FIELD OF THE INVENTION
The present invention relates to a method of heating of blast furnace stoves adapted to
achieve higher hot blast temperature. More particularly, the method of the invention is
directed to deploy more number of stoves on gas than on blast so that more gas input into
the stoves can be provided resulting in better heating of blast furnace stoves leading to
higher hot blast temperature (HBT), which is the most important controlling parameter to
regulate Blast Furnace hearth heat level. Advantageously, higher blast temperature or
higher heat input through tuyeres decreases the heat requirement into the furnace in the
form of coke or auxiliary fuels. The enhanced HBT also directly influences the combustion
raceway adiabatic flame temperature (RAFT). The method of the invention enables
increasing gas input by providing additional stove on gas even with partial choking of
refractory checker bricks after prolonged working or decrease in gas line pressure, which
restricts the gas input to the stoves. By putting three stoves on gas and one stove on blast,
the total BF gas input into the stoves increases significantly resulting in higher hot blast
temperature upto 1150°C. This heating practice for choked blast furnace stoves helps in
saving on capital repair cost of stove. The higher hot blast temperature facilitate the
injection of auxiliary fuel into the blast furnace and thus favouring lower energy cost for
production of hot metal. A rise of 10°C in blast temperature increases the combustion
raceway temperature by 8.4°C and decreases coke rate by 1.23 kg/ton hot metal (thm),
blast volume by 5.65 Nm3/thm and top gas volume (800Kcal/Nm3 basis) by 4.04 Nm3/thm.
The present method for heating of choked blast furnace stove to achieve higher hot blast
temperature is having prospects for application in blast furnaces in steel plants with
significant cost advantage and energy saving, extending the working life of stoves and
improving the productivity of Blast Furnace.
BACKGROUND ART
It is well known in art of iron and steel making that hot air blast through tuyeres at desired
rate and temperature is required for completion of blast furnace reaction. Many blast
furnaces are usually provided with four stoves for heating the cold blast. Normally, two
stoves are put on gas and two stoves on blast. Total gas input depends on numbers of
stoves on gas and the gas line pressure. When new stoves are installed, there occurs hardly
any chocking of checker bricks. Hence, quantity of gas input into the stoves is sufficient
resulting in higher waste gas temperature in the range of 350 - 400C, which indicates
proper soaking of checker bricks, which in turn helps achieving the higher HBT.
It has been experienced that due to long period of working over years, the gas input to the
stoves decreases due to chocking of refractory checker bricks and sometimes due to
decrease in the gas line pressure. The decrease in the gas input to the stoves adversely
affects the hot blast temperature (HBT) resulting in higher coke rate and lower furnace
productivity. In order to achieve higher hot blast temperature, it is essential to increase the
total gas input into the stoves. As the gas input to the stoves gets reduced due to chocking
of refractory checker bricks with two stoves on gas, resulting in lower waste gas
temperature in the range of 150°C-200°C, indicating inadequate soaking of bottom part of
checker. This results in lower hot blast temperature (HBT).
There has thus been a need to develop a method for heating of blast furnace stoves
adapted to provide sufficient gas input to the stoves, even in case of chocking of refractory
checker bricks of stoves on gas or if the gas line pressure is low, so as to increase the waste
gas temperature leading to achievement of higher hot blast temperature (HBT). The method
of the invention would also favour decreasing the heat requirement to be put into furnace in
the form of coke or auxiliary fuels by increasing HBT and resultantly enhancing raceway
adiabatic flame temperature (RAFT), and thus improving the productivity of furnace.
OBJECTS OF THE INVENTION
The basic object of the present invention is thus directed to develop a method for heating of
blast furnace stoves adapted to achieve desired higher hot blast temperature (HBT)
adequate to regulate BF hearth heat level, by increasing the number of blast furnace stoves
on gas, thereby increasing gas input into the stoves.
Another object of the present invention is directed to develop a method for heating of blast
furnace stoves adapted to achieve higher hot blast temperature (HBT) so that limitations on
gas input to stove due to chocking of checker bricks is avoided.
A further object of the present invention is directed to develop a method for heating of blast
furnace stoves adapted to achieve higher hot blast temperature (HBT) wherein quantity of
gas input to the stoves is sufficient resulting in higher waste gas temperature and proper
soaking of checker bricks.
