Experimental And Simulation Of PSA Process Enriching Low-Concentration Coalbed Gas

As unconventional natural gas,coalbed methane(CBM)is a low-carbon resource that is often overlooked and has abundant reserves.However,due to complex geological factors and mining technologies that have not yet broken through restrictions,its low concentration utilization is limited,and direct evacuation will cause serious Greenhouse effect,therefore,an efficient and economical separation technology is needed to achieve the enrichment and recovery of low concentration coal bed methane.The pressure swing adsorption(PSA)process can separate normal gas,with low energy consumption and simple operation,and shows a large competitive advantage under various gas separation conditions.Moreover,through the method of numerical simulation,the process of methane enrichment and denitrification can be studied to guide the design of low concentration coal bed methane enrichment and recovery process.The key to the application of PSA separation technology is to find a suitable adsorbent,and the most widely existing low concentration coal bed methane(CH₄ concentration is less than 30%)CH₄ and N₂ are both non-polar gases,and their dynamic diameters are similar(CH₄ is 3.8 nm,N₂ is 3.64 nm),and there is no nonpolar gas with dipole moment,making it difficult to develop an adsorbent with good separation performance.In many years of research on CH₄/N₂ separation,the research group found a zeolite material,Silicalite-1 adsorbent,with regular and ordered pore structure,high hydrothermal stability and hydrophobicity,especially for CH₄/N₂ has excellent separation performance,and developed a new synthesis method to reduce the synthesis cost of the adsorbent.,In this paper,a large amount(kg)of Silicalite-1 powder samples were bonded and molded and the samples before and after molding were analyzed and characterized by XRD,SEM,77 K nitrogen adsorption,etc.The morphology and pore structure of the samples were analyzed.The static adsorption amounts of CH₄ and N₂ were tested for the particles and powder samples,respectively.The static separation performance of the samples before and after molding is shown.The adsorption capacity of particles and powder samples at 5 bar is 35.8 and 36.5 cm³/g,respectively,and the IAST adsorption selectivity is 4.1 and 4.0,respectively.The test results show that the bonding method has no effect on the adsorption and separation performance of the adsorbent.Through the penetration experiment,the dynamic separation performance of the particle sample was evaluated,and the mixed gas without feed concentration was separated.The dynamic separation selectivity at different concentrations was higher than 3.0,indicating that the adsorbent can be fully applied to CH₄/N₂ adsorption separation Application.The self-designed and built pressure swing adsorption separation platform was used to evaluate the industrial use effect of Silicalite-1 particle samples,and the enrichment concentration and recovery rate of CH₄ were obtained through multiple cycle operations.The experimental results show that the enrichment result of 20%CH₄ concentration is40%,and the enrichment result of 30%CH₄ concentration is 50%.The enrichment effect is obvious,which reduces the restriction of CH₄ concentration on coalbed methane utilization.A one-dimensional adsorption bed mathematical model of the total mass transfer resistance model was established to study the loading and removal of CH₄ on the adsorbent surface during the adsorption separation process.The good agreement between the PSA experimental data and the numerical simulation results verifies the accuracy of the mathematical model.Further,we found the shortcomings in the original process during the simulation and developed a new process to improve the separation performance index.The enrichment results of 20%and 30%CH₄ concentration were increased to 45%and57%,respectively.And the recovery rate is still higher than 80%.As a new type of porous material,MOFs'ultra-high specific surface area and adjustable surface groups make the material highly selective for a variety of mixed gases.Imidazole grease framework materials(ZIFs),as a special MOFs material,have a zeolite-like structure.Studies have shown that the imidazole lipid group is conducive to the adsorption of CH₄.Based on this study,we explored the ZIF-8,ZIF-90 and SIM-1(ZIF-94)materials with six-membered rings and the ZIF-Study on the separation performance of 93 material for CH₄/N₂.The static adsorption capacity test results show that the CH₄ adsorption capacity at 5 bar,SIM-1(ZIF-94)material is 51.8 cm³/g is much higher than ZIF-8(29.7 cm³/g),ZIF-90(34.5cm³/g)And ZIF-93(31.3 cm³/g).The CH₄/N₂ static adsorption selectivity of SIM-(ZIF-94)material is as high as 6.6,which is higher than that of Silicalite-1,which makes us have high expectations for its application in the separation and enrichment of low concentration coal bed methane.We made the adsorbent particles using the method of tablet granulation,and discussed the CH₄/N₂dynamic adsorption separation selectivity of the above four materials through the penetration separation experiment.The volume ratio of CH₄/N₂ by penetration separation is 30/70.The selectivity of the mixed gas is obtained.The selectivity of CH₄/N₂ dynamic adsorption separation of SIM-1(ZIF-94)is 3.46,ZIF-8,ZIF-90 and ZIF-93 are 1.33,1.75 and 1.45,respectively.Further,we compared the application of SIM-1(ZIF-94)and ZIF-8 materials in the pressure swing adsorption process using simulation methods.The simulation results show that SIM-1(ZIF-94)enriches CH₄ The effect is remarkable,and the concentration of CH4 can be increased from 20%and 30%to 50%and 61%,while ZIF-8 don't show the effect of separation and enrichment.Compared with Silicalite-1,the CH₄/N₂ separation performance of SIM-1(ZIF-94)material is more advantageous.At the same volume,the processing efficiency of SIM-1(ZIF-94)material for raw gas is also higher.