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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Carbon capture and storage (CCS) requires captured CO2 to be purified and dried (i.e. conditioned) before it can be compressed or liquefied for transport, yet the adsorption dryers that remove water are routinely represented in process models as simplified separators with a fixed removal efficiency. Their regeneration energy, a contributor to the conditioning penalty that this study sets out to quantify, is left uncharacterised, because systematic dynamic data for commercial desiccants under CO2-conditioning conditions are largely absent from the open literature. This gap prevents reliable process design and, in particular, hides where the energy-optimal operating window of the dryer actually lies.

This thesis characterises two commercial adsorbents, silica gel and zeolite 4A, and integrates validated dryer models into complete conditioning chains that deliver a liquid or supercritical CO2 end product. Zeolite 4A is the industrial standard for this duty and, by virtue of its stronger affinity for water, is expected to outperform silica gel; it does so, however, at the cost of more demanding regeneration conditions, whereas silica gel regenerates at much lower temperatures and can potentially draw on low-grade waste heat. This raises the central question of whether, over the long run and at cyclic steady state, the milder regeneration requirements of silica gel make it the more efficient choice, or whether zeolite 4A retains its advantage.

Breakthrough experiments were carried out on a mixSorb L dynamic sorption analyser at pressures up to 10 bar across adsorption and regeneration temperatures, with a dedicated CO2-carrier run to bound competitive adsorption. Toth and dual-site Langmuir isotherms and LDF mass-transfer coefficients were fitted to the data in Python and validated in a cyclic bed model in Aspen Adsorption, which was then implemented in Aspen Plus flowsheets of three transport routes: subcritical liquefaction at 16 bar, low-pressure ship transport at 8 bar, and supercritical pipeline transport at 150 bar.

The results give explicit design rules: adsorb cold and at pressure, treat the dryer as a polishing step on a stream already dried by compression with intercooling, and regenerate hot with a minimal purge. Measuring the true working capacity and kinetics shows standard literature practice to be heavily oversized: a 2% purge suffices where 10% is customary, cutting dryer-loop energy fivefold, from 1.6 to 0.3 kWh/t, in the 16 bar case. At the process scale, the transport route dominates: roughly 30 kWh/t separates the chains, against 4 kWh/t or less between sorbents within a chain. Silica gel proves a genuine alternative to molecular sieves: where it can occupy the same downstream position as the zeolite, it matches its specific energy consumption while regenerating at less than half the temperature, so low-grade waste heat suffices. Its penalties in the other two routes are mechanical, set by the pressure tolerance of the pellet batch rather than by thermodynamics, which suggests a pressure-qualified grade would reduce the material choice to cost rather than energy. ... Read more

The market for light olefins—ethylene and propylene—is forecast to nearly quadruple between 2025 and 2050, yet remains heavily dependent on fossil feedstocks. This work presents an alternative route to synthesis polymer-grade light olefins, based on the gasification of commercial bio-oil and the use of electrolytic hydrogen within the Dutch electricity context. The methodology comprises: (1) TOPSIS-based selection among ten bio-oil alternatives against twelve criteria spanning physical, chemical, and economic aspects; (2) synthesis-route selection on the basis of commercial maturity; (3) flowsheet development in Aspen Plus™ V14 under primarily financial-benefit-driven optimisation; (4) a pinch-analysis heat-integration strategy to minimise the total annualised capital and utility cost; (5) techno-economic assessment using selected key performance indicators; and (6) optimisation of hydrogen generation and storage in response to the dynamic Dutch electricity price. The biomass-conversion literature has suggested bio-oil as an attractive intermediate feedstock for higher-value product synthesis; process-systems modelling of light-olefin production from non-fossil resources, however, has not yet addressed commercially produced bio-oil. This work addresses that gap.

The TOPSIS analysis identifies the commercial bio-oil produced at the Aracruz plant in Brazil as the most suitable feedstock, with a relative closeness coefficient of 0.828. The conceptual plant gasifies 100 000 t/yr of this bio-oil under autothermal conditions; the syngas stoichiometric number is then adjusted with electrolytic hydrogen from a twelve-stack, 58 MW alkaline water electrolyser to synthesise 94 181 t/yr of grade-AA methanol, which is converted via the DMTO-III process to 20 387 t/yr of polymer-grade ethylene and 14 581 t/yr of polymer-grade propylene. The plant adopts two process features not yet found in commercial practice: the use of electrolytic hydrogen as a stripping agent to remove dissolved CO₂ from the raw methanol, and membrane separators for the C₂ and C₃ olefin–paraffin separations as an alternative to the incumbent cryogenic separation. Heat integration lowers the annual utility cost from almost €6 million to −€0.78 million.

The principal performance indicators are: a light-olefin mass yield of 35% relative to the bio-oil feed; a carbon conversion of 81%; a conversion of 35% of the hydrogen input into light olefins; and energy and exergy efficiencies of 47.1% and 49%, respectively. The plant requires €474.6 million in total capital investment and €125.7 million in annual operating cost, while its annual revenue covers only 44% of the annual cost, corresponding to an annual loss of €70.3 million. This loss has two distinct origins—upstream, the high cost of bio-oil and electricity; and downstream, the low revenue from ethylene and propylene sales.

