Barbara Mazzarotta

Abrasion and breakage phenomena in agitated crystal suspensions

Abstract A technique is suggested for estimating the product-size distribution resulting from breakage and abrasion fracture occuring in agitated crystal suspensions. The contribution of each mechanism is highlighted, and the effects of some operating variables (time, suspension density, stirring intensity) are also shown with reference to potassium sulphate crystals of different size and morphology.

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.

Primary nucleation of citric acid monohydrate: influence of selected impurities

An experimental study is presented concerning solubility and primary nucleation kinetics of monohydrate citric acid from pure and selectively impure (KH2PO4, MgSO4·7H2O and FeSO4·7H2O) aqueous solutions. The metastable range of pure solutions is wide, ranging from 6 to 14°C, and the order of primary nucleation, equal to 2.51, is quite low. The addition of the tested impurities, which are usual fermentation aids, at concentrations lower than wt. 1%, produces negligible effects on the solubility and slightly enhances the primary nucleation rate. However, the presence of these compounds modifies the crystal habit at birth: in particular, the addition of MgSO4·7H2O and FeSO4·7H2O makes these crystals more elongated, but this effect diminishes as the crystals grow.

Size dependency of citric acid monohydrate growth kinetics

Abstract An experimental study concerned with the growth kinetics of citric acid monohydrate crystals is presented. Due to the properties of the system, which is very soluble, with low solid-liquid density difference and high liquid viscosity, two different techniques were used: large crystals (710–850 μm) were grown in a fluidized bed crystallizer; small crystals, belonging to three size ranges from 90 to 355 μm, were grown in the cell of a laser light diffraction granulometer. A first order growth kinetics resulted in both cases; a comparative analysis of both the present data and those reported in the literature relevant to larger or smaller crystals, indicates that the system exhibits size-dependent growth, which increases linearly with the crystal size.

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.

Growth kinetics of sodium perborate from batch crystallization

The size distribution of sodium perborate crystals was continually monitored using a Malvern sizer during batch crystallization from aqueous solutions carried out under falling supersaturation established at the experiment onset. The growth rate was determined from the time shift of the crystal size distribution expressed in cumulative oversize numbers. The size independent overall growth rate was first order with respect to supersaturation for crystals larger than 150 μm. Crystals between 20 and 150 μm exhibited a significant size-dependent growth rate. Furthermore, the fraction of crystals smaller than 20 μm, formed by primary nucleation, grew extremely slowly or did not grow at all.

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.