The separation distance (pitch) between obstacles is an area that has not received adequate attention by gas explosion researchers despite general recognition of the important role it plays in determining the explosion severity. Either too large or too small a separation distance between the obstacles would lead to lower explosion severity. Therefore obstacles would need to have “optimal” separation distance to produce the worst case explosions overpressures and flame speeds. Most studies to date with multi-obstacles had the obstacles too closely packed resulting in data that most likely do not represent the worst case scenarios. The major objective of this project was to investigate the influence of spacing between obstacles in gas explosions by systematically varying the distance in order to determine the worst case separation that will produce the maximum explosion severity. A long vented cylindrical vessel 162 mm internal diameter with an overall length to diameter ratio (L/D) of 27 was used in the experimental study. The vessel was closed at the ignition end and its open end connected to a large cylindrical dump-vessel with a volume of 50 m3. The spacing between the obstacles in the test vessel was systematically varied from 0.25 m to 2.75 m. The influence of obstacle spacing was studied with obstacles of different blockage ratios, shapes, number and scale. Tests were carried out with methane, propane, ethylene and hydrogen mixtures with air. A correlation was developed and applied in this research to predict the position to maximum intensity of turbulence downstream of an obstacle, xmax dimensionalised with obstacle scale, b as a function of obstacle blockage ratio, BR, using steady state experiments from the limited available data in the literature as, ( ) for t/d < 0.6 (thin/sharp obstacles) A clearly defined separation distance which gave the most severe explosions in terms of both maximum flame speed and overpressure was found in this research. The profile of effects with separation distance agreed with the cold flow turbulence profile determined in cold flows by other researchers. However, the present results showed that the maximum effect in explosions is experienced further downstream than the position of maximum turbulence determined in the cold flow studies. It is suggested that this may be due to the convection of the turbulence profile by the propagating flame, after the flame has moved passed the obstacle. The predicted model on position to maximum intensity of turbulence from cold flow data agreed with the worst case obstacle separation distance in the current research if multiplied by a factor of three. Turbulence parameters were estimated from pressure differential measurements and geometrical obstacle dimensions. This enabled the calculation of the explosions induced gas velocities, r.m.s turbulent velocity, turbulent Reynolds number and Karlovitz number. By expressing these parameters in terms of turbulent combustion regimes, the bulk of the tests in this study was shown to be within the thickened-wrinkled flames regime. Turbulent burning velocity, ST models with dependence on obstacle scale, higher than the ones in the existing gas explosion scaling techniques were obtained as, for single hole-obstacles for single flat-bar obstacles From the newly obtained ST correlation for single flat-bar obstacles, an overpressure correlation, P for scaling relationship was derived and validated against both small and large scale experimental data and the results were encouraging. [( √ ) ][ ] In planning the layout of new installations, it is appropriate to identify the relevant worst case obstacle separation in order to avoid it. In assessing the risk to existing installations and taking appropriate mitigation measures it is important to evaluate such risk on the basis of a clear understanding of the effects of separation distance and congestion. The present research would suggest that in many previous studies of repeated obstacles the separation distance investigated might not have included the worst case set up, and therefore existing explosion protection guidelines may not correspond to worst case scenarios.

