Uwe Gampe

Design and Operational Aspects of Gas and Steam Turbines for the Novel Solar Hybrid Combined Cycle SHCC

Solar hybrid power plants are characterized by a combination of heat input both of high temperature solar heat and heat from combustion of gaseous or liquid fuel which enables to supply the electricity market according to its requirements and to utilize the limited and high grade natural resources economically. The SHCC® power plant concept integrates the high temperature solar heat into the gas turbine process and in addition — depending on the scheme of the process cycle — downstream into the steam cycle. The feed-in of solar heat into the gas turbine is carried out between compressor outlet and combustor inlet either by direct solar thermal heating of the pressurized air inside the receivers of the solar tower or by indirectly heating via interconnection of a heat transfer fluid. Thus, high shares of solar heat input referring to the total heat input of more than 60% in design point can be achieved. Besides low consumption of fossil fuels and high efficiency, the SHCC® concept is aimed for a permanent availability of the power plant capacity due to the possible substitution of solar heat by combustion heat during periods without sufficient solar irradiation. In consequence, no additional standby capacity is necessary. SHCC® can be conducted with today’s power plant and solar technology. One of the possible variants has already been demonstrated in the test field PSA in Spain using a small capacity gas turbine with location in the head of the solar tower for direct heating of the combustion air. However, the authors present and analyze also alternative concepts for power plants of higher capacity. Of course, the gas turbine needs a design which enables the external heating of the combustion air. Today only a few types of gas turbines are available for SHCC® demonstration. But these gas turbines were not designed for solar hybrid application at all. Thus, the autors present finally some reflections on gas turbine parameters and their consequences for SHCC® as basis for evaluation of potentials of SHCC® .Copyright

Creep crack growth testing of P91 and P22 pipe bends

Laboratory component tests play an important role in the development of life assessment procedures for high temperature crack initiation and growth. Thus, the working programme of the project BE 1702 HIDA, which addressed the validation, expansion and harmonisation of existing procedures for high temperature defect assessment, included a comprehensive experimental programme with feature tests of components as its core. Because of their relevance for the high temperature industry, P91 and P22 were included in HIDA among five materials. This paper presents laboratory creep crack growth tests of P91 and P22 pipe bends, discusses the test experience and draws some conclusions for laboratory component tests in general. The components were prepared with spark-eroded notches at the outer surface. The test temperature was 625°C for P91 and 565°C for P22.

Parameterization of High Solar Share Gas Turbine Systems

Existing solar thermal power plants are based on steam turbine cycles. While their process temperature is limited, solar gas turbine (GT) systems provide the opportunity to utilize solar heat at a much higher temperature. Therefore there is potential to improve the efficiency of future solar thermal power plants. Solar based heat input to substitute fuel requires specific GT features. Currently the portfolio of available GTs with these features is restricted. Only small capacity research plants are in service or in planning. Process layout and technology studies for high solar share GT systems have been carried out and have already been reported by the authors. While these investigations are based on a commercial 10MW class GT, this paper addresses the parameterization of high solar share GT systems and is not restricted to any type of commercial GT. Three configurations of solar hybrid GT cycles are analyzed. Besides recuperated and simple GT with bottoming Organic Rankine Cycle (ORC), a conventional combined cycle is considered. The study addresses the GT parameterization. Therefore parametric process models are used for simulation. Maximum electrical efficiency and associated optimum compressor pressure ratio πC are derived at design conditions. The pressure losses of the additional solar components of solar hybrid GTs have a different adversely effect on the investigated systems. Further aspects like high ambient temperature, availability of water and influence of compressor pressure level on component design are discussed as well. The present study is part of the R&D project Hybrid High Solar Share Gas Turbine Systems (HYGATE) which is funded by the German Ministry for the Environment, Nature and Nuclear Safety and the Ministry of Economics and Technology.

Thermo-mechanical and low cycle fatigue behaviour of a nickel-base superalloy at elevated temperatures

Abstract Isothermal low cycle fatigue (LCF) and thermo-mechanical fatigue (TMF) tests were performed to investigate the deformation behaviour and fatigue life of the nickel-base Superalloy René 80 at elevated temperatures. The LCF test temperature was 950 °C. The TMF tests were performed in the temperature ranges 100–950 °C and 750–950 °C and both out-of-phase (OP) and in-phase (IP) shifts of mechanical and thermal loading. All LCF and TMF tests were conducted with a mechanical strain ratio Rε,me = −1, which allows using the mechanical strain range to compare the material behaviour under LCF and TMF stresses. With respect to the mechanical strain range, the material showed the shortest lifetime under TMF conditions for broad temperature ranges, whereas the TMF tests with narrow temperature ranges resulted in similar lifetimes to those in the LCF tests. Additionally, damage parameters were applied to assess the mean stress development during cycling and the different maximum stresses during IP and OP TMF testing. The Smith–Watson–Topper damage parameter is proposed for the assessment of fatigue life prediction because this parameter provides reasonable trends over the entire lifetime. Nevertheless, LCF and TMF cannot be combined in a single model.

