Browsing by Author "Oakey, John"

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    Biomass thermal conversion : pelletisation of lignocelluloses and the effect on the gasification process
    (Cranfield University, 2012-03) Kallis, Kyriakos Xenofon; Oakey, John; Simms, Nigel J.
    Agricultural residues and energy crops constitute an important part of the energy chain although they are not being used extensively in the energy generation processes since they are associated with disadvantages such as low bulk and energy densities and handling problems. One solution is the pelletisation of these residues, which solves a great deal of these problems and enables the competition of biomass with other types of fuels. A large amount of work, concerning the combustion of biomass pellets, has been done previously, however, studies on biomass pellet gasification are still limited. An effort is made, in the current project, to connect the pelletisation and the gasification processes so that the work presented here could constitute a guide to the industry. The quality of the pellets to be gasified is affected by the initial pelleting parameters, namely the feedstock moisture content, the feedstock particle size and the die diameter. These parameters in turn, affect the process of gasification. These relationships were studied with the purpose of finding an optimum behaviour in the pelleting process that would allow high efficiencies of pellet gasification. The agricultural residue investigated was oilseed rape due to high cultivation in the UK. Oilseed rape straw (OSRS) was pelletised and used in two types of gasifiers; a downdraft and a spouted fluidised bed gasifier. Other types of biomass pellets such as Miscanthus pellets and Dried Distillers Grains with Solubles (DDGS) pellets were also studied. The gasification performance of the OSRS pellets was compared with the performance during gasification of Miscanthus and DDGS pellets. The results showed that dry and large pellets required more energy to be manufactured than the wet and small pellets. In addition, the results revealed the connection of the initial pelleting parameters and the quality of pellets which was assessed in terms of the pellet density, the bulk density and the pellet durability. The wet pellets with a small particle size had the highest density and the dry pellets had the highest bulk density and durability. The effect of the initial pelleting parameters on the gasification was also studied. It was found that the high feedstock moisture content negatively affected the gasification performance in both downdraft and spouted fluidised bed gasification. The feedstock particle size did not have an effect on the downdraft gasification but a minor effect was identified for the spouted fluidised bed. Large pellets were unable to be processed in the downdraft gasifier due to the increased bed porosity and pellet density and decreased amount of active carbon sites, while both large and small pellets were successfully processed in the spout bed gasifier. The gas higher heating value (HHV) produced in gasification was typically quite low, of between 2-4 MJ/m3. The comparison of the pellets showed that Miscanthus pellets had the highest gasification performance followed by the dry OSRS pellets, the wet OSRS pellets and finally the DDGS pellets. The most important reason for these differences was identified to be the ash content of the pellets.
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    Deposition prediction in a pilot scale pulverized fuel-fired combustor
    (Elsevier, 2019-05-27) Chiara, Riccio; Simms, Nigel; Oakey, John
    Fossil fuels have traditionally been used in power generation systems and represent the main source of greenhouse gas emissions from this sector. Renewable fuels, especially biomass, are now being substituted for fossil fuels to reduce CO2 emissions. Co-firing biomass with coal, which has been widely practised in the UK and Europe, is one route to reduce the environmental impact of using coal. However, the deposition of ash particles and vapour species on heat exchanger surfaces during operation is a serious issue in pulverised coal and biomass fired power plant as this reduces the plant thermal efficiency and can cause fireside corrosion, which limits component lives. Deposit formation is difficult to predict as it varies with many factors including: boiler geometry, combustion conditions and fuel composition. Computational Fluid Dynamics (i.e. CFD) is one of the best modelling tools to study the flow behaviour of gases and particles around heat exchanger tubes and predict deposition. This work used an Eulerian-Lagrangian model to describe the gas flow field around tubes and the solid ash particle trajectories respectively. User Defined Functions (i.e. UDFs) were developed for the CFD package to enable the prediction of deposit growth, deposit shape and temperature gradients around superheater/reheater tubes. Deposit build up insulates such tubes from the flow of the hot combusted gas stream and reduces heat transfer between this gas stream and the steam coolant following within the tubes, thus raising the deposit temperature. The CFD-based predictions generated were consistent with available literature data. The CFD deposition model has been applied to predict deposition on air cooled ceramic probes in a 100 kWth pilot-scale, pulverized fuel (PF) combustor and compared to deposition data measured after the combustor rig runs. For modelling purposes, the geometry was simplified to a two-dimensional domain with inert spherical ash particles dispersed in air and injected at an inlet plane. Experimental data from a series of rig runs have been used to test this CFD deposition modelling approach
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    Development of a novel method for cross-disciplinary hazard identification
    (Cranfield University, 2013) Parchment, Ann; Oakey, John; Rocks, S.; Judd, Simon J.
