1,721,059 research outputs found
Off-design and annual performance analysis of supercritical carbon dioxide cycle with thermal storage for CSP application
Full text linkSupercritical Carbon Dioxide (sCO2) cycles can achieve higher efficiency compared to steam-Rankine or Air-Brayton cycles, therefore they are promising for concentrated solar power applications. Although sCO2 cycles show higher design efficiency, the off-design efficiency is highly sensitive to the ambient conditions, impacting the power block net-power and heat input. In the present work a recompression sCO2 cycle is connected to a central-tower solar field with two-tank thermal storage delivering molten chloride salt at 670 °C. The temperature of the molten-salt exiting from the power block and returning to the cold storage tank increases by 46 °C with respect to the design value when the compressor inlet temperature is raised by 13 °C relative to the design condition of 42 °C, which implies that the capacity of the thermal storage reduces by 25%. The main focus of this work is to investigate the off-design performance of a sCO2 recompression cycle under variable ambient temperature, molten-salt inlet temperature and molten-salt flow rate. Multi-objective optimisation is carried-out in off-design conditions using an in-house code to explore the optimal operational strategies and the Pareto fronts were compared. Since the power cycle can either be operated in maximum power mode or maximum efficiency mode, this study compares these two operational strategies based on their annual performance. Results indicate that the capacity factor of the concentrated solar power can be increased by 10.8% when operating in maximum power mode whilst the number of start-ups is reduced by about 50% when operating in maximum efficiency mode
Thermo-economic analysis, optimisation and systematic integration of supercritical carbon dioxide cycle with sensible heat thermal energy storage for CSP application
Full text linkIntegration of thermal energy storage with concentrated solar power (CSP) plant aids in smoothing of the variable energy generation from renewable sources. Supercritical carbon dioxide (sCO2) cycles can reduce the levelised cost of electricity of a CSP plant through its higher efficiency and compact footprint compared to steam-Rankine cycles. This study systematically integrates nine sCO2 cycles including two novel configurations for CSP applications with a two-tank sensible heat storage system using a multi-objective optimisation. The performance of the sCO2 cycles is benchmarked against the thermal performance requirement of an ideal power cycle to reduce the plant overnight capital cost. The impacts of the compressor inlet temperature (CIT) and maximum turbine inlet temperature (TIT) on the cycle selection criteria are discussed. The influence of the cost function uncertainty on the selection of the optimal cycle is analysed using Monte-Carlo simulation. One of the novel cycle configurations (C8) proposed can reduce the overnight capital cost by 10.8% in comparison to a recompression Brayton cycle (C3) for a CIT of 55°C and TIT of 700°C. This work describes design guidelines facilitating the development/ selection of an optimal cycle for a CSP application integrated with two-tank thermal storage
Integrated solutions of hydrogen storage materials
Full text linkLAUREA MAGISTRALELo stoccaggio di energia gioca un ruolo cardine nell'integrazione di domanda e offerta di energia,
sia sul breve sia sul lungo termine, specialmente nel settore dei trasporti dove mostra il
suo più elevato potenziale.
Questo progetto di tesi ha come scopo l'indagine dei correnti e nuovi materiali di stoccaggio
di idrogeno ad alta capacità per applicazioni distribuite, nello specifico il settore dei trasporti.
Materiali ad alta capacità di idrogeno (ad esempio gas compresso, idruri metallici e ammoniaca)
e la loro abilità di stoccare idrogeno saranno valutati, così come la loro futura implementazione
commerciale come mezzi di stoccaggio di idrogeno, anche paragonando le loro proprietà con il
documento del US Department of Energy `Targets for Onboard Hydrogen Storage Systems for
Light-Duty Vehicles'. In particolare, il progetto di tesi studierà lo stoccaggio di idrogeno applicato
ad un caso automobilistico, ovvero il rilascio di idrogeno gassoso a bordo. La conversione
di ammoniaca in idrogeno puro e le sue condizioni termodinamiche saranno valutate attraverso
il software MTData e Aspen Plus .
