With availability of natural gas at competitive prices and increased scrutiny of coal-fired generation, conversion of coal-fired units to natural gas-firing is a popular option to consider as an alternative to capital-intense environmental equipment upgrades or even retirement. Many owners are considering this option as a way to keep an existing plant open while meeting new and pending environmental regulations. There are many technical challenges associated with such a conversion and the owner should consider them all carefully on a case-by-case basis. This paper will present an overview of these challenges, with a focus on the steam generator and what an owner/operator needs to understand when considering conversion to natural gas-firing.
Typical effects of a conversion to natural gas-firing for a utility-scale coal-fired steam generator are discussed along with potential operational effects of such a project. A general discussion of differences in furnace and convective pass performance characteristics for the different fuels is presented along with a discussion of how these differences can translate to technical challenges in a conversion project. Typical effects on boiler efficiency and emissions as well as the most commonly required modifications are reviewed. Finally, a comprehensive review of the operational affects of the converted unit is presented.