Biogas plant for methanizing biomass having a high solids fraction

A biogas plant for methanizing biomass having a high solids fraction includes a digestion tank system having a plurality of digestion tanks adapted to be closed in a gas- and liquid-tight manner, each of which includes a charging and withdrawing opening for charging with biomass and withdrawing the biomass, a biogas discharge means, a percolate reservoir, a percolate drainage means for discharging percolate from the plurality of digestion tanks and supplying the percolate to the percolate reservoir, a percolate distributing means for distributing the percolate from the percolate reservoir over the biomass in the plurality of digestion tanks, and a percolate regulating means for regulating the percolate level in the plurality of digestion tanks. The percolate reservoir includes a first and a second percolate container, and supplying and discharging of percolate to/from the first and/or the second percolate container takes place with the aid of the percolate regulating means.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is based on, and claims priority to German Patent Application No. 202008017049.4, filed Dec. 23, 2008 and German Patent Application No. 102009011868.3, filed Mar. 5, 2009 the disclosures of which are incorporated herewith in their entirety.

FIELD

The present invention relates to a biogas plant for methanizing biomass, in particular biomass having a high solids fraction, in accordance with the preamble of claim1.

BACKGROUND

The expression “biomass having a high solids fraction” is to be understood as meaning the opposite of liquid, pumpable biomass, such as is used in wet fermentation processes. “Biomass having a high solids fraction” should therefore be understood as non-pumpable biomass.

A biogas plant in accordance with the preamble of claim1is known from WO 2007/096392. This known biogas plant includes a plurality of digestion tanks which are adapted to be closed in a gas- and liquid-tight manner, each of which includes a percolate discharge conduit having a percolate pump and opening into a common percolate reservoir. Percolate may be conveyed back from the common percolate reservoir into the digestion tank via a percolate return line in which a percolate recirculation pump is provided and which branches toward the individual digestion tanks. The filling level or percolate level of the individual digestion tanks is detected by respective filling level sensors having the form of pressure sensors.

This known biogas plant has the drawback that the plurality of digestion tanks has to be considered as a homogeneous overall system, for each digestion tank receives the same percolate, with substantially identical conversion processes taking place in every digestion tank in this overall system. This known biogas plant is therefore homogeneous in terms of process technology and is cumulatively composed of a plurality of partial systems (the individual digestion tanks) as regards its capacity.

SUMMARY

Starting out from the biogas plant according to WO 2007/096392, it is an object of the present invention to specify a biogas plant having a plurality of digestion tanks which is more flexible with a view to the conversion processes in the individual digestion tanks while forming a heterogeneous overall system in terms of process technology.

This object is achieved through the features of claim1.

In accordance with the present invention, the percolate reservoir includes a first and a second percolate container that are each adapted to be connected via a system of conduits to each single one of the plurality of digestion tanks, wherein feeding and discharging of the percolate to and from the percolate containers may be regulated separately for each digestion tank. Accordingly, there exist two separate percolate circuits, so that a first subset of the digestion tanks may receive percolate from the first percolate container, and a second subset of the digestion tanks may receive percolate from the second percolate container. Analogously, the percolate is conveyed from the first subset of the digestion tanks back into the first percolate reservoir, and the percolate from the second subset of the digestion tanks is conveyed back into the second percolate container. In this way it is possible, for instance, for Nawro's (nachwachsende Rohstoffe=renewable resources) to be converted to biogas in the first subset of digestion tanks, whereas the organic fraction of domestic waste is converted in the second subset of the digestion tanks. If both types of biomass were to receive the same percolate, the percolate from the contaminated organic fraction of the domestic waste would “pollute” the “purer” percolate of the renewable resources. The production of biogas would not unfold optimally in either type of digestion tank, for neither the renewable resources nor the organic fraction of the domestic waste receives the percolate that is particularly suited for each one of them. As a result of the percolate circuits being separated from each other, the percolate may be adapted to the respective biomass to be fermented—e.g., renewable resources or separately collected organic waste and organic domestic waste fraction. As it were, in terms of process technology one biogas plant thus becomes two biogas plants which jointly produce biogas.

In accordance with claim12it is also possible to provide more than two separate percolate circuits. The number of separate percolate circuits having associated percolate containers determines the number of different biomasses that can be fermented in the biogas plant of the invention.

In accordance with the features of claim2, a first and a second main drainage line coming from the first and second percolate containers branch into respective digestion tank drainage lines, so that every digestion tank may be connected to the first and/or the second percolate container. In operation, a separation of the first and second conversion processes is realized, to the effect of any digestion tanks in which the first conversion process takes place being connected to the first percolate container, and any digestion tanks in which the second conversion process takes place being connected to the second percolate container. What process takes place in which digestion tank may be determined at will in accordance with the invention.

