HAYNES® 282™ Alloy: A New Wrought Superalloy Designed for Improved Creep Strength and Fabricability

A new wrought, gamma-prime strengthened superalloy, HAYNES 282 alloy, has been developed for high temperature structural applications, especially those in aero and land-based gas turbine engines. The new alloy possesses a unique combination of creep strength, thermal stability, and fabricability not found in currently available commercial alloys. The new alloy has excellent creep strength in the temperature range of 1200 to 1650°F (650 to 900°C), surpassing that of Waspaloy alloy and approaching that of R-41 alloy. This level of creep strength is realized despite the alloy having a significantly lower volume fraction of the strengthening gamma-prime phase. The lower gamma-prime content of the new alloy provides a considerable improvement in terms of fabricability and resistance to strain-age cracking, a problem often associated with this class of alloys. In this paper, the major characteristics and attributes of the new alloy including mechanical properties, oxidation resistance, thermal stability, and weldability are presented.

Conceptual Analysis of Air Supply Systems For In-Flight PEM-FC

To cover the increasing demand of on-board electrical power and for further reduction of emissions, the conventional auxiliary power unit (APU) shall be replaced by a fuel cell system. The main components are a compressor-turbine unit, a kerosene reformer, and the fuel cell. Polymer exchange membrane fuel cells (PEM-FC) are favoured because of their currently advanced level of development. During in-flight operation, the inlet conditions of the PEM-FC system must be kept constant in order to avoid mechanical and thermal damage of the membrane and to ensure low levels of pressure fluctuations in the reformer section. A centrifugal compressor is chosen for pressurization of the system. The advantages of turbomachinery are low specific weight, high efficiency, and good controllability by inlet guide vanes and/or adjustable diffuser vanes. To drive the compressor, a radial turbine is used so that the air supply system resembles the turbocharger for a combustion engine (Fig. 1). A steady state thermodynamic evaluation of the entire system is carried out to identify an optimal system configuration that covers the large range of pressure, temperature, and humidity of ground operation of the aircraft in various regions on the earth as well as take-off, cruise, and landing. A catalytic combustion chamber is located between the PEM-FC and the radial turbine. In this combustion chamber, the hydrogen which is not used in the fuel cell is used to raise the turbine inlet temperature (TIT) and thus the mechanical power delivered by the turbine. To overcome an additional pressure loss of the reformer section, which occurs in the anode stream, an additional low-pressure-ratio compressor is used. The result is a highly thermally integrated PEM-FC system with three centrifugal turbomachines.

Management Strategies for a Compressed Air Energy Storage Plant

Energy storage can balance supply and demand over different time scales, with technical and economical benefits. In the present paper, commercial gas turbines, just modified for storage purposes, are considered. The possibility to improve their profitability in an utility perspective is investigated. The adopted strategy is based on a fair mix of different working states (charging, discharging, stand by or mere Brayton cycle operation), according to the instant energy market price, the previous history (storage level) and the plant features (reservoir and GT size). A simple mathematical model of the plant was conceived and a dynamic self-adjusting abacus was developed in order to select a suitable sequence of working ways. The expected results consist in the improvement of the daily cash flow and in the peak power augmentation. Both of them are due to the chance of exploiting a turbo expander not loaded with the compressor driving during the hours when energy price is the highest.

A Solar Gas Turbine Cycle With Super-Critical Carbon Dioxide as a Working Fluid

Solar thermal power generation system equipped with molten salt thermal storage offers continuous operation at a rated power independent of the variation of insolation. A gas turbine cycle for solar applications is studied which works in a moderate temperature range (600–850K) where molten salt stays as liquid stably. It is found that a closed cycle with super-critical state of carbon dioxide as a working fluid is a promising candidate for solar application. The cycle featured in smaller compressor work would achieve high cycle efficiency if cycle configuration and operation conditions are chosen properly. The temperature effectiveness of a regenerative heat exchanger is shown to govern the efficiency. Under the condition of 98% temperature effectiveness, the regenerative cycle with pre- and inter-cooling provides cycle efficiency of as much as 47%. A novel heat exchanger design to realize such a high temperature effectiveness is also presented.

Flow Reversal in a Horizontal Type Natural Circulation Heat Recovery Steam Generator

Natural circulation heat recovery steam generators (HRSG) are used in many applications for the thermal recycling of the waste flue gas. Many of these boilers are designed as a horizontal type HRSG (see fig. 1). The evaporator of such a steam generator is characterized by an array of parallel tubes with different heat input. The paper presents the results of a theoretical stability analysis for a HRSG with a vertical tube bank. For the horizontal type HRSG the static instability, namely the reverse flow was analysed. The study was done at low system pressures and under hot start-up conditions for the boiler. The investigations show the influence of the geometry, the system pressure and the heat absorption of the individual tubes in the evaporator on the stability of the boiler. The aim of the study was to find design criteria to avoid reverse flow in the tubes of the evaporator. Addition of flow resistance at certain locations of the evaporator can improve the stability. A higher stability will be also achieved by the homogenization of the heat absorption in the individual layers of the bundle heating surface.

Heavy Duty Gas Turbine Simulation: Global Performances Estimation and Secondary Air System Modifications

This paper reviews a modular-structured program ESMS (Energy System Modular Simulation) for the simulation of air-cooled gas turbines cycles, including the calculation of the secondary air system. The program has been tested for the Ansaldo Energia gas turbine V94.3A, which is one of the more advanced models in the family Vx4.3A with a rated power of 270 MW. V94.3A cooling system has been modeled with SASAC (Secondary Air System Ansaldo Code), the Ansaldo code used to predict the structure of the flow through the internal air system. The objective of the work was to investigate the tuning of the analytical program on the basis of the data from design and performance codes in use at Ansaldo Energy Gas Turbine Department. The results, both at base load over different ambient conditions and in critical off-design operating points (full-speed-no-load and minimum-load), have been compared with APC (Ansaldo Performance Code) and confirmed by field data. The coupled analysis of cycle and cooling network shows interesting evaluations for components life estimation and reliability during off-design operating conditions.

