GB2144767A - Methane fermenter - Google Patents

Abstract

A methane fermenter using wastes of the agriculture and domestic livestock industry, has improved fermentation efficiency and facilitates maintenance and inspection. The fermenter includes a horizontal, cylindrical tank (20), an inlet (23) provided at the top of the tank (20), a supporting flange (24) integral to the inlet (23), and a detachable heating and agitating unit (25) including a spacer (32) removably engaging the flange (24), a supporting framework (28) fixed to the spacer (32) and extending downward into the tank (20) and a heater (31) and an agitator (29) both fixed to the framework (28). <IMAGE>

Description

SPECIFICATION Methane fermenter BACKGROUND OF THE INVENTION 1. Field of the invention The present invention relates to a methane fermenter of a methane fermentation system.

2. Description of the Prior Art Methane fermentation using wastes from the agriculture and domestic livestock industry has recently received much attention as a source of locally generated energy and as a means of limitting pollution and development of various large and small methane fermentation systems for practical use continues.

In the present state of the art, a methane fermentation system for large-scale businesses accommodating more than 10,000 hogs must be similar to the sludge digestion system of a sewage treatment plant and so the cost of building such a methane fermentation system is correspondingly high. Potential customers who can afford such large-scale methane fermentation systems are few in number.

On the other hand, there are many potential customers who can afford smaller methane fermentation systems for smaller businesses accommodating 500 to 5,000 hogs. However, such small-scale potential customers have less capital available for building a methane fermentation system. Additionally, since the methane fermenter itself constitutes a large part of the total cost of the methane fermentation system, the cost peformance of the methane fermenter itself is the key to introduction of small-scale methane fermentation systems.

Figure 1 shows an example of a prior-art small scale methane fermentation system using a vertical, right circular-cylindrical methane fermenter.

This methane fermentation system will be described briefly hereinafter.

Feces and urine 3 (hereinafter referred to as waste) are drawn from a waste reservoir 2. The raw liquid phase of the waste is raised to the methane fermenter 5 by means of a raw waste raising pump 4. A vertical hot-water heating coil 6 is provided at the center of the methane fermenter 5 which retains the raw waste and a submerged agitating pump 7 separated from the heating coil 6 draws in fermenting liquid from the bottom of the tank and discharges it at the top. The agitating pump 7 includes an electrical motor (not shown), the electrical cable 8 for which runs out of the methane fermenter 5. Methane gas generated within the methane fermenter 5 is supplied to a water-sealed gas holder 11 through a dehydrator 9 and a desulfurizer 10. Part of the methane gas stored by the gas holder 11 is used as fuel for a boiler 12.The hot water produced by the boiler 12 is delivered to the hot-water heating coil 6.

The above-described methane fermenter 5 entails the following drawbacks: 1) In view of price, a right-circular cylindrical tank comprising a dual-walled structure is used, inner and outer walls of which are made of a fiber reinforced plastic plate with a thermal insulator disposed therebetween. The tank becomes more difficult to transport as its unobstructed capacity increases. Additionally, an erected tank becomes more susceptible to damage from earthquakes or typhoons as its height increases. In a 500 hog-scale methane fermentation system, the capacity of the methane fermenter 5 must be at most 20 m3, requiring, for example, an outer diameter and height of 2,280 mm and 5,921 mm, respectively. On the other hand, if the height of the tank is reduced, the outer diameter of the tank must be increased, so that transport becomes more difficult.

2) The pressure of the fermenting liquid within the methane fermenter 5 increases with the height of the tank. It accordingly becomes more difficult to pressure-proof the bottom of the methane fermenter 5.

3) The heads of the raw waste raising pump 4 and the agitating pump 7 must increase with the height of the tank, which reduces the efficiency of the pumps 4 and 7.

4) Measures, such as lighting conductors, must be taken to protect tall tanks against lighting.

5) Maintenance of the hot-water heating coil 6 and the agitating pump 7 is difficult.

6) The fermentation performance is lowered, so that the hot-water heating coil 6 necessarily has a multi-structure of concentric circles in order to uniformly heat the fermenting liquid at the same height within the methane fermenter 5.

Figure 2 shows an example of a prior-art horizontal cylindrical methane fermenter. The fermenter 15 includes three agitating pumps 16 of submerged type which are integrally fixed to the bottom 15b of a tank 15a at regular longitudinal intervals. The agitating pumps 16 are of the same type as the above-described agitating pump 7. A hot water heating coil 17 extends coaxially along the bottom 15b of the tank 15a. Two conduits 17a of the coil 17 pass through one end 15c of the tank 15a to the outside. The hot-water heating coil 17 is integrally fixed to the tank 15a, similarly to the agitating pumps 16.

The above-described methane fermenter 15 entails the following drawbacks: 1) Maintenance and inspection of the agitating pumps 16 and the hot-water heating coil 17, which are integrally fixed to the tank 15a, is difficult.

