Vent sizing for gas-generating runaway reactions

Exothermic runaway reactions that generate non-condensible gas as the temperature increases, as is typical of decompositions for example, can reach extremely high rates of pressure rise necessitating emergency relief of the process vessel containing the reactant. Sizing of a relief device using presently recommended methods (e.g. DIERS) frequently leads to extremely large and expensive vents. This paper presents a methodology that leads to a simple but much improved method for vent sizing, fully allowing for two-phase release of the gas—liquid mixture. A number of examples are presented which lead to interesting conclusions about the influence of plant variables.     

Calorimetric study of the inhibition of runaway reactions during methylmethacrylate polymerization processes

Reaction inhibition was adopted as a method to halt runaway phenomena during polymerization experiments. Use of reaction calorimetry coupled with a particular system for early detection of the onset of runaway (early warning detection system) has allowed to investigate the behaviour of two substances that can influence the reaction rate: hydroquinone and 1,4-benzoquinone. The process studied was the free-radical polymerization of methylmethacrylate carried out under batch conditions in bulk or in emulsion. The results show that hydroquinone and 1,4-benzoquinone behave differently: the first is an inhibitor because it completely stops the process; the second behaves as a retarder and could be used industrially to control the process and keep the reactor temperature within safe limits.     

CFD simulation of shortstopping runaway reactions in vessels agitated with impellers and jets

Runaway reactions are continuing to be a problem in the chemical industry. A recent study showed that 26% of our major chemical plant accidents are due to runaways. The consequences of runaway reactions are usually mitigated with (a) reliefs and containment systems or (b) shortstopping (reaction inhibition). This study covers the concept of shortstopping.

One of the major reasons for runaways is power failure. In the advent of a power failure, mixing an inhibiting agent with the reactor contents is challenging. However, jets or impellers driven by a small generator can be used for mixing. This study compares shortstopping results in vessels agitated with jets and impellers using computational fluid dynamics (CFD). A commercial CFD code, Fluent is used.

For shortstopping systems relying on jet mixing, angle and diameter of jet nozzle and jet velocity are the key design/operating parameters. For the systems with impellers, type, size and RPM of impeller are the key parameters. In this work, mixing with a jet mixer is first investigated for three nozzle diameters and two angles of injection. The best jet mixer configuration on the basis of mixing time is used for shortstopping studies. The simulated shortstopping results with the jet mixer are then compared with those obtained with impeller (Rushton and pitched blade turbine) stirred vessels. Our results identify the conditions for effective shortstopping; i.e., agitation requirements, locations for adding the inhibitor, and the quantity of inhibitor.

The distribution of excess inhibitor is shown to be an important and essential design criterion for effective shortstopping when using impeller stirred vessels. The comparative study with a single jet shows that jet mixer is ineffective when used for shortstopping. Efforts such as adding excess inhibitor and inhibition with higher reaction rates at the same power, proved to be ineffective when using jet mixer compared to the results with impellers.     

关于围填海工程的生态环境保护措施

以洋山深水港区围填海活动为例,结合工程对周边海域生态环境造成的一定的影响,提出围填海工程的生态环境保护措施。从宣传力度、环境监测工作全方位监控、环境保护监理工作、填海工程环保机构、水环境保护、大气环境保护、声环境保护、固废处置、保护生态环境的影响、敏感目标保护、风险事故环保应急、生态修复等方面做出相应的保护措施方案,以期为和谐海洋的构建、海洋资源的有效利用以及海洋生态环境可持续发展提供借鉴意义。     

探究林业生态保护与天然林保护的具体措施

在我国长期的发展与建设过程中,林业生态保护与天然林保护在很长的一段时期内被忽视,部分地区的环保设施与政策严重影响了当地甚至是全国的林业生态环境状况。     

Predictive accuracy of simplified vent area sizing methods for the case of thermal runaway reactions

A systematic comparison of the predictive accuracy of simplified design methods with respect to the relief diameter and the discharged mass flow on the basis of experimental results obtained in reactors with volumina ranging between 0.01 and 10 m³ allow for the conclusion that empirical design rules are not suited for an extrapolation. The preliminary recommended method in case of vapour systems is this of J.C. Leung and for use with gassy or hybrid systems the method by H.K. Fauske and J.C. Leung is promoted. Indeed, partly non acceptable overpredictions are evident. By using SAFIRE/VENT reasonable predictions are possible though still an oversizing can not be cut off.     

