Cupola is the most common type of melting
furnace used for the production of grey iron
castings in foundries. In the past few years,
TERI conducted energy audits of a range of
cupolas in Howrah and Agra foundry clusters.
The most energy-efficient cupola audited by
TERI used 13.6% charge coke (coke.:.metal
ratio of 1.:.7.5). The figure for the least
energy-efficient cupola was found to be as
high as 26.5% (coke.:.metal ratio of 1.:.4).
Some of the contributing factors that were
identified for this poor energy performance
are listed below.
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Incorrect blast rate |
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Lower blast air pressure |
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Incorrect distribution of air between
the top and lower tuyeres |
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Turbulent (non-linear) entry of air
into the cupola |
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Incorrect sizing of cupola
parameters such as tuyere area, well
depth,
and stack height among others |
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Poor operating and maintenance practices |
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Poor control of feed materials (shape,
size, weight, sequence) |
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Divided blast cupola (DBC) or twin blast cupola
is a proven techno-logy for improving the
energy performance at a modest investment.
As is evident from its name, a DBC supplies
blast air to the cupola furnace at two levels
through a double row of tuyeres. The advantages
of a DBC, compared to a conventional cupola,
are as follows.
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A higher metal tapping temperature
and higher carbon pick-up are obtained
for a given charge- coke consumption. |
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Charge-coke consumption is reduced
and the melting rate is increased, while
maintaining the same metal tapping temperature. |
The design being promoted by TERI captures
the above advantages by optimizing the design
parameters.
- Optimum blower specifications (quantity
and pressure)
- Optimum ratio of the air delivered to the
top and bottom tuyeres
- Minimum pressure drop and turbulence of
the combustion air
- Separate wind-belts for top and bottom tuyeres
- Correct tuyere area, number of tuyeres,
and distance between the two rows of tuyeres
- Optimum well capacity
- Higher stack height
- Mechanical charging system
- Stringent material specifications. |
 To
showcase the benefits of an optimal DBC design,
a demonstration plant has been installed at
Bharat Engineering Works, Howrah, a unit nominated
by the IFA (Indian Foundry Association). The
foundry, manufacturing ingot moulds, initially
had a charge-coke percentage of 13.6% (coke.:.metal
ratio of 1.:.7.5), which was brought down
to 8% (coke.:.metal ratio of 1.:.12.5). Hence,
the energy saving achieved in the new plant
was about 35% compared to their earlier cupola.
On an average monthly melting of 430 tonnes,
the yearly saving in coke is 270 tonnes. Additionally,
there was an increase in metal tapping temperature
and reduction in silicon and manganese losses.
Encouraged by the success of the demonstration
plant, a foundry unit located in Nagpur
has recently set up a DBC with technical
assistance of TERI. This unit, which makes
thin-walled sanitary castings, has been
able to reduce the charge-coke consumption
from 22% (coke.:.metal ratio of 1.:.4.5)
to 13% (coke.:.metal ratio of 1.:.7.7),
which is equivalent to energy savings of
about 40%. This translates to a coke saving
of 280 TPA (tonnes per annum) worth about
Rs 11 00 000 on a melting of 300 tonnes
per month in the foundry. In the two units,
the total capital investment of the DBC,
inclusive of civil work, plat-forms, bucket
charging system, etc., was about Rs 11 00
000. Thus the payback on the investment
is one year considering saving in coke alone.
TERI has also provided technical assistance
for replacing hot blast cupola with DBC
to a foundry unit near Kolkata. The imported
hot blast cupolas operating in the foundry
had a charge coke consumption of about 16%
(coke : metal ratio of 1 : 6.3) with beehive
coke. Implementation of DBC reduced the
charge coke consumption to 13% (coke : metal
ratio of 1 : 7.7) which is equivalent to
energy savings of 28%. Additionally, the
unit saved a substantial sum of money from
the diesel consumed earlier in the recuperator
used in the hot blast system.
A foundry unit located at Rajkot has recently
commissioned a DBC designed by TERI. The
foundry, which manufacturers electric motor
bodies, has been able to reduce the charge
coke consumption from 9.1% (coke : metal
ratio of 1: ) to 7.8% (coke : metal ratio
of 1: ) which is equivalent to energy savings
of about 15%. There have been substantial
savings in from reduction of alloying elements
in the foundry unit. |
