Browsing by Subject "Energie"

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    Auswirkungen der flexiblen Biogasproduktion auf die Effizienz von landwirtschaftlichen Biogasanlagen
    (2020) Kress, Philipp; Jungbluth, Thomas
    In future energy systems based on renewable energies, biogas plants can make a significant contribution to stabilizing the electricity grids. However, this requires demand-flexible and load-driven electricity production, which is only made possible by flexible biogas production with extremely versatile feed management. From the process engineering and process biology point of view, this demand-flexible operation represents a major challenge for the operation of biogas plants. Technically, this demand-flexible biogas production requires a complete utilization of the existing fermenter volume, which in turn requires an optimal mixing of the substrates in the fermenter. Similarly, a continuous high-resolution monitoring of the produced biogas composition is also necessary to detect process disturbances or overloads that begin at an early stage. The objective of this work was to test and optimize new measuring methods for the flow velocity measurement and the mixing quality in the biogas reactor. Furthermore, to achieve a high-resolution gas quality measurement, practical scale tests were conducted. From these results, conclusions about possibilities and limitations of a flexibilisation of the biogas production shall be derived. Stirring is one of the most important processes in biogas production. The power input was intended to generate turbulent flows and thus ensure uniform distribution of nutrients and homogeneous temperatures throughout the reactor and avoid sinking and floating layers. In order to be able to assess and optimize these mixing processes, investigations of flow velocities in the fermenter were carried out using a magnetic-inductive measuring system. Additionally, flow profiles were created as a function of the DM content and the viscosity of the fermentation substrate. At a DM content of 9.45% in the fermenter, the average flow velocity measured was 87.5 cm/s. The DM content and the viscosity of the fermenting substrate were also taken into account. This dropped to 0.96 cm/s with a DM content of 9.95%. For the further description of the mixing quality, spatially dissolved nutrient samples were taken from the entire fermenter to determine the biological parameters. It was proven that the punctual input of the solid biomass via the solid input leads to a locally increased DM content and increased concentrations of organic acids in the vicinity of the input. In contrast to the laboratory tests using the process tomography method, no zone was found in the fermenter at which process disturbances were present. Furthermore, in contrast to laboratory tests, no biologically inactive zones could be detected in the fermenter of the research biogas plant. In further investigations, a photoacoustic sensor with a newly developed measuring system for determining the methane and carbon dioxide concentrations of the biogas was installed, tested and optimized for the first time in a biogas plant in the field. The basic applicability of such a system in biogas plants could be demonstrated. The achieved data density was significantly higher than that of conventional devices with a very high precision of the measured values. Using this innovative measuring technique, a flexible substrate supply and its influence on the product gas quality was subsequently evaluated. Substrates with different degradation behavior and different specific methane yields were fed to the fermenter. The influence of the specific substrate used in biogas production was reflected in the biogas quality. In particular, the relation between the relative change in gas quantity and quality makes it possible to detect process changes at an early stage. The presented studies have created a basis that enables a demand-oriented biogas production: Even with high substrate quantities that are fed to the fermenter, a high mixing quality can be achieved in the fermenter with an appropriate design of the agitators, which also prevents local process overloads. The investigations prove that, despite very low flow rates, there is sufficient nutrient supply for the microorganisms. The newly developed sensors for determining the biogas composition provide measured values with high precision and high temporal resolution, so that possible process disturbances can be detected very early. The investigations contribute to optimizing future demand-oriented electricity production on the basis of demand-flexible feeding in biogas plants. As a result, biogas plants can fulfil an important system service in a renewable energy based grid by decentrally stabilizing the electricity supply.
