Plasma Processing in

Extractive Metallurgy

DEPARTMENT OF METALLURGUCAL AND

MATERIALS ENGINEERING

INDIAN INSTITUTE OF TECHNOLOGY

KHARAGPUR

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”.

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

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

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

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.

Plasma Furnace Design

Transferred DC Plasma Torch

Non transferred DC plasma torch

AC Plasma Torch

RF Plasma torch

Heating of the tube graphite anode

Plasma Metallurgy Process

PLASMA REDUCING TECHNOLOGY

• SHAFT FURNACE

• FALLING FILM PLASMA FURNACE

Shaft Furnace

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

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.

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

PLASMA MELTING TECHNOLOGY

• PLASMA ARC MELTING

• PLASMA INDUCTION FURNACE

• PLASMA ARC REMELTING

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.

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

Plasma Arc Melting

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

Applications

• Scrap Recycling

• Production of Special alloys

• Ultra low Carbon Stainless Steels

• Production of alloys used in High Temperature or Cryogenic Conditions

Plasma Arc Remelting

Plasma remelting furnaces are multi—duty systems.

Utilized for :

Simple and complex castings

Near—net shapes

Finished shapes.

Applications

• Production of high temperature alloys

• Processing of high melting and reactive metal alloys.

• Melting ceramic materials and glass.

Plasma Arc Remelting

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.

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.

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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