Description:
FIELD OF THE INVENTION
The present invention relates to co-injection of calcined dolomite (dolo) along with pulverized coal injected through tuyeres in the Blast Furnace, resulting in enhanced combustion characteristics and metallurgical benefits. The present invention particularly relates to a system and method co-injection of calcined dolomite along with pulverized coal into the tuyeres of the Blast Furnace for improving the performance of Blast Furnaces (BF) in steel plants, specifically addressing the challenges associated with combustion efficiency, sulphur content reduction, and slag basicity control.

BACKGROUND OF THE INVENTION
Blast furnace is basically a counter current apparatus, composed of two truncated cones placed base to base and having the main parts like Bosh, Hearth, Belly, Shaft and Throat. The entire furnace is lined with suitable refractory and in addition to refractory lining, there are external water coolers, designed to enhance the life of the furnaces. In the hearth, there is a taphole of suitable dimension and length for the purpose of tapping the hot metal.

Blast Furnace uses highly pure copper (>99.7 %), water-cooled nozzles (tuyeres) as the injection point for high velocity, pre-heated air mixture to the blast furnace for iron oxide reduction. The tuyere is the device that allows heated air to be blown into the combustion raceway of the blast furnace.

Pulverized coal injection (PCI) is a process which involves injecting large volumes of fine coal particles into the raceway of the blast furnace (BF). Pulverized coal is an important auxiliary fuel used in the BF ironmaking. PCI provides auxiliary fuel for partial coke replacement and has proven both economically and environmentally favourable. It can result in substantial improvement in the BF efficiency and thus contribute to the reductions of energy consumption and environmental emissions.

When the pulverized coal is injected into the BF through blowpipes and tuyeres, the coal is a source of heat and a reductant, because of the reactions of devolatilization, gasification, and combustion as well as the formation of unburned char. In the present day environment, pulverized coal is extensively used in BFs as a partial replacement of the metallurgical coke. PCI is a well-established technology today for the production of hot metal (HM) in a BF. The composition and properties of the coal used for injection can influence the operation, stability and productivity of the BF, the quality of the HM, and the composition of the BF gas.

IN 202131013521, of the applicant, describes a system for storage and controlled feeding of flux materials onto existing coal conveyor for mixing, grinding and injection into Blast furnace. In this system, Calcined Dolomite brought from raw material plant is stored in dolomite storage bin and Dolomite from the storage bin is discharged by belt weigh feeder in a desired ratio onto the existing underground inclined coal conveyor carrying the coal. The said application relates to system installation for controlled addition of calcined dolo with PCI coal

Cohesive zone (2) is one of the zones of the blast furnace. The inventors of the present invention found that introduction of fluxes (such as calcined dolomite) through the tuyeres (4), instead of charging them from top, to improve slag formation in the blast furnace decrease the variations in slag basicity and the slag amount in the cohesive zone.

In Fig 1, the basicity of slag formed at different locations in the blast furnace is compared for normal blast furnace operation and operation with injection of fluxes through the tuyeres.

In order to achieve smooth slag formation, the use of injection of flux via tuyeres (4) in the blast furnace results in a decrease in volume of bosh slag and its excessive basicity. Injection of iron ore and different fluxes has been tested in some blast furnaces to adjust the sulphur and silicon content of hot metal. At normal blast furnace operation, the tuyere slag, formed by the ashes of coke & coal combusted in front of tuyeres, is very acidic and has a high viscosity.

The injection of fluxes (calcined dolomite) via the tuyeres (4) makes it possible to increase the basicity of the tuyere slag (7) to an appropriate level and improve its melting properties.

A lower tuyere slag viscosity might improve the drainage of the slag through the voids in the coke bed.

At normal blast furnace operation, with tuyeres that only allow hot air, the tuyere slag, formed by the ashes of coke and coal combusted in front of tuyeres, is very acidic and has a high viscosity.

