The utilisation of waste materials as precursors for generating low-cost and effective carbonaceous materials, which can be used on a large scale, is very attractive and would help to solve the issues associated with waste disposal. In this work, scrap tyre, municipal solid waste in the form of refuse derived fuel (RDF) and date stones were selected for char and activated carbon production. The produced carbons were investigated as valuable adsorbent materials for control of (i) a problematic industrial nitric oxide (NO) gaseous pollutant or alternatively (ii) as a low-cost catalyst for tar cracking in relation to cleaning up the syngas produced from the gasification of biomass. The investigated carbonaceous materials were prepared using a fixed bed reactor. (i) The use of waste derived activated carbons as an adsorbent for NO removal under different test conditions at a low temperature of 50 ºC was investigated using a fixed bed reactor. The activated carbons were synthesised through carbonisation of the precursor at a temperature of 600 ºC, followed by subsequent physical activation with steam at 900 ºC. The NO removal efficiency of the waste-derived activated carbons was compared with different commercial carbons with varied porous texture and surface chemistry. Date stones activated carbon exhibited the highest NO removal efficiency of 40%, whereas a lower NO removal efficiency of 23% and 21% was obtained with RDF and tyre activated carbons respectively at 120 minutes time on stream. Commercially produced activated carbons had NO removal efficiencies of between 40% and 60%. The lower NO sorption of waste tyre and RDF activated carbons compared to those of commercial activated carbons or date stones was because of the difference in porous texture. Considering the Kinetic diameter of NO is 0.317 nm, effective adsorbents should exhibit a large volume of micropores. It was shown that the pores of the commercial activated carbons and date stones are mostly located in the micropore range of 1-2 nm (micropores), whereas RDF and waste tyre derived activated carbons have a much greater number of pores with diameters in the range of 2-10 nm (mesopores). Chemical activation can greatly alter the pore size and characteristics of the produced carbon. Therefore, surface modification of waste tyre was investigated via chemical activation to develop the porous texture and thereby enhance the NO adsorption capacity of tyre derived activated carbon. Thus, the influence of chemical activation of the waste tyre with KOH, K2CO3, NaOH and Na2CO3 on porosity development and the corresponding NO adsorption was investigated. It was shown that the activation of waste tyre with KOH favored the production of activated carbon with high micropore volume, which has been considered a key feature affecting NO adsorption at low temperature. Therefore, waste tyre activated with KOH at a char: KOH ratio of 1:3, with a total micropore volume of 0.437 cm3 g-1 and surface area of 621 m2 g-1 gave the highest NO adsorption capacity (17.23 mg g-1), which was double that of the physically activated tyre derived activated carbon. The results obtained in this study have shown that the adsorption capacity of carbonaceous sorbents relies greatly on the porous texture, in particular, the micropore structure of the carbon, as well as on the method of activation, but to a lesser extent on the BET surface area and acid-base surface groups on the carbon surface. (ii) Char materials derived from the pyrolysis of scrap tyre, RDF and date stones were also investigated in term of their use as a catalyst for the catalytic cracking of biomass pyrolysis gases during the two-stage pyrolysis/gasification of biomass. Biomass was used to generate a range of hydrocarbon gases typically found in biomass gasification tars through the pyrolysis of biomass. Among the investigated chars for bio-oil/tar decomposition, at a char cracking temperature of 800 ºC, tyre-derived pyrolysis char presented the highest activity resulting in a 70% reduction in bio-oil/tar yield compared to the non-char catalytic experiments. The results suggest that tar decomposition by char materials is mainly ascribed to the catalytic conversion of tar species, as the decrease of the hydrocarbon tar yields was accompanied with a consequent increase in total gas yield. Analysis of the tar composition showed the presence of naphthalene, fluorene and phenanthrene as the major polyaromatic hydrocarbon (PAH) components at the higher cracking temperature. To understand the tar decomposition mechanism and to further investigate the influence of porous texture and oxygen functional groups of char on tar decomposition process, the catalytic cracking of tar model (furfural, phenol, toluene, methylnaphthalene) over tyre char was investigated. The most reactive compound was furfural, followed by phenol and toluene, whereas methylnaphthalene presented the lowest reactivity. The results also indicated that both the porous texture and the oxygen functional groups of the carbonaceous materials had a marginal effect on tar decomposition. Additionally, tyre char was used as a sacrificial catalyst for the reforming/gasification of tars from the gasification of biomass to produce a hydrogen-rich syngas and also to contribute to the yield of biomass syngas through tyre char gasification reactions. The influence of tyre ash metals, catalyst bed temperature, steam to biomass ratio and reaction time were investigated. The metallic mineral content of tyre char has been shown to contribute significantly to the tar degradation. The maximum H2 content of the product syngas of 56 vol.% was obtained at a reforming temperature of 900 ºC and with steam to biomass ratio of 6 g g-1. Tyre char was also subjected to steam gasification during the process, whereby the tyre pyrolysis char catalyst is sacrificed to produce hydrogen and carbon monoxide to enhance the yield of the syngas. Overall, this research work shows that waste derived carbonaceous materials are low-cost promising adsorbents for NO control and tar removal from the syngas produced from biomass gasification.

