Browsing by Subject "Erneuerbare Energien"

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Agent-based modeling of climate change adaptation in agriculture : a case study in the Central Swabian Jura
(2014) Troost, Christian; Berger, Thomas
Using the MPMAS multi-agent software, the present thesis implements an agro-economic agent-based model to analyze climate change adaptation of agricultural production in the Central Swabian Jura. It contributes to the DFG PAK 346 FOR 1695 research projects dedicated to improve the understanding of processes that shape structure and functions of agricultural landscapes in the context of climate change at regional scale. In the context of this example, this thesis discusses, develops and tests novel approaches to deal with four notorious challenges that have so far hampered the empirical use of agent-based models for applied economic analysis: data availability, process uncertainty, model validity and computational requirements. The model is used to examine climatic effects on agriculture, changes in agricultural price responses and biogas support and agri-environmental policies illustrating the applicability of the model to adaptation analysis. The first part of the thesis is dedicated to a methodological discussion of the use of mathematical programming-based multi-agent systems, such as MPMAS, for the analysis of agricultural adaptation to climate change. It synthesizes knowledge about the potential impacts of climate change and processes of farmer adaptation and reviews existing agent-based models for their potential contribution to adaptation analysis. The major focus of the first part is a discussion of available approaches to model validation, calibration and uncertainty analysis and their suitability for the use with mathematical programming-based agent-based models. This discussion is based on four principles required to ensure the validity of conclusions drawn from modeling studies: (i) a transparent model documentation, (ii) that the invariant elements of the model can really be expected to be invariant between scenarios assessed, (iii) that empirical calibration of the model is limited to the extent warranted by available observation and knowledge about the expected error distribution, and (iv) that the effect of process uncertainty on the conclusions is evaluated and communicated. Based on these conclusions, generic extensions of the MPMAS toolbox are developed to allow the application of suitable approaches for validation and uncertainty analysis. The second part of the thesis describes the application of the newly developed methodology in the construction and use of the Central Swabian Jura model. The model focuses on an endogenous representation of heterogeneity in agent behavior, an empirical parameterization of the model, and an incorporation of climate effects on possible crop rotations and suitable days for field work besides the expected effects on yields. It extends the demographic, investment and land market components of MPMAS to improve the simulation of structural change over time. The model was used to analyze potential effects of climate change adaptation on agricultural production and land use in the study area. The results show that besides effects on yields also other climate change-induced effects on the conditions of agricultural production may have important impacts on land use decisions of farmers and deserve more attention in climate change impact analysis. Potential impacts of changes in the time slots suitable for field work and an additional rotation option are predicted to be comparable to the impact of the changes in yields predicted by a crop growth model. Results point to an expansion of wheat and silage maize areas at the expense of barley areas. The partial crowding out of summer barley by wheat area held for current price relations and is less strong at higher relative prices for summer barley. Price response analysis indicated that winter wheat production enters into a substitutive relationship with summer barley production under climate change conditions, while competition with winter barley area diminishes. This leads also to a higher elasticity of the wheat area with respect to relative summer barley prices. The model was then used to analyze biogas support through the Renewable Energy Act (EEG) and the support for grassland extensification and crop rotation diversification through the MEKA scheme. Especially simulated participation in crop rotation diversification is strongly reduced in the climate change scenarios, while the investments in biogas plants are slightly increased. The conditions established by the latest EEG revision imply that further development of biogas capacity will crucially depend on the existence of demand for excess process heat, because the alternative option of using high manure shares seems to be rather unattractive for farmers in the area according to the simulation results.
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.
