ACARP ACARP ACARP ACARP
Coal Preparation

Quality Of Dense Medium

Coal Preparation » Gravity Separation

Published: October 08Project Number: C15053

Get ReportAuthor: Michael O'Brien, Bruce Firth | CSIRO Energy Technology

The objective of this project was to quantitatively detail the impact the particle characteristics constituting the dense medium in a coal preparation plant have on the properties which are key in defining the performance of a dense medium circuit; that is the viscosity and medium stability.  Secondary objectives were:

  • The critical evaluation of methods to quantitatively measure the values for viscosity and medium stability; and
  • The development of a Handbook for assisting plant staff in the operation of their dense medium cyclone circuits.

Background

The use of a dense medium provides the most efficient and cost effective approach for the separation of clean coal from raw coal. Finely ground magnetite has become the medium of choice for the Australian coal preparation industry. While the magnetite being supplied to the plant has a nominal size distribution, the actual characteristics of the steady state medium found in the plant will be a balance between a number of activities occurring within the circuit :

  • Some of the material in the feed magnetite has poor magnetic susceptibility and is quickly lost by the magnetic separators.
  • The operation of the magnetic separators is such that complete recovery of magnetite is not possible.
  • The desliming screens do not remove all of the particles less than the nominal bottom size set for the DMC circuit.
  • Some of the magnetite is not recovered from the drain and rinse screens.

The clay bands and shale tend to disintegrate in the water as they pass through the DMC circuit and, since the majority of the medium reports to the 'correct' medium stream from the drain and rinse screens, there is accumulation of this material.

To control the level of 'build up' of material, some of the 'correct' medium is also sent to the magnetic separators to reduce the level of contamination from non-magnetic material.

In some plants water carry over on the drain and rinse screens can cause detrimental effects to the medium as the non-mags within the medium are diluted which can lead to an unstable medium.

The presence of slimes in the medium will increase its stability by virtue of the particle size and low mineral density, and on operating plants the level of build up of these slimes is normally closely controlled. In some cases a build up of slimes to increase suspension stability is desirable, and clay is sometimes added for this purpose.  

Conclusions and recommendations

The F5 settling test was found to be unreliable for the medium suspensions used in Australia with dense medium cyclones. It may have relevance to suspensions used in dense medium baths. Comment on this test should be removed from the technical information used in the industry for the education of new practitioners.

From the extended Einstein equation the calculated viscosities for plant samples were expected to be in the range of 1.4 cp to 2 cp. This indicates that the amount of material in the colloidal size range is relatively small and thus would have little effect on the flow of solids in a dense medium cyclone. The measured viscosities of the synthetic medium samples were within this range and showed no correlation with the stability as measured with settling tests.

Settling tests on the synthetic medium slurries showed some distinct linkages to the measured parameters, particularly the volume fraction of the non-magnetics present.

The results suggest that the major factors that influence the settling behaviour of the medium are the volume fraction of the non-magnetics and the mean size of the magnetite particles. There is therefore potential for improving stability, and hence performance, through tailoring and controlling the size distribution and the proportions of magnetics and non-magnetics.

These results show that more experimental work is required to produce a handbook for use in the coal preparation industry. This report goes someway to providing the required data but other factors such as the rate of build up of fines in the medium circuit and consideration of differing fines build up within loops is not addressed. Furthermore the effect of plant stoppages on the medium quality is not addressed. The measurement of the DMC underflow density to determine density differential should also be investigated as a means to establish the medium stability.

The potential for improving stability by tailoring and controlling the size distribution and proportions of  magnetics and non-magnetics should also be investigated.

Underground

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...

C27049Mine Machine Radar Sensor Integration

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

C29007Innovative Coal Burst System To Investigate The Influence Of Confinement Loss And Pre-Conditioning On Coal Burst Mechanism

The challenges associated with designing and operating a safe and pr...

Underground

Open Cut

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

Recently Completed Projects

C33035High Water Recovery, Low Cost Desalination Using PV-Powered Membrane Capacitive Deionisation (Mcdi)

Capacitive deionization is a robust, energy efficient and cost effec...

C28035Topsoil Deficits In Site Rehabilitation Accelerated Transformation Of Spoils To Functional Soils

The incorporation of commercial biological amendments (compost, worm...

C34036Tyre Handler Testing Rig Stage 2: Lifting Trials

Tyre handling is a major source of risk in surface mining operations...

Open Cut

Coal Preparation

Maximising throughput and yield while minimising costs and emissions.

Coal Preparation

Technical Market Support

Market acceptance and emphasising the advantages of Australian coals.

Recently Completed Projects

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...

C29071Source Of Variability Of Reactivity Of Coke In The CSR Test

The Coke Strength after Reaction (CSR) test is used worldwide to det...

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

NERDDC

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

NERDDC