Utilizing waste and wood pellets in gasification reactors is a promising solution to the waste and energy problem. However, plant shutdowns often occur due to failures in the feedstock handling systems. Unfortunately, research focusing on the flow properties and the impact of mechanical degradation on the flow properties of pellets is lacking. In this study, the flow properties of RDF, fresh wood pellets, and waste wood pellets with fines contents ranging from 0% to 30% were analyzed by Schulze Ring Shear Testing, angle of repose, angle of tilt, and Hausner ratio. The collected data was used to design a mass flow hopper and establish relationships between flowability and the angle of repose, angle of tilt, and Hausner ratio.

Our findings revealed that the fines fraction significantly influenced wall friction at a fines content of just 10%. The fines could increase or decrease the wall friction angle depending on the material. Additionally, the fines content adversely affected the flowability, with flowability reaching the flowability of the fines fraction at 30% fines content. Mixtures of RDF with waste or fresh wood pellets showed consistent wall friction and flowability similar to the base materials. We observed that a higher angle of repose, angle of tilt, and Hausner ratio indicated lower flowability. However, their predictive accuracy was limited, and we do not recommend relying on them for hopper design.

Sodium borohydride (NaBH4) is a potential material-based hydrogen storage solution. However, a lack of information regarding its bulk material properties poses a challenge in designing storage and handling equipment. This report addresses this gap by conducting a series of tests to analyse the bulk material properties of NaBH4 powder and granules, with a specific interest in how these properties change under varying humidity conditions.
Since humidity does not have a direct effect on material properties, but moisture content does, the report first investigates the effect of humidity on moisture content in the material. The second set of experiments is then designed to determine the bulk material properties with varying moisture content, establishing a link between humidity and bulk material properties.
The findings reveal that prolonged exposure to ambient humidity negatively affects the cohesion and flowability of NaBH4. This effect is more pronounced in powdered NaBH4 compared to its granulated form. However, these adverse effects can be mitigated by storing the material in a closed environment. The study concludes by emphasizing the importance of a closed storage environment and the need for further research on NaBH4’s behaviour under a wider range of conditions for its storage and handling.

Large-scale hydrogen storage is a crucial part of the energy transition. The usage of salt caverns has a great potential in this process, but there are open questions regarding the construction’s lifetime which need to be investigated prior to their implementation. In this work, potential construction steels were studied. The conditions in a salt cavern were imitated on laboratory scale with an experimental high-pressure setup. Two steels, J55 and H2-ready X56, were systematically exposed to pressure/temperature cycles, gas (H2 and N2), water and brine. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) techniques were used for the characterisation of the steels’ surface, focussing on corrosion effects and crack formation. For both steels, a significant impact of moisture and salt ions could be shown. However, only for J55, intensification of corrosion and cracking on the surface due to hydrogen gas exposure was found. Pronounced crack formation over the entire surface of J55 was revealed. For X56 significantly less crack formation could be observed. Overall, the results strongly indicate better resistance of X56 than J55 against the conditions in a salt cavern, used for hydrogen storage.

Electrochemical CO₂ reduction may present a solution to close the carbon cycle and to utilise CO₂ emissions. However, for this technology to have a significant impact, it has to be successfully implemented on an industrial scale. Numerical simulations can aid with the study of process parameters and reactor design.

The overall aim of this project is to develop and utilise a numerical model that can describe phenomena arising in the CO₂ electrolyser inside the flooded catalyst layer (CL). First, the general operation of the electrolyser is addressed, and this is extended for the effect of liquid flow rate, electrolyser length, and operating pressure. To investigate the performance and limitations arising at the large-scale, the model is scaled-up to describe a one meter long electrolyser. The study is concluded with two considerations that could improve the electrolyser performance. These points were addressed by developing a 2D numerical model of a gas diffusion-based CO₂ electrolyser in COMSOL Multiphysics. We assessed the performance of the electrolyser in terms of current density, reflecting rate of species formation, and of faradaic efficiency for CO (FE), reflecting selectivity towards the desired product.

