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: akshaya.saxena@bhushansteel.com

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