DE2916261A1 - Sludge combustion process - involves adding coal dust to thickened sludge and combusting - Google Patents

Abstract

Sludge, derived from industrial wastes and municipal sewage treatment, is first thickened, conditioned by an admixture of coal dust and dewatered. Dewatering process takes advantage of the structural framework, supplied by the coal dust. Sludge is finally burned with a raised calorific value by the earlier addn. of coal. This is a simple and efficient way of utilising the calorific value of sludge from an effluent treatment.

Description

The invention relates to a method for the recovery of

Sludge, especially from industrial work processes, as well as from municipal wastewater, in which the sludge is first thickened, then through a Conditioned additive and then further dehydrated. The invention relates also an installation for carrying out the procedure.

The method according to the invention is used to eliminate this in industry and in connection with the treatment of municipal, especially domestic, wastewater resulting fine-grained sludge, which is also referred to as sewage sludge. They initially have a very high water content, which is initially reduced must before the sludge can be dumped or otherwise removed.

It is known that such sludges can be produced by adding flocculants to thicken and then to drain further, in order to then spread them as fertilizer or to deposit. In order to achieve increased degrees of dewatering, the thickened Sludge often conditioned with organic or metal salts as well as with lime. A sludge containing up to 40% dry matter is then obtained.

However, the organic or metal salts as well as the lime pollute the cost of the process is considerable. Because of the still relatively high water content such sludges are difficult to incinerate due to their low oleic value. Only small amounts can be used as fertilizer in agriculture; the bigger one Share must be deposited with considerable costs and possibly also difficulties will.

The invention is based on the object of clear sludge cleaning in particular of the origin mentioned at the beginning to be treated in such a way that their calorific value can be used can.

The object is achieved according to the invention in that ~ the thickened Mud conditioned with coal dust and drained using the is carried out by the coal dust formed scaffolding, whereupon the sludge with the calorific value increased by the addition of coal is burned. Used preferably a coal dust in the elder # 75 with a grain size of 50 - 100 lm Ver) 0n,: 1bis 2 1 preferably 1.5: 1 to the dry matter of the sludge.

The method according to the invention allows the production of a fuel its calorific value from the increased in relation to the added amount of coal dust The calorific value of the sludge exists and, moreover, dehydrates much more is, so that by saving heat of vaporization a more effective combustion is achieved.

It is known that coal dust, especially anthracite coal dust or sludge can be used with advantage as filter aids (Dt-PS 1 257 071). On the one hand, however, the coal then has to undergo a separate calcination before it can be used and additional ferric sulfate can be added. On the other hand is the addition of coal is limited to small amounts, and by the addition of ferric sulphate as well as the calcination, the overall process is considerably burdened.

In contrast, the invention is based on the surprising finding that coal dust in sludge provides a framework for form the drainage can, which can be exploited in particular on chamber filter presses, to increased To achieve degrees of dewatering and the previously necessary conditioning agents dispensable power. The invention uses the coal dust twice in this way, namely for Drainage and to increase the calorific value.

Depending on the type and composition of the sludge, i.e. depending on the calorific value of the sludge, it is more advantageous and at the same time sufficient if the thickened Sludge is conditioned with a coal dust-ash mixture. For this purpose, e.g. the fine coal from classifying or air sifting without further processing be used. The ash content of this coal is usually in a size ratio from 20 - 30%. Such a method has the particular advantage that a Part of the otherwise necessary processing steps for the coal can be omitted.

To improve the filtering effect and especially the detachment of the filter cake from the filter surfaces is provided that the coal dust or an additive is added to the coal dust-ash mixture before or during conditioning will. The addition of the additive to the coal dust or coal dust-ash mixture has the advantage that it is thoroughly mixed during the subsequent conditioning is guaranteed.

The smoke gases produced during combustion or those contained therein Heat can advantageously be used to dry or warm up the coal dust or the coal dust-ash mixture can be used. According to the invention is to provided that the coal dust or the Coal dust-ash mixture dried before conditioning and mixed into the sludge while it is still warm will.

The subsequent filtration process can be improved by the heat supplied will.

The process is optimized when the two essentials Components on an ongoing basis with regard to their composition, in particular with regard to the combustible components and the grain size are analyzed before conditioning. On the basis of this analysis carried out, e.g. the amount or composition of coal dust or

Coal dust-ash mixture can be adjusted so as to be as possible to achieve optimal calorific value.

The so conditioned sludge shows due to the contained therein Coal dust has a kind of scaffolding that has a positive effect on the subsequent drainage. Such a conditioned sludge is, according to the invention, between filter cloths filled and then drained under pressure. This type of drainage is special suitable because it does not destroy the coal dust framework, but rather on it builds up.

The filter cake obtained in this way, i.e. the sludge-coal dust mixture is then burned.

This is possible without further pretreatment according to the invention, by placing the sludge-coal dust mixture on a bed of coal and together with the coal is burned. In this way it is possible to remove the sludge-coal dust mixture to be burned on the grates provided for the burning of lump coal. It is so there is no need for a separate one expensive incineration too develop or build.

The sludge-coal dust mixture still has a residual moisture that causes a certain #cohesion of the filter cake. This good can after a Another embodiment of the invention can be burned in the fluidized bed.

