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.

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...


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


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