Tubular waterwall structure in a fluidized bed reaction chamber and a fluidized bed reaction chamber

A fluidized bed reaction chamber comprising:

• a tubular waterwall structure, the tubular wall structure comprising:
• multiple vertically extending tubular waterwalls defining the fluidized bed reaction chamber, the tubular waterwalls comprising horizontally adjacent first and second wall portions forming a corner structure and being constituted by vertical tubes interconnected by fins centrally attached to the tubes and having a first width,
• wherein (i) the first wall portion has an outermost tube next to the corner structure, an upper portion defining an upper vertical plane in an upper level range and a lower portion defining a lower vertical plane in a lower level range, the lower portion having a refractory lining and each of the tubes of the first wall portion being bent in an intermediate level region between the upper level region and the lower level region so that the lower vertical plane is shifted outwards from the upper vertical plane, (ii) the second wall portion is vertical and has an outermost tube next to the corner, and (iii) the outermost tube of the second wall portion is in the lower level region connected to the outermost tube of the first wall portion by a planar lower beveled corner fin having a refractory lining and a width that is larger than the first width.