ZA200907579B

ZA200907579B - An anaerobic digester

Info

Publication number: ZA200907579B
Application number: ZA200907579A
Authority: ZA
Inventors: Gregory Alan Austin
Original assignee: Gregory Alan Austin
Priority date: 2008-08-11
Filing date: 2009-10-28
Publication date: 2010-07-28
Also published as: AP2009004951A0; AP2595A

Description

) RE | le *2009/075;

AN ANAEROBIC DIGESTER

FIELD OF INVENTION

This invention relates to an anaerobic digester for the anaerobic digestion of organic matter.

BACKGROUND TO INVENTION

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In an anaerobic digestion process, microorganisms transform organic matter into biogas and other digested matter. The biogas produced during this process is a mixture of carbon dioxide and methane and may be used as a fuel. A typical known fixed dome anaerobic digester may include a reactor chamber in which organic matter can undergo anaerobic digestion and an expansion chamber which is horizontally offset at a location alongside the reactor chamber and which is in flow communication therewith to receive organic matter overflowing under pressure, from the reactor chamber.

Such an anaerobic digester occupies a relatively large area with a correspondingly large footprint.

i -3- "5 Jtisan object of the present invention to provide an anaerobic digester which is relatively inexpensive to produce and install and which, once installed, occupies a relatively small area when compared to anaerobic digesters of the type referred to above. «2000/0757 9

SUMMARY OF INVENTION

According to the invention there is provided an anaerobic digester which includes a vessel having a lower reactor chamber in which organic matter can be digested and an upper expansion chamber which is disposed adjacent to and above the reactor chamber, the expansion chamber being in flow communication with the reactor chamber thereby to permit an overflow of organic matter from the reactor chamber, under pressure, into the expansion chamber, the vessel including feed means for introducing organic matter to be digested, into the reactor chamber; and biogas extraction means for permitting the extraction of biogas generated in the reactor chamber.

The vessel may comprise a base, an upper wall, at least one surrounding wall which extends between the base and the upper wall and an internal dividing wall which is disposed between the upper wall and the base and which divides the vessel into said reactor and expansion chambers.

The upper wall and the dividing wall may be generally dome-shaped and the upper wall and the dividing wall may each define a central opening, the biogas extraction means being in a form of a biogas discharge conduit which extends between the central openings in the upper wall and the dividing wall. :

The dividing wall may define a conduit opening and the vessel may include an overflow conduit which extends downwardly from the conduit opening into the reactor chamber to a level at a lower end of the overflow conduit, which is spaced a predetermined distance below the dividing wall.

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The vessel may define an overflow opening which is in flow communication ) with the expansion chamber and which is disposed at a predetermined height above the dividing wall.

The lower end of the conduit may be spaced said predetermined distance below the dividing wall and the overflow opening may be spaced said predetermined height above the dividing wall, such that a gas collecting zone is defined in the reactor chamber between the dividing wall and said level at which the lower end of the overflow conduit is disposed; and an organic matter overflow zone is defined in the overflow conduit and in the expansion chamber between the overflow opening and the dividing wall, the volume of the gas collecting zone and of the organic matter overflow zone being substantially similar thereby to provide a substantially linear reduction in pressure when biogas is discharged from the reactor chamber, in use.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features of the invention are described hereinafter by way of a non- limiting example of the invention, with reference to and as illustrated in the accompanying diagrammatic drawings. In the drawings:

Figure 1 shows a top plan view of a typical prior art fixed-dome anaerobic digester;

Figure 2 shows a sectional side view of the prior art fixed-dome anaerobic digester of Figure 1;

Figure 3 shows a top plan view of an anaerobic digester in accordance with the invention;

Figure 4 shows a sectional side elevation of the anaerobic digester of Figure 3, sectioned along section line IV-1V;

Figure 5 shows a side elevation of the anaerobic digester of Figure 3, as viewed along direction indicator V;

) Figure 6 shows a side elevation of the anaerobic digester of Figure 3, as viewed along direction indicator VI,

Figure 7 shows a perspective view of the anaerobic digester of Figure 3, showing hidden detail;

Figure 8 shows a sectional side elevation of the anaerobic digester of Figure 3, sectioned along section line IV-1V, illustrating the different volumes defined by the chambers of the anaerobic digester;

Figure 9 shows a top plan view of another embodiment of an anaerobic digester in accordance with the invention;

Figure 10 shows a perspective view of the anaerobic digester of Figure 9; and

Figure 11 shows a sectional side elevation of the anaerobic digester of Figure 9, sectioned along section line Xl - XI of Figure 9.