Biologische Wasserstoffmethanisierung in Hochdruck-Rieselbettreaktoren für Power-to-Gas-Konzepte
(2018) Ullrich, Timo; Jungbluth, Thomas
In order to achieve climate protection targets, intermittent and decentralised energy sources such as wind power and photovoltaics will be expanded in the future. However, the power grids are not designed for the large-scale expansion and connection of different decentralised and fluctuating generation plants. This represents a major challenge for grid stability and requires an increasing expansion of energy storage. Power-to-Gas technology, a process for converting electrical energy into chemical energy, will play a central role in this process. In this two-stage process, hydrogen is first produced by electrolysis, which then reacts with carbon dioxide to form methane. It can be stored and transported in the natural gas grid almost indefinitely and can be used flexibly in a wide variety of applications. In addition to the chemical-catalytic methanation of hydrogen, there is also the biological methanation process. Characteristic features are a flexible load change behaviour and a marked robustness regarding the educt gas composition. Compared to chemical-catalytic methanation, however, the gas flow rates are significantly lower, which is the greatest challenge of this process. For this reason, the aim of this work was to optimize the performance of trickle-bed reactors for biological hydrogen methanation. The focus was on improving the gas-liquid-mass-transfer as described in the literature, but not yet which has not yet been investigated in the context of this promising concept. In an automated and continuous test plant, the operating pressure was initially varied in stages of 1.5, 5 and 9 bar in the first publication. With increasing pressure, conversion rates were improved and gas quality increased by 34%. Furthermore, the circulation of the process liquid to the trickling bed of the reactors was paused for periods up to 1440 min in the second publication. As the circulation pause rose, there was a noticeable increase in all performance parameters with maximum methane contents > 97 Vol.-%. Finally, different temperature levels of 40 - 55 °C were also examined. In spite of the continuous increase in gas volumes in the three publications, the performance parameters increased again. Overall, the combined optimization measures more than doubled the output with an MFR of 4.28 ± 0.26 m3 m-3 d-1 to 8.85 ± 0.43 m3 m-3 d-1, while simultaneously increasing the methane content in the product gas. Periodical analyses of the process liquid, especially the acid concentrations, as well as the stable conversion rates indicated a stable biological process in all experiments. The tests were done with three identical reactors, underlining the high degree of reproducibility. It was noticeable that the microorganisms quickly adapted to the changing operating parameters within a maximum of 24 hours. The performance increases could thus be related to the successful increase in the gas-liquid-substance exchange rate and not to a changed microorganism concentration or selection. The studies have also revealed further optimisation potential. In particular, the properties of the process liquid with regard to pH and nutrient composition should be the subject of further investigations. Thus, the present study not only successfully demonstrated the goal of increasing performance; with stable and uncomplicated operation over several months and a wide range of operating parameters, it also demonstrated that trickle bed reactors for the biological methanation of hydrogen are a reliable, flexible and thus promising concept in the context of power-to-gas applications.
Biomethane production in an innovative two-phase pressurized anaerobic digestion system
(2015) Chen, Yuling; Jungbluth, Thomas
Generation of biogas from biomass through anaerobic digestion is receiving increasing attention. Over the past decade, the biogas industry has been developing rapidly in Germany, as well as the rest of the world. In Germany, biogas is generally used in a heat and power plant (CHP) for electricity and heat production. However, most biogas plants are located in a rural area, where heating demands are quite low. Except for biogas plant thermal control, a huge amount of cogenerated heat is often wasted. In order to increase the overall energy utilization efficiency, biogas can be alternatively converted to biomethane of natural gas quality and injected into existing gas grids. By making use of the mature gas transportation and storage systems, biogas production and end utilization can be temporally and spatially separated. Therefore, it is regarded as an efficient and flexible solution to energy issues. Nevertheless, in terms of this application, raw biogas requires, above all, gas purification and upgrading. Carbon dioxide content, in particular, must be reduced from 40–50% in the raw biogas to approximately 4% in the purified gas. Conventional technologies are generally expensive in investment and/or operation. Therefore, an economical option is desired. Within this research project, a two-phase pressurized anaerobic digestion system was developed. The innovative concept aimed to reduce the cost involved in biomethane conversion and injection into the natural gas grids by integration of biogas production, purification and compression in one system. It was expected that a great amount of carbon dioxide could be directly removed from the pressurized digester due to its high solubility. In addition, the methane-rich biogas could be produced at an elevated pressure which could meet the injection standard, and therefore could reduce or even avoid the expenses for further compression. In order to gain better understanding of two-phase pressurized anaerobic digestion, three major studies were conducted: - The pressure effects on two-phase anaerobic digestion - Effects of organic loading rate (OLR) on the performance of a pressurized anaerobic filter in two-phase anaerobic digestion - Effects of liquid circulation on two-phase pressurized anaerobic digestion By this means, the system performance could be examined and the technical feasibility and potential of the new concept could be explored. Moreover, an optimization of the process in a two-phase pressurized anaerobic digestion system could be realized. From both economic and ecological perspective, two-phase pressurized anaerobic digestion offers an interesting process option for biomethane production, making a great contribution to sustainable energy supply.
