Publications Search Results

Now showing 1 - 10 of 57
  • Publication
    Aqueous phase of thermo-catalytic reforming of sewage sludge - quantity, quality, and its electrooxidative treatment by a boron-doped diamond electrode
    Pyrolysis is a promising conversion technology to produce biofuels from residues such as sewage sludge. In this study, the chemical composition and the amount of the resulting aqueous phase from the thermo-catalytic reforming process of sewage sludge at different process parameters are compared to those of non-catalytic fast pyrolysis processes from literature. Furthermore, electrooxidation using a boron-doped diamond (BDD) electrode was investigated as purification technology for the resulting aqueous phase. The results of this study show that the quantity of the aqueous phase strongly depends on the temperature of the thermo-catalytic reforming process and is presumably governed by the influence of secondary gas-carbonisate reactions like the water gas shift reaction. Higher reaction temperatures result in a reduced amount of the aqueous phase. The chemical composition of the aqueous phase of fast pyrolysis processes was comparable to that obtained at the thermo catalytic reforming process. To reduce the chemical oxygen demand (COD) and the number of refractory sub stances to a level at which the aqueous phase can be discharged into a conventional wastewater treatment plant, electrooxidation experiments with the aqueous phase of the thermo-catalytic process were carried out using a BDD electrode. The treatment efficiency was investigated in galvanostatic operation varying the applied current density and the flow rate of the aqueous phase. A COD removal of 94.6 % was achieved after 0.54 kWh at an instantaneous current efficiency of 0.47 at a current density of 50 mA/cm2 and a flow rate of 3.7 L/min. This indicates that electrooxidation by a BDD electrode can be a promising purification technology for the aqueous phase from pyrolysis of sewage sludge. However, the high energy consumption of the process will need to be addressed in future studies to make the process economically feasible.
  • Publication
    Design and Performance Analysis of a Latent Heat Storage for the Operation of a High-Temperature Methanol Fuel Cell
    ( 2021)
    Deinert, Lisa
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    Due to ever stricter economical and legislative regulations, the efficiency of technical processes has to be constantly increased. Besides many other efficiency enhancing methods, the use of waste heat has a great potential to save energy. In particular, the use of waste heat at temperatures above 373 K offers many possibilities, as it is mostly unused today. In order to exploit these potentials, a new latent heat storage system using a polymer as a phase change material has been developed during the R&D project ""eleMeMe - Decentralized decoupling of power generation and energy supply through onsite electrochemical methanol production and methanol fuel cells"". The storage is used to operate a high-temperature methanol fuel cell. Usually the fuel cell must be electrically preheated before the start to reach its optimum operating temperature. During operation, heat is generated and the system has to be air cooled to maintain its temperature. Instead of cooling the system with air, the heat is now stored in a latent heat storage system to start the fuel cell later.
  • Publication
    Development of a purification strategy for the aqueous phase from biomass pyrolysis - recovery of valuable products
    The aqueous phase from biomass pyrolysis is until today mostly seen as worthless by-product and has to be costly disposed. However, it can be a valuable resource for the recovery of products. For this, the composition of the aqueous phase must be known and a suitable purification strategy, adjusted to the pyrolysis feedstock, has to be developed. The aim of this investigation is to introduce a multi-level purification strategy for the aqueous phase gained from the thermo-catalytic reforming of sewage sludge, which allows also the recovery of products. The purification strategy consists out of an electrooxidation step, the decarbonisation of the aqueous phase and the stripping of ammonia by air. By means of this, 44 l hydrogen, 69 g calcium carbonate and 264 g ammonium sulfate can be recovered from 1 l of the aqueous phase. In the medium term, purification strategies like this will lead to a reduction of the overall pyrolysis process costs and decrease the specific costs of targeted pyrolysis products like char, bio oil and syngas.
