The Sines H2 Hub aims to take advantage of Portugal’s solar resources and push for a green hydrogen hub centred in Sines. To do so, a 1GW electrolyser is expected to be built by 2030. The gas produced, which will have the same production profile as the solar irradiance, can be injected in the gas grid, distributed by truck or shipped to the Netherlands. Due to hydrogen’s high volumetric energy density, ammonia is considered a suitable energy carrier for the ship­ping option. However, ammonia production requires a stable hydrogen supply ­ which is not compatible with a profile dependant on solar irradiance. To face this issue, a technological option that stands out is using the existing Carriço salt caverns, located 280km north of Sines and connected by pipeline, as a buffer to store the hydrogen during the day and supply it back to Sines at night. This research aims to calculate the levelized cost of hydrogen transmission by pipeline from Sines to Carriço, storage in the Carriço salt caverns and transmission back to Sines. Based on the stabilized hydrogen production, a model is developed and 4 pathways are considered for each of the possible infrastructure combinations: new or retrofitted transmis­sion and new or retrofitted storage. Dependant on the infrastructure selected, the cost model developed found a total levelized cost of hydrogen transmission and storage of: 0.17­-0.25 [€ ⋅ kg(H2)−1]. By considering a competitive green hydrogen production cost of 1­-1.5[€ ⋅ kg(H2)−1], the transmission & storage costs along with the rest of the direct hydrogen supply, will translate into an added 10% expense ­ on top of production ­ to provide a stable hydrogen supply to the ammonia plant. The result, which is aligned with literature, is expected to provide solid input in assessing hydrogen’s price competitiveness and contribute to the decision process of using retrofitted or new infrastructure.

The concept of coproduction has been explored in combined heat and power applications. It is a method of improving the efficiency of the energy generating system by utilising waste heat. In the coming years hydrogen is expected to play an important role in decarbonization as it does not emit greenhouse gas at the point of application. Hydrogen today is primarily generated from fossil fuels and the processes of producing hydrogen are energy intensive, while also emitting large quantities of greenhouse gases into the atmosphere. As the amount of hydrogen generated today is limited, it has restricted the growth of industries such as the automobile industries producing fuel cell vehicles that are to use hydrogen as fuel. In this thesis report a coproduction concept using high temperature molten carbonate fuel cell has been examined. The molten carbonate fuel cells operate at very high temperature, and it is possible to utilise the waste heat for internal reforming reaction of a fuel such as natural gas to liberate hydrogen required by the fuel cell. Excess hydrogen can also be produced from such fuel cell systems when the fuel utilisation in the fuel cell is reduced. This concept has been studied with solid oxide fuel cells and a paper published in 2008 by Hemmes et al. titled "Flexible Coproduction of Hydrogen and Power Using Internal Reforming Solid Oxide Fuel Cells System" has served as the inspiration for this thesis report. Three modes of operations have been simulated in this thesis on the Cycle-Tempo software with varying fuel utilisations, similar to what has been shown with the solid oxide fuel cells in that paper. With molten carbonate fuel cells, overall efficiency of up to 80% was obtained in terms of electricity and hydrogen coproduction. By doing so it is also possible to produce overall power output of nearly three times than what can be achieved by conventional electricity production. The results obtained have also been compared with the solid oxide fuel cells in this report. While high coproduction efficiencies for flexibly coproducing hydrogen and power have been shown to be possible, other factors would also play important roles in the success of this technology. In this report some of those factors such as the status and expected growth of the hydrogen market, molten carbonate fuel cell market, role of actors, role of policy makers have also been examined. As this technology does rely on a fossil fuel that is natural gas, the benefits of using natural gas in hydrogen production has also been highlighted along with the positive effects these systems could have on the society.

