This is a good question and it will lead me to investigate our sintered product with respect to the kinetics in the melting furnace. We produce magnetic iron from a laterite ore with basically FeO and Fe2O3 material where we convert to magnetics and produce a concentrate that is relatively porous with high surface area. The kinetics of the furnace reaction could possibly have favorable effect. We are able to increase the grade from 40% Fe in the feed material to 58-60% Fe in final product after beneficiation.

100% pellet as feed to furnace will have good surface area, but porosity also play a major role in reaction, hence the mix of lumps and pellets is good.

Have you determine the effect of porosity or surface area for that matter on the melting kinetics of the furnace feed? This would be interesting as the product we produce is porous and definitely has higher surface area than the normal pellet feed.

What is the effect? On the kinetics? On Power?

Pellets are used in blast furnace should not be porous? And if we are talking about lumps so sintering is another option also it needs to shutter tumbler test before feeding. But don't have any idea about kinetics effects.

I think there hasn't been much studied on the effect of surface area on the reaction kinetics in blast furnace. But then it confuses me on what basis the lump size for blast furnace feed is chosen?

Because I thought the lump size was chosen for maintaining balance between maximum surface area (meaning minimum size) and appropriate void and porosity.

POROSITY and surface area: Here we want to discuss mineral surface area or internal porosity surface area. Which minerals have porosity? Till date all were interested to know more about inter spaces between two particles. That is why it is a standard practice to feed LUMPS and not fines. Fines also have mare surface area, but breathing becomes difficult. The principle question is not clear. If you want to discuss on inter spaces or porosity of minerals

Please excuse me if I am wrong but isn't the size of 10-40 mm (it’s a range in which mostly furnaces take their feed) is decided after carefully considering the balance between the surface area provided by the iron lumps and the void spaces between them?

Because from what I understand, we would want to feed the smallest size possible in blast furnace because it will make melting easier and increase the reaction rate, however if very small size lumps are fed, they would not be able to sustain the weight and will compact resulting in blockage of reducing gas rising from below. So from what I understand, the size 10-40 mm was a compromise between the surface area and the void space provided. Also not to forget some other constraints which we are not accounting here.

Have you looked at any of the shrinking core models? There's different equations based on the rate controlling steps: diffusion, ash layer and chemically rate control. You might find this article useful:http://nopr.niscair.res.in/bitstream/123456789/8411/1/IJEMS%2012(1)%2037-41.pdf

Shrinking core models don't work if there's large temperature differences (you get different kinetics at various points), only heat is required for the reaction or if reactions aren't occurring at a sharp interface (such as in a very porous solid with slow reactions - you'll have to look at a continuous reaction model instead).