To anticipate for future demand of sustainable liquid fuels, Zero Emission Fuels B.V. develops a solar powered micro plant which produces methanol from water and carbon dioxide captured from outside air. An intermediate step in this process is the electrolysis of water to create hydrogen which reacts with carbon dioxide to methanol. This study encompasses an integration of the pressurised alkaline electrolysis system, in which problems observed in previous generations of the electrolyser have been solved and functionalities have been added. In addition to that, electrolyte samples are taken after different periods
of operation to investigate electrolyte deterioration over time.

A new Balance of Plant (BoP) has been designed, realised and tested. Eight new features to the system can be distinguished, two of which are included to add functionality: the degasser to decontaminate the carbon dioxide-rich
feed water and the pressure booster to replenish the consumed water at system
pressure. The other features are integrated to enlarge the operational envelope, the determination of which was central to the experiments conducted in this research.
Experiments are conducted to find and characterise the four limitations to the operational envelope: the relative valve opening duty (RVOD), flow stagnation, temperature control and crossover.

The RVOD experiments showed deviations from the modelled valve opening cycles, attributed to additional pressure drops, valve opening interference and smaller discharge volumes. Subsequently a corrected model is presented to improve valve cycle time predictions.
Flow stagnation was investigated at various current densities, pressures and temperatures using camera images and a characteristic temperature response to establish flow stagnation. The results showed a minimum volume flow rate decrease in comparison to the previous system, expressed in parameter 𝑋 which decreased from 3.4 to 0.74 A K bar^-1 cm^-2. The minimum volume flow rate decrease is attributed to the larger number of cells and the increase of the height difference between the stack and buffer tanks.
In the temperature control experiments, steady state temperatures were monitored at different current densities, with and without crossflow fan operation. This resulted in a temperature control map, in which the reachable temperatures for different current density are depicted. Furthermore, electrolyte mass flows are determined and pressure dependency of temperature control was investigated at low current densities, concluding that steady state temperatures are independent from pressures in the 10 bar to 50 bar regime. 
Hydrogen crossover was tested by taking gas samples at different operating conditions and subsequent gas composition analysis in a gas chromatograph; oxygen crossover was determined by an oxygen sensor implemented downstream the hydrogen exhaust. All steady state crossovers values were found to be below the safety limits, concluding that crossover is not limiting in the acquired system on all possible operating points. Overnight diffusion crossover experiments showed that maintaining the system under pressure overnight, keeps crossover values below the safety limit.
In addition to the operational envelope, complementary general characteristics such as power consumption and efficiency are presented and compared to industry and literature. On top of that, unexpected findings, design deficits and other relevant phenomena are described to complete the perspective on system performance and behaviour of the electrolysis system. Due to the electrolyte mist purged into the degasser and pressure booster, the electrolyte deterioration experiments are deemed inconclusive. Moreover, a demister is found to be an essential system feature to include in the next generation electrolyser, because both degasser and pressure booster were damaged by the electrolyte spill.

When experimenting with the compression of a gas similar to the output of a CO2 Direct Air Captureunit using an off-the-shelf lubricated compressor, Zero Emission Fuels B.V.(ZEF) encountered severecondensation, damaging the compressor. This explorative study aims to identify the cause of thisproblem, create a concept solution, and test this concept based on model-supported experimentation.Based on a literature study all theoretical concepts are divided into three solution classes. Twoconcepts are then created and theoretically compared. A concept is selected that is based on theadsorption of water into a solid desiccant.As the concept solution is to operate in a closed system, regeneration of the desiccant needs to befaster than its utilization. For this, an experiment is made where a controlled quantity of inert gas ismoisturized, dried, and used to regenerate a second column. From this it can be concluded that thegas can be dried adequately, and that regeneration can be done thoroughly.A model is made to verify the experiment’s workings, based on models from literature. This modelis then validated using literature, and then fitted to experimental data. Combining experiment andliterature data, three key performance indicators are calculated: Cyclic capacity, energy usage, anddesorption rate. The design tools and models developed throughout this thesis are used to size thenext iteration of the concept according to the needs of ZEF.From this, it is concluded that the presented concept is indeed viable to prevent, rather than solve,the problem stated at the start of this thesis. Recommendations are done concerning further develop-ment of the prototype, experiments, model, and overall system

Flash calculations are used for the dynamic simulation of vapor-liquid phase equilibria (VLE) in many chemical processes. When used to predict the composition of mixtures in VLE, the repeated applicatino of these flash calculations, particularly in dynamic cases can cause small inaccuracies to cascade. One way to prevent this, is to have strong predictions and initial guesses for what a mixture in equilibrium will look like. For this, stability tests can be employed. Stability tests require the minimisation of the tangent plane distance, which is derived from the excess Gibbs Energy. The VLE problem and stability tests have been approached from a viewpoint based in mathematical optimisation, not one based in thermodynamics. As such, this work provides a slightly different description of flash calculations and stability tests, and can serve as both an introduction to the problems, as well as an approach to the problem in a different way than is traditionally done. In this report, the tangent plane distance function has been studied and applied to an example to gain intuition on the problem, and different optimisation methods were considered for minimising this function. A stochastic- and a deterministic method were applied to the stability problem to gain a better understanding of which type of method will work better for minimising the tangent plane distance. Both methods seem sufficient, but the scalability to higher dimensions is lacking, especially in the deterministic case.

Power-to-gas (PtG) technology represents a promising route in providing long-term energy security and involves pairing volatile sources of renewable energy (solar and wind energy) with alkaline water electrolysis (AWE) to create a wide range of products based on intermediate hydrogen gas for end-users across various industries such as in fuels, chemicals and power sectors. However, PtG currently lacks the technical adaptability to match the intermittency of these sources caused by daily and seasonal weather patterns, and suffers from a low turndown ratio (TDR) as a consequence.

