Download - Plasma processing in extractive metallurgy
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Plasma Processing in
Extractive Metallurgy
DEPARTMENT OF METALLURGUCAL AND
MATERIALS ENGINEERING
INDIAN INSTITUTE OF TECHNOLOGY
KHARAGPUR
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PLASMA
• Plasma is considered to be the 4th state of matter next to solid, liquid and gas.
• “A gas in which an appreciable number of atoms or molecules are ionized is called Plasma”.
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PROPERTIES OF PLASMA
• Exists at temperatures over 10,000 K
• It is electrically neutral
• Electrons in it have highest energy and molecules the least
• Electrically conductive
• Responds to Electric and Magnetic Fields
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1. As a heat source and
2. As a carrier medium.
In material processing plasma is used both as a heat source and a carrier medium.
UTILIZATION OF PLASMA
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Plasma Furnace Design Plasma Torch
• Heat source in the plasma furnace.
• Used for generating a direct flow of plasma.
Types of Plasma Torches
Electrode
AC
DC Industrially used
• Transferred • Non transferred
No Electrode
Radio Frequency (RF) Used in Lab furnaces
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Plasma furnace design
DC Plasma Torch
• Electric arc is formed between electrodes made up of Cu, W, Mo, graphite etc.
• Carrier gas used is Oxygen, Hydrogen, Helium, Nitrogen etc along with Ar or He.
• The electrodes are continuously cooled.
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Plasma Furnace Design
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Transferred DC Plasma Torch
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Non transferred DC plasma torch
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AC Plasma Torch
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RF Plasma torch
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Heating of the tube graphite anode
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Plasma Metallurgy Process
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PLASMA REDUCING TECHNOLOGY
• SHAFT FURNACE
• FALLING FILM PLASMA FURNACE
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Shaft Furnace
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Mechanism of Shaft Furnace
Step 1: Shaft Furnace is filled with coke
Step 2 : 3 plasma torches of 6 MW each are installed
Step 3 : The powdered initial raw material is reduced by fluidized bath of plasma gas, i.e. Carbon dioxide.
USES
reduce for Pig Iron , Non-Ferrous metals, Fe-Cr processing
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Falling Film Plasma Furnace
Step1 : Fine raw material with reducing agent is tangentially introduced .
Step 2 : The intensely whirled gas dispersed flow forms a metal film on the wall of the reactor anode.
Step 3 : The film falls on the bottom part of the furnace and gets reduced on the way.
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Falling Film Plasma Furnace
Hem
etit
e+H
2+N
atu
ral G
as 0.07%Cu
0.06%C
0.06%Si
S & P=0.01%
Remaining was Fe
Reduction of hematite: • Very pure Fe was
obtained. • Electrical energy
consumption was 3.9KW/kg Fe.
Mass Balance
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PLASMA MELTING TECHNOLOGY
• PLASMA ARC MELTING
• PLASMA INDUCTION FURNACE
• PLASMA ARC REMELTING
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Plasma Arc Melting
Plasma Arc Melting (PAM): Utilises an arc in
a non-reactive gas, as a heat source and is
applied to the melting of reactive and
refractory metals.
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Advantages :
• Improves quality of the produced metal
• Decreases the specific electric energy consumption
under increased output
• Enables production of low carbon alloys
Disadvantages :
• Working life of plasma electrodes is short under high
power density and in case of high capacity steel
formation.
Plasma Arc Melting
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Plasma Arc Melting
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Plasma Induction Melting
Mostly used in foundries for the preparation of molten alloys in quantities up to 3 tons.
COMPONENTS
• plasma torch of power capacity 100 KW up to 400 KW
• plasma gas argon
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Applications
• Scrap Recycling
• Production of Special alloys
• Ultra low Carbon Stainless Steels
• Production of alloys used in High Temperature or Cryogenic Conditions
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Plasma Arc Remelting
Plasma remelting furnaces are multi—duty systems.
Utilized for :
Simple and complex castings
Near—net shapes
Finished shapes.
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Applications
• Production of high temperature alloys
• Processing of high melting and reactive metal alloys.
• Melting ceramic materials and glass.
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Plasma Arc Remelting
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Fundamental studies of plasma heat generation and application
(a) Investigation of physical problems of plasma arc in the power range 1 MW to 10 MW;
(b) Pilot scale investigations of kinetics, thermodynamics of gas exchange processes, evaporation processes, deoxidation , decarburization, during plasma heating;
(c) Investigations of electrode erosion, process and methods of extending electrode life or improving its thermal stability in industrial scale systems;
(d) Reduction of cooling requirements of the bottom electrode in transferred arc plasma melting systems for overall improvement of electrical efficiency and maintenance requirements;
(e) Development of methods for the intensification of energy—mass exchange between the plasma arc and the heated body;
(f) Design, development of high response plasma power sources for plasma torch operations in a wider voltage range,different gas atmospheres and pressure conditions within the melting chambers.
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Advantages • The atmosphere can be controlled to meet any process
requirement.
• No need for pelletization or agglomeration as fine ore particles can be used.
• More efficient than other processes at Higher Temperatures
• Processing rate is very high.
• Total enclosure: avoids contamination.
• High value metals can be recovered from waste.
• Can process low grade complex minerals.
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Disadvantages and Scope for
Improvement
•Heat recovery: Products have a high latent
heat.
•Electrode life: Electrodes have to be
regularly replaced thus inhibiting continuous
operation.
•High cost of maintenance.
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