The Experimental Study Of Low-temperature Vapor-liquid Equilibrium Apparatus And Vapor-liquid Equilibrium For LNG Mixture

Natural gas is the one of the three conventional energy sources, the main components of natural gas is methane, it also includes a certain amount of nitrogen, ethane. With the energy crisis and environmental deterioration, natural gas becomes a very attractive source of energy in an environmental perspective as it can reduce emissions of carbon dioxide, nitrogen oxides, and particulates. The market for natural gas has been rapidly increasing due to projected increase in energy demand and the global natural gas consumption by end-use sector is expected to increase more from the present over the next20years. The merits of the storage and transportation of liquefied natural gas (LNG) are quite obvious. In order to minimize the energy consumption in separation, storage and transportation process, the simulation and optimization of the liquefaction process are necessary to be developed. The accurate vapor-liquid equilibrium data of natural gas at low temperature (110-120)K are a basis for the design and operation of low temperature processes involving natural gas. Therefore, the knowledge about phase equilibrium of the binary mixture (N2+CH4),(CH4+C2H6) over extensive ranges of pressure and temperature is extremely important for the optimization of the LNG system. Based on these, the main contents in this paper include:(1) A high accuracy experimental apparatus of vapor-liquid equilibrium is designed and set up. It mainly consists of the thermostatic control system and the measurement system. The main part of the thermostatic control system is the thermostated bath; and measurement system consists of a high accurate temperature measure system (temperature uncertainty is less than±10mK), a high accurate pressure measure system (the total pressure uncertainty is±0.65kPa), and a composition measure system (the overall uncertainty is estimated to be within±0.004 mole fraction).(2) The experimental data of binary mixture (N2+CH4) in the temperature of (110.01-130.01) K are obtained by the apparatus. Using PR equation of state, combined with the MHVlmixingrule and Wilson model, the vapor-liquid equilibrium data are correlated. The results reveal that they have a good agreement with the experiment results. And average deviation of pressure is0.75%, the maximum relative pressure deviation is2.55%, the average deviations of vapor composition is0.0057, the maximum composition deviation is0.0166. The results suggest that the model used by this work has a good prediction capability.(3) The experimental data of binary mixture (CH4+C2H6) in the temperature of (126.01-140.01) K are obtained by the apparatus. Using PR equation of state, combined with the MHVlmixingrule and Wilson model, the vapor-liquid equilibrium data are correlated. The results reveal that they have a good agreement with the experiment results. And average deviation of pressure is1.45%, the maximum relative pressure deviation is2.18%, the average deviation of vapor composition is0.0010, the maximum composition deviation is0.0120. The results suggest that the model used by this work has a good prediction capability.