The scarcity of water is a major global concern in the modern times. Hence, the judicial use of water must be coupled with water reuse to counteract the water depletion. To reuse water, we eye on available treatment technologies which can guide us to circular use and reuse of water and nutrients. Anaerobic digestion, is known for producing better quality effluent with a possibility of energy generation through biogas. It can also be coupled with post-treatment techniques to extract nutrients. Anaerobic membrane bioreactors have been used to treat high-strength wastewater to obtain higher particle and organic removal. Introducing limited aeration to such an anaerobic environments have been studied earlier to enhance the degradation process. Depending on the quantity of aeration added and the mechanism of aeration, studies have reported both positive and negative effects on the organic degradation. The existing studies only cover the effects of the applied aeration on the Anaerobic Digestion process. Little is talked about its effect on the sludge characteristics such as particle size and sludge rheology. This research focuses on studying the effect of applied aeration on the AnMBR performance, based on the effect of aeration on substrate degradation and on sludge characteristics. To study this, an AnMBR is operated with laboratory-made synthetic blackwater treating 5gCOD/l. A 2% increase in oxygen with respect to the sludge VSS is introduced through added air. The effect of this added aeration to the system is studied. The organic removal was enhanced by 11% when compared to the observed removal during the non-aerated phase. Ammonium concentration increased by 24% and sulphate concentration reduced by 12% in the effluent. The size of the coarser fraction of sludge, D90 increased by 13% and that of the finer fraction D10 increased by 15%. The viscosity profile of the sludge after aeration also increased. Inhibition caused to the Methanogenic activity of the sludge reduced as the sludge started adapting to the applied aeration. Activity changes to higher sets of aeration matching that of a Dissolved Aeration and Flotation system was studied. The feasibility of such a system is still a work in progress for the future. The obtained results are for an adapting sludge, and has to be continued for a better adapted sludge. Recommendations based on this study to future works on the same line, is given.

Although the Dutch energy supply is gradually progressing from fossil fuels to renewable energy sources, the consequences for the grid are becoming increasingly evident. Meanwhile, the gas extraction from the Groningen natural gas reserve is de- clining as the induced earthquakes in the northern Netherlands persist. Hydrogen, as a flexible carbon-free molecule, offers a potential solution to the overcapacity of the electricity grid and thus has the potential to fulfill an important role in the fu- ture energy supply. It has recently been proved that by making few adjustments in the grid assets, the existing gas grid can be made compatible with hydrogen. A relating issue to hydrogen distribution through the gas grid is the resulting hydrogen qual- ity. Similarly to natural gas, the roll-out of a national hydrogen grid needs a national quality standard. There will be a variety of end-use applications, such as hydrogen boilers and fuel cell technologies that have different quality requirements.
This report researches the influences of the distribution of hydrogen through the existing gas grid. There are five sources of contamination: odorant, inward permeation of air through polymer pipelines, particles circulating in the grid, leaks causing an entrance for contaminants and byproducts from hydrogen production technologies. All five sources are considered, but the focus of this report is on inward permeation of air through low pressure polymer pipelines. There are three significant risks which are linked to the permeation of air: feed dilution, explosion risk and damage to fuel cells. Fick’s laws for diffusion were used to create a computation model, from which relationships were found between seven variables and the amount of contamination. Correlations were found between the amount of permeated air and the pipeline material, pressure, inner diameter, wall thickness, flow velocity, temperature and soil type. Pure hydrogen was modelled to be distributed through the low pressure grid at different conditions. After traveling 100 meters through an MDPE pipeline with 26 mm inner diameter and wall thickness of 3 mm at a flow velocity of 1 m/s, 1.4 mg oxygen and 1.9 mg of nitrogen per m3 hydrogen will have diffused into the pipeline. The results have been implemented in a case study in Stad aan ’t Haringvliet in Goeree-Overvlakkee, and the contamination for the farthest distance in the grid was found to be 0.057 ppm oxygen and 0.085 ppm nitrogen at a flow velocity of 1 m/s. Following the research set out above, no issues were found in connecting hydrogen boilers to the existing grid. Low temperature PEM fuel cells are more sensitive to impurities than boilers and some concerns were found under certain specific conditions with exceeding the current hydrogen fuel contamination limit for oxygen stated in ISO 14687-2. After traveling 529 m through MDPE and 5.8 km through HDPE the oxygen limit was exceeded. This is not considered as a constraint for the development of a future hydrogen grid, as this upper limit was set for the fuel requirement of metal hydride storage, and existing hydrogen road vehicles have another means of storage. A positive side effect of the presence of oxygen in the hydrogen feed is that it reacts with carbon monoxide, thereby decreasing fuel cell poisoning effects. Nitrogen contamination of the hydrogen feed can dilute the fuel and only at high concentrations increase fuel cell cathode poisoning caused by carbon monoxide. These high concentrations are not expected to be achieved as a result of inward permeation of nitrogen. Consequently, through the obtained results in this research it is believed that a sufficiently high purity hydrogen can be achieved in the existing distribution grid.

