Claims:WE CLAIM:

1. A system for the pelletization of different types of iron ore comprising of :

a hot air generator (for low temperature updraft drying);

a pelletization chamber including bottom and top chambers with hydraulic lifting arrangement from bottom for arresting leakages of hot air;

a pellet hardening pot with an hydraulic system for pellet pot movement;

a combustion system including a gas burning system (for high temperature downdraft firing) and a gas exit system; and

a plurality of pneumatically operated gate valves and gas circuit for controlled LPG, oxygen and nitrogen supply.

2. The system for the pelletization of different types of iron ore as claimed in claim

1, wherein the LPG gas circuit is connected to the hot air generator and gas burning system.

3. The system for the pelletization of different types of iron ore as claimed in claim

1, wherein the nitrogen gas circuit is connected to the seven numbers of pneumatically operated gate valves.

4. The system for the pelletization of different types of iron ore as claimed in claim

1, wherein the oxygen gas system is connected to the gas burning system.

5. The system for the pelletization of different types of iron ore as claimed in claim

1, wherein the hot air generator is connected to the bottom chamber to pellet pot to top chamber.

6. The system for the pelletization of different types of iron ore as claimed in claim

1, wherein the gas burning system is placed above the top chamber.

7. The system for the pelletization of different types of iron ore as claimed in claim

1, wherein the gas exit system is connected to a chimney through an ID fan.

8. The system for the pelletization of different types of iron ore as claimed in claim

1, wherein the hot air is generated in hot air generator through the mixing of air and

LPG and air is supplied by a blower and wherein the hot air is diluted by another blower.

9. The system for the pelletization of different types of iron ore as claimed in claim

8, wherein the temperature of hot air is kept to about 400ºC and this hot flue air is flown to the pellet pot for updraft drying.

10. The system for the pelletization of different types of iron ore as claimed in claim

1, wherein pellet hardening pot the bottom chamber and top chamber are a flanged circular shell with mullite based insulation lining suitable for temperature up to1500°c.

11. The system for the pelletization of different types of iron ore as claimed in claim

1, wherein the pellet hardening pot is a flanged circular shell with mullite based insulation lining suitable for temperature up to 1500°c.

12. The system for the pelletization of different types of iron ore as claimed in claim

11, wherein the pellet hardening pot is hydraulic and mounted on wheels supported over a structure for positioning & retracting with hydraulic power pack, instruments & electrics.

13. The system for the pelletization of different types of iron ore as claimed in claim

11, wherein the combustion system includes LPG burners of suitable capacity with common combustion air (ca) fan, combustion air line, excess air line, LPG gas line, valve train & burner management system for automatic operation of heating cycle, flue gas discharge and change over.

Dated: this 20th day of March, 2017.

(N. K. Gupta)
Patent Agent
Of NICHE
For SAIL

To,
The Controller of Patents,
The Patent Office, Kolkata.
, Description:A SYSTEM FOR THE PELLETIZATION OF DIFFERENT TYPES OF IRON ORE FIELD OF INVENTION

The present invention relates to system for pelletization of different types of iron ores. More particularly, the present invention relates in treating of iron ore fines obtained from beneficiation of the low grade iron ores or slime to improve the overall quality of blast furnace burden feed as pellets and also to enhance the overall performance of blast furnace.

BACKGROUND ART

Iron ore IS upgraded to a higher iron ore content through beneficiation. This process generates iron ore filter cake which needs to be pelletized to be used in the steel making process. Also during the processing of high grade iron ores which don’t need beneficiation, fines which are generated can be pelletized and used instead of being disposed of.

Iron Ore Pellets are formed from beneficiated or run of mine iron micro-fines. The iron is usually ground to a very fine level and mixed with limestone or dolomite as a fluxing agent and bentonite or organic binders as a binding agent. If the ore is a Hematite ore, coke or anthracite coal can be added to the mix to work as an internal fuel to help fire the pellets. This mixture is blended together in a mixer and fed to balling discs or drums to produce green pellets of size typically about 9-16 mm. The green pellets are then fed to the induration machine. Both straight grates and grate kilns strengthen the pellets in a drying section, then bring the pellets up to a temperature of about 800-900
°C in a preheat zone, then finish the induration process at roughly 1200-1350 °C. The pellets are then cooled to a suitable temperature for transporting to a load out facility. Both processes recycle the heat from the pellet back through the process to aid in energy efficiency and decrease fuel usage.

Both processes can be used to generate almost any type of desired pellet chemistry, from direct reduction pellets (DR pellets) to blast furnace pellets. By adjusting the amount of fluxing agent or limestone added, pellets can be made that are anywhere from acid (or non-fluxed) pellets to heavily fluxed pellets.

Mixing is where the properly ground ore is combined with binding agents like Bentonite or organic binders, fluxing agents like limestone or dolomite, and if the ore is a Hematite with coke or anthracite coal as an internal fuel. The mixing is done usually in vertical or horizontal high intensity mixers to achieve a homogenous blend of ore and additives.

