Inject steam in a gas turbine - but not just for NO/sub x/ control

Most cogeneration systems installed today use gas turbines with heat-recovery steam generators partly because the turbine operates on a wide range of liquid and gaseous fuels and its exhaust contains the high-temperature heat necessary to produce adequate levels of steam. As long as the steam demand of the accompanying process plant is compatible with the required electric power production, the thermal efficiency of this combination rates as high as 70-80%; however, when the electric and steam loads greatly differ, thermal efficiency can drop from 70-80% to 20-30%. Injecting superheated steam into the gas turbine from the heat recovery boiler can be used to boost efficiency and match load output to demand with less cycling of the turbine inlet temperature. Although the steam-injection technology described in this study is based on Detroit Diesel Allison's 501K machine without aerodynamic modifications, it has the potential to be retrofitted to most other gas turbines, with some changes.