Thermal plasma applications · - Plasma definition Langmuir (Nobel prize) 1932 . 6. 1950 – 1970 - Cutting torch Gage 1955 - Plasma spraying Thermal Dynamics 1968 - Few tens of manufacturers

1

Thermal plasma applications

Prof. P. FauchaisSPCTS (CNRS and Univ. of Limoges)

France

2

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

63

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

64

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

66

Induction Plasma Synthesis of Nano Powders75 kW, 3 MHz Induction Plasma Reactor at Tekna Plasma Systems Inc.

Evaporation and Condensation Filtration and Collection

67

Plasma assisted CVD

68

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

69

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

71

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

73

Extractive metallurgy

74

• 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

75

• 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

76

• 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

77

���������� �������������������������

-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

78

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

79

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

81

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

83

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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������������ � ����������� �

84

AlcanAlcan’’ss Aluminum Dross recovery plasma processAluminum Dross recovery plasma processGuillomGuillom TremblaitTremblait JonquiereJonquiere, Quebec 20 000t/year, Quebec 20 000t/year

85

The SKF The SKF PlasmadustPlasmadustprocessprocess

Zinc and Lead Recovery from E.A.F. Dusts

86

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

88

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

90

Air

Plasma torchArc

Anode

CathodeRefractory

Ash

Liquid glassT > 1300°C

Solidifiedglass

Schematic of Europlasma Cenon Incinerator of flying ashes

Thermal plasma waste treatment

91

Europlasma Cenon Incinerator

Calcia

Glass composition

Heavy metal composition

Thermal plasma waste treatment

92

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

93

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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,