ACARP Project Number: C22035
Published: December 14
Lauren Johnson, Philip Bennett, Sarah
Grimish
Extended
Abstract
The stamp charging of coal has emerged as a
widely-used, effective treatment to improve the quality of coke
produced in coke-making operations. Traditionally, expensive prime
hard coking coal has been used to make coke with the required
properties to operate blast furnaces effectively. Through the use
of stamped charging technology cheaper, lower quality coals can be
used in larger amounts increasing the flexibility and cost
efficiency of coke-making operations along with maximising oven
throughput. An important consideration for the use of a coal in a
stamped charged operation is weighing up the cost of the energy
used for stamping with the improvement in coke quality and
reduction in raw material costs.
The defining factor in determining a coal's
suitability for stamp-charging treatment is the stampability, which
is the amount of energy required to pack the coal to a target bulk
density. Coal properties and factors which can influence
stampability include coal type and rank, moisture content and size
distribution. One purpose of this project is to develop a
small-scale stampability apparatus for determining the stampability
of single coals and coal blends. As well as devising standard
procedure for the operation of the apparatus. The project also aims
to improve the understanding of the relationship between bulk
density and coke quality at small scale for Australian Coals.
The objectives of this project were to:
- Develop
a standard procedure to determine the stampability of a coal or
coal blend;
-
Demonstrate the use of stamp charging at small scale to investigate
coals being considered for stamp charging operations;
- Relate
the stampability of a coal to coal quality; and to
- Improve
understanding of the relationship between coal bulk density and
coke quality.
The stampability of single coals has been found
to be related to the moisture at which the coal is tested, the size
distribution and coal type. In general coals with a low Hardgrove
Index (HGI) were found to require lower energy to stamp. Stamping
is also less energy intensive when the size distribution (measured
by Rosin Rammler n) is broader. The stampability of a coal blend is
related to the moisture and size distribution of the resulting
blend. However the limited data in this project does not allow a
conclusion to be drawn on which parameter is of greater
significance in a blending scenario. The maximum compressive
strength of the coal cake occurs at an optimum moisture and this
moisture differs coal by coal. The compressive strength is also
influenced by the size distribution of the feed. However it is
important to ensure that increased moisture to create a stable coal
cake does not require excess energy for carbonisation. As with the
stampability the compressive strength of coal blends is related to
the moisture and size distribution of the coals.
All coals tested in this project showed
improvement in coke quality with stamped charging. Though the
improvement in coke quality did differ depending on the individual
coal and the improvement in quality for some coals did plateau as
the charge density increased. Coal G was shown to produce coke that
has adhesion controlled strength. For these coals the mechanism for
improvement in coke quality is via increased contact between coal
particles with increasing bulk density. This type of coal is more
likely to be of higher rank (lower volatile matter) and are more
easily stamped, this is very favourable as significant improvement
in coke quality can be achieved whilst lower energy is required for
stamping. The improvement in coke quality for Coals F, H, I & J
with stamp charging is due to reduced porosity. Despite the
significant improvement in the quality for coal H, the initial
quality was very low. Also this coal is low rank (high volatile
matter), which means that more energy would be required for
stamping. From the testing of coal blends it is evident that the
addition of small proportions of a hard coking coal are able to
improve the structure of a coke which can be further improved by
stamped charging.