Natural gas is a troublesome and ‘wayward’ material (Bridge, 2004; 396). Amongst other qualities, it is invisible, intangible, naturally odorless, highly inflammable, and constantly resistant to the forces that contain it. This thesis provides an account of how these qualities both introduce a series of insecurities to everyday social environments, and also make it a challenging material to govern. Specifically, I examine the way that security is performed around gas circulations in the UK’s transmission and distribution pipelines, and I describe how a range of specialized security practices have been developed according to the particular challenges that gas’s materiality presents. In developing this account, I make two claims. First, I argue that performances of security cannot be adequately understood without attending to the specific qualities of the circulating elements around which it is practiced. Here I build upon Dillon’s (1996) observation that security has tended to be treated as a noun that is independent of the elements that it is practiced in relation to. As a consequence, it has typically been framed as a broadly transferrable set of practices that can be more-or-less unproblematically applied to very different elements. I suggest that this abstraction has resulted in the further reduction of security into two broad practices: acts of circulatory filtration (in which risky elements are separated from flows of safe bodies, materials and things), and acts of circulatory maintenance (whereby security is performed by ensuring the continuity of particular circulations). It is my contention in this thesis that security scholars need to pay better attention to the ways in which the specific material qualities of circulating elements are generative of particular forms of securing practice. Indeed, by examining the way that security is performed around gas, I describe a series of practices that far exceed those described in accounts that present security as a matter of circulatory filtration or maintenance. My second claim is that the spaces and scales at which security is analyzed need to be expanded. I demonstrate how the critical security studies and energy security literatures have both tended to focus on security’s practice within particular nodes, at the exclusion of the performances of security (and forms of insecurity) that develop across the journeys of circulating elements; as they move between nodes. Indeed, I suggest that circulation has often been reduced in these accounts to thin, straight, and featureless lines that are largely inconsequential for performances of security. I seek to trouble this reduction, following gas as it travels through the UK gas transport infrastructures, tracing the various forms of (in)security that develop across these journeys. As a consequence of these two claims, security takes quite a different form in this account to its various depictions in the existing security literatures. I describe it as consisting of a series of ontological projects that are enacted across the lengths and breadths of gas’s circulations, and through which the material reality of natural gas is constantly (re)organised in attempts to facilitate, ‘compensate for’, and ‘cancel out’ particular kinds of perceived potential phenomena (Foucault, 2007; 36). Significantly, these performances are shown to be structured, or ‘programmed’ (Latour, 1991), through the coming together of multiple interests that pertain to a variety of heterogeneous actors and manifold referent objects. Different interests are shown to come together across gas’s journeys, and to undergo ongoing processes of negotiation that result in a variety of security performances, through which different imperatives are pursued. As such, I suggest that gas becomes ‘modulated’ (Deleuze, 1992) – it is constantly transformed from moment to moment, across the full duration of its circulatory journeys.

