Large Industrial Gas Turbines Research Articles

Evolution of Turbine Cooled Vanes and Blades Applied for Large Industrial Gas Turbines and Its Trend toward Carbon Neutrality

Photovoltaics and wind power are expected to account for a large share of power generation in the carbon-neutral era. A gas turbine combined cycle (GTCC) with an industrial gas turbine as the main engine has the ability to rapidly start up and can follow up to load fluctuations to smooth out fluctuations in power generation from renewable energy sources. Simultaneously, the system must be more efficient than today’s state-of-the-art GTCCs because it will use either Carbon dioxide Capture and Storage (CCS) when burning natural gas or hydrogen/ammonia as fuel, which is more expensive than natural gas. This paper describes the trend of cooled turbine rotor blades used in large industrial gas turbines that are carbon neutral. First, the evolution of cooled turbine stationary vanes and rotor blades is traced. Then, the current status of heat transfer technology, blade material technology, and thermal barrier coating technology that will lead to the realization of future ultra-high-temperature industrial gas turbines is surveyed. Based on these technologies, this paper introduces turbine vane and blade cooling technologies applicable to ultra-high-temperature industrial gas turbines for GTCC in the carbon-neutral era.

Unsteady phenomena at the combustor-turbine interface

The combustor-turbine interface in a gas turbine is characterised by complex, highly unsteady flows. In a combined experimental and large eddy simulation (LES) study including realistic combustor geometry, the standard model of secondary flows in the nozzle guide vanes (NGV) is found to be oversimplified. A swirl core is created in the combustion chamber which convects into the first vane passages. Four main consequences of this are identified: variation in vane loading; unsteady heat transfer on vane surfaces; unsteadiness at the leading edge horseshoe vortex, and variation in the position of the passage vortex. These phenomena occur at relatively low frequencies, from 50–300 Hz. It seems likely that these unsteady phenomena result in non-optimal film cooling, and that by reducing unsteadiness designs with greater cooling efficiency could be achieved. Measurements were performed in a high speed test facility modelling a large industrial gas turbine with can combustors, including nozzle guide vanes and combustion chambers. Vane surfaces and endwalls of a nozzle guide vane were instrumented with 384 high speed thin film heat flux gauges, to measure unsteady heat transfer. The high resolution of measurements was such to allow direct visualisation in time of large scale turbulent structures over the endwalls and vane surfaces. A matching LES simulation was carried out in a domain matching experimental conditions including upstream swirl generators and transition duct. Data reduction allowed time-varying LES data to be recorded for several cycles of the unsteady phenomena observed. The combination of LES and experimental data allows physical explanation and visualisation of flow events.

Loss in Axial Compressor Bleed Systems

Abstract Loss in axial compressor bleed systems is quantified and the loss mechanisms are identified to determine how efficiency can be improved. For a given bleed air pressure requirement, reducing bleed system loss allows air to be bled from further upstream in the compressor, with benefits for the thermodynamic cycle. A definition of isentropic efficiency, which includes bleed flow is used to account for this. Two cases with similar bleed systems are studied: a low-speed, single-stage research compressor, and a large industrial gas turbine high-pressure compressor. A new method for characterizing bleed system loss is introduced, using research compressor test results as a demonstration case. A loss coefficient is defined for a control volume including only flow passing through the bleed system. The coefficient takes a measured value of 95% bleed system inlet dynamic head and is shown to be a weak function of compressor operating point and bleed rate, varying by ±2.2% over all tested conditions. This loss coefficient is the correct nondimensional metric for quantifying and comparing bleed system performance. Computations of the research compressor and industrial gas turbine compressor identify the loss mechanisms in the bleed system flow. In both cases, approximately two-thirds of total loss is due to shearing of a high-velocity jet at the rear face of the bleed slot, one-quarter is due to mixing in the plenum chamber, and the remainder occurs in the off-take duct. Therefore, the main objective of a designer should be to diffuse the flow within the bleed slot. A redesigned bleed slot geometry is presented that achieves this objective and reduces the loss coefficient by 31%.