From mixing the filter cake is sent to the balling area where the ore is agglomerated on balling discs or balling drums into green(or unfired) pellets. Both drums and discs ball the ore to about 9-16mm size. Drums typically have very high recycle rates so have a screening circuit to screen out undersize and oversize pieces to be put back through the drum. Discs usually do not have a separate screening circuit itself.

Green pellets are then transported to the induration process. Pellets that are oversized or undersized and any fines generated during the balling or transporting process are screened right before entering the induration machine and sent back to the mixer or the balling area. The on-size pellets are then fed to the induration machine. Both straight grates and grate kilns dry the pellets out in a drying section, then bring the pellets up to a temperature of about 800-900 °C in a preheat zone, then finish the induration process at roughly 1200-1350 °C. The pellets are then cooled to a suitable temperature for transporting to a load out facility. Both processes recycle the heat from the pellet back through the process to aid in energy efficiency and decrease fuel usage.

SUMMARY OF INVENTION

The present invention is directed to pelletization system wherein iron ore green pellets are indurated. Actually the disclosed system is employed to harden the green pellets to a level of 250 kg/pellet produced from the beneficiation of any type of iron ore. Advantageously, the system of the present invention is capable to use the beneficiated micro-fines of low grade iron ore which has limited option to utilize in the sintering process.

In actual practice, iron ore green pellets are dried to 120ºC. Thereafter, the pellets are preheated to 950-1000ºC and finally fired at 1250-1300ºC followed by cooling to 50ºC. The scope of this work is limited to heat hardening of the green pellets. This innovative work focused in utilizing the goethite type of iron ore which creates several problems during heat hardening of green iron ore pellet due to sudden evolution of the entrapped chemically bonded water between 300-400ºC. In the present work, process parameters can be optimized for the pelletization of any type of iron ore. The basic objective of the present invention is directed to providing a system and process for the simulation of the heat hardening process of green iron ore pellets and optimization of heat hardening parameters such as time, temperature, duration of soaking, heat input rate, heat transfer rate, etc.

BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS

Fig. 1 illustrates Schematic Representation of the Innovative Pilot Pellet Heat

Hardening System in accordance with the present invention;

Fig. 2 illustrates Pictorial view of the Innovative Pilot Pellet Heat Hardening System in accordance with the present invention;

DETAILED DESCRIPTION

As there was no facility for heat hardening of green iron ore pellets, an innovative system has been conceptualized and implemented. The schematic representation of the entire system is shown in Fig. 1. The main equipments of the system are Hot Air Generator, LPG-Oxygen Circuit & Burners, Top Chamber, Bottom Chamber, Pellet Pot, unique leak proof system, Hot Flue Gas Flow Circuit, Gas Exit and Control Panel to run the system in auto mode. After erection, installation and commissioning of the system several trials and tests were conducted. Pellets obtained by optimizing process parameters exhibit the properties like strength, porosity, RDI, RI, etc. in line with the commercial grade pellets. The pictorial view of the innovative system is shown in Fig. 2.

The system consists of a Hot Air Generator (for low temperature updraft drying), Bottom Chamber with hydraulic lifting arrangement for arresting leakages of hot air, Top Chamber, Pellet Pot, Hydraulic System for Pellet Pot Movement, Gas Burning System (for high temperature downdraft firing), Gas Exit System, Pneumatically Operated Gate Valves and Gas Circuit for LPG, Oxygen and Nitrogen.

The LPG gas circuit is connected to the Hot Air Generator and Gas Burning System. The Nitrogen Gas Circuit is connected to the seven numbers of pneumatically operated Gate Valves. The Oxygen Gas System is connected to the Gas Burning System. The Hot Air Generator is connected to the Bottom Chamber to Pellet Pot to Top Chamber. The Gas Burning System is placed above the Top Chamber. The Gas Exit System is connected to a Chimney through an ID Fan.

Functions of the Components:

1. Gas Circuit: LPG is supplied to the Hot Air Generator and Gas Burning System. Nitrogen Gas is supplied to pneumatic valves. Oxygen Gas is supplied to the Gas Burning System.

2. Hot Air Generator: Hot air is generated through the mixing of air and LPG. Air is supplied by a blower. The hot air is diluted by another blower. The temperature of hot air is kept to about 400ºC and this hot flue air is flown to the pellet pot for updraft drying.

3. Bottom Chamber and Top Chamber: It is a flanged circular shell with mullite based insulation lining suitable for temperature up to1500°C.

4. Pellet Hardening Pot: Flanged Circular shell with mullite based insulation lining suitable for temperature up to 1500°C. Hydraulic, mounted on wheels supported over a structure for positioning & retracting with hydraulic power pack, instruments & electrics.

5. Combustion System: LPG Burners of suitable capacity with common

Combustion air (CA) Fan, combustion air line, excess air line, LPG gas line, valve train

& burner management system for automatic operation of heating cycle, flue gas discharge and change over. Oxygen enrichment has also been provided.

