Semester

Spring

Date of Graduation

2012

Document Type

Thesis

Degree Type

MS

College

Statler College of Engineering and Mineral Resources

Department

Mechanical and Aerospace Engineering

Committee Chair

Andrew C. Nix

Committee Co-Chair

Seth A. Lawson

Committee Member

Gary J. Morris

Committee Member

Edward Sabolsky

Abstract

Use of coal syngas for Integrated Gasification Combined Cycle (IGCC) industrial gas turbines introduces contaminants into the flow that can deposit onto the components of the first stage of the turbine. These deposit structures may create alterations in the cooling scheme and can erode or react with thermal barrier coatings (TBC). A study was performed to examine the evolution and contributing factors to the growth of deposit structures in a simulated gas turbine environment. Tests were performed in the high pressure/temperature aerothermal facility at the Department of Energy's (DoE) National Energy Technology Laboratory (NETL) in Morgantown, WV. The facility was operated at a pressure of 45 psig and temperatures ranging from 1950°F to 2350°F. Two test article geometries with four film cooling holes non-dimensionally matched to a large-scale industrial gas turbine were created to simulate the pressure side of a first stage vane. A high pressure seeding system was developed to inject coal fly-ash to simulate the build-up of particulate matter experienced by industrial gas turbines into the high pressure facility to perform accelerated deposition of the fly-ash onto the test articles. A method was developed to process the fly-ash to match the theoretical size distribution and particle flow dynamics representative of an industrial gas turbine scaled. Analyses were performed to determine whether the particles reached thermal equilibrium before impacting the test article and to estimate the penetration depth of the particles from the injection tube into the mainstream flow of the facility cross flow. Five independent variable effects were studied; impaction angle, freestream temperature, blowing ratio, surface (TBC or no TBC), and increases in simulated operating hours. In studying the effects of surface impaction angle, deposition increased as the face angle of the test article increased from 10° to 20°. Variation of the freestream temperature showed that the deposition was dependent on a theoretical sticking freestream temperature of 2315oF. Deposition resisted forming at temperatures below the theoretical sticking temperature. In studying the effects of blowing ratio, deposition formation increased as the blowing ratio (mass flux of cooling flow/mass flux of the mainstream flow) decreased from M=1.0, 0.25 and finally to 0.0 (no cooling). The study of the effects of the surface coating on deposition showed that TBC's increased the rate of deposition over the exact same test article that was not coated. Instead of forming new deposits with twice the run time, the deposits started forming on top of other deposits showing that even at high particulate loadings the deposition did not affect the film cooling downstream of the cooling holes. Post test surface roughness scans were planned and performed on the test articles that didn't have deposits break off as they were removed from the facility. Most test articles were not scanned due to the flyash deposits breaking or "sluffing" off as the test article cooled after the conclusion of the test. In contrast, the flyash deposits that formed on the interior (non-TBC coated) walls of the test section did not display any sluffing during cool down. This research is valuable to gas turbine manufacturers and operators to understand the variables that promote deposition so appropriate mitigations can be put in place to prevent engine downtime and component failures.

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