Abstract
The waste gas streams from Upgrading processes pass as primary energy sources to two CO boilers. As Upgrading feedrates have increased, the volume flowrate, and properties of the streams have changed to such extent that the boilers have suffered severe reliability problems due to the new, and adverse fireside conditions. Heat flux rates have increased in critical sections of the boiler with consequent disruption in thermal hydraulic flow in water and steam circuits. Departure from nucleate boiling (DNB) and steam blanketing in generating bank tubes have resulted, causing treatment chemicals to precipitate, deposit, and react on the internal surfaces of the water wall tubes.
This paper discusses the use of computational fluid dynamic simulation and other techniques to assess water and fireside conditions for the original, current, and future operating conditions (prior to and post boiler design modifications). The engineered changes required to correct the combustion and thermal hydraulic problems are described, as well as the rationale for introducing equilibrium phosphate treatment as the boiler water chemistry control corrective action. Micro-Raman spectroscopy was used for the first time to confirm the presence of maricite when investigating the root cause of generating bank tube failures. Maricite is one of the definitive corrosion products resulting from acid phosphate corrosion. The paper also discusses the use of the latest Electrical Power Research Institute guidelines for failure mechanism identification in boiler tubes and for monitoring cycle chemistry.
