thermal plasma applications · - plasma definition langmuir (nobel prize) 1932 . 6. 1950 – 1970 -...
TRANSCRIPT
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Thermal plasma applications
Prof. P. FauchaisSPCTS (CNRS and Univ. of Limoges)
France
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Main applications of thermal plasmas:
- Cutting- Welding- Transferred arc reclamation- Particle spheroidization- Spraying- Metallurgical processing- Chemical synthesis- Nano particle generation- Thermal plasma CVD- Processing of hazardous wastes
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History
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19th Century
- 1st arc experiment Davy (GB) 1813
- Arc melting L. Clerc (F) 1880
- Calcium carbide production William (USA) 1882Moissan (F) 1882
- Arc Welding E. Thomson(USA) 1887
- Melting furnace (100 kW) Stassano (I) 1898
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1900 - 1950- Development of electricity →→→→ circuit breakers
- Arc Furnace Heroult (F) 20 MW – 100 tons 1900
- NO production →→→→ 73 g HNO3/kWh 1902 – 1940
- C2H2 production 1925 –1939
- German academician: « Everything is known about arcs » ! 1928
- Plasma definition Langmuir (Nobel prize) 1932
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1950 – 1970
- Cutting torch Gage 1955
- Plasma spraying Thermal Dynamics 1968
- Few tens of manufacturers of plasma torchesin USA and Europe 1960-1970
- Development of inductively coupled dischargesBabat (Leningrad) 1940MIT (USA) and Stel + CNRS (F) →→→→ first industrial torches 1960
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1950 – 1970
- Development of electricity →→→→ circuit breakers
- Aerospace research: Reentry phenomena – Torches up to 40 MW
- Industrial processes (P > few MW)•••• Ferro-chromium reduction Bethlehem Steel (USA)•••• Direct melting of iron Linde, Freihtal (A)•••• TiO2 production (Tioxide UK)•••• Acetylene Huls Marl (G) (165 MW !),
Dupont de Nemours (USA)
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Plasma cutting
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Cutting world market 2003: 2.4 B€
FlamePlasmaLaser
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Plasma cutting : − Metals and alloys : Transferred arc (98%)− Dielectric materials : blown arc− Current source :
• open circuit voltage up to 400 V, working voltage up to 100 V
Current source
Work piece
Cooling water
Plasma forming gas
High plasma velocity�small nozzle i.d. v ~ 1/d²
Tungsten electrode Current
source
W cathode:Ar-H2, N2; Hf or HfC cathode (vortex injection):O2,air
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Cathode
Laminar injection Vortex injection
Exit nozzle
gas gas
Cathode Water cooling
Nozzle
Plasma forming gas
with wortex injection
Water vortex inlet
Principle of an additional water vortex
Water
Types of plasma torches :
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Plasmaforming
gasOxygen Cathode-nozzle
Nozzle
Annulararc
plasma
New cutting process: OXYPLASMA (Air Liquide)
Metal sheet
Flame 6 kW ~ Plasma (1 kW) + O2
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Dust, fumes, noise limitations over 200 A – noise higher than 100 db– very high quantity of fumes and dusts :
Cutting underwater
Water inlet
Water chimney
Support Support
Water
Cutting direction
Part
Cutting direction
Part
Water chamber Water
Support Support
Waterchimney
60-80 mm
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• Chopped power units (switching amplifier,chopped secondary) with Insulated Gate Bipolar Transistor,resulting in almost constant current characteristic• Complex gas mixtures (N2-O2-CH4) for shielding gas• Sensors
•spectral analysis of cutting area•geometry oriented :
optical : front and back sensing• Robots to cut complex shapes•Expert systems•Artificial neural networks for control application
Cutting improvements
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Performances of plasma cutting
Thickness (mm)
Plasma forming gas
Current (A)
Cutting velocity
(cm/min) 5 O2
Ar-H2
40 120
250 300
100 Ar-H2 compressed
air
120 160
120 250
Typical example: black steel
O2: steels with low % of Ni, Cr, …..Ar-H2: stainless steelAr-H2 ,N2 + water vortex: steel, stainless steel, aluminium and its alloys,Ti and alloys, Ni and alloysAir: steel, stainless steel
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Plasma welding
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Arc column
Welding bead
Piece to be welded
Principle– Transferred arc but low velocity gas �large nozzle i.d.– Shielding gas to protect the material from oxidation ����
acts also on wettability, welding bead aspect and welding speed
– Arc started with a high frequency discharge– For thin sheets (<3mm) the arc works as in TIG
(Tungsten Inert Gas) operation
