Runaway reactions prevention

Comenges, J. M. Z. (1991). "Fundamentals on Runaway Reactions Prevention and Protection Measures." Safety of Chemical Batch Reactors and Storage Tanks, ed. A. Benuzzi, and J. M. Zaldivar, 19-47. Dordrecht, The Netherlands Kluwer Academic... 

Zaldivar, J.M. (1991) Fundamentals on runaways reactions prevention and protection measures, in Safety of Chemical Batch Reactors and Storage Tanks, Benuzzi, A. and Zaldivar, J.M. (eds.) ESCS, EEC, EAEC, Brussels, 19 17. 

R. D. Coffee, in H. H. Fawcett and W. S. Wood, Safety and Accident Prevention in Chemical Operations, 2nd ed., Wiley-Interscience, New York, 1982, p. 305 International Symposium on Runaway Reactions, Center for Chemical Process Safety, New York, 1989, pp. 140, 144,177, 234. 

Many runaway reactions can be prevented by changing the order of operations, reducing the temperature, or changing another parameter. 

A polymerization process involving a monomer, an organic peroxide initiator and an organic solvent underwent an energetic runaway reaction. All the contents in the polymerization reactor were lost. The emergency relief system prevented major damage to the equipment. 

Short-Stop Agent A material added to a reaction mixture to stop or greatly reduce the reaction rate. This is usually done to prevent a runaway reaction. 

While alkyl cyanoacrylate-based adhesives are used globally in a large variety of domestic and commercial settings, their physical and toxicological properties must be considered. Alkyl cyanoacrylate polymerization is a very exothermic reaction, so care must be taken to prevent the contamination of large quantities with any materials, which might initiate a very rapid, runaway reaction. Also, alkyl cyanoacrylate monomers and the polymers which they form, will burn, and users should avoid their use near sparks or open flames. 

Anonymous, How to Prevent Runaway Reactions, EPA 550-F99-004, U.S. Environmental Protection Agency Office of Solid Waste and Emergency Response, August 1999. In addition to the accidents mentioned in the reference, a significant number occurred prior to the 1989 time frame. Serious incidents arc recorded as early as 1957. Accident recording before 1957 was incomplete. 

Overheating can result in overpressure due to reduction of allowable stress. Therefore, flie design must include monitoring and control features to prevent the occurrence of decompositions and runaway reactions, since conventional pressure reheving devices cannot normally provide protection against these contingencies. 

Figure 12-7. Simplified scenario of a thermal runaway. (Source T. Hoppe and B. Grob, Heat flow calorimetry as a testing method for preventing runaway reactions," Int. Symp. on Runaway Reactions, OCRS, AlChE, March 7-9, 1989.)...

In scale-up, runaway exothermic chemical reactions can be prevented by taking appropriate safety measures. The onset or critical temperature for a runaway reaction depends on the rate of heat generation and the rate of cooling, which are closely linked to the dimensions of the vessel. 

Procedural The same reactor described in Example 3 above, but without the 5 psig high pressure interlock. Instead, the operator is instructed to monitor the reactor pressure and stop the reactant feeds if the pressure exceeds 5 psig. There is a potential for human error, the operator failing to monitor the reactor pressure, or failing to stop the reactant feeds in time to prevent a runaway reaction. 

The basic requirements of a reactor are 1) fissionable material in a geometry that inhibits the escape of neutrons, 2) a high likelihood that neutron capture causes fission, 3) control of the neutron production to prevent a runaway reaction, and 4) removal of the heat generated in operation and after shutdown. The inability to completely turnoff the heat evolution when the chain reaction stops is a safety problem that distinguishes a nuclear reactor from a fossil-fuel burning power plant. 

The immediate cause of the disaster was the contamination of an MIC storage tank by several tons of water and chloroform. A runaway reaction occurred, and the temperature and pressure rose. The relief valve lifted, and MIC vapor was discharged to atmosphere. The protective equipment, which should have prevented or minimized the release, was out of order or not in full working order the refrigeration system that should have cooled the storage tank was shut down, the scrubbing system that should have absorbed the vapor was not immediately available, and the flare system that should have burned any vapor that got past the scrubbing system was out of use. 

