Containment relief systems

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. 

Large-scale storage containers are usually of metal and equipped with pressure-relief systems. 

Grossel, S. S., Vn Overriew of Equipment for Containment and Disposal of Emergency Relief System Effluents, y(ntrnaZ Loss Prevention Process Industries, (3), 112-124, January 1990. 

A pressure relief system must be designed to protect the beverage bottle from overpressure. The relief device will be installed in the C02 line where it enters the beverage container. 

The reactor system in a pilot plant contains stock tanks that are 24 in in diameter and 36 in high. A relief system must be designed to protect the vessel in the event of fire exposure. The vessel contains a flammable polymer material. What rupture disc diameter is required to relieve the vessel properly Assume a discharge pressure of 10 psig. The molecular weight of the liquid is 162.2, its boiling point is 673°R, the heat of vaporization is 92.4 Btu/lb, and the heat capacity ratio of the vapor is 1.30. 

Containment within the vessel for the credible worst-case scenario reducing the design requirements for the emergency relief system this step is frequently too expensive and impractical in a multipurpose facility. 

The term pressure relief refers to the automatic release of fluids or gases from a system or component to a predetermined level. Pressure relief systems are designed to prevent pressures in equipment or processes reaching levels where rupture or mechanical failure may occur by automatically releasing the material contained within. 

Results for thermal expansion coefficient of liquids are presented for major organic chemicals. The results are especially helpful in the design of relief systems for process equipment containing liquids that are subject to thermal expansion. 

Physical and thermodynamic property data, such as thermal expansion coeffici t, are important in process engineering. The following brief discussion illustrates such importance. Liquids contained in process equipment will expand with an increase in temperature. To accommodate such expansion, it is necessary to design a relief system which will relieve (or vent) the thermally expanding liquid and prevent pressure build-up from the expansion. If provisions are not made for a relief system, the pressure will increase from die diermally expanding liquid. If the pressure increase is excessive, damage to the process equipment vtdll occur. 

Direct scale-up may be used to obtain a relief system size that is less conservative than the DIERS equation. Direct scale-up and its many conditions of applicability are detailed in A5.12. A direct scale-up test is only applicable if the test reactor empties totally by two-phase relief161, and the applicability of the method can therefore only be assessed after the scale-up test has been performed. Direct scale-up may not be feasible if the reacting system contains solids with a particle size similar to or larger than the diameter of the small-scale relief system. 

Many computer simulation codes (see Annex 4 and 7.4.2) allow the option of specifying a bottom relief system. This can be particularly useful if the effects of simultaneous venting from the top of the reactor needs to be assessed, provided that the code selected contains this option. Again, it will usually be safe to assume liquid only flow if dumping occurs well before the maximum rate.. 

The void fraction at the inlet to the relief system will be estimated assuming the reactor contains a homogeneous two-phase mixture. This is consistent with the assumptions of the relief sizing method used. 

It should be noted that "rules of thumb" giving a ratio of the volume of the containment/ disposal system to the volume of the reactor may result in vast undersizing and could lead to overpressurisation of the reactor and relief system during a runaway incident. 

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