1,720,967 research outputs found
Partially Cracked Ammonia for Micro-Gas Turbine Application
No full textDuring the last decades, CO2 emissions have increased by 42% with respect to the pre-industrial era. The anthropogenic CO2 is the main source of GreenHouse Gas (GHGs) emissions, contributing, alone, to nearly 30% of global warming effects. The reduction in GHGs emissions to contain the increase in global temperature below 2°C, represents one of the greatest challenges of the XXI century, to ensure the survival of the planet and future generations. In this energy context, Power to X to Power (P2X2P) solutions are gaining more and more importance in the market considering that, in recent years, the market scenario is increasingly driven by Renewable Energy Sources (RESs). The possibility of storing the exceeding electrical energy production, mainly due to RESs, into hydrogen (H2) or ammonia (NH3) and then turning it back into electricity when RESs power production falls below demand, can improve grid resilience and stability, ensuring, in the meanwhile, a lower environmental impact. Even more, P2X2P represents an innovative solution to increase the flexibility of Gas Turbine (GT) plants, extending their operative range by using alternative carbon-free fuel. Attaining this goal would make GT plants more suitable to trade on the ancillary services market guaranteeing a more secure and clean power system. This study focuses on the use of partially cracked NH3 in micro-Gas Turbine (mGT) applications. To carry out the analysis, a MATLAB/Simulink model has been developed, including also the NH3 storage and the ammonia cracking reactor to simulate an Ammonia To Power (A2P) system. The main thermodynamic parameters, system features, and critical aspects have been evaluated (e.g. the global efficiency, the turbine inlet and outlet temperatures, the power output, etc.) and a comparison between the same system fueled by natural gas and hydrogen has been carried out from the technical and environmental point of view. Copyright © 2023 by ASME
Components and Architecture optimisation for marine fuel cell systems
No full textThe energy transition to zero emission maritime transport implies a central role for hydrogen as an energy carrier of choice for multiple applications and use cases. Among the power conversion technologies fuel cell systems can combine unrivalled performance and zero tailpipe emission.
Nonetheless the state-of-the-art architectures of fuel cell modules are largely driven by requirements related to the on-road applications, while the maritime applications with their specific performance indicators are expected to be suitable for alternative designs.
In this context, the thesis is focusing on the architecture of the fuel cell module, the fundamental functions carried out by the subsystems within it and the design choices to be made in a defining an architecture suitable for installation in conjunction with a marine propulsion system.
Moreover, the defined design is modelled and analysed to evaluate its performance and the ability of all subsystems to perform the assigned functions, at steady state and in transient conditions
EFFICIENCY ENHANCEMENT IN PRESSURE GAIN COMBUSTION COMBINED CYCLE GAS TURBINE BY BLADE COOLING INTEGRATION WITH BOTTOMING CYCLE
No full textThis paper investigates the potential advantages of
integrating turbine blade cooling with bottoming cycle in
Combined Cycle Gas Turbine (CCGT) with Pressure Gain
Combustion (PGC) for land-based power generation application.
PGCs have recently emerged as a promising solution to achieve
significant performance gains in current Gas Turbines (GT) and
CCGTs in terms of efficiency and power output. However, GTs
with PGC combustors require higher cooling flow compared to
conventional GTs, due to the increased temperature of cooling
flow from its secondary compression that is necessary for
admission in the turbine. The present work aims to address this
issue by utilizing the working fluid from the steam cycle for
cooling stator and rotor vanes or to decrease the cooling air
temperature. PGC is represented by a steady-state zero dimensional
constant volume combustion (CVC) model based on
the Humphrey cycle. The PGC combustor model is simulated with
different injection pressure losses to investigate the impact of
pressure gain on steam cooling integrated CCGT. Different
approaches of turbine blade cooling through the bottoming cycle
are investigated in this work, such as (i) cooling of compressor
bleed air through steam/water, ii) open-loop steam cooling
(OLSC) for stator and vanes, iii) closed-loop steam cooling
(CLSC) for stator and vanes and iv) mixed loop steam cooling
(MLSC) where stator is steam cooled while rotor is air cooled. A
heavy-duty industrial H-class CCGT with a PGC combustor and
a three-pressure level heat recovery steam generator (HRSG)
was modelled in WTEMP (Web-based Thermo-Economic
Modular Program) software, an original modular cycle analysis
tool developed at the University of Genova. Thermodynamic
analysis of the CCGT cycle was performed with realistic
component efficiencies at a wide range of operating conditions,
with methane as the fuel. The impact of different cooling
approaches on the cycle performance was analyzed in terms of
efficiency, specific work and practical feasibility of the solution.
