MOVING CAR FURNACE FOR IRON ORE PELLETIZATION PROCESS

FIELD OF THE INVENTION

The present patent application relates iron ore pelletization process. More particularly, it relates to a process for iron ore pelletization in a moving car furnace. Further, it also relates to the moving car and its use in the iron ore pelletization process in an induration furnace setup.

BACKGROUND OF THE INVENTION

Increasing demand for steel in the domestic and international markets, depleting reserves of precious iron ore has made it necessary to find usage of fines and conserve the iron ore.

Pelletization is an essential alternative process for dwindling stocks of iron ore as the pellets have better porosity and reactivity as compared to lump ore.

The iron ore feed is extremely fine in nature with majority of particles smaller than micron. Generally, the iron ore feed that is used to produce iron ore pellets is a multi component mixture of ores, coke breeze or coal fines, limestone or dolomite and bentonite as a bonding medium.

Pellets are produced by a process called pelletization process. This process essentially makes iron ore from very fine powder in to porous, partially fused and sufficiently hard agglomerates or balls of certain diameter also known as pellets.

Pelletization typically consists of two steps, a) balling of fine powder in a rotating disk or drum to produce green pellets (balls); and b) Induration or thermal hardening of wet pellets at an elevated temperature to produce fired pellets.

Several procedures for iron ore pelletization are described in the literature including US 4257806, US 4684549, US 5908166 and WO 2009/119291Al.

The reported technologies for producing pellets include Combined Grate Kiln Process; Straight Grate Induration Process; and Vertical Shaft Furnace. Even though there technologies are used in some industries, they suffer from several disadvantages when used in large scale industry.

In Combined Grate Kiln Process, drying, preheating, Indurations and cooling cycles are carried out in different units like straight grate for drying and preheating, rotary kiln for roasting and annular cooler for cooling. The green pellets are fed in to Straight Grate and the pellets are moved along with the grate in to different zones such as drying zone and preheating zones till it attains about 800°C to 1000°C. Thereafter it is transferred to rotary kiln where the temperature is further raised up to about 1250 - 1300°C and then it is transferred to annular cooler for cooling. The major disadvantages of this process includes: heavy generation of fines causing accretion and pollution; Need more fuel as less efficient thermal process; shut down the furnace for maintenance; and all the parts are imported.

Straight Grate Indurations Process involves drying, preheating, indurations and cooling cycles are carried out in single straight grate. The green balls are fed in to straight grate and the pellets are moved along with the grate in to different zones like drying zone, preheating zone, firing zone and cooling zone. This process also has some disadvantages such as Need more fuel as less efficient thermal process; shut down the furnace for maintenance; and all the parts are imported.

Hence, there is a long felt need to develop a process which obviate the aforesaid disadvantages and yet suitable for manufacturing in large scale industry.

SUMMARY OF THE INVENTION

The present patent application provides a process for iron ore pelletization, which process comprises of:

providing green balls in a car, which is provided with a provision for movement;

moving the car along the furnace through various reaction zones over a period time at a specified temperature and pressure; and

collecting the fried pellets of required quality.

The present application also relates to moving car and its use in the iron ore pelletization process. Further it also relates to a moving car induration furnace its use in the iron ore pelletization process.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a schematic diagram of a typical moving car induration furnace along with flow directions.

Fig. 2a and Fig 2b are schematic diagrams showing cross-section view and top view of a moving pellet car.

DETAILED DESCRIPTION

The present patent application provides a process for iron ore pelletization, which process comprises of:

providing green balls in a car, which is provided with a provision for movement;

moving the car along the furnace through various reaction zones over a period time at a specified temperature and pressure; and

collecting the fired pellets of required quality.

The green balls that may be used in the current process are produced using a typical process such as balling of fine powder in a rotating disk or drum or by any other process described in the art for producing green ball. The iron ore used for producing green balls may be selected from magnetite and hematite ores

The green ball may also be obtained by adding binder comprising water, organic polymer and the like to the fine powder.

The moving car as used herein is a car provided with a provision for movement along the length of the furnace. A typical moving car setup is described in fig.2a and 2b.

The car is made of steel perforated plate in bottom and side wall plate. The car will be moved over the railing by drive arrangement the furnace is designed in easy to operate, maintenance and flexibility.

Several such cars will be moved sequentially from one end to other end by means of drive arrangement. Furnace is designed in different zones such as UDD (up draught drying zone), pre heating zone, firing zone, cooling zone. Sealing arrangements are provided in between zones in bottom and top of the furnaces.

The moving car induration furnace is a cross-current packed bed gas - solid reactor. While the pellets or solids move along the length of the furnace, gases flow in upward or downward directions in different zones on the moving car furnace.

The schematic of a typical moving car induration furnace along with gas flow directions is shown in Fig. 1. The furnace top is a completely covered with gas hoods and at the bottom of the furnace is covered with wind boxes.

The moving car pelletization furnace may be suitably divided in to five zones namely UDD zone (1), pre heating zone (2), firing zone (3), cooling zone-A (4) and cooling zone-B (5). The wet pellets or green balls (6) are charged to a specific bed height in to the each moving car (7) at the feed end (8) of the moving car furnace.

The aforementioned zones are being fed by a gas circulation of required temperature i.e hot gases in drying zone, heating and firing zones where as cold gases in cooling zones.

These various zones are provided with provisions for measuring temperatures. The process is controlled by measuring temperature in the aforementioned zones or portions of zone and controlling the gas circulation and the car speed between a predetermined maximum value and a minimum values.

