Once-through steam generator having spirally disposed evaporator tubes

A once-through steam generator, comprising:

• a gas flue having a firing region, steam generator tubes with a length L and an outside diameter d, and fins gas-tightly welding said steam generator tubes to one another;
• said steam generator tubes connected in parallel for a throughflow of a flow medium;
• said steam generator tubes having an inner wall surface and an inner surface structure for generating a high heat transfer from said inner wall surface to the flow medium;
• said steam generator tubes disposed approximately in a spiral coil in said firing region;
• and
• each of said steam generator tubes constructed in such a way that points in a coordinate system, determined by pairs of values of said tube length L in said firing region and said outside diameter d of said tube, lie approximately along a straight line defined as follows:
• points determined by pairs of values L=59.7 m, d=31.8 mm and L=93.6 m, d=44.5 mm for a fin width of 12 mm;
• points determined by pairs of values L=64.7 m, d=31.8 mm and L=99.8 m, d=44.5 mm for a fin width of 16 mm;
• and
• points determined by pairs of values L=70.6 m, d=31.8 mm and L=106.9 m, d=44.5 mm for a fin width of 20 mm.