Plasmacolumn
Part to be welded
Welding bead
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For thickness > 3 mm key hole system :plasma parameters regulated to achieved a tiny hole in the
molten metal through which the plasma flows
Key hole welding achieved by increasing the arc current. For thicknesses over 2-3 mm metal addition with a welding wire is needed: for example TIG+wire
Plasma gas Water Nozzle
Shielding gas
Part
Plasma jet flowing through the hole formed in
the molten bath
Key hole
Molten bath Welding bead
Cathode
Crosssection
Top view
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– Power sources– current type - Max current ~ 400 A– electronic power sources– open circuit voltage 70 - 75 V– working voltage 20 - 30 V
– High Frequency, high voltage ignition source– Pilot arc with low current – Arc transferred to the piece to be welded– Progressive power increase– Automation to reduce the power when beads overlap or
shift from a key hole jet to a non-emerging one
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Plasma welding
• Welding quality depends strongly on the welded material,
its preparation, the choice of the welding material supplied
, the sheath gas, the welding parameters:
• Welded materials: low carbon steel, stainless steels,
light alloys, copper alloys, Cu-Ni alloys, metals very
sensitive to oxidation: Ta, Ti, Zr, ……………….
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Plasma transferred arc reclamation: PTA
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Principle: deposition of a welded coating on a metallic part� use of transferred arc (P~10kW up to 30kW):
• Workpiece or substrate is part of electrical circuit (anode) • Anode heat transfer � improved energy utilization• High heat transfer rates possible
Shield gas
Cathode
Coolingwater
Powderinjection
Pilot arc power Mainpower
Coating
Substrate
Substrate movement
Welding pool
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• Main arc is transferred to substrate• maximum heating, surface melting
• Pilot arc for process initiation, arc stabilization• avoids arc quenching by powder
• Powder injection into transferred arc, melting on substrate• metallurgical bond
• Coating/filler material can be introduced in form of wires, cored wires or rods
Substratemovement7 - 10 cm/min
PTAtorch
Oscillatorymovement
Weldingbead
Torch movement: - vertical for adjustment of arc length
- transverse oscillatory during deposition
± 5 - 15 mm, frequency ~ 0.5 - 1 Hz
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Dilution
dilution defined as
dilution generated by mixing of moltensubstrate metal with coating metal
• high dilution can reduce coating values• several passes are needed
• higher velocities, powder flow rates reduce dilution• typical dilution values for PTA deposition: 5 - 15%
D =B
A + B× 100 %[ ]
B mix zone between substrate and coating materials
B
A
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Dual Powder PTA for Composite Coatings
• powder for metal matrix injected into arc • carbide powder injected into molten metal layer� homogeneous mixture of carbide in metal matrix• significantly improved wear characteristics
Metal matrix
Cooling water
Shield gas
Molten pool Coating
Displacement
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• Rebuilding of eroded surfaces• various Fe alloys, Al alloys, other metals
• Wear and abrasion resistant coatings• Ni alloys + WC, Cr alloys + VC• cobalt alloys for impact resistant and steam corrosion resistant coatings• FeCrC with 33% C for economical wear protection
Wide Range of Industries• construction, mining, agriculture
• reinforcing rods, drills, plow shares• automobile and aircraft industries
• valves, valve seats, turbine parts• chemical, nuclear and oil industries
• pump parts, corrosion protection of vessels
Applications
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Abrasion + frottement
Dent d ’excavateur. Dépôt PTA (25 kg/h) base Ni +CW
Micrographie du dépôt
Example of PTATooth of excavator : Ni base coating + WC (25 kg/h)
micrograph
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Plasma spraying
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ThermalSpray
Combustion
Wire Powder
Flame
D-Gun
HVOF
Plasma
Air Chamber
Shroud
Vacuum
Inert
Underwater
ElectricWire-Arc
Air Chamber
Shroud
Vacuum
Inert
APS
VPS
Plasma Technology Applications in the Thermal Spray IndustryPlasma Technology Applications in the Thermal Spray Industry
In 2005, these techniques represented about 5 BUS$ of sales world-wide
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THERMAL SPRAYING
Group of processes in which finely divided metallic or non-metallic surfacing materials are deposited in a molten or semi-molten condition on a prepared substrate to form a spray deposit.
