The fouling behaviour of sodium aluminosilicate polytypes in high ionic strength caustic media heat exchangers
Date
2006
Authors
Addai Mensah, J.
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Asia-Pacific Journal of Chemical Engineering, 2006; 14(1-2):323-336
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Sodium aluminosilicate (SAS) scale formation, simulating high ionic strength caustic media process heat exchanger fouling, has been investigated for a temperature range of 30-240°C. Findings from several studies performed with a variety of liquor, substrate-type and agitation conditions show that SAS polytypes; i.e. amorphous, zeolite A, sodalite and cancrinite phases, differing in thermodynamic stability and kinetic behaviour may deposit. The polytypes formed and subsequent transformations to more thermodynamically stable phases are strongly dependent on liquor composition, temperature and time. The scale deposition process is substrate mediated heterogeneous nucleation and particle growth (precipitation fouling, which may be accompanied by bulk liquor-nucleated solids adsorption (particulate fouling) at sufficiently high supersaturations. Liquor seeding with stable SAS solid phases is found to be effective in mitigating fouling. The precipitation fouling behaviour is principally determined by the crystallo-chemical nature of the SAS polytype and the solution conditions. The substrate (mild steel, 316 stainless steel, nickel and teflon) surface physico-chemical structure has a significant impact on the scale particle morphology and layer structure, particularly at high temperatures.
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Copyright 2006 John Wiley & Sons Ltd.