Generación de hidrógeno en buques GNL

Programa Oficial de Doutoramento en Enerxía e Propulsión Mariña. 5014P01[Resumen] Debido a la evolución de las estrictas normativas anticontaminación, los sistemas de propulsión a bordo de buques GNL (Gas Natural Licuado) están en una época de cambios tecnológicos y económicos. Los motores DF (Dual Fuel) se establecieron como el sistema de propulsión más utilizado debido a la posibilidad que ofrecen de consumir diferentes combustibles, proporcionando una gran versatilidad al buque. Pero se debe prestar especial atención al sistema de gestión de gas en los buques GNL sin planta de relicuefacción, debido a que el exceso de BOG (Boil Off Gas) generado es quemado en la GCU (Gas Combustion Unit) sin ningún aporte energético, con lo que es evidente la necesidad de mejorar el sistema. Esta tesis se centra en el estudio del aprovechamiento del exceso de BOG generado en buques GNL, para mejorar la eficiencia de las plantas. Se revisan los diferentes sistemas de propulsión a bordo de buques GNL y se analiza el proceso de la gestión de gas, para determinar la energía disponible del BOG y la que se puede recuperar. Lo anterior tiene como objetivo proponer una nueva configuración de la planta de gestión de gas para aprovechar el exceso de BOG generado y aumentar el rendimiento de la planta. Las planta propuesta es modelizada termodinámicamente y analizada con el software EES (Engineering Equation Solver) para realizar un análisis paramétrico y optimizarla bajo el punto de vista de la eficiencia. La planta tratada se basa en el aprovechamiento del exceso de BOG en un sistema de reformado con vapor para la obtención de hidrógeno, un combustible limpio que nos permite navegar sin limitaciones en zonas con estrictas normativas anticontaminación.[Resumo] Debido a evolución das estritas normativas anticontaminación, os sistemas de propulsión a bordo dos buques GNL (Gas Natural Licuado) están nunha época de cambios tecnolóxicos e económicos. Os motores DF (Dual Fuel) establecéronse como o sistema de propulsión mais empregado debido a posibilidade que ofrecen de consumir diferentes combustibles, proporcionando unha gran versatilidade ao buque. Pero se debese prestar especial atención ao sistema de xestión de gas nos buques GNL sen planta de relicuefacción, debido a que o exceso de BOG (Boil Off Gas) xerado é queimado na GCU (Gas Combustion Unit) sen ningún aporte enerxético, polo que é evidente a necesidade de mellorar o sistema. Esta tese centrase no estudio do aproveitamento do exceso de BOG xerado en buques GNL, para mellorar a eficiencia das plantas. Revísanse os diferentes sistemas de propulsión a bordo dos buques GNL e analízase o proceso de xestión de gas, para determinar a enerxía dispoñible do BOG e a que se pode recuperar. O anterior ten como obxectivo propoñer unha nova configuración da planta de xestión de gas para aproveitar o exceso de BOG xerado e aumentar o rendemento da planta. A planta proposta é modelizada termodinámicamente e analizada con software EES (Engineering Equation Solver) para realizar un análises paramétrico e optimizala baixo o punto de vista da eficiencia. A planta tratada baséase no aproveitamento do exceso de BOG nun sistema de reformado con vapor para a obtención do hidróxeno, un combustible limpo o que nos permite navegar sen limitacións en zonas con estritas normativas anticontaminación.[Abstract] Amendments to strict anti-pollution maritime regulations have given rise to the shipping industry having to undertake costly technological investments in propulsion systems aboard LNG (Liquefied Natural Gas) vessels. The flexible fuel consumption of DF (Dual Fuel) engines have resulted in them becoming the main choice as the prime propulsion system, providing great versatility to the ship. However, particular attention should be given to gas management systems on those LNG vessels without a reliquefaction plant, as the excess BOG (Boil Off Gas) produced is burned in the GCU (Gas Combustion Unit) without any energy input, thereby determining a clear need to improve the system. To this end, this thesis focuses on the study of the use of excess BOG generated on LNG vessels, with the aim of improving plant efficiency. Thus, the different propulsion systems on board LNG ships are reviewed and the gas management process is analysed to determine the available energy of the BOG, as well as the amount that can be recovered. Such analysis is aimed at proposing a new gas management plant configuration to exploit the excess BOG produced and hence increase the performance of the plant. The proposed plant is thermodynamically modelled and analysed using EES (Engineering Equation Solver) software to perform a parametric analysis and optimisation thereof in terms of efficiency. The plant concerned is based on the use of excess BOG in a steam reforming system in order to obtain hydrogen, a clean fuel that allows vessels to navigate without limitations in areas with strict anti-pollution regulations

Thermodynamic and Environmental Analyses of a Novel Closed Loop Regasification System Integrating ORC and CO2 Capture in Floating Storage Regasification Units

