Hydrocarbon Processing - December 2021 - GP-29

TREATING & NGL
Facility
TABLE 6. Total water contents at the outlet of separators
Sample temperature, o
PS-1 Sample 1
PS-1 Sample 2
PS-1 Sample 3
PS-1 Sample 4
PS-1 Sample 5
47
45
40
46
48
C Solubility (soluble water), ppmw Water content measured by KFT, ppmw Free water content, ppmw
405
371.7
288.4
388.4
421.7
3,000
2,876
339
2,987
1,012
2,594.5
2,504.3
50.6
2,598.6
590.3
FIG. 3. Water solubility curve of GPP-1.
For example, if the sample contains a total water content of
250 ppm at 30°C, then 34.4 ppmw of water will be in the form
of free water and 215.6 ppmw will be in the soluble form. As
shown in FIG. 3, once the temperature rises, the solubility of
the water NGL will also increase, and vice versa. The solubility
limit of water in NGL depends on the temperature-i.e.,
the higher the temperature, the higher the solubility of water
in NGL. FIG. 4 represents the solubility curve of samples from
other sample points.
Sample from downstream of inlet separators. The condensate
from downstream of the inlet separators will contain
a high water content, including free and soluble water. One
sample point was selected for this study at different periods of
time, and the results are summarized in TABLE 6. To calculate
the Cs values, the composition was obtained from gas chromatography
analysis. As shown in the table, total water concentrations
were varied from a few hundred ppmw up to 0.3%. For
illustration, the recorded temperature of Sample 1 is 47°C; at
this temperature, the total water content measured by KFT is
3,000 ppmw. The solubility curve shows that the soluble water
content of this sample will be 405.5 ppmw, and the free water
content will be 2,594.5 ppm.
FIG. 5 shows the solubility curve of the sample from PS-1.
In this sample point, it is recommended to design a facility to
remove the free water by additional cooling upfront so that it
can remove any free water early on.
Recommendations. This study concluded that the solubility
of water in NGL at varying process temperatures can be easily
calculated, based on the NGL composition and the water saturation
values of the pure components present.
The solubility curve can guide engineers in understanding
the importance of improving the existing condensate dehydration
step and the selection of the appropriate technology or
technologies for processing NGL. From the solubility curve, it
FIG. 4. Water solubility curves of samples from GPP-2, GPP-3, GPP-4
and GPP-5.
FIG. 5. Solubility of water in NGL vs. temperature
can be seen that if the plant engineer can maintain a total water
concentration of 10 ppmw or below in processed NGL, then
free water formation at the pipeline will not occur even if the
ambient temperature of the pipeline goes to 0°C. GP
ACKNOWLEDGMENTS
The author would like to express his sincere thanks to SAOO TSD management
for their generous support and encouragement during this work.
LITERATURE CITED
Complete literature cited available online at www.GasProcessingNews.com.
JOSEPH J. PUTHUVELIL works as a Senior Scientist in the
SAOO technical support department of Saudi Aramco and
has been with the company for almost 8 yr. He holds an
MS degree in chemistry and a PhD in environmental science
from Cochin University of Science and Technology (CUSAT)
in India. He has 23 yr of analytical experience in the oil and
gas, power plant, chemical and petrochemical industries.
Dr. Puthuvelil specializes in separation science (i.e., chromatography) and
has worked on analytical investigations of gas and liquids, including water
and solids. He has also given presentations at several national and international
conferences and has published papers in local and international journals.
He is a member of the Society of Petroleum Engineers (SPE).
Gas Processing & LNG | NOVEMBER/DECEMBER 2021 29

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