European Community Project of Fifth Framework Programme
Dec. 2000 - Nov. 2003
TECHNION ISRAEL INSTITUTE OF TECHNOLOGY
Israel Institute of Technology (Technion) ISRAEL
Imperial College of Science Technology & Medicine (ICSTM) UK
CINAR Ltd. (CINAR) UK
Instituto Superior Técnico (IST) PORTUGAL
Institute of Fundamental Technological Research (IPPT-PAN) POLAND
ANSALDO Ricerche Srl. (Ansaldo) ITALY
B&B AGEMA Gmbh (B&B_AGEMA) GERMANY
Aachen University GERMANY
The primary objective of the proposal is to develop innovative combustors for small gas turbines, suitable for safe and reliable operation at high temperatures while maintaining low NOx level (typically less than 20 ppmv). The method proposed in the FLOXCOM program for clean and efficient gas turbines, operating at high temperatures, is based on a technologically innovative combustion solution, the FLameless OXidation - FLOX(r) method. This promising technology allows operation of the combustor at high temperatures with ultra-low NOx levels. In addition, this combustion mode has further advantages over other advanced NOx reduction technology such as safety, reliability and the possibility for its incorporation in a heat exchanger cycle using high air temperatures at the combustor inlet. Other objectives are to improve the internal combustor aerodynamics in order to obtain a more uniform wall temperature for lower thermal stresses, and to lower the values of the exhaust gas pattern factors for more circumferential uniformity at the combustor exit for increased Mean Time Between Failure (MTBF) and reliability of the gas turbine. An additional objective is to gain advanced engineering expertise in combustion related subjects. These include modelling of combustion chemistry–turbulence interaction, integrated wall cooling and combustion aerodynamics, high momentum and uniform fuel stream injection and more.
The proposed investigation will be distributed between the different participants while guidance, coordination and integration will be performed by the coordinator. The investigation is directed toward the completion of the studies required to validate the engineering feasibility of the Flameless Oxidation technology and to produce operating pilot combustors that will demonstrate its improved performance. The program will make use of innovative combustion predictions and advanced technologies of fuel injection and cooling, developed to fit the Flameless Oxidation combustor’s specific needs. The theoretical results will be validated through detailed experimental analysis of different sector combustors and full-scale tests of pilot combustors. The work is equally divided between theoretical studies and experimental verifications. It commences with basic studies required to improve understanding on the interactions between turbulence and combustion. This study will be coupled to well defined and controlled combustion laboratory experiments. Basic studies will also be performed of an innovative fuel atomisation method, which will also serve as a momentum accelerator for the main vortex playing a major role in the operation of the newly developed combustor, while maintaining circumferential uniformity. An additional, detailed investigation will be conducted to develop wall-cooling methods where the small-wall jets are optimised for maximising the combined effects of the vortex momentum augmentation and wall temperature reduction and unification. The effect of wall cooling and fuel injection on the vortex characteristics will be quantitatively visualised within transparent flow models using the PIV technique. The results of these investigations will be integrated within existing CFD codes that allow analysing and predicting the complete 3D-combustor performance. Prediction results will be used to optimise the combustor geometry for minimum emission and maximum combustion stability, uniformity of wall temperature and circumferential distribution of exhaust gas temperature profiles. Different combustor sectors will be produced, for detailed point measurements of velocities, temperatures and species concentration. The tests will be performed under a variety of operating parameters including chemical reactive flows and pressurised conditions. These will be used for further adjustments of the different models and for comparison with the CFD predictions. A complete pilot combustor prototype will be produced and tested under realistic pressure and temperature conditions. These will be used for global performance measurements such as combustion efficiency and stability, emission, circumferential variation of the exhaust gases temperature and wall temperature distribution.
The major goal of this program will be an advanced, extensively tested and validated, operating pilot combustor. Significant progress is also expected in combustion engineering related technologies through the gained knowledge. This program will test and verify the new combustor technology. However, some optimisations of various design parameters and endurance testing will still have to be performed to complete the combustor design.
