A system for feeding a primary oxidant to an oxy-fired circulating fluidized bed (CFB) boiler. The system includes a plurality of bubble cap assemblies each comprising a stem and a bubble cap with at least one exit hole, each bubble cap connected via a stem to at least one windbox, the windbox containing at least one manifold. A plurality of pipes are provided, each pipe located within a bubble cap assembly with an open end located either at, above or below the exit holes of the bubble caps and an opposite end connected to the manifold located inside each windbox. Recycle gas is piped into the windbox, to the stem, and exiting from the exit holes located in the bubble cap into the CFB. Oxygen is piped into the manifold, through the pipes and exiting through the exit holes located in the bubble cap. The pipe may further contain means placed at its open end, to prevent accidental inlet of hot particles into the pipe, such as a debris shield placed above and proximate to the open end of the pipe or by having the open end oriented in a downward direction. An insulating gap may also be placed inside the bubble cap to reduce thermal conductance between the bubble cap outer surface that is exposed to hot bed material and the inner surface of the bubble cap, being in contact with oxygen.