Coal Preparation

Product Moisture After Centrifuging Coarse Coal

Coal Preparation » Dewatering

Published: August 95Project Number: C3003

Get ReportAuthor: Bruce Firth, T White, B Stanmore | CSIRO Energy Technology, University of Queensland

High moisture content in export coals increases transport and handling costs and invokes contract penalties. Considerable effort has been focussed on fine coal dewatering, but significant variation in the moisture content of the coarse product is also important.  Very little work has been carried out to determine the magnitude and causes of these variations. ACARP supported this AMIRA project which was established to investigate the problem.

The moisture content of coarse coal after centrifugation has been found to vary significantly:  

The Grubbs estimation technique has shown that the MCI Model TBM101 on-line moisture meter is capable of providing accurate and precise (plus/minus 0.3%) information in real plant environments. It is not significantly affected by the presence of magnetite or thin (about 65mm) beds of coal.  The meter is capable of maintaining its calibration over significant time periods (a number of months).  

Normal distributions or multiple normal distributions for multiple seam mines, appear to provide a convenient method of describing the plant, fine coal and coarse coal moistures. This could be of use in determining real changes to plant operations and the application of statistical process control procedures.  

Little dependence of coarse coal moisture was found with respect to time of plant operation. There was a small positive correlation with the feed rate to the plant. The product ash value for the two coals examined also had little impact.  

Laboratory centrifuge technique has been developed, which for relatively coarse coal feeds, has identified that there are three types of water associated with a coal with respect to its potential for removal by centrifugation:  

There is an amount of water removed easily with centrifugation. This excess water appears to have little relationship with the coal.

There is an amount of water which is closely related to the coal surface, causing a slower rate of removal.

There is a Non-Centrifugable Moisture (NCM) which cannot be removed by centrifugation even using much longer times. It comprises a small amount of surface water, as well as an amount of internal water within the coal structure. Particular coals have different capacities for holding internal water.  

It has been found that the results from the laboratory centrifuge are erroneous when the samples have been allowed to begin drying. This is considered to be due to problems of rewetting the coal, particularly with respect to water being unable to penetrate the dried internal pore structure of the coal.  

The Non-Centrifugable Moisture results from the laboratory centrifuge work can be interpreted as the coal having an internal moisture, NCM i , (which is unaffected by particle size) and an external moisture, NCM s , which varies with particle size, and is proportional to the surface area. Values of NCM i and NCM s are given for the coals tested.  

Four boreholes were obtained form the coal seams involved in the plant investigations. There are significant differences between the NCM i values, with the Goonyella Middle seam having a substantially higher value (4.2%) than the Goonyella Lower (3.1%) and the Middle seam from the Isaacs Pit (3.4%). All the Goonyella cores are much higher than that for the Dysart seam at Norwich Park (2.3%). The surface moistures were similar for all the material from the boreholes.  

The mercury porosimetry tests provide relative internal pore volumes for the different coals tested. All the Norwich Park samples have lower internal porosities than those from Goonyella. For both coals, the dull material has a higher pore volume than the bright, and also retains more mercury during extrusion. The dull coal from the Goonyella Middle seam contains significantly higher porosity than the Lower dull and all the bright samples. The dull material from the Isaacs pit had a porosity between the Middle and Lower seams.  

Analysis of the results from the major samples obtained from the two plants, as well as samples obtained at five other mine sites has indicated that the moisture level of the coal after centrifugation and its propensity to vary, is controlled by:  

  • the amount of moisture held internally within the coal;
  • the specific surface area of the coal being presented to the centrifuge;
  • the hydrophobicity of the coal as indicated by the rank (reflectance);
  • the amount of ultra-fine (slimes) material associated with the coarse coal, which appears to affect the drainage of water from the coal particle surface.  

The overall range of the rank of the coals involved in this investigation, as measured by reflectance, varied from 0.7 to 1.65. The model was able to explain 80% of the variation in the 25 samples investigated.  

At all sites investigated, it was found that there was a significant amount of coal breakage in the centrifuge. Evidence suggests that the majority of the breakage occurred as the coal leaves the centrifuge, and any analysis based on the final product size distribution could be erroneous.  

At Goonyella, washing the coal (ie the removal of the ultra-fine particles led to decreases in moisture level.  

Scanning electron microscopy has identified that the surface of the coarse particles is covered by a layer of ultra-fine particles, with the majority of these being carbonaceous in nature.  

A model incorporating the above factors has been developed. It provides an approach for estimating the moisture level which can be achieved by centrifugation of coarse coal.


