1,721,034 research outputs found
Safety Challenges on Runaway Reactions: The Esterification of Acetic Anhydride with Methanol
No full textEsterification reactions are commonly used in industrial practice. These reactions are fast and moderately exothermic thus they are prone to exhibit a runaway behavior, that is a thermal loss of control of the synthesis reactor. This scenario may lead to either quality issues, such as formation of undesired side products, or safety concerns, as pressurization and rupture of the reactor itself.
To mitigate the risk, proper recipes should be designed and optimized for a safe conduction of the reaction at the full-plant scale. This can be done by knowing the kinetics of the involved reactions, both desired and undesired.
The aim of this work is to determine the kinetic parameters of the esterification of acetic anhydride with methanol (forming methyl acetate) in the presence of sulfuric acid as a catalyst to be used in a cost-effective safe optimization protocol. This reaction has been analyzed in the past because of its exothermicity, but without fully describing the involved reactions (both desired and side).
In this work, calorimetric measurements are used to observe both the thermic and quality characteristics of the overall synthesis run in a semi-batch, lab-scale reactor. Both a detailed kinetic scheme and the associated parameters are determined to provide safe and productive operating conditions for the process, properly considering all the side reactions than could emerge during the synthesis. The study also required the implementation of a dedicated mathematical model for the simulation of the lab-scale semi-continuous reactor
Detailed reconstruction and safety analysis of a pre–Seveso accident
Full text linkIndustrial safety has been a topic of growing interest during the last decades, mainly because of the increased awareness and knowledge about safety issues. In this framework, the detailed reconstruction of the dynamics of an explosion (1 killed and 8 injured) occurred, on the 26th of June 1971, at Noury Italy (a plant dedicated to the production of chemicals for hardening plastics) is worth of interest and it could be used to improve actual safety guidelines related to the storage of peroxides. The accident happened before whatever Seveso Directive release. Therefore, root-causes reconstruction and related risk assessment were carried out making a comparison between a hypothetical plant layout at that time and a modern plant layout implemented with minimum safety systems, such as acoustic alarms and adequate bypass lines. The accident reconstruction was carried out by doing a deep literature research, mainly based on newspaper clippings of the time, to both remodel the accident at best and draw the most likely layout of the plant. The latter is of fundamental importance to carry out a risk assessment procedure by applying the Recursive Operability Analysis (ROA), which allows for a direct generation of the fault trees that can provide an easy estimation of the probability of occurrence of all unwanted events. This method was applied to the Noury Italy case study to show the criticalities of the storage equipment also underlining the possible improvements which could be implemented also in the ‘70s, therefore preventing the fatal explosion
Study of the performance of disinfection with sodium hypochlorite on a full-scale sewage treatment plant
Full text linkA full-scale sewage treatment plant was investigated to assess the performance of the disinfection stage. Sodium hypochlorite was used as a disinfectant agent and the process efficiency was evaluated by E.coli removal. The research took place over a period of two years in order to evaluate the effect of retention time (t) and residual chlorine (Cr) under different seasonal conditions. The effectiveness of E.coli removal with sodium hypochlorite proved to be strictly dependent on the factor CR t (product of residual chlorine with the contact time). The regression line of the experimental points was, on the whole, well comparable with the model proposed by Collins, especially in the field of CRt lower than 30 mg L-1 min
Recursive operability analysis as a tool for ATEX classification in plants managing explosive dusts
Full text linkSafety and prevention in workplaces are important issues, especially regards to risks with serious consequences for health and infrastructures, such as dust explosions, which have caused several industrial accidents during the last centuries and, actually, represent a critical issue in the industrial framework. The current European legislation, referred to as ATEX directive, identifies ATEX zones as parts of the plant where explosive atmospheres can be generated. In this work, a modified version of the classic Recursive Operability Analysis method, specifically tailored to define with an automatic procedure the ATEX zones related to flammable dust clouds, is proposed. The method is fast and effective, allowing for an automatic generation of fault trees from which the probability of occurrence defining the specific ATEX zone type can be estimated. This technique was successfully implemented in a chemical plant dedicated to the mixing of inert powders with a stearate powder, a hazardous dust classified as strongly explosible. The extent of all the ATEX zones identified within the plant was simulated with the ALOHA software, treating the dispersed dust cloud of stearate as a dense gas cloud. From the results, it was possible to identify not only type and extension of all the ATEX zones but also either the most critical parts of the plant or the most dangerous activities (e.g. human errors in the use of the forklift was found to account for about 97.7% to explosion probability in this type of plant)
Increasing Safety by Shifting Semi-Batch Polymerizations into Semi-Continuous Production
No full textRandomized, Double-blind, placebo-controlled study of pivagabine in neurasthenia.
