DEVELOPMENT AND APPLICATION OF TUBE FURNACE TO REPLICATE GAS TURBINE COMBUSTION ENVIRONMENT

Abstract

Implementation of hydrogen in gas turbines has garnered significant attention over recent years. However, the effects of moisture as a byproduct of the flue gas caused from the combustion of hydrogen enriched natural gas in a gas turbine is detrimental to the health of the gas turbine. Specifically, the thermal barrier coatings used to protect the gas turbine’s fins from extreme heat tend to oxidize and degrade when encountering moisture or steam. A tube furnace or dual furnace apparatus was developed to test novel thermal barrier coating materials for extended periods of time at various moisture levels. In addition to the novel thermal barrier coating materials, the conventional thermal barrier coating materials were tested in the tube furnace for a quantitative comparison of the results. After thermal barrier coating materials were tested inside the tube furnace, analysis of the samples were performed using Scanning Electron Microscopy with Energy-Dispersive X-ray Spectroscopy to observe the development of the oxidization layer within the thermal barrier coating materials.In order to replicate gas turbine combustion environments, strategic design constraints and limitations were implemented. Specifically, a constraint to maintain stable temperature at approximately 1500 °C and a constraint to maintain stable moisture concentration was considered. To further replicate the conditions that a thermal barrier coating would be subjected to, the specific concentrations of flue gases from a flame that is created within a gas turbine needed to be calculated. ANSYS CHEMKIN a chemical kinetics solver, was utilized to perform equilibrium calculations on a flame with set input conditions to get the desired moisture concentration and flue gas concentration. An equivalence ratio of 0.4 was maintained across each moisture condition, while the oxidizer mixture (oxygen & nitrogen) and fuel mixture (methane & hydrogen) were varied iteratively to attain the desired moisture concentration. After performing CHEMKIN simulations, moisture concentrations of 10.5%, 18.1%, 36.1%, and 44.0% as well as the corresponding flue gas concentrations for each moisture concentration were extracted to be utilized in the dual furnace apparatus. The thermal barrier coating materials were tested inside the dual furnace apparatus for each of the conditions for test times of 15, 30, 45, 60, and 180 minutes. This enables an investigation of the effects of moisture concentration and exposure duration on the different thermal barrier coating materials. Results indicate a significant reduction in interfacial layer growth for novel thermal barrier coating materials compared to conventional thermal barrier coating materials during the early oxidation stage.