Iron Ore Pellets Screening Solutions

The productive operation of a pelletizing plant is closely linked with its capacity to effectively screen green balls prior to their induration. The narrower the pellet size distribution is within the required pocket size range, the higher the plant efficiency will be. Better pellet sizing leads to improvement in plant productivity, reduction in induration costs (fuel for instance) and higher pellet quality.

Furthermore, the requirement for better sizing of pellets goes beyond the operational needs of the pelletizing plant.  It is also one of the main quality criteria for the steel making plant buying the pellets.

Screening through roller screens is known for decades.  But many roller types and roller screen designs are available on the market.  They provide large differences in the segregation efficiency of the pellet sizes.  Few roller screen designs really perform in service. 

 

The challenge is to develop a screening solution that would:

-    Increase productivity of the pelletizing line;
-    Recover all the good size pellets;
-    Provide size distribution within the narrowest bell-curve shape (for instance pellets between 10 – 12.5 mm);
-    Reduce to a minimum the pellet breakage occurring in the green pellet handling, screening and discharging;
-    Distribute pellets on the grate in order to ensure their uniform firing in the furnace;
-    Optimize pellet bed permeability – one of the most, if not the most, important function of a screening solution;
-    Low maintenance and high availability of the pellet screening line;

Metal 7 has concentrated its efforts in the last 40 years on roller screens, since this is still the best known system for the segregation of the pellets according to their size.

The company at first focussed on the rollers as they are the most important component on any roller screen.

The constant improvement of their rollers also led them to design their own roller screen system to get even better screening performance out of its rolls. Existing designs in the industry had limitations. They could not accommodate the smaller diameter rolls developed by Metal 7. They did not provide the versatility of adjustment in service (RPM of the rolls, inclination, etc.) and they had lower availability in operation.

Its roller screen systems have become the most cost-effective solution and even the standard in the iron ore industry. No one attains the same efficiency thanks to the combination of their special rolls and well-designed equipment.

 

METAL 7 solution for rolls:

-    Roller material 

Through its expertise in material and surface engineering, Metal 7 selects the most appropriate material for the manufacturing the rolls for every application. In most projects, our objective is to use the smallest possible roll. The smaller the rolls, the more rolls and more gaps in the screen.. We pay close attention to the eventual deformation during service, and particularly for the longer rolls of the roller feeder at sometimes more than 4 meters long.

Other suppliers compensate for the lower strength of their roll by increasing the diameter of the roller. This goes counter to the maximisation of the screening surface in the design of a roller screen (bigger rolls equal less gaps per screen).

 

-    Roller surface

The engineering team develops the specifications of the rollers to ensure the adequate transportation of the pellets from one roller to the other without generating sticking on the roller surface.  The characteristics of the ore and pellet content are taken into consideration.  Pellet breakage is also considered.

 

-    Construction of the rolls

Rolls are assembled with shafts. We offer different fixed or removable shaft arrangements (bolted, central screw types, etc.). We determine what is most suitable according to the specific needs of a roller screen, including the size of the rolls, the driving mechanism, the location, etc.

 

-    Selection of the wear protection

Metal 7 has distinguished itself in the industry with its protective coatings for roller screen rolls. Its coated rolls are used in over 40 pelletizing plants.

Different types of coatings are available.  Metal 7 will select the one appropriate for your operation whether it is for a retrofit on your existing equipment or for a new screen supplied by Metal 7.

The coated rolls do not really wear. Therefore, they last much longer than uncoated rolls found in the market. Experience has shown increases in life expectancy by a factor of up to 10 when converting to such coated rollers of Metal 7. The coated roller replacement will not be related with wear. Other mechanical related causes will provoke the replacement of coated rolls (shaft problems, damages of the coating surface, etc.).

Most coated rollers could be reconditioned to give them a second or third life in service.  It is more popular for larger rolls of the roller screen/feeder located at the entrance of the indurating surface. 

However, the increase in the workign life expectancy is not the main contribution to the coating. The fact they do not wear means also that the gaps between rolls stay constant all through the life of the rolls. Therefore, the screening performance remains at its best without requiring periodic calibration of the gaps. That is by far the most important feature of the coated rolls.

The wear resistance of the coated rolls is also a key contributor to the use of smaller diameter rolls on Metal 7’screens. It is not necessary to provide extra material on the roller diameter to compensate the wear. They will retain their integrity for the entire life of the roller.

