GOALI: Collaborative Research: Fundamental Studies of water-hydrocarbon condensation

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Currently, natural gas supplies ~23% of U.S. energy needs. In addition to CH4, raw natural gas contains water, higher hydrocarbons, and other substances that must be removed before the gas is transported and used. For off-shore wells, treatment near the wellhead is critical to prevent clathrates from forming and plugging the pipeline as gas flows to the mainland. The raw gas is normally treated by adding chemicals or reducing its dew point, but standard processing equipment is often large and requires manned platform operation. An alternative approach is to use supersonic natural gas separators that (1) cool the gas in a supersonic expansion to induce droplet formation and growth, (2) separate the droplets from the gas, and, (3) recompress the dried gas using a diffuser to minimize pressure losses. These separators are smaller than traditional process equipment, have no moving parts, and require no chemicals. Thus, they are suited for both off-shore and sub-sea applications. Worldwide, three of these devices are now in commercial operation. Twister BV, the industrial partner for this proposal, is at the forefront of developing and implementing this technology. As these devices are adopted, however, critical questions remain regarding droplet formation and growth in these complex vapor mixtures, and these questions are related to the structure of the droplets.Intellectual Merit: With an overarching goal of improving the efficiency of natural gas production, this proposal examines droplet formation, growth, and structure in highly non-ideal water hydrocarbon systems under conditions that mimic those found in the supersonic separators. The experimental program will characterize the condensation process in supersonic nozzles, at Mach numbers comparable to the real separators, using pressure measurements and spectroscopy. The resultant aerosols will be characterized using small angle x-ray and/or neutron scattering. The theoretical program will focus on understanding droplet structure, formation and growth rates as a function of the key parameters, i.e., the vapor phase compositions and temperature. Combining the experimental results with the theoretical calculations and detailed modeling will result in more robust descriptions of multicomponent droplet formation and growth that can then be incorporated into the computational fluid dynamics codes used to describe and optimize the performance of supersonic separators. This novel application of computer simulation techniques and density functional theory and of small angle neutron and x-ray scattering experiments is helping transform the field of aerosol science by enabling the solution of problems that previously defied investigation.Broader Impacts: In a broader context, this work is directed toward improving the energy efficiency of natural gas production. In addition to their relevance to the domestic natural gas industry, as well as to Twister BV, the results stemming from this work are of interest to other researchers in nucleation, aerosol science, and cloud and atmospheric physics. In the area of education and training, this project will provide a rich, highly interdisciplinary research environment for all students and will incorporate a unique international experience for graduate students. Participation in the research by undergraduate students, particularly from minority and underrepresented groups, will be fostered. As an important outreach activity, table top diffusion cloud chambers will be built so that students and teachers can visualize cloud formation in the classroom, a process that is of great interest in elementary and high school education but is not easily realized.