Results showed that implementing both PGC technology and
steam cooling together in a CCGT can significantly enhance
efficiency and work output due to the synergistic effect of both
technologies. The efficiency of an H-class CCGT can be
increased from 62.6 to 67.2% (4.54 percentage points increment)
and specific work by 194.5 kJkgair by using CLSC and PGC
combustor with a pressure gain of 0.40. MLSC was identified as
the most practical solution, which, when augmented with a PGC
combustor with 0.26 pressure gain, can improve the overall
CCGT efficiency by 2.9 percentage points and specific work by
104.6 kJ/kgair. Overall, the study demonstrates the theoretical
potential of integrating turbine cooling in the PGC combined
cycle with steam bottoming cycle as a potential pathway towards
CCGTs with more than 65% efficiency
Optimal energy management techniques for island applications
No full textThe global imperative to address climate change and pollution has catalysed the development of innovative and environmentally sustainable energy systems, with polygeneration microgrids emerging as a leading technology due to their high energy conversion efficiencies and low emissions. This thesis focuses on the integration of electrical and thermal technologies in isolated maritime environments, an area of increasing interest in
both academia and industry. The primary challenge addressed herein is the development of an energy management system capable of optimizing power flows and storage operations while ensuring robustness.
Drawing from practical experience, this thesis aims to advance the current understanding of energy management systems and control for microgrids, particularly in maritime applications such as islands and ships. The central objective is to conceptualize and test an energy management system tailored to these environments, considering operational constraints and optimizing overall system performance. These efforts are supported by
simulation tools and cyber-physical tests conducted in the Innovative Energy System laboratory of the Thermochemical Power Group at the University of Genoa. The methodology begins with the introduction of the isolated microgrid layout, incorporating industrial symbiosis principles. Dynamic models of each component are then developed and validated using Matlab-Simulink®. These models serve as the basis for designing and fine-tuning the Energy Management System, which controls each prime mover to fulfil the customer demand meeting operational constraints and minimizing costs. Comparative analyses are conducted between scenarios with and without the EMS, utilizing both simulations and real-world tests over typical operational periods. Additionally, the
robustness of the EMS is thoroughly tested and validated, ensuring its efficacy in practical applications. In conclusion, this thesis highlighted the great potential of microgrids with EMS, showing high energy conversion efficiencies in a wide operative range in terms of load and ambient conditions. It also showed that the proper operation of the system is possible during various transient scenarios, implementing proper control strategy in order to face each scenario
Dynamic analysis and energy management strategies of micro gas turbine systems integrated with mechanical, electrochemical and thermal energy storage devices
No full textThe growing concern related to the rise of greenhouse gases in the atmosphere has led to an increase of share of renewable energy sources. Due to their unpredictability and intermittency, new flexible and efficient power systems need to be developed to compensate for this fluctuating power production. In this context, micro gas turbines have high potential for small-scale combined heat and power (CHP) applications considering their fuel flexibility, quick load changes, low maintenance, low vibrations, and high overall efficiency. Furthermore, the combination of micro gas turbines with energy storage systems can further increase the overall system flexibility and the response to rapid load changes. This thesis aims to analyse the integration of micro gas turbines with the following energy storage systems: compressed air energy storage (CAES), chemical energy storage (using hydrogen and ammonia), battery storage, and thermal energy storage.
In particular, micro gas turbines integrated with CAES systems and alternative fuels operate in different working conditions compared to their standard conditions. Applications requiring increased mass flow rate at the expander, such as CAES and the use of fuels with low LHV, such as ammonia, can potentially reduce the compressor surge margin. Conversely, sudden composition changes of high LHV fuels, such as hydrogen, can cause temperature peaks, detrimental for the turbine and recuperator life. A validated model of a T100 micro gas turbine is used to analyse transitions between different conditions, identify operational limits and test the control system.
Starting from the dynamic constraints defined in the related chapters, in the final part, an optimisation tool for energy management is developed to couple the micro gas turbine with energy storage systems, maximizing the plant profitability and satisfying the local electrical and thermal demands. For the modelling of the CAES system and alternative fuels, the operating constraints obtained from the initial analyses are implemented in the optimisation tool. In addition, a battery and thermal energy storage system are also considered.
