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The Fouling Behaviour of Sodium Aluminosilicate Polytypes in High Ionic Strength Caustic Media Heat Exchangers
Author(s) -
AddaiMensah J.
Publication year - 2006
Publication title -
developments in chemical engineering and mineral processing
Language(s) - English
Resource type - Journals
eISSN - 1932-2143
pISSN - 0969-1855
DOI - 10.1002/apj.5500140128
Subject(s) - fouling , sodium aluminosilicate , chemical engineering , nucleation , precipitation , ionic strength , sodalite , materials science , zeolite , aluminosilicate , substrate (aquarium) , particle (ecology) , adsorption , amorphous solid , heat exchanger , chemistry , thermodynamics , catalysis , organic chemistry , aqueous solution , geology , engineering , biochemistry , physics , oceanography , membrane , meteorology
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 foulin&, which may be accompanied by bulk liquor‐nucleated solids adsorption (particulate fouling) at suficiently high supersaturations. Liquor seeding with stable SAS solid phases is found to be efective in mitigating fouling. The precipitation fouling behaviour is principally determined by the clystallo‐chemical nature of the SAS polytype and the solution conditions. The substrate (mild steel, 316 stainless steel, nickel and tef2on) surface physico‐chemical structure has a signlficant impact on the scale particle morphology and layer structure, particularly at high temperatures.