The relative erosivity of limestone, dolomite and coal samples from an operating boiler

The erosivity of limestone, dolomite and coal samples retrieved from an operating boiler was determined in an elevated-temperature laboratory erosion tester. Test conditions attempted to simulate the erosion conditions found at the tubes in the bare tube-refractory interface area of CFBC boilers. Elevated-temperature erosion tests were conducted on AISI 1018 steel. Test results were compared to erosion test data for bed ash, limestone and dolomite samples retrieved from other plants and tested under similar conditions. Data comparison indicated that all five samples tested in this work had relatively low erosivity and the erosivity of limestones (or dolomites) retrieved from different sources varied widely. The value difference between the highest erosive dolomite and the lowest erosive one may reach 100-fold. Some high erosive dolomites may even show higher erosivity than the high erosive bed ashes. Therefore, some limestones (or dolomites) can contribute to the erosivity of the ash in FBCs. Among the three coal samples tested, the Hawthorn coal (Indiana coal) caused the highest wastage, whereas the Rochelle coal (Western coal) caused the lowest erosion wastage, with 5-fold difference between the highest and lowest values. Higher wastage was associated with lower moisture content, higher ash content and the higher concentration of hard erosive species in the coal ash, such as SiO 2, Al 2O 4 and Fe 2O 4. The influence of limestone and coal mineralogy was discussed with regards to erosion potential in the boiler.