Options and Evaluations on Propulsion Systems of LNG Carriers

The LNG carriers are undergoing a period of rapid and profound change, with much larger size ships and novel propulsion systems emerging for fulfilling the market trends of LNG shipping industry. There are various proposed propulsion solutions for LNG carriers, ranging from the conventional steam turbine and dual fuel diesel electric propulsion, until more innovative ideas such as slow speed dual fuel diesel engine, combined gas turbine electric & steam system, and hybrid propulsion based on steam turbine and gas engine. Since propulsion system significantly influenced the ship’s capital, emission regulation compliance and navigation safety, the selection of a proper propulsion option with technical feasibility and economic viability for LNG carriers is currently a major concern from the shipping industry and thus must be comprehensively assessed. In this context, this chapter investigated the main characteristics of these propulsion options in terms of BOG treatment, fuel consumption, emission standards compliance, and plant reliability. Furthermore, comparisons among different propulsion system were also carried out and related evaluation was presented

An analysis of the propulsion and powering options for LNG carriers

The work presented in this thesis provides a comprehensive analysis of the propulsion and powering options for future LNGCs (Liquid Natural Gas Carriers) using academic methods and operational measurements. An analytical study of the LNGC fleet using the EEDI methodology was used initially from which it was concluded that the legislated performance requirements of the current EEDI protocol is insufficient to stimulate the design improvements needed to reduce the CO2 footprint of the LNGC fleet. The research further demonstrated that multiple baselines for different LNGC propulsion technologies would yield improved reductions of CO2 more compatible with the long term IMO (International Maritime Organisation) goal of reducing CO2 emissions by 50%. The issue of methane slip was also considered in the analysis because it has an impact on propulsion efficiency and the knowledge that methane is also a greenhouse gas. A method of calculating methane slip was developed to be included in proposed modified EEDI calculations revealing the need to ensure a holistic approach to atmospheric emissions impact is needed. Using modelling and simulation methods, case studies were undertaken to explore improvements to the current designs. Furthermore, when a comparative analysis of the different modern designs and upgraded options were carried out, it was seen that modern DFDE (dual fuel diesel engine) designs showed the highest efficiency and operational flexibility of the various options, due to its flexibility in the use of multiple prime movers which increases the reliability of these engines. By analysing the operational data carried out during practical case studies on-board LNGCs, it was determined that the operational profile differs markedly from the design profiles often presented in the literature. Sea trials conditions were found to be non-representative of realistic operational conditions hence the research focused on identifying methods where trial profiling could be better used to predict actual performance. Finally, the research also highlighted the specific operational safety practices carried out by ship operators which reduce the efficiency of the vessel below the design point and identified tested methods to reduce inefficiencies in these practices

LNG-fueled vessels in the Norwegian short-sea market : a cost-effective response to environmental regulation

The objective of this thesis is to assess the environmental and economic advantages of using LNG as fuel for ships. Air emissions from ships are an increasing environmental concern. Since the shipping sector can expect to face more stringent environmental regulations in the future, LNG’s potential as a response to these regulations is analyzed. This study offers an overview of present environmental regulations as well as a description of the properties of LNG. The aim of the final analysis is to identify the cost position of LNG-fueled vessels within different sectors of the Norwegian short-sea shipping market. Net present value (NPV) analysis sets the technical framework for the economic evaluation. The analysis comes to the conclusion that using LNG as fuel for ships offers the potential for significant environmental improvement, regarding both air quality and climate protection, in all sectors subject to the analysis. Economically, LNG as fuel can compete with conventional marine fuel (MGO), at oil prices around approximately 60 $/bbl. Hence, the results of this study indicate that from both an environmental- and economic perspective the investment in LNG powered ships is strongly recommendable. The study also presents some potential barriers with regards to commercial viability and technological feasibility that need to be overcome before LNG becomes fully competitive with other fuels

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

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

Biofuel as an alternative shipping fuel : technological, environmental and economic assessment

© Royal Society of Chemistry 2019Fossil derived fuels available for application within the maritime sector have been dominated by heavy fuel oil (HFO), which is conventionally used in low speed (main) engines, and more refined fuels such as marine diesel oil (MDO), which is consumed in fast or medium speed engines. However, increasing fuel costs and regulatory pressure such as the restrictions placed on sulphur content have increased interest in the use of alternative fuels. A number of alternative fuels have been identified and may be viable for use within the maritime sector including straight vegetable oil (SVO) as an alternative to HFO in low speed engines, biodiesel to replace MDO/MGO in low to medium speed engines and bio-liquefied natural gas (bio-LNG) in gas engines using LNG. The potential sources of biomass feedstocks, conversion pathways and technologies are identified. The key parameters limiting their potential application are examined, in particular, availability, technological development, technical integration, and operational consequences. A proposed solution to overcome these limitations is recommended. The effective implementation of these strategies will enable the more widespread use of biofuels in marine applications, significantly reducing emissions from ships and improving global air quality and also protecting the ecological environment.Peer reviewe

An empirical analysis on the operational profile of liquefied natural gas carriers with steam propulsion plants

Liquefied natural gas (LNG) offers negligible NO_{x} and SO_{x} emissions as well as reductions in CO_{2} compared with other liquid hydrocarbons. LNG is a significant player in the global energy mix, with a projection of 40% increase in demand for the next two decades. It is anticipated that the expected rise in demand will cause the fleet of LNG carriers (LNGC) to expand. This work concentrates on steam-powered LNGC, which accounted for 47% of the LNGC fleet in 2018. It performs an empirical analysis of continuous monitoring data that provide high levels of accuracy and transparency. The analysis is done on data collected from 40 LNGCs for over a year to estimate the fleet's operational profile, fuel mix and energy performance. The findings of this work are relevant for bottom-up analysis and simulation models that depend on technical assumptions, but also for emission studies such as the upcoming Fourth International Maritime Organization Greenhouse Gases study

How to decarbonise international shipping: Options for fuels, technologies and policies

International shipping provides 80–90% of global trade, but strict environmental regulations around NOX, SOX and greenhouse gas (GHG) emissions are set to cause major technological shifts. The pathway to achieving the international target of 50% GHG reduction by 2050 is unclear, but numerous promising options exist. This study provides a holistic assessment of these options and their combined potential to decarbonise international shipping, from a technology, environmental and policy perspective. Liquefied natural gas (LNG) is reaching mainstream and provides 20–30% CO2 reductions whilst minimising SOX and other emissions. Costs are favourable, but GHG benefits are reduced by methane slip, which varies across engine types. Biofuels, hydrogen, nuclear and carbon capture and storage (CCS) could all decarbonise much further, but each faces significant barriers around their economics, resource potentials and public acceptability. Regarding efficiency measures, considerable fuel and GHG savings could be attained by slow-steaming, ship design changes and utilising renewable resources. There is clearly no single route and a multifaceted response is required for deep decarbonisation. The scale of this challenge is explored by estimating the combined decarbonisation potential of multiple options. Achieving 50% decarbonisation with LNG or electric propulsion would likely require 4 or more complementary efficiency measures to be applied simultaneously. Broadly, larger GHG reductions require stronger policy and may differentiate between short- and long-term approaches. With LNG being economically feasible and offering moderate environmental benefits, this may have short-term promise with minor policy intervention. Longer term, deeper decarbonisation will require strong financial incentives. Lowest-cost policy options should be fuel- or technology-agnostic, internationally applied and will require action now to ensure targets are met by 2050