CLIAMS:We Claim:
1. A method for ensuring connectivity of tuyeres and taphole in a blown down blast furnace by freeing blocked voidages in the hearth comprising:
(i) measuring the voidage of the settled dead man zone in the hearth;
(ii) heating up the coke inside the hearth and in the vicinity of taphole to free interstitial congestion between coke particles; and
(iii) selectively filling up the hearth for desired block free voidage for the initial melt and lowered viscosity of the slag formed with upto the tuyere level with large size +80 -100 mm coke blank mixed with fluorspar.

2. A method as claimed in claim 1 wherein said measuring of the voidage is done involving drill machine accompanied with N2 and/or air purging.

3. A method as claimed in anyone of claims 1 or 2 wherein large size coke is provided to ensure that there is enough voidage for the initial melt to trickle down towards tap hole when the furnace restarts and fluorspar is charged in the range of 10-80 kg per ton of coke.

4. A method as claimed in anyone of claims 1 to 3 wherein the opening of the tuyeres is done selectively depending upon the working conditions of the furnace including temperature of liquid slag and metal and its drainage from the tap hole.

5. A method as claimed in anyone of claims 1 to 4 wherein the initial fill up of large sized coke is done upto belly region after which DRI and fluxed coke are charged in the furnace.

6. A method as claimed in claim 5 wherein said fluxed coke comprises coke plus LD slag to meet set slag composition with said LD slag containing Fe alongwith calcined CaO in solution.

7. A method as claimed in anyone of claims 5 to 6 wherein said selectively filling up the hearth for desired block free voidage for the initial melt and lowered viscosity of the slag formed further comprises introducing after DRI and fluxed coke crushed graphite/carbon electrodes (CRE) of size 10-25 mm containing > 98% C and about 20-30 tonnes depending upon the furnace to provide for the required instant heat to the furnace.

8. A method as claimed in anyone of claims 1 to 7 wherein said selectively filling up the hearth comprising after DRI and coke providing lean burden comprising lean ore with variable coke rate.

9. A method as claimed in claim 8 wherein said lean ore with variable coke rate comprises providing after fluxed coke and DRI, the lean coke burden comprising of lean ore with coke rate of 1250 Kg/THM, lean ore with coke rate of 950 Kg/THM and lean ore with coke rate of 650 Kg/THM.

10. A method as claimed in anyone of claims 1 to 9 wherein the liquid metal formed initially on the furnace passes through the voidage created in the deadman zone and owing to its lower melting point does not solidify and and therefore gets easily tapped from the taphole, the hot metal owing to its good conductivity providing for transfer of heat to the coke in the deadman zone and thus maintain its thermal requirement and keeping permeability of the dead man zone.

Dated this the 20th day of December, 2014

Anjan Sen
Anjan Sen & Associates
(Applicants Agent)
,TagSPECI:FIELD OF THE INVENTION
The present invention relates to a method for ensuring connectivity of tuyeres and taphole in a blown down blast furnace by freeing blocked voidages in the hearth. More particularly, the present invention is directed to smooth restarting of a blowndown blast furnace ensuring connectivity of tuyere and taphole post shutdown to prepare an easy melt to have proper drainage of liquid into the hearth region so that blocking of the tuyeres as well as the blanketing of the coke surface by slag near the tuyere zone is avoided. After ensuring the dead man voidage is good, the coke present near the taphole and the tuyere zone inside the hearth is heated to free the interstitial congestion between coke particles by lancing through taphole. After that large size handpicked coke in the size range of 80 – 100 mm mixed with fluorspar (10 – 80 kg per ton of coke) is charged to fill the cavity formed during heating of coke bed and raking out. Furnace is then filled with special burden recipe/ composition of blowing in through these tuyeres above the taphole with which the connectivity with the taphole has been established. Opening of tuyeres are planned depending on working condition of the furnace i.e. temperature of liquid slag and metal and its drainage from the taphole. The liquid metal formed initially in the furnace passes through the voidage created in the dead man zone and owing to its lower melting point won’t solidify and therefore easily tapped from the taphole. Hot metal owing to its good conductivity will transfer heat to the coke in dead man zone and thus maintain its thermal requirement and thus help in keeping the permeability of the dead man zone.

