VOLUME PERCENT VAPORIZED Figure 2.1. TBP and EFV Curves for a typical crude oil and product yield by volume.
intermediate fractions. These procedures were developed by the American Society for Testing Materials and are called ASTM distillations. These methods are rapid batch distillations employing no trays or reflux between the stillpot and the condenser. The only reflux available is that generated by heat losses from the apparatus. These test methods are used in control laboratories throughout the world.
The third type of laboratory distillation which is used in discussing petroleum fractionation is the equilibrium flash vaporization (distillation) commonly called the EFV. The procedure is also discussed in Chapter 4 of Nelson. This distillation can be run at pressures above atmospheric as well as under vacuum, whereas the TBP and ASTM distillations are run either at atmospheric pressure or under vacuum. EFV curves are seldom run because of the time and expense involved and are almost exclusively limited either to crude oil or to reduced crude samples (atmospher ic tower bottoms liquid) which are being evaluated as vacuum tower charge stocks. The EFV initial boiling point is the bubble point of the fraction under study, and the EFV final boiling point is its dew point. If desired, a family of EFV curves can be run at a series of pressures encompassing the envisioned operating pressure. This will allow a more accurate estimate of phase behavior thai,can be attained from calculations.
The purpose for running these various distillations is to characterize the composition of the material under study, and, for this reason, the boiling range of petroleum liquids is of primary importance. For example, kerosene will have an ASTM boiling range of approximately 325 to 525 degrees F which corresponds to a TBP boiling range on the order of 275 to 575 degrees F. While the latter is theoretically indicative of actual composition, the former is the one used by both designers and operators in discussing distilla
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