    Hazards and risks are currently identified in generic risk silos using top-down tools and methods which are incorporated into whole system risk management frameworks such as enterprise risk management. The current methods of identification and documentation are linear in approach and presentation. However, the world is multi-dimensional requiring a method of identification which responds to complex non-linear relationships. A method is required to identify cross- disciplinary hazards and formulate a register method to evidence the identified hazards. This study uses expert elicitation, web, survey and case studies to develop a method for cross-disciplinary hazard identification by application of the dimensions of generic, interface, causation and accumulation. The results of the study found many of the tools and methods used for hazard and risk identification such as hazard and operability studies took a top down approach commencing with a known failure and establishing cause and effect. The starting position of a known failure or event precludes identification of new types of failure or events and perpetuates a linear approach to hazard identification. Additionally the linear design of a risk register does not facilitate the presentation of multidimensional hazards. The current methods do not accommodate multiple lifecycles and components within cross discipline relationships. The method was applied to three case studies. The first case study had an existing risk register of 50 risks, post method application an additional 531 hazards were identified; case study (2) a register of 49 hazards and post method application additional hazards of 261; case study (3) an initial register of 45 hazards and an additional 384 hazards after method application. The impact of the method application highlights inconsistencies in the initial risk register and provides a tool which will aid the identification understanding and communication of hazards. Additionally it documents previously unidentified cross-disciplinary hazards and provides a proactive register method for identification and documentation by application of the dimensions of interface, causation and accumulation.
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    Development of safe and reliable operations in large-scale CO₂ shipping: an experimental approach.
    (2021-01) Al Baroudi, Hisham; Patchigolla, Kumar; Oakey, John
    A successful worldwide implementation of Carbon Capture, Utilisation and Storage largely relies on the establishment of a safe and reliable CO₂ transmission network. CO₂ shipping hereby represents a promising transport option, characterised by a high degree of flexibility in sink-source matching. This study addressed some key knowledge gaps that currently pose a limitation on large-scale commercialisation of this technology by providing information on operational and maintenance challenges in the chain. Firstly, an extensive review of technological advancements and future projections in large scale CO₂ shipping drew the attention to the fact that key technical challenges still need to be addressed in both pipeline and sea vessel systems in order to establish a worldwide network of CO₂ transport infrastructure. In particular, significant dearth concerns the adoption of appropriate safety protocols during accidental scenarios and selection of suitable materials to ensure integrity of transport infrastructure throughout real operations. Thus, an experimental lab scale rig was built and commissioned, capable of handling refrigerated carbon dioxide batches (up to 2.25 L) at conditions typical of sea vessel transport (~0.7 - 2.7 MPa, 223 - 259 K); the facility was designed to permit investigation of accidental leakage behaviour and to determine the qualification assessment of elastomer materials exposed under real shipping conditions. A technical qualification of elastomer materials for CO₂ transport systems was then performed with the aim of assessing their suitability in the intended systems and propensity for degradation. Such elastomers are used as seals in pressure- relief valves, providing elastomer-to-metal shutoff and eliminating leakage around stem during relief mode. Samples previously tested under pipeline conditions (9.5 MPa, 318 K) at exposure times of 50 – 400 h were characterised for a visual inspection, mechanical and thermo-analytical properties. Based on the suitable performance of the elastomers under such pipeline conditions, Ethylene Propylene Diene Monomer was selected for testing under operations typical of CO₂ shipping; constrained (25% compression) samples thereby underwent 20 – 100 CO₂ loading and offloading cycles at average decompression rates of 1.6 MPa/min; tested materials were then qualified through the aforementioned characterisation methodology, demonstrating a satisfactory resistance to rapid gas decompression and mechanical stability. A detailed experimental campaign was considered to assess the accidental leakage behaviour of CO₂ under shipping conditions; the main risks associated with CO₂ are asphyxiation due to displacement of oxygen to critically low levels, and exposure to concentrations of 15% or above in air are deemed life threating due to toxicological impacts on humans. The study highlighted that selection of initial fluid conditions significantly affects the propensity for solid formation in the vessel and blockages in the pipe section, thus resulting in significantly diverse leakage behaviours. Low-pressure decompression tests (0.7 – 0.94 MPa) resulted in the highest amount of inventory solidification (36 – 39 wt%) while high- pressure decompression scenarios (1.8 – 2.65 MPa) demonstrated the lowest (17 – 22 wt%). Lastly, a real-scale investigation on liquid CO₂ discharge from the coupler of an emergency release system was undertaken in order to scrutinise the applicability of such spillage containment measure to CO₂ shipping operations. The study focused on two refrigerated states, namely low- (0.87 – 0.94 MPa, 227 – 231 K) and medium-pressure conditions (1.62 – 1.65 MPa, 239 – 240 K) typical of shipping transport; findings demonstrated the presence of an abrupt outflow behaviour, characterised by full inventory discharge form the coupler in less than 1 s and achievement of peak depressurisation rates of 6 MPa/s. Moreover, the discharge behaviour showed considerable variations in relation to the selected initial conditions.
