Purification method and junction for related apparatus

A method of purifying a gas stream by removing oxygen from the gas stream to produce a purified gas stream, said method comprising:

• dividing the gas stream into subsidiary gas streams, introducing the subsidiary gas streams into primary oxygen separation elements to separate a primary portion of the oxygen from the gas stream, and collecting a partly purified gas stream from the primary oxygen separation elements after separation of the primary portion of the oxygen from the gas stream;
• introducing the partly purified gas stream into a secondary oxygen separation element, separating a secondary portion of the oxygen from the partly purified gas stream, thereby to produce the purified gas stream and discharging the purified gas stream from the secondary oxygen separation element;
• each of the primary oxygen separation elements and the secondary oxygen separation element being configured to separate the oxygen through electrically driven oxygen ion transport occurring within the primary oxygen separation elements and the secondary oxygen separation element, being heated to an operational temperature at which the oxygen ion transport can occur and having a first electric potential applied to the primary oxygen separation elements and a second electric potential applied to the secondary oxygen separation element to drive the oxygen ion transport;
• the subsidiary gas streams flowing through the primary oxygen separation elements under conditions of laminar flow;
• and
• the secondary oxygen separation element being sized such that a turbulent flow condition exists within the secondary oxygen separation element.