Two-phase ow analyses are critical to successful design and operations of liquid-gas pipe ow applications found in major industrial fields, such as petroleum, nuclear, chemical, geothermal and space industries. Due to diffculties in obtaining analytical solutions, approximate solutions have been applied to two-phase flows. However, several limitations still exist, and categorised into three prediction models, namely: ow regime, pressure gradient, and transient models. Previous studies show that existing ow regime models and maps for horizontal flows under-predicts transition from stratified to annular flow. Furthermore, there is requirement to include criteria for identifying mist and plug flows in unified flow regime model. In order to improve under-prediction in stratified to annular prediction, nondimensional liquid lm height in original criterion is replaced with nondimensional liquid holdup. This shifts stratified to annular transition line towards higher gas superficial velocity thus improving prediction. Using experimental data available in literature, a simple flow rate dependent criterion is proposed for identifying the existence of mist flow. Two criteria are proposed for identifying plug flow in horizontal and inclined flows. The first criterion is the exact criterion for identifying bubble flow in vertical flows. The second criterion is also based on bubble flow criterion but fitted to experimental data. Transition criterion for the existence of dispersed-bubble flow is also proposed, based on stability of gas bubble in liquid ow. These flow regime criteria are combined in a solution algorithm to obtain a unified flow regime model, which has been verified using existing unified flow regime models and map, and validated using experimental data. Mechanistic or phenomenal methods are generally applied in predicting pressure gradient in two-phase liquid-gas pipe flow. These methods relies on prior knowledge of prevalent flow regime, and subsequent application of flow regime specific pressure gradient model. This approach is susceptible to error should wrong flow regime be selected. In order to overcome this problem, a Single Equation Two-Phase Mechanistic (SETM) model is proposed. SETM is obtained by combining: liquidgas momentum equations, existing and modified flow regime criteria, and new flow regime boundaries at the initiation and completion of transition to annular flow. Thus, SETM implicitly determines pressure gradient and flow regime in liquid-gas pipe flow, and also captures liquid-gas interface transition from at to curved interface. SETM is applicable to all pipe inclination, and has been validated using experimental data available in literature. Further, prediction of flow characteristic features per ow regime, such as identified flow regime, liquid holdup in slug lm region, ratio of slug regions, and apparent liquid heights, have been verified against theoretical limits for different flow regimes. Alternative to SETM, modified homogeneous pressure gradient model is also proposed for liquid-gas pipe flow. Existing homogeneous models are applicable to dispersed bubble flow, and slug flow with low or negligible liquid-gas slip. The modified homogeneous model is obtained by correcting mixture fanny friction factor using error between experimental pressure gradient and unmodified homogeneous pressure gradient; observed error is particularly large at high liquid-gas slip values. The modified homogeneous model is therefore applicable to all flow regimes, including stratified, annular, and mist flows. The modified model has been verified against existing homogeneous model, and validated using published experimental data. Transient analysis is critical to liquid-gas pipe flow design. Rigorous analytical solution is generally not available. Alternative solution method is full numerical solution approach, which is subject to high demand on computational resources and time, especially for long pipelines. Hence simplified transient methods are sort. Existing simplified transient liquid-gas pipe flow models assume quasi-steady state conditions for liquid-gas momentum equations, thus neglecting convective terms in the momentum equations. The simplified transient liquid-gas pipe ow model proposed in this study include: (a) transient liquid-gas continuity equations, (b) transient convective terms of liquid-gas momentum equations, and (c) steady state pressure gradient terms of liquid-gas momentum equations. The proposed transient model captures gas and/or liquid flow variations at coarse pipe discretisation, and has been validated against published experimental data and verified with a proprietary program (OLGA).

No description available.

