From oil to gas firing of large utility boilers: How to improve both environmental impact and operating costs

In the 80s, Middle East Countries commissioned hundreds of oil-fired utility boilers, to support their tremendous economic development. Twenty years later, these assets are aging. Owners seek ways to improve their availability and reduce operating costs. In addition development must now be sustainable, i.e. environmentally friendly: reduction of NOx, SOx and particulate emissions is now a priority. A new fuel, suitable to meet these new economical and environmental challenges is now widely available and competitive: natural gas. Switching to natural gas can follow two options: scrap the aging boilers and replace them with heavy-duty gas turbines, or modify the boilers to burn natural gas. The latter solution allows continued use of the existing plant infrastructure while meeting the goals of improved performance and reduced emissions. Such conversions are not, however, only a simple matter of straight burner replacement, as some owners unfortunately discovered. Gas firing is significantly different compared to oil. Complete re-check of the boiler design is necessary, and may lead to significant modifications of the surperheaters and reheaters. It makes sense, at fast, to combine such fuel switching with a rehabilitation of other boiler components and pressure parts within a comprehensive package, supported by full performance guarantees. The paper will summarize our wide experience in this field. Then, the boiler gas conversion currently implemented by ALSTOM at TABRIZ power station will be presented, as well as other examples in Jordan and Venezuela.

Keywords:

natural gas firing , utility boiler , fuel switching , dual firing