Development and evaluation of methods for assessing the efficiency of biogas plants
(2022) Hülsemann, Benedikt Werner; Müller, Joachim
Biogas is a renewable energy source with main advantages compared to other renewable energy sources. The advantages include the use of organic waste as a substrate, local power and heat production, rural job creation, the possibility of a flexible gas production and a product which can easily stored and transported in a gas grid or on the roof of a digester. However, the development of the biogas sector is highly dependent on the costs of producing gas, electricity and heat. The production costs are higher than the costs for other energy sources. Growth of the biogas sector is therefore only possible if there is political promotion for biogas as there was in Germany through the EEG. Nowadays, due to the reduction of bonus payments in the EEG 2017 and EEG 2021 in Germany as well as the lack of policy promotion in several other countries, lower production costs based on a higher efficiency are essential to help the biogas sector grow further. In order to achieve higher efficiency and to tap the full potential of biogas, the efficiency has to be determined, which is done in this thesis. The input methane potential is determined using 6 different methods. These methods are compared on the basis of an investigation of 33 German agricultural BPs as well as one German and one US BP using food waste as feedstock. The four methods based on the batch test show a high sensitivity. Unfortunately, they also show efficiencies greater than 100% for most BPs, clearly indicating an underestimation of the degradable potential. Only for the US BP can an efficiency less than 70% be reported. This result is probably based on the lack of heating system corresponding to the lack of promotion of heat recovery in the US. The CE according to the BMP method also reveals an average efficiency of 95% for the German BPs. The values of the two gross calorific value-based methods show efficiencies below 100%, but with low sensitivity. The results of these methods can be used to determine the further potential of a bioeconomic process and to compare the biogas process with other industrial processes. There are several impact factors that affect the accuracy of the efficiency measurements. The installed meters are not frequently calibrated at most BPs. Also, some meters are almost completely missing, as only few BPs in Germany have a gas flow meter. Thus, assumptions and calculations are required to determine the efficiency. In the developed method, the gas flow must be calculated from the amount of the power production, the calorific value, the gas quality, the CHP unit efficiency and the conversion loss at the transformer. The last two values must be assumed, even if the database is small. Another important parameter is the feeding mass. It is measured by the German BPs, but in some cases, the data quality is low. For example, different crops are mixed in the silos and measurement of each substrate is not possible. This leads to measurement errors shown by the organic dry matter mass balance, which has a residual value of up to 24%, while only 11% can be occur based on water incorporation into the ODM. Another factor having an impact is the sampling. The results of a monthly sampling throughout the year show a fluctuation in the DM/ODM values. To investigate the accuracy of the methods used to determine the SMP of the substrate, the biochemical methane potential test is examined in detail. The BMP consists of the used inoculum, the substrate, the digestion system and the calculation. The impact of the used inoculum and the digestion system is investigated by using different inocula in one digestion system as well as by using the same inoculum in multiple digestion systems. The inocula used in this thesis are well-known and have been used in interlaboratory tests for several years. Thus, outliners were excluded. A CV of 4.8% can be reported between the different inocula, which is lower than reported in most other publications before. The use of different digestion systems shows a higher CV of up to 12.8%. For the inoculum and the digestion system, the deviation varies strongly and no clear correlation can be identified. Therefore, a correction of this effect is not possible. The biological yield efficiency of 21 of the investigated BPs is in the range of 100 ± 12.8%. This reveals the need of stricter rules for the digestion system. All digestion systems used in this thesis are described in the German guideline VDI 4630. The calculations were also done according to the German guideline VDI 4630. An influence can be neglected. However, if the results of a measurement with already dried gas are compared with the results of a calculation according to VDI 4630, which is based on the measurement with wet gas, a discrepancy can be found. Although, the CV using only one digestion system and one inoculum is only 1-7%. A comparison of the efficiency of different BPs by using the same inoculum and digestion system is hence recommended.
