Landesanstalt für Agrartechnik und Bioenergie

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A full-scale study on efficiency and emissions of an agricultural biogas plant
(2013) Nägele, Hans-Joachim; Jungbluth, Thomas
In this study we focused on process engineering for the conversion of biomass, and utilization of the gas obtained by fermentation. Several topics regarding efficiency and emissions have been addressed by conducting intensive and long-term measurements. In detail, our objectives were (1) to conduct long-term measurements of the electric energy consumption of the biogas plant and its individual components and examination of energy-saving potentials; (2) to develop a method to measure mixing quality in the digester and to examine the mixing quality by measuring nutrient distribution in the digester with different agitator setups; (3) measure the influence of maintenance strategies on efficiency and emissions at long-term operation in practical application; (4) examine the efficiency of an external biological desulfurization plant under practical conditions to enhance biogas fuel quality. The results of electric energy measurement over a period of two years showed that a percentage of 8.5% (in 2010) and 8.7% (in 2011) of the produced electric energy was required to operate the biogas plant. The consumer unit agitators with 4.3% (in 2010) and 4.0% (in 2011) and the CHP unit with 2.5% (in 2010 and 2011) accounted for the highest electrical power demand, in relation to the electric energy produced by the CHP unit. Calculations show that the agitators consumed 51% (in 2010) and 46% (in 2011) of the total electric energy demand. The results stress the need for further research in the fields of substrate homogenization in biogas plants in order to reduce the demand for electric energy. Based on the results of electric energy consumption, follow-up studies have been conducted on nutrient distribution, which depends on agitator type and agitator regime. The investigation showed that significant differences in local concentrations of organic acids, which are not correlated to DM content, are found in dependence on agitator type and agitation regime. Measurements on electric energy consumption of the different agitator types verified that, depending on the agitator type, the saving potential rises up to 70%. The results for emissions and efficiency of the CHP unit confirm the fact that after readjustment of the air-fuel ratio (Lambda value), the emission values for NOx decline while CO increases. However, the emission-optimized operation mode leads to lower engine efficiency. The permanent measurements proved their legitimacy showing various emission deviations from the limiting values prior and post maintenance. In addition, the results show that by monitoring the lubricating oil quality, the oil change intervals can be maximized, while ensuring that engine performance is not endangered. This allows the operator to reduce maintenance expenditures while minimizing wear. To increase engine efficiency, the reduction of the lambda value combined with exhaust gas scrubbing and exhaust gas power generation is a promising approach. However, that would presuppose a permanent and almost total removal of H2S from the biogas. The fourth part of the study examined the technical and economic feasibility of a Fixed Bed Trickling Bioreactor (FBTB) for external biological desulfurization of biogas. In contrast to well-established biological methods to oxidize H2S, the FBTB allows removal of these from the biogas process, thus ensuring a constant low H2S concentration in the biogas. The FBTB showed H2S removal efficiencies (RE) of 98% at temperatures between 30-40°C. A major decline in RE in a range of 21-45% was observed when temperature in the FBTB dropped to a range of 5-25°C. The results revealed that different pH values of the percolation fluid and air ratios have little effect on RE. The practical use of the investigated FBTB system is an interesting technological alternative as disadvantages of internal biological desulfurization methods are being avoided. Due to high expenditures for operation resources and maintenance for FBTB operation during the research, a technical optimization is necessary to ensure economical operation. The results presented in this thesis show that the scientific instrument ?research biogas plant? is the ideal supplement to methods such as laboratory scale research and measuring programs. Research at full scale offers an entirely new opportunity to determine the interaction of process technique and process biology and to conduct long-term studies of gas utilization. Compared to measuring programs at commercial biogas plants, the research biogas plant has the advantage of being significantly better equipped with measurement technologies and that economic success is not the overall goal.
Einsatz von Spurenelementen bei der Vergärung von nachwachsenden Rohstoffen in Biogasanlagen
(2014) Vintiloiu, Anca; Jungbluth, Thomas
The operational agricultural biogas plants in Germany are fed mainly with renewable raw materials. During substrate addition, several micro and macro elements enter the digester. These elements are essential nutrients for the methanogens. If their concentration is too low, the production of biogas can be disrupted. A large number of agricultural biogas plants use therefore commercially available trace element solutions to optimize the process and to achieve higher methane yields. When the fermentation is complete, the digestate containing these trace elements (mostly heavy metals) is spread on fields as fertilizer. The amounts added to the biogas process should be kept as low as possible in order to minimize the environmental damage. The purpose of this study was to investigate the cause of trace elements deficiency in renewable raw materials fed biogas plants. It was also tested whether the chelation of the nutrients could increase their bioavailability for microorganisms and thus lead to a reduction of the amounts needed for the stabilization of the fermentation process. The effect of the complexing agent ethylenediaminetetraacetic acid (EDTA) on the bioavailability of metal ions was tested. The sole addition of EDTA to an undersupplied substrate increased the methane yield by up to 32 %. When trace elements were also added, their amounts could be reduced by up to 75 % with no negative consequences for the fermentation process. EDTA is a persistent chelating agent and so it was further tested, whether readily biodegradable chelating agents (ethylenediaminedisuccinic acid (EDDS) and iminodisuccinic acid (IDS)) could have the same effect. During the investigation, IDS had a high statistically significant positive effect on the bioavailability of the metal ions, which exceeded the effect of EDTA. IDS represents therefore a good alternative to EDTA. The bioavailability of the metal ions in the digester was increased by the use of complexing agents, which made the reduction of the trace elements amounts needed to compensate for substrate-related deficiency symptoms possible. This reduces the pollution on the agricultural land on which the digestate is used as fertilizer.
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.
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.

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