CLIAMS:We Claim:

1. A process for integrated leak test in a blown down non empty blast furnace comprising

(a) capping of the deadman by gunning refractory material for preventing gases to come in contact with air during test;

(b) allowing cold blast from blowers to pass through the furnace, by passing the stoves, and finally exit through flare-stack;

(c) maintaining furnace top pressure and various network pressure alike to the normal operation conditions;

(d) providing nitrogen curtaining just above coke in dead man to dilute the percentage of CO gas inside furnace and avoid the LEL and UEL(lower and upper explosive limits) range during the process;

(e) detecting any leakage at any location of furnace causing loud hiss sound for any major leakage followed by slight pressure drop in that region and/or involving use of soap solution at the flanges and edges for minor leakage, in the area of maintenance ;

(f) sealing the leak so detected, thus making it leak proof; and

(g) optionally,in case any leak is detected and sealed in step (f) above repeating said steps (a) to (f) till all leak points are detected and rectified and sealed satisfactorily.

2. A process for integrated leak test in a blown down non empty blast furnace as claimed in claim 1 comprising

said step of Nitrogen curtaining comprising:
purging nitrogen involving coal injection lance and purging nozzles in the bosh belly and stack to dilute the percentage of CO gas inside furnace; and

providing a nitrogen curtain just above the coke in dead man involving coal injection lance to dilute the concentration of CO gases emitted from coke bed to avoid the LEL and UEL(lower and upper explosive limits) range during the process.

3. A process as claimed in anyone of claims 1 or 2 , wherein said cold blast is made to pass from the blower to the mixer valve, by-passing the stoves completely and from there to inside the blast furnace through tuyeres and finally made to exit through flare stack after coming out of the furnace.

4. A process as claimed in claim 1 to 3 wherein furnace top pressure and network pressure controls are tuned to the normal operating condition and are measured by pressure transmitters (PT).

5. A process as claimed in anyone of claims 1 to 4, wherein initially the blast pressure is kept low and is slowly brought up to the normal blast pressure.

6. A process as claimed in anyone of claims 1 to 5, wherein cold blast is passed through tuyeres and inside the furnace in such a way that the percentage value of CO is never in the 12.5% – 74% range(lower and upper explosive limits) such as to avoid explosion during testing.

7. A process as claimed in anyone of claims 1 to 6, comprising opening some peep holes to allow sufficient air to pass inside the furnace (a) at the start of the test when cold blast is fed directly from the blower to the furnace, by-passing the stoves, having deficiency of air/oxygen in the beginning which may lead to formation of CO gases and again (b) at the end of the test when cold blast is being cut down, to allow sufficient air to pass inside the furnace to prevent the formation of CO.

8. A process as claimed in anyone of claims 1 to 7, wherein said capping of the deadman zone is done with 45% Al2O3 castable material of 100 mm thick.

9. A process as claimed in claims 1 to 8, comprising placing chains under the capped material which spreads from center of the furnace over deadman to a few numbers of tuyeres to facilitate easy removal of castable after the leak test is completed by pulling out the chain.

Dated this the 7th day of January, 2014
Anjan Sen
Of Anjan Sen & Associates
(Applicants Agent)
,TagSPECI:FIELD OF THE INVENTION

The present invention relates to a method for integrated leak test in a blast furnace. More particularly, the present invention is directed to a method for integrated leak test with cold blast in blow down non empty blast furnace, where coke in the dead man and hearth continues emitting gases to determine the various leakages present in the furnace and its peripherals at different locations so that they can be made leak proof as a prerequisite step prior to the blowing in of the furnace. The method for integrated leak test using cold blast in blow down blast furnace according to the present invention thus helps to avoid disruption during the blow-in of the furnace on account of leakages post blow down maintenance. Importantly, the present leak test process according to the invention is made safe and reliable by capping of the deadman is done by gunning refractory castable over the incandescent coke below the tuyere level to prevent the CO gas produced from coming in contact with air and also nitrogen purging is done just above the dead man to dilute the gases coming out of dead man coke and act as a curtain against them so as to avoid possibility of any explosion. This ensures trouble free and safe blow-in by detecting any leakage and sealing it prior to start-up.

