363 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
Fibers Explosion Severity: a Parametric Study on the Fiber Geometry
No full textEven though explosive incidents involving organic fibrous materials have happened in a number of industries, the literature has very few research about the explosibility of fibers. This may have to do with people's lack of awareness of the possibility of explosions caused by fibers, which are frequently thought to be unlikely to explode. Nevertheless, they may provide a significant risk which needs to be taken into account throughout a risk assessment process. More specifically, only a small number of studies regarding fiber explosion modelling has been published in order to gain a better understanding of the primary controlling factors which can affect the explosion severity. Such studies primarily refers to an equivalent diameter approach, in which the elongated fiber is modelled as an equivalent sphere with an effective diameter. This approach, while useful in calculating the primary explosion characteristics, is inherently incapable of differentiating between the effects of increasing either the fiber length or the diameter. A variety of physical and chemical processes, including heat transfer between external and internal particles, pyrolysis and/or devolatilization reactions, and the combustion of volatiles, take place during a fiber explosion. These processes exhibit distinct characteristic times which vary depending on the fiber diameter and length. A comprehensive mathematical model that can account for the cylindrical-like geometry of a fiber can explain this discrepancy. This makes possible to differentiate between the effects of varying both the fiber length and the diameter, so demonstrating through a parametric analysis how such parameters can affect the severity of the explosion
Detailed reconstruction and safety analysis of a pre–Seveso accident
No full textIndustrial 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
Recursive operability analysis as a tool for ATEX classification in plants managing explosive dusts
No full textSafety 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)
Facial animation in patients with Moebius and Moebius-like syndromes.
No full textMoebius syndrome, a rare congenital disorder of varying severity, involves multiple cranial nerves and is characterised predominantly by bilateral or unilateral paralysis of the facial and abducens nerves. Facial paralysis causes inability to smile and bilabial incompetence with speech difficulties, oral incompetence, problems with eating and drinking, including pocketing of food in the cheek and dribbling, as well as severe drooling. Other relevant clinical findings are incomplete eye closure and convergent strabismus. The authors report on 48 patients with Moebius and Moebius-like syndromes seen from 2003 to September 2007 (23 males and 25 females, mean age 13.9 years). In 20 cases a reinnervated gracilis transplant was performed to re-animate the impaired sides of the face. In this series, all free-muscle transplantations survived the transfer, and no flap was lost. In 19 patients complete reinnervation of the muscle was observed with an excellent or good facial symmetry at rest in all patients and whilst smiling in 87% of cases. In conclusion, according to the literature, the gracilis muscle free transfer can be considered a safe and reliable technique for facial reanimation with good aesthetic and functional results
Un approccio «safety-based» per ridurre il contagio da virus respiratori
No full textLa distanza di sicurezza con cui abbiamo imparato a convivere durante la pandemia è un valore mediato e approssimativo che può garantire ai diversi individui di non venire raggiunti da droplet respiratori emessi da altre persone. Tuttavia, tale valore può cambiare molto a seconda di parametri ambientali quali temperatura e umidità relativa dell’aria, oltre che chiaramente alla velocità dell’aria stessa. Un valore ragionevolmente conservativo può essere calcolato tramite un apposito modello matematico di veloce risoluzione basato sui fenomeni di trasporto ed evaporazione coinvolti, implementabile in semplici dispositivi portatili
Safe optimization of potentially runaway processes using topology based tools and software
No full textIn chemical industries, fast and strongly exothermic reactions are often to be carried out to
synthesize a number of intermediates and final desired products. Such processes can exhibit a phenomenon
known as “thermal runaway” that consists in a reactor temperature loss of control.
During the course of the years, lots of methods, aimed to detect the set of operating parameters (e.g., dosing
times, initial reactor temperature, coolant temperature, etc..) at which such a dangerous phenomenon can
occur, have been developed. Moreover, in the last few years, the attention has been posed on safe process
optimization, that is how to compute the set of operating parameters able to ensure high reactor productivity
and, contextually, safe conditions.
To achieve this goal, with particular reference to industrial semibatch synthesis carried out using both
isothermal and isoperibolic temperature control mode, a dedicated optimization software has been
implemented. Such a software identifies the optimum set of operating parameters using a topological
criterion able to bind the so-called “QFS region” (where reactants accumulation is low and all the heat
released is readily removed by the cooling equipment) and, then, iteratively searching for the constrained
system optimum. To manage the software, only a few experimental parameters are needed; essentially:
heat(s) of reaction, apparent system kinetics (Arrhenius law), threshold temperature(s) above which
unwanted side reactions, decompositions or boiling phenomena are triggered, heat transfer coefficients and
reactants heat capacities. Such parameters can be obtained using simple calorimetric techniques (DSC, ARC,
RC1, etc..). Over the optimization section, the software posses a simulation section where both normal and
upset operating conditions (such as pumps failure and external fire) can be tested
Study of the performance of disinfection with sodium hypochlorite on a full-scale sewage treatment plant
No full textA 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
Integrating Recursive Operability Analysis with Different Risk Assessment Methods: Analysis of the Historical BP American Refinery Explosion
No full textThe British Petroleum (BP) American Refinery accident, back in 2005, was one of the most severe explosions recorded in any industrial accident database. According to both the reconstruction and the interviews with the company, it was found that the causes of the accident where both technical, with the failure of a level controller, which was also badly designed for the isomerization unit, and human, with a very stressed and undersized personnel. In this work, a Quantitative Risk Assessment (QRA) based on the Recursive Operability Analysis (ROA), as hazards and accidental scenarios identification tool, was performed on the unit (BP isomerization unit) involved in the accident. The analysis was carried out exploiting many different techniques, to provide a proper assessment. The quantification of all node-deviation-variables (necessary to establish the real behaviour of the system) was performed by implementing the BP plant in CoCo simulator. Basic events were identified using a simplified Failure Mode and Effects Analysis (FMEA). Then, the magnitude of fire and explosion was estimated basing on the simulation results provided by the ALOHA software. Finally, a Fault Tree Analysis for the BP isomerization unit was performed, quantifying the probability of occurrence of all the most credible scenarios. Probabilities, magnitudes, and risk indexes (function of the distance with respect to the source point) were also estimated. From the analysis, the importance of redundant measurements of the most crucial variables, such as liquid level, and the impact of human errors was highlighted
Online model-based optimization and control for the combined optimal operation and runaway prediction and prevention in (fed-)batch systems
No full textAn advanced model-based strategy for the online optimization and/or optimal control of (fed-)batch systems, the BSMBO&C, is applied to discontinuous equipment that can be subject to runaway phenomena. The aim is that of showing that it is simultaneously possible to provide profitable online optimization and/or optimal control policies, predict possible future hazardous situations in advance and automatically decide whether and when to (optimally) stop a production cycle in order to prevent safety risks (unavoidable runaways). All these actions are performed online, thus allowing for the effect of any external perturbation. A fed-batch process based on a well-known example of runaway reaction, i.e. the oxidation of 2-octanol to 2-octanone with nitric acid in aqueous solution, is selected as a benchmark to test the real attainability of simultaneous process profitability and safety
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