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Adiabatic Calorimetry: A Must for Linking Laboratory Data and Plant Scaleup

A presentation delivered at the 1998 Process Plant Safety Symposium in Houston, TX. Read more

An Advanced Method for the Estimation of Reaction Stoichiometry and Rates from ARC Data

Effect design of emergency relief systems requires accurate modeling. In particular, the PVT relation of such systems is fundamental and unique. This relation must be accurately represented during direct scale-up or computerized simulation. Variables which can significantly alter the PVT behavior of a system should be quantified, and included in the design. The pressure/temperature (PT) relation is a function of thermal inertia, liquid fill level (vessel void fraction), composition and chemical identity (vapor-liquid equilibrium, liquid/vapor density, heat of formation, etc). For a specified relief device set pressure, there is a unique corresponding system temperature. For reactive systems, this temperature corresponds to a reaction state. Small errors in estimating this temperature can lead to inadequate sizing and potential catastrophic vessel failure. Estimation of fluid flow rates and their associated energy depletion rates is a strong function of chemical identity. Often, simple reaction models are used which ignore this fact. If the reaction model only fits the observed constant PVT relation nd PT time histories, it will yield inaccurate predictions. The model may assume, for example, that the reaction products are made of a heavy and a light component. It may also specify a heat of reaction independently. However, these assumptions are often thermodynamically inconsistent and do not guarantee a unique solution, i.e., the chemical identities of the products are not unique. As a result, the estimated flow rates are often in error. This paper presents a method that guarantees a thermodynamically consistent and unique solution. Read more

Butadiene Thermal DimerizationTrimerization, Free-Radical Polymerization, and Polymer Decomposition Reactions

1,3-butadiene monomer undergoes thermally initiated, reversible dimerization/trimerization reactions with essentially the same kinetics in both the gaseous and liquid phases. Kinetics for formation of the dimer and the trimer are available from the open literature. The rate of reaction becomes significant (0.02°C/min = 29°C/day) at temperatures above 70-80°C. Inhibitors (t-butylcatechol, et al.) are used to prevent/minimize free-radical polymerization reactions in the liquid phase and to maintain product quality at ambient or subambient temperatures. These inhibitors do not prevent dimerization/trimerization reactions. Unless adequate emergency relief is provided, emergency relief is provided, the adiabatic temperature rise from the dimerization/trimerization reactions can lead to both a free-radical polymerization, initiated by adventitious peroxides, and a thermal decomposition of the resultant polymer to produce residues, volatiles, and not condensable gases. Temperatures of 600°C and pressures of over 2,000 psig are possible. Heat rates of 10,000°C/min pressure rise rates of 10,000 psig/min are also possible in unvented/undervented vessels. Emergency relief devices protecting vessels containing high concentrations of 1,3-butadiene should be reviewed to identify potentially reactive cases. This review is recommended to ensure that current that current emergency relief system designs are adequate and that equipment is being operated with an adequate margin safety. Read more

CEP Sizing Relief Systems for High Viscosity Two-Phase Flow

High viscosity two-phase (HVTP) flow occurs in many industrial scale reactors, particularly when runaway reactions (e.g. during polymerizations) are vented through an emergency relief system. The design of a relief system for two-phase discharge can be complicated, as it involves a fluid with a liquid-like density and a gas-like compressibility. This paper will help you qualify your design methods for high-viscosity two-phase relief systems against these simple benchmarks. Read more

Chemical Reactivity Data in PSM and RAGAGEP

Chemical reactivity is addressed throughout OSHA’s PSM Standard. A chemical reactivity hazard is a situation with the potential for an uncontrolled chemical reaction: Temperature increase, pressure increase, gas evolution. Chemical reactivity incidents can be initiated by various process upsets: Unintentional interaction, self-reactivity, accumulation of reactants, loss of cooling, catalyst mischarge, fire. The first step is understanding where a chemical reactivity hazard might exist. Read more

Combustible Dust: What You Should Know About NFPA 652

NFPA 652: Standard on the Fundamentals of Combustible Dust, 2016 Edition became effective on September 7, 2015. NFPA 652 is intended to provide the minimum requirements for managing fire, flash fire, and explosion hazards associated with combustible dusts. After establishing the minimum requirements for combustible dust in general, the standard then refers to other NFPA standards that may be required based on the specific dust you're handling in your plant. Read more