Viscosity studies of prepared samples of coal ash and coke ash at high temperature viscometer at RDCIS were carried out and results showed higher level of viscosity. The injection of fluxes via the tuyeres (4) makes it possible to increase the basicity of the tuyere slag to an appropriate level and improve its melting properties. Improvement of slag formation in front of the tuyeres can be expected with flux injection. Basic oxygen furnace (BOF) slag, lime and dolomite can decrease the melting point of tuyere slag significantly and narrow softening-melting interval possibly due to lower viscosity at all injection level previously studied through different laboratory studies. This will improve the drainage of slag from the raceway area of the BF. Results also confirmed that presence of BOF slag, burnt lime or dolomite with coal & coke ash lowers the melting temperature significantly. HGI studies of calcined dolo confirmed no problem of grinding calcined dolo with PCI coal.

The inventors of the present invention have surprisingly found that injection of some amount of flux through tuyeres helps in better slag formation inside blast furnace. Co-injection of pulverized coal and calcined dolomite-bearing flux via tuyeres of blast furnace improves metallurgical properties of BF slag with respect to fluidity and desulphurization ability.

In the present invention dolomite is used as a fluxing material. Preferably, calcined dolomite is used as the fluxing agent/material. A fluxhas ability to react with acidic impurities, forming a basic slag that can be easily removed from the steel. This helps to improve the efficiency of the steelmaking process and ensure a high-quality final product.

Need of the present invention:
The goal of the present invention is to develop a process route for better combustibility of Pulverized coal injection (PCI) coal and improve quality of hot metal mainly with respect to sulphur content in hot metal.

OBJECTS OF THE INVENTION
It is an object of the present invention to overcome the shortcomings of the prior art.

It is another object of the present invention to provide a method to achieve smooth slag formation by injection of fluxes via the tuyeres.

It is yet another object of the present invention to provide a method to preparebetter slag formation inside blast furnace.

It is yet another object of the present invention to improve the hot metal quality and PCI rate.

It is further an object of the present invention to increase the basicity of the tuyere slag to an appropriate level and improve its melting properties by injection of fluxes via the tuyeres.

SUMMARY OF THE INVENTION
According to an aspect of the present invention there is provided a method of co-injection of calcined dolomite with Pulverized Coal Injection (PCI) coal in Blast Furnace (BF) comprising granular zone (1), cohesive zone (2), active coke zone (3), tuyeres (4), stagnant coke zone (5), or hearth zone (6);
characterized in that the calcined dolomite with PCI coal is co-injected through tuyeres (4)

According to another aspect of the present invention there is provided a method of co-injection of calcined dolomite with Pulverized Coal Injection (PCI) coal in Blast Furnace (BF) comprising the steps of:
a) receiving calcined dolomite in the blast furnace via highway;
b) loading the calcined dolomite of step (a) to calcined bunker;
c) discharging the calcined dolomite of step (b) to the PCI coal conveyor;
d) grinding the calcined dolomite and PCI of step (c) to 70-80 micron size and discharged to fine coal silo;
e) mixing the mixture of step (d) and transporting it to injection vessel;
f) transporting the mixture of step (e) through pipeline and PCI lance ;
wherein the calcined dolomite with PCI coal is co-injected in to the blast furnace through tuyeres (4).

BRIEF DESCRIPTION OF FIGURES
Fig 1: Slag Basicity across the height of Blast Furnace
Fig 2: Blast Furnace layout scheme of the invented system showing the tuyeres.
Fig 3: Blast Furnace Process: that depicts co-injection of calcined dolomite with PCI through tuyeres
Fig 4: Arrangement of the system according to the present invention

DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to the co-injection of calcined dolomite along with pulverized coal into the tuyeres of the Blast Furnace, resulting in enhanced combustion characteristics and metallurgical benefits. The present invention particularly relates to a system and method co-injection of calcined dolomite along with pulverized coal into the tuyeres of the Blast Furnace for improving the performance of Blast Furnaces (BF) in steel plants, specifically addressing the challenges associated with combustion efficiency, sulphur content reduction, and slag basicity control.

The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary.

Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope of the invention. In addition, descriptions of well-known functions and constructions are omitted for clarity and conciseness.

The invention addresses the need for improved slag formation and metallurgical properties within blast furnaces by introducing calcined dolomite alongside pulverized coal through the tuyeres. This method aims to enhance hot metal quality, particularly with respect to sulphur content. Grindability studies confirm that calcined dolomite can be smoothly ground with PCI coal. Industrial trials demonstrate successful co-injection of calcined dolomite and PCI coal, with no operational issues encountered during mixing, grinding, transportation, or injection into the blast furnace.

