thumb|Modular HRSG

A heat recovery steam generator (HRSG) is a heat exchanger that recovers heat from a hot gas stream, such as waste gas from combustion turbine. It produces steam that can be used in a process (cogeneration) or used to drive a steam turbine (combined cycle).

HRSGs

thumb|Modular HRSG GA

HRSGs consist of four major components: the economizer, evaporator, and the superheater and water preheater. The different components are put together to meet the operating requirements of the unit. See the attached illustration of a Modular HRSG General Arrangement.

Modular HRSGs can be categorized by a number of ways such as direction of exhaust gas flow or number of pressure levels. Based on the flow of exhaust gases, HRSGs are categorized into vertical and horizontal types. In horizontal type HRSGs, exhaust gas flows horizontally over vertical tubes whereas in vertical type HRSGs, exhaust gas flows vertically over horizontal tubes. Based on pressure levels, HRSGs can be categorized into single pressure and multi pressure. Single pressure HRSGs have only one steam drum and steam is generated at a single pressure level, whereas multi pressure HRSGs employ two (double pressure) or three (triple pressure) steam drums. As such, triple pressure HRSGs consist of three sections: an LP (low pressure) section, a reheat/IP (intermediate pressure) section, and an HP (high pressure) section. Each section has a steam drum and an evaporator section where water is converted to steam. This steam then passes through superheaters to raise the temperature beyond the saturation point.

The steam and water pressure parts of an HRSG are subjected to a wide range of degradation mechanisms, for example creep, thermal fatigue, creep-fatigue, mechanical fatigue, Flow Accelerated Corrosion (FAC), corrosion and corrosion fatigue, amongst others.

Additionally, HRSGs can include cold water heat exchangers designed to condense moisture in flue gases, reducing emissions and increasing efficiency.

Packaged HRSGs

Packaged HRSGs are designed to be shipped as a fully assembled unit from the factory. They can be used in waste heat or turbine (usually under 20 MW) applications. The packaged HRSG can have a water-cooled furnace, which allows for higher supplemental firing and better overall efficiency.

Applications

  • Heat recovery can be used extensively in energy projects.
  • In the energy-rich Persian Gulf region, the steam from the HRSG is used for desalination plants.

Block diagram

thumb|left|800px|Block diagram of [[Integrated gasification combined cycle|IGCC power plant, which utilizes the HRSG]]

thumb|left|800px|Block diagram of HRSG in Combined Cycle

See also

  • Exhaust heat recovery system
  • BMW Turbosteamer
  • Oxygenated treatment
  • Monotube steam generator

References

  • HRSG Users