Multiscale Modeling and Simulation of Directional Solidification Process of Ni-Based Superalloy Turbine Blade Casting

Ni-based superalloy turbine blades have become indispensable structural parts in modern gas engines. An understanding of the solidification behavior and microstructure formation in directional solidified turbine blades is necessary for improving their high-temperature performance. The multiscale simulation model was developed to simulate the directional solidification process of superalloy turbine blades. The 3D cellular automaton-finite difference (CA-FD) method was used to calculate heat transfer and grain growth on the macroscopic scale, while the phase-field method was developed to simulate dendrite growth on the microscopic scale. Firstly, the evolution of temperature field of an aero-engine blade and a large industrial gas turbine blade was studied under high-rate solidification (HRS) and liquid-metal cooling (LMC) solidification processes. The varying withdrawal velocity was applied to change the curved mushy zone to a flat shape. Secondly, the grain growth in the aero-engine blade was simulated, and the grain structures in the starter block part and the spiral selector part in the HRS process were compared with those in the LMC process. The simulated grain structures were generally in agreement with experimental results. Finally, the dendrite growth in the typical HRS and LMC solidification process was investigated and the simulation results were compared with the experimental results in terms of dendrite morphology and primary dendritic spacing.

Novel casting processes for single-crystal turbine blades of superalloys

This paper presents a brief review of the current casting techniques for single-crystal (SC) blades, as well as an analysis of the solidification process in complex turbine blades. A series of novel casting methods based on the Bridgman process were presented to illustrate the development in the production of SC blades from superalloys. The grain continuator and the heat conductor techniques were developed to remove geometry-related grain defects. In these techniques, the heat barrier that hinders lateral SC growth from the blade airfoil into the extremities of the platform is minimized. The parallel heating and cooling system was developed to achieve symmetric thermal conditions for SC solidification in blade clusters, thus considerably decreasing the negative shadow effect and its related defects in the current Bridgman process. The dipping and heaving technique, in which thinshell molds are utilized, was developed to enable the establishment of a high temperature gradient for SC growth and the freckle-free solidification of superalloy castings. Moreover, by applying the targeted cooling and heating technique, a novel concept for the three-dimensional and precise control of SC growth, a proper thermal arrangement may be dynamically established for the microscopic control of SC growth in the critical areas of large industrial gas turbine blades.

Investigation of Effective Groove Types for a Film Riding Seal

Over the past two decades, significant efforts have been made to introduce film riding sealing technology on large industrial or aerospace gas turbines. The main challenge comes from the high surface speeds and high temperatures, which lead to large thermal distortions. One approach to tackle the effect of thermally induced distortion is to design a seal to operate at a large film to limit the viscous heat generation. To design a seal pad that maximizes force at relatively high film heights, it is important to select the seal groove type that looks the most promising to deliver this characteristic. Several groove types have been assessed as part of this study. The most promising groove type is the Rayleigh step, which gives the strongest level of combined hydrostatic and hydrodynamic load support while also being easier to tessellate on individual seal segments. The results generated using a uniform grid Reynolds equation method show reasonable agreement with computational fluid dynamics (CFD) calculations. This provides confidence in the validity of the method, approach, and results.

A222 大型ガスタービンの高温部品の信頼性評価手法について(OS2 保全・設備診断技術(4))

A222 大型ガスタービンの高温部品の信頼性評価手法について(OS2 保全・設備診断技術(4))

Intergranular Corrosion in Retaining Rings Made of X39CrMo17-1 and X39Cr13

Abstract A number of retaining rings used in fuel gas piping assemblies of large stationary heavy-duty industrial gas turbines were found broken upon reception at the gas turbine manufacturer's plant. While the pipes were made of AISI 321 austenitic stainless steel, 1.4541, X6CrNiTi18-10, the specified material of the subject locking rings is the martensitic stainless chromium steel X39CrMo17-1, 1.4122. In fact, however, the failed snap rings consisted of the lower-chromium X39Cr13, 1.4031. The fractured retaining rings all originated from a particular North American supply chain. In contrast, the same pipe assemblies delivered by an alterna­tive second-source European supplier did not show these remarkable fractures in their retain­ing rings. Also, they were indeed made of the specified higher-chromium material. It was later discovered that the supplier that shipped the faulty product employed a peculiar wet cleaning process without proper post-cleaning drying. The conclusion of the metallurgical failure analysis was that the subject retaining rings failed by intergranular corrosion due to sensitisation from heat treatment and wet cleaning residues that remained on the product and caused corrosion during shipment. The erroneous material selection, violating the specifica­tion, contributed to the failure.

