Reheaters

In modern high pressure steam electric generating systems, steam exhausting the high pressure section of the turbine at around 600 psig and 590 °F is often returned to the boiler to be reheated back to the superheat temperature.

The section of the boiler where this occurs is known as the reheat section. The material of construction of the tubes is gener­ally type 321 stainless or Croloy. The reheat section is in the convection pass, usually lo­cated between the secondary and primary superheater sections.

Reheat temperature control is similar to that in the superheater section in that feedwater is sprayed into the steam path to control outlet temperature. In reheaters, the attemperation spray is generally to the inlet rather than the outlet to reduce the potential for thermal stress.

In addition to contamination in the attemperation spray water, sloughage of turbine deposits is a source of reheater deposits. While any deposition in the reheat section is detrimental, greater tolerance to deposits is exhibited by reheat tubes due to the lower operating pressures than in the Superheater section.

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