Abstract
A commercial high temperature fluidized bed has been modified to accept two contra-rotating rotor arms of either a single alloy or small cylindrical sections of different alloys.
Two austenitic steels, type 347 stainless steel and Incoloy 800H, and bright mild steel have been tested at temperatures up to 600°C, a fluidizing velocity of 1.2 x Umf (the minimum fluidizing velocity) and at a rotor speed of 250 rpm which gives a range of particle impact velocities up to 2.5 ms-1. In one experimental run the effect of particle impingement velocity can be determined. Patterns of wear have been observed that closely match those found in industrial fluidized bed combustors.
For the austenitic steels a peak in the wastage rate was found at ~450 °C and for bright mild steel a peak was found at ~300 °C. For each of the steels the wastage fell rapidly with temperature either side of the maximum.
At temperatures above 100 – 200 °C wastage involves the formation and removal of oxide. Tribological enhancement of oxidation is an important feature of the wastage process, and oxide is formed at much greater rates than would be the case during static oxidation.
The mechanisms of erosion-corrosion are discussed in terms of the growth rates of the oxide and its response to low velocity impact. Simply, the peak in wastage rates may be understood in terms of competition between increasing oxidation rates and increasing oxide plasticity as the temperature is raised.
