ACARP ACARP ACARP ACARP
Technical Market Support

Demonstration of the True Ash Fusibility Characteristics of Australian Thermal Coals. Stage 2: Prov

Technical Market Support » Thermal Coal

Published: April 98Project Number: C5060

Get ReportAuthor: S Gulpta, Terry Wall, R Gupta, Bob Creelman, R Sanders, A Lowe, J Saxby | University of Newcastle, RA Creelman & Associates, Quality Coal Consulting, CSIRO Energy Technology

The current ash fusibility temperature (AFT) test can give differences in estimates of up to 300°C for some coal ashes. This irreproducibility led to the testing of a range of methods for determining the fusibility temperatures of coal ashes.  The use of shrinkage levels for an ash sample measured using thermo-mechanical analysis (TMA) is shown to be a valid method of characterising ash fusibility behaviour. Thermo-mechanical analysis is shown to be a reliable procedure, with a typical accuracy of ± 10oC for a particular shrinkage level.

Alternative ash fusibility temperatures based on the TMA test are proposed. These temperatures correspond to particular shrinkage levels (denoted as T(S%) for S of 25%, 50%, 75% and 90%). The new temperatures suggested as indicators are:

  • Initial melting (T25%, ~25% melting),
  • Intermediate melting (T50%, ~60% melting), completion of melting (T75%, ~80% melting),
  • slag flow (T90%).

These new temperatures are shown to correlate with the observed extent of melting and calculated viscosity, which is an indication of particle stickiness in a furnace.

Project Objectives

  • to investigate alternative procedures, for characterising ash fusibility.
  • establish the scientific understanding necessary to explain the results, including relationships with plant performance as well as with the standard AFT procedure.
  • develop a correlation between ash shrinkage and ash stickiness, and therefore between shrinkage and ash deposition in furnaces

Project Method

Various approaches to evaluating the ash deposition tendencies of a coal were reviewed:

  • simultaneous electrical resistance-shrinkage measurement (HRL test)
  • improved ash fusion test (ACIRL test)
  • thermomechanical analysis (CSIRO test)

The effect of particle size, heating rate, ash chemistry and the sample configuration on the various ash fusion events observed during a measurement for each technique have also been discussed.  The samples used in the study were far ranging, but were grouped into Australian export coals, overseas export coals and Australian power station feed coals. Base data on all coals and blends have been collected and collated. Combustion ashes from a selection of power stations, mineral mixtures and synthetic glasses supplemented the coal ashes studied.  For the TMA work, the behaviour of specific ash classes was investigated and compared to AFT results. The classifications include: 

  • refractory ashes, further divided into low basic components and high basic components, where the basic components are K2O and Fe2O3
  • ashes which contain Fe2O3 and CaO as the major fluxing components
  • ashes with unusual chemistries eg very high CaO, or Na2O
  • pure mineral mixtures and synthetic glasses

The study of melting was undertaken using ash pellets a technique successfully used in previous projects.

Project Outcomes

The data and observations show that the measured shrinkage reflects the extent of melting.  An initial shrinkage event (ie minor peak temperature) in the TMA test is shown to relate to significant particle deformation. This event can account for up to 25% shrinkage, therefore the deformation temperature measured using the traditional AFT test does not necessarily represent the initial melting events.

Shrinkage at around the 50% level can be related to substantial melting. These events are related to the ash chemistry - mineralogy. The temperature of these peaks relate to the various eutectic temperatures from the known system SiO2-Al2O3-X where X = FeO, CaO, K2O.

In general, the major peak temperature for refractory ashes ranges from 1400-1600oC. However, there is a modification of the observed TMA behaviour with K2O content. The “K2O effect” is proportional to the absolute K2O content of the ash. Ashes with a high K2O content demonstrate major peaks up to 1200oC. Ashes with low K2O contents have weak peaks in the low temperature regions for deformation temperature, resulting in poor precision for deformation temperature measurement. The deformation temperature is found to represent the appearance of a substantial melt phase. The melt is the result of low melting point minerals containing K2O such as illite.

A major peak and substantial melting is observed in the temperature interval of 1100oC to 1200oC for ashes that contain high amounts of combined Fe2O3 and CaO (total basic components >10wt%). Ashes with a low SiO2/Al2O3 ratio and small amounts of Fe2O3 or CaO show a wide range of melt temperatures, whereas those with high SiO2/Al2O3 ratios or with high iron contents show a narrow range of melt temperatures. For these types of ashes shrinkage measurements adequately reflect the extent of melting.

The effect of particle size is found to be of secondary importance compared to ash chemistry when determining the rapid shrinkage events, with fine particles giving rapid shrinkage events only 10oC lower in temperature than coarser particles.

TMA shrinkage at a temperature greater than the major peak temperature is mainly associated with the dissolution of SiO2 into the existing melt phases.

Underground

Health and safety, productivity and environment initiatives.

Recently Completed Projects

C27039True Triaxial Strength Of Coal Measure Rocks And Its Impact On Roadway Stability And Coal Burst Assessment

Rocks in the ground are subject to a range of stresses. The stresses...

C3063Underground Vehicle Design Standards And Statutory Implications

The Australian underground diesel vehicle fleet has evolved since di...

C3064Conveyor Belting And Lagging Shear Characteristics - Drive Drum Slip

The primary aim of this project was to investigate the relationsh...

Underground

Open Cut

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

Recently Completed Projects

C29021Assessing The Impact Of Consecutive Night Shifts On Night-Time Alertness, Daytime Sleep And Timing Of The Circadian System

In the Australian coal mining industry, most guidelines for managing...

C33037Quantifying Recharge To Groundwater Systems In The NSW Coalfields (Sydney, Gunnedah And Gloucester Basins)

The purpose of this project was to estimate the rate of diffuse rec...

C26029Geological Controls On Fluorine And Phosphorus In Bowen Basin Coals

Increasing global restrictions on fluorine in product coal prompted ...

Open Cut

Coal Preparation

Maximising throughput and yield while minimising costs and emissions.

Recently Completed Projects

C27064Dry Beneficiation Using FGX And X-Ray Sorters

Conventional dry processing methods engage a single beneficiation de...

C26010Multi-Sloped Screening Efficiency With Changing Strokes, Frequencies, Feed Solids And Feed Rates-Pilot Plant Study

Optimising multi-sloped screens is often described as an art and the...

C28059Impact Of Water Quality In Coal Handling And Preparations Plants

The objective of this project was to deliver a concise reference do...

Coal Preparation

Technical Market Support

Market acceptance and emphasising the advantages of Australian coals.

Technical Market Support

Mine Site Greenhouse Gas Mitigation

Mitigating greenhouse gas emissions from the production of coal.

Recently Completed Projects

C23052Novel Stone Dust Looping Process For Ventilation Air Methane Abatement

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

C27054Optimisation Of A Thermal Flow Reversal Reactor For Ventilation Air Methane Mitigation

Ventilation air methane (VAM) generally accounts for 50-85% of the t...

C28076Selective Absorption Of Methane By Ionic Liquids (SAMIL) - Phase 2 Demonstration In A Packed Bed Reactor

An alternative approach to high temperature oxidation of ventilation...

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