The green balls are first moved in to UDD Zone where the moisture from the pellets is removed by utilizing waste gases from cooling zone-B. Thereafter it is moved in to pre heating zone where the pellets are preheated to 800 - 1000°C by using gasses coming out from the firing zone.

Thereafter it is moved in to firing zone where the pellets are heated up 1200 - 1300° C by firing furnace oil/pulverized coal. Thereafter it is moved in to cooling zone for cooling the pellets.

The drive arrangement (9) in the moving car furnace is designed in such a way that the car will be moved over the railing through the furnace in uniform speed and it consists of 1) Electric motor to drive the driving mechanism 2) Gear Box 3) Driving Mechanism and 4) Driving mechanism sprockets.

The driving mechanism is made of chain and pushing arrangement on the chain. The pushing mechanism is arranged in such a way that the movement of the car is continuous and constant speed to obtain by the way of adjusting the motor speed.

The pellet feeding in to car is arranged such a way that the Green balls (Pellets) is fed in to the car with uniform bed height and width. It contains of pellet feeding conveyor and leveler.

The roasted pellets are cooled in a closed chamber without moving the pellets in its position and cooled by forced Air. After cooling, the pellets are discharged in the bunker (10) by hydraulic lifting arrangement (11).

The car travelling arrangement throughout the furnace over the railing, the car will be moved from one end to another end.

As the cars moves pellets undergoes various stages of drying, preheating firing and cooling sequentially. In order to optimize energy consumption off gases from one section are re circulated and utilized in another section. Hot air from second cooling zone is recycled to the UDD zone to reduce the moisture content of the fresh pellets in the lower part of the bed. This in turn reduces the tendency of pellet deformation and breaking of pellets into small pieces due to excessive internal water vapour pressure (spalling).

The air flow to UDD is controlled to avoid lifting of the bed. The hot air from the cooling zone-A is fed to the firing zone through ducting.

The overall objective of pelletization plant operation includes maximizing productive, minimizing fuel consumption maintaining roasted or fired pellet quality within limits specified by blast furnace or DRI units requirement and also minimize green house gas and sulfur emissions to the environment.

This process is directly linked to process variables such as wet pellet or green ball sizes distribution and strength, time temperature profile etc.

The moving car furnace is a cross current packed bed gas solid reactor. In this process the green balls are fed in to a moving car furnace at a required bed thickness. The green pellets are moved along the furnace with moving car in to different zones for various thermal processes.

Sealing arrangement is very important role in the pellet roasting process to avoid the false air entry in to furnace and air short circuits. The sealing is arranged in such a way that the gap between moving car and furnace wall is kept at minimum level to avoid the false air entry.

Furnace bottom sealing is arranged to avoid the false air entry in to the furnace. The sealing is made with high alloy steel sheet strips to with stand high temperature and it will be guided through the car bottom support channel.

Zone sealing has important role in the pellet roasting process between the up draught and down draught zones. The sealing is adjustable depending upon pellet bed height the sealing black is made of refractory black and both the sides fixed with adjustable screws for adjust the height.

ADVANTAGES OF MOVING CAR INDURATING FURNACE

Pellets remain undisturbed thought the process.
Generation of fines is bare minimum as there is no transfer of materials Minimized dust generation and uniform heat treatment. Drying, Preheating, Firing and cooling process are carried out in a single unit.
More thermal efficiency and lesser fuel consumption.
Lesser power consumption for car movement and easy maintenance of of the car.
No down time required for maintenance of grate car as independent car can be replaced without stopping the process or reducing the temperatures because there are no chain links are involved
Controlling of temperature, air and gas flow in different zones is easy. Suitable for Both the hematite and magnetite ores. No moving or rotating parts are exposed to high temperature.
Compact and suitable for small capacity, capacity starts from 1 lakh tones per annum.
Lowest Investment and all the required machinery is available in domestic markets.

We Claim:

1. A process for iron ore pelletization, which process comprises of: providing green balls in a car with a provision for movement; moving the car along the furnace through various zones over a period time at a specified temperature and pressure;
collecting the fried pellets of required quality.

2. A process for iron ore pelletization, which process comprises of: providing green balls in the form of a bed in a car with a provision for movement;
moving the car along with various zone comprising UDD zone (1), pre
heating zone (2), firing zone (3), cooling zone-A (4) and cooling zone-B (5) at
a specified temperature and pressure; and
collecting the fired pellets of required quality from the car at the end of the furnace.

3. The process of claims 1 and 2, wherein the specified temperature range varies between 10°C and 1300°C.

4. The process of claims 1 and 2, wherein the car travelling arrangement throughout the furnace over the railing and moved from one end to another end.

5. The process of claims 1 and 2, wherein several cars are moved sequentially from one end to the other end by means of drive arrangement.

6. A moving car that is used for iron ore pelletization process which is according to Fig 2a and 2b.

7. The car of claim 6 which is made of steel perforated plate in bottom and side wall plate.

8. The car of claim 6 which is moved over the railing by drive arrangement along the length of the furnace.

9. A moving car furnace installation set up comprising
UDD zone (1), pre heating zone (2), firing zone (3), cooling zone-A (4) and cooling zone-B (5) with a provision for circulation of gases at specified temperature and pressure;
several cars with a provision for sequential movement over the railing by drive arrangement along the length of the furnace; and
provision for recirculation of gases used in one zone to another zone.

10. The moving car furnace installation setup of claim 9 which is according to Fig. 1 and the moving car setup which is according to Fig. 2a and 2b.