EP2401552B1 - Method for autolytic combustion of sludge - Google Patents

Description

The invention relates to a method for the automatic combustion of sludge.

In the process in question, sludges for their disposal are self-contained, that burned without external thermal energy. Such sludges can be formed in particular by sewage sludge.

After mechanical dewatering by means of presses, decanters or the like, these typically have a solids content of about 18 to 30 percent. To further treat these sludges for disposal purposes, the mechanically dewatered sludge is fed to a dryer, for example a drum, disc or stacker dryer, by methods known in the art. The sludge dried there is then fed to a combustion unit, for example a fluidized bed furnace, where it is incinerated. The running of the combustion unit, hot flue gas is used in these methods as a heating medium in the dryer.

A major disadvantage here is that the design effort and thus the cost of implementing the method is undesirably large. A further disadvantage is that during drying of the sludge in the dryer, in particular when the sludge is sewage sludge, exhaust gases with organic constituents are formed which have to be filtered out with an exhaust system such as activated carbon filters. This represents another significant cost factor.

In particular sewage sludge, but also other protein-containing sludges change their physical properties at a solids content of about 30-70% in the way that they go through the so-called glue phase. Here, the viscosity of the sludge increases significantly and there are problems in conveying the sludge. However, if the sludge is heated to a temperature of, for example, greater than 180 ° C, the long-chain molecules contained in the sludge break up and the sludge hydrolyzes, and thus no glue phase is produced when the dry matter increases and the sludge has a much lower viscosity.

The DE 31 03 417 A1 relates to a process for the oxidation of solids and aqueous sludges, in particular solid waste such as waste and sewage sludge in an oven. According to this method, aqueous sludges, especially sewage sludge, in a predetermined amount with solids, especially crushed combustible solid waste (garbage), mixed intensively, fed without dewatering in the oven and burned under pressure, verschwelt or gasified.

The EP 0 304 783 A1 relates to a process for burning aqueous sewage sludge in fluidized bed, wherein aqueous mixtures of sewage sludge and TDI residues having a solids content of 25 to 98 wt .-% and their content of TDI residue 25 to 95 wt .-%, based on The solids content is burned without further input of energy carrier.

The invention has for its object to provide a method of the type mentioned, by means of which a cost-effective and efficient combustion of sludge is made possible without additional thermal energy supply.

To solve this problem, the features of claim 1 are provided. Advantageous embodiments and expedient developments of the invention are described in the subclaims.

The inventive method is used for the automatic combustion of sludge with a high water content. The sludge is heated under pressure before being fed to a combustion unit in a heat exchanger, so that the water contained in the sludge does not evaporate but remains in a liquid phase.

By heating the sludge in a heat exchanger according to the invention before it is fed to the combustion unit, a significant reduction in the cost of self-contained sludge incineration can be achieved. This is essentially due to the fact that in the process no costly dryer for drying sludge must be used more. The fact that in the method according to the invention no more dryer is needed, is particularly advantageous in the combustion of sewage sludge. The in a dryer when drying sewage sludge striking exhaust gases are now eliminated, so that there is no corresponding Exhaust gas treatment, especially for the separation of organic constituents and odors must be provided more, since they are completely decomposed during combustion.

In addition, the problems associated with the glue phase in increasing the solids content are solved.

The sludge to be incinerated has a high water content because prior mechanical dehydration typically can not lower the water content of the sludge to below about 75%. The feed of this hydrous sludge to the incineration unit takes place in conduits through which the sludge is pumped at high pressures, typically at least 40 bar. In these lines, the sludge is heated by means of the heat exchanger. Due to the high pressure, the sludge can absorb large amounts of heat without the water evaporating in the sludge. The sludge water thus remains in the liquid phase and the sludge thus remains pumpable. When the sludge is heated under pressure, it hydrolyzes, ie large organic molecules are broken up and the viscosity of the sludge decreases considerably. This is an essential prerequisite for a controlled supply of sludge to the combustion unit and a compact design of the system components. There, the pre-heated sludge can be burned energy-efficient.