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    Demand-driven biogas production in anaerobic filters
    (2017) Krümpel, Johannes; Jungbluth, Thomas
    Fluctuating energy sources, namely wind turbines and photovoltaic, will be the mayor contributors to the increase in share of renewable energies. The intermittent energy supply by these sources poses challenges for the power grid and need to be counter balanced. A demand-driven energy supply by weather independent biomass conversion can offer these grid services. Flexible energy production from biogas has been identified as a vital approach to provide the grid with positive and negative balancing power. The two-staged anaerobic digestion may be especially suitable for demand orientated gas production due to the advantages of the anaerobic FIlters to withstand high organic loading rates and shock loading. Two staged anaerobic digestion is characterized by a spatio-temporal separation of acidification and methane production. A liquid rich in soluble products, such as volatile fatty acids, alcohols and sugars is produced in the first stage and and is subsequently converted to biogas in the second stage. The methanation stage as the main gas producing unit in such a system is in the focus of this research.The ability to react to sudden changes in demand might be influenced by substrate composition and controlled hydrolysis towards certain intermediates could improve the reaction times towards increased demand. It is therefore one focus of this research work to examine intrinsic methane production kinetics of common intermediates of anaerobic digestion. Other major questions are how fast the methane production can be adapted to sudden changes in demand and to what extent these adaptions are reproducible. It was therefore of interest to demonstrate the feasibility, reproducibility and the possible extent of demand-driven biogas production in anaerobic filters, with respect to changing substrate composition. Furthermore the evaluation of the process effciency based on carbon fluxes should be examined to unfold effects resulting from changing operational conditions. With a newly developed methodology, introduced in the publication "Kinetics of Biogas Production in Anaerobic Filters" kinetic parameters of methane production for individual volatile fatty acids (VFA) could be determined. The bandwidth of tested intermediates was broadened in the second research paper "Intrinsic Gas Production Kinetics of Selected Intermediates in Anaerobic Filters for Demand Orientated Energy Supply". It has been found that intermediates could be ordered according to their half-lives of methane production. The apparent order, beginning with the fastest was acetic acid >ethanol >butyric acid >iso-butyric acid> valeric acid> propionic acid> propanediol> lactic acid. However the mixture of these individual components administered as a naturally produced hydrolysate revealed the fastest methane production kinetics. Differences in the absolute values of determined kinetic parameters between the two experiments can be attributed to variations in organic loading rate (OLR), since degradation rates of a specific substrate are determined by substrate concentration. But also other parameters influence the absolute rate at which methane is produced, such as the concentration of products or unionized substrate itself, pH, nutrient availability, bioenergetics, temperature, inhibition, mass transfer and microbial population. In the third research paper "Demand-Driven Biogas Production in Anaerobic Filters "the previous findings have been put to the test by applying changes in OLR throughout the day and examining different substrate compositions with respect to the methane production rates. As demonstrated, the gas production followed the applied OLR with a distinctive expression of each change in the OLR. That marks the process as highly predictable and defined boundaries within safe operation of AD, in terms of VFA accumulation,can possibly be satisfied by process control. The inclusion of three reactors in the analysis emphasizes the repeatability and therefore the predictability of such an approach of operation. Feasibility and reproducibility of demand-driven biogas production by anaerobic filters could thus be demonstrated. It has been found that the hydrolysate composition has no significant influence on methane production kinetics for demand orientated gas production, since the maximum rate is limited by acetoclastic methanogenesis. The control of the hydrolysis should focus on high overall degradation, rather than towards the production of specific intermediates. A key factor in order to prevent large fluctuation in gas composition is alkalinity, specifically the provision of nitrogenous compounds is vital to maintain stable conditions. Anaerobic filters or attached biomass reactors in general seem to exhibit superior performance towards shock loading and are therefore especially suited for demand orientated gas production as they recover quickly from overloading.Formation of soluble microbial products (SMP) and extracellular polymeric substances (EPS) may be influenced or exaggerated by constantly changing HRT and OLR. Further research in order to evaluate the limits of safe operation is recommended as more extreme scenarios than the ones examined in this work are imaginable in practice.
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    Effects of low dietary levels of saponins on two common culture fish - common carp (Cyprinus carpio L.) and Nile tilapia (Oreochromis niloticus (L.))
    (2001) Francis, George; Becker, Klaus
    Saponins are a group of compounds present in many wild plants and cultivated crops and are commonly found in traditional medicinal preparations. Feeding experiments using saponin-supplemented (commercial Quillaja saponin) feeds were conducted in two commonly cultured fish species, namely common carp (Cyprinus carpio L.) and tilapia (Oreochromis niloticus (L.)). Quillaja saponins (QS) at dietary levels of 150 mg kg-1 and 300 mg kg-1 significantly increased body weight gain in common carp and Nile tilapia compared to controls. When fed to tilapia fry QS (700 mg kg-1) altered the normal 1:1 sex ratio. In separate, in vitro measurements it was found that QS stimulated the release of leutinising hormone (LH) from cultured tilapia pituitary cells, but apparently this did not happen in vivo since serum levels of LH were not found to be elevated in the saponin fed fish. Dietary saponins were also found to affect serum and muscle cholesterol levels. Adult tilapia - but not tilapia fry - fed a dietary level of 300 mg kg-1 QS were found to have significantly higher muscle cholesterol levels than fish fed the control diet. In tilapia fry, the average serum cholesterol levels in males showed a steady increase from dietary QS levels of 0 to 700 mg kg-1, while no such trend existed among the females. Supplementation with 50 and 100 mg kg-1 of Yucca schidigera butanol extract (containing steroidal saponins) did not significantly promote the growth of carp despite showing initial promise. The purified haemolytic fraction of triterpenoid Gypsophila saponin extract (isolated using column chromatography) did not produce any toxic effects in carp at dietary levels up to 250 mg kg-1 in a preliminary feeding trial. A growth promoting effect was however evident at the very low level of about 5 mg kg-1 when the purified fraction was used. More research needs to be done to determine the mechanisms of action of QS and to test whether saponins from other sources have similar effects.