DESCRIPTION OF PREFERRED EMBODIMENTS

With reference to Figures 1 and 2 of the drawings, a prior art fixed-dome anaerobic digester is illustrated. The anaerobic digester is designated generally by the reference numeral 1 and is installed below ground. The ground surface is indicated in Figure 2 of the drawings by reference numeral 2. The anaerobic digester 1 comprises, broadly, a dome-shaped reactor vessel 3 which defines a reactor chamber 4 in which anaerobic digestion of organic matter takes place, a waste loading chute 5 covered by a manhole cover 6 for feeding organic waste material into the reactor chamber 4, a sewer inlet pipe 7 which allows for sewerage to be deposited into the waste loading chute 5, and an overflow reservoir 8 which defines an expansion chamber 9 which is in flow communication with the reactor chamber 4 and which receives organic matter overflowing under pressure, from the reactor chamber. The anaerobic digester 1 further includes a service chute 10 which is covered by a to ° 2000/0757 9 manhole cover 11. The anaerobic digester 1 yet further includes a gas outlet 12 allowing for the takeoff of biogas generated in the reactor chamber as a result of the digestion of organic waste matter therein.

It will be appreciated that as the overflow reservoir 8 is located alongside the reactor vessel 3, the anaerobic digester 1 occupies a relatively large area with a correspondingly large horizontally-extending “footprint”.

With reference to Figures 3 to 8 of the drawings, an anaerobic digester in accordance with the invention, is designated generally by the reference numeral 20. The anaerobic digester 20 comprises, broadly, a vessel 22 which defines a lower reactor chamber 24 in which organic waste material can be digested and an upper expansion chamber 26 which is disposed adjacent to and above the reactor chamber 24.

The vessel 22 is of low density polyethylene and includes waste material feed means in the form of an organic waste-loading chute 28 which extends into the reactor chamber 24 for introducing organic waste matter into the reactor chamber. The waste-loading chute 28 includes a side opening 30 to which a sewerage pipe or the like, can be connected for depositing sewerage into the waste-loading chute 28.

The vessel 22 includes a service chute 32 providing access to the expansion chamber 26. The service chute 32 defines an overflow opening 34 through which waste material can be discharged from the expansion chamber 26.

The vessel 22 has a base 36; a cylindrical side wall 38 which extends upwardly from the base and which defines the outer sides of the reactor chamber 24 and the expansion chamber 26; a dome-shaped upper wall 40 which defines the top of the vessel 22; and a dome-shaped internal dividing wall 42 which separates the reactor chamber 24 from the expansion chamber 26.

The vessel 22 includes biogas extraction means in the form of a biogas discharge conduit 44 which is centrally disposed within the vessel 22 and

' "5 which extends between the dividing wall 42 and the upper wall 40 of the vessel 22. More particularly, the dividing wall 42 defines a central opening 46 to which a lower end of the discharge conduit 44 is connected and the upper wall 40 defines a central opening 48 to which an upper end of the discharge conduit 44 is connected. The central opening 48 is closed airtight by means of a closure 49 which can be removed to allow the discharge of biogas from the reactor chamber.

The vessel 22 includes an overflow conduit 50 which extends downwardly from a conduit opening 41 in the dividing wall 42 into the reactor chamber 24.

The overflow conduit 50 provides for an overflow of organic waste material from the reactor chamber 24 into the expansion chamber. The waste-loading chute 28 is located in an opening 31 defined in the dividing wall 42 and extends downwardly into the reactor chamber.

In use, biodegradable organic waste material such as kitchen scraps, animal manures etc. can be deposited into the reactor chamber 24 via the organic waste loading chute 28. Over the course of time, the waste material is digested giving off biogas which can be discharged from the reactor chamber via the central opening 48 after removal of the closure 49. The discharged biogas can be used, for example, to provide a source of cooking energy for rural households.

Due to increased pressure within the reactor chamber 24, caused by a build- up of biogas within the reactor chamber, the level of the waste material within the reactor chamber 24 may rise, overflowing into the expansion chamber 26 via the overflow conduit 50. The length of the overflow conduit 50 is designed such that biogas generated by the digestion of organic waste material within the reactor chamber, will collect at a level above the lower end of the overflow conduit 50. 1t will be appreciated also that the lower end of the waste-loading chute 28 will also be disposed at a height within the reactor chamber 24, which is below the biogas collection volume above the waste material.

With reference to Figure 8 of the drawings, the maximum level of organic waste material within the reactor chamber 24 is designated by “B”, while the minimum level of organic waste material within the reactor chamber 24 ) required for harvesting biogas from the reactor chamber, is designated by “C".

The volume provided in the expansion chamber 26 into which organic waste material from the reactor chamber can overflow, is designated by “V2, whereas the overflow level is designated by "A" at the level of the overflow opening 34. Clearly, an overflow volume “V3” will also be defined in the chute 28 above the level B, into which organic waste material can overflow from the reactor chamber 24. The volumes “V2” and “V3” thus provide an organic matter overflow zone between the dividing wall and the level of the overflow opening 34, whereas a gas collection zone is defined between level B defined by the dividing wall and level C defined by a lower end of the overflow conduit 50.

