JPS58205597A - Method and device for drying sewage sludge preparatorily dehydrated - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for drying pre-dewatered sewage sludge.

An important part of the treatment of municipal and industrial wastewater is the removal of substances separated from the wastewater during wastewater treatment. These substances are present in the form of sludge with a high water content of 95 to 99%.

Generally, sludge refers to sewage sludge discharged from wastewater purification devices such as pre-clarification tanks, post-clarification tanks, activation tanks, and sedimentation tanks of biological purification devices. Economical removal of these sludges requires severe water reduction to reduce sludge volume and change consistency. Concentration, dewatering, and drying are distinguished as sludge treatment methods for reducing water content.

For example, the water content of digested sewage sludge from municipal wastewater is reduced by 95 to 90% by thickening, by about 40 to 75% by dewatering, depending on the method used, and by about 40 to 30% by drying. . The final moisture content of sewage sludge that can currently be achieved by these dewatering methods is
It is still considered too much as there is no longer a sufficient number of open spaces for accumulation. Sedimentation creates economic, technical and ecological problems. A temporary solution is to further dewater the sewage sludge during sludge drying, followed by decomposition and combustion. Drying, for example in rotary dryers, is known, but requires high technical outlays, especially because of the environmentally harmful emissions. Even with this method, the reassuring energy that should be generated can only be used on a large scale. The resulting vapors must be cleaned through suitable cleaning equipment and the large elbow fumes must be cleaned up through effective dust removal equipment.

On the other hand, sludge combustion, which is a possible solution, likewise has the serious disadvantage that added fuel is required and the cost is related to the water content and exothermic sensitivity of the wastewater sludge. For example, a fluidized bed reactor often used as a reactor is 450'C and 1
Operating at temperatures between 150° C. requires significant use of natural gas or fuel oil as additive fuel. Furthermore, high equipment costs are a disadvantage. Many equipment parts must be made fireproof and require complicated preheating! A position, an inlet bottom with special nozzles, an air distribution device, an afterburning chamber and a recuperator are required. Equipment costs are a necessary consequence of incomplete pre-dewatering and drying of sewage sludge according to the prior art.

The problem on which the present invention is based is to further dewater mechanically pre-dewatered sewage sludge to an almost 100% dry substance by eliminating the capillary action of the solid cells, while avoiding the disadvantages mentioned in J-. It is to be.

In order to solve this problem, according to the invention, the pre-dewatered sewage sludge is placed in a first process step 1 with continuous swirling or rolling, and at the same time the product temperature is brought down to the level of the mixture. boiling point, while the resulting vapor is transferred to a second
The dry material obtained on the other hand is combusted in a third process step in order to obtain heat which increases the product temperature. By this method according to the invention, the pre-dewatered sewage sludge is further dewatered to approximately +oo96 dry matter. Mechanical dehydration not only separates the water that has accumulated on the surface, but also the residual water that is bound to the cells, which has hitherto been an unsolvable problem in all decanter devices. Stir or knead;
Mixing, U compound treatment temperature as high as boiling point, and optionally aromatic and/or in the second stage
By the combined action of the addition of solvents containing aliphatic hydrocarbons,
Since the capillary action of solid cells is eliminated, this water can also be separated.

Pre-dewatering is preferably carried out mechanically to a dry matter value of 25% to 50%, and the pasty M compound is therefore the basis for the treatment according to the invention.

According to an advantageous embodiment of the invention, it is proposed to carry out the treatment of the sewage sludge under vacuum conditions. The application of negative pressure significantly lowers the required boiling point, so that trans-M'fCJ advantages are obtained without the consequences of the combined effects of mechanical treatment, temperature and possibly solvent. Negative pressure treatment also significantly improves the energy balance. Depending on the type of solvent consisting of aromatic and/or aliphatic hydrocarbon groups and the degree of negative pressure applied, the product source of the mixture □□□ is between 60 °C and 200 °C. is appropriate.

The device according to the invention for carrying out this drying method, a supply of sewage sludge and optionally a solvent, a heating device,
a reactor having a stirring mechanism and a steam outlet line to a distillation tank;
and a device for discharging the dehydrated product. Thermal pretreatment steam is conducted via the jacket pipe of the sewage sludge feed line, so that the heat capacity can be utilized to simply bring the sewage sludge to a suitable temperature before introduction into the reactor.

