1. electrodes and smelting of charge takes place.

1. Introduction

 

India
is the third highest global producer of Chromium Ore and Chrome Alloys. Chrome Ore
is used in the production of chromium metal and various alloys of chromium with
iron, nickel, cobalt, tungsten, molybdenum etc. Chromium imports strength,
hardness, toughness, magnetism, and offers resistance to abrasion, corrosion
and also acts as a de-oxidant.Despite its rich ore deposits and low cost manpower,
Ferro alloys industry in India has never been globally competitive. The high
cost of production of Ferro Chrome essentially attributed to

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a) High Power Cost

b) Increasing cost of Chrome ore and reductant

c) Non-availability of low ash, low phos. Coking coal in the country for
the production of desired coke with low ash, and low phos contents, making
import of such coke.

d) High-cost and insufficient infrastructural facilities

 

2.
Economics of Ferro Chrome Production

 

Major cost components of Ferro
Chrome production can be segregated in to three parts, i.e., Raw material,
Power cost, other costs. The contribution of each component to the total
variable cost is as under. The raw material cost consist
of Cost of coke, Flus, EC paste and Chrome ore where as the other variable
costs include maintenance, stores consumables, packing, loading, labor charges,
material handling etc.

There are about 15 to 20 varieties of
raw materials that are used for manufacturing Ferro alloys. The charge mix
can be divided in to three broad categories as under.
Basic Ore – Chrome Ore. The ore may be
in its natural form or in the form of Briquettes – About 12 varieties of
materials in this category are used.
Reductants – Coke, about four verities
of coke (Low Ash Metallurgical Coke) in this category are used.
Fluxes – Quartz, Dolomite and Magnetite-
about four verities of materials in this category are used.
 

 

Raw material (Charge
Mix) is fed to the Furnace. Electrode paste goes to form soderberg electrode,
which is submerged in the charge. Current is supplied through electrodes and
smelting of charge takes place. Reduced metal forms alloy, and impurities join
to form Slag. Ferro Alloys Industry is very much power intensive. Power cost is
about 40 to 45% of the product cost.

 

3. Energy Consumption and Conservation measures

Energy in terms of electricity and
Caron is the major input to Ferro Chrome manufacturing. The productivity of the
industry solely depends upon effective and efficient use of energy. Some
activities for reducing energy consumption are discussed below.

 

a.     Maintaining Slag Volume at an Optimum Level.

 

Ferro Chrome production being a slag
process, equal or more volume of slag is also generated along with the
metal. The power consumption is influenced by the
raw material mix in the sense that higher the volume of slag higher is the
power consumption. The skill of the
metallurgist to maintain a lower slag volume results in lower cost of
production.

 

 

Since the cost and royalty of
low-grade ore is less, compared to that of high-grade ore, the raw material
cost may decrease but slag volume will increase due to use of low grade
ore. As the total charge volume increases it requires more power for
smelting and results in increasing in cost of power. The charge balance should
be selected in such a manner so as to maintain an optimum slag volume at a
level where the total cost will be minimum.
 

 

Study shows
a direct relationship between slag volume, raw material and consumption of power
. Fig.1 and Fig 2 shows the relationship between the slag volume, raw material
and consumption of power and between the slag volume and total cost. Higher
gang material in the ore leads to increases in slag volume. Higher volume of
low grade ore with high alumina content along with flux, may increase the slag
volume.

Fig. 2 Relationship between the
slag volume and total cost.

 

b.
Installation of auto furnace control system with auto on-load tap changers and
HT capacitor banks to obtain effective power utilization

 

Installation of auto furnace control equipment coupled with auto load
tap changers and H.T Capacitor banks are today’s common feature of modern
furnaces which contribute towards enhancing productivity by minimizing consumption
of unproductive power.

 

c. Minimizing heat losses in
furnace

 

Today there are several open furnaces operating in the country
today. Closed furnaces should be envisaged during modernization/expansion or
new projects for manufacturing of Chromium alloys. This will not only reduce
the heat losses from the furnace but also enable recovery of sensible and
latent heat in exhaust gases. This will bring down the volume of gases and will
impact in reducing the size of gas cleaning units.

 

d. Control of Moisture in
Raw materials

 

Often moisture content in chrome ore , coke and other raw materials goes
beyond acceptable limits particularly during rainy season and impacts in increasing
specific power and reductant requirement. Drying operation is imperative for
lowering down the moisture level in input materials since it will help not only
to bring down the specific power consumption but also reduce the specific
consumption of reductants, besides maintaining a steady slag volume and metal
composition.

 

e. Use of agglomerated feed
to the Furnace.

 

Agglomerates, being consistent in size and uniform in chemical
composition, are better than natural lumps in their reducibility and therefore
use of agglomerates lowers the specific power consumption, as well as helps to
attain smooth furnace operation. Sinters can be used in the production of chrome
alloys in order to bringing down the specific power consumption.

 

f) Other Energy conservation
measures

 

In addition to the above practices there are many other energy
conservation measures which can be implemented in order to minimize energy
consumption. Some of these are listed below:

• Use of exhaust gases from chimney to produce
electricity. Further the exhaust gases can be utilized for heating the raw
materials before feeding to the furnaces which will enhance chromium recovery
and reduction in power consumption.

• Use of the excess heat to melt secondary materials
without the use of additional fuel

• Heat recovery by using hot gases from melting stages
to preheat the furnace charge. The recovered heat is approximately 4 – 6 % of
the furnace fuel consumption

• collecting monoxide from closed Furnaces and burning as
a fuel for several different processes or to produce steam or other energy

 

4. Conclusion

India has rich mineral resources as it stands 2nd to South Africa in
chrome ores production. In spite of having natural resources, the Indian
ferroalloys industry is facing many challenges for its survival.   The Indian Ferro Alloy Industry has a lot of
potential to be energy efficient. With the implementation of energy
conservation measures, the position of the industry can be strengthened in the global
market.

 

References

·        
World Steel Association/Statistics March 2010. In:
http://www.worldsteel.org/?action=stats_search

 http://www.worldsteel.org/pictures/publicationfiles/Sustainability
Report2008_English.pdf;

·        
USGS 2007 Minerals Yearbook, U.S. Geological Survey,
FERROALLOYS Advance releaseSept. 2009. In:
http://minerals.usgs.gov/minerals/pubs/commodity/ ferroalloys/
myb1-2007-feall.pdf

·        
C.N. Harman 
“Innovations In Ferro Alloys Technology In India”INFACON XI

·        
IEA, 2009. World Energy Outlook 2009, Executive Summary,
International Energy Agency. In:http://iea.org/textbase/npsum/weo2009sum.pdf

·        
Kim, Y. and E. Worrell, 2002. International comparison of CO2
emissions trends in the iron and steel industry. Energy Policy, 30, pp.
827-838.

·        
L. Holappa “Toward Sustainability In Ferroalloys Production”
INFACON XII

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