The aim of this work was to develop an intensified syngas cleaning system for different applications of the cleaned gas. The main target of syngas cleaning is the destruction of tars although the removal of heavy metals is also important. The syngas cleaning strategies include water scrubbing followed by further cleaning and moisture reduction, low temperature capture of tars and destruction of tars at high temperatures preferably at the gasifier exit temperature. In the present study, initially a novel downdraft intensive 50kWe air-blown auto-thermal gasifier was used for the gasification of refinery sludge indicating that refinery sludge could be gasified with low levels of tar as a result of catalytic tar cracking during gasification since refinery sludge initially contained large amounts of catalytic rare earth elements. It contained tar and particulate matter of less than 90 ± 6.0 mg/Nm3 and calorific value of 3.71 ± 0.4 MJ/Nm3 (wet gas), which is sufficient for power generation using an internal combustion engine (ICE). Gas composition, tar content and heat content of the produced gas were determined. Results were compared with those obtained with wood chips (reference feedstock). In the development of intensified syngas cleaning systems, we used a model syngas (carbon dioxide) and model tar (crude oil). A new/novel, multi-functional tar removal rig was designed and fabricated. It can be used as a water scrubber or for tar removal under electric field in the absence or presence of biphilic (both hydrophilic to adsorb water and lipophilic to adsorb tars) adsorbents in the form of functionalized PolyHIPE Polymers (PHPs). These PHPs were produced, functionalized and characterized using environmental scanning electron microscopy (ESEM) and surface area analysis (SAA) and then used in the form of packed bed for the adsorption of model tars from model syngas. According to the literature, using the syngas in a power production application, the tar concentration in syngas needs to be less than 100 mg/Nm3 which requires particle and tars reduction efficiencies of 90 % for a satisfactory operation of an Internal Composition Engine (ICE) using syngas produced in a downdraft gasifier. vii Maximum tar removal efficiencies under the prevailing process conditions were: water scrubbing 45.9 ± 4.5 %; adsorption by the sulphonated PolyHIPE Polymers (s-PHP) 61.8 ± 2.5 %; high voltage application with conductive electrodes 97.5 ± 1.5 % at 25kV; and the combination of s-PHP with electric field resulted in 96.7 ± 1.9 % % tar removal efficiency. The advantage of high voltage gas cleaning is that it can be used at high temperatures and that no other material is used as adsorbent which requires regeneration once they are saturated with tar, etc. Finally, another electrical method was designed to crack the model tars using plasma induced catalytic conversion. The results indicate that hydrocarbon profile of crude oil in the model syngas shifted towards low carbon number.

Improved catalytic routes could help to transform the exploitation of the large worldwide natural gas reserves, whose principal component is methane. They transform methane into more valuable chemicals and fuels through carbon dioxide reforming of methane (CDRM), steam reforming of methane (SRM) and partial oxidation of methane (POM). These reactions facilitate the formation of syngas, which is subsequently converted to fuels through the Fischer-Tröpsch synthesis. Mixed Ionic and Electronic Conducting (MIEC) membrane reactors are of interest because they have the potential to produce high purity oxygen from air at lower costs and provide a continuous oxygen supply to reactions or/and industrial processes, and hence avoid sourcing the pure oxygen from air by conventional cryogenic separation technology. In addition, the MIEC ceramic membrane shows the ability to carry out simultaneous oxygen permeation and hydrocarbons oxidation into single compact ceramic membrane reactor at high temperature. This can reduce the capital investment for gas-to-liquid (GTL) plants and for distributing hydrogen. This study compares the oxygen release and oxygen uptake obtained through a LaSrCoFeO hollow fibre membrane (referred as LSCF6428-HFM) under an 0.60.40.20.83-δ Air/He gradient at 850°C and 900°C. The separation and quantification of these two processes permitted the determination of the oxygen incorporated into LSCF6428 structure and the development of a model for apparent overall rate constant using the molar flow of the oxygen at the inlet and outlet in different side