Economizers, evaporators, superheaters, and
reheaters are specific heat transfer sections
within the HRSG. Economizers heat the incoming
boiler feedwater to just below the saturation
temperature and supply water to the steam
drum. Evaporators draw water from the steam
drum and heat the water to saturation temperature,
producing a steam-water mixture that is
separated in the steam drum. Evaporators can
have either natural or forced circulation.