Relief discharges

M. Kneale, The Safe Disposal of Relief Discharges, Selection Use of Pressure Relief Systems for Process Plants, Institution of Chemical Engineers North Western Branch, Manchester. UK, 1989, Paper 7. 

First and foremost these venting ducts should be as straight as possible, with few, if any elbows, and even these should be sw eeping bends. There should be no valves of any type to keep flow resistance as low as possible, as this creates friction that creates backpressure on the relief de ice and raises burst conditions, which can be terribly dangerous. Figure 7-66 and 7-67 are used to assess the increased pressure due to ducts on relief discharge as affected by duct length. (This data is limited. See Ref. [56 and 53].)... 

Types of Equipment Equipment for handling emergency relief discharge streams can be divided into two classes ... 

Sparger piping to be supported to control vibration and the suddenly applied load from the relief discharge. 

Emergency Scrubbers (Absorbers) Emergency relief discharges are often passed through scrubbers (also called absorbers, or absorption columns or towers) for removal of flammable, corrosive, or toxic chemicals. The removal mechanism in some scrubbers involves physical absorption in a solvent, whereas in others chemical absorption (reactive scrubbing) is required. 

A G Keiter, "Emergency Pressure Relief Discharge Control by Passive Quenching", International Symposium on Runaway Reactions, 425-450, AlChE, 1989, ISBN 0-8169-0460-X... 

Figure 9.4 Techniques for reducing distillation relief discharges. See text for explanation.

The main disadvantage of this technique is that in many cases (particularly with wide-boiling mixtures), its effectiveness in reducing relief discharge rate may be limited. This technique can also be expensive when column pressure exceeds 100 to 150 psig. 

Providing secondary relief at a lower pressure A relief device is usually sized to accommodate the failure that is expected to generate the largest relief discharge rate. This failure may rarely occur, and even when it does, quick operator intervention may reduce the discharge rate. However, once the relief device is sized for this failure, it will discharge this flow rate each time it opens. 

X 100 ft distillation column Column relirf requirement was based on failure of Ibe steam flow controller. The rdief requirmnent was more than halved by adding a restriction orifice in the steam supply line. A method for reducing relief discharge requirements. 

Pressure relief discharges but with different threshold quantities. 

Burgoyne, J.H., 1987, Review paper safe disposal of relief discharges. Hazards from Pressure, Symposium Series No. 102. 201-214 (IChemE. Rugby. UK). 

Process instrumentation for the overpressurization protection equipment that is associated with the Reactor Coolant System is shown in Figure 5.1.2-1 and described in Chapter 7. Instrumentation associated with pressurizer relief discharge is described in Section 5.4.11. 

Relief discharge piping adequately supported and drained... 

Vent/relief discharges - treatment/containment/recovery E... 

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