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    Engineering scale-up and environmental effects of the calcium looping cycle for post-combustion carbon dioxide capture
    (Cranfield University, 2013-08) Cotton, Alissa; Oakey, John; Patchigolla, Kumar
    This thesis has addressed several gaps in the knowledge with regards to the calcium looping cycle for carbon dioxide capture, including identification of engineering challenges associated with the scale-up of the technology to pilot scale and beyond; assessment of changes in sorbent morphology during the pilot scale capture process; and partitioning of elemental impurities in the limestone between the solid and gaseous phase during the carbon dioxide capture process. Hydrodynamic investigations identified the optimum superficial velocities required for the reactor in order to optimise solids entrainment and flux, and to minimise gas bypassing. Estimations made in determining how particle attrition would affect minimum fluidisation velocity confirmed a decrease of approximately 0.09m/s for every 5 % reduction in particle size. Amendments made to the exhaust diameter and position, and the loop seals, improved the pressure balance of the system thus enhancing solids transfer. Reactor and process modifications, including modification of carbonator temperature, and maintenance of temperature above 420°C in standpipes resulted in improved carbon dioxide capture %. Increasing bed inventory had a positive effect of carbon dioxide capture % due to an increased Ca looping ratio. Steam addition also benefitted the carbonation process, due to improved sorbent morphology and therefore carbon dioxide diffusion into the sorbent. Sulfur dioxide was considered to have a detrimental effect on carbon dioxide capture due to pore pluggage, although burner- derived steam had a positive effect in maintaining capture %. Gaseous elemental emissions from the process were low for all elements, but concentrations of elements in the solid sorbent phase were influenced by bed inventory, implying that filtering systems may be required in industry for the large masses of sorbent required. Concentrations of elements in the sorbent were identified to be below levels typical of cement, with the exception of Ni, implying that there is potential for spent sorbent to be used in the cement industry with adequate mitigation measures in place.
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    Experimental and modelling studies of coal/biomass oxy-fuel combustion in a pilot-scale PF combustor
    (Cranfield University, 2014-08) Jurado Pontes, Nelia; Oakey, John; Darabkhani, Hamidreza Gohari
    This thesis focuses on enhancing knowledge on co-firing oxy-combustion cycles to boost development of this valuable technology towards the aim of it becoming an integral part of the energy mix. For this goal, the present work has addressed the engineering issues with regards to operating a retrofitted multi-fuel combustor pilot plant, as well as the development of a rate-based simulation model designed using Aspen Plus®. This model can estimate the gas composition and adiabatic flame temperatures achieved in the oxy-combustion process using coal, biomass, and coal-biomass blends. The fuels used for this study have been Daw Mill coal, El Cerrejon coal and cereal co-product. A parametric study has been performed using the pilot-scale 100kWth oxy-combustor at Cranfield University and varying the percentage of recycle flue gas, the type of recycle flue gas (wet or dry), and the excess oxygen supplied to the burner under oxy-firing conditions. Experimental trials using co-firing with air were carried out as well in order to establish the reference cases. From these tests, experimental data on gas composition (including SO3 measurement), temperatures along the rig, heat flux in the radiative zone, ash deposits characterisation (using ESEM/EDX and XRD techniques), carbon in fly ash, and acid dew point in the recycle path (using an electrochemical noise probe), were obtained. It was clearly shown during the three experimental campaigns carried out, that a critical parameter was that of minimising the air ingress into the process as it was shown to change markedly the chemistry inside the oxy-combustor. Finally, part of the experimental data collected (related to gas composition and temperatures) has been used to validate the kinetic simulation model developed in Aspen Plus®. For this validation, a parametric study considering the factor that most affect the oxy-combustion process (the above mentioned excess amount of air ingress) was varied. The model was found to be in a very good agreement with the empirical results regarding the gas composition.
