Metallurgy

University of Chemical Technology and Metallurgy,
8 Kl. Ohridski, 1756 Sofia, Bulgaria
E-mail: vps@uctm.edu

Received 20 November 2000 Accepted 30 November 2000

The oxidation processes of the mineral bornite have been studied under simulating flash smelting conditions.

The influence of the following parameters on the degree of bornite oxidation has been determined: i) the temperature - in the range from 733K to 1473K; ii) the partial oxygen pressure in the gaseous phase (3.5 kPa and 21 kPa); iii) the particles diameter (fractions: 315+125 mm, 125+75 mm, and 75 mm).

Considering the experimental results, a mechanism of bornite oxidation under flash smelting condition has been proposed and discussed. The features of the mechanism proposed are as follows:

· Iron ions migration toward the periphery of bornite particles leads to their decomposition to spatially separated oxysulphide crust and digenite core. Oxy-iron core is not formed on the particles surface and the oxidation process takes part in the solid phase.

· The melt phase formation is typical only for the last oxidation stage when the oxy-sulphide ) melt is transformed to spinel () melt.

R. Paunova*, K. Todorov*, D. Damgaliev*, V. Petkova**

* University of Chemical Technology and Metallurgy
Kl. Ohridski 8, Blvd., 1756 Sofia, Bulgaria
E-mail: rossy@uctm.edu
** Bulgarian Academy of Sciences, Sofia 1113, Bulgaria

Received 16 October 2000
Accepted 28 November 2000

Some results of the influence of copper, lead, zinc and silver oxides on the kinetics and the degree of ferrous oxide reduction with solid carbon have already been published. These non-ferrous metals are contained in already studied synthetical mixtures. They have a similar content as the slurries and waste dusts in the basic metallurgical productions in “Kremikovtzi-AD”. It is well known that the iron content in blast furnace production slurries is considerably lower (35-39%) than in steel-making production (49-54%). In order to work out an effective technology of waste materials utilization, the reduction of mixtures with small fraction of coke has been studied.

A distinctive peculiarity of these by-products is their fine-dispersed composition, the form and content of iron and the non-ferrous metal admixture content. It is found out that the highest degree of ferrous oxides reduction with small fraction of coke can be reached in mixtures of converter and blast furnace slurries. Good reducing also possesses a mixture of 40% blast furnace slurry, 40% converter slurry and 8% electric steel-making slurry. The calculated values of activation energy show the possibility that the direct reduction runs in a kinetic field with a limiting stage of indirect reduction within the temperature range 293K - 1183K and the reaction of solid carbon gasification within temperature range 1183K - 1473K.

University of Chemical Technology and Metallurgy,
8 Kl. Ohridski, 1756 Sofia, Bulgaria
hadjiski@hpap1.uctm.edu, venko@uctm.edu,
mil@uctm.edu

Received 20 November 2000
Accepted 30 November 2000

The combustion of pulverized low-caloric coal in power plant boilers is still a complicated problem. There are scientific and commercial software tools for steady state calculation of gas, oil and high caloric coal combustion. Low-grade lignite combustion in the furnace chamber possesses a lot of peculiarities caused by the low temperatures, strong influence of the ballast components in the coal (water, ash) on the combustion process and its stability. Some of the model parameters are known with large number uncertainties. The aim of this contribution is to present the software developed for simulation and forecasting of low-caloric coal combustion in steam generators. The adjustment of off-line low-grade lignite firing steam boiler model is under consideration as a stage of global strategy for on-line approximate model design. Some problems of the strategy of model parameter estimation by optimization are considered taking into account the extremely time-consuming processing of numerical plant models.