Interaction of dust with the DC plasma arc - a computational modelling investigation
QG Reynolds
The presence of dust and fume suspended in the freeboard region is a
common feature of the operation of direct current (DC) plasma smelting
furnaces. This occurs primarily as a result of the use of fine feed materials
together with the open-arc, open-bath operation of such smelters, and is
exacerbated by the high velocities and turbulent mixing of the gas in the
vicinity of the arc jet. Dust and fume losses into the furnace off-gas system
can be significant in some cases and may have economic, operational, and
environmental impacts on the process. A computational modelling study is
presented in which the concentration of dust material was considered as a
continuous field subject to a governing partial differential equation.
Settling behaviour was calculated as a function of particle size, local
gas/plasma temperature, and other physical properties. Development of
the coupling between the concentration field and a magnetohydrodynamic
description of the arc is shown, and the resulting models were used to
compute various aspects of the behaviour of the concentration field in the
arc region for a variety of furnace conditions. Time-averaged as well as
transient models of the arc were used to generate the results presented.
Qualitative case studies produced several practical suggestions for furnace
operation, including increased dust capture by the bath when feed ports
are located closer to the electrode, and the possible effects of feed
segregation in the furnace freeboard based on dust particle size and
density.
Keywords: DC furnace, arc plasma, dust entrainment, continuumcomputational
model, freeboard flow, arc flow.