chemeng_201001-aa2bc0b481-pp

Feature Report Engineering Practice

Pressure Relief Requirement During External Pool-Fire Contingency Santosh Arvind Katkar Jacobs Engineering Group Inc.

A practical overview of the important factors that need to be considered when designing a pressure relief system

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Codes and standards

BACKGROUND

The most important codes, standards and recommended practices that provide basic information on relief system design are as follows: t

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TFMFDtion, and installation of pressurerelieving devices in refineries t

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and installation of pressure-relieving devices in refineries t

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and low-pressure storage tanks t

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relief-system design using DIERS (Design Institute of Emergency Relief System) Technology [2] t

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well as local codes are also used in relief system design. Most process engineers base their relief-system calculations on API standards and recommended practices. Guidelines and equations from these standards are referred to in this article, but no attempt is made to cover each design situation or confirm any design standard or recommended practice.

elief system design is an important engineering activity throughout the chemical process industries (CPI). The main purpose of this task is to design a system that protects process equipment and piping against all possible causes of overpressure. It should relieve the excess pressure safely so as to protect personnel working in the facility from accidents, prevent damage to equipment and adjoining property, and comply with government regulations. The principle causes of overpressure and guidance of plant design to minimize the effect of these causes are discussed in-depth in API STD 521 [1]. Among these causes, the external pool fire is a contingency that is very complex and dynamic in nature. (A pool fire is a turbulent diffusion fire burning above a horizontal pool of vaporizing hydrocarbon fuel where the fuel has zero or low initial momentum.) Although it is very difficult to cover every aspect of this contingency, important aspects are presented in this article for non-reactive systems. Reactive systems are beyond the scope of this article and interested readers should refer to DIERS Methodology [2]. A sample calculation and modeling results using commercial software are also presented at the end of this article.

Relief system design involves enormous efforts by process engineers who need to refer to all major engineering documents [such as process flow diagrams (PFDs), piping and instrumentation diagrams (P&IDs), heat and material balance and layout] as well as applicable codes, practices and standards. Among the tasks involved are the design of pressure relief devices, inlet-outlet piping, knockout drums, flares and vent stacks. 42

Important definitions The definitions of important terms used in this article are as follows: Relieving pressure is the pressure at the inlet of the pressure-relief device during relieving conditions and is equal to the sum of the valve set pressure and the overpressure. Refer UP
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