Surfacing material: powder, rod, or wireSpraying gun generates heat by combustible gases, arcs or
RF discharges.Particles (molten or semi-molten) strike the surface,
flatten and form thin platelets (splats) that conform and adhereto the irregularities of the prepared surface and to each other.
Any material which does not sublime or decompose before melting (at least 300K difference) can be sprayed.
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316L SS on 1040 steel
(APS)Surface OpticalMicroscopeSurface OpticalMicroscope Cross Section OpticalMicroscopeCross Section OpticalMicroscope
The coating has a lamellar structure
316L SS on 1040 steel
(APS)Surface OpticalMicroscopeSurface OpticalMicroscope Cross Section OpticalMicroscopeCross Section OpticalMicroscope
Substrate
Unm
eltedparticle
Void
Oxidized
particle
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Substrates: metals, ceramics, glasses, composites, woods, or plastics.Preparation prior to spraying (most critical step for bonding and adhesion) in most cases:
* cleaning the surface to eliminate contamination
* roughening the surface to provide asperities or irregularities to enhance coating adhesion and provide a greater effective surface area. However, some substrates (composites, etc.) require special preparations.
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d.c. AIR PLASMA SPRAYING
Powder injector
Substrate
Air engulfment
d.c. torch
Coating:50-3000 µm
Flattening particles
Particles injected: 22-45 µm,5-25 µm, 10-110 µm
100-120 mm P < 60 kW
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Example of an EPI LLPS chamber with six preheat chambersd.c. SOFT VACUUM (20-60 kPa) PLASMA SPRAYING
3510 cm
5 kPa
20 kPa
95 kPa
195 kPa
4000
3000
2000
1000
0te
mpe
ratu
re [°
C]
distance fromtorch exit [mm]
200 400
101.3 kPa39.4 kPa6.6 kPa5.3 kPa
0
10 cm
5 kPa
20 kPa
95 kPa
195 kPa
10 cm
5 kPa
20 kPa
95 kPa
195 kPa
4000
3000
2000
1000
0te
mpe
ratu
re [°
C]
distance fromtorch exit [mm]
200 400
101.3 kPa39.4 kPa6.6 kPa5.3 kPa
0
4000
3000
2000
1000
0te
mpe
ratu
re [°
C]
distance fromtorch exit [mm]
200 400
101.3 kPa39.4 kPa6.6 kPa5.3 kPa
0
Influence of pressure on d.c. plasma jet lengths
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Repartition of the 615 M euros coating activities across end-use sectors (source : MAGETEX study) M. Ducos ITSC 2002
Applications
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Estimated repartition of the 1998 park of operating units in Europe by techniques (MAGETES – M. Ducos ITSC 2002)
Park of Units
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Plasma sprayed coatings on aircraft turbine engine partsPlasma sprayed coatings on aircraft turbine engine parts
Mid Span Support
Root Section
CompressorHub
CompressorHub Bushing
CompressorBlade Airfoil
Air Seals
Guide Vanes
CombustionChamber
Liner
Turbine BladeShroud Notch
Turbine BladeAirfoil
Oil Tubes BossCover & Sleeve
Fuel Nozzle Nut/Pin& Stator
Seal Seats, Spacers,Bearing
Housings & Liners
FAN LOW PRESSURECOMPRESOR
HIGH PRESSURECOMPRESOR
COMBUSTOR TURBINE
Outer Casing Turbine BladeSnap DiameterCourtesy of Sulzer Metco
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Plasma sprayed coatings in the automotive industryPlasma sprayed coatings in the automotive industry
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Plasma spray applications in the paperPlasma spray applications in the paperand printing industryand printing industry
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Medical applications of plasma Medical applications of plasma spray technology for the coating spray technology for the coating of hip and dental implantsof hip and dental implants
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Suspension or solution plasma spraying
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Suspension injection
Suspension Plasma Spraying
DC plasma torch Substrate
Cathode
Anode
Plasma
Coating buildingon the substrate
- Deposition efficiency ∼ 50%, rate ∼ 10µm.m-2.h-1
- Dense or porous coatings by adjusting the deposition parameters- Coatings with gradients of properties (porosities, chemical compositon) with one or several suspensions
- Suspensions of sub-micronic particles
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0.1-2 µm
Suspension droplets
Vaporizationof the solvent
0.3-6 µm
300 µm
Agglomeration of nanoparticles
Molten particle
Fragmentation ≈1 µs « vaporization ≈ 1ms
(300 �m)
Vaporization ≈1 µs (3 �m)
Acceleration + Heating
0.1-2 µm
Suspension droplets
Vaporizationof the solvent
Suspension droplets
Vaporizationof the solventVaporizationof the solventVaporizationof the solvent
0.3-6 µm
300 µm
Agglomeration of nanoparticles
Molten particle
Fragmentation ≈1 µs « vaporization ≈ 1ms
(300 �m)
Vaporization ≈1 µs (3 �m)
Acceleration + Heating