Entwicklung und Erprobung eines Online-Messsystems für Biogasanlagen auf Basis der Nah-Infrarot-Reflexionsspektroskopie (NIRS)
(2013) Stockl, Andrea; Jungbluth, Thomas
Due to the EU?s and Germany?s political goals of expanding the use of renewable energy sources, the utilization of biomass for energy supply is expected to continue growing in the coming years. Consequently, the efficiency of biogas plants will have to be improved further. This applies both to raising the energy yield from the input materials and exploiting the full potential of the technical installations. During the four phases of the anaerobic digestion (AD) process, volatile fatty acids such as acetic and propionic acids are produced as intermediates. These compounds can be used as indicators of the function and stability of the digestion process. So far, volatile fatty acids have to be determined by sampling the digester content and analyzing the sample in the laboratory (e.g., by gas chromatography). It is thought that by using near-infrared-reflection spectroscopy (NIRS) for online measuring, the management and control of biogas plants could be facilitated, considerably. This was to be investigated in a project funded by the Baden-Württemberg Ministry of Rural Areas and Consumer Protection within the ?research platform on bioenergy? Baden-Württemberg?. In this study, a NIR-measurement system was calibrated for determining the concentration of volatile fatty acids in two semi-continuously operated, bench-scale digesters at mesophilic and thermophilic temperature level. For each of the two digesters, one NIR-sensor was calibrated for acetic and propionic acid, and a second one for total acid equivalents. The experimental studies were divided into three stages. The chapters of this research work consist of three peer-reviewed papers that describe these experiments.
Experimentelle Entwicklung einer modellbasierten prädiktiven Regelung für den flexiblen Betrieb von Biogasanlagen
(2023) Dittmer, Celina; Lemmer, Andreas
The transformation of the energy system requires controllable producers due to increasingly decentralised, fluctuating electricity generation from wind turbines and photovoltaics. Biogas plants can make a substantial contribution here by making plant operation more flexible and thus providing electricity as needed. Technical adjustments, such as the expansion of gas storage capacities and CHP output, can compensate for short-term fluctuations. However, in order to be able to shift the potential of electricity generation over longer periods of time, an adapted feed-in strategy is essential. The control of biogas production poses several challenges in practical implementation. First, the conversion of biomass into biogas is a complex process and must be considered individually for each biogas plant. Models developed so far use parameters for all characteristic process phases and influencing variables in order to be able to model anaerobic digestion. In contrast, biogas plants are often only rudimentarily equipped with measurement technology, so that corresponding parameters are not available. In this work, a model-predictive control of biogas plant operation was developed to enable demand-driven electricity generation. The aim was to develop models that are particularly well suited for practical use. Thus, for the first time, a successful application on almost all biogas plants could be possible without or with only minor adaptations to the existing measurement technology. All studies carried out in this thesis are based on a real-world laboratory, the "Unterer Lindenhof". This includes a practical biogas plant as well as an electrical consumption corresponding to that of a village with about 125 inhabitants. In a first step, forecasting models were evaluated to predict the electricity demand of the real-world laboratory over 48 hours in advance. Four models from the field of time series analysis were examined, one TBATS and three different ARIMA models. In an evaluation of 366 forecasts each, all four models performed sufficiently well to provide a set point for biogas plant operation, with average MAPE values of 13-16 %. Further investigations showed that forecasts can also be carried out over a period of up to 14 days without significant losses in forecast quality. In a further step, a model was developed to simulate biogas production. This is also based on time series analysis, or more precisely on a regression model. Thus, it differs significantly from previous developments in this field, which are mostly based on the complex ADM1. It turns out to be very advantageous that the developed simulation model uses as input parameters only historical data of the last four weeks of biogas production and the amount of solid substrates fed in, without considering their composition. The simulation of biogas production over 48 hours in advance is based on correlations resulting from these two data sets. An evaluation of the model over 366 simulations resulted in an average MAPE of 14-18 %. Data from both digesters of the biogas plant were used, which can be considered as independent systems, demonstrating the adaptability of the model. In a third step, the feeding schedule was developed for demand-based biogas production. For each 48 hours in advance, 1500 randomised feeding schedules were calculated. Some constraints were imposed, such as the maximum amount of substrate that is technically possible in the biogas plant. The biogas production expected from the feeding schedules could be calculated using the simulation model. By comparing the simulation with the desired biogas demand profile, the simulation with the least deviations could be determined and the appropriate feeding plan selected and implemented. The entire model predictive control system was used and thoroughly tested in a field trial at the real-world laboratory "Unterer Lindenhof". Over a period of 36 days, an average MAPE of less than 20 % was achieved in comparison between the real biogas production and the desired biogas demand. During the test period, the biogas demand was derived from the predicted electricity demand of the real-world laboratory. The investigations carried out show that the model-predictive control system developed enables demand-oriented electricity generation on full-scale and that, due to the models being very close to practice for the first time, adaptation to almost all biogas plants is possible.