In the first part, a comprehensive analysis of the T100 combined with a second-generation CAES system showed enhanced efficiency, reduced fuel consumption, reduced thermal power output and increased maximum electrical power output due to the reduction of the rotational speed. The study identified optimal air injection constraints, demonstrating a +3.23% efficiency increase at 80 kW net power with a maximum mass flow rate of 50 g/s. The dynamic analysis exposed potential instabilities issues during air step injections, mitigated by using ramps at a rate of +0.5 (g/s)/s for safe and rapid dynamic mode operation. The second part explored the effects of varying H2-NG and NH3-NG blends on the T100 mGT. Steady-state results showed increased power output with hydrogen or ammonia, notably +6.1 kW for 100% H2 and up to +11.3 kW for 100% NH3. Transient power steps simulations showed surge margin reductions, especially at lower power levels with high concentrations of ammonia, highlighting the need for controlled transitions. Controlled ramps were effective in preventing extreme temperature peaks during fuel composition changes. The final chapter focused on developing an energy scheduler for different plant setups, evaluating four configurations. For a typical day of the month of April of the Savona Campus, the integration of the CAES lead to relative savings of +8.1% and power-to-H2 of +5.3% when surplus electricity was not sold to the grid. Conversely, with the ability to sell excess electricity, CAES and battery energy storage (BES) systems exhibit modest savings of +1.2% and +2.4%, respectively, while the power-to-H2 system failed to provide economic advantages
Thermoeconomic impact on combined cycle performance of advanced blade cooling systems
No full textIn this work the thermoeconomic features of two different combined cycles using air "open loop" and steam "closed loop" cooled gas turbines are presented and compared in depth. In order to properly estimate both thermodynamic and thermoeconomic performance of the different combined cycles an analytical model of the blade cooling system has been developed in details and outlined in the paper. Internal Thermoeconomic functional analysis is not performed here, as only economic results are shown and discussed. The blade cooling detailed model, originally developed by TPG researchers, has been integrated into the web based modular code WTEMP, already validated for GT based cycles, developed in the last ten years by TPG. It is shown that the closed loop blade cooling configuration has the greatest potential in terms of thermodynamic efficiency and economic competitivity in the mid-term.Cooled gas turbine Combined cycles Open loop Closed loop Thermoeconomics
Experimental and Numerical Analysis of Torsional—Lateral Vibrations in Drive Lines Supported by Hydrodynamic Journal Bearings
No full textThe driving and resistance torques of some rotating machinery for industrial applications are nonstationary and affect system dynamics. Under such operating conditions, coupling between torsional and lateral vibrations may become significant for drive lines supported by hydrodynamic bearings in particular design configurations. Indeed, the occurrence of fluid–structure interactions causes a reduction in the stability threshold of the journal bearings. A hypothesis based on Hopf bifurcation theory (HBT), which justifies how the coupling phenomenon develops, is validated by means of overall experimental observations and a suitable numerical model. When the pulsating driving torque induces significant angular speed oscillation, the rotor-bearing system lateral operating response becomes more complex, and bearing instability onset is detected. Such observation proves the influence of bearings in converting torsional oscillations to lateral vibrations. Particularly, during run-up and run-down tests, localized hysteresis is observed in trends of fundamental order contents. The numerical model of the hydrodynamic bearings solves the Reynolds equation in unsteady conditions to quantify the lateral vibrations amplitude in the presence of both angular speed oscillation and dynamic perturbation. The proposed approach proves the onset of torsional–lateral vibration coupling due to hydrodynamic bearings, to a certain extent. The detected hysteresis phenomena can also be explained by the onset of journal bearing instability
Influence of pressurization for fuel cell systems fed with alternative fuels for maritime applications.
No full textThe maritime sector, characterized by its reliance on conventional fossil fuels, is undergoing a decarbonization process towards cleaner and more sustainable energy sources. This thesis investigates the potential utilization of fuel cells as alternative energy power systems for maritime applications, with a particular emphasis on both low-temperature Proton Exchange Membrane Fuel Cells (PEMFC) and high-temperature Solid Oxide Fuel Cells (SOFC).
The study begins with a comprehensive review of the current composition of power energy systems in the maritime field, analysing existing propulsion systems and their environmental impact. To complete this first part, the software HELM (developed by the Thermochemical Power Group) was adopted to carry out a multicriteria analysis on few case studies to have a better understanding on the range of applicability of these innovative technologies.
The work includes the simulation of the fuel cells system through numerical models to evaluates the feasibility, advantages, and challenges associated with integrating PEMFC and SOFC systems into maritime vessels. Special attention is given to the study of pressurization of both PEMFC and SOFC systems. The performance of the system increases but the complexity of the BoP, the costs and the volumes and weights are influenced negatively. The pressurization is achieved for both cases, hybridizing the fuel cell with a turbocharger.