BACKGROUND OF THE INVENTION

Integrated leak test in the blast furnace in general is carried out at the start of any new furnace, where the furnace is completely empty i.e. devoid of any raw material. The integrated leak test with cold blast is carried out to determine the various leakages present in the furnace and its peripherals at different locations so that they can be made leak proof. Any kind of leakage is not only detrimental for the functioning of the furnace while startup, but it can prove to be very hazardous for the area around the furnace. Once the furnace starts, any leak detected later on is not only difficult to mend but also time consuming. In worse case scenario it may even require to stop the plant several times to attend the leakage during the course of ramp up of the furnace. Therefore, integrated leak test is a prerequisite step prior to the starting of the furnace.

In the existing leak test procedure, the cold blast from the blowers is passed through cold blast mixing line; from there it is taken to the bustle main which surrounds the blast furnace circumferentially. From the bustle pipe to the furnace the cold blast enters through the various tuyeres encircling the furnace. Inside the empty furnace the cold blast moves upwards to the uptakes and then to dust catcher followed by gas cleaning plant. Finally it exits from the flare stack. Furnace top pressure and various network pressure is maintained alike to the normal operation conditions. The whole set up is akin to passing gases through an empty tube in order to detect any leakages. In case of any major leakage a loud hiss sound is generated followed by slight pressure drop in that region. As for minor leakage, soap solution at the flanges and edges is used in the area of maintenance. Once the leak area is localized, it is attended and sealed, thus making it leak proof.

Maintenance jobs are carried out in the furnace from time to time for the general upkeep of the furnace. The furnace is taken for a blow down prior to starting the maintenance job in the furnace. In case of blow down of the furnace, the charges inside the furnace are only up to or just below the tuyere zone. In this case the furnace contains only slow burning coke up to tuyere level. After the blow down on many occasions the furnace is opened at various locations from blower to gas cleaning plant and critical jobs like replacement of top charging gear box is carried out. Post maintenance the furnace blow-in starts without conducting any leak test.

During the maintenance of the furnace at various locations in the furnace there is a possibility of leakage formation especially at the weld edges and flanges of the repaired or replaced equipments. This not only leads to leakages of gases through it but also disturbs the pressure dynamics of the furnace during ramping-up stage. Therefore, any leakage found will lead to unwanted stoppages which will retard the stabilization process of the furnace. Therefore ensuring leak proof furnace becomes a pre requisite before starting the furnace post maintenance. Conventionally no one does integrated leak test post maintenance, as the furnace in blow down condition contains incandescent coke at the tuyere level.

There has been thus a need in the art of blast furnace operation and maintenance to develop a method for integrated leak test of non empty blow down blast furnace in a safe and reliable manner wherein coke in the dead man and hearth continues emitting gases, ensuring trouble free and safe blow-in post blow down maintenance by detecting any leakage present in the furnace and its peripherals at different locations and sealing it prior to start-up.

OBJECTS OF THE INVENTION

The basic object of the present invention is thus directed to a method for integrated leak test with cold blast in blow down non empty blast furnace, where coke in the dead man and hearth continues emitting gases, to detect and seal any leak present prior to blowing in a safe and reliable manner.

A further object of the present invention is directed to a method for integrated leak test with cold blast in blow down non empty blast furnace to avoid disruption during the blow-in of the furnace on account of leakages post blow down maintenance.

A still further object of the present invention is directed to a method for integrated leak test with cold blast in blow down non empty blast furnace which ensures trouble free and safe blow-in by detecting any leakage prior to start-up.

A still further object of the present invention is directed to a method for integrated leak test with cold blast in blow down non empty blast furnace wherein cold blast from blowers is made to pass through the furnace maintaining normal operating pressure for leak detection and finally made to exit through flare-stack.

A still further object of the present invention is directed to a method for integrated leak test with cold blast in blow down non empty blast furnace wherein capping of the deadman is done by gunning refractory castable material that helps in preventing the gases from coming in contact with air during test.

A still further object of the present invention is directed to a method for integrated leak test with cold blast in blow down non empty blast furnace wherein peep holes are opened at the start and end of the cold blast to allow sufficient air to pass into the furnace to prevent formation of CO gas.

