DE102008030957A1 - Preparation of fermentation residues from biogas production, comprises making a separation into a solid phase and a liquid phase and undergoing the liquid phase of a membrane separation processes using membrane elements - Google Patents

Abstract

Procedure for the preparation of fermentation residues from biogas production, comprises making a separation into a solid phase and a liquid phase (liquid sludge) by pressing and undergoing the liquid phase of a membrane separation processes using membrane elements, which it make a chemical cleaning of the modules with the membrane elements in the reactor in periodical spacing, where a cleaning solution is flowed from a purification tank by the membrane elements.

Description

The The present invention relates to a process for the preparation of digestate from the biogas production, in which one in through a first step Press a separation into a solid phase and a liquid phase (Dilute sludge) and you in a later Step the liquid Phase a membrane separation process using membrane elements subjects.

The Significance of the production of biogas (mainly methane) by fermentation of Biomass with the aim of generating electricity from renewable energies, takes in recent Time from the point of view of the rapidly increasing conventional fuels Petroleum and Natural gas is becoming increasingly important. In the production of biogas remains the so-called digestate, the usual in compliance with the Fertilizer Ordinance on agricultural land is applied. However, since the application areas are becoming scarcer or in High population density areas not enough to disposal stand, the technology of digestate treatment is becoming more important. The question of residue management already plays a role in proceedings today to approve a biogas plant a role. The cost of reprocessing of the fermentation residue lie in a not insignificant order of magnitude. After a separation of the digestate in a solid and a liquid Phase, the recovery of solids is still relatively easy, for example, as aggregates to compost substrates. More difficult is the preparation and subsequent use of the liquid phase due to their high water content. You can, for example, through Reverse osmosis concentrates gain, as a medium with high nutrient concentration are usable.

conventional Process for the preparation of the liquid phase from the above Separation of the digestate include in particular steps in which pressure-driven pore membranes and / or Reverse osmosis membranes are used. Problematic in particular in systems with overpressure-driven Porous membranes is that the membranes used by solid components enforce comparatively quickly, so that only very short operating times possible are before the procedure for cleaning or replacement of the filter devices must be interrupted.

Here uses the present invention. Starting from the mentioned The problem is the object of the present invention is that a process for the treatment of fermentation residues from biogas production to provide the type mentioned, which longer operating times at allows the membrane elements.

The solution This task provides a method for the treatment of digestate from the biogas production of the aforementioned type with the characterizing Features of the main claim. According to the invention, it is provided that at periodic intervals a dry cleaning of the modules with the membrane elements in makes the reactor containing the membrane elements, wherein a cleaning solution flows from a cleaning tank through the membrane elements.

at come the process of the invention preferably membranes with pore diameters between 0.02 microns (molecular weight cut-off about 15,000 g / mol) and 1 μm in question.

The Membrane separation process according to the invention is usually a low pressure separation process, in which preferred working with submerged Niderdruckmembranmodulen.

A another preferred or alternative measure to support the Cleaning of the membrane elements is that in the filtration operation at periodic intervals the flow direction reverses and makes a backwash, at the one for a defined period of time filtrate counter to the filtration direction promotes through the membrane elements.

Preferably is according to one Further development of the method further provided that as membrane elements Hollow fiber membranes are used and one in filtration operation by means of a sucking pump the medium to be filtered from the outside to inside through the hollow fiber membranes sucks. This has the advantage that the fine inner tube of the hollow fiber membranes remains clean while the dirt phase in the room outside the hollow fiber membranes is concentrated.

A Particularly preferred variant of the method according to the invention provides that one over a fan Introducing air into the container containing the medium to be filtered, and creates a turbulence behavior in the medium. The container according to the invention (reactor), in which the microfiltration is done so is a kind of turbulence reactor. This usually has several chambers containing microfiltration modules which in turn preferably consist of an array of hollow fiber membranes. The turbulence behavior in the medium to be filtered acts pollution the membranes opposite.

