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A method and apparatus for fractionating a mixture of gasses, by using a bed of sorbent which is conditionally depressurized and purged after adsorption intervals of a predetermined time duration, varies the time duration in response to demand as indicated by the decisions of whether purging is requ

A method and apparatus for fractionating a mixture of gasses, by using a bed of sorbent which is conditionally depressurized and purged after adsorption intervals of a predetermined time duration, varies the time duration in response to demand as indicated by the decisions of whether purging is required. Preferably a historical record is kept of the recent purge decisions, and based upon this historical record, the duration of the adsorption interval is increased at a limited rate up to a maximum duration when purging is infrequently required, and is decreased at a limited rate down to a minimum duration when purging is frequently required. The method and apparatus is particularly suited to drying air or other gasses using a heaterless pressure-swing dehydrator of the kind having two alternately-switched desiccant beds, and capacitance probes inserted in the middle of each bed for sensing the advance of the moisture fronts to determine whether purge is required at the end of the respective adsorption interval.

대표청구항 ▼

A process for reducing the concentration of first gas in mixture thereof with a second gas to below a limiting maximum concentration thereof in the second gas, which comprises the steps of: (a) during a predetermined time interval, passing an influent flow of the mixture through a bed of a sorbent h

A process for reducing the concentration of first gas in mixture thereof with a second gas to below a limiting maximum concentration thereof in the second gas, which comprises the steps of: (a) during a predetermined time interval, passing an influent flow of the mixture through a bed of a sorbent having a preferential affinity for the first gas, adsorbing the first gas thereon to form a gaseous effluent having a concentration thereof below the maximum, and forming a concentration gradient of first gas in the bed progressively decreasing from one end to the other end as the adsorption continues and an increasing concentration of first gas in the second gas defining a concentration front progressively advancing in the bed from one end to the other end as sorbent capacity thereof decreases; (b) sensing whether the first gas front in said sorbent bed has advanced by a predetermined extent at the end of said first predetermined time interval to decide whether purging of said sorbent bed is required after said predetermined time interval; (c) at the end of said predetermined time interval, closing off the influent flow of gas, and in response to the decision in step (b), conditionally depressurizing the bed of said sorbent and introducing a purge gas to regenerate said sorbent; and thereafter, (d) repeating steps (a), (b) and (c) above; wherein said process further comprises, recording a history of the decision in step (b) of whether purging of said sorbent bed is required, and during the repetition of steps (a), (b) and (c) above, decreasing the duration of said predetermined time interval based upon said recorded history indicating that purging of said sorbent bed is frequently required, and increasing said predetermined time interval based upon said recorded history indicating that purging of said sorbent bed is infrequently required. A control system for a pressure-swing desiccant gas dryer having a first desiccant bed and a second desiccant bed, gas to be dried being alternately directed by valves to pass through one of the beds providing adsorption of vapor while the other desiccant bed is being regenerated after depressurization or is in an idle condition in response to at least one cyclic bed select signal and at least one regeneration enable signal, respectively, the control system comprising, in combination, a capacitance probe in each desiccant bed so that the level of condensate saturation of the desiccant in each bed is indicated by the capacitance of the respective probe, a probe interface for generating a digital signal indicating the capacitance of the probe in the desiccant bed undergoing regeneration, a microcomputer executing a stored sequence of instructions, said microcomputer comprising means for generating said bed select signal to switch the bed providing adsorption after a predetermined adsorption time interval, means for receiving said digital signal generated by said probe interface at the end of said adsorption time interval, comparing said digital signal to a predetermined threshold signal representative of the condensate saturation level for which regeneration is required, and generating said regeneration enable signal in response to said means for comparing the final count to the predetermined threshold indicating that regeneration is required, and means for conditionally changing the duration of said adsorption time interval in response to said regeneration enable signal so that said duration of the adsorption interval decreases at a limited rate when purging is frequent and increases at a limited rate when purging is infrequent, and for limiting the duration of said adsorption time interval so as not to exceed a predetermined maximum and so as not to be less than a predetermined minimum.