DE2019731C3 - Process for treating sewage sludge to improve its drainage properties and device for carrying out the process - Google Patents

Description

The invention relates to a method for processing of sewage sludge to improve its drainage properties, in which in continuous Passage the sewage sludge is subjected to thermal conditioning and in which the heat of the outflowing conditioned sewage sludge largely on the inflowing Raw sludge is transferred. The invention also relates to a device for performing this Procedure.

In such methods, the in the sewage sludge, such. B. in the primary sludge, secondary sludge, digested sludge and similar sludge, contained colloids destroyed under increased pressure and temperature, whereby a very easy separation of the sludge solids from the rest union water by z. B. settling, filtering or centrifuging becomes possible. For this method to operate economically, it is also necessary to keep the amount of heat necessary for generating alien sleep as possible. In a known method that meets these requirements, the sewage sludge is under

δ increased pressure in the closed reactor for 30 to 45 minutes at a temperature of about 170 to 200 ° C, after which the sludge solids can be separated very easily from the remaining water. As part of an economical mode of operation

te the process is carried out continuously and the conditioned sludge in countercurrent to the raw sludge passed through a double tube heat exchanger, whereby the conditioned sludge cools down and the raw sludge is heated (brochure from Technfina S. A., 1200 Geneva / Switzerland, printing sign SCH 68/2000, pp. 2, 5 and 6. with reference to the Hritische patent specification 909 872).

In the known process, the double tube heat exchanger is under the prevailing in the reactor

Ao seeing high system pressure of rt »'a 15 to 25 atm. Particularly disadvantageous is the fact that, particularly at temperatures of the sewage sludge of over 100 ^° C, the heat-transferring surfaces quickly become encrusted, which reduces the heat transfer and increases the pressure loss in the double-tube heat exchanger. The tubes of the double tube heat exchanger can even become completely clogged. The cleaning of such pipes is very complex.

The invention is based on the object of modifying the known method so that the structural Reduced expense for the devices for recovering the heat from the condensed sludge is avoided and in particular high pressure losses in the heat exchanger heat-transferring surfaces that are encrusted by the sewage sludge. be brought in discontinuation.

This object is achieved according to the invention solved that the Rohschlamvi over at least one intermediate stage from the initial state to the im Reactor for conditioning brought the prevailing pressure and the conditioned sewage sludge is released from the reactor pressure via the same intermediate stages and that the raw sludge in these intermediate stages through direct contact with the vapors of the condensed sewage sludge released during the relaxation in each case is heated to the corresponding saturation temperature.

The direct heat exchange between the vapors and the raw sludge not only avoids the heat transferring surfaces required in the known method, but also ensures very good heat transfer. The expansion or pressure increase in intermediate stages makes it possible to achieve a higher outlet temperature of the raw sludge from the heat exchanger than is possible with the heat exchanger through tension from the reactor pressure to external pressure (or vice versa for the pressure increase) without the intermediate stages. The flake structure of the conditioned sludge is also protected more by the relaxation through intermediate stages than with relaxation in a single pressure stage.

In the device for carrying out this method , a pressure vessel divided into two rooms is provided according to the invention for each pressure stage,

3 4

its lower tree as the evaporator and its table in the drawing v> and is shown in the following

upper space is designed as a mixing condenser. described in more detail below. The drawing is worth it

These pressure vessels thus replace the parts of a device that are essential in conventional for the invention.

