Emergency relief venting

Fauske, H. K, et al, Emergency Relief Vent Sizing for Fire Emergencies Invoking Liquid-Filled Atmospheric Storage Vessels, Plant/Operations Progress, 5 (4), 205-208, October 1986. 

Leung, J. C., Overpressure During Emergency Relief Venting In Bubbly and Churn-Turbulent Regimes, AIChEJ, 33 (6), 952-958, June 1987. 

The task of specifying the design, operation, and control of a reactor with stirrer, heating, or cooling coils, reflux facilities, and emergency relief venting can pose a problem if all the time-dependent parameters are not considered. The use of batch processing techniques in the fine chemical industry is often characterized by ... 

Leung JC (1987) Oveipressure during emergency relief venting in bubbly and churn-turbulent flow. AIChE J 33(6) 952-958... 

In the event of an alarm, an automatic sequence of actions should make the plant safe without the intervention of an operator. The sequence is likely to be simplest for continuous or semi-batch processes typically it may involve no more than stopping the reactant feeds, provided there are no problems with accumulation of reactants. Batch reactors are more difficult, particularly if they contain large amounts of unreacted material and are more likely to require the provision of protective measures such as emergency relief venting, or the provision of dump tanks with drown out facilities. 

Protection of a reactor against runaway chemical reaction by emergency relief venting poses the additional problem of the safe disposal of the resulting relief stream. If the reactor contents or products formed during the runaway reaction are toxic, corrosive, flammable or foul smelling, it is unlikely that venting directly to atmosphere will be acceptable. 

Many emergency relief vents are therefore connected to a disposal system which may include knock-out dmms. quench tanks, flare stacks and scrubbers. The size and capacity of such systems needs to be checked once the relief area has been calculated, particularly where a new reaction is being sited in an existing reactor unit. In addition, consideration has to be given to the possibility of the reaction continuing in the disposal system. 

In the manufacture of a phenol-formaldehyde resin, the temperature was allowed to rise to 341 K. Attempts to control it failed, despite addition of water. Insufficient thought had been given in scaling-up. The lack of emergency relief venting resulted in failure of the vessel. 

Thermal stability testing showed that the reaction mixture could decompose exothermically with self heating occurring on the plant scale from 145°C (the boiling point of the mixture is about 160°C). Decomposition of the reactant mass would lead to a runaway reaction with the generation of a toxic and irritant gas. This would be vented safely, as far as protecting the reactor from overpressure is concerned, by the emergency relief vent, but would cause a serious toxic and corrosive aerosol emission. 

E) The total emergency relief venting capacity for any specific stable liquid may be determined by the following formula ... 

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