of membrane (i.e. shell side and lumen side). The results show that the oxygen flux is enhanced by rising helium flow rates, this is due to an increased driving force for oxygen migration across the membrane and also the air flow determines the oxygen amount that permeates across the membrane. In addition, the oxygen flux improves at higher temperatures, due to its dependence on bulk oxygen diffusion and the oxygen surface reaction rates. The temperature increase improves the mobility of the lattice oxygen vacancies and also the concentration of lattice oxygen vacancies in the perovskite. The impact of surface modification was also studied by coating CoO and 5%Ni-LSCF6428 34 catalysts on the shell side surface of the LSCF6428 hollow fibre membrane for oxygen permeation. It was found that the oxygen flux significantly improved under Air/He gradient for catalyst-coated LSCF6428-HFM. However, under continuous operation conditions over a long time both the unmodified and the modified perovskite LSCF6428-HFM reactors suffered segregation of metal oxides or redistribution of metal composition at the surface membrane, although the bulk LSCF6428 membrane stoichiometry did not change. The apparent overall rate constants for oxygen permeation of the CoO/LSCF6428-HFM and 34 5%Ni/LSCF6428-HFM were enhanced 3-4 fold compared to unmodified LSCF6428-HFM. Comparison of both modified HFM reactors revealed that the apparent overall rate constants for CoO/LSCF6428-HFM were 2 fold higher than those obtained for 5%Ni- 34 LSCF6428/HFM. According to the distribution of total oxygen permeation residence for unmodified and modified LSCF6428-HFM reactor, the oxygen permeation rate is limited by surface exchange on the oxygen lean side or lumen side (R) at 850°C and 900°C and the ex contribution of bulk diffusion on the oxygen permeation rate increased with a rise in the temperature (900°C). The methane oxidation reaction was studied in unmodified and modified 5%Ni- LSCF6428/LSCF6428 hollow fibre membrane in reactors at 850°C. The results suggest that catalytic pathways in methane oxidation depended upon flow operation modes, oxygen concentration, Htreatment and on the type of catalyst. The performances in methane conversion of LSCF6428-HFM and 5%Ni/LSCF6428-HFM modules facilitated the formation of SrCO3 because of the reaction of CO2 with segregated strontium oxide.

Biogas is generated during anaerobic digestion (AD) of sewage sludge at wastewater treatment works (WWTW) and consists of approximately 50-70 % methane (CH4) balanced primarily by carbon dioxide (CO2). It is commonly used directly as a fuel gas for the renewable generation of electricity on-site by combined heat and power (CHP) engines. However, as a result of governmental incentivisation, biogas possesses a greater value when applied to the national gas grid as a natural gas substitute. However, this requires enhancement of the CH4 content to that comparable to natural gas by selective removal of CO2; a process known as biogas upgrading. This thesis explores the potential of hydrophobic micro-porous hollow fibre membrane contactors (HFMCs) to biogas upgrading. HFMCs allow non-dispersive contact between the biogas and a liquid solvent for the preferential absorption of CO2, which is conventionally facilitated by packed-column gas scrubbing technology. However, recent gas absorption literature has demonstrated many practical and operational advantages of HFMCs, which suggests they may be effective for biogas upgrading at WWTW. In this thesis, HFMCs were used to explore the mechanism and controllability of the undesirable co-absorption of CH4, known as methane slip. This was found to be attributable to the phase limiting mass transfer, with liquid-limited physical absorption in water exhibited 5.2 % slip whereas gas-limited chemical absorption displayed just 0.1 %. Ammonia-rich wastewaters were investigated as sustainable chemical absorbents using HFMCs and exhibited comparable chemically enhanced absorption to analogue synthetic ammonia solutions. The recovery of the subsequent reaction product (ammonium bicarbonate) by crystallisation facilitated by the membrane was also examined. The potential of this approach was summarised within two hypothetical wastewater flowsheets, where upgrading using a return liquor absorbent acts as a return liquor treatment and where ion exchange allows 100 % application of wastewater derived ammonia to biogas upgrading. These both offered potential economic advantages versus conventional flowsheets with 100 % biogas application to CHP.