Borrowed systems required long double pipes with three pressure levels.

cables. This reduces the structural effort

considerably reduced. Heat exchange surfaces are not disintegrated at increased pressure and temperature.

longer available, so that incrustations are no longer a problem. Three direct heat ex-

may occur. The previously provided in the heat exchanger 2a, 2b, 2c . In these the

shear unavoidable high pressure losses are raw sludge, which with the help of pumps 3a, 3b, 3c,

largely avoided. Operation and maintenance * - ία 3d in pressure stages in the direct heat exchange 2c,

costs are reduced. 2b, 2a and the reactor 1 is pumped, staged

To make a mixture of the raw sludge with the wise warmed. Expansion valves 4β, 4b, 4c, 4 <f conditioned sludge to avoid, at the same time ensure the gradual pressure reduction of the condenser to direct the vapors from the evaporator into the mixed sludge from the reactor pressure to the condenser, is between the lower and withdrawal pressure of the device . A partition wall is provided above the gas outlet and the upper space, and a connecting pipe is provided in the valves 5a, Sb, Sc, Sd , exhaust gas from the reactor 1 partition wall. The direct heat exchangers 2n, 2b, 2c are left from the arrangement of the connecting pipe in the partition. The exhaust gas consists of carbon dioxide-rich, has the advantage that pressure-bearing walls, non-condensable gas, which comes from organic sludge components caused by welds or the like for the connecting pipe 20, mixed with water. steam.

According to a further embodiment of the invention, pipes 6a, fl ·, 6c, 6d serve for the supply of the raw sludge in the upper space of the pressure vessel to the direct heat exchangers for generating a cast sludge upper exchanger 2c, 2b, 2a and the reactor 1 area, such as B. cascade plate, nozzles or ro- 25 the pipeline 6e is the supply of foreign animal plates, provided to steam an intimate mixture in the reactor 1. Through pipelines 7a, the raw sludge m ^; t to allow the vapors Ib, Ir, TJ will be the conditioned sludge from the

It is true that the German patent specification reactor 1 via the direct heat exchangers 2a, 2b. 1 241 381 describes a continuous process. 2r derived from the device. The exhaust gas from where the sludge - after mixing 30 the reactor 1 and the direct heat exchangers 2a, with an oil - under gradual pressure and temperature 2b, 2c is subjected to a heat treatment through pipes 8a, Sb, Sc, 8d over temperature increase. the gas discharge valve 5a, 5b, 5c, Sd of a pipeline9 is pulled. The heat supply is supplied at the highest level, through which the exhaust gas allows the device to be switched by supplying live steam from one. The partition 10 divides the Direklwärmeaus boiler, in each of the further stages by exchangers 2c, 2b, 2c in the lower room 11 . Sludge evolved steam. It is designed as a mixing capacitor. However, by a method in which the sludge the connecting pipe 13, the spaces 11 and 12 are dewatered by evaporation. The heat with each other, wodi ~ z \\ the transition in the space 11 in the individual stages can therefore the space werindirekt fed only 12 40 vapors liberated. ie with the interposition of \ on wä ^r mcden. For the fine distribution of the raw sludge in the transferring surfaces, there is a direct space! 2, the cascade plates 14α, 14Λ are in it to heat exchange, which is brought about with a condensate absorption. The raw sludge can also be connected with the aid of the purpose of the process, namely by nozzles, rotating parts or otherwise sprayed, a dehydration by evaporation to be carried out. The number of pressure points for the heat pipes would run counter to this known interchange is three in the example, and could therefore not give the person skilled in the art any suggestion. fewer pressure levels are sent. Preferential

Also the warming \ on raw sludge by wise three to three to six pressure levels for the

(Direct contact with vapors is known per se. 5 ° heat exchange is used.

(see Swiss patent specification 458 226). In the new device operates as follows: the contrast to the invention by the familiar comparison Rohschiamm However, from the pump 3a through the drive not continuously, but batch pipeline since in Raun; 12 of the direct warming pass. In this case, the completion of an under exchanger 2c is promoted, wc he treatment of a 55 die Khskadcnblechc 14t; 14 '> is distributed and the charge in the reactor and, after extensive pressure, the heat of condensation from the expansion from the room IS heats the vapors from the reactor into a rising vapor. Which is routed to this pressure storage tank, in which there is already the next stage heated raw sludge and the vapor condensate charge / preheating. However, the expert cannot provide any information from this pressure from the pump 2 through the pipe opening ⁶ ° conveyed into the next direct heat exchanger 2b , then see how a direct heat exchange can be carried out in this and in the direct heat exchanger 2a again with a continuous process, the process described gets carried out. Finally will is. The particular difficulty involved was the fact that the raw sludge preheated in this way was brought by the pump 3d to bridge the pressure difference with continuous pressure in reactor 1 and pushed in there slightly and the demand for a ⁶ 5. By mixing the reactor, the heat recovery is as complete as possible with external steam that comes through the pipe. line 6c is supplied , the required

