20160914 owi red · 2016. 9. 14. · • flat-flame burner for liquid fuels • fully premixed...
TRANSCRIPT
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NORA Technical WorkshopNewport, RI
September 14, 2016
Vaporizing Burners-Concepts for Premixed Combustion of Liquid Fuels
Dr. Klaus LuckaDipl.-Ing. David Diarra
Oel-Waerme-Institut GmbH
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• Introduction
• partially premixed combustion• flat-flame burner for liquid fuels
• fully premixed combustion
• small scale radiant burner
• small scale porous burner
• Ongoing research projects
Outline
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• Introduction
• partially premixed combustion• flat-flame burner for liquid fuels
• fully premixed combustion
• small scale radiant burner
• small scale porous burner
• Ongoing research projects
Outline
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• Premixed combustion has been identified as one of the key technologies in combustion engineering
• to reduce emission of pollutants.
• to increase fuel flexibility
• To make gaseous fuel technology accessible for liquid fuels
• Whereas premixed combustion for gaseous fuels is state of the art in many applications, the implementation of premixing technology for liquid fuels reveals significant challenges.
• Suitable atomization/evaporation technology for various fuels (viscosity, boiling range)
• Need for energy efficient and residue free evaporation
• Preventing early ignition (during mixing, prior to combustion)
Introduction
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In premixing burners for liquid fuels (vaporizing burners), evaporation zone
and combustion zone are fully separated
Two characteristic premixing types for liquid fuel combustion shall be
defined:
• Partially premixed Combustion: The fuel is completely vaporized
and partially mixed with air/off gas before it reaches the reaction
zone.
• Fully premixed Combustion: The fuel needs to be completely
evaporated and fully mixed with combustion air before it reaches the
reaction zone.
Introduction
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• Introduction
• partially premixed combustion• flat-flame burner for liquid fuels
• fully premixed combustion
• small scale radiant burner
• small scale porous burner
• Ongoing research projects
Outline
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partially premixed combustion
FuelMixing zone(vapor, air, off gas)
Reaction zone (blue, faintyellow)
recirculation (ext) recirculation (int.)
partially premixed combustion
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characteristics of partially-premixed combustion:
• separation of evaporating- and combustion zone, distinct premixing zone
• Separation achieved by high recirculation fluxes (inertisation and cooling of the reaction zone)
• large blueish flames, low energy density due to high recirculation rates
• moderate temperatures reduced risk for high temperature NOx - formation
• Application: burners for tight emission regulations (domestic application in the EU)
main drawbacks
• increased noise emissions due to higher flow speeds and turbulent combustion
• additional parts for flame stabilisation might be necessary (flame tube, higher costs), as well increased blower powers to achieve higher impulses are t. b. prov.
partially premixed combustion
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partially premixed operation of a flat flame burner
(power max. 180 kW)
partially premixed combustion
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flat flame burner for liquid fuels: concept
rezirculation
• flame orientation in radial direction
• flame mainly directed throughshape of the burner-stone
• flame is heating the furnace wall, heat transfer to melter via radiation
• application: zinc-galvanizing plant
partially premixed combustion
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Flat flame burner: start modeLeistung 90 kW, non premixed operation
partially premixed combustion
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recirculation
P = 90 kW P = 160 kW
transition from non premixed to partially
premixed operation mode
partially premixed combustion
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burnercool flame evaporizer
fully premixed operation for a flat flame burner
(power max. 180 kW)
partially premixed combustion
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experimental setup, premixing device
premixing device
Burner housing
partially premixed combustion
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Premixed operation with external premixing device (cool flame reactor)
partially premixed combustion
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• Introduction
• non premixed combustion• Industrial scale burner with air staging
• partially premixed combustion• flat-flame burner for liquid fuels
• premixed oil burner for radiant tubes
• fully premixed combustion
• small scale radiant burner
• small scale porous burner
• Ongoing research projects
Outline
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Atomization, Evaporation Mixing
Combustion on/in porous media(e.g. meshsurface, ceramicfoam)
fully premixed combustion
fully premixed combustion
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characteristics of fully-premixed combustion:
• Complete separation of evaporating/mixing- and combustion zone
• fully homogenious mixture allows for extensive control of the combustion process
• Laminar combustion, flame stabilization on/in porous media very silent flames
• Generally low NOx - emissions
• Application: burners for tight emission regulations (domestic application in the EU), fuel processor for fuel cell systems, catalytic burners
main drawbacks
• Very complex thermal management in the premixing zone, strongly depending on the operational area
• Risk of unintended ignition of the fuel air mixture in the mixing area due to flash back or insufficient thermal management (self ignition)
• Porous media may show limited lifetime when exposed to high temperatures
fully premixed combustion
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Auto ignition temperatures and boiling ranges in °C
temperature in °C
boiling range
auto ignition temperature
H2
• The temperatures needed for complete evaporation of technical fuels like diesel and IGO are associated with the boiling range which lies between 100 °C and 350 °C.
• However, the auto ignition temperature for Diesel fuel lies far below the upper limit of the boiling range. • Hence premixing of diesel/igo and air is a critical process as temperatures beyond auto ignition
temperature are needed and the risk of ignition is given.
fully premixed combustion
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examples for premixingtechnology for liquid fuelcombustion
- Combustion in porousmedia
- Reforming, catalyticcombustion
fully premixed combustion
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The radiant burner-a concept for surface small scale
combustion of liquid fuels
fully premixed combustion
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view on a typical air inlet plate(through the flame tube)
flame tube
air inletplate
burner surface mesh
Schematic sketch of a combustion process
burner in operation
fully premixed combustion
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small scale burner
for light fuel oil in the power range
1 kW to 8 kW
for a solar heating storage
fully premixed combustion
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‹Nr.›/4
Concept
110
mm
230 mm
Light fuel oil
Air
Coo
l Fla
me
Vapo
risat
ion
in
poro
us m
edia
Fuel
/Air
mix
ture
radiation
Exha
ust
radiation
Porous burner +Recuperator
Cool Flame-Vaporiser
Vaporizing burner module 1 kW – 8 kW
solar heating storage
fully premixed combustion
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Values corrected to a N-Content of 140 mg/kg (DIN EN 267)
excess air ratio: 1.6
fully premixed combustion