A Novel Approach for Measuring the Thickness of Refractory of Metallurgical Vessels

The advancement of metallurgical vessels, such as blast furnaces, shaft furnaces, and torpedo ladles, can be better controlled and expanded for a greater lifespan if the thickness of the refractory lining wear is known and predicted. In the past, various methods including radioactive tracers, infrared (IR) thermography, electromagnetic waves, ultrasonic tomography, and temperature field have been tested to determine the thickness of the refractory wall. However, for various reasons, these methods have failed to be effective. This paper presents a novel method—electromotive force (EMF)—for predicting the thickness of refractory lining wear in vessels, including a small-scale vessel in the laboratory, an industrial torpedo ladle, and in the two refining hearths of blast furnaces. The experimental results show that the magnitude of the EMF signal increases with a decrease in wall thickness. Prediction values of the refractory wall thickness are consistent with measured ones. The relative error of EMF measurement for the torpedo ladle is around 6.8%. The EMF measurement of blast furnace hearths is quite accurate, and the relative error is less than 11%.

The Impact of Critical Operational Parameters on the Performance of the Aluminum Anode Baking Furnace

Minimizing energy consumption and reducing pollutant emissions during the carbon anode baking process are critically important for the aluminum industry. The present study investigates the effects of oxidizer inlet temperature, inlet oxygen concentration, equivalence ratio, refractory wall thermal conductivity, and refractory wall emissivity on the baking process using unsteady Reynolds-averaged Navier–Stokes (URANS)-based simulations in conjunction with the presumed probability density function method. Numerical results are combined with a response surface methodology (RSM) to optimize the anode baking process. The advantage of the coupled method is that it can adequately provide information on interactions of different input parameters. It is remarked that the significance level of the studied parameters varies drastically for different outputs. It is noted that diluting inlet oxygen concentration (from 23% in atmospheric air to 15%) at an elevated oxidizer temperature leads to enhanced furnace fuel efficiency, more uniform temperature distribution, and lower pollutant emissions. A linear model is detected to be adequate for response surface modeling of the anode baking furnace NOx formation. On the other hand, furnace soot formation is modeled with a higher-order model due to the quadratic behavior of the response.

Development of Probability Concept for Thermal Fatigue Life Cycle Prediction

Furnaces are most commonly used for melting of Ferrous Metals and its alloy materials. Induction furnaces use Electrical Power so that they are more advantageous as no fuel is required. It is a very critical problem to find life span of Induction Melting Furnace Wall under thermal load variation. The life cycle of induction furnace refractory wall is a variable as minor variation is always present due to effect of skill of workers and many other factors. The life cycle of furnace wall will vary minor with some miscellaneous factors and cannot be justified as a single value always. The probability concept is utilized here in the forecast of life cycle calculation to justify the miscellaneous factors effected for the damage of the induction furnace refractory wall. The probability concept initially defines a minimum life of induction furnace wall for a certain case then it is assumed to vary with different probability as given below. So, all the cases of induction furnace wall are having minimum life always but some cases of induction furnace wall are having much longer life. It is due to effect from many miscellaneous factors like skills of workers, efficiency of workers, raw material quality used for construction of wall, tools applied for ramming of it, row material employed for melting, etc.

A Computational Heat Transfer and Optimization Study of Drying of Peas and Rice in a Rotary Dryer