A still further object of the present invention is directed to develop a method for heating of
blast furnace stoves adapted to achieve higher hot blast temperature (HBT) wherein higher
input through tuyeres decreases the heat requirement to be put into furnace in the form of
coke or auxiliary fuels leading to lower coke rate and higher productivity of furnace.
A still further object of the present invention is directed to develop a method for heating of
blast furnace stoves adapted to achieve higher hot blast temperature (HBT) wherein the
heating practice enables achieving desired increased gas input to the stove and higher HBT
even when desired gas line pressure is not maintained.
A still further object of the present invention is directed to develop a method for heating of
blast furnace stoves adapted to achieve higher hot blast temperature (HBT) wherein higher
HBT facilitates higher rate of auxiliary fuel injection through tuyeres the blast furnace.
A still further object of the present invention is directed to develop a method for heating of
blast furnace stoves adapted to achieve higher hot blast temperature (HBT) wherein
increased HBT is achieved by firing BF gas alone into the stoves.
A still further object of the present invention is directed to develop a method for heating of
blast furnace stoves adapted to achieve higher hot blast temperature (HBT) wherein higher
HBT is achieved with very old used stoves and with low gas line pressure.
A still further object of the present invention is directed to develop a method for heating of
blast furnace stoves adapted to achieve higher hot blast temperature (HBT) wherein the
method results in lowering energy cost for production of hot metal in blast furnace.
SUMMARY OF THE INVENTION
The basic aspect of the present invention is directed to a method of heating for blast
furnace stoves adapted to achieve higher hot blast temperature (HBT), comprising
increasing the gas input into the stoves by putting more numbers of stoves on gas
than on the blast;
increasing the waste gas temperature and ensuring proper soaking of checker bricks;
and
attaining higher hot blast temperature (HBT).
Another aspect of the present invention is directed to a method of heating for blast furnace
stoves adapted to achieve higher hot blast temperature (HBT) in blast furnaces having four
stoves and with preferably three stoves put on gas and one stove on blast to obtain desired
increased gas input to stoves.
A further aspect of the present invention is directed to a method of heating for blast furnace
stoves adapted to achieve higher hot blast temperature (HBT), wherein gas input to the
stove is increased by 20-30% which meets HBT of 1000°C or more with blast furnace gas
alone.
A still further aspect of the present invention is directed to a method of heating for blast
furnace stoves adapted to achieve higher hot blast temperature (HBT), wherein the hot
blast temperature is increased up to 1150°C.
A still further aspect of the present invention is directed to a method of heating for blast
furnace stoves adapted to achieve higher hot blast temperature (HBT), wherein higher HBT
facilitates higher rate of auxiliary fuel injection into the blast furnace, lowering the energy
cost for production of hot metal.
A still further aspect of the present invention is directed to a method of heating for blast
furnace stoves adapted to achieve higher hot blast temperature (HBT), wherein due to
increased HBT, coal dust injection (CDI) in blast furnace is increased from 50 Kg/thm to 100
Kg/thm.
Advantageously, in said method of heating for blast furnace stoves adapted to achieve
higher hot blast temperature (HBT) according to the invention, wherein said method
ensures achieving the hot blast temperature even with partial chocking of refractory checker
bricks that restrict gas input to stove and when gas line pressure is lower than the desired
gas line pressure.
According to an important aspect of the present invention directed to said method of
heating for blast furnace stoves adapted to achieve higher hot blast temperature (HBT),
wherein a rise of 10°C in blast temperature increases the combustion raceway adiabatic
flame temperature (RAFT) by 8.4°C, decreases coke rate by 1.23Kg/htm, decreases blast
volume by 5.65Nm3/thm and top gas volume (800Kcal/Nm3 basis) by 4.04 Nm3/thm.
A still further aspect of the present invention is directed to a method of heating for blast
furnace stoves adapted to achieve higher hot blast temperature (HBT), wherein said method
extends the life of the existing blast furnace stoves thereby saving capital repair cost of
stoves.
The present invention and its objects and advantages are described in greater details with
reference to the following accompanying illustrative drawings and examples.
BRIEF DESCRIPTION OF ACCOMPANYING FIGURES
Figure 1: is the schematic illustration of the deployment of the blast furnace stoves on gas
and on blast according to the present invention vis-a-vis existing practice, showing how the
higher gas input to the stove is increased leading to desired higher HBT.
