Technical Market Support » Metallurgical Coal
The introduction of renewable biomass into coal blends is regarded as a promising approach to increase the sustainability of the cokemaking process. However, due to the adverse impacts of biomass derived materials on blend thermoplasticity and resultant coke quality, it is crucial to select and study the performance of suitable biomass species. This project examines the impact of microalgae addition on coking performance and quality of cokes made from four coking coals ranging in rank, maceral composition and fluidity.
The overall objective of the project was to evaluate the influence of microalgae addition on carbonisation behaviour, thermoplasticity and internal gas pressure development, the mechanism of microstructure and microtexture formation, and reactivity and strength of resultant coke. This was achieved by a comprehensive investigation of the coal-to-coke transformation and coke quality evaluation using a range of in-situ analysis techniques and high temperature reactivity testing.
Results showed that coals vary greatly in their carrying capacity for microalgae. Prime coking coals with higher rank and fluidity were less impacted by microalgae addition. In contrast, the quality of cokes made from coals with lower rank and high inertinite content deteriorated rapidly at low microalgae addition levels. These findings suggest that selection of prime coking coals is essential to ensure a high biocoke quality.
One key objective of the project was to understand the impact of microalgae on the development of thermoplasticity and IGP during the coking process. It was found that the thermoplasticity of coals with higher initial dilatation and fluidity was less impacted by microalgae, up to 10 wt% addition. The coking tests in the 4kg oven showed lower IGP for blends incorporating microalgae, indicating that microalgae can reduce the IGP of high pressure coals. Further increasing the blend microalgae content to 20 wt%, led to a complete loss of thermoplasticity and IGP during the coke formation. The consequence was the disappearance of the plastic layer and the formation of biocoke with severe structural defects, as analysed by 3D micro-CT image analysis.
Key drivers were investigated for increased biocoke reactivity and it was found that increased coke porosity and increased concentration of alkali species in coke with the addition of microalgae are they key factors leading to higher biocoke reactivity.