Dynamic Behaviour of a Continuous Heat Exchanger/Reactor after Flow Failure

The intensified technologies offer new prospects for the development of hazardous chemical syntheses in safer conditions: the idea is to reduce the reaction volume by increasing the thermal performances and preferring the continuous mode to the batch one. In particular, the Open Plate Reactor (OPR) type “reactor/ exchanger” also including a modular block structure, matches these characteristics perfectly. The aim of this paper is to study the OPR behaviour during a normal operation, that is to say, after a stoppage of the circulation of the cooling fluid. So, an experiment was carried out, taking the oxidation of sodium thiosulfate with hydrogen peroxide as an example. The results obtained, in particular with regard to the evolution of the temperature profiles of the reaction medium as a function of time along the apparatus, are compared with those predicted by a dynamic simulator of the OPR. So, the average heat transfer coefficient regarding the “utility” fluid is evaluated in conductive and natural convection modes, and then integrated in the simulator. The conclusion of this study is that, during a cooling failure, a heat transfer by natural convection would be added to the conduction, which contributes to the intrinsically safer character of the apparatus

Evaluation of an intensified continuous heat-exchanger reactor for inherently safer characteristics

The present paper deals with the establishment of a new methodology in order to evaluate the inherently safer characteristics of a continuous intensified reactor in the case of an exothermic reaction. The transposition of the propionic anhydride esterification by 2-butanol into a new prototype of ‘‘heatexchanger/ reactor’’, called open plate reactor (OPR), designed by Alfa Laval Vicarb has been chosen as a case study. Previous studies have shown that this exothermic reaction is relatively simple to carry out in a homogeneous liquid phase, and a kinetic model is available. A dedicated software model is then used not only to assess the feasibility of the reaction in the ‘‘heat-exchanger/reactor’’ but also to estimate the temperature and concentration profiles during synthesis and to determine optimal operating conditions for safe control. Afterwards the reaction was performed in the reactor. Good agreement between experimental results and the simulation validates the model to describe the behavior of the process during standard runs. A hazard and operability study (HAZOP) was then applied to the intensified process in order to identify the potential hazards and to provide a number of runaway scenarios. Three of them are highlighted as the most dangerous: no utility flow, no reactant flows, both stop at the same time. The behavior of the process is simulated following the stoppage of both the process and utility fluid. The consequence on the evolution of temperature profiles is then estimated for a different hypothesis taking into account the thermal inertia of the OPR. This approach reveals an intrinsically safer behavior of the OPR

A mechanistic and experimental study of the diethyl ether oxidation

International audienceThis work presents the results of the theoretical investigations on autoxidation process of diethyl ether (DEE), a chemical largely used as solvent in laboratories and considered to be responsible for various accidents. Based on Density Functional Theory (DFT) calculations, the aims of this study were the identification of all the most probable reaction paths involved in DEE oxidation (at ambient temperature and under conditions that reflect normal storage conditions) and the characterization of products and all potential hazardous intermediates, such as peroxides. Results indicate that industrial hazards could be related to hydroperoxide formation and accumulation during the chain propagation step. A detailed kinetics model of DEE oxidation in the gas phase was then developed from all energetic and kinetics parameters collected during the mechanistic study. Outputs of the kinetics model, in terms of time of evolution of product concentrations, have been then compared with the experimentally measured concentration of products (notably hydroperoxides) issued from tests on DEE oxidation conducted under accelerated conditions with autoclaves

Experimental study of CH4/O2/CO2 mixtures flammability

International audienceThe oxy-combustion process uses CH4/O2/CO2/H2O mixtures at various concentrations, according to the different operation phases. To analyze the risks associated to this process, the safety characteristics of these explosive mixtures have to be taken into account. A literature review showed that some safety features of methane in oxygen or in air were not available. Thus, the flammability ternary diagram of CH4/O2/CO2 mixtures was determined at room temperature and 1 bar pressure. Furthermore, the influence of oxygen content on the explosion severity (Pmax; dP/dt) was investigated. The ternary mixtures were prepared directly in a 20 L spherical test vessel. The concentrations of reactants were adjusted using the relationship between the partial pressure and the molar fraction of gas. The ignition source used was an alumel fusing wire. The flammability limits of methane in oxygen were extrapolated at 5 and 68% vol., by using the established CH4/O2/CO2 mixtures ternary diagram. It also confirmed that when the carbon dioxide concentration increases, the flammability range decreases: no ignition was observed when carbon dioxide content exceeded 73%. A significant influence of the oxygen concentration on the explosion severity has been highlighted for CH4/O2/CO2 mixtures containing respectively 10, 25, 45 and 65% vol. of carbon dioxide. The maximal explosion overpressure and the maximum pressure rise were both measured near the stoechiometry. Maximum values of Pmax and dP/dt measured for a 10% vol. carbon dioxide concentration were 11.2 bar rel. and 5904 bar/s respectively, while they were 3.6 bar rel. and 72 bar/s respectively in the case of a 65% vol. carbon dioxide content in the mixture

Antioxidant activity and chemical constituents of Anthriscus vulgaris Bernh. (Apiaceae) from Algeria