According to the invention, the pumpability of the sludge to be supplied to the heat exchanger is considerably improved by recycling a portion of the sludge heated in the heat exchanger and mixing it with fresh sludge forming sludge before being fed to the heat exchanger under pressure. As a result, the temperature of the raw sludge mixed with the recycled sludge is increased so that in this case the formation of a glue phase in the heat exchanger

Shape of a tough mud avoided or at least partially reduced.

By returning a portion of the heated in the heat exchanger sludge and its mixture with raw sludge, that is new, the first time the heat exchanger supplied sludge, this raw sludge is preheated before entering the heat exchanger. Preferably, the raw sludge is heated to such an extent by the mixture with sludge already passed through the heat exchanger that the mixture thus obtained is at such a high temperature that it no longer passes through any glue phase in the heat exchanger. Alternatively, the mixture is made so that it passes through the glue phase only very short and incomplete in the heat exchanger. In any case, achieved by the sludge recirculation avoidance of the glue phase is achieved, that the sludge remains well pumpable when passing through the heat exchanger and thus can pass well this.

Essential for an automatic combustion of the sludge without external thermal energy supply in this case is that the heat exchanger for heating the sludge, the flue gas is supplied as a heat exchange medium.

According to a further variant of the invention, the heat exchanger for heating the sludge is designed as a thermal oil heat exchanger, wherein the thermal oil is heated by means of the flue gas. Instead of the thermal oil heat exchanger and a heat exchanger with high-pressure steam or high-pressure hot water can be used as a heat exchange medium.

Already with this variant, an efficient and cost-effective combustion of the sludge is possible.

The use of thermal oil as a heat carrier between the flue gas and the sludge is an alternative embodiment of the method. It is particularly advantageous, however, that the heat exchanger for heating the Sludge the flue gas is supplied as a heat exchange medium. Coils are expediently installed for heating the sludge under pressure in the flue gas duct behind a fluidized bed combustion as a combustion unit. This could also be realized by immersion heating surfaces built into the fluidized-bed combustion or by radiant heating surfaces in the combustion chamber.

This method has as an additional advantage that the sludge can be heated directly by the exhaust gas stream, so that it is possible to dispense with thermal oil heat exchangers or a corresponding unit.

Thus, the system for implementing this method variant on a particularly compact and inexpensive construction, in particular, the sizes and weights of the system components compared to the variant with an intermediate heat transfer medium are further significantly reduced.

Figur 1:

Anlage zur selbstgängigen Verbrennung von Schlamm gemäß dem Stand der Technik.

Figur 2:

Erstes Ausführungsbeispiel einer erfindungsgemäßen Anlage zur selbstgängigen Verbrennung von Schlamm.

Figur 3:

Zweites Ausführungsbeispiel einer erfindungsgemäßen Anlage zur selbstgängigen Verbrennung von Schlamm.

Figur 4:

T-Q-Diagramm für die Anlage gemäß Figur 2.

Figur 5:

T-Q-Diagramm für die Anlage gemäß Figur 3.

The invention will be explained below with reference to the drawings. Show it:

FIG. 1:

Plant for the automatic incineration of sludge according to the prior art.

FIG. 2:

First embodiment of a plant according to the invention for the automatic combustion of sludge.

FIG. 3:

Second embodiment of a plant according to the invention for the automatic combustion of sludge.

FIG. 4:

TQ diagram for the system according to FIG. 2 ,

FIG. 5:

TQ diagram for the system according to FIG. 3 ,

FIG. 1 shows schematically the structure of a known from the prior art plant 1a for the spontaneous combustion of sludge. In the following, sewage sludge is always mentioned as an example of a sludge to be disposed of.

The sewage sludge is first supplied from a reservoir 2 of a mechanical drainage 3, which is formed by a press or the like. There, the water content of sewage sludge is reduced by mechanical means to about 75%. From the mechanical dewatering the sewage sludge is fed to a system 4a for self-combustion to burn the sewage sludge without additional thermal energy supply. The sewage sludge is first fed via a line 5 to a dryer 6, which is typically designed as a tube dryer. In the dryer 6, the sewage sludge is dried. In order to filter the resulting exhaust gases, the dryer 6 is associated with a filter system, not shown, such as an activated carbon filter. The exhaust air of the dryer 6 is discharged from the system 4a via a line 7.