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    Fate of nitrogen/trace metals species during combustion and gasification of biomass
    (Cranfield University, 2010-06) Petrolati, Andrea; Oakey, John
    This thesis focused on the fate of nitrogen and trace metals species from combustion and gasification of biomass. The effect of process parameters on the release of these species during pilot-scale combustion and gasification of biomass was investigated and the information used to identify methods for the reduction of these species. The investigation focused on Miscanthus and Dried distillers’ grains with solubles (DDGS). The pilot-scale test rigs used were a fluidised-bed combustor and a fixed-bed downdraft gasifier. The two fuels were analysed by means of proximate, ultimate and ash analysis. The process parameters monitored were temperatures, gas flow, gas composition and ash composition and the process parameters studied are bed temperature and equivalence ratio. The different nitrogen content of the two fuels plays an important role in the emission. Both bed temperature and air to fuel ratio have demonstrated to have an important influence in the release of nitrogen oxides in combustion and ammonia in gasification, therefore they can be used to mitigate the emission of these species in the flue gas. Both processes are affected by the high alkali metals content of the fuels for the tendency to form low melting composites. Differences have been highlighted in the metal distribution between combustion and gasification. The different nitrogen and ash content of the two fuels make the results of the present thesis applicable to predict the behaviour of other biomass fuels according to the fuel characteristics. The scale of the tests performed allowed highlighting which methods can be used to control the emission of nitrogen and trace metal species. Moreover, the investigation highlighted major drawbacks in the use of biomass fuels in both fluidised bed and fixed bed technology due to ash properties.
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    Fireside corrosion in biomass combustion plants
    (Cranfield University, 2008-04) Coleman, K; Simms, Nigel J.; Oakey, John
    In recent years concerns over global warming and escalating worldwide energy consumption have sparked an interest in C02-neutral energy sources for power production. Historically biomass-fired boilers have been operated at low steam temperatures (below 450°C) mainly for heat production. For electricity generation from fossil fuels maximum steam temperature of up to 620°C are used today. At these heat exchanger conditions there are severe high temperature corrosion issues when burning biomass. The potentially high levels of alkali chlorides and low levels of sulphates in deposits formed during combustion of biomass fuels can result in chemically aggressive low melting point deposits. The aim of this study was to investigate the effect of the combustion of biomass fuels on heat exchanger materials currently used in power generation. To achieve this a series of pilot scale combustion trials and laboratory corrosion tests have been carried out. The deposits formed during the combustion trials were analysed to identify their composition and provide a basis for the simulated deposits used in the corrosion 'testing. The corrosion testing investigated the effects of potential exposure conditions on the corrosion levels of the 5 candidate materials. The tests were carried out using simulated deposit compositions and gaseous environments (selected on the basis of potential fuel compositions). As well as weight change data, these tests yielded statistical data on actual metal loss from the materials allowing the performance of the material to be determined from dimensional metrology before and after exposure. Analysis of the data obtained has enabled an investigation into the sensitivity of the corrosion damage of the candidate heat exchanger materials to changes in temperature, gas environment and deposit composition. This has in tum permitted the development of an initial model for fireside corrosion damage of biomass combustion heat exchangers and identification of routes to improve this model.
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    Fireside corrosion of heat exchanger materials for advanced solid fuel fired power plants
    (Springer, 2021-12-18) Mori, Stefano; Pidcock, Andy; Sumner, Joy; Simms, Nigel; Oakey, John
    To address the challenge of climate change, future energy systems need to have reduced greenhouse gas emissions and increased efficiencies. For solid fuel fired combustion plants, one route towards achieving this is to increase the system’s steam temperatures and pressures. Another route is to co-fire renewable fuels (such as biomass) with coals. Fireside corrosion performance of two candidate superheater/reheater alloys has been characterised at higher heat exchanger surface temperature. Samples of the alloys (a stainless steel, Sanicro 25 and a nickel-based alloy, IN740) were exposed in fireside corrosion tests at 650 °C, 700 °C and 750 °C, in controlled atmosphere furnaces using the ‘deposit recoat’ test method to simulate superheater/reheater exposure for 1000 h. After exposure, the samples were analysed using dimensional metrology to determine the extent and distributions of corrosion damage in terms of surface recession and internal damage. At 650 °C, the stainless steel and nickel-based alloy performed similarly, while at 700 °C and above, the median damage to the steel was at least 3 times greater than for the nickel-based alloy. Optical and electronic microscopy studies were used to study samples’ damage morphologies after exposure. Intergranular damage and pits were found in sample cross sections, while chromium depletion was found in areas with internal damage. For high-temperature applications, the higher cost of the nickel-based alloy could be offset by the longer life they would allow in plant with higher operating temperatures.