1.1 Issues involved - state of the art
The need for reducing the global impact of the power industry is obvious. This was quantified in the Kyoto objectives, which implies for the EU a reduction of greenhouse gas emissions by 8%. In general, the technology developed within the FLOXCOM project will assist in achieving the following objectives:
The main objective of this program is the development of an innovative combustor for gas turbines. It can also be applied to aero-engines for both helicopters and jet engines. The distinct advantages of this innovative design arise from the new ability to apply the FLOX(r) combustion concept to gas turbine combustors. The FLOX(r) combustor design results in significant performance improvements mainly due to the lower NOx emission levels in comparison to those existing in alternative dry-low NOx combustion techniques, running under similar operating conditions (temperature and pressure).
The application of the FLOX(r) combustion concept to gas turbine combustors and the role of the FLOX(r) mode in NOx emission reductions were already confirmed by computer simulations performed at the Technion. FLOX(r) is also being currently used in industrial furnaces with regenerative burners in non-adiabatic cycle, indicating extremely low NOx emission levels (typically less than 5 ppmv), well below the requirements specified in Key Action 5.1.3.
The technological objectives of the present proposal are to design, build and test a pilot combustor using the FLOX(r) combustion concept. For the completion of the above objectives some basic study in the field of combustion theory and design optimisation have to be performed. In addition, due to the unique internal flow structure inside the combustor that is characterised by a large vortex, an improved wall cooling and fuel injection method can be integrated into its design. Consequently the methodology adopted to achieve the above scientific and technological objectives includes the following studies:
1. To improve combustion modelling according to engineering recommendations for the enhancement of mixing, combustion and emissions performance of gas turbine combustors. This is to be achieved by improved modelling of the turbulence/chemistry interaction applicable to diffusion and partially premixed flames. It also concerns the development and validation of a NOx prediction model using suitable chemistry for the FLOX(r) mode with vitiated air. These models will be incorporated in an existing three-dimensional computational fluid mechanics (CFD) prediction code. The resulting prediction procedure will be tested against laboratory data for turbulent combustion.
2. To get physical insights of the main vortex by detailed whole field cold flow measurements in a transparent combustor sector.
3. To improve fuel injection and distribution. This is to be done by numerical and experimental investigation of the flow-field and combustion features for different atomisation and vaporisation systems. This specific study will conclude by selecting the best fuel supply system for the FLOX(r) combustor and for optimisation of its design.
4. To improve wall cooling. This is to be done through detailed investigation, conducted to develop wall-cooling methods where the jets are optimised for maximising the combined effects of the vortex momentum augmentation and wall temperature reduction and unification.
5. To optimise the combustor design. This is to be done by implementation of the results from all the detailed investigations described in the above scientific and technological objectives (1-4) within current CFD codes that are capable of analysing and predicting the complete 3D-combustor performances. The results of these predictions will be used for optimisation of the combustor geometry. This includes the minimum pollutant emissions, maximum combustion stability, uniformity of wall temperature and smooth profiles of the circumferential distribution of exhaust gas temperature.
6. To perform combustor sector testing. Two combustor sectors will be produced with optical windows, for detailed point measurements of velocity vectors, temperatures and species concentrations distributions under reactive and pressurised conditions. These will be used for further adjustments of the different models and for comparisons with the CFD predictions.
7. To assemble the pilot combustors. This requires detailed design specifications of the pilot combustor; negotiations with the manufacturing sub-contractors; definition of the experimental conditions.
8. To perform pilot combustor testing. One complete pilot combustor prototype will be produced and tested under realistic pressure and temperature conditions. These will be used for global performance measurements such as combustion efficiencies and stability, emission, circumferential variation of the exhaust gases temperature and of the wall temperature. This validation stage is essential for further commercial exploitation.
9. To deduce conclusions from comparison between predictions and tests, suggest design modifications and devise a plan for a continuation program leading to completion of the combustor development. This plan should lead to design optimisation for production cost reduction. The next stage being the commercial manufacturing of the FLOX(r) combustor for a specific gas turbine and performance of a test program for endurance testing.
FLOX(r) is a registered trademark of WS Wärmeprozesstechnik GmbH, Renningen.