Effects of Particle Size, Gas Temperature and Metal Temperature on High Pressure Turbine Deposition in Land Based Gas Turbines From Various Synfuels

Four series of tests were performed in an accelerated deposition test facility to study the independent effects of particle size, gas temperature, and metal temperature on ash deposits from two candidate power turbine synfuels. The facility matches the gas temperature and velocity of modern first stage high pressure turbine vanes while accelerating the deposition process. This is done by matching the net throughput of particulate out of the combustor with that experienced by a modern power turbine. In the first series of tests, four different size particles were studied by seeding a natural-gas combustor with finely-ground coal ash particulate. The entrained ash particles were accelerated to a combustor exit flow Mach number of 0.25 before impinging on a thermal barrier coated (TBC) target coupon at 1183°C. Particle size was found to have a significant effect on capture efficiency with larger particles causing significant TBC spallation during a 4-hour accelerated test. In the second series of tests, different gas temperatures were studied while the facility maintained a constant exit velocity of 170m/s (Mach = 0.23–0.26). Coal ash with a mass mean diameter of 3 μm was used. Particle deposition rate was found to decrease with decreasing gas temperature. The threshold gas temperature for deposition was approximately 960°C. In the third and fourth test series impingement cooling was applied to the backside of the target coupon to simulate internal vane cooling. Ground coal and petcoke ash particulates were used for the two tests respectively. Capture efficiency was reduced with increasing massflow of coolant air, however at low levels of cooling the deposits attached more tenaciously to the TBC layer. Post exposure analyses of the third test series (scanning electron microscopy and x-ray spectroscopy) show decreasing TBC damage with increased cooling levels. Implications for the power generation goal of fuel flexibility are discussed.