Green hydrogen produced by alkaline water electrolysis may contain residual water vapour and other impurities that must be removed before use in fuel-cell applications. This study investigated adsorption-based hydrogen drying using Pressure Swing Adsorption (PSA) and Temperature Swing Adsorption (TSA), with particular attention to process modelling in Aspen Adsorption.

Zeolite 4A was selected because of its strong affinity for water at low partial pressures. Water adsorption equilibrium was represented using a Dual-Site Langmuir 2 model, while mass transfer was described using the Linear Driving Force model. A non-isothermal packed-bed model was developed for a hydrogen feed containing 872 ppmv water at 25 bar, 298.15 K, and a flow rate of 0.0223 kmol s−1. Several PSA configurations were tested, including conventional pressure regeneration, vacuum regeneration, and temperature-assisted vacuum regeneration. Conventional regeneration at 1 bar produced only limited reduction in solid water loading, while deep-vacuum simulations showed numerical convergence problems during multi-cycle operation. Therefore, the detailed cyclic and economic assessment was continued using TSA.

For the TSA process, the simulated breakthrough time was approximately 19 250 s, and an adsorption time of 14 000 s was selected to provide a safety margin before water breakthrough. Regeneration w
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This thesis assesses the techno-economic viability of large-scale ammonia cracking as a hydrogen import pathway for industrial clusters, using a 100-ton-per-day hydrogen plant at the Port of Rotterdam as the case study. An integrated process uses catalytic cracking over Ni/Al2O3 in a fired multi-tubular reactor at 10 bar and 689 °C, water absorption of unconverted ammonia, pressure swing adsorption to 99.5 mol% hydrogen, and compression to 50 bar. This process is simulated in Aspen HYSYS and costed to AACE Class 4 accuracy. The reactor design rests on a published Langmuir-Hinshelwood rate expression that, after correction of a reparametrisation error in earlier work, predicts an independent set of 63 high-pressure measurements to within 7.1 conversion points with no fitted parameters. Pinch analysis identifies the flowsheet as a threshold problem requiring no cold utility, in which the process supplies 88% of its own heating; with adsorption tail gas and recovered ammonia fired as internal fuel, the plant converts ammonia to hydrogen at 91.6% efficiency on a lower heating value basis, consuming 7.04 kg of ammonia per kilogram of hydrogen. The levelised cost of hydrogen is €6.47/kg at a delivered ammonia price of €800/t, of which the feedstock contributes 87%. Sensitivity analysis shows that no design variable can materially alter this outcome: viability reduces to a single break-even condition, requiring green ammonia below approximately €796/t at current hydrogen prices. The market-discovered price for RFNBO-compliant ammonia delivered to Rotterdam, at €1000/t, lies outside this envelope, while lower-cost supply routes reported in the literature fall within it. The competitiveness of ammonia cracking is therefore determined by the ammonia supply chain, not by the design of the cracking plant.
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This study investigates the influence of sodium thiocyanate (NaSCN) as chaotropic electrolyte additive on the physicochemical properties and electrochemical performance of aqueous NaOH for alkaline water electrolysis. Density, viscosity, and electrical conductivity were measured experimentally and compared with empirical correlations and classical MD simulations. A biased-random walk model was used to estimate the contribution of Grotthuss-type transport to OH^– mobility. Electrochemical performance was evaluated on Pt-mesh electrodes using cyclic voltammetry. NaSCN addition increased electrolyte density and generally increased viscosity. Although it increased the number of charge carriers, its effect on conductivity depended strongly on composition. Positive conductivity increments were observed in some diluted mixtures, whereas concentrated mixtures exhibited reduced conductivity because of increased viscosity, ionic crowding, and correlated ion motion. Classical simulations reproduced NaSCN conductivity but underestimated NaOH conductivity because the nonreactive force field excluded structural OH^– transport. The conductivity-based analysis indicated that NaSCN decreased the corrected OH^– self-diffusion coefficient and increased its estimated hopping lifetime, suggesting suppression of Grotthuss transport. NaSCN also substantially inhibited the electrochemical reactions on Pt. The HER overpotential magnitude at –10 mA/cm2 increased approximately from 116 mV to 300–310 mV, while the apparent OER overpotential at 10 mA/cm2 increased approximately from 459 mV to as much as 1082 mV. These effects are attributed to a combination of reduced ionic mobility, increased transport resistance, modification of the electrical double layer, and specific adsorption of SCN^– on Pt. Sulfate detected after cyclic voltammetry further supported the occurrence of parasitic SCN^– oxidation, indicating that part of the anodic current could not be assigned exclusively to OER. Overall, NaSCN did not improve alkaline water electrolysis performance under the investigated conditions. The results demonstrate that chaotropicity alone is insufficient for selecting electrolyte additives; ionic transport, catalyst interactions, and electrochemical stability mas also be considered. ... Read more