Drops � droplets � particles treatment
Main problem: short spray distance (40-60 mm) � high heat fluxes: 15-25 MW/m2 � sintering or melting of deposited pass
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Low porosity < 3 %
Polished coating
10 µm
Example: YSZ (8 wt %) narrow size distribution (0.06-0.4 µm)
Ar-He 40-80 slpm 13 MJ.kg-1��V/V < 0.5
Conventional coatingwith 5-22 µm particles
15 % porosity
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Precursordroplet Evaporation
BreakupGelation
Precipitation Pyrolisis Sinter Melt
A B C
Solution plasma sprayingSolution injection
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Typical YSZ coating (8 wt%) obtained with solution
Vertical cracks due to pyrolysis of previously deposited and un-pyrolysed splats
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Particles spheroidization
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Integrated Induction Plasma Systems forPowder Spheroidization on an Industrial Scale
Objectives
- Improve Flowability- Lower Porosity
- Higher Powder Density- Less Friable
- Less Abrasive- Increase Purity
Powder spheroidization using induction plasma technologyPowder spheroidization using induction plasma technology
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Vacuum
Sintered metal filter
CycloneChamberbottom
Powdercollectionchamber
Powder + Carrier gas Sheath gas Central
gas
Torch
Induction plasma powder spheroidization and densificationInduction plasma powder spheroidization and densification
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Optical micrographs of metallic powders before and Optical micrographs of metallic powders before and after plasma processingafter plasma processing
Ni
Mo
W
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Powder Powder spheroidization using spheroidization using induction plasma induction plasma technologytechnology
Al2TiO6 Cr/Fe/C
SiO2 Re/Mo
WC TiN
Re
YSZZrO2
CaF2
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Metals and alloys purification
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Inert atmosphere: high purity, specialty metals, alloysPlasma Arc Remelting (PAR) of Specialty Metals
Precision alloys, CP titanium,
Ti alloysIngots: ø = 125 mm,L = 500 mm ~ 50 kg
Electrode:ø = 90 mm,
l = 1000 mm
P ~ 500 kWto 3 torches
2000 - 2500 kWh/ton,50 - 70 kg/h
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Retech Ti Remelting Furnace
P ~ 500 kW –mi ~ 250 - 500 kg/h
Ti alloys electrodes 2.5 to 5 tons
Losses after plasmatreatment (wt%)
Al ~ 0.05, V ~ 0.05, Sn < 0.01,Mo < 0.01,
Fe 0.01
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Plasma heating
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14 ton tundish,1 MW Tetronics R&D transferred heater5,000 A, Argon gas,Temperature control, +/- 5°CTemperature control, +/- 2°C, with melt stirring and plug flow
Tundish Heating with Plasma Torches
Ar
WatertankPump
Laddle Anode
Mold
Heatingchamber
Gas bubbling
Thermocouple
Thermocouple
Torch
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Plasma chemistry
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The The HHüülsls plasma furnace (oneplasma furnace (one--stagestage����for acetylene for acetylene production since 1939production since 1939
Each torch 8.5 MWInlet gas: methaneYield: 12.5 kW.h/kg120,000 ton/yAdvantage adaptproduction to needs(5 min to start)
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The TIOXIDE Titanium oxide pigment plasma processThe TIOXIDE Titanium oxide pigment plasma process
TiCl4
Chlori-nation
CokeOre
O2
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The TIOXIDE Titanium oxide pigment plasma processThe TIOXIDE Titanium oxide pigment plasma process
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Ultrafine or nano particles
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Principal steps involved in the plasma synthesis of Principal steps involved in the plasma synthesis of ultrafineultrafine nano powders (UFP) of metals and ceramics:nano powders (UFP) of metals and ceramics:
Plasma reactorPlasma reactor
Liquid or vaporprecursor
Solid precursor
Nano-powder
Quench
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UFP Basic concept involvedUFP Basic concept involved�� DC transferred arc plasmaDC transferred arc plasma
Quench Gas
Metal vapour
Transferred arc
Cathode
Ultrafinenanometricpowder
Molten metal Anode
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The use of a reactive quench allows for the synthesis of new nano-powders
Nano-powder
ReactionZone
QuenchZone
Quench GasReaction Gas
In-flight particle melting and vaporization
Ultra Fine Particles production
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Induction Plasma Synthesis of Nano Powders75 kW, 3 MHz Induction Plasma Reactor at Tekna Plasma Systems Inc.
