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Investigation of a prototype industrial gas turbine combustor using alternative gaseous fuels

Sigfrid, Ivan LU (2013)
Abstract (Swedish)
Popular Abstract in Swedish

Jordens totala energiförbrukning stiger. Samtidigt förbrukas primärt fossila naturresurser som kan anses ändliga, så som olja, kol eller naturgas, för att tillgodose energibehovet. Även andra energikällor används, t.ex. kärnbränsle, vind och vatten. Denna avhandling fokuserar på energi som omvandlas vid förbränning av gas i gasturbiner. Eftersom naturgas är ett fossilt bränsle riktas forskning åt nyttjandet av alternativa gaser, vilket är tänkt minimera nettoproduktionen av koldioxid. Sådana alternativa gaser kan exempelvis vara förgasningsgas från kol där koldioxiden separerats innan förbränning eller biogas vars konsumtion och produktion av koldioxid tar ut vartannat. De mest grundläggande... (More)
Popular Abstract in Swedish

Jordens totala energiförbrukning stiger. Samtidigt förbrukas primärt fossila naturresurser som kan anses ändliga, så som olja, kol eller naturgas, för att tillgodose energibehovet. Även andra energikällor används, t.ex. kärnbränsle, vind och vatten. Denna avhandling fokuserar på energi som omvandlas vid förbränning av gas i gasturbiner. Eftersom naturgas är ett fossilt bränsle riktas forskning åt nyttjandet av alternativa gaser, vilket är tänkt minimera nettoproduktionen av koldioxid. Sådana alternativa gaser kan exempelvis vara förgasningsgas från kol där koldioxiden separerats innan förbränning eller biogas vars konsumtion och produktion av koldioxid tar ut vartannat. De mest grundläggande förutsättningarna för att sådana gaser ska kunna användas kommersiellt är att de ska kunna förbrännas kontrollerat, utan avbrott och utan att bidra till att farliga avgaser så som kväveoxider (NOX), kolmonoxid eller oförbrända kolväten kommer ut i naturen. För att nå kommersiell framgång fordras även att den för stunden ekonomiskt sett mest fördelaktiga gasen kan användas. För att kunna nyttja olika gaser fordras en bränsleflexibel brännare vars befintliga brännkammare kan anpassas eller enkelt bytas ut beroende bränslets egenskaper. Denna avhandling redogör för undersökningen av hur en prototyp av en nydesignad brännkammare kan hantera alternativa gaser. De gaser som undersökts är syntetiska gaser så som förgasningsgaser med högt vätgasinnehåll och metanbaserade gaser med lågt energiinnehåll, vilka imiterar biogas. De ekonomiska aspekterna ligger utanför avhandlingens omfattning.