Parametric sensitivity analysis for thermal runaway in semi-batch reactors: Application to cyclohexanone peroxide reactions

The semi-batch reactors (SBRs) system, which is widely used in industrial processes, possesses an intrinsic parametric sensitivity, in which infinitesimal disturbances of input parameters can result in large variations in output variables. In this work, local parametric sensitivity analysis (PSA) was used to understand parameter variations and global PSA was conducted to examine the interaction of input parameters. The effects of these parameters on the output of the system model were analyzed based on the Monte Carlo method with Latin hypercube sampling and the extended Fourier amplitude sensitivity test model. The results showed that the evolution of thermal behaviors in SBRs were observed: marginal ignition; thermal runaway; and the quick onset, fair conversion, and smooth temperature profile. The threshold point of transition from marginal ignition to thermal runaway was at the maximal value of local sensitivity, for which the slope with respect to cooling temperature equaled zero. Moreover, the sequence of the global sensitivity of six common input parameters was computed and evaluated. The reliability of the numerical models was verified by using our previous experimental results of cyclohexanone peroxide reaction. This comprehensive sensitivity analysis could provide valuable operating information to improve chemical process safety.     

Study on the early stage of runaway reaction using Dewar vessels

In this paper, compared with a UN cylindrical 500 mL Dewar (H.4 in the UN tests), a spherical 1 L Dewar vessel was used to study the early stages of runaway reactions of several liquid and solid samples, including three organic peroxides and a reactive material. The samples were filled in the vessels and the temperature profiles versus times at different positions of the samples were measured. As a result, the minimum temperatures, defined as the SADT, were averagely 10 K lower than those measured in the cylindrical Dewar vessels. At the same time, the temperature profiles of solids in the spherical Dewars tended to be homogeneous. The heat transfer coefficient of a spherical Dewar is only 0.18 W/K/m, one-eighth of a conventional cylindrical Dewar vessel. Meanwhile it has a low phi factor. These factors are essential to simulate low heat loss bulk conditions in the equilibrium process and at the early stage of a runaway reaction. To characterize the ability of the adiabaticity of a storage vessel, it can be seen that a spherical Dewar could simulate the plant process having critical storage size of a reactive-material, r₀, approximately 0.6 m. It is recommended that such a technique is used to investigate the SADT of an unstable material in larger scale packaging or a material with very weak heat release in industry.     

电磁辐射对人的危害与防护

随着计算机通讯网络、移动电话、视听设备、空调器、微波炉等电子产品的日益普及,为我们在工作和生活中带来极大便利的同时,一种新型污染源——电磁辐射正悄然向人们袭来,成为继大气污染、水污染和噪音污染后的第四种污染。这些有害的电磁辐射不仅影响了电子设备的正常工作,还污染了我们赖以生存的环境,威胁着人类的健康。为此,各国政府采取了一系列措施来防治它。20世纪90年代以来,美国、欧盟、日本、澳大利亚、新西兰、韩国等国家和地区还相继采取法律形式宣布禁止产生电磁污染的产品(即电磁兼容不合格产品)进入市场。专家们强调市民应树立预防为先的意识,注意减少同电磁波的长期接触,采用某些方法对电磁波进行屏蔽,长期接触电磁波辐射的工作人员应穿用特殊的防护服装。     

基于职能控制下的环境保护和管理措施

当今世界面临的环境危机使人类认识到人必须和环境和谐发展。环境保护人人有责,企业应做好环境保护的事前和过程的控制,要用新的理论技术充实环保管理的内容,强化环境控制职能。本文用环境工程、系统工程、控制论的原理和方法探讨研究企业在环保管理中如何强化控制职能的理论和方法,为企业在"环境和发展"所面临的挑战中采取相应的管理对策抛砖引玉。     

Preparing for major terrorist attacks against chemical clusters: Intelligently planning protection measures w.r.t. domino effects

Chemical industrial areas or so-called chemical clusters consist of hundreds, and sometimes thousands, of chemical installations situated next to each other. Such areas can thus be seen as the summation of a large number of structures exhibiting danger to a certain degree for initiating or continuing accident domino effects or knock-on effects. In this article, an approach to investigate in a systemic way the vulnerability of each installation within the larger chemical cluster context, is developed. Our suggested method results in a prioritization of chemical installations with respect to their vulnerability for domino effects. The method can be used for intelligently designed protection of chemical industrial areas against terrorist attacks.     