Adopting an IRR of 10% as the threshold for financial feasibility, a sensitivity analysis shows that reducing the bio-oil and electricity prices simultaneously to zero—i.e. virtually free bio-oil and electricity—yields an IRR of only 7.59%, which renders the plant financially unattractive. On the product side, the ethylene and propylene prices would need to rise by 250% and 500%, respectively, to reach financial feasibility, implying a reliance on the price premium for non-fossil-derived products. Finally, equipping the plant with hydrogen storage to limit its exposure to high electricity prices, and optimising accordingly, sets the electrolyser and storage capacities to 62.6 MW and 3393 kg; this configuration nonetheless lowers the annual electricity cost by only 7%, insufficient to render the plant financially viable. ... Read more

Light olefins, namely ethylene, propylene, and 1-butene, are essential building blocks of the chemical industry, yet their production remains almost entirely reliant on fossil feedstocks through steam cracking and fluid catalytic cracking. As the chemical sector seeks to reduce its carbon footprint, the direct conversion of captured CO₂ into light olefins via Fischer–Tropsch synthesis (CO₂-FT) has emerged as a promising Power-to-X pathway. Despite its potential, comprehensive process-level assessments integrating reactor modeling, process design, energy integration, and techno-economic analysis remain limited.

This thesis develops and evaluates two process configurations for the production of C₂–C₄ olefins from direct air-captured CO₂ and renewable hydrogen using Aspen Plus. The base configuration consists of a kinetic iron-based CO₂-FT reactor model integrated with a complete product recovery train comprising CO₂ removal and cryogenic separation to produce polymer-grade ethylene and propylene together with chemical-grade 1-butene. A second configuration extends the process by incorporating a downstream steam-cracking unit to convert the C₅–C₁₀ Fischer–Tropsch products into additional light olefins. Both configurations are evaluated within a consistent Power-to-X framework through process simulation, pinch-based heat integration, and techno-economic assessment.

The developed CO₂-FT reactor model operates at an optimal temperature of 350°C, a pressure of 15 bar, a H₂/CO₂ molar ratio of 3, and a chain-growth probability of α = 0.6, achieving a single-pass CO₂ conversion of 39%. The FT-only configuration produces 10.28 t/h of light olefins with a carbon efficiency of 43%, whereas integration of the steam-cracking section increases olefin production to 13.49 t/h and improves carbon efficiency to 56%, while reducing the specific CO₂ consumption from 7.38 to 5.70 tCO₂ per tonne of product. Following heat integration, the FT-only and FT-cracking configurations achieve overall fuel energy efficiencies of 73% and 58%, respectively, corresponding to light-olefin energy efficiencies of 31% and 40%.

The techno-economic assessment indicates that integrating steam cracking decreases the net light olefin production cost from €8.02/kg to €7.03/kg, representing a 12.3% reduction primarily through improved carbon utilization and increased product yield. In both configurations, renewable hydrogen dominates the operating expenditure, and sensitivity analysis identifies hydrogen price as the principal economic driver, substantially outweighing the influence of electricity and CO₂ prices. Although the calculated production costs remain significantly higher than those of conventional fossil-based olefin production, the results demonstrate that economic competitiveness is primarily constrained by hydrogen costs and reactor selectivity.

Overall, this work provides an integrated process design and evaluation of direct CO₂-to-olefins production, combining detailed reactor modelling, process simulation, heat integration, and techno-economic analysis within a unified framework. The results demonstrate that downstream steam-cracking integration significantly enhances carbon utilization and economic performance, while identifying hydrogen cost reduction and improved Fischer–Tropsch catalyst selectivity as the key priorities for the industrial deployment of defossilised olefin production.
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Low-temperature electrochemical CO₂ conversion has gained growing attention as a potential route towards a more circular and electrified chemical industry, particularly for producing carbon-based chemicals under mild operating conditions. Most progress remains focused on electrochemical reactor performance or lower-order products, while industrial feasibility also depends on process integration, separation, recycle design, purification, and economic performance. It therefore remains unclear whether coupling CO₂ electrolysis with electrocarboxylation can provide feasible pathways to higher-value circular chemicals at industrial scale.

This study assessed the techno-economic feasibility of producing ethylene carbonate (EC) and succinic acid (SA) via direct and tandem low-temperature electrochemical CO₂ conversion pathways in an industrial-scale plant in North-West Europe. A structured screening framework compared CO₂-derived products and pathway concepts using complete CO₂ utilisation, technological readiness, continuous operation, electricity demand, economic attractiveness, strategic fit, and sustainability by design. This led to the selection of EC as the strongest near-term product candidate and SA as a complementary high-value case, with ethylene and carbon monoxide (CO) retained as key intermediates. Four routes were then defined: direct and tandem pathways to EC, and direct and tandem pathways to SA.