The inventive chemical cleaning of the membrane elements usually takes place at relatively long intervals. The cleaning is usually done for each chamber. All other chambers remain in operation. The cleaning is preferably carried out in the so Crossflow method mentioned, and particularly preferably in the manner described below. The cleaning solution is applied in a cleaning tank. From the cleaning tank, the cleaning solution is conveyed to the modules. There it enters a first filtrate outlet, flows in the axial direction through the hollow-fiber membranes, exits at the other filtrate outlet and flows back into the purification tank. As a result of the overpressure acting within the hollow-fiber membranes, cleaning solution passes from the inside to the outside through the pores of the membrane. After completion of the cleaning, the module is thus in the chamber in cleaning solution. This then possibly dissolves on the diaphragm outer wall existing deposits.

following is a preferred sequence of process steps in a method according to the invention for the treatment of digestate described in more detail. The first separation stage is, for example, a press screw separator used in the digestate separated coarse solids such as vegetable fibers or husks. The press screw separator can be pumped, for example, by means of progressing cavity pumps be fed. Promote the pumps the digestate or the oversize from procedural steps later to be described on the press screw separator. A pressure transmitter on the inlet side of the press screw separator serves as a setpoint generator for the frequency on the motor of the eccentric screw pumps. The pressure is monitored continuously and evaluated. This ensures that the press screw separator not too high is applied. The usual target pressure for the inlet the press screw separator is for example about 0.2 bar.

in the Press screw separator, for example, to be drained Product in a cylindrical sieve drum by means of a screw against a resistance of a weighted discharge flap promoted. The material to be sieved is pressed, the liquid passes through the Columns of the screening drum in the shell space and is deducted there. One for the digestate treatment suitable gap width is for example in the range of 0.5 mm. The filtrate of the press screw separator arrives in free fall in one Collection container. This serves as a storage container for the subsequent process step. The filtrate of the screw extruder becomes common as a thin sludge designated.

Of the Separator is preferably equipped with an additional unbalance motor, which causes the drum to vibrate and thus the drainage result improved. The solid falls at the discharge flap and can then spent again on fields or further dried and otherwise used.

Of the Press screw separator is preferred for safety with a mechanical Limit switch protected against excessive vibration, which in case of clogging or plant defect can occur.

According to one preferred further development of the method according to the invention is provided, that in at least one step subsequent to the pressing step the filtrate obtained in the pressing sieves, preferably by means of at least a vibrating screen. The loading of the vibrating screen is done for example via a feed pump from the thin sludge tank of the Pressschneckenseparators. The inlet is in the upper part of the vibrating screen given and in a coarse grained and a fine-grained Separated fraction. The oversize leaves over free gradient the sieve and can be collected for example in an oversized grain tank. The filtrate falls into a vibrating screen filtrate container. At this point, for example, a mesh size of the order of 250 μm be used.

It was mentioned earlier, that is preferably the filtration with submerged low-pressure membranes in a so-called turbulence reactor. This can be for example include the membrane modules, a working vessel and a turbulence fan. If For example, the screening step described above is provided, then the filtrate of the vibrating screen is first pumped into the working container. This is about Pore membranes (for example, with a pore size in the range of about 0.4 microns) a practical solids-free filtrate produced. For this must over the pore membranes a Pressure difference applied. This is preferred by the generation a negative pressure on the filtrate side achieved by a sucking Pump is used, by means of which the medium to be filtered sucks through the hollow fiber membranes from outside to inside.

By specific selection of the shape and dimensions of the working container can For example, in conjunction with appropriate setting the supply quantity and the air quantity produce a turbulence behavior, that counteracts membrane contamination.

The solids-enriched phase, the retentate, is discharged from the process vessel and may, for example, be partially recycled to the digesters of biogas production. The other part of the retentate can be pumped, for example, in a possible variant of the method from the working container to another vibrating screen. The feed is placed in the upper part of the vibrating screen and separated into a coarse-grained and a fine-grained fraction. The oversize ver leaves the sieve over free slope and is also collected in the oversize tank. The filtrate returns in free fall back into the working container. At this point, for example, one can use a mesh size in the order of about 75 microns.