Per- and polyfluoroalkyl substances (PFAS) are persistent contaminants that occur throughout the water cycle, and European drinking water limits for them keep tightening. Foam fractionation concentrates PFAS into a small volume of foam by using their surface activity, but reaching the short-chain compounds takes a cationic co-surfactant on top of that. The one normally used, cetyltrimethylammonium bromide (CTAB), is toxic to aquatic life and poorly biodegradable. This work tests whether biosurfactants from algae can take its place.
Reverse-osmosis concentrate from a Dutch drinking water plant was treated in a 1 L batch column and analysed by LC-MS/MS across a 32-compound PFAS panel. Two algae were compared first, and the better of the two was then combined with three bio-based cationic co-surfactants. Spirulina held a foam for a full run and removed the short-chain PFBS at 32, 45 and 59% across its three doses, where Tetraselmis foam thinned within ten minutes and gave no removal above what bare bubbles achieve on their own. Neither alga matched CTAB on the short chains, because algal biosurfactants carry no positive charge. A bio-based cation closed that gap: PFBS rose from 48% with the alga alone to above 99%, beating the CTAB benchmark, while PFOS stayed above 85% in every run. LAE is the recommendation, as the only option classed as readily biodegradable. Every run in the second phase contained Spirulina, so whether the alga is still needed alongside a co-surfactant remains untested. ... Read more

Large-scale import of green hydrogen is expected to become essential for the Netherlands to achieve its climate targets and secure its future energy supply, as domestic hydrogen production alone will not be sufficient to meet projected demand. However, hydrogen gas has a very low volumetric energy density, making direct long-distance transport economically challenging. To overcome this limitation, hydrogen can be compressed, liquefied, or converted into a chemical carrier. Although these transport pathways have been extensively studied, the conversion and reconversion stages are often treated as a black box, making a transparent comparison between different hydrogen carriers difficult. This study addresses this gap by developing detailed models of these stages under identical assumptions to determine which hydrogen carrier provides the most cost-effective import pathway to the Netherlands. Following a screening of multiple candidates, ammonia and a liquid organic hydrogen carrier (LOHC), in the form of methylcyclohexane (MCH), were selected for further evaluation.

A case study is considered in which hydrogen is imported from Brazil, where lower production costs are expected due to abundant renewable energy resources. The conversion and reconversion processes are modelled in Aspen Plus, including reaction kinetics, to quantify energy consumption and determine equipment requirements. Combined with shipping and storage costs, these results are used to calculate the total landed cost of hydrogen delivered to the Dutch hydrogen network.

At an assumed hydrogen production cost of 6 $/kg, both the ammonia and LOHC pathways result in a landed cost of approximately 11 $/kg, which is below the expected domestic production cost and therefore indicates a potential economic incentive for import. However, when a more conservative production cost of 8 $/kg is assumed, the landed cost exceeds the domestic production cost, removing this incentive. The two pathways show very similar overall costs, as the lower hydrogen efficiency of the ammonia route is largely offset by the lower energy density of MCH and its resulting transport requirements. Since neither carrier is clearly superior from an economic perspective, the final selection is likely to depend on additional factors such as technological maturity, safety considerations, and existing infrastructure.

It should be noted that these conclusions are specific to the Brazil-to-Netherlands case study. Due to the lower energy density of MCH, the LOHC pathway requires more shipping capacity and becomes increasingly sensitive to transport distance. For longer transport routes, the ammonia pathway is therefore expected to become the more economically favourable option. ... Read more

Heating and cooling represent about half of Europe’s final energy consumption, with industry using a large share and fossil fuels still supplying most heat demand. This makes reliable industrial heat pump operation important for improving efficiency and reducing emissions. However, faults, degradation, sensor issues, and changing operating conditions can reduce system performance and increase the need for manual diagnosis.

This thesis develops a digital-twin-based hybrid fault detection and diagnosis methodology for industrial thermal systems. The Digital Twin part focuses on a component-level empirical model of an air-cooled condenser that estimates expected behaviour using manufacturer data. The fault detection and diagnosis part focuses on an alarm-assisted hybrid framework that interprets existing industrial alarms and warnings using operational measurements, thermodynamic principles, rule-based logic, and Digital Twin models.

To support performance monitoring, a general methodology for developing component-level empirical Digital Twin models was created using manufacturer and operational data. The methodology includes automatic extraction of healthy performance data, identification of dominant operating variables, normalization with respect to design conditions, and correction-based empirical modelling to estimate expected component behaviour. As an application example, the methodology was implemented for an air-cooled condenser and applied to operational data from three plants, where it identified one condenser with clear signs of underperformance.