Evaporation and Condensation Filtration and Collection
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Plasma assisted CVD
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DC-Arc Jet Reactor
Specific Advantages
• high energy density permits high heating rates
• high flow rates compress stagnation boundary layer
• higher precursor concentrations possible
• wider range of substrates possible– deposition rate higher
than diffusion into solid
Thermal Plasma Chemical Vapor Deposition
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RF Induction TPCVD Reactor
Advantages
• minimizes film contamination
• more uniform substrate heating due to larger plasma volume
• good reactant-plasma mixing
70TiTech plasma jet diamond deposition (Ohtake)
TPCVD example
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New technology: LPPS thin films by Sultzer-Metco
• In “soft” vacuum chamber (0.1-0.2 kPa) high enthalpy plasma jet (torch power 180 kW) obtainedwith new nozzle design � long jets: 100-150 cm
Conventional LPPSp = 30 kPA
LPPS thin filmp = 0.1 kPA
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• Use of fine powder (1.5-11 µm) � evaporation �vapor phase deposition � non line of sight capability
• With YSZ powders � TBCs with columnar structures similar to those obtained with EBPVD
• Deposition rate:10 µm/mm.m2
• Layer thickness: 0.2-30 mm
New technology: LPPS thin films by Sultzer-Metco
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Extractive metallurgy
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• Potential: plasma reduces processing steps, capital investment– Directly from ore to metal
• “Electric Economy” spawned many developments– Most of them technically successful, but
economically not viable• Significant shift in steel industry to increased
use of scrap– Plasma technology shifted to remelting
Main problem: most techniques require P ~ 100 MW� graphite electrodes: non-consumable electrodeslimited to 7-8 MW
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• Electric Arc Furnace (EAF) represents oldest plasma processing technology
• Bulk heating of material with A.C arc, graphite electrodes: 1% of world electricity consumption in 2000!
