DE2754070B2 - Process for treating sewage sludge - Google Patents

Description

The invention relates to a method for processing of sewage sludge, in which Jer fresh sewage sludge rotted in a digester and is then mechanically pre-dewatered, whereupon the mechanically pre-dewatered sewage sludge under Use of combustion heat obtained from digester gas, thermally dried and pelletized in the process will.

A similar process is from DE-OS 15 84 991 known. However, the fresh sewage sludge with a high water content becomes thermal dried by ir. A circuit of the thermal drying system is introduced into which there is also a carrier material. The carrier material is dried from the pelletized material by sieving End product separated and reused. The pelletized end product can also be put in the incinerator thermal drying. However, this incinerator becomes preferable heated with waste oil. But it can also come from the plant dried sludge or digester gas or normal heating oil can be burned.

DE-AS 17 29 240 shows a method for drying sewage sludge using it the resulting vapor heat by transferring the heat content of the vapor to the sewage sludge. Here, too, a drum dryer is used for thermal drying using combustion gases is heated.

With the known methods it is possible to use the fresh sewage sludge as a soil improver to reshape and dry the final product to be used. In doing so, however, oil is used as an energizing agent

ίο Medium used when the oil price is relatively high these processes can therefore not be operated economically.

The invention is based on the object of providing a method of the type described at the outset design so that it is energy self-sufficient - i.e. economically feasible even with high oil prices

According to the invention this is achieved by the fact that only that which arises in the digester Digester gas to cover the entire heat balance

2f> the thermal drying and heating of the Digester is used, with the digested sludge in the digester at a few temperature degrees above 38 = C is digested, the digester gas obtained in the digester initially only for thermal drying is used and the heat content of the exhaust gases from thermal drying to a heat transfer medium is transferred, "by which the digester and, if necessary, the operating buildings of the sewage treatment plant are heated.

It was surprisingly found that the

i »digester gas continuously produced in the digester in its amount is sufficient to first carry out the thermal drying and then the heating of the digester without the use of other heating media being necessary. This became a

Ji overcome prejudice according to which adopted was that the amount of digester gas from sewage sludge does not exceed 20% of the heat requirement of the thermal drying could cover. It is essential in the invention that the entire digester gas initially at thermal drying is used and the exhaust gases from thermal drying are then used transferred remaining heat content to a heat transfer medium, with which the maintenance of the required temperature in the digester secured> and, if necessary, the operating building of the sewage treatment plant is also heated can be.

The temperature of the exhaust gases of the thermal drying can be heated with digester gas Hot gas generator increased and thereby a dew point

■> o below this in all parts of the system up to the heat exchanger be prevented. The digester gas that is continuously generated in the digester is stored and fed to the discontinuously operated drying. A gas container is expediently used for this purpose

^Γ > ί as well as an upstream compressor.

The process management is based on a block flow diagram further explained:

The sewage sludge 1 arrives in a heating device 2 and from there into a digester 3.

ho Through the heating device 2, the sewage sludge 1 kept in the digester 3 at a temperature higher than 38 ° C, preferably 40 ° C, at which the amount of the developing digester gas 4 is particularly high and the calorific value of this digester gas is also increased.

μ The digester gas 4 is drawn off with the aid of a compressor 5 and stored in a compressed state in a gas container 6, where it is available if, for example, the thermal drying is discontinuous.

Hch is operated.

The digested sewage sludge arrives from the digester 3 via a pump 7 optionally into one of two thickeners 8. The thickeners work according to the settling process, so that here part of the water can be withdrawn. The sludge treated in this way becomes a mechanical one via a further pump 9 Drainage 10 supplied, which may for example consist of a belt press. Before being flok Kmittel üDer a metering device 11 is added. In the mechanical dewatering 10, part of the water is discharged according to arrow 11 '. The sludge reaches a mixer 13 according to arrow 12, where it is mixed with return material according to arrow 14 of a drying device 15 the thermal drying is reinstated. The drying device 15 can consist for example of a drying unit operated with digester gas. In this drying unit, the sludge is thermally dried and pelleted It then reaches a cyclone separator i7 according to arrow 16. The pelletized product becomes according to arrow 18 in a sieve device 19 ″ and from there stored or packed in silos. The hot gases from the cyclone separator 17 are according to arrow 20 a dedusting device 21 is supplied. There it is separated into returned goods, which is fed to the mixer 13 according to arrow 22 and in hot gases, which according to arrow 23 to a fan 24 arrive, which sends the hot gases into a heat exchanger 26 according to arrow 25. From there the cooled exhaust gases according to arrow 27 into an exhaust gas scrubber 28 and according to arrow 29 in a cleaned state Fireplace or the atmosphere.

Downstream of the heat exchanger 26 is a storage device 37 for the heat transfer medium, for example Water that makes it possible for the discontinuous operation of thermal drying and you also discontinuous heat recovery

ί continuous supply of digester and To ensure operational buildings with thermal energy. A pump 38 circulates the heat transfer medium between heat exchanger 26 and heat storage 37. About the heat transfer medium is the Heating of the sewage sludge operated in the heating device 2. The heat transfer medium is also used to heat the company building

The digester gas stored in the gas container 6 is sufficient

π off to meet the entire heat demand of the process cover. It is burned in a hot gas generator 31, which is used for thermal drying and for heating the Drying device 15 is used. It goes without saying that the hot gas generator 31 combustion air according to the arrow 32 and mixed air according to arrow 33 is supplied.

There is another hot gas ore 34 to increase the exhaust gas temperature provided, mi 'which can optionally be heated before the exhaust gases in the Dedusting device 21 arrive. on the other hand

2ί the temperature of the exhaust gases can be raised if they are additionally heated by the hot gas generator 34. In addition, the hot gas generator 34 ensures the heating operation for the digester and operating building, if the thermal

jo drying device 15 with the hot gas generator 34 is not in operation for a long time. Diverter flaps 35 and 36 control the flow of hot gas in the preselected direction.

1 sheet of drawings

Claims (4)

Patent claims: 1. Process for the treatment of sewage sludge, in which the fresh sewage sludge in one Digestion tank is rotten and then mechanically pre-drained, whereupon the mechanically pre-drained Thermal sewage sludge using combustion heat obtained from digester gas is dried and pelletized, characterized in that only the digester gas produced in the digester to cover the entire heat balance of the thermal drying and heating of the digester is used, with the digested sludge in the digester at some temperature degrees is digested above 38 ° C, the digester gas obtained in the digester is initially used solely for thermal purposes Drying is used and the heat content of the exhaust gases of thermal drying to a Heat transfer medium is transferred, with which the digester and, if necessary, the operational building of the Wastewater treatment plant to be heated. 2. The method according to claim 1, characterized in that the temperature of the exhaust gases thermal drying increased by a hot gas generator heated with digester gas and thereby a Falling below the dew point is prevented in all parts of the system up to the heat exchanger. 3. The method according to claim 1 or 2, characterized in that the digester is continuously resulting digester gas is stored and the discontinuously operated thermal drying fed wire. 4. The method according to; inem of claims 1 to 3, characterized in that! ie in the case of discontinuous thermal drying and discontinuous Heat recovery accumulating thermal energy stored and for the continuous Heating of digestion towers and operational buildings is released again.