The routes were developed as process flow diagrams and implemented as steady-state Aspen Plus models, including electrolysers, electrocarboxylation cells, gas and liquid separation sections, recycle structures, and final purification. The resulting mass and energy balances were used in a techno-economic assessment (TEA), with net present value (NPV) as the main feasibility indicator. Under the base-case assumptions, none of the four routes reached economic feasibility, as expected for early-stage low-temperature CO₂ electrolysis and electrocarboxylation at industrial scale. This result should be interpreted as a current feasibility benchmark rather than as a rejection of the route concepts. Route 1, the direct pathway to EC, showed the strongest process-design and mass-balance performance, while Route 2, the tandem pathway to EC, was the strongest near-term techno-economic option. The SA routes showed higher product-revenue potential and the strongest optimistic-case upside, but were constrained by dry-solvent operation and losses, raw material demand, product purification, and downstream separation uncertainty.

The case analysis showed that technology improvements alone were insufficient, whereas improved economic conditions had a stronger effect and the combined optimistic case made all four routes economically feasible. Overall, the selected routes are technically credible early-stage pathways, but not yet techno-economically feasible under current base-case assumptions in North-West Europe. The main bottlenecks were electrochemical cost, economic exposure, dry-solvent demand, product purification uncertainty, and separation and recycle uncertainty. Future research and development should therefore prioritise integrated electrochemical and separation improvements, focusing on lower stack cost, lower cell voltage, stable high-current operation, dry-solvent recovery, electrolyte-compatible product purification, recycle validation, and realistic North-West European market conditions. ... 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 increased emission of carbon dioxide (CO2) derived from the use of fossil fuels has a major in fluence on global warming and climate change. In order to reduce these emissions, carbon dioxide can be capture from the air and converted into useful products. This can be done for example using the Sabatier reaction, in which CO2 and hydrogen (H2) are converted into methane (CH4) and water (H2O). This reaction is reversible and it is therefore desirable to adsorb the water to shift the reaction equilibrium to the product side, applying Le Chatelier’s principle. Water adsorption is achieved using zeolites, which are hydrated minerals with an open crystal structure. There are many zeolite types, both natural and artificial. This study will focus on determining which zeolite type is the most suitable for water adsorption in the Sabatier reaction at relevant process circumstances and which properties account for this superior performance. ... Read more

With increasing climatic changes due to greenhouse gas accumulation, there is an urgent need for sustainability improvements across many sectors of society, including chemicals manufacturing. One ubiquitous chemical feedstock in need of a cleaner production method is hydrogen (H2), commonly produced by the environmentally unfriendly steam-methane reforming reaction. The production of H2 could be made far more sustainable by instead using alkaline water electrolysis powered by renewable energy, but the process economics are unfavorable, with so-called “green” hydrogen from water electrolysis costing much more than less sustainable “gray” hydrogen. The majority of the costs of green hydrogen arise from the balance of plant surrounding the electrolyzer, and recent research has made only incremental progress in improving the efficiency of either the balance of plant or the electrolyzer itself. Driving down the cost of green hydrogen will require a more innovative approach. Electrolysis splits water into high-value H2 but also low-value oxygen (O2). A creative approach to lowering costs would be to replace the anodic reaction producing low-value O2 with a reaction to produce high-value hydrogen peroxide (H2O2). The H2O2 could then be separated and sold, offsetting the higher cost of the green hydrogen produced at the cathode. This method of paired electrolysis to simultaneously produce H2 and H2O2 has been the subject of much study with respect to its electrochemistry, but very little with regards to the electrochemical engineering. If we are to scale this reaction and offset the cost of green hydrogen by co-production of a valuable side product, we also need to understand the electrochemical engineering of the reaction, from the scale of operational devices to the complete process plant.... ... Read more

This study concerns the dynamic operation of methanol steam reforming in fixed bed reactors for shipboard hydrogen production. The work is motivated by the need to reduce greenhouse gas emissions and harmful exhaust pollutants from the maritime sector, while also addressing the practical difficulty of storing hydrogen directly on board ships. Methanol is considered a promising alternative fuel and hydrogen carrier because it is liquid under ambient conditions, has relatively high energy density, is already handled at industrial scale, and can be used both in combustion-based transition technologies and in future fuel cell systems. In this context, methanol reforming offers a route to produce hydrogen on demand, avoiding some of the storage challenges associated with compressed or cryogenic hydrogen.

The dissertation focuses specifically on methanol steam reforming for polymer electrolyte membrane fuel cell systems. This reforming route is attractive because it provides a high hydrogen yield and comparatively low carbon monoxide selectivity. This is important because PEM fuel cells require pure hydrogen feed. The selected reactor type is a fixed randomly packed catalytic bed. This a configuration is widely used and commercially relevant for reforming applications.

The shipboard operation introduces requirements that are not prioritized in conventional land-based chemical plants. A ship power system must respond to changing loads, and therefore the reformer must be understood in transient operation, in addition to steady state operation. The central question of this dissertation is how fixed-bed methanol reformers behave dynamically, what limits their response time, and what modelling or experimental tools are needed for their reliable analysis.

