CFD evaluation of waterwall wastage in coal-fired utility boilers

With the advent of substoichiometric low NOx combustion in coal-fired utility boilers during recent years, problems with waterwall corrosion have increased. A predictive tool capable of assessing corrosion potential and aiding in the design of problem solutions could help alleviate the utility downtime and cost associated with waterwall wastage. Waterwall wastage has been associated with various mechanisms, including gaseous phase reducing sulfur species, wall deposition of unoxidized sulfur fuel, and fuel chlorine. Integration of predictive correlations for corrosion into a computational fluid dynamics ( CFD) code can provide a framework for evaluation of corrosion potential. In this paper, CFD studies and predictions of corrosion in five utility boilers are examined and compared with observed wastage. The CFD code makes use of approximations of empirically developed corrosion correlations for gaseous phase reducing sulfur species, wall deposition of unoxidized sulfur fuel, and fuel chlorine. Model corrosion predictions are compared with observed or measured wastage in several coal-fired utility boilers, including tangentially fired, wall-fired, and cyclone-fired units.