(19a) A Practicable Approach to Reactive Pressure-Relief System Design for Multi-Purpose Vessels

Chemical process industry (CPI) companies, particularly toll or contract manufacturing and blending facilities, often utilize vessels and reactors in multiple services that may include runaway reactions. Performing calorimetry testing and sizing relief systems for every potential mode of operation is often unrealistic and costly.

A practicable approach to pressure-relief system design for reactive hazards is a multistep procedure. First, the process information, including the potential chemical inventories, equipment design conditions, and operating conditions, is gathered and structured.

From the identified chemical inventories, the potential reactive chemistry is screened starting with a review of the safety data sheets (SDS) and reference literature including Sax’s Dangerous Properties of Industrial Materials, Bretherick’s Handbook of Reactive Chemical Hazards, the “Process Safety Progress” archives, and the AIChE Design Institute for Emergency Relief Systems (DIERS) online knowledgebase. Chemical incompatibility databases are referenced, and reactivity matrices are constructed from readily available resources (U.S. EPA, NOAA, and Coast Guard, for example). With the potential reactions identified, a review of relevant process safety incidents specific to the chemical inventories is catalogued.

The potential reactivity is then classified according to characteristics such as the calculated adiabatic reaction temperature (CART), the Melhem Index, and the Vent Area Pressure Index. In addition to the severity of the reaction, equilibrium estimates are also performed to identify potentially hazardous reaction products, further potential side reactions, and toxic or flammable compounds that require special effluent handling.

Based on the identified worst-case reactive inventories, a minimum set of calorimetry tests can be performed. From the results of the calorimetry tests, the pressure-relief system requirements are assessed and the vessel, relief-device, and effluent handling system combinations appropriate for a given inventory are identified.

This paper demonstrates applying the multistep procedure to an example slate of organic peroxides in a battery of pressure vessels at a typical toll blending facility.