Measurement and Calculation of Surface Tension of Oil, Gas and Glycol
The importance of surface tension in separation design was evaluated in this report.
Surface tension was found to have importance when calculating essential
design parameters, like droplet size, which is is fundamental in several vessel design
operations. Other impacts of surface tension in separation are the ability to
sustain a liquid film and avoid droplet re-entrainment into the gas flow, both being
discussed in the report. Miscalculation of surface tension could lead to incorrect
sizing of separation equipment, subsequently causing expensive fault in operation
and decreased separation effect.
The main objective of this thesis was to experimentally measure surface tension
with the pendant drop technique. Although surface tension was the main task,
density and solubility data were also collected and evaluated, as they too are
important parameters in separator design. The measurements were carried out
on MEG/water systems because of low availability of such data in the literature.
The deviation of the surface tension measurements was calculated on the basis of
recommendations from ISO, and the total average deviation for all mixtures was
stated to be 2.00%.
The second objective was to evaluate models for the calculation of surface tension
in process simulation software. The simulation tools PRO/II, HYSYS, PVTSim
and NeqSim were used for calculation. PRO/II and HYSYS use simple models that
are based on pure component values. PVTsim utilizes the well-known parachor
method when simulating hydrocarbon systems, while for MEG/water systems it
uses a model based on the corresponding state theory. NeqSim uses the most complicated
and computational demanding model, the gradient theory, which is based
on thermodynamics. Some of the software have additional models implemented,
but in this thesis the default models have been used.
The MEG/water and hydrocarbon systems were simulated in the software, and
thereafter compared against the experimental data.
The results of the comparison regarding hydrocarbon systems showed two distinct
tendencies. Firstly, the performance of PRO/II and HYSYS was not adequate.
They both were, with a few exceptions, overestimating the surface tension for all
mixtures. Second, even though the performance of both PVTsim and NeqSim
could be termed satisfactory, NeqSim was superior to the estimations of PVTsim
throughout most of the experimental data. The only exception was for the ternary
systems, on which the base of surface tension data was rather insufficient.
The results of the comparison regarding glycol systems showed that all software
overestimate the surface tension. NeqSim was once again the software with the
best accuracy, and the CPA equation of state was the overall preferred choice. In
contrast to hydrocarbon mixtures PVTsim now has a large discrepancy throughout.
However, the accuracy improved drastically for the 50 wt% MEG/50 wt%
water mixture. PRO/II and HYSYS performed better than they did on hydrocarbon
mixtures, especially for the 100wt%MEG mixture. However, as water was
added to the composition, PRO/IIs deviation increased substantially.
Place, publisher, year, edition, pages
Institutt for energi- og prosessteknikk , 2014. , 152 p.
IdentifiersURN: urn:nbn:no:ntnu:diva-26343Local ID: ntnudaim:11052OAI: oai:DiVA.org:ntnu-26343DiVA: diva2:746608
Solbraa, Even, Professor II