ACARP ACARP ACARP ACARP
Technical Market Support

Stage One - Assessment of In Situ High-Temperature Strength of Cokes

Technical Market Support » Metallurgical Coal

Published: April 17Project Number: C25045

Get ReportAuthor: Pramod Koshy, Michael Drew, Sushil Gupta and CC Sorrell | University of New South Wales and Australian Nuclear Science and Technology Organisation

A typical high-CSR Australian coke was subjected to high-temperature tests to determine its compression and creep-compression properties and the associated microstructural and mineralogical modifications.  The major findings are as follows:

· The unique high-temperature facilities at ANSTO were capable of producing valid and reliable measurements of the high-temperature compression and creep-compression behaviour of high-CSR cokes with good repeatability.  The rates of thermal expansion of the tested coke samples varied with the test temperature, with a significant decrease above 1200°C, followed by a constant rate to ~1550°C at which there was a second decrease.  A testing protocol was developed to compare the compression strength and creep-compression behaviour of the cokes at different temperatures.  On the basis of repeated preliminary trials (25°C to 1800°C) as well as experimental limitations, three test temperatures (1400°, 1550°, and 1700°C) were identified for creep-compression and compressive strength measurements.

· The present work confirmed the hypothesis that the compression strength of the coke increases significantly with increasing temperatures for at least high-CSR cokes such that the ultimate failure stress at 1400°C (30 MPa) was almost three times the value at room temperature (~13 MPa).

· The stress-strain behaviours observed at room and high temperatures are significantly different.  At high temperatures, the samples showed steady elastic and plastic deformation prior to sudden failure while at room temperatures the steady-elastic part was followed by brittle failure and uneven load fluctuations owing to self-compression.

· Microstructural analysis showed an increase in the extent of porosity after high-temperature testing and this is attributed to crack and pore formation from the well-known in situ reduction of quartz and other oxide species in the coke.  At 1400°C, the glassy silicate phases can undergo plastic flow, which can contribute to enhancement of the plastic deformation of the coke samples at these temperatures.  However, at higher temperatures, the graphitisation degree of the coke would also increase, reaching a maximum at the highest testing temperature of 1800°C (as expected).  Increasing graphitisation would result in decreasing load-bearing capacity owing to decreasing bonding and abrasion strength of the graphitic material.

· The stress relaxation test done at a constant stress of 13 MPa at 1550°C was able to identify the overall strain from elastic and plastic deformation to be ~1.19% and the elastic spring-back deformation on unloading was clearly seen from the deformation data.

 

IMPLICATIONS

In the published literature, brittle deformation of coke had been observed previously at room temperature and at 1000°C while plastic deformation has been observed during creep tests at constant stresses at 1300°, 1500°, and 1600°C and during compression testing in a Gleeble machine at 1600°C.  However, studies reporting the effect of temperature on the failure stresses of cokes have not always shown consistent trends.  This may be due partly to the variety of test methods used, specimen pre-conditioning, and definition of failure and temperature ranges assessed.  Some axial compression tests have given higher strengths at 1400°C than at room temperature [Grant 1986, Grant et al. 1991].  However, a range of different failure modes has been observed and Haapakangas [Haapakangas et al 2014] has classified two different room-temperature and four different high-temperature deformation modes from fifty tests each on three grades of coke.  In these tests, the coke specimens generally had lower strengths at 1600° and 1750°C than at room temperature while other work has found lower ultimate strength at 1600° than at 1000°C [Haapakangas 2013].

Failure strains observed in the current work were broadly similar at room and high temperature (~3.6 to 4.9%) and these were similar to other published data (e.g., 2.5 to 3.0% by Haapakangas et al. (2014) and 2.2 to 3.0% by Kim and Sazaki (2010)).  The slopes of the initial elastic loading in these tests were similar between 1400° and 1700°C; however, these were almost twice the slope of the room temperature tests.  Other published axial compression elastic moduli reported by Sato (1999) have been ~1500 MPa and ~1300 MPa.  These were slightly lower than those of the present high temperature test data.  The room-temperature tests by Amanat et al (2009) indicate an elastic modulus of ~900 MPa, which is broadly in agreement with the present room-temperature test data.  The measured failure strains in the present work are consistent with values expected for foam-like materials at high temperatures and this further confirms the reliability of the data and the testing methods.

Underground

Health and safety, productivity and environment initiatives.

Recently Completed Projects

C23005Use Of Plastic Metal In Underground Coal Mines For Minor Repair On Flameproof Equipment

The potential for a gas or dust explosion arising from hot work and ...

C25070Shuttle Car Steering System Optimisation

The condition of roadways in underground mines is of great importance, a...

C20041Polymer-Based Alternative To Steel Mesh For Coal Mine Strata Reinforcement

The report details work undertaken to develop a polymer-based alternativ...

Underground

Open Cut

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

Recently Completed Projects

C19023MWD For Super-Resolution Control Of R.A.B. Drilled Blast-Hole Stand-Off Distances

Open-cut coal mine blasting losses are serious. Incorrect blast stan...

C21005RAB Drill Rig Top Of Coal Detection While Drilling

Accurately detecting the approaching top of a coal seam prior to blastin...

C24064Top Of Coal Detection In A Rotary Air Blast Drill Rig

Accurately detecting the approaching top of a coal seam prior to bla...

Open Cut

Coal Preparation

Maximising throughput and yield while minimising costs and emissions.

Recently Completed Projects

C24046Online Particle Size Monitoring In Coal Preparation

The principle of using laser diffraction as a means of measuring a v...

C24048Thickener Underflow Monitor

The aim of this project was to develop an instrument that is capable of ...

C24044RFID Residence Time Modelling

The project had two main objectives, the first to provide residence ...

Coal Preparation

Technical Market Support

Market acceptance and emphasising the advantages of Australian coals.

Recently Completed Projects

C24060Structural Differences Between Coking Coals Of The Sydney Basin And Other Sources

Cokes made from Australian coals of relatively low fluidity can have...

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

A typical high-CSR Australian coke was subjected to high-temperature...

C24056Relationship Between Internal Pressure And Coke Strength And Implications For Semi Soft Coking Coals In Blends

The objective of this project was to explore the relationships between t...

Technical Market Support

Mine Site Greenhouse Mitigation

Mitigating greenhouse gas emissions from the production of coal.

Recently Completed Projects

C24017Improving Methods For Quantifying Fugitive Emissions From Open Cut Coal Mining

Fugitive emissions from open cut coal mines are usually estimated fo...

C21065Flame Arresting Mechanisms And Flameproof Device For VAM Mitigation

The overall goal of this project was to study the gas flammability limit...

c21064Development Of A Catalytic Mitigation System For VAM - Stage 3 - 20 Litre Per Min VAM Flow Technical Development Unit

This report describes work undertaken towards the development of a p...

Mine Site Greenhouse 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

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 ...

C19025Governance Strategies To Manage And Monitor Cumulative Impacts At The Local And Regional Level

ACARP levy contributors should order this report in the normal manner – ...

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