Jenny Larfeldt

Investigation of Hydrogen Enriched Natural Gas Flames in a SGT-700/800 Burner Using OH PLIF and Chemiluminescence Imaging

The effect of hydrogen enrichment to natural gas flames was experimentally investigated at atmospheric pressure conditions using flame chemiluminescence imaging, planar laser-induced fluorescence of hydroxyl radicals (OH PLIF) and dynamic pressure monitoring. The experiments were performed using a 3rd generation dry low emission (DLE) burner used in both SGT-700 and SGT-800 industrial gas turbines from Siemens. The burner was mounted in an atmospheric combustion test rig at Siemens with optical access in the flame region. Four different hydrogen enriched natural gas flames were investigated; 0 vol.%, 30 vol.%, 60 vol.% and 80 vol.% of hydrogen. The results from flame chemiluminescence imaging and OH PLIF show that the size and shape of the flame was clearly affected by hydrogen addition. The flame becomes shorter and narrower when the amount of hydrogen is increased. For the 60 vol.% and 80 vol.% hydrogen flames the flame has moved upstream and the central recirculation zone that anchors the flame has moved upstream the burner exit. Furthermore, the position of the flame front fluctuated more for the full premixed flame with only natural gas as fuel than for the hydrogen enriched flames. Measurements of pressure drop over the burner show an increase with increased hydrogen in the natural gas despite same air flow thus confirming the observation that the flame front moves upstream towards the burner exit and thereby increasing the blockage of the exit. Dynamic pressure measurements in the combustion chamber wall confirms that small amounts of hydrogen in natural gas changes the amplitude of the dynamic pressure fluctuations and initially dampens the axial mode but at higher levels of hydrogen an enhancement of a transversal mode in the combustion chamber at higher frequencies could occur.

Setup for microwave stimulation of a turbulent low-swirl flame

An experimental setup for microwave stimulation of a turbulent flame is presented. A low-swirl flame is being exposed to continuous microwave irradiation inside an aluminum cavity. The cavity is designed with inlets for laser beams and a viewport for optical access. The aluminum cavity is operated as a resonator where the microwave mode pattern is matched to the position of the flame. Two metal meshes are working as endplates in the resonator, one at the bottom and the other at the top. The lower mesh is located right above the burner nozzle so that the low-swirl flame is able to freely propagate inside the cylinder cavity geometry whereas the upper metal mesh can be tuned to achieve good overlap between the microwave mode pattern and the flame volume. The flow is characterized for operating conditions without microwave irradiation using particle imaging velocimetry (PIV). Microwave absorption is simultaneously monitored with experimental investigations of the flame in terms of exhaust gas temperature, flame chemiluminescence (CL) analysis as well as simultaneous planar laser-induced fluorescence (PLIF) measurements of formaldehyde (CH2O) and hydroxyl radicals (OH). Results are presented for experiments conducted in two different regimes of microwave power. In the high-energy regime the microwave field is strong enough to cause a breakdown in the flame. The breakdown spark develops into a swirl-stabilized plasma due to the continuous microwave stimulation. In the low-energy regime, which is below plasma formation, the flame becomes larger and more stable and it moves upstream closer to the burner nozzle when microwaves are absorbed by the flame. As a result of a larger flame the exhaust gas temperature, flame CL and OH PLIF signals are increased as microwave energy is absorbed by the flame.

Extended Fuel Flexibility Testing of Siemens Industrial Gas Turbines: A Novel Approach

Opportunity gaseous fuels are of great interest for small and medium sized gas turbines. The variety of gaseous fuels that Siemens Industrial Turbomachinery AB (SIT) is requested to make judgments on is continuously expanding. From such requests follows an increasing need for testing new fuels.The SIT novel approach for fuel flexibility testing, EBIT, has been to combine the single burner rig testing with a full scale engine test to give a cost effective and flexible solution. The combination of the two approaches is accomplished by using a separate feed of testing fuel to one or more burners in a standard gas turbine installation where the other burners use standard fuel from standard fuel system for engine operation. The separate feed of testing fuel can be operated as a slave to engine governor heat demand, but can also be controlled independently.This paper describes how EBIT has been implemented and tested. Combustion monitoring techniques and measurements to check behavior and predictions for full scale engine tests are presented. Results from testing with a blended natural gas with more than 50% of heat input from pentane, C5H12, in a SGT-700 engine shows that the EBIT concept is possible and powerful.The SIT 3rd generation DLE burner proves to be very fuel flexible and tolerant to high levels of pentane in the fuel. Less than 20% increase in NOx emissions can be expected when using pentane rich fuels. The burner is used in the SGT-800 47MW engine and the SGT-700 31MW engine.Copyright

Investigations of microwave stimulation of turbulent flames with implications to gas turbine combustors

Efficient and clean production of electrical energy and mechanical (shaft) energy for use in industrial and domestic applications, surface- and ground transportation and aero-propulsion is currently of significant general concern. Fossil fuels are mainly used for transportation and aero-propulsion, but also for power generation. Combustion of fossil fuels typically give rise to undesired emissions such as unburned hydrocarbons, carbon dioxide, carbon monoxide, soot and nitrogen oxides. The most widespread approach to minimize these is to apply various lean-burn technologies, and sometimes also dilute the fuel with hydrogen. Although efficient in reducing emissions, lean-burn often results in combustion instabilities and igniteon issues, and thus become challenging itself. Another desired aspect of today’s engines is to increase the fuel flexibility. One possible technique that may be useful for circumventing these issues is plasma-assisted combustion, i.e. to supply a small amount of electric energy to the flame to stimulate the chemical kinetics. Although not new, this approach has not yet been fully explored, partly because of it’s complexity, and partly because of apparent sufficiency. Recently, however, several research studies of this area have emerged. This paper attempts to provide a brief summary of microwave-assisted combustion, in which microwaves are utilized to supply the electrical energy to the flame, and to demonstrate that this method is useful to enhance flame stabilization, delay lean blow-off, and to increase combustion efficiency. The main effect of microwaves (or electrical energy) is to enhance the chemical kinetics, resulting in increased reactivity and laminar and turbulent flame speeds. Here we will demonstrate that this will improve the performance of gas turbine combustors. (Less)

