An Advanced Method for the Estimation of Reaction Kinetics, Scale-up and Pressure Relief Design

This paper presents an advanced modeling approach which significantly improves predictions of reaction rates and critical data that engineers need to design effective pressure relief systems. Ideally, pressure relief systems are sized exactly for the reaction characteristics of the chemicals in the vessel. However, with many chemicals and chemical mixtures, reaction chemistry is difficult to characterize because the individual components interact in complex ways. 

Furthermore, the high cost and risk of full-scale reactivity experiments make test data scarce. Chemical engineers bridge this gap in part with small-scale tests and modeling computer codes such as the one developed by DIERS. The comprehensive approach developed in this paper provides a reliable design basis for difficult systems, including highly energetic and nonideal reactions, systems with continuing reactions in piping and containment vessels, and systems where homogeneous bubble collapse caused by rapid depressurization could cause a catastrophic vessel failure. We first examine possible mechanisms for catastrophic vessel failure and associated consequences. Next, we outline a detailed approach for emergency relief design and reactivity testing.

Vessel rupture is caused by an increase in the internal energy of the contents and insufficient emergency relief. When a vessel ruptures, the internal energy of the contents provides a source of fragmentation/deformation energy for the shell, kinetic energy imparted to contents and fragments, and blast wave energy. Clearly this process is not reversible as some internal energy will be dissipated as turbulence and heat transferred to the surroundings. Under external heating by fire or internal heating by a runaway reaction or both, the temperature of the tank walls increases, the yield and tensile strength of the vessel walls decrease, and resistance to internal pressure decreases as well.