ACARP Project Number: C19053
Published: July 12
Lauren Johnson Philip
Bennett
Note project was published in two parts-
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Influence of bulk density
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Understanding the Sapozhnikov Test and factors that influence the
determination of Plastic Properties
Extended
Abstract
The force that a coal exerts on the coke oven
walls can have deleterious effect on coke batteries if it is
excessive. The most common method of controlling oven wall pressure
is blending. However predicting the expected oven wall pressure
(OWP) is complex as there is no one coal property that is known to
directly indicate OWP. Additionally, the oven design and charging
conditions such as bulk density are important.
Previous research has demonstrated that the
properties of the plastic layer influence both OWP and the
structure of the final coke, thus coke strength. The plastic layer
properties can be assessed by a Plastometer test that measures the
thickness (Y, mm) of the plastic layer and the degree of
contraction (X, mm) that occurs when a coal sample is heated
unidirectionally. There are two national standards that describe
this test (Russian & Chinese), in those countries the plastic
properties are used in the classification of coals. This test is
known as the Sapozhnikov test.
In Part 1 of this project the influence of bulk
density on contraction and plastic layer thickness was studied
using an automated commercial Sapozhnikov apparatus. In Part 2, a
number of parameters affecting the test results of the Sapozhnikov
and Chinese Plastometer test were considered and the repeatability
of these tests assessed. Recommendations are made in respect of
technical factors that should be considered in any future ISO
standard
The Edinburgh Cohesion Tester (ECT) was used to
investigate the influence of size distribution, moisture content
and coal properties on bulk density. There was good correspondence
between the increased bulk density caused by a consolidation load
determined in the ECT and the Sapozhnikov apparatus. However, it
was found difficult to predict the loosely packed bulk density of
different coals based just on their size distribution and coal
properties and, as the bulk density after application of a
consolidation load is related to the loosely packed bulk density,
that also cannot be predicted based on coal properties.
It was found that the bulk density of the packed
coal has an influence on the contraction and the thickness of the
plastic layer in the Sapozhnikov retort. This influence was
different for each coal. There is also evidence that the bulk
density influences the heat transfer from the base of the retort
thus impacting on the size of the region that is undergoing plastic
deformation. Again this influence may be dependent on the coal
properties. As found by others the contraction as measured by the
Sapozhnikov test is a good indication of the coking pressure that
may be generated by a coal.
The effect of automation was found to be minimal,
with four out of the five coals tested having results within the
published repeatability, assuming that the plastometer needle is
aligned correctly at the beginning of the automated test.
Coal tested at 5% moisture had increased
contraction compared to coal tested at air dried moisture, the
magnitude of the increase in contraction varied with each coal (due
to the varying effect of moistures on bulk density), plastic layer
thickness was also affected by moisture but this effect was also
inconsistent.
Due to the effect that moisture and bulk density
have on the results of the plastometer test it is recommended that
the moisture level that the test is conducted at be specified and
the packing bulk density be defined, additionally the final bulk
density (after the load has been added) that the test is conducted
at should be recorded.
For a coal tested at various intervals over a one
month period with one subsample stored at ambient temperature and
another subsample kept in cold storage there was no significant
difference in the measured contraction. For samples stored for an
extended period of time in cold storage there was also no
significant change however a sample that had been stored at ambient
temperature for an extended period showed a significant increase in
contraction.
The measurement uncertainty of the automated
plastometer method was investigated experimentally. It was found
that for contraction the uncertainty (u) was 2.28mm and the
expanded uncertainty (U) was 4.57mm. For plastic layer thickness
the uncertainty (u) was 1.33mm and the extended uncertainty (U) was
2.66mm. These numbers are higher than those published in the
standards, possible reasons for this are discussed.