Gas Turbine Combined Cycle With CO2-Capture Using Auto-Thermal Reforming of Natural Gas

A concept for capturing and sequestering CO2 from a natural gas fired combined cycle power plant is presented. The present approach is to decarbonise the fuel prior to combustion by reforming natural gas, producing a hydrogen-rich fuel. The reforming process consists of an air-blown pressurised auto-thermal reformer that produces a gas containing H2, CO and a small fraction of CH4 as combustible components. The gas is then led through a water gas shift reactor, where the equilibrium of CO and H2O is shifted towards CO2 and H2. The CO2 is then captured from the resulting gas by chemical absorption. The gas turbine of this system is then fed with a fuel gas containing approximately 50% H2. In order to achieve acceptable level of fuel-to-electricity conversion efficiency, this kind of process is attractive because of the possibility of process integration between the combined cycle and the reforming process. A comparison is made between a “standard” combined cycle and the current process with CO2-removal. This study also comprise an investigation of using a lower pressure level in the reforming section than in the gas turbine combustor and the impact of reduced steam/carbon ratio in the main reformer. The impact on gas turbine operation because of massive air bleed and the use of a hydrogen rich fuel is discussed.

Determination of Thermoacoustic Response in a Demonstrator Gas Turbine Engine

This paper describes an analytical and experimental investigation to obtain the thermoacoustic response of a demonstrator gas turbine engine combustor. The combustor acoustic response for two different fuel injector design configurations was measured. It was found that the combustor maximum peak to peak pressure fluctuations were 0.6 psi to 2 psi for configuration A and B respectively. Based on the measured acoustic response, another experimental investigation was conducted to identify the design features in configuration B that caused the increase in the acoustic response. The data showed that by changing the fuel injector swirler’s vane to inner passage discharge area ratio, the engine acoustic response could be lowered to an acceptable level. A simplified analytical model based on the lumped-parameter approach was then developed to investigate the effect of geometrical changes upon the engine response. The analytical model predicted the fuel injector/swirlers acoustic response as a function of the swirlers inner passage discharge area ratio and frequency. The predictions were consistent with the experimental observations, in particular, it was predicted that as the area ratio was increased, the system reactance was decreased and as a result the system changed from a damping to an amplifying system.

Operation Experiences of Siemens IGCC Gas Turbines Using Gasification Products From Coal and Refinery Residues

The Integrated Gasification Combined Cycle concept is an emerging technology that enables an efficient and clean use of coal as well as residuals in power generation. After several years of development and demonstration operation, now the technology has reached the status for commercial operation. SIEMENS is engaged in 3 IGCC plants in Europe which are currently in operation. Each of these plants has specific characteristics leading to a wide range of experiences in development and operation of IGCC gas turbines fired with low to medium LHV syngases. The worlds first IGCC plant of commercial size at Buggenum/Netherlands (Demkolec) has already demonstrated that IGCC is a very efficient power generation technology for a great variety of coals and with a great potential for future commercial market penetration. The end of the demonstration period of the Buggenum IGCC plant and the start of its commercial operation has been dated on January 1, 1998. After optimisations during the demonstration period the gas turbine is running with good performance and high availability and has exceeded 18000 hours of operation on coal gas. The air-side fully integrated Buggenum plant, equipped with a Siemens V94.2 gas turbine, has been the first field test for the Siemens syngas combustion concept, which enables operation with very low NOx emission levels between 120–600 g/MWh NOx corresponding to 6–30 ppm(v) (15%O2) and less than 5 ppm(v) CO at baseload. During early commissioning the syngas nozzle has been recognised as the most important part with strong impact on combustion behaviour. Consequently the burner design has been adjusted to enable quick and easy changes of the important syngas nozzle. This design feature enables fast and efficient optimisations of the combustion performance and the possibility for easy adjustments to different syngases with a large variation in composition and LHV. During several test runs the gas turbine proved the required degree of flexibility and the capability to handle transient operation conditions during emergency cases. The fully air-side integrated IGCC plant at Puertollano/Spain (Elcogas), using the advanced Siemens V94.3 gas turbine (enhanced efficiency), is now running successfully on coal gas. The coal gas composition at this plant is similar to the Buggenum example. The emission performance is comparable to Buggenum with its very low emission levels. Currently the gas turbine is running for the requirements of final optimization runs of the gasifier unit. The third IGCC plant (ISAB) equipped with Siemens gas turbine technology is located at Priolo near Siracusa at Sicilly/Italy. Two Siemens V94.2K (modified compressor) gas turbines are part of this “air side non-integrated” IGCC plant. The feedstock of the gasification process is a refinery residue (asphalt). The LHV is almost twice compared to the Buggenum or Puertollano case. For operation with this gas, the coal gas burner design was adjusted and extensively tested. IGCC operation without air extraction has been made possible by modifying the compressor, giving enhanced surge margins. Commissioning on syngas for the first of the two gas turbines started in mid of August 1999 and was almost finished at the end of August 1999. The second machine followed at the end of October 1999. Since this both machines are released for operation on syngas up to baseload.

