Claims:We Claim :

1. A process for manufacture of good quality pellets with reduced cracks from green pellets including Loss on Ignition (LOI) iron ores comprising:

step of subjecting the green pellets including Loss on Ignition (LOI) iron ores to step of heating such as to favour releasing the LOI in green iron ore pellets before the green pellets are subjected to firing in firing zone of induration furnace.

2. A process as claimed in claim 1 comprising heating the green pellets including said Loss on Ignition (LOI) iron ores by pre-heating the same in a pre-heating zone prior to subjecting dried pellets to said firing in said firing zone.

3. A process as claimed in anyone of claims 1 or 2 comprising pre-heating said green pellets including said Loss on Ignition (LOI) iron ores in high temperature in a preheating zone in the temperature range of 650 to 1000 0C.

4. A process as claimed in anyone of claims 1 to 3 wherein said green pellets including Loss on Ignition (LOI) iron ores used include high LOI iron ore consisting of goethite and kaolinite phases in pellet.

5. A process as claimed in anyone of claims 1 to 4 involving

green pellets having the composition :
Fe(T) in amounts of 56.02 – 60.69 % by wt,
SiO2 in amounts of 3.45 - 5.26 % by wt,
Al2O3 in amounts of 1.31 – 2.75 % by wt,
MgO in amounts of 0.61 – 1.2 % by wt,
LOI in amounts of 4.61 – 7.6 % by wt,
Carbonin amount of 0.80-1.0 by wt,
and the green pellets moisture is maintained in the range of 10.0 to 10.2%

6. A process as claimed in anyone of claims 1 to 5 wherein

maintaining other regular operating stages and parameters for 3 % LOI in concentrate, rise in preheating temperature from 550 to 800 °C was carried out to improve CCS from 237 to 251 kg/pellets and TI (+6.3 mm) from 89 to 92 %; and

maintaining other regular operating stages and parameters for 6 % LOI in concentrate, rise in preheating temperature from 550 to 800 °C resulted in improvement in CCS from 222 to 236 kg/pellets and TI (+6.3 mm) from 88 to 91 %.

7. A process as claimed in anyone of claims 1 to 6 comprising apart from said step of pre heating carrying out pelting under regular operating stages and parameters comprising:
Drying of pellets in the range of 240 to 300 0C,
Preheating of pellets in the range of 550 to 800 0C,
Firing of pellets at temperature up to 1330 0C, and
Subsequent cooling in two stages down to room temperature.

8. A straight grate induration furnace system for manufacture of good quality pellets with reduced cracks from green pellets including Loss on Ignition (LOI) iron ores as claimed in anyone of claims 1 to 7 comprising:

preheating zone of straight grate induration furnace of pellet provided with enhanced heat input to the pellet bed including heat system , installed in preheating zone of the induration furnace to maintain temperature in preheating zone in the range of 650 to 1000 0C ahead of the firing zone in the induration furnace.

9. A straight grate induration furnace system as claimed in claim 8 wherein

heating system of preheating zone of travelling grate induration furnace comprise burners on both sides of the wind box of induration machine, said burners adapted for attaining the higher temperature of 650 to 1000 °C in preheating zone favouring complete removal of LOI vis-à-vis rise in pellet temperature.

10. A straight grate induration furnace system as claimed in anyone of claims 8 or 9 comprising :

four gas burners installed on both side of the induration machine.

11. A straight grate induration furnace system as claimed in anyone of claims 8 to 10 comprising
Heat resistant alloy basket for keeping/charging prepared green pellets for placing in the raising hearth furnace for induration.

12. A straight grate induration furnace system as claimed in anyone of claims 8 to 11 comprising:

mixed gas tapping lines;
combustion air tapping lines ;
Orifice plates in the tapping gas lines.

a tapping (mixed gas tapping line) from mixed gas main line is taken upto flow control valve , Butterfly valves are used in mixed gas tapping line;

mixed gas tapping line starts after flow control valve and ends at butterfly valve and similarly a further mixed gas tapping line starts after flow control valve and ends at butterfly valve ;

such that the operation of butterfly valves enables start and stop the flow of mixed gas to burners , said mixed gas tapping line selectively reduced involving reducers to connect the flow control valve, also said mixed gas tapping lines of selective configurations connect to shut-off valves to allow to continue and discontinue the gas flow to individual burners;

after shut off valves, orifice plates are installed with desired orifice for burner to allow required gas flow to burner ports;

combustion air line tapping from pre-existing combustion air main line, butter fly valves installed at the end of combustion air lines to control the combustion air flow to the burner;

pressure gauges installed in the combustion air taping lines to measure the flow of combustion air to the burners ;

