IBRAHIM, AKEEM OSAMWONYI

This study presented a comprehensive investigation into the failure mechanism and performance modelling of the combustion and emission characteristics of an industrial dualfired steam boiler operating on natural gas and diesel. The study was driven by the reoccurring failure on the third pass, operational inefficiencies and concerns over the environmental performance observed in the boiler system of a bottling company in Nigeria The failure investigation component of the study involved a systematic diagnostic assessment of the third-pass tubes including visual inspection, chemical composition analysis, micro- structural analysis and water chemistry analysis. For performance evaluation, the study employed experimental measurements and computational fluid dynamics (CFD) simulations using ANSYS Fluent to model combustion dynamics, temperature distribution, pollutant formation, and flue gas flow behaviour under various operating loads and fuel combinations. The models were validated against plant data, Furthermore, parametric studies were conducted to optimize key operational boiler control parameters such as air flow, load, variable frequency drive (VFD) and fuel flow rate using Taguchi methodology. Failure investigation results revealed key degradation phenomena due to due to thermal stresses, corrosive water chemistry, tube fouling, scaling, fouling-induced heat transfer impairment. Also, micro-structural examination showed thermal degradation, including decarburization, grain growth, and oxidation, alongside pitting corrosion, indicating high-temperature exposure and scale deposition weakened the metal. The water chemistry analysis revealed elevated levels of total dissolved solids, P-alkalinity, chloride, and silica in the boiler drum water, which contribute to scaling and localized overheating. Major failures was traced to inadequate water treatment and poor combustion control. CFD simulations revealed that scale layers significantly reduces heat transfer, leading to increased failure risk. An optimal water mass flow rate of 0.454kg/s was determined as the effective mass flow rate to attain the desired outlet steam temperature. The study revealed load as the most influential factor, leading to reduced emissions, improved combustion, operational stability and prolonged component life. The findings provide insights into enhancing boiler reliability, thermal efficiency, and environmental compliance.

This study presented a comprehensive investigation into the failure mechanism and performance modelling of the combustion and emission characteristics of an industrial dualfired steam boiler operating on natural gas and diesel. The study was driven by the reoccurring failure on the third pass, operational inefficiencies and concerns over the environmental performance observed in the boiler system of a bottling company in Nigeria The failure investigation component of the study involved a systematic diagnostic assessment of the third-pass tubes including visual inspection, chemical composition analysis, micro- structural analysis and water chemistry analysis. For performance evaluation, the study employed experimental measurements and computational fluid dynamics (CFD) simulations using ANSYS Fluent to model combustion dynamics, temperature distribution, pollutant formation, and flue gas flow behaviour under various operating loads and fuel combinations. The models were validated against plant data, Furthermore, parametric studies were conducted to optimize key operational boiler control parameters such as air flow, load, variable frequency drive (VFD) and fuel flow rate using Taguchi methodology. Failure investigation results revealed key degradation phenomena due to due to thermal stresses, corrosive water chemistry, tube fouling, scaling, fouling-induced heat transfer impairment. Also, micro-structural examination showed thermal degradation, including decarburization, grain growth, and oxidation, alongside pitting corrosion, indicating high-temperature exposure and scale deposition weakened the metal. The water chemistry analysis revealed elevated levels of total dissolved solids, P-alkalinity, chloride, and silica in the boiler drum water, which contribute to scaling and localized overheating. Major failures was traced to inadequate water treatment and poor combustion control. CFD simulations revealed that scale layers significantly reduces heat transfer, leading to increased failure risk. An optimal water mass flow rate of 0.454kg/s was determined as the effective mass flow rate to attain the desired outlet steam temperature. The study revealed load as the most influential factor, leading to reduced emissions, improved combustion, operational stability and prolonged component life. The findings provide insights into enhancing boiler reliability, thermal efficiency, and environmental compliance.