CLIAMS:We Claim:

1. A process for blowing down of a blast furnace below tuyere level comprising

controlling the top gas temperature by controlled and selective segment wise spraying of water avoiding chances of water droplets landing on the burden and thereby controlling hydrogen generation ;
diluting the concentration of hydrogen in the exit gas and maintaining hydrogen level below LEL value; and
carrying out blow down at normal blast.

2. A process as claimed in claim 1 wherein dead man is completely consumed or eliminated.

3. A process as claimed in anyone of claims 1 or 2 wherein said controlled and selective segment wise spraying of water comprises spraying through multiple nozzle water injection means during blow down of blast furnace whereby individual segment with higher exit temperature are controlled without disturbing the other segments.

4. A process as claimed in anyone of claims 1 or 2 wherein the diluting of the concentration of hydrogen in the exit gas is carried out by nitrogen purging at various stack level as well as by coal injection lances across the length of the furnace.

5. A process as claimed in anyone of claims 1 to 4 wherein pressure cycle at the last stages of blowing down process consumes coke in the dead man and tuyere area.

6. A process as claimed in anyone of claims 1 to 5wherein the burden level is brought down to a level of about 200-1200 mm below the tuyere level.

7. A process as claimed in anyone of claims 1 to 6 wherein the blast furnace exit gas produced during blow down having similar composition and less moisture is utilized except for the last 2-3 hours of blow down.

8. A method as claimed in anyone of claims 1 to 7 wherein water mist is formed in such a way as to cover the complete surface area of the throat region of the furnace.

9. A system to carry out the process for blowing down of a blast furnace below tuyere level with normal blowing rate as claimed in anyone of claims 1 to 8 comprising
means for controlled and selective segment wise spraying of water avoiding chances of water droplets landing on the burden and thereby controlling hydrogen generation ;
means for nitrogen purging for diluting the concentration of hydrogen in the exit gas and maintaining hydrogen level below LEL value; and
means for carrying out blow down at normal blast.

10. A system as claimed in anyone of claims 9 wherein said means for controlled and selective segment wise spraying of water comprises spray means involving spray nozzles, wherein in said spray arrangement of the nozzles – comprises combinations of 1000 and 600 spray angles preferably four are at 100° and four are at 60° arranged alternately with solenoid valve based individual control and said spray nozzles cover the entire top cone area with water in the furnace.

Dated this the 20th day of February, 2014
Anjan Sen
Of Anjan Sen & Associates
(Applicants Agent)

,TagSPECI:FIELD OF THE INVENTION
The present invention relates to a method for blowdown of blast furnace. More particularly, the present invention is directed to a process for blowing down of a blast furnace below tuyere level with normal blowing rate. This also results in greatly reducing the blowing down time. Also by subsequent pressure cycles of blowing at the end, the dead man is completely consumed or eliminated. This elimination of dead man leads to time saving as there is no need to rake out coke through the tuyeres. Also this process intends to achieve the target by completely eradicating the chances of any kind of explosion as such.

BACKGROUND OF THE INVENTION

A blast furnace is lined with a refractory material, which provides insulation and structural support. The refractory material needs to be replaced every few years.
Blast furnaces are used to turn iron ore into pig iron by combining the ore with charcoal and limestone at extremely high temperatures. The pig iron can then be used to make cast iron or steel. Periodically, blast furnaces must be shut down, or blown out, to allow for cleaning and repairs. It is extremely dangerous to shut down a blast furnace, not just because of the intense heat of the furnace but also because of the presence of the LP gas in the furnace without the other elements to help control a possible explosion.

Another issue is that lower portions of blast furnaces contain "deadman" coke of which permeability for gas and liquid affect the performance and life time of the furnaces significantly. Especially, the deadman coke determines the flow of gas and hot metal in the lower portion of a blast furnace, and deterioration of the gas permeability increases gas flow along the furnace wall, resulting in poor furnace conditions.

