Evaluation of CH4/NOx Reduced Mechanisms Used for Modeling Lean Premixed Turbulent Combustion of Natural Gas

1998 ◽  
Vol 120 (4) ◽  
pp. 703-712 ◽  
Author(s):  
H. P. Mallampalli ◽  
T. H. Fletcher ◽  
J. Y. Chen
Keyword(s):  
High Pressure ◽  
Natural Gas ◽  
Gas Turbine ◽  
Turbulent Combustion ◽  
Gas Turbines ◽  
Flame Structure ◽  
Computational Cost ◽  
Premixed Turbulent Combustion ◽  
Reduced Mechanism ◽  
Lean Premixed

This study has identified useful reduced kinetic schemes that can be used in comprehensive multidimensional gas-turbine combustor models. Reduced mechanisms lessen computational cost and possess the capability to accurately predict the overall flame structure, including gas temperatures and key intermediate species such as CH4, CO, and NOx. In this study, four new global mechanisms with five, six, seven, and nine steps based on the full GRI 2.11 mechanism, were developed and evaluated for their potential to model natural gas chemistry (including NOx chemistry) in gas turbine combustors. These new reduced mechanisms were optimized to model the high pressure and fuel-lean conditions found in gas turbines operating in the lean premixed mode. Based on perfectly stirred reactor (PSR) and premixed code calculations, the five-step reduced mechanism was identified as a promising model that can be used in a multidimensional gas-turbine code for modeling lean-premixed, high-pressure turbulent combustion of natural gas. Predictions of temperature, CO, CH4, and NO from the five-to nine-step reduced mechanisms agree within 5 percent of the predictions from the full kinetic model for 1 < pressure (atm) < 30, and 0.6 < φ < 1.0. If computational costs due to additional global steps are not severe, the newly developed nine step global mechanism, which is a little more accurate and provided the least convergence problems, can be used. Future experimental research in gas turbine combustion will provide more accurate data, which will allow the formulation of better full and reduced mechanisms. Also, improvement in computational approaches and capabilities will allow the use of reduced mechanisms with larger global steps, perhaps full mechanisms.

Sequential Combustion in Gas Turbines: The Key Technology for Burning High Hydrogen Contents With Low Emissions

2019 ◽  
Author(s):  
Mirko R. Bothien ◽  
Andrea Ciani ◽  
John P. Wood ◽  
Gerhard Fruechtel
Keyword(s):  
High Pressure ◽  
Natural Gas ◽  
Gas Turbine ◽  
Gas Turbines ◽  
Tuning Parameter ◽  
High Hydrogen ◽  
Stable Combustion ◽  
Second Stage ◽  
In Series ◽  
Exit Temperature

Abstract Excess energy generation from renewables can be conveniently stored as hydrogen for later use as a gas turbine fuel. Also, the strategy to sequestrate CO2 from natural gas will require gas turbines to run with hydrogen-based fuels. In such scenarios, high temperature low emission combustion of hydrogen is a key requirement for the future gas turbine market. Ansaldo Energia’s gas turbines featuring sequential combustion have an intrinsic advantage when it comes to fuel flexibility and in particular hydrogen-based fuels. The sequential combustion system is composed of two complementary combustion stages in series: one premix stage followed by an auto-ignited second stage overcoming the limits of traditional premix combustion systems through a highly effective extra tuning parameter, i.e. the temperature between the first and the second stage. The standard Constant Pressure Sequential Combustion (CPSC) system as applied in the GT36 engine is tested, at high pressure, demonstrating that a modified operation concept allows stable combustion with no changes in combustor hardware for the whole range of natural gas and hydrogen blends. It is shown that in the range from 0% to 70% (vol.) hydrogen, stable combustion is achieved at full nominal exit temperature, i.e. without any derating and thus clearly outperforming other available conventional premixed combustors. Operation between 70% and 100% is possible as well and only requires a mild reduction of the combustor exit temperature. By proving the transferability of the single-can high pressure results to the engine, this paper demonstrates the practicality of operating the Ansaldo Energia GT36 H-Class gas turbine on fuels containing unprecedented concentrations of hydrogen while maintaining excellent performance and low emissions both in terms of NOx and CO2.