Working Principle

The pilot pellet plant has been installed to reproduce the commercial scale pellet plant conditions i.e. it is a simulator of straight grate green pellet heat hardening system. The capacity of the pilot plant is for production of 40-60 kg hardened pellets. The diameter of the green pellets is in the range of 8 to 16 mm. The process of hardening consists of drying, preheating, firing, cooling and soaking in between at different stages. Precise control of time and temperature for drying, heating, soaking and cooling is the key to achieve the desired hardness and other properties of the pellet. The flue gases after cooling will exhaust through chimney.

Results

Two types of indurations have been planned. One type of experiments were conducted through conventional hardening process i.e. Drying at 250°C for 15 min, Preheating at
1000°C for 20 min and Firing at 1350°C for 15 min. The other type of experiments were conducted through special hardening process i.e. Drying at 250°C for 15 min, After Drying at 400°C for 15 min, Preheating at 1000°C for 20 min and Firing at
1350°C for 15 min. In the second case an extra hardening treatment i.e. after drying treatment was given at 400°C for 15 min. The experimental methodology is given in Table 1.

Table 1: Different methods of Pellet Indurations

Pellet Induration
Conventional Method Special Method

Drying at 250°C for 15 min Drying at 250°C for 15 min
After drying at 400°C for 15 min
Preheating at 1000°C for 20 min Preheating at 1000°C for 20 min
Firing at 1350°C for 15 min Firing at 1350°C for 15 min

The results different tests conducted after hardening of the pellets i.e. Cold Crushing Strength (CCS), Porosity, Reduction Degradation Index (RDI), Reducibility Index (RI) is given in Table 2.

Table 2: Salient Properties of the Roasted Iron Ore Pellets

Properties Values
Traditional

Method Special

Method Commercial

Grade
CCS, kg per Pellet 180 240 230-260
Porosity, % 15 18 18-20
RDI, % 8 7 6-8
RI, % 58 61 58-62

After-drying treatment during induration results in higher CCS value and the pellets also exhibit better properties (porosity, RDI, RI, etc) compared to the traditional hardening treatment. This may be due to smooth evolution of chemical water of goethite ores. It can be assumed that constant rate of heat transfer from the pellet surface to interior results in smooth evolution of chemical water which in turns results superior properties of the roasted pellets. Table 2 also reveals that pellets obtained in special hardening treatment method i.e. with after drying treatment exhibit the properties in line with the commercial grade.

Salient features

a. Using this system desired quality of heat hardened pellet can be prepared in fully automated manner, with only initial setting up of desired time-temperature profile. b. This system has the capability to optimize heating cycle as per DTA-TG curve of input raw material to be pelletized. This system has capability to provide maximum temperature up to 1400°C to the material to be pelletized.
c. This system has a capability of optional purging of oxygen enrichment (up to

10%) at any temperature level of thermal cycle for betterment of final pellet.

d. The system has a capability to provide up to 8 numbers of temperature soaking duration in stage wise after surface moisture drying to remove inter molecular volatile matter to optimize the heating cycle for desired quality of heat hardened pellet.
e. Parameters like time temperature curve, machine speed, yield and productivity of any straight grate commercial pelletize machine can be optimized in pilot scale using this system with a limitation of maximum temperature of 1400°C.

Experimental Observations

The representative iron ore samples were collected from Gua, Bolani, Kiriburu and Meghahatuburu mines for in-depth investigation at RDCIS laboratory. The samples were ground to micron level and beneficiated through hydro-cyclone and magnetic separator. Then the samples were analyzed using DTA/DTG, XRD, mineralogical microscope and XRF equipment. After characterization of the samples, green pellets of size 9-16 mm were prepared by a laboratory disc pelletiser of 1m diameter using the ore fines of minimum blaine value of 2000 cm2/g with 0.6% bentonite as binder and thereafter, drying, pre-heating and firing were conducted in a tailor made laboratory scale horizontal zone furnace by varying the main process parameters such as temperature and duration of soaking. Thereafter, the same pellets were heat hardened under the same conditions in the innovative pilot scale system of capacity 60 kg per batch i.e. straight grate pelletization simulator for the production of commercial grade pellets. This unique pilot pellet heat hardening system has been designed, developed, erected, installed and commissioned at RDCIS, Ranchi complex by employing in- house technology. Pellets obtained by optimizing the above process parameters exhibit the properties like strength, porosity, RDI, RI, etc. in line with the commercial grade pellets.

Although the foregoing description of the present invention has been shown and described with reference to particular embodiments and applications thereof, it has been presented for purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the particular embodiments and applications disclosed. It will be apparent to those having ordinary skill in the art that a number of changes, modifications, variations, or alterations to the invention as described herein may be made, none of which depart from the spirit or scope of the present invention. The particular embodiments and applications were chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such changes, modifications, variations, and alterations should therefore be seen as being within the scope of the present invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.