Relief system design

Figure 3.3 shows the typical behaviour of both tempered and untempered systems during relief, with a properly designed relief system. The information that is required for the purposes of relief systerrrdesign will depend upon how the system pressure is generated and whether or not the system is tempered. 

Properly designed relief systems, taking into account two phase flow and reactions if appropriate... 

Once the process route has been chosen, it may be possible to synthesize flowsheets that do not require large inventories of materials in the process. The design of the reaction and separation system is particularly important in this respect, but heat transfer, storage, and pressure relief systems are also important. 

Designers of emergency pressure relief systems should be famihar with the fohowing hst of regulations, codes of practice, and industiy standards and guidehnes. 

DIERS. 1992. Emergency Relief System Design Using DIERS Technology, DIERS Project Manual. American Institute of Chemical Engineers, New York. 

Water addition to vessels that have been steam-purged If vacuum conditions can develop, then either the equipment must be designed for vacuum conditions or a vacuum relief system must be instiled. 

Since discharges of vapors from highly hazardous toxic materials cannot simply be released to the atmosphere, the use of a weak seam roof is not normally acceptable. It is best that tanks be designed and stamped for 15 psig to provide maximum safety, and pressure relief systems must be provided to vent to equipment that can collect, contain, and treat the effluent. 

Unwanted reaction Clean and inspect equipment after each use Design with compatible materials contaminants. Maintain integrity of the system Design emergency relief system (ERS) for runaway scenario CCPS G-13 CCPS G-22 CCPS G-23 CCPS G-29... 

Wilday, A.J. 1991. The Safe Design of Chemical Plants with No Need for Pressure Relief Systems. Elazards IX—New Directions in Process Safety. IChemE Symposium Series. No. 124, pp. 243-253. Institute of Chemical Engineers, IChemE, Rugby, U.K. 

Design Institute for Emergeney Relief Systems (DIERS) Institute under the auspices of the American Institute of Chemical Engineers founded to study relief requirements for reactive chemical systems and two-phase flow systems. 

DIERS Design Institute for Emergency Relief Systems... 

The maximum pressure from an explosion of a hydrocarbon and air is 7 x initial pressure, unless it occurs in a long pipe where a standing wave can be set up. It may be cheaper to design some small vessels to withstand an explosion than to provide a safety relief system. It is typical to specify %" as minimum plate thickness (for carbon steel only). 

Rearick, How to Design Pressure Relief Systems, Parts I and II, Hydrocarbon Processing, August/ September 1969. 

Many columns have water removal trays designed into the column. Top or bottom temperatures may have to be changed to expel the water if the column isn t provided with water removal trays. In some instances, the water can be expelled by venting the column through the safety relief system. 

In applying this rule, the capacity of the pressure relief system must also be sized to handle the quantity of fluid released at this pressure (together with other expected loads during this contingency), so that the built-up back pressure will not result in exceeding 1.5 times the design pressure. This additional load need not, however, be considered in calculations of flare and PR valve radiant heat levels. 

Liquid Drainage from Closed Relief System - Accumulation of liquid in closed rehef systems can impose appreciable back pressure and reduce relieving capacity. The following design features must be included to avoid these problems ... 

Design of the relief system including discharge ducting and safe discharge area... 

Design Institute for Emergency Relief Systems (DIERS) Institute under the auspiees of the Ameriean Institute of Chemieal Engineers funded to investigate design requirements for vent lines in the ease of two-phase venting. 

Fisher, H., et ah, Emergeney Relief System Design Using DIERS Teehnology, AIChE s Design Institute for Emergeney Relief Systems, DIERS, AIChE, New York, 1992. 

Fisher, H. G., An Overview of Emergeney Relief System Design Praetiee, Plant/Operations, Prog., 10 (1), pp. 1-12, January 1991. 

Fauske, H. K., Emergeney Relief System Design for Runaway Chemieal Reaetion Extension of the DIERs Methodology, Chem. Eng. Res. Des., Vol. 67, pp. 199-202, 1989. 

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