Technical Market Support » Metallurgical Coal
Assessment of increasingly subtle changes in coal quality, either potential improvements or deteriorations, is clouded by the deficiencies in drum tests routinely conducted on pilot scale coke. When coking tests are performed on coke produced at the small scale (8kg feed coal) the comparison between relatively small differences in coke strength of different coals is tenuous. This project demonstrates that a coke strength index (JKCSI) developed by Julius Kruttschnitt Mineral Research Centre (JKMRC) and determined from drum testing can aid in the evaluation of coke quality. The objectives of the project were to:
· Test the applicability of the JKCSI model to cokes that exhibit adhesion controlled breakage;
· Extend the modelling of breakage to include coke produced in the small scale coke oven (8kg) where the strength of the coke is determined by the modified Micum or the I-Drum tests;
· Recommend a suitable method for the preparation of coke from small scale coke testing for the NSC Reactivity test.
To achieve these objectives JKMRC undertook a series of tasks on coke samples supplied by ALS Coal.
In the project, the JKCSI model developed from data on strong cokes in ACARP Project C20009 was applied to a weak coke produced from lower volatile coal that undergo adhesion controlled breakage. It was proved that the JKCSI model can work for both strong and weak cokes with equally good model fitting qualities. From the data in this project the transition point between adhesion controlled to porosity controlled breakage occurs when the JKCSI decreases below 200. There is insufficient data to extend this finding to small scale data. While the data in this report does indicate there is a sharp transition from adhesion control to porosity control breakage there is insufficient data in this transition region to categorically state that there is fixed transition point.
The use of JKCSI in routine testing will assist coal producers to better understand the coke quality and identify if the coke breakage is dominantly controlled by adhesion or porosity. This will allow producers to formulate better blending strategies to improve coke quality.
Work demonstrated that the JKCSI can be determined from small scale coke using a modified Micum test conducted at least two revolutions or from an I-Drum test conducted at least two revolutions. The determination of JKCSI on small scale coke should add to the understanding of the coke quality of small scale results. On the limited small scale coke data on two coals examined in this project the JKCSI does indicate the expected changes in coke quality due to coking conditions.
The inclusion of a modified Micum test on small scale coke has been shown to effectively stabilise the coke thus ensuring the influences of fissures on coke breakage are minimised. This should lead to greater consistency in small coke testing especially for weaker cokes. Stabilisation had a greater effect on the CSR of the weakest coke compared to the stronger coke.
ALS Coal aims to implement the calculation of JKCSI from routine pilot scale drum testing data. This will allow validation of the different drum indices and give the client a useful parameter to better track how coal quality may be influencing coke quality.
The JKCSI could be applied to reduce the number of the routine drum tests to determine coke strength indices for pilot scale cokes. ALS Coal has a large data set of drum test results. This data set could be used to statistically examine the predicted results of a range of drum tests based on the JKCSI determined on suitable input drum test data.
There is also a potential to use a small amount of coke sample generated from a small oven and test with a new procedure to acquire the equivalent JKCSI measured by the standard drum tests. There are two issues to be addressed before this is feasible. Firstly, better understanding of how the coke quality differs between the small scale and pilot scale ovens. Second, clarification that the JKCSI as determined by modified Micum accurately predicts standard drum tests. To demonstrate the possible benefit of determining JKCSI on small scale coke it is recommended that the completed data sets from ACARP projects looking coking conditions (C22039) and stamp charging (C22035), where suitable modified Micum data exists for determination of JKCSI, be further evaluated. This evaluation will demonstrate if the JKCSI aids in a better understanding on how coking conditions can impact on the coke quality of small scale coke and if the small scale data can be used to predict standard drum test results. As this is a limited data set the above work will only demonstrate that prediction of standard drum indices from small scale coking is feasible. A large data set would be required to determine the statistical significance of the predictions.