The study investigates the impact of a nanofluid suspended in carbonated water (CW) on the CO2 mass transfer into hydrocarbon in a carbonated water/hydrocarbon system. Furthermore the study addresses into the influence of the nanofluid assisted CO2 mass transfer on the viscosity and density of hydrocarbon and its relevance to enhanced oil recovery (EOR). The experiments were carried out at 10-70 bar at 25°C and 45°C using an axisymmetric drop shape analysis (ADSA) for three concentrations of silica nanofluid (0, 0.05, 0.5, and 1.0 g/l). A pressure decay method was used to estimate the change in CO2 solubility in water in the presence of the nanofluid. A mathematical model coupled with experimental input was used to quantify the mass of CO2 transferred into the hydrocarbon from the CW. Although this work does not address the EOR process, it indicates its applicability for EOR. The results showed that the dispersed nanofluid in CW enhanced the CO2 mass transfer into the hydrocarbon, and reduced the hydrocarbon viscosity and density. The pressure decay experiments indicated that the nanofluid increases the mass of CO2 in water by 17% compared to that without nanofluid. Compared to CW, CNF (CW+nanofluid) increased the CO2 mass transfer into the hydrocarbon drop by approximately 2% at 10 bar and 45% at 60 bar, this leads to an increment in volume of the pendant drop by approximately 3% at 10 bar and 48% at 60 bar at 25°C. A similar observation was made at 45°C. The nanofluid through CO2 mass transfer was responsible for approximately 40% and 29% reduction in the viscosity and density respectively, when compared with CW. Compared to CO2/hydrocarbon the CNF/hydrocarbon lead to a 17.3% volume increase at 30 bar to 91.2% at 50 bar. The increase in the drop volume is unlikely to be due to the migration of nanofluid across the interface into the hydrocarbon drop as indicated by analysis done using UV spectrophotometry and may be due to increase in the CO2 concentration gradient across the interface due to increase in the CO2 solubility in CW.
Conventional deaeration of seawater for water injection use expensive chemical scavengers and heavy vacuum towers, which occupy valuable space on offshore installations. The scope of this study is to investigate, compare, and further advance the development of two state-of-the-art deaeration technologies which solve the aforementioned issues. The first method, compressorless deaeration with the use of stripping gas is a newly developed modification of an already efficient, light, compact, and worldwide implemented technology. This technology uses pure nitrogen in a regeneration loop, together with static mixers which allow oxygen mass-transfer from seawater into the gas phase. The second method utilize the same proven nitrogen regeneration loop in combination with novel membrane deaeration technology. Advanced dynamic process simulations, combined with field data, mechanical design and process calculations are utilized to quantify process parameters and design requirements for the two technologies. The results are presented and used for discussing advantages, disadvantages, possibilities and further development needs of both the stripping gas- and membrane technology. Results show that it is possible to further increase the robustness of the stripping gas-technology by eliminating the compressor. A clever ejector system with turn-down capabilities ensures the technology's advantage of positive operating pressure and utilizes energy from the seawater flow to compress the nitrogen. Power calculations, turn-down possibilities and oxygen removal efficiency at various operating conditions are presented. A suggested design for membrane deaeration is also presented, along with calculations and comparisons to the stripping gas technology, especially regarding flow rate capacity and the economies of scale. The main advantage of the proposed membrane technique compared to existing membrane concepts is the high-purity nitrogen regeneration loop, which offers improved mass-transfer capabilities across the membrane. The novelty of this work the feasibility of successfully operating a compressor-less, efficient, compact deaeration system on positive pressure. Additionally, the stripping gas technology requires no chemical scavengers in order to obtain an oxygen concentration lower than 10 ppb. The membrane deaeration process can also achieve low oxygen concentrations without chemical scavengers and it is further found that the technology might be economically viable compared to stripping gas for low flow rates.
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