In an embodiment of the present invention theenhances blast furnace performance and hot metal quality, offering benefits such as reduced slag and coke rates, improved control over slag basicity, and enhanced blast furnace operability. These improvements extend to sinter quality, with potential downstream benefits in steelmaking processes.

The present invention will not only improve the performance of the blast furnaces but also will improve quality of sinter in an integrated steel plant. Blast furnaces can be operated with lower slag basicity with better control of quality of hot metal. These will lead to lower slag rate and coke rate in blast furnaces.

According to another aspect of the present invention there is provided a method of co-injection of calcined dolomite with Pulverized Coal Injection (PCI) coal in Blast Furnace (BF) comprising the steps of:
a) receiving calcined dolomite in the blast furnace via highway;
b) loading the calcined dolomite of step (a) to calcined bunker;
c) discharging the calcined dolomite of step (b) to the PCI coal conveyor;
d) grinding the calcined dolomite and PCI of step (c) to 70-80 micron size and discharged to fine coal silo;
e) mixing the mixture of step (d) and transporting itd to injection vessel;
f) transporting the mixture of step (e) through pipeline and PCI lance
wherein the calcined dolomite with PCI coal is co-injected in to the blast furnace through tuyeres (4).

According to an embodiment of the present invention there is provide a methodof co-injection of calcined dolomite with Pulverized Coal Injection(PCI) coal in Blast Furnace (BF) comprising the steps of
a. receiving calcined dolo of size 10-50 mm in ground via highway;
b. loading through telpher load the calcined dolo from ground to calcined dolo bunker;
c. discharging calcined dolo to PCI coal conveyor in the desired ratio depending upon rate of calcined dolo injection;
d. grinding both PCI and calcined dolo of step (c) together in 70-80 micron size and discharging in fine coal silo;
e. transporting the mixed materials of step (d) to injection vessel from fine coal silo; and
f. transporting the mixed materials of step (e) to tuyeres of BF via pipeline and PCI lance with nitrogen as carrier.

The co-injection process allows for varied injection rates of calcined dolomite, optimizing the ratio to meet specific furnace requirements. Trial results indicate improved coal combustibility, as evidenced by increased tuyere outlet temperatures and higher Coal Dust Injection system (CDI) rates. Hot metal sulphur content is significantly reduced, even when lowering BF slag basicity.

In an embodiment, the calcined dolomite and PCI of step (c) is grinded to 70-80 micros, preferably 75 micron size and discharged to fine coal silo.

Fig 4: Arrangement of the system according to the present invention : The general arrangement drawing of the system according to present invention.

A calcined dolo bunker with loading from ground with the help of telpher has been installed. The location of motorized R&P gate is below day bin hopper for opening and closing day bin opening for maintenance purpose. It has been provided with hand wheel with chain to operate it manually. A belt weigher has been installed in inclined conveyor which carries PCI coal to raw coal silo to know the rate of PCI coal. The belt weigh scale has been installed which works in automatic dual module and electronic type which is installed in coal conveyor to give a feedback of coal quantity to weigh feeder controller which controls the discharge of calcined dolomite based on set ratio of coal : dolomite. Belt scale is provided with flow rate total quantity etc. Remote flow rate indicators are provided in the Central Control Room (CCR). The capacity of belt weigh feeder is 15TPH having continuous flow characteristics. It has a VFD drive for AC motor to vary the flow rate. The weigh feeder has both remote and local control panel. Remote panel has the provision through the controller to set the desired quantity as set point and the weigh feeder is able to maintain the same within an accuracy of ±0.5%. The weigh feeder controller panel has the following displays: Feed rate indications in tons/hr, totalized display, Set point indicator, annunciations lamps and set point increase/decrease.

In an embodiment of the present invention the calcined dolomite with PCI coal is co-injected through tuyeres in to the cohesive zone of the blast furnace. Conventionally, the fluxes are introduced from the top of the blast furnace.

In an embodiment the mixture of the calcined dolomite and PCI is transported to blast furnace through pipeline and PCI lance with nitrogen as carrier;

During trials conducted in March 2020 and March 2021, calcined dolomite was co-injected at varying rates (3-4 kg/thm and 3-10 kg/thm in BF #1, 5-15 kg/thm in BF #5) alongside pulverized coal. The trials demonstrated an increase in the outlet temperature of tuyeres, validating the improved combustibility of coal.

