Medical oxygen is crucial for effective treatment of patients, yet many low- and middle-income countries (LMICs) without a good healthcare infrastructure have been unable to provide sufficient oxygen therapy for years now. The COVID-19 pandemic highlighted the critical need for more oxygen, leading to supply shortages and rising prices even in developed countries. Currently, most medical oxygen is produced by a few large companies using centralized Cryogenic Air Separation Units (CAS). Pressure Swing Adsorption (PSA) offers a promising alternative, enabling local production of medical oxygen without reliance on suppliers. PSA leverages the pressure dependency of adsorption isotherms to selectively adsorb nitrogen, concentrating the oxygen.

This research has investigated the possibilities of designing a system that not only meets the specific oxygen demands of a Dutch hospital but also complies with the Dutch legal frameworks and forms an economically feasible case. A case study at Reinier de Graaf hospital (RdGG) in Delft used real oxygen consumption data. The applicable regulatory frameworks have been obtained by research in literature and with help of a representative at RdGG. For the technical design and optimisation, a numerical model of the PSA-cycle has been developed. This model is based on the Ideal Adsorption Solution Theory (IAST) and makes use of the Linear Driving Force model for adsorption kinetics. The model behaviour has been validated by experiments within a self-built, small-scale PSA-unit in the Process & Energy (P&E) lab. After this, the setup was scaled to hospital size within the model. A schematic PSA-plant has been designed based on the regulatory frameworks and system requirements which came from the numerical modelling. The economic viability has been addressed based on quotes, consumption data and electricity prices which were provided by RdGG.

Dutch regulations require hospitals to have three oxygen sources, each capable of independently providing the full design flow, with PSA units obligated to produce 93% oxygen concentration (± 3%) and meet strict impurity limits. To achieve the required oxygen purity, a vacuum pressure of 0.05 bar and an adsorption pressure of 6 bar with Oxysiv MDX zeolite are optimal. Depressurization should occur close to atmospheric pressure (1.05 bar) for efficiency. The adsorption column is most effective with a diameter-to-length ratio of 0.1 and a dimensionless time, tc, of 9.56 seconds for maximum oxygen production. The dimensionless time represents the time it takes for the gas to pass through the length of the column based on its inlet velocity.
The PSA unit at RdGG must handle a normal demand of 10 Nm³/h and a peak demand of 80 Nm³/h for three consecutive days. The second source can handle peak demand for three days, while the backup source can manage only 9 hours (tvital). If the PSA-storage has been depleted and the second source fails, tvital is the maximum refill time of the PSA-storage. This requires a production rate of 0.40 mol/s and two packages of storage cylinders (1.6 m³) which store the oxygen at 200 bar. This setup necessitates two 336L columns (3.5m height, 0.35m diameter, 0.36 m/s inlet velocity) and an air inlet flow of 126 m³/hr, supported by a vacuum pump and a compressor. The cycle steps for the adsorption, depressurization and vacuum (tAD = 79 s, tDP = 67 s, tVC = 112.1 s) total 258.7 s, allowing two columns to run in parallel. A 3 m³ air pressure vessel at 10 bar maintains PSA operation for three minutes during compressor disturbances. This setup achieves 93.61% oxygen purity with 41% recovery for 93% oxygen concentration, increasing to 58% recovery for 90% oxygen concentration. Each column requires 127 kg of zeolite, producing 5.75 mol O₂ kg⁻¹h⁻¹ (0.66 m³ O₂ kg⁻¹h⁻¹ at adsorption pressure), with an energy consumption of 29.38 kJ per mole of oxygen, totalling 255 kWh/tO₂.

The total investment for a PSA plant is estimated at 215,190 EUR, with fixed equipment costs of 176,800 EUR. Using straight-line depreciation over 20 years results in annual depreciation of 9,890 EUR. Annual costs also include energy and maintenance.
For an oxygen demand of 234 tons in 2023, the annual cost would be 25,590 EUR using PSA, significantly less than the current 60,840 EUR with the Liquefied Oxygen (LOX) installation. The levelized cost of oxygen over a period of 20 years for PSA is 128.61 EUR/ton, which is 2.1 times lower than the LCOO of LOX which is 270.52 EUR/ton.

The implementation of PSA plants for localized oxygen production in the Netherlands is both technically and economically feasible. A case study at Reinier de Graaf hospital shows significant cost savings compared to current liquid oxygen setups, with potential annual savings of 35,250 EUR. Required equipment is available and the setup size allows it to be installed inside or next to the hospital. Regulatory frameworks are already present and define clear requirements for using a PSA system as primary source. When implementing the right flow and pressure mechanisms the PSA plant can be connected to the current second and backup source, minimizing system adjustments for a smooth integration.