Zero Emission Fuels (ZEF) B.V. aim to adapt this process to create an autonomous, dynamically operated solar panel add-on known as a micro-plant that will produce methanol from CO2 and H2O in the atmosphere. In doing so, the company looks to extend the TDR, but requires the micro-plant and by extension, its AWE unit to operate in wider partial load ranges, in which lower current densities dominate. These cause a rise in gas crossover within the electrolyser, creating impure and potentially flammable H2-O2 mixtures in the outlet that hinder the functionality of the micro-plant. Specifically within the AWE unit, the risk of oxygen crossover has been qualitatively identified as a likely safety hazard. Therefore, the focus of this thesis was set on studying the feasible development of a prototype (gas scavenger) that can remove trace O2 within the techno-economic scope of ZEF’s micro-plant and electrolyser.

To determine a viable method that meets ZEF’s constraints on cost, size, weight and efficiency, industry techniques were studied that either purify hydrogen gas streams or destructively remove flammable H2-O2 mixtures. Based on a subsequent numerical estimation on each method’s limiting factors, a local combustion process in the form of a micro-combustor was identified to be the most suitable method.

To quantitatively estimate the safety risk crossover poses, two models were developed: a non-dimensional model to analyse how 50 bar pressure influences crossover during operation, and a two-dimensional, transient diffusion model to analyse the extent of trace O2 contamination overnight. Results indicate that to mitigate dangerous impurity levels, a gas scavenger needs to be implemented: (a) above a 0.1% difference in pressure between electrolyser half cells during operation, and (b) upon start-up to remove overnight gas accumulation that may not pose an immediate severe risk at 0.079 mol% contamination relative to amount of stored hydrogen, but has the potential to build-up on a monthly timescale.

Finally, the feasibility of the micro-combustor was preliminarily characterised at 50 bar and 80 ⁰C through flame simulations. The variability in low amounts of trace oxygen content show that the mixture is normally non-flammable. Further studies on geometry design and control strategies of the micro-combustor must consider how to achieve optimal ignition conditions, determined to be at richer fuel mixtures between 휙 = 1.03−1.40, and how to contain the flame within a well-defined region. Initial suggestions include using a small volume to induce ignition and relying on wall effects to promote flame quenching.

The global energy transition from a fossil fuel base energy system to a renewable energy source base system is the key mission for a low-carbon future. The target of CO₂ emission reduction by 2050, following the Paris Climate Agreement, is 90% compared to the CO₂ level of 1990. Haber-Bosch process is the main industrial procedure for the production of ammonia today and about 80% of the global ammonia is consumed by the fertilizer industry. However, the century old Haber-Bosch process is normally energized by fossil fuel and it
releases about 3% of the global carbon footprint. In light of this fact, replacing the conventional fossil fueled Haber-Bosch process for manufacturing ammonia with renewable source powered ammonia production is the main goal of this study. Instead of obtaining H₂ from steam-reformed CH₄, H₂ is produced from electrolyzed H₂O. This transition enables the conventional ammonia manufacturing process transforming into a green Haber-Bosch production of ammonia. Two Dutch companies, TNO and Zero Emission Fuels, are cooperating
and developing a small scale of reactor system that can convert ammonia from air and water by using solar PV panels. In this work, a new design of ammonia reactor system is developed. Ammonia is typically formed at high pressure (150 - 250 bar) and high temperature (400 - 500^oC) using a promoted iron base catalyst. High temperature ensures rapid reaction kinetics, and high pressure boosts the product yield. Here a reactor system, that is operated at lower pressure (≤100 bar) and uses condensation to remove ammonia, is kinetically simulated in ASPEN. The effect of different operation conditions - reaction temperature (300^oC, 350^oC and 400^oC) , pressure (50, 75 and 100 bar) and feed gas (N₂ : H₂) ratio (1 : 3 and 1 : 5) - on the production rate in a small-scale ammonia reactor have been systematically computed. The mass flow rate of the single pass reactor is set to 50 g/h in this work. With a catalyst bed length of 15 cm and inner diameter of 3.6 cm, according to the simulation, reaction temperature of 400^oC and operating pressure of 100 bar can lead to the highest conversion (40%) in a single pass reactor. The average heat transfer area of the reactor system is to a great extend less than 50 m², therefore, the double pipe heat exchanger is a favorable heat exchange system for the proposed reactor system. In the reactor design validation section, the selected optimum operation conditions are tested in the same scale reactor laboratory setup. Experimental results show that the single pass conversion of nitrogen at 400^oC and 100 bar in such a small-scale reactor can reach 15.4% which is in the range of the industrial one pass conversion level. For reaction operated at 50 bar, 6% of ammonia yield is obtained. It is clear that ammonia production in small-scale and in milder operation condition is possible and the results are promising. The techno-economic analysis has been performed based on above mentioned outcome. The reactor system is integrated with ZEF AEC, ZEF compressor system and a membrane nitrogen separation system. With current ammonia design production (350 g/day), the cost of ammonia per kilogram can be achieved in the range of €1.8 to €2 depending on the operation condition. This is about 5 times more than fossil ammonia prices, but it is very competitive with biomass ammonia. In accordance with the sensitivity analysis, increasing the capacity of feed gas production or reducing the cost in plant equipment can remarkably reduce the ammonia price to less than 1 €/kg NH₃. Furthermore, recommendations in four categories are discussed in the last section of this work, which can lead to a further step towards a green ammonia plant in small-scale.