Reactor Network Modeling of Stability and Emissions of Hydrogen and Natural Gas Blends for a Piloted Gas Turbine Combustor

2020 ◽  
Author(s):  
Candy Hernandez ◽  
Vincent McDonell
Keyword(s):  
Natural Gas ◽  
Gas Turbine ◽  
Gas Turbines ◽  
Chemical Reactor ◽  
Experimental Results ◽  
Fuel Composition ◽  
Gas Turbine Combustor ◽  
Flammability Limits ◽  
Lean Premixed ◽  
Carbon Molecules

Abstract Lean-premixed (LPM) gas turbines have been developed for stationary power generation in efforts to reduce emissions due to strict air quality standards. Lean-premixed operation is beneficial as it reduces combustor temperatures, thus decreasing NOx formation and unburned hydrocarbons. However, tradeoffs occur between system performance and turbine emissions. Efforts to minimize tradeoffs between stability and emissions include the addition of hydrogen to natural gas, a common fuel used in stationary gas turbines. The addition of hydrogen is promising for both increasing combustor stability and further reducing emissions because of its wide flammability limits allowing for lower temperature operation, and lack of carbon molecules. Other efforts to increase gas turbine stability include the usage of a non-lean pilot flame to assist in stabilizing the main flame. By varying fuel composition for both the main and piloted flows of a gas turbine combustor, the effect of hydrogen addition on performance and emissions can be systematically evaluated. In the present work, computational fluid dynamics (CFD) and chemical reactor networks (CRN) are created to evaluate stability (LBO) and emissions of a gas turbine combustor by utilizing fuel and flow rate conditions from former hydrogen and natural gas experimental results. With CFD and CRN analysis, the optimization of parameters between fuel composition and main/pilot flow splits can provide feedback for minimizing pollutants while increasing stability limits. The results from both the gas turbine model and former experimental results can guide future gas turbine operation and design.

Performance and Cost Analysis of Advanced Gas Turbine Cycles With Precombustion CO2 Capture

2008 ◽  
Vol 131 (2) ◽  
Author(s):  
Stéphanie Hoffmann ◽  
Michael Bartlett ◽  
Matthias Finkenrath ◽  
Andrei Evulet ◽  
Tord Peter Ursin
Keyword(s):  
High Pressure ◽  
Power Plant ◽  
Natural Gas ◽  
Gas Turbine ◽  
Co2 Capture ◽  
Gas Turbines ◽  
High Efficiency ◽  
Combined Cycle ◽  
Co2 Separation ◽  
The Cost

This paper presents the results of an evaluation of advanced combined cycle gas turbine plants with precombustion capture of CO2 from natural gas. In particular, the designs are carried out with the objectives of high efficiency, low capital cost, and low emissions of carbon dioxide to the atmosphere. The novel cycles introduced in this paper are comprised of a high-pressure syngas generation island, in which an air-blown partial oxidation reformer is used to generate syngas from natural gas, and a power island, in which a CO2-lean syngas is burnt in a large frame machine. In order to reduce the efficiency penalty of natural gas reforming, a significant effort is spent evaluating and optimizing alternatives to recover the heat released during the process. CO2 is removed from the shifted syngas using either CO2 absorbing solvents or a CO2 membrane. CO2 separation membranes, in particular, have the potential for considerable cost or energy savings compared with conventional solvent-based separation and benefit from the high-pressure level of the syngas generation island. A feasibility analysis and a cycle performance evaluation are carried out for large frame gas turbines such as the 9FB. Both short-term and long-term solutions have been investigated. An analysis of the cost of CO2 avoided is presented, including an evaluation of the cost of modifying the combined cycle due to CO2 separation. The paper describes a power plant reaching the performance targets of 50% net cycle efficiency and 80% CO2 capture, as well as the cost target of 30$ per ton of CO2 avoided (2006 Q1 basis). This paper indicates a development path to this power plant that minimizes technical risks by incremental implementation of new technology.

