April 2015 Gas Processors Association (GPA) Conference in San Antonio
Thanks to everyone that stopped by our hospitality suite at GPA 2015. The cryogenic cocktails derived from a liquid nitrogen process where the ingredients are frozen at -321 F were a big hit. We hope you enjoyed your time with us we certainly enjoyed seeing friends and customers.
Congratulations to the winners of our drawings. The lucky winners received the Parrot AR.Drone 2.0 Power Edition and a Hat Trick BBQ tool set made from the US National Team Development Program hockey sticks, donning the official red, white and blue trim.
Read more for some important reflections on Methanol and Equations of State and PVT Characterization methodologies.
May, E., Hughes, T., Kandil, H., & Graham, B. (2015). Simulating Carbon Dioxide Recovery from Natural Gas: New Data and Improved Methods for Methane + Carbon Dioxide + Methanol. Gas Processors Association Conference. San Antonio, Texas (USA): Gas Processors Association, Tulsa, OK (USA).
This important paper provided new data collected by Eric May’s group at the University of Western Australia for the systems methane-methanol, methane-carbon dioxide and the key ternary methane-carbon-dioxide-methanol that can be used as a prototype to simulate the thermodynamic behavior of sour natural gas mixtures and processes involving the addition of methanol, either for hydrate control or gas conditioning such as the Rectisol process. The new data is a welcomed addition to the currently available experimental data set and valuable for testing the development of new thermodynamic models and evaluation of available equations of state.
May and co-workers showed that predictions from a commonly used process simulation using default interaction parameters were not adequate and that temperature dependent as well as composition dependent interaction parameters are necessary to accurately model this class of system.
Fortuitously VMG started a comprehensive maintenance program for the APR family of equations of state about 18 months ago aimed at improving the performance of these widely used models when dealing with polar compounds. Modeling decisions made more than a decade ago served our clients well but a comprehensive revamp of the thermodynamic model was required to prepare the field for comprehensive modeling developments on hydrates, freezing phenomena and multiphase equilibrium on water/oil/solvent systems as required by the industry.
As always these developments are carefully planned to ensure the widest coverage is provided to our clients and we started from the very basic issue of modeling water/hydrocarbon systems more accurately, including mutual solubility and water content, moving then to alcohols, glycols and mutual solubility issues of water hydrocarbons as well as water and important inorganic compounds such as carbon dioxide and hydrogen sulfide.
This development is available to our clients with VMGSim 9.0 when they select the APR for Natural Gas 2 model. It includes, amongst many other things, a consistent and flexible mixing rule that overcomes the issues pointed by Dr. May’s work. In addition, the mixing rule provides a consistent representation of systems of interest for gas processing across the critical point and avoids inconsistencies such as the Kistenmacher-Michelsen syndrome that is present in older models. This fits perfectly with our new multiphase PT diagram and users can now draw complex PT maps for mixtures that contain water, hydrocarbons and polar compounds of interest such as methanol and ethylene glycol.
Below you will find the comparisons between APR Natural Gas 2 and the data published by Eric May. The results are straight out of the box without any adjustment, and they are excellent as shown in figure 1.
Figure 1: VMGSim 9.0 - Average deviation 121 kPa, Average error = 6.4% (blue circles)
Other Simulator, Average error = 38.7% (red circles)
The paper shows composition deviations but they do not specify the feed, therefore only the Methane/Methanol binary mixtures can be directly compared as shown in figure 2.
Figure 2: VMGSim 9.0 - Experimental and Measured mole fractions of methane in the methanol rich phase.
The results for the ternary C1/Methanol/CO2 are even more impressive as shown in figure 3.
Figure 3: VMGSim 9.0 - VMGSim Average deviation = 155 kPa, Average error = 4.9%
If you are not running VMGSim, beware of other off the shelf equations of state when simulating mixtures containing polar solvents, such as methanol, glycols etc. We would like to stress that APRNG2 embodies a vast amount of quality experimental data carefully evaluated and processed to provide you with the best available property package system to model natural gas processes. Of particular importance in our opinion is the integration of the vapour-liquid equilibrium data for dry systems as the ones presented by Dr. May with data for wet systems as they occur in field operations while ensuring accuracy for VLLE calculations, hydrate calculations and freezing phenomena amongst other problems of interest for the process engineer such as:
Figure 4: VMGSim 9.0 - Methanol losses in gas phase from: VMG APRNG2-Technical Brief; Virtual Materials Group Inc.; Calgary, Alberta, Canada (2015).
