GB2046725A

GB2046725A - Tank for the Digestion of Organic Substances

Info

Publication number: GB2046725A
Application number: GB8011827A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1979-04-11
Filing date: 1980-04-10
Publication date: 1980-11-19
Also published as: NL180406C; PL223395A1; ES249925Y; NL180406B; CS214829B2; GB2046725B; LU82354A1; CH648058A5; ES249925U; YU97780A; SE446970B; NL8002122A; DE2914802A1; HU181095B; PL123080B1; SE8002619L; DE2914802C2; RO80002A; RO80002B; FR2453589A1

Abstract

A fermenting tank for the intermittent or continuous digestion of organic substances comprises a heat insulated tank provided with inlet pipes for fresh organic material, outlet pipes for digested material, means for heating and circulating the organic material, means for draining sludge from the bottom of the tank and means for drawing off floating material from the upper surface of the organic material.

Description

SPECIFICATION Fermenting Tank for the Digestion of Organic Substances A fermenting tank with devices for the continuous or intermittent digestion of organic substances.

The invention relates to a fermenting tank with devices for the continuous or intermittent digestion, of organic substances, consisting of a heat insulated tank (digestion tank) into which feed pipes for the inlet of fresh material and out of which flow pipes for the discharge of the digested material and inside the said tank devices for the heating and circulating of the digested material.

The object of the abovementioned fermenting tank is the manufacture of methane gas from organic substances, mainly stable manure, straw, faeces, green material, waste from households, gardens, agriculture and the foodstuff industry.

Furthermore the digested material supplied from the fermenting tank is a hygienically satisfactory natural manure low in odour and rich in nitrogen.

Practical experiments with homogenized, fibrerich digested material have shown that this material, even with progressive digestion, does not sink like a communal sewage sludge but ascends upwards. The continuous operation of upright fermenting tanks is therefore only possible with specifically light digested material even if floating material can be led off. Since, however, in the setting up of a biogas installation it is not certain whether only floating, only sinking or both upwards and downwards tending material will arrive for digestion, therefore a possibility for the sludge clearing of both alternatives must be provided for so that the process can be carried out free of disturbance.

The aim of the present invention is to develop further a fermenting tank of the abovementioned type such that floating digested material as well as sinking digested material can be utilized. The fermenting tank according to the present invention can therefore be employed universally, and will work with high efficiency and be transportable.

The problem is solved according to the present invention in that besides the discharge of sludge at the bottom of the tank there is a sludge discharge level with the upper limit of the digested material to provide for the alternative draining off of floating or ascending digested material.

Thus the essential feature of the present invention is that besides a discharge of sludge for the delivery of the digested material from the bottom of the container a further discharge of sludge for the delivery of the digested material floating in the fermenting tank is provided so that the fermenting tank is capable of being used universally (for all types of waste material).

The discharge pipes reaching from the bottom and from the upper surface sludge draw-off are guided laterally outwards in the upper third of the tank through the wall thereof into a static vessel This static vessel serves mainly as a gas seal and must always be filled with liquid above the upper edge of the entering and discharge pipes. It is either fixed on the outer wall of the container or set up freely in the vicinity. A discharge pipe leads from the static vessel into the cesspool. The static vessel as a gas seal corresponds to a syphon which may be formed otherwise and is flanged onto the outer casing.

In order to keep the upper limit of the digested material at a constant level even at high gas pressure, the pipe discharging from the static vessel into the cesspool protrudes upwards for a distance through the bottom of the static vessel so that with a tube piece (movable sleeve) pushed thereover the flow-over edge can be adjusted as desired.

In a preferred embodiment of the present invention the sludge discharge is formed at the bottom of the tank by means of a sludge guide cone with lateral openings parallel to the main opening on the bottom of the tank. From this sludge guide cone a discharge pipe ascends approximately vertically and in the upper third of the tank is guided laterally to run almost parallel with the equivalent pipe which has descended from the upper surface of the digested material into the static vessel.

The sludge discharge associated with the floating digested material is, in a preferred embodiment, effected by a funnel positioned with its flow-off edge level with the upper surface of the digested material. This funnel leads into a descending discharge pipe the other opening of which, below the upper surface of the digested material, leads into a static vessel. The openings from the bottom and the upper surface discharge pipes therefore both lead into the static vessel where they can be closed selectively by a slide valve. The slide valve is vertically movable in this example, the openings to be closed are disposed above one another.

