THE INFLUENCE OF ADDITIONAL NITROGEN CONTENT IN THE HEATED DUTTY ON THE PERFORMANCE OF THE BLOWING PERIOD OF BLAST FURNACES

An analysis of the effect of heated nitrogen and blowing temperature on the course of the blast furnace process was performed from the point of view of the developers of this technology and the theory of the blast furnace process. It is shown that enriching the blowing with nitrogen reduces the volume of the cavity in case of oxygen deficiency, and increasing the blowing temperature increases the volume and pressure of gases, both in the cavity and outside it. The mutual effect of the two listed factors significantly reduces the gas permeability of the charge, which is an obstacle to its uniform lowering. With regard to the mechanism of nitrogen influence, it is shown that, firstly, the acceleration of heat exchange should accelerate the formation of the primary cohesion zone, in which the processes of sticking together pieces of iron ore materials with the loss of gas permeability and macropores with the formation of a liquid phase will prematurely proceed, and secondly, the dilution of blowing oxygen and reducing agents in the furnace gas does not contribute improving recovery of iron ore materials, especially in the prematurely formed zone of cohesion. Additional nitrogen in the heated blast slows down the process of burning coke on the tuyeres, thereby delaying the start of movement of the charge, increasing its porosity and, accordingly, gas permeability. Focusing attention on the development of the temperature field in the charge column of the blast furnace during the blowing period should not exclude from consideration the dynamics of changes in the mechanics of the movement of the charge and the concentration field, because the problem of nitrogen blowing technology is the lack of relatively uniform lowering of the charge and its treatment with hot reducing gases. In addition, the simultaneous decrease in the mass of coke burning near the nozzles and the reduction in the size of the nozzle cavity, along with the increase in the output of nozzle gas as a result of nitrogen enrichment of the blast, worsens the gas permeability of the charge in the high temperature zone. On the other hand, the depletion of furnace gas by reductants and premature heating of iron ore materials with loss of their fluidity worsen the recovery process. Unprepared iron ore materials, when lowered down, cause an increase in direct recovery and cooling of the furnace. On the basis of the analysis of practical data on the use of nitrogen as an energy additive to atmospheric blasting when blasting blast furnaces, as well as on the basis of the analysis of the compliance of nitrogen blasting technology with the foundations of the theory of the blast furnace process, the negative influence of nitrogen on the course of the blasting period is shown, which calls into question the feasibility of using nitrogen in start-up period of blast furnaces.