Erosion of horizontal tubes in a pressurized fluidized bed Influence of pressure, fluidization velocity and tube-bank geometry
Artikel i vetenskaplig tidskrift, 1995
Measurements of local tube erosion were carried out in a cold pressurized bed with horizontal tubes. The influence of fluidization velocity, pressure and circumferential position was studied at different locations within tube banks for three different tube-bank geometries. The erosion results were correlated with the hydrodynamic properties of the bed obtained in a previous investigation under the same operating conditions. At high pressures, the erosion decreases with increasing pressure. Preliminary results from heat transfer measurements in the bed show a significant increase of the bed-to-tube heat transfer coefficient with increasing pressure. Thus, it should be favourable to operate a bed at high pressure levels. The erosion tests were carried out using target tubes coated with a thin layer of stearin. This coating wears rapidly and, thus, an exposure time of 1 h per operating condition was sufficient to obtain an accurately measurable erosion. This exposure time compares favourably with those reported in most other investigations using more erosion-resistant tube materials. The bed has a cross-section of 0.2 m x 0.3 m, and was operated at pressures between 0.1 and 1.6 MPa and at excess gas velocities of 0.2 and 0.6 m/s. Three different tube-bank geometries were used, one with a fairly dense pitch and two with more sparse configurations. The bed material was silica sand with a mean particle diameter of 0.7 mm and a shape factor of approximately 0.8. The erosion results presented here are generally in good agreement with results reported for real tubes under hot conditions, both from atmospheric and pressurized fluidized bed combustors.