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    Fireside corrosion study of superheater materials in advanced power plants
    (Cranfield University, 2011-10) Syed, Adnan; Simms, Nigel J.; Oakey, John
    Conventional power plants are major emitters of CO2 gases, which are believed to be contributing to global warming. An efficient, co-firing biomass-coal power plant with oxy-firing combustion system (running at high steam temperature and pressure), can play a vital role in CO2 emission reduction. However, these techniques will further worsen the issue of fireside corrosion of heat exchangers. An increase in fireside corrosion rates can cause short component lives and unexpected failures if not dealt with appropriately. The aim of this PhD study was to use laboratory-based testing to assess the performance of alloy materials under superheater conditions in simulated co-fired (biomass and coal) air and oxy-fired combustion. In this PhD project five different alloys were used. Synthetic deposits were also prepared to simulate superheater deposit compositions. Tests were carried out at temperatures appropriate for metal temperatures in superheaters/reheaters of future power plants. The performance of samples was determined using: mass change data, advanced microscopy techniques, x-ray diffraction and dimensional metrology. Additional tests were carried out to investigate deposit stability and the effect of high concentrations of salts. The results achieved have confirmed the hypothesis that increased fireside corrosion rates are due to the combined effect of extreme environment: high temperatures, SO2 and HCl gases, aggressive deposits. Corrosion damage follows trends that resembles ‘bell-shaped’ curve in both air and oxy-fired conditions. Alloy corrosion damage in novel oxy-firing compared to air-firing conditions was significantly higher at 700C. The peak of the curve shifts from 650 to 700C in oxy-fired conditions. The alloys with higher chromium content clearly showed better corrosion resistance. The work on deposit chemistry and exposure to high salt concentrations has improved the understanding of corrosion reaction mechanisms. Corrosion damage data have been used to produce basic fireside corrosion mathematical model; which can be used as a stepping stone towards further development of fireside corrosion models.
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    Fireside performance of different coatings in biomass power plant
    (Taylor & Francis, 2023-03-12) Mori, Stefano; Pidcock, Andy; Sumner, Joy; Simms, Nigel; Oakey, John
    The energy sector will need to employ novel strategies to reduce greenhouse gas emissions, such as the increase of steam temperatures/pressures or the use of low carbon fuels (i.e. biomass). Both cause heat exchanger materials’ degradation issues, due to the formation of more/different corrosive deposits, which requires the use of expensive nickel-based materials or coatings. This paper focuses on the behaviour of three different coatings (HVOF NiCrFeSi, laser clad FeCrAl and Laser Clad NiCrFeSi) deposited on TP347HFG, at 700°C (up to 1000 h exposure). Tests were performed using the ‘deposit recoat’ method (KCl deposit) in simulated biomass combustion environments. Cross-sections were analysed using dimensional metrology, to determine distributions of metal loss and internal damage. Intergranular damage and pits were identified using SEM/EDX. A ‘diffusion cell’ behaviour was observed, which led to depletion of alloying elements from the coating and consequent increase in damage. The results suggested a severe degradation of all coatings.
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    Generic framework for the reliability assessment of ageing offshore wind turbine jacket support structures.