Many accidents, particularly on batch plants, have been due to runaway reactions, that is, reactions that get out of control. The reaction becomes so rapid that the cooling system cannot prevent a rapid rise in temperature, and/or the relief valve or rupture disc cannot prevent a rapid rise in pressure, and the reactor ruptures. Examples are described in the chapter on human error (Sections 3.2.1 e and 3.2.8), although the incidents were really due to poor design, which left traps into which someone ultimately fell. 

Hoppe, T. and Grob, B., Heat Flow Calorimetry for Preventing Runaway Reactions, Chem. Eng. Prog., V. 89, No. 1, 1990. 

The same group showed (Baumeister et al., 1997) that addition of vanadyl compounds as cocatalysts solved a recurring problem in hydrogenations the build-up of arylhydroxylamine intermediates, which can lead to runaway reaction conditions. Vanadyl complexes catalyse the disproportionation of aiylhydroxylamines and, hence, prevent their build-up during... 

Cascade control, along with ratio control, is used to control the temperature. The cold-water line is to have an air-to-close control valve. In case of failure in the air supply, the valve would open fully and a runaway reaction would be prevented. The hot-water line will have an air-to-open valve for similar reasons. After the two streams are mixed, the temperature will be measured. If it is above the desired temperature, the amount of air supplied to the valves will be reduced. This will increase the cold-water flow rate, and decrease the hot-water throughput. The result will be a reduction in the inlet water temperature. The desired temperature will be determined from a measurement of the reactor temperature. A deviation from the desired temperature will cause the set point of the second controller to be changed. This will result in a change of the inlet water temperature. 

Such nuclear reactions are controllable by keeping the sample size small. Most of the neutrons escape from the sample instead of causing further reactions. The smallest mass of sample that can cause a sustained nuclear reaction, called a chain reaction, is called the critical mass. Another way to control the nuclear reaction is to insert control rods into the nuclear fuel. The rods absorb some of the neutrons and prevent a runaway reaction. 

Factors of importance in preventing such thermal runaway reactions are mainly related to the control of reaction velocity and temperature within suitable limits. These may involve such considerations as adequate heating and particularly cooling capacity in both liquid and vapour phases of a reaction system proportions of reactants and rates of addition (allowing for an induction period) use of solvents as diluents and to reduce viscosity of the reaction medium adequate agitation and mixing in the reactor control of reaction or distillation pressure use of an inert atmosphere. 

EPA, How to Prevent Runaway Reactions, Report 550-F99-004 (August 1999). Available at www.epa. gov/ceppo/. 

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). 

Use the paper developed by the EPA (see footnote 27) to state the EPA s recommendations for preventing runaway reactions. 

Now that some of the possible causes of a runaway reaction have been discussed, the question of preventive measures remains. The type of information needed can be grouped according to the triangle discussed in Chapter 1 (Figure 1.1). These parameters are as follows ... 

Techniques such as adiabatic calorimetry (Dewar calorimetry) were by then well established [2, 118, 119]. All these techniques can be used for obtaining data to design for the prevention of runaway reactions, that is, to design for inherent plant safety. 

In an early stage of warning for a runaway reaction, emergency cooling should be applied in an attempt to control the situation. This often is not sufficient to be a fully preventive measure, particularly if the runaway initiation was not identified quickly. Quenching of the reaction is the usual next step to take. The reaction can be quenched by using one or more of the following procedures ... 

Hoppe, T., and R. Bruderer, "Thermal Analytical Investigation into a Runaway Reaction," in Proceedings of the 6th Annual Symposium on Loss Prevention and Safety Promotion in the Process Industries, p. 37, Oslo,... 

Noronha, J. A., C. S. Brown, Jr., M. R. Juba, and J. Schmidt, "Kinetics of Runaway Reactions," CEP Technical Manual, Loss Prevention, 13 (1980), American Institute of Chemical Engineers, New York, NY. 

The information in this book is concerned primarily with prevention of runaway reactions rather than mitigation effects after such events have occurred. Further, this book covers technical issues and not specifically management techniques. 

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