I risultati del progetto suggeriscono come nessuno dei software utilizzati sia capace di modellare
la reazione adeguatamente. I risultati di MTData confermano la tesi del potenziale
dell'ammoniaca nell'economia dell'idrogeno, tuttavia la caratteristica più critica del processo
rimane la fornitura del calore di reazione necessario, calcolato nella simulazione di Aspen Plus,
nelle migliori condizioni economiche e di sicurezza dell'impianto.Energy storage plays a cardinal part in integrating energy demand and supply, both on a
short and long timeframe, especially in the transportation sector where it shows its highest
potential. Hydrogen plays an important role and might be one of the most important future
energy sources.
This thesis project aims at reviewing the current/new storage materials with high hydrogen
storage capacity for distributed level applications i.e. transport sector. High storage capacity
materials (ex. compressed gas, metal hydrides and ammonia) and their ability to store hydrogen
will be critically assessed and their future implementation as commercial hydrogen storage media
will be checked, also comparing their properties with the US Department of Energy `Targets for
Onboard Hydrogen Storage Systems for Light-Duty Vehicles'. In particular, the project will
study the storage of hydrogen in ammonia applied to an automotive case, i.e. the on-board
release of hydrogen. The conversion from ammonia to pure hydrogen and its physical conditions
will be evaluated with the software MTData and Aspen Plus .
The results of this project suggest that neither of the used software was able to model the real
reaction properly. The MTData results con rm the theory on the potential of ammonia in
hydrogen economy, however the most critical feature of the process remains the supply of heat
to the reaction, computed in the Aspen Plus simulation, in the most economical and safe
condition
Development of safe and reliable operations in large-scale CO₂ shipping: an experimental approach.
Full text linkA 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.PhD in Energy and Powe
Process engineering and development of post-combustion CO2 separation from fuels using limestone in CaO-looping cycle
Full text linkGlobal CO2 emissions produced by energy-related processes, mainly power plants, have increased rapidly in recent decades; and are widely accepted as the dominant contributor to the greenhouse gas (GHG) effect and consequent climate changes. Among countermeasures against the emissions, CO2 capture and storage (CCS) is receiving much attention. Capture of CO2 is the core step of CCS as it contributes around 75% of the overall cost, and may increase the production costs of electricity by over 50%. The reduction in capture costs is one of the most challenging issues in application of CCS to the energy industry. Using limestone in CaO-looping cycles is a promising capture technology to provide a cost-effective separation process to remove CO2 content from power plants operations. Limestone has the advantage of being relatively abundant and cheap, and that has already been widely used as a sorbent for sulphur capture. However, this technology suffers from a critical challenge caused by the decay in the sorbent capture capacity during cyclic carbonation/calcination, which results in the need for more sorbent make-up; hence a reduction in cost efficiency of the technology. The performance of sorbent influenced by several operating and reaction conditions. Therefore, much research involves investigation of influencing factors and different methods to reduce the sorbent deactivation. Cont/d
Engineering scale-up and environmental effects of the calcium looping cycle for post-combustion carbon dioxide capture
No full textThis 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
Annual performance of a novel configuration for an integrated solar combined cycle utilising municipal solid waste
Full text linkSansom, Christopher L. - Associate SupervisorClimate change has been a major incentive for the global power generation
industry to move towards the implementation of sustainable renewable energy
technologies in order to reduce the emissions of greenhouse gases, especially
carbon dioxide emissions. Concentrated solar power (CSP) has established itself
as one of the common renewable energy technologies for large scale power
generation. A further attractive feature of this solar technology is its hybrid
operation in the form of integrated solar combined cycle (ISCC) which facilitates
control and ensures that the power plant is available to meet demand whenever
it occurs. ISCC commonly uses natural gas to operate the combined cycle but
this CSP hybrid system also has the potential to limit its use of this fossil fuel with
a more environmentally friendly fuel, namely the produced syngas from solid
feedstock gasification which can be accomplished by further integration of the
gasification reactor with ISCC. The organic fraction of municipal solid waste
(MSW) was selected for this application, both to replace natural gas as well as
for its value as a waste management method. In the present work, the thesis
studies and contrasts four configurations of ISCC based on two factors, the type
of fuel and the level of solar thermal contribution. One configuration represents
the conventional form by using natural gas (ISCC 1) while another configuration
uses municipal solid waste (ISCC 2) and in both cases, the solar field generates
high -pressure saturated steam using parabolic trough with thermal oil. The last
two configurations are related to the research proposal for ISCC which states that
this hybrid system runs on municipal solid waste and utilises enhanced solar
thermal contribution. This enhanced thermal power from the solar field is used to
generate high-pressure superheated steam using parabolic trough with molten
salt (ISCC 3) or solar power tower with molten salt (ISCC 4). In all cases, the fuel
runs the combined cycle, and the solar field operates in parallel to provide extra
steam for the hybrid system. However, the use of gasification in ISCC 2, ISCC 3
and ISCC 4 generates extra steam for the hybrid system through syngas cooling
system which is attached to the low-pressure section of the steam turbine cycle.
