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SAFETY
A simple, pragmatic, and comprehensive approach relies on spreadsheets and established procedures to handle complex facilities, and tabulates worst-case data.
Developing a relief system design and its basis is a challenging task and becomes more cumbersome for multiple-process batch reactors. Conducting a complete evaluation for each process can be very time consuming and may seem of minimal value. However, personnel and equipment safety, and U.S. Occupational Safety and Health Administration (OSHA) regulations require complete evaluation and documentation of the relief system design basis (RSDB). Determining an adequate RSDB and documenting it is left to industry, with some broad guidelines set out and reference to AIChE's Design Institute of Emergency Relief Systems (DIERS) technology (1).
This article describes an approach that was applied by a large bulk pharmaceutical manufacturing company in developing an adequate RSDB for a multiple-process reactor. The method is applicable throughout the chemical process industries (CPI). An emphasis was made on the development of a simple, practical, yet thorough program that covers all the aspects of RSDB in an efficient and cost-effective manner, especially for situations such as evaluating and documenting worst-case scenarios, operating parameters (the pressure/temperature envelope) at relieving conditions, backpressure, reaction forces, and determining the flow phase (single- or two-phase).
Setting the relief requirements for two-- phase flow becomes more involved, particularly due to runaway reactions and, hence, may require special expertise. However, ascertaining whether the flow is single- or two-- phase should be fully comprehended by anyone who is involved in an RSDB. Relief system design steps and methodology as per this approach are described in the following. In addition to the DIERS methodology, the American Petroleum Institute's Recommended Practice RP 520 (2) was followed, and computational methods were used from Crowl and Louvar (3), and Creed and Fauske (4).
Developing the program
Commercial emergency-relief-system design programs were evaluated, and they varied in complexity. Simple ones did not have all the options and the more complex were too sophisticated to use in an efficient manner. Moreover, these programs did not provide options to address pertinent information such as worst-case scenarios, backpressure, reaction forces, and relief system evaluations.
We needed to find or develop a simple program that was easy to use, and could collect, calculate, and present...