Method according to one of the preceding claims, characterized in that the combustible gas is burned by means of at least one combined heat and power plant, wherein the cogeneration plant is always operated in the nominal load range, and wherein peak loads are covered by at least one natural gas-fired cogeneration plant.