The fault detection and diagnosis part was developed to reduce the dependence on manual alarm interpretation in industrial operation. For this purpose, an alarm-assisted hybrid framework was implemented using a Branch A / Branch B structure, where Branch A diagnoses existing alarms and warnings and Branch B is proposed as a future extension for hidden degradation detection. The first branch combines operational measurements, thermodynamic reasoning, rule-based diagnostic logic, and Digital Twin models to automatically translate alarms and warnings into structured diagnostic indications. The framework was implemented in Python in a modular form, so that new alarms, plant-specific settings, and additional diagnostic checks can be added without changing the overall structure. The results showed that the framework can provide transparent and physically traceable diagnostic support.

The most important conclusion of this thesis is that the methodology developed for component-level Digital Twin modelling, together with the proposed Branch A / Branch B FDD structure, showed strong potential for supporting monitoring and diagnosis in industrial heat pump systems. Additionally, Branch A provided a practical method for translating alarms and warnings into clear and traceable diagnostic indications. Overall, this methodology could help industrial operators diagnose faults more effectively while reducing the time and resources required for manual alarm interpretation.
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The transition towards carbon-neutral energy systems requires solutions capable of integrating large shares of variable renewable energy while simultaneously supplying multiple energy carriers. This thesis analyses sector coupling as an approach to increase system flexibility by linking the electricity, \ce{H2}, and heat sectors through energy conversion and storage technologies. The study investigates how sector coupling can enable a flexible, cost-optimal, closed-grid renewable energy system for the Rotterdam area.

A techno-economic optimisation model is developed to determine the optimal sizing of renewable generation, power-to-X technologies, and energy storage under a renewable-only energy supply. The system comprises onshore wind and photovoltaic generation, an electrolyser, heat pump, fuel cell, battery storage, H2 salt cavern storage, and thermal storage, and is evaluated using hourly supply and demand profiles. Besides the base optimisation and respective techno-economics, a sensitivity analysis is presented, which includes CAPEX sensitivity, component-removal scenarios, and a carbon break-even analysis to assess competitiveness against conventional energy pathways.

The results show that the cost-optimal system is characterised by oversizing of renewable generation relative to conversion capacity by a factor of approximately 5.2 Consequently, storage plays a complementary role by providing flexibility across different timescales. Wind generation is identified as the essential supply technology, while photovoltaic generation primarily complements battery operation. Moreover, the fuel cell serves mainly as a backup pathway, and battery and H2 storage provide complementary short- and long-term flexibility. Although the system achieves a net present value over its lifetime of 2\,995 M€, corresponding to a payback time of approximately 12 years, it is not yet competitive with conventional alternatives under current market conditions. The system-level carbon break-even analysis indicates that cost parity would require a carbon price approximately 5.4 times higher than the current EU Emissions Trading System level.

Overall, the results demonstrate that sector coupling can enable reliable and economically viable operation of closed-grid renewable energy systems while reducing dependence on large-scale energy storage through the strategic combination of renewable oversizing and energy conversion pathways. The findings provide insights into the role of individual technologies in integrated energy systems and identify key technological and policy developments required to improve their future competitiveness.
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Hydrogen is at a turning point in the global energy transition. Its high specific energy makes it attractive for weight- and range-constrained sectors such as long-distance transport and aviation, where liquid hydrogen (LH₂) provides the required compact storage medium. Liquefaction, however, remains the main challenge, as industrial plants consume 12-15 kWh per kilogram of liquid hydrogen, roughly three to four times the thermodynamic minimum. Conceptual designs promise to reduce this consumption, but they rest on idealized models. This thesis quantifies two of these idealizations for an 86 tonnes-per-day reference process. The first is the property and kinetic modeling of the cryogenic catalytic plate-fin heat exchanger (PFHX). The second is the assumption of full liquid yield, which ignores the boil-off gas (BOG) generated during storage and truck loading. An ejector-driven recovery cycle is then proposed and assessed for the BOG.

For the cryogenic cooling stage, the helium-neon refrigerant is modeled with an improved equation of state (SAFT-VRQ-Mie) and residual entropy scaling. This replaces the dilute-gas correlations used in earlier studies. The revised thermal conductivity diverges from those correlations by a factor of two at 30 K and underpredicts the measured mixture property by 20-22%. Because the cold-side heat transfer scales as the two-thirds power of conductivity, this increases the required heat exchanger length by about 30% to 7.8 m, and the updated ortho-para conversion kinetics push it to the 8.2 m single-unit manufacturing limit.

