Fuel Flexibility Influences on Premixed Combustor Blowout, Flashback, Autoignition and Instability (original) (raw)
Related papers
Fuel Flexibility Influences on Premixed Combustor Blowout, Flashback, Autoignition, and Stability
Journal of Engineering for Gas Turbines and Power, 2008
This paper addresses the impact of fuel composition on the operability of lean premixed gas turbine combustors. This is an issue of current importance due to variability in the composition of natural gas fuel supplies and interest in the use of syngas fuels. This paper reviews available results and current understanding of the effects of fuel composition on combustor blowout, flashback, dynamic stability, and autoignition. It summarizes the underlying processes that must be considered when evaluating how a given combustor's operability will be affected as fuel composition is varied. Fig. 15 Comparison of flow reactor data with kinetic modeling using different detailed mechanisms †35,40,56-59 ‡
Response of a Model Gas Turbine Combustor to Variation in Gaseous Fuel Composition
Volume 2: Coal, Biomass and Alternative Fuels; Combustion and Fuels; Oil and Gas Applications; Cycle Innovations, 2000
The effect of fuel composition on performance is evaluated on a model gas turbine combustor designed to mimic key features of practical devices. A flexible fuel injection system is utilized to control the placement of the fuel in the device to allow exploration and evaluation of fuel distribution effects in addition to chemistry effects. Gas blends reflecting the extremes in compositions found in the U.S. are considered. The results illustrate that, for the conditions and configuration studied, both fuel chemistry and fuel air mixing play a role in the performance of the device. While chemistry appears to be the predominant factor in stability, a role is noted in emissions performance as well. It is also found that changes in fuel distribution associated with changes in fuel momentum for fixed firing rate also have an impact on emissions. For the system considered, a strategy for sustaining optimal performance while fuel composition changes is illustrated.
Burner Development and Operability Issues Associated with Steady Flowing Syngas Fired Combustors
Http Dx Doi Org 10 1080 00102200801963375, 2008
This article addresses the impact of syngas fuel composition on combustor blowout, flashback, dynamic stability, and autoignition in premixed, steady flowing combustion systems. These are critical issues to be considered and balanced against emissions considerations in the development and operation of premixed combustors. Starting with blowout, the percentage of hydrogen in the fuel is suggested to be the most significant fuel parameter, which is more fundamentally related to the hydrogen flame's resistance to stretch induced extinction. Turning to flashback next, it is shown that multiple flashback mechanisms are present in swirling flows, and the key thermophysical properties of a syngas mixture that influence its flashback proclivity depend upon which flashback mechanism is considered. Flashback due to turbulent flame propagation in the core flow and the interaction of heat release with pulsations are less critical, whereas flame propagation in boundary layers and flashback due to the interaction of the heat release with vortex breakdown dynamics are most significant. Then, combustion instability is considered. The key flame parameter impacting the conditions under which instabilities occur is the spatial distribution of the flame. As such, fuel composition influences dynamics through impacts upon flame speed and the flame stabilization point. Furthermore, certain syngas fuel compositions are not more inherently stable than others-rather, each mixture has particular islands in the parameter space of, e.g., velocity and fuel/air ratio, at which instabilities occur. Changes in fuel composition move these islands around but do not necessarily eliminate or introduce instabilities. Relative to autoignition, measurements indicate that the ignition delay time exceeds typical premixer The first three authors of this article are participants in the University Turbine Systems Research (UTSR) program, a DOE-sponsored program that is investigating fundamental problems that are of interest to the gas turbine community, with particular focus upon coal-derived fuels. This publication was prepared with the support of the
Industrial combustion is still related to the majority of energy consumption in the world today and it is expected to continue to play a major role in the future due to the increasing global demand for electrical energy production. The cost-effective production and use of energy with reduced emissions is a key aim in Europe. This may be achieved by increasing the efficiency of fossil fuel based energy conversion processes and by increasing the utilization of renewable energy sources like wind turbines that, due to their unpredictable power fluctuation, need to be backed up by fast-reacting gas turbine power plants to avoid outages in the case of sudden wind velocity drops. Furthermore, gas turbines play a central role in power generation, due to their relatively low installed capital cost, their high flexibility, and their low emissions with respect to other energy conversion systems. Hence, as important parts of economic growth and increased quality of life, it is of upmost importance that they perform at maximum capacity and with minimum disruptions at all times. Lean Pre-Mixed (LPM) combustion is the state-of-the-art technology in stationary gas turbines for highly efficient low NO x emission power generation using natural gas. The counterpart for liquid fuels is the Lean Pre-mixed Pre-vaporized (LPP) strategy. By means of such technologies it is possible to operate gas turbines with pollutant emissions below the limits imposed by the European Industrial Emission Directives. However, especially when operated close to the lean blow out limit, these combustion strategies tend to experience large amplitude pressure oscillations due to the coupling of pressure waves, associated to the acoustics of the combustion system, and heat release fluctuations. These pressure oscillations can have amplitudes greater than 10% of the mean chamber pressure, however acceptable levels are much lower. Depending on the mechanical design of the combustion chamber and the frequency of the oscillations typical limits set by manufacturers can be more than an order of magnitude lower than this. These undesired oscillations reduce the stable operating range of gas turbines: they often tend to increase when working with leaner mixtures, but there are also combustion systems exhibiting some characteristic frequencies that increase with richer
The Fuel Flexibility of Gas Turbines: A Review and Retrospective Outlook
Energies
Land-based gas turbines (GTs) are continuous-flow engines that run with permanent flames once started and at stationary pressure, temperature, and flows at stabilized load. Combustors operate without any moving parts and their substantial air excess enables complete combustion. These features provide significant space for designing efficient and versatile combustion systems. In particular, as heavy-duty gas turbines have moderate compression ratios and ample stall margins, they can burn not only high- and medium-BTU fuels but also low-BTU ones. As a result, these machines have gained remarkable fuel flexibility. Dry Low Emissions combustors, which were initially confined to burning standard natural gas, have been gradually adapted to an increasing number of alternative gaseous fuels. The paper first delivers essential technical considerations that underlie this important fuel portfolio. It then reviews the spectrum of alternative GT fuels which currently extends from lean gases (coa...
