Runaway reactions protection

Protective measures mitigate the consequences of a runaway reaction. Protective measures are rarely used on their own some preventive measures are usually included to reduce the demand on the protective system. The options for protective measures are ... 

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. 

Improving the capability to detect a runaway reaction and terminate it (by emergency protection) significantly reduces risk. 

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. 

EPA 1999a. How to Prevent Runaway Reactions, Case Study Phenol-Formaldehyde Reaction Hazards. EPA 550-F99-004. U.S. Environmental Protection Agency. August. 

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... 

Pressure resistant construction or equipment protected by pressure relief devices are considered highly reliable where design measures are adopted to prevent unacceptable consequences of a runaway reaction. Design measures, especially the provision of pressure relief, may be appropriate and also required when a complete and reliable evaluation of deviations, their causes and consequences cannot be achieved. This can happen as a result of the complexity of the contributing causal chains. 

The protection principle of pressure relief is based on limiting the pressure to which equipment might be exposed by the removal of gaseous or multi-phase material flows from, in the case of an explosion or a runaway reaction by allowing certain predetermined openings to be opened in such a way that the pressure in the vessel does not exceed a predetermined permitted value. 

Processes susceptible to a runaway reaction during fire exposure shall be protected by water spray systems and fire monitors. 

Where the hazard is an exothermic runaway reaction, there are number, of alternative measures that may be used either to prevent or control runaway. Informatipn on the various options is in Annex 1. In the UK, one of the most commonly selected measures used to protect reactors from exothermic runaway is an emergency relief system. These have a number of advantages ... 

A detailed knowledge of the runaway reaction, in particular the rate of runaway, is needed for the specification or design of protective systems. With the exception of (a), these measures are normally reliant upon control systems to operate, and the... 

The international standard IEC 61511 [2] gives advice on the design of safety instrumented systems (SIS) and presents a layer concept to achieve reliability of protection systems. These principles can be applied to the protection of chemical reactors [3]. Figure 10.3 represents this layer of protection principles. The first layer is the process itself, meaning that it should be designed in such a way that it cannot give rise to a runaway reaction. Some concepts for achieving this objective are reviewed in Section 10.3. 

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. 

The probability of triggering a secondary decomposition reaction may be assessed using the time-scale as defined in Section 3.3.3. The principle is that the longer the time available for taking protective measures, the lower the probability of triggering a runaway reaction. The concept of Time to Maximum Rate (TMRld) was developed for this purpose and is presented in Section 2.5.5. The TMRld under adiabatic conditions is given by... 

For extremely exothermic reactions, emergency quench systems are sometimes used to protect against a runaway reaction. If the reactor temperature exceeds a predetermined maximum safe temperature, the reactor contents are rapidly... 

Extreme fast-acting pressure relief is required Rupture discs can be considered as process pressure protection when there is a potential risk for chemical runaway reactions. Depending on the choice of the SRV (for instance, a non-coded spring-operated valve), there could be a risk that they would... 

V. Tufano. Modeling runaway reactions in reactors protected with suppression systems. Journal of Hazardous Materials, 19 225-236, 1988. 

Consider a process that consists of a reactor used for the processing of a highly unstable chemical that is sensitive to small increases in temperature. The reactor is equipped with a quench tank to protect the system against a runaway reaction and is monitored by two temperature sensors (see Fig. 17) T, and T2. Sensor T, automatically activates the quench tank outlet valve when it detects a temperature rise above the specified upper limit. Sensor T2 sounds an alarm in the control room to alert the operator to the process upset. When the alarm sounds, the operator closes the reactor inlet valve. The operator also pushes a quench tank valve button in the control room in case the quench valve fails to open. Note that A is the reactant B, the product and C, the quench. 

Containment systems are only rarely designed with sufficient pressure and temperature rating to fully contain a runaway reaction. For this reason, overpressure protection is of obvious critical importance as a last line of defense against loss events that can result from runaway reactions. The latter sections in this chapter on Pressure Relief Systems and on Emergency Relief Device Effluent Collection and Handling address design basis selection, relief calculations, and effluent treatment system configurations for reactive system overpressure protection. 

Good processes are safe for the operators, the environment, and the consumer. OSHA has proposed exposure limits for many compounds, and worker safety considerations will only become more stringent with time. An out-of-control, runaway reaction can lead to fatal consequences and to spills and emissions that are injurious to the environment. Environmental emissions standards are posed and regulated by agencies at the federal (EPA), state, and local levels. Green chemistry is becoming more important. The consumer is protected by the effective process controls filed with the FDA, so that the purity and impurity levels of the API are held within specified ranges. 

M HNO3 and TBP enters into a runaway reaction when heated rapidly to 130°C, but not at 125 C. Protective measures recommended to prevent future explosive reactions were to (1) minimize the amount of TBP added to the evaporator (2) permit TBP to steam distiU during evaporation (3) hold the temperature below 130°C until all the TBP has been distilled. 

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