Gas stream purification method utilizing electrically driven oxygen ion transport

A method of purifying a gas stream by removing oxygen from said gas stream, said method comprising:

• introducing said gas stream into a series of electrically driven oxygen separation zones operating an elevated temperature to separate the oxygen from the gas stream, thereby to produce a purified gas stream;
• each of the electrically driven oxygen separation zones having an electrolyte and cathode and anode assemblies for applying a voltage to the electrolyte that such that the oxygen ions are transported through the electrolyte and emerge therefrom to recombine into elemental oxygen, thereby to separate the oxygen from the gas stream;
• the oxygen being separated from the gas stream at a successively lower partial pressure due to the separation of the oxygen within successive electrically driven oxygen separation zones;
• each of the electrically driven oxygen separation zones being capable of separating the oxygen as an increasing function of the voltage applied to the cathode and anode assemblies up to a level that induces an oxygen ion current that approaches a limiting oxygen ion current within the electrically driven oxygen separation zones at which a further increase in the voltage fails to produce an increase in oxygen separation, the limiting oxygen ion current limit being a function of the successively lower partial pressure such that the voltage applied decreases for each of the successive electrically driven oxygen separation zones;
• and
• applying the voltage to each of the electrically driven oxygen separation zones in an amount selected such that the oxygen ion current approaches the limiting oxygen ion current applicable thereto.