Oil sludges are composed mainly of crude oil, water and sediments. These are hazardous wastes from petroleum extraction and refining processes, and the worldwide generation of oil sludges is approximately 60 million tonnes per year. Treatment of oil sludges to date has been focused on physicochemical and biological remediation. Oil recovery methods including oil sludge washing with surfactants and co-solvents have also been applied for reusing the oil. However, there is a need to optimise the oil recovery in this process. The main aim of this research was to assess whether the addition of surfactants (Triton X-100 and X-114, Tween 80, sodium dodecyl sulphate, and rhamnolipid) and the co-solvents (n-pentane, nhexane, cyclohexane, toluene and iso-octane) in the oil sludge washing enhances the oil recovery and reduces the burden of hydrocarbon contamination. Specifically, three oil sludge washing parameters were considered: surfactant to oil sludge ratio, surfactant type and surfactant concentration. Also, the influence of the co-solvent type and ratio to oil sludge was investigated. Oil sludges from different sources were analysed, and the toxicity of the residuals from oil sludge washing was assessed with the impact on the soil microbial respiration (dehydrogenase activity test) and ryegrass germination. Rhamnolipid, Triton X-100 and Triton X-114 had the highest oil recovery rates (50 – 70%) compared to SDS and T80. These values were higher compared to other studies (30 – 40%). It was demonstrated that the ratio of surfactant to oil sludge factor had a high impact on the oil sludge washing. Particularly, it was found that the surfactant concentration did not have an effect on the oil recovery, and the addition of surfactant was not significantly different in most of the oil sludges analysed. Only one sludge had a highly significant oil recovery rate when surfactants were used. Cyclohexane, as a more benign co-solvent, was confirmed to have similar oil recovery values to toluene; approximately 75% of recovered oil was obtained with each co-solvent. This work has confirmed that oil sludge washing was an efficient pretreatment method which can reduce the organic contaminant. According to the oil hydrocarbon fractions analysed, the recovered oil had the potential to be reused as a feedstock for light fuel production. The oil sludge washing residuals had an adverse impact on the soil microbiota activity (percentage decrease of 40%), and ryegrass germination. However, some dehydrogenase activity by the soil bacteria and a germination higher than 70% were detected implying that bioremediation techniques can be applied to treat the oil sludge washing residuals further if necessary. Based on these studies, a systematic approach to the extraction of oil from sludges was proposed at both laboratory and large scales. First, a quick bench scale experiment can be done to assess the oil recovery rates with surfactant and without surfactant at a low and high surfactant to oil sludge ratios (e.g. 1:1 and 5:1). By doing this first assay, it can be established if the surfactant is needed or not. If the surfactant is not required, the costs can be reduced. For this first assay, the surfactant can be added at lower concentrations because the results of this thesis showed no significant difference in the surfactant concentrations. The proposed application of this method to a large scale mentioned the possibility of adapting surfactant and co-solvent recycling systems to reuse these reagents in more cycles of oil sludge washing. The residual water obtained from the surfactant recycling step and the sediments at the bottom layer of the oil sludge washing tank can be mixed and considered as oil sludge washing residuals. Finally, these residuals can be further treated if needed with the landfarming and phytoremediation combined method in a designated area. Moreover, the use of soybeans was proposed as the phytoremediator species because these plants can also be used for biodiesel production purposes. Even though the oil sludge washing is a low-cost process compared to other treatments, the cost of applying the surfactant and solvent recycling systems is high due to the expensive equipment. In fact, it was found that about 70% of the total cost of the proposed method at a large scale goes towards these recycling systems. Indeed, it is important to consider the surfactant and co-solvent recovery steps carefully. However, if the proposed method is used on a frequent basis, the investment may be recuperated due to the profit obtained with the use of recovered oil as a feedstock for fuel production. In addition, if the phytoremediation with soybeans of the oil sludge washing residuals is implemented, the production of biodiesel can be a profitable source.