Flameholding Tendencies of Natural Gas and Hydrogen Flames at Gas Turbine Premixer Conditions

2014 ◽  
Author(s):  
Elliot Sullivan-Lewis ◽  
Vincent McDonell
Keyword(s):  
Natural Gas ◽  
Gas Turbine ◽  
Gas Turbines ◽  
High Efficiency ◽  
High Reliability ◽  
Elevated Pressure ◽  
Inlet Temperature ◽  
Increased Risk ◽  
Wide Range ◽  
Lean Premixed

Ground based gas turbines are responsible for generating a significant amount of electric power as well as providing mechanical power for a variety of applications. This is due to their high efficiency, high power density, high reliability, and ability to operate on a wide range of fuels. Due to increasingly stringent air quality requirements, stationary power gas turbines have moved to lean-premixed operation. Lean-premixed operation maintains low combustion temperatures for a given turbine inlet temperature, resulting in low NOx emissions while minimizing emissions of CO and hydrocarbons. In addition, to increase overall cycle efficiency, engines are being operated at higher pressure ratios and/or higher combustor inlet temperatures. Increasing combustor inlet temperatures and pressures in combination with lean-premixed operation leads to increased reactivity of the fuel/air mixture, leading to increased risk of potentially damaging flashback. Curtailing flashback on engines operated on hydrocarbon fuels requires care in design of the premixer. Curtailing flashback becomes more challenging when fuels with reactive components such as hydrogen are considered. Such fuels are gaining interest because they can be generated from both conventional and renewable sources and can be blended with natural gas as a means for storage of renewably generated hydrogen. The two main approaches for coping with flashback are either to design a combustor that is resistant to flashback, or to design one that will not anchor a flame if a flashback occurs. An experiment was constructed to determine the flameholding tendencies of various fuels on typical features found in premixer passage ways (spokes, steps, etc.) at conditions representative of a gas turbine premixer passage way. In the present work tests were conducted for natural gas and hydrogen between 3 and 9 atm, between 530 K and 650K, and free stream velocities from 40 to 100 m/s. Features considered in the present study include a spoke in the center of the channel and a step at the wall. The results are used in conjunction with existing blowoff correlations to evaluate flameholding propensity of these physical features over the range of conditions studied. The results illustrate that correlations that collapse data obtained at atmospheric pressure do not capture trends observed for spoke and wall step features at elevated pressure conditions. Also, a notable fuel compositional effect is observed.

scholarly journals Development and Integration of the Dual Fuel Combustion System for the MGT Gas Turbine Family

2021 ◽  
Author(s):  
Bernhard Ćosić ◽  
Frank Reiß ◽  
Marc Blümer ◽  
Christian Frekers ◽  
Franklin Genin ◽  
...  
Keyword(s):  
High Pressure ◽  
Natural Gas ◽  
Gas Turbine ◽  
Distribution System ◽  
Gas Turbines ◽  
Liquid Fuel ◽  
Flame Stabilization ◽  
Experimental Investigations ◽  
Dual Fuel ◽  
Combustion System