Hybrid Heat Engines: The Power Generation Systems of the Future

A hybrid heat engine results from the fusion of a heat engine with a non-heat-engine based cycle (unlike systems). The term combined cycle, which refers to similar arrangements, is reserved for the combination of two or more heat engines (like systems). The resulting product of the integration of a gas turbine and a fuel cell is referred to here as a hybrid heat engine or “Hybrid” for short. The intent of this paper is to provide, to the gas turbine community, a review of the present status of hybrid heat engine technologies. Current and projected activities associated with this emerging concept are also presented. The National Energy Technology Laboratory (NETL) is collaborating with other sponsors and the private sector to develop a Hybrid Program. This program will address the issues of technology development, integration, and ultimately the demonstration of what may be the most efficient of power plants in the world — the Hybrid System. Analyses of several Hybrid concepts have indicated the potential of ultra-high efficiencies (approaching 80%). In the Hybrid, the synergism between the gas turbine and fuel cell provides higher efficiencies and lower costs than either system can alone. Testing of the first Hybrid concept has been initiated at the National Fuel Cell Research Center (NFCRC).

Computation of 3D Turbulent Not-Premixed Reacting Flows Using an Implicit Unstructured Solver

A 3D CFD simulation of turbulent reactive flows is discussed. The original compressible version of the solver HybFlow designed for turbine rows investigation is here applied for low speed burning flow. A conserved scalar approach is considered to simulate the turbulent reacting flow field of non-premixed flames. The spatial discretization is based on an upwind finite volume method for unstructured grids using the Roe’s Riemann solver with a non-linear TVD scheme. The steady state solution is computed by means of an implicit relaxed Newton method. The linear solver is GMRES coupled with an ILU(0) preconditioning scheme. The turbulence chemistry interaction is described using a presumed β-PDF Flamelet approach. Two test applications are here presented to verify the methodology characteristics for a pilot-jet turbulent flame and a bluff-body stabilized flame both using CH4. A model combustor supplied with propane is also briefly shown as an example of application to a more realistic configuration.

The Structure of Two-Stage Counterflow n-Heptane-Air Flames

Partially premixed flames are formed by mixing air (in less than stoichiometric amounts) into the fuel stream prior to the reaction zone, where additional air is available for complete combustion. Such flames can occur in both laboratory and practical combustion systems. In advanced gas turbine combustor designs, such as a lean direct injection (LDI) combustor, partially premixed combustion represents an impotent mode of burning. Spray combustion often involves partially premixed combustion due to the locally fuel vapor-rich regions. In the present study, the detailed structure of n-heptane/air partially premixed flame in a counterflow configuration is investigated. The flame is computed by employing the Oppdif code and a detailed reaction mechanism consisting of 275 elementary reactions and 41 species. The partially premixed flame structure is characterized by two-stage burning or two distinct but synergistically coupled reaction zones, a rich premixed zone on the fuel side and a ‘nonpremixed zone on the air side. The fuel is completely consumed in the premixed zone with ethylene and acetylene being the major intermediate species. The reactions involving the consumption of these species are found to be the key rate-limiting reactions that characterize interactions between the two reaction zones, and determine the overall fuel consumption rate. The flame response to the variations in equivalence ratio and strain rate is examined. Increasing equivalence ratio and/or strain rate to a critical value leads to merging of the two reaction zones. The equivalence ratio variation affects the rich premixed reaction zone, while the variation in strain rate predominantly affects the nonpremixed reaction zone. The flame structure is also characterized in terms of a modified mixture fraction (conserved scalar), and laminar flamelet profiles are provided.

