The article discusses the method of calculating the condensation of hydrocarbons contained in the gas-air mixture displaced from the tanks and vehicles when they are filled. Currently, there is a wide range of software products that allow high-precision modeling of various technological processes, including low-temperature condensation. However, foreign software products are expensive and therefore inaccessible for widespread use. At the same time, in the practice of designing and analyzing technological processes of oil and gas production and oil and gas processing, the equations of phase concentrations are widely used. They require a minimum amount of initial data for the calculation: information on the composition of the gas-air mixture, as well as on the thermodynamic conditions of the process (pressure and temperature). However, in most works, recommendations for calculating the phase equilibrium constants are given in relation to positive temperatures, which is typical for reservoir conditions and conditions for separation of reservoir fluids. Low-temperature separation processes of multicomponent hydrocarbon mixtures in the field are also common. For example, the extraction of hydrocarbon condensate from gas at complex treatment plants is carried out at temperatures up to -40 °C. However, according to foreign data, to ensure a high degree of capture of oil and gasoline vapors, it is necessary to cool the gas-air mixtures to a temperature of -60 °C or less. Therefore, the currently known methods for determining the phase equilibrium constants, which are not intended for a given temperature range, cannot be used in the calculations of condensation units for recovering hydrocarbons.
With the use of relatively complex well-known techniques a data bank was developed on the dependence of the value of the phase equilibrium constants of individual components of the gas-air mixture on temperature at atmospheric pressure, which takes place in condensation units for recovering vapors of oil and oil products. Then, the obtained numerical values of these constants were approximated by a fairly simple dependence that is convenient for use.
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