BACKGROUND OF THE INVENTION

After long shutdown of the blast furnace the liquid in the hearth level gets gradually solidified in due course of time. The voidage in this zone gets reduced as the materials such as coke along with solidified liquid coalesce to form a dense mass with lesser permeability. So when the furnace is restarted in such cases the impermeable hearth with low voidage hampers the trickling of molten liquid formed below the tuyere level. This leads to flooding of fresh melt close to tuyeres which creates problem in further blowing of the furnace. This leads to blocking of the tuyeres as well as the blanketing of the coke surface by slag near the tuyere zone. The coke that was supposed to burn near the tuyere and generate heat for the furnace fails to do so because of the thick layer slag formed all around it. The oxygen from the tuyere will then react with coke much ahead of the tuyere level, thus shifting the whole reaction upward. Slag formation will take place in the above region and as the slag drips down it will envelope the whole tuyere region. This will further hamper the blast intake into the furnace and as the hot blast temperature is lower than the slag melting temperature, the slag will begin to solidify thus bringing down the hearth temperature drastically. After accumulation of slag, the metal will also start accumulating near the tuyeres resulting in burning of the tuyeres due to metal contact at its surface. The burning of the tuyeres will lead to water seepage into the hearth zone. If the temperature falls below, this may lead to chilled hearth furnace.

Shortcomings associated with the present system are that the conventional start with coke filling may lead to uncertainty during the startup of the furnace post shutdown. More coke is required to help the melting of the solidified liquid in the tuyere hearth region leading to very high fuel rate. It may lead to delayed revival of the furnace post shutdown as the functioning is not smooth. Blocked voidages in the hearth may lead to overfilling and thus damaging the tuyeres of the furnace. The whole process of the restart is uncertain and takes long time to stabilize the process.

There has been thus a need to developing a methodology for smooth startup and faster revival of the furnace post shutdown overcoming blocked voidage of the impermeable hearth due to coke along with solidified liquid coalescing to form a dense mass with lesser permeability during long shutdown, by ensuring connectivity of tuyere and taphole post shutdown to prepare an easy melt to have proper drainage of liquid into the hearth region.

OBJECTS OF THE INVENTION

The basic object of the present invention is directed to developing a method for ensuring connectivity of tuyeres and taphole in a blown down blast furnace by freeing blocked voidages in the hearth favouring smooth starting and faster revival with stabilization of the process.

A further object of the present invention is directed to developing a method for ensuring connectivity of tuyeres and taphole in a blown down blast furnace by freeing blocked voidages in the hearth ensuring connectivity of tuyere and taphole post shutdown to prepare an easy melt to have proper drainage of liquid into the hearth region.

A still further object of the present invention is directed to developing a method for ensuring connectivity of tuyeres and taphole in a blown down blast furnace by freeing blocked voidages in the hearth with stabilized process whereby requirement of more coke for melting of the solidified liquid in the tuyere heart leading to high fuel rate can be avoided.

A still further object of the present invention is directed to a method for ensuring connectivity of tuyeres and taphole in a blown down blast furnace by freeing blocked voidages in the hearth whereby accumulation of slag and metal near the tuyeres resulting in burning of the tuyeres due to metal contact at its surface can be eliminated.

A still further object of the present invention is directed to a method for ensuring connectivity of tuyeres and taphole in a blown down blast furnace by freeing blocked voidages in the hearth wherein it is ensured that there is enough voidage for the initial melts to trickle down towards taphole when the furnace restarts.

A still further object of the present invention is directed to a method for ensuring connectivity of tuyeres and taphole in a blown down blast furnace by freeing blocked voidages in the hearth wherein the furnace is filled with special burden recipe/composition and blowing in through the tuyeres above the taphole with which the connectivity with the taphole has been established.

