Chemistry: molecular biology and microbiology – Apparatus – Bioreactor
Reexamination Certificate
2000-05-12
2002-05-21
Beisner, William H. (Department: 1744)
Chemistry: molecular biology and microbiology
Apparatus
Bioreactor
C435S300100, C435S262000, C366S262000, C366S270000
Reexamination Certificate
active
06391628
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a digester with an agitator and an associated method for the operation of an agitator in a digester. The agitator is arranged in a stirring shaft or pipe and has a drive axle.
BACKGROUND OF THE INVENTION
A digester with an agitator in a stirring shaft or pipe is conventionally used in agricultural biogas plants and communal clarification plants. In such digester, organic waste materials remain, on the average, for a few days at a temperature above atmospheric temperature, for example at approximately 35° C. The agitator provided in the digester, among other things, serves to distribute waste materials introduced through a filling standard support arrangement. The agitator is operated in timed cycles, so that an optimum temperature balance prevails throughout the digester and the newly introduced waste materials are distributed uniformly in the digester. Through this arrangement, the agitator serves to supply the bacteria contained in the digester regularly with nutrients, to prevent the formation of layers, especially to destroy floating and sinking layers which are forming continually, and to release the gas bubbles which are bound on sludge particles in deeper layers. Gas separation occurs during the fermenting process in the digester, whereby the biogas being generated can be collected in a storage container.
A mixing device for liquid-filled containers is disclosed in DE 94 04 188 U1. In this case, a circulating device connected immovably with a guide assembly is lowered and raised inside and along the container and outside of a guide pipe fastened on the bottom of the container. The spacing between the guide pipe and the wall of the container is selected to be of such dimensions that the circulating device includes the open chambers or free spaces on the suction side and radially which are required for its undisturbed operation.
WO 82/00299 discloses a ball-shaped digester with a helical screw pump arranged in a central pipe shaft and having a vertically running drive axle. The pipe shaft projects upward out of the digester, and includes a partition sealing the top part of the pipe shaft from the gas chamber of the digester. At the level of the equator of the ball or sphere, forming the fill level of the digester, the pipe shaft has a plurality of openings through which the screw pump suctions the material to be pumped. A filling pipe is built into the top part of the pipe shaft, through which material is to be fed into the digester.
A mixing device for liquid-filled containers is disclosed in DE 94 04 188 U1. A circulating device is securely connected with a guide assembly and is raised and lowered by means of a lifting device in the container, along and to the exterior of a guide pipe fastened on the bottom of the container. The distance between the guide pipe and the wall of the container is of such dimensions that the circulating device incorporates radial free spaces on the suction side required for its undisturbed function.
SUMMARY OF THE INVENTION
Objects of the present invention are to provide a digester having an agitator as well as a method for the operation of an agitator in a digester, which digester and method offer an improved thorough mixing of the waste materials in the digester, and therefore, increase the efficiency of the digester. Additionally, the gas separation is particularly improved as a result of an improved thorough mixing of the waste materials.
The foregoing objects are attained by a digester having with a bottom surface and its agitator is accommodated in a stirring conduit arranged beneath the filling standard inlet. The extended projection of the driving or stirring axle of the agitator intersects the periphery of the digester forming a secant thereof. In other words, the extended projection is not directed precisely to the midpoint of the digester.
The configuration of the digester generally involves a cylindrical, closed container, preferably with a circular bottom surface. The bottom surface, however, can have basically any desired contour. Rounded corners or a circular shape are advantageous because these configurations require the generation of rotary movement of the waste materials in the digester. In addition to a driving axle, the agitator also has one or more agitator blades or an agitation or stirring screw. The agitator is preferably mounted on the periphery or edge of the digester. Through the filling inlet, new waste materials are fed into the digester. The stirring pipe generally runs perpendicular and extends preferably as far as a distance of from 0.2 m to 1 m beneath the relevant filling level.
The agitator is generally arranged in a bent, horizontal segment of the stirring pipe, whereby the driving axle extends preferably in the middle and axially parallel to the horizontal segment of the stirring pipe. Alternatively, the agitator can be arranged to the exterior of the stirring pipe, but directly beneath its bottom end. Then, the driving axle of the agitator is not directly to the midpoint of the digester, but rather the extended driving axis intersects the periphery or the edge or the contour of the digester forming a secant.
Advantageously, a rotary or rotary agitating movement of the waste materials in the digester is attained. This rotary movement leads to an especially beneficial thorough mixing of the waste materials, and thus, to increased efficiency of the digester with regard to the development of gases. The arrangement of the agitator beneath the filling inlet provides the advantage that newly filled-in material is suctioned directly into the stirring pipe and then is mixed especially effectively with the waste materials found already in the digester. As a result of the arrangement of the present invention providing the stirring pipe beneath the filling inlet, the development of floating layers is effectively avoided by means of newly introduced waste materials.
When a certain distance is maintained between the agitator and the bottom of the digester, a sediment of digested waste materials can be formed on the bottom of the digester, where it is not whirlpooled up again by the agitation movement. Thus, any undesired mixing of the still gas-producing waste materials with the no longer gas-producing sediment in the bottom of the digester is effectively avoided. Finally, as a result of this, the efficiency of gas formation in the digester is further increased.
As a result of the height-adjustability of the agitator arrangement, the agitating or stirring effect can be set at various heights within the digester. This adjustment leads to an improved thorough mixing of the waste materials, and consequently, to increased efficiency of gas formation. The height adjustment can be executed either manually or mechanically, as well as together with the agitation or in some other relation to the agitation.
A sweeping or tilting of the driving axle out of the horizontal causes not only a horizontal rotary movement of the waste materials, but also a resulting thorough vertical mixing of the waste materials. The angle between the drive axis and the horizontal is preferably between 5° and 45°.
The motor unit can be arranged to the exterior of the digester, through the outwardly directed drive axis. This arrangement is advantageous especially with regard to maintenance work on the motor. By the provision of a gearing or transmission connection, different speed ratios, both faster and slower, and consequently, different rpm's of the agitator could be realized. The gearing or transmission connection can then also occur through a gear train. Preferably a chain connection or belt transmission is provided. A coupling, for example even a slip coupling, can be provided.
With the driving axle to the exterior of the digester as another drive shaft in addition to the main drive shaft for example through the electric motor, powering the drive is possible by means of a combustion engine, for example by a tractor. This agitating or stirring by means of a combustion engine allows for
Beisner William H.
Roylance Abrams Berdo & Goodman L.L.P.
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