[Abstract] Regasification systems in Floating Storage Regasification Units (FSRUs) that use the steam generated by the boilers as the heat source (closed loop) in the liquefied natural gas (LNG) regasification process are less detrimental to the marine environment than those systems that use seawater (open loop). Their drawback, however, lies in the significant increase in fuel consumption and, thus, CO2 emissions. The present paper performs an energy, exergy and environmental analysis of a novel closed-loop regasification system for FSRUs that integrates an organic Rankine cycle (ORC) and post-combustion CO2 capture system with a 30 wt% aqueous solution of monoethanolamine (MEA). LNG cold energy is utilised for power generation through the ORC as well as in the processes of CO2 capture, compression, drying and liquefaction. The system proposed is able to meet the electrical power demand of the FSRU without the use of dual fuel engines, while CO2 capture efficiency in the boiler flue gases exceeds 90%. Fuel consumption is cut by 18% in this system in comparison with existing closed-loop regasification systems, and exergy efficiency increases by 14%, while CO2 emissions decrease by approximately 75% compared to open-loop systems commonly installed on board.Funding for open access charge: Universidade da Coruña/CISUG

Energy Efficiency and Environmental Measures for Floating Storage Regasification Units

Financiado para publicación en acceso aberto: Universidade da Coruña/CISUG[Abstract] In view of the need to reduce greenhouse gas emissions from the maritime sector, this paper proposes design and operation indicators for the assessment of Floating Storage Regasification Unit (FSRU) energy efficiency and carbon footprint. Such indicators are applied to the study of five regasification systems: seawater system without recondenser (Case 0), seawater system (Case 1), open-loop propane system (Case 2), closed-loop water-glycol system (Case 3) and open-loop system with Organic Rankine Cycle (ORC) (Case 4). Of the regasification systems installed in FSRUs, Case 1 proves most energy efficient, closely followed by Case 2. If the cold energy of liquefied natural gas (LNG) were to be exploited in the regasification process, Case 4 would present an Energy Efficiency Design Index (EEDI) 41.25% lower than that of Case 1, whilst positioned at the opposite end of the scale is Case 3 with an EEDI of 347.98% higher. The Carbon Footprint Design Index (CFDI), in comparison with the EEDI, further includes emissions deriving from the methane slip from dual fuel engines and the CO2 capture ratio factor for the possible implementation of Carbon Capture and Storage (CCS) systems. In the cases analysed, the CFDI with a methane slip of 5.5 g/kWh represents an increase of 4–28% with regard to the EEDI

Thermodynamic and Economic Analyses of Zero-Emission Open Loop Offshore Regasification Systems Integrating ORC with Zeotropic Mixtures and LNG Open Power Cycle

[Abstract] The present study provides an energy, exergy and economic analysis of a seawater regasification system (open loop) combining stages of simple organic Rankine cycles (ORCs) arranged in series with an open organic Rankine cycle (OC) in order to exploit the cold energy of liquefied natural gas (LNG). The proposed system, termed ORC-OC, is implemented in a Floating Storage Regasification Unit (FSRU) to achieve the objective of zero greenhouse emissions during the regasification process. Configurations of up to three stages of ORCs and the use of zeotropic mixtures of ethane/propane and n-butane/propane as working fluids are considered in the study of the novel regasification system. Only the two-stage ORC-OC (2ORC-OC) and three-stage (3ORC-OC) configurations accomplish the objective of zero emissions, attaining exergy efficiencies of 61.80% and 62.04%, respectively. The overall cost rate of the latter, however, is 20.85% greater, so the 2ORC-OC results as being more cost-effective. A comparison with conventional regasification systems installed on board shows that the 2ORC-OC yields a lower total cost rate if the LNG price exceeds 8.903 USD/MMBtu. This value could be reduced, however, if the electrical power that exceeds the FSRU’s demand is exported and if compact heat exchangers are implemented

Entropies and IPR as Markers for a Phase Transition in a Two-Level Model for Atom–Diatomic Molecule Coexistence

This work is part of the I+D+i projects PID2019-104002GB-C22 and PID2020-114687GB-I00 funded by MCIN/AEI/10.13039/501100011033. This work is also part of grant Group FQM-160, EU FEDER funds US-1380840 and the project PAIDI 2020 with reference P20_01247, funded by the Consejería de Economía, Conocimiento, Empresas y Universidad, Junta de Andalucía (Spain) and “ERDF—A Way of Making Europe”.A quantum phase transition (QPT) in a simple model that describes the coexistence of atoms and diatomic molecules is studied. The model, which is briefly discussed, presents a second-order ground state phase transition in the thermodynamic (or large particle number) limit, changing from a molecular condensate in one phase to an equilibrium of diatomic molecules–atoms in coexistence in the other one. The usual markers for this phase transition are the ground state energy and the expected value of the number of atoms (alternatively, the number of molecules) in the ground state. In this work, other markers for the QPT, such as the inverse participation ratio (IPR), and particularly, the Rényi entropy, are analyzed and proposed as QPT markers. Both magnitudes present abrupt changes at the critical point of the QPT.Consejería de Economía, Conocimiento, Empresas y Universidad, Junta de AndalucíaSecretaría de Estado de Investigacion, Desarrollo e Innovacion FQM-160, MCIN/AEI/10.13039/501100011033, PID2019-104002GB-C22, PID2020-114687GB-I00European Regional Development Fund US-138084

