Emergency pressure relief discharge control by passive quenching—update

A recent runaway reaction emergency relief system design includes a passive quench tank to collect and contain the two-phase emergency relief discharge. This avoids the release of a large vapor cloud to the atmosphere and the attendant flammability and toxicity hazards. The feasibility of quenching is demonstrated with small scale experiments. A pressure relief simulation model is shown to accurately reproduce the observed temperature and pressure profiles in both the reactor and quench tank during relief. The model is then applied to the design of a full scale system. Quench system design considerations are discussed.     

The DIERS users group: A forum for development/dissemination of emergency relief system design technology

DIERS was formed in 1976 to develop methods for the design of emergency relief systems capable of handling runaway reactions [1, 2]. Of particular interest at the time were when tow-phase flow venting would occur and the applicability of different methods for sizing emergency relief systems for two-phase, vapor-liquid flashing flow. Approximately $1.6MM was devoted to investigations of two-phase, vapor-liquid onset/disengagement dynamics and the hydrodynamics of emergency relief systems.     

Application of the DIERS methodology to the study of runaway polymerization: Validation of the DIERS methodology using blow-down tests

The Design Institute for Emergency Relief Systems (DIERS) and more recently the DIERS Users Group have been investigating various aspects of emergency relief for more than 12 years. The DIERS programs have given rise to an in-depth understanding of the basic mechanism of how runaway thermal reactions are safely vented. In concert with the development of the understanding of the venting mechanism, DIERS also developed experimental procedures and computational techniques for estimating emergency vent sizes.     

The role of instrumentation and process controls in minimizing accidental releases

Most accidental releases are the result of either mechanical failures or measures taken to prevent such failures, such as, venting through emergency vents, relief valves, or rupture discs. Where the mechanical failure is the result of defective materials, inadequate design, or external factors, little can be done by means of instrumentation to prevent the release. It may be possible, however, to reduce the flow. Many failures are due to process upsets such as overpressure, internal explosions, and runaway reactions. The probability of these failures occurring can be substantially reduced by proper instrumentation.     

Batch runaway reaction relief: Re-evaluation of “Credible” scenario

Many chemical reactions in the fine chemical and related industries are performed in a semi-batch manner under isothermal conditions. Relief system design evaluation for runaway reactions, using DIERS methodology for example, is frequently studied adiabatically using data derived from batch mode testing. In many cases, however, evaluation of the process isothermally under the realistic semi-batch mode can be extremely useful, often helping to greatly reduce the vent size as a result of a better understanding of the process. In some cases, it is even possible to eliminate runaway reaction as a viable case for relief sizing. Such evaluations of venting are fully consistent with DIERS methodology. This paper presents the arguments for sizing vents for scenarios other than the very worst case, by objective evaluation of trips and interlocks, so that the level of risk is reduced to an acceptable level without the need for extremely large vents.     

Design charts for two-phase flashing flow in emergency pressure relief systems

The design charts of this paper apply to the high velocity flow of a boiling liquid and its vapor during two-phase emergency pressure relief events. These charts are used to size relief system components to handle a given minimum relief flow requirement. This flow requirement is determined by computer simulation programs such as that described in [1], or by special-case models [2, 3, 4]. Though intended for use in sizing pressure relief systems, the charts are applicable to high-velocity flashing flow problems.     

Design of quench system for runaway reactions using bench-scale equipment

Runaway chemical reactions are a potential problem in many sectors of the chemical industry. The typical hazard scenario involves a batch (or semi-batch) chemical reaction where, due to an operator error or instrument failure, the reaction temperature begins to accelerate rapidly. The rise in temperature is, of course, accompanied by a rise in pressure and in order to prevent vessel rupture, some means of protection must be provided. The common approach to overpressure protection in the industry is to fit a relief device to the reactor vessel in question; the device opens at a predetermined pressure and, provided it is sized correctly, the maximum pressure can be kept within acceptable limits. The Design Institute for Emergency Relief Systems (DIERS), organized through the auspices of the AIChE [1], undertook several years of research to develop the methodology for the sizing of relief systems to cope with runaway reactions. The emphasis in industry has changed so considerably since the DIERS work that companies are interested in avoiding the release of chemicals to the environment in addition to preventing equipment damage. This adds considerable complexity to the relief system and must be evaluated with the same thoroughness as the vent design.     

Design and sizing of knock-out drums/catchtanks for reactor emergency relief systems

Sizing criteria and design procedures for knock-out drums and catch tanks used in reactor emergency relief systems.     

Relief system design scope of CCPS effluent handling guidelines

The forthcoming CCPS Guidelines for Effective Handling of Emergency Release Effluents includes the methodology for defining effluent flow rates and characteristics during emergency pressure relief event. The intent is to provide the user with relief systems in a typical process unit without requiring expert assistance or access to other documents. Cases requiring special design training and methodology due to combinations of multi-phase, multi-component, reactive, geometric and thermodynamic complexities are identified and illustrated in the Guidelines. However, the complete design technology for such cases is beyond the scope of these Guidelines; reference is given to applicable documents.     

Reliable detection of runaway reaction precursors in liquid phase reactions

A theoretical approach for early on-line detection of runaway reactions based on temperature derivative estimates is described and shown to be feasible in the laboratory. On-line process measurements were processed to yield smoothed derivative estimates and confidence intervals. These estimates were then compared to characteristics of potentially hazardous situations. If a match was sensed, preventive or emergency measures could be initiated. The problem lies in the tradeoff between earliest possible detection and false alarm avoidance.     