Health and safety, productivity and environment initiatives.

Recently Completed Projects

C34019Longwall Bretby Cable Handling Monitoring With Fibre Optics

This project examined the potential of using fibre optic sensing tec...

C28028The Inclusion Of High Interest Native Plants In Mine Site Restoration Programs: Propagation, Translocation And Field Re-Introduction

This report synthesises over 10 years of ex situ and in si...

C27049Mine Machine Radar Sensor Integration

The aim of this project was to develop an integrated radar sensor an...


Open Cut

Safety, productivity and the right to operate are priorities for open cut mine research.

Recently Completed Projects

C34029Validation Of Laser Induced Breakdown Spectroscopy (LIBS) As A Rapidly Deployable Field Technology To Estimate Coal Quality

Rapid evaluation of a coal resource by in-situ characterisation dow...

C34028Guidelines For Assessment Of Geotechnically Safe And Stable Post-Mining Landforms

The purpose of this project was to develop a guidelines document as ...

C34016Elements In Coal – A Start-To-End Analysis

This project explores the fate and concentration potential of critical e...

Open Cut

Coal Preparation

Maximising throughput and yield while minimising costs and emissions.

Recently Completed Projects

C26016Determining The Benefits Of Online Thickener Underflow Rheology Measurements

The aim of this project is to determine how useful the rheology meas...

C33056Modelling And Control Of Classifying Cyclones

Hydrocyclones are one of the key technologies for the classification...

C28056Surface Alloying Of Centrifuge Baskets And Sieve Bends Screen Surfaces To Increase The Service Lifetime

The main objective of this project was to improve the wear resistanc...

Coal Preparation

Technical Market Support

Market acceptance and emphasising the advantages of Australian coals.

Recently Completed Projects

C33066Washability And Distribution Of Sulfur And Trace Elements For Different Size And Density Fractions Of Raw Coals

Based on the hypothesis that the levels of sulfur and other toxic tr...

C34060In-Situ Investigation Of Coke Structure Formation Under Stamp Charged Coking Conditions

Stamp charged cokemaking has emerged as an effective technique to im...

C34062Improving The Classification Of Microstructure Distribution In Coke CT Images Using Deep Learning And Lineal Path Calculations

This project builds on a number of earlier projects that have helped...

Technical Market Support

Mine Site Greenhouse Gas Mitigation

Mitigating greenhouse gas emissions from the production of coal.

Recently Completed Projects

C28076Selective Absorption Of Methane By Ionic Liquids (SAMIL)

This third and final stage of this project was the culmination of a ...

C29069Low-Cost Catalyst Materials For Effective VAM Catalytic Oxidation

Application of ventilation air methane (VAM) thermal oxidiser requir...

C23052Novel Stone Dust Looping Process For Ventilation Air Methane Abatement

This multi‐phase project is concerned with the mitigation of m...

Mine Site Greenhouse Gas Mitigation

Low Emission Coal Use

Step-change technologies aimed at reducing greenhouse gas emissions.

Recently Completed Projects

C17060BGasification Of Australian Coals

Four Australian coals were trialled in the Siemens 5 MWth pilot scale ga...

C17060AOxyfuel Technology For Carbon Capture And Storage Critical Clean Coal Technology - Interim Support

The status of oxy-fuel technology for first-generation plant is indicate...

C18007Review Of Underground Coal Gasification

This report consists of a broad review of underground coal gasification,...

Low Emission Coal Use

Mining And The Community

The relationship between mines and the local community.

Recently Completed Projects

C16027Assessing Housing And Labour Market Impacts Of Mining Developments In Bowen Basin Communities

The focus of this ACARP-funded project has been to identify a number...

C22029Understanding And Managing Cumulative Impacts Of Coal Mining And Other Land Uses In Regions With Diversified Economies

The coal industry operates in the context of competing land-uses that sh...

C23016Approval And Planning Assessment Of Black Coal Mines In NSW And Qld: A Review Of Economic Assessment Techniques

This reports on issues surrounding economic assessment and analysis ...

Mining And The Community


National Energy Research,Development & Demonstration Council (NERDDC) reports - pre 1992.

Recently Completed Projects

1609-C1609Self Heating of Spoil Piles from Open Cut Coal Mines

Self Heating of Spoil Piles from Open Cut Coal Mines

1301-C1301Stress Control Methods for Optimised Development...

Stress Control Methods for Optimised Development and Extraction Operations

0033-C1356Commissioned Report: Australian Thermal Coals...

Commissioned Report: Australian Thermal Coals - An Industry Handbook