Drying of steel-teeming ladle monolithic linings

Abstract

The use of moist unformed refractories for the production of steel-teeming ladle monolithic linings increases the role of drying as a production operation regulating the preparation of linings and influencing the life of the lining in service of the ladle.Until now the process of drying of linings with the use of the energy liberated in combustion of gas in the ladle has remained unstudied.In the few publications devoted to this operation, its disadvantages have been noted.Nonuniform heating of the surface with the flame of the burning gas leads to significant moistening of the reinforcing layer and formation of undried zones [i, 2], the occurrence of cracks on the whole surface, spalling, and screes in the lower portion of the ladle, and in some cases to collapse of the lining [3,4]. To eliminate the defects occurring attempts have been made to do the drying in two or more stages with different rates of gas consumption [5,6].However, the ladle drying programs developed in some plants have not been soundly based and opinions on the maximum temperature at the boundary of the lining working and reinforcing layers at the moment of completion of drying have been contradictory.We should also turn our attention to the long drying time, which involves significant losses of heat in combustion of gas in the ladle.The efficiency of existing drying equipment based on gas burners has been determined as not more than 5% [i].The basic reasons for the low effectiveness of drying of linings by the products of gas combustion are the result of the drying method itself.The input of heat to the moist surface from the high-temperature flame of the burning gas creates high gradients of temperature, capillary or chemical potential, and pressure of the stream-air mixture in the pores of the lining surface layer.Under the action of temperature and pressure gradients, filtration transfer of moisture in the form of water and steam into the depth of the lining predominates over diffusion mass transfer to the open surface of the lining under the action of the capillary or chemical potential gradient. As the result intense moistening of the reinforcing layer and accumulation of water at the ladle shell in the less heated zones of the monolithic layer occur.Evaporation of the moisture within the lining and removal through the steam holes in the shell require significantly more energy and time than evaporation of it from the open surface. This is responsible for the long drying time and the presence of undried zones in the lining of the lower portion of the ladle.Input of heat from the gas burner flame which is nonuniform over the surface creates in the monolithic lining nonuniform distributions of temperature, moisture content, and excess pressure of the steam-air mixture both across the wall thickness and in the height of the ladle.Nonuniform and sharply unsteady temperature and moisture content fields are the reason for the occurrence of temperature and moisture (mass-thermal) stresses [7] in the lining working layer.The mass-thermal stresse...

Development of a method of accelerated drying of casting ladle linings

“…In [2] the use of electric heating elements of current-conducting fabrics mounted in the lining was proposed. Such a solution made it possible to organize the flow of heat and the flow of moisture in the same direction, to obtain an ecologically clean oepration with controlled drying conditions, and to increase the efficiency to 50% and more.…”

“…About 80% of existing preparation operations are based on use of the combustion products of liquid or gaseous fuels as the energy carrier. This is related primarily to the accessibility of fuel sources and the relatively simple and reliable design of the equipment [i-4].Practical experience and service of drying equipment with fuel burners has revealed its primary disadvantages [2]: low efficiency in use of energy, which does not exceed 30% even with use of recuperator~ contamination of the atmosphere and working areas with the combustion products of fuel containing oxides of sulfur, nitrogen, and carbon and unfavorable working conditions in the zone of operation of the equipment as the result of increased temperatures.Preparation operations being developed and equipment being designed must be distinguished by high economy and ecological cleanliness. Therefore development of effective operations and equipment for drying the working layer of a lining requires more thorough study of the physicochemical processes occurring in removal of moisture from refractories.…”