The gas collection volume “V1” defined between levels B and C of the reactor chamber 24 and the sum of the volumes V2 and V3 of the expansion chamber 26 are similar, thereby providing for a linear reduction in pressure within the vessel 22 when biogas is discharged therefrom through the central opening 48.

It will be appreciated that the anaerobic digester 20 has a significantly smaller . 25 footprint than is the case with prior art fixed-dome digesters of the type as described hereinabove. This is achieved by providing an expansion chamber adjacent to and above the reactor chamber. It will further be appreciated that : the configuration of the vessel 20 provides a compact space-saving design which is relatively simple to install.

With reference to Figures 9 to 11, another embodiment of an anaerobic digester in accordance with the invention, is designated generally by the reference numeral 200. The digester 200 operates in the same way as the digester 20 and is also similar in construction to the digester 20. As such, in

Figures 9 to 11, features of the digester 200 which are similar to those of the digester 20, are designated by similar reference numerals.

As for the digester 20, the digester 200 comprises a vessel 222 which defines a lower reactor chamber 224 in which organic waste material is digested and an upper expansion chamber 226 which is disposed above and adjacent to the reactor chamber 224. The vessel further includes an organic waste-loading chute 228 having a side opening 30 and a service chute 232 having a discharge opening 290 through which organic waste material can be pumped from the digester 200.

The vessel 222 includes biogas extraction means in the form of a biogas extraction conduit 244 which is centrally disposed within the vessel. The vessel further includes a funnel 260 within which an upper and region of the biogas extraction conduit 244 is located. The biogas attraction conduit 244 has an opening 248 in a side thereof, through which biogas can be discharged. The opening 248 is closed airtight by means of a closure 249.

As for the vessel 22, the maximum level of organic waste material within the reactor chamber 224 is designated by “B”, while the minimum level of organic waste material within the reactor chamber 224 required for harvesting biogas, is designated by “C”". The overflow level is designated as “A” at the level of the overflow opening 234. As for the vessel 22, volumes V1, V2 and V3 are defined within the vessel 222, which serve the same purpose as in the vessel

Claims

TT cals Te” +2000/07579

1. An anaerobic digester which includes a vessel having a lower reactor chamber in which organic matter can be digested and an upper expansion chamber which is disposed adjacent to and above the reactor chamber, the expansion chamber being in flow communication with the reactor chamber thereby to permit an overflow of organic matter from the reactor chamber, under pressure, into the expansion chamber, the vessel including feed means for introducing organic matter to be digested, into the reactor chamber; and biogas extraction means for permitting the extraction of biogas generated in the reactor chamber.

2. The anaerobic digester as claimed in claim 1, wherein the vessel x comprises a base, an upper wall, at least one surrounding wall which extends between the base and the upper wall and an internal dividing wall which is disposed between the upper wall and the base and which divides the vessel into said reactor and expansion chambers.

3. The anaerobic digester as claimed in claim 1 or claim 2, wherein the upper wall and the dividing wall are generally dome-shaped and wherein the upper wall and the dividing wall each define a central opening, the biogas extraction means being in a form of a biogas discharge conduit which extends between the central openings in the upper wall and the dividing wall.

4. The anaerobic digester as claimed in any one of claims 1 to 3, wherein the dividing wall defines a conduit opening and the vessel includes an overflow conduit which extends downwardly from the conduit opening into the reactor chamber to a level at a lower end of the overflow conduit, which is spaced a predetermined distance below the dividing wall.

5. The anaerobic digester as claimed in any one of claims 1 to 4, wherein the vessel defines an overflow opening which is in flow communication with the expansion chamber and which is disposed at a predetermined height above the dividing wall.

6. The anaerobic digester as claimed in claim 5, wherein the lower end of the overflow conduit is spaced said predetermined distance below the dividing wall and the overflow opening is spaced said predetermined height above the dividing wall, such that a gas collecting zone is defined in the reactor chamber between the dividing wall and said level at which the lower end of the overflow conduit is disposed; and an organic matter overflow zone is defined in the overflow conduit and in the expansion chamber between the overflow opening and the dividing wall, the volume of the gas collecting zone and of the organic matter overflow zone being substantially similar thereby to provide a substantially linear reduction in pressure when biogas is discharged from the reactor chamber, in use.

7. The anaerobic digester as claimed in claim 1, substantially as described in the specification with reference to and as illustrated in the accompanying drawings. Dated this 27™ day of October 2009 ADAMS & ADAMS APPLICANTS’ PATENT ATTORNEYS