Gasification of coal or biomass can produce hydrogen rich synthetic gas (syngas) for use in fuel cells, liquid fuels or chemicals. While coal gasification is well established, biomass gasifiers have been hindered by costs and difficulties such as tar and ash deposition. Ultra-Superheated Steam (USS) has been proposed as an economical method to maximise gasification temperatures and hydrogen yields. A novel entrained flow USS gasification system showed promise with coal in a previous investigation. The main objectives were to investigate how a USS gasification system produced high hydrogen yields and feedstock conversion within a short residence time. Secondly, apply the system to biomass gasification for sustainable hydrogen production. The principle tasks were to identify the factors affecting the product composition, and experimentally compare the conversion and yields from coal and biomass materials. Numerical software was used to investigate gas and particle behaviour inside the burner. Coal and a unique high ash softwood char were successfully gasified. Char yielded up to 34.9%mol H2 and 25.1%mol CO in the dry gas, demonstrating higher conversion and yields than coal despite lower feedstock heating value and feeding rates. Biomass ash was considered to catalyse char conversion. No detrimental effect was observed from ash deposition, which was dry and easily removed. A fluid model mapped temperature distribution, showing good correlation with validation measurements and supporting the observation that wall temperature greatly affected particle conversion. Particle residence times were inversely proportional to particle diameter and density. High ash biochar showed greater conversion than coal. Economic analysis revealed the system would be most competitive on an existing site with available feedstocks and steam. A longer reactor would increase time for homogeneous reactions to play a greater role. With further development this technology has potential to produce hydrogen competitively on a commercial scale.

In this work an in-house code for large-eddy simulations of coal combustion is developed and tested, with a special focus on the issue of modelling radiative heat transfer effects inside a furnace. An Eulerian-Lagrangian approach is used to describe the continuous gas phase and the discrete particle phase, with a two-way coupling between the two phases (implemented by another group member). The radiative transfer equation is solved using the discrete ordinates method, testing several different angular and spatial discretisation schemes. The spectral properties of the participating media are approximated with different grey gas models of varying complexity and accuracy. The accuracy of the radiative solver is initially assessed on simple idealised static cases in both two- and three-dimensions, and validated against benchmark data found in literature. The code is then integrated, parallelised and optimised with the LES flow and combustion solver, and used to simulate a large 2.4 MW coal combustion furnace. The results of the simulations are compared quantitatively against experimental data in terms of velocity, temperature, species distribution and solid particle analysis, showing a good agreement overall. A parametric study is then also performed on the variables and parameters of the radiation solver, showing great sensitivity on the outcome of the simulations in certain cases, further highlighting the importance of accurate radiation modelling for closed coal combustion furnaces.

Liquid combustible fossil fuel empowers global society, yet is a non-renewable entity with time-constrained limits to supply. Advanced generation biofuel derived from microalgae could feasibly yield more than conventional biofuel crops, utilise non-agricultural land or the sea and remediate atmospheric carbon dioxide and anthropogenic waste. However, technical and economical limits have so far prevented the successful implementation of microalgae biofuels. This thesis exemplifies how apparently disconnected technologies are able to become united in their provision for the growth and processing of microalgae. In so doing, it employs unique experimental methodology which unites inter- disciplinary themes with the proposition to cultivate and process microalgae biomass in a manner which has never been done before. The novelty of this endeavour presents a unique set of challenges, reasoning and results with implications for future creative research and investigation. The philosophical approach to conception and achievement of the laboratory work intercedes with entirely new methodology. Selected examples of such methodology follow. In chapter 3, a newly developed bio-composite gel disk was processed aligning a new design of apparatus for a geotextile puncture resistance test. In chapter 3, a novel formulation for harvesting microalgae is described. In chapter 5, a modified methodology of the preceding chapter is used to investigate seawater ion remediation via ionic and density phase separation. Chapter 6 integrates waste components from 5 different industries, namely dairy farming, anaerobic digestion, brewing, steel slag aggregates and coal power combustion with no previously known unification of such technologies in scientific literature. Chapter 7 assesses the lipid quality of biomass harvested by the novel formulation of chapter 3, before and after exposure to hydrothermal liquefaction. Chapter 8 extrapolates findings from the thesis to define an economic appraisal and suggest a cost saving process.