Furthermore, the Calcined Dolomite Injection (CDI) rates exhibited significant increments, contributing to enhanced metallurgical efficiency.

For improving the performance of BF’s at Bhilai Steel Plant (BSP), a system for grinding and injection of calcined dolomite along with pulverized coal was installed in the BF.

In view of the above, a system for injection of calcined dolomite along with pulverized coal was installed in Coal Dust Preparation Plant -1 of BSP, first time in any Indian blast furnace.

The injection of calcined dolomite may be varied in ratio of calcined dolo:coal as per the requirements; preferably at 4:1 to 12.1.

Installed System can be run as per need without affecting coal grinding.

Grindability studies (HGI) of calcined Dolomite has been done and the study suggests no problem of grinding calcined dolomite with CDI. Initially Co-injection of Calcined dolo@ 3-4 kg/thm together with PCI coal was done without any problem. The system for co-injection of flux together with coal has run smoothly and poses no problem during mixing, grinding, transportation and injection in BF.

In an embodiment calcined dolo is used. Other flux material such as limestone, magnesite may also be used.

Performance Evaluation of the system and co-injection of calcined dolo with PCI coal at envisaged level was carried out. Calcined dolomite was injected @ 3-10 kg/thm and @5-15 kg/thm in BF # 1 and BF #5 respectively.

Increase in outlet temperature of tuyere was observed during trial period confirming better combustibility of coal.

CDI rate of BF # 1 and BF # 5 increased by 8 kg/thm and 16 kg/thm respectively during trial period during co-injection of calcined dolo with PCI coal.

Average Sulphur content of hot metal came down significantly from 0.024 to 0.014% in BF # 5.

Similarly, Sulphur content was within 0.020% even with BF slag basicity was lowered in the range of 0.90-0.95.

There are other benefits like less flux consumption; decrease in blowing time during steel making processes due to significant decrease in sulphur content of HM. Cost of running desulphurization units may also be reduced. Similarly Flux addition may also be decreased during sinter making by maintaining lower MgO in sinter and increase in Fe content of sinter.

Installed System can be run as per need without affecting coal grinding of CDPP-1. Grindability studies (HGI) of calcined Dolomite study suggests no problem of grinding calcined dolomite with CDI.

In the most preferred embodiment of the present invention calcined dolomite is co-injected along with pulverized coal for injection in tuyeres of BF.

Calcined dolomite was injected @ 3-4 kg/thm for around two weeks in the BF of BSP without any problem. The amount of calclined dolo injected in BF # 1 and BF #5.

The system for co-injection of flux together with coal has run smoothly and poses no problem during mixing, grinding, transportation & injection in BF.

Calcined dolomite was injected @ 3 to 15 kg/thm in BF.
Calcined dolomite was injected @ 3-10 kg/thm and @5-15 kg/thm in BF # 1 and BF #5 respectively.

Increase in outlet temperature of tuyere was observed during trial period confirming better combustibility of coal. CDI rate of two BFs increased by 8 kg/thm and 16 kg/thm respectively during trial period. Average Sulphur content of hot metal came down significantly from 0.024 to 0.014% in BF # 5. Similarly, Sulphurcontent was within 0.020% even with BF slag basicity was lowered in the range of 0.90-0.95. Table 1 describes the benefits of the invention.

Base period: No calcined dolo was introduced during the base period.

Trial period: Calcined dolomite with PCI coal co-injected through tuyeres of blast furnace #1 and #5.

Table 1 (below) provides comparative data between base and trial periods, showcasing the benefits of the invention

Table-1: Base and Trial period data with co-injection of calcined dolo with PCI coal

Parameters Unit Base Period Trial Period
HM Production ton/day 2456 2478
BF Productivity t/m3/day 1.65 1.67
Coke Rate kg/thm 491 458
CDI Rate kg/thm 49 65
Fuel Rate kg/thm 557 559
Cal dolo rate kg/thm 0 9
HBT oC 957 958
HM Analysis
HMT oC 1493 1494
Si % 0.84 0.81
S % 0.024 0.014
P % 0.21 0.16
BF Slag Analysis
Al2O3 % 18.3 17.8
MgO % 8.0 9.0
Basicity % 1.0 1.0

One notable result of the co-injection process was the substantial reduction in the average sulphur content of hot metal. BF #5 experienced a decrease from 0.024% to 0.014%, and even with lowered slag basicity (0.90-0.95), sulphur content remained within acceptable limits.