LPG gas main line including solenoid valves installed in LPG gas tapping lines, LPG gas from the LPG gas tapping lines (connecting to the burners via solenoid valves and during the cold start of the plant LPG gas being used as pilot gas inside the burner.

Dated this the 16th day of August, 2019
Anjan Sen
Of Anjan Sen & Associates
(Applicant’s Agent)
IN/PA-199

, Description:FIELD OF THE INVENTION
The present invention relates to a process for producing good quality pellets by induration of high loss on ignition(LOI) iron ore pellets through preheating zone temperature optimization and a modified heating system to carry out such process. More particularly, the present invention is directed to modification in preheating zone of straight grate induration furnace of pellet plant for enhanced heat input to the pellet bed in pre-heating zone. LOI in iron ore constitutes of chemically bonded water in the form of kaolinite, gibbsite and goethite phases present in iron ores which releases over a range of temperature (250 to 800 0C). The removal of LOI in iron ore is investigated through thermal analysis (thermo-gravimetric studies). Proper heating of dried pellets in pre-heating zone at 800 0C resulted in complete LOI removal from pellets and reduces the cracking of pellets. Additional heat source in the form of 4 burners for supplying mixed gas were installed in preheating zone of the induration furnace. This modification helped in maintaining adequate temperature in preheating zone. In present invention, preheating temperature was varied during induration of iron ore pellets containing LOI varying in the range of 3 - 6%. Complete removal of LOI from pellets before entering in the firing zone resulted in reduced cracking, unfired pellets, fines generation and required strength properties of fired pellets.

BACKGROUND OF THE INVENTION

Iron ore pelletization is a process which involves mixing of finely ground particles of iron ores of less than 150 microns with additives like coke breeze, bentonite, limestone and dolomite and then shaping them into spherical balls of 8-16 mm diameter with optimum moisture followed by induration. The green pellets are treated in induration furnace to achieve adequate strength, hardness, impact resistance etc. required for handling, transportation and charging into the furnace (BF, Corex or DRI). The loss on ignition (LOI) in iron ore constitutes of chemically bonded water in the form of kaolinite, gibbsite and goethite phases. High LOI in green pellets during induration results in generation of cracks and deteriorates the pellet properties. The removal of LOI in iron ore is investigated through thermal analysis (thermo-gravimetric studies) and found to release over a range of temperature (250 to 800 0C). In existing heat cycle (i.e., before modification) of the induration furnace, the temperature achieved in the preheating zone was in the range 450 to 550 °C only and therefore, complete removal of LOI was not taking place. Sudden release of LOI in firing zone (at high temperature of 1000 - 1320 °C) will develop cracks leading to lower strength and more fines generation. In order to achieve good quality pellets, the LOI in green iron ore pellets to be completely released before the pellets enter the firing zone of the induration furnace.

The state of the arts revealed in some prior patents relating to induration of iron ore pellets is summarized below.

US3245778A entitled “Method of indurating iron ore concentrates” stated a method of heating iron ore concentrate green balls which involve drying, preheating, ignition and cooling. First stage of down-draft drying zone maintained at a temperature of about 204 °C to 288 °C, second stage maintained at a temperature of about 288 °C to 371 °C and the third stage maintained at a temperature of about 371 °C to 510 °C. Next, bed moved into down-draft combustion zone containing a plurality of burners having the first stage maintained at a temperature of about 538 °C to 982 °C, second stage maintained at a temperature of about 982 °C to 1093 °C and the third stage maintained at a temperature of about 1204 °C to 1371 °C.

US3365339A entitled “Indurating ore fines pellets” stated a process for indurating a material consisting of initially moist green pellets of iron ore concentrates that contain an oxidizable fuel, comprising: drying the pellets, pre-indurating the pellets at a temperature between 538 °C to 1093 °C to provide sensible heat to the pellets while preserving a substantial portion of the oxidizable fuel, indurating the pellets by passing an oxidizing gas there through to oxidize the remaining fuel in the pellets and raise the temperature thereof to at least 1205 °C solely through oxidation of the remaining fuel in the pellets.