Investigating the small-scale electrolyser we find that at high current density (200 mA cm^-2), the pH in the CL immediately increases by 3 units and further diagonally increases from pH 10.1the inlet to 12.2 around the outlet. When operating the electrolyser with excess of CO₂ supply, we find the CL to perform the best near the gas phase boundary (311 mA cm^-2, 95% FE), while the regions close to the electrolyte are underperforming (250 mA cm^-2, 89% FE). This shows that the performance in certain regions of the CL needs to be improved.

When scaling-up the electrolyser to a length of one meter we find that the performance does not change dramatically when operating at excess of gas supply. However, if a high CO₂ conversion should be achieved, the long electrolyser shows a 10% decrease in FE, and CO₂ conversion compared to a small-scale electrolyser, at the same level of current density (115 mA cm^-2).  Analysing the current density locally, we find that difference between the inlet and outlet can be as large as 100 mA cm^-2. Next, we find that FE can fall to almost 50% around the outlet. This shows that when adding extra length to the long electrolyser, this extra length only adds a fraction of its potential performance.

The uneven utilization of the catalyst can be improved by varying the catalyst loading along the electrolyser length. This improves the FE by around 5% while using 40% less catalyst. We also find that while the current density is slightly lower, the amount of product generated per mass of catalyst has significantly increased. This shows that carefully engineering the catalyst loading can save the amount of catalyst needed and could potentially improve the cost-effectiveness of the CO₂ electrolyser.

In all cases the performance over the CL is unevenly distributed. To achieve a higher performance, research needs to find ways how to enhance the performance also in the poorly utilised regions of the CL. Scaling-up the electrolyser just by extending its length proves inefficient and inevitably leads to a lower performance. The beneficial buffering effect provided by the electrolyte at a small-scale does not translate to a large-scale. At this moment, performance of large-scale CO₂ electrolysers seems satisfactory only when operating at very low CO₂ conversion. From the investigated parameters that address the performance issues, higher operating pressure and smart catalyst loading seem only promising options, however, other options should be found to speed up the development.

This thesis aims to find out whether electrokinetic transport of a calcium chloride solution can be controlled by adding sodium ions by performing molecular dynamics simulations. The idea that electrokinetic transport control is a possibility originates from research that found that charge inversion is reduced when monovalent ions are added to a multivalent solution. Consequently, flow reversal suppression is expected. Many mechanisms are known to contribute to charge inversion and ion competition, but it is unclear how they exactly relate to charge inversion reduction and flow reversal suppression. This work aims to replicate charge inversion reduction and flow reversal suppression in a system with an amorphous silica interface for mixed electrolytes with calcium, sodium and chloride. To allow insight into the structural behaviour of the electrical double layer and the electrokinetic properties for varying concentrations, molecular dynamics simula- tions are used. No variation in charge inversion and flow reversal reduction was found for the simulated concentrations. However, the adsorption behaviour of ions in the electrical double layer changed due to ion competition between sodium and calcium, where sodium outcompetes calcium for inner sphere surface complex adsorption. This work also shows that the electroosmotic flow behaviour for mixtures is sensitive to the dynamic adsorption behaviour of ions, emphasizing the importance of correctly tuned force field parameters between surface and ions.