No full textARZNEIM.-FORSCH./DRUG RES
A normative study of a shorter version of Raven's progressive matrices 1938
No full textA shorter four-set (A, B, C, D) version of Raven's progressive matrices 1938 (PM38) has gained increasing use in neuropsychological assessment. No normative data spanning across a wide age range are, however, available. This study collected norms for the shorter version of PM38, established an inferential cut-off value and derived equivalent scores in a sample of 248 individuals from 20 to 89 years of age, evenly distributed across sex, age and education levels. Results showed significant effects of age and education but no effect of sex on performance. These normative data will complement existing norms for other tests, will increase the wealth of neuropsychological tools for which normative data are available for the Italian population, and may be useful in the early detection of individuals at risk of developing dementia
Application of Critical Energy Density concept for Minimum Ignition Energy determination
No full textThis study presents a new concept, referred to as Critical Energy Density (CED), for estimating the Minimum Ignition Energy (MIE) of organic powders. Only readily experimental data, such as granulometric analysis, thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC), are required for running the mathematical model. The algorithm simulates the heating of a dust cloud exposed to an electrical spark and detects the ignition by comparing the energy released by the volatiles’ homogeneous combustion with a threshold value corresponding to the minimum energy required to sustain the flame propagation (that is, the CED). Validation was performed on six different organic powders, with estimated MIE values showing good agreement with experimental data. This approach provides a cost-effective tool for early-stage hazard assessment in industrial environments where combustible powders are present and supports the development of a safer process design
Application of a Gaussian model to simulate contaminants dispersion in industrial accidents
No full textThe increase of the industrial production and the development of new processes led to the necessity of better regulations of activities concerning potential risks for human health and environment. Accomplishing such purposes requires studies on both the chemistry of the involved phenomenon and the dispersion mechanism in the surrounding environment. While the chemistry of reaction can be determined at small scale via laboratory experiments and models, the dispersion in the environment is an extremely complex phenomenon to model, because it is strongly affected by the atmospheric conditions. Several models with the purpose of simulating pollutants dispersion were developed (Gariazzo et al., 2012; Alemayehu et al., 2015; Fang et al., 2018); among those, Gaussian models found many applications in safety engineering, due to both their effectiveness and relatively low computational costs. The US-EPA recommends the use of the Gaussian model AERMOD for the simulation of dispersions within 50 km from the emission source. It is important to underline that most of these models were developed with the aim to simulate the dispersion of continuous emissions such as those from industrial chimneys. Such systems can be assumed to work under steady-state conditions, since they are supposed to work for a long time. Nonetheless, industrial accidents, which can have a severe impact on people and environment, generally occur at a relatively small time scale, thus their dispersion has not yet reached the steady state conditions. In this work, we developed a modified non-steady-state Eulerian Gaussian model able to simulate the dispersion of contaminants produced by an industrial accident, which is hypothesized to be a point source. The model requires as input data time-dependent meteorological conditions and topographic information of the site, concerning: the source, physical properties of the pollutant, emission height and release temperature. The proposed model was applied to the 2,3,7,8-Tetrachlorodibenzodioxin (TCCD) dispersion after the Seveso accident (1976) near the source (radius of about 4 km). Results highlighted a good agreement with available literature experimental data
Influence of Ground on Jet Fire Extension
Full text linkA common accident in the industrial process industry is the puncturing of storage tanks or rupture of process pipelines containing gases. In these scenarios, the gas will escape the piece of equipment producing a single-phase gas jet. If the fluid is flammable, an ignition source is most probably encountered during the accidental scenario and a jet-fire can follow the leak. Free jets of hazardous gases and free jet-fires have been extensively analyzed in the past literature to assess their shape and extension for safety purposes. Similar analyses have been conducted to observe the effect on shape/extension of neutral jets if obstacles were present. Also, the effect of the ground proximity to the jet source has been studied. In general, the presence of obstacles and the proximity to the ground lead to enlarged hazardous areas, mainly because of the Coandă effect. In this work, flammable jets igniting and forming a jet-fire were considered. The effect of the ground proximity was analyzed, to observe the extension of the flame. Two opposed phenomena were supposed to act on the fire, differently from non-ignited jets: the Coandă effect having an attractive nature towards the ground and the buoyancy effect on the opposite direction. The relevant methane jet-fires case study was considered carrying out computational fluid dynamics (CFD) simulations using the Fire Dynamics Simulator software. The study considered both the jet source height from the ground and the gas relief flowrate effects. CFD results were summarized basing on simple dimensionless parameters to determine the eventual variation of jet-fire extension for preliminary safety analyses
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