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Dimopoulos G.G.,DNV GL Maritime Research and Development | Stefanatos I.C.,DNV GL Maritime Research and Development | Kakalis N.M.P.,DNV GL Maritime Research and Development
Energy Conversion and Management | Year: 2016

In this paper we present the exergy analysis and design optimisation of an integrated molten carbonate fuel cell (MCFC) system for marine applications, considering waste heat recovery options for additional power production. High temperature fuel cells are attractive solutions for marine energy systems, as they can significantly reduce gaseous emissions, increase efficiency and facilitate the introduction of more environmentally-friendly fuels, like LNG and biofuels. We consider an already installed MCFC system onboard a sea-going vessel, which has many tightly integrated sub-systems and components: fuel delivery and pre-reforming, internal reforming sections, electrochemical conversion, catalytic burner, air supply and high temperature exhaust gas. The high temperature exhaust gasses offer significant potential for heat recovery that can be directed into both covering the system's auxiliary heat requirements and power production. Therefore, an integrated systems approach is employed to accurately identify the true sources of losses in the various components and to optimise the overall system with respect to its energy efficiency, taking into account the various trade-offs and subject to several constraints. Here, we present a four-step approach: a. dynamic process models development of simple and combined-cycle MCFC system; b. MCFC components and system models calibration via onboard MCFC measurements; c. exergy analysis, and d. optimisation of the simple and combined-cycle systems with respect to their exergetic performance. Our methodology is based on the thermofluid and chemical reactions modelling of each component, via our in-house ship machinery systems modelling framework, DNVGL COSSMOS. For the major system components spatially distributed exergy balances are considered in order to capture the coupling of the local process phenomena and exergy destruction with component design characteristics. Exhaust heat recovery is considered using a steam turbine combined-cycle module integrated with the rest of the MCFC system. Both the simple and combined cycle MCFC systems are optimised with respect to their overall exergetic efficiency subject to design, technical, operational and space constraints. The exergy analysis identified and ranked the sources of exergy destruction and the subsequent optimisation yielded significant improvement potential for both systems. The simple MCFC system optimisation yielded an exergy efficiency improvement of 7% with 5% more power produced. Heat recovery in the combined cycle MCFC resulted in 40% more power produced, with a 60% overall exergy efficiency (relative increase of 45%). Both MCFC systems outperform conventional dual-fuel engines with respect to efficiency, having also a positive impact on CO2 emissions with a relative reduction of about 30%. © 2015 Elsevier Ltd. All rights reserved.


Dimopoulos G.G.,DNV GL Maritime Research and Development | Stefanatos I.V.,DNV GL Maritime Research and Development | Kakalis N.M.P.,DNV GL Maritime Research and Development
International Journal of Thermodynamics | Year: 2016

The increasing seaborne transportation of Liquefied Natural Gas (LNG) in the current volatile global market and energy supply environment puts a pressure on LNG vessels to be more efficient, environmentally friendly, and costeffective. Modern LNG carriers feature complex and tightly integrated machinery systems to convert the onboard primary energy sources to useful energy demands for propulsion, electricity and heat. Therefore, process modelling and simulation techniques combined with an integrated systems approach is required for the evaluation of different configuration alternatives of LNG carriers. In this paper, we used our in-house process modelling framework DNVGL COSSMOS to develop a generic model of an LNG carrier integrated machinery system encompassing various propulsion and energy recovery technologies. The resulting system model was then coupled with a generic operational profile description accounting for various operating modes and intended trading routes of the vessel. The integrated LNG carrier machinery process model was subsequently used for the evaluation of different technology alternatives and machinery configurations. Namely, the model was used to size the gas-fuel compression trains; assess the introduction and optimal size of an LNG reliquefaction plant; compare electric and mechanical propulsion technologies; and, assess the introduction of energy recovery technologies such as shaft generators and exhaust gas economizers. The model-based studies resulted in an improved insight of this complex integrated machinery arrangement, revealing important performance trade-offs and interrelations between the vessel's sub-systems. The results revealed high energy savings potential of 5% to 8% depending on the energy recovery options implemented, operating profile and trading route. At the same time fuel savings of about 6% were identified, improving the overall cost-effectiveness of the integrated system.