Electrolyzers for CO2 reduction can be used to synthesize renewable fuels, as a route to replace fossil fuels in our everyday economy with the purpose of minimizing the effects of climate change. For a high-scale implementation of electrolyzers, high operation current densities and low overpotentials are essential. Currently available options do not offer this and are limited by the low mass transfer of CO2 in the system. We envision using catalyst-coated capacitive particles (slurry electrodes) to be a solution: a system where the reaction site can be brought to the reagent, instead of the other way around. This thesis is a first step in the direction of a slurry electrode flow cell and aims to produce silver nanoparticles deposited on activated carbon particles to function as catalysts in such a system. The goal of the synthesis procedures was to produce a capacitive powder (activated carbon) with efficient deposition of silver nanoparticles spheres) ranging 5-20 nm in diameter. Based on literature, the most interesting methods for synthesis were selected to be: solution-based methods with only activated carbon, with added polyvinylpyrrolidone, with added sucrose, electrodeposition and impregnation. The resulting powders were analyzed using ICP-OES and TEM, showing that only impregnation and electrodeposition can yield the desired powders with a near-100% silver deposition efficiency and particles < 20 nm in size. Next, the impregnation and electrodepostion samples were prepared into a 15 wt% slurry, and a third slurry was made with bare AC as a blank. The catalysis experiments were executed in a flow cell (electrode area = 4 cm2), with currents ranging from -5 to -15 mA/cm2. Within this range of currents, extreme potentials up to -10 V (measured over working electrode versus counter electrode) were measured. The potentials on the anode and cathode side of the cell were also measured individually using reference electrodes, showing that the anodic side of the cell reached +5 V, whereas the cathodic side of this cell reached only -1 V. Additionally, CV scans before and after the experiments confirm that the cell’s conductivity decreased within an experiment, however, this degradation is reversed for a new experiment. These observations combined lead us to believe that the cause of the cell problems is located on the anodic side of the system, and is most likely resistance from oxygen bubbles, which needs to be solved to allow cell operation at higher current densities. Since the aim of the project was CO2 reduction on the slurry electrodes, the outgoing gases from the cathode were measured in a GC. The blank was included to demonstrate the catalytic effect of the silver nanoparticles, yet the highest CO flow (around 0.05 ml/min) was measured at the lowest current density during this blank experiment. Calculating the Faradaic efficiency (FE) suggests that 33% of the electrons in that experiment was used for this conversion. The other measurements, at higher currents or with silver present, did not reach an FE of 10%. This combination leads to the conclusion that the observed CO is most likely not produced by CO2 reduction. A hypothesis was made that this CO was already present at the powder’s surface and released during the experiment, however XPS data showed that there were no noticeable differences in the content of oxygen-bound carbon between the coated samples and the bare sample. Thus, the source of the CO is at this stage unknown. Future work towards proving CO2 taking place on the slurry electrode should first investigate the source of the observed CO, which requires testing the influence of the different carbon sources present in the system. Additionally, the blank experiment should be improved: using a bare carbon slurry that underwent the same procedure as the coated slurry (without the precursor present) eliminates any differences in the powder.

The process in which a smooth laminar flow transits to a chaotic to a chaotic, turbulent state, is a topic of particular interest in the sectors of energy technology and aerodynamics. To study the different paths that can be followed during the transition process, various tools and methods have been developed. A preliminary investigation of the response of a laminar flow to an internal or external disturbance can be performed by applying Linear Stability Theory principles. In the recent years, the Direct Numerical Simulations of flows offer a more insightful method to study the transition process, since the flow fields are numerically solved using high computational power. Previous research has primarily focused on the stability and transition of Ideal Gas flows, with little attention to the effects of a highly Non-Ideal behaviour. The present work aims to develop a DNS code that can be used to investigate the stability of compressible boundary layers in the vicinity of theWidom Line. For the initialization of a DNS, a two dimensional base flow profile is required. For the calculation of the base flow, a self-similar solution is obtained, using a MATLAB script that has been developed for the purpose of this study. The DNS code is developed in FORTRAN. An inviscid characteristic wave analysis is utilized for the implementation of the boundary conditions, along with numerical sponges to avoid reflections. To trigger the instabilities, periodic suction and blowing is incorporated. For the simulations of non-ideal fluids, a thermodynamic table interpolation tool is incorporated. For the validation of the results obtained by the DNS code, an in-house MATLAB script is used to for the calculation of the growth rate and fluctuation amplitude profiles using LST. Initially, the FORTRAN code is used on ideal-gas simulations, to investigate how different computational parameters will affect the flow field. The parameters are related to mesh resolution, boundary conditions and numerical sponges. To investigate the stability of non-ideal fluids, cases of different free-stream temperatures and Eckert numbers are simulated. The free-stream temperature is altered to control the non-ideal gas effects, whereas the Eckert number is used to control the compressibility effects. In general, the flow is stabilized as non-ideal gas and compressibility effects become more prominent. However, a second unstable mode is observed in the case where the temperature profile crosses the pseudo-critical point. This second mode has a higher growth rate of instabilities, compared to the first mode. All the results are validated using the LST predicted profiles.