The special type of combustion allows it to be on a previous one refrain from further drying of the mixture.

In order to avoid the incineration of the sludge-coal dust mixture, To utilize the heat taken away from the flue gas is a system for the implementation of the Process provided in which the sludge treatment in such an incinerator is integrated.

The details, further features and advantages of the invention result from the following description of an exemplary embodiment with reference to the drawing; 1 shows a process diagram of a plant according to the invention.

Fig. 1 shows at 4 the sludge feed, in which a first Analysis device 2 is built in, with which the composition is determined at predetermined intervals of the sludge and e.g. the calorific value can be determined. The mud can initially e.g. be pre-drained in a sedimentation system (not shown). He will subsequently Pretreated in the thickener 1, the separated wastewater via the sewer pipe 3 is discharged. Thereafter, the sludge is fed to the conditioner 10, where the Sludge with the coal or coal fed in via the coal feeder 7.

is mixed with the coal dust. Here too is in the Coal feed 7 an analysis device 8 is provided over the regular Analyzes of the coal flow can be carried out at intervals. via the analysis device the coal feed 7 can then be controlled.

The sludge conditioned in this way is then passed to the filter press 12 fed and drained there. The draining clean water is via the sewage roller 13 discharged.

The largely dewatered sludge-coal dust mixture can then be poured into temporarily stored in a bunker 1 or directly in the incinerator 20 are fed. The flue gases produced during combustion can then e.g.

can be used to pre-dry the coal.

The invention is further illustrated by means of an example. Included is a municipal sludge with 95% WG conditioned with a coal-ash mixture and then dewatered on chamber filter presses and then incinerated.

The coal-ash mixture is made up as follows: Coal dust: 80 ash: 20% grain size 30 to 100 ß calorific value 26 800 KJ / Kg this mixture is used in a ratio of 1: 1 to the dry matter of the sludge for conditioning the municipal sludge used. Furthermore, an organic additive known per se is used admitted what better Solution of the filter cake from the Filter cloths leads.

The sludge is without prior thickening with the coal-ash mixture been conditioned.

After conditioning, the sludge-coal ash mixture becomes one Chamber filter press fed and treated there as usual. It turns out that the The filter cake obtained only has a water content of 30 to 35%. The calorific value of the filter cake is 13 140 R3 / kg.

The same sludge with the well-known metal salts and conditioned with lime, has a water content of 55% after leaving the chamber filter press and shows a calorific value of 5100 KJ / kg.

It follows that the additional costs for the coal conditioning thanks to the above-mentioned advantages, the proper combustion of the sludge allow more than to be caught.

If you go one step further and that with the coal dust-ash mixture conditioned sludge dewatered on filter presses is now still in the flue gas flow the incineration plant is dried to approx. 10% residual moisture, a sewage sludge dust is obtained with a calorific value of 17,816 KJ / kg. Such a dust can be conveyed pneumatically and burn in special burners without difficulty. This sewage sludge can be add burnt lime so that that is released during the incineration of the sewage sludge Sulfur is bound in the form of the resulting gypsum.

Cannot put sewage sludge treatment in an incineration plant should be integrated, the sewage sludge treatment at the sewage treatment plants should be carried out by means of Conditioning for dewatering to 30% residual moisture can be carried out. The drying and processing to the pulverulent fuel can then in the incinerator because, if the sludge is not incinerated, none are hot at the sewage treatment plant Flue gases are available. This process of special processing Sewage sludge is much more effective than sludge dewatering below 30% Flat share.

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Claims (9)

Process for the recovery of sludge "Patent claims 1. Process for the recovery of sludge, especially from industrial work processes, as well as from municipal wastewater, both of which the sludge is first thickened, then by one The additive is conditioned and then further dehydrated, so that it can be I do not know that the thickened sludge is conditioned with coal dust and dewatering using the framework formed by the pulverized coal is carried out, whereupon the sludge with the increased by the addition of coal Calorific value is burned. 2. The method according to claim 1, d a d u r c h g e k ennz e i c h n e t that the coal dust was added in a mixture with ash during conditioning will. 3. The method according to claim 1 and claim 2, d a d u r ch g e k e n n z e i n e t that the coal dust resp. Coal dust-ash mixture before or during conditioning an additive to facilitate the detachment of the filter cake formed during drainage is admixed. 4. The method according to claim 1 and claim 2, d a d ur c h g e k e It is not noted that the coal dust or the coal dust / ash mixture before the Conditioning dried and mixed into the mud while it is still warm will. 5. The method according to claim 1 and claim 2, d a -d u r c h g e k It is noted that the coal dust has a grain size of 30 - 120 ffi. 6. The method of claim 1 or claim 2, d a -d u r c h g e it does not indicate that the conditioned sludge is filled between filter cloths and then dewatered under pressure. 7. The method according to claim 1 and claim 2, d a -d u r c h g e k It is noted that the sludge-coal dust mixture was placed on a coal bed and burned together with the coal. 8. The method according to claim 1 and claim 2, d a -d u r c h g e k Note that the sludge-coal dust mixture in the fluidized bed is barred. 9 system for performing the method according to claim 1 to claim 8, it is not indicated that the sludge treatment (1, 10, 12) is integrated into an incinerator (15, 20).