Combustion Science and Technology, 1998
This paper presents the results of a study of the potential causes of frequently observed combustion instabilities in low NO x gas turbines (LNGT) that burn gaseous fuels in a premixed mode. The study was motivated by indications that such systems are highly sensitive to equivalence ratio perturbations. An unsteady well-stirred reactor model was developed and used to determine the magnitude of the reaction rate and heat release oscillations produced by periodic flow rate, temperature or equivalence ratio perturbations in the combustor's inlet flow at different mean equivalence ratios. This study shows that the magnitudes of the reaction rate and heat release oscillations produced by these perturbations remains practically unchanged, decreases, and significantly (i.e., by a factor of 5-100) increases, respectively, as the equivalence ratio decreases. These results strongly suggest that equivalence ratio perturbations, which are an indication of reactants unmixedness, playa key role in the driving of combustion instabilities in LNGT operating under lean conditions.
Combustion and Oxidation Kinetics of Alternative Gas Turbines Fuels
Volume 3A: Coal, Biomass and Alternative Fuels; Cycle Innovations; Electric Power; Industrial and Cogeneration, 2014
Heavy duty gas turbines are very flexible combustion tools that accommodate a wide variety of gaseous and liquid fuels ranging from natural gas to heavy oils, including syngas, LPG, petrochemical streams (propene, butane…), hydrogenrich refinery by-products; naphtha; ethanol, biodiesel, aromatic gasoline and gasoil, etc. The contemporaneous quest for an increasing the panel of primary energies leads manufacturers and operators to explore an ever larger segment of unconventional power generation fuels. In this moving context, there is a need to fully characterize the combustion features of these novel fuels in the specific pressure, temperature and equivalence ratio conditions of gas turbine combustors using e.g. methane as reference molecule and to cover the safety aspects of their utilization. A numerical investigation of the combustion of a representative cluster of alternative fuels has been performed, namely two natural gas fuels of different compositions, including some ethane, a process gas with a high butane content in, oxygenated compounds including methanol, ethanol, and DME (dimethyl ether). Sub-mechanisms have specifically been developed to include the reactions of C 4 species. Major combustion parameters, such as auto-ignition temperature (AIT), ignition delay times (AID), laminar burning velocities of premixed flames, adiabatic flame temperatures, and CO and NOx emissions have then been investigated. Finally, the data have been compared with those calculated for methane flames. These simulations show that the behaviors of alternative fuels markedly differ from that of conventional ones. Especially, DME and the process gases appear to be highly reactive with significant impacts on the auto-ignition temperature and flame speed data, which justifies burner design studies within premixed combustion schemes and proper safety considerations. The behaviors of alcohols (especially methanol) display some commonalities with those of conventional fuels. In contrast, DME and process gas fuels develop substantially different flame temperature and NOx generation rates than methane. Resorting to lean premix conditions is likely to achieve lower NOx emission performances. This review of gas turbine fuels shows for instance that the use of methanol as a gas turbine fuel is possible with very limited combustor modifications.
LES Analysis of a Syngas Turbulent Premixed Dump-Combustor at 5 Bar
1. General aspects It is well known that combustion in gas turbines may exhibit pressure oscillations due to poor flame stability. Flame anchoring and thermo-acoustic instabilities are, in fact, a major concern for modern and future combustors, as they tend to employ some form of premixing to reduce NO x . Efforts are currently focused on fuel lean premixed combustors or partially premixed combustors with rapid mixing after fuel injection, with the tendence to operate close to the Lean BlowOut limit (LBO). However, these combustion strategies are less stable than conventional ones because lean mixtures imply weaker combustion processes and can therefore be easily perturbed, thus increasing the risk of flame blowout. This scenario goes against an acceptable operation of gas turbines. Today the use of CCS (Carbon Capture and Sequestration) derived fuels is becoming more usual, especially in IGCC (Integrated Gasification Combined Cycle) power plants. The big difference between these fu...
Characterization of Fuel Composition Effects in H2∕CO∕CH4 Mixtures Upon Lean Blowout
Journal of Engineering for Gas Turbines and Power, 2007
This paper describes measurements of the dependence of lean blowout limits upon fuel composition for H2∕CO∕CH4 mixtures. Blowout limits were obtained at fixed approach flow velocity, reactant temperature, and combustor pressure at several conditions. Consistent with prior studies, these results indicate that the percentage of H2 in the fuel dominates the mixture blowout characteristics. That is, flames can be stabilized at lower equivalence ratios, adiabatic flame temperatures, and laminar flame speeds with increasing H2 percentage. In addition, the blowoff phenomenology qualitatively changes with hydrogen levels in the fuel, being very different for mixtures with H2 levels above and below about 50%. It is shown that standard well stirred reactor based correlations, based upon a Damköhler number with a diffusivity ratio correction, can capture the effects of fuel composition variability on blowoff limits.