Char Morphology and Reactivity in Coal Combustion

Char morphology and reactivity underpin the efficiency and emissions profile of coal‐fired processes. During combustion, the devolatilisation of coal yields a solid residue—char—whose physical form ranges from highly porous, thin‐walled fragments to dense, thick‐walled structures. These morphological features are determined by coal rank, maceral composition and heating regime, and they exert a defining influence on surface area, pore connectivity and gas–solid interactions. Reactive sites on char surfaces facilitate heterogeneous oxidation and gasification reactions; their number, accessibility and chemical nature govern burn‐out rates and pollutant formation pathways. Key descriptors of char behaviour include intrinsic reactivity, which measures conversion rate under defined conditions, and thermal swelling ratio, which reflects structural collapse or expansion at elevated temperatures. Advances in imaging, microscopy and surface analysis have revealed how mineral inclusions and structural heterogeneities dictate char fragmentation, pore evolution and catalytic effects on NOx formation. A detailed understanding of morphology–reactivity interrelationships informs the design of furnaces, fluidised beds and gasifiers to optimise combustion performance, reduce unburned carbon losses and mitigate emissions of nitrogen oxides and particulates.

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Char Morphology and Reactivity in Coal Combustion publication trend

The graph below shows the total number of articles in char morphology and reactivity in coal combustion across all publications each year (not limited to Nature Index journals).

Technical terms

Char: The solid carbonaceous residue remaining after coal devolatilisation.

Morphology: The study of the shape, size and pore structure of char particles.

Intrinsic reactivity: A measure of the rate of char conversion under specified conditions.

Thermal swelling ratio: The change in char dimensions upon heating, indicating structural collapse or expansion.

Drop‐tube furnace: An apparatus for rapid heating of char particles to study devolatilisation and combustion behaviour.

Micropore surface area: The area contributed by pores smaller than 2 nm, crucial for gas–solid reaction rates.

References

1. Automated image analysis techniques to characterise pulverised coal particles and predict combustion char morphology. Fuel (2020).
2. Effect of Temperature, Pressure, Feed Particle Size, and Feed Particle Density on Structural Characteristics and Reactivity of Chars Generated during Gasification of Pittsburgh No.8 Coal in a High-Pressure, High-Temperature Flow Reactor. Energies (2019).
3. Combined Effect of Pressure and Carbon Dioxide Activation on Porous Structure of Lignite Chars. Materials (2019).
4. The effect of pulverised coal’s devolatilisation conditions on char physical characteristics. Ingeniería e Investigación (2007).
5. Liberación de materia volátil y formación de carbonizados de pared gruesa y delgada en función del contenido de vitrinita, rango del carbón, tiempo y temperatura de desvolatilización. Ingeniería y Competitividad (1969).