Dredging is an energy-intensive operation and, due to the nature of the process, there are large and rapid fluctuations in the power requirement. With the signing of the Paris Agreement, implementation of IMO 2020 and expansion of ECAs, the external pressures for the reduction of different emissions(CO2, SO_x, PM, and/or NO_x) in dredging are rising. Additional motivating factors are the rise in the fuel expenses which form a major component of dredging project costs and the incentives from regulatory authorities to reduce the carbon intensity in dredging operations. Often, the achievement of one objective leads to deterioration of another, for example, the use of IMO-compliant fuel can increase the overall carbon emissions. In recent years, alternative fuels like LNG and biofuels have been explored. However, they suffer from their own set of issues and with the predicted trends, the usage of these alternative fuels would imply lower production and earnings, especially in large dredging projects. In this work, a marine power plant concept that has been rarely discussed in the context of dredging is explored and forwarded: a nuclear-based system. Fundamentally, such a power plant addresses the issues related to the emissions and essentially eliminates bunkering stops. This was the first study focused on nuclear-powered Trailing Suction Hopper Dredgers (TSHD), the most common type of dredging vessel. In this work, a system-level study was carried out to ascertain the retrofittability of a nuclear-based system on four existing TSHDs. The feasibility of retrofitting the nuclear-based system has been studied by comparison of mass and volume requirements of the nuclear power plant, with the mass and volume of the engine and fuel storage system of current dredging vessels. No re-design of the vessel was considered here.The ”inherently safe” High Temperature Gas-cooled Reactor (HTGR) with Nuclear Air-Brayton Cycle (NABC) was determined as the nuclear power system of choice. It appeared that for such a system,the TSHD sizes that are interesting for the deployment starts around 12000 m³ hopper capacities.The bigger the hopper capacities than this baseline, the better the nuclear system performed. It was found that despite the satisfaction of the mass and volume constraints, a redesign of the TSHD is required for the placement of the reactor and for the compliance with the nuclear related regulations.In addition to the nuclear power plant, the retrofitting of the TSHDs with Proton Exchange Membrane Fuel Cell (PEMFC) in combination with solid, compressed and liquid H₂ storage and batteries was considered. With the current commercially available offerings, PEMFC with liquid or 500 bar compressed H₂ storage were found to be suitable for maintenance dredging or capital dredging for a short duration(couple of days). However, it was established that the realisation of endurance level of current dredgers is not possible without a reduction of hopper capacities or factorial increase in energy density of storage. Further, the smaller TSHDs were found to be better suited to use PEMFC or battery-based systems.A part of this work also tried to answer the pertinent question of the third party liability insurance premiums for a nuclear-powered vessel and the regulations such a ship would be subjected to. Further, a preliminary business case was developed and the sustainability of the concept was evaluated. It was realised that the technological forces and trends like the development of Small Modular Reactors, deep-sea mining and autonomous ships, could favour the development of a fleet of nuclear-powered dredging vessels in the future. However, the regulations and the support for these vessels would be highly dependent on the flag country and operational location.