In accordance with an aspect according to claim3, the percolate is filtered prior to its introduction into the percolate reservoir. Such filtering may also be provided, alternatively or additionally, in the lines recirculating the percolate from the percolate reservoir to the digestion tanks. Filtering ensures that the distribution unit, e.g. a spraying unit, will not be clogged by the dirt particles, suspended matter, etc. that are present in the percolate. Furthermore it is possible to remove heavy metals and the like from the percolate by such filtering.

As a result of the features of claim4a constructive simplification is achieved, to the effect that—instead of a separate line leading from each one of the two main drainage lines into each one of the digestion tanks—a single line referred to as a main drainage section leads out from each one of the digestion tanks, which single lines then branch into respective lines that are referred to as a first and a second secondary drainage section and that are connected to the first and the second main drainage line, respectively. By controlling cut-off valves arranged in the secondary drainage sections it is possible to connect each one of the digestion tanks to the first and/or the second percolate container.

The features of claim5allow an arbitrary three-dimensional relationship between the digestion tanks and the percolate reservoir. In particular, the percolate reservoir may be disposed in a higher position than the digestion tanks, for the percolate may be transported to this higher position with the aid of the pumps.

As a result of the features of claim6, the digestion tanks may be charged and emptied independently of each other, for the percolate level of each individual digestion tank is detected. The data (height of the percolate level) detected by the percolate regulation unit with the aid of the filling level sensor are supplied, in accordance with the conditions in the digestion tanks, as an appropriate signal to the respective pumps which lower the percolate level to target level by pumping off percolate. The target level may be determined, e.g., on the basis of the charged quantity of the digestion tank or the composition of the biomass, or the like.

In the bioreactor of the invention, the percolate drainage means and the percolate distributing means for withdrawing the percolate from the percolate reservoir and distributing it over the biomass in the digestion tanks have a nearly symmetric construction—Claims7and8.

As a result of the advantageous aspect of the invention according to claim9having a plurality of main distributing sections which extend into each one of the digestion tanks while being distributed across the area of cross-section of the digestion tank, a uniform distribution of the percolate over the entire surface of the biomass in a respective digestion tank is facilitated. The uniform distribution of the percolate may furthermore be optimized by a rebounding plate being arranged in a suitable position for each main distributing section, independently of the number of the main distributing sections, on which rebounding plate the percolate exiting from this main distributing section impacts and, rebounding from the latter, is sprayed over the biomass.

Due to a corresponding valve assembly as defined in claims8and11, each one of the digestion tanks may be connected to the first and/or the second percolate container in analogy with the percolate drainage means. Advantageously, control of the valves takes place automatically, such that a respective digestion tank is not connected to different percolate containers via its drainage means and its percolate distributing means.

As a result of the arrangement of the percolate containers in accordance with claim13, the space demand for the percolate reservoir is reduced in comparison with a side-by-side arrangement of the percolate containers, for instance to about half in a special arrangement in accordance with claim14. This, moreover, involves a simplified system of conduits connecting the percolate containers to the digestion tanks. In addition, the outer percolate container acts as a thermal insulation jacket for the inner percolate container.

The features of claim15allow simple and thus safe charging of the digestion tanks with the aid of appropriate agricultural machines.

In accordance with claim17, the valves are adapted to be operated pneumatically, so that explosions of the gases developing during the conversion processes, which might be triggered by sparking of electrically operated valves, are excluded.

The remaining subclaims relate to further advantageous aspects of the invention.

DETAILED DESCRIPTION

In accordance with the schematic representation inFIG. 1, a biogas plant10in accordance with a preferred embodiment includes a percolate reservoir20, a percolate drainage means100, a percolate distributing means200, and a plurality (in this embodiment: seven) of digestion tanks106.

The percolate reservoir20includes a first—inner—column-type percolate container22and a second—outer—column-type percolate container24, wherein a partition wall26separating the percolate containers22,24from each other and an outer wall28of the percolate reservoir20form concentric circles in a sectional view.

The percolate drainage means100includes a first main drainage line102and a second main drainage line104which open into the inner22and the outer percolate container24, and a first and a second digestion tank drainage line108and110, wherein each one of the plurality of digestion tanks106is connected to the first main drainage line102via a first digestion tank drainage line108and to the second main drainage line104via a second digestion tank drainage line110. The first and the second digestion tank drainage line108and110of a respective digestion tank106include a common main drainage section112extending from a percolate region114inside the digestion tank106as far as a branching point116outside of the digestion tank106, and a first and a second secondary drainage section118and120extending from the branching point116to the first and the second main drainage line102and104, respectively. In other words, the first digestion tank drainage line108includes the main drainage section112and the first secondary drainage section118, and the second digestion tank drainage line110includes the main drainage section112and the second secondary drainage section120, as is shown more clearly (without valves) inFIG. 2.