A still further object of the present invention is directed to a method for integrated leak test with cold blast in blow down non empty blast furnace wherein cold blast is passed through tuyeres and inside the furnace in such a way that the percentage value of CO is never in the 12.5% – 74% range (which is the LEL and UEL respectively) to avoid explosion.

A still further object of the present invention is directed to a method for integrated leak test with cold blast in blow down non empty blast furnace wherein for desired dilution of the CO gas concentration, nitrogen purging with the help of coal injection lance and purging nozzles in the bosh belly and stack is done.

A still further object of the present invention is directed to a method for integrated leak test with cold blast in blow down non empty blast furnace wherein nitrogen purging is done just above the dead man to dilute the gases coming out of dead man coke and act as a curtain against them.

SUMMARY OF THE INVENTION

The basic aspect of the present invention is directed to a process for integrated leak test in a blown down non empty blast furnace comprising

(a) capping of the deadman by gunning refractory material for preventing gases to come in contact with air during test;

(b) allowing cold blast from blowers to pass through the furnace, by passing the stoves, and finally exit through flare-stack;

(c) maintaining furnace top pressure and various network pressure alike to the normal operation conditions;

(d) providing nitrogen curtaining just above coke in dead man to dilute the percentage of CO gas inside furnace and avoid the LEL and UEL(lower and upper explosive limits) range during the process;

(e) detecting any leakage at any location of furnace causing loud hiss sound for any major leakage followed by slight pressure drop in that region and/or involving use of soap solution at the flanges and edges for minor leakage, in the area of maintenance ;

(f) sealing the leak so detected, thus making it leak proof; and

(g) optionally,in case any leak is detected and sealed in step (f) above repeating said steps (a) to (f) till all leak points are detected and rectified and sealed satisfactorily.

A further aspect of the present invention is directed to said process for integrated leak test in a blown down non empty blast furnace comprising

said step of Notrogen curtaining comprising:
purging nitrogen involving coal injection lance and purging nozzles in the bosh belly and stack to dilute the percentage of CO gas inside furnace; and

providing a nitrogen curtain just above the coke in dead man involving coal injection lance to dilute the concentration of CO gases emitted from coke bed to avoid the LEL and UEL(lower and upper explosive limits) range during the process.

A still further aspect of the present invention is directed to said process wherein said cold blast is made to pass from the blower to the mixer valve, by-passing the stoves completely and from there to inside the blast furnace through tuyeres and finally made to exit through flare stack after coming out of the furnace.

A still further aspect said process wherein furnace top pressure and network pressure controls are tuned to the normal operating condition and are measured by pressure transmitters (PT).

Yet another aspect of the present invention is directed to said process wherein initially the blast pressure is kept low and is slowly brought up to the normal blast pressure.

A further aspect of the present invention is directed to said process wherein cold blast is passed through tuyeres and inside the furnace in such a way that the percentage value of CO is never in the 12.5% – 74% range(lower and upper explosive limits) such as to avoid explosion during testing.

A still further aspect said process comprising opening some peep holes to allow sufficient air to pass inside the furnace (a) at the start of the test when cold blast is fed directly from the blower to the furnace, by-passing the stoves, having deficiency of air/oxygen in the beginning which may lead to formation of CO gases and again (b) at the end of the test when cold blast is being cut down, to allow sufficient air to pass inside the furnace to prevent the formation of CO.

Yet another aspect of the present invention is directed to said process wherein said capping of the deadman zone is done with 45% Al2O3 castable material of 100 mm thick.

A still further aspect said process comprising placing chains under the capped material which spreads from center of the furnace over deadman to a few numbers of tuyeres to facilitate easy removal of castable after the leak test is completed by pulling out the chain.

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: is the schematic arrangement to perform the integrated leaktest according to the present invention showing the cold blast line as indicated by dotted lines that passes from the blower through the mixer valve, by-passing the stoves completely, to the tuyeres and then inside the blast furnace and lastly released through the flare stack.

Figure 2: shows the means for nitrogen purging with the help of coal injection(PCI) lance and purging nozzles in the bosh, belly and stack zone for diluting the concentration of CO gas during performing the integrated leak test of blow down blast furnace according to the present invention.