This thesis looks at creating a multidisciplinary simulation tool for rotating plant equipment selection, specifically gas turbines, for the liquefaction of natural gas (LNG). This is a collaborative project between Shell Global Solutions and Cranfield University in the UK. The TERA LNG tool uses a Techno-economic, Environmental and Risk Analysis (TERA) approach in order to satisfy the multidisciplinary nature of the investigation. The benefits of the tool are to act as an aid to selection, operations and maintenance planning and it also acts as a sensitivity tool for assessing the impact of changes in performance, environmental and financial parameters to the overall economic impact of technology selection. The aim is to not only select technology on the basis of techno-economics but also on the basis of risk analysis. The LNG TERA tool is composed of a number of modules starting with the performance simulation which calculates the thermodynamic conditions in the core of the engine. Next, life estimates of the hot gas path components are made using a mixture of parametric and probabilistic lifing models for the turbine first stage blades, coatings, and combustor liner. This allows for a risk analysis to be conducted before maintenance and economics issues are dealt with. In parallel, emissions estimations are made based on empirical correlations. The modelling exemplifies a methodology which is uniquely applied to this application and there are no studies previous to this which look at so many aspects before making conclusions on plant machinery selection. Comparisons have been done between industrial frame engines based on the General Electric Frame 9E (130 MW) and Frame 7EA (87 MW) engines as well as more complex cycles involving aero-derivation and inter-cooling such as the LM 6000 (42 MW) and LMS 100 (100 MW). Work has also been carried out to integrate the tool to Shell based systems in order to utilise the database of information on failure and maintenance of machinery as well as its performance. The results of the integrated TERA show a clear favour for the aero-derivative engines and the main benefit is the fuel saving, though the life of the hot gas path components is deteriorated much faster. The risk results show that the industrial frame engines have a wider variation in expected life compared to aero-derivatives, though the industrial frames have longer component lives. In the context of maintenance and economics, the aero-derivative engines are better suited to LNG applications. The modular change out design of the aero- derivatives also meant that time to repair was lower, thus reducing lost production. Application of the LNG TERA tool was extended to power generation whereby a series of 6 engines were simulated. The changes required to the modelling were minimal and it shows the flexibility of the TERA philosophy. This study was carried out assuming a given ratio of load split between the engines and hence is sensitive to the way an operator demands power of the engine as opposed to LNG application where the operator tries to drive the engine as hard as possible to get the most production out of the train. The study was limited in the modes of failure which were investigated, a major further work would be to extend the methodology to more components and incorporate fatigue failure. Further, the blade creep and probabilistic coating models were very sensitive to changes in their respective control parameters such as coating thickness allowances and firing temperature. The contribution to the project from the MBA is the statistical techniques used to conduct the risk analysis and data handling as well as financial management techniques such as the Net Present Value (NPV) methodology for project evaluations.

This work is to develop a passive slug mitigation technique based on a novel flow conditioner, wavy pipe, through laboratory experiment and numerical simulation. The wavy pipe has been applied to two types of slug flows: severe slugging in pipeline/riser systems and hydrodynamic slug flow in horizontal pipelines. The experiment of severe slugging mitigation was conducted on the 2” and 4” pipeline/riser systems in the Three-Phase Test Facility in PSE (Process Systems Engineering) Laboratory. The flow regimes in the pipeline/riser systems have been classified into four categories, i.e. severe slugging, transitional severe slugging, oscillation flow and continuous flow. Experimental results have revealed that: (1) the severe slugging region in the flow regime map can be reduced by applying a wavy pipe; (2) the wavy pipe is more effective when there is a pipe section of an appropriate length between its outlet and the riser base; (3) a smaller severe slugging region can be obtained with a longer wavy pipe (of more bends); (4) even if there is no flow regime transition due to the application of a wavy pipe, the severity of the severe slugging and oscillation flow can be reduced instead. The effects of the wavy pipe have been summarised as reducing the slug length in the pipeline/riser system. For severe slugging the wavy pipe works by accelerating the movement of the gas phase in the pipeline to the riser base to initiate the bubble penetration stage; for the oscillation flow the wavy pipe works by mixing the two phases of gas and liquid. Two-dimensional CFD models of the 4” pipeline/riser and pipeline/wavy-pipe/riser systems were developed in Fluent (Release 6.3.26) and the effects of the geometrical parameters and location in the pipeline of the wavy pipe on severe slugging mitigation were investigated numerically. The model predictions of the flow regime transition and slug frequency in the pipeline/riser system agree