Future research should focus on several key areas to enhance the feasibility of using PSA in Dutch hospitals. Regulatory frameworks need approval or revision by experts in medical oxygen production. Analysing zeolite degradation and validating its performance are crucial for simulating the PSA unit's lifecycle. Improved modelling techniques, considering temperature variations, research on the validity of current assumptions and preventing backflow in the experimental setup will yield more accurate results. Additionally, industry practices should be reviewed to refine the proposed setup and obtaining precise cost estimates from quotes or hospital bills will improve the economic analysis.

De-carbonizing aviation is necessary for a sustainable future, and using hydrogen in a fuel cell, that produces water, can greatly reduce greenhouse gas emissions. Achieving higher gravimetric energy density with hydrogen compared to conventional jet fuels, involves storing it in cryogenic liquid form. Along with it, its cryogenic temperature range not only enables its use as chemical energy storage but also as a potential heat sink. However, rapid vaporization, known as boil-off, limits the long-term storage of liquid hydrogen in fuel tanks, requiring regular venting due to self-pressurization over time. Additionally, hydrogen needs to be heated to the fuel cell’s operating temperature before being used as a reactant. Understanding these requirements, this thesis focuses on three areas: predicting the maximum boil-off rate of liquid hydrogen while charging the fuel tank using a MATLAB simulation and the boil-off rate during the flight journey using a validated software called BoilFAST to understand the feasibility of retrieving the boil-off for its integration with the fuel supply; designing a fuel supply system that integrates the boil-off gas with the vaporized liquid hydrogen supply line to the fuel cell system; and integrating the cryogenic energy of hydrogen with a ram air-cooled vapor compression refrigeration system (VCRS) based thermal management of fuel cell, with the intention of reducing its parasitic load and improving system compactness. Two methods were used for the thermal integration: VCRS involving fuel cooled heat exchangers that function as an intercooler and as a separate de-superheater before a ram air-cooled condenser; and VCRS with a separate single-phase, 52\% ethylene-glycol based serial cooling circuit with multiple fuel cooled heat exchangers (FCHX). This resulted in a significant reduction of parasitic load by 13.4% and 26% when integrated with the intercooler system and single-phase serial cooling system, respectively. The study also examined the expected additional component weight, considering the aviation sector's preference for lighter systems. The findings demonstrate that the holding time of the fuel for minimum 13 minutes after tank filling and before the start of the propulsion system unit can allow a controlled amount of boil-off gas to be integrated with the fuel supply. Utilizing cryogenic energy for thermal management can significantly enhance the system's coefficient of performance by 15.3% and 33.3% respectively. Future work should involve experiments to obtain actual boil-off rates at different ambient exposures of fuel tank, tests on sloshing effect due to turbulence during flight journeys, analysis of thermal stress effects in cryogenic heat exchangers due to high temperature gradients, and testing new compatible mixed refrigerants with improved thermal properties for optimum cryogenic heat exchange.

Rising global CO2 levels underscore the urgent need for effective carbon capture and utilization (CCU) technologies to support a circular carbon economy. This study evaluates the techno-economic per- formance of a novel integrated CCU system that combines a K2CO3-based capture column with a bicarbonate electrolyser for syngas production, specifically targeting applications in the steel industry. An ASPEN PLUS model of the capture column was developed and integrated with a pH-dependent Faradaic Efficiency (FE) model of the electrolyser in Excel. Five cases were defined: (I) 90 wt% CO2 capture, (II) syngas production with a 2:1 H2/CO ratio for the Fischer-Tropsch process, (III) electrolyser operation with FECO > 50%, (IV) syngas composition suited as feedstock for electric arc furnaces (EAF) in the Energiron III process, and (V) an intermediate pH step. A techno-economic analysis (TEA) was conducted across worst, base, and best-case scenarios for each case.  Key findings reveal a trade-off between achieving high FECO at low pH levels and maximizing CO2 capture efficiency at high pH levels. Systems operating with large pH steps demonstrated a lower Lev- elized Cost of Syngas normalized to the Lower Heating Value (LCOSLHV ), due to increased hydrogen output. In contrast, systems with smaller and narrower pH steps incurred higher LCOSLHV due to their output’s lower LHV. The techno-economic analysis (TEA) indicates that the operational expenditure (OPEX) for the integrated CCU system is currently too high to be cost-competitive with alternative solu- tions. Sensitivity analysis reveals that the integrated CCU system is competitive with other electrolysis methods only under best-case conditions. Electricity costs and a low CO2 utilization ratio are identified as the primary drivers of OPEX. Improvements in these areas result in the most significant reduction in LCOSLHV, making them critical enablers for the integrated CCU system. Additionally, the cost per kilogram of CO2 saved is high compared to EU CO2 Emission Trading System (ETS) prices.  Current bicarbonate electrolysers are more costly than gas-fed CO2RR systems in terms of Unit Capital Cost (UCC) per kilogram of CO produced, largely due to reduced performance at higher current den- sities (>100 mA/cm2). Achieving CAPEX parity with gas-fed CO2RR systems would require increasing current densities while maintaining high FECO and sustaining these efficiencies at alkaline pH levels.  Future work should prioritize reducing both OPEX and CAPEX for the system, with a particular focus on improving the technical performance of the bicarbonate electrolyser. Key objectives include increasing current density while maintaining high FECO at alkaline pH levels, improving the CO2 utilization ratio, and enhancing the stability of the electrolyser.  Keywords: Carbon Capture and Utilization, Bicarbonate Electrolysis, K2CO3-based CO2 Capture, Ben- field Process, Integrated CCU System, Techno-economic Analysis