The sewage sludge dried in the drier 6 is fed via a line 8 to a combustion unit, which is formed, for example, by a fluidized-bed furnace 9. Likewise, the combustion unit is supplied via a line 10 combustion air. The resulting in the fluidized bed combustion 9 hot flue gas is carried out via a line 11 from the fluidized bed furnace 9 and fed to the dryer 6 as a heating medium. By means of a heat exchanger unit 12, the combustion air is heated by using the heat of the noise gas.

The Figures 2 and 3 show embodiments of the system 1 according to the invention for the spontaneous combustion of sludge, which is again exemplified as sewage sludge. In both embodiments, the sewage sludge is supplied from a reservoir 2 to a mechanical drainage 3 such as a press. There, the mechanical content of the water content sewage sludge is reduced to about 75%. Then, in both embodiments, the sewage sludge is fed to a system 4 for automatic combustion. There, the sewage sludge in a line 5 at high pressures, which are typically about 40 bar, fed to a combustion unit, but the run in the line 5 sewage sludge is previously heated under pressure in a heat exchanger system. Due to the high pressure prevailing in the line 5, the sewage sludge remains liquid when heated and can thus be supplied with compact plant components, in particular lines 5 of the combustion unit. The emerging from the combustion unit hot flue gases are used to heat the sewage sludge, whereby a closed system 4 is obtained without external thermal energy supply.

In the embodiment according to FIG. 2 the sludge is fed in the line 5 a combustion unit in the form of a fluidized bed 9. Alternatively, the combustion unit (as in the following embodiment according to FIG. 3 ) be formed by a cyclone furnace or a rotary kiln. The sewage sludge in the line 5 is heated by means of a heat exchanger system in the form of a thermal oil heat exchanger 13. The heating of the sludge is carried out under high pressure, so that the water contained in the sludge remains in the liquid phase until it is released during combustion.

The flue gas generated in the fluidized bed combustion 9 during the combustion of the sewage sludge is fed via a line 14 to an air preheater 15 to heat there via a line 16 to the system 4 supplied combustion air which is fed to the fluidized bed 9. Then, the flue gas stream in the line 14 'is supplied to the thermal oil heat exchanger 13 for heating the thermal oil. Finally, the flue gas stream is fed via line 14 "to another air preheater 17 for a first heating of the combustion air and then via line 14"'out of the system executed. The air preheaters 15, 17 for heating the combustion air form further heat exchanger systems.

The embodiment according to FIG. 3 points to the embodiment according to FIG. 2 an even more simplified and therefore more cost-effective construction.

The sewage sludge is in turn supplied from the reservoir 2 to a mechanical drainage 3 and then fed via the line 5 of the fluidized bed furnace 9. In contrast to the embodiment according to FIG. 2 In the present case, no thermal oil heat exchanger 13 is required for heating the sewage sludge in the line 5, but only a simple heat exchanger 18. This heat exchanger 18, the flue gas generated in the fluidized bed 9, and performed via a line 19 is supplied as a heat exchange medium. In this case, the heat exchanger 18 is preceded by an air preheater 20 in the flue gas flow as another heat exchanger system, wherein in the air preheater 20 via a line 21 of the fluidized bed combustion 9 supplied combustion air is heated. The flue gas stream at the outlet of the heat exchanger 18 is discharged from the system 4 via a line 19 '. The heat exchangers for sludge heating and air preheating are usefully installed in the flue gas duct behind the combustion.

FIG. 4 shows a TQ diagram, that is, a temperature-heat diagram for the system 1 according to FIG. 2 , In the diagram according to FIG. 4 is denoted by I the temperature-heat curve of the discharged from the fluidized bed 9 flue gas. In this case, the direct outlet of the flue gas from the fluidized bed furnace 9 is designated by a. The temperature of the flue gas at the exit from the fluidized bed combustion 9 is about 800 ° C, as shown FIG. 4 is apparent. The temperature-heat curve forms a monotonically decreasing straight line up to the point b, which forms the exit of the flue gas from the system 4. There, the outlet temperature of the flue gas is about 270 ° C.

