A Comparative Analysis of Two Competing Mid-size Oxy-fuel Combustion Cycles

Conceptual turbine and compressor designs have been established for the semi-closed oxy-fuel combustion combined cycle and the Graz cycle. Real gas effects are addressed by extending cycle and conceptual design tools with a fluid thermodynamic and transport property database. Maximum compressor efficiencies are established by determining optimal values for stage loading, degree of reaction and number of compressor stages. Turbine designs are established based on estimates on achievable blade root stress levels and state of the art design parameters. The work indicates that a twin shaft geared compressor is needed to keep stage numbers to a feasible level. The Graz cycle is expected to be able to deliver around 3% net efficiency benefit over the semi-closed oxy-fuel combustion combined cycle at the expense of a more complex realization of the cycle

Multidisciplinary assessment of a year 2035 turbofan propulsion system

A conceptual design of a year 2035 turbofan is developed and integrated onto a year 2035 aircraft model. The mission performance is evaluated for CO2, noise and NOx and is compared with a notional XWB/A350-model. An OGV heat exchanger is then studied rejecting heat from an electric generator, and its top-level performance is evaluated. The fan, the booster and the low-pressure turbine of the propulsion system are subject to more detailed aero design based on using commercial design tools and CFD-optimization. Booster aerodynamic modelling output is introduced back into the performance model to study the integrated performance of the component. The top-level performance aircraft improvements are compared to top-level-trends and ICAO estimates of technology progress potential, attempting to evaluate whether there is some additional margin for efficiency improvement beyond the ICAO technology predictions for the same time frame

On Degradation and Monitoring Tools for Gas and Steam Turbines

The revenue from a power plant is strongly dependent on the life cycle cost. Today, when the market conditions for power-producing companies have shifted from a protected market to a deregulated market, the need for tools to monitor power plants has increased significantly. In this new competitive market, targeted revenues and operational economy drive the need for advanced monitoring tools. In this thesis, monitoring tools for both the gas turbine and the steam turbine are described. The thesis gives a thorough description of the state-of-the-art model-based gas turbine flow path analysis system. The underlying mechanisms for degradation are also described, together with some remedying actions. The main intention of the thesis is to provide guidance for the user of the plant on how a model-based system works. The information is presented in general terms, since it is impossible to cover all gas turbine based power plant configurations. The tools presented here have different levels of sophistication, from the most simple to state-of-the-art heat and mass balance programs. The level of sophistication that is achievable is dependent on the extent of knowledge about a specific engine type. The highest level of sophistication is reserved for systems delivered by the manufacturing companies (OEMs). This level of model-based monitoring system requires detailed propriety turbine data that are not available outside the OEM. A system delivered by an OEM is more costly in general, but the additional know-how is a very valuable commodity. When working with the operational aspects of a power plant, one needs to make quantitative estimations of the effects of deteriorated components. Usually, the software for more detailed analysis are not available to the users since they use in-house code developed by the manufacturers. Besides being proprietary, such code is normally neither user-friendly nor adapted for this type of analysis. However, there are commercially available software packages on the market, but these do not usually provide the required level of off-design prediction capability. Thus, it was decided to develop a flexible tool with open structure that would enable both general power plant simulation useful for the plant owners, and detailed component analysis that is of special interest for research purposes. This work resulted in three different tools, a gas turbine performance deck or off-design performance prediction tool, a steam cycle analysis tool, and a reduced-order through-flow program. The gas turbine performance deck is suitable for both gas turbine and complete combined cycle analysis. This tool has also been used to analyze the off-design behavior of advanced wet gas turbine based cycles. The steam cycle analysis tool was developed for general steam cycle studies, and is suitable for highly loaded turbine components such as control stages at partial load. This tool was calibrated against high-quality data measured from test code (DIN) performance tests, and the results are well within expectation. The steam cycle calculation tool has been used by the project partners as a tool for generating data for ANN training purposes and general power plant off-design performance studies. The first two calculation models presented are at the component level ? where the performance of a component is simulated ? rather than dealing with an individual stage in a compressor or a turbine. As a complement, the author developed a reduced-order through-flow program, where more detailed analysis at the stage level can be performed. This software can be used for an arbitrary number of cooled and choked turbine stages. The code was validated against data measured from a turbine test rig, and the results show that the accuracy is well within the figures expected. This program is available at the department's website as open source code in Matlab?. The theories behind these calculation programs are presented in this thesis in Chapters 5, 6 and 7. Knowing the underlying degradation mechanisms, and with the possibility of including these in a condition-monitoring system, the potential for improving the economics of operation is significant. The availability of a plant can be increased if early warnings can be obtained. Also, in the case of component breakdowns, the cost of secondary replacement parts can be avoided entirely

