THE INTERACTION OF SYNTHETIC PETCOKE SLAGS WITH ALUMINA CRUCIBLES
Open Access
- Author:
- Karri, Kashyap
- Graduate Program:
- Energy and Mineral Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- October 31, 2018
- Committee Members:
- Mort D Webster, Thesis Advisor/Co-Advisor
Chiara Lo Prete, Committee Member
Seth Adam Blumsack, Committee Member - Keywords:
- petcoke
slags
refractory
refractory depletion
slag interaction
high-temperature viscometry - Abstract:
- Entrained flow gasifiers generate ash as a byproduct while producing syngas. The high temperature inside the gasifier melts the ash and the resulting slag flows down along the refractory-lined (usually high alumina) walls of the gasifier. During high temperature viscosity measurement experiments simulating the conditions found inside gasifiers, it was found that the walls of the crucible, made of alumina lost thickness and developed perforations that cause the molten slag to leak out. The problem of depletion of refractory material when in contact with molten petcoke ash slags was investigated using thermodynamic equilibrium calculation software FactSage™ to identify the cause. Simulations were performed using synthetic petroleum coke ash slags in high density alumina crucibles. During the simulations to identify the thermodynamically stable phases at various temperatures in 1050-1650°C range, it was found that if the amount of alumina present in the initial slag was less than the equilibrium value, then the alumina from the crucible was dissolved into the slag to achieve the equilibrium levels. Simulations carried out in 100%H2, 5% H2/ 95% N2, ¬ 69.5% CO/ 30.5% CO2 and 100% O2 atmospheres showed that pure H2 atmosphere produced the least amount of alumina at equilibrium, suggesting that the atmosphere played a role in dissolution of alumina from the crucible. The simulations with varying contents of alumina suggested that a deficit of alumina in the starting mix favored the slag picking it up from the crucible. This hypothesis was tested experimentally by heating a synthetic slag mixture containing higher amount of alumina to 1500°C in 5% H2/N2 atmosphere, thus simulating the conditions encountered during the viscosity measurement experiment. During FactSageTM simulations, it was observed that 5% H2/N2 mixture was as reducing atmosphere as CO/CO2 (30.5%:69.5%) from the perspective of alumina dissolution into the slag. This was confirmed by x-ray diffraction (XRD) analysis of the two samples, as the patterns revealed the existence of similar compounds (anorthite, corundum, and crystobalite) in the bulk of the slags in both cases. Scanning electron microscopy- energy dispersive spectroscopy (SEM-EDS) analysis of the samples showed that the ash sample with lower initial content of alumina showed higher amounts of aluminum at the slag-crucible interface, thus confirming the hypothesis, while the concentration of alumina in the other case was very low, indicating very little, if any dissolution from the crucible surface. This study suggests that addition of alumina-rich material to slags with lower alumina contents helps minimize the interaction of slag with the refractory wall and its degradation. This leads to lower depletion of alumina from the wall material and reduces the degradation of refractory walls.