Arashk Memarpour, Voicu Brabie, and Pär G. Jönsson:
Studies on the decarburization of commercial submerged entry nozzles
Submerged entry nozzle (SEN), Al2O3-C, ZrO2-C, MgO-C, decarburization, reaction mechanism
The decarburization behaviour of Al2O3-C, ZrO2-C and MgO-C refractory materials constituting a commercial submerged entry nozzle (SEN) were investigated in different gas atmospheres consisting of CO2, O2 and Ar. The (CO2/O2) ratios were kept the same as for propane combustion flue gas at air-fuel-ratio (AFR) values equal to 1.5 and 1 for both air-fuel and oxygen-fuel combustion systems. Laboratory experiments were carried out for non-isothermal heating in the temperature range between 873 K and 1473 K at heating rates of 15 K·min-1 followed by isothermal heating at 1473 K for 60 min. The values of the decarburization ratio a of the three refractory types were determined by measuring the real time weight losses of the samples. The results showed that the a-values of the MgO-C refractory became 3.1 times higher for oxygen-fuel combustion compared to air-fuel combustion at an AFR of 1.5 in the temperature range 873 K to 1473 K. The values of the decarburization ratio for Al2O3-C samples were the same as for isothermal heating at 1473 K and non-isothermal heating in the temperature range from 1473 K to 1773 K with a heating rate of 15 K·min-1. It substantiates the SEN preheating advantage at higher temperatures for a shorter holding time instead of heating at lower temperatures for a longer holding time. Diffusion models were proposed for estimating the decarburization rates of Al2O3-C refractory in SEN. The activation energy for Al2O3-C samples heated at an AFR of 1.5 for air-fuel and oxygen-fuel combustion were found to be 81.8 kJ·mol-1 and 88.8 kJ·mol-1, respectively, during non-isothermal heating in the temperature range from 873 K to 1473 K.
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