Advancement of Experimental Methods and Cailletaud Material Model for Life Prediction of Gas Turbine Blades Exposed to Combined Cycle Fatigue

The European project PREMECCY has been conducted to enhance predictive methods for combined cycle fatigue (CCF) of gas turbine blades, i.e. interaction of low cycle fatigue (LCF) and high cycle fatigue (HCF). While design of CCF feature tests, comprising specimen and test rig design, has already been reported, this paper presents experimental HCF/ CCF test results and progress in life prediction.Besides standard lab specimen tests for characterization of single crystal and conventional cast material, also advanced specimens representing critical rotor blade features were tested in a hot gas rig.Based on these experimental data an extended Cailletaud material model for stress-strain analysis has been calibrated and combined with a modified ONERA damage model for creep-fatigue interaction to estimate the lifetime of the advanced test specimens.The model extensions address the effect of ratcheting, which is typical for CMSX-4 at asymmetric cyclic loading at elevated temperature. Caused by limitations of the Armstrong-Frederick kinematic hardening rule regarding ratcheting, three models for improved ratcheting simulation of isotropic material were adopted to anisotropic material. In addition multiple Norton-flow rules for the viscous part of the model are combined with time recovery terms in the kinematic hardening evolution to represent the behaviour of single crystal material in high temperature environment at a wide range of strain rates. Hence, an improved model for stress-strain and lifetime prediction for single crystals has been developed.Copyright

Dynamic Behavior of a Solar Hybrid Gas Turbine System

Solar hybrid gas turbine technology has the potential to increase the efficiency of future solar thermal power plants by utilizing solar heat at a much higher temperature level than state of the art plants based on steam turbine cycles. In a previous paper the authors pointed out, that further development steps are required for example in the field of component development and in the investigation of the system dynamics to realize a mature technology for commercial application [1].In this paper new findings on system dynamics are presented based on the simulation model of a solar hybrid gas turbine with parallel arrangement of the combustion chamber and solar receivers. The operational behavior of the system is described by means of two different scenarios. The System operation in a stand-alone electrical supply network is investigated in the first scenario. Here it is shown that fast load changes in the network lead to a higher shaft speed deviation of the electric generator compared to pure fossil fired systems. In the second scenario a generator load rejection, as a worst case, is analyzed. The results make clear that additional relief concepts like blow-off valves are necessary as the standard gas turbine protection does not meet the specific requirements of the solar hybrid operation. In general the results show, that the solar hybrid operational modes are much more challenging for the gas turbines control and safety system compared to pure fossil fired plants due to the increased volumetric storage capacity of the system.Copyright

Advanced Experimental and Analytical Investigations on Combined Cycle Fatigue (CCF) of Conventional Cast and Single-Crystal Gas Turbine Blades

Rotor blades are the highest thermal-mechanical loaded components of gas turbines. Their service life is limited by interaction of creep, low cycle fatigue (LCF), high cycle fatigue (HCF) and surface attack. Because assurance of adequate HCF strength of the rotor blade is an important issue of the blade design the European project PREMECCY has been started by the European aircraft engine manufacturers and research institutes to enhance the predictive methods for combined cycle fatigue (CCF), as a superposition of HCF and LCF. Although today’s predictive methods ensure safe blade design, there are certain shortcomings of assessing fatigue life with Haigh or “modified Goodman diagrams”, such as isolated HCF assessment as well as uni-axial and off-resonant testing. HCF and LCF are considered without taking into account their interaction. PREMECCY is aimed to deliver new and improved CCF prediction methods for exploitation in the industrial design process. Beside development of predictive methods the authors are involved in the design and testing of advanced specimens representing rotor blade features. In this connection the paper presents a novel test specimen type and a unique hot gas rig for CCF feature test at mechanical and ambient representative conditions.Copyright

CFD Analysis of Steam Turbines With the IAPWS Standard on the Spline-Based Table Look-Up Method (SBTL) for the Fast Calculation of Real Fluid Properties

