FIELD OF THE INVENTION

The present invention relates to a process for sinter production using granular burnt lime. More particularly, the present invention is directed to a process for sinter production using upto 10 mm size granular burnt lime adapted to improve sinter bed permeability while maintaining smooth flow of material in slaking unit to thereby allowing increased rate of lime addition and improve productivity of sinter plant.

BACKGROUND ART

It is well known that in sinter making, formation of balls facilitate bed permeability. Higher the extent of ball formation and bigger the size of balls, the higher is the bed permeability. Higher bed permeability favour achieving higher sinter productivity. Calcium Oxide due to its excellent binding properties tends to facilitate ball formation. Lime stone fines (CaO-45%) are conventionally used binder in sinter making. Limestone fines are replaced by burnt lime powder as it contains around 90% of CaO. Lime slaking is nothing but treating lime with water and in this process lime gets converted to calcium hydroxide. The resultant product is called slaked lime or hydrated lime, which is a very good binding agent. The calcium hydroxide forms a coating on the nuclei and helps in adhesion of super fines (minus 100 mesh size) on the surface of the nuclei to form a granule / ball.

Use of burnt lime powder with a size range of 0-3 mm leads to increased productivity due to increase in bed permeability compared to lime stone fines. But the use of burnt lime fines poses problems such as difficulty in handling during slaking and rate of lime addition could not be increased as per need. The handling problem was not due to any limitation in the charging system. The problem is due to the nature of the material and its granulometry. In the case of 0-3 mm burnt lime, during slaking, almost complete slaking takes place and the burnt lime powder becomes pasty. This pasty mass sticks to the walls of the slaker and hinders the movement of subsequent material, resulting in choking and interruption in lime dosing. Hence, lime addition poses problems for operations.

There has been therefore a need in the art to developing a process for producing sinter in sinter plant using burnt lime which would eliminate the problems of handling burnt lime in slaker and facilitate increased lime addition rate while maintaining desire enhanced permeability of sinter bed and consequent increased sinter productivity. Herein disclosed by way of the present invention a process for sinter making involving higher sized granular burnt lime replacing lime powder which avoids handling problem in slaker, allow increased rate of lime addition and improve bed permeability and sinter productivity significantly.

OBJECTS OF THE INVENTION

The basic object of the present invention is thus directed to providing a process for sinter production using selectively higher sized 0-10 mm granular burnt lime in sinter mill to improve bed permeability and sinter productivity.

A further object of the present invention is directed to providing a process for sinter production using higher sized granular burnt lime wherein the slaking process enables increased lime addition rate maintaining smooth flow of materials through the slaking unit.

A still further object of the present invention is directed to a process for sinter production using higher sized granular burnt lime wherein only partial slaking takes place in the slaker and the rest of the slaking and swelling in size takes place on transfer to conveyor, favouring formation of large green balls required for desired bed permeability during sintering.

A still further object of the present invention is directed to providing a process for sinter production using higher sized granular burnt lime which would favour reduced power consumption during sinter making.
A still further object of the present invention is directed to providing a process for sinter production using higher sized granular burnt lime wherein the sinter chemistry remains substantially unchanged.

A still further object of the present invention is directed to providing a process for sinter production using higher sized granular burnt lime wherein coke fines consumption per ton of sinter is reduced.
A still further object of the present invention is directed to providing a process for sinter production using higher sized granular burnt lime wherein sinter produced is stronger than the one produced by using burnt lime fines (0-3 mm), with reduced generation of sinter return fines, ensuring improved utilization in blast furnace.

A still further object of the present invention is directed to providing a process for sinter production using higher sized granular burnt lime wherein improved bed permeability results in lower suction pressure and higher gas temperature at the flue and thus decreasing the load on waste gas fan and increasing the efficiency of the dedusting electrostatic precipitator (ESP).