In a further embodiment the slide valve may also be arranged to move horizontally in this case the openings associated with ends of discharge pipes are arranged in a horizontal line next to one another.

In a further embodiment the bottom and the upper surface sludge discharges are effected by a pipe which passes from the bottom of the tank to a position above the top of the gas bell lid with lateral openings in the said pipe in the region of the bottom of the tank and in the region of the upper surface of the digested material. Below the gas bell lid gas outlet openings are provided and the pipe extending outside the gas bell lid is closed gas tight. Below the upper surface of the digested material an approximately horizontal pipe is extended from this vertical pipe and leads into the static vessel. Thus a particularly simple, effective method of draining off sludge from the bottom and upper surface is ensured because essentially only a vertical projecting pipe with a lateral branch must be disposed in the fermenting tank.

It is preferred that there should be some method of entering the fermenting tank in order to carry out repairs and this entry point may be disposed in the gas bell lid near the tank wall so that the operator upon entry would easily be able to go past the upper sludge discharge funnel. It is however, also possible to position the manhole to open laterally through the tank wall.

The advantage resulting from this is that the whole tank lid is welded gas tight in the region of the gas supply chamber and does not have any detachable connection.

In addition the immersion pump can be mounted without difficulty in a position which is favorable for transport. Similarly should this pump break down, it can be replaced from outside without difficulty or danger because the contents of the tank only reaches as far as the assembling height.

A further essential feature of the invention is that the aforementioned high-output fermenting tank is capable of being transported without difficulty by the conventional means on public roads because its diameter is within the officially prescribed limits for transportation without special approval. Thus the fermenting tanks can be mounted ready in series on the worksite. Then at the place of erection only the electricity cables, hot water pipes and digested material feed and discharge pipes are to be connected. These small dimensions result in the fact that a thermophilic fermenting method, that is, a heating of the contents of the tank being only applied over 500.

The scope of protection of the present invention extends not only to the subject matter of the individual claims but also to the combination of the claims with one another.

The invention will now be described with reference to the accompanying drawings illustrating only one method of construction.

The fermenting tank shown in the Figure is a cylindrical cross section with a tank inner wall 1 a, a tank outer wall 1 b and the insulation 1 c fixed between these two walls. On the tank 1 a, 1 b is arranged a gas bell lid 2a which is formed from a gas bell inner wall 2b and a gas bell outer wall 2c.

The gas bell lid 2a encloses the gas supply space 2 which is formed above the upper surface of the digested material 3. The fermenting substrate is pumped into the digestion tank 1 via the fresh material feed 4 and flows from the fresh material outlet openings 4a until the tank is filled almost to the upper permissible limit of the digested material 3.

In operation a constant circulation of the digested material is effected by means of an immersion pump 25 which is disposed inside the digestion tank 1 and sucks the digested material in through the suction foot 30 and it then flows via the circulation pipe 8 and outlet nozzles 8a into the tank again. Hereby, in a preferred embodiment of the present invention, a first outlet nozzle 8a is disposed in the bottom region and the digested material flows out through it in the direction of the arrow 32 whilst in the gas supply space 2 a second outlet nozzle 8a is provided which is directed at the floating cover forming on the upper surface of digested material 3 so that by means of the digested material emerging in the direction of the arrow 31 the floating cover is reduced to small dimensions.

The bottom of the tank 1 fis formed conically around the periphery of the digestion tank as bottom 1 g whereon a sludge guide cone 12 with base side openings 12a is positioned. The digested sludge reaching the middle of the bottom of the digestion tanks can finally be removed via the discharge pipe 5 in the direction of the arrow 33. The digested sludge is brought to a relatively high temperature by a heating coil 10 which is connected via the heating inflow current 1 Oa and the heating return 1 Ob to a central heater.

The gas forming in the gas supply space 2 can be removed via the gas outlet pipe 9 whereby the heating coil 10 arranged pyramide-like is connected via the heating inlet 1 Oa and the heating return 1 Ob to a central heater.

By means of the above heating arrangement around the sludge guide cone, a convection flow is obtained which results in the tank space being better utilized. The application of a thermophilia fermenting method (over 500) allows the use of smaller and thus transportable fermenting tanks.

Of course the fermenting substrate may also be pre-heated outside the tank.