Fouling of calcium sulphate is commonly observed in industrial heat exchangers and desalination membranes. The build-up of a fouling layer can reduce plant efficiency by a considerable extent resulting in higher energy demand, carbon footprint, and cost of operation. Traditional fouling mitigation methods are effective, but require maintenance downtime and use of hazardous chemicals. This project is aimed at exploring a novel approach in mitigating fouling through the addition of porous silica particles, which can help control the crystallisation process of calcium sulphate. Silica particles are a practicable alternative to traditional methods due to their low cost of production, tractability, and low environmental impact. The crystallisation of calcium sulphate is investigated using two primary experiments. The first experiment investigates the crystallisation of calcium sulphate inside a batch crystalliser. The progress of crystallisation is tracked online by measuring the variation of the solution's electrical conductivity in time, while the final crystal size distribution is measured externally using laser diffraction. The crystallisation process is modelled using the population balance equation, which considers the evolution of the crystal size distribution in time in the presence of nucleation, growth, agglomeration, and breakage. The model is solved numerically using the method of classes. Experiments show that porous particles can reduce the crystallisation induction time by enhancing the rate of homogeneous nucleation. Comparison between porous particles of various pore diameters and silica nanoparticles reveal that the pore volume is the significant parameter in nucleation enhancement (more so than pore diameter or surface area). Furthermore, gas sorption measurements showed a decrease in available pore volume, indicating that pores are blocked during crystallisation. Population balance modelling suggests that the confined space of the pore increases nucleation by increasing the frequency of collision between free ions. Pore deactivation is modelled through heterogeneous nucleation. The surface chemistry of the particles was functionalised to further enhance the pores' effect on nucleation. Amine functionalisation was observed to decrease the nucleation induction time by 26% at a loading of , whereas TAAcOH functionalisation was observed to increase nucleation induction time by a six-fold at a loading of . The second experiment investigates the surface crystallisation of calcium sulphate in the presence of continuous flow. The deposition of calcium sulphate crystals is measured using a microscope camera and a quartz crystal microbalance (QCM), which is capable of measuring the deposited mass in real-time by using a piezoelectric sensor. Measurements of surface crystallisation take place in a customised in-house designed flow cell that contains the QCM sensor. Raw QCM data (depicting complex frequency shifts) were translated into mass using an equivalent circuit model. A novel equivalent circuit equation was developed for the unique QCM data observed during the flow experiment. Together with imaging data, the model was used to calculate nucleation, growth, and mechanical properties of the crystals. The stiffness of the crystal was found to decrease with decreasing supersaturation.

Corrosion and scale deposition on pipelines are two of the major flow assurance issues which have been recognized in the oilfield. Corrosion control of carbon steel pipelines requires understanding of the simultaneous occurrence of both processes. To date there have been few studies demonstrating the interactions between surface scale deposition and corrosion processes. Combined scale/corrosion inhibitors (mixture of scale and corrosion inhibitors) are gaining in popularity in the oil and gas industry as one of many methods to mitigate both those processes. A newly developed methodology of combined bulk jar scaling/bubble cell technique (corrosion) was used to assess the corrosion rate, CaCO3 deposition on the material surface and bulk precipitation in a CO2 environment. In this study the effects of single components of scale and corrosion inhibitors on the corrosion processes (general and localized corrosion) and scale deposition (bulk and surface deposition) have been investigated. Surface analysis techniques (SEM, EDX and Light Interferometry) and bulk analysis (Turbidity meter and ICP-MS) enable the corrosion/scale mechanisms to be studied in detail for X65 pipeline material. An experimental design method has been used to evaluate single and/or synergistic effect of single components of combined scale/corrosion inhibitor on the corrosion and scale processes. The methodology used in this study a newly-developed combined bulk jar scaling/bubble cell prove that is very effective tool in assessment of corrosion and scale interactions when they occurs simultaneously. Assessment of calcium carbonate precipitation on the sample showed that scale plays an important role of accelerating pitting corrosion by providing a suitable environment. XRD analysis showed that the calcium carbonate crystals which formed on the metal sample in the tests with 2-mercapthoethanol were calcite crystals only. The simple linear regression model was developed to predict corrosion and scale when these process occur simultaneously. The model also enables the interactions between the corrosion and scale inhibitor components to be quantified.

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This work presents a novel method of Sn-infiltration on SOFC anodes for SOFC operation in biogas dry reforming. Using commercially available NiYSZ-based anode supported half cells with hand-painted LSM/YSZ cathode layers, Sn-infiltrated NiYSZ SOFCs containing different amounts of Sn were manufactured. These SOFCs were tested for their electrochemical performance and quantity of deposited carbon during operation on simulated biogas of 1:2 volume ratio of CO2:CH4 without humidification but with 25% Helium added to the feed stream to enable measurements of the fuel cell outlet gas composition using a quadrupole mass spectrometer. Most of the SOFCs were tested in biogas for 1 day (22 hours), but several cells were tested for 6 days (150 hours) to evaluate performance degradation. The electrochemical performance tests at 750 oC showed that with H2 as fuel the non-infiltrated NiYSZ SOFCs were able to reliably generate a moderate level of current of 350 mA cm-2 at 0.7 V; however when simulated biogas was introduced, current dropped significantly to 90-200 mA cm-2. Contrary to non-infiltrated cells, a series of Sn-infiltrated cells under the same operating conditions performed equally well both on H2 and biogas producing 310 to 420 mA cm-2 at 0.7 V. Several cells showed stable electrochemical performance over 150 hours of operation both on H2 and biogas. Using Temperature Programmed Oxidation (TPO), both Sn-infiltrated and non-infiltrated SOFCs showed low quantities of carbon formed during 22 hours operation on biogas. Visual observation and SEM images of the anode surface after 150 hours operation on biogas showed no sign of deposited carbon. The conclusion is that Sn-infiltrated NiYSZ-based SOFC can be operated on simulated biogas with significantly higher electrochemical performance and low carbon deposition, given the anode is adequately modified.

