Repowering Fossil Steam Power Plants With Combustion Turbine-Based Technologies

Increased competition fostered by changes in legislation governing power generation entities has engendered a need to closely assess the economics of operating older-electric generating units. Decisions must be made as to whether these units should be retired and replaced with new, greenfield generation capacity, whether capacity should be purchased from other generation companies, or whether such units should be repowered in some way. The repowering alternative has merit when economic factors and environmental considerations show it to project the least cost of electricity over other choices. The chief advantages of repowering, include use of existing real estate and infrastructure, existing transmission facilities and staffing. Since the repowered plant usually emits less stack gas pollutants per unit of energy generated then the original plant, environmental benefits can also accrue.Various types of gas turbine based repowering options for steam electric plants are presented. All the approaches discussed involve the addition of gas turbines to the cycle and the consequent benefit of some form of combined cycle operation. This option includes boiler retirement (and replacement with combined cycle), hot or warm windbox repowering (the boiler is retained and a gas turbine topping cycle is added), feedwater heating repowering (the gas turbine exhaust heats feedwater), and site repowering (only the site infrastructure is re-used as the site for a combined cycle). Business considerations are discussed in terms of their impact on the decision to repower and technology selection. An example involving feedwater heater repowering is used to illustrate the interaction between the business and technical aspects of repowering.Copyright © 1996 by ASME