Treated water is pumped under pressure via the water supply pump to the tube-in-tube water pre-heater. The tube-in-tube water pre-heater heats the supply water with hot water discharged from the economizer section. After discharging the tube-in-tube heat exchanger, the supply water flows to the economizer section, is further heated via flue gas, and then flows to the radiant section. The combustion gases from the burner heats the water into steam (80 quality).

The burner combusts fossil fuel and the hot combustion gases transfer the heat of combustion to the water/steam mixture in the radiant section and to the water in the convection section.