Figure 2: is the illustration of the chart showing the sequence of heating practices in
achieving the higher HBT with increased gas input to stoves according to the present
invention vis-a-vis the existing practice indicating reduction in blast period.
DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE
ACCOMPANYING FIGURE
The present invention is directed to develop a method for heating of Blast Furnace stoves in
order to increase the gas input to the stoves thereby to increase the hot blast temperature,
lower coke rate and higher productivity. The heating practice according to the present
invention is particularly suitable for blast furnace with four stoves. The method of the
invention is capable of providing higher hot blast temperature by increased gas input to the
stoves even when the stoves with partial chocking of refractory checker bricks and also with
low gas line pressure.
It has been experimentally verified under different blast furnace operating conditions by
way of the present invention that for blast furnace with four stoves, deployment of stoves in
higher numbers on gas increases the gas input rate as well as the HBT. Thus, instead of
conventional two stoves on gas and two stoves on blast, a method of heating using three
stoves on gas and one on blast, enhances the gas input rate to stoves and also favour
obtaining higher hot blast temperature. It is also a distinctive technical advancement over
the prevailing art that higher gas input to stoves helps in increasing the hot blast
temperature, lower coke rate, higher rate of auxiliary fuel injection into the blast furnace
and improved productivity of furnace, even with chocked checker bricks of stoves and low
gas line pressure. Thus the invention establishes that an increase in HBT is possible by firing
BF gas alone into the stoves. By providing an extra stove on gas, the gas input into the
stoves is increased by 25-30% that helps attaining increased HBT up to 1150°C.
Reference is now invited to the accompanying Figure 1 that shows two stoves are on blast
and two stoves on gas in the existing practice where as in the improved heating practice,
only one stove is on blast and three stoves are on gas which results in higher BF gas input
to the stoves thereby helping in achieving higher hot blast temperature.
Reference is next invited to the accompanying Figure 2 that shows the existing and
improved heating practices for stoves. In existing heating practice, at any point of time two
stoves are on blast for a blast period of Tb and two stoves on gas for a gas period of Tg with
stove change over time of Teh for changing stoves from blast to gas and vice versa.
In the improved heating practice, only one stove is on blast with a blast period of MTb and
three stoves are on gas for a gas period of MTg and the same stove change over period of
Tch. If total cycle time for both the cases is same and stove change over period is negligible
compared to gas/blast period, then blast period in the improved heating practice becomes
half of blast period of the existing practices as shown in Figure 2.
The objects and advantageous aspect of the invention directed to improved heating practice
of blast furnace stoves adapted to ensure higher HBT is illustrated with the help of the
following experiments/examples and observed results.
Example I:
According to an embodiment of the invention Blast Furnaces provided with four stoves and
when all the four are available, wherein three stoves can be put on gas, then total gas input
into the stoves increases by about 25 - 30%, which will meet the HBT of 1000C or more
with Blast Furnace gas alone [usually two stoves are on gas and the remaining two are on
blast]. Whenever only three stoves are available, two stoves are on gas and third stove is
on blast.
Example II:
Experiments with three stoves on gas and one stove on blast have been conducted in
another blast furnace to increase HBT from 960°C. The total gas input into the stoves
increased from 85,000 to 1,10,000 Nm3/nr, which resulted in increased HBT from 960°C to
1100 - 1150°C. This has also helped in increasing coal dust injection (CDI) from 50 to 100
Kg/thm. The same result has been observed while experimenting with other Blast Furnaces
where four stoves have been provided and stove availability is quite high.
Example III:
Similar exercise was carried out in another blast furnace in another steel plant of the
applicants where total gas input to stoves found to increase from 80,000 Nm3/hr to
1,00,000 Nm3/hr resulting in increased HBT from 900°C to 1000°C.