• Modern plasma furnaces are more flexible with regard to raw material input
• Maximum arc current 75 kA
[*D. Neuschütz, 1999]
Arc and Plasma Furnaces for Steel: Graphite Electrodes
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• EAF produced steel has increasing market share– 1960 = 10%; 1980 = 22%; 1997 = 33%*
• Energy cost reduced from >600 kWh/t to 320 - 500 kWh/t
• 100 MW � 90-150 tons of steel � 0,5 à 1,5 Mt/y
• In 1998 125 AC furnaces replaced by DC ones and since 75 % of those to bereplaced � DC
Arc and Plasma Furnaces for Steel: Graphite Electrodes
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���������� �������������������������
-Less flicker-Less noise-Less graphite consumption:1-1,5 kg/t against 1,8 à 3 kg/t
-Less refractorywear-Easier powercontrol
-Need foamy slag
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Blast furnaces:
- Boosting air temperature and powered coal injection
Use of blown arcs with cold cathode
1.8 MW torch/nozzle, 8/9 equipped
Coke reduction:200 kg/t
Economy linkedto coke/kWh
PricesElectrodes
lifetime~800-1000h
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SKF Swedechrome flow sheet: ferro-chromium smelting3 torches of 8 MW each[A.B. Wikander et al., 1987]
Use of blown arcs with cold cathode
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GM - Central Foundry at Defiance, Ohio
• Non-transferred arc, cold cathode torches
• Six Westinghouse 1.5 MW torches installed in one 4 m diameter, shaft furnace operating with air
• Successful operation since 1989
• Special electrode developments for long life (> 1000 hrs)
Cupola Plasma-Fired:
Use of blown arcs with cold cathode
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Shaft Furnace Comparison with Conventional
• Wind rate reduced to 1/3
• Metal to coke ratio increased to 70:1
• Top gas recycling
• Higher blast temperature (~ 1500°C)
• No briketting of fines• Lower back pressure
• 60% higher productivity• 10 - 30% lower iron cost
• Up to 40% CO content• Low oxidation losses
• Higher melt rates
Plasma-Fired Cupola
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Waste destruction
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AlcanAlcan’’ss Aluminum Dross recovery plasma processAluminum Dross recovery plasma processGuillomGuillom TremblaitTremblait JonquiereJonquiere, Quebec 20 000t/year, Quebec 20 000t/year
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AlcanAlcan’’ss Aluminum Dross recovery plasma processAluminum Dross recovery plasma processGuillomGuillom TremblaitTremblait JonquiereJonquiere, Quebec 20 000t/year, Quebec 20 000t/year
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The SKF The SKF PlasmadustPlasmadustprocessprocess
Zinc and Lead Recovery from E.A.F. Dusts
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1600 oC
EDF process for the treatment of PORCHEVILLEEDF process for the treatment of PORCHEVILLEwaste materialwaste material
87
RETECHRETECH’’ss Plasma Centrifugal FurnacePlasma Centrifugal Furnacefor hazardous Waste treatmentfor hazardous Waste treatment
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CFC treatment capacity50 kg/hDestruction efficiency+99.99%
CFC destruction using induction CFC destruction using induction Plasma TechnologyPlasma Technology
89
• Incineration ash contains hazardous materials
• Plasma melting and vitrification produces non-leaching slag– high plasma temperatures allow addition of high melting
point ceramics
• Medical wastes have wide range of compositions, high moisture content– plasma reduces off-gas flow– local destruction may be possible
• Numerous approaches exist, mostly based on transferred arc technology
Residues from Municipal Waste Incineration
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Air
Plasma torchArc
Anode
CathodeRefractory
Ash
Liquid glassT > 1300°C
Solidifiedglass
Schematic of Europlasma Cenon Incinerator of flying ashes
Thermal plasma waste treatment
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Europlasma Cenon Incinerator
Calcia
Glass composition
Heavy metal composition
Thermal plasma waste treatment
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Waste Treatment with Gasification
• installation in Japan (Hitachi)
• Westinghouse non-transferred plasma torches
• 300 tons/day municipal waste or165 tons/day automobile shredderresidue
• off gases of H2 + CO used togenerate steam, electricity
• 8 MW of power generated
• very low emissions
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Thermal plasma waste treatment
Georgia Tech Research Institute
94
Integrated Environmental Technologies Co.
Plasma between two graphiteelectrodesSteam injection to producesyn-gasThree graphite electrodes(3-phase) immersed withinliquid bath to control itstemperature
Thermal plasma waste treatment
95
YEAR 2020SELECTED RENEWABLE ENERGY SOURCES
Source Quads(1015 BTU)
Plasma Processed MSW(1) 0.90Geothermal(2) 0.47Landfill Gas(2) 0.12Solar(2) 0.09Wind(2) 0.04_____________________
(1) Assumes 1 million TPD(2) Extrapolated from 1999 statistics
Thermal plasma waste treatment
Georgia Tech Research InstituteAtlanta, GA
96
Conclusions
• Realization of plasma process advantages requires automated controls, or at least on-line monitoring, which is under development for cutting, welding, spraying, PTA, spheroidization,
• Electric Arc Furnace with D.C. graphite electrodes sees continuous growth in metallurgy,
• Several waste treatment processes are now commercial or in advanced stages of development but they depend on:
- stringent environmental conditions or low electricity cost
- waste treatment as part of production process
• Many works on thermal plasma CVD, nano particle production,