Comparison of criteria for prediction of runaway reactions in the sulphuric acid catalyzed esterification of acetic anhydride and methanol

Loss of temperature control is one of the major reasons that can lead to runaway reaction. This occurrence is commonly named thermal runway. The aim of this paper is the application of thermal runaway criteria in order to predict the onset of runaway phenomena and define the range of stability related to operating conditions in the reactor, with specific reference to the esterification of acetic anhydride and methanol catalysed by sulphuric acid tested in isoperibolic conditions. The isoperibolic calorimeter has also been used to obtain thermodynamic, kinetic and physical chemistry data necessary to develop a model for the reaction. Some runaway criteria applied in this work require a model for the process, so a model for the analyzed system been developed.Because of the modest reaction enthalpy and low activation energy this reacting system provide a severe test to the runaway criteria.In this work, various runaway criteria have been applied to the experimental and simulated data and the results obtained have been compared.     

石油化验室职业病危害分析与工程防护对策研究

石油化验室存在毒物种类多,毒物发生源多且不固定,逐一分析了毒物的来源以及职业病危害防护措施存在的主要问题及原因。最终给出了化验室采用既可高效通风排毒,又可满足工艺要求,且不影响工人操作、节能环保的不同形式推挽式通风排毒系统。并通过化学试剂柜顶部设置局部排风罩,使化学试剂柜内形成微负压系统的职业病危害工程防护。     

河道治理与水环境保护的措施研究

本篇文章主要是对河道治理和水环境的保护进行分析,并且提出相应的建议,帮助有关部门更好地加强对河流水污染问题的解决,给人们的生活提供一个优美的环境。     

建筑施工过程中环境保护措施应用研究

在改革开放高速的社会发展环境下,各行各业都在不断的变化,随着我国经济与科技的飞速发展,我国对各行业的环境保护越发重视,其中建筑行业是环境保护中的重要一环。本文对于建筑施工过程中环境保护技术的重要性进行了阐述,研究现代房建工程施工中普遍存在的环境问题,从而提出改善方案,保障建筑施工过程中环境保护技术措施的有效应用。     

环境检测的作用及环保措施分析

本文对环境检测的作用进行了总结,包括环境检测是环境影响评价的基础、环境检测是环境保护的依据、环境检测促进环境管理工作等,提出了环境保护措施,需要增加资金投入力度、完善环境检测法律保障体系、合理使用环境检测新技术、构建环境检测质量控制体系、完善环境监管保护方法来有效地保护环境,提升人们的生活质量。     

基于企业制造的人为差错及防范措施研究

以企业人为差错及其防范措施为研究对象,通过对人为差错成因、机理及影响等方面的分析,提出了降低或消除生产过程中人为差错的防错技术模型和防错设计方法,论述和总结了有效防范企业生产过程中人为差错的措施和建议,旨在不断提升企业生产过程的管理水平.     

化工安全生产与生态环境保护管理措施探究

现代社会进入一个科技化、现代化发展阶段,人们的生活条件不断提升,其中诸多民生相关的产业都发挥着关键作用。化工产业作为社会产业基础构成部门与民生息息相关。但从其基本属性来看,实践工作难免会遇到一些安全性的问题,以及相应的环境污染。需要探索生态环境保护管理与化工安全生产协调配合的有效措施,由此才能达成可持续化发展目标,提升其积极影响作用。     

环境监测在生态环境保护中的作用及发展措施

环境监测是对水体环境、大气环境、噪声环境、土壤环境的质量进行监视和测量,以确定环境质量变化趋势以及环境污染程度。近年来,自然生态环境日趋恶化,温室效应、土地沙漠化、水土流失、植被破坏等生态环境问题逐步浮出水面,给国民经济和社会的可持续发展带来严重的负面影响。而环境监测工作恰恰可以查找出导致生态环境污染的诱因,为制订针对性强、效果显著的生态环境保护方案提供真实、确凿的数据支持。因此,本文围绕环境监测在生态环境保护中发挥的重要作用和针对采取的发展措施展开论述。