Failure Analysis and Improvement Measures of Grate Bars Used in Iron Ore Pelletizing Plant

Stainless steel grate bars are one of the important components of pallet cars used in straight grate iron ore pelletizing plant. Their service life has a major influence on plant productivity and pellet quality. The objective of this work is to find the root cause of grate bars premature failure and suggest preventive measures. To reach this objective, failed grate bars were studied which includes examination of accumulated corrosives obtained from grate bars, surface and cross-sectional characterization of failed grate bars using scanning electron microscope equipped with energy-dispersive spectroscopy. The study also includes laboratory corrosion simulation tests on fresh grate bar samples using 1M Na 2 SO 4 solution, 1M NH 4 Cl solution and water associated with coal tar used in pellet plant. Failed grate bars from the pellet plant were compared with the corrosion exposed simulated grate bar samples. The study showed that the plant grate bar failure occurred due to intergranular corrosion caused by high-chloride input into the furnace wherein the major source of chloride was coal tar water. The damage was aggravated by the presence of alkalis and sulfur combined with the thermal cycling and erosive action in the furnace. Based on the findings, the water content of coal tar was reduced from ~ 6.0 to 1.0 (in wt.%) and stainless steel grate bar composition was modified. This combined effect led to an increase in the grate bar life from six months to ~ 16-18 months. It also resulted in a significant decrease in specific consumption of grate bar from ~ 120 g/ton of pellets to ~ 10 g/ton of pellets.