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Deposition of hydroxyapatite and calcium oxalate dihydrate on a heat exchanger tube

East, Chris P., Doherty, William O.S., Fellows, Christopher M. , & Yu, Hong (2011) Deposition of hydroxyapatite and calcium oxalate dihydrate on a heat exchanger tube. Asia-Pacific Journal of Chemical Engineering, 6(6), pp. 921-932.

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Abstract

Most studies on the characterisation of deposits on heat exchangers have been based on bulk analysis, neglecting the fine structural features and the compositional profiles of layered deposits. Attempts have been made to fully characterise a fouled stainless steel tube obtained from a quintuple Roberts evaporator of a sugar factory using X-ray diffraction and scanning electron microscopy techniques. The deposit contains three layers at the bottom of the tube and two layers on the other sections and is composed of hydroxyapatite, calcium oxalate dihydrate and an amorphous material. The proportions of these phases varied along the tube height. Energy-dispersive spectroscopy and XRD analysis on the surfaces of the outermost and innermost layers showed that hydroxyapatite was the major phase attached to the tube wall, while calcium oxalate dihydrate (with pits and voids) was the major phase on the juice side. Elemental mapping of the cross-sections of the deposit revealed the presence of a mineral, Si-Mg-Al-Fe-O, which is probably a silicate mineral. Reasons for the defects in the oxalate crystal surfaces, the differences in the crystal size distribution from bottom to the top of the tube and the composite fouling process have been postulated.

Impact and interest:

2 citations in Scopus
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2 citations in Web of Science®

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ID Code: 34322
Item Type: Journal Article
Keywords: fouling, heat exchangers, calcium oxalate, silica, hydroxyapatite, elemental mapping
DOI: 10.1002/apj.487
ISSN: 1932-2135
Subjects: Australian and New Zealand Standard Research Classification > CHEMICAL SCIENCE (030000) > OTHER CHEMICAL SCIENCES (039900) > Industrial Chemistry (039903)
Australian and New Zealand Standard Research Classification > ENGINEERING (090000) > INTERDISCIPLINARY ENGINEERING (091500) > Heat and Mass Transfer Operations (091505)
Divisions: Past > Schools > Chemistry
Current > Research Centres > Centre for Tropical Crops and Biocommodities
Past > QUT Faculties & Divisions > Faculty of Science and Technology
Deposited On: 03 Sep 2010 11:35
Last Modified: 23 Oct 2013 11:56

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