For the LH₂ storage stage, validated two-phase models show that the loading process dominates the boil-off losses and vents about 2.3% of each delivered load. A one-dimensional ejector model then shows that this BOG, together with the separator flash vapor, can be entrained and returned to the cycle in a single pass. This raises the net liquid product from 86 to 104 tonnes per day. In the adapted cycle, the binding constraint is the downstream PFHX and not the ejector. At the original 75 bar feed pressure, the heat exchanger exceeds the 8.2 m single-unit limit. Only when lowering the feed pressure to 40 bar, which also removes one feed-compression stage, it becomes buildable as a single unit at 8.19 m.

A techno-economic analysis of the isolated cryogenic section quantifies the cost of this recovery. Capital cost rises by 24% and specific energy consumption by 56%. The specific liquefaction cost increases from 0.432 to 0.593 USD per kilogram, an increase of 37.4% that holds across all tested cost assumptions. Ejector-based BOG recovery is therefore technically feasible and increases liquid yield, but it is not economically justified within the cryogenic boundary on its own. ... Read more

The Netherlands is transitioning towards a fully renewable energy system, aiming to achieve an almost entirely renewable energy supply by 2050. Green hydrogen, produced via water electrolysis powered by renewable energy, offers a key solution for decarbonising energy-intensive sectors. However, high production costs remain a major barrier to widespread adoption. This study investigates the cost-optimal design of a hybrid renewable energy system combining solar PV, onshore wind, and battery storage to supply a 200 MW electrolyser in De Koog, the Netherlands.
A simulation model was developed in Python, incorporating hourly wind and solar generation data, electrolyser operation with on/off stack control, battery charging and discharging, and system degradation over a 20-year lifetime. Multiple system scenarios were evaluated by varying installed capacities, battery sizes, and minimum stack operation rules. Economic performance was assessed using key indicators, including hydrogen sales price, levelised cost of hydrogen (LCOH), net present value (NPV), internal rate of return (IRR), and payback time. Additionally, stack and battery replacement costs were considered. Results show that the cost-optimal system for the chosen location, De Koog, is dominated by wind-only systems, with the electrolyser operating at a capacity factor of 0.659. Inclusion of a small battery provides
minor operational flexibility, increasing annual hydrogen production slightly from 22.98 to 22.99 million kg, but has a negligible effect on hydrogen sales price (7.442–7.444 €/kg), NPV, LCOH, IRR, or payback time. From year 8 onwards, stack replacement costs remain constant, as stacks are replaced annually and battery replacement is scheduled after 13.5 years, leading to only a limited and predictable increase in total system costs. Electrolyser stack granularity affects operational efficiency: smaller stacks reduce curtailment without storage but slightly limit battery utilisation when included.
The findings indicate that the economic performance of green hydrogen production is primarily driven by the balance between renewable generation and electrolyser operation. In particular, the renewable to-electrolyser capacity ratio plays a key role, while battery storage has only a minor influence in the cost-optimal configuration. For the analysed Dutch coastal site, the lowest hydrogen production costs are achieved with a moderately oversized wind capacity, an electrolyser operating at an intermediate capacity factor, and minimal battery integration. However, the optimal capacity ratio and the economic value of battery storage are strongly location-specific and depend on local resource conditions and system design assumptions. This study provides a comprehensive techno-economic assessment of hybrid renewable energy system design, offering practical guidelines for optimising component sizing to achieve cost-efficient green hydrogen production in the Netherlands and supporting the transition to a low-carbon energy system. ... Read more

The Levelized Cost of Hydrogen (LCOH) is commonly used to evaluate the economic performance of electrolytic hydrogen production. In many studies, electricity costs are represented by static average prices, while assuming simplified operating profiles. This simplification neglects the temporal variability of electricity prices in liberalized power markets and limits the representation of flexible electrolyzer operation.

This thesis develops a techno-economic LCOH framework that incorporates hourly electricity prices, renewable generation profiles, and operational constraints of an alkaline electrolyzer. A bottom-up modeling approach is applied, aggregating hourly operating decisions into discounted lifetime costs. A daily dispatch optimization algorithm is introduced to determine the operation of the electrolyzer based on electricity prices, expected hydrogen revenues, and solar availability, while accounting for start-up penalties, efficiency degradation, and stack replacement.

The framework is applied to a case study of a 1.2 MW alkaline electrolyzer coupled with a large solar field in the Netherlands using historical market data. The results indicate that price-responsive operation can reduce LCOH relative to continuous operation, primarily by avoiding periods of high electricity prices, although this leads to lower overall hydrogen production volumes. Compared with purely solar-following operation, cost reductions are achieved at the expense of higher carbon emissions as a result of increased reliance on grid electricity.

Overall, the study shows that incorporating electricity price dynamics and operational constraints can materially affect LCOH estimates and provides a more transparent basis for evaluating grid-connected electrolytic hydrogen production under volatile electricity markets. ... Read more

As the energy transition accelerates, there is growing interest in exploring different renewable energy sources to help reduce emissions from heating and electricity. One of the more promising options, under the right conditions, is geothermal energy, which can provide a stable and relatively low-carbon supply of heat and/or power. In the Netherlands, medium-depth (>500 m) geothermal heat has mostly been used for heating greenhouses, with electricity production from geothermal sources not yet explored.