An example of completion of the invention is achieved in the schematic reactor temperature. After a necessary

Residence time of the raw sludge supplied above, the now conditioned sludge leaves the reactor 1 at the bottom through the pipeline Ta and is expanded in the expansion valve Aa to the pressure prevailing in the direct heat exchanger 2a. The conditioned sludge cools down with the formation of steam. In room 11 of the direct heat exchanger, conditioned sludge and steam are separated from one another, with the vapors rising into room 12 and mixing there with less warm raw sludge, while the conditioned sludge flows down through pipeline Ib from direct heat exchanger 2a and is again expanded in expansion valve 4b will. The process described is repeated in the direct heat exchangers 2b and 2c , and a largely cooled, conditioned sludge then leaves the device through the pipeline Id.

The pressure in the reactor and the individual direct heat exchangers 2a, 2b, 2c is set with the aid of the respective gas discharge valve Sa or Sb or Sc or Sd. High pressure in reactor 1 results in low steam losses through the exhaust gas, but also requires a correspondingly higher pump capacity. For the pressure in the respective direct heat exchangers 2a, 2b, 2c , the highest possible temperature of the raw sludge emerging from the space 12 is the decisive criterion under given conditions.

Ideally, i. H. inter alia in the complete absence of inert exhaust gas and with complete heat exchange, z. B. the following Temperatures on:

6th designation Direct"
lc j »Poor
lh I suschcr
la reactor
1 Raw sludge
⁵ entry
temperature
⁰ C 55 100 138 171 Exit
temperature
^{10 0} C 100 138 171 Conditioned
mud
Entry
temperature
»5» c 138 171 200 Exit
temperature
^C C 100 138 171 200

In fact, the exit temperature of the raw sludge from any direct heat exchanger is negligible for the reasons given above lower than the outlet temperature of the conditional

»5 nated sludge from the same direct heat · exchanger.

If, on the other hand, the heat exchange were carried out in a single stage, only result in an outlet temperature of 138 ° C, d. H.

the raw sludge would be at a significantly lower temperature than with the three-stage process get into the reactor.

1 sheet of drawings

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Claims (4)

Patent claims: 1. A method for processing sewage sludge to improve its dewatering properties, in which the sewage sludge is subjected to thermal conditioning in a continuous flow and in which the heat of the outflowing conditioned sewage sludge is largely transferred to the incoming raw sludge, characterized in that 4 raw sludge via at least one Intermediate stage brought from the initial state to the pressure prevailing in the reactor for the conditioning and the conditioned sewage sludge is relaxed by the reactor pressure via the same intermediate stages and that the raw sludge in these intermediate stages through direct contact with the vapors of the conditioned sewage sludge released during the relaxation in each case is heated to about uie the corresponding saturation temperature. 2. Apparatus for carrying out the method according to claim 1, c IBy in that for each pressure stage is provided a partitioned into two spaces pressurized container, the lower space (II) is formed as Ausdampkr and the upper space (12) as a mixing condenser. 3. Apparatus according to claim 2, characterized in that between the spaces (11, 12) a Tren .. * and (10) and a connecting pipe (13) are provided in the partition (10). 4. Apparatus according to claim 2 or 3, characterized in that in the P ium (12) of the pressure vessel devices for generating a large sludge surface, such. B. cascade plates (14a, 146), nozzles or rotating plates are provided.