Effect of Coal Constituents on the Liquid-Assisted Capture of Impacting Ash Particles in Direct Coal-Fired Gas Turbines

With the growing interest in burning pulverized coal directly in gas turbines, the problem of fouling--blockage of hot-gas pathways by thick ash deposits--is receiving increased attention. The inertial deposition rate of supermicron ash, which determines the fouling propensity of the coal via the thickness of the deposit, depends linearly on the sticking fraction of ash material arriving at the cooled surfaces, e.g., turbine blades and guide vanes. The magnitude and temperature-dependence of the sticking coefficient will depend on the inventory, composition and physico-chemical properties of the liquid glue consistent with the prevailing temperature, pressure and trace inorganic elemental compositions. As the deposit evolves in time, it encounters several deposition regimes in the order of increasing surface temperature, each characterized by a different source of liquid glue. The effect of coal-ash constituents on the extent of each of these sticking regimes is investigated theoretically here by means of a model of self-regulated ash deposition.