The paper reports a numerical simulation study of drying of peas and rice grains in a rotary dryer with superheated steam, dry air, and humid air (20%, 40%, 60% and 80% moisture content by volume) at 1 bar as the drying media. The initial water contents in peas and rice grains are 75% and 13% (by weight), respectively. The thermal model includes turbulent convection heat transfer from the gas to the refractory wall and solids, radiation exchange among the gas, refractory wall and the solid surface, conduction in the refractory wall, and mass and energy balances of the gas and the solids. In the absence of experimental data of food drying, the present model has been satisfactorily validated with the experimental and numerical results reported in Sass (1967, Sass, A., “Simulation of Heat-Transfer Phenomena in a Rotary Kiln”, Industrial & Engineering Chemistry Process Design and Development, 6(4), pp. 532–535) for iron ore and cement. It is found that for superheated steam there is an optimum kiln inner diameter at which the predicted kiln length is the highest. For dry air, the predicted kiln length monotonically decreases with a decrease in kiln inner diameter. A detailed parametric study lent a good physical insight into the drying process. An optimization study has been conducted for superheated steam as the drying medium using the Univariate Search method to minimize the length of the kiln with an upper limit on the inlet gas temperature as the constraint.

Computer Simulation of Heat Transfer in a Rotary Lime Kiln

In the present work, a steady-state, finite difference-based computer model of heat transfer during production of lime in a rotary kiln has been developed. The model simulates calcination reaction in the solid bed region of the rotary kiln along with turbulent convection of gas, radiation heat exchange among hot gas, refractory wall and the solid surface, and conduction in the refractory wall. The solids flow countercurrent to the gas. The kiln is divided into axial segments of equal length. The mass and energy balances of the solid and gas in an axial segment are used to obtain solids and gas temperature at the exit of that segment. Thus, a marching type of solution proceeding from the solids inlet to solids outlet arises. To model the calcination of limestone, shrinking core model with surface reaction rate control has been used. The output data consist of the refractory wall temperature distributions, axial solids and gas temperature distributions, axial percent calcination profile, and kiln length. The kiln length predicted by the present model is 5.74 m as compared to 5.5 m of the pilot kiln used in the experimental study of Watkinson and Brimacombe (1982, Watkinson, A.P. and Brimacombe, J. K., “Limestone Calcination in a Rotary Kiln,” Metallurgical Transactions B, Vol. 13B, pp. 369–378). The other outputs have been also satisfactorily validated with the aforementioned experimental results. A detailed parametric study lent a good physical insight into the lime making process and the kiln wall temperature distributions.

Computer Simulation of Drying of Food Products With Superheated Steam in a Rotary Kiln

The present work reports a computer simulation study of heat transfer in a rotary kiln used for drying and preheating food products such as fruits and vegetables with superheated steam at 1 bar. The heat transfer model includes radiation exchange among the superheated steam, refractory wall and the solid surface, conduction in the refractory wall, and the mass and energy balances of the steam and solids. The gas convection is also considered. Finite-difference techniques are used, and the steady state thermal conditions are assumed. The false transient approach is used to solve the wall conduction equation. The solution is initiated at the inlet of the kiln and proceeds to the exit. The output data consist of distributions of the refractory wall temperature, solid temperature, steam temperature, and the total kiln length. The inlet of the kiln is the outlet of the gas (superheated steam), since the gas flow is countercurrent to the solid. Thus, for a fixed solid and gas temperature at the kiln inlet, the program predicts the inlet temperature of the gas (i.e., at the kiln exit) in order to achieve the specified exit temperature of the gas. In the absence of experimental results for food drying in a rotary kiln, the present model has been satisfactorily validated against numerical results of Sass (1967, “Simulation of the Heat-Transfer Phenomena in a Rotary Kiln,” Ind. Eng. Chem. Process Des. Dev., 6(4), pp. 532–535) and limited measured gas temperature as reported by Sass (1967, “Simulation of the Heat-Transfer Phenomena in a Rotary Kiln,” Ind. Eng. Chem. Process Des. Dev., 6(4), pp. 532–535) for drying of wet iron ore in a rotary kiln. The results are presented for drying of apple and carrot pieces. A detailed parametric study indicates that the influence of controlling parameters such as percent water content (with respect to dry solids), solids flow rate, gas flow rate, kiln inclination angle, and the rotational speed of the kiln on the axial solids and gas temperature profiles and the total predicted kiln length is appreciable. The effects of inlet solid temperature and exit gas temperature on the predicted kiln length for carrot drying are also shown in this paper.