Exhaust Diffuser Characteristics at Off-Design Conditions

2014 ◽  
Author(s):  
Vladimir Vassiliev ◽  
Thomas P. Sommer ◽  
Andrei Granovsky ◽  
Sergey Prozorov
Keyword(s):  
Numerical Model ◽  
Mass Flow ◽  
Electricity Market ◽  
Gas Turbines ◽  
Central Body ◽  
Part Load ◽  
Operational Window ◽  
Diffuser Flow ◽  
Low Load ◽  
Base Load

In todays electricity market with a strong mix of renewables and traditional energy sources, heavy-duty gas turbines often have to operate at part load with decreased exhaust mass flow. Decreased mass flow leads to reduced Mach number and this factor drives the exhaust loss down. At the same time off-design conditions lead to reduction of diffuser pressure recovery, and this factor drives loss up. The latter is normally stronger, and therefore the losses at GT low load are higher than at base load. Traditionally exhaust diffusers were optimised for base load operation, and their characteristics were analysed in range close to this regime. However with increased part load operation it became important to investigate strong off-design conditions as well. In this work the numerical analysis of diffuser flow at different conditions corresponding to GT base load and different part loads is performed. In the first part of the paper the numerical model and results of calculations are discussed. The calculations are compared with measurements in real engine, and this comparison demonstrates that numerical model provides good predictions not only for design conditions, but for off-design conditions as well. The validated numerical model was then applied to analysis of diffuser geometry impact on the off design conditions, and the second part of the paper describes the results of these calculations. The analysis showed that modification of central body and front part of diffuser have negligible impact on losses at off design conditions, but significantly reduce performance at base load leading to non-optimal redistribution of losses between different regimes. Therefore original diffuser configuration provides the best compromise for wide operational window.

Turn-Down Capability of Ansaldo Energia’s GT26

2021 ◽  
Author(s):  
Ralf Jakoby ◽  
Jörg Rinn ◽  
Christoph Appel ◽  
Adrien Studerus
Keyword(s):  
Mass Flow ◽  
Gas Turbines ◽  
Development Project ◽  
Combined Cycle ◽  
Operational Flexibility ◽  
Part Load ◽  
Single Feature ◽  
Low Load ◽  
Fast Start ◽  
Base Load

Abstract The operational flexibility of heavy-duty gas turbines is of increasing importance in today’s power generation market. Fast start-up, fast loading, grid frequency support, fuel flexibility and turn-down capability are only some of the keywords that describe the challenges for GT manufacturers. This paper reports Ansaldo Energia’s activities to further reduce the Minimum Environmental Load (MEL) of the GT26. The difficulties related to operation at very low loads and the solutions that were developed are explained. Furthermore, the results of engine validation tests of the new extended Low Load Operation (eLLO) and extended Low Part Load (eLPL) operation concepts are presented. The enhancement of the operational flexibility of the GT26 is in the focus of Ansaldo’s development activities since many years. Its sequential combustion system is a very good basis for flexible and emission compliant operation down to very low loads. Ansaldo Energia’s Low Part Load (LPL) and Low Load Operation (LLO) concepts are standard products in the GT26 flexibility portfolio and established in the market for many years. Low Part Load (LPL) operation extends the standard operating range down to low loads by switching off individual burners in the second combustor (SEV combustor). The compressor mass flow can be varied between idle and base load levels. Low Load Operation is characterized by a combination of idle compressor mass flow and base load temperatures in the first Combustor (EV combustor). The SEV combustor is switched off. LLO is intended to be a “parking point”, where the plant can operate in combined cycle mode during times of low electricity demand. Ansaldo Energia has conducted a development project in the past two years in order to further reduce the minimum simple cycle and combined cycle loads. The extension of the LLO and LPL operating ranges and their combination into one single feature are the main targets of the project.

