A device for the injection and mixing of steam into a fluid stream. The device is intended to be used in a substantially cylindrically-shaped primary conduit having a longitudinal axis and circular cross-section for carrying the fluid stream. The primary conduit is provided with an inlet for accepting the fluid stream and an outlet for discharging the fluid stream along the longitudinal axis. A secondary conduit is joined to the primary conduit for discharging steam within the fluid stream along the longitudinal axis. A biscuit element is provided of sintered tungsten having upstream and downstream circular faces sized to fit within the primary conduit along its interior wall having a geometric center coincident with the longitudinal axis and having a plurality of openings, each having a longitudinal axis parallel to the longitudinal axis of the primary conduit. Each opening is provided with a mixing element that induces a rotational angular velocity to the fluid stream passing therethrough. Conically-shaped features extend from the circular faces and are centered along the longitudinal axis at the geometric centers thereof.