The PEMFC-TC system was analysed using the commercial software GT-Power while the SOFC was investigated with the use of TRANSEO which relies on MATLAB-Simulink.
The actual state of art for SOFC provides for the use of methane that is converted with a reforming process into hydrogen but in the recent years other hydrocarbons or hydrogen carriers are considered as alternative fuels. The last chapter of this thesis explores the potential of utilizing innovative fuels such as ammonia in SOFC systems. The feasibility and advantages of using ammonia as a fuel source are examined, considering its potential for reducing greenhouse gas emissions relying on the fact that its production is widely diffused.
Overall, this thesis contributes to the research on alternative systems that will be part of the energy mix of the next years to reach the emissions limits imposed by regulations for a more sustainable maritime transportation by offering a comprehensive analysis of the opportunities and challenges associated with fuel cell technologies in this field
Feasibility assessment of retrofitting ships with fuel cell-based hybrid systems to decarbonize the domestic maritime sector
No full textIl trasporto marittimo rappresenta un canale vitale per l’economia a livello mondiale e all’interno dell’Unione Europea (UE), tuttavia contribuisce al 3% delle emissioni di CO2 dell’UE e al 14,33% delle emissioni di gas serra legate ai trasporti. Per rendere il trasporto marittimo più sostenibile ed efficiente dal punto di vista energetico, è essenziale retrofitting le navi alimentate a diesel di sistemi innovativi. In questo contesto, l'interesse per la tecnologia delle celle a combustibile ad alta efficienza e basse emissioni per applicazioni marittime è aumentato nell'ultimo decennio.
Come parte della tesi, è stata condotta una revisione comparativa dei sistemi di celle a combustibile adatti per applicazioni marittime, con un'attenzione ai tipi più promettenti per le navi, celle a combustibile a membrana a scambio protonico (PEMFC) e celle a combustibile a ossidi solidi (SOFC). La tesi contribuisce al crescente corpus di conoscenze sviluppando un quadro di valutazione multi-aspetto per il retrofitting delle navi con sistemi ibridi basati su celle a combustibile e altri sistemi di alimentazione avanzati. Questo quadro integra valutazioni energetiche, tecniche, economiche e di sensibilità per identificare il sistema di alimentazione più fattibile da implementare a bordo.
La prima parte della tesi esamina due casi di studio, un traghetto passeggeri a corto raggio e un rimorchiatore portuale. Vengono esaminati diversi tipi di soluzioni (PEMFC, SOFC, motore a combustione interna (ICE) e batterie) e combustibili (idrogeno, ammoniaca, gas naturale e metanolo) per identificare la tecnologia più fattibile in base a diversi criteri. Per il traghetto passeggeri, PEMFC alimentato a idrogeno è emerso come la soluzione più fattibile per il tempo di resistenza identificato, offrendo compatibilità con i requisiti di peso e volume rispetto ad altre soluzioni alternative. Il sistema a batteria completa e il sistema PEMFC alimentato a idrogeno hanno dimostrato un'efficienza energetica superiore, fattibilità tecnica, sostenibilità ambientale e costi inferiori rispetto ai sistemi basati su SOFC. L'analisi del rimorchiatore ha identificato i sistemi ibridi, in particolare il sistema ibrido PEMFC-batteria, come la soluzione più equilibrata per garantire una propulsione a zero emissioni, ottenendo al contempo efficienza energetica, fattibilità tecnica e prestazioni economiche ottimali rispetto ad altre soluzioni. Questi risultati sottolineano il potenziale dei sistemi ibridi basati su celle a combustibile nella decarbonizzazione delle navi portuali.
La seconda parte della tesi esplora un innovativo sistema ibrido basato sull'integrazione di SOFC con ICE su due traghetti RoPax (traghetti Island e Lake). Attraverso analisi on-design e off-design, lo studio identifica l'innovativa integrazione tra SOFC turbocompresso e ICE come una configurazione interessante con una quota di potenza SOFC del 20% come ottimale, ottenendo un'efficienza del sistema fino al 53,2%. Questa configurazione è studiata in dettaglio attraverso un modello 0D sviluppato utilizzando il software interno WTEMP e un modello 1D più dettagliato sviluppato nell'ambiente Matlab-Simulink. L'analisi dimostra significativi risparmi di carburante e guadagni di efficienza, in particolare per le navi con elevate ore di operatività portuale, come il traghetto Island. I risultati dell'analisi tecnico-economica rivelano che mentre questo sistema ibrido comporta costi di capitale più elevati, i suoi vantaggi operativi e i miglioramenti dell'efficienza lo rendono un'opzione competitiva per le navi con sostanziali profili operativi giornalieri. I risultati della tesi offrono approfondimenti scalabili su applicazioni marittime più ampie, nonché una metodologia per il retrofitting delle navi per operazioni a zero emissioni.Waterborne transport is a vital conduit for the economy globally and inside the European Union (EU), however, it contributes to 3% of the EU's carbon dioxide emissions and 14.33% of transport-related greenhouse gas emissions. To make waterborne transport more sustainable and energy efficient, retrofitting diesel-powered ships with advanced power systems is essential. In this context, the interest in high-efficiency and low-emission fuel cell technology for maritime applications has been rising during the last decade.
