After the steam has been generated from the heat of combustion of the fuel, flue gases created from the process go through the HRSG before exiting the system. The HRSG has the flue gas inlet from one side and the water inlet from the opposite. There are different zones, each having multiple passes for the water, and due to the heat exchange from the hot waste gases to the water, you get super-heated or saturated steam at the end.
Because flus gas generated from Gas engine or Gas turbine is higher than saturated steam.
The stack gases can reach temperatures over 1000°C, and they will all go to waste if not used properly. With HRSG, the heat in those flue gases will be used again to generate more steam, which will save additional fuel costs, reduce overall energy consumption and increase the overall efficiency of the whole system.
Greenhouse gases raise average temperature of our planet, we are trying to take care of this environmental issue. HRSG get the heat from gas engine or gas turbine reduce fuel consumption in factory which also reduce CO2 emission and the greenhouse effect.