A simplified steady-state model for air,water and steam curtains

Curtain mitigation systems are modeled here since they have experimentally shown their efficiency in reducing the concentration of certain toxic gases within dense gas clouds. Air, water and steam are analyzed in a model as the physical barriers to decrease the gas concentration. The model, developed for a steady-state mitigation process, is based on the mass, energy and momentum conservation laws. Concentration estimations during the dispersion before and after the mitigation are performed with a SLAB type model. A sensitivity analysis for each model is given to detect which variables have bigger effects. A release of chlorine is used as an example and the results are calculated in a prototype developed in Visual C++, where the model is solved using the Runge–Kutta 4th order method. The results include the effects of composition, speed, temperature and height of the releasing point as well as a comparison with CFD simulations. The proposed model is simplified and it cannot reproduce eddy effects but it is fast and robust enough. The model provides a set of equations that can be used in numerical problems where explicit derivatives are required, e.g. optimizations procedures.     

Inherently safer reactors: Improved efficiency of 3-picoline N-oxidation in the temperature range 110–125 °C

Alkylpyridine N-oxides are important intermediates in the pharmaceutical and agrochemicals industries. The N-oxides are produced via the homogeneously catalyzed oxidation of the respective alkylpyridines using a 50% excess of hydrogen peroxide. The competitive hydrogen peroxide decomposition produces oxygen in the flammable environment of alkylpyridines and thus forms a key hazard for this reaction. In this work, the N-oxidation was performed under pressure in the temperature range of 110–125 °C with different catalyst concentrations. It was shown that temperature had an undisputable positive effect on the N-oxidation efficiency. The accurate measurement of the pressure rise due to decomposition was difficult. However, only 5% of the added H₂O₂ decomposed when stoichiometric quantities were employed, even in the temperature of 110 °C. The N-oxidation was very efficient, even when the lowest concentration of catalyst employed in this study was used.     

Distribution and ecology of leptocephali of the congrid eel, Ariosoma scheelei, around Sulawesi Island, Indonesia

A survey for leptocephali around Sulawesi Island in the central Indonesian Seas during May 2001 found that the leptocephali of the congrid eel, Ariosoma scheelei, were present in all seven areas that were sampled. A total of 551 leptocephali (22–166 mm TL) were collected, and A. scheelei was by far the most abundant species of leptocephali collected during the survey. The wide range of sizes in most areas indicated that spawning had occurred during a period of several months in many different areas, although the exact spawning locations were not determined. The larger size classes were more abundant in all areas except in Tomini Bay on the northeast side of Sulawesi Island. The highest catch rates were observed at the eastern edge of the Java Sea and to the north in the Celebes Sea near Makassar Strait. Premetamorphic leptocephali were also collected in surface samples at 11 stations (N=62), but metamorphosing leptocephali (N=86) were only caught in IKMT tows that fished from the surface to about 200 m. Metamorphosing leptocephali were collected primarily at two stations in the Java Sea and Makassar Strait where a surface layer of lower-salinity water was detected. Their total lengths (105.3–153.3 mm) and the largest premetamorphic individuals suggested that this species can reach maximum sizes of about 165 mm before beginning to metamorphose. It is hypothesized that this species may be abundant in the Indonesian Seas region and that it has ecological traits such as large size at recruitment and a small size at reproduction that have made it successful in many regions of the Indo-Pacific.     

Ecology, management and monitoring of grey dunes in Flanders

Grey dunes are a priority habitat type of the European Union Habitats Directive and demand special attention for conservation and management. Knowledge of the ecology of coastal grey dunes can contribute to this policy. Dune grassland succession is initiated by fixation and driven by the complex of soil formation (humus accumulation) and vegetation development. Leaching and mobilization of CaCO₃. which are important in nutrient dynamics, complicate the picture. At present, grass- and scrub encroachment greatly overrules these fine scaled soil processes and causes substantial loss of regional biodiversity. Belgium has an international responsibility in grey dune conservation because of the limited range of its characteristic vegetation, flora and fauna. As biomass removal seems essential in grassland preservation, grazing is an important management tool. Evaluation of management measures focuses on biodiversity measurements on the levels of landscape, community and species.     