Experimental Study on Low Load Operation Range Extension by Autothermal On-Board Syngas Generation

2018 ◽  
Vol 141 (1) ◽  
Author(s):  
Max H. Baumgärtner ◽  
Thomas Sattelmayer
Keyword(s):  
Mass Flow ◽  
Power Output ◽  
Gas Turbines ◽  
Power Plants ◽  
Renewable Energy Sources ◽  
Thermal Power ◽  
Combined Cycle ◽  
Range Extension ◽  
Nox Emissions ◽  
Low Load

Volatile renewable energy sources induce power supply fluctuations. These need to be compensated by flexible conventional power plants. Gas turbines in combined cycle power plants adjust the power output quickly but their turn-down ratio is limited by the slow reaction kinetics, which leads to CO and unburned hydrocarbon emissions. To extend the turn-down ratio, part of the fuel can be converted to syngas, which exhibits a higher reactivity. By an increasing fraction of syngas in the fuel, the reactivity of the mixture is increased and total fuel mass flow and the power output can be reduced. An autothermal on-board syngas generator in combination with two different burner concepts for natural gas (NG)/syngas mixtures was presented in a previous study (Baumgärtner, M. H., and Sattelmayer, T., 2017, “Low Load Operation Range Extension by Autothermal On-Board Syngas Generation,” ASME J. Eng. Gas Turbines Power, 140(4), p. 041505). The study at hand shows a mass-flow variation of the reforming process with mass flows, which allow for pure syngas combustion and further improvements of the two burner concepts which result in a more application-oriented operation. The first of the two burner concepts comprises a generic swirl stage with a central lance for syngas injection. Syngas is injected with swirl to avoid a negative impact on the total swirl intensity and nonswirled. The second concept includes a central swirl stage with an outer ring of jets. For this burner, syngas is injected in both stages to avoid NOx emissions from the swirl stage. Increased NOx emissions produced by NG combustion of the swirl pilot were reported in last year's paper. For both burners, combustion performance is analyzed by OH*-chemiluminescence and gaseous emissions. The lowest possible adiabatic flame temperature without a significant increase of CO emissions was 170–210 K lower for the syngas compared to low load pure NG combustion. This corresponds to a decrease of 15–20% in terms of thermal power.

Low Load Operational Flexibility for Siemens F- and G-Class Gas Turbines

2010 ◽  
Author(s):  
Pratyush Nag ◽  
David Little ◽  
Adam Plant ◽  
Douglas Roth
Keyword(s):  
Power Generation ◽  
Gas Turbine ◽  
Gas Turbines ◽  
Power Plants ◽  
Power Demand ◽  
Operational Flexibility ◽  
Low Load ◽  
Natural Gas Prices ◽  
Carbon Dioxide Co2 ◽  
Base Load

The US gas turbine (GT) power generation market has seen significant volatility in recent years due to climate changes, changes in natural gas prices and the uncertain future of nuclear and coal power generation. Many gas turbine power plants originally intended to operate on a more continuous basis (base load) are operating in intermittent dispatch mode which has caused some operators to frequently shut down their units. This frequent cycling of units can increase start-up and maintenance costs. It could be beneficial to these plants to operate at lower loads when power demand is low and ramp up to higher loads as demand increases. A key issue in operating at lower loads is an increase in carbon monoxide (CO) emissions. When the engines are base loaded, the combustion system operates at high firing temperatures and most of the CO is oxidized to carbon dioxide (CO2). However, at part loads — when the firing temperature is lower — the CO to CO2 oxidation reaction is quenched by the cool regions near the walls of the combustion liner. This results in increased CO emissions at low loads. In order to provide greater operational flexibility to its F- & G-class gas turbine operators, Siemens has developed an upgrade for the engine system designed to allow the gas turbine to operate at lower loads while maintaining emissions. This low load turndown upgrade has been installed, tested and is currently in operation at 8 F and 4 G class Siemens operating gas turbines. These plants were previously operating typically between 70% and 100% of GT base load. Sometimes, when the demand for power was low, typically at night and on weekends, these plants would shut down. During these low power demand periods — with this upgrade installed — these plants continue to operate down to lower loads while maintaining CO emissions and with a capability to more quickly ramp-up to full load when the demand for power increases. This paper details the installation, testing results and continued validation of the Low Load Turndown upgrade.

Premixed Pilot Flames for Improved Emissions and Flexibility in a Heavy Duty Gas Turbine Combustion System

2015 ◽  
Author(s):  
William D. York ◽  
Bryan W. Romig ◽  
Michael J. Hughes ◽  
Derrick W. Simons ◽  
Joseph V. Citeno
Keyword(s):  
Gas Turbine ◽  
Gas Turbines ◽  
Hydrogen Gas ◽  
Operating Conditions ◽  
Nox Emissions ◽  
Combustion System ◽  
Heavy Duty ◽  
Low Load ◽  
Gas Turbine Combustion ◽  
Base Load

