A Heat Recovery Steam Generator (HRSG) is a boiler that gets energy from hot gas source. It could be the exhaust gas from a Gas Turbine, Diesel Engine or process plant. There are several applications of a HRSG boiler, the two most common are Combined Cycle Power Plant (CCPP) and Cogeneration Plant.
In a CCPP, everything focuses on electricity production. The boiler is designed to produce steam for a steam turbine. This increases the overall efficiency of the plant. For small to medium size gas turbines the efficiency goes up to app. 55 %.
In a Cogeneration Plant the process are similar to the CCPP but the HRSG has a Heat exchange module incorporated that also generates heat. This allows for a much lower final outlet temperature of the exhaust gas, thus increasing the overall efficiency up to and above 90%.
The heat generated are commonly used for process heating or district heating/cooling supplying a cheap solution compared to other heating/ cooling processes.