Plasma Processing inExtractive MetallurgyDEPARTMENT 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
UTILIZATION OF PLASMA 1. As a heat source and 2. As a carrier medium.In material processing plasma is used both as a heat sourceand a carrier medium.
Plasma Furnace Design Plasma Torch• Heat source in the plasma furnace.• Used for generating a direct flow of plasma. Types of Plasma Torches Electrode No Electrode AC Radio Frequency (RF) DC Used in Lab furnaces Industrially used • Transferred • Non transferred
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.
Mechanism of Shaft FurnaceStep 1: Shaft Furnace is filled with cokeStep 2 : 3 plasma torches of 6 MW each are installedStep 3 : The powdered initial raw material is reduced by fluidized bath of plasma gas, i.e. Carbon dioxide.USESreduce for Pig Iron , Non-Ferrous metals, Fe-Crprocessing
Falling Film Plasma FurnaceStep1 : 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 FurnaceReduction of 0.07%Cu Hemetite+H2+Natural Gashematite: 0.06%C• Very pure Fe was obtained.• Electrical energy 0.06%Si consumption was 3.9KW/kg Fe. S & P=0.01% Remaining was Fe Mass Balance
Plasma Arc MeltingPlasma Arc Melting (PAM): Utilises an arc ina non-reactive gas, as a heat source and isapplied to the melting of reactive andrefractory metals.
Plasma Arc MeltingAdvantages :• Improves quality of the produced metal• Decreases the specific electric energy consumption under increased output• Enables production of low carbon alloysDisadvantages :• Working life of plasma electrodes is short under high power density and in case of high capacity steel formation.
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 latentheat.•Electrode life: Electrodes have to beregularly replaced thus inhibiting continuousoperation.•High cost of maintenance.