    (Cranfield University, 2020-12) Ivanhoe, Oribi Richard; Oakey, John; Mehmanparast, Ali
    Wind Europe annual report for 2019 shows that a significant amount of installed offshore wind turbines will reach their design service life in the next decade. Most of these structures will remain in service if granted permission for life extension. Life extension remains a complex decision given the limited experience in the offshore wind industry, and so structural integrity assessment of ageing structures is seen as a potential upcoming challenge. While the existing guidelines provide a general process for assessment, it is crucial to have robust offshore wind-specific guidelines by including relevant concepts and notation of the wider structural integrity assessment and models that can adequately account for the time-dependent degradation mechanism more accurately. Offshore wind turbine (OWT) support structures are exposed to harsh marine environments with considerable uncertainties in the environmental loads and soil properties, making structural integrity assessment difficult. Hence, reliability assessment is seen as the most suitable approach to methodically account for these uncertainties. In this thesis, a generic framework for assessing the reliability of ageing OWT jacket support structures is developed based on a non-intrusive formulation. A parametric finite element analysis (FEA) model of a typical OWT jacket support structure was developed incorporating operational and environmental load and soil-structure interactions in order to map its response under varying input conditions appropriately. The results from several FEA simulations have been analysed through multivariate regression, deriving performance functions and formulation of relevant limit states. for this assessment, five limit states were considered: deflection, buckling, vibration, ultimate and fatigue limit states. The reliability index under each limit state is then calculated using the first-order reliability method (FORM). The developed reliability assessment framework has been applied to the NREL 5MW OWT OC4 jacket design to determine the reliability of critical components of the structure. The results of this reliability assessment show that, for the given stochastic conditions, the structural components of the OWT jacket support structure are found to be within acceptable reliability levels as defined in DNV-OS-J101 Offshore wind turbine design standards. A robust inspection, maintenance and repair (IMR) plan, adequately executed, proved to boost the remaining life of the structure, thus, making life extension of ageing offshore structures more economical for owners of wind turbines and operators. The validity and applicability of the framework to the OWT industry were reviewed, and recommendations were made on the next steps required for the deployment of this framework in the offshore wind energy sector.
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    High temperature corrosion of HVOF coatings in laboratory-simulated biomass combustion superheater environments
    (Springer, 2022-12-26) Pidcock, Andy; Mori, Stefano; Sumner, Joy; Simms, Nigel; Nicholls, John; Oakey, John
    This study examines the fireside corrosion of FeCrAl, NiCr, NiCrAlY and A625 coatings applied by ‘high velocity oxy fuel’(HVOF) and exposed to simulated biomass firing conditions (gas composition CO2, N2, SO2 and HCl). The coatings and a typical base steel alloy (T92) were exposed to simulated conditions at 600 °C for 1000 h in a laboratory scale furnace. Samples were coated with a potassium chloride deposit. Samples were then cold mounted in a low-shrinkage epoxy resin and then cross-sectioned. Corrosion was assessed by dimensional metrology comparing the coating thickness change of the samples. The cross-sections of the ‘worst’ and ‘best’ coatings were examined. Results show that all but one coating (HVOF NiCr) outperformed the T92 alloy. No coating composition or method was conclusively better. Evidence of Cr depletion as well as the formation of a sulphidation layer have been found in the exposed samples with coatings. The formation of a K2SO4 layer has also been observed on all coated specimens.
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    Hydrogen production with integrated CO2 capture via sorbent enhanced reforming
    (SSRN, 2022-11-10) Lesemann, Markus; Mays, Jeff; Clough, Peter T.; Oakey, John; Adedipe, Tosin; Duncan, Angus
    GTI Energy has been developing a novel process technology for hydrogen production from natural gas with inherent carbon capture. The GTI process, based on sorbent enhanced reforming (SER), has the advantage that it captures CO2 inherently in the process via a pre-combustion technique instead of secondary capture from a flue gas stream. This approach is fundamentally different from conventional technologies such as steam methane reforming (SMR) and autothermal reforming (ATR) which require additional process steps to avoid CO2 emissions. The inherent carbon capture capability results in step-out economics of the GTI process. The GTI process is based on GTI’s Hydrogen Generator (CHG) technology which converts natural gas and steam into H2 and CO2 in separate streams. The inherent carbon capture in the GTI process leads to its higher carbon capture potential, its substantially lower capital cost (by 40-60%) and substantially smaller footprint compared to the conventional approaches, resulting in overall lower levelized cost of hydrogen (by 10-30%). In its optimized configuration, carbon capture rates over 97.5%, with 10% lower levelized cost of hydrogen (LCOH) and ~50% reduction in CAPEX compared to conventional SMR with CO2 capture are achievable. By relaxing the carbon capture rate to 96%, a LCOH ~20% lower than the SMR case can be achieved. LCOH and CAPEX advantages of the process compared to Autothermal Reforming (ATR) are even more pronounced. Development of the process technology is currently supported by the U.S. Department of Energy (DOE) and by the U.K. Department for Business, Energy, and Industrial Strategy (BEIS). DOE has been supporting the development and operation of a 0.071 MWth pilot plant at GTI’s main test facility near Chicago, USA, to demonstrate the process chemistry and fluidized bed operation. Under BEIS funding, a team comprised of Cranfield University, GTI Energy, and Doosan Babcock has been developing a 1 MWth pilot plant at a dedicated new test site at Cranfield University in the UK (“HyPER Project”).
