ACARP ACARP ACARP ACARP
Coal Preparation

Dry Classification of Fine Coal

Coal Preparation » Environmental Improvement

Published: May 07Project Number: C15055

Get ReportAuthor: KJ Walton, Kevin Galvin, AM Callen | University of Newcastle

The classification and beneficiation of coal with spirals or cyclones inherently involves high water consumption. The issue of water supply, particularly in arid areas, is further complicated by problems associated with waste tailings generation and disposal. The development of alternative dry processing methods would alleviate these water consumption and tailings disposal issues. This study examines the application of dry beneficiation technology to separation of coal and mineral matter samples using a novel gas-solid fluidised bed.

The innovative device, known as the Reflux Classifier (RC), combines a conventional fluidised bed with a set of parallel plates. An internal particle recycling mechanism develops from the continual upwards fluidisation of particles into the inclined channels formed between the plates, and the downwards segregation of the particles via the inclined surfaces. The self-recycling effect helps prevent misplacement of particles during the classification process and consequently improves the separation quality. The focus of the study is on evaluating the potential of the device for pneumatic size classification and gravity beneficiation of nominally -2mm coal particles. The study also examined particles up to 4 mm in size.
 
Size classification in the RC relies on the complex particle elutriation mechanism where high gas flow rates initially launch particles into the inclined channels. Here, the coarser particles segregate from the gas flow and return to the bed, whereas the finer particles are entrained by the gas and removed from the system. Hence, relatively higher flow rates are capable of suspending larger particles which, in turn, can be transported from the apparatus.

Using compressed air as the fluidisation gas, a series of flow rates were studied to examine the size classification of -2 +0mm coal samples in the RC. The underflow and overflow samples were collected and the partition data calculated, in turn the equilibrium size separation cut point (S50) was determined. A data set is shown in Figure 1. The RC generated separation cut points ranging from 0.06 - 1.1mm for the 0.903 – 2.917 m/s flow rates investigated. The imperfection (I = (S75-S25)/2S50) of each classification experiment was also determined using the partition data. This study has shown that a typical separation cut point of 0.25mm was achieved with an imperfection value of I = 0.12. Generally, the imperfection term increases as the gas flow rate increases. The equilibrium separation cut point was used to establish a relationship between the S50 and the velocity.

 

Figure 1: The effect of flow rate on the S50 for experiments with a 6 minute run time. The graph depicts an exponential increase in the cut point, S50, as the flow rate is increased.

This study also investigated the gravity beneficiation of nominally -2 +0.25mm coal and mineral matter samples in the RC. Air was used as the fluidisation gas but it was discovered that a dense medium was required in the apparatus to promote a density separation rather than a size classification. Illminite was originally used as the dense medium but was later substituted by magnetite due to the likelihood that magnetite would be preferred in the coal industry. A range of variables were studied which included the dense medium quantity, size range and the variation in the medium inventory throughout the experiment, the solids inventory, and the particle size range analysed, the gas velocity, the particle residence time in the vessel, and the RC channel geometry. Several different multistage process systems were examined to identify any improvement in quality of the separation by reprocessing either the product or reject streams, or by simulating a continuous process. Results from all the methods are shown in Figure 2.

The amount of magnetite required was related to the physical dimensions of the RC. Under excessive medium conditions, the RC had a tendency to entrain solids with the overflow by plug flow, whereas insufficient media promoted size separation. The ideal dense medium particle size range was -0.212 +0.150 mm. A medium that was too fine was impossible to retain in the system and suffered from its cohesive nature. The use of an excessively coarse medium was problematic to recover from either the overflow or underflow and also prevented fine particles from escaping the bed. Each experiment processed typically 200 g of feed. The feed particle size range for this study was varied to determine the optimum size range the RC could process. Although it was discovered that a range from -2 +0.5mm provided the best result, separations of particles covering the range -8 +0.25 mm were achievable.

Multistage process systems were examined to improve the results from a single stage split operation. Here either the products continued to the cleaner or the reject would be directed to a rougher, for reprocessing after the first separation was completed. While these multistage operations had several process advantages, the best performing arrangement was the system that reprocessed the product in a series of cleaners. This system was called the Product Fractionation path way. In this process, the continual removal of the reject material from the product stream reduced the likelihood of misplacement of mineral matter and ensured a higher quality product. Figure 2, which compares yield-ash results with the washability curve, shows that this method was significantly more effective than all of the other methods investigated.

Figure 2: Comparison of all the different methods investigated with reference to the Float/Sink washability Curve. The particle size range was -2+0.25 mm. The Product Fractionation method shows the best separation of all the different methods.

In general, the dry beneficiation results are poorer than the separations possible using a water based separation. However, the higher mineral matter content obtained for a given yield may be offset against the reduction in the moisture content.

 

Underground

Health and safety, productivity and environment initiatives.

Recently Completed Projects

C26059Proof Of Concept Of The Electronic Spark Test Apparatus On Existing Known Power Supplies

This project continued a long running research program into an elect...

C26070Industrialisation Of Proof Of Concept Wall-Flow DOC + Filter System

The need to protect workers from diesel particulate matter (DPM) had...

C25001Ventilation And Gas Management - Underground Coal Mines

This planning guideline has been prepared to assist mine operators t...

Underground

Open Cut

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

Recently Completed Projects

C26034Coking Properties Deterioration In Small Samples

Accurate evaluation of coking coal parameters at the exploration sta...

C23029Alternative And Sustainable Explosive Formulations To Eliminate Nitrogen Oxide Emissions

This technical report describes the technology of a novel mining exp...

C25005Site Based Trials Of Alternative Explosive Formulations To Eliminate Nitrogen Oxide Emissions

This report documents the outcomes of Phase 3 of this project and b...

Open Cut

Coal Preparation

Maximising throughput and yield while minimising costs and emissions.

Recently Completed Projects

C26009Improved Precision Of Determining Coal In Urban Dust

Dust samples collected in coastal locations using High Volume Air Sa...

C26015Novel Characterisation Of Coal Petrography For Improving The Dewatering Of Fine Coals Using Chemicals

This project aimed to develop alternatives to existing mechanical de...

C26014Low Cost Online Measurement Of Particle Size And Density For Diagnostics Across The Fine Coal Circuit

This project has developed a novel prototype optical system for prof...

Coal Preparation

Technical Market Support

Market acceptance and emphasising the advantages of Australian coals.

Recently Completed Projects

C26045Mineralogy Effects On The 3D Porosity Evolution Of Coke And Coke Reactivity

CRI/CSR CO2 combustion data are key metrics of coke quality and perf...

C25049Fusibility Of Coal Blends And Minerals In Coking

The CSIRO optical reflected light imaging CGA (Coal Grain Analysis) ...

C25045Stage Two - Assessment Of In Situ High-Temperature Strength Of Cokes

Stage I of this project established a reliable and repeatable proces...

Technical Market Support

Mine Site Greenhouse Gas Mitigation

Mitigating greenhouse gas emissions from the production of coal.

Recently Completed Projects

C27058Technological Assessment Of A Recycle Reactor For VAM Abatement

Underground coal mining emits high volumes of methane, diluted in ve...

C27008Selective Absorption Of Methane By Ionic Liquids

The connection of a ventilation air methane (VAM) abatement plant di...

C24061Proof-Of-Concept Photocatalytic Destruction Of Methane For Coal Mining Fugitive Emissions Abatement

Australia's fugitive emissions in 2015 were 41 Mt CO2-e (representin...

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