Reduction of Ash Deposition in Pulverized Coal Fired Boilers

Abstract

This study proposes reduction technology of ash deposition on the heat exchanger tube in pulverized coal fired (PCF) boilers. Thermal spraying technique is adopted to change the surface properties of tube to reduce the ash deposition. As a result, Ni alloy as a thermal spraying material played an effective role to reduce the deposition under both the ash deposition experiments and the actual coal combustion experiments. However, it is necessary to change ash types in order to evaluate that the thermal spraying technology is universally useful or not. If this technology will be applied to the commercialized PCF boilers, additionally, the effectiveness for the long-term will also be studied as well as the theoretical elucidation on the reduction of ash deposition must be discussed. In this study, therefore, four types of coal ash with different melting points were tested as samples for the ash deposition experiments. The long-term ash adhesion experiments were also carried out, using a precise tension tester at high temperature. As the theoretical approaches, the compositions of each ash particle depositing on the tube surface were analyzed by a computer-controlled scanning electron microscope (CCSEM) with electron dispersive spectroscopy (EDS) detector, thereby the interfacial reactions between the ash deposition layer and the heat exchanger tube were discussed. Those results obtained were also compared to the results obtained by the thermal equilibrium calculations.