SUMMARY OF THE INVENTION

The basic aspect of the present invention is thus directed to a process for sinter production with improved bed permeability and sinter productivity comprising:

providing granular burnt lime upto 10 mm size in slaker and allowing the granular lime to come in contact with water particles to get wet on the surface before it is discharged onto a belt conveyor to thereby avoid flying off of fine burnt lime particles;

said surface wet granular lime particles on the conveyor allowed to expand and become wet powder ;and
the thus expanded wet powder of granular lime particles with desired heat content adapted to mix well with other raw materials in a mixer and upon spraying of water for nodulization adapted to react rapidly to form better granules /bigger green balls thereby enabling improved raw mix bed permeability and increased sinter productivity.

A further aspect of the present invention is directed to said process wherein 220 to 350 ml, preferably 250 ml of water is mixed per kg of lime in slaker for said partial slaking of said granular burnt lime and preferably 350 ml of water is mixed per kg of raw mix in the mixer for complete slaking for producing desired bigger and harder green balls and improved permeability of sinter bed.

Advantageously in said process, the bed height is increased to a level of 550 to 600 preferably about 600mm.

A still further aspect of the present invention is directed to said process, wherein as the partially slaked lime is discharged onto the belt conveyor, it mixes well with other raw mix and the heat released by slaking increases the initial temperature of sinter raw mix thus reducing the fuel demand (coke fines consumption).

Yet another aspect of the present invention is directed to said process, wherein bigger ball formation and improved permeability of sinter bed leads to higher rate of airflow across the raw mix and improved suction leads to lower power consumption.

A further aspect of the present invention is directed to said process, wherein improved bed permeability results in lower suction pressure and higher gas temperature at the flue reducing the load on waste gas fan and increasing the efficiency of dedusting electrostatic precipitator (ESP).

A still further aspect of the present invention is directed to said process, wherein charging of 0-10 mm granular lime fine into the slaker is carried out at desired rate using Hanging chute system (with chute vibrators and liners) avoiding choking or interruption.

Also in said process, increased sinter bed height of 550 to 600mm preferably about 600mm is maintained during sintering.

According to another aspect of the present invention directed to said process, wherein said granular burnt lime fine are provided such as to produce stronger sinter limiting the return sinter fines to 26%.

A still further aspect of the present invention is directed to said process, wherein use of granular burnt lime powder in the size range of upto 10mm in the slaking process enables increased lime dosing rate in the range of 40 to 60 preferably about 50 kg / ton of sinter enabling maintaining smooth flow of material in the slaking unit and also in the transfer chutes and productivity in the range of 1.45 to 1.55 preferably about 1.50 tons of sinter /m2/hr.

According to yet further aspect of the invention there is provided a system for sinter production with improved bed permeability and sinter productivity involving the process as above comprising:

Lime Slaker, conveyor, mixer and sinter bed involving any conventional sinter system wherein said slaker is fed with 0-10 mm granular lime to a charging system (wherein said charging system consisting of bucket arrangement for charging burnt lime into the storage bin in proportioning system).

The various other objects and advantages are described in greater details with reference to the following accompanying non limiting illustrative drawings.

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES

Figure 1: is the schematic diagram for sinter process flow diagram for conventional burnt lime fines based sintering plant.

Figure 2: is the schematic diagram of (a) conventional chute before modification for charging lime fines and (b) chute configuration after modification for charging of higher size granular burnt lime according to the present invention.

Figure 3: is the schematic diagram for sinter process flow diagram for modified sinter plant involving modified Chute for charging of higher size burnt lime fines according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS

The present invention is directed to providing a process for sinter production using higher sized granular burnt lime so as to improve flow of material in slaking unit and enabling increased lime addition while ensuring improved permeability of sinter bed and increased sinter productivity.

Accompanying Figure 1 shows the schematic diagram for sinter process flow diagram for conventional burnt lime fines based sintering plant operation using 0-3mm size burnt lime fines. In Figure 1, reference signs A,B,C,D,E,F indicates the discharge chutes of various conveyors.

