Experimental Research On Pressure Swing Adsorption Of Methane/Nitrogen Mixture In Coalbed Methane

Methane contained in coalbed methane(CBM) is not only a valuable fuel, but also a greenhouse gas. Liquefaction is a prospective way of utilizing CBM. In China, CBM often contains air when it comes out of the well. The effective enrichment of methane from CH₄/N₂ is one of the most important issues in the liquefaction of CBM.In this paper, experiments have been carried out to study the separation of CH₄/N₂ by pressure swing adsorption(PSA). The breakthrough curves of CH₄ and N₂ on a single fixed adsorption bed packaged with different adsorbents were measured to find a suitable adsorbent. The influence of regeneration condition was investigated. The influence of pressure, feed gas velocity and methane concentration in feed gas on separation performance were studied. A two-bed Skarstorm cycle was used to produce continuous enriched methane under different experimental conditions. The experimental results show that:(1) The separation effect was better while the adsorbents were regenerated at high temperature and low pressure(150℃, 1.0kPa, 12h).(2) After regenerated, SL-CMS3 carbon molecular sieve(CMS) can separate CH₄/N₂ effectively. There is nearly no N₂ at the exit of the fixed bed during the initial breakthrough period.(3) Breakthrough curves on single-bed experiment device show: the feed gas velocity has a greater influence on separation than that of pressure, and it is adverse to the separation when the velocity is too large. While the methane content in feed gas reduces from 50% to 30%, the methane concentration can be enriched up to 90% too, and the influence of each parameter is similiar.(4) The CH₄ recovery rate decreases as the velocity or pressure or methane concentration in feed gas increases, yet the productivity of SL-CMS3 increases.(5) The two-bed experimental results show: methane concentration in products can be up to 84% under all conditions. The highest methane purity of 94.37% was obtained; the shorter the adsorption time is in a cycle, the greater the methane concentration is in the product, yet the slower the methane content increases in the buffer tank.(6) The methane concentration is remakeblely enriched through a single set of two-bed PSA apparatus. The experimental results are better than most published articles focused on methane-nitrogen separation. This research brings the prospect of effective utilization of low concentration CBM.