ENVIRONMENTAL AND COST-EFFECTIVENESS COMPARISON OF DUAL FUEL PROPULSION OPTIONS FOR EMISSIONS REDUCTION ONBOARD LNG CARRIERS

The selection of the suitable propulsion system for LNG carrier highly affects the ship capital and life cycle costs. The current paper compares between the available propulsion systems for LNG carriers from environmental and economic points of view operated with heavy fuel oil (HFO) and marine gas oil (MGO). In addition, the cost-effectiveness for emission reduction due to using dual fuel propulsion options using natural gas fuel (NG) is calculated. As a case study, large conventional LNG carrier class has been investigated. The results show that steam turbine (ST), Ultra-ST, dual fuel diesel engine (DFDE), and combined gas and steam (COGAS) propulsion options can comply with NOx and SOx emissions regulations set by IMO using dual fuel mode with NG percentages of 87.5%, 82%, 98.5% and 94%, respectively. DFDE operated with pilot HFO and NG is the most economic propulsion option. It reduces the dual fuel costs by 1.37 MUS$/trip compared with HFO cost. The annual cost-effectiveness for the most economic and emission compliance propulsion option is 6.07$/kg, 6.39 $/kg, and 0.55$/kg for reducing NOx, SOx, and CO2 emissions, respectively

Greenhouse Gas Reduction by Utilization of Cold LNG Boil-off Gas

AbstractThis paper present the analysis of utilization the cryogenic temperature of Boil off Gas (BOG) from Liquefied Natural Gas (LNG) to flow air inside insulation space of LNG. Three Dimensional geometry of the tank are model in Computational Fluid Dynamic (CFD) ANSYS Fluent software package using steady state and K-Epsilon turbulence model. Result shows that almost 60% of BOG can be prevented from flared to the atmosphere thus will reduce Greenhouse Gas (GHG) emission and pollution

Greenhouse Gas Reduction by Utilization of Cold LNG Boil-off Gas

This paper present the analysis of utilization the cryogenic temperature of Boil off Gas (BOG) from Liquefied Natural Gas (LNG) to flow air inside insulation space of LNG. Three Dimensional geometry of the tank are model in Computational Fluid Dynamic (CFD) ANSYS Fluent software package using steady state and K-Epsilon turbulence model. Result shows that almost 60% of BOG can be prevented from flared to the atmosphere thus will reduce Greenhouse Gas (GHG) emission and pollution

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

Holistic modelling of LNG carrier systems

PhD ThesisAs the human population increases in parallel with an increase in the standard of living, the world energy demand also continually grows every year. Fossil fuels are the major components contributing to this energy supply. Natural gas, one of the fossil fuels, has shown promising growth due to it price and lower pollutant emissions compared to other fossil fuels. One option for transporting natural gas is the use of Liquefied Natural Gas (LNG) carriers. The LNG carrier is one of the most expensive, complex and potentially hazardous cargo carriers that are operating across the world’s oceans due to its cargo, thus proven components are required to build this type of ship. There are seven main components involved in constructing an LNG carrier and they are manufactured by a range of different companies. This situation has created a competitive environment for this industry; however it has also introduced a new challenge to the shipbuilder, engineer and ship-owner in terms of selecting the right components. For a new ship design, there would typically be an incremental change in one or more technology elements from a base design and over time this may result in a less than optimum design. This thesis therefore aims to develop a holistic methodology that can be employed in order to help the ship-owner in particular to select the right combination components for an LNG carrier to rationalise the fleet size, minimise overall costs of construction and operation, and control the total mass of pollutant emission products in preliminary design stage. This methodology is based on the mutual symbiosis between the tools used: namely a comprehensive ship system simulation method, an artificial neural network (ANN) evaluation process and an integrated ANN based multi-objective optimisation process. It is a comprehensive methodology that can be applied to all types of ships, although in this study, it focuses on LNG carrier

Improving ship maintenance : a criticality and reliability approach

Ship maintenance has evolved through the years incorporating tools and techniques already applied in other industrial sectors. The obvious benefits from such an application include improved safety, environmental protection, asset integrity, minimisation of downtime and increased operability. In this paper, a predictive maintenance approach is described employing reliability and criticality analysis tools. Its application on the Diesel Generator (DG) system of a motor cruise ship is also presented. Well known tools such as Failure Modes, Effects and Criticality Analysis (FMECA) and Fault Tree Analysis (FTA) using static and dynamic gates together with reliability Importance Measures (IMs) are applied. The results of this research paper include the estimation of the reliability of the main system and sub-systems and the identification of their critical components as well as suggesting measures in order to prevent and/or mitigate the failures of the under-performing equipment

Reducción de los costes en el transporte marítimo mediante la optimización de la planta de propulsión de un buque de transporte LNG