Metallurgical Failure Investigation of Overheated and Fractured Investment Cast Nickel-base Bolts Made of Inconel 939

Abstract A number of small investment cast nickel-base bolts used for fastening metallic heat shields in combustion chambers of large industrial gas turbine engines were found fractured upon a regular hot gas path inspection in one particular engine. No similar findings were reported from any other engine in the field. The fracture of a single-digit number of these fasteners in an individual engine did not cause the liberation of the respective heat shields, hence no secondary damage occurred. The subject bolts were fractured in the head region that is also used to apply the fastening torque upon assembly of the heat shields. No evidence of fatigue, creep or hot corrosion damage was found. From the results of the metallurgical failure investigation described in this paper it was concluded that the subject bolts failed by torsional and/or tensional overload. Severe embrittlement by precipitation of secondary phases due to long-term high temperature service exposure contributed to the failure. The bolts ran hotter than intended by design. It is likely that cracks were induced in the bolt heads by over-torquing them upon assembly. Those cracks later grew in service.

Compressor Efficiency Variation With Rotor Tip Gap From Vanishing to Large Clearance

Compressor efficiency variation with rotor tip gap is assessed using numerical simulations on an embedded stage representative of that in a large industrial gas turbine with Reynolds number ∼ 2 × 106 to 7 × 106. The results reveal three distinct behaviors of efficiency variation with tip gap. For relatively small tip gap (less than 0.8% span), the change in efficiency with tip gap is nonmonotonic with an optimum tip gap for maximum efficiency. The optimum tip gap is set by two competing flow processes: decreasing tip leakage mixing loss and increasing viscous shear loss at the casing with decreasing tip gap. An optimum tip gap scaling is established and shown to satisfactorily quantify the optimal gap value. For medium tip gap (0.8%–3.4% span), the efficiency decreases approximately on a linear basis with increasing tip clearance. However, for tip gap beyond a threshold value (3.4% span for this rotor), the efficiency becomes less sensitive to tip gap as the blade tip becomes more aft-loaded thus reducing tip flow mixing loss in the rotor passage. The threshold value is set by the competing effects between increasing tip leakage flow and decreasing tip flow induced mixing loss with increasing tip gap. Thus, to desensitize compressor performance variation with blade gap, rotor should be tip aft-loaded and hub fore-loaded while stator should be tip fore-loaded and hub aft-loaded as much as feasible. This reduces the opportunity for clearance flow mixing loss and maximizes the benefits of reversible work from unsteady effects in attenuating the clearance flow through the downstream blade-row. The net effect can be an overall compressor performance enhancement in terms of efficiency, pressure rise capability, robustness to end gap variation, and potentially useful operable range broadening.

TMF Cracking in Metallic Heat Shields of Gas Turbine Combustion Chambers

Abstract Several metallic heat shields of the combustion chamber of a large industrial gas turbine were affected by thermo-mechanical cracking after long service exposure. The base metal Alloy 617 is coated with a thermal barrier system. While microstructural evidence allowed the exclusion of creep damage as the metallurgical cause of failure, other microstructural features led to the conclusion that the affected components were massively overheated and experienced service temperatures of up to 1100 °C. There are several possible reasons for such overheating, ranging from burner failure and lack of cooling to abuse in service. A discussion of these factors is not the subject of this case study.

The Influence of the Total Pressure Profile on the Performance of Axial Gas Turbine Diffusers

Large industrial gas turbines for combined heat and power generation normally have axial diffusers leading to the heat recovery steam generator. The diffusers operate with high inlet axial Mach number (0.6) and with a nonuniform inlet total pressure profile from the turbine. Tests have been carried out on a generic highly loaded axial diffuser in a scaled axial diffuser test rig, with different inlet total pressure profiles including those that might be met in practice. The results show that the inlet total pressure profile has a strong effect on the position of flow separation, whereby a hub-strong profile tends to separate at the casing and the tip-strong profile on the hub. Steady computational fluid dynamics (CFD) simulations using the shear stress transport (SST) turbulence model have been carried out based on extensive studies of the best way to model the inlet boundary conditions. These simulations provide good agreement with the prediction of separation in the diffuser but the separated regions often persist too long so that, in this highly loaded case with flow separation, the calculated diffuser pressure recovery can be in error by up to 30%.

