SK6793A3 - Method and instalation for the treatment of sludge or filter cakes - Google Patents

Abstract

The invention concerns a method of treating sludge or press cakes, produced from suspensions or similar sludge-like mixtures, above all sewage sludge from local-authority sewage plants, by compressing the sludge or press cake and subsequently drying it. The sludge or press cake is dried in a multi-stage process by heating in a vacuum. Preferably before the first and optionally before the subsequent vacuum-drying stage, a dry material, e.g. filter dust, is mixed into the sludge or press cake in a mixing zone, said dry material being taken from the drying zone and fed to the mixing zone.

Description

Technical field

The invention relates to a method and an apparatus for treating sludge or filter cake with a slurry or similar mixtures containing sludge, in particular sewage sludge from municipal sewage treatment plants, by pressing the sludge or filter cake and then drying it.

BACKGROUND OF THE INVENTION

Conventional centrifuges or screen belt presses are used to dewater the sewage sludge, but often do not achieve the solids content as required by the deposition management. Improvement of sludge dewatering is achieved by the use of high-pressure net belt presses as disclosed by the applicant in DE-P S27 20 178. For example, high-pressure net belt presses achieve a solids content in the filter cake which is 5-10% higher than dewatering with conventional net belt presses, provided that the dewatered sewage sludge is dewatered of sufficient quality so that the pressures achieved in the high-pressure screen belt presses can even be used. High pressure net belt presses can also be used for sludge difficult to process, such as sludge from biological residues that have very low compression stability. Even at low pressures, they begin to lose their thixotropic and viscous properties, and are therefore usually admixed as a fabric, sawdust or peat meal to push through the mesh of the filter cloth. The disadvantage of this method is that, on the one hand, a large amount of additives causes an increase in costs, since it has to be transported to the sewage treatment plant, and on the other hand, the amount of waste deposited is considerably increased by the additives. The addition of 10 kg of sawdust per m ^and thin sludge increases the deposited amount by 33% by three percent solids.

It is also known to introduce filter sludge into a reserve heat dryer with direct or indirect heating. The municipal sewage sludge dryer and the industrial sewage dryer generally operate at atmospheric pressure in an open system, i.e., to displace water, the entire product in the dryer is heated to at least 100 ° C while evaporating the water. Water vapor can be sucked out of the dryer by a fan and condensed in the cooler. At the same time as the water vapor, a large amount of non-condensed air is sucked out and must also be cooled in the cooler. This large amount of air is saturated with other gases released from the sludge and must only be passed through a large absorber for odorless discharge into the atmosphere.

SUMMARY OF THE INVENTION

Based on the knowledge of this prior art, the object of the invention is to improve the processing of the sludge cake or filter cake, in particular by increasing the degree of drying.

This object is solved in the independent claim. According to this, the sludge cakes or filter cakes are thermally dried under vacuum in several stages, preferably with a dry substance being admixed to them before the first and / or subsequent vacuum drying stage.

In particular, it has proven to be suitable to introduce into the mixing zone an equally dry substance, for example filter dust, taken separately from the drying process, i.e. to recycle the raw material.

Further features and improvements are set forth in the dependent claims.

According to the invention, the sludge or filter cakes from a centrifuge or press containing 30% dry substances are thermally dried to 90 to 95% dry substances in a closed system of a multi-stage vacuum drying device.

In the heated dryer, the pressure is also reduced so that the water in the sludge evaporates at about 80 ° C. However, when the boiling point is reduced, the entire amount of product may not be heated to 100 ° C. Water vapor flows into the condenser and condenses there. A small amount of non-condensed gases are extracted with water vapor through a sealed tight system. According to the invention, a pre-dryer serves as a condenser. In this pre-dryer, water vapor condenses in the double jacket, which determines the condensation heat transferred in the product pre-dryer, so that most of the heat is recovered. The product, such as sewage sludge, is heated to about 50 ° C in a pre-dryer with a temperature of about 80 ° C. Under a vacuum of about 100 mbar, the water is already partially evaporated in the pre-dryer. On the other hand, this steam, which is approximately 50 [deg.] C., is fed to a preheater, e.g.

The pre-heated product is filled into a pre-dryer, pre-dried and dried to the desired final moisture in the main dryer.

This system is serially connected in three stages and thus achieved recycling compared to known systems energy-saving. Approximately 50% energy is saved compared to other drying processes. A small amount of inert gas is sucked through a vacuum pump and is also cleaned on an activated carbon filter and released into the atmosphere without odor.

Dried sludge from municipal sewage treatment plants has a calorific value of 12 000 to 18 000 KJ / kg and can be burnt in energy production. Dry and granulated sludge can also be deposited very well. It is also possible to sterilize the product by briefly applying the temperature, by heating from 121 ° C, to render it hygienically safe and almost odorless, so that it can be used as fertilizer.

Since the final weight represents only about 30% of the initial weight, the cost of the deposit is greatly saved, so that the cost of the equipment is amortized quickly.

Dried industrial sludge without said heating value can also be used as a filler, for example in cement plants.

The device according to the invention can continue to operate automatically. Operation and supervision is performed from the control center by microprocessors. Possible faults are localized and reported, making the whole system easy to operate and maintain.

By the above-described measures, the drying time can be considerably shortened, so that the size of the device at the same power is considerably smaller, and a considerably smaller area at the installation site is also required. Overall, the described method or the device conceived according thereto has the following additional advantages:

- the closed vacuum drying system does not cause any odor load when properly operated,

- the resulting product is hygienically sound, sterile and almost odorless,

- the dry powder product has a low residual moisture, up to 98% of the dry substance can be achieved,

- in the production of steam from dried sludge, additional energy costs are small,

- Reduction of labor costs by the automatic operation and maintenance of the whole installation,

- low energy costs, thereby rapidly depreciating low investment and input costs.