US 4278462 entitled “Process for upgrading iron ore pellets” stated that in a process for hardening oxidizable green iron ore pellets in a vertical shaft furnace, said process comprising passing the pellets through the furnace wherein said pellets are heated by contact with hot combustion gases and air, the furnace having a zone which is downstream of the introduction of the combustion gases, said zone having an average temperature in the range of 1100 0F to 2200 0F., the improvement comprising directing a plurality of oxygen streams at the pellets passing through the periphery of said zone in such a manner that (a) each stream penetrates into the furnace about one to about six inches measured from the inside surface of the furnace wall; (b) the velocity of each stream is sufficient to substantially prevent the stream from flowing up the furnace wall; (c) the points of introduction of the streams are on the inside surface of the furnace wall located in the zone; and (d) any theoretical vertical line, which is parallel to the theoretical vertical axis of the furnace.

US 9752206 B2 titled “Plasma heated furnace for iron ore pellet induration” stated that the induration of iron ore pellets is achieved in a tunnel furnace heated by plasma torches, wherein the generation of CO2 by the conventional iron ore pelletizing process is reduced by using electricity powered plasma torches instead of burning natural gas, heavy oil or pulverized coal in burners, thereby reducing considerably industrial pollution of the atmosphere.

IN0072/MUM/2012 entitled “A pellet induration system and a process for improving the induration of pellets involving the same” discussed a pellet induration system in a straight grate machine. The traveling grate carries the pellets through the indurating furnace where they are subjected to the sequential zones of updraft drying, downdraft drying, preheating, firing and after firing and first and second cooling. The first stage of drying is updraft to prevent the condensation of the water. The drying is continued in a subsequent downdraft stage to remove free water of the top of the bed. In these two zones, it is necessary to use drying air of sufficient temperature to cause rapid water evaporation yet not so high that the pellets are destroyed by high internal pressures.

The above referred patents disclose that heat hardening of green pellets is must to attain the required strength. Before the modification in preheating zone, pellets bed in the preheating zone was subjected to only recuperation header gases coming from cooling zone 1. In the present invention, modification in heating system of preheating zone of travelling grate induration furnace is made by incorporating burners on both sides of the wind box (e.g. 20 and 21) of induration machine. The installation of burners helped in attaining the higher temperature of 700 to 1000 °C in preheating zone. This increased temperature in preheating zone resulted in complete removal of LOI vis-à-vis rise in pellet temperature.

OBJECTS OF THE INVENTION

The basic object of the present invention is directed to a process for induration of high LOI iron ore pellets to utilize high LOI iron ore consisting of goethite and kaolinite phases in pellet making without affecting the pellet quality and a system to carry out such process with modification in preheating zone to achieve higher temperature.

Another object of the present invention is directed to a process for induration of high LOI iron ore pellets to utilize high LOI iron ore to increase the temperature of pre-heating zone of induration furnace by supplying additional heat through the installed burners.

A still further object of the present invention is directed to a process for induration of high LOI iron ore pellets to utilize high LOI iron ore to achieve complete removal of LOI in green pellets in the preheating zone, i.e., before the entry of pellets in firing zone of induration furnace.

A further object of the present invention is directed to a process for induration of high LOI iron ore pellets to utilize high LOI iron ore to minimize the generation of cracks and fines during pelletization.

SUMMARY OF THE INVENTION

The basic aspect of the present invention is directed to a process for manufacture of good quality pellets with reduced cracks from green pellets including Loss on Ignition (LOI) iron ores comprising:

step of subjecting the green pellets including Loss on Ignition (LOI) iron ores to step of heating such as to favour releasing the LOI in green iron ore pellets before the green pellets are subjected to firing in firing zone of induration furnace.

A further aspect of the present invention is directed to said process comprising heating the green pellets including said Loss on Ignition (LOI) iron ores by pre-heating the same in a pre-heating zone prior to subjecting dried pellets to said firing in said firing zone.