The loss of methanol injected to prevent the formation of gas hydrates is an important aspect of hydrocarbon processing affecting economics, environment and tower performance.
Methanol distribution in vapour and multiple liquid phases
Figure 5: VMGSim 9.0 - Methane losses in liquid phase from: VMG APRNG2-Technical Brief; Virtual Materials Group Inc.; Calgary, Alberta, Canada (2015).
The distribution of methanol in gas and liquid phases is important for the determination of appropriate methanol injection rates for the prevention of hydrate formation in pipelines.
Methanol distribution in Demethanizers, Deethanizers and Depropanizers
Small amounts of methanol resulting from hydrate inhibition may be carried to the demethanizer, deethanizer and depropanizer towers. Due to the non-ideality of methanol / hydrocarbon mixtures the presence of small amounts of methanol in the gas feed presents a strict test for the thermodynamic model. Methanol behaves in a way similar to water in an atmospheric crude tower and its high activity coefficient in hydrocarbon mixtures results in volatilities significantly higher than what you would expect based on its boiling point as shown in figure 6.
Figure 6: Non-ideal behavior of methanol in depropanizers, from: VMG APRNG2-Technical Brief; Virtual Materials Group Inc.; Calgary, Alberta, Canada (2015).
APR Natural Gas 2
The Advanced Peng-Robinson for Natural Gas 2 is a new property package system based on the APR equation of state developed by Virtual Materials Group as the new standard for thermodynamic calculations of gas and hydrocarbon systems. APRNG-2 was specifically designed to provide consistent modeling for hydrocarbon-rich and water-rich phases using a flexible and consistent mixing rule, capable of representing hydrocarbon or aqueous systems, in particular systems containing methanol, glycols, water and hydrocarbons.
APR Natural Gas 2 is fully integrated with VMG’s multiphase envelope calculator and can provide a rich picture of highly complex mixtures of interest for the hydrocarbon processing industry. The mixing rule formulation in APRNG-2 can handle non-polar or polar mixtures in a consistent manner and fully supports the construction of multiphase phase diagrams In addition to its flexible mixing rule for vapour-liquid-liquid equilibrium computations, APRNG-2 accurately models vapour pressures of non-polar and polar compounds and it includes the same special algorithms for the calculation of accurate enthalpies and liquid heat capacities used in APRNG for mixtures of water and glycols.
Throughout this work we have used the Gas Processors Association (GPA) Research Reports and the National Institute of Standards and Technology’s (NIST) Thermo Data Engine Version 8.0  for the location of and evaluation of experimental data high quality scientific journals and NIST’s TDE 8.0.
Conder, M. W., Schroer A. D., (2015). Design of Gas Handling Facilities for Shale Oil Production Gas Processors Association Conference. San Antonio, Texas (USA): Gas Processors Association, Tulsa, OK (USA).
This paper stressed the importance of process and mechanical design for multi-well field production. Shale Oil production facilities are large and expensive, requiring significant investment, and increasing air emission requirements require careful attention to flash gas handling to minimize or eliminate gas venting. A number of designs of shale oil production facilities were reviewed. In addition this article contained some excellent insight into real world facility design.
With the increasing need for tighter design of these facilities comes the need for accurate simulation, which is highly dependent on the thermos-physical behavior of the oil. The new VMGSim PIONA/Oil Source characterization methodology was highlighted as an approach that provides a more accurate description of the fluid and consequently a framework for improved simulation accuracy in design and operation. VMG has been doing a lot of work in this area and have applied this approach in all aspects of unconventional plays from well head recombination to sales product specification estimation to field wide composition tracking. Additional information of how PIONA characterization and VMGSim can be of use to you in these application can be found at www.virtualmaterials.com/Upstream.
The Parrot AR.Drone 2.0 Power Edition, the BBQ tool set and other free giveaways
Our "cryogenic cocktail": a frozen Caipirinha with the consitency of a sorbet