Ash Deposition at Coal-Fired Gas Turbine Conditions: Surface and Combustion Temperature Effects

Abstract

A study of ash deposition from a cleaned bituminous and conventional bituminous coal is presented. An electrically heated drop tube furnace is used to burn the coal and provide deposition conditions representative of proposed coal-fired gas turbines. Variations in the combustion temperature and deposit surface temperature demonstrate that surface cooling may significantly reduce ash deposition, or may provide little benefit, depending on the combustion conditions. Lower temperature combustion produced larger ash particles, with a greater fraction of ash adhering to the deposition test surface. Although the sticking coefficient was higher at the lower combustion temperature, the deposits were readily removed. A modest numerical simulation suggests that the smallest ash particles can experience significant boundary layer cooling and may account for the reduction in sticking observed at some conditions.

Simulations of Multiphase Particle Deposition on a Showerhead With Staggered Film-Cooling Holes

“…Deposition in turbomachinery from ingestion of foreign particles, such as sand, into the engine intake is highly dependent on factors such as combustion temperature and particle melting temperature. Experiments conducted by Wenglarz and Fox [5], Richards et al [6], and Wenglarz and Wright [7] explored the effects of gas and surface temperatures on deposition in turbomachinery. Wenglarz and Fox [5] found that an increase in gas temperature resulted in an increase in the number of molten particles that deposit upon impaction of a turbine surface.…”

“…Wenglarz and Fox [5] found that an increase in gas temperature resulted in an increase in the number of molten particles that deposit upon impaction of a turbine surface. Richards et al [6] found that deposition rates on a surface could be decreased by increasing cooling near the surface. The increased cooling near the surface served to cool particles to a solid state preventing them from sticking to the surface upon impaction.…”

The Effect of Film Cooling on Nozzle Guide Vane Deposition

“…The temperature of the vane was also found to have a direct effect on the amount of deposition. Richards et al [3] isolated and studied two variables of importance in coal ash deposition, surface temperature and combustion temperature. The group showed that deposition at relatively low combustion temperature was insensitive to surface temperature, but at high combustion temperatures low surface temperature reduced sticking probability.…”

“…al. [3] Richards developed governing equations for a particle going through a stagnation flow field with a thermal boundary layer that was developed due to a constant surface temperature boundary condition. Changes in velocity and temperature of the particle were taken into consideration when tracking the particle through the thermal boundary layer.…”

Ash Deposit Formation and Deposit Properties. A Comprehensive Summary of Research Conducted at Sandia's Combustion Research Facility

“…,, ,[, ,,, Recent literature discussing deposit radiative properties indicates their dependence on chemical composition and structure [Goodwin 1986;Wall, Bhattacharya et al 1994]. and for ash deposits in more recent work [Richards, Logan et al 1992;Richards, Slater et al 1993;Wall, 13hattacharya et al 1994] [Boow and Goard 1969]. More formal relationships between composition and emissivity have been investigated [Goodwin 1986], and experimental data illustrating the dependence of emissivity on structural properties [Markham, Best et al 1992] have been reconciled with published theoretical treatments indicating similar trends [Bohren and Huffman 1983].…”