A still further aspect of the present invention is directed to saidprocess comprising pre-heating said green pellets including said Loss on Ignition (LOI) iron ores in high temperature in a preheating zone in the temperature range of 650 to 1000 0C.

A further aspect of the present invention is directed to saidprocess wherein said green pellets including Loss on Ignition (LOI) iron ores used include high LOI iron ore consisting of goethite and kaolinite phases in pellet.

Another aspect of the present invention is directed to saidprocess involving green pellets having the composition :
Fe(T) in amounts of 56.02 – 60.69 % by wt,
SiO2 in amounts of 3.45 - 5.26 % by wt,
Al2O3 in amounts of 1.31 – 2.75 % by wt,
MgO in amounts of 0.61 – 1.2 % by wt,
LOI in amounts of 4.61 – 7.6 % by wt,
Carbonin amount of 0.80-1.0 by wt,
and the green pellets moisture is maintained in the range of 10.0 to 10.2%

yet another aspect of the present invention is directed to said process wherein

maintaining other regular operating stages and parameters for 3 % LOI in concentrate, rise in preheating temperature from 550 to 800 °C was carried out to improve CCS from 237 to 251 kg/pellets and TI (+6.3 mm) from 89 to 92 %; and

maintaining other regular operating stages and parameters for 6 % LOI in concentrate, rise in preheating temperature from 550 to 800 °C resulted in improvement in CCS from 222 to 236 kg/pellets and TI (+6.3 mm) from 88 to 91 %.

A further aspect of the present invention is directed to said process comprising apart from said step of preheating carrying out pelletizing under regular operating stages and parameters comprising:
Drying of pellets in the range of 240 to 300 0C,
Preheating of pellets in the range of 550 to 800 0C,
Firing of pellets at temperature up to 1330 0C, and
Subsequent cooling in two stages down to room temperature.

A further aspect of the present invention is directed to a straight grate induration furnace system for manufacture of good quality pellets with reduced cracks from green pellets including high Loss on Ignition (LOI) iron ores as described above comprising:

preheating zone of straight grate induration furnace of pellet provided with enhanced heat input to the pellet bed including heat system, installed in preheating zone of the induration furnace to maintain temperature in preheating zone in the range of 650 to 1000 0C ahead of the firing zone in the induration furnace.

A still further aspect of the present invention is directed to said straight grate induration furnace system wherein

heating system of preheating zone of travelling grate induration furnace comprise burners on both sides of the wind box of induration machine, said burners adapted for attaining the higher temperature of 650 to 1000 °C in preheating zone favouring complete removal of LOI vis-à-vis rise in pellet temperature.

A still further aspect of the present invention is directed to said straight grate induration furnace system comprising:

four gas burners installed on both side of the induration machine.

Another aspect of the present invention is directed to said straight grate induration furnace system comprising Heat resistant alloy basket for keeping/charging prepared green pellets for placing in the raising hearth furnace for induration.

Yet another aspect of the present invention is directed to said straight grate induration furnace system comprising:

mixed gas tapping lines;
combustion air tapping lines;
Orifice plates in the tapping gas lines.

a tapping(mixed gas tapping line) from mixed gas main line is taken upto flow control valve, Butterfly valves are used in mixed gas tapping line;

mixed gas tapping line starts after flow control valve and ends at butterfly valve and similarly a further mixed gas tapping line starts after flow control valve and ends at butterfly valve ;

such that the operation of butterfly valves enables start and stop the flow of mixed gas to burners , said mixed gas tapping line selectively reduced involving reducers to connect the flow control valve, also said mixed gas tapping lines of selective configurations connect to shut-off valves to allow to continue and discontinue the gas flow to individual burners;

after shut off valves, orifice plates are installed with desired orifice for burner to allow required gas flow to burner ports;

combustion air line tapping from pre-existing combustion air main line, butter fly valves installed at the end of combustion air lines to control the combustion air flow to the burner;

pressure gauges installed in the combustion air taping lines to measure the flow of combustion air to the burners ;

LPG gas main line including solenoid valves installed in LPG gas tapping lines, LPG gas from the LPG gas tapping lines (connecting to the burners via solenoid valves and during the cold start of the plant LPG gas being used as pilot gas inside the burner.