Georgopoulou C.,DNV GL Maritime Research and Development | Jain S.,DNV GL Strategic Research and Innovation | Agarwal A.,DNV GL Strategic Research and Innovation | Rode E.,DNV GL Strategic Research and Innovation | And 3 more authors.
Computers and Chemical Engineering | Year: 2016

This paper presents a model-based approach on the analysis of complex multidisciplinary electrochemical processes, with implementation on a reactor for the electrochemical conversion of CO2 to formate/formic acid. The process is regarded as a system of interacting physical and electrochemical mechanisms. A process model is developed by combining individual mathematical sub-models of the mechanisms, organised at groups of compartments following the physical process structure. This approach results in a generic reconfigurable model that can be used as a part of integrated systems, and to test design modifications. The approach is demonstrated on an electrochemical cell, where CO2 is converted to formate/formic acid. The model captures the molar transportation under electric field, the two-phase flow effects, and the key electrochemical reactions. The model is calibrated and validated against experimental data obtained from a continuous flow cell. The key parameters affecting the process performance are discussed through scale-up analysis. © 2016 Elsevier Ltd


Stefanatos I.C.,DNV GL Maritime Research and Development | Dimopoulos G.G.,DNV GL Maritime Research and Development | Kakalis N.M.P.,DNV GL Maritime Research and Development
ECOS 2015 - 28th International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems | Year: 2015

This paper presents the thermoeconomic assessment and design of alternative cargo unloading system configurations of crude oil tanker vessels via modelling and simulation techniques. A typical-in-practice Rankine-cycle system was synthesised in our modelling framework DNV GL COSSMOS to describe the thermodynamic behaviour of the baseline system. Then, three alternative configurations were examined: A) the addition of a micro steam turbogenerator to utilise the potential steam rejection that may take place during an operation at low load; b) the addition of superheaters in the boiler to drive the steam turbines; c) the replacement of one steam turbine driven pump by a variable frequency electric driven pump. To assess the system for the actual operation, a realistic operating profile was used based on on-board measurements from discharge operations of an Aframax cargo-oil tanker over one year. The thermoeconomic comparison of the alternative designs is based on operational, capital, and installation costs. The operational costs of each design (fuel and energy consumption) were estimated based on the simulation of system performance. Capital and installation costs were estimated based on economic data from similar previous applications. The alternative designs were assessed both for new built vessels and as potential retrofit solutions for existing vessels. Sensitivity analysis with respect to capital costs and the fuel oil price complete this study.


Georgopoulou C.A.,DNV GL Maritime Research and Development | Dimopoulos G.G.,DNV GL Maritime Research and Development | Kakalis N.M.,DNV GL Maritime Research and Development
Proceedings of the Institution of Mechanical Engineers Part M: Journal of Engineering for the Maritime Environment | Year: 2014

Exhaust gas scrubber is one of the options to comply with the new regulations for sulphur emissions in the shipping industry. This article presents a model-based approach to assess the energy and environmental performance effects from the installation of a seawater flue gas desulphurisation scrubber on a marine two-stroke diesel engine propulsion plant. A mathematical model was built that describes the governing physical and chemical behaviour of the integrated machinery system. The model was used to examine the impact of main scrubber design characteristics on the engine fuel consumption under different engine loads. The results indicate that the desulphurisation system causes an increase in the engine fuel consumption, for constant power output. This is due to the increased back-pressure to the turbocharging system caused by the pressure drops in the desulphurisation system. This effect can be partly mitigated by the installation of forced-draft fans after the desulphurisation system limiting the negative impact on the overall system efficiency to half of its initial value. © Institution of Mechanical Engineers.

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