In the case of conventional method of blowing down of the blast furnace, the raw material inside the furnace is brought down up to the tuyere level. The area above the tuyere zone is kept clean in case of any maintenance job needs to be carried out. The charging into the furnace is stopped and the remaining material inside the furnace is consumed to bring down the burden level. The blowing rate is cut down to as much as 40-50% of normal blast while controlling the top gas temperature and H2 in the exit gases in order to avoid any explosion (the LEL and UEL value of H2 is 4% and 76%). This whole process of blowing down of the furnace with a lower blowing rate up to tuyeres level takes about 16-24 hrs.
In the above case the time duration for blowing down is very high. Also exit gas temperature is controlled by spraying water throughout the top layer cross section of the raw material without any control over any particular segment, lest there the temperature shoots up as compared to other section. Excessive water spraying across all zones to control the rise in temperature results in an increase in H2 concentration in the exit gas, leading to higher chances of explosion. Therefore, the process has certain limitation in case of any deviation in the process parameters. Also in this process the dead man remains as it is and therefore it requires raking out of coke through the tuyeres which just prolongs the blowing down time for the furnace. The BF gases produced during the process have to be flared and therefore remain unutilized due to high variation in composition along with high moisture content. The hot metal chemistry also gets highly deviated from the normal values. Since this process is carried out at 40-50% blowing rate, excess coke is required to compensate for the heat loss due to cut in blast volume during the blow down of the furnace. Even after complete blow down, at times the material level in the furnace remains above the tuyeres. In this case a lot of effort is required to ignite the burden top which consumes time.

There has been thus a need in the existing art to developing a process for blow down of a blast furnace below tuyere level with normal blowing rate, substantially reducing the blowing down time, also consuming or eliminating the deadman by subsequent pressure cycles of blowing at the end, and avoid chances of explosion.

OBJECTS OF THE INVENTION

The basic object of the present invention is thus directed to provide a process for blowing down of a blast furnace below tuyere level with normal blowing rate, substantially reducing the blowdown time.

A further object of the present invention is directed to provide a process for blowing down of a blast furnace below tuyere level with normal blowing rate wherein pressure cycles at the last stages of blowing down process consumes coke in the dead man and tuyere area.

A still further object of the present invention is directed to provide a process for blowing down of a blast furnace below tuyere level with normal blowing rate wherein elimination of dead man leads to time saving without needing to rake out coke through the tuyeres.

A still further object of the present invention is directed to provide a process for blowing down of a blast furnace below tuyere level with normal blowing rate wherein chances of any kind of explosion is completely eradicated.

A still further object of the present invention is directed to provide a process for blowing down of a blast furnace below tuyere level with normal blowing rate wherein any chance of H2 generation due to water droplets landing on the burden is minimized.

Yet another object of the present invention is directed to provide a process for blowing down of a blast furnace below tuyere level with normal blowing rate wherein nitrogen purging at various stack level as well as by coal injection lances results in diluting the concentration of the H2 in exit gases, favoring to keep the hydrogen level in check and below the LEL value.

A further object of the present invention is directed to provide a process for blowing down of a blast furnace below tuyere level with normal blowing rate wherein with shorter dead man residual there is easy access to the tuyere zone repairs.

A further object of the present invention is directed to provide a process for blowing down of a blast furnace below tuyere level with normal blowing rate wherein no excess coke is required to compensate for the heat loss as in case of conventional cut in blast volume during the blow down of the furnace.

A still further object of the present invention is directed to provide a process for blowing down of a blast furnace below tuyere level with normal blowing rate wherein segment wise control of top gas temperature is implemented through multiple nozzle water injection during blow down of blast furnace.

SUMMARY OF THE INVENTION

The basic aspect of the present invention is directed to a process for blowing down of a blast furnace below tuyere level comprising

controlling the top gas temperature by controlled and selective segment wise spraying of water avoiding chances of water droplets landing on the burden and thereby controlling hydrogen generation ;

diluting the concentration of hydrogen in the exit gas and maintaining hydrogen level below LEL value; and

carrying out blow down at normal blast.

A further aspect of the present invention is directed to said process wherein dead man is completely consumed or eliminated.

A still further aspect of the present invention is directed to said process wherein said controlled and selective segment wise spraying of water comprises spraying through multiple nozzle water injection means during blow down of blast furnace whereby individual segment with higher exit temperature are controlled without disturbing the other segments.

A still further aspect of the present invention is directed to said process wherein the diluting of the concentration of hydrogen in the exit gas is carried out by nitrogen purging at various stack level as well as by coal injection lances across the length of the furnace.

Yet another aspect of the present invention is directed to said process wherein pressure cycle at the last stages of blowing down process consumes coke in the dead man and tuyere area.

A further aspect of the present invention is directed to said process wherein the burden level is brought down to a level of about 200-1200 mm below the tuyer level.

A still further aspect of the present invention is directed to said process wherein the blast furnace exit gas produced during blow down having similar composition and less moisture is utilized except for the last 2-3 hours of blow down.

A still further aspect of the present invention is directed to said process wherein water mist is formed in such a way as to cover the complete surface area of the throat region of the furnace.