The above and other 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: Process flow for green pellet production and firing at lab scale.
Figure 2: Schematic diagram of process flow for iron ore pellet making.
Figure 3: Photograph of the actual location of installed burners in the induration furnace at pellet plant.
Figure 4: Schematic diagram of present invention comprising of the modification. in gas flow and improvement in temperature by burners installation in wind box 20 & 21 in Zone Zero, i.e., Preheating zone of Induration system.
Figure 5: Installed burners on North side of induration furnace in preheating zone.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO ACCOMPANYING DRAWINGS

The present invention is directed to a process for induration of high LOI iron ore pellets to utilize high LOI iron ore consisting of goethite and kaolinite phases by modifying the preheating process of pellets inside the induration furnace of pellet plant by installing burners in preheating zone to supply extra heat so that the complete removal of LOI could take place within the preheating zone of the induration furnace. The green pellets were prepared in laboratory disc pelletizer followed by screening (8 to 16 mm) to remove the over size and under size pellets. The screened pellets were subjected to firing in raising hearth furnace.

At pellet pant#2 indurating furnace, wind box number 18 to 21 constitutes the preheating zone. Prior to design modification in preheating zone, hot gas from recuperation header was the only source of heat in preheating zone. In order to achieve the desired temperature for complete removal of LOI from the dried pellets bed, four gas burners (two in each wind box number 20 and 21) were installed on both side of the induration machine. The modification in preheating zone helped in achieving the preheating temperature in the range of 650 to 800 °C. These additional burners supply extra heat resulting in the required temperature rise in preheating zone for removal of LOI.
Two iron ore sources (iron ore concentrates 1and 2 having LOI, <10 µ size particles and Blaine number 8.69 %, 37.77 % & 3400 cm2/gm and 3.0 %, 32.84% & 2100 cm2/gm respectively) were used for making green pellets having composition as under.
Fe(T) in amounts of 56.02 – 60.69 % by wt,
SiO2 in amounts of 3.45 - 5.26 % by wt,
Al2O3 in amounts of 1.31 – 2.75 % by wt,
MgO in amounts of 0.61 – 1.2 % by wt,
LOI in amounts of 4.61 – 7.6 % by wt,
Carbonin amount of 0.80-1.0 by wt,

The size distribution of the iron ore concentrates is given in Table 1.
Table 1: Size distribution of iron ore concentrates, %
Iron ore samples -10 µ -25 µ -45 µ -75 µ -150 µ
Iron Ore Concentrate 1 37.77 58.72 72.04 85.23 98.01
Iron Ore Concentrate 2 32.84 43.78 69.26 95.00 98.50

The experimental plan and blend for green mix is given in Table 2 and 3 respectively.

Table 2: Experimental Plan
Parameter UOM Value
Moisture wt. % 10.0 – 10.2
Iron ore LOI wt. % 3, 4, 5, and 6
Drying temperature OC 240, 270 and 300
Pre-heating Temperature OC 550, 600, 650, 700, 750,800
Firing Temperature OC 1300

Table 3: Blend for green pellets production

Constituent Wt. %
Blend No. A B C D
Iron Ore Concentrate 1 0.0 16 32 48
Iron Ore Concentrate 2 94.4 78.2 62 46.2
Limestone 1.0 1.2 1.4 1.6
Dolomite 2.8 2.8 2.8 2.8
Coke breeze 0.8 0.8 0.8 0.8
Binder 0.6 0.6 0.6 0.6
Overall LOI in iron ore concentrate 3.0 4.0 5.0 6.0

The present invention is directed to heating cycle time used in laboratory scale Raising Hearth Furnace (RHF) for pellets induration for 11.3 minutes drying time, 1.9 minutes of preheating time and 11.9 minutes of firing time and further cooling inside the furnace.

Another aspect of the present invention is directed to said modified process resulting in improved CCS and TI of fired pellets. Yet another aspect of the present invention is directed to the said process for reduction in cracks and unfired product pellets.

