Heat Recovery Steam Generators

The Heat Recovery Steam Generator (HRSG) is a critically important subsystem of a Combined Cycle or Cogeneration Power Plant. In most of these plants the HRSG uses the exhaust gas from the gas turbine as the energy source for the production of high pressure and temperature steam. The main difference in these plants is that in a combined cycle power plant the steam generated in the HRSG is used solely in the production of power while in a cogeneration plant the steam can be used for process as well as power production. The Combined Cycle Power Plant uses the steam in a large condensing steam turbine that produces about 40% of the power generated at design conditions, while in a cogeneration application it is not uncommon to bleed the steam from an extraction steam turbine for process purposes. In the cogeneration mode if a steam turbine is used these extraction type steam turbines are usually smaller and may be of a backpressure type.