För att undersöka hur alternativa gaser beter sig vid förbränning undersöktes först deras flamhastighet i en simpel brännare av Bunsen typ. En sådan undersökning visar hur pass reaktiv en gas är, vilket kan användas till att förutse om en flamma vid förbränning av gasen kommer att stabiliseras i det tilltänkta förbränningsområdet eller om flamman riskerar att placera sig upp- eller nedströms. Att erhålla sådan information är av vikt eftersom felaktig placering av flamman kan leda till ostabil förbränning eller orsaka skador på brännkammaren. Därefter undersöktes själva brännaren vid både atmosfäriskt och högre tryck. Undersökningarna omfattade lokalisering av stabilitetsgränser, minimering av emissioner, visualisering av själva flamman och mätning av strömningsfält. Stabilitetsgränserna och emissionerna undersöktes genom tillförsel av olika mängder luft och bränsle i brännarens enskilda delar. Flammans positionering diagnosticerades med hjälp av laser som skapar ett fluorescerande ljus från molekyler som enbart fanns i flamman. För att mäta strömningsfältet tillsattes partiklar till förbränningsluften. Genom att använda laserljus och ett kamerasystem kunde sedan partiklarnas rörelse dokumenteras. De två laserteknikerna gav möjligheten att visualisera flammas placering och strömningsmönster. Ett ytterligare mål med de lasermätningar som genomfördes var att skapa mätresultat som kan nyttjas för validering av såkallade CFD-beräkningar, avancerade datorbaserade beräkningsmodeller för flöden. (Less)
Abstract
In this thesis, the effect of alternative gaseous fuels, with high hydrogen content and lower calorific value, on gas turbine combustion was investigated experimentally. The aim of the investigation was to find operational limitations for an experimental burner and to supply data for validation of computational fluid dynamics (CFD). Before examination of the actual burner, the laminar flame speed was measured for a range of gases. The measurement technique was based on Schlieren imaging which is a measure of the density gradient through a flame surface. A Bunsen type burner was used to measure the angle of a conical flame from which the laminar flame speed was calculated. In order to improve the comparability of these measurements with... (More)
In this thesis, the effect of alternative gaseous fuels, with high hydrogen content and lower calorific value, on gas turbine combustion was investigated experimentally. The aim of the investigation was to find operational limitations for an experimental burner and to supply data for validation of computational fluid dynamics (CFD). Before examination of the actual burner, the laminar flame speed was measured for a range of gases. The measurement technique was based on Schlieren imaging which is a measure of the density gradient through a flame surface. A Bunsen type burner was used to measure the angle of a conical flame from which the laminar flame speed was calculated. In order to improve the comparability of these measurements with other measurement methods the laminar flame speed was corrected for the influence of stretch. The effect of stretch will increase or decrease the flame speed depending on the curvature of the flame and the physical properties of the gases involved in the combustion, e.g. the Lewis number and preferential diffusivity.



The gas turbine burner examined was a downscaled version of the burner that is now found in the commercial gas turbine, SGT-750. The burner consists of three concentric sections. The central part is a precombustor called rich-pilot-lean (RPL). The purpose of the RPL is to supply heat and radicals to the other sections to stabilize combustion. The next section is the Pilot, which serves as an intermediate burner in which the equivalence ratio can be optimized to stabilize combustion and minimize NOX emissions. The outermost section is the Main. For the experimental burner approximately 79% of the mass flow passes through this section. All sections have their own swirlers that create recirculation zones for flame stabilization. The experimental work in this thesis includes measurements of the lean stability limit, emission optimization (primarily NOX), flame diagnostic through OH-Laser induced fluorescence (LIF) and particle image velocimetry (PIV). Tests were conducted at both atmospheric conditions with preheated air (650 K) and at elevated pressure up to 9 bar. Results from the experimental investigations were also used to validate CFD computations using reduced chemical kinetic schemes, and to validate reactor network calculations based on perfectly stirred reactors (PSR) and plug flow reactors (PFR).



Lean stability limit experiments showed how the RPL equivalence ratio could be optimized to lower the lean blowout limit. Increasing the RPL equivalence ratio was shown to extend the lean blowout limit, up to a limit after which the RPL flame was quenched. Reactor network modelling showed that the stabilizing effect of the RPL was a combination of thermal energy and reactive radicals supplied to the flame zone. The important radicals were shown to be H, O and OH.