The present invention is thus directed to provide modification in preheating zone of induration furnace and a process for usage of high LOI iron ore concentrate in pellet making without impacting the fired pellet properties, i.e., CCS, TI, % fines generation and % unfired pellets which is described hereunder with reference to following accompanying figures to illustrates the working of the invention:

Accompanying Figure 1 shows the process of green pellet making and firing of the same at lab scale. The raw materials were ground in ball mill to achieve the required fineness and size distribution (-150 micron passing 100%). As per design of experiment, for each experiment, a pellet blend (101) of 10 kg was prepared for green pellets preparation in balling disc (102) having the disc diameter of 700 mm, disc angle of 440, and the disc rotation of 24 rpm for all the experiments. The green pellet moisture was maintained between 10 - 10.2 %. Prepared green pellets (103) were kept in the heat resistant alloy basket 105 and placed in the raising hearth furnace (104) for induration. After the completion of induration cycle, indurated pellets (106) were allowed to cool in the furnace followed by characterization studies (107).

Accompanying Figure 2 shows a schematic diagram of pelletization process in pellet plant#2. It shows the flow of materials from the bunkers 101,102,103, and 104 and the equipment. The raw materials are fed through (105) to high intensity paddle mixer (202). Water from the industrial water tank (201) is added to the mixer (202). Output of the mixer 202 goes to the surge bin (301) with the help of conveyer (203). Surge bin (301) discharges the wet mix to the balling disc through conveyer (303). Water is also sprayed in the balling disc through water nozzles, if required, to maintain the required moisture in green balls. Green pellets formed in the balling disc is transferred to the induration machine (402) through conveyer (401) after removing +16 mm and -8mm size pellets in double deck roller screens. Only 8 to 16 mm size pellets are fed to induration machine. The undersize and oversize pellets are recirculated. Output of the induration machine (402) goes to stock yard or iron making units.
Accompanying Figure 3 shows the exact location of design modification performed in pre heating zone of induration machine. Preheating zone consists of 4 wind boxes from wind box number 18 to 21. In Figure 4, design and working of the invention is explained. For mixed gas tapping lines (102) and (104) & (104’), pipes of 200 mm and 150 mm respectively were selected. For combustion air tapping lines 202 & 202’ and 204 & 204’, pipes of 150 mm and 100 mm respectively were selected. Reducers for 200 to 150, 150 to 100, and 100 to 50 diameter reduction were used in the tapping lines. Orifice plates (107) and (107’) of 3 mm thickness were added in the tapping gas lines.

In Figure 4, mixed gas main line (101) of nominal bore 600 mm was already there at both sides of Induration furnace before this innovation to supply gas to furnace as a fuel. In this innovation, a tapping (mixed gas tapping line 102) of nominal bore of 200 mm from mixed gas main line is taken upto flow control valve (103). Butterfly valves (105) & (105’) are used in mixed gas tapping line (104) & (104’) respectively. Mixed gas tapping line (104) starts after flow control valve (103) and ends at butterfly valve (105) and similarly mixed gas tapping line (104’) starts after flow control valve (103) and ends at butterfly valve (105’). The operation of butterfly valves (105) & (105’) helps to start and stop the flow of mixed gas to burners. Then mixed gas tapping line (102) is reduced from 200 mm to 50 mm by using reducers to connect the flow control valve (103) of 50 mm diameter. Again the mixed gas tapping lines (104) & (104’) size is increased to 150 mm from 50 mm diameter to connect shut-off valves (106) & (106’) of 150 mm diameter respectively, which allows to continue and discontinue the gas flow to individual burners. After the shut off valves (106) & (106’), orifice plates (107) & (107’) are installed with an orifice diameter of 35.21 mm for burner (401) and 40.01 mm for burner (401’) respectively to allow required gas flow to burner ports.

Further, tapping (combustion air line tapping (202) & (202’) of 150 mm nominal bore diameter and tapping (204) & (204’) of 100 mm nominal bore) from pre-existing combustion air main line (201) of 500 mm nominal bore pipe line is taken. Butter fly valves (203) & (203’) of 100 mm are installed at the end of combustion air lines (202) & (202’) to control the combustion air flow to the burner. Pressure gauges (205) & (205’) are installed in the combustion air taping lines (204) & (204’) respectively to measure the flow of combustion air to the burners (401) & (401’). From LPG gas main line (301) of 40 mm diameter, LPG gas tapping lines (302) & (302’) of 12.7 mm diameter is taken. Solenoid valves (302) & (303’) are installed in LPG gas tapping lines (302) & (302’). LPG gas from the LPG gas tapping lines (302) & (302’) goes to the burners (401) & (401’) via solenoid valves (302) & (303’) and during the cold start of the plant this LPG gas is used as pilot gas inside the burner.
Accompanying Figure 5 shows the digital photographs of preheating zone with and without modification. Figure 5A shows the portion of the induration furnace starting from the preheating zone to the cooling zone. Digital photograph Figure 5B shows the burner ports (BP 20 and BP 21) with burners before the invention. Digital photograph Figure 5B shows the burner ports (BP 20 and BP 21) after the addition of new burners in BP20 and BP 21 in WB 20 and WB 21 respectively.