Technology options and plant design issues for fuel-flexible gas turbines

Abstract Gas turbines are continuously flowed through machines with high power densities. Their application area is widening from natural gas-fired base-load operation to fuel-flexible base load or plants for flexible operation. Gas turbines can offer low emissions in a wide operating range with the prevailing lean, premixed combustion systems. Gas turbines can be integrated in plants for power generation and sometimes heat. A natural gas-fired gas turbine in a combined cycle has less than half the CO2 emissions in grams per produced kWh compared to a coal-fired conventional plant. With carbon capture and storage technology, the CO2 footprint of a plant can be even lower. Gas turbines are challenged to handle reactive gaseous fuels containing heavy hydrocarbons and/or hydrogen as well as fuels with high inert content. The combustion properties will vary with the fuel composition and need to be considered to avoid flashback, lean blow out and combustion dynamics.

Investigation of ozone stimulated combustion in the SGT-800 burner at atmospheric conditions

The effect of ozone (O3) in a turbulent, swirl-stabilized natural gas/air flame was experimentally investigated at atmospheric pressure conditions using planar laser-induced fluorescence imaging of formaldehyde (CH2O PLIF) and dynamic pressure monitoring. The experiment was performed using a dry low emission (DLE) gas turbine burner used in both SGT-700 and SGT-800 industrial gas turbines from Siemens. The burner was mounted in an atmospheric combustion test rig at Siemens with optical access in the flame region. CH2O PLIF imaging was carried out for four different seeding gas compositions and seeding injection channel configurations. Two seeding injection-channels were located around the burner tip while the other two were located along the center axis of the burner at different distances upstream the burner outlet. Four different seeding gas compositions were used: nitrogen (N2), oxygen (O2) and two ozone/oxygen (O3/O2) mixtures with different O3 concentration. The results show that the O3 clearly affects the combustion chemistry. The natural gas/air mixture is preheated before combustion which is shown to kick-start the cold combustion chemistry where O3 is highly involved. The CH2O PLIF signal increases with O3 seeded into the flame which indicates that the pre-combustion activity increases and that the cold chemistry starts to develop further upstream. The small increase of the pressure drop over the burner shows that the flame moves upstream when O3 is seeded into the flame, which confirms the increase in pre-combustion activity. (Less)

Hydrogen Enriched Combustion Testing of Siemens Industrial SGT-400 at Atmospheric Conditions

In order to further extend the turbine fuel flex capability, a test under atmospheric conditions of a full-scale SGT-400 burner was performed to study the combustion behavior when operating on hydrogen enriched natural gas.A high speed camera was installed in the rig to investigate the flame dynamics on different operation conditions. NOx emissions were measured for all presented conditions. The combustion system was instrumented with thermocouples on all the key locations to allow flame position monitoring and to avoid flame attachment on the hardware. Further measurements included static pressure probes to monitor combustor pressure drop.The test was conducted in a systematic matrix format to include the most important combustion parameters in order to identify their individual effects on the combustion behaviors. The quantity of hydrogen in natural gas, fuel split, air preheat temperature, air reference velocity and flame temperature were the combustion related variables studied in the presented test campaign. The volumetric hydrogen quantity could be increased to 30% maintaining stable operation for all measured conditions. Higher hydrogen contents up to 80 vol-% were reached without flash back tendency. A glowing spark igniter prevented testing at even higher hydrogen contents. Hydrogen enriched gas showed higher NOx emissions and improved blowout limit. Hydrogen blending in the fuel also reduced the combustor pressure drop, lowered the prechamber temperature and raised the pilot tip temperature.Copyright

Experiments on plasma assisted combustion using a dielectric barrier surface discharge

Summary form only given. Plasmas in thermal equilibrium have been in use in different kinds of combustion systems since the invention of the internal combustion engine and the spark ignition systems. Recently the possibility of using plasmas in non-thermal equilibrium for energy-efficient production of radicals and excited species that increase the combustion speed has attracted attention. This interest stems not only from the need for more efficient combustion but also from a wish to increase fuel flexibility with a minimum of modification in existing combustor designs. This paper report experiments performed using a dielectric barrier surface discharge to increase the combustion rate in a Bunsen type burner. The burner has a coaxial geometry where premixed fuel-air flows in the outer annular tube while a jet of air can be injected through the central tube, thus increasing turbulent mixing and flame speed. When the central jet is used the power density but not the total power of the flame increases and gives the possibility of studying the influence of the discharge as a function of power density in the flame. Measurements of the electrical parameters together with two-dimensional distributions of OH, CH2O and CH using Planar Laser-Induced Fluorescence have been used to analyze the influence of the electrical energy on the combustion process. It is found that, although the total power in the flame is held constant, when the power density in the flame increases the influence of the electrical power on the flame characteristics decreases.