It is thus possible by way of the present invention to develop a method for heating of blast
furnace stove by providing increased number of stoves on gas compared to blast so that the
gas input to the stoves is increased, even in case of chocking of refractory checker bricks for
old stoves and low gas line pressure. The increase in gas input to stove helps in increasing
waste gas temperature and the hot blast temperature and also achieve lower coke rate,
higher injection of auxiliary fuel e.g. coal dust and improved furnace productivity. For
achieving higher hot blast temperature, it is essential to increase the total gas input into the
stoves. By putting three stoves on gas and one stove on blast, the total gas input into the
stoves resulting in higher hot blast temperature upto 1150°C, even with the stoves being
very old and with low gas line pressure. The method of the invention thus favours extending
the life of the stoves and thus saving on capital repair cost of stoves. Moreover, enhanced
HBT enables the injection of auxiliary fuel into the blast furnace, which results in lower
energy cost for hot metal production. The heating method for stoves of blast furnaces
according to the present invention thus having the potential for wide application in energy
efficient Blast furnace operation in steel plants.
We Claim:
1. A method of heating for blast furnace stoves adapted to achieve higher hot blast
temperature (HBT), comprising
increasing the gas input into the stoves by putting more numbers of stoves on gas
than on the blast;
increasing the waste gas temperature and ensuring proper soaking of checker bricks;
and
attaining higher hot blast temperature (HBT).
2. A method of heating for blast furnace stoves adapted to achieve higher hot blast
temperature (HBT) as claimed in claim 1, adapted for blast furnaces with four stoves
and with preferably three stoves put on gas and one stove on blast to obtain desired
increased gas input to stoves.
3. A method of heating for blast furnace stoves adapted to achieve higher hot blast
temperature (HBT) as claimed in claims 1 or 2, wherein gas input to the stove is
increased by 25-30% to meet HBT of 1000°C or more with blast furnace gas alone.
4. A method of heating for blast furnace stoves adapted to achieve higher hot blast
temperature (HBT) as claimed in anyone of claims 1 to 3, wherein the hot blast
temperature is increased up to 1150°C.
5. A method of heating for blast furnace stoves adapted to achieve higher hot blast
temperature (HBT) as claimed in anyone of claims 1 to 4, wherein higher HBT
facilitates higher rate of auxiliary fuel injection into the blast furnace, lowering the
energy cost for production of hot metal.
6. A method of heating for blast furnace stoves adapted to achieve higher hot blast
temperature (HBT) as claimed in anyone of claims 1 to 5, wherein due to increased
HBT, coal dust injection (CDI) in blast furnace is increased from 50 Kg/thm to 100
Kg/thm.
7. A method of heating for blast furnace stoves adapted to achieve higher hot blast
temperature (HBT) as claimed in anyone of claims 1 to 6, wherein said method
ensures achieving the hot blast temperature even with partial chocking of refractory
checker bricks that restrict gas input to stove and when the gas line pressure is
lower than the desired gas line pressure.
8. A method of heating for blast furnace stoves adapted to achieve higher hot blast
temperature (HBT) as claimed in anyone of claims 1 to 5, wherein a rise of 10°C in
blast temperature increases the combustion raceway adiabatic flame temperature
(RAFT) by 8.4°C, decreases coke rate by 1.23Kg/htm, decreases blast volume by
5.65Nm3/thm and top gas volume (800Kcal/Nm3 basis) by 4.04 Nm3/thm.
9. A method of heating for blast furnace stoves adapted to achieve higher hot blast
temperature (HBT) as claimed in anyone of claims 1 to 5, wherein said method
extends the life of the existing blast furnace stoves thereby saving capital repair cost
of stoves.
10. A method of heating for blast furnace stoves to achieve higher hot blast temperature
(HBT) as herein described with reference to the accompanying illustrative examples
and drawings.

The invention relates to a method of heating for blast furnace stoves adapted to achieve
higher hot blast temperature, by deploying preferably more number of stoves on gas than
on blast results in increased gas input into the stoves, higher hot blast temperature (HBT)
and combustion raceway adiabatic flame temperature (RAFT). Advantageously, higher HBT
or higher heat input through tuyeres decreases the heat requirement put into the furnace in
the form of coke or auxiliary fuels. By putting three stoves on gas and one stove on blast,
the total BF gas input into the stoves increases significantly resulting in higher HBT upto
1150°C. The higher HBT favours injection of coal dust with lower energy cost for production
of hot metal. A rise of 10°C in blast temperature increases the combustion raceway
temperature by 8.4°C and decreases coke rate by 1.23 kg/ton hot metal (thm), blast
volume by 5.65 Nm3/thm and top gas volume (800Kcal/Nm3 basis) by 4.04 Nm3/thm. The
method is capable of wide application with significant cost advantage and energy saving,
extending stove life and improving BF productivity.