Coupled and Uncoupled CFD Prediction of the Characteristics of Jets From Combustor Air Admission Ports

The paper focusses attention on alternative approaches for treating the coupling between the flow in the annulus supply ducts and the jets which enter combustor primary and dilution zones through air admission ports. Traditionally CFD predictions of combustor flows have modeled this in a very weakly-coupled manner, with the port flow conditions being derived from 1D empirical correlations and used as boundary conditions for an internal-flow-only combustor CFD prediction. Recent work by the authors and others has introduced the viewpoint that fully-coupled external-annulus/internal-combustor predictions is the way forward. Experimental data is gathered in the present work to quantify the strength of the interaction between annulus and core flows, which ultimately determines the jet characteristics at port exit. These data are then used to illustrate the improvement in the prediction of port exit jet characteristics which is obtained by adopting fully-coupled calculations compared to the internal-flow-only approach. As a final demonstration of the importance of a fully coupled approach, isothermal calculations are presented for a single sector generic annular combustor. These show that quite different primary zone flow patterns are obtained from the two approaches, leading to considerable differences in the overall mixing pattern at combustor exit.

Conceptual Design for Medium Size Combined Cycle Plants Improved by Recent Research and Innovation

A conceptual design study for a 120 MW combined cycle plant is presented here. Values of 60% thermal efficiency are at present the realm of very large gas turbines of most advanced design with power outputs of 300 to 500 MW. For industry and district heating plants it would be of most economic value to achieve similar thermal efficiencies in medium size gas turbines and combined cycle plants as they are being installed in Central European cogeneration and district heating plants. The authors propose by concerted application of recent research results to achieve this goal for medium size combined cycle plants. Design measures incorporated are transonic turbine stages, an innovative cooling system and a 600 degree reheat steam turbine.

Investigation Concerning the Aerothermodynamic Performance Perturbation of a 19MW Intercooled Air Compressor

This paper investigates the performance problem of a large capacity multistage centrifugal air compressor when operated continuously for an extended period of time without overhauling. The compressor flow constitutes fifty percent of the plant production and plays a critical role in meeting the annual contract capacity and can not tolerate performance instability due to high intercooler temperatures, ambient conditions and, fouling of the internal components. During a recent harsh summer operation, the compressor was undergone to surge many times and prompted to initiate a performance evaluation study to identify the cause(s) of surge and the extent of performance deterioration. High cooling water supply temperature and ambient conditions crippled the performance of the compressor. Engineering analysis identified the excessive accumulation of condensed water in the water chamber of the second intercooler as the most logical reason of the compressor surge during the instances of high ambient conditions i.e. relative humidity and temperature greater than 80% and 35°C, respectively. During heavy load of condensed water, the blockage and insufficient size of the condensate drain caused build up of water level in the water collecting chamber which offered instantaneous hindrance to airflow to the next section and, hence, led to the compressor surge. During normal ambient conditions, the overall performance of the compressor was found satisfactory when compared with the commissioning after a long term of continuous operation without maintenance.

Life Extending Advanced Component Repairs — Field Operating Experience

Advanced repair technologies have been introduced to the gas turbine industry over recent years. An increasing selection of coating systems is available which can be tailored to the specific operating environment. Automated welding systems and the use of custom weld filler metals for enhanced component life provide a means of reliably welding the new generation of high strength turbine blade alloys. Powder metallurgy processes have been introduced as an alternative to welding and have been used to upgrade certain components by employing higher strength repair materials than the original castings. In the paper, these and other technologies are assessed based on engine operating experience with direct comparison to the conventional repair techniques which they have replaced.