Phosphorites electric conductivity and structures specifics at high temperature heating


Аuthors

Bobkov V. I.

Branch of the National Research University Moscow Power Engineering Institute in Smolensk, Smolensk, Russia

e-mail: vovabobkoff@mail.ru

Abstract

The article studies specifics of electric conductivity and dilatometric characteristics of thermally activated processes occurring in phosphate raw materials while thermal preparation and yellow phosphorus sublimation in ore heat-treating furnaces. It presents the results of experimental studies of electric conductivity dependence on CaO, MgO and SiO2 concentrations sum, and relative elongations on temperature. These results are necessary for modeling and quantitative calculations of electro-thermal units, as well as while developing the new chemical-energy-technological systems for phosphate raw materials treatment. The developed rather simple and accurate method for electrical conductivity determining can be applied for studying phosphorus bearing ore and rock structure and content, as well as physic-chemical transformations occurring in them while heating.

Significant effect of admixtures on the electrical conductivity was revealed. It was established, that the thermal expansion temperature dependence character depends notably on phosphorus bearing ores and rocks content. Deformations in high temperature region herewith increase with the carbonates content built-up. Phosphorites with high natural acidity module transfer into liquid melt, uninterruptedly increasing in size. This is stipulated by superimposition of temperature ranges of thermal decarbonization of the basic phosphate substance , and formation of, significant in a quantitative sense, liquid phases. Reprocessing of lumpy phosphorites with high natural acidity module in a phosphorus furnace causes phenomena affecting negatively the furnace stable operation. Grains swelling before transition into liquid melt reduces the layer porosity and deteriorates the conditions of gaseous products seepage from the reaction zone, and may facilitate the gas-permeable “coving”, disrupting the heat exchange in electric furnace and complicating the furnace charge yield to the reaction zone. The phosphorites with high natural acidity module reprocessing in the ore-thermal furnace is accompanied by significant thermal expansions, furnace charge layer compacting and occurrence of conducting layer in the top zone of the phosphorus ore-thermal furnace. Consequently, it leads to formation of a parasitic current path, electrodes’ envelope burning-out under the liquid melt zone and their breaking, as well as furnace envelope warming-up.

Keywords:

modeling, heat and mass exchange, electrical conductivity; temperature expansion; sintering; kinetics; phosphorite

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