Operators of heavy duty gas turbines desire more flexibility of operation in compliance with increasingly stringent emissions regulations. Delivering low NOx at base load operation, while at the same time meeting aggressive startup, shutdown, and part load requirements for NOx, CO, and unburned hydrocarbons is a challenge that requires novel solutions in the framework of lean premixed combustion systems. The DLN2.6+ combustion system, first offered by the General Electric Company (GE) in 2005 on the 9F series gas turbines for the 50 Hz market, has a proven track record of low emissions, flexibility, and reliability. In 2010, GE launched a program to incorporate the DLN2.6+ into the 7F gas turbine model. The primary driver for the introduction of this combustion system into the 60 Hz market was to enable customers to capitalize on opportunities to use shale gas, which may have a greater Wobbe range and higher reactivity than traditional natural gas. The 7F version of the DLN2.6+ features premixed pilot flames on the five outer swirl-stabilized premixing fuel nozzles (“swozzles”). The premixed pilots have their roots in the multitube mixer technology developed by GE in the US Department of Energy Hydrogen Gas Turbine Program. A fraction of air is extracted prior to entering the combustor and sent to small tubes around the tip of the fuel nozzle centerbody. A dedicated pilot fuel circuit delivers the gas fuel to the pilot tubes, where it is injected into the air stream and given sufficient length to mix. Since the pilot flames are premixed, they contribute lower NOx emissions than a diffusion pilot, but can still provide enhanced main circuit flame stability at low-load conditions. The pilot equivalence ratio can be optimized for the specific operating conditions of the gas turbine. This paper presents the development and validation testing of the premixed pilots, which were tested on E-class and F-class gas turbine combustion system rigs at GE Power & Water’s Gas Turbine Technology Lab. A 25% reduction in NOx emissions at nominal firing temperature was demonstrated over a diffusion flame pilot, translating into more than 80% reduction in CO emissions if increased flame temperature is employed to hold constant NOx. On the new 7F DLN2.6+, the premixed pilots have enabled modifications to the system to reduce base load NOx emissions while maintaining similar gas turbine low-load performance and bringing a significant reduction in the combustor exit temperature at which LBO occurs, highlighting the stability the pilot system brings to the combustor without the NOx penalty of a diffusion pilot. The new combustion system is scheduled to enter commercial operation on GE 7F series gas turbines in 2015.

A Higher Turndown Flexibility on AE64.3A Gas Turbine: Design and Operating Experience

2011 ◽  
Author(s):  
Federico Bonzani ◽  
Luca Bozzi ◽  
Alessia Bulli ◽  
Andrea Silingardi ◽  
Domenico Zito
Keyword(s):  
Gas Turbine ◽  
Gas Turbines ◽  
Energy Demand ◽  
Power Plants ◽  
Operating Experience ◽  
Maintenance Cost ◽  
Power Demand ◽  
Service Market ◽  
Low Load ◽  
Base Load

Italian power generation market is living today a period of substantial changes due to the liberalization process, climate issues, natural gas price fluctuation and the uncertain future of nuclear and coal. In this framework, many gas turbine power plants, originally designed to operate mainly at base load, feel the necessity to be flexibly and profitably operated into the dispatch and ancillary energy service market. In particular, many operators ask for the possibility to operate their gas turbines intermittently, frequently cycling and quickly ramping up and down to satisfy energy demand. Such using drafts new trade off between profitability and maintenance cost. From this point of view it’s not unusual to shut down the engine when the power demand is low if the unit cannot be cost effectively parked at a suitable low load and then quickly ramped up to base load when the power demand is higher. The main barrier against lowering the minimum load of the gas turbines is the increase of the CO emission. When the engine operates close to its turndown load the compressor airflow is such that the heat released by the flame cannot properly support the conversion of CO into CO2. In such a condition, the power plant will not comply with the environmental legislation and must be operated at a higher load or, worse, shut down. An operating strategy has been devised to face up such problem. It is based on the adjustment of compressor IGV (Inlet Guide Vanes) and the optimisation of cooling air consumption in order to keep the proper amount of combustion air close to the turndown load. This paper shows the feasibility check, the installation and final field tests of the low load turndown upgrade on a AE64.3A gas turbine which allowed to operate the unit in a more cost effective way even when the power demand is low.

