Siemens Power Generation Research Articles

Design and Analysis of High-pressure Casing of a Steam Turbine

Contact pressure and pretension in bolts-analysis has been made easier in recent years due to the availability of high computational capabilities and flexibility in the computational methods using finite element analysis. In the present work, one such analysis is carried out blending the hand calculations and steady-state finite element analysis to evaluate the contact pressure in a high pressure steam turbine casing. The work involves design considerations, design checks, validation and sensitivity analysis to achieve the design criteria to fulfill the structural requirements for mechanical integrity. During the last several years the primary changes to the design of steam turbines have focused on improving their efficiency, reliability and reducing operating costs. Siemens Power Generation, for example, has improved the overall efficiency and availability of its steam turbines by decreasing the steam flow energy losses in each of the steam turbines components. The steam turbine unit largely influences the efficiency and reliability of power stations. Any improvement in the design of steam turbine enables more efficient use of fuel and results in reduced cost. The high pressure steam at 565°C and 156bar pressure passes through the high pressure turbine. The exhaust steam from this section is returned to the boiler for reheating before being used. On leaving the boiler reheater, steam enters the intermediate pressure turbine at 565°C and 40.2bar pressure. From the intermediate pressure turbine, the steam continues its expansion in the three Low pressure turbines. The steam entering the turbine is at 306°C and 6.32bar. To get the most work out of the steam, the exhaust pressure is kept very low. The casing thus witnesses, energy of the steam turned into work in HP and IP stages. So, the design of the casing is a very important aspect.

Dynamic modeling, simulation, and MIMO predictive control of a tubular solid oxide fuel cell

Solid oxide fuel cells are a promising option for distributed energy stationary power generation that offers efficiencies up to 50% in stand-alone applications, 70% in hybrid gas turbine applications and 80% in cogeneration. To advance SOFC technology sufficiently for widespread market penetration, the SOFC must demonstrate improved cell lifetime from the status quo. Much research has been performed to improve SOFC lifetime using advanced geometries and materials, and in this research, we suggest further improving lifetime by designing an advanced control algorithm based upon preexisting mechanical stress analysis [1]. Control algorithms commonly address SOFC lifetime related operability objectives using unconstrained, SISO control algorithms that seek to minimize thermal transients. While thermal fatigue may be one thermal stress driver, these studies often do not consider maximum radial thermal gradients or critical absolute temperatures in the SOFC. In addition, researchers often discuss hot-spots as a critical lifetime reliability issue, but as previous stress work demonstrates, the minimum cell temperature is the primary thermal stress driver in tubular SOFCs modeled after the Siemens Power Generation, Inc. design. In this work, we present a dynamic, quasi-two-dimensional model for a high-temperature tubular SOFC combined with ejector and prereformer models. The model captures dynamics of critical thermal stress drivers and is used as the physical plant for closed-loop simulations with a constrained, MIMO model predictive control algorithm. Closed-loop simulation results demonstrate effective load-following, operability constraint satisfaction, and disturbance rejection.

Numerical Investigation of a Delta High Power Density Cell and Comparison With a Flattened Tubular High Power Density Cell

The thermal, electrical, and fluid flow fields associated with a Siemens Power Generation Inc., Stationary Fuel Cells, flattened tubular high power density (HPD) solid oxide fuel cell (SOFC) were investigated comprehensively in a previous study. The present computational investigation is the subsequent part of an ongoing numerical pursuit at Siemens of an optimized cell geometry, commercialization of SOFC technology being the ultimate objective. A Delta type HPD cell featuring eight air channels was investigated and compared with a flattened tubular HPD cell. The computational models were developed using the commercial computational fluid dynamics software FLUENT 6.2 along with its SOFC user defined routine to model the electrochemical effects. The SOFC model parameters were derived from experimental data. The cathode, the anode, and the interconnection layers of the cell were resolved in the model and all modes of heat transfer, conduction, convection, and radiation were included. The resulting electrical performance and the thermal hydraulic characteristics of the cells for fully reformed natural gas fuel flow (reformed external to the cell) are presented and discussed. It was clear from these studies that the Delta HPD cell has distinct advantages over the flattened HPD cell in terms of system electrical performance as well as power density.