Metal 7 will review the specific operating conditions in your pelletizing plant and will propose the most adapted coating option. Different coating options are available including the :

•    The M7-C21: Ceramic coating with high hardness (70 HRc), very good pellet transport, high longevity.  The most cost-effective coating and its most popular;

•    M7-A19 (or M7-C19 for smaller rolls): Carbide base coating with high hardness (68 HRc), good transport property, high impact resistance, etc.  This coating option is particularly adapted to plants handling material with more contaminants or leading to more building-up on roller surface.

•    M7-D130: Metallic base coating with material hardness increasing with the contact of pellets, very high transport property, etc. It is considered only for handling dry pellets (very low moisture). Other coatings are available including many variations of the above coating families.

Other coatings are available including many variations of the above coating families.    

ROLLER SCREEN SYSTEMS

The involvement of Metal 7 in the production of rollers for roller screen for the last 40 years had exposed us to a lot of different roller screen designs and technologies.   However, its engineering team did not find one that was addressing all their concerns to really provide the end users with all the possible benefits our special rolls could provide.  

So, in the 1990’s they developed their own design gathering all the best features found on different screen technologies and in innovating with their own ideas. In the last 25 years, the company has invested major resources in the constant improvement of its most popular product family, the roller screen.

Beside the impressive contribution of the rolls themselves, the roller screen systems of Metal 7 is the most popular on the market thanks to the following:

-    We optimise the screening surface. They can accommodate the smallest available rolls, which provides more screening gaps. The screen width (roller length) is also lengthened to the maximum allowed by the plant layout and limitations;

-    Metal 7 offers a wide range of options and features in the design.  Each screen is customised for every application to maximise productivity, lower CAPEX, OPEX and maintenance costs and surpass the expectations of the end users;

-    Reduced pellet breakage (lower pellet drops, EPSILON discharge end, etc.);

-    High equipment availability is our trademark;

-    Energy efficient design;

-    Lower vibration and noise level;

-    Simple design and rapid roller gap adjustment, roller replacement and screen maintenance;

-    Critical components are sealed and protected against dust contamination;

-    Creative design and use of material for the chutes, skirtboards, chain take-up, sprockets, bearings, etc.

-    A dedicated engineering team support all through the process (design of the solutions, implementation, commissioning and post-sale service);

 

Metal 7 offers all the screening solutions for your pelletizing plant whether it is for your balling department (single deck roller screen – two product or tri-product versions) or for your induration furnace grate feeding station (roller feeder).  In this latter case, several configurations are available with the individual drive or chain driven options including the :

-    Single deck roller feeder (removing only the fines/undersize);

-    Double deck roller screen/feeder (removing the oversize pellets and the fines/undersize pellets), or;

-    The new triple deck version for the segregation of pellet size in the pellet bed on the grate.

 

A comprehensive screening solution is also offered to Metal 7’s customers optimizing the complete green pellet screening function and the pellets discharge on the grate of induration furnace. Its project scope could include the roller screens and roller feeders but also all other related equipment involved in the screening operations, including:

 

-    The specialized belt conveyors feeding the pellets to the roller screens/feeders and returning the off-size pellets;

-    The charging system feeding the green pellets on the wide belt conveyor (reciprocating belt conveyor or shuttle belt conveyor);

-    The oversize pellet shredders or squeezers;

-    Etc.

 

This comprehensive approach permits a complete integration of the equipment without interference. It also optimises the overall performance of the screening function. Improved pellet quality and productivity, lower pellet breaking and the uniform laying of the pellets on the grate according to the desired profile are the main focus of this integrated approach.

Improvement of green pellet screening leads to very significant for the pelletizing line and for the steel making plants using the pellets.

Better pellet sizing enhances the productivity of the plants with better circulation of the hot gases in the furnaces. That is the most obvious gain.

Green pellet screening solutions of Metal 7 also provides:

-    Larger screening surface allowing higher throughput of the line, the screening capacity often being a bottleneck in plants;
-    Higher productivity of the pelletizing plant with a better sizing and superior bed permeability in the surface;
-    More cost-effective machines with lower and easier maintenance and higher equipment availability through less maintenance (or calibration) related interruption of the pelletizing line;

-    Gains in efficiency: All good pellets go to the induration instead of being wrongly recirculated in the process (wear resistant rolls equal constant gaps);
-    Smarter use of the energy.  Better sizing reduces the consumption of fuel.
-    Better quality: final product is more attractive for the steel making plants with a narrower sizing and better firing of the pellets;

Just for the pelleting plant operation, benefits in terms of millions of dollars per year are attainable with the conversion to a better green pellets sizing system.