Steam Turbines for Flexible Load Operation in the Future Market of Power Generation

2012 ◽  
Author(s):  
Michael Wechsung ◽  
Andreas Feldmüller ◽  
Heiko Lemmen
Keyword(s):  
Electricity Market ◽  
Power Plants ◽  
Point Of View ◽  
Plant Performance ◽  
Future Market ◽  
Plant Design ◽  
Steam Turbines ◽  
Load Range ◽  
Part Load ◽  
Base Load

In a liberated electricity market with a steadily growing percentage of fluctuating renewables the load related requirements of modern steam power plants are noticeably changing. Whereas the past has seen mainly coal-fired units being operated in base load now highly efficient part load behavior becomes more and more important as well as quickly responding frequency support at minimized investment costs. …In the article various approaches will be identified, discussed and evaluated under economical criteria focused on the above described challenges for future power generating technologies. One central idea is to shift the pure sliding pressure mode down to an intermediate load range where the upper limit is reached at around 70% and optimize the blade path efficiency according to this point. Along with this strategy concepts are presented which allow frequency support from primary to hour- reserve of maximized load steps. Moreover it shall be explained how it is principally possible to use the same cycle conditions for load steps and increasing part load efficiency at the same time. Another idea is to improve the plant performance at lower load ranges by raising the main and reheat steam temperature accompanied by special maintenance concepts. The ideas presented in this article are mainly derived from a steam turbine point of view. Nevertheless some requirements and effects on the overall plant are taken into account additionally. The presented approaches can be applied for new apparatus as for the upgrade of existing units. As the drivers for a more flexible operation of steam plants are especially strong in markets which do not guarantee an attractive utilization of the plant in produced MWhrs/year, investment decisions for new plants have been delayed or cancelled due to the difficult market conditions. Therefore special attention will be paid in this paper to the application of the new flexibility features in power plants which are already in operating and which have been designed originally with the main focus on highest efficiencies in base load operation. The difficulties and limitations given with the existing plant design will most likely be compensated by the economical advantages of the more flexible plant operation after the modernization.

scholarly journals Flow Characteristics of an Annular Intercooler-Diffuser for Gas Turbines

1998 ◽  
Author(s):  
Ajay K. Agrawal ◽  
Alejandro Tinneti ◽  
Surbamanyam R. Gollahalli
Keyword(s):  
Gas Turbines ◽  
Pressure Loss ◽  
Stagnation Pressure ◽  
Pressure Recovery ◽  
Scale Model ◽  
Airflow Rate ◽  
Mean Velocity ◽  
Part Load ◽  
Diffuser Flow ◽  
Inlet Conditions

Benefits of intercooling in power generating gas turbines can be maximized by reducing stagnation pressure loss in the intercooler flow path without adversely affecting the flow pattern in compressors. The intercooler-diffuser isolates the low pressure compressor from the intercooler, recovers the static pressure by decelerating the compressor discharge flow, and uniformly supplies low speed air to the intercooler for effective heat exchange. An experimental investigation was carried out to obtain data in a conceptual design with two sections: an outwardly canted prediffuser and a dump. The test-section was a one-fourth scale model of a typical industrial gas turbine. The diffuser flow is described in terms of the pressure recovery and loss coefficients, velocity vectors, static and stagnation pressure distributions, and the mean velocity and turbulence intensity profiles. The flow resistance by the intercooler was simulated to assess its effects on the upstream diffuser flow. The airflow rate was varied to obtain data at full and part-load operations. The inlet conditions corresponded to naturally developed axisymmetric annulus flow. Results show high stagnation pressure loss and distorted velocity profiles in the dump because of flow recirculation next to the casing. Pressure recovery was confined to the prediffuser and a tail-section downstream of the dump where the flow reattached. Results show that the diffuser flow was practically unaffected by the intercooler and by operation at part-load.

Experimental Study on Low Load Operation Range Extension by Autothermal On-Board Syngas Generation

2018 ◽  
Author(s):  
Max H. Baumgärtner ◽  
Thomas Sattelmayer
Keyword(s):  
Natural Gas ◽  
Mass Flow ◽  
Power Output ◽  
Gas Turbines ◽  
Power Plants ◽  
Combined Cycle ◽  
Nox Emissions ◽  
Gas Combustion ◽  
Low Load ◽  
Natural Gas Combustion