The second chapter examines the broader problem of dynamic operation in fixed bed reactors. It shows that dynamic behaviour can arise from several motivations, including process flexibility, periodic operation, and on-demand production. These different cases require different performance metrics, modelling approaches, and measurement strategies. The dissertation points how dynamic reactor analysis cannot simply reuse steady state design priorities. Moreover, the objective of the transient analysis must first be clearly defined in each case. This chapter also reviews available numerical modelling approaches and analytical techniques for measuring changing gas compositions. A key point is that models of higher fidelity than 1D are often necessary for dynamic analysis, but not always readily available or computationally convenient. Likewise, transient experiments require instruments with suitable sampling rates, and often a combination of analytical techniques is more likely than using a single method.

To demonstrate the importance of model fidelity, this study develops and applies a dynamic 2D fixed bed reactor model for methanol steam reforming. A comparison with a 1D plug flow model shows that models may agree reasonably well at steady state but differ during transients, especially when predicting local temperature fields and species selectivity. This is important because transient CO formation and hydrogen production are directly relevant to operation and control in fuel cell systems. The 2D model therefore becomes the central tool for the later chapters, which focus on origins of reformer response time.

The second major part of the dissertation, starting with chapter 3, investigates the internal heat transfer dynamics of the fixed bed reactor. Methanol steam reforming is endothermic, so reactor performance depends strongly on heat transport from the reactor wall into the catalyst bed. For this work, the model only deals with the internal packed bed behaviour by imposing changes directly in wall temperature and reactant throughput. Thus the limitations of the external heating system influence is excluded. This allows for an estimation of a theoretical lower limit for the reactor transient time. The results show that, for typical tube diameters of 2-3 cm, internal heat and mass transfer lead to transient times of up to about one minute. This suggests that internal radial heat transfer alone is unlikely to explain the much slower response times often associated with practical methanol reformer systems. The packed bed may only amplify slow external heat supply changes, but it is probably not the dominant source of long load-change durations.

Chapter 4 combines experiments and modelling to study external heat transfer effects and validate the dynamic reactor model. A laboratory fixed bed methanol steam reformer is used for gathering steady state and transient data, mainly consisting of internal bed temperatures and reformate carbon monoxide content. The model is adapted to include all detected experimental non-uniformities and heat transfer imperfections. This enables a complete comparison between simulated and measured reactor behaviour. The results show that the model can capture the main dynamic trends, but they also reveal a strong influence of practical heating details during transient operation. Important external factors include the heat capacity of the reactor and supporting structure, axial heat loss profiles, non-uniform axial heat supply, and instability in inlet reactant temperature. Among these, the heat capacity of the reactor assembly is especially influential because it stores and releases heat during load changes, thereby prolonging the transient response even in a relatively small and well-insulated laboratory reactor.

Overall, the conclusions of this study is that dynamic shipboard methanol reformer design requires a broader approach than conventional steady state reactor sizing. A comprehensive analysis includes definition of the cause and purpose of dynamic operation, selection of a model with sufficient spatial and temporal fidelity, and finally the use analytical instruments fast enough to validate transient predictions. From this study it is also concluded that the intrinsic internal dynamics of typical fixed bed reformer tubes are relatively fast compared with the load change times reported for practical systems. Therefore, future improvements in transient performance should focus strongly on the external heating arrangement, reactor thermal mass, heat integration strategy, and system level control. These findings are relevant not only for methanol reforming but also for other shipboard chemical reactors that may become part of future low emission maritime energy systems. ... Read more

Fluidized beds for large-scale biomass gasification are among the most efficient and widely used reactor types for converting solid biomass into syngas or for biofuel production via Fischer-Tropsch or methanol synthesis. Several fluidized bed designs have focused primarily on conventional geometries, such as cylindrical and conical beds, typically with a distributor plate at the bottom. Many studies have been devoted to correlating the interplay of hydrodynamics and heat & mass transfer in fluidized beds, both from an experimental and computational point of view. Several direct correlations for full-scale reactors already exist. These are typically
only applicable to conventional reactor geometries. There is, though, a dearth of information on how other methods of fluidization, such as using nozzles/orifices at different locations within the bed, influence fluidization and the interplay between the gas and the solid phases. It is therefore needed to provide a better understanding of the physics in industrial-scale fluidized bed reactors by creating lumped models that sit between single correlations for full fluidized beds and detailed CFD simulations, and that can provide predictions in a matter of minutes rather than days or weeks.

The main aim of this research is to gain insight into the hydrodynamics of a novel conical, jet-spouted, bubbling fluidized bed using different bed materials, namely corn grits (polenta) and porous alumina (widely used in industries as a catalyst support material). The novel idea described in this thesis is to develop a well-validated model that can provide deeper insights into the hydrodynamics of such less-studied bed configurations, thus helping to improve their scaling and design. Furthermore, this can be used to improve lumped modelling work in future studies.

While lumped models are used extensively in the literature, they are also a source of confusion, especially for people entering the field who are looking for relatively fast models, because the term ‘lumped model’ has different meanings. Chapter 1 of this thesis, therefore, discusses the various lumped models available in the literature for fluidized bed reactors and critically analyzes the developments necessary to apply them to high-temperature processes.

