Roberto Bubbico

Process optimisation in sunflower oil extraction by supercritical CO2

Abstract A continuous process for the extraction of sunflower oil using supercritical CO 2 , featuring multiple extractors, one oil separator and three cascaded CO 2 recovery vessels operating at different pressures, was devised and studied. For every single equipment of the plant making up the process a mathematical model was built. Experimental tests—consisting in measurements of oil solubility in supercritical CO 2 —were carried out in a laboratory-scale apparatus to characterise the behaviour of sunflower oil in the separation from the supercritical fluid. The mathematical model of the whole process was coded in the commercial gPROMS process modelling environment where both its simulation and optimisation—this latter assuming the overall oil production cost as the objective function—were carried out. The process- and economics-related results are discussed and compared with those obtained with traditional and cold-pressing extraction.

Assessment of an explosive LPG release accident: a case study

In the present paper, an accident occurred during a liquefied petroleum gas (LPG) tank filling activity has been taken into consideration. During the transfer of LPG from the source road tank car to the receiving fixed storage vessel, an accidental release of LPG gave rise to different final consequences ranging from a pool fire, to a fireball and to the catastrophic rupture of the tank with successive explosion of its contents. The sequence of events has been investigated by using some of the consequence calculation models most commonly adopted in risk analysis and accident investigation. On one hand, this allows to better understand the link between the various events of the accident. On the other hand, a comparison between the results of the calculations and the damages actually observed after the accident, allows to check the accuracy of the prediction models and to critically assess their validity. In particular, it was shown that the largest uncertainty is associated with the calculation of the energy involved in the physical expansion of the fluid (both liquid and vapor) after the catastrophic rupture of the tank.

Heat transfer in water-based SiC and TiO2 nanofluids

The article reports the results of heat transfer experimental tests on water-based TiO2 (9 wt%) and SiC (3, 6, 9 wt%) nanofluids. Measurements were performed in a two-loop test rig for immediate comparison of the thermal performances of the nanofluid with the base fluid. The convective heat transfer is evaluated in a circular pipe heated with uniform heat flux (from 20 to 240 kW/m2) and flow regimes from laminar to turbulent. Tests have been performed to compare the heat transfer of nanofluids and water at the same velocity (from 0.7 to 1.6 m/s) or Reynolds number (from 300 to 6000), and they have also been compared with values calculated from some of the most widely used correlations. The analysis of the experimental data shows a strong dependence on the parameter used, while both the nanofluid and water data have the same agreement with the calculated values. Nanofluids were manufactured through a two-step procedure: laser synthesis of nanoparticles followed by dispersion in water.

Risk analysis of LPG transport by road and rail

Abstract Historical data concerning more than 130 LPG rail and road transport accidents were critically examined, identifying the scenarios, following their evolution into the final accidental events, and determining their theoretical probabilities of occurrence. In principle, rail accidents are rather hazardous, the most probable scenario being a major release followed by an UVCE. However, in order to discriminate among road and rail transport, the relevant number of trips and accident rates should be taken into account. In fact, the application, concerning the transport of 5700 ton/year of LPG in Italy along one rail and two different road itineraries, showed that the risk for rail transport was more than one order of magnitude lower than that for those on the roads. The population density along the route and the accident rate, rather than the length of the route, appear the most important factors for discriminating between different itineraries.

Preliminary study on the transport of hazardous materials through tunnels

The risk associated to road and rail transportation of some hazardous materials along two routes, one including a significant portion in tunnels, and the other following the same path, but running completely in the open, is assessed. The results show that, for rail transport, no particular risk increase or mitigation is associated to the circulation of the dangerous goods through tunnels; on the contrary, for road transport, a risk increase is generally observed in the presence of tunnels. However, for LPG, the risk curve in the open lies above that in tunnels in the high frequency-low fatality zone, according to the different evolution of the accidental scenarios in the tunnel (assuming no ventilation). The transportation of liquefied nitrogen, not hazardous in the open but potentially asphyxiating in a tunnel, gives rise to a negligible risk when performed by rail, but to a not negligible one, when performed by road. These preliminary results focused on the risk for the exposed population, suggest that it may be unnecessary to limit dangerous goods circulation through rail tunnels, while, at least for some types of dangerous goods, the circulation through road tunnels may be allowed/forbidden based on the results of a specific risk analysis.

