GB638745A - Adsorption process and apparatus - Google Patents

Abstract

<PICT:0638745/III/1> <PICT:0638745/III/2> A process and apparatus for separating a gaseous mixture containing gases of different adsorbabilities comprises contacting the mixture with a solid adsorbent, e.g. silica gel, granular carbon, animal or vegetable charcoal, preferably activated in a continuously moving bed preferably countercurrent to the gas to adsorb gases of higher adsorbability, separating unadsorbed gases of lower adsorbability, rectifying the adsorbent, stripping the adsorbed gases from the adsorbent by heat and steam or other stripping gas, and returning a portion of the stripped gas to rectify the adsorbent by preferentially desorbing gases of lower adsorbability; the regenerated adsorbent is cooled before re-use. The separation is increased by multiplying the rectifying sections to give more fractions. In Fig. 1, granular charcoal passes down an adsorption column 10 at such a rate that substantially all the C2 and heavier hydrocarbons in a feed gas containing C1-C4 paraffins and C2-C4 olefin introduced at 12 are adsorbed in adsorption section 11, while lean gas, e.g. methane, nitrogen, and oxygen is withdrawn at 15, although some assists in drying out charcoal in cooling section 56 and is withdrawn at 52. The enriched charcoal is then refluxed in rectifying section 19 with a C2 fraction, produced lower down the column, to release more lean gas which passes back into the adsorption section, while the charcoal is refluxed in the second rectifying section 21 with heavier hydrocarbons introduced at 35 from the stripping section 25 to preferentially desorb C2 hydrocarbons of which, a portion is allowed to pass back up the column as reflux in section 19 while the remainder is withdrawn as intermediate fraction at 22. The charcoal then passes to stripping section 25 where steam introduced at 26 and indirect heating by combustion gases combine to strip the adsorbed gases which pass off at 34 to be dried prior to return of a portion to rectifying section 21. The regenerated adsorbent passes to the bottom of the column, where its flow is controlled by, e.g. rotating vane or apportioning means operated by level control 39, and thence by elevator 41, hopper 51, and cooler 56, back to the adsorption section. Disengagers are fitted between the sections and charcoal may be withdrawn at 58 for reactivation. Alternative arrangement, Fig. 2, is placed in an adsorption column 10 between the adsorption section and second rectifying section, and enables some of the adsorbent to byepass the first rectifying section, and comprises primary and secondary tubes 100, 109 closed one end and of smaller diameter than the adsorption column and joined by third tube 104. Feed gas is introduced at 101 and meets charcoal travelling through annular space between primary tube 100 and the column; all the heavier components are adsorbed below the entrance to tube 104. Thus the charcoal in the annular section carries the heavier fraction and that in tube 104 the lighter fractions. The charcoal is refluxed in 110 with heavier fraction desorbing an intermediate fraction which refluxes with charcoal in 106 and 104 desorbing the lighter fraction while the intermediate fraction may be withdrawn at 112. More than one of the units in Fig. 2 may be used at the same or different levels in one column. The charcoal may be lifted by gas stream, e.g. lean gas, instead of by the mechanical elevator 41; the adsorption and stripping sections may be separate columns, and a separate secondary adsorption column supplied with adsorbent from the main column may be used for purifying the intermediate fraction; the stripping zone may work on concurrent flow. Reference has been directed by the Comptroller to Specification 650,095.