Hydrogen has emerged as a promising candidate for energy storage, offering an alternative to fossil fuels as a primary fuel source. It can be safely stored in a liquid organic hydrogen carrier (LOHC) and recovered upon demand through the reversible hydrogenation/dehydrogenation of the LOHC. Voyex, a technology-driven startup, is developing a novel LOHC that can be loaded onto ships and dehydrogenated onboard, providing hydrogen for ship propulsion as an alternative to fossil fuels. The successful implementation of this new technology requires a dehydrogenation reactor that may provide the conditions necessary for LOHC dehydrogenation to meet the ship's power demand.

This work develops a computational fluid dynamics (CFD) model to simulate the LOHC dehydrogenation reaction within a cocurrent upward-flow fixed-bed reactor. While lab-scale studies have examined the effect of operating conditions on the dehydrogenation of specific LOHCs, only a few works have studied LOHC dehydrogenation reactors and the inner flow details have yet to be understood. A CFD model will allow for a better understating of the flow, temperature, and species distribution within the reactor, and help gain more insight into the design and operating parameters on the reactor performance as measured by conversion and hydrogen yield.

This thesis delves into the distinct phenomena at play within an LOHC dehydrogenation reactor including hydrodynamics, heat transfer, species transport, and reaction kinetics, discussing ways to incorporate them into a numerical model. These effects are brought together in an Eulerian multiphase CFD model, as this approach is found to provide a good balance between modelling accuracy and computational demand.

The result of this research is a computationally inexpensive Eulerian multiphase CFD model capable of adapting to various LOHC systems and reactor configurations. Through multiple sensitivity analyses, the impact of design variables including reactor dimensions, temperature, flow rate, and catalyst pellet diameter on reactor performance is explored. These analyses yield valuable insights and design parameters to enhance reactor efficiency. Additionally, these analyses lead to several design improvement proposals such as raising the reactor inlet temperature, using a low inlet LOHC mass flux, incorporating gas-liquid separation methods, adding internal heating mechanisms, and employing internal baffles to disrupt flow and enhance heat transfer. The findings underscore potential for reactor design improvements, thereby proving the CFD model as a research and design tool for packed-bed multiphase reactors.

Particle-laden pipe flows are ubiquitous in industrial applications. Examples are industries like dredging, slurry transport, and the transport of reactants and products in chemical industries. One of the most important factors in these transport processes is the friction coefficient which relates directly to the pumping power which is a significant parameter for industries when viewed from an economic standpoint. The migration of particles in dense suspensions can significantly impact the friction coefficient in pipe flow. The clustering of particles in the core can lead to a reduction in the friction factor compared to a well-mixed particle suspension. This reduction is attributed to the decreased effective viscosity near the pipe wall. While the development lengths of single-phase flows are well known, limited knowledge exists regarding the development of velocity and concentration profiles in suspension flows.

The goal of this thesis is to study the development of neutrally buoyant suspension pipe flows. The experimental setup was validated using pressure drop measurements and the entrance length for single-phase pipe flow was obtained. The experiments for suspension flows involved varying the suspension Reynolds number and volume fractions keeping the particle size constant. Ultrasound imaging technique is used to circumvent the opacity of the suspension to study the development of suspension pipe flow. The inlet conditions for concentration were characterized, obtaining a uniform distribution at the inlet. Measurements are conducted at various locations downstream of the pipe and the velocity of the dispersed phase is obtained using ultrasound imaging velocimetry. Additionally, insights into the development of the concentration profile are obtained by checking the convergence towards a fully developed intensity profile, despite the fact that the image intensity doesn’t directly correlate to concentration profiles. The velocity profiles and intensity profiles were analyzed to understand the effect of radial migration on both concentration and velocity profiles. The entrance lengths for concentration and velocity were obtained for volume fractions ranging from 0.17 to 0.25 and suspension Reynolds numbers ranging from 500-2000. The results obtained revealed that the entrance length for concentration was greater than the entrance length for velocity. Scaling of the concentration entrance length with suspension Reynolds number and volume fractions were determined, and suspension Reynolds number scaled with an exponent of -1.62 and volume fraction scaled with an exponent of -2.1. This implies that the entrance length decreases with an increase in suspension Reynolds number and volume fraction. However, no definite trend was observed for the velocity entrance length.