Yet another aspect of the present invention is directed to a system to carry out the process for blowing down of a blast furnace below tuyere level with normal blowing rate as described above comprising
means for controlled and selective segment wise spraying of water avoiding chances of water droplets landing on the burden and thereby controlling hydrogen generation ;

means for nitrogen purging for diluting the concentration of hydrogen in the exit gas and maintaining hydrogen level below LEL value; and

means for carrying out blow down at normal blast.

According to a further aspect of the invention directed to said system which comprises PLC operated flow control valve.

A further aspect of the present invention is directed to said system wherein said means for controlled and selective segment wise spraying of water comprises spray means involving spray nozzles with solenoid valve based individual control and said spray nozzles cover the entire top cone area with water in the furnace.

A still further aspect of the present invention is directed to said system wherein in said spray arrangement of the nozzles – comprises combinations of 1000 and 600 spray angles preferably four are at 100° and four are at 60° arranged alternately.

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 DRAWINGS

Figure 1: shows the top spray Schematic arrangement fitted with special spray nozzles with segment wise individual control of water through each solenoid operated valve.

Figure 2: shows the spray nozzle arrangement.

Figure 3 (a): shows the arrangement of the nozzles - four at 100° and four at 60° arranged alternately.

Fig. 3 (b) shows the top view of the cloud of water mist formed by the arrangement of the nozzles in such a way as to cover the complete surface area of the throat region of the furnace.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS

The present invention relates to a method for blowdown of blast furnace below tuyere level with normal blowing rate, substantially reducing the blowing down time, completely consuming the coke in dead man zone by subsequent pressure cycles of blowing at the end, avoiding any chance of explosion.

Accompanying Figure 1 shows schematically the arrangement of top spray water spray header and nozzles fitted with special spray nozzles with segment wise individual control of water through each solenoid operated valve(1). By using control valves(5) for each segment in the top spray arrangement fitted with special spray nozzles(6), there is a better control over the top gas temperature. Total 8 spray nozzles(6) are there to cover entire top cone area with water in the furnace. The flow of the water is controlled by isolation valve(3) and flow control valve(5) through PLC (Programmed Logic Controller) and measured with flow meter(4). The chance of water droplets landing on the burden, which results in H2 generation, is minimum. Accompanying Figure 2 shows the spray nozzle(6) mounting arrangement with respect to top core shell(7) of furnace. Accompanying Figure 3 (a) shows the arrangement of the nozzles(6) with selective orientation wherein four at 100° and four at 60° spray angles arranged alternately and Figure 3 (b) shows the top view of the water mist formed by the arrangement of the nozzles(6) in such a way as to cover the complete surface area of the throat region of the furnace.

Also, nitrogen purging at various stack level as well as by coal injection lances results in diluting the concentration of the H2 in exit gases. This helps in keeping the hydrogen level in check and below the LEL value. The blow down is carried out at normal blast therefore the speed of blow down is fast and takes lesser time. Pressure cycle at the last stages of blowing down process consumes coke in the dead man and tuyere area. This leads to bringing down the burden level about 200 – 1200 mm below the tuyere level. This pressure cycle method is so efficient that the whole dead man coke can be consumed if carried for a long period.

Blowing down period is reduced along with improvement in safety aspects. The control over the hydrogen generation by water gas reaction helps in minimizing any chances of explosion; also there is better control over the top gas temperature. Extra coke consumption for blowing down is minimum since the hot blast volume is kept normal which provides for the heat requirement of the ore burden in the furnace. The certainty to achieve the target level in blow down is higher. No coke raking is required as the dead man is consumed in last stages of blowing down of the furnace and therefore the down time is reduced. With shorter dead man residual there is easy access to the tuyere zone repairs. It also minimizes the salamander liquid in the hearth level due to pressurizing drainage of liquid in last tapping. With a control over the top gas temperature and a control over the water gas reaction the generation of hydrogen is always kept under control because of which the exit gas composition remains almost same throughout the whole process of blow down. Therefore the BF exit gas produced during blow down owing to similar composition and less moisture can be utilized except for in the last 2-3 hrs of the blow down.

There is segment wise control of top gas temperature through multiple nozzle water injection during blow down of blast furnace. This helps to regulate the water flow in various segments independent of each other and therefore an individual segment with higher exit temperature can be taken care of without disturbing the other segments.

Nitrogen purging through coal injection lances in tuyeres and across the length of furnace to control in the event of interruption in blow down process. This arrangement helps in controlling the concentration of hazardous gases such as H2 by diluting them.