Integrated rural and urban agricultural systems for the sustainability transition towards the bioeconomy
(2021) Winkler, Bastian; Lewandowski, Iris
The goal of the bioeconomy is a fundamental transition of both the economy and society towards sustainability. Replacing fossil resources by biomass for the provision of food, feed, fibre and fuel/energy (the 4F’s) will result in a substantial increase in demand for agricultural products. The consequent intensification of agricultural production, however, needs to be achieved while alleviating the societal challenges of the 21st century. The bioeconomy provides a knowledge-based, cross-sectoral and systemic pathway to increase agricultural production that involves all relevant stakeholders in the sustainability transition. This interdisciplinary thesis investigated the contribution that three selected bioeconomic approaches can make to the sustainable intensification of agricultural production, encompassing the growing urban population on the demand side and the numerous smallholder family farmers in countries of the global South on the supply side. The first study develops the ‘Integrated Renewable Energy Potential Assessment’ (IREPA) approach that involves smallholder farmers in planning and selection of renewable energy (RE) technologies for implementation into their agricultural systems. The bottom-up potential assessment, participatory learning and action research and multi-criteria decision analysis supported the smallholders in two case studies in rural South Africa and India in the identification of locally appropriate RE technologies. The second study uses IREPA to explore smallholders’ perception of agricultural RE production. Social, environmental, technical, institutional and economic factors are analysed to identify drivers of and barriers to RE implementation into smallholder agricultural systems. Mainly environmental factors, in particular climate change impacts, motivate smallholders to produce RE, while social factors (social cohesion, gender aspects, well-being, food and water security) determine the actual change. The barrier of high upfront investment costs can be eliminated by falling RET prices, the development of novel rural RE business models and institutional support. In addition, growing smartphone penetration rates in rural areas and open-access online information enables do-it-yourself RET operation and maintenance. Integrated approaches and such insights are crucial for the targeted formulation of agricultural development policies and stakeholder involvement in the sustainability transition towards a bioeconomy. The third study investigates the characteristics of urban gardening in Germany and its potential to encourage sustainable consumer behaviour, based on a review of 657 urban gardening project websites and an online survey involving 380 project participants. The results reveal multiple social, environmental and economic benefits of urban gardens for sustainable city development. The diverse gardener communities actively promote sustainable consumer behaviour by (unintentionally) applying several methods known to encourage pro-environmental behaviour. Hence, urban gardens are transformative spaces that involve the growing urban population in the societal transition towards a bioeconomy. In the context of sustainable intensification of biomass production in rural areas, the fourth study investigates the contribution of environmental service assessment and monetization in agricultural systems, using the example of the perennial biomass crop miscanthus for biofuel production. The valorisation makes environmental services - such as soil fertility improvement, carbon sequestration, water and air purification – tangible. This can incentivise payments to farmers for the provision of these public goods. Enhancing and utilising environmental services through nature-based solutions is a promising pathway to sustainable intensification, providing a shift from input-based towards process-based agricultural production. Finally, it can be concluded that integrated approaches which connect different production systems, disciplines and stakeholders are central for the development of the bioeconomy: - The integration of sustainable technologies, such as RE, into agricultural systems requires case-based research and participation of local stakeholders in project planning, decision making and targeted policy formulation. - The integration of the growing urban population in the sustainability transition can be supported by urban gardening because it promotes sustainable consumer behaviour. - The integration of nature-based solutions into agricultural systems enhances environmental service provision and supports the shift from input-based towards process-based agricultural systems. The approaches discussed in this thesis can support the sustainable intensification of agriculture, serve to re-connect the perspectives of rural producers and urban consumers, and enable the involvement of large portions of society in the sustainability transition towards the bioeconomy.