Validation of CESI Blade Life Management System by Case Histories and in situ NDT

A life management system was developed for hot components of large industrial gas turbines, in the form of a software tool for predicting component lives under typical operational transients (normal and also abnormal) and steady-state periods. The method utilizes results of previous thermo-mechanical finite element and finite volume fluid mechanics analyses. The basic idea of this method is using data from structural and aero-thermal analyses (pressures and temperatures), blade life theory, and material properties as an input to algorithms, and using operational and historical data to validate the predicted damage amounts. The software developed in this project, of general applicability to all GT models, has been implemented with reference to the geometries, materials, and service conditions of a Fiat-Westinghouse model.

Flow and Heat Transfer in an Industrial Rotor-Stator Rim Sealing Cavity

Flow and heat transfer in the row-1 upstream rotor-stator disk cavity of a large 3600-rpm industrial gas turbine was investigated using an integrated approach. A two dimensional axisymmetric transient thermal analysis using aeroengine-based correlations was performed to predict the steady-state metal temperatures and hot running seal clearances at ISO rated power condition. The cooling mass flow and the flow pattern assumption for the thermal model were obtained from the steady-state two dimensional axisymmetric CFD study. The CFD model with wall heat transfer was validated using cavity steady-state air temperatures and static pressures measured at inlet to the labyrinth seal and four cavity radial positions in an engine test which included the mean annulus static pressure at hub radius. The predicted wall temperature distribution from the matched thermal model was used in the CFD model by incorporating wall temperature curve-fit polynomial functions. Results indicate that although the high rim seal effectiveness prevents ingestion from entering the cavity, the disk pumping flow draws air from within the cavity to satisfy entrainment leading to an inflow along the stator. The supplied cooling flow exceeds the minimum sealing flow predicted from both the rotational Reynolds-number-based correlation and the annulus Reynolds number correlation. However, the minimum disk pumping flow was found to be based on a modified entrainment expression with a turbulent flow parameter of 0.08. The predicted coefficient of discharge (Cd) of the industrial labyrinth seal from CFD was confirmed by modifying the carryover effect of a correlation reported recently in the literature. Moreover, the relative effects of seal windage and heat transfer were obtained and it was found that contrary to what was expected, the universal windage correlation was more applicable than the aeroengine-based labyrinth seal windage correlation. The CFD predicted disk heat flux profile showed reasonably good agreement with the free disk calculated heat flux. The irregular cavity shape and high rotational Reynolds number (in the order of 7×107) leads to entrance effects that produce a thicker turbulent boundary layer profile compared to that predicted by the 1/7 power velocity profile assumption.

TBC experience in land- based gas turbines

This paper summarizes prior and on-going machine evaluations of thermal barrier coatings (TBC) for power generation, that is large industrial gas turbine applications. Rainbow testing of TBCs on turbine nozzles, shrouds, and buckets are described along with a test of combustor liners. General Electric Power Generation has conducted more than IS machine tests on TBC turbine nozzles with various coatings. TBC performance has been quite good, and additional testing, including TBCs on shrouds and buckets, is continuing. Included is a brief comparison of TBC requirements for power generation and aircraft turbines.

Particulate and Alkali Capture from PFBC Flue Gas Utilizing Granular Bed Filter (GBF)

Abstract Abstract— The adequacy of a high-temperature, high-pressure gas cleanup system in protecting a large industrial gas turbine in a combined PFBC cycle can be evaluated by determining the dust and alkali loading into and out of the hot-gas cleanup unit. Sub-pilot plant experiments were performed at the New York University (NYU)-DOE PFBC facility to evaluate Ihe performance of the Granular Bed Filter (GBF) designed by Combustion Power Company, Inc., Menlo Park, California, in terms of its ability to capture dust and alkali. The inlet to and outlet of the GBF were isokinetically sampled for alkali and dust loadings. The particulate sampling system consisted of a total filter and a cascade impactor. The total filter collected the dust in a microfiber tube. In Ihe impactor, the particles collected are separated according to their size. Alkali emissions were measured using two techniques, namely. NYU total vapor condensation method and METC/INEL on-line alkali monitor. The results show that the dust and ...