[Resumen]: En este proyecto se analizará la reducción del coste de operación de los buques de transporte de gas natural licuado (LNG) optimizando su planta de propulsión, mediante el estudio de tipos de diseño diferentes al más habitual de los presentes en este tipo de buques (planta de propulsión a vapor). El estudio incluirá además la influencia de la reducción del uso del gas procedente del boil-off mediante un proceso de relicuefacción. Para realizar este estudio será necesario conocer: Estado actual del mercado del gas natural Características de la flota actual de Buques LNG Construcción de estos tipo de buques Evaluación técnica de las diferentes plantas propulsoras Evaluación económica de los costes de construcción, mantenimientos y costes de carga.Traballo fin de mestrado (UDC.EPS). Enxeñaría naval e oceánica. Curso 2016/201

An early-stage approach to optimise the synthesis, design and operation of a marine energy system for liquefied natural gas carriers

Since decisions of the greatest impact are made in early stages of ship design, developing design tools to make more information available sooner is desirable. Moreover, there is still room for improvements on the optimisation of energy system selection considering an integrated approach. Therefore, the present work aims to provide a comprehensive early-stage approach to perform the optimisation of design, synthesis and operation, considering economic and technical aspects as well as route weather. Constraints are used to avoid propellers that could present issues concerning strength, cavitation and vibration. Various propellers, sixteen engines and four operational profiles are assessed. A differential evolution optimisation algorithm whose objective function to be maximised is the net present value is applied. The case study is designed using a liquefied natural gas carrier of 175,000 m3 sailing between Lake Charles (USA) and Tokyo Bay (Japan), via Panama Canal. All suitable matchings for 15,023 propellers are found. The approach shows a gain of 22% between the worst individual of the initial population and the worst individual of the final population. The required brake power is approximately 22% higher for rough weather than for still water. A difference of over 120% was found by comparing varied matchings of economic scenes and fuel profiles. The approach shows a significant gain and highlights the value of exploring a broad range of energy system configurations in an integrated manner, considering the weather condition.Uma vez que as decisões de maior impacto são feitas nos primeiros estágios do projeto do navio, o desenvolvimento de ferramentas de projeto para disponibilizar mais informações mais cedo é desejável. Além disso, ainda há margem para melhorias na otimização da seleção do sistema de energia, considerando uma abordagem integrada. Portanto, o presente trabalho visa proporcionar uma abordagem preliminar e abrangente para a otimização de projeto, síntese e operação, considerando aspectos econômicos e técnicos, bem como o estado do mar ao longo da rota. Para evitar hélices que possam apresentar problemas de resistência, cavitação e vibração, são usadas restrições. Vários hélices, dezesseis motores e quatro perfis operacionais são avaliados. Um algoritmo de otimização do tipo evolução diferencial, cuja função objetivo a ser maximizada é o valor presente líquido, é aplicado. O estudo de caso foi projetado usando um transportador de gás natural liquefeito de 175,000 m3 que navega entre Lake Charles (EUA) e Tokyo Bay (Japão), através do Canal do Panamá. Todas as combinaçõe adequadas para 15,023 hélices são encontradas. A abordagem mostra um ganho de 22% entre o pior indivíduo da população inicial e o pior indivíduo da população final. A potência no freio necessária é aproximadamente 22% maior para mar agitado do que para água parada. Uma diferença de mais de 120 % foi encontrada comparando combinações variadas de cenas econômicas e perfis de combustível. A abordagem mostra um ganho significativo e destaca o valor de explorar uma ampla gama de configurações de sistemas de energia de forma integrada, considerando a condição climática

Comparative safety assessment of LNG re-liquefaction systems applied on LNG carriers

This research was aimed to evaluate the safety of the LNG cargo compressor room against unwanted gas leakage from two different re-liquefaction systems applicable for an LNG carrier: 1) the Partial (Full) Re-liquefaction System (P(F)RS) and 2) the combination of Partial Re-liquefaction System and Mixed Refrigerant Re-liquefaction system (PRS+MRS). To achieve this goal, quantitative risk assessment was carried out with the integration of system hierarchical modelling, statistical analysis, and CFD simulation. The frequency of initial leakages, occurring to each component of the re-liquefaction systems, was analysed, whereas for the consequence analysis, a CFD program of PyroSim was employed to simulate the gas dispersion in the confined room fitted with mechanical ventilation systems. In addition, various ventilation capacities were investigated with changes in their allocations in the room in order to determine these parametric influences on the results. The risk level of re-liquefaction systems was determined in a quantitative way. Research results clearly presented the importance of the proper arrangement of the ventilation systems. The risk levels were estimated at 5.6 E-3/year for P(F)RS whereas about 9.6 E-3/year for the PRS+MRS in consideration of current regulations. However, the increase in the ventilation capacity was found to reduce the risk levels. The research findings are highly believed to offer meaningful guidance into future safety regulatory frameworks