GB2149815A - Anaerobic fermenter - Google Patents

Abstract

Anaerobic fermentation apparatus comprises a generally cylindrical shell (1) having its longitudinal axis generally horizontal and provided with a pair of end walls (2, 2a) closing the shell; a dividing partition (3) extending the width and length of the shell and dividing the interior of the shell into two superposed fermentation spaces, each of which spaces is provided with a generally horizontal liquid-pervious layer of packing material (6a, 6b) extending across the space and dividing it into an upper (4a, 4b) and a lower (5a, 5b) portion; means (9a, 9b) for introducing liquid substrate into the lower portion of each of the spaces; means (10a, 10b) for removing sludge from each of the lower portions; means for removing gas from each of the upper portions and means (12a, 12b) for removing treated liquid from each of the upper portions.

Description

SPECIFICATION Anaerobic fermenter This invention is concerned with improvements in and relating to anaerobic fermenters and to anaerobic fermentation processes carried out therein.

The anaerobic fermentation of liquid substrates, such as aqueous liquid wastes or effluents, is a well-established process. Typically, such a process comprises feeding the liquid substrate, continuously or semi-continuously, to a closed fermentation vessel in which the substrate is subjected to anaerobic fermentation often at moderately elevated temperatures whereby a gaseous product, commonly methane, is produced. During the course of the fermentation solid material, unfermented material and/or fermentation residue, set tles to the bottom of the vessel as a sludge and excess fermented liquid substrate is removed from the fermenter vessel. The fermentation may be carried out with the liquid in the vessel in a more or less quiescent condition or under stirred conditions.One problem encountered in such a process is that particles of solid matter, possibly bearing the microorganisms responsible for the fermentation, may be upwardly entrained in the body of liquid in the vessel especially by the flotation action of gas evolved during the course of the fermentation.

It has now been found, in accordance with the present invention, that particles of solid material may be de-entrained from the liquid by means of a liquid-pervious layer of packing material, that is a layer formed of randomly arranged (dumped) or regularly arranged pieces of fluid-fluid contact elements such as are used in fluid-fluid contact apparatus in the chemical engineering industry, for example in distillation columns, absorption columns and humidifiers.

Such fluid-fluid contact elements may, for example take the form of regularly arranged grids or regularly arranged arrays of generally vertical shaped sheets. Preferably, however, the fluid-fluid contact elements are discrete elements such as Raschig rings, Lessing rings, Pall rings, Tellerete rings, saddles (for example Berl or Intalox saddles) or Cascade mini-rings (i.e. rings having an overall length less than their diameter). When the fluidfluid contact elements are discrete elements it is preferred that the layer of packing material take the form of a randomly arranged (dumped) layer of the elements supported on a perforated support.

It is an object of the present invention to provide anaerobic fermentation vessel containing a plurality of fermentation zones, each containing a layer of packing material as described above.

According to the invention there is provided anaerobic fermentation apparatus comprising a generally cylindrical shell having its longitudinal axis generally horizontal and provided with a pair of end walls closing the shell; a dividing partition extending the width and length of the shell and dividing the interior of the shell into two superposed fermentation spaces, each of which spaces is provided with a generally horizontal liquid-pervious layer of packing material extending across the space and dividing it into an upper and a lower portion; means for introducing liquid substrate into the lower portion of each of the spaces; means for removing sludge from each of the lower portions; means for removing gas from each of the upper portions; and means for removing treated liquid from each of the upper portions.

The partition dividing the shell of the apparatus into two portions may be flat or, preferably, arcuate as viewed in a transverse cross-section through the shell. In this latter case, the partition is preferably so curved that it concave downwards when viewed in cross-section.

It has further been found that the average depth of the volume of liquid below the layer of packing material is suitably from 100 to 3000 mm, preferably from 200 to 1500 mm. Thus, by employing the depth of liquid below about 1500 mm, the rate of fermentation per unit volume of the fermenter is increased whilst employing depths above 3000 mm, no useful increase in that rate of fermentation is obtained, i.e. increasing the total volume of liquid in the reactor below the packing material over a certain amount does not lead to a concomitant increase in overall fermentation rate per unit volume.

In order that the invention may be well understood reference will now be made to the accompanying diagrammatic drawings in which: Figure 1 is a transverse cross-section through a fermentation apparatus according to the invention and Figure 2 is a longitudinal cross-section through the fermentation apparatus shown in Figure 1.

As shown in the drawings, fermentation apparatus in accordance with the invention comprises a generally cylindrical shell 1 closed by a pair of end plates 2 and 2a. A downwardly concave arcuate partition member 3 spans the width of shell 1 and divides its interior into an upper and a lower space. Each of the two spaces is divided into an upper, gas, zone, 4a and 4b and a lower liquid, zone, 5a and 5b, by means of liquid pervious beds or layers, 6a and 6b, of dumped discrete fluid-fluid contact elements supported on perforate supports 7a and 7b. Gas zones 4a and 4b are connected via ports in end wall 2 to valved gas discharge conduit 8.A set of liquid feed pipes 9a and 9b extend along the length of liquid zones 5a and 5b and through end wall 2 where they are connected to manifolds (not shown) and in turn connected to a valved liquid feed supply conduit (not shown).