with the experimental data well. It has been concluded from the simulation that: (1) for a given pipeline/riser system experiencing severe slugging, the severe slug length can be reduced further by increasing the amplitude or length of the wavy pipe, respectively; however, the mean, maximum and fluctuation amplitude of the drag and lift forces on the wavy pipe increase with the increase of the wavy pipe amplitude and the mean, maximum and fluctuation amplitude of the differential pressure across the wavy pipe increase with the increase of the wavy pipe length; (2) the location of the wavy pipe relative to the riser base has significant effects on the performance of wavy pipe; an optimum location of the wavy pipe exists for a pipeline/riser system at given operating conditions. The wavy pipe in a horizontal pipeline experiencing hydrodynamic slug flow was tested on a two-phase test facility in PSE Laboratory. The wavy pipe has been found to be able to mitigate the adverse impacts of hydrodynamic slug flow on the downstream facilities. It has been concluded that the wavy pipe works as a mixer which is able to agitate the gas/liquid two phases by its upward and downward limbs. More gas entrainment is introduced into the slug body in the wavy pipe. The entrained gas distributes in the slug body extensively due to the agitation effects of the wavy pipe. However, the flow tends to recover after a certain distance downstream of the wavy pipe. The horizontal wavy-pipe systems under hydrodynamic slug flow were modelled applying STAR-OLGA coupling. The mixing effects of the wavy pipe on gas/liquid two-phase flow identified in the experiment can be presented by the coupling model reasonably well. The effects of the geometrical parameters of the wavy pipe, i.e. amplitude and length, on hydrodynamic slug mitigation were examined. It has been concluded that: (1) a wavy pipe of higher amplitude does not always introduce better mixing effects because the longer upward limbs allow more liquid to accumulate thus the liquid slugs tend to reform; a wavy pipe with amplitude of 1.8d is more desirable than those of 1.1d and 2.5d (d the pipe diameter); (2) a wavy pipe of more bends (7 bends, L/d = 20.4, L the length of wavy pipe) is more favourable to mix the gas/liquid two phases than the shorter ones (5 bends, L/d = 16.5; 3 bends, L/d = 11.1) because more space and time can be provided for the two phases to interact with each other. The forces acting on a single bend induced by hydrodynamic slug flow were investigated using STAR-OLGA coupling. The predicted peak force on the bend agrees with the experimental data in the literature. The force components on different areas of the bend wall can be presented by the 3-D STAR model. The pressure-induced force contour plots have shown the most vulnerable part on the bend wall prone to mechanical damage.

Slugging is one of the challenges usually encountered in multiphase transportation of oil and gas. It is an intermittent flow of liquid and gas which manifests in pressure and flow fluctuations capable of causing upset in topside process facilities. It can also induce structural defects in pipeline-riser system. The threat of slugging to oil and gas facilities has been known since the early 1970s. This study investigated a new method for slug flow stability analysis and proposed the use of active feedback control and intermittent absorber (a passive device) for hydrodynamic and severe slugging attenuation. The geometry impact on the hydrodynamic slug flow in pipeline-riser systems was established using modelling (LedaFlow and OLGA) and experimental studies. The unit cell model in both software packages, the slug tracking model of OLGA and slug capturing model of LedaFlow were employed for hydrodynamic slug modelling. Three distinct slug regions were reported for a typical pipeline-riser system. The H-region typifies the slug flow regime in the pipeline-riser system due to slug formed in the horizontal pipeline upstream the riser pipe. The V-region represents the slug flow regime due to the riser pipe while the I-region describes slug flow regime where both horizontal and vertical pipes contributes to the dynamics of the slug flow in pipeline-riser system. A simple but yet robust methodology that can be used for pipeline-riser system and slug controller design was proposed. The active feedback control was shown to help stabilise hydrodynamic slug flow at larger valve opening compared with manual valve choking. For the case study, a benefit of up to 5% reduction in riserbase pressure was recorded for the proposed method. This in practical sense means increase in oil production. The analysis also showed that the new slug attenuation device (intermittent absorber) possesses the potential for slug attenuation. Experimental studies showed that the device was able to reduce the magnitude of riserbase pressure fluctuation due to hydrodynamic slugging up to 22%. The absorber enables larger valve opening for both hydrodynamic and severe slugging stabilisation. For severe slugging attenuation for example, a benefit of 9% reduction in riser base pressure was recorded for the case studied. This is of great benefit to the oil and gas industry since this translates to increased oil production. Slug attenuation index (SAI) and pressure benefit index (PBI), have been proposed to quantify the slug attenuation potential and the production benefits of the intermittent absorber respectively. The SAI and the PBI provided consistent results and methods for estimating the slug attenuation potential of the intermittent absorber concept. They could also be used to quantify the slug attenuation benefits of other slug mitigation techniques.

