Marine Radiant Reheat Boilers

To increase plant efficiency reheat systems are used. In this the exhaust from the HP Turbine is led back to the furnace and reheated to superheat temperatures. This allows the steam to be expanded to lower pressures in the LP turbine with reduced need for blade taper twist and other efficiency degrading designs to cope with the steam wetness.

The boiler design is of a standard roof fired radiant furnace with a gas tight membrane water wall and single row of screen tubes. The convection space is devided into a superheater and reheater secion and a section containing superheat and reheat temperature control by-pass economisers. Gas dampers allow cooling air from the windbox to pass over the reheater section during astern manouevres to prevent overheating and thermal shocking when the plant is moved ahead.
An alternate design using water drum attemperation for superheat control rather than by-pass economisers splits the convective zone into two parts

The superheaters in the reheat section ensure that gas is cooled sufficiently to prevent overheating in the reheat in the event of gas dampler leakage. Provision is made to allow windbox air into the reheat space in the event of damper failure.

• Advatages of MRR boiler. These are common with any radiant boiler over the convective type design
  • Increased plant efficiency
  • Improved combustion
  • Less excess air requirement. This has the additional advantage of reducing dew point corrosion in the uptake
  • Refractory limited to burner quarls and exposed section of water drum and bottom header. This allows for poor quality fuels due to reduced slagging
  • Furnace Gas tight