When maintenance and inspection are to be performed, the tank 15a must be emptied.

2) The contents of the methane fermenter 15 are difficult to heat and agitate uniformly over the length of the methane fermenter 15 even though the fermenter 15 is so designed that the outer diameter of its tank is no more than 2.8m and the length of its tank is no more than 10m so that it can be transported by means of a normal truck while maximizing the capacity of the fermenter 15.

SUMMARY OF THE INVENTION An object of the present invention, overcoming drawbacks of vertical, cylindrical methane fermen ters and horizontal, cylindrical methane fermenters of the prior art, is to provide a horizontal, cylindrical methane fermenter with enhanced heating and agitating effects so as to increase fermentation peformance.

Another object of the present invention is to provide a horizontal, cylindrical methane fermenter which facilitates maintenance and inspection of a heating device and an agitating device.

For accomplishing the objects, the methane fermenter of the present invention comprises a horizontally aligned cylindrical tank, at least one inlet provided at the top of the tank, a supporting flange integrated to the periphery of the inlet, a spacer displaceably attached to the supporting flange, a supporting framework fixed to the spacer and extending downward into the tank, and a heating and agitating unit comprising a heater and an agitator both fixed to the supporting framework. In accordance with the present invention, any of a number of heating and agitating units, which are easily interchangeable, may be freely selected according to conditions such as the capacity of the tank, the properties of the fermenting liquid and the climatic conditions of the local area. Additionally, transportation, maintenance and inspection of the methane fermenter are facilitated.Additionally, since the methane fermenter of the present invention can easily be designed as modular units comprising a tank with a maximum capacity of 50 m3 for example, it is also easy to add to an existing methane fermentation system.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic view of the methane fermentation system using the vertical, cylindrical methane fermenter of the prior art; Figure 2 is a schematic view of the horizontal, cylindrical methane fermenter of the prior art; Figure 3 is a cut-away plan view of the methane fermenter of the present invention; Figure 4 is a sectional view taken along the line IV-IV in Fig. 3; Figure 5 is a cross-sectional view taken along the line V-V in Fig. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to Figs. 3 to 5, the preferred embodiments of the present invention will be described in detail hereinafter. A horizontal, generally cylindrical tank 20 of a methane fermenter is fixed to the ground 22 by means of a plurality of legs 21. The wall of the tank 20 comprises an inner wall and an outer wall both made of fiber-reinforced plastic and separated by a layer of a thermal insulator such as polystyrene foam or polyurethane foam (not shown). The outer diameter and the length of the tank 20 are suitably selected in accordance with the scale of the methane fermentation system.

In particular, the outer diameter is preferably no more than 2.8m in view of transport of the tank 20 by means of a large-scale low floored truck rather than by means of a special transporting car such as a large-scale trailer.

A plurality of inlets 23 which are spaced at regular intervals longitudinally along the tank 20 extend slightly upward from the top of the tank 20. Each inlet 23 has an opening with a square cross-section and a supporting flange 24 integrally fixed to the upper edge of the periphery of the opening.

A heating and agitating unit 25 supported by the supporting flange 24 extends through the inlet 23 near to the bottom of the tank 20. The heating and agitating unit mainly comprises a framework 28 consisting essentially of a plurality of vertical rods 26 and a bottom plate 27 attached to the lower ends of the rods 26, an agitating pump 29 of submerged type fixed to the bottom plate 27 and serving as an agitator, a discharge pipe 30 extending upward from the agitating pump 29 within the framework 28, a hot-water heating coil 31 serving as a heater, and spiralling upward in contact with the inner surfaces of the rods 26 and around the agitating pump 29 and the discharge pipe 30, and a rectangular spacer 32 placed on the supporting flange 24 of the inlet 23 and displaceably fixed to the flange 24, for example by means of bolts and nuts.

One or more than one heating and agitating units 25 are provided in accordance with the capacity of the tank 20 and required heating and agitating capacities.

Elements of the above-described heating and agitating unit 25 will be described in detail hereinafter.

A fermenting liquid circulating inlet 33 is provided at the bottom of the agitating pump 29 and opens through the underside of the bottom plate 27 of the framework 28.

As best shown in Fig. 3, a cross-shaped discharge nozzle 34 having four openings is attached to the upper end of the discharge pipe 30. The openings of the discharge nozzle 34 lie above the level of the fermenting liquid 35.

Three openings lie inside of the hot-water heating coil 31 in order to improve circulation efficiency and on the other hand, the remaining opening 34a projects outside of the hot-water heating coil 31. The opening 34a is supported by one of the rods 26.

The spacer 32, which is in the shape of a box, has the same dual-walled structure as the tank 20.