This thesis provides a techno-economic assessment of medium-depth geothermal energy systems in South Holland, the Netherlands, evaluating their potential to meet local heat and electricity demands sustainably and with a profit. Two case studies were analyzed in this thesis. The first investigated a geothermal district heating system for the TU Delft campus, incorporating a large-scale heat pump to increase heat extraction from the reservoir. The second examined a combined heat and power (CHP) system for the Royal IHC facilities in Kinderdijk, based on an Organic Rankine Cycle (ORC). The work relied on thermodynamic modeling together with subsurface and economic simulations to select working fluids, size the main components, and assess economic indicators such as Levelized Costs of Heat/Electricity (LCOH/LCOE), Net Present Value (NPV), payback times, and internal rate of return (IRR).

The findings reveal a sharp difference in feasibility between the two cases. The geothermal heat pump project in Delft proved to be promising for district heating applications, whereas the ORC-based power generation system proved to be both technically and economically unviable under the assessed conditions, mainly due to the low temperature of the geothermal brine and the small scale of the project. A subsequent evaluation of a heat pump alternative for the Kinderdijk site indicated limited economic competitiveness under the current market price assumptions for heating.

Overall, the work suggests that the viability of geothermal projects is highly dependent on the quality of the geothermal resource, the scale of implementation, and the end-use requirements. Integrating heat pumps with medium-depth hydrothermal resources appears as a technically promising and financially attractive strategy for decarbonizing district heating networks, whereas low-temperature ORC systems for power generation remain unsuitable in regions with insufficient subsurface temperatures. The study shows the importance of site-specific assessments in ensuring the successful deployment of geothermal energy systems. ... Read more

The economic viability of a hydrogen economy revolves around efficient and scalable methods for its transportation and storage. Liquefaction presents a key pathway by increasing hydrogen’s volumetric energy density, though current industrial plants are hampered by high energy consumption and costs.
While conceptual models offer pathways to higher efficiency, they often lack the detailed technical and economic analysis needed to validate their feasibility, particularly for systems based on the Brayton cycle.
This thesis presents a comprehensive framework for the process modeling, viability assessment, and techno-economic analysis of a large-scale hydrogen liquefaction plant based on a conceptual Brayton cycle. A central contribution is the detailed modeling of the critical ortho-para hydrogen conversion, which was simulated within a catalytic Plate-Fin Heat Exchanger (PFHX) using a specialized Python-based model integrated with a full-plant Aspen HYSYS simulation. The study also addresses the effective management of excess cold hydrogen gas; an initial investigation into using an ejector for recirculation was conducted, but this approach was ultimately discarded as it did not yield economic improvements. A final, optimized hybrid Brayton-Claude cycle featuring an efficient cold gas recirculation loop was developed, enabling a plant capacity of 86 tonnes per day (TPD).

The techno-economic analysis of the final design was performed using the Aspen Process Economic Analyzer (APEA). In the baseline scenario, assuming an electricity price of 0.1 €/kW h, the plant achieved a Specific Liquefaction Cost (SLC) of 1.51 €/kgLH2 and a Specific Energy Consumption (SEC) of 6.983 kWh/kgLH2 in the baseline scenario.

Moreover, sensitivity analyses show a further reduction in SLC and SEC in the scenario using power recovery from the turbines: 1.49 €/kgLH2 and 6.723 kWh/kgLH2 respectively. Additionally, electricity price is the dominant factor influencing plant economics, with the long-term cost target of below 1.00 €/kgLH2 being achievable at an electricity price of 0.035 €/kW h. Future projections, which account for reduced design allowances as the technology matures to a ”Proven Process,” suggest a potential SLC reduction of 4.64%.

In summary, this thesis establishes a robust techno-economic framework for Brayton-cycle based liquefaction, demonstrating its viability while highlighting the critical interplay between advanced process modeling, component efficiency, and energy costs in achieving a competitive large-scale liquid hydrogen supply chain. ... Read more

Hydrogen is getting great attention as a key energy carrier for a cleaner energy future, with demand projections up to 20% of global energy demand by 2050. However, the low volumetric density of hydrogen leads to a challenge for storage and transport purposes, making liquefaction a promising solution that also ensures high purity. However, at the current time, the high energy consumption of liquefaction remains a major obstacle. Within this process, the precooling stage is the second most energy-intensive step, covering the broadest temperature range but offering flexibility in terms of refrigerant choice, cycle configuration, and operating conditions.

