The primary causes of damage to the refractory lining in the gasifier furnace are mainly attributed to several factors. One key issue is excessive thermal stress. The Texaco burner's cooling coils cause the upper part of the refractory bricks near the burner mouth to remain at a relatively low temperature, while the lower section is exposed to high-temperature radiation and convective heat from the furnace. This significant temperature difference leads to thermal stress, which can result in cracking and spalling of the refractory bricks.
Another major factor is frequent start-up and shutdown cycles. During normal operation, the refractory lining remains at a high temperature, but when the system is shut down—especially during burner maintenance—the cooling effect of the burner cooling coils or the influx of cold air causes a rapid temperature drop. When the system restarts, the temperature rises quickly again. Each cycle resembles an emergency condition, leading to repeated thermal shock. For example, corundum bricks were found to crack after only four quenching and heating cycles. Between 1983 and April 1991, two gasifiers experienced 195 start-stop cycles, with an average of 19.4 days per cycle. Such frequent cycling accelerates the degradation of the refractory material, causing it to crack and lose structural integrity over time.
Additionally, during shutdowns, moisture from the process can condense inside the furnace, especially near the burner area due to the cooling effect of the coils. This condensation, combined with carbon black and slag, contributes to the erosion of the refractory bricks, leading to spalling and loss of material.
A third contributing factor is the insufficient expansion joint size. Original designs featured a 40mm expansion gap, but field observations showed that corundum bricks and castables often protruded above the flange surface, indicating that the joints were too small. Calculations confirmed this issue, and as a result, the expansion of the bricks was restricted, leading to increased mechanical stress and eventual damage.
To address these issues, improvements were implemented starting in January 1988. The number of corundum brick rings was increased from three to five, and the height of each brick was reduced from 123mm to 70mm, which helped reduce thermal stress and minimize cracking. The mortar used was changed from high-sintering alumina to a lower-temperature insulation brick, and the joint between the corundum and corner bricks was redesigned from a flat to a grooved surface to prevent choking.
In the space between the furnace shell and the refractory bricks, 50mm-high white corundum was poured, reinforced with stainless steel wire for added strength. Above this, additional bricks were laid to provide double insulation and prevent the loss of castables. Based on the expansion coefficient of the corundum bricks, the appropriate expansion joint height was calculated to ensure proper alignment and avoid pressure buildup.
Since June 1992, these measures significantly improved the performance of the refractory lining. Cracking and castable loss were largely eliminated, and overheating alarms at the furnace wall were no longer a concern. While the top and upper sections of the cylinder showed minimal thinning (typically 10–30mm), the middle and lower parts experienced faster wear due to direct flame exposure. Despite this, most corundum bricks lasted over 8,000 hours, and the service life of the refractory lining was greatly extended.
Damage to the refractory lining can also be caused by impurities in the raw materials, such as Ni, V, Ca, Na, Fe, and Mg, which react with Al₂O₃ to form low-melting compounds. These compounds can melt and erode the refractory material, especially under high temperatures and gas flow. Additionally, impurities can penetrate the brick pores and react to form new minerals, leading to volume changes and thermal expansion mismatches. This results in cracks and eventual spalling, particularly during temperature fluctuations, start-ups, and shutdowns.
Accidental events, such as burner nozzle damage, cooling coil leaks, misaligned burners, oxygen over-temperature, quench ring failure, or water leakage into the combustion chamber, can also contribute to refractory damage. Poor quality of refractories, improper construction, or inadequate baking processes further exacerbate the problem.
Improvements focused on replacing damaged or thinned corundum bricks in the lower part of the combustion chamber. At this point, the upper sections were still in good condition, so only the most vulnerable areas were addressed, extending the overall service life of the refractory lining.
After years of implementing these improvements, issues like overheating of the furnace wall, short service life of lower corundum bricks, and thermocouple hole overheating were largely resolved. This led to fewer production interruptions and maintenance downtimes. With optimized fuel selection, better operational practices, improved masonry quality, and higher-quality corundum bricks from Luoyang Refractories Research Institute, the refractory lining now lasts up to two years. These advancements have created favorable conditions for stable, long-term fertilizer production.
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