Page 322 - Characterization and Properties of Petroleum Fractions - M.R. Riazi

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302 CHARACTERIZATION AND PROPERTIES OF PETROLEUM FRACTIONS

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FIG. 7.2—Effect of pressure on the liquid density at 60 F (15.5 C). Unit conver-
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3
3
sion: ρ [g/cm ] = ρ [lb/ft ]/62.4; F = ( C) × 1.8 + 32; psia = bar × 14.504. Taken
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with permission from Ref. [8].
to specific volume (V s = 1/ρ)as For example, Eq. (2.111) can be used to estimate density at
temperature T from SG. The general formula for calculation
1 x wi
(7.4) = of d T (density at T and 1 atm) from known density at a refer-
ρ mix ρ i ence temperature T o can be derived from Eq. (2.110) as
i
3 −3
where ρ mix is the mixture liquid density (i.e., g/cm ) and x wi (7.5) d T = d T o − 10 × (2.34 − 1.9d T o ) × (T − T o )
is weight fraction of component i in the liquid mixture. ρ i
should be known from database, experiment, or may be cal- where both T and T o are in kelvin or in C and d T and d T o
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3
culated from Rackett equation. Equation (7.4) can be applied are in g/cm . This method provides reliable density values at
to specific gravity but not to molar density. This equation is temperatures near the reference temperature at which density
particularly useful for calculation of specific gravity and den- is known (when T is near T o ). When the actual temperature is
sity of crude oils with known composition at atmospheric far from the reference temperature, this equation should be
pressure, as it is shown later in this chapter. used with caution.
When only a minimum of one data point for liquid density For quick density calculations several graphical methods
of a petroleum fraction at atmospheric pressure is known (i.e., have been developed, which are less accurate than the meth-
SG, d 20 ,or d 25 ), then Eq. (2.110) may be used to calculate liq- ods outlined above. Graphical methods for liquid density cal-
uid density at atmospheric pressure and other temperatures. culations recommended by GPA [8] are shown in Figs. 7.1–7.3.

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