PHYSICAL PROPERTIES OF HYDROCARBON e SYSTEMS A reliable estimate of physical properties is required in order to obtain reliable calculations.. Tables 3.1 and 3.2 are examples of such d
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e
SYSTEMS
A reliable estimate of physical properties is required in order to obtain reliable calculations For single component systems data are readily available Tables 3.1 and 3.2 are examples of such data that will be used for calculations References 3.1-3.3 may be used to estimate properties of pure paraf- fins heavier than decane
Note: Table 3.2 is in two parts Table 3.2(a) is in SI units and Table 3.2(b) is in FPS units This is the system used throughout this book when corresponding tables and figures are shown in sepa- rate units
TABLE 3.1 Physical Constants
ncs
nC9
nC1o
n c l l nC12 N2
c o 2 H2S
0 2 H2
- 3 0 -
=.- -
-Molecular Weight
16.043 30.070 44.097 58.124 58.124 72.151 72.151 86.178 100.205 114.232 128.259 142.286 156.302 170.338
-
28.016 44.010 34.076 32.000 2.016
1 8.015-
Acentric Factor - o
0.0104 0.0979 0.1522 0.1852 0.1995 0.2280 0.2514 0.2994 0.3494 0.3977 0.4445 0.4898 0.5350 0.5620
- -
0.0372 0.2667 0.0948 0.02 16 -0.2202
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.5
Nonideal P-V-T Equations
A large number of P-V-T equations have been developed to describe nonideal, real gas behav- ior Each is empirical in that it correlates a specific set of data using one, or more, empirical constants There can be as many such equations as there are people who correlate data Some of the most com- mon equations are summarized below The inclusion, or exclusion, of an equation is not a reflection of the worth of an equation It merely reflects degree of recognition in this industry
van der Waals
Where: a & b = correlation constants
Equations 3.2, 3.4 and 3.5 are called cubic equations of state because they are cubic when writ- ,ten in terms of volume The constants a and b are a hnction of the critical properties T, and PC and a third parameter, usually the acentric factor, a For mixtures, mixing rules are necessary to determine the values of a and b Mixing rules will be discussed briefly in a later section
A number of nlodifications to these equations of state have been published and are used in the oil and gas industry The purpose of the nlodifications is to improve the validity of the model Exam- ples include the Soave modification to the RK equation (SRK) and the Starling modification to the BWR equation (BWRS)
The above equations are used primarily as a basis for computer solutions They tend to offer more precision, but the real accuracy of the results may be no better than the simpler methods when
actual systems