However, most of the study of the hydrogen precooling omits economic analysis, refrigerant freeze-out discussion, and employs a portion of a non-environmentally sustainable substance as the refrigerant. This study focused on addressing the gap by conducting multi-objective optimization (MOO) on specific energy consumption (SEC) and levelized precooling cost (LPC) to find out the optimal trade-off between the technical and economic competitiveness of the precooling stage, while ensuring the freeze-out risk in the streams was avoided and using environmentally friendly mixed refrigerant (MR) mixtures.

Two cycles, namely single mixed refrigerant (SMR) and dual mixed refrigerant (DMR), are modeled in Aspen HYSYS V12, where the configurations are defined based on freeze-out consideration. Nine MR mixtures for SMR and DMR are defined based on their thermophysical properties. A Non-dominated Sorting Genetic Algorithm-II (NSGA-II) algorithm was used for MOO through the pymoo library package in Python, which was then coupled with Aspen HYSYS. The decision variables to be optimized include MR composition, MR flow rate, compressor discharge pressure, and JT valve outlet pressure. Several constraints are also introduced, such as vapor fraction at the inlet compressor, minimum internal temperature difference (MITD) of heat exchangers, JT valve temperature difference, and several temperature constraints to ensure thermodynamic behavior is not violated.

In this study, Mixture 8 (for SMR) and Mixture 6 (for DMR) appear to be the top-performing mixtures, achieving specific energy consumptions (SEC) of 1.25 kWh/kg_H2 and 1.13 kWh/kg_H2, respectively, with levelized precooling costs (LPC) of €0.47/kg_H2 and €0.60/kg_H2. The study indicates that aligning the boiling points of mixed refrigerant components to enhance temperature glide, combined with tuning of operating conditions, is the key to achieving both energy efficiency and cost competitiveness. Furthermore, the optimized results in DMR also suggest that the intermediate-compression stage in the MR2 cycle could be removed.

From the sensitivity analysis, it was observed that as the precooling temperature target increased, the gap in SEC between the SMR and DMR configurations narrowed. Starting from 95 K, both systems reached similar SEC values, highlighting equal technical performance. However, the LPC further SMR dominant over the DMR. This indicates that beyond this temperature target, DMR was no longer economically competitive. Additionally, variations in pressure drop across heat exchangers and coolers had a stronger impact on the SMR configuration. The percentage increase in SEC and LPC was more severe due to the accumulation of pressure losses within a single-loop cycle. In contrast, the DMR system distributes losses across two separate loops, making it less sensitive to pressure drop effects. ... Read more

This thesis evaluates the technical and economic feasibility of producing methane (CH4) via the electrochemical reduction of carbon dioxide (CO2), offering a pathway to valorize captured CO2 while integrating surplus renewable electricity into established natural gas infrastructure. A dual-modeling framework was developed: an Excel-based electrolyzer model captures key electrochemical parameters including Faradaic efficiency (FE), current density (CD), cell voltage, and resulting power demand while an ASPEN Plus simulation rigorously models downstream separation, employing cryogenic distillation to achieve high-purity CH4 and co-products. The study systematically investigates multiple operational scenarios, reflecting variations in electricity pricing (including projected low-LCOE renewables), CO2 feedstock costs (derived from different capture strategies), and market values for methane and by-products. A detailed techno-economic assessment quantifies capital expenditure (CAPEX) requirements, dominated by electrolyzer sizing due to constraints on CD and FE, and operational expenditure (OPEX), primarily driven by electricity consumption. Sensitivity analyses reveal that electricity price, electrolyzer CAPEX (tied to CD and cell voltage), and product stream valuations are the most influential parameters affecting the net present value (NPV). Base case simulations show that under current market conditions (25=C/MWh electricity, 9,000=C /m2 electrolyzer CAPEX), the process yields a strongly negative NPV. However, scenario analyses demonstrate that moderate improvements across several fronts, reducing cell voltages to 2.5V, increasing CDs beyond 5000 A/m2, and securing electricity prices under 15=C /MWh can collectively transition the process towards economic breakeven within a 30-year project horizon. Environmental performance was assessed via a simplified CO2 balance, indicating that for each ton of CH4 synthesized, approximately 2.75 tons of CO2 are sequestered. However, this benefit is partially offset by indirect emissions from electricity generation, underscoring the need to combine the process with low-carbon power sources to ensure genuine climate mitigation. This comprehensive analysis highlights both the promise and the formidable challenges of industrialscale CO2 electroreduction to methane. It underscores the critical need for integrated approaches combining advancements in catalyst selectivity and stability (to improve FE toward CH4), process intensification to achieve higher CDs with minimized overpotentials, and supportive policy mechanisms such as carbon pricing or renewable integration incentives. Ultimately, the findings provide quantitative benchmarks and strategic direction for advancing CO2-to-CH4 electrolysis towards economically and environmentally viable deployment. ... Read more