A heat exchanger is provided between the reactor and the distillation vessel, the heat transfer medium of which, in particular the pre-heat transfer, being circulated to a tube furnace with a multi-fuel burner, to which optionally the heat transfer medium is circulated. can be connected to a solvent evaporator. As a result, the dewatering of the aqueous sludge takes place in a mechanically closed system, and environmental damage in the area of the reactor is completely avoided.

The liberated water can be used for separation, drainage, irrigation, or introduced into any waste water, and the solvent can be continuously recycled and used up, reducing material loss. All the solvent present in lA in the solid reaches the combustion chamber of the tube furnace and burns out there, so that according to the energy balance, additional primary energy only has to be used for starting the device.
The use of eliminated products is advantageous.

In a preferred embodiment, a vacuum system is further provided, and the heating system of the reactor is likewise connected to the tube furnace.

Further details, features and advantages of the invention will emerge from the following description of the accompanying drawing, which schematically shows a drying device according to the invention for pre-dewatered sewage sludge.

The important part of the device is six reactors L connected in parallel.
6a; L 7ai sl 8a, and our reactor is constructed as shown in FIG. 3 in detail.

The reactors 6 to 8 have a Wc connection to the main pressure line 16 in the upper region.
This main pressure feed pipe 1! +6
The sewage sludge is pumped from the transport vehicle 17 through the transport pipe 5 to the reactor. Screw conveyors can also be used to convey the sewage sludge according to its consistency. However, in the exemplary embodiment, the pressure line 1 is constructed as a jacket pipe.
6 is used and the heat capacity of the vaporous water-molten mixture exiting the reactor can be used to preheat the sewage sludge. Alternatively) the solvent consisting of aliphatic hydrocarbons is removed from the solvent tank 4 via a pump device and line 19. A tubular heating furnace 2 connected to the evaporator 3, in which the solvent is heated above its boiling point to about 150"C and is thus injected through the bottom of the reactor in the form of solvent vapor,
The heat transfer medium oil exiting from the expansion vessel 1 is contained within the coiled tube. This heat transfer medium oil is used not only for heating the evaporator 3, but also for the heating device of the reactor 1.
The closed circuit of the heat transfer medium oil is indicated in the flow diagram by a line segment with an arrow and representing a pipe line. 4. Each reactor 6 to 8 contains a stirring mechanism which constantly swirls the mixture until the fed sewage sludge is completely dewatered.6 Preferably with edge scraping as the stirring mechanism. Two further connections are made in each reactor, namely a bottom outlet 2 in the center of the bottom, in order to draw off the process product, in which a cross-blade stirrer 20 is used.
The dehydrated product can be transported to the container 13 via this outlet 21 by means of a screw conveyor. Since the sewage sludge thus dehydrated has sufficient calorific value to be combusted together with the residual solvent attached to it, the receiving container 13 is connected to the tube heating furnace 2 and is combusted in its multi-fuel burner, thereby transferring heat. Generates the heat necessary to heat the medium oil. Since the start-up of the device and the fluctuation of the calorific value may require the use of primary energy depending on the circumstances, the receiver connects a mixer 15 after the vessel 13, and this mixer 15
The calorific value of dry matter generated from sewage sludge can be increased by powdered coal.

A further water vapor/solvent mixture must be drawn off from each reactor 6 to 8. For this purpose, a line connection 22 is provided in the lid area of each reactor, which leads the steam-solvent mixture via a heat exchanger 9 to the distillation tank IO. This line 6 (as a jacket pipe) is combined with the feed line 16 to preheat the pre-dewatered sewage sludge. In the heat exchanger 9 the water vapor-solvent mixture condenses. Separation of both components takes place in the distillation tank 10, so that, on the one hand, the W9 medium is fed from there to the tank 1' 4, and on the other hand, the water is fed to the water separator 11.
It reaches the drainage canal through.

A vacuum pump 12, shown on the right side of Figure 1 of the drawings, allows the entire system to be evacuated to 20% of atmospheric pressure, allowing the system to operate at relatively low temperatures.

The devices described above are fed with a starting product which is usually sewage sludge with a dry matter value of 1 to 1091 I dry matter. This sewage sludge is mechanically pre-dewatered so that a pasty mixture of 25 to 50% dry matter is obtained.

This product is then fed via belt conveyor 5 to a heat spreader where it is further dehydrated to approximately 10% dry pulp material. This treatment is carried out in reactors 6 to 8 which allow the combined use of aromatic or aliphatic hydrocarbon-based solvents at operating temperatures that are above the boiling point of the mixture. For this purpose, the pre-dewatered sewage sludge is fed to the reactor tank via the pressure line 16, whereupon a solvent can be injected via a dosing nozzle (not shown) into the product entering 1) u on a specific request. can.