Hot metal (HM) productivity also increased from 2456 ton/day to 2478 ton/day. The Co-injection of the PCI coal with calcined dolo by tuyeres resulted in an increase of 22 tons per day.

To take care of high alumina in Blast Furnaces, BF slag with respect to slag fluidity and melting temperature, higher amount of MgO is being maintained in sinter. Different types of slag are formed at different locations inside the blast furnace. Normally the bosh slag has a higher basicity compare to primary, tuyere and final slag. Very high basic slag has normally high melting point and its viscosity varies significantly in cohesive zone and thus permeability of the furnace gets deteriorated.

Detailed Laboratory Studies and industrial trials in some of abroad blast furnaces has explained that injection of some amount of flux through tuyeres helps in reduction in excessive basic bosh slag formation, decreases bosh slag volume, better tuyere slag formation and keeping basicity of slag formed across the height of the furnace evenly and at proper level with good melting properties.

Slag volume and Slag properties have significant influence on BF operation. Charging low MgO content sinter with co-injection of pulverized coal and MgO-bearing flux via tuyeres of Blast Furnace can improve metallurgical properties of BF slag such as fluidity and desulphurization ability, especially for the slag of high Al2O3 content. Co-injection of the PCI coal with calcined dolo in existing grinding mills can thus be attempted with minimum investment with substantial benefits.

The present invention finds applicability in integrated steel plants seeking to address challenges related to slag fluidity, melting temperature, and sulphur content in hot metal. Co-injection of calcined dolomite with PCI coal results in appreciable enhancement in per-day productivity. Co-injection of calcined dolomite with PCI coal offers a cost-effective solution with substantial benefits, requiring minimal investment for retrofitting existing grinding mills.

It is to be understood that the present invention is susceptible to modifications, changes and adaptations by those skilled in the art. Such modifications, changes, adaptations are intended to be within the scope of the present invention.
, Claims:
1. A method of co-injection of calcined dolomite with Pulverized Coal Injection (PCI) coal in Blast Furnace (BF) comprising granular zone (1), cohesive zone (2), active coke zone (3), tuyeres (4), stagnant coke zone (5), or hearth zone (6);
characterized in that the calcined dolomite with PCI coal is co-injected through tuyeres (4).

2. A method of co-injection of calcined dolomite with Pulverized Coal Injection (PCI) coal in Blast Furnace (BF) comprising the steps of :
a) receiving calcined dolomite in the blast furnace via highway;
b) loading the calcined dolomite of step (a) to calcined bunker;
c) discharging the calcined dolomite of step (b) to the PCI coal conveyor;
d) grinding the calcined dolomite and PCI of step (c) to 70-80 micron size and discharged to fine coal silo;
e) mixing the mixture of step (d) and transporting it to injection vessel;
f) transporting the mixture of step (e) through pipeline and PCI lance
wherein the calcined dolomite with PCI coal is co-injected in to the blast furnace through tuyeres (4).

3. The method of co-injection of calcined dolomite with Pulverized Coal Injection(PCI) coal in Blast Furnace (BF) as claimed in claim 1 comprising the steps of
a. receiving calcined dolo of size 10-50 mm in ground via highway;
b. loading through telpher load the calcined dolo from ground to calcined dolo bunker;
c. discharging calcined dolo to PCI coal conveyor in the desired ratio depending upon rate of calcined dolo injection;
d. grinding both PCI and calcined dolo of step (c) together in 70-80 micron size and discharging in fine coal silo;
e. transporting the mixed materials of step (d) to injection vessel from fine coal silo; and
f. transporting the mixed materials of step (e) to tuyeres of BF via pipeline and PCI lance with nitrogen as carrier.

4. The method as claimed in claim 1 wherein the calcined dolomite is injected at a variable rate ranging from 3 to15 kg/thm.