The oversize grains of both Sieves can then for example be pressed again on the press screw.

Of the particular advantage of the method according to the invention is the particular economical handling of the membrane modules. As already stated For example, the pore membranes are in the described submerged low pressure membrane separation process treated in a special way.

The in the subclaims described features relate to preferred developments of the task solution according to the invention. Further Advantages of the present invention will become apparent from the following Detailed description.

following The present invention will be described with reference to exemplary embodiments explained in more detail in the accompanying drawings. Showing:

1 a schematic representation of an exemplary inventive method in a block diagram;

2 a view of a turbulence reactor used for microfiltration;

3 a top view of the in 2 represented turbulence reactor;

4 an enlarged detail view of a detail from 3 in the upper area;

5 a side view of the representation of 4 ;

6 a schematic representation of the method for cleaning one of the membrane modules;

7 a partial view of the turbulence reactor, in which a chamber is cut longitudinally and one recognizes the filtration module.

First, on the 1 Reference is made and explained with reference to the block diagram of the sequence of the method according to the invention with the various separation stages. The from a biogas plant 10 originating fermentation residue passes via a pipe 11 and a feed 12 in a press screw separator 13 in which a separation into a solid phase and a liquid phase takes place. The solid is separated and can be used, for example, as a fertilizer, optionally after further drying. It may be the immediate application to fields provided or the solid is used elsewhere.

With the press screw separator 13 accumulating liquid phase, the so-called thin sludge, via a feed pump is a vibrating screen 14 fed, by means of which a separation into a coarse-grained and a fine-grained fraction takes place. The coarse-grained fraction, called oversize grain, can be over the line 15 in the press screw separator 13 be returned or it is collected in a (not shown here) oversize tank.

The filtrate from the screening process passes into a vibrating screen filtrate container and can then via the line 16 the microfiltration reactor 17 be forwarded. The separation with submerged low-pressure membrane is preferably carried out in a so-called turbulence reactor, which will be explained in more detail later. The retentate obtained in the microfiltration can via the line 18 be attributed to another vibrating screen 19 from where the fines on the line 20 can be fed back into the biogas plant 10 , The oversize from the screening process can be over the line 21 back to the supply of digestate to press screw separator 13 conduct and treat again.

The filtrate from the membrane separation 17 leads you over the line 22 a reverse osmosis system 23 to. There, by means of reverse osmosis, a separation into a permeate and a concentrate, which are removed by means of pumps separately from the reverse osmosis system.

Hereinafter, referring to FIGS 2 to 5 the one for microfiltration 17 used turbulence reactor explained in detail in the passes to the pre-treatment of the digestate described above. The turbulence reactor 24 comprises a roughly rectangular in plan view of the container which consists of several adjacent chambers. In the present embodiment, there are five such chambers, each by transversely extending partitions 25 are separated from each other. The total receiving volume of such a container according to the embodiment is for example 23.5 m ³ . In each chamber is a microfiltration module, which is not shown here for reasons of clarity. The chambers are connected to each other via communicating pipelines or via overflow weirs.

The microfiltration modules, for example, have a rectangular outline and have approximately a cuboid shape. Each module may, for example, be provided with feet. At the bottom of the frame, a foot is installed at each corner of the frame. Within the stainless steel frame of the modules, the membrane elements are arranged with the hollow fiber membranes. The hollow fiber membranes are arranged horizontally across the width. A module preferably has more than 200 m ² membrane area.

The cuboid chambers of the turbulence reactor, which are also roughly cuboidal, are designed to match the module and for the application case fermentation treatment. On a longitudinal side of the turbulence container - the operating level - are preferably various holes for the filtrate removal or cleaning, input / output, the inlet, the level measurement and the retentate removal arranged. The corresponding holes are present in each chamber of the container. These are like in 2 recognizable in detail, the holes 26 , which are intended for the filtrate removal and for the backwashing and are also used in the purification for the feed. At a distance next to it at about the same height are holes 27 provided, which are also used for the filtrate removal, and the backwashing and serve as a drain in the cleaning of the filter modules. The feed to microfiltration via the holes 28 slightly laterally offset and below the holes 26 and 27 each lie in the edge area. About further drilling 29 In the lower area, level measurements can be made. The holes 30 in the lower part of the container are provided for the expiration of the retentate from the microfiltration.

