Abstract

Certain types of fuel used for combustion in land-based gas turbines can contain traces of ash when introduced into a gas turbine. Examples include synfuel, from the gasification of coal, and heavy fuel oil. When these ash particles travel through the hot gas path of the gas turbine they can deposit on turbine vanes and blades. As deposits grow, they can reduce turbine efficiency and damage turbine hardware. As turbine inlet temperatures increase, ash deposition rates increase as well.Experiments were conducted in the Turbine Accelerated Deposition Facility (TADF) at Brigham Young University to better understand ash deposition behavior at modern turbine inlet temperatures. Experiments were conducted that varied deposition duration, gas temperature, surface temperature, ash type and characteristics, and film-cooling blowing ratio. Analysis included measuring and calculating the capture efficiency, deposit surface roughness, deposit density, and deposit surface temperature. Test results indicate that capture efficiency increases with time and as the gas temperature increases. Previous studies have shown that the capture efficiency increases with increasing surface temperature as well, but the results from this study show that at a gas temperature of 1400°C, the capture efficiency of the ash used in these tests initially increased but then began to decrease with increasing surface temperature. It was also shown that different ashes, with differing ash chemistries and densities, deposit at very different rates and produce different surface structures. The film-cooling tests showed that film cooling does reduce the capture efficiency at modern turbine temperatures, but has a smaller relative effect than at lower temperatures. Tests performed with heavy fuel oil ash and increased SO2 levels (similar to those found in heavy fuel oil combustion environments) indicate that the increased sulfur levels result in the formation of more sulfur compounds in the deposit and change which elements are dissolved by water, but has little effect on the amount of deposit that dissolves. CFD simulations were performed to model the fluid dynamics and particle trajectories in the TADF. The resulting particle impact data (particle impact velocity, temperature, diameter, etc.) were used in sticking models to evaluate the models' performance at high temperatures. Results indicate that while the models can be fit fairly well to specific data, they need to be able to better account for changing surface conditions and high temperature particle behavior to accurately model deposition at high temperatures.

Degree

PhD

College and Department

Ira A. Fulton College of Engineering and Technology; Chemical Engineering

Rights

http://lib.byu.edu/about/copyright/

Date Submitted

2017-07-01

Document Type

Dissertation

Handle

http://hdl.lib.byu.edu/1877/etd9471

Keywords

coal, ash, deposition, turbines, IGCC, HFO, film cooling, high temperature

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