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International Heat Transfer Conference 13

ISSN: 2377-424X (online)
ISSN: 2377-4371 (flashdrive)

EXPERIMENTAL INVESTIGATION OF PARTICULATE FOULING IN WASTE HEAT RECOVERY FROM THE ALUMINUM INDUSTRY

Erling Naess
Department of Energy and Process Engineering, Norwegian University of Science and Technology, N-7491 Trondheim, Norway

T. Slungaard
Department of Energy and Process Engineering, Norwegian University of Science and Technology, 7491 Trondheim, Norway

B. Moxnes
Hydro Aluminium, Norway

Otto K. Sonju
Department of Energy and Process Engineering, Norwegian University of Science and Technology, 7491 Trondheim, Norway

DOI: 10.1615/IHTC13.p19.20
11 pages

Abstrakt

The main objective of the present study is to establish criteria for energy recovery from dust-laden off-gases from aluminum electrolysis cells. No earlier measurements have been reported in the literature for this application.
An experimental investigation of particulate fouling from a real industrial gas stream on bare and finned tubes in crossflow has been performed. The gas stream is an exhaust gas from an aluminum smelting plant, containing approximately 200 mg/Nm3 dust particles with a cut size of ca. 0.5 μm. A small test section consisting of a bare tube and an annular-fin tube were used for the tests.
The heat transfer degradation as a function of time at various gas approach velocities and temperatures was recorded for experiments with duration from 40 to more than 2000 hrs. A simplified data reduction procedure provided quantitative information on the effect of deposit formation.
Fouling resistances increased with time during the first period of operation. Asymptotic fouling resistances were obtained for superficial flow rates above ca 10 kg/m2s, but did not stabilize for the lower flow rates. The net fouling rates decreased with increasing flow velocities. The annular-fin tube experienced a slightly higher fouling rate than the unfinned tube.
Visual observations of the deposit showed that the major part of the particle deposition was on the downstream side of the tubes. For the annular-fin tube, the flow passages between the fins were completely blocked by deposits in the shadow region of the tube. On the upstream side, fluffy deposits were obtained both on the tube and fin surfaces at low velocities. At higher velocities, the deposit became harder, but significantly thinner.

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