The present research extends the application of the “slug capturing” technique, already extensively validated for the prediction of horizontal slug flow, to the case of vertical pipes. In this technique, the one-dimensional two fluid model is solved numerically in order to simulate mechanistically the growth and development of the structures which characterise the vertical intermittent flow, such as slugs and waves. In this work the technique is first successfully applied to the prediction of vertical slug flow: it is shown here that, when the appropriate correlation for the interfacial friction forces is used, the slug capturing technique is able to simulate correctly – even in vertical configurations - the complete evolution of the slugs and to predict their key characteristics with a notable accuracy when compared against experimental data. This represents certainly the most important achievement of this work. The one-dimensional two-fluid model is well known to be ill-posed and hence, as the mesh is refined, artificial instabilities may grow so as to render the simulation unreliable. For this reason, a Von Neumann analysis of the discretized form of the model is presented. It is shown that the discretization introduces a cut-off limit for short wavelengths, below which all the perturbations are damped. It is suggested here that this effect, for practical sizes of the mesh, is sufficient to stabilize the system. Furthermore, this work presents preliminary results of the application of the technique to churn flow. It is shown that, although the results may be considered promising, the model still needs development.

Natural gas being the cleanest fossil fuel today is receiving tremendous rise in demand for both industrial and domestic energy requirements. The availability of natural gas requires it to be transported from the production area through pipeline in most cases to the consumers; this requires compressor station mostly driven by gas turbine. The development of gas pipeline system requires important data such as appropriate pipe sizes, gas rate, required delivery pressure, appropriate compressor and gas turbine sizes. The investment for the pipeline and compressor station is capital intensive and therefore the techno-economic and environmental risk assessment tool to rapidly assess the pipeline becomes imperative. The objective of this project is to look at advanced pipelines and the close coupling of the compression system with advanced prime mover cycles. The investigation offers a comparative assessment of traditional and novel prime mover options including the design and off-design performance of gas turbine engine and the economic analysis of the system. The originality of the work lies in the technical and economic optimization of gas turbines and fluid movers, based on current and novel cycles for a novel pipeline application in a wide range of climatic conditions. The techno-economic and environmental risk assessment (TERA) tool created is made up of a number of modules, starting with the pipeline and compressor station modules which compute the necessary flow parameters and compressor performance, as well as the required compressor power. The next is the gas turbine performance simulation module, TURBOMATCH software was used to simulate the performance of the selected gas turbine engines at design and off-design conditions and it computes the thermodynamic conditions in the core of the engine. Receiving information from the performance simulation module, the emission module, which is based on combustion equations, estimates the amount of emission over the period of operation of the gas turbine. The economic module, which is essential to the tool, receives information from all the other modules to establish the life cycle cost and use the net present value (NPV) methodology to assess the plant. It also calculates all associated costs, as well as the cost of transporting natural gas. The economic module establishes the economic pipe size for any particular throughput. The electric motor drive module is the parallel arm of the methodology, handling all the modules as explained earlier except the gas turbine performance and emission modules. This allows a comparative assessment of gas turbine and electric motor drives to be carried out under any prevailing conditions. This methodology is unique to natural gas pipeline techno-economic assessment and no previous studies have looked at various aspects of the pipeline project before selecting a prime mover or an economic pipe size. This study further uses a genetic algorithm optimization tool to optimize gas turbine selection and compressor station location along the pipeline, based on total cost objective function. The optimization is limited to a particular pipe size and gas throughput. The use of various pipe sizes as well as varying throughput will be a major area for further studies. The results from the individual models are presented in chapters 3, 4 and 5. The result of the integrated modules under case study one and two shows that the transportation of 0.5 million cubic meter per day of natural gas over long distance interstate pipeline for both prime movers is uneconomical. The economic pipe size for 3.0 million cubic meter per day of natural gas is 609.6 mm (24”) pipe size for the two prime movers with transportation cost of $0.063/m3 and $0.056/m3 for gas turbine and electric motors respectively. This is equivalent to $1.46/GJ and $1.30/GJ which agrees with the cost of natural gas transportation in literature. The result of the optimization shows a clear preference for the selection of a 34 MW plant for the pipeline and throughput considered since this presents the minimum cost which is the definition of the genetic algorithm optimizer. It is worth noting that this techno-economic tool, which is made of many modules, can be used to rapidly assess the profitability or otherwise of a natural gas pipeline project.