As shown in Figs. 4 and 5, the spacer 32 has a cable terminal 36 on one wall and a hot water inlet 37 and a hot water outlet 38 on the opposite wall and has two gas outputs 39, one on each of the remaining walls.

An electrical cable is connected to the electrical motor (not shown) within the agitating pump 29 and to the cable terminal 36. Both the hot water inlet 37 and the hot water outlet 38 are connected to the hot-water heating coil 31. The gas outlets 39 are connected to a gas refining and storing apparatus (not shown) constituting another part of the methane fermentation system.

A square cap 41 is placed over the upper edge of the spacer 32. A pipe 41b leading from the tank 20 for sampling fermenting gas has a valve 41a and is provided at the center of the cap 41. The fermenting gas sampling pipe 41b is used to sample gas in the tank 20 before the normal methane fermentation within the tank 20 begins.

One end of the tank (in Fig. 4, the left end) has a raw waste inlet 42 near its upper edge and a drain 43 near its lower edge.

The other end of the tank (in Fig. 4, the right end) has a waste liquid outlet 44 and a level meter 45 near its upper edge and another drain 43 near its lower edge.

The operation of the above-described methane fermenter of the present invention will be described hereinafter. The raw waste is shot into the tank 20 through the raw waste inlet 42 by means of a raw waste raising pump 4, such as shown in Fig. 1, provided outside of the methane fermenter.

The received raw waste is subjected to methane fermentation for a residence period depending on the nature of the raw waste and then overflows through the waste liquid outlet 44. That is, after the methane fermenter achieves static equilibrium, the same amount of waste as received is discharged and the level of the fermenting liquid 35 within the tank 20 is held constant.

The received raw waste is sufficiently heated and agitated by the heating and agitating unit 25. Thus, the fermentation of the received raw waste is promoted under an anaerobic environment within the tank by methane generating fungi in the fermenting liquid 35. The fermenting liquid 35 emits methane gas into the chamber above the level of the fermenting liquid 35 and slowly flows from the side of the raw waste inlet 42 to the opposing waste liquid outlet 44. The above-mentioned methane gas is delivered to the gas refining and storing apparatus via the gas outlet 39.

In the methane fermenter, the fermenting liquid 35 near the bottom of the tank 20 is raised by the agitating pump 29 through the discharge pipe via the fermenting liquid circulating inlet 33 and dispersed to the inside and outside of the hot-water heating coil 31 by the discharge nozzle 34. The fermenting liquid 35 dispersed to the outside of the heating coil 31 descends outside of the heating coil 31, and the fermenting liquid 35 dispersed to the inside of the heating coil 31 descends inside of the heating coil 31 and then is descended to the outside by the bottom plate 27 of the supporting framework 28 subject throughout to heating by the heating coil 31. The dispersed fermenting liquid reaches the fermenting liquid circulating inlet 33 again. Thus, the agitation and the heating are efficiently repeated.

The heating and agitating unit 25, the spacer 32 of which is removably attached to the supporting flange 24, can be easily removed from the tank 20, which facilitates transportation of the methane fermenter. Additionally, when the heating and agitating unit 25 is removed during operation of the methane fermenter, the anaerobic environment within the tank 20 will not be violated because the cap 41 forms a seal with the supporting flange 24.

Claims (6)

1. A methane fermenter comprising a horizontally aligned cylindrical tank, at least one inlet provided at the top of the tank, a supporting flange integral to the periphery of the inlet, and a heating and agitating unit including a spacer removably engaging the supporting flange when in operating position, a supporting framework fixed to the spacer and extending downward into the tank and a heater and an agitator both fixed to the supporting framework.

2. A methane fermenter as defined in claim 1, characterized in that the heater is a hot-water heating coil fixed to the supporting framework, a hot water inlet and a hot water outlet of the hot-water heating coil being disposed in the spacer and in that the agitator comprises a submergeable agitating pump including an electrical motor, a discharge pipe for conducting fermenting liquid upward from the agitating pump, and a discharge nozzle connected to the discharge pipe and in that a terminal of an electrical cable connected to the electrical motor is disposed in the spacer.

3. A methane fermenter as defined in claim 1, characterized in that the supporting framework comprises a bottom disposed near the bottom of the tank when the heating and agitating unit is in operating position, and a plurality of rods, upper ends of which are fixed to the spacer and in that the agitating pump is fixed to the bottom of the framework with an intake port exposed to underside of the bottom of the framework and in that when the heating and agitating unit is in operating position the discharge nozzle lies above the level of fermenting liquid and opens to the inside and outside of the hot-water heating coil.

4. A methane fermenter substantially as described hereinbefore with reference to the accompanying drawings.

5. A methane fermenter according to claim 4 and as shown in Figures 3 to 5 of the accompanying drawings.

6. Any other novel feature or combination disclosed hereinbefore or shown in the accompanying drawings.