Experimental research of LNG accidental underwater release and combustion behavior

Evaluating potential hazards caused by accidental LNG release from underwater pipelines or vessels is a significant consideration in marine transportation safety. The aim of this study was to capture the dynamic behavior of LNG jet released under water and to analyze its vapor dispersion characteristics and combustion characteristics on the water surface during different release scenarios. Controlled experiments were conducted where LNG was jet released from a cryogenic storage tank. The dynamic process of LNG being jet released from orifices of different sizes and shapes, as well as the rising plume structure, were captured by a high-speed camera. The leakage flow rate and pipeline pressure were recorded by a flow meter and pressure gauge, respectively. The concentration distribution that emanated from the water surface was measured utilizing methane sensors in different positions with various wind speeds. The flame combustion characteristics of LNG vapor clouds, which immediately ignited upon the enclosed water tank, were also recorded. Additionally, the mass burning rate of the flame on the water surface was evaluated, and a new correlation between the ratio of flame length and width was established. The results indicated a large dimensionless heat release rate (Q*) and a continuous release flow rate in a limited burning area. This study could provide greater understanding of the mechanisms of LNG release and combustion behavior under water.     

Underwater towed video: a useful tool to rapidly assess elasmobranch populations in large marine protected areas

Elasmobranch stock assessment studies are usually made through fisheries surveys data. However, in large marine protected areas (MPAs) the use of destructive techniques must be dismissed in order to avoid population impacts. In 2005, while conducting a marine habitat survey in two marine Special Areas of Conservation (Sebadales de Playa de Inglés and Franja Marina de Mogán) in south Gran Canary Island (Canary Islands, Spain) with underwater towed video (UTV) and underwater visual census (UVC) transects, we recognized the opportunity rose to assess elasmobranch populations through UTV. Number of observed species and specimens, overall field work effort and total surveyed area were determined and compared between methods. Mean observations per day per unit of time (MOPUT) and mean observations per day per unit of surveyed area (MOPUA) were also compared through Mann–Whitney rank sum statistical test (α = 0.05). Data analysis demonstrated that UTV is a very useful tool to rapidly assess elasmobranch populations in large MPAs in good visibility underwater environments. It can assess larger areas than UVC with the same effort (statistically significant difference found for the MOPUT; p =< 0.001), leading to more observed species (5 vs 2) and specimens (46 vs 3) per day of work, with no loss in resolution power (MOPUA values were not significantly different between UTV and UVC; p = 0.104).     

海洋风电场水下噪声评估与管理研究

总结了海洋风电场建设中水下噪声的主要类型与声学特性,基于国内外水下噪声对海洋生物影响的最新研究成果,分析了海洋风电场噪声对生态环境的可能影响,尤其是近岸海域海洋风电施工期冲击式打桩噪声对海洋生物的影响。在此基础上,参考《海上风电工程环境影响评价技术规范》的相关内容,提出了海洋风电场水下噪声测量与评估方法,以及控制与降低噪声的措施建议。     

Mapping of the benthic communities in the Taranto seas using side-scan sonar and an underwater video camera

Side-scan sonar and underwater video camera records as well as dredging samples were used to map the bottom morphology and biocoenoses in the Taranto seas. A 1:20,000 scale chart has been produced with all the data recorded. Most of the study area consists of biocoenoses affected by the anthropogenic activities of the town of Taranto. Some native broadly tolerant species seem to benefit from these activities and become increasingly dominant. Environmental modifications also seem to favour the settlement of exotic species.     

Dynamic response and effect of apertures on explosion parameters of flameproof apparatus

Explosion parameters for closed flameproof apparatus are changed when apertures like gap (e.g. push button) and porous structures (breathing element) are introduced on the cover or wall of the flameproof enclosures. Similarly, an interconnecting tube between two enclosures, results in significant change in explosion parameters. It is observed that the maximum explosion pressure, maximum rate of pressure rise and severity index are higher for enclosures with apertures on cover or body than that of enclosures without apertures. In case of two interconnected identical enclosures, the explosion parameters are increased in the secondary enclosure and higher than that of primary enclosure and also of isolated enclosure.     

电厂燃煤的安全贮存管理

电厂燃煤的安全贮存管理是发电用煤的质量保障.燃煤的贮存点选择,库存组成定额及煤的组堆等防损耗方法直接关系到电力生产的安全和效益.     