Abstract Industrial gas turbines like the MGT6000 are often operated as power supply or as mechanical drives for pumps and compressors at remote locations on islands and in deserts. Moreover, small gas turbines are used in CHP applications with a high need for availability. In these applications, liquid fuels like ‘Diesel Fuel No. 2’ can be used either as main fuel or as backup fuel if natural gas is not reliably available. The MAN Gas Turbines (MGT) operate with the Advanced Can Combustion (ACC) system, which is already capable of ultra-low NOx emissions for a variety of gaseous fuels. This system has been further developed to provide dry dual fuel capability to the MGT family. In the present paper, we describe the design and detailed experimental validation process of the liquid fuel injection, and its integration into the gas turbine package. A central lance with an integrated two-stage nozzle is employed as a liquid pilot stage, enabling ignition and start-up of the engine on liquid fuel only, without the need for any additional atomizing air. The pilot stage is continuously operated to support further the flame stabilization across the load range, whereas the bulk of the liquid fuel is injected through the premixed combustor stage. The premixed stage comprises a set of four decentralized nozzles placed at the exit of the main air swirler. These premixed nozzles are based on fluidic oscillator atomizers, wherein a rapid and effective atomization of the liquid fuel is achieved through self-induced oscillations of the liquid fuel stream. We present results of numerical and experimental investigations performed in the course of the development process illustrating the spray, hydrodynamic, and thermal performance of the pilot injectors. Extensive testing of the burner at atmospheric and full load high-pressure conditions has been performed, before verification of the whole combustion system within full engine tests. The burner shows excellent emission performance (NOx, CO, UHC, soot) without additional water injection, while maintaining the overall natural gas performance. Soot and particle emissions, quantified via several methods, are well below legal restrictions. Furthermore, when not in liquid fuel operation, a continuous purge of the injectors based on compressor outlet (p2) air has been laid out. Generic atmospheric coking tests were conducted before verifying the purge system in full engine tests. Thereby we completely avoid the need for an additional high-pressure auxiliary compressor or demineralized water. We show the design of the fuel supply and distribution system. We designed it to allow for rapid fuel switchovers from gaseous fuel to liquid fuel, and for sharp load jumps. Finally, we discuss the integration of the dual fuel system into the standard gas turbine package of the MGT6000 in detail.

Chemical Kinetic Modeling of Ignition and Emissions From Natural Gas and LNG Fueled Gas Turbines

2012 ◽  
Author(s):  
P. Gokulakrishnan ◽  
C. C. Fuller ◽  
R. G. Joklik ◽  
M. S. Klassen
Keyword(s):  
Natural Gas ◽  
Gas Turbine ◽  
Gas Turbines ◽  
Chemical Kinetic ◽  
Higher Order ◽  
Premixed Combustion ◽  
Nox Emissions ◽  
Lean Premixed Combustion ◽  
Lean Premixed ◽  
Combustion Systems

Single digit NOx emission targets as part of gas turbine design criteria require highly accurate modeling of the various NOx formation pathways. The concept of lean, premixed combustion is adopted in various gas turbine combustor designs, which achieves lower NOx levels by primarily lowering the flame temperature. At these conditions, the post-flame thermal-NOx pathway contribution to the total NOx can be relatively small compared to that from the prompt-NOx and the N2O-route, which are enhanced by the super-equilibrium radical pathway at the flame front. In addition, new sources of natural gas fuel (e.g., imported LNG) with widely varying chemical compositions including higher order hydrocarbon components, impact flame stability, lean blow-out limits and emissions in existing lean premixed combustion systems. Also, the presence of higher order hydrocarbons can increase the risk of flashback induced by autoignition in the premixing section of the combustor. In this work a detailed chemical kinetic model was developed for natural gas fuels that consist of CH4, C2H6, C3H8, nC4H10, iC4H10, and small amounts of nC5H12, iC5H12 and nC6H14 in order to predict ignition behavior at typical gas turbine premixing conditions and to predict CO and NOx emissions at lean premixed combustion conditions. The model was validated for different NOx-pathways using low and high pressure laminar premixed flame data. The model was also extended to include a vitiated kinetic scheme to account for the influence of exhaust gas recirculation on fuel oxidation. The model was employed in a chemical reactor network to simulate a laboratory scale lean premixed combustion system to predict CO and NOx. The current kinetic mechanism demonstrates good predictive capability for NOx emissions at lower temperatures typical of practical lean premixed combustion systems.