In an effort to replace fossil fuels by more sustainable solutions, the demand for green hydrogen hasgrown significantly over the last few years. This has raised the interest in electrolysis and has boostedits development. Water electrolysis produces hydrogen and oxygen from water using direct current,nowadays often with an electrochemical efficiency of around 80%. Although much effort has beenmade to reach such high efficiencies little research has been done on the excess heat produced byelectrolysis. This thesis intends to cover this topic, mainly focussing on Proton Exchange Membrane(PEM) electrolysis. All of the inefficiencies of the electrolyser translate into heat and it is the objective ofthis research to investigate how much of this heat can be extracted and contained for use in a separateapplication. Furthermore, in the second part of this thesis, the available applications are studied in anoffshore and onshore production scenario to better understand potential of this heat.In order to accurately simulate the thermal behaviour of a stack of PEM cells an electrochemical andthermal model was created representing the average largescalePEM electrolyser of today. Furthermorea basic integrated cooling system was designed in order to assess how much heat can be extractedfrom the stack and at what temperature. The system consists of separate channels for coolingwater inside the bipolar plates that separate the individual cells. It was found that well over 90% ofthe heat produced by the stack can be extracted in the form of cooling water at a few degrees (<3표퐶)below stack temperature without impeding the performance of the stack. The largest contributor to heatbeing lost, was found to be the production of water vapour on the anode side of the cells which can bereduced significantly by operating with an elevated pressure in the anode chamber (5 bar).In the onshore case study it was found that an electrolyser is very well suited to be connected to adistrict heating network. The low temperature heat serves well for applications such as space heatingand/or water heating. In an offshore scenario the excess heat can serve to aid in thermal desalinationhowever it proved to be more difficult to find an adequate application for the full amount of producedheat.In conclusion, the models presented in this thesis have shown very satisfactory results in terms potentialof excess heat. It has proved to be a very interesting field of study and more indepthresearchas well as broader studies on possible heat applications can be conducted to fully understand thepotential of excess heat from electrolysis.

Climate change, depletion of fossil fuels, and economic concerns are among the main drivers of sustainable energy transition. The Netherlands has drawn up ambitious goals in the energy transition. However, numerous studies have shown that there is a lack of space in the Netherlands to adapt to a 100% green economy. To solve this dilemma it is necessary to import renewable energy from other countries. Solar electricity prices are dropping rapidly in high solar irradiation areas and are currently the worlds cheapest source of electricity, likewise this is in places where space is often abundant. This thesis examines the techno-economical feasibility of importing solar energy from Morocco to the Netherlands. As subsidized solar electricity is bought by the Dutch government for 0.125 e/kWh, the target is to find a solution below this demand. All energy storage systems are analyzed thoroughly and an energy and cost analysis is performed for a cable, chemical energy storage, thermal energy storage and liquid air energy storage.
A HVDC submarine power cable between Morocco and the Netherlands is compared in proportion to the costs and distance of the NorNed cable. A HVDC submarine power cable over a distance of 2600 km results in a LCoE of 0.113 e/kWh. Other energy storage systems use a tanker to transport the stored energy. In this thesis liquid hydrogen, ammonia and methanol are analyzed as chemical energy storage systems. Liquid hydrogen is produced by cooling and expanding hydrogen, ammonia is produced by the Haber-Bosch process and methanol is formed by reacting H2 and CO2. Fuel cells are used to convert fuels back into electricity. The most efficient and cost effective solution for chemical energy storage is storing electricity in the form of liquid hydrogen. A round-trip efficiency of 27% with a LCoE of 0.491 e/kWh is obtained in 2015, from the predictions of 2030 a round-trip efficiency of 40% with a LCoE of 0.159 e/kWh is derived. The next concept is based on thermal energy storage with Solar Salt as energy carrier. Solar Salt is heated in the receiver of a solar tower where heat from the sun is concentrated to by heliostats. Hot Solar Salt is transported to the Netherlands by a tanker and a steam cycle is driven utilizing the heat of hot Solar Salt. The energy efficiency obtained from solar irradiation to electricity in the Netherlands is 28%, the output power is only 1% less than the output power should be if the power block was located in Morocco. An electricity price of 0.164 e/kWh is obtained, but if heat is delivered a heat price of 0.069 e/kWh can be realized. The final designed energy storage system combines liquid air with the heat of hot Solar Salt. Liquid air and hot Solar Salt are produced in Morocco and in the Netherlands electricity is produced with high efficiencies due to the large temperature differences. The system described results in a electricity price of 0.108 e/kWh with an energy efficiency of 58.7% from electricity and hot Solar Salt to electricity in the Netherlands.
It is concluded that storing electricity in chemical energy storage via the processes described in this thesis will lead to too high costs to be used as energy storage solution. There are possibilities in direct fuel conversion technologies due to high conversion efficiencies, only developments are still in its experimental phase. The combination of liquid air with Solar Salt complies to the cost requirement, some more research is required on the electricity generation process described, but the concept shows a lot of potential. Finally, heat of Solar Salt can be provided at a price of 0.069 e/kWh, subsidized solar heat is bought by the Dutch government for 0.095 e/kWh. This gives possibilities to effectuate a business case.