LABORATORY SCALE TRIALS

To investigate the effect of high LOI in the iron ore concentrate on fired pellets properties, iron ore concentrate of LOI 3 to 6 wt. % with and interval of 1 % was used for pellet production. During green pellets production, moisture in the green pellets was maintained 10.0 - 10.2 wt. %. Chemical analysis of fired pellets produced at various levels of LOI in the iron ore concentrate was conducted and is tabulated in Table 4:

Table 4: Chemical analysis of fired pellets, %
Blend No. Fe(total) SiO2 Al2O3 CaO MgO MnO LOI
A 62.76 4.24 3.14 1.51 0.54 0.27 0.13
B 62.54 5.01 3.07 1.62 0.38 0.29 0.14
C 62.65 4.62 3.11 1.69 0.46 0.28 0.18
D 61.59 5.72 3.02 1.74 0.36 0.24 0.18

Tables 5, 6, 7 and 8 show the properties of fired pellets made out of iron ore concentrates containing 3, 4, 5 and 6 % LOI respectively.
Table 5: Fired pellets properties produced with 3.0 wt. % LOI in IO concentrate

Drying Temperature, °C Preheating Temperature, °C Firing temperature, °C CCS, Kg/pellet TI,+6.3 mm wt. % FeO, wt. % Cracked pellets, wt.% Unfired pellets, wt.%
240 550 1300 237 89.13 0.56 5.16 8.23
270 244 89.67 0.52 4.96 8.11
300 246 90.19 0.52 4.63 7.93
240 600 238 89.41 0.58 5.03 7.89
270 245 89.91 0.56 4.86 7.56
300 250 90.26 0.55 4.51 7.06
240 650 243 89.88 0.56 4.91 8.16
270 249 90.31 0.55 4.12 7.26
300 251 91.26 0.56 3.26 6.98
240 700 244 90.76 0.54 4.78 7.56
270 251 91.98 0.53 3.91 6.92
300 253 92.27 0.51 3.08 5.96
240 750 246 91.54 0.56 4.06 6.23
270 254 92.49 0.55 3.19 5.19
300 258 93.36 0.56 2.88 4.78
240 800 251 92.31 0.56 3.96 6.17
270 256 92.87 0.57 3.11 5.01
300 263 93.88 0.58 2.71 4.33

It is observed from Table 5 that for 3 % LOI, 240 °C drying temperature, 1300 °C firing temperature; rise in preheating temperature from 550 to 800 °C resulted in improvement in CCS from 237 to 251 kg/pellets and TI (+6.3 mm) from 89 to 92 %.
Table 6: Fired pellets properties produced with 4.0 wt. % LOI in IO concentrate

Drying Temperature, °C Preheating Temperature, °C Firing temperature, °C CCS, Kg/pellet TI,+6.3 mm wt. % FeO, wt. % Cracked pellets, wt.% Unfired pellets, wt.%
240 550 1300 235 88.97 0.58 5.75 9.21
270 242 89.43 0.51 5.56 9.15
300 244 89.98 0.56 5.14 8.92
240 600 236 89.26 0.59 5.62 8.79
270 243 89.71 0.56 5.19 8.55
300 247 90.09 0.59 5.11 8.11
240 650 239 89.63 0.58 5.13 8.91
270 247 90.13 0.56 4.73 7.76
300 250 91.04 0.57 3.82 7.32
240 700 242 90.59 0.55 5.09 8.51
270 249 91.77 0.59 4.18 7.93
300 251 92.09 0.54 3.67 6.71
240 750 244 91.42 0.53 4.65 7.56
270 252 92.31 0.50 3.77 6.23
300 256 93.21 0.52 3.21 5.79
240 800 249 92.09 0.56 4.36 7.11
270 253 92.38 0.56 3.87 6.23
300 259 93.61 0.57 3.02 5.19