Exploitation of Liquefied Natural Gas Cold Energy in Floating Storage Regasification Units

[Abstract] This paper aims to review regasification technology installed in Floating Storage Regasification Units (FSRUs) and the potential offered by the exploitation of cold energy from liquefied natural gas (LNG) in these vessels. The assessment describes the main characteristics of regasification systems along with their respective advantages and limitations. Regasification systems in direct exchange (seawater and steam) and systems with intermediate fluids that use propane or water-glycol in the heat transfer process are studied. In recent years, water-glycol systems have cornered the market. The mixture, besides reducing the risk of freezing, is non-flammable, economical and highly available. Thermodynamic analysis of the regasification process shows that LNG cold energy is the main source of residual energy in these vessels; the specific energy and exergy content is more than double that of engine exhaust gases. Exploitation of this cold energy in power cycles could significantly reduce FSRUs harmful emissions and electrical energy could even be exported to shore. The organic Rankine cycle technology is the most well-known and widely studied, although scientific literature is scarce and there is a need to propose new regasification systems with cold energy exploitation that can be adopted on these vessels

Entropies and IPR as Markers for a Phase Transition in a Two-Level Model for Atom–Diatomic Molecule Coexistence

A quantum phase transition (QPT) in a simple model that describes the coexistence of atoms and diatomic molecules is studied. The model, which is briefly discussed, presents a second-order ground state phase transition in the thermodynamic (or large particle number) limit, changing from a molecular condensate in one phase to an equilibrium of diatomic molecules–atoms in coexistence in the other one. The usual markers for this phase transition are the ground state energy and the expected value of the number of atoms (alternatively, the number of molecules) in the ground state. In this work, other markers for the QPT, such as the inverse participation ratio (IPR), and particularly, the Rényi entropy, are analyzed and proposed as QPT markers. Both magnitudes present abrupt changes at the critical point of the QPT.Ministerio de Ciencia e Innovación PID2019-104002GB-C22, PID2020-114687GB-I00, 10.13039/501100011033Junta de Andalucía US-1380840, P20_0124

Generation of H₂ on Board Lng Vessels for Consumption in the Propulsion System

[Abstract] At present, LNG vessels without reliquefaction plants consume the BOG (boil-off gas) in their engines and the excess is burned in the gas combustion unit without recovering any of its energy content. Excess BOG energy could be captured to produce H₂, a fuel with high energy density and zero emissions, through the installation of a reforming plant. Such H₂ production would, in turn, require on-board storage for its subsequent consumption in the propulsion plant when navigating in areas with stringent anti-pollution regulations, thus reducing CO₂ and SOₓ emissions. This paper presents a review of the different H₂ storage systems and the methods of burning it in propulsion engines, to demonstrate the energetic viability thereof on board LNG vessels. Following the analysis, it is identified that a pressurised and cooled H₂ storage system is the best suited to an LNG vessel due to its simplicity and the fact that it does not pose a safety hazard. There are a number of methods for consuming the H₂ generated in the DF engines that comprise the propulsión plant, but the use of a mixture of 70% CH₄-30% H₂ is the most suitable as it does not require any modifications to the injection system. Installation of an on-board reforming plant and H₂ storage system generates sufficient H₂ to allow for almost 3 days’ autonomy with a mixture of 70%CH₄-30%H₂. This reduces the engine consumption of CH₄ by 11.38%,thus demonstrating that the system is not only energy-efficient, but lends greater versatility to the vessel

Premature termination of psychological treatment for anxiety disorders in a clinical setting

Background: Empirically supported psychological treatments (ESTs) have demonstrated their effectiveness and clinical utility for the treatment of anxiety disorders (AD) but few studies have assessed the factors associated with premature termination in ESTs for AD. Method: The goals of this study, which involved 291 patients with a diagnosis of anxiety who had received outpatient psychological care, consisted of examining premature termination of treatment (PTT), comparing the individual characteristics of the patients who successfully completed treatment with those who terminate it prematurely, and analyzing the predictors of PTT. Results: Of the sample, 8.2% refused to start treatment, 28.5% dropped out before completing it, and 63.2% successfully completed treatment. In 50% of the cases, PTT occurred during the first 7 sessions, and in 80%, before the 15th session. Alternatively, 76.4% of the patients who complete treatment successfully do so before session 20. We found that patients with PTT attended a significantly lower number of treatment sessions and attended the sessions more irregularly and unpunctually. Presenting a generalized anxiety disorder (GAD), problems with punctuality and with task performance were predictors of failure to complete treatment. Conclusions: These findings suggest the need to reinforce early adherence to treatments to help patients remain in treatment