A pig is a maintenance tool used in the Oil and Gas Industry, chiefly to remove solids or liquids from pipelines. It is in essence a sliding seal, which moves due to the action of the fluid pushing it. The aim of this work is to describe the steady state motion of the pipeline pig in terms of several key characteristics. An analytical model of the pig motion has bey prepared to calculate these parameters. The model also shows how these characteristics vary with velocity and distance due to wear. All assumptions and limitations are listed. The model has been verified by tests performed on a 10' carbon steel pipeline. The model works by f rstly calculating the force exerted by the pig seal on the pipe wall. A generalisation of the seal shape allows calculation of the contact parameters. A simplified lubrication analysis ensues, enabling calculation of the seal film profile. Knowledge of film thickness allows estimation of friction, differential pressure and leakage rates. Varying pig velocity affects the film shape and thickness, which in turn affects seal friction and therefore alters the program output. Changes in pig characteristics due to abrasive wear are accounted for using a wear coefficient and estimating the volume of material removed over successive distance increments. The model compares well with the experimental remits for characteristics such as differential pressure and friction For this reason the wall force, contact and surface roughness models (i.e. the mechanical We of the problem) are considered to be accurate. However, agreement between leakage test results and the model was less well defined and it is apparent that the hydrodynamic analysis requires further study.

Chapter 1 provides an overview of the past developments in the field of syngas conversion. Previously developed heterogeneous and homogeneous catalytic systems for syngas conversion are discussed along with the different mechanisms proposed for these processes. The use of main group and metal hydrides in CO reduction is covered, along with hydrogen activation chemistry and their application for syngas conversion. Step-wise systems for indirect syngas conversion are also described. Chapter 2 describes the synthesis and characterisation of novel transition metal complexes bearing substituted bipyridyl ligands with pendant basic groups. The reactivity of the complexes towards carbon monoxide and hydrogen is also investigated. Chapter 3 describes the synthesis and characterisation of novel transition metal pincer complexes. The reactivity of these complexes with hydrogen and carbon monoxide is reported and the fluxionality of a Ru(II) complex is studied. In Chapter 4, the reduction of carbon monoxide at a metal centre with metal hydride complexes is described, along with in situ hydrogen activation to form the hydride donors. The mechanisms and products of the reactions are investigated, and the implications with regard to syngas conversion discussed. The CO tolerance of novel transition metal complexes in the hydrogenation of carbonyl substrates is also reported. Experimental details relating to the synthesis and characterisation of the novel compounds in Chapters 2 to 4 are detailed in Chapter 5.

Injection of supercritical CO2 allows us to sequester an important component of the greenhouse gases in the subsurface to reduce emissions of CO2 in the energy sector. In light of global environmental change, it is of utmost importance to reliably predict the fate and containment of injected CO2 at geological time scales. Therefore, modelling of the CO2 plume migration and its containment within geological carbon storage repositories helps to uncover and understand challenges arising during injection and post-injection phase. Discrete fracture and matrix (DFM) simulations have emerged as a powerful technology to analyse the fundamental flow and transport properties in naturally fractured reservoirs and bridge gaps between geosciences and reservoir engineering: they help to validate upscaling workflows, improve the analysis of pressure transients from welltests, and allow to explore how uncertainties in fracture network properties impact hydrocarbon recovery. The key difference between DFM simulations and traditional dualporosity approaches is that the structurally complex fracture geometries are explicitly discretised as 2D surfaces in a 3D reservoir model, hence provides a more geologically realistic representation of the fracture patterns and rock matrix as compared to dualporosity models. Here I extend the DFM simulation workflow to account for capillary trapping of CO2 in fractured porous media. Fluid flow is described by a fully compositional model including an equation of state for CO2-H2O-NaCl fluids. The governing equations are discretised in space using unstructured and mixed-dimensional finite element - finite volume techniques. An Operator splitting approach is used to decouple capillary diffusion from the mass balance equation. For the first time, relative permeability hysteresis within the DFM method has been performed. I demonstrate how my new DFM approach can be applied to simulate CO2 injection and trapping of CO2 in fractured geological formations with geologically realistic fracture networks. I show how matrix diffusion and capillary forces influence the rate at which CO2 is trapped in the rock matrix.