Improved load control for a steam cycle combined heat and power plant

The problem of optimum load control of steam power plants has been dealt within many technical papers during the last decades. Deregulation of the power markets and close to the (bio-) fuel source thinking has lead to a trend of small scale combined heat and power plants. These plants are usually operated according to the heat demand and therefore they spend a significant time on partial load. The load control of such plants is in general done by partial arc control. This work applies a hybrid control strategy, which is a combination of partial arc control and sliding pressure control. The method achieves further improvement in performance at partial load. Hybrid control itself is not novel and has earlier been used on traditional coal-fired condensing plants. This has, to the author's knowledge, not earlier been applied on combined heat and power plants. The results show that there is a potential for improved electricity production at a significant part of the load range. (C) 2009 Elsevier Ltd. All rights reserved

A Novel Approach For Gas Turbine Condition Monitoring Combining Cusum Technique And Artificial Neural Network

Investigation of a novel condition monitoring approach, combining artificial neural network (ANN) with a sequential analysis technique, has been reported in this paper. For this purpose operational data from a Siemens SGT600 gas turbine has been employed for the training of an ANN model. This ANN model is subsequently used for the prediction of performance parameters of the gas turbine. Simulated anomalies are introduced on two different sets of operational data, acquired one year apart, whereupon this data is compared with corresponding ANN predictions. The cumulative sum (CUSUM) technique is used to improve and facilitate the detection of such anomalies in the gas turbine's performance. The results are promising, displaying fast detection of small changes and detection of changes even for a degraded gas turbine

Temporary CO2 capture shut down: Implications on low pressure steam turbine design and efficiency

The Natural gas Combined Cycle (NGCC) with post combustion capture using liquid solvents may in some cases be of interest to design with a flexible steam bottoming cycle, so that it can operate both with and without CO2 capture. It is then important that the choice of the low pressure (LP) steam turbine exhaust size is made accordingly. The paper describes why a flexible NGCC requires a LP steam turbine with smaller exhaust than the corresponding NGCC without CO2 capture, and how this will affect the LP turbine exhaust loss and NGCC process efficiency. Handling large variations in LP steam flow is in fact wellknown technology in combined heat and power (CHP) plants, and the use of 3D simulation tools can further help making the best LP steam turbine design choice.publishedVersio

Aerodynamic turbine design for an oxy-fuel combined cycle

The oxy-fuel combined cycle (OCC) is one of several carbon capture and sequestration (CCS) technologies being developed to reduce CO2 emissions from thermal power plants. The OCC consists of a semi-closed topping Bryton cycle, and a traditional bottoming Rankine cycle. The topping cycle operates with a working medium mixture of mainly CO2 and H2O. This CO2-rich working fluid has significantly different gas properties compared to a conventional open gas turbine cycle, which thereby affects the aerodynamic turbine design for the gas turbine units. The aerodynamic turbine design for oxyfuel gas turbines is an unexplored research field. The topic of this study was therefore to investigate the aerodynamic turbine design of turbines operating with a CO2-rich working fluid. The investigation was performed through a typical turbine aerodesign loop, which covered the 1D mid-span, 2D through-flow, 3D blade profiling design and the steady-state 3D analysis. The design was performed through the use of conventional design methods and criteria in order to investigate if any significant departures from conventional turbine design methods were required. The survey revealed some minor deviations in design considerations, yet it showed that the design is feasible with today's state-of-the-art technology by using conventional design practice and methods. The performance of the oxy-fuel combined cycle was revised based on the performance figures from the components design. The expected total performance figures for the oxy-fuel combined cycle were calculated to be a net electrical power of 119.9 MW and a net thermal efficiency of 48.2%. These figures include the parasitic consumption for the oxygen production required for the combustion and the CO2 compression of the CO2 bleed stream