As part of the thesis, a comparative review of the fuel cell systems suitable for maritime applications was conducted, with a focus on the most promising types for ships, Proton Exchange Membrane Fuel Cells (PEMFC) and Solid Oxide Fuel Cells (SOFC). The thesis contributes to the growing body of knowledge by developing a multi-aspect assessment framework for retrofitting ships with fuel cell-based hybrid systems, as well as other advanced power systems. This framework integrates energy, technical, economic, environmental, and sensitivity assessments to identify the most feasible power system to be implemented on board.
The first part of the thesis examines two case studies, a short-sea passenger ferry and a port tugboat. Different types of solutions (PEMFC, SOFC, internal combustion engine (ICE), and batteries) and fuels (hydrogen, ammonia, natural gas, and methanol) are investigated to identify the most feasible technology according to different criteria. For the passenger ferry, PEMFC powered by hydrogen emerged as the most feasible solution for the identified endurance time, offering compatibility with the weight and volume requirements compared to other alternative solutions. The full battery system and PEMFC system powered by hydrogen demonstrated superior energy efficiency, technical feasibility, environmental sustainability, and lower costs compared to SOFC-based systems. The tugboat analysis identified hybrid systems, particularly the hydrogen PEMFC-battery hybrid system, as the most balanced solution to guarantee zero-emission propulsion while achieving optimal energy efficiency, technical feasibility, and economic performance compared to other solutions. These findings underscore the potential of fuel cell-based hybrid systems in decarbonizing port-operating vessels.
The second part of the thesis explores an innovative hybrid system based on the integration of SOFC with ICE on two RoPax ferries (Island and lake ferries). Through on-design and off-design analyses, the study identifies the innovative integration between turbocharged SOFC and ICE as an attractive configuration with a 20% SOFC power share as optimal, achieving a system efficiency of up to 53.2%. This configuration is investigated in detail through a 0D model developed using the in-house software WTEMP and a more detailed 1D model developed in the MATLAB-Simulink environment. The analysis demonstrates significant fuel savings and efficiency gains, particularly for vessels with high port operation hours, such as the Island ferry. The techno-economic analysis results reveal that while this hybrid system incurs higher capital costs, its operational benefits and efficiency improvements make it a competitive option for vessels with substantial daily operating profiles. The thesis findings offer scalable insights into wider maritime applications as well as a methodology for retrofitting ships for zero-emission operations
Combined Cycle, Heat Pump, and Thermal Storage Integration: Techno-Economic Sensitivity to Market And Climatic Conditions Based on a European and United States Assessment
No full textThe integration of a Heat Pump with a Combined Cycle Gas Turbine (CCGT) to control the inlet air temperature is a promising technology to meet the requirements imposed by the current electricity systems in terms of efficiency and flexibility. If the HP is coupled with a Thermal Energy Storage (TES) in an Inlet Conditioning Unit (ICU), it can be exploited in different modes to enhance the off-design CCGT’s efficiency or to boost the power output at full load. Furthermore, fuel-saving would be reflected in avoided emissions. The optimal sizing of the ICU, as well as an accurate estimation of the benefits, is a complex problem influenced by several factors such as the local climate and electricity market prices. The paper aims to systematically investigate, utilizing a MILP model for optimal dispatch, the feasibility of an ICU integration in different scenarios (EU and US). Different electricity markets have been analyzed and classified according to the parameters describing the average and variability of prices, the interdependency with the gas market, the ambient temperature, or the local carbon pricing policy. The most favorable conditions are identified and the dependency of the optimal ICU sizing on the climate and the electricity market is highlighted. The paper provides information for a first viability assessment: the concept appears to be highly profitable in hot regions with high price variability. Additionally, even in less profitable conditions (i.e., stable low prices in a cold climate), the system increases operating hours and reduces economic losses
- …
