Process
The pellet plant facility is conceived as versatile operation capable of producing a variety of product types, as predicated by the ore supply and/or the market demand. Thus, from time to time, campaigns may be run to produce varieties ranging from acid pellets, pellets with nominal limestone addition or fluxed pellets.
The Pelletization Plant is provided with single strand indurating machine to achieve the uaranteed capacity as mentioned above.
Bentonite / Hydrated lime & ground coal is used as additive for Pelletizing.
The Pelletizing Plant can be broadly classified into the following sections
- Ore Beneficiation & Grinding Section
- Storage Silo & Bins Section
- Weighing & Mixing Section
- Balling (Green Pelletizing) & Screening Section
- Indurating Section
- Dedusting Section
ORE BENEFICIATION & GRINDING SECTION
Iron Ore received from the mines needs to be beneficiated & ground. The process of Beneficiation depends upon quality of Iron Ore. The ore with Fe content of + 63% can be beneficiated by washing & to be ground upto 300 mesh for Pelletization.
For Iron Ore with low Fe content, Beneficiation can be done by various alternatives like Gravity Separation, Magnetic Separation, etc. Grinding of Iron Ore can be done by Dry grinding or Wet grinding depending on the process of Beneficiation. For wet grinding filtration is required after grinding.
Beneficiation process will ensure good and consistant quality of Pellets having Fe always more than 65%.
STORAGE SYSTEM & BINS
Storage systems are large Silos/ Bins with aeration & extraction System to store raw material, binding, etc.
The Storage System comprises of:
- RCC Storage Silo with aeration & extraction System along with Bag Filter
- Ground Bentonite Bin with bag filter.
- Ground Coal Bin with inert gas purging & bag filter
- Organic Binder bin.
WEIGHING & MIXING SECTION
Accurately weighed quantity of ground iron ore with binders / additives from respective bins are conveyed to mixer via a belt conveyor & all ingredients are mixed in Intensive mixer. Normally iron ore is mixed with water, bentonite & ground coal. Set points are adjusted as per balling performance / requirement. Intensive mixing is necessary with the following explanation:
To achieve a uniform growth and control of green pellets within the pelletizing disc as well as a uniformity in relation to physical properties of the green pellets.
For Chemical reaction between additive and ore during the firing process. This reaction is more uniform, if better mixing take place. It also influences physical properties of the fired pellets.
BALLING & SCREENING SYSTEM
The green Pelletizing Section has Pelletizing discs. One Pelletizing disc serves as a stand by unit. All the Pelletizing Units are identical. Mixed material is discharged from bin via vibrating mouthpiece and the Dozing Belt Weigher. The amount discharged is controlled in accordance with the set point fixed in the process control room. In the feeding chute to the Pelletizing disc, a fluffer and adjustable guide plates are installed to allow in a certain range the charging point of mixed material onto the Pelletizing disc. The function of the fluffer mainly is to disintegrate the fed material from the Weigh Feeders and spreading the mixed material on a certain area of the Pelletizing disc. The Rotary movement of the disc produces the green Pellets. The disc’s rotational speed is below the critical, so that the material carried along can roll down from the highest point of the disc to the lowest. The rolling motion of the material and the surface tension of the water in the individual particles of material lead to forming of micro Pellets. As the disc carries them along and as they roll down again, due to tumbling action, these micro pellets grow until they reach a specific size & then spill over the edge of the disc (separating out effect).
The pellets discharged from the discs are directed to the roller screen conveyor. The roller screen conveyor separates the fraction Minus 6, 6 to 16, and + 16 mm. The fraction 6 - 16 mm is fed onto the green Pellet collecting conveyor. The fraction 0 - 6 mm is fed to a recirculating belt conveyor whereas the fraction + 16 mm is fed onto another recirculating belt conveyor. The green pellet collecting belt conveyor feeds the green pellets having the fraction 6 - 16 mm onto the moving belt conveyor, which discharges the green pellets onto the descending belt conveyor & from there to the roller conveyor.
Belt conveyors for collecting the undersize & over size green pellets from roller screen conveyor feed the material into the mixer with plough scrapper. The recirculated under and oversize green pellets as well as the total disc discharge of the disc can be dumped in case of emergency or during disc adjustment.
The undersize fraction from the roller screen conveyor is collected by a belt conveyor and fed via other belt conveyors onto required belt conveyor. Two belt scales are installed in the recycling conveying system to indicate the amount of screened out undersize material & total amount of recirculated material of the green pellets section onto the concentrate belt conveyors. Transporting units distribute the green pellets onto the indurating machine with required width as evenly as possible.
PELLET INDURATION SECTION
Travelling Grate - Machine is basically an endless chain of Pellets. The lifting wheel guides the pellets up onto the rails of the upper strand, and the lowering wheel guides them down again at the discharge end onto the rails of the lower strand. Each Pellet consists of two end sections & a center part. The end sections incorporate the running and pressure rolls.
The Indurating machine has nos. of wind boxes, connected to the process gas/air lines and fitted with dust removal equipment. Wind boxes are equipped with Motorised throttle dampers, so as to be able to adapt the flow of gases in these sections to the process requirements. All wind box pipes are fitted with compensators to allow for thermal expansion between the wind boxes and gas mains. Vaned sealing plates between the wind boxes are position in certain area, where the gas flow reverses. These sealing plates restrict the extent to which the gases take shortcuts at these points.
Above the Indurating machine, hoods with refractory material are installed. Burner chambers are arranged along both sides of the hood in alternative sections. These Burner chambers are connected to the direct recuperation line via connecting pipes.
Dividing walls with refractory cladding are situated between various zones in the hoods. To restrict the movement of infiltrating air or process air between hood and moving pellets to a minimum, sealing air is blown in special sealing elements. Cooling water system is installed to cool the traveling grates. Burners with flame detectors are installed for firing of fuel from burner hoods.
PELLET TRANPORT SYSTEM
Vibrating Feeder, Belt Conveyor, Bucket Elevator are installed at various locations for Transportation of Pellets.
DEDUSTING EQUIPMENT FOR INDURATING SECTION
Utmost care is taken in ensuring the proper environment by installing the Pollution Control Equipment at various points.
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