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Technical Market Support

An In-situ Study of the Plastic Layer Formation in Coking Coals Using a Lab-scale Test Furnace

Technical Market Support » Metallurgical Coal

Published: February 18Project Number: C24054

Get ReportAuthor: Soonho Lee, Yunze Hui, Merrick Mahoney, Jianglong Yu | The University of Newcastle

The main objectives of this project were to investigate:

  • Formation, migration and characteristics of the plastic layers of Australian coking coals during coking (in-situ);
  • Improved understanding of the chemistry and formation mechanism of plastic layer and its impact on coke quality;
  • Validation of the quality of cokes produced from the 4kg coke oven by comparing them with final product cokes prepared in CSIRO's 450 kg pilot-scale coke oven.

A lab-scale double-heated-wall 4kg coke oven was built and fully functioning at NIER, University of Newcastle during the early stage of the project. Main features of this coke oven include providing the equivalent conditions to the practical coke ovens, in-situ measurements of temperature of five locations of the coal charge and direct sampling of plastic layer during coking process.

A series of experiments have been carried out using six coal samples supplied by the industrial monitors. Good quality coke samples have been produced at a heating rate of 10°C/min. The temperature profile and Internal Gas Pressure (IGP) were measured in-situ at five locations in the coal bed inside the reactor. The plastic layer samples were obtained during heating and quenched in nitrogen gas. The plastic layer samples have been systematically analysed using various advanced analytical techniques, including TGA-FTIR, ART-FTIR, and Synchrotron-micro-CT, etc. The results have shown that dramatic changes in both physical and chemical structures in the plastic layer take place during coking and the analyses significantly improved the fundamental understanding the plastic layer formation and its behaviour. The aliphatic and aromatic components in the volatile matter have given good trends with respect to the plastic layer positions. The thickness, internal gas pressure, the behaviour and chemical structure of the plastic layer vary significantly with coal type such as rank and vitrinite content. It has been found that there is correlation between some generic properties of coking coal and the nature of their plastic layer; maximum IGP and thickness of the plastic layer.

The temperature profile and Internal Gas Pressure (IGP) were measured in-situ at five locations in the coal bed inside the reactor. The plastic layer samples were obtained during heating and quenched in nitrogen gas. The plastic layer samples have been systematically analysed using various advanced analytical techniques, including TGA-FTIR, ART-FTIR, and Synchrotron-micro-CT, etc. The results have shown that dramatic changes in the plastic layer take place during coking and the analyses significantly improved the fundamental understanding the plastic layer formation and its behaviour. The aliphatic and aromatic components in the volatile matter have given good trends with respect to the plastic layer positions. The thickness, internal gas pressure, the behaviour and chemical structure of the plastic layer vary significantly with coal type such as rank and vitrinite content. It has been found that there is correlation between some generic properties of coking coal and the nature of their plastic layer; maximum IGP and thickness of the plastic layer.

In the extension part, a series of experiments have been carried out using six coal samples and two coal blends supplied by the industrial monitors. Coke samples produced from the 4kg coke oven sent to CSIRO to test their CRI, CSR and I600 and the coke quality testing results were compared with that of the coke samples produced from the sample coals on the CSIRO's 450 kg pilot-scale coke oven. It has been concluded that by the CSIRO report that the CSR and CRI values obtained by the two different ovens agreed within experimental error and ISO standard repeatability limits. No statistically significant differences were found between the CSR and CRI results of the cokes prepared at the two ovens of different scale. It was concluded that the coke samples prepared on the UON 4kg coke oven were essentially the same as those from the large pilot scale coke oven.

A few highlights of the research are given below:

  • Success in developing the 4kg UoN lab-scale coke oven rig which allows in-situ measurement of both temperature and IGP, high quality coke samples being produced, and direct sampling of the plastic layer as well as potentially providing a small scale pilot coking facility;
  • Postulation of a combined physical and chemical structure changes in plastic layer during pyrolysis process as described in section 3.2.2 advances the fundamental understanding of coke formation;
  • The coke samples prepared on the UON 4kg coke oven were essentially the same as those from the large pilot scale coke oven in terms of coke quality;
  • There appears to be correlation between coal properties during coking stage to plastic layer width and IGP.

The benefits from this project are:

  • Provide lab-scale coke oven tests on a range of Australian coking coals simulating large scale coke ovens. Temperature and internal gas pressure (IGP) have been measured and plastic layer samples have been obtained and analysed.
  • Provide better understanding of underlying chemistry of the plastic layer, which is important stage during the coking process.
  • Establish a methodology of quantitatively linking the chemistry of coal to the characteristic parameters of plastic layers during the coking process.

The outcomes of the project have raised importance of further work such as effects of coal blending, coal rank, self-heating and coal maceral composition on plastic layer formation for future ACARP projects. There is also a potential of commercialization of this lab-scale coke oven technology and to partially replace the large pilot scale coke oven for some coking tests.

A comprehensive literature review is provided in the Appendix of this report.

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