As one of the carbon-free emission transportation method, fuel cell electric vehicles (FCEV) have become a very popular research topic for the recent years. However, as the fuel of FCEV, the hydrogen is usually produced by traditional steam reforming method, which is still not an environmentally friendly process.

This report focuses on the study of infrastructure for hydrogen producing and refueling with zero carbon emission. An on-site water electrolysis hydrogen producing and refueling system powered by wind energy is designed and simulated in this study.

The hydrogen is produced by on-site PEM electrolyzer powered by distributed wind turbine. First of all, the suitable petrol stations for such hydrogen refueling station modification are selected by GIS data analysis in Germany. By applying the constraints for safety and noise consideration, about 500 stations are selected from over 10000 petrol stations in Germany.

Furthermore, the hydrogen producing and refueling system is designed and simulated by MATLAB modelling. The system is composed of five main components: wind turbine, PEM electrolyzer, compressors, storage tank and hydrogen dispenser. The technical and economic details for each of these devices are defined by a series of literature review. Besides, some parameters are from the real commercial products to make the system model more practical.

A case study is built to validate the designed model for a 330kg/day H2 refueling station in Germany based on both current and future scenarios. The results show that more than 170 tons hydrogen can be produced annually. It can cover most of the hydrogen demand for the refueling throughout the year, which eliminates most of the hydrogen delivery cost from the other producer to the refueling station.

In addition, by using the optimal pre-allocation control strategy, the system can become partially stand-alone with the grid. Only the high-pressure compressor system and cooling system for dispenser need energy supply from the grid, which is less than 1% of the system energy consumption. It means no extra grid reinforcement is needed. The wind energy can be used in a very efficient way. More than 95% of wind energy can be used for hydrogen producing while the other 5% supplies for the compressors as the electricity. The sensitivity research is also performed based on the climate data in a different year, which shows the stable operational behavior for the system.

Last but not least, the economic analysis is carried out based on the case study. For the current scenario, the hydrogen production cost of the system is €6.1/kg and the overall dispensing price is €10.9/kg. It is expensive because the distributed wind turbine and on-site PEM electrolyzer are still costly technologies for now.

However, with the R&D progress of these technologies, the production cost and the dispensed hydrogen fuel cost price for the future scenario will reduce to €2.6/kg and €5.1/kg respectively, which makes the hydrogen a very competitive fuel for the vehicles in the future.

New technologies are being developed to produce electricity cleaner and more efficient. A promising technology among these is the solid oxide fuel cell (SOFC). It electrochemically converts chemical energy into electricity. This process is highly efficient and several types of fuel are suitable. Furthermore, the SOFC operates at a high temperature, thus producing high quality excess heat which can be converted into electricity in a thermodynamic power cycle to increase the efficiency. Commonly this is done by a directly coupled gas turbine (GT).
The supercritical carbon dioxide (sCO2) Brayton cycle has recently received attention for its potential as a next generation power cycle. It combines the advantages of the steam Rankine cycle and air Brayton cycle. So far, two heat sources are mainly considered for this cycle: Nuclear and concentrated solar power (CSP).

