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Study On Pressure-Swing-Adsorption Enrichment Of Coalseam Methane

Posted on:2005-07-28Degree:DoctorType:Dissertation
Country:ChinaCandidate:M L YangFull Text:PDF
GTID:1101360125463638Subject:Mining engineering
Abstract/Summary:PDF Full Text Request
In the experiments, anthracite with typical low reactivity and lignite with high reactivity are respectively use to produce coal-based activated carbon by one-step alkali-activation process, and the structural properties are characterized.Then it is found that the BET surface area and the pore volumes of the raw coal, its carbonized sample and coal-based activate carbon are all increasing in their above order,and the anthracite is almost the same with its carbonized anthracite in the most probable pore size,which can be explained by the activation mechanism of potassium steam squeezing into the space between graphite sheets,making micropore number increasing. This is due to the inactivity and the low volatility of anthracite.A model called Hybrid Lusheng is proposed in the paper to describe the pore distribution of the activate carbon-like heterogeneous porous solids,in which all pore in an activated carbon particle can be in fact considered as the collection of different size round holes just like a Lusheng,an ancient Chinese traditional musical instrument. And with Kelvin Equation describing the capillary filling mechanism and with fractal theory, it is found that the anthracite based activate carbon has double surface fractal dimension values. The surface modification on activate carbon is carried out with n-C24H50 to promote the affinity to hydrocarbon.The results demonstrate that acidic functional groups on activate carbon after modification is decreased and the affinity of its surface to methane is increased,which leads the enforced separating properties of surface modified activated carbon for methane from N2 in the wider range of pressure,the mimic coalseam gas of about 60% methane can be enriched into methane of about 90% after two PSA cycles.An idea is put forward in the paper that surface inhomogeneity and the caused heterogeneous distribution in surface energy of porous solids may be considered as results from the inhomogeneous distribution of those adsorption sites at the same level of energy.Concentration or pressure of absorbates may be used as a probe to detect those adsorption sites,number of which is genernally larger in smaller pores.A promoted Langmuir isothermal adsorption model is then proposed and applied in describing the adsorption behaviors of methane,nitrogen,and carbon dioxide on activated carbon before and after surface modification: A novel dual-column PSA system with a preset pretreatment colmn and automatically controlled unit was designed and manufactured.The PSA system has more excellent properties in airtight properties,automation level,pressure range,flexibility,and mimic gas preparation than that the original single-column PSA device in our laboratory as well as those PSA devices in the market.The experiments are made with the PSA system,of mimic coalseam gas breaking through adsorption column filled with above surface modified activate carbon.The breakthrough curves are got.According to the facts that the temperature fluctuation at lower,middle,and upper site of the column is within one degree centigrade during experiments and the adsorption isotherms of the activated carbon for methane appear S type,a nonlinear kinetic model under the following hypothesis as (1)ideal gases,(2)piston fluid,and (3)linear deriving force.The numerical analysis for the model is carried on Microsoft Visual Foxpro 6.0.The analysis results is in keeping with experimental breakthrough curves.
Keywords/Search Tags:pressure swing adsorption(PSA), coalseam methane, activated carbon, surface modification, breakthrough curve, kinetic simulation
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