Optimierung der Konservierung und der anaeroben Konversion von Zuckerrüben zur Nutzung in flexiblen Biogassystemen
(2019) Kumanowska, Elzbieta Joanna; Jungbluth, Thomas
Biogas production is well suited to balance the fluctuating electricity production from the renewable energy sources sun and wind. Due to the currently unfavorable conditions in the renewable energy supply policy in Germany, time is spent looking for alternatives for electricity production from biogas. The preparation for natural gas quality for fuel production or for natural gas grid injection would be such an alternative but requires process improvements to reduce costs. One approach would be to use two-stage biogas production, as there is a high methane content in the produced biogas, thus reducing the cost of processing to natural gas quality. A suitable substrate for both applications would be sugar beet, due to its fast biodegradability and good methane yields. The preservation of sugar beets for year-round provision has so far been problematic because it can cause high losses. In addition, it can cause process biological problems, if it is used in high proportions. In the context of this work, the use of sugar beets for biogas production was tested using these promising methods. For this purpose, storage experiments were carried out and new storage methods for the practice were developed and tested, all of which are primarily aimed at the use of sugar beet silage effluent. Practice-based point-feeding experiments were used to test its suitability for demand-oriented biogas production. Furthermore, the optimization of the two-stage biogas production from sugar beet was carried out. For this purpose, an experiment was conducted in the biogas laboratory to determine the optimum hydrolysis pH during the fermentation of sugar beet silage. In order to develop a new, optimal method for the storage of sugar beets, further knowledge regarding the process of ensiling sugar beets, the silage effluent formation and the influencing parameters was required. Therefore, mass balances were carried out in the column experiments in the laboratory of the State Institute of Agricultural Engineering and Bioenergy to determine the influence of the parameters stack height and sugar beet chips size on the silage effluent formation during the ensiling process of the chopped sugar beets. Silage effluent was produced in amount about 50% of the stored mass. About half of the silage effluent production took place during the first three weeks of storage. The produced silage effluent was characterized over the entire storage time by extremely high COD-values of 250 g l-1. The parameters stack height and particle size had no significant influence on the mass balance. On the basis of the results of the column experiments, a mobile and a stationary method on a technical scale for the storage of sugar beets were investigated. In the mobile variant, the flexible tanks, washed, chopped sugar beet was ensiled. Considering the goal to maximize silage effluent yield, the ensiling of chopped sugar beet was superior to the ensiling of whole beet. Also, soil removal is advantageous for silage effluent production as well as for silage quality. Storage in the stationary pit silos proved to be technically advantageous, and it promises to be well suited for the intended applications when in combination with washed and chopped beets. The application of produced silage effluent for demand-oriented biogas production was carried out at the research biogas plant of the University of Hohenheim. The system’s response observed as an increase in biogas production took place a few minutes after the point feeding with sugar beet silage effluent. As a result of the point feeding, the produced volumetric biogas flow rate was doubled without endangering the stable biogas plant operation. The maximum gas production was reached after about 1:45 h. In this work, a concept for the use of sugar beet for the production of high calorific biogas was tested, based on the two-stage anaerobic digestion. The experimental plants consisted of a horizontal stirred tank reactor for hydrolysis and two combined fixed bed reactors used as a methane reactor. The influence of the pH value in the hydrolysis stage on the anaerobic digestion of sugar beet silage was tested. High degradation rates and methane yields demonstrated the overall suitability of this system for sugar beet silage digestion. The best compromise of the process parameters degradation rate in complete system and methane yield was achieved at a pH value of 6. The investigation carried out for this work shows, that the concept of a new sugar beet storage method, with a focus on sugar beet silage effluent production, is well suited for demandoriented biogas production as well as for the production of a high calorific biogas by means of the two-stage biogas process.