SUMMARY OF THE INVENTION

The basic aspect of the present invention is directed to a method for ensuring connectivity of tuyeres and taphole in a blown down blast furnace by freeing blocked voidages in the hearth comprising:
(i) measuring the voidage of the settled dead man zone in the hearth;
(ii) heating up the coke inside the hearth and in the vicinity of taphole to free interstitial congestion between coke particles; and
(iii) selectively filling up the hearth for desired block free voidage for the initial melt and lowered viscosity of the slag formed with upto the tuyere level with large size +80 -100 mm coke blank mixed with fluorspar.

A further aspect of the present invention is directed to said method wherein said measuring of the voidage is done involving drill machine accompanied with N2 and/or air purging.

A further aspect of the present invention is directed to said method wherein large size coke is provided to ensure that there is enough voidage for the initial melt to trickle down towards tap hole when the furnace restarts and fluorspar is charged in the range of 10-80 kg per ton of coke.

A still further aspect of the present invention is directed to said method wherein the opening of the tuyeres is done selectively depending upon the working conditions of the furnace including temperature of liquid slag and metal and its drainage from the tap hole.

A further aspect of the present invention is directed to said method wherein the initial fill up of large sized coke is done upto belly region after which DRI and fluxed coke are charged in the furnace.

Yet another aspect of the present invention is directed to said method wherein said fluxed coke comprises coke plus LD slag to meet set slag composition with said LD slag containing Fe alongwith calcined CaO in solution.

A further aspect of the present invention is directed to said method wherein said selectively filling up the hearth for desired block free voidage for the initial melt and lowered viscosity of the slag formed further comprises introducing after DRI and fluxed coke crushed graphite/carbon electrodes (CRE) of size 10-25 mm containing > 98% C and about 20-30 tonnes depending upon the furnace to provide for the required instant heat to the furnace.

A still further aspect of the present invention is directed to said method wherein said selectively filling up the hearth comprising after DRI and coke providing lean burden comprising lean ore with variable coke rate.

Another aspect of the present invention is directed to said method wherein said lean ore with variable coke rate comprises providing after fluxed coke and DRI, the lean coke burden comprising of lean ore with coke rate of 1250 Kg/THM, lean ore with coke rate of 950 Kg/THM and lean ore with coke rate of 650 Kg/THM.

A still further aspect of the present invention is directed to said method wherein the liquid metal formed initially on the furnace passes through the voidage created in the deadman zone and owing to its lower melting point does not solidify and therefore gets easily tapped from the taphole, the hot metal owing to its good conductivity providing for transfer of heat to the coke in the deadman zone and thus maintain its thermal requirement and keeping permeability of the dead man zone.

The objects and advantages of the present invention are described hereunder in greater details with reference to the following accompanying non limiting illustrative drawings.

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES

Figure 1: shows schematically the arrangement to check the dead man permeability according to the method of restarting the blast furnace post blow down using the drill machine accompanied with air blowing at high pressure such that if the bed is loose, dust smoke and gas comes out from the top which can be observed from the open tuyeres.

Figure 2: shows the arrangement for heating of hearth bed with oxygen blowing through tuyeres and taphole to enhance the permeability of the bed according to the method of the present invention.

Figure 3: shows the special recipe burden to start the furnace post blowdown according to the method of the present invention.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS

The present invention is directed to a method of a method for ensuring connectivity of tuyeres and taphole in a blown down blast furnace by freeing blocked voidages in the hearth, ensuring smooth restarting of a blowndown blast furnace wherein connectivity of tuyere and taphole is maintained post shutdown to prepare an easy melt to have proper drainage of liquid into the hearth region and flling up furnace with special burden recipe/composition for smooth start up and faster stabilization of process.

Blowing down of the furnace well below the tuyere level is a prerequisite for this novel process. It facilitates the raking out of the coke as well as rebound material of gunning castable easier. The furnace is cleared from any kind of maintenance job and no work is allowed inside or around it. The bleeder of the furnace is kept open to maintain proper suction into the furnace through tuyeres opening. 3-4 tuyeres in the area around the taphole are removed.