Each of feed pipes 9a and 9b is provided with perforations or nozzles for the discharge of liquid feed from the pipes into zones 5a and 5b. These perforations or nozzles are preferably so arranged that liquid is discharged into the zone either horizontally or downwardly.

Sludge withdrawal pipes 10a and 10b extend longitudinally through liguid zones 5a and 5b, below the level of liquid feed pipes 9a and 9b, and close to the bottom parts of zones 5a and 5b. The sludge discharge pipes 10a and 10b extend through end wall 2 and are connected to appropriate valved sludge withdrawal conduits 11a and 11b.

Upwardly open channel members 12a and 12b extend longitudinally of shell 1 in the upper portion of packed beds 6a and 6b respectively and are connected via ports in end wall 2 to valved treated liquid discharqe conduits 13a and 13b. Thus the upper edges of channel members 12a and 12b serve as weirs defining the upper liquid of level in each of the two spaces in the fermenter and for the removal of treated liquid from those spaces.

As it will be appreciated, in operation of an apparatus in accordance with the invention sludge will deposit in the lower parts of zones 5a and 5b (as generally indicated by broken lines 14a and 14b) and the height of the lower surface of packed beds 3a and 3b above this level represents the effective average depth of liquid below the beds and is preferably, as discussed above, from 200 to 1500 mm.

The overall diameter of shell 1 is suitably from 2 to 4 m, preferably about 3 m, and the overall length of the shell may, for example, be from 5 to 30m, preferably from 10 to 20m. Thus, as will be appreciated, the fermentation apparatus of the invention forms. a unit package containing two fermentation zones and which can be readily fabricated and assembled off-site and subsequently delivered to the desired site. Further, it will be appreciated, a complete fermentation installation may be built up comprising a number of fermentation apparatus in accordance with the invention, the number of the individual units depending, of course, upon the total amount of substrate to be fermented.

In operation, liquid feed is fed to each of the upper and lower spaces defined by partition 3, via liquid feed pipes 9a and 9b, and flows upwardly through zones 5a and 5b (wherein it undergoes fermentation) and thence through packed beds 6a and 6b, treated liquid being discharged via channels 12a and 12b and gas evolved being discharged via gas discharge conduits 8a and 8b.

Sludge is removed from lower zones 5a and 5b by means of sludge withdrawal pipes 10a and lob, generally on an intermittent basis.

A fermentation process carried out using the fermentation apparatus of the invention may be carried out moderately elevated temperatures, for example from 10 to 700C, and in this case the upper and lower spaces in the fermentation apparatus may be provided with internal or external heating means and, further, the shell 1 may be provided with external insulation.

Suitable substrates which may be fermented in accordance with the invention include effluents from citric acid production, effluents from paper and pulp production, effluents from molasses fermentation and effluents from the edible oil industry, dairy, pharmaceutical, brewing and food industries.

Whilst the invention has been particularly described with reference to the fermenter divided only into a pair of zones by means of an internal partition it will be appreciated that it may be divided for example, into three spaces by means of a pair of partitions, each space being provided with a liquid-pervious layer of fluid-fluid contact elements and appropriate means for feeding and removing liquid, withdrawing sludge and removing gas.

Using the fermenter in accordance with the invention it is possible to carry out two separate fermentation processes, possibly on different substrates. Alternatively the fermentation portion of the apparatus may be connected in series to carry out successive fermentations on a single substrate.

Claims (6)

1. Anaerobic fermentation apparatus comprising a generally cylindrical shell having its longitudinal axis generally horizontal and provided with a pair of end walls closing the shell; a dividing partition extending thetwidth and length of the shell and dividing the interior of the shell into two superposed fermentation spaces, each of which spaces is provided with a generally horizontal liquid-pervious layer of packing material extending across the space and dividing it into a upper and a lower portion; means for introducing liquid substrate into the lower portion of each of the spaces; means for removing sludge from each of the lower portions; means for removing gas from each of the upper portions; and means for removing treated liquid from each of the upper portions.

2. Fermentation apparatus as claimed in claim 1 in which the liquid-pervious layer of packing material is formed of dumped discrete fluid-fluid contact elements.

3. Fermentation apparatus as claimed in claim 1 or claim 2 in which the average depth of the liquid below the layer of packing material in each space of the apparatus above the floor of that space is from 100 to 3000 mm.

4. Fermentation apparatus as claimed in any one of the preceding claims in which the partition is curved so that it is concaved downwardly when viewed in cross-section.

5. Fermentation apparatus as claimed in claim 1 substantially as hereinbefore described with reference to the accompanying drawings.

6. A process of anaerobically fermenting a liquid substrate which comprises fermenting it in an apparatus as claimed in any one of the preceding claims.