In recent decades, Computational Fluid Dynamics (CFD) has become a popular tool for studying fluidized beds. The two-fluid model is one of the most popular modelling approaches, but it is unclear how reliable this type of modelling is for more challenging non-standard geometries. Hence, in Chapter 2, we delve into a numerical study of a novel, conical, multi-jet fluidized bed, with three different solvers used to predict the hydrodynamics. All three solvers use the same two-fluid model, the same parameters, and the same computational mesh, yet lead to different results, especially in the lower bed regions, highlighting the effects of differences in numerical discretization approaches. These differences indicate how these approaches preserve momentum injection, capture centerline spouting, and stabilize dense-phase transport. A good agreement of a solver with experiments on a simple, standard (cylindrical/conical with a distributor plate for fluidization) geometry does not guarantee agreement when the same solver is applied to a more complex geometry. This reinstates the well-known importance of experimental validation.

Experimental validation of the dynamics in such complex industrial geometries is often a challenge due to operational and computational limitations. Therefore, scaling down such beds becomes crucial. Hence, in Chapter 3, a scaled-down reactor is made from the scaling analysis of the larger reactor described in Chapter 2. In this chapter, three-dimensional CFD simulations of the reactor bed under various operating conditions using ANSYS Fluent are performed and validated using novel experimental techniques previously unexplored for bubbling fluidized beds, such as wire mesh sensors (WMS) and gamma-ray computed tomography (GCT). Simulations and experiments are performed for different operating conditions. The comparisons show good agreement for different physical parameters for different flow rates. However, some simulation cases show significant deviations from experiments, even for numerically better-resolved computational grids. While the results of a novel design of experiments for maldistribution also show good agreement with experiments performed, it is still too early to decide how reliable the measurements are because of experimental uncertainties and numerical inaccuracies.

To provide a good characterization of the hydrodynamics inside novel configurations and explore the uncertainties involved in them, two experimental methods in such novel configurations, WMS and GCT, are compared to each other in Chapter 4. These are used to obtain the time-resolved void fraction distribution. Used for both static and dynamic experiments, representative of different fluidization regimes, two bed-filling heights are compared. The results demonstrate the potential use of WMS in gas-solid flows and its capability to determine phase distribution.

Once a well-validated numerical model is obtained from novel experimental methods, validated with each other, the numerical and experimental data can be provided as input to parametrize or train a lumped model. Chapter 5 explores this for the novel fluidized bed configuration described in Chapter 2, using pressure sensor data obtained from experiments. This is done using an Artificial Neural Network (ANN), and subsequently for a Gaussian Process Regression (GPR). The idea is to show how Machine Learning (ML) models can be trained using data and how this could be applied to make predictions much faster than with experiments or CFD
simulations.

Lastly, Chapter 6 discusses a valorization study for plastic waste gasification conducted at KNUST, Ghana. Plastic waste has been handled in Ghana largely through the involvement of local governments and private-sector authorities. Many policies have been enacted in West Africa for plastic waste management. However, despite many policies being passed in the last three decades, both at the national and urban levels, there is still a strong focus on the inability to develop rural areas. Several processes, from collection to recycling, are discussed to examine the plastic waste collected and which processes use the most energy. It was observed that 15% of plastic waste is removed from landfills for further processing (pelletization, shredding, etc.). However, this remains a key hotspot in a technology chain in which plastics could be further utilized to produce high-value end products, such
as liquid or gaseous fuels. Furthermore, a quantitative assessment of local waste management infrastructure reveals that mechanical recycling, although operational, entails a 15% material loss rate during pelletization and relies heavily on a thermally
dominated electricity grid. These factors introduce a latent carbon footprint into the recycling value chain. Future strategies must therefore prioritize technologies capable of valorizing the non-recyclable fractions quantified in this study via thermochemical conversion, for example, via fluidized-bed gasification. ... Read more

The transition toward a circular economy necessitates efficient energy recovery technologies for biomass and plastic waste. Fluidized bed reactors (FBRs) provide excellent gas–solid mixing and thermal efficiency; however, their scale-up is often limited by complex hydrodynamics. This study examines the hydrodynamics of a scaled-down tapered bubbling fluidized bed (BFB) through combined experimental and numerical analyses. A scaling methodology based on Glicksman’s inertial law was employed to design a small-scale reactor that replicates the flow characteristics of a large facility. Experimental investigations using γ-ray computed tomography (CT) and radiographic scans were conducted to quantify solid fraction distributions and visualize bed expansion under varying gas velocities, revealing axial variations in particle-phase packing and gas–solid interactions. Parallel computational fluid dynamics (CFD) simulations, carried out in Ansys Fluent using a two-fluid Euler–Euler framework with the kinetic theory of granular flow (KTGF), successfully captured the onset of fluidization and the
evolution of gas inlet jets along the axial height. Nonetheless, extending the simulation runs to longer physical times would provide deeper insights into the underlying flow physics. ... Read more

Adipic acid (AA), a critical precursor for nylon-6,6 and other industrial applications, is currently produced at over 3 million tons annually, with projected revenues reaching $6 billion by 2030. However, an alternative to the dominant industrial process, accounting for 95% of global production, has been sought due to inefficiency and significant environmental impact. This conventional route relies on petroleum-derived benzene as a feedstock and involves multiple hydrogenation and oxidation steps, notably utilizing nitric acid, which produces stoichiometric amounts of nitrous oxide (N₂O), a potent greenhouse gas. Furthermore, the high energy feedstocks like benzene, hydrogen, and nitric acid contribute significantly to Scope 3 emissions.