The global energy transition is one of the most urgent technological and societal challenges of the 21st century. To achieve climate goals, it is essential to reduce the use of fossil fuels and replace them with sustainable alternatives. In this context, green hydrogen is receiving increasing attention, particularly as asolution for sectors where direct electrification is difficult or unfeasible, and as a means to balance the intermittency of renewable energy sources. However, hydrogen production via water electrolysis remains energy-intensive and costly, particularly when powered by fluctuating sources like wind. To improve economic viability, system-level optimisation must account for technical phenomena such as dynamic efficiency, degradation, gas crossover, and the performance of power electronics.
This thesis investigates the dynamic behaviour and optimal sizing of a directly coupled wind-powered alkaline electrolyser system, with the aim of minimising the Levelized Cost of Hydrogen (LCOH). Although static operating conditions are often assumed in existing models, this work addresses gaps in the literature by developing a time-resolved simulation model that includes wind variability, dynamic efficiency, degradation effects, realistic operational limits of the electrolyser, and time-dependent efficiency of power electronics.
An electrolyser model was developed and implemented in Python using an Electrical Equivalent Circuit (EEC) approach. An initial analysis compared intra-hour wind power fluctuations with hourly averages, revealing that the impact on hydrogen conversion efficiency was negligible (<0.06% over three 3-hour periods). Given this minimal difference and the widespread availability of hourly wind data across numerous locations, hourly wind data was deemed sufficiently accurate for system-level analysis.
The model was subsequently applied to evaluate system performance across 38 onshore European locations using 2015 wind data, assuming a constant configuration of a 2MW wind turbine coupled to a 1380kW electrolyser (69% ratio). For each location, the wind turbine and electrolyser capacity factors were calculated to assess the geographical variability in system utilisation. In addition, two Dutch sites, one coastal and one inland, were studied in greater detail to analyse annual operational behaviour, power electronics impact, conversion efficiency, hydrogen yield, and degradation patterns. Finally, lifetime simulations over 20 years were performed to evaluate system economics under varying electrolyser sizes, three cost scenarios, and two discount rates. Results showed that optimal electrolyser sizing is highly location-dependent and influenced by design objectives: the size yielding the highest hydrogen production is not necessarily the one that results in the lowest LCOH. In fact, the LCOH-optimal size was consistently smaller. Moreover, cost scenarios affected optimal sizing, with higher capital costs favouring slightly larger systems to offset investment through increased hydrogen output.
Time-resolved modelling further revealed the importance of minimum load constraints (to avoid gas crossover) and degradation effects, which influence system utilisation and stack replacement timing. While lifetime hydrogen production estimates from the dynamic model did not deviate significantly from those based on static assumptions, the dynamic approach enabled more accurate performance forecasting and degradation tracking. This research highlights the necessity of time-resolved modelling for techno-economic assessment of wind-powered hydrogen systems. The developed framework provides a comprehensive foundation for future optimisation studies and supports more accurate design and investment decisions for renewable hydrogen deployment. ... Read more

Catalytic methane pyrolysis (CMP) is a potential method to produce clean hydrogen without direct COx emissions, but is not cost-competitive with current hydrogen production techniques yet. A strategy to increase the cost-competitiveness is to purify and sell the nanocarbon by-product. This paper outlines the process design, modelling and analysis of purifying carbon nanofibre (CNF), produced by CMP, with acid leaching.

CNF produced by CMP with a Ni-SiO2 catalyst was used for this study and initially contains 4700 ppm of nickel. The baseline scenario of the designed process has a production capacity of 20,000 tonnes per year and includes acid leaching with HCl, liquid removal and post-treatment steps. The techno-economic analysis showed a Levelized Cost of Purification (LCOP) of 10.09 $/kg and a Net Present Value (NPV) of 1.48 billion $ for the baseline scenario. The process is very profitable due to the assumed high selling price of 25 $/kg. However, the conversion of nickel is only equal to 5.15 %, leaving 4460 ppm of nickel in the CNF product while the desired nickel content is below 300 ppm. The low conversion indicates that the quality of the CNF product is barely improved and that the assumed selling price is probably too high. The acid leaching kinetics are modelled using literature on acid leaching with HCl of nickel from a Ni-Al2O3 spent catalyst. Acid leaching experiments of nickel from CNF with H2SO4 showed a more positive average nickel conversion of 70.9 % so far. The leaching kinetics still have to be determined for a variety of acids and will be necessary to model the leaching more accurately.

