Swelling, calculation

The method uses the dnft-fhix level swell calculation models to take into account there being more vapor in the inlet stream to relief device than average for the vessel. 

Further information on level swell calculations and the determination of vessel flow regimes is given in Annex 3. 

A description of level swell is gjjven in 4.3.1. Level swell calculations do not apply to inherently foamy systems as these always vent a homogeneous two-phase mixture. 

Calculation methods are given here for cases (a) to (c). In section A3.4 below, references are given to a calculation method for case (d). The level swell calculation methods presented here use the drift flux correlations developed by DIERS[11. The DIERS correlations apply to a vertical cylindrical vessel, which is most often the case for chemical reactors. Modifications for horizontal cylindrical vessels are given by Sheppard[2,3]. 

Where it is uncertain whether thle system is inherently foamy, it is recommended that the worst case assumption is used (see 4.3.2(1)). For tempered systems, the worst case will be inherent foaminessl Where tempered systems are not inherently foamy, the level swell calculations described in this Annex may lead to a reduction in calculated relief system size. For untempered systems, the worst case is vapour/ liquid disengagement causing reduced mass loss from the reactor during relief. In this case, dynamic simulation (see A3.4) may be needed to take account of level swell in relief sizing. 

The different flow regimes during level swell (churn-turbulent, bubbly and droplet) were described in 4.3.1. In order to perform a level swell calculation, it is necessary to decide the flow regime. 

Figure A3.2 illustrates terminology used in level swell calculations. Annex 10 gives...

WORKBOOK FOR CHEMICAL REACTOR RELIEF SYSTEM SIZING Figure A3.2 DEFINITION OF TERMS IN LEVEL SWELL CALCULATIONS... 

In order to use the sizing method, the reactor, void fraction, aD, at which total vapour/ liquid disengagement is expected at the maximum accumulated pressure, must first be evaluated. This may be done by level swell calculation (see Annex 3) or by small-scale experiment with the same vapour superficial velocity as will occur at plant-scale (see Annex 2). Equation (A5.7)can then be used to find the relief area ... 

The void fraction at disengagement has been estimated by level swell calculation (not shown here) as 0.9. 

Before using the method, the void fraction at disengagement must be evaluated at conditions corresponding to the maximum accumulated pressure during relief. This can be done by level swell calculation (see A3.3) or possibly by a small-scale experiment that uses depressurisation to achieve the same vapour superficial velocity as in the full-scale reactor during relief (see Annex 2). The required relief rate can then be calculated fromt31 ... 

This example is also used as a worked example for level swell calculations in A3.3.6. A reactor of volume 3.6 m3 contains 2610 kg of reactants under worst case runaway conditions. The relief pressure is 5.5 bara and the maximum accumulated pressure is 7.0 bara. 

A level swell calculation (see A3.3.6) indicates that disengagement will occur at the maximum accumulated pressure at a void fraction of 0.271. 

FIGURE 9.8 Concentrations inside droplets after osmotic swelling calculated by solving Equation 9.16 for 5, using the interface tension from Figure 9.3. The radius of the droplets prior to swelling was 10 pm and the phase volume fraction of the droplet phase was 0.5. 

Understanding the thermophysical and thermodynamic properties of polymer/gas mixtures is critical for controlling cellular morphology. This paper describes measurements of pure polypropylene (PP) density and PP/CO2 volume swelling at elevated temperatures and pressures using a newly developed method. Also, measured volume swelling is compared with the swelling calculated from SL and SS EOS. 

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