An oxyfiring system and method for capturing carbon dioxide in a combustion process is disclosed. The oxyfiring system comprises (a) an oxidation reactor for oxidizing a reduced metal oxide; (b) a decomposition reactor wherein a decomposition fuel is combusted and oxidized metal oxide sorbents are reduced with oxygen being released and a flue gas with an oxygen enriched carbon dioxide stream is produced; (c) a fuel combustion reactor for combusting a primary fuel and the oxygen enriched carbon dioxide stream into a primary flue gas; and (d) separation apparatus for separating a portion of the primary flue gas so that a carbon dioxide enriched stream can be prepared. The method comprises providing a primary fuel and an oxygen enriched carbon dioxide stream to a fuel combustion reactor. The primary fuel and oxygen enriched carbon dioxide stream are combusted into a primary flue gas stream which is split into a first flue gas portion and a second flue gas portion. The first flue gas portion is processed to produce a high purity carbon dioxide stream suitable for sequestration. The second flue gas portion is sent to the decomposition reactor to provide heat and serve as a fluid stream. The primary flue gas may include oxygen or else synthesis gas depending on whether the oxygen enriched carbon dioxide stream contains a stoichiometric excess or deficit of oxygen needed for complete combustion.