Multiphase Equilibrium Prediction For Ill-defined Asymmetric Hydrocarbon Mixtures
Figure 3: Experimental and Predicted (Based on Refinery-type Characterisation) Phase Boundaries for Athabasca Vacuum Residue + N-decane Mixtures
A
1,000 1,500 2,000 2,500 3,000
500 0 100 150 C
1,000 1,500 2,000 2,500 3,000 3,500
500 0 100 150 E
1,000 1,500 2,000 2,500 3,000 3,500
500 0 100 150 Experimental L1L2V/L1L2 boundary13 200 250 300 Temperature (ºC) (red dots); experimental L1V/L1 boundary13 (green dots); computed LV/L boundaries (red dashed line). A: 10 wt% athabasca vacuum residue (AVR); B: 20 wt% AVR; C: 30 wt% AVR; D: 40 wt% AVR; E: 70 wt% AVR; F: 90 wt% AVR. 350 400 450 200 250 300 Temperature (ºC) F L LV
1,000 1,500 2,000 2,500 3,000 3,500
500 0 100 150 200 250 300 Temperature (ºC) 350 400 450 350 400 450 200 250 300 Temperature (ºC) D L LV
1,000 1,500 2,000 2,500 3,000 3,500
500 0 100 150 200 250 300 Temperature (ºC) 350 400 450 350 400 450 B L LV
1,000 1,500 2,000 2,500 3,000
500 0 100 150 200 250 300 Temperature (ºC) 350 400 450
L LV
LV LV
L
LV
adaptation that preserves the generality and the integrity of the computed results; recognition of the varied nature and quality of the fluid characterisation and phase behaviour data; minimisation of tuning with fluid-specific phase equilibrium data are all major guiding principles. For example, the sets of values in Tables 1 and 2 reflect two of many possible pseudomolecular representations for the same ill-defined hydrocarbon – AVR. These sets of values were derived from different data and are in turn inputs for stability and flash calculations based on one of many possible equations of state. With diverse inputs and mathematical treatments, diverse outputs are
HYDROCARBON WORLD – VOLUME 6 ISSUE 2
to be expected. Ideally, individual calculation steps should not be viewed in isolation and the number of adjustable parameters should be minimised. Computations should be based on general theoretical principles where parameters, rooted in high-quality data, constrain the number of adjustable parameters used in calculations.
Binary interaction parameters are an illustrative example, as they can introduce large numbers of parameters into phase equilibrium calculations. For a sixteen component mixture there are 120 interaction parameter values. Gao et al.’s10
correlation, Equation 1: 55
Pressure (kPa)
Pressure (kPa)
Pressure (kPa)
Pressure (kPa)
Pressure (kPa)
Pressure (kPa)
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