Why iron bearing materials should be pelltized or briquetted before they are introduced to the blast furnace?
- Why they cannot be added in a powder form, what is the effect of briquette size on the iron extraction process?
-What is the effect of moisture content on the process and what is the highest acceptable range of moisture content of briquettes?
iron making process basically blast furnace worked on counter current reactor mechanism where the reducing gas at high velocity comes in contact with iron bearing raw material.If fine where used there will not sufficient permeability of material for interaction of gases with the solid iron bearing material.If excess fines will used it tends to attain the terminal velocity of upwards flowing gas and went out of the system called as flooding.
the size of briquette plays a vital role on reduction kinetic.Before material reaching to the Thermal reserve zone of bf it should get reduced and stats soften.the lengthy of thermal reserve zone decide the coke requirement in blast furnace.
the size of briquette for blast furnace will +10mm -20 mm or less than 25 mm size with sufficient porosity of 25-30% will considered suitable for blast furnace.the optimium moisture for briquetting is the range of 7.5-9%.
iron making process basically blast furnace worked on counter current reactor mechanism where the reducing gas at high velocity comes in contact with iron bearing raw material.If fine where used there will not sufficient permeability of material for interaction of gases with the solid iron bearing material.If excess fines will used it tends to attain the terminal velocity of upwards flowing gas and went out of the system called as flooding.
the size of briquette plays a vital role on reduction kinetic.Before material reaching to the Thermal reserve zone of bf it should get reduced and stats soften.the lengthy of thermal reserve zone decide the coke requirement in blast furnace.
the size of briquette for blast furnace will +10mm -20 mm or less than 25 mm size with sufficient porosity of 25-30% will considered suitable for blast furnace.the optimium moisture for briquetting is the range of 7.5-9%.
Iron ore pellets and briquettes must have properties that match the conditions in the aggregate in which they are processed. Each of these conditions is highlighted through specific tests. In the particular case of the blast furnace are required characteristics that correspond to: a thermal heating gradient of about 450 - 500 kg C / h, compressive strength - kgf / pellet / lighter, sufficient mechanical resistance under temperature conditions and modification of the internal structure due chemical gas reduction - Nagoya test after chemical reduction at 550 gr.C.
Pellets dedicated to use in blast furnaces are usually calcined at 1300 gr.C to obtain mechanical strengths of approx. 200 - 220 kgf / pellet. Shock and abrasion resistance tests are made in standardized drums: IRSID, MICUM. The reductibility tests are carried out in reduction plates and then mechanical shock resistance. The briquettes have not yet been established for use in medium and large capacity furnaces (over 750 m3). Technological manufacturing conditions are chosen to achieve these characteristics.
Why they cannot be added in a powder form, what is the effect of briquette size on the iron extraction process?
As Dhiraj sir said, it has impact on reducibility of iron oxides. The other major concern of pellet/sinter feed in blast furnace is size distribution. It affects the radial distribution of burden. for example, lesser particle size tends to segregate either at the center or to the wall. It affects the cohesive zone properties of the materials and it will affect the blast furnace performance.
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