AbstractThe chloroform and ethyl acetate extracts obtained from the aerial parts of Anthriscus vulgaris Bernh. were analyzed by gas chromatography-mass spectrometry (GC-MS). 36 components have been identified in each extract. The major constituents were 1-monooleoylglycerol (20.72%), caffeic acid (15.20%), cinnamic acid (11.31%) and benzene acetic acid (10.95%). The phytochemical study led to the isolation and structural elucidation of three compounds, scopoletin, umckalin and 1-(3',4'-dihydroxycinnamoyl) cyclopentane-2,3-diol. Moreover the ethyl acetate extract was screened for its possible in vitro antioxidant activity by 2,2-diphenyl-1-picrylhydrazy l(DPPH) and lipid peroxidation inhibition assays in which it displayed a noticeable activity. This study provides the first biological and chemical investigation on Anthriscus vulgaris Bernh. in Algeria

A HAZOP-like risk analysis method for intensified and multi-scale processes

Technology under development for process intensification using multi-scale equipment will contribute significantly to provide a safer design by going from batch/semi-batch to continuous operation while reducing inventory of hazardous substances in critical stages. On the other hand, the shift to higher space-time-yields adds new risks such as runaway reactions with hot spot formation or handling an explosive atmosphere in the presence of potential permanent ignition sources, etc. A new method was developed for preliminary risk assessments, called HAZOP-LIKE study, to cover the characteristic and specific features of micro-designed equipment that are relatively unimportant when employing conventional equipment. Another advantage is that the method can be employed in the early stages of development of the process to point out as early as possible the areas of concern in terms of safety. The method uses a guide-word approach with ranking the risks in terms of probability and severity. It was developed as part of the European research project IMPULSE (Integrated Multiscale Process Units with Locally Structured Elements) whose overall objective was the effective and targeted integration of innovative process equipment such as micro-reactors, compact heat exchangers and other micro- and/or meso-structured components to attain radical performance enhancement for whole process systems in chemical production. The risk analysis method is described in detail and case studies are presented concerning a generic liquid-liquid reaction and the production of vinyl acetate to demonstrate the method. The results show that the created generic templates support comprehensive risk analysis studies with hidden deviations not obviously following traditional HAZOP studies

Experimental study of ignition of bulk storage by hot points

International audienceFire and explosion risk is generated by chemical or biological oxidation of combustible materials. An experimental study of ignition risk due to hot points in the storage of bulk materials is required to ensure fire safety. Many parameters are involved in this phenomenon: nature of the material, storage volume and temperature, type and size of hot point, etc. The aim of this study is to describe an adapted experimental procedure to determine critical ignition temperatures of powders for different conditions and with several types of hot points. Material selected for this study is a powder of " Lucy coal ". Ignition is carried out in 1000 and 2700 cm3 cubic baskets for two sizes of inert cylinders at a given temperature and for an inert sphere at a given initial temperature. The critical ignition temperature is defined as the hot point temperature in the middle of a 5°C interval of both temperatures: 1) ignition and 2) no ignition. First results demonstrate that the set-up procedure is relevant. Critical temperatures measured for both cylinders and for the sphere are in the same range. Discrepancies between the results obtained under these three test conditions have been explained by different basket sizes and hot points geometry. Data obtained need now to be compared to available theoretical modelling. These results will then allow predicting material behaviour under other storage conditions

Développement d'une méthodologie pour la conduite en sécurité d'un réacteur continu intensifié

L'objectif de la thèse est de développer une méthodologie d'étude de sécurité pour la mise en oeuvre d'une réaction exothermique dans un réacteur continu intensifié. Elle est établie sur un cas modèle : la transposition de l'estérification de l'anhydride propionique par le butanol dans un nouveau concept de réacteur/échangeur. La démarche se décline en trois étapes. La première passe par l'acquisition de données calorimétriques permettant de caractériser la dangerosité des composés et de la réaction et inclut la validation d'un modèle cinétique. La deuxième phase comprend la détermination de conditions opératoires pour un fonctionnement sûr en marche normale à l'aide d'un modèle de simulation et la réalisation d'expériences. La dernière partie concerne l'évaluation du caractère intrinsèquement plus sûr du réacteur en marche dégradée (arrêt des fluides) lié à l'inertie thermique de l'appareil. Le simulateur dynamique est utilisé pour prédire l'évolution des températures en cas de dériveThe aim of this study is to develop a methodology in order to carry out safely an exothermic reaction in an intensified continuous reactor. It is established on a case study: the transposition of the esterification between propionic anhydride and 2-butanol in a new prototype of heatexchanger/reactor. The approach is divided in three steps. In a first part, experimental data obtained by calorimetry allow to determine the potential hazard of the compounds as well as the reaction and a kinetic model is validated. In a second stage a dedicated software model is used to calculate optimal operating conditions for safe control. Experiments are then achieved to test these conditions. In the last step, the inherently safer behaviour of the reactor is evaluated in the case of probable malfunctions (fluids shutdown) due to the thermal inertia of the apparatus. Finally, the evolution of the temperature profiles is obtained by dynamic simulation.TOULOUSE-ENSIACET (315552325) / SudocSudocFranceF