Performance and Cost Analysis of Advanced Gas Turbine Cycles With Pre-Combustion CO2 Capture

2008 ◽  
Author(s):  
Ste´phanie Hoffmann ◽  
Michael Bartlett ◽  
Matthias Finkenrath ◽  
Andrei Evulet ◽  
Tord Peter Ursin
Keyword(s):  
High Pressure ◽  
Power Plant ◽  
Natural Gas ◽  
Gas Turbine ◽  
Co2 Capture ◽  
Gas Turbines ◽  
High Efficiency ◽  
Combined Cycle ◽  
Co2 Separation ◽  
The Cost

This paper presents the results of an evaluation of advanced combined cycle gas turbine plants with pre-combustion capture of CO2 from natural gas. In particular, the designs are carried out with the objectives of high efficiency, low capital cost and low emissions of carbon dioxide to the atmosphere. The novel cycles introduced in this paper are comprised of a high-pressure syngas generation island, in which an air-blown POX reformer is used to generate syngas from natural gas, and a power island, in which a CO2-lean syngas is burnt in a large frame machine. In order to reduce the efficiency penalty of natural gas reforming, a significant effort is spent evaluating and optimizing alternatives to recover the heat released during the process. CO2 is removed from the shifted syngas using either CO2 absorbing solvents or a CO2 membrane. CO2 separation membranes, in particular, have the potential for considerable cost or energy savings compared to conventional solvent-based separation and benefit from the high pressure level of the syngas generation island. A feasibility analysis and a cycle performance evaluation are carried out for large frame gas turbines such as the 9FB. Both short term and long term solutions have been investigated. An analysis of the cost of CO2 avoided is presented, including an evaluation of the cost of modifying the combined cycle due to CO2 separation. The paper describes a power plant reaching the performance targets of 50% net cycle efficiency and 80% CO2 capture, as well as the cost target of 30$ per ton of CO2 avoided. This paper indicates a development path to this power plant that minimizes technical risks by incremental implementation of new technology.

Flameholding Tendencies of Natural Gas and Hydrogen Flames at Gas Turbine Premixer Conditions

2014 ◽  
Vol 137 (1) ◽  
Author(s):  
Elliot Sullivan-Lewis ◽  
Vince McDonell
Keyword(s):  
Natural Gas ◽  
Gas Turbine ◽  
Gas Turbines ◽  
High Efficiency ◽  
High Reliability ◽  
Elevated Pressure ◽  
Inlet Temperature ◽  
Increased Risk ◽  
Wide Range ◽  
Lean Premixed

Ground-based gas turbines are responsible for generating a significant amount of electric power as well as providing mechanical power for a variety of applications. This is due to their high efficiency, high power density, high reliability, and ability to operate on a wide range of fuels. Due to increasingly stringent air quality requirements, stationary power gas turbines have moved to lean-premixed operation. Lean-premixed operation maintains low combustion temperatures for a given turbine inlet temperature, resulting in low NOx emissions while minimizing emissions of CO and hydrocarbons. In addition, to increase overall cycle efficiency, engines are being operated at higher pressure ratios and/or higher combustor inlet temperatures. Increasing combustor inlet temperatures and pressures in combination with lean-premixed operation leads to increased reactivity of the fuel/air mixture, leading to increased risk of potentially damaging flashback. Curtailing flashback on engines operated on hydrocarbon fuels requires care in design of the premixer. Curtailing flashback becomes more challenging when fuels with reactive components such as hydrogen are considered. Such fuels are gaining interest because they can be generated from both conventional and renewable sources and can be blended with natural gas as a means for storage of renewably generated hydrogen. The two main approaches for coping with flashback are either to design a combustor that is resistant to flashback, or to design one that will not anchor a flame if a flashback occurs. An experiment was constructed to determine the flameholding tendencies of various fuels on typical features found in premixer passage ways (spokes, steps, etc.) at conditions representative of a gas turbine premixer passage way. In the present work, tests were conducted for natural gas and hydrogen between 3 and 9 atm, between 530 K and 650 K, and free stream velocities from 40 to 100 m/s. Features considered in the present study include a spoke in the center of the channel and a step at the wall. The results are used in conjunction with existing blowoff correlations to evaluate flameholding propensity of these physical features over the range of conditions studied. The results illustrate that correlations that collapse data obtained at atmospheric pressure do not capture trends observed for spoke and wall step features at elevated pressure conditions. Also, a notable fuel compositional effect is observed.

Sign in / Sign up

Export Citation Format

Share Document