Turbine Accelerated Deposition Facility Research Articles

Formation of deposits from heavy fuel oil ash in an accelerated deposition facility at temperatures up to 1219 °C

Some industrial gas turbines are currently being fired using heavy fuel oil, which contains a small percentage of inorganic material that can lead to fouling and corrosion of turbine components. Deposits of heavy fuel oil ash were created in the Turbine Accelerated Deposition Facility (TADF) at Brigham Young University under gas turbine-related conditions. Ash was produced by burning heavy fuel oil in a downward-fired combustor and collecting the ash from the exhaust stream. This ash was then introduced into the TADF and entrained in a hot gas flow that varied from 1101 °C to 1219 °C. Sulfur dioxide was introduced to the system to achieve 1.1 mol% SO2 in the exhaust to simulate SO2 levels in turbines burning heavy fuel oil. The gas and particles were accelerated to over 200 m/s before impinging on a nickel-based superalloy coupon and forming deposits. The ash deposits were collected and the capture efficiency, surface roughness, and deposit composition were measured. The deposits were then washed with deionized water, dried, and the analysis was repeated. As the gas temperature increased, there was no effect on capture efficiency and the post-wash roughness of the samples decreased. Washing aided in the removal of sulfur, magnesium, potassium, and calcium.

Independent Effects of Surface and Gas Temperature on Coal Fly Ash Deposition in Gas Turbines at Temperatures up to 1400 °C

Deposition of coal fly ash in gas turbines has been studied to support the concept of integrated gasification combined cycle (IGCC). Although particle filters are used in IGCC, small amounts of ash particles less than 5 μm in diameter enter the gas turbine. Previous deposition experiments in the literature have been conducted at temperatures up to about 1288 °C. However, few tests have been conducted that reveal the independent effects of gas and surface temperature, and most have been conducted at gas temperatures lower than 1400 °C. The independent effects of gas and surface temperature on particle deposition in a gas turbine environment were measured using the Turbine Accelerated Deposition Facility (TADF) at Brigham Young University. Gas temperatures were measured with a type K thermocouple and surface temperatures were measured with two-color pyrometry. This facility was modified for testing at temperatures up to 1400 °C. Subbituminous coal fly ash, with a mass mean diameter of 4 μm, was entrained in a hot gas flow at a Mach number of 0.25. A nickel base super alloy metal coupon 2.5 cm in diameter was held in this gas stream to simulate deposition in a gas turbine. The gas temperature (and hence particle temperature) governs the softening and viscosity of the particle, while the surface temperature governs the stickiness of the deposit. Two test series were therefore conducted. The first series used backside cooling to hold the initial temperature of the deposition surface (Ts,i) constant at 1000 °C while varying the gas temperature (Tg) from 1250 °C to 1400 °C. The second series held Tg constant at 1400 °C while varying Ts,i from 1050 °C to 1200 °C by varying the amount of backside cooling. Capture efficiency and surface roughness were calculated. Capture efficiency increased with increasing Tg. Capture efficiency also initially increased with Ts,i until a certain threshold temperature where capture efficiency began to decrease with increasing Ts,i.

Time-Dependent Deposition Characteristics of Fine Coal Fly Ash in a Laboratory Gas Turbine Environment

Time-dependent deposition characteristics of fine coal fly ash were measured in the Turbine Accelerated Deposition Facility (TADF) at Brigham Young University. Two samples of subbituminous coal fly ash, with mass mean diameters of 3 μm and 13 μm, were entrained in a hot gas flow with a gas temperature of 1288 °C and Mach number of 0.25. A nickel-based, superalloy metal coupon approximately 0.3 cm thick was held in a hot particle-laden gas stream to simulate deposition in a gas turbine. Tests were conducted with deposition times of 20, 40, and 60 min. Capture efficiencies and surface roughness characteristics (e.g., Ra) were obtained at different times. Capture efficiency increased exponentially with time, while Ra increased linearly with time. The increased deposition with time caused the surface temperature of the deposit to increase. The increased surface temperature caused more softening, increasing the propensity for impacting particles to stick to the surface. These data are important for improving models of deposition in turbines from syngas flows.

