NOVELTY - System (100) comprises: a chemical looping system (200) comprising an oxidizer (102) in fluid communication with a reducer (104), where the oxidizer is operative to oxidize a multivalent metal oxide or a calcium sulfide to higher valent metal oxide or to a calcium sulfate respectively, the reducer is operative to reduce the metal oxide to a lower valent metal oxide or the calcium sulfate to calcium sulfide, and the chemical looping system generates a flue gas stream comprising carbon dioxide during reducing of metal oxide or reducing of calcium sulfate; and a gas purification unit (300).    USE - The system is useful for producing a lift gas for the fuel reactor (claimed).    ADVANTAGE - The system utilizes vent gas that: provides lift to the solids, thus reducing utilization of other primary gases; and contains carbon compounds which act as a fuel source, thus improving the overall conversion of fuel to carbon dioxide as well as facilitating an increase in the overall efficiency of the process.    DETAILED DESCRIPTION - System (100) comprises: a chemical looping system (200) comprising an oxidizer (102) in fluid communication with a reducer (104), where the oxidizer is operative to oxidize a multivalent metal oxide or a calcium sulfide to a higher valent metal oxide or to a calcium sulfate respectively, the reducer is operative to reduce the metal oxide to a lower valent metal oxide or the calcium sulfate to calcium sulfide, and the chemical looping system generates a flue gas stream comprising carbon dioxide during the reducing of the metal oxide or the reducing of the calcium sulfate; and a gas purification unit (300) in a recycle loop with the chemical looping system, where the gas purification unit comprises at least one compressor, at least one dryer, and at least one distillation purification system, where the gas purification unit is operative to separate carbon dioxide from other contaminants present in the flue gas stream, and the gas purification unit is operative to recycle the contaminants to the chemical looping system in the form of a vent gas that provides lift for reactants in the reducer. An INDEPENDENT CLAIM is also included for producing a lift gas for the fuel reactor in the chemical looping system, comprising: discharging a flue gas stream from the chemical looping system to the gas purification unit; compressing the flue gas stream in the gas purification unit; separating carbon dioxide from other contaminants present in the flue gas stream; and recycling the contaminants to the chemical looping system in the form of the vent gas that provides lift for reactants in the reducer.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic description of a chemical looping system in fluid communication with a gas purification unit that generates vent gases that can be used for producing a lift gas for use in the reducer of the chemical looping system.    System (100)    Oxidizer (102)    Reducer (104)    Chemical looping system (200)    Gas purification unit (300)