System for combusting a methane stream and a method of combustion

A method of combusting a methane stream with an oxygen transport membrane assembly comprising

• a vessel with an internal cavity having a feed side and a combustion side that are separated by an oxygen transport membrane having a composition with a general formula AxA′x′ByB′y′O3−z,
• wherein each of A and A′ is selected from the group consisting of Sr, Ba, La, and Ca, and each of B and B′ is selected from the group consisting of Fe, Co, Cr, and Ga, and wherein each of x, x′, y, and y′ has a value between 0 and 1, such that x+x′=1 and y+y′=1, and z is a number that varies to maintain electro-neutrality of the oxygen transport membrane,
• the method comprising:
• delivering an oxygen-containing stream to the feed side of the vessel, wherein molecular oxygen present in the oxygen-containing stream is transported to the combustion side through the oxygen transport membrane;
• and
• delivering a methane stream to the combustion side of the vessel, wherein methane in the methane stream is combusted with the molecular oxygen to form an exhaust stream that comprises water vapor, carbon dioxide, and molecular oxygen,
• wherein a molar flow rate ratio of methane to the molecular oxygen is in the range of 1:2.1 to 1:3 to provide greater than 7.5 vol % and up to 15 vol % molecular oxygen in the exhaust stream.