Effect of Surface Temperature on Coal Mineral Deposition in Heat Engines

Growing interest in the utilization of coal as a primary fuel for power-generating gas turbines has emphasized the need for further investigation of the problem of mineral ash deposition. In particular, it has been demonstrated [1] that successful operation of a coal-fired gas turbine will require some method to reduce the fraction of ash which adheres to the surfaces of the turbine blades. In a gas turbine application, the products of coal combustion will be directed through a series of stators and vanes which comprise the turbine. Referring to Figure 1, mineral ash deposits have been observed to form on the surface of the blade by particle impaction and capture on the surface of the blade. Not all of the ash particles which collide with the blade stick to form a deposit; some particles rebound and are carried away by the main flow. It has become customary [2,3] to denote the fraction of impacting particles which actually adhere as the sticking fraction, or sticking coefficient. In an effort to find a method to reduce the sticking coefficient to levels acceptable for gas turbine applications, this paper considers the effect of actively cooling the deposition surface. The results suggest that careful control of blade temperatures and combustion temperatures may be part of an effective strategy to control ash deposition.