Decarburization Efficiency in EAF With Hot Metal ... - Steel Library

injectors had to be always operated at maximum available
capacity. In case of lower charge carbon contents
(20–40% hot metal), the deviations are more significant.
It is believed that the deviations were caused by
inconsistent process conditions, among them manual
control of power and chemical energy input, as well
as incorrect identification of decarburization reaction
launch.
The decarburization reaction efficiency was also evaluated
using an alternative method, based on sampleto-sample
carbon content difference and elapsed time
between the samples. This method could not be used
for higher carbon contents.
The first sample used to be taken when more or less
flat bath conditions were identified, i.e., when the progress
of decarburization reaction reached 60% or more
for charges with 35–40% hot metal. The second sample
was usually taken close to the superheating end.
Although the accuracy of carbon content evaluation
in the first sample can be questionable, the obtained
results (Figure 9) are very interesting. Similarly, as in
the previous case, the relation between carbon content
in the liquid bath and the actual decarburization rate
is rather clear. Moreover, the trendline for all available
results is almost identical to the one indicated in
Figure 8.
The decarburization rates estimated by the second
method are higher than in the first case. This can
probably be explained by too-high carbon content
analyzed in the initial samples, which were not fully
representative of the whole volume of the liquid bath
in the furnace.
Performance Data
All three furnaces presented in this paper are almost
identical from the design point of view. The difference
between adopted hot metal charging practice has
been considered less significant for such performance
indexes as specific energy consumption, lance oxygen
consumption and productivity. Therefore, the available
performance data have been evaluated jointly.
Figure 11
Specific lance oxygen consumption.
Figure 10
Specific energy consumption results (to liquid steel).
The specific electrical energy consumption results
are shown in Figure 10.
For the most frequent charge configuration of
30–40% hot metal, the energy consumption is 220–180
kWh/ton, respectively. With 70% hot metal, it is practically
“zero consumption.” For this charge configuration,
practically observed, very limited energy was consumed
in the initial part of the heat or before tapping for the
fine adjustment of required tap temperature.
The lance oxygen consumption results are shown in
Figure 11. The deviations observed on the graph are
related to the fact that oxygen consumed for silicon
oxidation could not be filtered out in a predictable way.
Also, the earlier mentioned inconsistency in injection
system operation with manual control is significant.
Increase of the hot metal share in the furnace charge
to 70% dramatically increases the oxygen consumption.
The required oxygen volume in lance mode is about
6,000 Nm 3 per heat. With six CONSO units operating
at 2,500 Nm 3 /hour, lance oxygen injection can be
completed in less than 25 minutes, with the average
decarburization rates of 0.12–0.14% C/minute, which
corresponds to the values practically observed during
normal operation.
Figure 12
EAF productivity results.
68 ✦ Iron & Steel Technology A Publication of the Association for Iron & Steel Technology