Methylmercury, fish consumption, and the precautionary principle

This paper considers several broad issues in the context of probabilistic assessment of the benefits of curtailing mercury (Hg) emissions from U.S. coal-fired power plants, based on information developed from recent literature and epidemiology studies of health effects of methylmercury. Exposure of the U.S. population is considered on the national scale, in large part because of recent questions arising from survey and experimental data about the relative importance of local deposition of airborne Hg. Although epidemiological studies have provided useful information, safe levels of Hg exposure remain uncertain, in part because of other dietary considerations in the populations that were studied. For example, much of the seafood consumed in one of the major studies was also contaminated with polychlorinated biphenyls, as are fish taken from some U.S. fresh waters. The primary epidemiological approach involves cross-study comparisons in relation to mean exposures, rather than detailed critiques of individual effects reported in each study. U.S. exposures are seen to be well below the levels at which adverse health effects are reported. This analysis supports the conclusion that unilateral reduction of Hg emissions from U.S. coal-fired power plants alone is unlikely to realize significant public health benefits.     

Uncertainty aspects in process safety analysis

Uncertainties of input data as well as of simulation models used in process safety analysis (PSA) are key issues in the application of risk analysis results. Mostly, it is connected with an incomplete and uncertain identification of representative accident scenario (RAS) and other vague and ambiguous information required for the assessment of particular elements of risk, especially for determination of frequency as well as severity of the consequences of RAS. The authors discuss and present the sources and types of uncertainties encountered in PSA and also methods to deal with them. There are different approaches to improve such analysis including sensitivity analysis, expert method, statistics and fuzzy logic. Statistical approach uses probability distribution of the input data and fuzzy logic approach uses fuzzy sets. This paper undertakes the fuzzy approach and presents a proposal for fuzzy risk assessment. It consists of a combination of traditional part, where methods within the process hazard analysis (PHA) are used, and “fuzzy part”, applied quantitatively, where fuzzy logic system (FLS) is involved. It concerns frequency, severity of the consequences of RAS and risk evaluation. In addition, a new element called risk correction index (RCI) is introduced to take into account uncertainty concerned with the identification of RAS. The preliminary tests confirmed that the final results on risk index are more precisely and realistically determined.     

Flammability of heat transfer fluid aerosols produced by electrospray measured by laser diffraction analysis

Accidental release of pressurized high flash point heat transfer fluids can result in fire and explosion hazard scenarios in the process industry. An experimental investigation on ignition of aerosols of a heat transfer fluid is carried out, and characterization of aerosol and its ignition process by non-intrusive laser diffraction technique is reported. Propagation speed of the aerosol combustion flame front as analyzed from the laser diffraction measurement agrees with high-speed visual camera observation. Flammability of the aerosol, which is based on the chances of the global flame appearance in the aerosol, is mainly controlled by aerosol droplet size and the droplet volume concentration.     

Risk measures constituting a risk metrics which enables improved decision making: Value-at-Risk

In this work, a novel approach is proposed for expressing the risks of process plants consisting of a large number of scenarios, in the form of a risk metrics of leading indicators to prevent potential high profile industry accidents. The methodology includes: 1) risk estimation of a portfolio by CPQRA (or QRA), 2) monetization of the tangible risks with the inclusion of the lost time of production, 3) estimation of the maximum portfolio loss using Value-at-Risk approach, 4) inclusion of intangible risks using FN-curve and, 5) generation of F$-curve of tangible risks. The proposed methodology can particularly help in understanding the stakes at risk by performing the overall cost-benefit analysis, for identifying the most risky scenarios and identifying critical equipments to enable better risk-informed decision making in order to adopt appropriate risk mitigation measures. This work establishes the groundwork for developing measures for understanding and comparing the large number of risk values derived from QRA studies for large portfolios. It will aid in less subjective decision making as it enables the decision maker to choose the most preferred portfolio option among alternatives. Decisions made with the accurate understanding of the consequences of risks can significantly reduce potential work-related fatalities, property losses and save millions of dollars.     

Melt Strength and Rheological Properties of Biodegradable Poly(Lactic Aacid) Modified via Alkyl Radical-Based Reactive Extrusion Processes

Poly(lactic acid) (PLA) has been modified using twin-screw reactive extrusion to improve its melt properties and crystallinity. In this work lauroyl peroxide was used as an alkyl free radical source, abstracting hydrogen atoms from the PLA backbone leading to branching and chain extension reactions. Once the linear viscoelastic region was determined for these polymers, changes in dynamic rheology (dynamic viscosity real and loss modulus) were measured. Gel permeation chromatography showed that the molecular weight and polydispersity increased to a maximum with the addition of 1.00 and 0.50?wt% peroxide, respectively. Low temperature ?? transitions in dynamical mechanical thermal traces gave further evidence that branching had also occurred. G?ttfert Rheotens measurements showed a three fold increase in melt strength due to both increased chain length and branching. Thermal analysis showed the level of crystallisation had decreased also possibly due to branching. Reductions in crystallinity and improved melt strength are known to be critical for film and foam formation.