The supply of air into the turbulence reactor via the pipe in the upper area approximately centrally arranged 31 , Each of the chambers of the container is each with a hood 32 covered. In the upper part of this hood 32 there is a threaded connector 33 , via which a conduit for the removal of air blown into the container can take place. The hoods 32 and the threaded connectors 33 You can also good from the top view 3 detect.

In four places of the container 24 are lifting and transport traverses 34 provided so that you can lift the container for transport. In addition, the container indicates 24 various stiffeners 35 for stabilization, which is partly in 2 as in 3 can recognize.

The 4 and 5 each show enlarged detail views each one of the cover of the container 24 serving domes 32 , once in the front view and once in the side view. One recognizes in 4 that the hood 32 has a kind of lower flange and therefore screws 36a can be attached to the top of the container. About seals can be the connection between hood 32 and containers 24 be sealed. In the side view according to 5 is the position of the threaded neck 33 clearly visible in the rear central region of the container, through which the injected air can be derived.

The turbulence reactor is therefore closed in operation at the top. After removal of the hood, the installation or removal of the microfiltration modules is possible. The position of the pipe socket 31 for the air supply into the container is behind the hood in the region of a cover plate of the container, as can be seen from the top view 3 can recognize.

The membrane modules, for example, have a rectangular outline and have approximately a cuboid shape. Each module may, for example, be provided with feet. At the bottom of the frame, a foot is installed at each corner of the frame. Within the stainless steel frame of the modules, the membrane elements are arranged with the hollow fiber membranes. The hollow fiber membranes are arranged horizontally across the width. A module preferably has more than 200 m ² membrane area.

The Retentate removal preferably takes place centrally under the modules. By the holes are routed pipelines. For filtrate removal or cleaning Input / output and for the air supply, the pipes are connected to the modules.

Each module can be flown to generate the turbulence with a sufficient amount of air, for example, about 80 Nm ³ / h. During operation, the modules are sucked by means of a self-priming pump. Due to the negative pressure within the hollow fibers, the digestate filtrate then penetrates through the membrane pores. The filtration direction for the hollow fiber membranes is thus from outside to inside. Thus, then the fine inner tube remains clean. The Schmutzfase is concentrated in the diffuse space outside the hollow fiber membranes. The pore size used in the present embodiment is 0.4 microns.

In periodic intervals is for short time the filtration direction reversed. Then it becomes filtrate from the filtrate container conveyed through the membrane pores in the chamber of the module. This Operation is referred to as backwashing. In general, the backwash is in of the order of magnitude of about 1.5 times the amount of filtrate.

At longer intervals, the individual modules should be chemically cleaned. The Reini supply is preferably carried out for each chamber. All other chambers then remain in operation. The cleaning can be done for example in the so-called crossflow process. The cleaning solution is applied in a cleaning tank. From the cleaning tank, the cleaning solution is conveyed to the modules.

you For example, the system can operate in such a way that in a first Membrane module, the filtration is operated while in a second membrane module the backwashing expires and again in a third membrane module the chemical described above Cleaning takes place.

The procedure and the flow conditions in the chemical purification of a membrane module will be better understood from the following description, which is based on the schematic representation of 6 Refers. Shown is the cleaning tank 36 in which there is a supply of cleaning solution 37 located. This is done by means of the cleaning pump 39 over the line 38 pumped into the container in which the submerged membrane module 40 located with the hollow fiber membranes. The solution occurs at the filtrate outlet 41 a, then flows in the axial direction through the individual hollow-fiber membranes 42 through, occurs at the second Filtratausgang 43 out and over the line 44 back to the cleaning tank 36 , It is clear from the double arrows shown that the overpressure within the hollow-fiber membranes acts as a result 42 the cleaning solution passes from the inside to the outside through the pores of the membrane. After completion of the cleaning, the module is thus in the chamber in cleaning solution. This then possibly dissolves on the diaphragm outer wall existing deposits.

