Finding the key transition states and intermediates controlling net reaction rates and selectivity

In this paper Campbell's degree of rate control is extended to introduce the concepts of degree of kinetic rate control, degree of kinetic selectivity control, degree of thermodynamic rate control and degree of thermodynamic selectivity control. It is demonstrated by applying hypothetical but realistic kinetic models of varying complexity that the new methods offers a rigorous framework to analyze the importance of kinetic and thermodynamic parameters i.e. establishing the critical parameters of the kinetic model. The methods are general and can be applied to complex reaction networks with multiple overall reactions not only in heterogeneous catalysis but for all sorts of chemical kinetic models

On the Adequacy of API 521 Relief-Valve Sizing Method for Gas-Filled Pressure Vessels Exposed to Fire

In this paper, the adequacy of the legacy API 521 guidance on pressure relief valve (PRV) sizing for gas-filled vessels subjected to external fire is investigated. Multiple studies show that in many cases, the installation of a PRV offers little or no protection—therefore provides an unfounded sense of security. Often the vessel wall will be weakened by high temperatures, before the PRV relieving pressure is reached. In this article, a multiparameter study has been performed taking into consideration various vessel sizes, design pressures (implicitly vessel wall thickness), vessel operating pressure, fire type (pool fire or jet fire) by applying the methodology presented in the Scandpower guideline. A transient thermomechanical response analysis has been carried out to accurately determine vessel rupture times. It is demonstrated that only vessels with relatively thick walls, as a result of high design pressures, benefit from the presence of a PRV, while for most cases no appreciable increase in the vessel survival time beyond the onset of relief is observed. For most of the cases studied, vessel rupture will occur before the relieving pressure of the PRV is reached