Underground coal gasification (UCG) has the potential to access vast resources of stored fossil energy in a safe, clean and environmentally sound manner. Previous experiments have however led to concerns around surface subsidence, groundwater pollution and water table lowering. These issues can be prevented through the use of appropriate site selection and an understanding of the processes which cause these effects. Numerical simulations provide a cost effective means of predicting these issues without the need for costly and publically opposed field trials. This work uses a commercially available discrete element code to simulate the coupled thermal, hydraulic and mechanical phenomena which cause environmental damage. Surface subsidence is predicted through the displacements of fully deformable discrete elements separated by a network of fractures. The flow of groundwater through these fractures is simulated in order to predict the effects of water table lowering and the inflow of groundwater into the UCG cavity. Heat conduction from the cavity walls is simulated using an explicit finite difference algorithm which predicts both thermal expansion effects and the influence of temperature on rock material properties. Comparison of results with experimental observations in the literature show good agreement for subsidence and groundwater behaviour, while initial predictions for a range of designs show clear relationships between environmental effects and operating conditions. Additional work is suggested to incorporate groundwater contaminant transport effects, and it is envisioned that the overall model will provide a valuable screening tool for the selection of appropriate site designs for the future development of UCG as an economically viable and environmentally sound source of energy.

While the individual need for dosage of nickel and cobalt in anaerobic digesters has been established, together with the biochemistry underpinning such need; their co-requisite in anaerobic digestion of acetate has not been extensively studied. In addition, the balance between the catalytic and toxic concentrations of nickel and cobalt in anaerobic acetate digesters is not well documented. The aim of this study was to examine and evaluate the effects of individual and combined dosage of nickel and cobalt on biogas production as well as on methanogenic population balance of a mesophilic (37°C) anaerobic acetate digester so as to determine their catalytic and toxic concentrations. Four semi-CSTR digesters were daily fed acetate at a loading rate of 1.8 g L-1 d-1 and were operated at a HRT of 10 days for this investigation. Co-dosage of nickel and cobalt in anaerobic acetate digesters were found to lead to increased biogas production in an additive manner, with the sole dosage of nickel resulting in more biogas production than that of cobalt. At a large enough concentration, these elements were found to inhibit biogas production.

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Slugging involves pressure and flowrate fluctuations and poses a major threat to optimising oil production from deepwater reserves. Typical production loss could be as high as 50%, affecting the ability to meet growing energy demand. This work is based on numerical simulation using OLGA (OiL and GAs) a one- dimensional and two-fluid equations based commercial tool for the simulation and analysis of a typical field case study in West Africa. Numerical model was adopted for the field case. Based on the field report, Flow Loop X1 consisted of well X1 and well X2, (where X1 is the well at the inlet and X2 is the well connected from the manifold (MF)). Slugging was experienced at Flow Loop X1 at 3000 BoPD; 4MMScf/D and 3%W/C. This study investigated the conditions causing the slugging and the liquid and gas phase behaviour at the period slugging occurred. The simulation work involved modelling the boundary conditions (heat transfer, ambient temperature, mass flowrate e.t.c). Also critical was the modelling of the piping diameter, pipe length, wall thickness and wall type material to reflect the field geometry. Work on flow regime transition chart showed that slugging became more significant from 30% water-cut, especially at the riser base for a downward inclined flow on the pipeline- riser system. Studies on diameter effect showed that increasing diameter from 8” – 32” gave rise to a drop in Usg (superficial velocity gas) and possible accumulation of liquids on the riser- base position and hence a tendency for slugging formation. Depth effect study showed that increasing depth gave rise to increasing pressure fluctuation, especially at the riser- base. Studies on the Self-Lift slug mitigation approach showed that reducing the internal diameter of the Self-lift by-pass pipe was effective in mitigating slug flow. S3 (Slug suppression system) was also investigated for deepwater scenario, with the results indicating a production benefit of 12.5%. In summary, the work done identified water-cut region where pipeline-riser systems become more susceptible to slugging. Also, two key up-coming slug mitigation strategies were studied and their performance evaluated in-view of production enhancement.

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