Figure 3: shows the schematic view of capping of the deadman zone by 45% Al2O3 castable material of 100 mm thickness prior to performing the integrated leak test according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING FIGURES

The present invention is directed to a method of integrated leak test with cold blast in a blow down furnace and more particularly to a method for integrated leak test of blow down non empty blast furnace carried out using cold blast air, where coke in the dead man and hearth continues emitting gases, directed to avoid disruption during the blow-in of the furnace on account of leakages post blow down maintenance. This ensures trouble free and safe blow-in by detecting any leakage prior to start-up.

In this test, cold blast from blowers is made to pass through the furnace and finally made to exit through flare-stack. Furnace top pressure and network pressure controls are tuned to the normal operating condition. Though initially the blast pressure is kept low, it is slowly brought up to the normal blast pressure. This test is repeated till all leak points are detected and rectified up to the satisfactory limits.

Accompanying Figure 1 shows the schematic arrangement to perform the integrated leak test of blast furnace using cold blast. It can be seen in Figure 1 that the cold blast is indicated by dotted lines which passes from the blower(1) to the mixer valve(5), by-passing the stoves(S1, S2, S3) completely. From there it passes to the tuyeres(7) and then inside the blast furnace. After coming out of the furnace it again follows the path air passage (4) as indicated by dotted lines to finally exit through flare stack(12). In between all pressures are maintained as in normal conditions and are measured by pressure transmitters (11).

Thus according to the present invention, the method of integrated leak test is applied to a furnace which is not completely empty but contains coke (dead man) up to the tuyere level. The burning coke produces small amount of CO and CO2 gas inside the furnace. The coke in the dead man zone(8) generally produces CO2 in the presence of sufficient air. Capping(9) of the deadman is done by gunning the refractory material. This helps in preventing the gases from coming in contact with air during test. Accompanying Figure 3 shows the schematic view of capping(9) of the deadman zone(8) by 45% Al2O3 castable material of 100 mm thickness prior to performing the integrated leak test according to the present invention.

At the start of the test when cold blast is fed directly from the blower to the furnace, by-passing the stoves, there is deficiency of air/ oxygen in the beginning and it may lead to formation of CO gases. To prevent the formation of CO the peep holes(10) are opened to allow sufficient air to pass into the furnace. Slowly the blast volume along with blast pressure is increased and finally all peep holes(10) are closed down. Similarly at the end of the test when cold blast is being cut down, we again open some peep holes(10) to allow sufficient air inside to prevent the formation of CO. CO being flammable gas has LEL & UEL (lower & upper explosive limit) value of 12.5% and 74% which on coming in contact with oxygen in the range can lead to explosion. The cold blast is passed through bustle main(6), down leg(14), blow pipe(13) and tuyeres(7) to inside the furnace in such a way that the percentage value of CO is never in the 12.5% – 74% range and for further dilution nitrogen purging with the help of coal injection lance(15) and purging nozzles in the bosh belly and stack is done. Accompanying Figure 2 shows the means for nitrogen purging with the help of coal injection(PCI) lance(15) and purging nozzles in the bosh, belly and stack zone across the length of the furnace for diluting the concentration of CO gas during performing the integrated leak test of blow down blast furnace according to the present invention. Also since the dead man zone is lowered below the tuyeres zone when cold blast is passed through, it does not come in contact with dead man as happens in case of normal running furnace. The nitrogen purging is done just above the dead man to dilute the gases coming out of dead man coke and act as a curtain against them.

The present invention thus provides a unique and safe methodology in which cold blast is sent inside the blow down furnace which contains coke up to or just below tuyeres level emitting gases.

A nitrogen curtaining is done just above the coke in dead man with the help of coal injection lance. The coke in dead man continues burning and emitting CO & CO2 gases. The purpose of nitrogen curtaining is to dilute the concentration of gases emitted from coke bed to avoid the LEL and UEL range during the process.

Capping of the deadman is done by gunning the refractory material. This helps in preventing the gases from coming in contact with air during test. Also chains are placed under the capped material which spreads from center of the furnace over deadman to a few numbers of tuyeres. This facilitates the easy removal of castable after the leak test is completed by pulling out the chain.