Table 7: Fired pellets properties produced with 5.0 wt. % LOI in IO concentrate

Drying Temperature, °C Preheating Temperature, °C Firing temperature, °C CCS, Kg/pellet TI,+6.3 mm wt. % FeO, wt. % Cracked pellets, wt.% Unfired pellets, wt.%
240 550 1300 231 88.57 0.56 6.72 9.43
270 237 88.92 0.52 6.51 9.36
300 239 89.46 0.55 6.15 9.12
240 600 230 88.77 0.58 6.66 8.98
270 238 89.22 0.57 6.18 8.76
300 243 89.62 0.53 6.11 8.11
240 650 236 89.19 0.51 6.12 9.06
270 243 90.02 0.55 5.71 7.96
300 248 90.88 0.56 4.92 7.53
240 700 241 90.26 0.52 6.08 8.62
270 246 91.41 0.58 5.22 7.98
300 248 91.99 0.59 4.66 6.96
240 750 240 91.12 0.61 5.63 7.88
270 249 92.06 0.53 4.71 6.47
300 253 92.89 0.51 4.22 6.23
240 800 243 91.33 0.6 5.39 7.34
270 251 92.27 0.59 4.47 6.02
300 256 93.05 0.54 3.97 5.89

Table 8: Fired pellets properties produced with 6.0 wt. % LOI in IO concentrate

Drying Temperature, °C Preheating Temperature, °C Firing temperature, °C CCS, Kg/pellet TI,+6.3 mm wt. % FeO, wt. % Cracked pellets, wt.% Unfired pellets, wt.%
240 550 1300 222 88.03 0.55 9.76 9.92
270 226 88.47 0.54 9.52 9.81
300 228 89.03 0.56 9.22 9.63
240 600 223 88.28 0.54 8.61 9.19
270 229 88.78 0.58 8.52 9.16
300 234 89.19 0.56 8.13 8.6
240 650 225 88.38 0.53 7.65 9.55
270 235 89.57 0.54 7.26 8.41
300 237 90.33 0.58 6.43 8.03
240 700 228 89.83 0.52 7.11 9.04
270 236 91.01 0.51 6.31 8.43
300 238 91.54 0.52 5.73 7.19
240 750 232 90.89 0.54 6.14 8.36
270 237 91.57 0.53 5.81 6.91
300 240 92.44 0.55 5.78 6.76
240 800 236 91.13 0.57 5.89 7.89
270 241 91.81 0.52 5.37 6.37
300 245 92.71 0.53 5.11 6.11

It is observed from Table 8 that for 6 % LOI, 240 °C drying temperature, 1300 °C firing temperature; rise in preheating temperature from 550 to 800 °C resulted in improvement in CCS from 222 to 236 kg/pellet and TI (+6.3 mm) from 88 to 91 %.
PLANT SCALE IMPLEMENTATION:
Additional heat input through the newly installed burners in preheating zone of induration furnace helped in achieving the desired temperature in the range of 650 - 800 °C. In order to assess the quality of product pellets, analysis of data before and after implementation was carried out and the results are shown in Figures 6 to 9.

As shown in Figure 6, average CCS of fired pellets increased to 238 from 231 kg/pellet. Average TI (+6.3 mm) of fired pellets increased to 89.78 from 89.27 % as shown in Figure 7.
Figure 8 shows the average unfired pellets reduction to 2.5% from 2.88 %. As shown in Figure 9, the average fines generation reduced by 0.71 % (i.e., from 10.44 to 9.73 %).
It is thus possible by way of the present invention to provide a process for indurating high LOI pellets by modifying the preheating process of pellets inside the induration furnace of pellet plant by installing additional burners in preheating zone to supply extra heat so that the complete removal of LOI could take place within the preheating zone of the induration furnace. These additional burners supply extra heat resulting in the required temperature rise in preheating zone for removal of LOI. The process favoured improved pellet product properties with increased average CCS and Average TI (+6.3 mm) of fired pellets and reduction in unfired pellets and fines generation.