In one aspect, a grate segment for a burner, comprises a substantially rigid body (30) having a dispersed array of cavities (38) filled with a refractory material. In another aspect, a solid fuel gasifier includes a housing (12) defining a gasifier chamber (14), and a solid fuel inlet (21), grate structure (22, 24) in the gasifier chamber. The grate structure includes base means, a plurality of agitator segments (32) positioned relative to the base means for reciprocating movement to agitate a fuel load in the gasifier, and means to support the base means and the agitator segments so that the latter reciprocate in a direction at a substantial inclination to both horizontal and vertical. In use of the gasifier a deep burden of fuel accumulates on the grate structure and the outward stroke of the reciprocation of the agitator elements is in the overall direction of flow of the fuel burden or generally oppositely thereto.