Pressure cycles at the end of the process to ensure shorter dead man. When the burden material in the furnace has reached up to the tuyere level, by blowing sporadically the dead man is consumed.

It is thus possible by way of the present invention to provide a process for blowing down of a blast furnace below tuyere level with normal blowing rate so as to greatly reducing the blowing down time. Also by subsequent pressure cycles of blowing at the end, the dead man is completely consumed or eliminated, leading to time saving as there is no need to rake out coke through the tuyeres. Also this process is safe by completely eradicating the chances of any kind of explosion as such. With a control over the top gas temperature and a control over the water gas reaction the generation of hydrogen is always kept under control because of which the exit gas composition remains almost same throughout the whole process of blow down. Therefore the BF exit gas produced during blow down owing to similar composition and less moisture can be utilized except for in the last 2-3 hrs of the blow down. With shorter dead man residual there is easy access to the tuyere zone repairs. The blowdown process according to the present invention is thus suitable for industrial application with significant economic advantage with reduced downtime of furnace, easy, safe and faster repair/maintenance, ensuring improved productivity.

We Claim:

1. A process for blowing down of a blast furnace below tuyere level comprising

controlling the top gas temperature by controlled and selective segment wise spraying of water avoiding chances of water droplets landing on the burden and thereby controlling hydrogen generation ;
diluting the concentration of hydrogen in the exit gas and maintaining hydrogen level below LEL value; and
carrying out blow down at normal blast.

2. A process as claimed in claim 1 wherein dead man is completely consumed or eliminated.

3. A process as claimed in anyone of claims 1 or 2 wherein said controlled and selective segment wise spraying of water comprises spraying through multiple nozzle water injection means during blow down of blast furnace whereby individual segment with higher exit temperature are controlled without disturbing the other segments.

4. A process as claimed in anyone of claims 1 or 2 wherein the diluting of the concentration of hydrogen in the exit gas is carried out by nitrogen purging at various stack level as well as by coal injection lances across the length of the furnace.

5. A process as claimed in anyone of claims 1 to 4 wherein pressure cycle at the last stages of blowing down process consumes coke in the dead man and tuyere area.

6. A process as claimed in anyone of claims 1 to 5wherein the burden level is brought down to a level of about 200-1200 mm below the tuyere level.

7. A process as claimed in anyone of claims 1 to 6 wherein the blast furnace exit gas produced during blow down having similar composition and less moisture is utilized except for the last 2-3 hours of blow down.

8. A method as claimed in anyone of claims 1 to 7 wherein water mist is formed in such a way as to cover the complete surface area of the throat region of the furnace.

9. A system to carry out the process for blowing down of a blast furnace below tuyere level with normal blowing rate as claimed in anyone of claims 1 to 8 comprising
means for controlled and selective segment wise spraying of water avoiding chances of water droplets landing on the burden and thereby controlling hydrogen generation ;
means for nitrogen purging for diluting the concentration of hydrogen in the exit gas and maintaining hydrogen level below LEL value; and
means for carrying out blow down at normal blast.

10. A system as claimed in anyone of claims 9 wherein said means for controlled and selective segment wise spraying of water comprises spray means involving spray nozzles, wherein in said spray arrangement of the nozzles – comprises combinations of 1000 and 600 spray angles preferably four are at 100° and four are at 60° arranged alternately with solenoid valve based individual control and said spray nozzles cover the entire top cone area with water in the furnace.

Dated this the 20th day of February, 2014
Anjan Sen
Of Anjan Sen & Associates
(Applicants Agent)

ABSTRACT

TITLE: PROCEDURE FOR BLOWING DOWN OF BLAST FURNACE BELOW TUYERE LEVEL WITH NORMAL BLOWING RATE.

The present invention relates to a method for blowdown of blast furnace. More particularly, the present invention is directed to a process for blowing down of a blast furnace below tuyere level with normal blowing rate. This also results in greatly reducing the blowing down time. The process controls the top gas temperature by controlled and selective segment wise spraying of water avoiding chances of water droplets landing on the burden and thereby controlling hydrogen generation. Moreover, involves nitrogen purging for diluting the concentration of hydrogen in the exit gas and maintaining hydrogen level below LEL value. Also by subsequent pressure cycles of blowing at the end, the dead man is completely consumed or eliminated. This elimination of dead man leads to time saving as there is no need to rake out coke through the tuyeres. Also this process intends to achieve the target by completely eradicating the chances of any kind of explosion as such.