Carbon Capture and Utilisation (CCU) is seen globally as one of the available technologies that can contribute to avoiding the effects of global warming while securing energy supply by utilising CO2 as a carbon source for chemical and fuel production. This thesis has measured the technical and economic performance of seven Carbon Capture and Utilisation (CCU) process designs (Base Case Models) based on best available technology. This was the first attempt to compare different routes of similar Technology Readiness Level to manufacture a liquid fuel from CO2. In addition, this thesis also examines the techno-economic feasibility of selective CO2 capture processes from biogas streams using ionic liquids as physical absorbents to assess the potential improvements that this developing technology could have on process performance. The selected Base Case Models were modelled using the process simulation software Aspen Plus to determine mass and energy balances. In addition, an economic assessment was developed using Aspen Plus Economic Analyzer (APEA) and MS Excel to determine capital, operating and production costs. The results revealed that the synthetic route based on CO2 capture and steam methane reforming was the most promising CO2-to-fuels route since it was able to achieve the highest overall plant energy efficiency (17.9%) and the lowest fuel production costs (£95.46 per GJ [LHV]); however this process cannot currently compete commercially with conventional fossil fuels. Further research in the specific areas suggested in this work is encouraged in order to bring fuel production costs down. It was also demonstrated that the evaluated ionic liquids cannot compete with MEA in terms of bio-methane production costs; however, the simulation methodology developed in this study can be used as a basis for further work in the area since it allows consideration of ionic liquids made of any combination of cation and anion as well as different gas streams.

Wax formation in diesel and biodiesel fuels at low temperatures is one of the major problems faced by the fuels industry as crystallisation of the saturated compounds present in these solutions can plug up filters and obstruct pipelines. Preventing wax formation in these multicomponent mixtures requires a good understanding of the crystallisation behaviour of both n-alkanes and Fatty Acid Methyl Esters (FAMEs). This work studies solutions of methyl palmitate and stearate in representative mixtures of diesel fuels and unsaturated esters solvents, providing an overall assessment of their solubility and nucleation kinetics. An in-depth analysis of the growth kinetics and crystal morphology for methyl stearate crystallising from n-dodecane, kerosene and toluene solvents is also presented. To perform this study methodologies are developed for the assessment of nucleation kinetics and morphological indexation of crystal specific faces. Models for the analysis of crystal growth kinetics are also derived. These describe the effect in series of the diffusion of growth units within the bulk of the solution and a rate of incorporation of these units which is associated to the molecular structure of the crystal faces´ surface. It was found that the solubility and crystallisation kinetics of methyl palmitate and stearate is very dependent on the solution environment in particular solvent type. Solubilities are higher in solvents whose molecules have more compact structures, such as in the case of toluene and methyl-cyclohexane and are lower in unsaturated methyl ester type solvents. The nucleation process in these systems is found to be much more thermodynamically controlled in the case of diesel type solvents and show a greater kinetic influence in the case of unsaturated methyl esters solvents. The growth kinetics of methyl stearate crystals is found to be strongly associated to the level of solvation of these solutes molecules as well as to the chemical structure of the crystal-solution interface. Accordingly, the rate limiting step is suggested to be the integration of growth units to the surface of the crystal in the case of methyl stearate growing from n-dodecane solvent, and more diffusional controlled in the case of methyl stearate growing from kerosene and toluene solvents. The morphology of methyl stearate crystals however is not found to be strongly influenced by solvent type, only showing changes as a function of supersaturation in the case of kerosene solvent.

