An Approach for the Laboratory Investigation of Coarse Coal Dewatering by Centrifugation

Abstract

In many coal preparation plants, basket centrifuges are used for dewatering coarse coal after it has been cleaned. As part of a large Australian Minerals Industries Research Association (AMIRA) project, a laboratory batch centrifuge test has been developed to provide a reproducible procedure to quantify the moisture retention properties of black coals. The final moisture content after prolonged centrifugation, termed the non-centrifugable moisture, NCM, has been found to be independent of the batch size and the amount of initial moisture. It only varies slightly with the magnitude of the applied centrifugal force. The rate of drainage falls exponentially with time, and can be described by a time constant, τ, and an exponentially centrifugable moisture, ECM. Both NCM and ECM vary markedly with the particle size of the coal, being linearly related to the specific surface area. This allows the NCM to be divided into one component for the internal moisture, NCMi. and another for the external film moisture, which can be expressed by an effective external moisture film thickness,δN. The ECM has a corresponding moisture film thickness, δE. The quantities NCM_i, ;δN and δE are properties of a coal. Given a reliable size distribution of a particular clean coal fed to a centrifuge, an estimate of the final moisture content can be made.

Key words:

• Coarse coal
• dewatering
• moisture
• centrifuge
• laboratory