Risk analysis study of road transport of ethylene oxide

Abstract A quantitative risk analysis is presented for road transportation of ethylene oxide. The procedure is outlined, discussing the amount and depth of information required. Based on analysis of the data relevant to accident frequency, consequences of historical accidents, meteorological conditions and resident population, the route was divided into a number of portions. Then, reference was made to a couple of weather conditions, assuming two typical release sizes and the complete series of possible outcome predictions for each release, which were estimated using a commercial software package for consequence analysis. All the information was combined to give, directly, the individual risk, as a function of the distance from the route, and the societal risk ( F – N curve), using a simple computer routine. The results showed that the examined transportation case represented a real hazard for the population and some mitigative actions were proposed, testing their effectiveness.

Vulnerability of the Environment in the Proximity of an Industrial Site

This work is carried out in the framework of the ARAMIS project, which aims at developing a comprehensive procedure for assessing the risk level associated to an industrial site with respect to the surrounding environment. To this end, an index is defined which consists of the contribution of three terms, expressing the scenario consequence severity, the safety management efficiency and the vulnerability of the surrounding environment. The present work focuses on this last aspect by determining the vulnerability of the area in the proximity of an industrial site from the contribution of classes of elements belonging to the categories of human, environmental and material targets. The applied methodology consists in identifying and quantifying the targets by means of a geographical information system (GIS) and in assessing the contribution of each target on the basis of a multicriteria decision approach (Saaty method). The result is an operational tool allowing competent authorities, industrialists and risk experts to assess the vulnerability of the area surrounding an industrial site.

Computer aided transportation risk assessment

The assessment of the hazard represented by the transportation of dangerous goods is the only reasonable basis for any policy of risk management and reduction. The use of such a quantitative approach, on the other hand, requires both the acquisition and the manipulation of a very large number of information: these steps are always time-consuming and seldom very accurate, since the need of limiting the calculation burden generally imposes the use of simplifying assumptions. This work presents a computer aided approach to transportation risk analysis coupling a risk assessment program with a Geographic Information System (GIS), providing accurate local information. The obtained benefits are more accurate risk estimates, a substantial cut of the time required to perform the analysis, a simplification of the data input step, and the possibility of displaying the results on the area map, together with other information, useful in the case of an emergency (location of fire brigades stations, hospitals, etc.).

Calculation of the Flame Size from Burning Liquid Pools

The calculation of the consequences associated with a pool fire consists in a stepwise procedure where a number of parameters must be characterized, which depend on the geometrical size and shape of the flame. A number of calculation models exists in the literature, characterized by different levels of accuracy and complexity.In the present work we will focus on the characterization of the geometrical configuration of the flame generated from a pool fire: some of the most commonly adopted models will be shortly recalled, and compared against experimental data taken from the literature. It is expected that this would provide useful information about the range of applicability and the level of accuracy of these models. Also, it will help improve the quality of the results, and reduce the time required for carrying out important applications such as consequence assessment and risk analysis, where a large number of calculations must be run.

Security risk assessment of process plants: The role of layout

After the accident of Toulose and the terrorist attack of September 11, interest is growing about the security of process plants: recommendations [1], guidelines [2] and standards [3], have been issued and security risk assessment (SRA) approaches have been proposed in the literature [4-10]; other works assess the attractiveness and/or vulnerability of industrial targets [11-13]. Among the various factors affecting the security of a process plant, the layout of the plant may play a significant role, since the different parts of the installation may be more or less easily reached by a terrorist attack and present different potentials for causing a major accident, including the possibility of domino effects. The present work will focus on the influence of the layout of a process plant on its security and on its possible impact on the external environment: the different approaches will be critically examined to extract the essential information concerning this issue, in order to derive some general guidelines to support the choice of a layout contributing not only to the safety but also to the security of the installation. Study cases, relevant to some existing Italian installations, will be then examined to assess the efficacy of their layout from the security point of view.