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    Investigation of a radial turbine design for a utility-scale supercritical CO2 power cycle
    (MDPI, 2020-06-17) El Samad, Tala; Teixeira, Joao Amaral; Oakey, John
    This paper presents the design procedure and analysis of a radial turbine design for a mid-scale supercritical CO2 power cycle. Firstly, thermodynamic analysis of a mid-range utility-scale cycle, similar to that proposed by NET Power, is established while lowering the turbine inlet temperature to 900 ◦C in order to remove cooling complexities within the radial turbine passages. The cycle conditions are then considered for the design of a 100 MWth power scale turbine by using lower and higher fidelity methods. A 510 mm diameter radial turbine, running at 21,409 rpm, capable of operating within a 5% range of the required cycle conditions, is designed and presented. Results from computational fluid dynamics simulations indicate the loss mechanisms responsible for the low-end value of the turbine total-to-total efficiency which is 69.87%. Those include shock losses at stator outlet, incidence losses at rotor inlet, and various mixing zones within the passage. Mechanical stress calculations show that the current blade design flow path of the rotor experiences tolerable stress values, however a more detailed re-visitation of disc design is necessitated to ensure an adequate safety margin for given materials. A discussion of the enabling technologies needed for the adoption of a mid-size radial turbine is given based on current advancements in seals, bearings, and materials for supercritical CO2 cycles
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    Investigation of the feasiblity of employing a radial turbine for a utility-scale supercritical CO₂ power cycle.
    (2020-04) El Samad, Tala; Oakey, John; Teixeira, Joao Amaral
    With the current growth rate of world population, comes a high demand on electric energy generation. Technological advancements in metallurgy, fuel conversion, heat transfer, and turbomachinery design allow the continuous dominating rule of fossil fuel energy resources and the expansion of non-renewable based power cycles. The challenges arising due to greenhouse gas emissions from fossil fuel combustion necessitate regulated policies to limit CO₂ emissions in particular. Design considerations and issues in power plants revolve around increasing efficiencies, reducing noise pollution and land footprint, while mitigating emissions. An example of advanced power configurations include the supercritical CO₂ cycle that has gained much interest in recent years due to its compact-size turbomachinery, increased efficiencies compared to other conventional steam or gas cycles, and its ability to be coupled with a wide range of heat sources. Another avant-garde technology is an oxy-combustion cycle that proves more favourable than the other carbon capture and storage routes of gasification and absorption. A proposed NET Power (Allam) cycle, which combines both technologies of using supercritical CO₂ conditions in an oxy-combustion gas-fired power plant, seems promising with claims of cycle efficiencies reaching 55%. However, the Allam cycle is still in a pre-mature phase due to the barriers that inhibit its full-scale development; challenges include the design of a high-pressure, high-temperature turbine which dictates cooling requirements, material considerations, and number of stages to name a few. A radial turbine, which generally has a simpler construction and fewer stages when compared to an axial turbine, is suggested as a superior candidate configuration for cycles of high fluid density. A thermodynamic analysis of a mid-range cycle similar to that proposed by NET Power is established while lowering the turbine inlet temperature to 900 C in order to remove cooling complications within the radial turbine passages. The cycle conditions are then considered for the design of a 100 MWth power scale turbine by using preliminary and higher fidelity methods. Two radial turbine designs are illustrated; the first, whilst not satisfying the cycle operating conditions, is used to showcase the detailed 1D design as well as the 2D and 3D analyses procedures followed during this work. A second 510 mm diameter turbine, running at 21,409 rpm, capable of operating within a 5% range of the required cycle conditions, is designed and presented. Results from computational fluid dynamics simulations indicate the loss mechanisms responsible for the low-end value of the turbine total-to-total efficiency which is 69.87%. Mechanical stress calculations show that the aerodynamic flow path of the rotor blades experience tolerable stress values, however a more detailed disc design is required to meet actual material constraints.