Depletion of conventional fossil fuel resources, as well as concerns regarding their environmental impact is a driving factor in the search for cleaner alternative fuels. Through the gasification of solid fuels, the produced syngas can be reacted to produce a cleaner, alternative liquid fuel. This thesis presents the development and use of a combination of fundamental and process models to evaluate alternative fuel production through a pressurised entrained flow gasification process. These include an equilibrium model, a one dimensional model and a process model. An equilibrium model using the non-stoichiometric approach based on the minimisation of Gibbs free energy and the Lagrange multipliers was established. A series of evaluations were performed to study the impact of the process conditions related to the entrained flow gasification, at the same time validating the model through comparisons with commercial software. It was shown that the model was not only quick to be developed, the results were also in excellent agreement with the commercial software it was compared to. A detailed one dimensional model of an entrained flow gasifier was developed from first principles. It is more complex than the equilibrium model, as it allows for evaluation of the variables along the length of the gasifier. Review of the available one-dimensional models of entrained flow gasifiers in the literature revealed inconsistent implementation of heat transfer mechanisms. The study showed that the solid-wall radiation along with the heterogeneous heat of reactions were the dominant heat transfer mechanisms in the entrained flow gasifier. In addition, although this model was developed specifically for a coal gasification process, assessment of biomass addition was also studied. ]t was shown that the best biomass mixtures were between 25% - 50%. A process model was developed in AspenHYSYS, which has enabled the entrained flow gasifier to be integrated with related auxiliary process equipment to model desired operating conditions. Implementation of the coal and biomass gasification for a polygeneration process is promising. Technoeconomic studies reveal that although biomass introduction may increase the costs of fuel, they are more environmentally-friendly as negative carbon emission can be achieved.

Anaerobic digestion with biogas production has both economic and environmental benefits. 25 % of all bioenergy in the future could potentially be sourced from biogas (Holm-Nielsen et al., 2009). Although anaerobic digesters have seen wide applicability, they typically perform below their optimum as a consequence of the complexity of the underlying process. This work involves the development of a generic advanced process control system for the optimisation of the performance of anaerobic digesters. There is a requirement for a configurable monitoring and optimisation system with associated sensors to optimise the production of biogas, combined with a degree of flexibility for quality and content of the digestate. Several analyses are conducted to establish the baseline performance of the four benchmarked sites. Significant findings are revealed which include lack of superior technology between the four varying processes, differing performance due to optimisation activities through increased monitoring and whole plant optimisation such as energy usage and production. Potential improvements are presented including increased monitoring and a reduction in the variability of key parameters such as thicker percentage dry solids (% DS), steady feed rate, and temperature. The lack of instrumentation in anaerobic digestion processes is a key bottleneck as sensors and analysers are necessary to reduce the uncertainty related to the initial conditions, kinetics and the input concentrations of the process. Without knowledge of the process conditions, the process is inevitably difficult to control. Financial gains that can be achieved through increased instrumentation were calculated to justify the business case for the need for process improvement. An instrumentation review is presented with the minimum and ideal instrumentation requirements for the AD process. Improved monitoring is achieved through soft sensor development for volatile solids (VS), an important variable that is currently only monitored offline. The inferential sensor is developed using data from an industrial process and compared with the results from a simulation study where feed flow and biogas production rate are used for modelling VS. This theme of improving monitoring with inferential sensors is continued with development of soft sensors with microbial data and data from different reactor designs.