Abstract
From the total electricity generated in South
Africa, about 85% is coal based. Coal powder is a solid fuel
used in injectors for electricity production. The coal powder is
extremely abrasive therefore it is important to maintain a
minimum admissible flow speed. As the most severe pipe wall
erosion takes place in bends, the most significant factor
influencing wall erosion is the solid particle velocity. The aim
of this research was to reduce the wall erosion through flow
velocity control. Computational fluid dynamics (CFD)
simulations, showed that for the same velocity, the erosion is
dependent on flow direction change and the ratio between the
radius of the bend and pipe diameter. The reduction of flow
velocity was achieved by subtracting a spiral volume, from the
inner volume of a horizontal pipe, just before an upward or
downward bend. The modified volume geometry generated a
vortex flow in the bend, achieving a more even distribution of
maximum erosion points over the bend surface. The wall
erosion, expressed in mm–wall thickness loss/hour, in the
modified volume decreased by about 28,8 % while the
installation life expectancy increased significantly.
Furthermore the bend radius was proved to influence the
erosion magnitude and location.