Optimierung der primären Gärung bei zweistufigen Biogasanlagen
(2016) Lindner, Jonas Philipp; Jungbluth, Thomas
The microbial conversion of biomass into biogas generally comprises several steps. These steps, are divided in accordance to the involved microorganisms and are often referred to as primary fermentation, secondary fermentation and methane formation. In contrast to single-stage, two-stage biogas system performs primary fermentation spatially separated from the methanogenesis in order to provide optimal milieu conditions for each group of microorganisms. There are many different reactor settings outlined in scientific literature for two-stage biogas production. For the digestion of energy crops or biowaste, discontinuously charged leach-bed reactors are often combined with anaerobic filters. The main disadvantage of this setup is the impossibility of regulating the pH-value in the first step, thus leading to fluctuating acid and gas production rates. To avoid this, new approaches aim to use continuous flow stirred-tank reactors for the process of primary fermentation, using chemical additives for the pH regulation. In the framework of this research, a process automation for a continuous two-stage system was developed and implemented in two lab scale plants at the State Institute of Agricultural Engineering and Bioenergy. Each laboratory plant comprised of a continuous stirred-tank reactor with an integrated filtration for solid-liquid separation and an anaerobic filter. In the primary fermentation stage, the adjustment of the pH-value was made by an indicatorbased return of alkaline effluent from the anaerobic filter. In order to evaluate and optimize the newly developed and completely automated pH-regulation system, this study investigated the (I) influence of the substrate characteristics on the degree of degradation and the biogas yields, (II) optimal pH-value for biomass degradation in the primary fermentation and (III) the possibility of enhancing methane yields by combined mechanical and enzymatic treatment of digestates with a subsequent refeeding into the process. The results of the investigations clearly showed the suitability of the system for a highprecision pH-regulation in primary fermentation for the tested pH-values 5.5, 6.0, 7.0 and 7.5. This unique technique enabled the continuous formation of organic acids and biogenic gases. Hay/straw, maize silage and sugar beet silage were digested at a pH-value of 5.75 in order to investigate the influence of different substrates on the two-stage system performance. Compared to the determined potential biogas yields, the recorded methane yields were 70.6 % lower for the hay/straw substrate and 31.3 % lower for maize silage in the two-stage system. Contrary to this, for sugar beet silage no difference in the gas yields between the batchtest and the two-stage system could be detected. Further investigations on the influence of pH-value on the degradation rate of lignocellulosic substrates showed an optimum pH between 7 and 8. The mechanical treatment of the digestates with the ball mill exhibited no losses of volatile solids through warming. The application of this procedure enhanced the specific methane yield from 9 to 17 % for maize silage digestate and hay/straw digestate respectively from the described laboratory plant. The treatment of the digestate obtained from a full-scale plant permitted a triplication of the specific methane yield at very low level. The combined mechanical and enzymatic treatment through the aerobic fungi “lentinula edodes” resulted in losses of volatile solids between 58.2 and 86.4 % for the hay/straw digestate and between 10.8 and 18.4 % for the substrate from the full-scale biogas plant depending on the incubation time. Furthermore, the investigations determined an increase in the lignin content of the hay/straw digestate by the combined treatment. Overall, using the digestate of the two-stage system, the mechanical/enzymatic treatment attributed to a methane yield loss by 86.4 %. In contrast, an increase of methane production by 134.5 % was observed with the full-scale digestates. This study has revealed that two-stage biogas systems are favorable only for easily degradable substrates. The phase separation was not beneficial for fiber rich substrates. Based on the results, a reactor cascade consisting of a continuous stirred-tank reactor and an anaerobic filter with similar milieu conditions seems to be well suited for the digestion of organic wastes. Due to the extraordinary high process stability, flexibility and high load capacity this system is very suitable for the treatment of substrates with extremely varying compositions. Moreover, within the study essential basics for the application of innovative fermentation procedures (e.g. pressure fermentation) were investigated. The combined mechanical and enzymatic treatment of digestates seems to be an interesting alternative to the established substrate pretreatment systems and it can be recommended also for single-stage biogas plants.