The aim of this study is to investigate the potential of integrating a SOFC with a sCOs Brayton cycle. A thermodynamic model of the SOFC- sCOኼ Brayton cycle hybrid system (SSHS) is developed to explore and analyze different concepts that effect the integration of both systems. Methane is converted to syngas in an indirect internal reforming (IIR) setup. The steam required for this process is either fed by a heat recovery steam generator (HRSG) or supplied by recirculating
anodic exhaust gas. Both options are considered. Recirculating the exhaust of the cathode is another options that is explored and analyzed. Two sCO2 cycle setups are analyzed in combination with the SOFC system: A simple recuperative
cycle and a recompression cycle.
Different setups of the SSHS are compared on efficiency, complexity of the system and size of the exchangers. For comparison, a directly coupled solid oxide fuel cell (SOFC)- GT hybrid system is considered as well.

It is found that the recompression cycle in combination with SOFC system is more efficient than the simple recuperative cycle but significantly increases the complexity of the heat exchanger network, recirculating cathodic air decreases the size of the heat exchangers and increases the efficiency and supplying steam through a HRSG decreases the efficiency. Compared to a directly coupled SOFC-GT system the SSHS is a significantly more complex system. However, it does not require a pressurized SOFC since the sCO2 Brayton cycle is indirectly coupled
to the SOFC. The most efficient setup of the SSHS, combining the recompression cycle with cathode recirculation, has a higher LHV efficiency than the directly coupled SOFC- GT hybrid system, 66.58% over 62.38%. This setup of the SSHS is rather complex though. Other setups of the SSHS show efficiencies similar to that of the directly coupled SOFC- GT hybrid system.
A promising result, but the practical feasibility of the SSHS is something that should be carefullyconsidered in future research and practice.

Transitioning from a heavily fuel reliant economy to a sustainable future is one of the major challenges of our time. The high energy density and good storage properties of fossil fuels have made them the most important energy source for the last centuries. Moving away from fossil fuels towards greener, biomass-based energy and energy carriers is hindered by the technological gap due to the maturity of conventional processes compared to sustainable ones. This thesis focuses on a process of converting biomass into methanol. The process is a small-scale application which is mobile so it can be moved towards the source of the biomass, with the aim to reduce transportation costs. The specific focus lies on the conversion of the gasification-derived syngas into methanol. For this an extensive literature study was conducted to find suitable technologies and process kinetics. Aspen Plus® with the integration of Excel was used to model the chosen technologies. The process was divided into three unit operations. The methanol reactor unit with a recycle stream, the CO2-removal unit to prepare the gas for the reactor unit and a H2-recycle unit to increase the utilisation of the hydrogen. Each unit operation was modelled separately to study the influence of their parameters and to determine which parameters have the largest influence. Finally, when integrating all unit operations within one model, these selected parameters were used to determine the operating conditions and process design.

The aim of the developed model was to predict and improve the process for different applications with integrated hydrogen supply from renewable sources. The disadvantage of utilising renewable energy sources for the production of hydrogen is the intermittent supply of electricity for the electrolysis of hydrogen. Therefore the process needs to be able to accommodate different levels of hydrogen production. The first case is the base case without any hydrogen input. It is given a syngas-input and the CO2-removal unit runs at full capacity. Building upon this model, the behaviour of the system for hydrogen supply integration was modelled in the second and third case. The second case introduces additional hydrogen and therefore the CO2-removal unit can be turned down. The third application adds CO2, which was removed in case one, to the system and increases the hydrogen input. The study of these processes shows, that the operating pressure of the methanol reactor unit has a very large influence on the energy requirements of the process but also on the production of methanol. In respect to the power and cooling requirements of the process a low pressure is favoured but much larger quantities of methanol can be produced at higher pressures. With the chosen designs for the cases a respective methanol production of 47.6 t/d, 96.8 t/d and 180.6 t/d is reached. The integration of hydrogen leads to two major concerns for the process. The integration requires much larger equipment due to higher flowrates and the quality of the product decreases as a higher CO2/CO-ratio produces more water. The thesis served its purpose by developing a model of the process which can be further used to optimise the process on a techno-economic level.

