DE2746317A1 - METHOD OF Sludge Preparation and Apparatus for Carrying Out the Method - Google Patents

Description

DR. BERCi DiPL-INCi. STAPF DIPL-ING. SCHWAbE DR. DR. SANDMAIR 27 46317 PATENT LAWYERS

8 MUNICH 86, POST BOX 8602 45

Attorney file 28 557

ITEM S.p.A. Impianti Technologici Ercole Marelli, MILAN,

Italy

Method for sludge treatment and device for Implementation of the procedure

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r <0M) VK «2 72 8 Munich 80. MaucrkWiMsÄmW W / U ö HÜtken: Bayerische Vereinsbank Munich 453

9K7043 Telegrams: BKR (JSTAPI-'PATI-NT Munich Hypo-Bank Munich .W92f> 23

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The invention is concerned with the treatment of sludge and in particular relates to a method and an apparatus for drying sludge resulting from the treatment of Industrial water originate.

It is known that the processes for the treatment and treatment of sewage sewage, both civil and are also of industrial origin, which result in the formation of considerable amounts of sludge, for which additional Preparations are required before they are finally removed from the plant concerned.

Among the systems for processing such sludges, the one in which drying and drying has been preferred so far Settling beds are used, on which the sludge, when it is still wet, settle and then natural Way to dry off. In such beds, the water contained in the sludge becomes partial withdrawn by dewatering and partly by evaporation, so that the water content is reduced by approximately 50% can be.

However, such a method leads, despite its advantages in view of technically desirable results, which it is beneficial, to considerable effort, the with increasing output of the plant for processing

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of water increases sharply, both under the aspect of the area required for the drainage beds and also under the aspect of removing the dried sludge.

Finally, it must not be overlooked that the considerable drying which takes place in this way is quite a requires a long period of time so that the facilities are occupied for a long time.

As an alternative solution to the dewatering bed systems, systems based on the mechanical Drying based.

For the stabilization of wet sludge, an anaerobic digestion process is usually used, the not only readily provides a technically stable sludge that can be dehydrated in a simple manner and has a minimal content of small particles (which are difficult to separate even from the water), but also provides a considerable volume of biological gas as an add-on product, which is useful for the Operation of the sewage treatment plant can be exploited as such.

These systems, commonly used for mechanical

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Dehydration can be used in filtration systems (Vacuum filters and filter presses) as well as in centrifugal systems (Centrifuges or fast-acting decanting systems). These systems have their own corresponding advantages and disadvantages, insofar as they on the one hand make it possible for the drying times to be drastic and mechanized the loading of wet sludge and the recovery of dried sludge can be. On the other hand, however, they have a drying efficiency that is considerably lower than that of the drying beds lies. In the latter, as described above, the evaporation is in fact accompanied by the dewatering effect, whereas in the case of the mechanized ones Systems that completely lack evaporation.

It will of course be seen that the treatment of the sludge to a substantial extent is a function of the The final intended use of the sludge in question is depending on whether the sludge is just being dumped or whether it is are subsequently to be processed in an incineration furnace.

Within the framework of the previous design practice, from the theoretical point of view, the solution of the Preference is given, according to which the sludge is subjected to a stabilization and a composite drying process

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that is a drying step that is partly mechanical and partly thermal. The latter is, in fact, practically impaired by the low efficiency of the dehydration caused by the mechanical drying process is achieved. However, thermal drying has not yet led to results which, although suggested, are entirely satisfactory for reasons of process economy to use the biological gas generated in the digestion stage as fuel that is suitable for the thermal drying to donate the required amount of heat.

It has been found, and in particular this is an essential feature of the invention, that an advantageous Solution is achieved by a method and a device for thermal drying of sludge, which from the treatment of industrial water, preferably from sludge, which undergoes a stabilization treatment and / or subjected to mechanical dehydration when, according to the invention, the sludge is in contact with be brought into a gas stream that has a low moisture content and a high temperature, wherein the gas flow is given a high speed, so that the sludge in question thereby correspondingly in very small particles are split up while simultaneously evaporating their own water content becoming dehydrated.

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According to the preferred embodiment of the invention In the process, the gas stream used consists of hot air with a moisture content controlled to a low value and serves to atomize the sludge, which is achieved at the same time by supplying the heat necessary for evaporation of the water is required. The latter is discharged together with the air flow, while the finely ground sludge residues are stripped out of the air stream and collected separately.

From Fig. 1 of the accompanying drawing, an embodiment of the invention is schematically and only for better understanding Device shown.

The device has a large container 5, which is connected to an atomizing channel 2 at its inlet end stands in which the sludge is pumped in by a metering pump 1. The speed of the dosing pump is variable. The air heated by a burner 4 and conveyed by a fan 3 is also introduced into the duct 2.

