The thesis is devoted to increase of energy efficiency of electric arc steelmaking furnaces (EAF) based on development of theoretical ideas about processes of heat transfer, hydromechanics and electrovortex flows in the EAF working space.
Theoretically substantiated and experimentally confirmed the optimal, by criterion of energy efficiency, ratio of diameter and depth of the bath, equal to 2.5-1.8 for various EAF energy-technological modes, which reduces the heat loss with cooling water by 8.5-49 %, increase the bath heating and scrap melting rate by 12-25 %.
Based on mathematical modeling of scrap melting and liquid bath heating processes, it was found that arc energy efficiency decreases from 0.92-0.94 to 0.68-0.70 as the individual wells evolve to a common one. The maximum relative reduction of specific electric power consumption of 2.5-7.5 % in EAF of various capacities is achieved with the electrodes pitch diameter 0.42-0.49 of the working space internal diameter.
It has been established that in the EAF working space a tubular surface of the water-cooled elements (WCE) perceives the effective values of heat flux, determining the thermal stress and stability of WCE, 12-55 % higher than the the heat flux, evaluated for a flat surface, and the part of convective and condensation components of the thermal load on the WCE add up to 31-37 % of the irradiation heat flux.
The WCE with a spatial tubular structure have been elaborated, for which theoretical and experimental data on the thermal state were obtained, confirming the reduction of irradiation heat loss with cooling water by 20-35 % due to the created conditions for the formation of a heat-accumulating and heat-insulating layer of the crust.
By numerical studies of heat exchange in the foundry class EAF, for the conditions of non-rhythmic operation, it has been determined and experimentally confirmed, that the use of WCE with a spatial structure in the places of critical durability of the lining, does not increase the energy consumption, comparing to the traditional fully refractory shell, with a relative area of WCE in the roof not higher than 15-20 %, while reducing refractories consumption by 1.4-2.5 times.
The concept of the EAF aspiration system has been developed based on the joint gas-dynamic effect of dispersal and increasing the suction surface with approaching it to the electrode gaps. The possibility of reducing fugitive emissions by 15-29 %, air inflow by 20-25 %, dust removal from the EAF by 20-50 % was experimentally shown.
The energy-ecological concept of the EAF exhaust gases heat utilization is developed. Based on the study of two-stage CO burning process in the EAF afterburning chamber, the ratio of primary and secondary air 1 to 3.5 is determined, which ensures achievement of the MPC of CO due to organization of a steady burning zone and obtaining a heat carrier for scrap preheating with the temperature up to 500 °C, making impossible the formation of toxic PCDD/F.
Based on thermodynamic analysis, it is grounded that utilization of the heat and chemical potential of the EAF exhaust gases for thermochemical regeneration of natural gas, followed by preheating of the scrap due to burning of synthesis gas, increases the thermal efficiency of the «flat bath» EAF process by 5-6 %, reduces the consumption of natural gas by 21 % and CO2 emission by 9.8 %.
For elaborated liquid-phase carbon-thermal smelting-reduction process in a heat-generating slag bath of an electric furnace with two bottom electrodes (BE), it was found that to obtain a liquid metallized product in the hearth separated from the BE by a slag layer, the factor taking into account the effect of convection in the bath at a coefficient of stationary thermal conductivity should be at least 2.7.
Based on numerical study of electrovortex flows (EVF) in the DC EAF of a foundry class, the use of a "deep" bath has been substantiated, which allows to increase the EVF-mixing capacity for various BE types by 1,3-8,4 times, and, by intensification of steel refining process, promotes to reduce the specific EAF energy consumption by 3-9 %. The processes of heat exchange with the phase transition of bimetallic BE in the conditions of EVF in the anode well of high power DC EAF are investigated and it is shown that the equilibrium thickness of BE solid steel part is in critical dependence on the width of the transition copper-steel zone, which, for stable BE operation, should not exceed 20-25 mm. The concept of BE with a convective mechanism of heat transfer is substantiated.
The developments have been brought to industrial implementation at 7 plants equipped by the EAF with a capacity from 3 to 120 tons. High technical and economic indicators of elaborations ensure a payback period of investments, as a rule, up to 1 year.
Key words: electric arc furnace, energy efficiency, numerical modeling, heat-mass transfer, deep bath, water-cooled elements, aspiration of dust-gas environment.
