ACARP Project Number: C20009
Published: May 13
Philip Bennett, Frank Shi, Nick
Andriopoulos
Extended
Abstract
Coke quality is commonly characterised by tumble
drum strength tests, typically on coke produced in pilot scale coke
ovens. The empirical nature of the commonly used suite of tests
usually requires that all the major coke tests need to be completed
for a single coke. Additionally, the variability of each test
measurement can be high, and comparison between different tests
remains problematic. It is becoming more common for coking coal
producers, cokemakers and ironmakers to try to understand how
different blending or washing practices will influence coke
quality. The identification of increasingly subtle potential
improvements or deteriorations in coke quality is clouded by the
deficiencies in drum tests.
This problem is further exacerbated by different
sub samples of the same coke being used in the different drum tests
and differences in the feed sizing. It is reasoned that the
difference in the drum indices obtained by various drum tests is
caused by the difference in applied tumbling energy due to
variations in drum diameter and tumbling time.
This project proposed that a unified index or
indices can be generated once the size reduction and energy
relationship is established and the applied energy in various drum
tests is corrected.
The project investigated whether the coke
size data, normally collected when a set of drum tests are
performed, can be used to determine a theoretically based strength
index based on sound breakage theory and, since it is determined
from all the data generated, is a better representation of the coke
strength for the whole coke sample than is possible with individual
drum indices.
The objectives of this project were to:
- Review
particle breakage theories and select the most suitable theory for
the determination of a coke strength index or indices based on drum
test results;
-
Formulate mathematical procedures for the determination of the
index or indices based on a set of drum test data and implement
those procedures; and
-
Demonstrate that such an index can be used for the evaluation of
coking coals.
The JKMRC developed a unified Coke Strength Index
(CSI) from a theoretically based breakage model which takes into
account the coke feed size distribution, product size distribution
and the total effective energy applied in a range of drum tests. It
has been demonstrated that this model agrees with the work of other
researchers for volume breakage and can be used to predict the
different volume breakage drum indices (such as Stability, M40,
I40, I20, DI3015and DI15015) used by the international steel and
coal industries. This project has demonstrated that the coke size
data, normally collected when a set of drum tests are performed,
can be used to determine the CSI and, since it is determined from
all the data generated, it is a better representation of the coke
strength for the whole sample than individual drum indices.
The use of the CSI will greatly assist in the
identification of any potential improvements or deteriorations in
coke quality where the coke strength data is clouded by the
deficiencies in drum tests. The results of this work can make it
possible to develop a drum testing procedure with smaller amounts
of coke being required and still being able to calculate all the
volume breakage drum indices. This can be done using smaller
compartments within pilot scale coke ovens, for example using a
multi-compartment coke charge. While the amount of coke produced
does depend on the yield of coke and mean coke size after
stabilisation, a revised coke testing procedure will reduce the
coke requirements needed to determine the tumble drum strength of
cokes and therefore lower the cost of the coking coal
evaluation.