The flue gas is supplied within the system 4 the two air preheaters 15, 17 and the thermal oil heat exchanger 13, where the flue gas emits heat to the local heat exchanger media. In FIG. 4 is denoted by II the temperature-heat curve of heated in the air preheater 15, the fluidized bed combustion 9 supplied combustion air. Next is in FIG. 4 III denotes the temperature-heat curve of the thermal oil of the thermal oil heat exchanger 13. Finally, in FIG. 4 IV denotes the temperature-heat curve of the heated in the air preheater 17, introduced into the system 4 cold air.

Due to the heat input of the flue gas, the combustion air to be supplied to the fluidized bed furnace 9, which is already preheated in the air preheater 17, is heated further in the air preheater 15 from a temperature of about 320 ° C. (lower end of the curve II) to a temperature of about 734 ° C. ( upper end of the curve II). Accordingly, the flue gas cools from the starting temperature of 800 ° C (point a of curve I) to a temperature of about 654 ° C as (point c on the curve I) from.

The slope of the curve II is greater than the slope of the curve I, since the amount of air in the air preheater 15 is considerably less than the amount of flue gas.

After heating the air in the air preheater 15, the flue gas is fed to the thermal oil heat exchanger 13. The flue gas releases heat to the thermal oil so that the flue gas cools from the temperature of 654 ° C (point c on curve I) to a temperature of about 375 ° C (point d on curve I).

Finally, the flue gas is supplied from the outlet of the thermal oil heat exchanger 13 to the further air preheater 17, where the introduced into the system 4 cold air is heated. How out FIG. 4 can be seen by the heat emission of the flue gas, the air in the air preheater 17 from the temperature 375 ° C (point d on the curve I) to the outlet temperature 270 ° C (point b cooled on the curve I). As a result, the air in the air preheater 17 is heated from the inlet temperature 20 ° C (right end of the curve IV) to about 319 ° C (left end of the curve IV).

The components of Appendix 1 are to be interpreted as meaning that the exit temperature of the flue gas at exit from the system 4 is as low as possible, so that much heat of the flue gas is transferred to the components of the system 1, namely the thermal oil heat exchanger 13 and the air preheaters 15, 17. This requirement is in accordance with Appendix 1a FIG. 2 relatively well fulfilled, since the starting temperature of the flue gas (point b on the curve I) is about 270 ° C. Another requirement is that the distances between the curves II, III, IV to the temperature-heat curve of the flue gas are as large as possible, since then large temperature differences are realized in the system components, whereby the sizes of the system components can be selected small. Also this requirement is how out FIG. 4 can be seen in Appendix 1 according to FIG. 2 relatively well met.

FIG. 5 shows a TQ diagram for the system 1 according to FIG. 3 , Analogous to FIG. 4 is also referred to in the TQ diagram with I the temperature-heat curve of the flue gas. Again, a is the direct exit of the flue gas from the fluidized bed 9, where the temperature of the flue gas is about 800 ° C. By using the flue gas as the heat exchanger medium for the air preheater 20 and the heat exchanger 18, the temperature of the flue gas decreases until it leaves the system 4 to an outlet temperature of 182 ° C (point b of the curve I).

In FIG. 5 II denotes the temperature-heat curve of the combustion air in the air preheater 20. Finally, in FIG. 5 III denotes the temperature of the sewage sludge, denoted by d (right end of curve III) the entry of the sewage sludge in the heat exchanger 18, and e designates the exit of the sewage sludge from the heat exchanger 18 or the inlet of sewage sludge in the fluidized bed 9 is. By heating the combustion air for the fluidized bed combustion 9 in the air preheater 20 by means of the flue gas, the flue gas is cooled from 800 ° C (point a of the curve I) to a temperature of about 615 ° C (point c of curve I). Accordingly, the combustion air for the fluidized bed combustion 9 in the air preheater 20 from a starting temperature of 20 ° C when entering the system 4 (right end of the curve II) is heated to a temperature of 548 ° C (left end of the curve II). Since the amount of flue gas is considerably larger than the amount of combustion air, the slope of the curve I for the flue gas is smaller than the slope of the curve II for the combustion air.