Hydrogen can be used as fuel for power generation; however current hydrogen production processes are not sustainable as they involve considerable CO2 emissions, and are mostly based on production from fossil fuels. Municipal solid waste (MSW) in the form of refuse derived fuel (RDF) can be subjected to thermal processes such as pyrolysis and/or gasification to produce a hydrogen rich syngas. Nevertheless some operational problems associated with tar formation arise, which significantly reduces the overall process yield. In this work a two-stage reaction system was used for hydrogen production and tar reduction, during the pyrolysis/gasification of RDF, using different types of catalysts. Firstly RDF was pyrolyzed at 600ºC, the pyrolysis gases were then passed through a second gasification stage where the catalytic steam reforming process took place at 800ºC, in order to generate hydrogen and promote tar cracking reactions. Different analytical techniques were used in this work to characterise RDF, product gases, tars/oils, and fresh/reacted catalysts. Initially two different Ni/Al2O3 catalysts were prepared, and their catalytic activity towards hydrogen production and tar reduction were assessed during the pyrolysis/gasification of RDF. The results were compared with those obtained using a bed of sand. Using a 10 wt.% Ni/Al2O3 catalyst, about 45 vol.% of hydrogen in the syngas was obtained together with other gases: CO2, CO, CH4, C2-C4. Also the condensed tar fraction was analysed and was found to contain polyaromatic hydrocarbon (PAH) constituents included naphthalene, fluorene and phenanthrene as the major components. Additionally, diverse Ni/SiO2 catalysts were prepared using different synthesis methods, including sol-gel,impregnation and homogenous precipitation. Among the catalysts tested for tar reduction, a 20wt.% Ni/SiO2 catalyst presented the highest activity resulting in a tar concentration of 0.15mgtar g-1RDF; PAH and oxygenated tar compounds were also identified within the analysed samples. For the catalysts tested in relation to hydrogen production, using a 10wt.% Ni/SiO2 catalyst prepared by homogeneous precipitation-sol-gel based method, resulted in a H2 concentration of 59 vol.%. Finally different Fe/SiO2 and Ni/SiO2 catalysts were prepared using nano-porous silica as the oxide support. Better catalyst activity in relation to H2 production was observed for the Ni/SiO2 catalysts. However the maximum H2 concentration obtained was around 44 vol.%. It was found that using calcination temperatures higher than 700ºC, both the surface area and the catalytic activity for hydrogen production was diminished for this series of catalysts.

No description available.

Weathering occurs in stored liquefied natural gas (LNG) due to the removal of the boil-off gas (BOG) from the LNG container and results in the remaining LNG being richer in heavier components. A model has been developed to predict stored LNG weathering in containment tanks, typically used in regasification. The model integrates a vapour-liquid equilibrium model, and a realistic heat transfer model. It provides a number of advances on previously developed models: (i) heat ingress is calculated based on outside temperature and LNG composition, allowing for daily/seasonal variations; (ii) boil-off-ratio is not an input; (iii) LNG density is estimated using an experimentally based correlation. The model was validated using real industry data and the agreement obtained in predicting overall composition, density and amount vaporized was within industry requirements. Two modelling approaches have been developed: (i) assuming thermodynamic equilibrium between vapour and liquid; and (ii) assuming heat exchange between the two phases. Both models were run in a predictive mode to assess the BOG under different scenarios. One of the main results of this work is that the BOG generation is 25% less when considering the non-equilibrium approach, which will have a significant impact on industry where simple equilibrium models are used. In the initial stages of weathering nitrogen content of LNG has a marked effect on BOG generation. Even 0.5% mol of nitrogen leads to nearly 7% BOG decrease, making the initial BOG unmarketable. That is a result of preferential evaporation of nitrogen and increase in the direct differential molar latent heat. In the final stages of weathering the heavier hydrocarbons govern the BOG dynamics, which becomes a strong function of initial composition and the LNG remaining in the tank.