Runaway analysis

Tables IV and V contain appropriate balance equations for nonisothermal free-radical polymerizations and copolymerizations, which are seen to conform to equation 2k. Following the procedure outlined above, we obtain the CT s for homopolymerizations listed in Table VI. Corresponding CT s for copolymerizations can be. obtained in a similar way, and indeed the first and fourth listed in Table VII were. The remaining ones, however, were derived via an alternate route based upon the definitions in Table VI labeled "equivalent" together with approximate forms for pj, which were necessitated by application of the Semenov-type runaway analysis to copolymerizations, and which will subsequently be described. Some useful dimensionless parameters defined in terms of these CT s appear in Tables VIII, IX and X.

Hazards Hang-fires, Runaways Analysis Procedures, Records, Feedback... 

Consequence Phase 3 Develop Detailed Quantitative Estimate of the impacts of the Accident Scenarios. Sometimes an accident scenario is not understood enough to make risk-based decisions without having a more quantitative estimation of the effects. Quantitative consequence analysis will vary according to the hazards of interest (e.g., toxic, flammable, or reactive materials), specific accident scenarios (e.g., releases, runaway reactions, fires, or explosions), and consequence type of interest (e.g., onsite impacts, offsite impacts, environmental releases). The general technique is to model release rates/quantities, dispersion of released materials, fires, and explosions, and then estimate the effects of these events on employees, the public, the facility, neighboring facilities, and the environment. 

Analysis of thermal runaway reactions is reviewed in Chapter 12. Table 4-6 gives various guidelines for the design of reactors and Figure 4-26 illustrates various reactor configurations. 

The ARC analysis has been extended to determine the eonditions that may lead to thermal runaway in reaetors or storage vessels [10]. The equipment timeline is defined by the ratio of the heat eapaeity of the reaetor and its eontents to the reaetor heat transfer area and heat transfer eoeffieient. This is expressed by... 

Complete and accurate written documentation of chemicals properties, process teclinology, and process equipment is essential to the PSM program and to a process hazards analysis (PrHA). This information serves many users including the PrHA team. The needed chemical information includes fire and explosion characteristics, reactivity hazards, safety and health hazards and the corrosion and erosion effects. Current material safety data sheet (MSDS ) information helps meet this requirement, but must be supplemented with process chemistry information regarding runaway reactions, and over-pressure hazards. 

Liquid nitrogen should always be analyzed before it is off-loaded. The same applies in other cases where delivery of the wrong material could have serious unwanted results, such as a fire or runaway reaction, as in the two incidents that follow. If analysis causes too much delay, the new load should be put in a holding tank. 

Tlie fourth case study (Section 21.5) was a haztird and risk analysis of the potential impiict of the caiastropliic release of llie chemical contents of a holdup lank because of a runaway reaction. The study traced calculations leading to a risk curve portraying the healtli impact in lenns of tlie frequency with which the number of people affected exceeded various amounts. 

During the development of these criteria the Semenov analysis was extended to systems with heat-exchanger reservoir temperatures different from feed temperatures (Tr < Tq) and with delayed runaway (larger value of e), which resulted In significant concentration drift prior to runaway. Since values of e for chain-addition polymerizations are not nearly as small as those for the gaseous explosions Investigated by Semenov, R-A Is not as sensitive nor Is It as early In terms of extent of reaction. 

We started this study by developing a computer model to predict the kinetic conditions during the runaway stage of a reaction. The computer model is based on an iterative analysis which permits a step-by-step computation of various variables. 

This event tree analysis shows that a dangerous runaway reaction will occur on average 0.025 time per year, or once every 40 years. This is considered too high for this installation. A possible solution is the inclusion of a high-temperature reactor shutdown system. This control... 

The other root causes were (1) the poor understanding of the chemistry, (2) an inadequate risk analysis, and (3) no safeguard controls to prevent runaway reactions. This EPA case history also summarized seven similar accidents with phenol-formaldehyde reactions during a 10-year period (1988-1997). 

Historical perspective An analysis of thermal runaways in the United Kingdom (Barton and Nolan, Incidents in the Chemical Industry due to Thermal Bunaway Chemical Reactions, Hazards X Process Safety in Fine and Specialty Chemical Plants, IChem 115 3-18) indicated that such incidents occur because of the following general causes ... 

Schisla, R. M., P. N. Lodal, and M. A. Paulonis (1996). "Use of the Semenov Model for the Analysis of Runaway Reactions Induced in Pipelines by Electrical Tracing." Proceedings of the 30th Annual Loss Prevention Symposium, February 26-28, 1996, New Orleans, LA, ed. R. P. Benedetti, J. J. Rooney, and K. Chatrathi, Paper 13d. New York American Institute of Chemical Engineers. 

A common perception is that reactive incidents are primarily the result of runaway reactions. In fact, analysis of data from the 167 incidents suggests that other types of reactive hazards should also be of concern. CSB data analysis identified three common types of reactive hazards (see Appendix A for definitions) ... 

In 55% of the cases, the accidents could have been foreseen by use of risk analysis, and in 35% of the cases by thermal stability testing. Different methods of stability testing were evaluated comparatively during the investigation of a runaway exothermic reaction which occurred during the preparation of a component mixture for a sealing composition in a 1200 1 reactor only DSC was effective in identifying the cause of the hazard. 

This sort of analysis could be extended to any metal-catalyzed chemistry in which a large runaway chiral excess is induced in the product by way of a small chiral excess of the molecules that serve as ligands to the metal. It is only necessary that the D,L-metal center be kinetically slower and thermodynamically more stable than the d,d- or L,L-complexes in order that any small e.e. of a chiral ligand be translated into chiral dominance of the reaction product. That the initial e.e. resulting in chiral takeover within a reacting system can be induced by asymmetric mineral surfaces indicates that a general chemical route to the asymmetry of life may exist. 

The experimental techniques described above of charge—discharge and impedance are nondestructive. Tear-down analysis or disassembly of spent cells and an examination of the various components using experimental techniques such as Raman microscopy, atomic force microscopy, NMR spectroscopy, transmission electron microscopy, XAS, and the like can be carried out on materials-spent battery electrodes to better understand the phenomena that lead to degradation during use. These techniques provide diagnostic techniques that identify materials properties and materials interactions that limit lifetime, performance, and thermal stabiity. The accelerated rate calorimeter finds use in identifying safety-related situations that lead to thermal runaway and destruction of the battery. 

A hazard analysis has identified the following failures and maloperations which may give rise to a runaway reaction . ... 

Closed system tests, using an unvented test cell (see Figure A2.5) or Dewar flask, can be used for vapour pressure systems. The runaway is initiated in the way that best simulates the worst case relief scenario at plant-scale. The closed system pressure and temperature are measured as a function of time. Most commercial calorimeters include a data analysis package which will present the data in terms of rate of temperature rise, dT/dt, versus reciprocal temperature (-1 / ), and pressure versus reciprocal temperature (see Figure A2.10). However, it is important to correct the temperature data for the effects of thermal inertia. See 2.7.2. 

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