The sewage sludge is first brought to a temperature below 140° C., for example the boiling point of the mixture, through a heating jacket while being constantly stirred in a reactor vessel. At that time, the device is operated by a vacuum pump 12.
% atmospheric pressure, while an injection nozzle at the bottom of the reactor introduces vaporous solvent. The stirring mechanism ensures continuous swirling of the mixture until complete dehydration.

The solvent vapor injected from the bottom of the reactor eliminates capillary action in the pre-dewatered sewage sludge so that the water bound to the cells is separated and can be discharged along with the solvent vapor as a water vapor-solvent mixture. Condensation of the mixture then takes place in heat exchanger 9, and finally separation of the two components of the mixture takes place. The remaining solvent is fed back into the process.

The dehydrated dry product is transferred to the receiving container 13 via the pressure equilibrium outlet of the reactors 6 to 8 and the screw conveyor.
and finally burned in a tube heating furnace 2. Only ash remains as the final product to be deposited.

The device shown in FIG. 2 of the drawings operates on the same principle as the device already described, but with additional reactors 6a, 7a.
and 8a it is possible to configure for approximately 70,000 tons of dry matter per year.

FIG. 4 is an elevational view of such a device 6.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of the sewage sludge drying equipment, and Figure 2 is the sewage sludge drying equipment.
FIG. 3 is a vertical sectional view of the reactor, and FIG. 4 is an elevational view of the apparatus. 2... Tubular heating furnace, 3... Evaporator, 4... Solvent tank, 5... Sewage sludge transport pipe, 6.6a+7+7a
+ s, 8a...reactor, 9...heat exchanger, 10
... Distillation tank, 14 ... Sludge connection part, 18 ... Solvent connection part, 20 ... Cross-blade stirrer, 21 ... Recirculation outlet.

Claims (1)

[Claims] l The pre-dewatered sewage sludge is stirred or kneaded in a first process step with continuous swirling, and at the same time the product temperature is raised approximately to the boiling point of the mixture, so that -10,000 is obtained. Pre-dewatered sewage sludge, characterized in that the steam is condensed in a second process step and the dry material obtained on the other hand is combusted in a third process step in order to obtain heat that increases the product temperature. drying method. 2. In the first process step aromatic and/or
Claim 1, characterized in that a solvent containing aliphatic hydrocarbons is added and in a second process step is condensed with the vapor, the solvent is separated off again and fed back to the process.
The method described in section. 3. Process according to claim 1, characterized in that the sewage sludge to be dried is pre-dewatered to a dry matter value of 25 to 50%. 4. The method according to any one of claims 1 to 3, characterized in that the treatment of sewage and water sludge is carried out under vacuum conditions. 5. Process according to claim 1, characterized in that the temperature at which the mixture is produced is adjusted between 60°C and 200°C. 6 The pre-dewatered sewage sludge is continuously stirred or kneaded with swirling, while the product temperature is raised to approximately the boiling point of the mixture, while the resulting vapor is
On the other hand, in an apparatus in which the dry material obtained is combusted in order to obtain heat which increases the product temperature, a supply of sewage sludge and optionally a solvent, a heating device, a stirring or kneading mechanism, a distillation basin (, 10 ) A drying device for pre-dehydrated sewage sludge, characterized in that it is equipped with a reactor having a steam outlet line to the drain pipe, and a device for discharging the dehydrated product. 7. The device according to claim 6, characterized in that the steam is led through a jacket pipe of the sewage sludge supply pipe. 8 A heat exchanger (9) is provided between the reactor (6, 7, 8) and the distillation basin (10), in which the heat transfer medium, in particular the heat transfer oil, is provided in a tube with a multi-heel fuel burner. Type heating furnace (2)
a solvent evaporator (3) is optionally connected to this tubular heating furnace (2,), and the dehydrated product can be fed to this tubular heating furnace (2) for combustion. 7. A device according to claim 6, characterized in that: 9. The device according to claim 8, characterized in that it has a vacuum device. 10. Device according to claim 8, characterized in that the heating device for the reactor is also connected to the tube heating furnace (2). 11. Device according to claim 6, characterized in that the supply of solvent to the reactor takes place via an injection nozzle located at the bottom. +2 Device according to claim 6, characterized in that the stirring mechanism is a cross-blade stirrer (20) with edge scrapers.