Process Simulation And Optimization Of Methane Purification By Pressure Swing Adsorption

With the rapid growth of energy demand worldwide,mankind has begun to look for alternative energy sources.In addition,because of the uneven distribution of fossil fuel resources around the world,human beings began to exploit and utilize unconventional and renewable energy.Therefore,the use of non-fossil and alternative resources to produce energy development technologies is essential to alleviate environmental problems and reduce human dependence on fossil fuels.As a clean energy source,coal seam gas can meet the growing energy demand,reduce greenhouse gas emissions and air pollution.However,because the existence of N₂ in the mixture reduces the overall energy,large amounts of coal seam gas cannot be used efficiently.Therefore,CH₄ must be recovered from coal seam gas before the energy in it can be used.Metal-Organic Framework（MOF）has been widely studied for its ability to meet the requirements of high CH₄/N₂ selectivity and high CH₄ working capacity.Pressure swing adsorption（PSA）is widely used in gas separation on account of its flexible manipulation,above the average degree of automatic control,below the average degree of capacity spend and low capital investment.Process simulation is a powerful tool for optimizing energy requirements and process performance and reducing the level of experimental work required,considering the considerable resources and time required to perform real-world variable pressure adsorption experiments.In this paper,using Aspen Adsorption software,a model of pressure swing adsorption process of MOF material as an adsorbent for CH₄/N₂ separation is established,and pressure swing adsorption process is analyzed,the main contents are as follows:（1）First of all,the PSA model applied to CH₄/N₂ separation is established.Through the analysis of mass balance,energy balance,momentum balance,adsorption dynamics and adsorption thermodynamic model,a suitable mathematical imitation model is gained,and then we can analyze the performance of product gas and the economic behavior of process.The validity of the model is proved by force of contrasting the examination results.We can acquire some new information which is difficult to measure in experiment from the model.（2）Based on the established PSA model,the breakthrough curve is simulated and the influence of each parameter is studied and analyzed.The study of breakthrough curve is an important transition between adsorption balance and process research and design.Through the simulation of breakthrough curve,the time of the first breakthrough of the adsorbent bed,the saturation time and the length and width of the reaction zone are learned,and these data can be used as the process design basis for the fixed bed adsorbent in the industrial scale.According to the variation law of each parameter,the adsorbent can be selected and the equipment can be debugged to achieve the desired effect.（3）For PSA upgrade CH₄ process design,we establish single-column,double-column and multi-column PSA system and discuss the parameters which have greater impact on product gas performance and process economy in each process.Through single-column PSA simulation,it is found that the addition of product gas for purging and vacuum pumping is effective for the system.Through double-column,it is found that the pressure equalizing step has a great influence on the product gas.Finally,through multi-column PSA simulation,through parameter optimization,CH₄ has a purity of 89.368%,recovery of 95.827%,process yield of 18.596 mol/kg/h and energy consumption of 0.319 kWh/m³.Through the research and analysis of the influence of various parameters and steps on the performance of product gas,the process parameters are optimized,the utilization rate of adsorbent is improved,and the production practice is guided.