7 shows a detailed view of a part of the turbulence reactor, in which the left-hand chamber is cut open, so that the filtration module 45 inside can recognize. This is on feet 46 in the container on its bottom 47 , The filtration module 45 comprises two vertically extending lateral hollow plates 48 in which the filtrate is collected. A variety of membrane elements 49 runs between these two hollow plates 48 , In the hollow slabs 48 the filtrate flows through the corresponding Filtratausgänge 41 . 43 , (see also 6 ) and from there to the in 2 shown holes 26 . 27 the container through which the Filtratentnahme takes place.

In the lower part of the chamber you can see under the filtration module 45 located pipelines 50 , via which the air supply to the module takes place. These conduits then extend in the direction of the depth of the container below the filtration module and have small openings where the air can escape, rising upwards and the medium swirling up to produce the turbulence.

10

biogas plant

11

management

12

Intake

13

screw extractor

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vibrating Screen

15

management

16

management

17

Microfiltration reactor

18

management

19

vibrating Screen

20

management

21

management

22

management

23

Reverse osmosis system

24

turbulence reactor

25

partition wall

26

drilling

27

drilling

28

drilling

29

drilling

30

drilling

31

pipe socket

32

Hood

33

threaded connector

34

lifting and transport traverses

35

stiffeners

36

cleaning tank

36a

screw

37

cleaning solution

38

management

39

cleaning pump

40

membrane module

41

filtrate outlet

42

Hollow fiber membranes

43

filtrate outlet

44

management

45

filtration module

46

foot

47

ground

48

hollow plate

49

membrane element

50

pipeline

Claims (11)

Process for the treatment of fermentation residues from the production of biogas, in which in a first step a separation into a solid phase and a liquid phase (thin sludge) is carried out by pressing and in a later step the liquid phase is subjected to a membrane separation process using membrane elements, characterized in that at periodic intervals a chemical cleaning of the modules with the membrane elements in the reactor is provided takes, which contains the membrane elements, wherein a cleaning solution flow from a cleaning tank through the membrane elements. Method according to the preamble of claim 1 or according to claim 1, characterized in that in the filtration operation at periodic intervals the flow direction reverses and makes a backwash, at the one for a defined period of time filtrate counter to the filtration direction promotes through the membrane elements. Method according to claim 1 or 2, characterized that the reactor comprises several separate chambers and the chemical Cleaning only in one chamber or only in part the chambers takes place while the remaining Chambers continue to be driven in filtration operation. Method according to one of claims 1 to 3, characterized that the cleaning takes place in the so-called crossflow method, wherein the cleaning solution is conveyed from a cleaning tank to filtration modules in the chambers and she enters there at a Filtratausgang, in the axial direction flows through the membrane elements in the form of hollow fiber membranes, at one exits the other filtrate outlet and flows back into the cleaning tank. Method according to claim 4, characterized in that that by the overpressure within the hollow fiber membranes cleaning solution from inside to outside the pores of the membrane elements occurs. Method according to one of claims 3 to 5, characterized that after completion of the flow through the cleaning solution by the membrane elements, the filtration module in the chamber a time long in cleaning solution is, which on the membrane outer wall remaining coverings dissolves. Method according to one of claims 1 to 6, characterized that are used as membrane elements hollow fiber membranes and in the filtration operation by means of a suction pump to be filtered Medium from the outside sucks inward through the hollow fiber membranes. Method according to one of claims 1 to 7, characterized that you over a fan Introducing air into the container containing the medium to be filtered, and creates a turbulence behavior in the medium. Method according to one of claims 1 to 8, characterized that in a first step a press screw separator is used to those in the fermentation residues Separate coarse solids contained. Method according to one of claims 1 to 9, characterized that in at least one step subsequent to the pressing step the filtrate obtained in the pressing sieves, preferably by means of at least a vibrating screen. Method according to claim 10, characterized in that that the filtrate of the screening step a separation process with submerged Low pressure membranes is subjected.