In the case of 0-3 mm burnt lime, during slaking, almost complete slaking takes place and the burnt lime powder becomes pasty. This pasty mass sticks to the walls of the slaker and hinders the movement of subsequent material, resulting in choking and interruption in lime dosing through transfer chutes. In the case of 0-3 mm lime powder, as slaking is almost completed inside the slaker and hence maximum amount of heat is released inside the slaker itself. Thus, this heat could not be effectively utilized for making bigger green balls. This leads to the formation of smaller sized green balls (and hence smaller voids between the balls) resulting in decreased gas permeability.

Burnt lime (along with water) is used mainly as a binder to facilitate ball formation. Higher the extent of ball formation and stronger the balls formed, the higher is the bed permeability. Furthermore, permeability of the raw mix is directly influenced by the addition of water in the mixing drum. A lack of surface moisture leads to a drop in bed permeability and the presence of excess moisture also leads to poor permeability. Hence, a number of trial experiments were needed to be conducted, to optimize the size of lime and quantity of water to be added in slaker and in the mixer drum. Permeability of various sinter raw mix used in our trial experiments was measured using Permeability meter.

It was determined through the trials that introduction of granular burnt lime in the size range 0-10mm in the slaking process enables increased lime addition rate apart form maintaining smooth flow of material in the slaking unit and in the transfer chutes. This granular lime comes into contact with water particles in the slaker and becomes wet on its surface before it is discharged onto the belt conveyor, which prevents the flying off of fine burnt lime particles during transfer between chutes. On the belt conveyor, it starts expanding and becomes wet powder, which gets mixed with the other elements of raw mix in the mixer.

In the mixer, when water is sprayed further for nodulisation, it reacts rapidly to make better granules due to higher heat content of the powder. This phenomenon helps in producing bigger green balls favouring in turn to improve raw mix bed permeability, which results in increased sinter productivity.

Importantly, in the case of 0-10 mm granular burnt lime (as most of the particles are granular in shape), only partial slaking takes place in the slaker and there is no sudden formation of sticky mass. Hence, even increased lime dosing could be effected without any problem.

In the modified process, due to partial slaking, heat is released gradually. Once, granular, the burnt lime
gets discharged onto the belt conveyor, it mixes well with other raw mix and the heat released by slaking increases the initial temperature of sinter raw mix. Higher initial temperature of sinter raw mix lowers the fuel demand (coke fines consumption). Furthermore, bigger ball formation and improved permeability lead to higher rate of airflow across the raw mix. Improved suction leads to lower power consumption. Better bed permeability results in lower suction pressure and higher gas temperature at the flue. Thus, the load on waste gas fan comes down and the efficiency of the dedusting electrostatic precipitator (ESP) increases.

Accompanying Figure 2 illustrates the modified chute with bin vibrator provided to feed the burnt lime granules. Hanging chute system (with chute vibrators and liners) is being used for charging 0-10 mm granular lime as depicted in Figure 2. Accompanying Figure 3 shows the schematic diagram for sinter process flow diagram for modified sinter plant involving modified chute for charging of higher size burnt lime fine according to the present invention wherein reference signs G,H,I,J,K,L indicates discharge chutes of various conveyors (such that reference signs A, B, C, D, E, F in Figure 1 corresponds to reference signs G, H, I, J, K, L in Figure 3 respectively) .

A comparative trial data involving 0-3 mm burnt lime powder and 0-10 mm granular burnt lime and their effect on permeability is presented in Table 1.

The advantages achieved by using 0-10 mm granular burnt lime under similar perating conditions is illustrated by data presented in the following Table 2 showing Operating parameters during the use of (0-3 mm) lime powder & Table 3 showing Operating parameters during the use of (0-10 mm) granular lime.

The data as given in the Tables 2 & 3 above reveal that, the following advantages have been achieved by using higher sized (0-10mm) granular burnt lime:

1. Increase in bed height: Bed height could be increased from 500 mm to 550 mm.

2. Sinter return fines: Generation of return fines came down from 38% to 26%. A reduction in sinter fines generation indicates that the sinter produced by using 0-10 mm lime is stronger than the one produced by using 0-3 mm. The stronger the sinter, the better is its behavior in the blast furnace.

