Modeling And Simulation Of Absorption-Adsorption / Absorption–Hydration Hybrid Process For The Separation Of CH₄-H₂

The refinery produces a large amount of dry gas by-products,such as catalytic reforming of dry gas,hydrogenation unit tail gas,cracked dry gas,etc.,which contain components with high economic value such as H₂ and C2.The separation process should be used to separate the gas mixtures,especially methane and hydrogen.Various traditional techniques are used for this type of separation,including cryogenic fractionation,pressure swing adsorption,and membrane separation,etc.However,these techniques have limitations,for example,cryogenic fractionation has a drawback of high energy consumption and cost,PSA can produce hydrogen in a high purity but a low hydrogen recovery ratio,membrane separation achieves a high hydrogen recovery ratio but low composition of hydrogen product.In recent years,the absorption-adsorption and absorption-hydration hybrid processes have received extensive attention in the academic community.The two hybrid processes can achieve the separation of gas mixtures at around 0°C,which greatly reduce energy consumption and save cost.The absorption-adsorption and absorption-hydration processes for separate methane and hydrogen is modeled and simulated respectively in this paper,and optimizes the processes operation parameters and evaluate the energy comsumption so that it can provide guidance in future industrial applications.The main research contents in this paper are as follows:（1）Thermodynamics and property method.The multiphase equilibrium problem in absorption-adsorption and absorption-hydration processes is simplified to the gas-liquid two-phase equilibrium problem.The physical properties of water are used as those of the slurry.The Peng-Robinson equation of state（PR EOS）coupled with the van der Waals mixing rule is used to calculate the fugacity for both the gas phase and the liquid phase.According to the phase equilibrium experimental data of hydrogen and methane in the slurry,the fitting method and calculation process are determined.The binary interaction parameters of hydrogen-slurry and methane-slurry are fitted.（2）Process modeling and simulation.The combination of multiple equilibrium stage is used to model the absorption-adsorption column and absorption-hydration column;the multi-stage pseudo-absorption separation processes are simulated in Aspen plus by multiple flash modules.The binary interaction parameters in the flash modules are determined according to composition calculation;sorption enthalpy effect is analysized to determine column temperature rise and the optimal operating conditions are discussed,such as equilibrium stages,the required flowrate of slurry and desorption pressure,for absorption-adsorption process,pressure of the circulating flash tank is also discussed.（3）Energy analysis.Calculate the total energy consumption per unit hydrogen product of two hybrid processes.Sensitivity of key parameters is carried out,such as operating pressure of column,methane composition in feed gas stream,the composition of hydrogen product.The effects of them on hydrogen recovery ratio and total energy consumption are evaluated.For the absorption-adsorption process,influence of pressure of the circulating flash tank on process energy consumption is also analyzed.