A water-cooled column (4) used in a circulating fluidized bed boiler furnace is disclosed, wherein the water-cooled column is formed by connecting membrane water-cooled walls (41). The water-cooled column (4) includes a lower section (A), an upper section and a transition section. The lower section (A) is a single column and is provided with inner secondary air ports (400) on a side wall thereof. The upper section includes a plurality of sub-columns (B, C). The membrane water-cooled walls at the lower section (A) extend to the upper section through the transition section. Each of the sub-columns (B, C) is formed by connecting extension portions extending upward from respective membrane water-cooled walls (41) in the membrane water-cooled walls (41), which are connected to form the lower section (A), and the plurality of sub-columns (B, C) are separated from each other.

A watertube panel portion for a fluidized bed reactor and a corresponding method. The watertube panel portion includes multiple parallel metal tubes having a tube length L1, an outer surface, an original outer diameter OD1, and an original wall thickness WT1, and a circumferentially extending recess formed in a central portion of each of the tubes, between first and second end portions. The recess has a constant depth D that is less than the wall thickness WT1. The recess encircles the outer surface of the central portion of the metal tube. A circumferentially extending metal coating has a constant thickness of at most the depth D of the recess to blanket the recess of each of the multiple metal tubes. A fin is continuously welded between each pair of adjacent tubes.

A watertube panel portion for a fluidized bed reactor and a corresponding method. The watertube panel portion includes multiple parallel metal tubes having a tube length L1, an outer surface, an original outer diameter OD1, and an original wall thickness WT1, and a circumferentially extending recess formed in a central portion of each of the tubes, between first and second end portions. The recess has a constant depth D that is less than the wall thickness WT1. The recess encircles the outer surface of the central portion of the metal tube. A circumferentially extending metal coating has a constant thickness of at most the depth D of the recess to blanket the recess of each of the multiple metal tubes. A fin is continuously welded between each pair of adjacent tubes.

A steam generator is provided. The steam generator has a combustion chamber having a peripheral wall formed at least partially from gas-proof, welded steam generator pipes, at least two additional inner walls formed at least partially from additional steam generator pipes which are arranged inside the combustion chamber. The inner walls are connected one behind the other on the flow medium side by an intermediate collector. The steam generator has a high service life and is reliable. The flow medium on the inlet of the inner wall upstream of the intermediate collector has a lower temperature than that of the flow medium on an inlet of the peripheral wall.