Simulation Of Pressure Swing Adsorption Separation Process Of Coalbed Methane Based On New Porous Materials

As an associated resource of coal,coal bed methane（CBM）is a kind of unconventional natural gas,which has gradually become an important clean,renewable energy and chemical raw material.However,due to the low concentration of methane in low-concentration CBM and the risk of explosion in the purification process,it is often difficult to use efficiently and directly discharged into the atmosphere,which will undoubtedly exacerbate global warming and other environmental problems.Therefore,the purification and recycling of low concentration CBM is of great significance to alleviate the energy and environmental problems.The existence of N₂and O₂is an important factor restricting the enrichment of low concentration CBM.Pressure swing adsorption（PSA）has the advantages of low energy consumption,low cost and diversity of adsorbing materials,and has a broad prospect in gas purification.New porous materials（MOFs）have the advantages of large specific surface area,high porosity,adjustable pore size and flexible surface properties,which have become the most promising adsorption materials for CH₄purification from low concentration CBM.In this paper,new porous materials are selected as adsorbent to establish a pressure swing adsorption process model for the separation of low concentration coal bed methane.The main research content is as follows:（1）Adopted a systematic mathematical model of low concentration CBM PSA process,and selected 12 kinds of porous composites synthesized in the laboratory with good separation performance for CH₄/N₂system.Various isotherm equations were used to fit and compared the experimental isotherm data.It was determined that the IAS-Langmuir-Freundlich adsorption model was suitable for fitting the single fraction data of CH₄and N₂of various materials.Using this isotherm model,a fixed-bed breakthrough model was established in Aspen Adsorption,and the breakthrough curves of two components were simulated and compared with those of real experiments to verify the accuracy of the model in describing the multi-component adsorption behavior.A double-tower and six-step pressure swing adsorption process model was established to verify the enrichment effect of various porous materials on low concentration of coal bed methane CH₄in the adsorption process.It can be known that the selectivity and saturation adsorption capacity of adsorbent materials for CH₄/N₂system jointly affect the separation performance of the process.Establishing process flow simulation can show the separation effect of new porous materials in actual process and reduce the huge input of resources.（2）The new porous material was coupled with the dual reflux pressure swing adsorption（DR PSA）process,and the double-tower and eight-step vacuum dual reflux PSA process was established.NKMOF-8-Br was used as adsorbent for purification of low concentration coal bed methane（CH₄/N₂,5:95,vol%）.The heavy product gas containing 55.69 vol%CH₄was obtained,and the recovery rate was higher than 60%.Single variable analysis method was used to investigate the effects of adsorption time,feed position,pressure equalization position,gas flow rate of recombined component product and reflux flow rate of light component product on the separation effect of DR VPSA process,and the process was optimized,which has guiding significance for the improvement of experimental performance and industrialization of real DR PSA process.（3）Aiming at the problems of low enrichment efficiency of low concentration oxygenic coalbed methane and the explosion risk of methane in PSA process,a double-tower and six-step pressure swing adsorption pilot process with Al-MOF as adsorbent was constructed to simulate the process of low concentration oxygenated CBM（CH₄/N₂/O₂,30/57.3/12.7,vol%）.The explosion triangle was modified according to the temperature and pressure changes of the process system at each stage and the safety analysis of the process was carried out.In order to achieve safety production,inerting dilution methane enrichment process was designed and optimized.Nitrogen inerting dilution of raw gas was used to reduce O₂concentration and avoid explosion risk,and the heavy product gas containing 71.06 vol%CH₄was obtained,and the CH₄recovery rate reached 74.93%,which verified the feasibility and safety of the process.