电力应急物资联合储备管理系统设计

系统地分析了电力应急物资的特点、储备现状及存在的问题,针对电力应急物资管理的复杂性、储备资金占用较大以及利用率不高等问题,提出了建立电力应急物资联合储备管理系统的设想,并系统地阐述了联合储备管理系统的设计思想、运作方式和流程,指出当出现突发性电力事故而局部短时应急物资储备不足时,联合储备管理系统的启动可以提升突发事故应急处理的质量和效率,缩小事故范围,加快恢复速度,节约应急成本。     

Measurement of flow resistance of rupture disc devices

Present codes and practices for the design of relief systems in which rupture discs are used are based either on non-typical system configurations or on “rule of thumb” default values of rupture disc flow parameters. There is a need to develop code methods and common practices based on actual relief system configurations, as well as test methods for determining the actual flow resistance of specific rupture disc devices. The methodology reported here is appropriate for these needs.     

Procedures for preventing pilot plant runaways

During the nitration of a substituted benzoic acid, a runaway reaction occurred. The reaction had been run without incident many times in the laboratory and once in the pilot plant on a 50 gallon scale. As a result of the runaway, the procedures for running reactions in the pilot plant were thoroughly reviewed. The review resulted in eliminating some practices, reemphasizing some existing procedures, establishing a new review system, and formalizing a standard operating procedure for all reactions to be run in the pilot plant.     

一种应急救援索系统的开发应用研究

在地形、地势复杂的地区输送应急救援人员或物资面临着道路中断等情况。为了解决这类问题,依据国标规范和实地工况,提出了小型救援系统的基本设计要求和工作原理,设计了结构参数。针对该救援系统的承载索部件,阐述了其设计方法和力学计算过程,并建议采用超高分子量纤维绳替代钢丝绳的设计,以降低系统成本,提高工效,然后对该救援索系统的牵引驱动模块进行了设计计算。在湖北省某地,采用机械提升倒装法对该救援索系统进行了现场组装、调制和试验,证实了在复杂的地理条件下利用临时组装架空索道实现小型物资应急输送的可行性,为实现经济物资的远距离、快速架设索道应急输送技术开发提供了数据支持及设计试验方法,具有一定的推广应用意义。     

大面积停电应急监控与启动机制设计的探讨

应急机制是应急管理体系的核心内容之一。大面积停电的应急监控与启动机制是启动应急方案之前的基础性机制,探讨其设计形式和内容具有重要意义。介绍了应急机制的含义,在此基础上讨论了在应急监控与启动机制设计中需要注意的预警及其分级、风险源辨识和事件评价指标等问题,以期完善应急方案,提高应急管理水平。     

QRA of chemical reaction systems: The state of the practice

This paper discusses a quantitative risk assessment (QRA) of an exothermic chemical process. Fault tree/event tree techniques were used to estimate the frequency of runaway reactions that could result in over-pressure and vessel rupture. The paper focuses on the current methodology used in performing this type of study, emphasizing analytical techniques that help avoid potential time-consuming pitfalls. The challenging problem of predicting how rare sequences of events (e.g., involving failure of several engineered control and safety systems) will develop is systematically modeled using fault trees/event trees, which makes the QRA process a unique and powerful analytical tool. The results of this study provided the guidance for selecting the most appropriate action(s) to implement from a set of various design options for improving the safety of this system. Use of QRA has enabled plant management to have confidence that they are selecting the most cost-effective safety improvement option.     

Alleviating rural poverty in sub-Saharan Africa

This analysis of rural poverty and hunger in Africa discusses the intertemporal and cross-sectional dimensions of poverty as an aid to policies and programs to alleviate hunger. Since nutritional adequacy of diets varies according to season, seasonality is an important cause of poverty especially in countries with 1 major harvest. In agricultural communities the wet season brings on food shortages and high prices, requiring assistance programs to concentrate on alleviating hunger at this time of year. Drought places a similar demand on resources. People may be poorer in 1 section of a country than another if they have no access to the existing power system, depriving them of services and assistance. There are forgotten regions of Africa where people are poor due to physical isolation, increasing the risk of drought and impeding emergency relief. Production in these areas may be low because there are no consumer goods to buy with surplus. It is important to identify target groups for financial assistance which will change with time and environmental conditions.     

浅谈海洋平台应急电源系统检验

应急电源系统作为海洋平台上在紧急状态下的重要电源，必须在平台处于异常状态下能发挥重要作用，以保证平台应急系统的用电要求。因此海洋平台上的应急电源系统必须要满足有关安全标准规范的要求。     

Runaway system characterization and vent sizing based on diers methodology

This article reveals the diverse nature of runaway systems as well as some general trends. In addition, it also serves to point out the usefulness of such an apparatus in characterizing virtually unknown systems.     

浅谈如何提高环境应急监测能力

针对环境应急监测在突发性环境污染事件中的作用、要求、现状以及管理特点,分别论述了风险源识别、敏感环境调查、污染预防、应急监测体系建设、软硬件建设、应急监测演练等环节对提高环境应急监测速度及应急监测能力的重要性。研究结果对应急监测机构快速、高效地应对环境应急监测工作和保证应急监测质量具有一定的现实指导意义。