Runaway prevention

Strozzi, F., Zaldivar, J.M., Kronberg, A. and Westerterp, K.R. (1997) Runaway prevention in chemical reactors using chaos theory techniques. American Institution of Chemical Engineers Journal, 45, 2394-408. 

Westerterp, K.R. (2006) Safety and runaway prevention in batch and semibatch reactors-a review. Chemical Engineering Research and Design, 84 (A7), 543-52. 

This would give a tube diameter dt = 0.14 m, whereas our selectivity requirement asks for a tube diameter < 0.06 m. Although the one-dimensional pseudo-homogeneous model is no more valid for dt = 0.14 m, this proves that maintaining the selectivity asks for much smaller tube diameters than the runaway prevention. 

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. 

The above statement is obvious. Almost as evident is the statement that since heat generation rate increases with temperature, heat removal rate should increase even faster. This would eliminate continued temperature increase and prevent temperature runaways. 

Prevent runaway of the string in the case of a generator load loss. The large amount of available energy upstream of the expander must be dissipated. 

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. 

Similar approaches are applicable in the chemical industry. For example, maleic anhydride is manufactured by partial oxidation of benzene in a fixed catalyst bed tubular reactor. There is a potential for extremely high temperatures due to thermal runaway if feed ratios are not maintained within safe limits. Catalyst geometry, heat capacity, and partial catalyst deactivation have been used to create a self-regulatory mechanism to prevent excessive temperature (Raghaven, 1992). 

Raghaven, K. V. (1992). Temperature Runaway in Fixed Bed Reactors Online and Offline Checks for Intrinsic Safety. Journal of Loss Prevention in the Process Industries 5, 3,153-59. 

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. 

Inhibitors are usually added to butadiene and acrolein to prevent polymerization, but the system is not foolproof. Several runaways have occurred in tank trucks or tank cars containing acrolein. As it cooled, some of the liquid crystallized, leaving the inhibitor in solution. In other cases impurities have been left behind in the bulk liquid, and their concentration has risen sufficiently to start a runaway. 

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

Fauske, H. K, Relief System Design for Runaway Chemical Reactions, CCPS International Symposium On Preventing Major Chemical Accidents, Washington, DC, February 3-5, 1987. 

The system can prevent explosion, fire, and venting with fire under conditions of abuse. These batteries have a unique battery chemistry based on LiAsF6/l,3-di-oxolane/tributylamine electrolyte solutions which provide internal safety mechanism that protect the batteries from short-circuit, overcharge and thermal runaway upon heating to 135 °C. This behavior is due to the fact that the electrolyte solution is stable at low-to-medium temperatures but polymerizes at a temperature over 125 °C... 

UL also requires overcharge testing. Here the PTC may not be activated by the low currents used in charging and thermal runaway might be prevented by fusing of the separator [5]. 

Equation (8.29) provides no guarantee of stability. It is a necessary condition for stability that is imposed by the discretization scheme. Practical experience indicates that it is usually a sufficient condition as well, but exceptions exist when reaction rates (or heat-generation rates) become very high, as in regions near thermal runaway. There is a second, physical stability criterion that prevents excessively large changes in concentration or temperature. For example. An, the calculated change in the concentration of a component that is consumed by the reaction, must be smaller than a itself Thus, there are two stability conditions imposed on Az numerical stability and physical stability. Violations of either stability criterion are usually easy to detect. The calculation blows up. Example 8.8 shows what happens when the numerical stability limit is violated. 

Control systems can fail in many ways, and highly energetic reactions like the styrene polymerization in Examples 5.7 and 14.8 raise major safety concerns. The contents of the vessel are similar to napalm. Discuss ways of preventing accidents or of mitigating the effects of accidents. Is there one best method for avoiding a disastrous runaway ... 

Proceedings of Conference Technical for the Control and Prevention of Runaway Chemical Reaction Hazards, London Dec. 1987. 

---