Volatile renewable energy sources induce power supply fluctuations. These need to be compensated by flexible conventional power plants. Gas turbines in combined cycle power plants adjust the power output quickly but their turn-down ratio is limited by the slow reaction kinetics which lead to CO and unburned hydrocarbon (UHC) emissions. To extend the turn-down ratio, part of the fuel can be converted to syngas, which exhibits a higher reactivity. By an increasing fraction of syngas in the fuel, the reactivity of the mixture is increased and total fuel mass-flow and the power output can be reduced. An Autothermal On-board Syngas Generator in combination with two different burner concepts for natural gas/syngas mixtures was presented in a previous study [1]. The study at hand shows a mass-flow variation of the reforming process with mass-flows which allow for pure syngas combustion and further improvements of the two burner concepts which result in a more application-oriented operation. The first of the two burner concepts comprises a generic swirl stage with a central lance for syngas injection. Syngas is injected with swirl to avoid a negative impact on the total swirl intensity and non-swirled. The second concept includes a central swirl stage with an outer ring of jets. For this burner, syngas is injected in both stages to avoid NOx emissions from the swirl stage. Increased NOx emissions produced by natural gas combustion of the swirl pilot was reported in last year’s paper. For both burners, combustion performance is analyzed by OH*-chemiluminescence and gaseous emissions. The lowest possible adiabatic flame temperature without a significant increase of CO emissions was 170 K – 210 K lower for the syngas compared to low load pure natural gas combustion. This corresponds to a decrease of 15–20 % in terms of thermal power.

Turn-Down Capability of Ansaldo Energia's GT26

2021 ◽  
Author(s):  
Ralf Jakoby ◽  
Jörg Rinn ◽  
Christoph Appel ◽  
Adrien Studerus
Keyword(s):  
Gas Turbines ◽  
Development Project ◽  
Combined Cycle ◽  
Operational Flexibility ◽  
Part Load ◽  
Fuel Flexibility ◽  
Single Feature ◽  
Low Load ◽  
Fast Start ◽  
Validation Tests

Abstract The operational flexibility of heavy-duty gas turbines is of increasing importance in today's power generation market. Fast start-up, fast loading, grid frequency support, fuel flexibility and turn-down capability are only some of the keywords that describe the challenges for GT manufacturers. This paper reports Ansaldo Energia's activities to further reduce the Minimum Environmental Load (MEL) of the GT26. The difficulties related to operation at very low loads and the solutions that were developed are explained. Furthermore, the results of engine validation tests of the new extended Low Load Operation (eLLO) and extended Low Part Load (eLPL) operation concepts are presented. The enhancement of the operational flexibility of the GT26 is in the focus of Ansaldo's development activities since many years. Its sequential combustion system is a very good basis for flexible and emission compliant operation down to very low loads. Ansaldo Energia's Low Part Load (LPL) and Low Load Operation (LLO) concepts are standard products in the GT26 flexibility portfolio and established in the market for many years. Ansaldo Energia has conducted a development project in the past two years in order to further reduce the minimum simple cycle and combined cycle loads. The extension of the LLO and LPL operating ranges and their combination into one single feature are the main targets of the project.

scholarly journals Numerical Investigation of a Radially Cooled Turbine Guide Vane Using Air and Steam as a Cooling Medium

Computation ◽  
2021 ◽  
Vol 9 (6) ◽  
pp. 63
Author(s):  
Sondre Norheim ◽  
Shokri Amzin
Keyword(s):  
Numerical Model ◽  
Gas Turbines ◽  
Guide Vane ◽  
Axial Direction ◽  
Average Error ◽  
Inlet Temperature ◽  
Average Temperature ◽  
Cooling Medium ◽  
Turbine Guide Vane ◽  
Steam Cooling

Gas turbine performance is closely linked to the turbine inlet temperature, which is limited by the turbine guide vanes ability to withstand the massive thermal loads. Thus, steam cooling has been introduced as an advanced cooling technology to improve the efficiency of modern high-temperature gas turbines. This study compares the cooling performance of compressed air and steam in the renowned radially cooled NASA C3X turbine guide vane, using a numerical model. The conjugate heat transfer (CHT) model is based on the RANS-method, where the shear stress transport (SST) k−ω model is selected to predict the effects of turbulence. The numerical model is validated against experimental pressure and temperature distributions at the external surface of the vane. The results are in good agreement with the experimental data, with an average error of 1.39% and 3.78%, respectively. By comparing the two coolants, steam is confirmed as the superior cooling medium. The disparity between the coolants increases along the axial direction of the vane, and the total volume average temperature difference is 30 K. Further investigations are recommended to deal with the local hot-spots located near the leading- and trailing edge of the vane.

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