A staged complementary pressure swing adsorption system and method for low energy fractionation of a mixed fluid. Two beds in a four-column PSA system are selective for component A, and another two columns are selective for component B. The cycle creates an intermittent A and B product, using the purge effluent from the complementary product fed at an intermediate pressure. This intermittent product is used as purge gas for low-pressure purged elsewhere in the cycle using appropriate storage tanks. The use of an intermediate pressure in this cycle enables continuous production of purified component A and B without the use of compressors. Columns may also be configured to enable pressure to equalize between complementary columns.

The invention relates to a method for regulating a unit for separating a gas stream, having P adsorbers, where P2, each following a PSA-type adsorption cycle with a phase time shift, the method involving the steps of operating the unit according to the nominal cycle when the required flow rate is equal to a nominal flow rate or optionally when the required flow rate is higher than the nominal flow rate, and operating the unit according to the reduced cycle when the required flow rate is lower than or equal to a predetermined flow rate, the predetermined flow rate being lower than the nominal flow rate.