Supercritical water gasification is a process in which wet biomass is converted to bio-syngas. In this process the temperature and pressure are raised above the critical point of water (374 C, 221 bar), creating a supercritical medium in which a high conversion and energetic efficiency of biomass to bio-syngas is realized. Due to these high efficiencies supercritical water gasification has received much attention as a potential treatment technique for sewage sludge from wastewater treatment plants.
To design a supercritical water gasification process kinetic models are used. They provide predictions on the decomposition products of the organic components of the biomass during treatment. However, kinetic data on lipids, which can make up to 25% of the organic matter in sewage sludge, are not available yet. This study aims to identify main reaction pathways and corresponding kinetic parameters that describe the decomposition of lipids in supercritical water.

Experiments were performed to provide data of decomposition products yields and find the dominant reaction pathways. Oleic acid was used as a model compound for lipids from sewage sludge. Experiments were conducted in a stainless steel batch reactor which was heated by immersion in a fluidized hot sand bath. Investigated temperatures and residence times were 400, 420, 460 and 520 C and 15, 35 and 65 min, respectively. Oleic acid feed concentration was 10 wt% and a pressure of 25 MPa was applied.

From experimental results the decomposition of oleic acid into aliphatic hydrocarbons and shorter chain fatty acids was identified. With increasing time and temperature these products would either gasify or the aliphatic hydrocarbons would dehydrogenate to cyclic and (poly)-aromatic compounds. A remarkably high selectivity towards the light hydrocarbon gases (C2H6, C2H4, C3H8, C3H6) compared to an earlier study into the decomposition of oleic acid in supercritical water was observed for all temperatures and residence times.

Parameters for a kinetic model, build up from the identified reaction paths, were fitted to the experimental data using Matlab. The Arrhenius equation was used to describe the reaction constants as function of temperature. For the oleic acid decomposition an activation energy of 151 kJ/mol was fitted first with a percentage output variation of 82% between 420 C and 520 C. Parameters for the other reactions were fitted using this activation energy as constraint.
Qualitative trends on the gas and liquid decomposition products distribution over time and temperature were predicted well by the model, but predictions on the quantitative yield of them were concluded to be inaccurate. Largest differences between experimental and model yields were observed for CH4 and the light hydrocarbon gases.

One reason for these model errors is the scarcity of data points in the 0-15 min time-scale, where the process was highest in reactivity. Also some of the reaction pathways in the model might have been oversimplified, neglecting certain dominant decomposition reactions.

The world is moving towards a cleaner future. With the increasingly stringent emission regulation in maritime field and the limitation of marine diesel engine systems, the shipbuilders may start to seek cleaner solutions rather than modifying the currently prevailing internal combustion engine systems (ICE). According to previous researches, a tandem fuel cell system power plant, which uses LNG as fuel, has a very good overall emission performance in comparison to marine LNG based ICE systems, and can achieve an overall efficiency of more than 60%. To study whether the tandem fuel cell system can be an alternative for marine LNG engine systems, two models are built in this master thesis to study the performance of the system under stationary operation and transients. The first model is built to study the stationary performance of the system, and to verify the result of high efficiency from previous researches. The result shows that indeed an efficiency of almost 60% can be reproduced. The second model is built to study the transient behaviour of the system, and to compare it with that of marine LNG engine systems. The result shows that the system has a better transient response than the recommended transient response for current marine LNG engine systems. Since the SOFC in the tandem fuel cell system has a slow transient behaviour, a hydrogen tank is added between the SOFC system and the PEMFC system as an energy buffer. A design assistance tool is developed to assist in sizing the hydrogen tank and the fuel (LNG) tank in design phase.

Low-grade heat sources are abundant on earth but are majorly untapped due to lower thermodynamic efficiency at low temperatures and cost considerations. A cost-effective technology is needed to convert this energy resource into useful forms of energy. This work aims at optimizing Organic Rankine Cycle (ORC) based heat engine and a cogeneration system developed to produce electricity and refrigeration from a heat source below 100℃, from both thermodynamic and economic point of view. Exergoeconomics, an algebraic thermoeconomic method, was used to analyze and optimize the systems for cost-effectiveness and exergetic efficiency. Also, the prototype of the cogeneration system was experimentally tested. The results exergoeconomic optimization show that the cost-effectiveness of the cogeneration system can be significantly improved by design parameter changes. The experimental results obtained were comparable with the results obtained from theoretical simulations.