Given these concerns, there is a strong incentive to develop more energy-efficient and environmentally suitable processes. This thesis addresses the gap in comprehensive techno-economic assessments of emerging alternatives, which often overlook practical implementation challenges such as downstream separation, feedstock pretreatment, and overall carbon footprint.

The overarching research question guiding this study is: "How do various electrochemical based alternatives to current AA production compare on an economic and emissions basis from a process systems modeling prospective?". To this end, two promising alternatives were selected for evaluation through the key performance indicators of; profitability in the form of minimum selling price (MSP), emissions based on kg CO₂, and material efficiency based on the excess ratio of theoretical main feedstock to actual main feedstock.

The first modeled process was that of the conventional route. This was done to ensure a consistent feedstock price component in the final adipic acid cost across all assessed production methods, thereby providing valuable validation for modeling assumptions. Furthermore, it serves as a benchmark for comparing the economic and emissions performance of various electrochemical-based alternatives, offering insights into their relative strengths and weaknesses. The results attained were consistent with those of literature, with a minimum selling price of $1.58/kg

The first alternative route employs an electrocatalytic oxidation cell to replace the nitric acid oxidation step of the conventional process. Experimental work of previous researchers was used to create an approximate model of the cell and the electrodialyzer used for the recovery of KOH electrolyte. This was implemented within Apsen Plus along with upstream and downstream processing. The resulting model and subsequent TEA predicted an adipic acid price of $2.33/kg or a 45% increase over the results of the conventional route. However, assuming the use of renewable electricity, the CO₂ equivalent emissions dramatically reduced by half when compared to the conventional process.

The second alternative was the use of biomass based fermentation and subsequent electrochemical oxidation to produce a adipic acid alternative of similar value to industry. Once again, the experimental work of previous researchers was used to predict a final minimum selling price of around $3.97/kg; however, these results are highly susceptible to variations in input parameters. Both alternatives showed lower emissions when compared to the conventional process. ... Read more

This thesis investigates the techno-economic feasibility of an integrated process that captures post-combustion CO₂ and converts it into carbon monoxide (CO) via electrochemical reduction powered by renewable electricity. The approach is intended to reduce the high regeneration energy of conventional amine-based capture while producing a valuable chemical feedstock. A hybrid solvent of 0.5 M MEA in a choline chloride–ethylene glycol deep eutectic mixture was evaluated, showing comparable capture performance to aqueous MEA and a lower heat of absorption (–59.8 kJ/mol), indicating potential energy savings.

Electrolysis was assessed under worst, baseline, and best-case scenarios with current densities between 100 and 300 mA/cm², voltages of 2.5–4 V, and CO faradaic efficiencies of 20–60%. Projected annual CO production ranged from 69.8 to 174.4 kt, with energy efficiencies of 10–48%. A semi-empirical vapor–liquid equilibrium model was applied, achieving high accuracy (R² > 99%, AARD < 3%).

Economic analysis shows that none of the scenarios achieve positive net present value at current market prices (CO: €0.64/kg, H₂: €4/kg). Electricity accounts for about 98% of operating costs, making the system highly sensitive to power price and product value. The best case becomes feasible at €0.06/kWh electricity or €0.96/kg CO, while the baseline requires €1.43/kg CO. The worst case remains unviable under all tested conditions.

In conclusion, the system demonstrates strong technical potential but limited economic feasibility under present conditions. Viability depends on access to low-cost renewable electricity, improved electrolyzer efficiency, and supportive policy or market frameworks. Further research on solvent properties, process integration, and pilot-scale demonstrations is recommended to advance this concept toward industrial application. ... Read more

As global regulations and International Maritime Organization (IMO) targets intensify, the maritime sector faces increasing pressure for decarbonization, reduction of greenhouse gas emissions and improvement of energy efficiency. Conventional marine auxiliary power systems, typically marine diesel generators, operate at low electrical efficiencies (25–45 %) and produce significant emissions. Bio-methanol, a renewable liquid fuel produced from biomass or renewable electricity, offers an attractive alternative for the yachting sector due to its high energy density, ambient-condition storage, compatibility with existing infrastructure, and ability to yield hydrogen-rich reformate gas for fuel cells. However, integrating methanol steam reforming (MSR) with solid oxide fuel cells (SOFCs) in marine environments remains largely unexplored in the literature.

This thesis investigates the design and modeling of an integrated bio-methanol steam reforming (MSR)–solid oxide fuel cell (SOFC)–Organic Rankine Cycle (ORC) system for a Feadship superyacht, developed in Aspen Plus. The bio-methanol reformer supplies hydrogen-rich gas to the SOFC stack, which subsequently drives both electric generation and heat recovery. Component integration includes thermal coupling between the MSR reactor, the afterburner, preheaters, and the ORC. The system meets auxiliary power demands from 225 kW to 325 kW and is modeled at three representative auxiliary power levels: 225 kW, 275 kW, and 325 kW. Motivated by the need to optimize both system efficiency and heat management, this work addresses a critical research gap in the techno-economic assessment of renewable methanol-based SOFC power systems for maritime applications.