The voidage of the settled dead man zone in the hearth needs to be checked. Method of knowing the voidage of the dead man zone is done by drilling with the drill machine accompanied with flushing air or nitrogen. If the bed is loosely packed, air mixed with dust generated from drilling can be observed from the tuyere openings. If not, more raking of coke from the dead man has to be carried out. Accompanying Figure 1 shows schematically the arrangement to check the dead man permeability according to the method of restarting the blast furnace post blow down using the drill machine(1) accompanied with air blowing at high pressure. After ensuring the dead man voidage is good, the coke present near the taphole and the tuyere zone inside the hearth is heated to free the interstitial congestion between coke particles by lancing through taphole. Accompanying Figure 2 shows the arrangement for heating of hearth bed with oxygen blowing from oxygen headers(2) and connecting metallic pipes(3) through tuyeres and taphole to enhance the permeability of the bed.

After that large size handpicked coke in the size range of 80 – 100 mm mixed with fluorspar (10 – 80 kg per ton of coke) is charged to fill the cavity formed during heating of coke bed and raking out. The large size cokes are filled there to ensure that there is enough voidage for the initial melts to trickle down towards taphole when the furnace restarts. The fluorspar ensures low viscosity of the initial formed slag. Furnace is then filled with special burden recipe/ composition of blowing in through these tuyeres above the taphole with which the connectivity with the taphole has been established. It should be done without much delay, thus ensuring smooth liquid drainage. Further opening of other tuyeres can be planned depending on working condition of the furnace i.e. temperature of liquid slag and metal and its drainage from the taphole.

Accompanying Figure 3 shows the special recipe burden to start the furnace post blowdown as per the method according to present invention comprising from top downwards(a)Lean ore with coke rate of 650 Kg/THM, (b)Lean ore with coke rate of 950Kg/THM,(c) Lean ore with coke rate of 1250Kg/THM, (d) DRI, (e) Fluxed coke, (f) Blank Coke,(g) Crushed electrode and (h) Hand picked coke. Post blowdown of the furnace when the furnace is to be restarted, it is first filled up with large size coke (80-100mm) up to the belly region. After which DRI and fluxed coke are charged in the furnace. The advantage with DRI is that it consumes less heat to melt and easily forms initial fluid melt which improves the heat levels of the furnace hearth. The fluxed coke contains coke plus LD slag in it to meet the set slag composition. The advantage of having LD slag is that it contains Fe along with calcined CaO in solution and thus provides the flux ingredient without the requirement of calcinations which is again endothermic reaction. Then CRE (crushed graphite/carbon electrodes) of size 10-25mm and about 20-30 tones, depending on the furnace size is charged in the furnace which contains >98% C which provides instant heat to the furnace. Since there is no ash content in the CRE charged, it does not lead to any kind of slag formation unlike in case of burning of coke to produce heat. Lean burden is charged initially in the furnace with high coke rate. As the level of the burden goes up the coke rate charged in the furnace is brought down from 1250kg/thm initially to 650kg/thm in steps. The liquid metal formed initially in the furnace passes through the voidage created in the dead man zone and owing to its lower melting point won’t solidify and therefore easily tapped from the taphole. Hot metal owing to its good conductivity will transfer heat to the coke in dead man zone and thus maintain its thermal requirement and thus help in keeping the permeability of the dead man zone. On the other hand if conventional method is followed, sole presence of slag may re-solidify and choke the voidages in the dead man zone; it may as well envelope the coke in the dead man zone and thus inhibits its proper combustion resulting in uncertainty in bringing back the furnace to normal.

It is thus possible by way of the present invention to provide a method of restarting of a blown down blast furnace free of blockage near tuyeres and maintaining voidage of deadman zone, ensuring smooth restarting of a blowndown blast furnace wherein connectivity of tuyere and taphole is maintained post shutdown to prepare an easy melt to have proper drainage of liquid into the hearth region. Importantly, a technique is adopted prior to filling of blown down furnace, to establish, confirm and ensure the permeability of deadman for smooth drainage of the initial melts, and simultaneously creating an initial melt which is more lean and fluid to facilitate drainage to taphole with usage of special recipe burden. Thus according to the method of restrating a blowdown blast furnace for smooth start up and faster stabilistaion of the process, the essential steps include measuring the voidage of the settled dead man zone in the hearth by using drill machine accompanied with N2/air purging, then heating up of the coke inside the hearth and in the vicinity of taphole to free the interstitial congestion between coke particles, followed by filling up the hearth up to tuyere level with +80 -100 mm coke blank mixed with fluorspar and startup recipe of CRE and DRI to ensure good voidage for the initial melt and lowered viscosity of the slag formed. This leads to easy drainage of liquid from taphole and thus favouring wide application of the method of restarting blown down blast furnace in iron and steel industry.

