The present invention relates to a biogas plant and a servicing device for a biogas plant.
Various biogas plants and servicing devices for biogas plants have become known in the prior art. Biogas plant are as a rule provided with one or more fermenter tanks for fermenting the fermenting substrates and as a rule with an agitator provided for stirring and at least partially homogenising the fermenting substrates in the fermenter tank.
Most of these agitators have agitator blades with which to mix and agitate the fermenting substrates. In dependence on the substrates to be fermented and further ambient conditions and on the materials employed the agitators require inspection and if necessary maintenance at specified intervals. Some or all of the agitator blades may be exchanged for example.
For maintenance on an agitator the agitator which is disposed on a mounting or holding rod or the like is traversed from the lower fermentation section in which the fermenting substrates are located, to the upper gas section. For gaining access to the agitator, for example a biogas plant equipped with a flexible top sheeting may be opened and the top sheeting removed entirely to thus gain easy access to the agitator. This method, however, involves the drawback of considerable work for removing the top sheeting. Also, the biogas collecting in the gas section above the fermentation section escapes as the top sheeting is removed.
For biogas plants having a concrete top, DE 199 51 959 A1 has made known a rectangular maintenance shaft inserted in the concrete top allowing maintenance of the agitator without significantly compromising the gas production. In the case of fermenters having a high solids content the maintenance shaft is bipartite with the top part terminating approximately 10 cm above the normal liquid level. In the case of maintenance a lower shaft portion is inserted into the top shaft portion for immersing in the fermenter mass. For sealing the top shaft portion is provided with a circumferential sealing channel with which when assembled a sealing collar of the lower shaft portion engages. These two-part maintenance shafts involve the drawback that each case of maintenance requires newly inserting the lower shaft portion and sealing against the top shaft portion and removing again after maintenance. Also, the fermenter filling volume must be kept within narrow limits for achieving reliable sealing. Therefore this document proposes for fermenters having a low solids content a one-piece maintenance shaft reaching at least 10 cm beneath the normal liquid filling level. For balancing the gas a shut-off pipe connection to the gas headspace of the fermenter is provided. In the case of maintenance the work involved is reduced compared to a two-piece maintenance shaft. The drawback of this is, however, that these maintenance shafts are suitable for low solids contents only. Also, deposits may accumulate on the immersed shaft. Another drawback is a permanent increase in the agitating resistance and thus in energy consumption.
EP 1 717 305 B1 has made known a biogas plant servicing shaft for a fermenter of a biogas plant with a top sheeting with the servicing shaft being provided as a gas-tight, dome-shaped cover across a servicing opening in the fermenter tank cover. The agitating unit held vertically in the fermenter tank can be moved upwardly from the lower fermentation section into the servicing shaft interior. After opening a servicing flap at the servicing shaft the agitator device can be serviced in the interior of the dome-type servicing shaft and one or all of the agitator blades may be exchanged as needed.
A biogas plant servicing shaft according to EP 1 717 305 B1 operates reliably, allowing servicing the agitator device while involving little work wherein maintenance does not require removal of the entire top sheeting. However, as the servicing flap is opened, the biogas which has collected in the upper gas section of the fermenter tank and which is under overpressure, escapes while air and thus a considerable amount of oxygen enters the fermenter tank requiring removal prior to restarting operation.