Detection and interactive isolation of faults in steam turbines to support maintenance decisions

The maintenance of steam turbines is expensive, particularly if dismantling is required. A concept for the provision Of Support for the maintenance engineer in determining steam turbine status in relation to the recommended maintenance interval is presented here. The concept embodies an artificial neural network which is conditioned to recognise patterns known to be related to faults. The faults Simulated are not known to be recognized on-line and the concept is in an early stage of development, An example of a Bayesian network structure containing expert knowledge is proposed to be used, in a dialogue with the operator, to isolate the root causes of a number Of fault types. The aim is to be well informed about the statue of the turbine in order to take earlier and better informed maintenance actions. The detection procedure has been validated in a Simulation environment. (C) 2008 Elsevier B.V. All rights reserved

Reduced-order through-flow design code for highly loaded cooled gas turbines

The development of advanced computational fluid dynamic codes for turbine design does not substitute the importance of mean-line codes. Turbine design involves mean-line design, through-flow design, airfoil design, and finally 3D viscous modeling. The preliminary mean-line design continues to play an important role in early design stages. The aim of this paper was to present the methodology of mean-line designing of axial turbines and to discuss the computational methods and procedures used. The paper presents the Lund University Axial Turbine mean-line code (LUAX-T). LUAX-T is a reduced-order through-flow tool that is capable of designing highly loaded, cooled axial turbines. The stage computation consists of three iteration loops – cooling, entropy, and geometry iteration loop. The stage convergence method depends on whether the stage is part of the compressor turbine (CT) or power turbine (PT) stages, final CT stage, or final PT stage. LUAX-T was developed to design axial single-and twin-shaft turbines, and various working fluid and fuel compositions can be specified. LUAX-T uses the modified Ainley and Mathieson loss model, with the cooling computation based on the m*-model. Turbine geometries were established by applying various geometry correlations and methods. The validation was performed against a test turbine that was part of a European turbine development program. LUAX-T validated the axial PT of the test turbine, which consisted of two stages with rotational speed 13000 rpm. LUAX-T showed good agreement with the available performance data on the test turbine. The paper presented also the mean-line design of an axial cooled twin-shaft turbine. Design parameters were kept within limits of current practice. The total turbine power was 109 MW, of which the CT power was 55 MW. The CT was designed with two stages with a rotational speed of 9500 rpm, while the PT had two stages with a rotational speed of 6200 rpm. The total cooling mass flow was calculated to 31 kg/s, which corresponds to 23 % of compressor inlet mass flow. LUAX-T proved capable of designing uncooled and cooled turbines

Numerical investigation of the effect of different back sweep angle and exducer width on the impeller outlet flow pattern of a centrifugal compressor with vaneless diffuser

This paper presents a numerical investigation of the effect of different back sweep angles and exducer widths on the steady-state impeller outlet flow pattern of a centrifugal compressor with a vaneless diffuser. The investigations have been performed with commercial CFD and in-house programmed 1-D codes. CFD calculations aim to investigate how flow pattern from the impeller is quantitatively influenced by compressor geometry parameters; thereby, the location of wake and its magnitude (flow angle and relative velocity magnitude) are analyzed. Results show that the increased back sweep impeller provides a more uniform flow pattern in terms of velocity and flow deviation angle distribution, and offers better potential for the diffusion process inside a vaneless (or vaned) diffuser. Secondary flux fraction and flow deviation angle from CFD simulation arc implemented into the 1-D two-zone program to improve 1-D prediction results. Copyrigh