The bottom sludge discharge 5, 12, 1 2a will now be explained as following:~ As stated above this sludge discharge serves to remove digested material which sinks to the bottom of the digestion tank. One end of the discharge pipe 5 opens into the sludge guide cone 12 whilst the other end 21 discharges into the static vessel 26. If at this point in time digested sludge deposit from the digestion tank is to be removed then the slide valve 34 blocking off the opening 21 of the discharge pipe 5 is moved upwards so that the opening 22 of the upper surface discharge pipe 5a is closed.Due to the liquid pressure (upper surface of digested material 3 is above the opening 21 of the discharge pipe 5 the digested material deposited on the bottom of the digestion tank is forced in the direction of the arrow 33 through the discharge pipe 5 and flows into the static vessel 26.

As the openings 21. 22 of the discharge pipes 5, 5a are always below the upper surface of the digested material 3 the static vessel forms a gas seal and there is a ventilation connection member 44 extending from the upper part of the static vessel 26.

The material flowing into the static vessel 26 fills the static vessel 26 until it reaches above the edge 38 of a sleeve 36 which is movable along the discharge pipe 5b. At this point the material falls downwards in the direction of the arrow 39 via the discharge pipe Sb.

As stated above, the movable sleeve 36 serves for maintaining the constant height of the upper surface of the digested material 3 independently of the gas pressure inside the gas supply tank 2. If the gas pressure is zero inside the gas supply tank then a similar liquid height exists inside the digestion tank 1 as well as in the static vessel 26.

For example, if the gas pressure in the gas supply tank 2 is a 250 mm column of water then the water level in the static vessel is higher, theoretically, by 250 mm.

The path of the displacement of the sleeve 36 depends therefore on the gas pressure inside the digestion tank 1.

In a further development of the present invention it is arranged for the displacement of the sleeve 36 to be effected automatically, corresponding to the gas pressure in the gas supply tank 2. However, it is possible to displace manually the sleeve 36. A certain maximum pressure is permitted in the fermenting tank. If the gas pressure gauge shows that the maximum pressure is exceeded, then the liquid level in the fermenting tank must be lowered. In order to accomplish this the sleeve 36 is moved downwards in the direction of the arrow 37 so that the edge 38 is likewise displaced downwards and the liquid level in the static vessel 26 drops because more liquid now flows from the static vessel in the direction of the arrow 39 via the pipe Sb.

The liquid level in the static vessel must never sink so low that the openings of the discharge pipes are uncovered because if this should happen the gas is forced from the gas supply tank into the static vessel.

So that this is less likely to happen it is suggested that the openings of the discharge pipes are arranged horizontally next to one another and the slide valve 34 is likewise horizontally moveable. In this way, a relatively low liquid level in the static vessel can be achieved without the openings being exposed above the liquid surface.

The upper surface discharge is described as follows: It is essential that the upper surface discharge should be level with the upper surface of the digested material and this is obtained by a funnel arranged with its flow-off edge level with the upper surface of the digested material. This funnel discharges into the pipe the other opening of which discharges, below the upper surface of digested material, into the static vessel. The shape of the funnel is important: On the lower edge of the funnel an inclined face is formed. The ascending fermenting material is guided upwards on this inclined face and collides there with the cover of floating material forming on the upper surface of the digested material.There then takes place a breaking of the digested material over the edge of the funnel as well as a degasification at the edge 46 so that the material of the floating cover falls, in broken form, into the funnel and moves in the direction of the arrow via the discharge pipe into the static vessel. A breaking into pieces of the floating cover is thus effected in conjunction with the outlet nozzle of the circulating pipe.

The funnel is fixed to the gas bell lid by struts.

In the representation shown the slide valve is in its lowermost position and closes the opening associated with the discharge pipe. In the representation, therefore, the material forming at the upper surface of the digested material is discharged from the fermenting tank via the funnel and the pipe in the direction of the arrow.

Instead of the arrangement of a funnel with one edge and a discharge edge 40 it is also possible, to effect the division of the floating matter by means of a stirring worm wheel or other mechanical breaking-up devices. Likewise several nozzle openings may be provided in order to break up the floating cover by the nozzle jet from the circulation pipe. The discharge edge of the funnel may also be provided with projections and prongs in order to ensure an additional mechanical breaking up.of the material falling into the funnel. Also the immersion pump may be positioned outside the fermenting tank. - It is also within the scope of the present invention that instead-of a cylindrical tank a spherical tank may be used. It is likewise possible that instead of the solid connection between the gas bell lid and the vertically ascending side wall of the tank, a gas bell lid floating on a liquid closure may be used.