Accurate simulations of non-stationary processes in steam turbines by means of Computational Fluid Dynamics (CFD) require precise and extremely fast algorithms for computing real fluid properties. To fulfill these requirements, the International Association for the Properties of Water and Steam (IAPWS) issues the “Guideline on the Fast Calculation of Steam and Water Properties with the Spline-Based Table Look-Up Method (SBTL)” as an international standard. Through the use of this method, spline functions for the independent variables specific volume and specific internal energy (v,u) are generated for water and steam based on the industrial formulation IAPWS-IF97. With these spline functions, thermodynamic and transport properties can be computed. The desired backward functions of the variables pressure and specific volume (p,v), and specific internal energy and specific entropy (u,s) are numerically consistent with the spline functions from (v,u). The properties calculated from these SBTL functions are in agreement with those of IAPWS-IF97 within a maximum relative deviation of 10 to 100 ppm depending on the property and the range of thermodynamic states spanned under the given conditions (range of state). Consequently, the differences between the results of process simulations using the SBTL method and those obtained through the use of IAPWS-IF97 are negligible. Moreover, the computations from the (v,u) spline functions are more than 200 times faster than the iterative calculations with IAPWS-IF97.In order to demonstrate the efficiency and applicability of the SBTL method, the SBTL functions have been implemented into the CFD software TRACE, developed by the German Aerospace Center (DLR). As a result, the computing times required for the simulations of steam flow in a turbine cascade considering real fluid behavior are reduced by a factor of 6–10 in comparison to the calculations based on IAPWS-IF97. Furthermore, computing times are increased by a factor of 1.4 only with respect to CFD calculations where steam is considered to be an ideal gas, through the use of the SBTL method.© 2015 ASME

Modeling and Simulation of the Dynamic Operating Behavior of a High Solar Share Gas Turbine System

Solar gas turbine (GT) systems provide the opportunity to utilize solar heat at a much higher temperature than solar thermal power plants based on steam turbine cycles. Therefore, GT technology has the potential to improve the efficiency of future solar thermal power plants. Nevertheless, to achieve mature technology for commercial application, further development steps are required. Knowledge of the operational behavior of the solar GT system is the basis for the development of the systems control architecture and safety concept. The paper addresses dynamic simulation of high solar share GT systems, which are characterized by primary input of solar heat to the GT. To analyze the dynamic operating behavior, a model with parallel arrangement of the combustion chamber and the solar receiver was set up. By using the heaviside step function, the system dynamics were translated into transfer functions which are used to develop controllers for the particular system configuration. Two operating conditions were simulated to test the controller performance. The first case is the slow increase and decrease of solar heat flow, as part of a regular operation. The second case is an assumed rapid change of solar heat flow, which can be caused by clouds. For all cases, time plots of critical system parameters are shown and analyzed. The simulation results show much more complex system behavior compared to conventional GT systems. This is due to the additional solar heat source, large volumes, and stored thermal energy as well as the time delay of energy transportation caused by the piping system.

Development of a Generalized LCF-TMF Lifing Model for a Nickel-Base Superalloy

The growing share of power generation from volatile sources such as wind and photovoltaics requires fossil fuel fired power generation units be available and capable of high load flexibility to adjust to the changing capacity of the electrical grid. Additionally, back-up units with quick start capability and energy storage technologies are needed to fill the power shortfall when volatile sources are not available. Gas turbine and combined-cycle gas and steam turbine power plants are able to meet these demands. However, safe component design for improved cycling capability, combined with optimum utilization of material regarding its mechanical properties, requires design procedures and lifing models for the complex loadings resulting from this increased volatility of power demand. Since hot gas path components like turbine blades and vanes are highly stressed by cyclic thermal and mechanical loadings, resulting Thermo-Mechanical Fatigue (TMF), life prediction models such as the classic strain-life Coffin-Manson-Basquin method do not capture the influences of thermal cycling satisfyingly. Advanced TMF prediction models are thus necessary to accurately predict the durability of hot section components.This paper addresses life prediction of the Nickel-base superalloy Rene 80 at elevated temperature for various loading conditions. For this purpose, isothermal Low Cycle Fatigue (LCF) and corresponding TMF tests, with various temperature ranges and thermal-mechanical phase shifts, have been performed. On this basis, a systematic approach has been developed which allows assessing the key influences on TMF life. Moreover, a generalized model for fatigue has been derived, which has the potential to predict TMF life on the basis of LCF data. The knowledge gained from the model development allows an improved life prediction and better utilization of the material capabilities. Additionally, the required number of material tests for a general insight in the materials behaviour can be reduced significantly.Copyright