Optimization of drying through analytical modeling: clays as bonding agents in refractory materials

The objective of this study was to investigate the clay drying as a unit operation in the refractory materials processing. Two clays that varied in chemical and mineralogical compositions were experimentally tested in a laboratory dryer. The results obtained on the green samples prior to drying indicated that clays have adequate plasticity and refractoriness for application in shaped refractories. The operating parameters of the dryer were regulated: temperature ranged from 40 to 60 °C, humidity increased in the interval 30-70%; and the airstream rate was 1.3 m/s. The correlation analysis between operating parameters and calculated and/or measured drying outputs was conducted for better comprehension of the clay׳s role as a refractory binder. Subsequently, a mathematical optimization of the drying regime was conveyed. The effect of the variables (operation parameters) on the drying parameters (critical moisture, equilibrium moisture, dryness degree, etc.) was compared and evaluated. The response surface method, standard score analysis, cluster method, and principal component analysis were used as a means of the drying regime optimization. Assessment of the drying regime impact on the dried samples quality highlighted optimal result for both clay types: SS=0.95, temperature 50 °C, and humidity 40%. Multiple comparison analyses pointed out that optimized combination of the drying operation parameters decreases the quantity of conducted tests. Furthermore, optimal combination of drying parameters reduces negative effects of clay binder inherent properties on the resulting product which in return improves energetic and economic sustainability of refractories production.