The emission optimization measurements showed that lowering the equivalence ratio in both the RPL and the pilot minimized the NOX emissions. CFD simulation showed that the degree of mixing of both the RPL and the Pilot at point of ignition was not perfect. Imperfect mixing causes pockets of stoichiometric mixtures to react, which in turn create hot spots where thermal NOX can be formed. At rich RPL equivalence ratios, a flame could be visualized with OH-LIF after the RPL exit. This flame probably to some extent combusts closer to stoichiometry, which increases thermal NOX. These theories of how NOX is formed were confirmed by reactor network calculations. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Tekn. Lic. & fd. adj. Prof Strand, Torsten, Energiteknik, KTH, Stockholm
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Combustion, Gas Turbine, Laminar flame speed, Stretch, Lean blowout, Emissions
pages
96 pages
publisher
Ivan Sigfrid
defense location
Lecture hall MA1 in Matteannexet, Sölvegatan 18-20, Lund University Faculty of Engineering
defense date
2013-09-17 10:15
external identifiers
  • other:ISRN LUTMDN/TMHP-13/1096-SE
ISSN
0282-1990
ISBN
978-91-7473-607-6
978-91-7473-608-3
language
English
LU publication?
yes
id
2624218b-afe4-44f5-8118-c70cabe4f4c0 (old id 3972178)
date added to LUP
2013-08-15 16:11:03
date last changed
2018-11-21 20:19:58
@phdthesis{2624218b-afe4-44f5-8118-c70cabe4f4c0,
  abstract     = {In this thesis, the effect of alternative gaseous fuels, with high hydrogen content and lower calorific value, on gas turbine combustion was investigated experimentally. The aim of the investigation was to find operational limitations for an experimental burner and to supply data for validation of computational fluid dynamics (CFD). Before examination of the actual burner, the laminar flame speed was measured for a range of gases. The measurement technique was based on Schlieren imaging which is a measure of the density gradient through a flame surface. A Bunsen type burner was used to measure the angle of a conical flame from which the laminar flame speed was calculated. In order to improve the comparability of these measurements with other measurement methods the laminar flame speed was corrected for the influence of stretch. The effect of stretch will increase or decrease the flame speed depending on the curvature of the flame and the physical properties of the gases involved in the combustion, e.g. the Lewis number and preferential diffusivity.<br/><br>
<br/><br>
The gas turbine burner examined was a downscaled version of the burner that is now found in the commercial gas turbine, SGT-750. The burner consists of three concentric sections. The central part is a precombustor called rich-pilot-lean (RPL). The purpose of the RPL is to supply heat and radicals to the other sections to stabilize combustion. The next section is the Pilot, which serves as an intermediate burner in which the equivalence ratio can be optimized to stabilize combustion and minimize NOX emissions. The outermost section is the Main. For the experimental burner approximately 79% of the mass flow passes through this section. All sections have their own swirlers that create recirculation zones for flame stabilization. The experimental work in this thesis includes measurements of the lean stability limit, emission optimization (primarily NOX), flame diagnostic through OH-Laser induced fluorescence (LIF) and particle image velocimetry (PIV). Tests were conducted at both atmospheric conditions with preheated air (650 K) and at elevated pressure up to 9 bar. Results from the experimental investigations were also used to validate CFD computations using reduced chemical kinetic schemes, and to validate reactor network calculations based on perfectly stirred reactors (PSR) and plug flow reactors (PFR).<br/><br>
<br/><br>
Lean stability limit experiments showed how the RPL equivalence ratio could be optimized to lower the lean blowout limit. Increasing the RPL equivalence ratio was shown to extend the lean blowout limit, up to a limit after which the RPL flame was quenched. Reactor network modelling showed that the stabilizing effect of the RPL was a combination of thermal energy and reactive radicals supplied to the flame zone. The important radicals were shown to be H, O and OH.<br/><br>
<br/><br>
The emission optimization measurements showed that lowering the equivalence ratio in both the RPL and the pilot minimized the NOX emissions. CFD simulation showed that the degree of mixing of both the RPL and the Pilot at point of ignition was not perfect. Imperfect mixing causes pockets of stoichiometric mixtures to react, which in turn create hot spots where thermal NOX can be formed. At rich RPL equivalence ratios, a flame could be visualized with OH-LIF after the RPL exit. This flame probably to some extent combusts closer to stoichiometry, which increases thermal NOX. These theories of how NOX is formed were confirmed by reactor network calculations.},
  author       = {Sigfrid, Ivan},
  isbn         = {978-91-7473-607-6},
  issn         = {0282-1990},
  keyword      = {Combustion,Gas Turbine,Laminar flame speed,Stretch,Lean blowout,Emissions},
  language     = {eng},
  pages        = {96},
  publisher    = {Ivan Sigfrid},
  school       = {Lund University},
  title        = {Investigation of a prototype industrial gas turbine combustor using alternative gaseous fuels},
  year         = {2013},
}