Interaction of olive pomace ash and coal ash with magnesium oxide based refractories

• In quicklime production, limestone is calcined at temperatures above 1000°C, depending on the desired product quality. Heat is supplied to the process from combustion inside the kilns that are insulated to reduce heat loss. The kilns are lined with insulating refractory bricks to withstand the hot, chemically aggressive, and mechanically abrasive environment. Magnesia bricks have emerged as well-performinglining materials, but they are still prone to extensive wear in kilns that are operated at higher temperatures. In particular, refractory corrosion can be caused by fuel ash infiltration that results inmaterial wear, which can incur high maintenance and operational costs through unplanned shutdowns of the kilns. At the same time, to reduce the release of fossil-based carbon to the atmosphere, it is of interest to introduce bio-based fuels into the kilns with only relatively small modifications to the process. Biobased waste streams from existing industries are preferable rather than biomass grown with the sole purpose of combustion. The ash content and properties of these types of waste residues do, however, tend to be problematic from a fuel ash chemistry point of view. Therefore, before introducing a new fuel, their potential effects on kiln lining material should be investigated. In this study, the infiltration of olivepomace ash and coal ash into commercially available refractory materials composed of mainly periclase(MgO) with minor amounts of spinel (MgAl2O4) were compared. They were exposed to the fuel ashes under a simulated lime kiln high CO2 atmosphere at 1200 and 1400°C for 15 and 60 minutes. The morphology and elemental composition of the exposed samples were investigated with scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy. Ash-forming elements infiltrated the porous parts of the materials. The analytical results are complemented with thermodynamic equilibrium calculations to investigate the ash melting behavior. Crystalline phases in the residual ashes were investigated with X-ray diffraction. Refractory phases could be found in both ashes, indicating migration of refractory constituents. Olive pomace ash formed new crystalline compounds together with the refractory components whereas this was not observed for the coal ash, indicating that the former is more of a risk for material failure.  

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Kemiteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Chemical Engineering (hsv//eng)

Nyckelord

Coal ash

Olive pomace ash

MgO refractory

Corrosion

Slag intrusion

Potassium

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