Abstract: There is provided a circulating fluidized bed steam generator (CFB) having an improved structural support system and an improved combined hot solids-gas separator for separating gas and solids from a combined gas-solids stream. The combined hot solids-gas separator is in the form of a cyclone assembly having a plurality of wall portions forming a separation chamber and an inlet for passage of a combined gas-solids stream into the separation chamber. The lowermost extent of the inlet forms a threshold over which the combined gas-solids stream flows in entering the separation chamber. The separation chamber is operable to separate the combined gas-solids stream into a predominantly gas exit stream and a predominantly solids exit stream in a manner by which separated out solids to be discharged from the separation chamber via the predominantly solids exit stream are collected within the separation chamber at a location lower than the inlet.