  • Publication
    Development of a New Sensor Module for an Enhanced Fuel Flexible Operation of Biomass Boilers
    The heterogeneity of biogenic fuels, and especially biogenic residues with regard to water and ash content, particle size and particle size distribution is challenging for biomass combustion, and limits fuel flexibility. Online fuel characterization as a part of process control could help too ptimize combustion processes, increase fuel flexibility and reduce emissions. In this research article, a concept for a new sensor module is presented and first tests are displayed to show its feasibility. The concept is based on the principle of hot air convective drying. The idea is to pass warm air with 90 °C through a bulk of fuel like wood chips and measure different characteristics such as moisture, temperatures and pressure drop over the bulk material as a function over time. These functions are the basis to draw conclusions and estimate relevant fuel properties. To achieve this goal, a test rig with a volume of 0.038 m3 was set up in the laboratory and a series of tests was performed with different fuels (wood chips, saw dust, wood pellets, residues from forestry, corncobs and biochar). Further tests were carried out with conditioned fuels with defined water and fines contents. The experiments show that characteristic functions arise over time. The central task for the future will be to assign these functions to specific fuel characteristics. Based on the data, the concept for a software for an automated, data‐based fuel detection system was designed.
  • Publication
    Analysis of the Thermal Management of a High-Temperature Methanol Fuel Cell Using a Latent Heat Storage
    ( 2021)
    Deinert, Lisa
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    Komogowski, Lars
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    HHornung, Andreas
    Waste heat from industrial applications offers a high but mostly unused potential due to the time differences between its generation and possible consumption. By using waste heat, the energy efficiency can be increased and therefore, the overall costs and emissions can be reduced. This work shows the feasibility of increasing the energy efficiency of a high-temperature methanol fuel cell using a latent heat storage with the help of full-scale experiments. The fuel cell needs to be preheated for start up to reach its operation temperature. During operation, heat is generated at a temperature of 433 K and the system needs to be air-cooled to maintain its temperature. Instead of cooling the fuel cell with air and losing the heat to the environment, the waste heat is now stored in a latent heat storage to later be used for preheating the fuel cell. Different experiments are conducted to find the optimum operation point of the latent heat storage in combination with the fuel cell. The aging and the cycling stability of high density polyethylene, which is used as phase change material in the latent heat storage, is monitored as well as the mechanical stability of the system.
  • Publication
    Numerical Simulation of the Thermo-catalytic Reforming Process: Up-scaling Study
    The up-scaling of the pyrolysis technologies is the next step to achieve the industrial scale and to fulfill the energy and petrochemical demand in large-scale units. The overall goal of this study is to up-scale the Thermo-Catalytic Reforming (TCR)technology from the laboratory to the pilot unit. In the previous part of the study, the up-scaling was studied experimentally in regard to the product yields and qualities. Therefore, a computational fluid dynamics (CFD) study is carried out to investigate the effects of upscaling of the TCR system on the temperature distribution through the intermediate pyrolysis and the catalytic reforming process. A multifluid model and K-e model are employed to simulate the TCR process for the mixture flow of sewage sludge as a solid phase and pyrolysis vapor as a gas phase. The results reveal a CFD model that can predict the heat distribution and flow velocities through the TCR system, while the deviations between simulation data and experimental work are considered small. The errors in the maximum biomass temperature within the auger reactor are 0.0 and 4.2%for TCR2 and TCR30, and the deviations in the solid residence time are about 0.8 and 0.74 s, respectively. Furthermore, the deviations in the vapor residence time within the post-reformer are 0.35 and 0.81 s for TCR2 and TCR30, respectively. Additionally, the CFD model provides a good platform for further simulation of the chemical reaction kinetics.
  • Publication
    Development of a mathematical model to calculate the energy savings and the system running costs through hydrogen recovery in wastewater electrolysis cells
    Electrooxidation of wastewater using a wastewater electrolysis cell is known to effectively oxidize persistent organics. However, like other chemical physical treatment methods, the treatment costs are high. The separation of the evolving hydrogen using a diaphragm and the subsequent use of it can help to lower the operational costs of such systems. This paper provides a theoretical basis of the benefits of hydrogen recovery in wastewater electrolysis cells using a diaphragm. The paper discusses all main parameter contributing to the energy demand of the cell as well as to the energy saving potential through hydrogen recovery. The paper lays the theoretical foundation for qualified experiments and is meant to stimulate researchers to proof the proposed concept. The calculations show a maximum theoretical energy saving potential of 45% through the recovery of hydrogen at a minimum cell potential of 2.8 V. The calculations also highlight, that the theoretical energy recovery proportion decreases with rising cell potential as the energy demand of the cell depends on the cell voltage, the hydrogen production rate however does not. In summary, it can be concluded that hydrogen recovery in wastewater electrolysis cells is an effective way of reducing the operational costs and increasing the economic feasibility of electrooxidation systems. Finally, the running costs of the system are compared to wastewater disposal costs.