Heat recovery steam generator

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

Some may contain a selective catalytic reduction system to reduce nitrogen oxides (a large contributor to the formation of smog and acid rain) or a catalyst to remove carbon monoxide.

Some low-temperature NOx catalysts have recently come to market that allow for the SCR to be placed between the evaporator and economizer sections (350–500 °F [177–260 °C]).

In this design, the inlet feedwater follows a continuous path without segmented sections for economizers, evaporators, and superheaters.

This provides a high degree of flexibility as the sections are allowed to grow or contract based on the heat load being received from the gas turbine.

The absence of drums allows for quick changes in steam production and fewer variables to control, and is ideal for cycling and base load operation.

This eliminates the need for a bypass stack and exhaust gas diverter system which is required to operate a combustion turbine with a drum-type HRSG out of service.