B.F. Pellets are agglomerated fines for use in Blast furnaces like any other material like calibrated lumpy ore or sinter.

Initially pelletizing process was developed for fines (with significant fraction of minus 100 mesh) which could not be sintered (like taconite concentrate). These type of conentrates had very low alumina.

Pellets have a higher manufacturing cost and BF users wanted better performance with respect to coke rate, production rate from pellets to justify higher price. As bigger and bigger blast furnaces were built post reduction properties of pellets also gained importance. Flux had to added to achieve these properties - low alumina and good SiO2 : Al2O3 ratio helped in achieving these goals. Removal of Alumina in earthy hemetite ores is a costly process.

Earlier Pellet plants were near mines. Now Chinese Steel mills have started installing pellet plants (instead of sinter plants) in the steel mills. In this case There is no degradation of pellets in transport. and economics will depend of relative costs of coke, pellets, fluxes etc ■

my experience is all with taconite pellets. they tend to have very low alumina. However, the question pertains more to how the blast furnace is operated than anything. Blast furnace slags are usually designed with a 1 ratio between the basic components (CaO and MgO) and the acid components (SiO2 and Al2O3), depending on the sulfur they are trying to get out of the metal product. Taconite comes in several "flavors." An acid pellet would be one with more alumina and silica. A basic or fluxed pellet would have added CaO to balance the acids. This changes pellet softening and melting properties and lets the furnace operator feed less trim materials like stone. Some taconite producers even make a superfluxed pellet, that has flux required for the coke included. So, your question is basically, what plant will be using this material and how will they choose to operate their blast furnace.

Hugh Crosmun ■

Allumina is normally considered a contaminant, as you don't want this in your final product. Although an HYL plant in Rusia used Allumina in their pellet, in the belief that it would increase hardness, and solve the solids flow problems that they were experiencing during start-up.

If it was my choice, I would use Dolomite to form spinnels and increase the melting point and, in consequence, avoid the softening of the pellet at high temperatures. Dolomite, as well as Lime will increase the Ph of the pellet making it easier on the refractories.

The problem in Rusia, from my point of view, was related to the start-up loading through one of the 4 legs that subsequently polished one side only of the reactor cone.

Being the HYL reactor marginal in the solid flow properties, the cones need to be homogenous in roughness, at least. Ideally, they should be polished to avoid channelling during start-uip.

After a few months, the reactor will polish itself and there will be no more channelling, or there will be isolated events. Nevertheless, HYL reactors always suffer during start-up and as a normal corrective action, people tend to work with the pellet properties to make them harder, etc.

Swelling is another problemk that has to be dealt with iron pellets as well as sticking, if they are going to be used in direct reduction. Sticking is a frequent problem not onl with pellets, but wih iron fines or dusts in fluidized reactors and dust collectors.

Regards,

Marco A. Flores ■

Expanding on the previous

This is the article on russian describing the use of alumina at the HYl plant in Levedinsky.

Improving the performance of the HYL-III unit at OAO Lebedinskii GOK.

Intersesting as it is . you have to read between lines .

check the price of gas at that time and the price of scrap at the same time , and you might beguin to understand why a New plant (not quite yet pased the acceptance test) had touble to start up.

there are many things behind that , that meets the eye.

Marco ■