A drumless natural circulation boiler system has a furnace enclosure with wall tubes and upper and lower headers connected to respective upper and lower ends of the wall tubes. At least one tangential steam/water separator is connected to a plurality of riser tubes that are also connected to the upper headers. The riser tubes return a steam/water mixture to the separator. Each riser tube is connected to the separator at a tangential nozzle for swirling the steam/water mixture in the separator for separating steam from water in the separator. At least one saturated connecting tube is connected to the separator for conveying steam therefrom. A downcomer is connected to the separator for conveying water from the separator and a plurality of supply tubes are connected between the downcomer and the lower headers. The separator includes a vertically extending cylindrical enclosure and a feedwater conduit is connected to the separator for supplying feedwater to the separator.