Computational Analysis of Conjugate Heat Transfer and Particulate Deposition on a High Pressure Turbine Vane

Numerical computations were conducted to simulate flash deposition experiments on gas turbine disk samples with internal impingement and film cooling using a computational fluid dynamics (CFD) code (FLUENT). The standard k-ω turbulence model and Reynolds-averaged Navier–Stokes were employed to compute the flow field and heat transfer. The boundary conditions were specified to be in agreement with the conditions measured in experiments performed in the BYU turbine accelerated deposition facility (TADF). A Lagrangian particle method was utilized to predict the ash particulate deposition. User-defined subroutines were linked with FLUENT to build the deposition model. The model includes particle sticking/rebounding and particle detachment, which are applied to the interaction of particles with the impinged wall surface to describe the particle behavior. Conjugate heat transfer calculations were performed to determine the temperature distribution and heat transfer coefficient in the region close to the film cooling hole and in the regions further downstream of a row of film cooling holes. Computational and experimental results were compared to understand the effect of film hole spacing, hole size, and TBC on surface heat transfer. Calculated capture efficiencies compare well with experimental results.

Effect of Hole Spacing on Deposition of Fine Coal Flyash Near Film Cooling Holes

Particulate deposition experiments were performed in a turbine accelerated deposition facility to examine the nature of flyash deposits near film cooling holes. Deposition on both bare metal and thermal barrier coating (TBC) coupons was studied, with hole spacing (s/d) of 2.25, 3.375, and 4.5. Sub-bituminous coal ash particles (mass mean diameter of 13 μm) were accelerated to a combustor exit flow Mach number of 0.25 and heated to 1183°C before impinging on a target coupon. The particle loading in the 1 h tests was 310 ppmw. Blowing ratios were varied in these experiments from 0 to 4.0 with the density ratio varied approximately from 1.5 to 2.1. Particle surface temperature maps were measured using two-color pyrometry based on the red/gree/blue (RGB) signals from a camera. For similar hole spacing and blowing ratio, the capture efficiency measured for the TBC surface was much higher than for the bare metal coupon due to the increase of surface temperature. Deposits on the TBC coupon were observed to be more tenacious (i.e., hard to remove) than deposits on bare metal coupons. The capture efficiency was shown to be a function of both the hole spacing and the blowing ratio (and hence surface temperature). Temperature seemed to be the dominant factor affecting deposition propensity. The average spanwise temperature downstream of the holes for close hole spacing was only slightly lower than for the large hole spacing. Roughness parameters Ra and Rt decreased monotonically with increased blowing ratio for both hole spacing analyzed. The roughness for s/d=3.375 was lower than that for s/d=4.5, especially at high blowing ratio. It is thought that these data will prove useful for designers of turbines using synfuels.

Effect of Particle Size and Trench Configuration on Deposition From Fine Coal Flyash near Film Cooling Holes

Particulate deposition experiments were performed in a turbine accelerated deposition facility to examine the effects of flyash particle size and trench configuration on deposits near film cooling holes. Deposition on two bare metal Inconel coupons was studied, with hole spacings (s/d) of 3.4 and 4.5. Two sizes of sub-bituminous coal ash particles were used, with mass mean diameter of 4 and 13 μm, respectively. The effect of a cooling trench at the exit of the cooling holes was also examined in this deposition facility. Experiments were performed at different angles of impaction. Particles were accelerated to a combustor exit flow Mach number of 0.25 and heated to 1183 °C before impinging on a target coupon. The particle loading in the 1-h tests was 160 ppmw. Blowing ratios were varied in these experiments from 0 to 4.0. Particle surface temperature maps were measured using two-color pyrometry based on RGB signals from a camera. Deposits generated from finer particles were observed to stick to the surface more tenaciously than larger particles. The capture efficiency measured for the small particles was lower than for the larger particles, especially at low blowing ratios. However, the finer particles exhibited a greater variation in deposition pattern as a function of hole spacing than seen with larger particles. The effect of trench configuration on deposition was examined by performing deposition tests with and without the trench for the same hole spacing and blowing ratio. The effects of trench configuration on capture efficiency, deposition pattern, and surface topography are reported. Deposition experiments at impingement angles from 45° to 15° showed changes in both deposit thickness and temperature. The trench increased cooling effectiveness, but did not change the particulate collection efficiency because the trench acted as a particulate collector.