In this work, models are developed to investigate the differences between the
various configurations in terms of technical and economic performances using
Spain and Saudi Arabia as case studies. The results indicate that the use of a
solar power tower in the proposed concept, ISCC 4, gave the highest electricity
production at 646 GWh with a solar share of 12.80% under Spanish weather and
644 GWh with a solar share of 15.24% under the Saudi Arabian weather.
Furthermore, ISCC 4 offered the lowest levelised cost of electricity at 28.45
/MWh for Saudi Arabia and Spain, respectively, when the
novel concept (ISCC 3 and ISCC 4) is compared to the conventional concept
(ISCC 1). The main thesis contribution was to reveal the impact of coupling the
ISCC using enhanced solar thermal power with municipal solid waste gasification
and its potential as Waste-to-Energy plant. Based on the study presented
outcomes, The proposed concept of integrated solar combined cycle (ISCC 3 and
ISCC 4) demonstrated its practicality against conventional concept (ISCC 1) due
to achieving higher performance outcomes with lower costs. The outcomes of
ISCC 2 in both countries presented slightly lower LCOE values than the novel
concept indicating that the replacement of fuel alone did not show a significant
impact against the novel concept in terms electricity production cost.PhD in Energy and Powe
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Formation of SO3 under oxy-fired fluidised beds - POSSIBLE RESTRICTED THESIS
No full textPOSSIBLE RESTRICTED THESIS – refer to Clare GrimesIn oxy-fuel combustion, fuel is burned in the presence of higher concentrations
of oxygen diluted with the recycled flue gas (RFG). The nitrogen fraction in the
air is replaced by the recycled flue gas to moderate the combustion temperature
in the furnace. Nitrogen is removed from the mainstream by the air separation
unit (ASU) to provide nearly pure oxygen. However, combustion environment of
fuel with RFG differs significantly from conventional air combustion due to the
high heating capacity of CO2. In typical air combustion process, sulfur in fuel is
converted to sulfur dioxide (SO2), while a smaller fraction is converted to the
sulfur trioxide (SO3). However, during the oxy-fuel combustion with RFG tends
to increase the SO2 concentrations in the combustion furnace. Thus, higher
concentrations of SO3 along with SO2 and steam may increase risks associated
with the corrosion of metal surfaces in the boiler. This occurs as the fraction of
SO3 reacts with steam to form sulfuric acid at low temperatures.
The aim of this PhD thesis is to evaluate the formation of SO3 concentrations
during the oxy-fuel combustion. Thus, SO3 concentrations were measured
experimentally under air and oxy-fuel environments. To reach the goals of this
work, bench-scale bubbling fluidised bed and fixed bed rigs were used to
measure SO3 concentrations. At a larger scale, a pilot-scale 50 kW circulating
fluidised bed rig (CFB) was employed. The PhD thesis provides a literature
survey on SO3 formation in air and oxy-fuel combustion environments, the
development of SO3 sampling train and an experimental description of the tests.
Finally, the results obtained from each rig have been discussed. As supporting
case, fly ashes were analysed in TGA to investigate the amount of unburnt
carbon content. The collected fly ash after the tests was scanned by using X-ray
fluorescence (XRF) to evaluate the change of metal oxides
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