In the quest to mitigate demand for conventional petroleum derived transportation fuels and reduce their associated CO2 emissions, there are an increasing number of alternative fuels being proposed. Blending of such alternatives necessitates a comprehensive understanding of their combustion behaviour for effective and efficient commercial deployment. Therefore, characterisation of such blends fundamental combustion parameters relative to their constituents, under different operational conditions, is of essential importance. Two key parameters are that of laminar burning velocity and ignition delay time. The present work predominately focused on investigations of the former and the theoretical development of a universal predictive laminar burning velocity blending law, suitable for all commercial fuel types and those from chemically dissimilar families, such as methane and hydrogen. Aiding this development, an array of pure fuel/air mixtures and their blends burning velocities were measured by means of a constant volume combustion vessel, at a temperature of 360K, for pressures of 0.1, 0.5 and 1.0 MPa, at equivalence ratios from 0.8 to 1.3. Blends comprised of pure fuels representative of the major chemical families found within Fischer-Tropsch synthetic gasoline, namely, iso-octane, n-heptane, toluene, 1-hexene, and that of promising bio-derived alcohols, namely, ethanol and n-butanol. A proposed laminar burning velocity blending law was evaluated against existing laws, using the measured blend data, and existing data from other researchers, and on average, outperformed all. The acquired data also allowed investigations into linear and nonlinear flame speed/stretch relationships, and correlations between the critical Peclet and Karlovitz numbers with Markstein numbers, as a function of fuel type, pressure and equivalence ratio. Furthermore, during the present work, considerable efforts were made towards commissioning a rapid compression machine, which served to allow the concurrent collection of ignition delay data for the same blends by other researchers. This gave the opportunity for a conjoint investigation into the comparative effects of ethanol and n-butanol addition to a TRF gasoline surrogates burning velocity and ignition delay behaviour.

The main aim of the present work is to investigate the applicability of Large Eddy Simulations to pulverised coal combustion. The Navier-Stokes equations that describe an incompressible tur- bulent reactive flow are presented, with a source term which ac- counts for the effect of the coal particles on the gas phase. Both a Eulerian and Lagrangian approach are presented to describe the coal particles motion and their heat exchange with the gas phase. The main processes that characterise pulverised coal combustion: devolatilisation, volatile combustion and char combustion are described and the main models to represent them are presented. The performance of the numerical approximation is tested on two main experimental cases: 1) a pulverised coal jet flame surrounded by a methane pilot and 2) a 100 kWth swirling burner operating in an O2/CO2 environment. The results of the simulations are com- pared to qualitative and quantitative experimental measurements for both test cases. Finally a parametric study is performed on both test cases to understand firstly, which combustion processes are dominant and secondly to understand which models perform best for each experimental set-up. The results showed the Lagrangian approach to be more representative of the pulverised coal combustion process. The analysis for the pulverised coal jet flame, showed that the radiation and char combustion processes have almost negligible effect. Instead, the simulation results were highly sensitive to variations in the devolatilisation and volatile combustion models and model parameters. For the second test case, char combustion was dominant throughout most of the domain as the coal particles had a longer time to burn. The devolatilisation and volatile combustion processes were dominant at the initial stages of the combustion process and characterised the initial flame bhevaiour.

The economic viability for a microalgae production facility for the production of algal oil and bioproducts remains challenging and unanswered. Important aspects not investigated in assessment of the economic viability of algal oil are the social benefits, such as employment, local earnings and outputs created from such facilities. A model that is able to include both techno-economic and social benefits can help provide answers on the future of these technologies. The development of this type of model requires a combination of techno-economic and social impact theory. This thesis presents an integrated model that estimates the social (employment earnings, and output) and techno-economic impacts generated from a microalgae production facility. A process and system configuration of the algal production chain is selected first. The construction costs of the equipment are then calculated, followed by overall capital cost calculation. Then, the operating costs are estimated by multiplying the resources and energy usage rate by a unit price. Employment, earnings, and output generated from constructing and operating the facility is then calculated using output from the capital and operating cost with input – output multipliers to measure the impact of the series of effects generated by expenditure. The model as far as the author knows, is the first techno-economic model that addresses the social impact. A parametric analysis is carried out using two different methods to determine the viability of an algal oil production facility. Taking the economic costs and the operating parameters from the socio- techno-economic model, some key parameters are changed across a range of values, and their influence on the final cost of algal oil and job impact are analysed. The results shows highest cost contributor to the algal oil cost comes from capital costs. Productivity rate and lipid content have the highest impact both on the final algal oil costs, and the social impact outputs. Improvement would need to be made both in biology and system units.

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