A new peroxide injection system for use in the production of poly olefins was being tested. Six different peroxides were being evaluated for use in the process. An on-site engineering and construction firm retained ioMosaic to complete an evaluation of the peroxide storage vessels to ensure compliance with the PSM standard.
OSHA 29 CFR 1910.119 Process Safety Management (PSM) requires, under the Process Safety Information (PSI) element, that employers compile information pertaining to the equipment in the process including relief system design and design basis.
First, it was desired to determine the minimum set of peroxides to be evaluated to ensure a safe relief system design for the pilot plant facility. With the fewest compounds identified, the adequacy of the existing relief system on a repurposed vessel was to be evaluated. After the adequacy of the pilot plant system was verified, the relief system for the production system was to be designed.
In an effort to minimize the simulations, the six potential peroxides were classified using three methods: adiabatic temperature increase (dTa), adiabatic temperature increase with initial concentration (X0 dTa), and the vent area pressure index (VAP).
The adiabatic temperature increase provides a rule of thumb for the worst case without considering the tempering effects of the solvents, which may be relevant if the solvent is preferentially depleted (resulting in concentrated peroxide). Including the peroxide initial concentration (X0) in the estimate of the theoretical adiabatic temperature increase defines the total energy concentration of the product. The vent area pressure index is calculated based on the concentration at predicted maximum reaction rate, an estimate of the decomposition product molecular weight, and the amount of non-condensable gas created.
For the pilot plant study, the classification eliminated one peroxide from consideration. Of the remaining five peroxides, two were not in the SuperChems™ databanks. Thermophysical properties, including temperature dependent properties were estimated using Cranium™ software by Molecular Knowledge Systems for use in the evaluation.
Runaway reaction kinetics were based on “Pressure Relief Requirements for Organic Peroxides and Other Related Compounds” by Michael A. Grolmes from 1998 DIERS 2nd International Symposium. Reaction stoichiometry was based on minimization of Gibbs free energies with the following potential decomposition products: Acetone, Methane, Ethane, Ethylbenzene, tert-Butanol, and Carbon Dioxide. Meteorological data for the solar heat input for the loss of cooling scenarios was based on historical data from the nearby airport SAMSON data. The solar flux is based on historical data for July 15th with the scenario starting at noon.
Based on the provided P&IDs ioMosaic identified and documented the overpressure scenarios. For each scenario that may result in pressure exceeding the design pressure of the system, ioMosaic quantified the relief system performance. As the runaway reaction, decomposition of various peroxides, was evaluated dynamically, the adequacy of the existing relief system to limit the pressure within ASME code limits was evaluated.
The goal of the classification was to minimize the necessary simulations. Based on the three criterion, it was safe to exclude peroxide number four from the simulations; however, the remaining five compounds are similar enough in their respective indices to warrant evaluation.