The impact of agrivoltaics on crop production
(2022) Weselek, Axel; Lewandowski, Iris
Facing the consequences of global warming and climate change, the reduction of greenhouse gas emissions is one of the most prior tasks of todays society and policymakers. To achieve this, energy generation is currently transformed towards a reduced utilization of fossil fuels and its replacement through an increased expansion of renewable energy sources. In this context, one challenge will be to spare land resources and diminish potential land use conflicts, in particular between food and energy production. An approach to accomplish this, can be the utilization of production-integrated technologies such as agrivoltaic systems (AV). Agrivoltaic systems are photovoltaic systems specifically adapted for its application in combination with agricultural production. For this, AV systems are installed above or on agricultural fields with certain technical adaptions, enabling agricultural production to be continued. First described in 1981, this approach was taken up in the early 2000s with first AV pilot systems being developed. In first experiments in South-France it has been shown, that through the combined utilization of agricultural land for food and energy production, AV can contribute to an increment of total land productivity. While electrical yields can be increased with an increasing density of the photovoltaic modules mounted above, the proportion of light available for the plants grown underneath and consequently also agricultural yields are reduced. The aim of the present work was to examine, whether the results from these first experiments on crop production under AV can also be transferred to conditions in more moderate climates and also account for crops other than the so far investigated ones. The following four research objectives were defined: 1.) To what extent is plant-available radiation reduced by the solar panels of the AV system? 2.) How does this effect parameters of aerial and soil climate? 3.) How do the cultivated crops respond to the altered cropping conditions with regard to plant growth and development? 4.) Which consequences does this have regarding the yields and the chemical composition of the investigated crop-species? In order to examine these research objectives, a field experiment has been established underneath an experimental AV pilot facility in Southwest-Germany, near Lake Constance. Four different types of crops (grass clover, potatoes, celery and winter wheat) have been selected and cultivated underneath the AV system and on an adjacent reference area for comparison within a two-year experiment. Various microclimatic parameters were recorded in a high-resolution monitoring including all investigated crops on both sites. Crop growth and development was monitored in regular intervals during vegetation period. The harvestable yields of both experimental sites, including crop-specific yield components, were recorded and partially supplemented with an analysis of chemical compounds. The results show, that crop production under an APV system is affected in several ways. Under the given climatic conditions, losses in harvestable yields as a consequence of a reduction of crop-available radiation are most likely. Exceptional years such as 2018 suggest however, that cultivation under AV can have advantages for crop production, in particular under dry and hot climatic conditions. In order to fully exploit this potential, the application of the APV thus seems to be most suitable for more dry climatic regions, whereby innovations and developments in AV technology as well as an improved water management can facilitate a further optimization. Regardless of this, potential conflicts of interest with regard to land use cannot be ruled out and require the integration of agrivoltaics in the existing legislation.
Two-stage high pressure anaerobic digestion for biomethane production
(2017) Merkle, Wolfgang; Jungbluth, Thomas
The use of natural gas for power and heat generation in the EU has become particularly prominent since the 1990s. As a result, the whole natural gas infrastructure has been continuously expanded and today has a total length of 2.15 million km and a storage capacity of about 108.3 billion m³. The production of biomethane in the EU and its distribution by natural gas network offers an interesting alternative for the reconfiguration of EU’s energy supply system. Up to now, biomethane is obtained by purifying and upgrading raw biogas in a complex process. In this study, a novel two-stage high pressure anaerobic digestion system was developed. This innovative concept aims to integrate biogas production, purification and pressure boosting within one system. The process is based on the enhanced water solubility of carbon dioxide compared to methane. By operating the methane reactor for biogas production at increased pressures, high amounts of dissolved carbon dioxide can be removed with the liquid effluent from the reactor, resulting in a high-calorific biogas. In batch experiments at pressures up to 30 bar, a significant influence of pressure on the pH-value in the reactor was observed, due to the augmented formation of carbon hydroxide. The study on the effect of a rapid pressure increase up to 100 bar showed no inhibition of the microorganisms in the batch-rigs too, although the microorganisms were not adapted to these environmental conditions. Furthermore, a continuously operated methane reactor was run at pressures up to 50 bar for the first time. The experiments showed that a stable anaerobic digestion process could be run at these pressures nearly without any problems and methane contents above 90% could be achieved. The promising results showed that this technology has great potential in producing on-site high calorific gas also in smaller units. In addition, the costs of post-production gas purification can be significantly reduced, due to the fact that the size of a subsequent gas purification unit can be decreased. Furthermore, the produced gas can be injected into the transnational gas grids without post pressurization or can be used in the transportation sector.