Claims

1. A fermenting tank with devices for the continuous or intermittent digestion of organic substances consisting of a heat insulated tank into which feed pipes for the inlet of fresh material and discharge pipes for leading away the digested material and in which are arranged devices for the heating and circulating of the digested material, characterised by the alternate drawing off of floating or ascending digested material and the draining off of sludge from the bottom of the container, and also a sludge drain at the level of the upper surface of the digested material.

2. A fermenting tank according to Claim 1, characterised by the sludge being drawn off from the bottom of the tank through a sludge guide cone with lateral openings parallel to the opening on the bottom of the tank and from this sludge guide cone leads a discharge pipe standing approximately vertical with its other opening below, the upper surface of the digested material discharging into a static vessel.

3. A fermenting tank according to Claims 1 or 2, characterised in that the sludge discharge is accomplished by means of a funnel (126) arranged with its discharge off edge (40) level with the upper surface of the digested material (3) and which leads into a discharge pipe (5a) the other opening (22) of which is below the upper limit of the digested material leads into a static vessel.

4. A fermenting tank according to Claim 1, characterised in that the sludge discharge from the bottom of the tank and level with the upper surface of the digested material is achieved by a continuous tube with lateral openings in the region of the bottom of the tank (1f) and in the region of the upper surface of the digested material (3) is extended from the bottom of the tank as far as beyond the top of the gas bell-lid (2a) whereby under the gas bell-lid (2a) openings for the gas outlet are provided and the pipe outside the gas bell-lid (2a) is closed gas-tight and that below the upper surface of the digested material (3) an approximately horizontal branch extends from the pipe and leads into a static vessel (26) (not shown).

5. A fermenting tank according to one of the Claims 1 to 4, characterised by openings (21,22) of the discharge pipes (5a, 5) are selectively closeable by means of a slide valve (34) adjustable electrically, hydraulically or manually and that the slide valve is disposed in the static vessel (26).

6. A fermenting tank according to one of the Claims 1 to 5, characterised for keeping constant a uniform upper surface height of the digested material (3) in the digestion tank (1). There is arranged independently of the gas pressure in the gas supply chamber (2) a discharge apparatus (5b, 3b, 38) with variable discharge height in the static vessel.

7. A fermenting tank according to Claim 6, characterised in that the discharge apparatus (5b, 3b, 38) in the static vessel (26) is formed from a flow discharge pipe (5b) leading from the static vessel (26) and on the upper end of the pipe is a sleeve (36) movable in the vertical direction.

8. A fermenting tank according to any of Claims 1 to 7, characterised in that there is diagnosed in the digestion tank (1) an immersion pump (25) or outside an arrangement which circulates the digested material via circulating pipes (8) inthe digestion tank (1).

9. A fermenting tank according to Claim 8, characterised in that there is dispersed above the upper limit of the digestion tank (3) a circulating pipe (8) with a nozzle (8a) directed onto the floating cover of the digested material.

10. A fermenting tank according to Claim 1, characterised in that the dimensions of the thermophilically heatable fermenting tank are adapted to the usual transport conditions (maximum 3000 mm diameter and 7,500 mm height).

11. A fermenting tank according to Claim 1 and 10, characterised in that the heating coils (10) arranged pyramid-shaped are disposed between the sludge guide cone (12) and the upper funnel (12b).

12. A fermenting tank according to any of the claims 1, 10 and 11, characterised in that the heating coils (10) arranged spaced apart from one another are located in the region of the fermenting substratum flow openings (4a, 8a).

13. A fermenting tank according to Claims 1 to 1 2, characterised by, in the bottom of the container (if) a reinforcement (23) running around is arranged which at the same time serves for the supporting of the sludge guide cone (12) and the heating cone (24).

14. A fermenting tank according to Claims 1 and 13, characterised in that the reinforcement (23) has guide faces (24) which point towards the base or openings (12a) in the sludge guide cone (12).

1 5. A fermenting tank according to Claim 1, characterised in that the static vessel (26) is connected to the housing casing of the fermenting tank by means of flange connections.

16. A fermenting tank for the continuous or intermittent digestion of organic substances s.a.d.

with reference to the accompanying drawings.