The model incorporates MSR kinetics, SOFC electrochemistry—including activation, ohmic, and concentration losses—and waste heat recovery. Iterative SOFC area sizing and heat integration strategies are developed and validated, while an analysis of the operational expenditure of the system is also included. Sensitivity analyses investigate the influence of SOFC fuel utilization and operating temperature on the system’s performance and consumption of resources. Analyzing key performance indicators, such as electrical generation efficiency and combined heat and power (CHP) efficiency, under different load conditions, has revealed that at the 225 kW partial-load condition, the system achieves a maximum electrical generation efficiency of 57.2% and a CHP efficiency of 79.4%, significantly outperforming conventional marine diesel generators. At the intermediate 275 kW load, the system reaches an electrical generation efficiency of 54.3% and a CHP efficiency of 71.5%. At full load (325 kW), the corresponding efficiencies are equal to 52.0% and 65.9% respectively.

The results confirm the technical feasibility of bio-methanol-fueled SOFC systems for superyacht applications and demonstrate their potential for significant efficiency gains. The developed model provides a foundation for future optimization, hybridization strategies, and onboard integration, supporting sustainable decarbonization in the maritime sector.
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As the energy demand is growing rapidly across the globe due to industrialization and higher living standards, along with the depletion of fossil fuel reserves and the effect of climate change more evident than ever [1], there is an urgent need to transition to sustainable methods of energy production. Among various sustainable energy alternatives, bio-energy is expected to play a significant role in the energy transition. Gasification constitutes a thermochemical way of converting carbonaceous feedstock into useful energy. When implemented with biogenic or waste-derived fuels, gasification can provide a promising sustainable energy solution, while it can also simultaneously deal with the landfill waste problem when utilizing feedstocks like Solid Recovered Fuel (SRF). Despite the fact that gasification of coal is often featured in literature, the use of biomass or SRF in gasification practices is still limited. Specific areas like the handling of tars, detailed modeling of the hydrodynamics in the fluidized bed and the freeboard of the reactor, as well as the implementation of chemical kinetics specific to wastederived feedstocks remain underexplored in literature. Furthermore, many studies completely ignore the freeboard region in their models, where critical reactions still occur. Therefore, the aforementioned research gaps are aimed to be answered to in the current thesis project. The purpose of this Master Thesis was to study bubbling fluidized bed gasification and develop a model of its processes using the Python programming language. The open-source software ”Cantera” was used [2], which contains tools for dealing with reaction kinetics, thermodynamics and transport phenomena. To be more exact, the python model includes the chemical reaction kinetics, the mass transfer, and finally the fluid mechanics in the reactor and calculates the composition of the final exiting gas, as well as other physical parameters of the process. The added value of this thesis project lies in the validation of the developed model against experimental results obtained from a series of tests carried out at the TU Darmstadt gasification facility, when experimental gasification campaigns were conducted using Solid Recovered Fuel (SRF) [3]. In addition, this work contributes to the modernization and further development of the model originally presented in Hamel’s PhD thesis [4]. The modeling approach that was followed for the construction of this model was based on a 1-D cell model, where the fluidized bed and the freeboard were discretized in control volumes. Within these control volumes, the local hydrodynamics and the gasification reactions were applied, through mass balance equations. As initial conditions for the gasification model, the outputs of a pyrolysis model were used, applied to the incoming feedstock. The final results of the numerical model show good agreement with the experimental set of data from the TU Darmstadt gasification campaign. More specifically, the model manages to predict with reasonable accuracy the concentrations of four out of the five major syngas species considered. The most notable shortcoming of the model lies in the prediction of the methane content in the final syngas, as this was completely depleted inside the bed, which is an unrealistic behavior given the operating temperature range of the gasification process. This deviation likely lies in the fast kinetics of the steam methane reforming and methane oxidation reactions, pinpointing the need for more accurate reaction kinetics. However, the content of CO, H2, CO2 and H2O were captured reasonably well. In addition, the model predicted a carbon conversion efficiency of 100%, which is unrealistic compared to typical values of around 70-90 % that are observed in real-life applications. This value overestimation lies in the fact that carbon is treated as a pseudo-gaseous species in the model, as well as in the fact that incomplete carbon conversion mechanisms, such as bottom ash removal or particle entrainment with the syngas, are not being considered. Different tests of sensitivity analysis were also conducted to assess the effect of different key parameters on the final product, including the freeboard temperature, the initial gasification conditions, the gaseous distribution through the nozzles and different kinetic parameters. Overall, the model managed to come close to the experimental results, demonstrating its potential in simulating the use of waste-derived fuels in a bubbling fluidized bed gasifier. Therefore, it provides a strong basis for further exploration and development. ... Read more

Transitioning the global energy system from finite fossil fuels towards renewable energy resources is probably the most pressing issue of the 21^st century. To mitigate the variability in typical sustainable electricity generation technologies, such as solar and wind power, on-demand generation methods are needed, powered by renewable sources such as biomass. As biomass may be converted into conventional types of fuel, methane (CH₄) for example, it could additionally help minimize the financial investment needed to complete the energy transition.