Description of the drawings

Further advantages, features and details of the invention are set forth in the following description of a preferred exemplary embodiment by means of the drawing. This drawing shows schematically an apparatus for vacuum drying of sewage sludge from municipal sewage treatment plants which are not shown in the drawing for the sake of clarity.

DETAILED DESCRIPTION OF THE INVENTION

From the settling tank 10, the sludge cake, together with the dry substance, is fed to the granulator 14, a mixing conveyor, where also the dust from the main drying is introduced from the silo 12, and the bubbling granulate is also mixed there. This granulator 14 is associated with a pre-dryer 18, which is designed as a conical dryer with additionally heated surfaces and a double jacket, below the intermediate container 16. The heated surfaces are heated by vapors from a main dryer 20 formed by a segmental disc dryer. Water vapor condenses in the double jacket. Most of the vapors from the main dryer 20 condense in the pre-dryer 18 and take away the product heat of vaporization.

The main dryer 20 is sprayed with the steam supplied via the conduit 21 from the boiler 22, the waste steam from the main dryer 20 being returned to it via the return conduit 23.

From the complete portion of the granulator 14 also including the pre-dryer 18, the product is emptied into the main dryer 20 without interruption of the vacuum and without interruption of vacuum, and the pre-dryer 18 can be refilled.

From the outlet opening 24 of the main dryer 20, the dust is transferred to the dust filter 26, whose lower outlet 27 is connected to the dust silo 12. Further, the dust filter 26 is connected by its filter guide 28 to the intermediate reservoir 16 as well as to the pre-dryer 18.

The outlet 30 of the main dryer is connected to a discharge auger 32 by which the discharging dry substance is conveyed to the cargo container 34.

Not only the intermediate reservoir 16, but also the pre-dryer 18 is connected to the condenser 38 by the condenser line 36, whose condenser outlet conduit 40 is connected with the intermediate condensation pump 41 to the condensation tank 42. In the condenser 38 condensation is condensed. the pre-dryer 18 is then concentrated in the condensation tank 42.

A cooling tower 48 is connected to the condenser 38 of the main dryer 20.

Both dryers 48, 20 are provided with their own vacuum system with a dust filter 26 in which all dust particles larger than 10 microns are separated. The separated condensate can be conducted for further processing.

The BSB a and CSB hodnoty values determined by experiments are below 15 and 50 mg / l, respectively, in the device according to the invention.

Each capacitor 38 is connected to the activated carbon filter 46 by a second condenser outlet line 44 and a vacuum pump 45. The ring pump vacuum pump 45 is used as a vacuum pump 45 which, in conjunction with the cooling tower 48, ensures the circulation of domestic water. Condensate may also be used as process water under specified conditions, also to cool the condenser 38, so that it is not always necessary to use fresh fresh water. The non-condensed gases exiting the vacuum pump 45 may be passed through the activated carbon filter 46 described above or may be combusted in an oven (not shown).

The device is controlled from the fault control and signaling panel 50.

Claims (12)

P A T E N T E N T R O L IN'' 1) A process for treating sludge cake or slurry filter cake or similar mixtures containing sludge, in particular sewage sludge from municipal sewage treatment plants, by pressing the slurry cake or filter cake and then drying it, characterized in that the slurry cake or filter cake is thermally dried under vacuum. in several stages. The process according to claim 1, characterized in that a dry substance is admixed to the sludge or filter cake before the first or subsequent vacuum drying stage. The process according to claim 2, characterized in that a product of a drying process, for example filter dust, is fed into the mixing zone as a dry substance. The process according to claims 1) to 3), characterized in that the sludge or filter cake is passed from the pre-drying stage to the main drying stage without interrupting the action of vacuum. Process according to at least one of Claims 1 to 4), characterized in that the vapors from the main drying are condensed during the pre-drying and transfer the evaporating heat of the mixture containing the sludge or filter cake. The process according to claims 1) to 5), characterized in that the sizing phase is exceeded during drying with a proportion of dry substance. The process according to at least one of claims 1 to 6, characterized in that the sludge or filter cake is dried to 90 to 95% of the dry substance. Apparatus for treating sludge cake or slurry filter cake or similar mixtures, in particular sewage sludge from municipal sewage treatment plants, pressing the slurry cake or filter cake and subsequently drying it, in particular for carrying out the method according to one of the preceding claims, characterized in that it consists of at least two vacuum stages, wherein a main dryer (20), for example a segmented disk dryer, is associated with the pre-dryer (18), for example a conical dryer. Apparatus according to claim 8, characterized in that a granulator (14) is formed in front of the dryer (18, 20), in particular in front of the dryer (18), which is connected to the settling tank (10) and also to the force (12). . Device according to claims 8) or 9), characterized in that the silo (12) is controlled by a dryer (18, 20). Device according to claims 8) to 10), characterized in that the pre-dryer (18) is provided with a double jacket and / or additionally heating surfaces. Device according to at least one of claims 8) to 11), characterized in that the heating surfaces and / or the double jacket of the pre-dryer (18) are connected to at least one vapor outlet of the main dryer (20). List of reference numbers used 10 settling tank 12 silo 14 granulator 16 intermediate tank 18 pre-dryer 20 main dryer 21 leadership 22 boiler 23 return line 24 outlet opening 26 dust filter 27 lower output 28 filter guide 30 main dryer outlet 32 emptying auger 34 cargo container 36 Condenser line 38 capacitor 40 Condenser output line 41 condensation pump 42 condensation tank 44 shows the second condenser output line 45 vacuum pump 46 activated carbon filter 48 cooling tower 50 Control and fault signaling desk