Gas Hydrate Equilibrium Measurement of Methane + Carbon Dioxide + Tetrahydrofuran+ Water System at High CO₂ Concentrations

AbstractApplication of gas hydrate in separation of carbon dioxide (CO2) form nitrogen in Carbon Capture and Storage (CCS) chain is recently studied by many researchers. Tetrahydrofuran (THF) is suggested as promoter for this process. The same process can be suggested for separation of CO2 from methane (CH4) for gas treatment and sweetening, especially for high CO2 content mixtures such as landfill gas. The first step in development of such process is understanding of the phase boundary of this mixture at different pressure-temperature condition and gas/liquid composition. In this work, gas hydrate phase boundary of CH4, CO2, THF and water at different pressure from 4.5 to 8.1 MPa is experimentally measured. CO2 mole fraction in gas phase is fixed at 0.7 and THF concentration in the liquid phase set at 0.03 mole fraction. Results show that presence of THF in the mixtures shift the phase boundary to the lower pressure / higher temperature condition. This effect is favorable for industrial applications

Experimental and numerical evaluation of the energy requirement of multi-stage vacuum membrane distillation designs

Although vacuum membrane distillation (VMD) has a high distillate flux, its potential is limited by its high specific heat consumption (SHC). Flat sheet VMD systems recover the brine energy by employing a cascade system to improve the SHC. Hollow fiber VMD systems, however, have not yet been optimized for energy recovery. To overcome this knowledge gap, four multi-stage configurations (with and without brine energy recovery) were investigated via experimentation and through numerical simulations. The results show that having permeate flux promoting conditions, such as high feed temperature or lower vacuum pressure, improves the SHC for VMD configurations without brine recirculation, but have little impact for configurations with brine energy recovery. A Pareto multi-objective optimization showed that the optimized first-stage heating MS-VMD without brine recirculation has the highest SHC (908 kWh/m3) but one of the lowest LCOW (2.37 USD/m3). In contrast, the configuration with the first-stage heating with brine recirculation provided the lowest SHC (585–629 kWh/m3) and an acceptable LCOW (2.27–8.30 USD/m3). This study reveals that the development of MS-VMD represents a promising direction for thermal desalination technologies, particularly for high saline water applications