This thesis designs and analyzes a process for making Liquefied Natural Gas (LNG) from Dutch domestic biomass resources, modeled in Aspen Plus process simulation software. Specifically, the process design combines gasification of biomass pyrolysis oil, desalination and electrolysis of sea water, and Sorption-Enhanced Methanation, as well as cryogenic liquefaction to produce bio-LNG, a renewable liquid fuel. This bio-LNG may then be used to generate electricity, to fuel heavy road traffic, or whatever application might be found for it.

Based on a 6 kg/s intake of wood pyrolysis oil, nearly 12 t/h LNG can be produced, in addition to useful side products such as sea salt and drinking water. Economic evaluation yields a project NPV of nearly €4 billion, and an IRR of 36.7%. Furthermore, the LCOM of this process is lower than several biomass-to-X processes, at €190/MWh. ... Read more

In the context of maritime decarbonization, methanol has emerged as a promising alternative fuel due to its favorable storage properties and potential for renewable production. This thesis investigates the techno-economic performance of integrating methanol steam reforming with low-temperature proton exchange membrane fuel cells (LT-PEMFCs) for on-board power generation on a super-yacht. The primary objective is to conduct a comparative analysis of two distinct system architectures: an integrated membrane reactor where reaction and separation occur simultaneously (Configuration A), and a conventional packed-bed reactor followed by a separate membrane purification unit (Configuration B).

To evaluate these systems, two detailed, steady-state process models were developed using the Aspen Plus V12 simulation software. The core unit operations, including the coaxial membrane reformer and the PEM fuel cell, were modelled using custom-developed User2 Fortran subroutines. These subroutines implement detailed, literature-based models for the MSR kinetics (Peppley et al.), hydrogen permeation (Sieverts’ Law), and PEMFC electrochemistry (Correa et al.). The systems were sized to meet a 325 kW net power demand derived from real-world Feadship vessel load data, and comprehensive heat integration strategies were implemented for both.

The simulation results reveal a fundamental trade-off between unit-level conversion efficiency and system-level thermal efficiency across the different power loads. While the membrane reactor (Configuration A) achieved superior methanol conversion due to in-situ hydrogen removal, its fuel-depleted retentate stream necessitated a significant supplementary fuel flow to the burner for heat integration. In contrast, the conventional packed-bed reactor (Configuration B), despite a lower conversion, produced a fuel-rich retentate that greatly improved the effectiveness of its heat recovery loop.

Consequently, Configuration B demonstrated a higher overall system efficiency (59%) and lower specific methanol consumption compared to Configuration A (57%) at the design point. The operational cost analysis further confirmed this advantage, showing lower annual fuel and membrane replacement costs for Configuration B. This study concludes that for an integrated onboard power system where retentate fuel value is critical for thermal self-sufficiency, the conventional reactor with a separate purification unit represents the more efficient and economically viable architecture. Both modelled systems, however, show significant efficiency and emissions advantages over traditional marine diesel engines, validating the promise of methanol-reforming PEMFC technology for sustainable maritime applications. ... 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

Traditional carbon capture processes require large amounts of energy to regenerate the solvents used. Recent research has proposed to decrease the energy requirements of this process by integrating the system of carbon capture and electrochemical conversion, removing the need for the traditional regeneration step. The integration of these two steps involves the use of the same medium for both the carbon capture solvent and for the electrolyte for electrochemical conversion of the captured CO2. The proposed methodology takes advantage of the inherent elevated temperatures resulting from ohmic losses in the electrochemical system, especially at an industrial scale and helps optimize the efficiency of the conversion process. This study investigates the use of non-aqueous solutions of 1:4 choline chloride to ethylene glycol coupled with monoethanolamine as the medium for this process, particularly focussing on its use as the catholyte in this system. Specifically, this project targets the production of carbon monoxide using silver cathodes in small laboratory scale compact H-cells, with an anolyte of 0.5 M sulphuric acid and a Nafion-117 cation exchange membrane separating the compartments. Different operating conditions, including pulsed electrolysis, are utilised to attempt to modify the levels of carbon monoxide production and stabilise the system for long term operation.
Initial investigations into this system found that carbon monoxide could successfully be produced at constant reduction potentials vs. Ag/AgCl of -1.5 V and -1.7 V for approximately 10 minutes of operation when operating at 65 °C. Pulsed electrolysis has been proven to be able to increase the stability of carbon monoxide production for up to an hour of operation. The study found that the most promising conditions for the pulsed electrolysis are using positive anodic potentials vs. Ag/AgCl of either + 0.1 V or + 1.5 V for between 5 and 40 seconds in combination with cathodic potentials vs. Ag/AgCl of - 1.5 V. The faradaic efficiency of carbon monoxide production was able reach up to 24 % for one hour of operation with relatively stable production profiles when using pulsed electrolysis.
The results of this project show that this system can produce the desired carbon dioxide reduction reaction and with the use of pulsed electrolysis this can be achieved for at least one hour with faradaic efficiencies of carbon monoxide production greater than 20%. These findings showed a better overview for the next stage of this research. In particular, further work involving longer term operation of the cells is of interest after this research.
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