Regression Models Analysis and Optimization of a SOFC SFC 5 kWe Field Unit

The EOS Project carries on an industrial research on Stationary Fuel Cells based on the SOFC technology developed by Siemens Power Generation Stationary Fuel Cells, through a co-operation between TurboCare S.p.A. (a subsidiary of Siemens Power Generation) and Politecnico di Torino. Two SOFC units have been installed and are currently in operation in the TurboCare workshop. The CHP100 generator was commissioned on June 19, 2005, and to date has shown more than 36,000 operating hours at this scale (record availability of 99.5%); the SFC5 alpha6 Generator is in operation since more than 7,000 hours. In the paper the performance of the 5 kW generator are analyzed. First, we have made two experimental analysis of the main variables of the generator with perturbation of the fuel utilization, the generator temperature and the management of the air distribution. Then, the regression models, obtained from the first test campaign and describing the behaviour of the generator, have been used to optimize the system.

Analysis of the cooling transient of a large SOFC generator

The EOS Project conducted an industrial research on stationary fuel cells based on the SOFC technology developed by Siemens, through a co-operation between TurboCare S.p.A. (TurboCare, a subsidiary of Siemens Power Generation) and Politecnico di Torino. Two SOFC units (CHP 100 and SFC 5) have been installed in the TurboCare workshop. To date, the CHP 100 generator has operated in Torino for more than 16,000h, producing more than 1.5million kWh of electric energy.After a failure of the UPS, a commercial component, the system for the first time performed a complete thermal cycle from operating temperature to ambient temperature.The shutdown has been a great opportunity of experimental analysis of the thermal cycle inside the generator. One topic has been considered: the analysis of air distribution in different sectors of the generator; this analysis gives information about the behaviour of the air cooling. The results obtained can be helpful to improve the cool down strategy in order to avoid thermal stress to stack tubes and to try to analyse the effect of the air distribution.

Experimental evaluation of the sensitivity to fuel utilization and air management on a 100 kW SOFC system

The tubular SOFC generator CHP-100, built by Siemens Power Generation (SPG) Stationary Fuel Cells (SFC), is running at the Gas Turbine Technologies (GTT) in Torino (Italy), in the framework of the EOS Project. The nominal load of the generator ensures a produced electric power of around 105 kW e ac and around 60 kW t of thermal power at 250 °C to be used for the custom tailored HVAC system. Several experimental sessions have been scheduled on the generator; the aim is to characterize the operation through the analysis of some global performance index and the detailed control of the operation of the different bundles of the whole stack. All the scheduled tests have been performed by applying the methodology of design of experiment; the main obtained results show the effect of the change of the analysed operating factors in terms of distribution of voltage and temperature over the stack. Fuel consumption tests give information about the sensitivity of the voltage and temperature distribution along the single bundles. On the other hand, since the generator is an air cooled system, the results of the tests on the air stoichs have been used to analyze the generator thermal management (temperature distribution and profiles) and its effect on the polarization. The sensitivity analysis of the local voltage to the overall fuel consumption modifications can be used as a powerful procedure to deduce the local distribution of fuel utilization (FU) along the single bundles: in fact, through a model obtained by deriving the polarization curve respect to FU, it is possible to link the distribution of voltage sensitivities to FC to the distribution of the local FU. The FU distribution will be shown as non-uniform, and this affects the local voltage and temperatures, causing a high warming effect in some rows of the generator. Therefore, a discussion around the effectiveness of the thermal regulation made by the air stoichs, in order to reduce the non-uniform distribution of temperature and the overheating (increasing therefore the voltage behavior along the generator) has been performed. It is demonstrated that the utilization of one air plenum is not effective in the thermal regulation of the whole generator, in particular in the reduction of the temperature gradients linked to the non-uniform fuel distribution.

