Densification characteristics of chromia/alumina castables by particle size distribution
© Zhao et al; licensee Springer. 2012
Received: 9 September 2011
Accepted: 5 January 2012
Published: 5 January 2012
The quality of the refractories applied on integrated gasification combined cycle should be a key factor that affects both the reliability and the economics of gasifier operation. To enhance the workability of chromia/alumina castables, three types of ultrafine alumina powder were added to improve the workability. Densification behavior of such castables in the presence of ultrafine alumina was assessed through the measurement of parameters like flow value, viscosity, bulk density, apparent porosity, and microstructure evaluation by an SEM study. It's proved that the specific surface area and particle size distribution of ultrafine powders in matrix parts greatly influence the densification behavior of these castables.
The gasification process converts carbonaceous materials such as coal, petroleum coke, and biomass to synthesis gas consisting of H2 and CO that can be utilized as a chemical feedstock or for powder generation. The ash from the carbon feedstock is liquefied into slag in the gasification chamber and can corrode, penetrate, and interact with the refractory liner at the elevated temperatures, severely limiting refractory service life and gasifier operation . Reaction can occur between refractory materials and slag oxides of Fe, Si, and/or V or with H2 and CO gasification products.
Chromia/alumina castables have been widely used in integrated gasification combined cycle [IGCC]. It provides a number of advantages such as high resistance to slag corrosion and low slag penetration. However, the current generation refractory liners installed in gasifier systems have a short service life . This paper discusses efforts to increase refractory service life through the development of refractory densification. The densification effect was examined by adding ultrafine alumina powder to reduce the amount of water and improve the flow ability of the chromia/alumina refractory castable.
The properties of active alumina
Specific surface area/BET
Particle size distribution
The prepared mix was poured into steel molds with dimensions of 150 × 15 × 15 mm and 50 × 50 × 50 mm for bending and compressive strength tests, respectively. After being cured for 1 day in air, the demoded samples were put into a drying oven for 24 h at 110°C. Then, the dried samples were sintered at 1,300°C and 1,600°C, respectively for 3 h with a temperature elevation of 5°C/min.
Physical properties such as apparent porosity, bulk density, and water absorption were measured. CCS was carried out, and the CAS formation was observed by a scanning electron microscope.
Result and discussion
With the ultrafine alumina addition, the amount of water could be controlled below 5% even in chromia containing alumina castables so that it can fabricate the densified refractory structure.
Ultrafine alumina powder added into the chromia/alumina castable can greatly increase the strength of specimens after sintering; the workability can be enhanced so that it can show high densification and high strength after firing.
Comparing the three ultrafine alumina powders, multimodal alumina is recommended to get a dense body because of the good particle size distribution in the castable.
The bulk density was increased especially at 50% chromia contents so the strength shows high values after firing at a high temperature.
This research was supported by a grant from the Korean Energy Management Corporation (KEMCO) in Korea (2010).
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