This thesis describes a study into pairwise particle interactions within a Hele-Shaw geometry, using stop-flow lithography. By exposing a photoreactive mixture to a strong UV-pulse, a hydrogel is formed. The shape of this hydrogel is controlled by masking part of the light beam. This process takes place while the Hele-Shaw channel is placed on the stage of a microscope, which allows these hydrogel particles to be viewed and tracked. Improvements were made to increase the accuracy and precision of the experimental set-up. No- tably, the initially present mismatch of intra-pair particle thickness was greatly reduced by changing the method of particle pair production. By tracking these pairs of particles, information is obtained regarding their motions and velocity relative to one another. Experiments were performed for a selection of particle shapes and compared to numerical simulations of identical geometries. Simulations predicted that attractive and repulsive velocities should be noticed depending on the separation distance and shape of the particles. Qualitatively, the experiments agree to a certain extent with the simulations. It was demonstrated that the pairwise interactions are indeed dependent on their shape. Furthermore, the magnitude of these interactions qualitatively matched with the experimental data. Quantitatively, the experimental data did not agree with the simulations, but strong evidence was presented to indicate that the UV-light hitting the sample was not uniformly distributed. This results in a discrepancy in particle thickness between the pair, which skews the experimental data. Novel insights were gained on the applicability of the current literature model on hydrogel particle propagation. In contrast to the current model, it was experimentally demonstrated that the shape and (in-plane) size of the particle affects its thickness.

The effort to reduce global anthropogenic carbon dioxide emissions has caused a growing interest in the use of sustainable energy sources. One of the potentially sustainable energy sources considered as an alternative for the currently used fossil sources is biomass. Biomass is organic matter that originates from plants or animals which can be used as chemical energy carrier for fuels or for the production of chemical feed stock[Basu, 2010]. Gasification is a thermochemical process that converts materials like biomass into useful convenient gaseous fuels or chemical feedstock[Basu, 2010]. Gasification takes place at high temperature in the presence of a gaseous agent. Gasification is aimed at increasing the overall energy density of biomass by producing gaseous energy carriers with a higher energy density than the original biomass feed. Conventional gasifiers combust a fraction of the biomass or char in order to provide heat to the reduction reactions. This has two disadvantages. First, the flue gasses are mixed with the product. Secondly, the air that is used for partial biomass combustion mainly consists out of nitrogen. The nitrogen dilutes the gasification product significantly. The Indirectly Heated Bubbling Fluidized Bed Steam Reformer [IHBFBSR] set-up at the TU Delft is a novel indirectly heated gasifier or allothermal gasifier. The combustion of natural gas takes place in a separate combustion chamber inside the reactor chamber. Steam gasification can therefore be performed in the absolute absence of oxygen. A radiant tube facilitates heat transfer from the combustion to the reaction chamber. The radiant tubes are installed at the top and bottom of the IHBFBSR and work according to the heat from inside to outside principle. The aim of this study is to assess the performance of the IHBFBSR set-up at the TU Delft and compare its performance with other existing allothermal gasifiers. The main research question of this study is stated as: "How does the Indirectly Heated Fluidized Bed Reactor perform in terms of product yield, product quality and energy efficiency and how does its performance compare to other indirectly heated gasifiers?". In order to answer this question, both an equilibrium model and a kinetic model have been designed. Sub-optimal conditions for the IHBFBSR take place at a reactor temperature of 850 degrees C, which is the maximal controlable temperature of the reactor. At this temperature, the carbon limit is reached for an equivalent ratio of 0.23. The CGE at the carbon limit equals 69.7%. Optimal process conditions are where the particle size of the bed material is maximized without losing the fluidization behaviour of the bed. The maximum particle size equals 600 micron. The overall efficiency of the system can be increased by heat transfer between the inlet and outlet gasses of the burners and by the separation and combustion of tars and char to add heat to the process. This study shows that the pyrolysis step in the IHBFBSR is rate limited by internal heat transfer. In addition, the char oxidation reaction is limited by mass transfer of oxygen to the char particle.