New Cathode and Interlayer Materials Development at Siemens Power Generation

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Web4diagnostics experience with web-based diagnostic systems in power plants

At SMORN 8, a new web-based diagnostic system – web4diagnostics – was presented (Kunze, 2002). During the last two years, this system became the standard diagnostic system infrastructure for internal use in Siemens Power Generation, which integrates a large data archive of measured data and capabilities for data analysis and evaluation. Besides this internal use, today some 15 power plants worldwide use web4diagnostics in their companies communication network. Essential features are: monitoring and diagnostic information are provided in HTML page format; diagnosis can be performed on any suitable machine in the computer network; a 'central diagnostic laboratory' can be configured as a virtual facility using the existing IT infrastructure; analysis results can be accessed from any computer in the information network, only a web browser is required. The system employs well-known standard diagnostic modules and also owns tools such as operational based limit surveillance, automatic report generation and automatic information in case of deviations.

Performance Benefits Using Siemens Advanced Compressor Cleaning System

Extensive operational performance data from the Siemens Power Generation V64.3 unit in Obernburg, Germany (operated by Kraftwerk Obernburg GmbH) is evaluated. The unit was commissioned in 1996 and has been running continuously in base load operation with fuel gas to supply heat and power to a nearby chemical plant. In rare cases, fuel oil is used as a backup fuel. During the first major outage after approximately 25,000 equivalent operating hours (EOH), the Siemens PG Advanced Compressor Cleaning System (ACCS) was implemented at Obernburg. ACCS features separate nozzle systems for online and offline compressor cleaning accounting for different operating conditions. For online cleaning, the droplet size is optimized for the droplets to remain in the main air flow in order to minimize erosion effects while providing a homogeneous field over the whole air intake. With reduced rotational speed during offline compressor cleaning, erosion is less critical. Offline nozzles therefore provide higher mass flow and larger droplets in order to maximize cleaning performance for all compressor stages. ACCS, in its maximum automated version, features operation from the control room, online-washing at low ambient temperatures (officially released down to −15 °C without GT anti-icing) and minimum use of manpower. The ACCS system in Obernburg was operated according to the recommended online washing procedure. By June 2002, the V64.3 unit in Obernburg reached 50,000 EOH and the second major inspection was carried out. For this paper, operational data from the second inspection intervals (24,350–49,658 EOH) and from three performance tests with calibrated equipment are compared in order to evaluate the effectiveness of the advanced compressor cleaning system. Statistical evaluation of single-wash performance recovery and the evolution of long-term performance are presented. The effects of degradation and fouling are differentiated. It is shown that ACCS has a significant benefit for long-term engine performance.

Weir, Siemens launch global healthcare network

Weir Group’s Services Division and the Industrial Applications Division of Siemens Power Generation, Germany, have entered into a worldwide co_operation agreement covering joint marketing and sales activities for the maintenance of a wide range of rotating equipment, including pumps, industrial turbines, turbo compressors and technical accessories for industrial plants. This is a short news story only. Visit www.worldpumps.com for the latest pump industry news.

Structural design of modern steam turbine blades using ADINA ™

The present paper provides an overview of the structural design of modern steam turbine blades at Siemens power generation using the finite element code ADINA™. The different types of blades are described in detail regarding their geometry and loading. The modular building block approach of modelling is shown to be of essential importance. For the different analyses a fatigue post-processor has been implemented as well as an optimization tool. Both of these in-house codes will be briefly presented.

Development and Evaluation of a High-Resolution Turbine Pyrometer System

Optical pyrometers provide many advantages over intrusive measuring techniques in determining the spatial and time varying temperature distribution of fast rotating components in gas turbines. This paper describes the development and evaluation of a versatile high-resolution pyrometer system and its application to radial turbine rotor temperature mapping as has been done in a R&D project at the Technical University Berlin under funding from Siemens Power Generation (KWU). The development goal was a pyrometer system with a temporal resolution of 1 μs, a minimum field of view of 1 mm, and a measurement range from 600 to 1500°C. A prototype of the pyrometer system has been built and tested at the small gas turbine test facility of the Technical University Berlin. The system yielded excellent results with respect to measurement uncertainty, resolution, and reliability. Finally, measurement results obtained with the new system on a radial turbine rotor and on a heavy duty industrial gas turbine are compared with measurements conducted with a commercially available turbine pyrometer system.