Abstract: A heater for heating turbine exhaust gas (TEG) flowing in a downstream direction through a duct formed by sets of opposing side walls is described. A flame shield has first and second plates which extend symmetrically with respect to a horizontal center line substantially across the duct, diverge in the downstream direction, and terminate in plate edges which are spaced from proximate duct side walls. Each plate defines spaced-apart, first and second slits which communicate an upstream side of the plate with a downstream side thereof. The slits are spaced from the center line and from the plate edges. A heating gas supply pipe extends parallel to the center line across the duct and has a plurality of spaced-apart orifices that face in a downstream direction and are in flow communication with the downstream side of the plate.