Search Results (4)

In this study, cargo boil-off gas (BOG) re-liquefaction systems for ammonia-fueled liquefied carbon dioxide (LCO₂) carriers were analyzed. These systems use cold energy from ammonia to reliquefy the CO₂ BOG. In this study, a system that can completely reliquefy the CO₂ BOG at all engine loads using only one heat exchanger is proposed, instead of the existing cascade system that requires multiple components. R744, which has a low global warming potential, was used as the working fluid for the refrigeration cycle in the CO₂ BOG re-liquefaction system. The organic Rankine cycle (ORC) was used to reduce the net power consumption of the system. The existing and proposed systems were classified into Case 1 (existing system), Case 2 (our proposed system), and Case 3 (Case 2 combined with an ORC). Thermodynamic and economic analyses were conducted. Case 2 is a system with a simpler configuration than Case 1, but it has a similar thermodynamic performance. Case 3 has a higher exergy destruction rate than Cases 1 and 2, owing to the ORC, but it can significantly reduce the net power consumption. The economic analysis shows that Cases 2 and 3 reduce the total annual costs by 17.4% and 20.1%, respectively, compared to Case 1. The proposed systems are significantly more advantageous for long-term operation than existing systems. Full article

Damages in port facilities during past seismic events have led to widespread direct and indirect losses, with serious impact on the economic, operational, and emergency management of the port itself and, as a consequence, on the related society. Ground shaking is among the most widespread sources of seismic damage to port structures and infrastructure, together with the induced phenomena principally associated with the liquefaction of loose, saturated soils that often prevail in coastal areas. This study presents a methodology for the seismic risk assessment of port facilities which considers the combined effects of ground shaking and liquefaction as well as various interdependencies among port elements, which affect the port’s operation and, consequently, the total risk impact. The methodology, based on either probabilistic or deterministic scenario-based approaches, is demonstrated through an application to the Thessaloniki port, one of the most important ports in Southeastern Europe and the largest transit-trade port in Greece. The systemic risk analysis of the port is carried out using as a performance indicator the reduction in the container and bulk cargo movements affected by the seismic performance of the piers, the waterfront, and container/cargo handling equipment, as well as their interaction with the seismic performance of the electric power system. Two different functionality analyses of the port system are performed, one basic and one less conservative alternative. The results of the probabilistic seismic risk assessment are illustrated in terms of annual probabilities of collapse and loss exceedance curves for each individual port component as well as normalized performance loss for the whole port system for the container and cargo terminal. For the scenario-based deterministic approach, the results are given in terms of risk maps presenting the spatial distribution of damages/losses for all components as well as in terms of the expected loss of performance of the port system. The proposed methodology may provide the basis for an efficient seismic risk management of ports. It may also be adjusted and applied to other port infrastructures in Greece and worldwide considering additional components, interactions among elements, and different earthquake induced hazards. Full article

A “Well-to-Propeller” Life Cycle Assessment of maritime transport was performed with a European geographical focus. Four typical types of vessels with specific operational profiles were assessed: a container vessel and a tanker (both with 2-stroke engines), a passenger roll-on/roll-off (Ro-Pax) and a cruise vessel (both with 4-stroke engines). All main engines were dual fuel operated with Heavy Fuel Oil (HFO) or Liquefied Natural Gas (LNG). Alternative onshore and offshore fuel supply chains were considered. Primary energy use and greenhouse gas emissions were assessed. Raw material extraction was found to be the most impactful life cycle stage (~90% of total energy use). Regarding greenhouse gases, liquefaction was the key issue. When transitioning from HFO to LNG, the systems were mainly influenced by a reduction in cargo capacity due to bunkering requirements and methane slip, which depends on the fuel supply chain (onshore has 64% more slip than offshore) and the engine type (4-stroke engines have 20% more slip than 2-stroke engines). The combination of alternative fuel supply chains and specific operational profiles allowed for a complete system assessment. The results demonstrated that multiple opposing drivers affect the environmental performance of maritime transport, a useful insight towards establishing emission abatement strategies. Full article

China imports a large quantity of bauxite each year. Bauxite in fine particles with high moisture has a high risk of liquefaction during the maritime transportation process, which is harmful to the stability and safety of the carrier. To ensure safe shipping, it is necessary to pay attention to the effects of the operation of cargo, the ship’s maneuvering and the ocean environment during the whole transportation process. The simulation of the process risk helps to develop measures to intervene with the cargo behavior to keep the risk to an acceptable level. This study examined the transportation process of a bauxite carrier using the Markov Chain method at different stages of loading, unberthing, departure and sea navigation. Based on the risk transfer matrix of the operational status at different stages of transportation, a cloud simulation model was developed to analyze the transportation process risk of a ship carrying bulk bauxite. Results: the research revealed that the risk evolution rule of the solid bulk cargoes with potential liquefaction during the transportation process, especially bauxite. The risk alteration during the prophase of the transportation process conforms to the rule of the “spoon curve”. Conclusions: a simulation model of the process risk based on the Markov Chain Cloud is suitable for the simulation analysis of the transportation risk of the bulk bauxite carrier. The outcomes of this study may contribute to better safety management to prevent the occurrence of ship capsizing. Full article