Worked example of.Relief system sizing for a gassy runaway reaction

6 WORKED EXAMPLE OF RELIEF SYSTEM SIZING FOR A GASSY RUNAWAY REACTION 

A reactor of volume 3.5 m3 has a design pressure of 14 barg. A worst case relief scenario has been identified in which a gassy decomposition reaction occurs. The mass of reactants in the reactor would be 2500 kg. An open cel test has been performed in a DIERS bench-scale apparatus, in which the volume of the gas space in the apparatus was 3,800 ml, and the mass of the sample was 44.8 g. The peak rate of pressure rise was 2,263 N/m2s at. a temperature of 246°C, and the corresponding rate of temperature rise was 144°C/minute. (These values include corrections for thermal inertia.) The pressure in the containment vessel corresponding to the peak rate was 20.2 bara. 

The problem is to evaluate the relief size required. Relief is to be via a bursting disc system with an overall length of 12 metres and two 90° bends with a velocity head 

The peak rate of gas evolution in the reactor can be calculated using an equation from Annex 2  

Ve is the volume of the gas space in the containment vessel, and Tc is the containment vessel temperature. An average has been taken between ambient (20°C) and the maximum test cell temperature of 2460C, i.e. a value of 133°C. The calculation is carried out at the maximum accumulated pressure. Thus  

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