Technical Market Support

The Improved Grindability Test: Comparisons with HGI

Technical Market Support » Thermal Coal

Published: June 05Project Number: C13065

Get ReportAuthor: Dick Sanders | QCC Resources

The Hardgrove Grindability Index test, developed in 1932, is universally used in specifications for coal purchase and power station pulveriser design, to indicate the grinding property of coal and other commodities. It has, however, three deficiencies:

  • it uses only the coarse (harder) part of the sample - producing biased (low) results
  • it grinds a standard mass rather than a volume - producing low values for stone bands
  • it reports the result as an arbitrary index - giving no direct indication of the physical properties of the coal tested.

In the initial project, C12063, a test was developed and demonstrated, which overcame all of the deficiencies of the Standard Hardgrove Grindability Index (HGI) Test. It uses a standard volume of a representative by-zero sample, and expresses the results of the standard grind in terms of the Sauter mean diameter, SMD (in µm). The test is called the Improved Grindability Test (IGT).

In the project reported, the test was applied to a larger number of coals, covering a wide range of rank, coal type, and mineral matter content and type. These comprised eleven from NSW, ten from Queensland, one from West Australia, and four from ACARP Project C13063 Milling of Blends (plus six blends made from these four coals).

  • A Standard procedure, based on modifications to the current HGI Standard, was prepared for consideration by the committee of Standards Australia.
  • The results confirmed the IGT result i.e. the SMD after grinding, to be an excellent indicator of the grindability of a coal, and in good general agreement with the HGI.
  • However, crushing pre-history was considered to affect the result and a modification to the method, to provide more initial crushing steps, and/or a slightly longer grind time, is needed to overcome this.
  • Petrographic tests confirmed that the HGI test portion contains less of the soft components (mono-macerites) and more of the hard components (tri-macerites) than the discarded portion, which comprises about half of the prepared sample.
  • An interrupted IGT, where the 0.75 µm material was removed twice during the test and recharged each time with an equivalent mass of feed material (-2+0 mm), showed that the overall sizing after grinding was little different to that from the Standard IGT. The IGT results correlated closely with the mass of recharge material, giving rise to confidence in the IGT as an indicator of power station mill capacity. The mass% of fines removed trended towards steady state after 4 to 5 minutes.
  • The precision of the test, in an experienced laboratory, was found to be similar to that for the HGI, but unsatisfactory in another two laboratories doing the test for the first time.
  • Sizings of blends prepared at 4.75 mm top size were coarser before and after the IGT than calculated from the individual components.


Health and safety, productivity and environment initiatives.


Open Cut

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

Recently Completed Projects

C19024Establishing Ecologically Sustainable Mine Water Release Criteria In Seasonally Flowing Streams

Extreme rainfall conditions in the Fitzroy Catchment over an approxi...

C25030Coal Mine Open Pit Final Void Closure And Relinquishment - Addressing Uncertainty In Coal Mine Environmental Planning

This report addresses uncertainties faced by coal mine operators whe...

C27046Estimation Of True Deformation Vector From Slope Radar Monitoring

Slope deformation radar monitors are now widely used in open cut coa...

Open Cut

Coal Preparation

Maximising throughput and yield while minimising costs and emissions.

Recently Completed Projects

C27004Improving Coal Flotation With Oscillatory Air Supply

This report provides detailed information on coal flotation with os...

C25018Improving Solids Recovery And Moisture Reduction In Ultrafine Coal Dewatering

This report provides detailed information on fine coal dewatering in...

C27028Lab Froth Flotation Testing Guide With Coal Quality

Correct outcomes from laboratory froth flotation testing in coal bor...

Coal Preparation

Technical Market Support

Market acceptance and emphasising the advantages of Australian coals.

Recently Completed Projects

C26039Nanoporosity In Cokes: Their Origin, Control And Influence On CO2 Reactivity

This project using the outcomes of previous project C24060, examine...

C28063A Comprehensive Technical Review Of High-Efficiency Low-Emission (HELE) Pulverised Coal Combustion Technologies For Power Generation

Research and development has been undertaken worldwide to realise co...

C28064Carbon Structure Transformation During Coking Of Australian Coking Coals: Better Understanding The Coke Formation

Carbon structures of coke that are formed during the plastic layer a...

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) - Phase 2 Demonstration In A Packed Bed Reactor

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

C26004CFD Modelling Of Reverse Thermal Oxidisers For VAM Abatement - CFD Modelling Of Fixed-Bed RTO Devices

The project is part of a larger multi‐phase program of study a...

C27058Technological Assessment Of A Recycle Reactor For VAM Abatement

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

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