It is thus possible by way of the present invention to provide for a method of integrated leak test of a non empty blow down blast furnace ensuring leak proof furnace in a reliable manner after long shutdowns and safe blowing-in post blow down maintenance. It ensures trouble free startup and normalizes the furnace within 48 hours. Also it requires less coke during the start-up.
We Claim:

1. A process for integrated leak test in a blown down non empty blast furnace comprising

(a) capping of the deadman by gunning refractory material for preventing gases to come in contact with air during test;

(b) allowing cold blast from blowers to pass through the furnace, by passing the stoves, and finally exit through flare-stack;

(c) maintaining furnace top pressure and various network pressure alike to the normal operation conditions;

(d) providing nitrogen curtaining just above coke in dead man to dilute the percentage of CO gas inside furnace and avoid the LEL and UEL(lower and upper explosive limits) range during the process;

(e) detecting any leakage at any location of furnace causing loud hiss sound for any major leakage followed by slight pressure drop in that region and/or involving use of soap solution at the flanges and edges for minor leakage, in the area of maintenance ;

(f) sealing the leak so detected, thus making it leak proof; and

(g) optionally,in case any leak is detected and sealed in step (f) above repeating said steps (a) to (f) till all leak points are detected and rectified and sealed satisfactorily.

2. A process for integrated leak test in a blown down non empty blast furnace as claimed in claim 1 comprising

said step of Nitrogen curtaining comprising:
purging nitrogen involving coal injection lance and purging nozzles in the bosh belly and stack to dilute the percentage of CO gas inside furnace; and

providing a nitrogen curtain just above the coke in dead man involving coal injection lance to dilute the concentration of CO gases emitted from coke bed to avoid the LEL and UEL(lower and upper explosive limits) range during the process.

3. A process as claimed in anyone of claims 1 or 2 , wherein said cold blast is made to pass from the blower to the mixer valve, by-passing the stoves completely and from there to inside the blast furnace through tuyeres and finally made to exit through flare stack after coming out of the furnace.

4. A process as claimed in claim 1 to 3 wherein furnace top pressure and network pressure controls are tuned to the normal operating condition and are measured by pressure transmitters (PT).

5. A process as claimed in anyone of claims 1 to 4, wherein initially the blast pressure is kept low and is slowly brought up to the normal blast pressure.

6. A process as claimed in anyone of claims 1 to 5, wherein cold blast is passed through tuyeres and inside the furnace in such a way that the percentage value of CO is never in the 12.5% – 74% range(lower and upper explosive limits) such as to avoid explosion during testing.

7. A process as claimed in anyone of claims 1 to 6, comprising opening some peep holes to allow sufficient air to pass inside the furnace (a) at the start of the test when cold blast is fed directly from the blower to the furnace, by-passing the stoves, having deficiency of air/oxygen in the beginning which may lead to formation of CO gases and again (b) at the end of the test when cold blast is being cut down, to allow sufficient air to pass inside the furnace to prevent the formation of CO.

8. A process as claimed in anyone of claims 1 to 7, wherein said capping of the deadman zone is done with 45% Al2O3 castable material of 100 mm thick.

9. A process as claimed in claims 1 to 8, comprising placing chains under the capped material which spreads from center of the furnace over deadman to a few numbers of tuyeres to facilitate easy removal of castable after the leak test is completed by pulling out the chain.

Dated this the 7th day of January, 2014
Anjan Sen
Of Anjan Sen & Associates
(Applicants Agent)

ABSTRACT

TITLE: A PROCESS FOR INTEGRATED LEAK TEST IN A BLOWN DOWN NON EMPTY BLAST FURNACE.

The present invention relates to a method for integrated leak test with cold blast in blow down non empty blast furnace, where coke in the dead man and hearth continues emitting gases so that the furnace can be made leak proof as a prerequisite step prior to the blowing in of the furnace. The method thus helps to avoid disruption during the blow-in of the furnace on account of leakages post blow down maintenance. Importantly, the leak test is performed by capping of the deadman by gunning refractory castable over the incandescent coke below the tuyere level to prevent the CO gas produced from coming in contact with air and also nitrogen purging is done to form a curtain over dead man coke and through coal injection lance and purging nozzles in the bosh belly and stack so as to avoid possibility of any explosion. This ensures trouble free and safe blow-in by detecting any leakage and sealing it prior to start-up.