Hydrocarbon Processing - December 2021 - GP-28

TREATING & NGL
TABLE 3. Water saturation value calculation for GPP-1
Component
Methane
Ethane
propane
isobutane
n-butane
iso-pentane
n-pentane
Hexane
Heptane
Octane
Nonane
Decane
Total
Volume,
%
1.28
60.04
24.45
3.75
6.84
2.14
1.24
0.17
0.09
100
Volume
fraction
0.01
0.6
0.24
0.04
0.07
0.02
0.01
1
Molecular
weight,
g/mol
16.04
30.07
44.097
58.124
58.124
72.151
72.151
86.178
100.205
114.232
128.259
142.286
Volume
fraction,
mol wt
0.21
18.05
10.78
2.18
3.98
1.54
0.89
0.15
0.09
37.87
Weight
fraction
0.005
0.476
0.284
0.057
0.105
0.041
0.024
0.004
0.002
1
0°C
14.8
15.9
1.4
2.1
1.3
0.7
0.1
0.1
36.4
TABLE 4. Water saturation value (ppmw) of NGL samples at various locations
0°C
10°C
Temperature
GPP-1
GPP-2
GPP-3
GPP-4
GPP-5
GPP-6
36.39
38.59
36.63
35.79
37.72
41.07
TABLE 5. Water saturation value by KFT
Sample point
GPP-3, Sample-1
GPP-3, Sample-2
GPP-3, Sample-3
GPP-3, Sample-4
Sample temperature, o
22
25
28
32
are given in TABLE 1. Énglin et al.21
67.05
64.67
61.78
67.74
69.18
69.02
20°C
122.28
108.66
104.46
126.13
125.62
116.05
10°C
0.1
30.9
26.4
2.4
3.6
2.2
1.2
0.2
0.1
67
Average Cs value
20°C
0.2
61.9
43.8
4.1
6.3
3.7
1.9
0.4
0.2
122.3
30°C
0.4
119
68.2
6.9
10.9
6.3
3.2
0.7
0.4
215.6
40°C
0.7
190.4
109.4
11.6
19.4
10.6
5.3
1.2
0.7
348.7
50°C
1.1
285.6
164.9
19.5
32.
17.7
8.9
2.2
1.1
531.9
30°C
40°C
Water saturation values Cs, ppmw
215.62
175.72
171.22
226.76
220.11
187.7
348.69
290.93
286.4
365.3
355.49
310.50
C Water content, ppmw
117.4 ± 0.8
137.7 ± 1.3
158.2 ± 1.5
194.8 ± 1.8
have tabulated water solubilities
in wt% for a number of hydrocarbons at 10°C intervals
between 0°C and 50°C. For this study, we selected only water
saturation values of pure components (i.e., methane, ethane,
propane, i-butane, n-butane, i-pentane, n-pentane, etc.), that
are present in NGL at various temperatures (TABLE 2). To
calculate the solubility of water in NGL, the water saturation
values of pure components are multiplied with the weight fraction
of the components in NGL.
NGL water saturation value calculation. For a mixture
of organic liquids like NGL, an average saturation value is calculated
from the weight fractions and saturation values of the
pure components by using Eq. 1:
Average Cs = ∑n
where:
28 NOVEMBER/DECEMBER 2021 | GasProcessingNews.com
i = 0 Xi(Cs)i
(1)
Xi = Weight fraction of the ith component
(Cs)i = The saturation concentration (ppmw)
of the ith component
n = The total number of components.
TABLE 3 illustrates the steps followed to calculate average
saturation values for each component of NGL sampled from
the sample point GPP-1. TABLE 4 summarizes the water saturation
value of NGL sampled from various locations.
Water in NGL may exist under different forms, such as dissolved,
emulsified or free water state. Once the water content
increases above its solubility limit, then emulsified or free water
will appear in the NGL. FIG. 3 shows the water solubility
curve of NGL sampled from the facility GPP-1, containing
1.28% of CH4
3.75% of i-C4
plus 60.04% of C2
plus 1.24% of C5
H6 plus 24.45% of C3
H10 plus 6.84% of n-C4
H12 plus 0.17% of n-C6
H10 plus 2.14% of C5
H8 plus
H12
H14 plus 0.09% of nC7H16
with temperature ranges from 0°C to 50°C. In the region
below the curve (Cs line), the soluble water alone can exist;
above the line, both free water and soluble water can co-exist.
As shown in FIG. 3, once the water content of the sample
increases above its solubility limit, the free water will appear
along with NGL. FIG. 3 shows that the solubility of water
in NGL at 30°C is 215.6 ppmw. If the total water content
rises above this value (at 30°C), then free water formation
will occur.
50°C
531.85
459.15
460.53
553.61
540.46
491.88
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