In channel 2, the sludge is atomized at the same time as its water content evaporates. Thereafter the already dried sludge and the air stream flows through the container 5, in which a separation plate 6 is attached is. The sludge hits the separation plate 6

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on, whereas the air flow flows off the side of the plate and leaves the system through a duct 7.

The sludge drips due to the action of gravity and / or by pushing it off the plate 6 into the collecting funnel 8, from which it is drawn off by a screw 9.

In all and every heat exchange process, there is one of the criteria for achieving the best possible thermal Efficiency in the best possible contact surfaces between the two phases involved in the heat exchange to enlarge. The phases involved in this case are the sludge and the hot air flow.

By introducing the mud into a stream of air that flows at a very high speed, the mud becomes in broken up very small droplets, each of which has an extremely small diameter, the smaller the smaller the the airflow is faster and is on the order of a few tenths of a millimeter at any rate. In addition, innumerable droplets are distributed almost suddenly in the air mass that causes them Generated droplets.

If this is done, a very large and evenly distributed interface is created.

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On closer inspection of the particles into which the sludge has broken up, it can be seen that they can be grouped into three classes:

a) Particles composed of coarser grains of mud are; these particles can be slightly larger than 1 mm in size, but small in amount contained in water;

b) Particles made up of very small particles of sludge and Water are formed;

c) particles that are composed entirely of water,

The latter two types of particles can be a few tenths of a millimeter in size.

After the sludge has thus been divided into so many droplets, the evaporation of the water, i.e. the Drying of the sludge results in a decrease in the diameter of each droplet.

The time it takes to reduce the diameter of an airborne drop of water from a value d .. on a value d- is required is defined by the following formula:

X = 0.0036 * ^ - ^(d 1 " ^d 2>

8 k (t _g - t)

whereby,

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L = time in seconds

λ = latent heat of vaporization, in kilocalories per kilogram £ = specific weight of water, in kilograms per cubic meter

d ₁ = initial diameter of the drop, in millimeters k = thermal conductivity of the air, in kilocalories per hour

and meters and degrees Celsius of the temperature difference t = temperature of the air in ⁰ C
t = temperature of the water in ⁰ C.

Using such a formula, it is readily apparent that the thinner the particles are into which the sludge is is split, the shorter the evaporation time. Likewise, the higher the temperature of the air, the shorter it is is the evaporation time.

For example, for values of t in the range of 400 ^° C., it can be seen that in order to reduce the diameter d .. of the particles into which a sludge having an initial moisture content of 75% is divided, to diameters corresponding to the achievement of a sludge corresponds to the final moisture content of 35%, a time of the order of a few tenths of a second is sufficient.

A device of the type described above was used in a plant for an experimental preparation of industrial

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Sewage sewage tested, which is processed at a flow rate of approx. 50 liters per second.

It was made with slurries of different characteristics and by changing from one to the other of the three main working parameters of the drying plant carried out operational investigations. The three main working parameters are the temperature, the flow rate of the air and the flow rate of the sludge.

The following values were measured for each examination:

1) Ambient humidity and temperature

2) Moisture content of the incoming sludge

3) Moisture content of the exiting sludge

4) the humidity and temperature of the vented air.

The results of one of such investigations are plotted in a graph shown in FIG. 2, in which also shows the theoretical curves, which can be derived from the Mollier table, the investigation was carried out under the following conditions:

Relative ambient humidity 62%

Ambient air temperature 24 ⁰ C

Incoming sludge moisture content 74%. Incoming air flow rate 1,400 m ³ / hour

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In the graph, the abscissa is the moisture of the exiting sludge and the ordinate is the feed flow rate of the mud applied.

The curve not only shows the close agreement between the experimentally obtained values and the theoretical ones Values again, but it also shows adaptability both the method and the system according to the invention, so that a sludge to the desired moisture content can be dried, particularly to any fourth in the range of 25 to 50%.

Finally, it should be noted that for the above-described Device theoretically and technically equivalent embodiments are conceivable without that of departing from the spirit of the present invention.

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Claims (4)

Expectations (1. ^ Process for the thermal drying of the slurry, the originate from the treatment of industrial water, characterized in that the sludge with a gas stream, which has a low moisture content and a high temperature, are brought into contact, wherein the gas stream flows at such a flow rate and at such a speed that the Sludge is atomized into tiny particles and dehydrated by evaporation of the water contained in the particles will. 2. The method according to claim 1, characterized in that the gas stream consists of air and that the to be processed Mud has been stabilized beforehand. 3. Device for drying sludge for performing the method according to claim 1, characterized by a channel, in the interior of which the sludge and the gas flow are fed, and through a separating device for separating the dried sludge from the gas stream after a predetermined contact time between Gas and mud. 809816/0885 -3- ORIGINAL INSPECTED 4. Apparatus according to claim 3, characterized in that the separating device is a chamber or a large container has, in the interior of which a sludge separation plate transversely to the direction of flow of the sludge and of the gas flow is arranged, which flow out of the channel. -4- 8Q9816 / 0885