An antifouling catechol/chitosan-modified polyvinylidene fluoride membrane for sustainable oil-in-water emulsions separation

• Underwater superoleophobic membrane was fabricated by deposition of catechol/chitosan. • The membrane had ultrahigh pure water flux and was stable under harsh pH conditions. • The membrane exhibited remarkable antifouling property in O/W emulsion separation. • The hydration layer on the membrane surface prevented oil droplets adhesion. Low-pressure membrane filtrations are considered as effective technologies for sustainable oil/water separation. However, conventional membranes usually suffer from severe pore clogging and surface fouling, and thus, novel membranes with superior wettability and antifouling features are urgently required. Herein, we report a facile green approach for the development of an underwater superoleophobic microfiltration membrane via one-step oxidant-induced ultrafast co-deposition of naturally available catechol/chitosan on a porous polyvinylidene fluoride (PVDF) substrate. Membrane morphology and surface chemistry were studied using a series of characterization techniques. The as-prepared membrane retained the original pore structure due to the ultrathin and uniform catechol/chitosan coating. It exhibited ultrahigh pure water permeability and robust chemical stability under harsh pH conditions. Moreover, the catechol/chitosan hydrophilic coating on the membrane surface acting as an energetic barrier for oil droplets could minimize oil adhesion on the surface, which endowed the membrane with remarkable antifouling property and reusability in a cyclic oil-in-water (O/W) emulsion separation. The modified membrane exhibited a competitive flux of ~428 L/(m²·h·bar) after three filtration cycles, which was 70% higher than that of the pristine PVDF membrane. These results suggest that the novel underwater superoleophobic membrane can potentially be used for sustainable O/W emulsions separation, and the proposed green facile modification approach can also be applied to other water-remediation materials considering its low cost and simplicity.     

A mechanistic model for hydrocarbon plumes rising through water

For releases of hydrocarbons from a subsea pipeline, riser, or production facility, the shape of the plume rising through the water must be predicted prior to any assessment of gas dispersion, liquid pools, or fire above the water surface. The location and size of the plume at the water surface are key parameters for subsequent consequence modeling. A mechanistic model has been developed to predict the plume trajectory and size, based on mass and momentum balances and an empirical water entrainment ratio from the literature. With suitable physical property values available, the model is applicable to releases of gas and/or liquid hydrocarbons, predicting the vaporization and vapor expansion due to decreasing hydrostatic pressure as the plume rises through the water. Some validation of the model was obtained with 16 tests in a small-scale transparent tank. The data cover a wide range of flow rates, including both choked and unchoked flow. The predicted and measured trajectories (centerline displacement) agreed reasonably well. Predictions of the model are presented for three fluids. The model is valuable for assessing the consequences of underwater hydrocarbon releases, providing input for subsequent modeling of gas dispersion or liquid pools and pool fires.     

Numerical modelling of the effects of vessel length-to-diameter ratio (L/D) on pressure piling

Pressure piling presents a major explosion hazard in interconnected process vessels. Pressure enhancement in the secondary vessel due to the acceleration of the flame through the connecting pipe can generate a disproportionately more violent explosion than would have been expected based on the concentration of dust in the secondary vessel. Pressure piling is a very complex phenomenon that is difficult to investigate through experimentation. Advanced computational fluid dynamics (CFD) modelling is a promising route to accurately account for all the complexities associated with pressure piling.In this paper, the current state of knowledge concerning pressure piling is presented. Further, the effects of varying the length-to-diameter ratio (L/D) of the primary vessel (Vessel 1) on pressure piling was investigated using numerical modelling. The volumes and volume ratio of the interconnected vessels were kept constant while the L/D of Vessel 1 was varied from 0.5 to 15. The simulations of coal dust explosion were performed using the coalChemistryFoam solver from OpenFOAM version 5.0.1. It is hoped that the findings from this study provide insight into the effects of the geometrical design of interconnected vessels, particularly L/D, on pressure piling. Additionally, this work has implications for the optimal placement of explosion isolation devices intended to actuate before the flame front and pressure escape to downstream vessels.     

Framework for the environmental impact assessment of operational shipping

Shipping is an important source of pollution affecting both atmospheric and aquatic environments. To allow for efficient mitigation of environmental degradation, it is essential to know the extent of the impacts of shipping in relation to other sources of pollution. Here, we give a perspective on a holistic approach to studies of the environmental impacts of operational shipping through presentation of an assessment framework developed and applied on a case of shipping in the Baltic Sea. Through transfer of knowledge and concepts, previously used in assessments of air pollution, now applied to assessments of marine pollution and underwater noise, the horizon of understanding of shipping-related impacts is significantly improved. It identifies the main areas of environmental degradation caused by shipping and potential improvements through legislation and technological development. However, as the vast majority of contaminants discharged into the sea are not routinely monitored and assessed, the links between pressure of contaminants from shipping and environmental state and impacts will not be caught in the current environmental regulatory frameworks.