It's all about chemistry. Exothermic reactions generate heat, which causes the temperature in the vessel to rise. Typically, a reaction rate doubles with every 10° temperature rise. If there is insufficient cooling, these phenomena lead to an exponential increase in temperature and pressure ― an uncontrollable runaway reaction.
The importance of understanding the reaction kinetics cannot be overemphasized. It often means the difference between adequately venting a reaction and an uncontrolled runaway.
Reaction chemistry is challenging because reaction rates are sensitive to temperature, contamination, interactions, and more. For example, ppm levels of contaminant can change the flow behavior of a system from non-foamy to foamy, which has a significant impact on the size of the required relief device. Furthermore, it can catalyze the reaction, or react with materials present to form a catalyst that can greatly accelerate reaction rates. These catalysts can also lower the temperature at which the reaction rates become significant, which can make an otherwise non-credible runaway reaction become credible.
Because of the complexity of the reaction dynamics and the reaction rate's dependence on temperature and concentration, it is rarely possible to design a proper relief system involving runaway reaction without dynamic simulation tools and/or adiabatic calorimetry testing.
Adiabatic calorimetry is an important tool that is widely used to quantify and understand the potential hazards of runaway reactions under adiabatic conditions. The Accelerating Rate Calorimeter (ARC) and Automatic Pressure Tracking Adiabatic Calorimeter (APTAC) by TIAX, LLC, and EuroARC from Thermal Hazard Technology are used by many companies and ERS consultants around the world to collect thermo-kinetic data under near-adiabatic conditions required to size relief devices for reactive systems. The Reaction Calorimeter (RC1) from Mettler-Toledo is also used (with caution) to obtain heats of reaction data and to simulate actual reaction processes on a 1-L scale. Vent sizing instruments, such as the Advanced Reactive Systems Screening Tool (ARSST) and the Vent Sizing Package (VSP2) from Fauske and Associates, Inc. and PHI-TEC from Hazard Evaluation Laboratories (HEL), are also useful.
Managing the safe handling of reactive chemicals depends on a thorough understanding and evaluation of chemical reactivity hazards and thermokinetics. ioKinetic’s approach includes a combination of experimental and theoretical methods. Experimental methods may include small- and/or large-scale testing, while theoretical methods involve the application of both short-cut methodologies or dynamic simulation, chosen based on the complexity of the system. Our multi-faceted approach has been applied to all areas of chemical reactivity hazard management, including pressure relief and flare system (PRFS) design.
Our professionals at ioKinetic conducted thermal hazard analysis and emergency relief device sizing for a 7-L pressure vessel owned by a chemical firm in the United States. The analysis involved multiple Accelerating Rate Calorimeter (ARC) tests to define the worst-case scenario for further use in the sizing calculation. By performing the ARC tests, we were able to understand the potential unwanted side reactions such as polymerizations and decompositions. The subsequent emergency relief sizing calculation involved the simulation of these undesired reactions, allowing the specification of the proper vent sizing for the reactive cases.
Specialists at ioKinetic conducted thermal hazard analysis and ERS device sizing of a polymerization reactor for a specialty chemical company in the United States. Using ARC tests, the published effect of oxygen on polyvinyl acetate stability was confirmed. Our experts analyzed the thermal hazards of the system using ARC data, developed a kinetic model, and completed the PRFS design including the blowdown calculations. The results indicated that thermal polymerization provides sample heat to trigger the polymer decomposition reaction, which is the main pressure generator. We were able to determine that the pressure generation rate becomes so fast at higher temperatures that the pressure cannot be controlled by a vent of any practical size. We recommended a relief strategy involving a reliable temperature-activated ERS and additional investigation of relief discharge handling.
The team at ioKinetic includes recognized experts who have written guidelines followed by industry, given expert testimony experience, participated in academic and industry partnerships, and consulted for major oil, gas and petrochemical manufacturers worldwide. Have a particular question on chemical reactivity? Contact the ioKinetic team online or call us at 1-844-ioKinetic today.
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