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Restart of BF#2 of Bhushan Steel Limited Using Durfee Method
AK Saxena , KL Sarda, VN.Giridhar, Rajesh Srivastava
Bhushan Steel Limited, Narendrapur, Dist Dhenkanal Odisha
Email: [email protected]
ABSTRACT
The paper describes the method used for restarting of the 3800 m3 Blast furnace which was
stopped unprepared 42 hrs after blow-in. The furnace was restarted after 5 months of
stoppage using the durfee pipe technology. The method of durfee involves installation of
special pipes for blowing in Hot Blast through the Tap hole of the blast furnace for certain
time period. This helps in heating up of the hearth and helps in early connection between
Tap hole and Tuyere. Special drilling tools were adopted for opening of the blanked
Tuyeres, without any wind reduction/shutdown. Thermocouples were installed in all the 34
Tuyeres to monitor the gas temperature at the Tuyeres. Special cast plugs were used to
ensure that Tuyeres open only as per schedule and premature opening was completely
avoided. The hot metal and slag separation was started through the pseudo skimmer
provided and metal was taken into ladle on the 4th day. Another 4 days the furnace was
operated through the pseudo skimmer and finally slag was taken into Inba Slag
Granulation system on the 8th day. The early separation of metal and slag helped in fast
stabilization of the blast furnace and filling of slag pits was avoided which was the major
concern. The blast furnace revival process was completed on the 8th day with all the
systems stabilised.
INTRODUCTION
BF#2 of Bhushan Steel is the latest generation of blast furnace designed and engineered
based on PWIT technology. The blast furnace is of 3800 m3 internal volume with 34
tuyere’s, 4 tap hole and 2 cast houses. The construction of the blast furnace started in
June 2009 and was completed in October 2013. The furnace was blown in during the
month of November 2013 however the furnace had to be shut down due to unavoidable
reasons unprepared. The furnace was subsequently started in the month of April 2014
using durfee pipe method.
Salient features of the Blast furnace are:
o Inner volume: 3,814 m3
o Working volume: 3,230 m3
o Number of tuyeres: 34
o Charging system: with belt conveyor and Paul Wurth Parallel hopper Bell Less Top®,
o Cooling system
o Under-hearth: water pipes
o Hearth: cast-iron staves
o from Bosh to lower Stack: copper staves
o Tuyere belt: cast iron staves
o Middle Stack to Throat: cast iron staves
PREPARATIONS FOR START UP
The major task of any recovery from a chilled hearth condition is establishing of
connection between the Tap hole and the Tuyeres so that the generated liquids can be
drained out.
The situation at BF#2 before starting the process of recovery was unique due to:
1. Furnace was stopped unprepared for a very long duration
2. Metal along with slag had solidified in the hearth and Tuyere area
Extensive discussions were held to find out whether to use the oxy-fuel burners in the tap
hole or to go for Durfee pipe method which involves blowing of oxygen enriched hot blast
through the tap hole. The Durfee method has been used extensively in Europe for revivals
after prolonged shutdown of blast furnace, however they have been mostly employed
when the shutdowns were prepared. The oxy-fuel method is a good choice when the
hearth is severely chilled as it brings in a very large amount of heat and melts away the
chilled metal and slag leading to a good connection between the tap hole and tuyere.
Based on lot of deliberations and critical analysis of the situation of burden inside the
blast furnace along with experts from PWIT it was concluded to go for the Durfee method
for revival of the blast furnace as it was felt that the coke inside may be just sufficient to
provide the energy for start of the revival process.
PREPARATION OF THE TUYERES
Any recovery process demands that Tuyeres don’t open up by itself
and create drainage issues or Tuyere Burnings leading to unplanned
shutdown. Tuyeres were carefully plugged with Ceramic Inserts and
gaps were filled up with mortar to ensure no blast can enter the
furnace even at higher blast pressures. Also to monitor the situation
inside thermocouples were installed in the ceramic plugs. This would give us a fair
indication of the status of the BF inside.
To ensure a fast recovery and to avoid any shutdown for opening the tuyeres special
drilling tools were used which could drill the ceramic plug even upto blast pressures of 2
bar.
INSTALLATION OF DURFEE PIPE
Tap hole No 2 and 3 were core drilled up to a depth of 4 m horizontally to install the
Durfee pipe as away from the hearth refractory to avoid burn out. Stainless steel tube of
special construction was pushed inside the tap hole and tightly sealed with castable to
avoid leakage of the gases. This was then connected to two modified peephole assembly
of Blow pipe with isolation valves.
Fig-1. Ceramic Plug
Fig-2 Durfee Installation
BUSTLE PIPE HEATING
12 hours before the blast was to be taken through the tap hole, Bustle Main heating was
started. 8 to 10 Tuyere peep-hole flanges were opened and hot blast was blown out to
heat up the bustle main to upto 650 deg C. After completion of the heating the peephole
flanges were closed and preparations were started to start the revival process.
THE START UP
Blast was introduced through both the Durfee’s at a pressure of 2.5 bar at a Temperature
of 550 deg C. No flow was observed even upto a pressure of 4.0 bar even after 6 hrs. This
indicated a very bad permeability in the hearth and it was decided to remove Durfee from
the tap hole and start lancing. It was inferred that slag within the coke interstices has
solidified in the lower heart just at the tap hole area and continuous lancing shall help
melt the slag and permeability can be achieved. The lancing in TH#2 was continued for
around 20 hrs Durfee was re-introduced into the Tap holes.
Blast was introduced into the Durfee pipes along with oxygen. A good delta P was
observed between the Durfee which implied a good permeability was present in the
hearth area. After around 12 hrs and cumulative flow of around 140000 Nm3 of blast
blown through the durfee pipes 4 Tuyeres above TH#2 were opened without reducing
blast by using the special drilling methods. Oxygen was introduced into the Tuyeres
through the peephole flange by installing branch pipes. 2 hours after opening of the 4
Fig-3 Durfee Installation at Tap hole and Tuyere connection
Tuyeres Slag was seen in TH#2 and durfee pipe was removed to divert the hot liquids into the
slag pit. Good flow of slag was obtained for around 30 minutes and cast closed.
However after removal of Durfee from TH#3 only gas blow was observed and no liquids
were obtained. It was decided to continue opening Tuyeres between TH#2 and TH#3 to
have an interconnection between them. TH#1 and TH#4 were not used in the revival
process. Further opening of Tuyere was executed based on the furnace working and
casting.
TH#2 was cast every two hours with good fluidity of slag and metal and taken into the
slag pit. After 71 hours from start up hot metal was tapped into ladle through the upper
skimmer and slag was diverted to the slag pit. Slag and Metal separation was good. Gas
Cleaning Plant was connected after 75 hrs from start up and gas connected to network.
TH#3 was continued to be lanced and after 135 hours of start up good stream of liquids
was obtained and diverted to the slag pit after which Main trough of TH#3 was cleaned of
Fig-5 Slag Filled up in Durfee Fig-6 Slag TappingFig-4 Oxygen in Tuyere
Fig-7 Trough Preparation with Sand and Ramming Mass
all sand and metal taken through bottom skimmer into ladle. Subsequently TH#2 also was
connected through the bottom skimmer.
Conclusion
On the 8th day after start up with 20 of 34 Tuyeres in operation the furnace was
successfully commissioned and put into operation. The authors would like to put on
record their deep appreciation for the help and support from PWIT team in smoothly
commissioning the furnace.
Fig-8 No OF TUYERE & BLAST INCREASE
Fig-9 TUYERE OPENING SEQUENCE
Fig-10 HOT METAL PRODUCTION TONS