By heating the sewage sludge in the heat exchanger 18 by means of the flue gas, the flue gas is cooled from the temperature 615 ° C (point c on the curve I) to the outlet temperature of the system 4 of 182 ° C (point b on the curve I). The sewage sludge is heated from a temperature of 20 ° C (point d on curve III) to a temperature of about 288 ° C (point e on curve III). Since the sewage sludge is under pressure, the water of the sludge remains in the liquid phase.

As from the comparison of FIGS. 4 and 5 can be seen, the Appendix 1 according to FIG. 3 better performance than Annex 1a FIG. 2 on. This is the case in the diagram according to FIG. 5 obtained at 182 ° C, an exit temperature of the flue gas at the exit from the system 4, which is considerably lower than the outlet temperature of 270 ° C in the diagram according to FIG. 4 , Furthermore, in the diagram according to FIG. 5 higher temperature differences between the curve I of the flue gas and the remaining curves II, III achieved, as in the diagram according to FIG. 4 the case is. It follows that for Annex 1, see FIG. 3 where no thermal oil heat exchanger 13 is needed, operates considerably more energy efficient than the plant 1 according to FIG. 2 where a thermal oil heat exchanger 13 is needed. In addition, the sizes of the system components in Appendix 1 can FIG. 3 are considerably smaller dimensions than in the Appendix 1 according to FIG. 2 ,

The invention is not limited to the specific designs of the systems according to the FIGS. 4 and 5 limited.

In particular, for the embodiment according to FIG. 5 Plant designs are possible in which an exit temperature of the flue gas is obtained from the system 4, which is at 80 ° C or even lower.

LIST OF REFERENCE NUMBERS

(1)

investment

(1a)

investment

(2)

reservoir

(3)

drainage

(4)

system

(4 ')

system

(5)

management

(6)

dryer

(7)

management

(8th)

management

(9)

fluidised bed combustion

(10)

management

(11)

management

(12)

heat exchangers

(13)

Thermal oil heat exchanger

(14)

management

(14 ')

management

(14 ")

management

(15)

air preheater

(16)

management

(17)

air preheater

(18)

heat exchangers

(19)

management

(19 ')

management

(20)

air preheater

(21)

management

Claims (12)

1. Method for self-feeding combustion of slurry with high water content, wherein the slurry prior to supply to a combustion unit is heated in a heat exchanger (18) under pressure so that the water contained in the slurry is not evaporated, but remains in liquid phase, characterised in that a part of the slurry heated in the heat exchanger (18) is fed back and new raw slurry is admixed under pressure prior to supply to the heat exchanger (18), wherein the temperature of the raw slurry mixed with the slurry fed back is increased to such an extent that prior to entry into the heat exchanger this hydrolises and thus the viscosity of the slurry is substantially reduced.
2. Method according to claim 1, characterised in that heat present in flue gas conducted out of the combustion unit is used for heating the slurry.
3. Method according to claim 2, characterised in that the flue gas is fed as heat exchange medium to the heat exchanger (18) for heating the slurry.
4. Method according to claim 3, characterised in that the heat exchanger (18) for heating the slurry is constructed as a thermal oil heat exchanger (13).
5. Method according to claim 4, characterised in that the thermal oil is heated by means of the flue gas.
6. Method according to one of claims 4 and 5, characterised in that a heat exchanger (18) with high-pressure steam or high-pressure hot water as heat exchange medium is used instead of the thermal oil heat exchanger (13).
7. Method according to any one of claims 2 to 6, characterised in that an air preheater (15, 20) for heating air fed to the combustion unit is arranged in the flue gas flow upstream and/or downstream of the heat exchanger (18) for heating slurry.
8. Method according to any one of claims 1 to 7, characterised in that a fluidised bed furnace (9), a cyclonic furnace or a drum furnace is used as combustion unit.
9. Method according to any one of claims 1 to 8, characterised in that a self-feeding combustion of sewage sludge is performed by that.
10. Method according to claim 9, characterised in that the sewage sludge is subjected to mechanical removal of water prior to the combustion.
11. Method according to claim 10, characterised in that the sewage sludge after the mechanical removal of water has a solids content in the range of 18 to 30%.
12. Method according to claim 11, characterised in that the sewage sludge after the mechanical removal of water has a solids content of approximately 25%.

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