Heat recovery steam generator

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A heat recovery steam generator or HRSG is a heat exchanger that recovers heat from a hot gas stream. It produces steam that can be used in a process or used to drive a steam turbine. A common application for a HRSG is in a combined-cycle power station, where hot exhaust from a gas turbine is fed to an HRSG to generate steam which in turn drives a steam turbine. This combination produces electricity more efficiently than either the gas turbine or steam turbine alone. The HRSG is also an important component in cogeneration plants.

HRSGs normally consist of three sections: an LP (low pressure) section, a reheat/IP (intermediate pressure) section, and a 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 and pressure past the saturation point.

Some HRSGs include supplemental, or duct, firing. These additional burners provide additional energy to the HRSG, which produces more steam and hence increases the output of the steam turbine. Generally, duct firing provides electrical output at lower capital cost but inferior efficiency compared with combined cycle generation. It is therefore often utilised for peaking.

Emissions controls may also be located in the HRSG. Some may contain a Selective Catalytic Reduction system to reduce nitrogen oxides (a large contributor to the formation of smog and acid rain) and/or a catalyst to remove carbon monoxide.

[edit] 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.