Sensitivity analyses showed that the impact of the acid waste price on the LCOP was the largest of the economic parameters with ±2.5 $/kg variation, followed by the electricity price. The acid feed price also had a significant impact on the LCOP. The high impact of the acid waste and feed price showed a need for the implementation of an acid recycle. A Monte Carlo analysis indicated a robust process design under economic uncertainties. The mean of the LCOP was equal to 10.12 $/kg and the standard deviation was equal to 0.90 $/kg.

Two improved design cases of the baseline scenario are presented. The first includes changes to the reactor temperature, residence time, acid molarity, ratio of CNF feed to acid feed and the inclusion of an acid recycle. The conversion is improved to 61.04 % with an LCOP of 24.68 $/kg. The second design case builds upon the first and includes further changes to the residence time and ratio of CNF feed to acid feed. Furthermore, the reactor setup is changed to three reactors placed in series for the second design case. The conversion is increased to 93.95 %, leaving only 285.66 ppm of nickel in the CNF product. The LCOP is equal to 21.84 $/kg, but a total of 90 reactors are required. While the process is profitable and the nickel content in the product is below 300 ppm, questions arise whether the second improved design is practical. ... Read more

The present work investigates the valorization of wine industry residues through the production of advanced biofuels, focusing on grape pomace as a representative lignocellulosic feedstock. The study aims to assess the technical and economic feasibility of converting this residue into liquid fuels via hydrothermal liquefaction (HTL)and to compareits performance against the bioethanol basedpathway currently implemented by Destilerías y Biorefinerías Zambrana, S.A. in the Basque Country. ... Read more

The increasing dependence on fossil fuels for energy and chemicals has caused a significant rise in atmospheric CO2 concentrations, leading to global warming and ecological imbalances. Electrochemical CO2 reduction (CO2R) has emerged as a promising technology to mitigate CO2 emissions while converting it into valuable chemicals and fuels, such as ethylene, ethanol, and acetic acid. With its compatibility with renewable energy sources, moderate operating conditions, and potential for high selectivity, CO2R is positioned as a key player in the transition toward a carbon-neutral economy. However, challenges such as mass transfer limitations, impurities in industrial CO2 feedstocks, and economic feasibility hinder its large-scale implementation. This thesis aims to address these challenges through experimental studies, process design, and techno-economic analysis. The combined findings also reveal key limitations that must be addressed for large-scale deployment. ... Read more

The viability of hydrogen as a sustainable energy carrier is significantly affected by the costs linked to its transportation and storage. Transporting and storing hydrogen in its liquid form offers remarkable advantages, as liquid hydrogen has unique characteristics, including lower weight and volume, as well as a higher energy content compared to gaseous hydrogen. However, current industrial hydrogen liquefaction processes face significant challenges related to efficiency and cost, with a second-law efficiency of less than 25% and costs ranging from 2.5-3.0 US$/kgLH2.

Large energy storage systems can address the issue of energy demand fluctuations in renewable energy grids by storing excess energy produced and compensating for any energy shortfalls. The development of hydrogen energy storage systems will thus support the advancement and increased utilization of renewable energy sources. The demand for liquid hydrogen is expected to rise in the near future, driven by environmentally friendly applications and use in mobility sector. As a result, large-scale hydrogen liquefaction (LHL) plants will become increasingly important in the clean energy efficient hydrogen supply chain.

This thesis aims to develop a Large-scale Hydrogen Liquefaction (LHL) plant based on the Brayton cycle concept of 86 TPD. The plant is modeled using Aspen HYSYS, with preliminary designs for key equipment—such as compressors, turbines, and plate-fin heat exchangers, ensuring compatibility with current technological constraints. State properties of the fluid used in the design of compressors and turbine equipment were obtained from REFPROP software, utilizing the Peng-Robinson Equation of State (EOS). For the design of plate-fin heat exchangers, Aspen Exchanger Design and Rating (EDR) was employed. Subsequently, a techno-economic analysis was conducted using the Aspen Process Economic Analyzer (APEA) to estimate both capital and operating expenditures, based on the process simulation model and preliminary equipment designs.

The specific energy consumption (SEC) of the plant, accounting for power recovery from turbine shafts, is determined to be 6.9025 kWh/kgLH2. The plant’s exergy efficiency is calculated at 43.665%, and the specific liquefaction power is found to be 3.014 kWh/kgLH2. Assuming an electricity price of 0.1 €/kWh, modelled 86 TPD Brayton-cycle concept yielded specific liquefaction cost (SLC) of 1.57 €/kgLH2.

A sensitivity analysis was conducted to identify the parameters that influence the specific liquefaction cost (SLC) of the plant. The analysis focused on two key parameters: 1) electricity price and 2) feed pressure. The results reveal that fluctuations in electricity prices have a substantial impact on the plant’s economic performance. Additionally, the analysis indicates that the plant’s efficiency and economic viability are significantly sensitive to decreases in feed hydrogen pressure. ... Read more