Hydrocracking unit, light gas fraction, calculation of vapor-liquid equilibrium

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The original process involved high-boiling-point oil entering a lower-temperature section where it flashed to produce low-boiling-point oil and low-boiling-point gas. The low-pressure gas is sent to the hydrogen purification unit as fresh hydrogen. Low-grade oil enters the distillation and light hydrocarbon recovery system to separate various products. From light to heavy, the products are: dry gas, LPG, light naphtha, heavy naphtha, jet fuel, light diesel, heavy diesel, and unconverted oil. Among them, the purity of the low-pressure hydrogen is about 90%, with the remainder being methane, ethane, propane, n-butane, isobutane, and small amounts of n-pentane and isopentane. The hydrogen purity of the dry gas is about 80%; the other components are mainly methane, ethane, propane, n-butane, isobutane, along with small amounts of n-pentane and isopentane. It should be noted that in low-pressure gas, the propane content is relatively high. In the dry gas, methane and ethane levels are high. Now, we want to change the process so that low-pressure gas does not go to other units, but rather returns to the inlet of the new hydrogen machine in its own unit. That is, to return the entire system. Please discuss the changes in the concentrations of the various components of the low-pressure gas when equilibrium is reached after the process modification. In terms of the processing methods, there are hot low-temp fractionation and cold low-temp fractionation; the temperature for hot low-temp fractionation is 250°C, while it is 25°C for cold low-temp fractionation. The pressure difference is not significant, at 2.38 MPa. How large is the error when simply using Henry’s law? What method should be used to calculate accurately? Using SRK’s equation of state to calculate fugacity? In fact, both the liquid phase and the gas phase are too complex, so simplified methods must be used.