At each one of the main drainage sections112a pump122for conveying percolate into the percolate reservoir20is arranged, and inside each secondary drainage section118,120there is a cut-off valve124whereby the flow through this section may be blocked or enabled. In particular, the percolate conveyed by the pump122may be supplied to the second percolate container24via the main drainage section112, the second secondary drainage section120, and the second main drainage line104by closing the cut-off valve124in the first secondary drainage section118and opening the cut-off valve124in the second secondary drainage section120, and may be supplied to the first percolate container22via the main drainage section112, the first secondary drainage section118, and the first main drainage line102by opening the cut-off valve124in the first secondary drainage section118and closing the cut-off valve124in the second secondary drainage section120.

As a result of corresponding switching positions of the cut-off valves124associated to the digestion tanks106it is moreover possible to supply the percolate of the ithdigestion tank106to the first percolate container22, and the percolate of the jthdigestion tank106to the second percolate container24, wherein i,jε{1, . . . , n}, with n=7 in this embodiment, and i=j (for the case of identical conversion processes in all of the digestion tanks106, i.e., if a separation is not necessary or desired), or i≠j (in cases of different conversion processes). Between the digestion tanks106and the percolate reservoir20, a first filter system126is arranged in the first and second main drainage lines102and104. Between the first filter system and the percolate reservoir20, a flow measuring device128is arranged which detects the throughput of percolate in the first and/or the second main drainage line102and104. On the basis of the detected data and of additional data, the valves may be controlled in an optimum manner.

In analogy with the first and second main drainage line102and104of the percolate drainage means100, the percolate distributing means200includes a first and a second main distribution line202and204(also cf.FIG. 3) which open into the first and the second percolate container22and24, respectively. Each of the digestion tanks106is connected to the first main distribution line202via two first digestion tank distribution lines208, and to the second main distribution line204via two second digestion tank distribution lines210(seeFIG. 3). One of the first digestion tank distribution lines208and one of the second digestion tank distribution lines210are connected to each other so as to include a common main distributing section212extending from a gas region of the digestion tank106as far as a connection point216, and a first and a second secondary distributing section218and220extending from the connection point216to the first and the second main distribution line202and204, respectively. The second one of the first digestion tank distribution lines208and the second one of the second digestion tank distribution lines210are connected to each other correspondingly. In other words, the first digestion tank distribution lines208each include a main distributing section212and a secondary distributing section218, and the second digestion tank distribution lines210each include a main distributing section214and a secondary distributing section220.

In each secondary distributing section218,220a respective flow control valve224is arranged, and in each main distributing section212a respective cut-off valve228is arranged. Between the digestion tanks106and the percolate reservoir20, a filter system226is arranged in the main distribution lines202,204. Furthermore, pumps230for conveying the percolate from the percolate reservoir20into the respective digestion tanks106as well as flow control valves232and cut-off valves234are arranged inside the main distribution lines202,204. In analogy with the percolate drainage means100, as a result of appropriate positions of the valves224and228it is possible to either jointly supply the percolate from the first and second percolate containers22and24or to separately supply the percolate from only one of the first and second percolate containers22and24to each one of the digestion tanks106. In other words, the valves224,228allow on arbitrary percolate mixture from the first and/or the second percolate container22and24to be supplied for each one of the digestion tank106, independently of the other ones of the digestion tanks106, with this mixture then being distributed over the biomass by means of the main distributing sections212. In analogy with the percolate drainage means100, a flow measuring device for detecting the throughput of percolate in the first and/or the second main distribution line202and204is arranged between the filter system226and the percolate reservoir20.

The digestion tanks106each include a biogas discharge conduit (not shown) through which the biogas generated in the respective digestion tank106is discharged.

In accordance with the embodiment, all of the valves and pumps are driven by a percolate regulation unit (not shown). Regulation is performed, for example, on the basis of the detected values of the percolate level which may be detected, e.g., with the aid of a pressure sensor, the temperature of the biomass, the composition of the discharged biogas, etc.

Although the present invention has been disclosed with reference to the preferred embodiments so as to enable an enhanced comprehension of these, it should be understood that the invention may be realized in various ways without departing from the scope of the invention. Accordingly, the invention should be construed to the effect of encompassing any possible embodiments and aspects for the shown embodiments which may be realized without departing from the scope of the invention as set forth in the annexed claims.