Emission Control for Gas Turbines

Johnson Matthey are reporting successful commercialisation of oxidation catalysts for the clean-up of gas turbine exhaust. The reduction of carbon monoxide and hydrocarbons is achieved with a platinum-rhodium catalyst which minimises the formation of sulphur trioxide. The catalyst system, supported on an energy saving, low pressure drop metal monolith, has been used continuously for five years on large industrial gas turbines.

Transonic Compressor Development for Large Industrial Gas Turbines

With increasing mass flow and constant rotational speed of the single shaft gas turbine, the diameters and tip speeds of compressor and turbine blading have to be enlarged. A significant further increase in mass flow can be achieved with transonic compressor stages, as they have been in service in aero gas turbines for many years. For industrial applications, weight and stage pressure ratio are not nearly as important as efficiency. Therefore, different design criteria had to be applied, which led to a moderate front stage pressure ratio of 1.5 with a rotor tip inlet Mach number of 1.37 and a high solidity blading. In order to simulate the first three stages of a 200-MW gas turbine, a test compressor scaled by 1:5.4 was built and tested. These measurements confirmed the aerodynamic performance in the design point very well. The compressor map showed a satisfactory part speed behavior. These results prove that the single-shaft industrial gas turbine still has a high development potential with respect to power increase. Additionally, with the higher pressure ratio, the cycle efficiency will be improved considerably.

Influence of coatings and hot corrosion on the fatigue behaviour of nickel-based superalloys

The fatigue behaviour of materials and components is strongly affected by the surface conditions, i.e. the surface finish and the materials properties in the near- surface region. Therefore any change in these conditions during fabrication or service may change the fatigue properties. It is common practice to coat turbine blades with materials that are resistant to hot corrosion. However, this treatment involves chemical and mechanical changes in the materials surface properties which could also change the fatigue properties of these components. The recommended heat treatment for the coating normally differs from that which produces the best mechanical or creep properties of the base metal and hence may cause additional changes in the fatigue properties. Chemical and mechanical changes in the surface conditions of an uncoated component may also take place during operation. Additionally, a large amount of notching may occur since oxidation and hot corrosion are not homogeneously distributed but take place preferentially at sites such as grain boundaries. In this work we investigate the effect of Pt-Al coatings on the high cycle fatigue (HCF) behaviour of the cast nickel-based alloys IN 738LC and IN 939 which are commonly used in large industrial gas turbines. A reduction in the fatigue life due to the coating was observed. However, the simultaneous occurence of hot corrosion attack and cyclic loading was much more detrimental. Fractographic and metallographic investigations showed that, in the as-coated condition, the crack initiation sites in the Pt-Al-coated alloys were internal pores situated just below the surface of the substrate. After aging or hot corrosion cracks initiate at the surface probably as a result of notch development by the attack. When HCF and hot corrosion are acting concurrently the coatings are expected to give a beneficial effect by protecting the surface from accelerated crack initiation.

Turbomachinery Design Considerations for the Nuclear HTGR-GT Power Plant

For several years, design studies have been underway in the U.S. on a nuclear closed-cycle gas turbine plant (HTGR-GT). This paper presents design aspects of the helium turbo-machine portion of these studies. Gas dynamic and mechanical design considerations are presented for helium turbomachines in the 400 MWe (non-intercooled) and 600 MWe (intercooled) power range. Design of the turbomachine is a key element in the overall power plant program effort, which is currently directed towards the selection of a reference HTGR-GT commercial plant configuration for the U.S. utility market. A conservative design approach has been emphasized to provide for maximum safety and durability. The studies presented for the integrated plant concept outline the necessary close working relationship between the reactor primary system and turbomachine designers. State-of-the-art technology from large industrial gas turbines developed in the U.S., considered directly applicable to the design of a helium turbomachine, particularly in the areas of design methodology, performance, materials, and fabrication methods, is emphasized.