German A Barrera
Consulting engineer, Cali, Colombia; germanabarrera@gmail.com
The effects of corrosion due to the presence of sulphur in fuel have been widely studied and recommendations have been made on the position of economizer-heater arrangement, minimum temperatures of air, water and gases and others. However, corrosion at the back of the boiler occurs in some equipment and can cause significant impacts on ducts and other structural elements when coal is not burned, or when mixtures with less than 5% by weight low-sulphur coals are burned; bagasse only fired boilers have back-end corrosion. What is the mechanism that generates corrosion and attacks structural surfaces and ducts?, What elements other than sulphur or associated with the presence of sulphur in low quantities can generate corrosion in the back end? Why the increase in the amount of ash and unburned fuel, even when typical rates for burning biomass are maintained in the furnace and residence times of 3 to 4 seconds are guaranteed with oxygen values measured at the boiler outlet that correspond to excess air values of 25 to 30%? These questions led me to look for changes associated with fuel such as the increase in the proportion of mechanized harvesting compared to manual harvesting, the decrease in pre-harvest burning, and the increase in milling in the rainy season and the impacts generated. Findings indicate that there is a generalized tendency to associate corrosion phenomena with the presence of sulphur and its dew point. There appears to be a lack of knowledge of the other corrosion mechanisms associated with ash and inorganic elements. Possible correlations are outlined and should generate follow-ups that will determine the cause of this corrosion of the back of the boiler.