Design Concept for Large Output Graz Cycle Gas Turbines

Introduction of closed cycle gas turbines with their capability of retaining combustion generated CO2 can offer a valuable contribution to the Kyoto goal and to future power generation. Therefore research and development work at Graz University of Technology since the nineties has led to the Graz Cycle, a zero emission power cycle of highest efficiency. It burns fossil fuels with pure oxygen which enables the cost-effective separation of the combustion CO2 by condensation. The efforts for the oxygen supply in an air separation plant are partly compensated by cycle efficiencies far higher than for modern combined cycle plants. Upon the basis of the previous work the authors present the design concept for a large power plant of 400 MW net power output making use of the latest developments in gas turbine technology. The Graz Cycle configuration is changed insofar, as condensation and separation of combustion generated CO2 takes place at the 1 bar range in order to avoid the problems of condensation of water out of a mixture of steam and incondensable gases at very low pressure. A final economic analysis shows promising CO2 mitigation costs in range of 20–30 $/ton CO2 avoided. The authors believe that they present here a partial solution regarding thermal power production for the most urgent problem of saving our climate.

Military Engine Response to Compressor Inlet Stratified Pressure Distortion by an Integrated CFD Analysis

Especially in aircraft applications, the inlet flow is quite often non uniform resulting in severe changes in compressor performance and hence, engine performance. The magnitude of this phenomenon can be amplified in military engines due to the complex shape of intake ducts and the extreme flight conditions. The usual approach to engine performance simulation is based on non-dimensional maps for compressors and turbines and assumes uniform flow characteristics throughout the engine. In the context of the whole engine performance, component-level, complex physical processes, such as compressor inlet flow distortion, can not be captured and analyzed. This work adopts a simulation strategy that allows the performance characteristics of an engine component, resolved from a detailed, high-fidelity analysis, to be transferred to an engine system analysis carried out at a lower level of fidelity. The methodology described in this paper utilizes an object-oriented, zero-dimensional gas turbine modeling and performance simulation system and a high-fidelity, three-dimensional, computational fluid dynamics (CFD), low-pressure compressor model. The CFD model is based on the overall geometry and performance of the low-pressure compressor of a modern, two-spool, low by-pass ratio (LBR) military turbofan engine and is subjected to both clean and distorted inlet flows. The analysis involves the generation of two characteristic maps for the first stage of the LP compressor from CFD simulations that account for a range of operating conditions and power settings with a uniform and a distorted inlet flow. The same simulation strategy could be adopted for other engine components such as the intake or the high-pressure compressor and for different magnitudes and types of distortion (i.e. radial, circumferential). By integrating the CFD-generated maps, into the 0-D engine analysis system, this paper presents a relative comparison between the ‘uniform-inlet’ engine performance (baseline compressor stage map) and the engine performance obtained after using the map accounting for a typical extent of stratified inlet distortion. The analysis carried out by this study, demonstrates relative changes in the simulated engine performance larger than 1%.

Advanced Gas Turbine and High Performance Gas-Steam Combined Cycle Plant With Blade Cooling Air Controlling

Air cooling blades are usually applied to gas turbines as a basic specification. This blade cooling air is almost 20% of compressor suction air and it means that a great deal of compression load is not converted effectively to turbine power generation. This paper proposes the CCM (Cascade Cooling Module) system of turbine blade air line and the consequent improvement of power generation, which is achieved by the reduction of cooling air consumption with effective use of recovered heat. With this technology, current gas turbines (TIT: turbine inlet temperature: 1350°C) can be up-rated to have a relative high efficiency increase. The increase ratio has a potential to be equivalent to that of 1500°C Class GT/CC against 1350°C Class. The CCM system is designed to enable the reduction of blade cooling air consumption by the low air temperature of 15°C instead of the usual 200–400°C. It causes the turbine operating air to increase at the constant suction air condition, which results in the enhancement of power and thermal efficiency. The CCM is installed in the cooling air line and is composed of three stage coolers: steam generator/fuel preheater stage, heat exchanger stage for hot water supplying and cooler stage with chilled water. The coolant (chilled water) for downstream cooler is produced by an absorption refrigerator operated by the hot water of the upstream heat exchanger. The proposed CCM system requires the modification of cooling air flow network in the gas turbine but produces the direct effect on performance enhancement. When the CCM system is applied to a 700MW Class CC (Combined Cycle) plant (GT TIT: 135°C Class), it is expected that there will be a 40–80MW increase in power and +2–5% relative increase in thermal efficiency.

Static and Dynamic Neural Networks for Simulation and Optimization of Cogeneration Systems

In this paper, the application of neural networks for simulation and optimization of the cogeneration systems has been presented. CGAM problem, a benchmark in cogeneration systems, is chosen as a case study. Thermodynamic model includes precise modeling of the whole plant. For simulation of the steady sate behavior, the static neural network is applied. Then using dynamic neural network, plant is optimized thermodynamically. Multi layer feed forward neural networks is chosen as static net and recurrent neural networks as dynamic net. The steady state behavior of CGAM problem is simulated by MFNN. Subsequently, it is optimized by dynamic net. Results of static net have excellence agreement with simulator data. Dynamic net shows that in thermodynamic optimization condition, σ and pinch point temperature difference have the lowest value, while CPR reaches a high value. Sensitivity study shows turbomachinery efficiencies have the highest effect on the performance of the system in optimum condition.