Performance and economic considerations of repowering steam power plants

Abstract

Repowering is broadly defined as an addition to or replacement of existing power plant equipment, retaining serviceable permitted components to improve generation economics, extend life, improve environmental performance, enhance operability and maintainability, and more effectively use an existing site. The most common form of repowering uses a gas turbine whose exhaust is used either as preheated combustion air, energy for feedwater heating or the displacement of steam from a fossil fuel fired boiler. Using the gas turbine exhaust as the steam supply in a conventional steam cycle results in the greatest increase in system output, most improved thermal efficiency and the greatest reduction in environmental emissions relative to the other available repowering options. Repowering may be an economically viable option at sites fuelled with natural gas and/or distillate oil, or coal or other solid or less desirable liquid fuels if a gasification system is included. This paper discusses the technical and economic aspects of available gas turbine-based repowering options focusing primarily on the steam displacement, or heat recovery repowering, alternative. Included are performance and operating characteristics as well as an example illustrating the economic merit of this technology. The environmental benefits of repowering and their impact on the generation system planning process in regions where environmental externalities are included in least cost planning evaluations are also illustrated. 20 figs., 7 tabs.