A method of assembling an injection device for use in a reactor injector feed assembly includes extending the injection device at least partially into a cavity. The injection device includes a plurality of substantially concentric conduits coupled to a modular tip that includes a plurality of cooling channels and a plurality of substantially annular nozzles defined therein. The method also includes coupling at least one coolant distribution device in flow communication with the plurality of cooling channels to facilitate removing heat from an outer surface of the injection device.