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    Kinetic simulation of a 100kWth oxy-combustor using Aspen Plus
    (C2ES, 2013-12) Jurado Pontes, Nelia; Gohari Darabkhani, Hamidreza; Anthony, Edward J.; Oakey, John
    Oxy-fuel combustion is a clean coal technology based on firing fuel in an enriched oxygen atmosphere to obtain high CO2 concentrations in the exhaust gas. Experimental tests were performed at Cranfield University using a 100kWth retrofitted oxy-combustor. In parallel, a kinetic simulation model using Aspen Plus was designed and validated to serve as a computer tool to predict the behaviour of the oxy-combustion process for a wide range of fuels and conditions. The main input parameters varied in the simulation study were: fuel type (El Cerrejon coal, Daw Millcoal, Cereal Co-product biomass, and coal/biomass blends); percentage of recycled flue gas (55, 60,and 65%); type of recycled flue gas (wet or dry); percentage of excess oxygen (0 and 5%), and the amount of air ingress into the process (0, 2, 10, and 18% of the total flue gas fed to the oxycombustor).The last input condition, percentage of air ingress, is of greater importance as a result of the unit being a retrofitted oxy-combustor; for which air ingress is more probable and this represents a situation likely to be an issue for any boiler retrofitted for oxyfuel firing. Results from the simulations as well as the definition of the operating conditions that best represents the behaviour of the rig are presented.
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    Modeling gas turbine materials’ hot corrosion degradation in combustion environments from H2‐rich syngas
    (Wiley, 2016-09-07) Sumner, Joy; Potter, Andrew; Simms, Nigel J.; Oakey, John
    Components of gas turbines (such as blades, vanes, combustor cans) exposed to combustion environments at high temperature are susceptible to hot corrosion attack. To successfully plan maintenance and to determine whether to operate in novel combustion modes (e.g., in integrated gasification combined cycles that incorporate pre-combustion carbon capture) predictions of hot corrosion component life must be made. In this paper, hot corrosion datasets relating to two alloys, MarM 509 (a cobalt-based superalloy), and Rene 80 (a nickel-based superalloy) form the basis of hot corrosion predictive lifetime models. The model framework is based on the two stages of incubation and propagation, with the transitions from incubation to propagation around the samples being based on Weibull statistics. The impact of a range of temperatures (including 700 and 900 °C), gas compositions (simulating the combustion of natural gas, H2-rich syngas, or partially cleaned syngas), and deposit chemistries/fluxes have been assessed. Predictions have been made including the expected damage spread for a range of different exposure conditions.
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    Numerical modelling of the electro-kinetic effect on pipe-soil interaction.
    (2017-10) Joshua, Hakuri Nwen; Kara, Fuat; Oakey, John
    The high pressure and high temperature (HP/HT) of operating fluid and soft soil content significantly account for the axial and lateral displacement of subsea pipelines. The ability of a pipeline to resist displacement depends on the soil strength. Due to low soil shear strength, the accumulation of displacement over a period of operating cycles leads to pipeline displacement. Increasing the pipe-soil interaction resistance will significantly reduce pipeline displacement. Soil contains solid, water and air particles. The levels of water, air and the solid particle size in the soil, govern its mechanical behaviour. Removal of pore water content from the soil voids may lead to consolidation with a resultant increase in effective stress. One of the methods used to increase soil strength is the Electro-Kinetic (EK) process. This is applied to increase the strength of onshore and offshore soil foundations. An important advantage is a reduction in time taken for the soil to consolidate. A Numerical model is developed for the determination of the EK effect on soft soil using the ABAQUS software tool. Two stages involved in the EK analyses are electro-osmotic consolidation and dynamic pipe-soil interaction. Three different test series each for electro-osmotic consolidation and dynamic analyses were built. The electro-osmotic consolidation analyses determined the soil consolidation followed by a dynamic pipe-soil interaction process. The electro-osmosis considered the effect of voltage variations, time taking for the soil to consolidate and variations with numbers of electrodes. The dynamic analyses consider the effect of electro-osmosis due to the displacement of pipeline in the vertical, axial, and lateral direction. From the electro-osmotic analyses, the soil settlement is due to its reduction in void volume as a result of the pore water pressure dissipation. A further interaction of pipeline on the (settled) consolidated soil indicates a significant improvement in the soil strength when compared with the non-treated soil.
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    Numerical prediction and mitigation of slugging problems in deepwater pipeline-riser systems
    (Cranfield University, 2015-11) Okereke, Ndubuisi Uchechukwu; Kara, Fuat; Oakey, John
    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.