3. Increase in productivity: Productivity was found to increase from 1.32 tons of sinter /m2/hr to 1.45 tons of sinter /m2/hr.

4. The suction pressure and BTP temperature were found to remain almost same.

It is thus possible by way of the present invention to providing a process for sinter production using higher sized (0-10mm) granular burnt lime, which would favour smooth flow of materials in slaker and feeding chutes resulting in increased rate of lime addition leading to formation of larger size green balls with improved bed permeability and enhanced sinter productivity. Moreover, the above process resulted in reduction in coal consumption by 2kg/t of sinter and reduction in power consumption by 4KWH/t of sinter, increased sinter usage in blast furnace by 6%, which leads to saving of 7.5kg of coke per ton of fuel, making the process capable of wide industrial application with significant cost advantage.

We Claim:

1. A process for sinter production with improved bed permeability and sinter productivity comprising:

providing granular burnt lime upto 10 mm in slaker and allowing the granular lime to come in contact with water particles to get wet on the surface before it is discharged onto a belt conveyor to thereby avoid flying off of fine burnt lime particles;

said surface wet granular lime particles on the conveyor allowed to expand and become wet powder ;and
the thus expanded wet powder of granular lime particles with desired heat content adapted to mix well with other raw materials in a mixer and upon spraying of water for nodulization adapted to react rapidly to form better granules /bigger green balls thereby enabling improved raw mix bed permeability and increased sinter productivity.

2. A process as claimed in claim 1, wherein 220 to 350 ml, preferably 250 ml of water is mixed per kg of lime in slaker for said partial slaking of said granular burnt lime and preferably 350 ml of water is mixed per kg of raw mix in the mixer for complete slaking for producing desired bigger and harder green balls and improved permeability of sinter bed.

3. A process as claimed in anyone of claims 1 or 2 wherein the bed height is increased (by a level of 10%) by 50mm where the normal bed height is 550 mm.

4. A process as claimed in anyone of claims 1 to 3, wherein as the partially slaked lime is discharged onto the belt conveyor, it mixes well with other raw mix and the heat released by slaking increases the initial temperature of sinter raw mix thus reducing the fuel demand (coke fines consumption).

5. A process as claimed in anyone of claims 1 to 4, wherein bigger ball formation and improved permeability of sinter bed leads to higher rate of airflow across the raw mix and improved suction leads to lower power consumption.

6. A process as claimed in anyone of claims 1 to 5, wherein improved bed permeability results in lower suction pressure and higher gas temperature at the flue reducing the load on waste gas fan and increasing the efficiency of dedusting electrostatic precipitator (ESP).

7. A process as claimed in anyone of claims 1 to 6, wherein charging of 0-10 mm granular lime fines into the slaker is carried out at desired rate using Hanging chute system (with chute vibrators and liners) avoiding choking or interruption.

8. A process as claimed in anyone of claims 1 to 7, wherein increased sinter bed height of 550 to 600 mm preferably about 600 mm is maintained during sintering.

9. A process as claimed in anyone of claims 1 to 8, wherein said granular burnt lime fines are provided such as to produce stronger sinter limiting the return sinter fines to 26%.

10. A process as claimed in anyone of claims 1 to 9, wherein use of granular burnt lime powder in the size range of upto 10mm in the slaking process enabies increased lime dosing rate in the range of 40 to 60 preferably about 50 kg/ton of sinter enabling maintaining smooth flow of material in the slaking unit and also in the transfer chutes and increased productivity by 10% (in the range of 1.45 to 1.55 preferably about 1.50 tons of sinter /m2/nr in the sinter plant used in trials).

11. A system for sinter production with improved bed permeability and sinter productivity involving the process as claimed in anyone of claims 1 to 10 comprising:

Lime Slaker, conveyor, mixer and sinter bed involving any conventional sinter system wherein said slaker is fed with 0-10 mm granular lime to a charging system (charging system consists of bucket arrangement for charging burnt lime into the storage bin in proportioning system).