We Claim:
1. A method for ensuring connectivity of tuyeres and taphole in a blown down blast furnace by freeing blocked voidages in the hearth comprising:
(i) measuring the voidage of the settled dead man zone in the hearth;
(ii) heating up the coke inside the hearth and in the vicinity of taphole to free interstitial congestion between coke particles; and
(iii) selectively filling up the hearth for desired block free voidage for the initial melt and lowered viscosity of the slag formed with upto the tuyere level with large size +80 -100 mm coke blank mixed with fluorspar.

2. A method as claimed in claim 1 wherein said measuring of the voidage is done involving drill machine accompanied with N2 and/or air purging.

3. A method as claimed in anyone of claims 1 or 2 wherein large size coke is provided to ensure that there is enough voidage for the initial melt to trickle down towards tap hole when the furnace restarts and fluorspar is charged in the range of 10-80 kg per ton of coke.

4. A method as claimed in anyone of claims 1 to 3 wherein the opening of the tuyeres is done selectively depending upon the working conditions of the furnace including temperature of liquid slag and metal and its drainage from the tap hole.

5. A method as claimed in anyone of claims 1 to 4 wherein the initial fill up of large sized coke is done upto belly region after which DRI and fluxed coke are charged in the furnace.

6. A method as claimed in claim 5 wherein said fluxed coke comprises coke plus LD slag to meet set slag composition with said LD slag containing Fe alongwith calcined CaO in solution.

7. A method as claimed in anyone of claims 5 to 6 wherein said selectively filling up the hearth for desired block free voidage for the initial melt and lowered viscosity of the slag formed further comprises introducing after DRI and fluxed coke crushed graphite/carbon electrodes (CRE) of size 10-25 mm containing > 98% C and about 20-30 tonnes depending upon the furnace to provide for the required instant heat to the furnace.

8. A method as claimed in anyone of claims 1 to 7 wherein said selectively filling up the hearth comprising after DRI and coke providing lean burden comprising lean ore with variable coke rate.

9. A method as claimed in claim 8 wherein said lean ore with variable coke rate comprises providing after fluxed coke and DRI, the lean coke burden comprising of lean ore with coke rate of 1250 Kg/THM, lean ore with coke rate of 950 Kg/THM and lean ore with coke rate of 650 Kg/THM.

10. A method as claimed in anyone of claims 1 to 9 wherein the liquid metal formed initially on the furnace passes through the voidage created in the deadman zone and owing to its lower melting point does not solidify and and therefore gets easily tapped from the taphole, the hot metal owing to its good conductivity providing for transfer of heat to the coke in the deadman zone and thus maintain its thermal requirement and keeping permeability of the dead man zone.

Dated this the 20th day of December, 2014

Anjan Sen
Anjan Sen & Associates
(Applicants Agent)

ABSTRACT

TILTLE: A METHOD FOR ENSURING CONNECTIVITY OF TUYERES AND TAPHOLE IN A BLOWN DOWN BLAST FURNACE BY FREEING BLOCKED VOIDAGES IN THE HEARTH.

The present invention relates to a method for ensuring connectivity of tuyeres and taphole in a blown down blast furnace by freeing blocked voidages in the hearth. More particularly, the method ensures that there is enough voidage for the initial melt to trickle down towards tap hole when the furnace restarts. After ensuring the dead man voidage is good, the coke present near the taphole and the tuyere zone inside the hearth is heated to free the interstitial congestion between coke particles by lancing through taphole. Then selectively filling up the hearth for desired block free voidage for the initial melt and lowered viscosity of the slag formed upto the tuyere level, with large size +80 -100 mm coke blank mixed with fluorspar, DRI and fluxed coke crushed graphite/carbon electrodes (CRE), and lean burden comprising lean ore with variable coke rate.