Efficiency of carbon utilization in blast-furnace heat consumption

Blast heating in the blast furnace saves as much heat as it supplies. However, to obtain such heat in a blast furnace, more fuel must be burned than in any air heater. The efficiency of a blast furnace as a heater is less than for any air heater and is no more than 12%, in some cases.     

Steady state segregation and heat flow in ESR

A combined theoretical and experimental study of steady-state heat flow and segregation in ESR is presented. The segregation model permits prediction of pressure gradients, hence, interdendritic flow velocities responsible for macrosegregation in the “mushy? zone of axisymmetric ESR ingots. The heat flow model considers the solidus isotherm as a moving boundary. The relationships between power and slag temperature as well as power and heat transfer coefficient are experimentally measured and included in the heat balance equation for the slag. Experiments on both a low-temperature simulated ESR apparatus and on a 200 mm diam ESR ingot mold verify both models.     

Steady state segregation and heat flow in ESR

A combined theoretical and experimental study of steady-state heat flow and segregation in ESR is presented. The segregation model permits prediction of pressure gradients, hence, interdendritic flow velocities responsible for macrosegregation in the “mushy≓ zone of axisymmetric ESR ingots. The heat flow model considers the solidus isotherm as a moving boundary. The relationships between power and slag temperature as well as power and heat transfer coefficient are experimentally measured and included in the heat balance equation for the slag. Experiments on both a low-temperature simulated ESR apparatus and on a 200 mm diam ESR ingot mold verify both models. S. CHAKRAVORTY formerly Research Associate, Department of Metallurgy and Mining Engineering, University of Illinois. J. D. NAUMAN formerly Engineering Associate, Cabot. Corporation     

Steady state hydrogen transport through zone refined irons

Hydrogen permeation from the gas phase through zone refined iron was measured with the electrochemical technique over 0 to 60°C and 0.01 to 1 atm. The surface impedance problems normally encountered in this pressure-temperature range were eliminated by a thin layer of electroplated palladium on the input surface of the permeation membrane. The steady state flux was propprtional to the square root of the pressure and inversely proportional to the membrane thickness. The permeability coefficient was 2.6× 10¹⁷ exp ((- 8500 ± 600 cal/mole deg)/RT) atom H/cm s atm^1/2, in good agreement with earlier results at higher temperatures. These results can be used to calibrate electrochemical charging experiments in terms of an effective hydrogen pressure. Formerly with the Department of Materials Science and Engineering, Cornell University, Ithaca, New York     

Steady state hydrogen transport through zone refined irons

Hydrogen permeation from the gas phase through zone refined iron was measured with the electrochemical technique over 0 to 60°C and 0.01 to 1 atm. The surface impedance problems normally encountered in this pressure-temperature range were eliminated by a thin layer of electroplated palladium on the input surface of the permeation membrane. The steady state flux was propprtional to the square root of the pressure and inversely proportional to the membrane thickness. The permeability coefficient was 2.6 × 10¹⁷ exp ((-8500 ± 600 cal/mole deg)/RT) atom H/cm s atm^1/2, in good agreement with earlier results at higher temperatures. These results can be used to calibrate electrochemical charging experiments in terms of an effective hydrogen pressure. Formerly with the Department of Materials Science and Engineering, Cornell University, Ithaca, New York     

Metal-Mold interfacial heat transfer

During the solidification of metal castings, an interfacial heat transfer resistance exists at the boundary between the metal and the mold. This heat transfer resistance usually varies with time even if the cast metal remains in contact with the mold, due to the time dependence of plasticity of the freezing metal and oxide growth on the surface. The present work has studied interfacial heat transfer on two related types of castings. In the first type, a copper chill was placed on the top of a cylindrical, bottom gated casting. Using the techniques of transducer displacements and electrical continuity, a clearance gap was detected between the solidified metal and the chill. The second type of casting had a similar design except that the chill was placed at the bottom. Owing to the effect of gravity, solid to solid contact was maintained at the metal-chill interface, but the high degree of interface nonconformity resulted in a relatively low thermal conductance as indicated by solution of the inverse heat conduction problem. Finally, the influence of interfacial heat transfer on solidification time with three mold ma-terials is compared by a numerical example, and criteria for utilizing Chvorinov's rule are discussed. Formerly Graduate Student.     

旋流叶片传热管内湍流强化传热数值模拟

基于管内核心流强化传热原理,在管内核心流布置旋流器以实现强化传热.建立了强化管内流体流动与传热的数学模型,结果表明:在强化传热管内布置旋流器可以显著强化湍流换热,而且其流动阻力增加幅度不大.当旋流器距圆管人口200mm,Re数为6000时,强化传热管的PEC值可达1.7.     

Regenerative heat transfer in rotary kilns

A mathematical model has been developed to determine the temperature distribution in the wall of a rotary kiln. The model, which incorporates a detailed formulation of the radiative and convective heat-transfer coefficients in a kiln, has been employed to examine the effect of different kiln variables on both the regenerative and the overall heat transfer to the solids. The variables include rotational speed, pct loading, temperature of gas and solids, emissivity of wall and solids, convective heattransfer coefficients at the exposed and covered wall, and thermal diffusivity of the wall. The model shows that the regenerative heat flow is most important in the cold end of a rotary kiln, but that generally the temperature distribution and heat flows are largely independent of these variables. Owing to this insensitivity it has been possible to simplify the model with the aid of a resistive analog. Calculations are presented indicating that both the shell loss and total heat flow to the bed may be estimated to within 5 pct using this simplified model.     

Radiative heat transfer in rotary kilns

Radiative heat transfer between a nongray freeboard gas and the interior surfaces of a rotary kiln has been studied by evaluating the fundamental radiative exchange integrals using numerical methods. Direct gas-to-surface exchange, reflection of the gas radiation by the kiln wall, and kiln wall-to-solids exchange have been considered. Graphical representations of the results have been developed which facilitate the determination of the gas mean beamlength and the total heat flux to the wall and to the solids. These charts can be used to account for both kiln size and solids fill ratio as well as composition and temperature of the gas. Calculations using these charts and an equimolar CO₂−H₂O mixture at 1110 K indicate that gas-to-surface exchange is a very localized phenomenon. Radiation to a surface element from gas more than half a kiln diameter away is quite small and, as a result, even large axial gas temperature gradients have a negligible effect on total heat flux. Results are also presented which show that the radiant energy either reflected or emitted by a surface element is limited to regions less than 0.75 kiln diameters away. The radiative exchange integrals have been used, together with a modified reflection method, to develop a model for the net heat flux to the solids and to the kiln wall from a nongray gas. This model is compared to a simple resistive network/gray-gas model and it is shown that substantial errors may be incurred by the use of the simple models.     

Improving blast-furnace heating

The possibility of raising the blast temperature by gas combustion in the air-supply line is considered. The prospect of replacing regenerative air heaters with recuperative heaters is discussed.     

Indirect reduction in blast-furnace smelting

The influence of the intensity of blast-furnace smelting on the effectiveness of the indirect reduction of iron from wustite is considered on the basis of the Rist model, for specially prepared batch and coke of satisfactory quality. In the case of practically stable and effective reduction, broad variation in the smelting intensity in terms of oxygen is associated with acceleration of the indirect reduction, on account of increase in the concentration of reducing agents in the gas, increase in their consumption, and increase in the gas–batch contact surface. These results do not confirm the finding from the 1950s and 1960s that the dependence of the productivity and coke consumption on the smelting intensity is extremal.